The document discusses drug delivery across the blood-brain barrier (BBB). It first provides background on the BBB and its role in strictly regulating molecular exchange between the blood and brain. It then outlines various transport routes that exist across the BBB, including carrier-mediated transport of small molecules via transport proteins, receptor-mediated transcytosis of larger molecules, and passage of monocytes/macrophages that can carry drugs. Finally, it discusses using biological and pathological properties of the BBB to design drug delivery systems, such as nanoparticles, that can exploit specific transport mechanisms to deliver drugs across the barrier for treating brain diseases.

1. 11/2015 :: National Institute of Science Education and Research ::
Aman Kumar Naik
Integrated M.Sc.
Drug Delivery across the
Blood–Brain Barrier(BBB)

2. onal adhesion molecule-1, occludin, and claudins) with cy-
mic accessory proteins (zonula occludens-1 and -2, cingulin,
and 7H6). They are linked to the actin cytoskeleton [9],
y forming the most intimate cell to cell connection. The TJ
ther strengthened and maintained by the interaction or
However, for almost all other substances, including essential mate-
rials such as glucose and amino acids, transport proteins (carriers),
specific receptor-mediated or vesicular mechanisms (adsorptive
transcytosis) are required to pass the BBB.
In the case of transport proteins or known as carrier-mediated
Fig. 1. Schematic representation of the blood–brain barrier (BBB) and other components of a neurovascular unit (NVU).
Reproduced with permission from reference [11].
Y. Chen, L. Liu / Advanced Drug Delivery Reviews 64 (2012) 640–665
Schematic representation of the blood–brain barrier (BBB)
REVIEWS© 2006 Nature Publi
*Wolfson Centre for Age-
Related Diseases, King’s
College London, UK.
‡
Institute of Clinical
Neuroscience, The
Sahlgrenska Academy at
Göteborg University,
Göteborg, Sweden.
Correspondence to N.J.A.
e-mail: joan.abbott@kcl.ac.uk
doi:10.1038/nrn1824
Neurovascular unit
A functional unit composed of
groups of neurons and their
associated astrocytes,
interacting with smooth muscle
cells and endothelial cells on
the microvessels (arterioles)
responsible for their blood
supply, and capable of
regulating the local blood flow.
Gliovascular unit
A proposed functional unit
composed of single astrocytic
glial cells and the neurons they
surround, interacting with local
segments of blood vessels, and
capable of regulating blood
flow at the arteriolar level and
BBB functions at the capillary
level.
in pathological conditions could lea
restorative therapies.
Neuroscience has traditionally focused on the
of the central and peripheral nervous system
increasingly, on their interactions with the gl
that support their function. It is now becomi
that neurons, glia and microvessels are organi
well-structured neurovascular units, which are i
in the regulation of cerebral blood flow1
.
this organization, further modular structure
detected; in particular, the proposed gliovascu
in which individual astrocytic glia support the f
of particular neuronal populations and territor
communicate with associated segments of the
vasculature2,3
. Several recent studies have high
the importance of the brain endothelial ce
form the blood–brain barrier (BBB) in this m
organization, and the physiology and pharm
of the signalling between glia and endothelium
involved in regulating the BBB. Here, we desc
properties of the brain endothelium that contr
its barrier function, and how cell–cell interacti
to induction of the specialized features of the B
associated cell types. We review work showing
BBB is a dynamic system, and discuss the ways i
BBB permeability and transport can be modula
then consider the important role of astrocytes
BBB in brain ion and volume regulation. Fin
discuss some of the pathologies that involve B
function, and the development of protective st
for the brain endothelium that may reduce sec
neural damage in both acute and chronic neur
conditions.
NATURE REVIEWS | NEUROSCIENCE
© 2006 Nature Publishing Group
*Wolfson Centre for Age-
Related Diseases, King’s
College London, UK.
‡
Institute of Clinical
Neuroscience, The
Sahlgrenska Academy at
Göteborg University,
Göteborg, Sweden.
Correspondence to N.J.A.
e-mail: joan.abbott@kcl.ac.uk
doi:10.1038/nrn1824
Neurovascular unit
A functional unit composed of
groups of neurons and their
associated astrocytes,
interacting with smooth muscle
cells and endothelial cells on
the microvessels (arterioles)
responsible for their blood
supply, and capable of
regulating the local blood flow.
Gliovascular unit
A proposed functional unit
composed of single astrocytic
glial cells and the neurons they
surround, interacting with local
segments of blood vessels, and
capable of regulating blood
flow at the arteriolar level and
BBB functions at the capillary
level.
Neuroscience has traditionally focused on the neurons
of the central and peripheral nervous systems, and,
increasingly, on their interactions with the glial cells
that support their function. It is now becoming clear
that neurons, glia and microvessels are organized into
well-structured neurovascular units, which are involved
in the regulation of cerebral blood flow1
. Within
this organization, further modular structure can be
detected; in particular, the proposed gliovascular units,
in which individual astrocytic glia support the function
of particular neuronal populations and territories, and
communicate with associated segments of the micro-
vasculature2,3
. Several recent studies have highlighted
the importance of the brain endothelial cells that
form the blood–brain barrier (BBB) in this modular
organization, and the physiology and pharmacology
of the signalling between glia and endothelium that is
involved in regulating the BBB. Here, we describe the
properties of the brain endothelium that contribute to
its barrier function, and how cell–cell interactions lead
to induction of the specialized features of the BBB and
associated cell types. We review work showing that the
BBB is a dynamic system, and discuss the ways in which
BBB permeability and transport can be modulated. We
then consider the important role of astrocytes and the
BBB in brain ion and volume regulation. Finally, we
discuss some of the pathologies that involve BBB dys-
function, and the development of protective strategies
for the brain endothelium that may reduce secondary
neural damage in both acute and chronic neurological
conditions.
Barriers of the CNS
The cerebral ventricles and subarachnoid space contain
cerebrospinal fluid (CSF), which is secreted by choroid
plexuses in the lateral, third and fourth ventricles4
. Three
barrier layers limit and regulate molecular exchange at the
interfaces between the blood and the neural tissue or its
fluidspaces(FIG. 1):theBBBformedbythecerebrovascular
endothelial cells between blood and brain interstitial
fluid (ISF), the choroid plexus epithelium between blood
and ventricular CSF, and the arachnoid epithelium
between blood and subarachnoid CSF5
. Individual neu-
ronsarerarelymorethan8–20µmfromabraincapillary6
,
although they may be millimetres or centimetres from a
CSF compartment. Hence, of the various CNS barriers,
the BBB exerts the greatest control over the immediate
microenvironment of brain cells.
The blood–brain barrier
The BBB is a selective barrier formed by the endothelial
cells that line cerebral microvessels7–10
(FIG. 2). It acts as a
‘physical barrier’ because complex tight junctions between
adjacent endothelial cells force most molecular traffic
to take a transcellular route across the BBB, rather than
moving paracellularly through the junctions, as in most
endothelia11,12
(FIG. 3). Small gaseous molecules such as O2
and CO2
can diffuse freely through the lipid membranes,
and this is also a route of entry for small lipophilic agents,
including drugs such as barbiturates and ethanol. The
presence of specific transport systems on the luminal
and abluminal membranes regulates the transcellular
traffic of small hydrophilic molecules, which provides
NATURE REVIEWS | NEUROSCIENCE VOLUME 7 | JANUARY 2006 | 41
© 2006 Nature Publishing Group
*Wolfson Centre for Age-
Related Diseases, King’s
College London, UK.
‡
Institute of Clinical
Neuroscience, The
Sahlgrenska Academy at
Göteborg University,
Göteborg, Sweden.
Correspondence to N.J.A.
e-mail: joan.abbott@kcl.ac.uk
doi:10.1038/nrn1824
responsible for their blood
supply, and capable of
regulating the local blood flow.
Gliovascular unit
A proposed functional unit
composed of single astrocytic
glial cells and the neurons they
surround, interacting with local
segments of blood vessels, and
capable of regulating blood
flow at the arteriolar level and
BBB functions at the capillary
level.
in the regulation of cerebral blood flow . Within
this organization, further modular structure can be
detected; in particular, the proposed gliovascular units,
in which individual astrocytic glia support the function
of particular neuronal populations and territories, and
communicate with associated segments of the micro-
vasculature2,3
. Several recent studies have highlighted
the importance of the brain endothelial cells that
form the blood–brain barrier (BBB) in this modular
organization, and the physiology and pharmacology
of the signalling between glia and endothelium that is
involved in regulating the BBB. Here, we describe the
properties of the brain endothelium that contribute to
its barrier function, and how cell–cell interactions lead
to induction of the specialized features of the BBB and
associated cell types. We review work showing that the
BBB is a dynamic system, and discuss the ways in which
BBB permeability and transport can be modulated. We
then consider the important role of astrocytes and the
BBB in brain ion and volume regulation. Finally, we
discuss some of the pathologies that involve BBB dys-
function, and the development of protective strategies
for the brain endothelium that may reduce secondary
neural damage in both acute and chronic neurological
conditions.
fluidspaces(FIG. 1):theBBBfo
endothelial cells between b
fluid (ISF), the choroid plexu
and ventricular CSF, and
between blood and subarach
ronsarerarelymorethan8–2
although they may be millim
CSF compartment. Hence, o
the BBB exerts the greatest
microenvironment of brain c
The blood–brain barrier
The BBB is a selective barrie
cells that line cerebral micro
‘physical barrier’ because com
adjacent endothelial cells fo
to take a transcellular route
moving paracellularly throu
endothelia11,12
(FIG. 3). Small g
and CO2
can diffuse freely th
and this is also a route of entr
including drugs such as bar
presence of specific transpo
and abluminal membranes r
traffic of small hydrophilic
NATURE REVIEWS | NEUROSCIENCE VO
Astrocyte–endothelial intera
at the blood–brain barrier
N. Joan Abbott*, Lars Rönnbäck‡
and Elisabeth Hansson‡
Abstract | The blood–brain barrier, which is formed by the endothe
cerebral microvessels, has an important role in maintaining a prec
microenvironment for reliable neuronal signalling. At present, the

3. g delivery typically involves either cationic proteins or cell- various CNS associated diseases. This section is focused on t
ort routes across the blood–brain barrier. Pathways “a” to “f” are commonly for solute molecules; and the route “g” involves monocytes, macrophages an
nd can be used for any drugs or drugs incorporated liposomes or nanoparticles.
m reference [11].
Y. Chen, L. Liu / Advanced Drug Delivery Reviews 64 (2012) 640–665
Transport routes across the blood–brain barrier
anced Drug Delivery Reviews 64 (2012) 640–665
nts lists available at SciVerse ScienceDirect
ced Drug Delivery Reviews
mepage: www.elsevier.com/locate/addr
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . .
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . .
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . .
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, au
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecule
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BC
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjuga
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS,
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experiment
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guano
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydr
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; IC
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprot
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipa
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mo
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotr
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-po
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycop
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activa
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nerv
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Austr
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Eng
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.addr.2011.11.010
e history:
ved 6 August 2011
pted 21 November 2011
able online 28 November 2011
ords:
d–brain barrier
delivery
ptor-mediated transport
mediated transport
particles
omes
ological conditions
The blood–brain barrier (BBB) is a highly regulated and efficient barrier that provides a sanctuary to the
brain. It is designed to regulate brain homeostasis and to permit selective transport of molecules that are es-
sential for brain function. Unfortunately, drug transport to the brain is hampered by this almost impermeable,
highly selective and well coordinated barrier. With progress in molecular biology, the BBB is better under-
stood, particularly under different pathological conditions. This review will discuss the barrier issue from a
biological and pathological perspective to provide a better insight to the challenges and opportunities asso-
ciated with the BBB. Modern methods which can take advantage of these opportunities will be reviewed.
Applications of nanotechnology in drug transport, receptor-mediated targeting and transport, and finally
cell-mediated drug transport will also be covered in the review. The challenge of delivering an effective ther-
apy to the brain is formidable; solutions will likely involve concerted multidisciplinary approaches that take
into account BBB biology as well as the unique features associated with the pathological condition to be
treated.
Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
ents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
bbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmunodeficiency syndrome; AJ, adherens junction;
adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of paclitaxel; Antp, Antennapedia; APP, amyloid beta
rsor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blood–cerebrospinal fluid barrier; BSA-NP, bovine
m albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG-PLA nanoparticles; CED, convection enhanced
ion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central nervous system; CPP, cell penetrating peptide;
cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoimmune encephalomyelitis; EO, ethylene oxide;
ndothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine monophosphate; HB-EGF, heparin binding epider-
rowth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–hydrophilic balance; HSA, human serum albu-
HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intracerebroventricular; IgG, immunoglobulin G; IL,
eukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein receptor; Lf, lactoferrin; LMV, large multilamellar
es; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic peptide; MAPK, mitogen activated protein kinase;
monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononuclear phagocytes; MRP, multidrug resistant pro-
MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferrin; PAI-1, plasminogen activator inhibitor 1;
CA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycaprolactone; PEG-G-CSF, PEGylated-recombinant
ionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein; PKA, protein kinase A; PKC, protein kinase C;
protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protein tyrosine kinase; Qdots, quantum dots; RAP,
tor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediated transport; R123, rhodamine 123; SA, sialic
esidue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmission electron microscopy; TER, transendothelial
ical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, vascular endothelial; VEGF, vascular endothelial
th factor; ZO, zonula occludens.
his review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous System”.
orresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.: +61 8 9266 2738; fax. +61 89266 2769.
-mail address: y.chen@curtin.edu.au (Y. Chen).
Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering, Curtin University.
-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
0.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain barrier☆
an Chen a,
⁎, Lihong Liu b,1
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Modern methods for delivery of drugs across the blood–brain barrier☆
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr

4. Tight junction opening
Biological stimuli
Zonula occludens toxin (Zot)
vasoactive compounds and
inflammatory stimuli such as
histamine, bradykinin and VEGF
H2 receptors NO and cyclic GMP production
Tight junction opening
Chemical stimuli
Arterial injection of hyperosmolar solution
(e.g., mannitol, arabinose) Shrinkage of endothelial cells Opening gaps between cells
Sodium dodecyl sulphate (SDS)
anced Drug Delivery Reviews 64 (2012) 640–665
nts lists available at SciVerse ScienceDirect
ced Drug Delivery Reviews
mepage: www.elsevier.com/locate/addr
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . .
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . .
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . .
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, au
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecule
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; B
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjuga
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experiment
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guano
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydr
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; IC
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprot
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphip
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mo
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanot
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-po
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycop
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PT
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activa
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nerv
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Austr
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Eng
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.addr.2011.11.010
e history:
ved 6 August 2011
pted 21 November 2011
able online 28 November 2011
ords:
d–brain barrier
delivery
ptor-mediated transport
mediated transport
particles
omes
ological conditions
The blood–brain barrier (BBB) is a highly regulated and efficient barrier that provides a sanctuary to the
brain. It is designed to regulate brain homeostasis and to permit selective transport of molecules that are es-
sential for brain function. Unfortunately, drug transport to the brain is hampered by this almost impermeable,
highly selective and well coordinated barrier. With progress in molecular biology, the BBB is better under-
stood, particularly under different pathological conditions. This review will discuss the barrier issue from a
biological and pathological perspective to provide a better insight to the challenges and opportunities asso-
ciated with the BBB. Modern methods which can take advantage of these opportunities will be reviewed.
Applications of nanotechnology in drug transport, receptor-mediated targeting and transport, and finally
cell-mediated drug transport will also be covered in the review. The challenge of delivering an effective ther-
apy to the brain is formidable; solutions will likely involve concerted multidisciplinary approaches that take
into account BBB biology as well as the unique features associated with the pathological condition to be
treated.
Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
tents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
bbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmunodeficiency syndrome; AJ, adherens junction;
adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of paclitaxel; Antp, Antennapedia; APP, amyloid beta
ursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blood–cerebrospinal fluid barrier; BSA-NP, bovine
m albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG-PLA nanoparticles; CED, convection enhanced
sion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central nervous system; CPP, cell penetrating peptide;
cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoimmune encephalomyelitis; EO, ethylene oxide;
ndothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine monophosphate; HB-EGF, heparin binding epider-
growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–hydrophilic balance; HSA, human serum albu-
HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intracerebroventricular; IgG, immunoglobulin G; IL,
eukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein receptor; Lf, lactoferrin; LMV, large multilamellar
les; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic peptide; MAPK, mitogen activated protein kinase;
monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononuclear phagocytes; MRP, multidrug resistant pro-
MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferrin; PAI-1, plasminogen activator inhibitor 1;
CA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycaprolactone; PEG-G-CSF, PEGylated-recombinant
ionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein; PKA, protein kinase A; PKC, protein kinase C;
protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protein tyrosine kinase; Qdots, quantum dots; RAP,
ptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediated transport; R123, rhodamine 123; SA, sialic
residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmission electron microscopy; TER, transendothelial
rical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, vascular endothelial; VEGF, vascular endothelial
th factor; ZO, zonula occludens.
This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous System”.
orresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.: +61 8 9266 2738; fax. +61 89266 2769.
-mail address: y.chen@curtin.edu.au (Y. Chen).
Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering, Curtin University.
-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
0.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain barrier☆
an Chen a,
⁎, Lihong Liu b,1
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Modern methods for delivery of drugs across the blood–brain barrier☆
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr

5. Physical stimuli
* FUS = Focused Ultrasound
Magnetic resonance monitoring of focused
ultrasound/magnetic nanoparticle targeting delivery
of therapeutic agents to the brain
Hao-Li Liua,b,1
, Mu-Yi Huac,1
, Hung-Wei Yangc,1
, Chiung-Yin Huangd
, Po-Chun Chua
, Jia-Shin Wua
, I-Chou Tsengd
,
Jiun-Jie Wange
, Tzu-Chen Yenb,f
, Pin-Yuan Chend,g,2,3
, and Kuo-Chen Weid,2,3
Departments of a
Electrical Engineering, c
Chemical and Material Engineering, and e
Medical Image and Radiological Sciences and g
Graduate Institute of C
Medical Sciences, Chang-Gung University, Taoyuan 333, Taiwan; b
Molecular Imaging Center and f
Department of Nuclear Medicine, Chang-Gung Me
Hospital, Taoyuan 333, Taiwan; and d
Department of Neurosurgery, Chang-Gung University College of Medicine and Memorial Hospital, Taoyuan 333, T
Edited by Ralph Weissleider, Harvard Medical School, Boston, MA, and accepted by the Editorial Board July 13, 2010 (received for review March 16,
The superparamagnetic properties of magnetic nanoparticles
(MNPs) allow them to be guided by an externally positioned magnet
and also provide contrast for MRI. However, their therapeutic use in
treating CNS pathologies in vivo is limited by insufficient local
accumulation and retention resulting from their inability to traverse
biological barriers. The combined use of focused ultrasound and
magnetic targeting synergistically delivers therapeutic MNPs across
the blood–brain barrier to enter the brain both passively and ac-
tively. Therapeutic MNPs were characterized and evaluated both
in vitro and in vivo, and MRI was used to monitor and quantify their
distribution in vivo. The technique could be used in normal brains or
in those with tumors, and significantly increased the deposition of
therapeutic MNPs in brains with intact or compromised blood–brain
barriers. Synergistic targeting and image monitoring are powerful
techniques for the delivery of macromolecular chemotherapeutic
agents into the CNS under the guidance of MRI.
blood–brain barrier | brain drug delivery | focused ultrasound | magnetic
nanoparticles | magnetic targeting
Within the CNS, the blood–brain barrier (BBB) excludes
larger (>400 Da) molecules from entering the brain pa-
renchyma, protecting it from toxic foreign substances (1). How-
ever, it also prohibits delivery of many potentially effective
diagnostic or therapeutic agents and restricts the enhanced per-
meability and retention (EPR) of therapeutic nanoparticles.
Many factors affect EPR, including the pH, polarity, and size of
the delivered substance. Even when pathologic processes com-
promise the integrity or function of the BBB, EPR can be limited
by microenvironmental characteristics such as hypovascularity,
fibrosis, or necrosis (2–4).
In the presence of microbubbles and with use of a low-energy
burst tone, focused ultrasound (FUS) can increase the perme-
ability of the BBB (5). This noninvasive procedure disrupts the
BBB locally rather than systemically, minimizing off-target
effects. Furthermore, the disruption is reversible within several
hours, providing a window of opportunity to achieve local delivery
of chemotherapeutic agents in brains with intact or compromised
BBBs. However, drug delivery in such cases is passive, relying on
the free diffusion of the agents across the barrier.
Advancesinnanotechnologyand molecularbiologyhaveallowed
development of novel nanomedical platforms (6–8). Such
approaches allow simultaneous diagnostic imaging and drug de-
liverymonitoringin vivo inrealtime (9, 10).Magneticnanoparticles
(MNPs) have intrinsic magnetic properties that enable their use as
contrast agents in MRI (8, 11). Because MNPs are also sensitive to
external magnetic forces, magnetic targeting (MT) actively enhan-
ces their deposition at the target site, increasing the therapeutic
dose delivered beyond that obtainable by passive diffusion (12).
This study combines FUS and MT of nanoparticles as a syn-
ergistic delivery system for chemotherapeutic agents concurrent
with MRI monitoring for treating CNS diseases. FUS creates the
opportunity to deliver therapeutic MNPs by passive local
and externally applied magnetic forces actively increase the
MNP concentration. When combined, these techniques p
the delivery of large molecules into the brain (Fig. 1). Fur
more, the deposition of the therapeutic MNPs can be moni
and quantified in vivo by MRI.
Results
Characterization of Therapeutic MNPs. The saturated magn
tion, mean hydrodynamic size, and particle size of the
mercially available MNP Resovist and the newly synthe
MNPs generated for this study are summarized in Table S
measured by transmission EM (TEM), MNP-3 had a mea
ameter of 12.3 nm (Fig. 2A). This was significantly smaller
the hydrodynamic sizes measured by dynamic light scatterin
nm for Resovist, 74–83 nm for MNPs-1–3; Fig. S1A and T
S1), although such differences could be attributable to so
effects. The measured zeta potentials of all of the synthe
MNPs were similar to that of Resovist (approximately 45 m
Magnetization of MNPs is crucial for their utility in MT
crystallinity significantly affects this parameter. During synt
the crystallinity of the MNPs was manipulated by controllin
reaction conditions. MNP-3 exhibited the best crystallinity a
the MNPs tested (Fig. S1C) and also displayed the highest d
of magnetization (Fig. S1B).
Administration of the MNPs into biological tissues profo
alters the spin–spin relaxation rate (R2), and thus can serve
indicator of the MRI contrast agent. The R2, and hence th
tection sensitivity, of MNP-3 was twice that of Resovist by
(Fig. 2 E and F and Table S1).
The polymer poly[aniline-co-N-(1-one-butyric acid)] a
(SPAnH) was used to encapsulate iron oxide (Fe3O4). This
cess decreases the aggregation typical of MNPs and imp
their stability in aqueous solutions. Fourier transform IR (FT
spectroscopy indicated that the surface of the Fe3O4 particle
covered with a layer of the SPAnH polymer, and that the
Author contributions: H.-L.L., M.-Y.H., H.-W.Y., P.-Y.C., and K.-C.W. designed re
H.-L.L., M.-Y.H., H.-W.Y., C.-Y.H., P.-C.C., J.-S.W., I.-C.T., J.-J.W., T.-C.Y., and P.-Y
formed research; H.-L.L., M.-Y.H., and H.-W.Y. contributed new reagents/analyti
H.-L.L., M.-Y.H., H.-W.Y., C.-Y.H., P.-C.C., J.-S.W., I.-C.T., J.-J.W., T.-C.Y., P.-Y.C., and
analyzed data; and H.-L.L., M.-Y.H., H.-W.Y., and K.-C.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. R.W. is a guest editor invited by the E
Board.
Freely available online through the PNAS open access option.
1
H.-L.L., M.-Y.H., and H.-W.Y. contributed equally to this work.
2
P.-Y.C. and K.-C.W. contributed equally to this work.
3
To whom correspondence may be addressed. E-mail: kuochenwei@adm.cgmh.or
pinyuanc@adm.cgmh.org.tw.
This article contains supporting information online at www.pnas.org/lookup/suppl
1073/pnas.1003388107/-/DCSupplemental.
www.pnas.org/cgi/doi/10.1073/pnas.1003388107 PNAS | August 24, 2010 | vol. 107 | no. 34 | 15205
development of novel nanomedical platforms (6–8). Su
approaches allow simultaneous diagnostic imaging and drug d
liverymonitoringin vivo inrealtime (9,10).Magneticnanopartic
(MNPs) have intrinsic magnetic properties that enable their use
contrast agents in MRI (8, 11). Because MNPs are also sensitive
external magnetic forces, magnetic targeting (MT) actively enha
ces their deposition at the target site, increasing the therapeu
dose delivered beyond that obtainable by passive diffusion (12).
This study combines FUS and MT of nanoparticles as a s
ergistic delivery system for chemotherapeutic agents concurre
with MRI monitoring for treating CNS diseases. FUS creates t
www.pnas.org/cgi/doi/10.1073/pnas.1003388107
development of novel nanomedical platforms (6–8). Such
approaches allow simultaneous diagnostic imaging and drug de-
liverymonitoringin vivo inrealtime (9,10).Magneticnanoparticles
(MNPs) have intrinsic magnetic properties that enable their use as
contrast agents in MRI (8, 11). Because MNPs are also sensitive to
external magnetic forces, magnetic targeting (MT) actively enhan-
ces their deposition at the target site, increasing the therapeutic
dose delivered beyond that obtainable by passive diffusion (12).
This study combines FUS and MT of nanoparticles as a syn-
ergistic delivery system for chemotherapeutic agents concurrent
with MRI monitoring for treating CNS diseases. FUS creates the
analyzed data; and H.-L.L., M.-Y.H., H.-W.Y., and K.-C.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. R.W. is a guest editor invited by the Editorial
Board.
Freely available online through the PNAS open access option.
1
H.-L.L., M.-Y.H., and H.-W.Y. contributed equally to this work.
2
P.-Y.C. and K.-C.W. contributed equally to this work.
3
To whom correspondence may be addressed. E-mail: kuochenwei@adm.cgmh.org.tw or
pinyuanc@adm.cgmh.org.tw.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.
1073/pnas.1003388107/-/DCSupplemental.
www.pnas.org/cgi/doi/10.1073/pnas.1003388107 PNAS | August 24, 2010 | vol. 107 | no. 34 | 15205–15210
MEDIC
ultrasound/magneticnanoparticletargetin
oftherapeuticagentstothebrain
Hao-LiLiua,b,1
,Mu-YiHuac,1
,Hung-WeiYangc,1
,Chiung-YinHuangd
,Po-ChunChua
,Jia-Shin
Jiun-JieWange
,Tzu-ChenYenb,f
,Pin-YuanChend,g,2,3
,andKuo-ChenWeid,2,3
Departmentsofa
ElectricalEngineering,c
ChemicalandMaterialEngineering,ande
MedicalImageandRadiologicalScien
MedicalSciences,Chang-GungUniversity,Taoyuan333,Taiwan;b
MolecularImagingCenterandf
DepartmentofNucl
Hospital,Taoyuan333,Taiwan;andd
DepartmentofNeurosurgery,Chang-GungUniversityCollegeofMedicineandMe
EditedbyRalphWeissleider,HarvardMedicalSchool,Boston,MA,andacceptedbytheEditorialBoardJuly13,2010(
Thesuperparamagneticpropertiesofmagneticnanoparticles
(MNPs)allowthemtobeguidedbyanexternallypositionedmagnet
andalsoprovidecontrastforMRI.However,theirtherapeuticusein
treatingCNSpathologiesinvivoislimitedbyinsufficientlocal
accumulationandretentionresultingfromtheirinabilitytotraverse
biologicalbarriers.Thecombineduseoffocusedultrasoundand
magnetictargetingsynergisticallydeliverstherapeuticMNPsacross
theblood–brainbarriertoenterthebrainbothpassivelyandac-
tively.TherapeuticMNPswerecharacterizedandevaluatedboth
invitroandinvivo,andMRIwasusedtomonitorandquantifytheir
distributioninvivo.Thetechniquecouldbeusedinnormalbrainsor
inthosewithtumors,andsignificantlyincreasedthedepositionof
therapeuticMNPsinbrainswithintactorcompromisedblood–brain
barriers.Synergistictargetingandimagemonitoringarepowerful
techniquesforthedeliveryofmacromolecularchemotherapeutic
agentsintotheCNSundertheguidanceofMRI.
blood–brainbarrier|braindrugdelivery|focusedultrasound|magnetic
nanoparticles|magnetictargeting
WithintheCNS,theblood–brainbarrier(BBB)excludes
larger(>400Da)moleculesfromenteringthebrainpa-
renchyma,protectingitfromtoxicforeignsubstances(1).How-
ever,italsoprohibitsdeliveryofmanypotentiallyeffective
diagnosticortherapeuticagentsandrestrictstheenhancedper-
meabilityandretention(EPR)oftherapeuticnanoparticles.
ManyfactorsaffectEPR,includingthepH,polarity,andsizeof
thedeliveredsubstance.Evenwhenpathologicprocessescom-
promisetheintegrityorfunctionoftheBBB,EPRcanbelimited
bymicroenvironmentalcharacteristicssuchashypovascularity,
fibrosis,ornecrosis(2–4).
Inthepresenceofmicrobubblesandwithuseofalow-energy
bursttone,focusedultrasound(FUS)canincreasetheperme-
abilityoftheBBB(5).Thisnoninvasiveproceduredisruptsthe
BBBlocallyratherthansystemically,minimizingoff-target
effects.Furthermore,thedisruptionisreversiblewithinseveral
hours,providingawindowofopportunitytoachievelocaldelivery
ofchemotherapeuticagentsinbrainswithintactorcompromised
BBBs.However,drugdeliveryinsuchcasesispassive,relyingon
thefreediffusionoftheagentsacrossthebarrier.
Advancesinnanotechnologyandmolecularbiologyhaveallowed
developmentofnovelnanomedicalplatforms(6–8).Such
approachesallowsimultaneousdiagnosticimaginganddrugde-
liverymonitoringinvivoinrealtime(9,10).Magneticnanoparticles
(MNPs)haveintrinsicmagneticpropertiesthatenabletheiruseas
contrastagentsinMRI(8,11).BecauseMNPsarealsosensitiveto
externalmagneticforces,magnetictargeting(MT)activelyenhan-
cestheirdepositionatthetargetsite,increasingthetherapeutic
dosedeliveredbeyondthatobtainablebypassivediffusion(12).
ThisstudycombinesFUSandMTofnanoparticlesasasyn-
ergisticdeliverysystemforchemotherapeuticagentsconcurrent
withMRImonitoringfortreatingCNSdiseases.FUScreatesthe
opportunitytodelivertherapeut
andexternallyappliedmagneticf
MNPconcentration.Whencom
thedeliveryoflargemoleculesi
more,thedepositionofthethera
andquantifiedinvivobyMRI.
Results
CharacterizationofTherapeuticM
tion,meanhydrodynamicsize,
merciallyavailableMNPResov
MNPsgeneratedforthisstudya
measuredbytransmissionEM(
ameterof12.3nm(Fig.2A).Th
thehydrodynamicsizesmeasured
nmforResovist,74–83nmforM
S1),althoughsuchdifferencesc
effects.Themeasuredzetapote
MNPsweresimilartothatofRe
MagnetizationofMNPsiscru
crystallinitysignificantlyaffectsth
thecrystallinityoftheMNPswas
reactionconditions.MNP-3exhib
theMNPstested(Fig.S1C)anda
ofmagnetization(Fig.S1B).
AdministrationoftheMNPsin
altersthespin–spinrelaxationrat
indicatoroftheMRIcontrastag
tectionsensitivity,ofMNP-3was
(Fig.2EandFandTableS1).
Thepolymerpoly[aniline-co-
(SPAnH)wasusedtoencapsulat
cessdecreasestheaggregation
theirstabilityinaqueoussolution
spectroscopyindicatedthatthesu
coveredwithalayeroftheSPA
Authorcontributions:H.-L.L.,M.-Y.H.,H.-W.
H.-L.L.,M.-Y.H.,H.-W.Y.,C.-Y.H.,P.-C.C.,J.-S
formedresearch;H.-L.L.,M.-Y.H.,andH.-W.Y
H.-L.L.,M.-Y.H.,H.-W.Y.,C.-Y.H.,P.-C.C.,J.-S.W
analyzeddata;andH.-L.L.,M.-Y.H.,H.-W.Y.,
Theauthorsdeclarenoconflictofinterest.
ThisarticleisaPNASDirectSubmission.R.W
Board.
FreelyavailableonlinethroughthePNASop
1
H.-L.L.,M.-Y.H.,andH.-W.Y.contributedeq
2
P.-Y.C.andK.-C.W.contributedequallytoth
3
Towhomcorrespondencemaybeaddressed
pinyuanc@adm.cgmh.org.tw.
Thisarticlecontainssupportinginformationo
1073/pnas.1003388107/-/DCSupplemental.
www.pnas.org/cgi/doi/10.1073/pnas.1003388107PNAS|August24,2010
Electromagnetic field (EMF) Pulse Protein kinase C signalling Translocation of tight junction's
Protein ZO-1
Tight Junction Opening
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Nanoparticles
Liposomes
Pathological conditions
a
in
tr
Contents
1. Introduction . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain
3. Transport routes across the blood–brain ba
4. Biological and pathological properties of BB
4.1. Physical barrier . . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amylo
AMT, adsorptive-mediated transport; AMP, adenosine mo
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine
serum albumin conjugated nanoparticles; cAMP, cyclic AM
diffusion; CHP, hydrophobic cholesterol groups; CMC, crit
CRM, cross reacting material; CSF, cerebrospinal fluid; DT,
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusi
mal growth factor; HIRMAb, human insulin receptor mono
min; HSP-96, heat shock protein 96; HUVEC, human um
interleukin; INF, interferon; JAM, junction adhesion mol
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein rece
MCP, monocyte chemotactic protein; MHC, major histoc
tein; MS, multiple sclerosis; NOS, nitric oxide synthes
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(but
methionyl human granulocyted colony stimulating facto
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolid
receptor associated protein; RES, reticuloendothelial sy
acid residue; SBP, sequence signal-based peptide; SUV, sma
electrical resistance; TfR, transferrin receptor; TJ, tight junc
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Rev
⁎ Corresponding author at: School of Pharmacy, Curtin
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctora
0169-409X/$ – see front matter. Crown Copyright © 2011
doi:10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain b
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
a b s t r a c ta r t i c l e i n f o
Article history:
Received 6 August 2011
Accepted 21 November 2011
Available online 28 November 2011
Keywords:
Blood–brain barrier
Drug delivery
Receptor-mediated transport
Cell-mediated transport
Nanoparticles
Liposomes
Pathological conditions
The blood–brain barrier (BBB) is a highly regulated and efficient ba
brain. It is designed to regulate brain homeostasis and to permit selec
sential for brain function. Unfortunately, drug transport to the brain is h
highly selective and well coordinated barrier. With progress in molec
stood, particularly under different pathological conditions. This review
biological and pathological perspective to provide a better insight to t
ciated with the BBB. Modern methods which can take advantage of
Applications of nanotechnology in drug transport, receptor-mediate
cell-mediated drug transport will also be covered in the review. The ch
apy to the brain is formidable; solutions will likely involve concerted
into account BBB biology as well as the unique features associated
treated.
Crown Copyright © 2011 Publish
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . . . .
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmunod
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of paclitax
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blood–
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG-PL
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central ner
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoimm
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine monop
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–hy
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intracere
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein recepto
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic peptid
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononuclear p
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferrin;
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycaprolact
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein; PKA
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protein ty
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediated tr
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmissio
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, vasc
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous System
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.: +
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering, Cu
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain barrier☆
Yan Chen a,
⁎, Lihong Liu b,1
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews 64
Contents lists available at SciVe
Advanced Drug Deliv
journal homepage: www.elsevi
Modern methods for delivery of drugs a
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, S
Advanced Drug Deliver
Contents lists availab
Advanced Drug
journal homepage: ww

6. Transport system-mediated drug delivery
Nanocarriers for brain drug delivery
mdpi.com
• Nontoxic, biodegradable and biocompatible
• Particle size less than 100 nm
• Stable in blood (no aggregation and dissociation)
• Non-immunogenic
• BBB-targeted moiety
• Applicable to carry small molecules, proteins, peptides or nucleic acids
Nano carriers May be Liposomes, Micelles, Polymeric Gels, Amphiphilic Gels
anced Drug Delivery Reviews 64 (2012) 640–665
nts lists available at SciVerse ScienceDirect
nced Drug Delivery Reviews
mepage: www.elsevier.com/locate/addr
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; A
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiope
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under cu
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum a
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, c
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, s
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human imm
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprot
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamell
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, my
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neu
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethy
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, pr
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evapo
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 t
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rig
doi:10.1016/j.addr.2011.11.010
treated.
Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
ntents
. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmunodeficiency syndrome; AJ, adherens junction;
T, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of paclitaxel; Antp, Antennapedia; APP, amyloid beta
ursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blood–cerebrospinal fluid barrier; BSA-NP, bovine
m albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG-PLA nanoparticles; CED, convection enhanced
usion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central nervous system; CPP, cell penetrating peptide;
M, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoimmune encephalomyelitis; EO, ethylene oxide;
endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine monophosphate; HB-EGF, heparin binding epider-
growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–hydrophilic balance; HSA, human serum albu-
; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intracerebroventricular; IgG, immunoglobulin G; IL,
rleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein receptor; Lf, lactoferrin; LMV, large multilamellar
cles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic peptide; MAPK, mitogen activated protein kinase;
P, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononuclear phagocytes; MRP, multidrug resistant pro-
; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferrin; PAI-1, plasminogen activator inhibitor 1;
CA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycaprolactone; PEG-G-CSF, PEGylated-recombinant
hionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein; PKA, protein kinase A; PKC, protein kinase C;
, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protein tyrosine kinase; Qdots, quantum dots; RAP,
ptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediated transport; R123, rhodamine 123; SA, sialic
residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmission electron microscopy; TER, transendothelial
trical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, vascular endothelial; VEGF, vascular endothelial
wth factor; ZO, zonula occludens.
This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous System”.
Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.: +61 8 9266 2738; fax. +61 89266 2769.
E-mail address: y.chen@curtin.edu.au (Y. Chen).
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering, Curtin University.
9-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain barrier☆
an Chen a,
⁎, Lihong Liu b,1
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Modern methods for delivery of drugs across the blood–brain b
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr

7. Transport vectors
Drugs
Molecular structure mimicking the endogenous nutrients
Prodrugs
BBB
Drugs
dvanced Drug Delivery Reviews 64 (2012) 640–665
ents lists available at SciVerse ScienceDirect
nced Drug Delivery Reviews
omepage: www.elsevier.com/locate/addr
Crown Copyright © 2011 Published by Else
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmunodeficiency sy
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of paclitaxel; Antp, A
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blood–cerebrospi
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG-PLA nanopart
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central nervous system
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoimmune enceph
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine monophosphate; H
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–hydrophilic ba
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intracerebroventricu
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein receptor; Lf, lactof
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic peptide; MAPK, m
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononuclear phagocytes
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferrin; PAI-1, plas
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycaprolactone; PEG-
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein; PKA, protein k
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protein tyrosine kin
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediated transport; R
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmission electron m
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, vascular endoth
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous System”.
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.: +61 8 9266 2
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering, Curtin Univer
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.addr.2011.11.010
an Chen a,
⁎, Lihong Liu b,1
chool of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
nstitute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
a b s t r a c tr t i c l e i n f o
icle history:
ceived 6 August 2011
cepted 21 November 2011
ailable online 28 November 2011
ywords:
ood–brain barrier
ug delivery
ceptor-mediated transport
ll-mediated transport
noparticles
osomes
thological conditions
The blood–brain barrier (BBB) is a highly regulated and efficient barrier that provides a sanctuary to the
brain. It is designed to regulate brain homeostasis and to permit selective transport of molecules that are es-
sential for brain function. Unfortunately, drug transport to the brain is hampered by this almost impermeable,
highly selective and well coordinated barrier. With progress in molecular biology, the BBB is better under-
stood, particularly under different pathological conditions. This review will discuss the barrier issue from a
biological and pathological perspective to provide a better insight to the challenges and opportunities asso-
ciated with the BBB. Modern methods which can take advantage of these opportunities will be reviewed.
Applications of nanotechnology in drug transport, receptor-mediated targeting and transport, and finally
cell-mediated drug transport will also be covered in the review. The challenge of delivering an effective ther-
apy to the brain is formidable; solutions will likely involve concerted multidisciplinary approaches that take
into account BBB biology as well as the unique features associated with the pathological condition to be
treated.
Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
ntents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmunodeficiency syndrome; AJ, adherens junction;
MT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of paclitaxel; Antp, Antennapedia; APP, amyloid beta
ecursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blood–cerebrospinal fluid barrier; BSA-NP, bovine
um albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG-PLA nanoparticles; CED, convection enhanced
fusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central nervous system; CPP, cell penetrating peptide;
M, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoimmune encephalomyelitis; EO, ethylene oxide;
endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine monophosphate; HB-EGF, heparin binding epider-
al growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–hydrophilic balance; HSA, human serum albu-
n; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intracerebroventricular; IgG, immunoglobulin G; IL,
erleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein receptor; Lf, lactoferrin; LMV, large multilamellar
sicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic peptide; MAPK, mitogen activated protein kinase;
CP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononuclear phagocytes; MRP, multidrug resistant pro-
n; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferrin; PAI-1, plasminogen activator inhibitor 1;
DCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycaprolactone; PEG-G-CSF, PEGylated-recombinant
ethionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein; PKA, protein kinase A; PKC, protein kinase C;
G, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protein tyrosine kinase; Qdots, quantum dots; RAP,
ceptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediated transport; R123, rhodamine 123; SA, sialic
d residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmission electron microscopy; TER, transendothelial
ctrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, vascular endothelial; VEGF, vascular endothelial
owth factor; ZO, zonula occludens.
This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous System”.
Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.: +61 8 9266 2738; fax. +61 89266 2769.
E-mail address: y.chen@curtin.edu.au (Y. Chen).
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering, Curtin University.
69-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
i:10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain barrier☆
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Modern methods for delivery of drugs across the blood–brain barrier☆
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Dopamine
Levodopa
Dopaminelevodopa
Decarboxylase
CNS
Type 1 l-type
Amino-acid transporter
Levodopa contains the carboxyl and α-amino groups

8. Adsorptive-mediated transcytosis
journals.cambridge.org/
Cell-penetrating peptides (CPPs)
The application of CPPs is based on the prem
active cargo can be attached to CPPs and translo
link between the CPPs and cargo is most comm
and seldom in non-covalent bond. A large va
cules/materials have been effectively delivered i
cluding small molecules, proteins, peptides,
liposomes and nanoparticles [204]. Some can ent
dothelia cells or are even translocated into the br
amples are highlighted here.
Table 3
Principle features of the selected cell penetrating peptides (
Peptide name Sequence
MAP KLALKLALKALKAALKLA
pAntp43–68 RQIKIWFQNRRMKWKK
Transportan GWTLNSAGYLLGKINLKALAALAKKIL
SBP MGLGLHLLVLAAALQGAWSQPKKKRKV
FBP GALFLGWLGAAGSTMGAWSQPKKKRKV
TAT48–60 GRKKRRQRRRPPQ
SynB1 RGGRLSYSRRRFSTSTGR
SynB3 RRLSYSRRRF
MAP: model amphipathic peptide; Antp: Antennapedia; SB
peptide; FBP, fusion sequence-based peptide; TAT, HIV-1 tra
The peptide residues in this table are expressed with one-
leucine; A—alanine; R—arginines; Q—glutamine; I—isoleu
phenylalanine; N—asparagine; M—methionine; G—glycines; S
was collected from references [204,206,221,222,312–314].
654 Y. Ch
The major dogma has
been that CPPs enter cells
by a receptor and energy-
independent process but
the exact mechanisms are
not yet fully understood
SynB1, SynB1
TAT derived CPPs Lipid raft-mediated macropinocytosis
Endosomal transport
All are having Net Positive Charge but Internalization differed in each case.

9. Endogenous receptor-mediated transcytosis
Receptor-ligand binding
Endocytosis at the luminal (blood) side
Movement through the endothelia cytoplasm
Exocytosis of the drug or ligand-attached
drug or cargo at the abluminal (brain) side
mdpi.com
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Contents
1. Introduction . . . . . . . . . . . . .
2. Physiology and biology of the blood–brai
3. Transport routes across the blood–brain b
4. Biological and pathological properties of B
4.1. Physical barrier . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amy
AMT, adsorptive-mediated transport; AMP, adenosine m
precursor protein; ApoE, Apolipoprotein E; ATP, adenosi
serum albumin conjugated nanoparticles; cAMP, cyclic
diffusion; CHP, hydrophobic cholesterol groups; CMC, c
CRM, cross reacting material; CSF, cerebrospinal fluid; D
EC, endothelial cell; EMF, electromagnetic fields; FBP, fu
mal growth factor; HIRMAb, human insulin receptor mo
min; HSP-96, heat shock protein 96; HUVEC, human u
interleukin; INF, interferon; JAM, junction adhesion m
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein re
MCP, monocyte chemotactic protein; MHC, major hist
tein; MS, multiple sclerosis; NOS, nitric oxide synth
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(b
methionyl human granulocyted colony stimulating fa
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glyco
receptor associated protein; RES, reticuloendothelial
acid residue; SBP, sequence signal-based peptide; SUV, sm
electrical resistance; TfR, transferrin receptor; TJ, tight ju
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery R
⁎ Corresponding author at: School of Pharmacy, Curt
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdocto
0169-409X/$ – see front matter. Crown Copyright © 20
doi:10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
a b s t r a c ta r t i c l e i n f o
Article history:
Received 6 August 2011
Accepted 21 November 2011
Available online 28 November 2011
Keywords:
Blood–brain barrier
Drug delivery
Receptor-mediated transport
Cell-mediated transport
Nanoparticles
Liposomes
Pathological conditions
The blood–brain barrier (BBB) is a highly regulated and efficient
brain. It is designed to regulate brain homeostasis and to permit se
sential for brain function. Unfortunately, drug transport to the brain
highly selective and well coordinated barrier. With progress in m
stood, particularly under different pathological conditions. This re
biological and pathological perspective to provide a better insight
ciated with the BBB. Modern methods which can take advantage
Applications of nanotechnology in drug transport, receptor-medi
cell-mediated drug transport will also be covered in the review. Th
apy to the brain is formidable; solutions will likely involve concert
into account BBB biology as well as the unique features associat
treated.
Crown Copyright © 2011 Pub
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . .
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmu
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of pac
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blo
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoim
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine mo
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intrac
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein rece
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic pep
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononucle
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferr
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycapro
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein;
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, prote
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediate
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmi
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE,
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous Sys
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain barrier☆
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews
Contents lists available at Sci
Advanced Drug Del
journal homepage: www.else
Modern methods for delivery of drugs
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Weste
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 13866
Advanced Drug Del
Contents lists avai
Advanced Dru
journal homepage: w

10. -
f
-
-
h
-
.
tyrosine. An alternative pathway is surface deiodination of the
intact peptide, possibly by ectoenzymes on the endothelial sur-
face of organ capillary beds. Evidence for this pathway is the
observation that the systemic clearance (C1, Table I) for the
125
I-bio-Ab1–40
/OX26-SA conjugate, 2.6 ml/min/kg, is approxi-
mately fourfold greater than the systemic clearance of the un-
conjugated 125
I-83-14 mAb in rhesus monkeys, 0.39–1.00 ml/
Figure 11. Scheme depicting the multifunctionality and three do-
mains of the peptide radiopharmaceutical conjugated to the BBB de-
livery system. The imaging agent is comprised of amyloid-binding do-
main, a linker domain, and a BBB transport domain, the last
constituted by the mAb to the HIR. The HIR is localized in human
brain capillary endothelium (reference 21), which forms the BBB in
vivo.
DrugTargeting of a Peptide Radiopharmaceutical through the Prima
Barrier In Vivo with a Monoclonal Antibody to the Human Insulin Re
Dafang Wu, Jing Yang, and William M. Pardridge
Department of Medicine, UCLA School of Medicine, Los Angeles, California 90095-1682
Abstract
Peptide radiopharmaceuticals are potential imaging agents
for brain disorders, should these agents be enabled to un-
dergo transport through the blood–brain barrier (BBB) in
vivo. Radiolabeled Ab1–40
images brain amyloid in tissue
sections of Alzheimer’s disease autopsy brain, but this pep-
tide radiopharmaceutical cannot be used to image brain
amyloid in vivo owing to negligible transport through the
BBB. In these studies, 125
I-Ab1–40
was monobiotinylated
(bio) and conjugated to a BBB drug delivery and brain tar-
geting system comprised of a complex of the 83-14 mono-
clonal antibody (mAb) to the human insulin receptor, which
is tagged with streptavidin (SA). A marked increase in
rhesus monkey brain uptake of the 125
I-bio-Ab1–40
was ob-
served after conjugation to the 8314-SA delivery system at
3 h after intravenous injection. In contrast, no measurable
brain uptake of 125
I-bio-Ab1–40
was observed in the absence
of a BBB drug delivery system. The peptide radiopharma-
ceutical was degraded in brain with export of the iodide ra-
dioactivity, and by 48 h after intravenous injection, 90% of
the radioactivity was cleared from the brain. In conclusion,
these studies describe a methodology for BBB drug delivery
and brain targeting of peptide radiopharmaceuticals that
could be used for imaging amyloid or other brain disorders.
(J. Clin. Invest. 1997. 100:1804–1812.) Key words: Alzhei-
mer’s disease • amyloid • monoclonal antibody • insulin re-
ceptor • avidin
Introduction
Peptide radiopharmaceuticals have potential for diagnostic im-
aging (1). The somatostatin receptor is overexpressed in cer-
tain neuroendocrine tumors, as well as brain tumors such as
meningiomas or gliomas, and 125
I- or 111
In-labeled octreotide, a
somatostatin peptide analog, has been used to image these tu-
mors (2, 3). Owing to the small size of the peptide radiophar-
maceutical, octreotide readily crosses the porous capillaries
perfusing tumors in the periphery, or certain brain tumors such
as meningiomas, which lack a bloo
However, well-differentiated gliomas
somatostatin receptors, have an intac
to image these tumors with octreotide
does not cross the BBB in vivo (5).
In addition to tumors, it should a
other medical disorders with peptid
such as amyloid. The deposition of
heimer’s disease correlates with the d
disorder (6, 7). Extracellular amyloid
comprised of two types: senile (neur
amyloid (8–12). Both types of amyloi
are comprised of a 43–amino acid am
nated Ab1–43
. There are as well Ab1–
the abnormal proteolysis of a normal
loid peptide precursor (13).
The Ab amyloid of tissue section
autopsy brain can be identified with
or with antibodies directed against
Ab1–42/43
peptide (14). However, the A
tions may also be identified in vitro
125
I-Ab1–40
, a peptide containing the f
Ab1–42/43
peptide that deposits with hi
ing Ab amyloid (15). Therefore, rad
tential peptide radiopharmaceutical
neurodiagnostic quantitation of the
Alzheimer’s disease brain of living su
ternal detection methodologies, such
computed tomography or positron
However, 125
I-Ab1–40
does not cross
vector-mediated BBB drug delivery
amyloid does not deposit in the brai
form in the brain of New World pri
(15–20 yr) squirrel monkey, as vascu
duced in the brain of Old World pr
(27–30 yr) rhesus monkey, in neuritic
These studies use 125
I-Ab1–40
adap
ery system that enables the peptide
blood to a high degree, allowing for im
of the peptide radiopharmaceutical in
(intravenous, i.v.) injection. The goa
fold: first, to prepare radiolabeled pep
jugated to the BBB delivery system;
that the deposition of 125
I-Ab1–40
on
Address correspondence to William M. Pardridge, M.D., Department
of Medicine, UCLA School of Medicine, Los Angeles, CA 90095-
1682. Phone: 310-825-8858; FAX: 310-206-5163; E-mail: wpardrid@
11/17/2015 Drug targeting of a peptide radiopharmaceutical through the primate blood-brain barrier in vivo with a monoclonal antibody to the human ins
J Clin Invest. 1997 Oct 1; 100(7): 1804–1812.
doi: 10.1172/JCI119708
PMCID: PMC508366
Drug targeting of a peptide radiopharmaceutical through the primate blood­brain
barrier in vivo with a monoclonal antibody to the human insulin receptor.
D Wu, J Yang, and W M Pardridge
Department of Medicine, UCLA School of Medicine, Los Angeles, California 90095­1682, USA.
Copyright notice
This article has been cited by other articles in PMC.
Abstract
Peptide radiopharmaceuticals are potential imaging agents for brain disorders, should these agents be enabled to
undergo transport through the blood­brain barrier (BBB) in vivo. Radiolabeled Abeta1­40 images brain amyloid
in tissue sections of Alzheimer's disease autopsy brain, but this peptide radiopharmaceutical cannot be used to
image brain amyloid in vivo owing to negligible transport through the BBB. In these studies, 125I­Abeta1­40
was monobiotinylated (bio) and conjugated to a BBB drug delivery and brain targeting system comprised of a
complex of the 83­14 monoclonal antibody (mAb) to the human insulin receptor, which is tagged with
streptavidin (SA). A marked increase in rhesus monkey brain uptake of the 125I­bio­Abeta1­40 was observed
after conjugation to the 8314­SA delivery system at 3 h after intravenous injection. In contrast, no measurable
brain uptake of 125I­bio­Abeta1­40 was observed in the absence of a BBB drug delivery system. The peptide
radiopharmaceutical was degraded in brain with export of the iodide radioactivity, and by 48 h after intravenous
injection, 90% of the radioactivity was cleared from the brain. In conclusion, these studies describe a
methodology for BBB drug delivery and brain targeting of peptide radiopharmaceuticals that could be used for
imaging amyloid or other brain disorders.
Full Text
The Full Text of this article is available as a PDF (354K).
Insulin receptor
Amyloid-β- peptide 125I-Abeta1–40
conjugated to 83–14 monoclonal antibody (mAb)
Insulin receptor
Diagnostic probe for ADReceptor mediated Endocytosis
11/17/2015 Drug targeting of a peptide radiopharmaceutical through the primate blood-brain barrier in vivo with a monoclonal antibody to the human in
J Clin Invest. 1997 Oct 1; 100(7): 1804–1812.
doi: 10.1172/JCI119708
PMCID: PMC508366
Drug targeting of a peptide radiopharmaceutical through the primate blood­brain
barrier in vivo with a monoclonal antibody to the human insulin receptor.
D Wu, J Yang, and W M Pardridge
Department of Medicine, UCLA School of Medicine, Los Angeles, California 90095­1682, USA.
Copyright notice
This article has been cited by other articles in PMC.
Abstract
Peptide radiopharmaceuticals are potential imaging agents for brain disorders, should these agents be enabled t
undergo transport through the blood­brain barrier (BBB) in vivo. Radiolabeled Abeta1­40 images brain amyloi
in tissue sections of Alzheimer's disease autopsy brain, but this peptide radiopharmaceutical cannot be used to
image brain amyloid in vivo owing to negligible transport through the BBB. In these studies, 125I­Abeta1­40
was monobiotinylated (bio) and conjugated to a BBB drug delivery and brain targeting system comprised of a
complex of the 83­14 monoclonal antibody (mAb) to the human insulin receptor, which is tagged with
streptavidin (SA). A marked increase in rhesus monkey brain uptake of the 125I­bio­Abeta1­40 was observed
after conjugation to the 8314­SA delivery system at 3 h after intravenous injection. In contrast, no measurable
brain uptake of 125I­bio­Abeta1­40 was observed in the absence of a BBB drug delivery system. The peptide
radiopharmaceutical was degraded in brain with export of the iodide radioactivity, and by 48 h after intravenou
injection, 90% of the radioactivity was cleared from the brain. In conclusion, these studies describe a
methodology for BBB drug delivery and brain targeting of peptide radiopharmaceuticals that could be used for
imaging amyloid or other brain disorders.
Full Text
The Full Text of this article is available as a PDF (354K).
Low-density lipoprotein receptor related proteins 1 and 2 (LRP1 and LRP2 receptors)
ApoE (Apolipoprotein E)
Tissue plasminogen activator (tPA)
Plasminogen activator inhibitor 1(PAI-1)
Amyloid precursor protein (APP)
Lactoferrin
Melanotransferrin
α2 macroglobulin (α2 M)
Receptor associated protein (RAP)
HIV-1 TAT protein
Heparin cofactor II
Heat shock protein 96 (HSP-96)
Engineered angiopeps
Binds to
Specific LRP1 and LRP2 receptors in BBB Receptor-mediated transcytosis

11. Diphtheria toxin receptor (DTR)
Transferrin receptor
Expert Review
Blood–Brain Barrier Transport of Therapeutics
Angela R. Jones1
and Eric V. Shusta1,2
Received March 29, 2007; accepted May 3, 2007; published online
Abstract. Drug delivery to the brain is hindered by the presen
Although the BBB restricts the passage of many substances, i
nutrients necessary for healthy brain function. To accomplish th
endothelium is endowed with a diverse collection of molecular
transport system, known as a receptor-mediated transcytosis (RM
machinery of the endothelium to transport substrates betwee
targeted, RMT systems can also be used to shuttle a wide rang
noninvasive manner. Over the last decade, there have been sign
RMT-based brain drug transport, and this review will focus o
validated in an in vivo setting.
KEY WORDS: antibody; blood–brain barrier; brain drug deliver
INTRODUCTION
The blood–brain barrier (BBB) provides the brain with
nutrients, prevents the introduction of harmful blood-borne
substances, and restricts the movement of ions and fluid to
ensure an optimal environment for brain function. As a
consequen
the movem
therefore
neurothera
soluble wit
penetratio
systems m
export the
many sma
pharmaceu
penetrate
Thus, alth
Pharmaceutical Research, Vol. 24, No. 9, September 2007 (# 2007)
DOI: 10.1007/s11095-007-9379-0
1
Department of Chemical and Biological Engineering, University of
Wisconsin-Madison, 1415 Engineering Drive, Madison, Wisconsin
53706, USA.
2
To whom correspondence should be addressed.(e-mail:shusta@
engr.wisc.edu)
Ex
Blood–Brain Barrier Transport of T
Angela R. Jones1
and Eric V. Shusta1,2
Received March 29, 2007; accepted May 3,
Abstract. Drug delivery to the brain is hi
Although the BBB restricts the passage o
nutrients necessary for healthy brain funct
endothelium is endowed with a diverse co
transport system, known as a receptor-med
machinery of the endothelium to transp
targeted, RMT systems can also be used
noninvasive manner. Over the last decade
RMT-based brain drug transport, and th
validated in an in vivo setting.
KEY WORDS: antibody; blood–brain barr
INTRODUCTION
The blood–brain barrier (BBB) provides the brai
nutrients, prevents the introduction of harmful blood-
substances, and restricts the movement of ions and fl
ensure an optimal environment for brain function.
1
Department of Chemical and Biological Engineering, Unive
Wisconsin-Madison, 1415 Engineering Drive, Madison, Wi
53706, USA.
2
To whom correspondence should be addressed.(e-mail:s
* Here TfR is BBB specific
CNS diseases such as AD,
Parkinson's disease,
multiple sclerosis(MS),
ischemia, encephalitis,
epilepsy, tumour and
lysosomal storage disease
Inflammation In BBB Upregulation of DTR
Diphtheria toxin
Mutated
Cross reacting material (CRM 197)
TargetAdvanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Accepted 21 November 2011
Available online 28 November 2011
Keywords:
Blood–brain barrier
Drug delivery
Receptor-mediated transport
Cell-mediated transport
Nanoparticles
Liposomes
Pathological conditions
Contents
1. Introduction . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain
3. Transport routes across the blood–brain b
4. Biological and pathological properties of B
4.1. Physical barrier . . . . . . . .
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amy
AMT, adsorptive-mediated transport; AMP, adenosine m
precursor protein; ApoE, Apolipoprotein E; ATP, adenosi
serum albumin conjugated nanoparticles; cAMP, cyclic
diffusion; CHP, hydrophobic cholesterol groups; CMC, c
CRM, cross reacting material; CSF, cerebrospinal fluid; D
EC, endothelial cell; EMF, electromagnetic fields; FBP, fu
mal growth factor; HIRMAb, human insulin receptor mo
min; HSP-96, heat shock protein 96; HUVEC, human u
interleukin; INF, interferon; JAM, junction adhesion m
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein rec
MCP, monocyte chemotactic protein; MHC, major hist
tein; MS, multiple sclerosis; NOS, nitric oxide synth
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(b
methionyl human granulocyted colony stimulating fa
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glyco
receptor associated protein; RES, reticuloendothelial
acid residue; SBP, sequence signal-based peptide; SUV, sm
electrical resistance; TfR, transferrin receptor; TJ, tight ju
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery R
⁎ Corresponding author at: School of Pharmacy, Curt
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdocto
0169-409X/$ – see front matter. Crown Copyright © 20
doi:10.1016/j.addr.2011.11.010
Modern methods for delivery of drugs across the blood–brain
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Singapore
a b s t r a c ta r t i c l e i n f o
Article history:
Received 6 August 2011
Accepted 21 November 2011
Available online 28 November 2011
Keywords:
Blood–brain barrier
Drug delivery
Receptor-mediated transport
Cell-mediated transport
Nanoparticles
Liposomes
Pathological conditions
The blood–brain barrier (BBB) is a highly regulated and efficient
brain. It is designed to regulate brain homeostasis and to permit se
sential for brain function. Unfortunately, drug transport to the brain
highly selective and well coordinated barrier. With progress in mo
stood, particularly under different pathological conditions. This re
biological and pathological perspective to provide a better insight
ciated with the BBB. Modern methods which can take advantage
Applications of nanotechnology in drug transport, receptor-medi
cell-mediated drug transport will also be covered in the review. The
apy to the brain is formidable; solutions will likely involve concert
into account BBB biology as well as the unique features associat
treated.
Crown Copyright © 2011 Pub
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Physiology and biology of the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Transport routes across the blood–brain barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Biological and pathological properties of BBB for drug transport . . . . . . . . . . . . . . . . . . . . .
4.1. Physical barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Advanced Drug Delivery Reviews 64 (2012) 640–665
Abbreviations: a2M, alpha-2 macroglobulin; Aβ, amyloid β; ABC, ATP binding cassette; AD, Alzheimer's disease; AIDS, autoimmu
AMT, adsorptive-mediated transport; AMP, adenosine monophosphate; ANG1005, angiopep 2 conjugated with 3 molecules of pacl
precursor protein; ApoE, Apolipoprotein E; ATP, adenosine triphosphate; AUC, area under curve; BBB, blood–brain barrier; BCSFB, blo
serum albumin conjugated nanoparticles; cAMP, cyclic AMP; CBSA, cationic bovine serum albumin; CBSA-NP, CBSA conjugated PEG
diffusion; CHP, hydrophobic cholesterol groups; CMC, critical micelle concentration; CMT, carrier-mediated transport; CNS, central
CRM, cross reacting material; CSF, cerebrospinal fluid; DT, diphtheria toxin; DTR, diphtheria toxin receptor; EAE, experimental autoim
EC, endothelial cell; EMF, electromagnetic fields; FBP, fusion sequence-based peptide; g7, similopioid peptide; GMP, guanosine mon
mal growth factor; HIRMAb, human insulin receptor monoclonal antibody; HIV, human immunodeficiency virus; HLB, hydrophobic–
min; HSP-96, heat shock protein 96; HUVEC, human umbilical vein endothelial cells; ICH, intercerebral haemorrhage; ICV, intrac
interleukin; INF, interferon; JAM, junction adhesion molecules; LDL, low density lipoprotein; LDLR, low density lipoprotein rece
vesicles; LPA, lysophosphatidic acid; LRP, lipoprotein receptor protein; LUV, large unilamellar vesicles; MAP, model amphipathic pep
MCP, monocyte chemotactic protein; MHC, major histocompatibility complex; MLCK, myosin light chain kinase; MP, mononucle
tein; MS, multiple sclerosis; NOS, nitric oxide syntheses; NP, nanoparticles; NVU, neurovascular unit; P97, melanotransferri
PHDCA, poly(hexadecylcyanoacrylate); PBCA, poly(butylcyanoacrylate); PEG, polyethylene glycol; PEG-PCL, PEG-polycapro
methionyl human granulocyted colony stimulating factor; PEG-PLA, polyethylene glycol-polylactic acid; P-gp, P-glycoprotein;
PKG, protein kinase G; PLGA, poly(D,L-lactide-co-glycolide); PO, propylene oxide; PTD, protein transduction domain; PTK, protei
receptor associated protein; RES, reticuloendothelial system; REV, reverse phase evaporation vesicles; RMT, receptor-mediate
acid residue; SBP, sequence signal-based peptide; SUV, small unilamellar vesicles; TAT, HIV-1 trans-activating transcriptor; TEM, transmi
electrical resistance; TfR, transferrin receptor; TJ, tight junction; TNF, tumour necrosis factors; tPA, tissue plasminogen activator; VE, v
growth factor; ZO, zonula occludens.
☆ This review is part of the Advanced Drug Delivery Reviews theme issue on “Delivery of Therapeutics to the Central Nervous Syst
⁎ Corresponding author at: School of Pharmacy, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. Tel.
E-mail address: y.chen@curtin.edu.au (Y. Chen).
1
L Liu is currently funded as an Australian Postdoctoral Fellow by ARC Discovery Project DP110104599 at Chemical Engineering
0169-409X/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.addr.2011.11.010
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Modern methods for delivery of drugs across the blood–brain barrier☆
Yan Chen a,
⁎, Lihong Liu b,1
Advanced Drug Delivery Reviews 64 (2012) 640–665
Contents lists available at SciVerse ScienceDirect
Advanced Drug Delivery Reviews
journal homepage: www.elsevier.com/locate/addr
Advanced Drug Delivery Reviews
Contents lists available at SciV
Advanced Drug Deli
journal homepage: www.else
Modern methods for delivery of drugs
Yan Chen a,
⁎, Lihong Liu b,1
a
School of Pharmacy, CHIRI, WABRI, Curtin University, GPO Box U1987, Perth, Weste
b
Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 13866
Advanced Drug Del
Contents lists avai
Advanced Dru
journal homepage: w

12. Inhibition of efflux Pumps
11/17/2015 PubMed Central, FIG. 1.: NeuroRx. 2005 Jan; 2(1): 86–98. doi: 10.1602/neurorx.2.1.86
<< Prev FIG. 1PMC full text: NeuroRx. 2005 Jan; 2(1): 86–98.
doi: 10.1602/neurorx.2.1.86
Copyright/License ► Request permission to reuse
FIG. 1.
Localization of selected drug efflux proteins on brain capillary endothelial cells that form the bloo
barrier. Only transporters that are localized on the apical (luminal) side of the brain capillary endot
would be in a position to restrict brain uptake of xenobiotics. Note that the exact localization in en
cells has not been demonstrated as yet for all transporters shown in the figure, but for some of the
transporters the localization (apical vs basolateral) was derived from studies on polarized epithelia
lines.6
Blood-Brain Barrier Active Efflux Transporters: ATP-B
Cassette Gene Family
Wolfgang Lo¨scher and Heidrun Potschka
Department of Pharmacology, Toxicology, and Pharmacy, University of Veterinary Medicine Hanno
Hannover D-30559, Germany
Summary: The blood-brain barrier (BBB) contributes to brain
homeostasis by protecting the brain from potentially harmful
endogenous and exogenous substances. BBB active drug efflux
transporters of the ATP-binding cassette (ABC) gene family
are increasingly recognized as important determinants of drug
distribution to, and elimination from, the CNS. The ABC efflux
transporter P-glycoprotein (Pgp) has been demonstrated as a
key element of the BBB that can actively transport a huge
variety of lipophilic drugs out of the brain capillary endothelial
cells that form the BBB. In addition to Pgp, other ABC efflux
transporters such as members of the multidrug resistance pro-
tein (MRP) family and breast cancer resistance protein (BCRP)
seem to contribute to BBB function. Consequences of ABC
efflux transporters in the BBB include minimi
neurotoxic adverse effects of drugs that other
etrate into the brain. However, ABC efflux t
also limit the central distribution of drugs that
treat CNS diseases. Furthermore, neurologica
as epilepsy may be associated with overexp
efflux transporters at the BBB, resulting in pha
to therapeutic medication. Therefore, modula
flux transporters at the BBB forms a novel str
the penetration of drugs into the brain and
therapeutic options for drug-resistant CNS
Words: P-glycoprotein, multidrug resistanc
lepsy, antiepileptic drugs, depression, AIDS.
INTRODUCTION
ATP-binding cassette (ABC) transporters are multido-
main integral membrane proteins that use the energy of
ATP hydrolysis to translocate solutes across cellular
membranes in all mammalian species.1
ABC transporters
form one of the largest of all protein families and are
central to many important biomedical phenomena, in-
cluding resistance of cancers and pathogenic microbes to
drugs.2
Elucidation of the structure and function of ABC
transporters is essential to the rational design of agents to
control their function.
ABC transporters are increasingly recognized to be
important for drug disposition and response.3–7
P-glyco-
protein (Pgp), the encoded product of the human multi-
drug resistance (MDR1) (ABCB1) gene, is of particular
clinical relevance in that this transporter has a broad
pression of this efflux transporter in certa
partments such as the gastrointestinal t
capillary endothelial cells limits oral absor
entry of many drugs.7
The use of Pgp-e
lines, the generation of Pgp knockout m
studies using Pgp inhibitors in animals, c
better understanding on the role of active
cesses for drug disposition.8
In addition to
transporters of the multidrug resistance
ABCC) family and the breast cancer res
(BCRP; ABCG2) have a role in drug disp
family of mammalian ABC transporters,
more extensive, and functionally highly d
review, we limit ourselves to the followi
porters: Pgp, MRPs 1-6, and BCRP, i.e., A
ers that are expressed at the blood-brain
and, particularly Pgp, are involved in th
Advanced Drug Delivery Reviews 55 (2003) 151–164
www.elsevier.com/loc

Pluronic block copolymers as modulators of drug effl
transporter activity in the blood–brain barrier
*Alexander V. Kabanov , Elena V. Batrakova, Donald W. Miller
Department of Pharmaceutical Sciences, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omah
USA
Received 6 July 2002; accepted 11 August 2002
Advanced Drug Delivery Reviews 55 (2003) 151–164
www.elsevier.com/locate/drugdeliv

Pluronic block copolymers as modulators of drug efflux
transporter activity in the blood–brain barrier
*Alexander V. Kabanov , Elena V. Batrakova, Donald W. Miller
Department of Pharmaceutical Sciences, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omaha, NE 68198,
USA
Received 6 July 2002; accepted 11 August 2002
Abstract
Drug efflux transporters can influence the absorption, tissue distribution and elimination of many therapeutic agents.
Modulation of drug efflux transporter activity is being explored as a means for improving the pharmacokinetic and
pharmacodynamic properties of various drugs. In this regard, several polymer formulations have been shown to inhibit drug

efflux transporters such as P-glycoprotein (P-gp). The current review will focus on Pluronic block copolymers in particular,

the mechanisms involved in the effects of Pluronic on drug efflux transporters, and the optimal polymer compositions

required for inhibition of drug efflux transporters. Special emphasis will be placed on the potential applications of Pluronic
Advanced Drug Delivery Reviews 55 (2003) 151–164
www.elsevier.com/locate/drugdeliv

Pluronic block copolymers as modulators of drug efflux
transporter activity in the blood–brain barrier
*Alexander V. Kabanov , Elena V. Batrakova, Donald W. Miller
Department of Pharmaceutical Sciences, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omaha, NE 68198,
USA
Received 6 July 2002; accepted 11 August 2002
Abstract
Drug efflux transporters can influence the absorption, tissue distribution and elimination of many therapeutic agents.
Modulation of drug efflux transporter activity is being explored as a means for improving the pharmacokinetic and
pharmacodynamic properties of various drugs. In this regard, several polymer formulations have been shown to inhibit drug

efflux transporters such as P-glycoprotein (P-gp). The current review will focus on Pluronic block copolymers in particular,

the mechanisms involved in the effects of Pluronic on drug efflux transporters, and the optimal polymer compositions

required for inhibition of drug efflux transporters. Special emphasis will be placed on the potential applications of Pluronic
in enhancing the blood–brain barrier (BBB) penetration of drugs.
 2002 Elsevier Science B.V. All rights reserved.
Keywords: Blood–brain barrier; Multidrug resistance (MDR); P-glycoprotein; Multidrug resistant protein (MRP); Block copolymer
Advanced Drug Delivery Reviews 55 (2003) 151–164
www.elsevier.com/locate/drugdeliv

Pluronic block copolymers as modulators of drug efflux
transporter activity in the blood–brain barrier
*Alexander V. Kabanov , Elena V. Batrakova, Donald W. Miller
Department of Pharmaceutical Sciences, University of Nebraska Medical Center, 986025 Nebraska Medical Center, Omaha, NE 68198,
USA
Received 6 July 2002; accepted 11 August 2002
Abstract
Drug efflux transporters can influence the absorption, tissue distribution and elimination of many therapeutic agents.
Modulation of drug efflux transporter activity is being explored as a means for improving the pharmacokinetic and
pharmacodynamic properties of various drugs. In this regard, several polymer formulations have been shown to inhibit drug

efflux transporters such as P-glycoprotein (P-gp). The current review will focus on Pluronic block copolymers in particular,

the mechanisms involved in the effects of Pluronic on drug efflux transporters, and the optimal polymer compositions

required for inhibition of drug efflux transporters. Special emphasis will be placed on the potential applications of Pluronic
in enhancing the blood–brain barrier (BBB) penetration of drugs.
 2002 Elsevier Science B.V. All rights reserved.
Keywords: Blood–brain barrier; Multidrug resistance (MDR); P-glycoprotein; Multidrug resistant protein (MRP); Block copolymer
Contents
1. Introduction ............................................................................................................................................................................ 151
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2. Overview of Pluronic block copolymers in pharmaceutics........................................................................................................ 152
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3. Pluronic block copolymers in drug resistant cancer.................................................................................................................. 152
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4. Effects of Pluronic on P-gp activity in the blood–brain barrier.................................................................................................. 154
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5. Mechanism of Pluronic -induced inhibition of P-gp in brain endothelial cells ............................................................................. 155

13. Cell-mediated drug transport across the blood–brain barrier
pharmacy.sites.unc.edu/
troy-movie.stasi.co.uk
Macrophages and monocytes/neutrophils are phagocytic and
have a tendency to endocytose colloidal materials, for
example, nano or microparticles, liposomes and subsequent
exo- cytosis to release drug and/or colloidal materials to
external media. A high payload of drug can be incorporated/
loaded into nanocar- riers or microcarriers, then taken up by
Trojan horse cells .

14. Thanks All
for a Patient Ear
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