The brain is a delicate organ with many vital functions and many formidable mechanisms, isolate and protect it from the outside world. Unfortunately, the same mechanisms that prevent environmental chemicals accessing the brain also prevent the access of therapeutic chemicals. The brain is segregated from the circulating blood by a unique membranous barrier i.e the blood brain barrier.

1. DRUG DELIVERY TO THE
BRAIN
BY
NADIKATLAANUSHA
M.Pharm

2. CONTENTS
 Introduction
 The Brain Microvasculature
 BARRIERS TO CNS DRUG DELIVERY
a) Blood-Brain Barrier
b) Blood-Cerebrospinal Fluid Barrier
c) Blood-Tumor Barrier
 PHYSIOLOGICAL APPROACHES: Transporter-mediated delivery
 INVASIVE APPROACHES
a) Blood brain barrier disruption
b) Intra-cerebro-ventricular infusion
c) Transporter-independent mechanisms to circumvent the BBB
d) Imaging in brain drug targeting
 PHARMACOLOGICAL APPROACHES
 Summary of the physiological approaches to deliver therapeutic molecules in the brain parenchyma.
 Commercially available drugs for brain targetting.
 In vivo model to study drug transport across the blood-brain and blood-csf barriers.
 Major unmet needs in brain drug targeting.
 Barriers to future progress in brain drug targeting.
 Important future research areas in brain drug targeting
 Conclusion.
 References.
ANUSHA NADIKATLA

3. INTRODUCTION
The brain is a delicate organ with many vital functions and many
formidable mechanisms, isolate and protect it from the outside world.
Unfortunately, the same mechanisms that prevent environmental
chemicals accessing the brain also prevent the access of therapeutic
chemicals. The brain is segregated from the circulating blood by a unique
membranous barrier i.e the blood brain barrier. BBB is a major
bottleneck in developing brain drug delivery and the most prominent
factor limiting the future growth of neurotherapeutics. Some small
molecules with appropriate lipophilicity, molecular weight (mw) and
charge will diffuse from blood into the CNS. However, the over
whelming majority of small molecules (mwN500 daltons,D), proteins
and peptides do not cross the BBB. Therefore, to reach the brain, most
molecules must cross the BBB through interaction with specific
transporters and/or receptors expressed at the luminal (blood) side of the
endothelial cells.
ANUSHA NADIKATLA

4. THE BRAIN MICROVASCULATURE
• The capillaries of the brain have evolved to constrain the movement of
molecules and cells between blood and brain, providing a natural
defense against circulating toxic or infectious agents. The relative
impermeability of the BBB results from tight junctions between
capillary endothelial cells which are formed by cell adhesion
molecules.
• The BBB also has additional enzymatic aspects which serve to protect
the brain. Solutes crossing the cell membrane are subsequently
exposed to degrading enzymes, ecto- and endo-enzymes, present in
large numbers inside the endothelial cells that contain large densities
of mitochondria, metabolically highly active organelles.
ANUSHA NADIKATLA

5. THE BRAIN MICROVASCULATURE
ANUSHA NADIKATLA

6. BARRIERS TO CNS DRUG DELIVERY
The failure of systemically delivered drugs to effectively treat many CNS
diseases can be rationalized by considering a number of barriers that
inhibit drug delivery to the CNS.
There are physical barriers that separate the brain extracellular fluid from
the blood, they are as follows:
I. Blood-Brain Barrier
II. Blood-Cerebrospinal Fluid Barrier
III. Blood-Tumor Barrier
ANUSHA NADIKATLA

7. Schematic representation of the two main barriers in the CNS
ANUSHA NADIKATLA

8. BLOOD-BRAIN BARRIER
• The blood brain barrier is discovered by Paul Ehrlich in 1929.
• BBB is a physical, metabolic and immunological barrier that protects
the brain micro environment from toxins.
• The BBB develops in the first trimester of fetal life.
• It utilizes 15% of the body glucose. The BBB is formed by the
combination of cerebral endothelial cells, pericytes, astrocytes,
microglia and neurons.
• The micro vascular endothelium shares a common basement
membrane with astrocytes and pericytes. Astrocytes send their foot
processes to invest more than 90% of endothelial capillaries.
• The BBB is a tight junction of brain capillary endothelial cells, which
abolish aqueous paracellular pathways across the cerebral
endothelium, and that prevent the free diffusion of solute into the
brain.
• Therefore, the diffusion or permeability is dependent on the
lipophillicity of drug and solutes. ANUSHA NADIKATLA

9. ANUSHA NADIKATLA

10. BLOOD-CEREBROSPINAL FLUID BARRIER
• The second barrier, located at the choroid plexus, is represented by the
blood-cerebrospinal fluid barrier (BCSFB) that separates the blood
from the cerebrospinal fluid (CSF) which, in turn, runs in the
subarachnoid space surrounding the brain.
• Unlike the capillaries that form the BBB, the capillaries in the choroid
plexus allow free movement of molecules via intracellular gaps and
fenestrations.
• The epithelial cells in the choroid plexus that form the BCSFB have
complex tight junctions on the CSF (apical) side of the cells.
• These tight junctions of the epithelial cells in the choroid plexus are
slightly more permeable than those found in the endothelial cells of
the BBB.
ANUSHA NADIKATLA

11. BLOOD-TUMOR BARRIER
• Drug delivery is even more challenging when the target is a CNS
tumor.
• Drug delivery to neoplastic cells in a solid tumor is compromised by a
heterogeneous distribution of microvasculature throughout the tumor
interstitial, which leads to spatially inconsistent drug delivery.
• Furthermore, as a tumor grows large, the vascular surface area
decreases, leading to a reduction in trans-vascular exchange of blood-
borne molecules.
• At the same time, intra-capillary distance increases, leading to a
greater diffusional requirement for drug delivery to neoplastic cells.
• As a result, the cerebral microvasculature in these tumor adjacent
regions of normal brain may be even less permeable to drugs than
normal brain endothelium, leading to exceptionally low extra-tumoral
interstitial drug concentrations.
• Brain tumors may also disrupt BBB, but these are also local and
nonhomogeneous disruptions. ANUSHA NADIKATLA

12. CROSSING THE BBB
• Crossing the BBB remains a key obstacle in the development of drugs
for brain diseases despite decades of research.
• The parameters considered optimum for a compound to transport
across the BBB are:
(a) Non-ionization.
(b) Log P value near to 2.
(c) Molecular weight less than 400 Da.
(d) Cumulative number of hydrogen bonds between 8 to10.
ANUSHA NADIKATLA

13. ANUSHA NADIKATLA

14. • Small hydrophilic molecules such as amino acids, glucose, and other
molecules necessary for the survival of brain cells use transporters
expressed at the luminal (blood) and basolateral (brain) side of the
endothelial cells.
• Larger and/or hydrophilic essential molecules such as hormones,
transferrin for iron, insulin, and lipoproteins use specific receptors that
are highly expressed on the luminal side of the endothelial cells. These
receptors function in the endocytosis and transcytosis of compounds
across the BBB.
• Small lipophilic molecules can diffuse passively across the BBB into
the brain but will be exposed to efflux pumps (P-glycoprotein [P-gp],
some Multidrug Resistance Proteins [MRP], Breast cancer Resistance
Protein [BCRP] and others) expressed on the luminal side of the BBB
and exposed to degrading enzymes (ecto- and endo-enzymes)
localized in the cytoplasm of endothelial cells before brain
penetration.
ANUSHA NADIKATLA

15. • It is also seen that some drugs like vincristine, vinblastine and
cyclosporine-A are highly lipophilic but the permeation is quite slow.
• The other biochemical entities present in the BBB include enzymes
like MAO-A & B, COMT; hormones like adrenaline, dopamine,
histamine, prostaglandins, bradykinins and proteins such as p-
glycoprotein also called multi drug resistant protein (MDRP) and
transferrin.
• To bypass the BBB and to deliver therapeutics into the brain,
three different approaches are currently used these are considered
below:
I. PHYSIOLOGICALAPPROACHES
II. INVASIVE APPROACHES
III. PHARMACOLOGICALAPPROACHES
ANUSHA NADIKATLA

16. • TRANSPORTER-MEDIATED DELIVERY:
• Carrier mediated transport systems (CMT)
• Receptor mediated transcytosis (RMT)
• Adsorptive mediated transcytosis (AMT)
PHYSIOLOGICAL
APPROACHES
• I. Blood brain barrier disruption:
• a) Osmotic blood brain barrier disruption.
• b) Bradykinin receptor-mediated BBB opening.
• c) Ultrasound-mediated BBB opening.
• d) Biochemical Blood-Brain Barrier Disruption.
• II. Intra-cerebro-ventricular infusion.
• III. Transporter-independent mechanisms:
• a ) Convection-enhanced delivery.
• b) Intranasal Delivery.
• IV. Imaging in brain drug targeting.
INVASIVE
APPROACHES
• Chemical delivery systems.
• Liposomes.
• Polymeric micelles.
• Nanoparticles.
• Monoclonal Antibodies.
PHARMACOLOGICAL
APPROACHES ANUSHA NADIKATLA

17. PHYSIOLOGICAL APPROACHES
• The brain requires essential substances for metabolism and survival,
such as glucose, insulin, growth hormone, low density lipoprotein
(LDL), etc.These substances are recognized by specific receptors or
transport mechanisms, resulting in specific transport into the brain.
• Since almost every neuron in the brain is perfused by its own
capillary as a result of the small distance separating capillaries (on
average 40 μm) and the brain's very high perfusion rate.Therefore, the
most effective way of delivering neuro-active drugs is via transporters
or internalizing receptors on these capillaries.
• Drugs can be modified to take advantage of native BBB nutrient
transport systems or by conjugation to ligands that recognize receptors
expressed at the BBB.This will result in their being carried across the
BBB after receptor-mediated transcytosis. This physiological
approach is recognized by the scientific community as the one with
the most likely chance of success. ANUSHA NADIKATLA

18. TRANSPORTER-MEDIATED DELIVERY
Peptides and small molecules may use specific transporters expressed on
the luminal and basolateral side of the endothelial cells forming the BBB
to cross into the brain. At least 8 different nutrient transport systems have
been identified, with each transporting a group of nutrients of similar
structure. Only drugs that closely mimic the endogenous carrier
substrates will be taken up and transported into the brain.
Limitations: To use a BBB transporter protein as a CNS drug delivery
vector, multiple factors must be considered. These include:
1) The kinetics available to transport physiologic molecules,
2) The structural binding requirements of the transporter
3) Therapeutic compound manipulation so that the compound binds but
also remains active in-vivo and
4) Actual transport of the molecule into the brain, as opposed to just
binding to the transporter.
ANUSHA NADIKATLA

19. Transport mechanisms operating at the BBB for peptides and proteins
can be classified into the following categories;
a) Carrier mediated transport systems (CMT)
b) Receptor mediated transcytosis (RMT)
c) Adsorptive mediated transcytosis (AMT)
ANUSHA NADIKATLA

20. CARRIER MEDIATED TRANSPORT SYSTEMS
In the braincapillary endothelial cells, which make up the BBB, there are
several transport systems for nutrients and endogenous compounds.They are:
 The hexose transport system for glucose and mannose.
 The neutral amino acid transport system for phenylalanine, leucine and
other neutral amino acids.
 The acidic amino acid transport system for glutamate and aspartate.
 The basic amino acid transport system for arginine and lysine.
 The b-amino acid transport system for b-alanine and taurine.
 The monocarboxylic acid transport system for lactate and short-chain fatty
acids such as acetate and propionate.
 The choline transport system for choline and thiamine.
 The amine transport system for mepyramine.
 The nucleoside transport system for purine bases such as adenine and
guanine, but not pyrimidine bases.
 The peptide transport system for small peptides.
 Utilization of differences in the affinity and the maximal transport activity
among these transport systems expressed at the BBB is an attractive
strategy for controlling the delivery and retention of drugs into the brain.
ANUSHA NADIKATLA

21. Peptide transport systems (PTS):
• These systems seen to be restricted to transportation of a limited
number of structurally related peptides. Peptides transport from
blood to brain and from brain to blood i.e bidirectional transport.
• Peptides transported from blood to brain via PTS include methionine
, enkephaline, orginine and vassopressin. The permeability coefficient
for peptide transport from blood to the brain via PTS usually ranges
between 1 to 10 ml/min/gm brain, which is about 10 fold faster than
could be predicted from their lipid solubilities.
• Transport from brain to blood is also mediated by PTS for methionine,
enkephaline, orginine, vassopressin, oxytocin and somatostatin with
half lives in the range of 10-50 min.
ANUSHA NADIKATLA

22. RECEPTOR-MEDIATED TRANSCYTOSIS
• The BBB expresses RMT systems for the transport of endogenous
peptides, such as insulin or transferrin.
• The RMT systems operate in parallel with the classical carrier-
mediated transporters (CMT).
• The RMT systems are portals of entry for large molecule drugs that
are attached to endogenous RMT ligands.
• These receptors are highly expressed on the endothelial cells forming
the BBB.
• These include the insulin receptor, transferrin receptor, LDL receptor
and its related protein, and others.
• Peptides such as insulin, transferrin, insulin like growth factor (IGF) I
& IGF II exhibit high affinity to receptors expressed on the brain
capillaries.
ANUSHA NADIKATLA

23. These receptors mediate the transcytosis of insulin, transferrin and IGF
through the BBB involving three successive steps :
• Step I: Receptor mediated endocytosis at the luminal or blood side of
BBB. Following the binding of ligand to its affinity receptor the
process of endocytosis is initiated.
• step 2: Movement of the ligand receptor complex through the
endothelial cytoplasm.
• Step 3: Receptor mediated exocytosis of the ligand into the brain
interstitial fluid at the antiluminal or brain side of the BBB.
ANUSHA NADIKATLA

24. TROJAN HORSES LIPOSOMES (THL)
TRANSFERRIN RECEPTOR (TR)
INSULIN RECEPTOR
ANTIBODIES AGAINST TR AND HIR FOR
BRAIN DRUG TARGETING
TARGETED NANOPARTICLE BRAIN
DRUG DELIVERY SYSTEMS
IN VIVO BRAIN IMAGING OF GENE
EXPRESSION
ANUSHA NADIKATLA

25. TROJAN HORSES LIPOSOMES (THL)
• These are liposomes coated with targeting molecules such as
antibodies.
• THL have been constructed by Pardridge et al. for the delivery of non-
viral plasmid DNA across the BBB for expression of interfering RNA
(shRNA).
• The plasmid DNA was encapsulated in the interior of a 100 nm
liposome, and the surface of the liposome was coated with 2000D
PEG.The ends of 1–2% of the PEG strands were conjugated with a
receptor (R) — specific mAb (HIR or TR).
• TR mAbs-targeted THL with expression plasmid for tyrosine
hydrolase (TH) has been shown effective in treating Parkinson's
disease (PD) in rat model.
• This approach has been used to deliver shRNA against EGFR and
resulted in the knock-down of EGFR expression and increased
survival of mice implanted intracranially with brain tumours.
ANUSHA NADIKATLA

26. TRANSFERRIN RECEPTOR (TR)
• The function of the TR is to provide iron to cells.
• Drug targeting to the TR can be achieved by using the endogenous
ligand transferrin, or by using antibodies directed against the TR.
• For transferrin (Tf) the in-vivo application is limited due to high
endogenous concentrations of Tf in plasma.
• Transferrin is an essential protein needed for iron delivery to cells and
is found at mg/ml amounts in plasma.
• Using the antibody approach against TR, the receptor specific mAb
binds to the receptor onthe endothelial cells, and allowsthe associated
therapeutic agent to cross the BBB via receptor-mediated transcytosis.
• For antibodies against the TR, proof of concept studies in rats have
demonstrated that mAb that binds to a distinct epitope from Tf
(OX26) can be used as a brain delivery agent.
ANUSHA NADIKATLA

27. INSULIN RECEPTOR
• Pardridge et al. have extensively documented the use of the insulin
receptor for the targeted delivery of drugs to the brain using specific
antibodies directed against the IR.
• For example, using the 83-14 mouse MAb against the human insulin
receptor (HIR) in rhesus monkey, shows that total uptake of the MAb
is 4%, which corresponds to 0.04%/g brain tissue 3 h after iv
injection.
• Both the chimeric antibody and a fully humanized form of the 83-14
antibody against HIR have been created and shown to be able to
transport an associated/conjugated molecule across the BBB.
ANUSHA NADIKATLA

28. ANTIBODIES AGAINST TR AND HIR FOR BRAIN DRUG
TARGETING
Applications of these antibodies to molecular Trojan horses (MTH) for
the delivery of therapeutics have been documented by Pardridge's group.
Different forms of fusion and conjugated proteins have been generated.
• VIP-TR mAb (vasoactive intestinal peptide conjugated to transferrin
receptor monoclonal antibodies [TRmAb])
• BDNF-HIR mAb (brain derived neurotrophic factors conjugated to
the human insulin receptor monoclonal antibodies [HIR mAb])
• FGF2-HIR mAb (fibroblast growth factor-2 conjugated to the HIR
mAb)
• EGF-TR mAb (epidermal growth factor conjugated to TR mAb)
• Aβ1-40 — TR mAb (amyloid β1–40 peptide conjugated to TR mAb)
• Peptide nucleic acid (siRNA) — HIR mAb
• β-galactosidase — TR mAb, IDUA- HIR fusion
• Neurotrophin — HIR fusion. ANUSHA NADIKATLA

29. TARGETED NANOPARTICLE BRAIN DRUG DELIVERY
SYSTEMS
• Nanoparticles are produced from polymeric precursors, and these
structures can be formulated to encapsulate a wide variety of
pharmaceuticals.
• The size of nanoparticles is typically 50-200 nm, and such structures
are too large to cross the BBB via free diffusion.
• However, the formulation of nanoparticles with polysorbate-80 has
shown to enable BBB transport.
• The conjugation of low density lipoprotein (LDL) apoproteins to the
surface of nanoparticles appears to trigger RMT across the BBB via
the BBB LDL receptor.
• Recent advances have loaded macrophages with nanoparticle/drug
complex ex-vivo, followed by the intravenous administration of the
cells.
• Since activated lymphocytes and/or macrophages cross the BBB,
these cells may be used as vehicles for drug delivery to the brain.
ANUSHA NADIKATLA

30. IN-VIVO BRAIN IMAGING OF GENE EXPRESSION
• Antisense radiopharmaceuticals hold promise for imaging gene
expression in the brain using nuclear medicine imaging modalities,
such as PET or SPECT.
• However, antisense radiopharmaceuticals do not cross the BBB on
their own and must be modified if they are to be useful brain gene
imaging agents.
• Peptide nucleic acids can be biotinylated and radiolabeled with 111-
indium.
• In parallel, a conjugate or fusion protein, of avidin and a BBB
molecular Trojan horse can by synthesized.
• The peptide nucleic acid is then coupled to the MTH via the avidin-
biotin bridge.
• Such targeted antisense radiopharmaceuticals cross the BBB, and the
brain cell membrane, and enable the in vivo imaging of gene
expression in brain.
ANUSHA NADIKATLA

31. ANUSHA NADIKATLA

32. ADSORPTIVE MEDIATED TRANSCYTOSIS
• Adsorptive mediated endocytosis (AME) and transcytosis involve
endocytosis in vesicles of charged substances, is similarly a receptor-
mediated mechanism, but not by a specific mechanism. Utilization of
the transcytosis mechanism for enhancement of the brain delivery of
peptides seems promising because of its applicability to a wide range
of peptides, including synthetic ones.
• Peptides and proteins with a basic isoelectric point (“cationic”
proteins) bind initially to the luminal plasma membrane (mediated by
electrostatic interactions with anionic sites), which triggers AMT. This
property is favorable for delivery of peptides to the brain.
• The examples of the peptides that penetrate the BBB via AMT
include; histone,avidine,cationized albumin,cationic peptides and
ebiratide. AMT of neuropharmaceutical peptides have the
characteristics of stability to enzymes and cationic charge as a
consequence of suitable chemical modifications of the native peptides.
ANUSHA NADIKATLA

33. • Ebiratide , a synthetic peptide analogous to ACTH that is used to
treat Alzheimers disease , is positively charged with an isoelectric
point of 10,its resistance to metabolism has been enhanced by
chemical modifications of the constituent natural amino acids.
• To prove the transcytosis of ebiratide across the BBB, brain
microdialysis study were performrd.
• This indicates that ebiratide crosses the BBB in an intact form very
effectively.
ANUSHA NADIKATLA

34. INVASIVE APPROACH
DISRUPTION OF THE BBB
ANUSHA NADIKATLA

35. DISRUPTION OF THE BBB
Disruption of the BBB can open access of the brain to components in
the blood by making the tight junction between the endothelial cells
of the brain capillaries leaky.
DISRUPTIONOFTHEBBB
OSMOTIC BLOOD BRAIN BARRIER
DISRUPTION
ULTRASOUND-MEDIATED BBB OPENING
BRADYKININ RECEPTOR-MEDIATED
BBB OPENING
BIOCHEMICAL BLOOD-BRAIN BARRIER
DISRUPTION
ANUSHA NADIKATLA

36. OSMOTIC BLOOD BRAIN BARRIER DISRUPTION
• The osmotic shock causes endothelial cells to shrink, thereby
disrupting the tight junctions.
• Intracarotid injection of an inert hypertonic solution such as mannitol
or arabinose has been employed to initiate endothelial cell shrinkage
and opening of BBB tight junctions.
• The BBB is opened to drugs, proteins, and nanoparticles for between
15minutes (for viral-sized agents) up to 4 hours (for low molecular
weight compounds) before returning to baseline permeability.
ANUSHA NADIKATLA

37. • BBBD currently is used clinically for the delivery of chemotherapy to
the CNS in patients with brain tumors. BBBD increases parenchymal
and CSF chemotherapy concentrations by 10-100 fold compared to
intravenous administration alone.
• Osmotic disruption of the BBB has also been suggested as a delivery
strategy for recombinant adenoviral vectors for gene transfer to
intracerebral tumors, and for magnetic resonance imaging agents for
diagnosis of brain metastases.
• Osmotic BBBD also has the potential for enhancing delivery of
therapeutics to the brain for treatment of brain infection, lysosomal
storage disorders, and neurodegenerative diseases.
ANUSHA NADIKATLA

38. ULTRASOUND-MEDIATED BBB OPENING
• BBB disruption by MRI-guided focused ultrasound can achieve focal
CNS delivery in animal models.
• Consistent vascular leak without tissue damage was achieved by
localizing cavitation-generated mechanical stresses to blood vessel
walls by IV injection of preformed gas bubbles just prior to pulsed
ultrasound treatment.
• The low power ultrasound caused reversible focal opening which was
completely healed within 24 hours.
• Marker dye extravasation was associated with widening of the tight
junctions and active vacuole transport across the endothelial cells.
• The ultrasound with micro-bubbles exposures did not cause neuronal
damage, apoptosis or ischemia, or long term vascular damage.
• Ultrasound BBB disruption produced clinically relevant levels of
liposomal doxorubicin and mAbs in the targeted local areas of the
brain in animals. It is as yet unclear whether this technique will show
any promise in humans. ANUSHA NADIKATLA

39. MRI-guided focused ultrasound BBB disruption technique:
Ultrasound
• The combination of micro
bubbles and manganese
(preformed micro bubbles
of ultrasound contrast
agent, optison, with a
diameter of 2–6 μm which
is injected into the blood
stream before exposures to
ultrasound).
• This technique has been
shown to increase the
distribution of Herceptin
in brain tissue by 50% in a
mice.
ANUSHA NADIKATLA

40. BRADYKININ RECEPTOR-MEDIATED BBB OPENING
• Bradykinin, an endogenous peptide mediator of the inflammatory
response, can induce transient increases in blood vessel permeability
that can be highly specific for tumor vasculature.
• There is evidence of the opening of the tight junctions to occur by
activation of bradykinin B2 receptors through a calcium-mediated
mechanism.
• RMP-7 (lobadimil) is a synthetic bradykinin analog that is specific for
the B2 receptor and is 100-fold more potent than bradykini in mice.
• Pharmacological manipulation of the BTB offers the possibility of
highly specific opening and targeted drug delivery to tumor, albeit
with the possibility that increases in delivery may only be modest and
dependent on the tumor type or model treated.
• Clinical studies in the past 5 years have demonstrated the safety of
concurrent RMP-7 and carboplatin, with or without radiation therapy,
for both adults and children with gliomas. ANUSHA NADIKATLA

41. • However, RMP-7 had no effect on the pharmacokinetics or toxicity of
carboplatin, and two studies have shown no objective responses of
RMP-7 and carboplatin in brain stem glioma or high-grade glioma.
• Higher doses of RMP-7 may be required to increase carboplatin
delivery to tumor, but may also result in increased toxicity in normal
brain.
• This technique was abandoned due to lack of efficacy in Phase II and
III studies when administered in combination with carboplatin.
Limitations:
• All these approaches are relatively costly, require anaesthesia and
hospitalization, and are non-patient friendly.
• These techniques may enhance tumour dissemination after successful
disruption of the BBB.
• Neurons may be damaged permanently from unwanted blood
components entering the brain.
ANUSHA NADIKATLA

42. BIOCHEMICAL BLOOD-BRAIN BARRIER DISRUPTION
• Recently, new and potentially safer biochemical techniques have been
developed to disrupt the BBB. Selective
• opening of brain tumor capillaries (the blood–tumor barrier), by the
intracarotid infusion of leukotriene C4 was
• achieved without concomitant alteration of the adjacent BBB. In
contrast to osmotic disruption methods, biochemical opening utilizes
the novel observation that normal brain capillaries appear to be
unaffected when
• vasoactive leukotriene treatments are used to increase their
permeability. However, brain tumor capillaries or injured brain
capillaries appear to be sensitive to treatment with vasoactive
leukotrienes, and the permeation is dependent on molecular size.
ANUSHA NADIKATLA

43. INTRA-CEREBRO-VENTRICULAR (ICV) INFUSION
• It has been reported that the concentration of a drug in the brain is
only 1–2% of the CSF concentration at just 1–2 mm from the surface.
• The drug eventually distributes to the general circulation, where the
drug then enters the brain parenchyma following transport across the
BBB.
• This result is similar to a slow intravenous infusion rather than a direct
administration of drugs into the brain.
• Pharmacologic effects can be seen after ICV administration, if the
target receptors of the drug for example, opioid peptides) are located
near the ependymal surface of the brain.
• Both the bolus injection of chemotherapy agents and the placement of
a biodegradable, chemotherapeutic impregnated, water into a tumour
resection cavity, rely on the principle of diffusion to drive the drug
into the infiltrated brain. ANUSHA NADIKATLA

44. Limitations:
• The diffusion of the drug in
the brain parenchyma is very
low. Unless the target is
close to the ventricles it is
not an efficient method of
drug delivery.
• Distribution in the brain by
diffusion decreases
exponentially with distance.
• The injection site has to be
very precisely mapped to get
efficacy and overcome the
problem associated with
diffusion of drugs in the
brain parenchyma. ANUSHA NADIKATLA

45. INTRA NASAL
DRUG
DELIVERY
CONVECTION-
ENHANCED
DRUG
DELIVERY (CED)
TRANSPORTER-INDEPENDENT
MECHANISMS TO CIRCUMVENT THE
BBB
ANUSHA NADIKATLA

46. CONVECTION-ENHANCED DRUG DELIVERY (CED)
The general principle of CED involves the stereotactically guided
insertion of a small-caliber catheter into the brain parenchyma. Through
this catheter, infusate is actively pumped into the brain parenchyma and
penetrates in the interstitial space. A continuous infusion pressure
gradient over hours to days results in distribution of therapeutic agents
into the interstitial space and the catheters are removed at the bedside. In
contrast to the mm distances obtained with simple diffusion, CED has
been shown in laboratory experiments to deliver high molecular weight
proteins 2 cm from the injection site in the brain parenchyma after as
little as 2 h of continuous infusion. The CED technique is used primarily
for large molecular weight agents that show minimal leakage across the
BBB and/or have significant systemic toxicity, including viruses,
oligonucleotides, nanoparticles, liposome, and targeted immunotoxins.
Animal studies have demonstrated that the volume of distribution
achieved by CED can be imaged by magnetic resonance in real time by
including contrast agents within the infusate. ANUSHA NADIKATLA

47. Parameters that affect CED volume of distribution include:
• Infusion parameters (rate, volume, duration, cannula size),
• Infusate characteristics (molecular weight, surface properties, tissue
affinity),
• Tissue properties (tissue density, extracellular space, vascularity, and
interstitial fluid pressure).
Limitations:
• Proper drug delivery depends on the precise placement of the
catheters and other infusion parameters for delivery into the correct
location in the brain parenchyma.
• Some areas of the brain are difficult to saturate fully with infusate,
particularly — infiltrated tissues surrounding a cavity.
• Distribution inhomogeneity, high interstitial fluid pressure, and rapid
efflux of agent from the injection site leads to CED treatment failure.
To overcome these issues, increased residence time must be achieved
to enhance targeted toxin receptor binding and uptake by the
cancerous cells. ANUSHA NADIKATLA

48. INTRA NASAL DRUG DELIVERY
• After nasal delivery, drugs first reach the respiratory epithelium,
compounds can be absorbed into the systemic circulation by
Transcellular and Para cellular passive absorption, carrier-mediated
transport, and absorption through trancytosis.
• This method allows drugs that do not cross the blood-brain barrier to
be delivered to the olfactory cerebrospinal fluid via transport across
the olfactory region of the nasal epithelium.
• The surface area of the olfactory region of the nasal epithelium in
rodents is large, about 50%, and is small in humans, about 5%,28
therefore intranasal delivery is not expected to achieve therapeutic
drug levels in most brain regions.
ANUSHA NADIKATLA

49. MAGNETIC
RESONANCE
IMAGING
IMAGING
DELIVERY
TECHNIQUES
POSITRON
EMISSION
TOMOGRAP
HY
IMAGING IN BRAIN
DRUG TARGETING
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50. MAGNETIC RESONANCE IMAGING
• Brain structural imaging data provide important metrics regarding the
extent of brain disease and objective surrogate markers for evaluation
of therapies.
• MRI has played an important role in evaluating new CNS therapies,
notably in multiple sclerosis, stroke, and brain tumor, and now in drug
trials of these disease states.
• Quantitative MRI techniques such as relaxography and diffusion
provide more complete assessment of total brain disease and also will
benefit from improved signal to noise associated with higher magnetic
field MRI instruments.
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51. • MRI techniques have been used to track cell migration in the CNS,
glioma invasion, and convincing evidence has been presented that
increased sensitivity afforded by ultra-high field MRI instruments,
may be sufficient to track single cells in vivo.
• Increasingly, functional imaging techniques have been used to
measure brain physiology in disease and changes associated with
treatment.
• Dynamic susceptibility contrast (DSC) and dynamic contrast
enhanced (DCE) MRI studies combined with time-series modeling
provide parametric maps of blood volume, blood flow, vascular transit
time, vascular permeability, interstitial volume, and water exchange
kinetics.
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52. IMAGING DELIVERY TECHNIQUES
• The distribution of drug within the brain using any of the BBB
circumvention strategies is complex and imaging information can be
used to optimize individual therapies, and importantly, also to
accumulate data to improve predictive (in silico) models.
• An important goal of imaging is to investigate the spatial and temporal
properties of BBB disruption to understand the potential distribution
volume of brain drugs.
• Contrast enhanced MRI has been used to monitor CED drug delivery
and revealed complex distribution patterns resulting from anisotropic
diffusion, vascular efflux, and other factors.
• MRI contrast agents range from the hydrophilic low-molecular weight
gadolinium based compounds to large molecular weight iron based
nanoparticles.
• These agents can serve as surrogate markers for drug distribution, and
can be used to probe small and large openings in the BBB.
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53. POSITRON EMISSION TOMOGRAPHY
• PET is non-invasive, has excellent sensitivity and specificity, and has
provided quantitative spatially resolved pharmacokinetic and
pharmacodynamic measurements on a wide range of small molecule
brain drugs in vivo.
• Advanced PET techniques have been used to determine
pharmacokinetics of brain drugs, pharmacodynamic response
following anti-cancer therapy, and even in investigations of fetal brain
pharmacokinetics following maternal drug administration.
• PET techniques have the ability to detect very low concentrations of
radiolabels, orders of magnitude below pharmacological dose, and are
inherently translational.
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54. PHARMACOLOGICAL APPROACH
The pharmacological approach to crossing the BBB is based on the
observation that some molecules freely enter the brain.
e.g: alcohol, nicotine and benzodiazepine.
This ability to passively cross the BBB depends on:
• The molecular size being less than 500 D.
• Charge (low hydrogen bonding capabilities).
• lipophilicity (the more lipophilic, the better the transport).
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55. CHEMICAL DELIVERY SYSTEMS
• This approach consists of modifying, through medicinal chemistry,
a molecule that is known to be active against a CNS target to
enable it to penetrate the BBB. Modification of drugs through a
reduction in the relative number of polar groups increases the
transfer of a drug across the BBB.
• LIPIDIZATION of molecules generally increases the volume of
distribution, the rate of oxidative metabolism by enzymes and
uptake into other tissues, causing an increased tissue burden.
• Lipid carriers have been used for transport, and there are
successful examples of this approach.
• Modification of antioxidants with pyrrolopyrimidines increases
their ability to access target cells within the CNS.
• Enhanced delivery of ganciclovir to the brain was observed by
covalently attaching 1-methyl-1,4-dihydronicotinate to an
hydroxymethyl group.
• Fatty acid such as N-docosahexaenoyl (DHA) have been
incorporated in small drugs to increase their brain uptake.
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56. ACTIVE EFFLUX TRANSPORT BY P-GLYCOPROTEIN AT THE
BBB
• Efflux transport system expressed at the luminal and/or albuminal
membranes of BCECs act to restrict the accumulation of some drugs.
• P-glyco protein(Pgp) is one such efflux transporter.
• Increasing the lipophilicity of a molecule to improve transport can
also result in making it a substrate for the efflux pump P-glycoprotein
(P-gp).
• Formulation of drugs facilitates brain delivery by increasing the drug
solubility and stability in plasma.
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57. Limitations:
• In contrast to the above hypothesis , it has recently been proposed that
active efflux of drugs by Pgp expressed at the luminal membrane of
the brain capillary endothelial cells accounts for the poor BBB
permeability to certain drugs.
• Results supporting the in vivo importance of Pgp –mediated efflux of
several drugs have been obtained in studies using rat brain, brain
microdialysis and mdr 1 a gene knockout mice.
• The concentrations of digoxin , doxorubicin, and cyclosporin A in the
brain of mdr 1 a gene knockout mice are significantly higher than
those in normal mice, clearly indicating that Pgp at the BBB mediates
efflux of these drugs from the brain.
• The modifications necessary to cross the BBB often result in loss of
the desired CNS activity.
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58. LIPOSOMES
• Liposomes are non-toxic, biocompatible and biodegradable lipid body
carrier made up of animal lipid like phospholipids, sphingolipids, etc.
• The basic mechanism is by coupling with brain drug transport vector
via receptor-mediated transcytosis or by absorptive-mediated
transcytosis.
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59. POLYMERIC MICELLES
Incorporation of low molecular mass drugs into pluronic micelles can
increase drug solubility and drug stability, and can improve drug
pharmacokinetics and biodistribution.
Polymeric micelles have been utilized for delivery of CNS drugs across
the BBB, and for oral delivery of drugs and tumour-specific delivery of
antineoplastic agents.
Examples:
• pluronic P85 micelles loaded with a neuroleptic drug were targeted to
the brain by conjugating micelles with neurospecific antibodies, or
using insulin as targeting moieties.
• Amphiphilic chitosan-based polymers (mwb20 kD) self-assemble in
aqueous media at low micromolar concentrations to give previously
unknown micellar clusters of 100–300 nm of size.
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60. • Intravenous anaesthetic propofol was used as a model drug. It is
known that the sleep times obtained with the carbohydrate propofol
formulations are up to 10 times those obtained when using either the
commercial Fresenius or Diprivan formulations.
• A loss of righting reflex time could not be recorded as animals were
asleep by the end of the injection period; evidence that delivery of the
centrally active drug across the blood–brain barrier is rapid and
efficient.
Limitations:
• The exact mechanism by which these specific nanoparticle-based
formulations cross the BBB is not known, and may involve the
induction of increased leakiness of the BBB and inhibition of efflux
pumps.
• In addition the application of nanoparticles to large hydrophilic
therapeutic molecules has not been proven.
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61. NANOPARTICLES
• Nanosystems employed for the development of nano drug delivery
system in the treatment of CNS disorders include polymeric
nanoparticles, nanospheres, nanosuspensions, etc.
• Nanoparticles enter into the brain by crossing the BBB by various
endocytotic mechanisms.
• Nanoparticles can be designed from albumin attached with
apoliprotein E (Apo E-albumin nanoparticles).
• After IV administration, Apo E-albumin nanoparticles are internalized
into the brain capillary endothelial cells by transcytosis and release
into brain parenchyma.
• The first drug that was deliverd to brain using nanoparticles was the
hexapepttidedalargin
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62. MONOCLONALANTIBODIES
• Monoclonal antibodies for targeting are usually prepared by
hybridoma technology.
• Combining malenoma (tumor) cells with antitumor antibodies against
a particular type of antigens found on malignant cells in animals like
rat.
• But instead of using mAb directly for brain targeting, they are
modified structurally to get genetically engineered monoclonal
antibodies.
• Cross the BBB by receptor mediated endocytosis.
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63. SUMMARY OF THE PHYSIOLOGICALAPPROACHES TO
DELIVER THERAPEUTIC MOLECULES IN THE BRAIN
PARENCHYMA
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64. ANUSHA NADIKATLA

65. COMMERCIALLY AVAILABLE DRUGS FOR BRAIN
TARGETTING
DRUG
MECHANISM OF
TRANSPORT
USE OF DRUG
GLUCOSE, MANNOSE
HEXOSE TRANSPORT
SYSTEM
SOURCE OF
CARBOHYDRATE IN
PARENTRAL NUTRITION
FLUOROURACIL.RANIM
USTIN
PHARMACOLOGICAL
OPENING OF BBB BY
INHIBITION OF PGP
ANTICANCER
ROVASTATIN
MONO CARBOXYLIC
ACID TRANSPORT
SYSTEM
TREATMENT OF
HYPERLIPIDAEMIAS
EBIRATIDE
ADSORPTIVE MEDIATED
ENDOCYTOSIS
ALZHEIMERS DISEASE
β-LACTAM ANTIBIOTIC
OLIGOPEPTIDE
TRANSPORTERS
ANTIBIOTIC

66. IN VIVO MODEL TO STUDY DRUG TRANSPORT ACROSS THE
BLOOD-BRAIN AND BLOOD-CSF BARRIERS
Brain Efflux Index (BEI)
The efflux transport across the BBB is a very important process for
explaining the mechanism of the apparent restricted cerebral distribution
of drugs after their systemic administration. In order to examine the BBB
efflux transport mechanism under in-vivo conditions, the intracerebral
microinjection technique has been developed and recently established as
the BEI. The BEI value is defined as the relative percentage of drug
effluxed from the ipsilateral (that is, they do not cross to the opposite
hemisphere) cerebrum to the circulating blood across the BBB compared
with the amount of drug injected into the cerebrum, i.e.:
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67. MAJOR UNMET NEEDS IN BRAIN DRUG TARGETING
i. Need to target therapeutics to specific brain regions or cell types.
ii. Need to understand toxicity associated with brain drug delivery
iii. Need to improve understanding of BBB transport systems.
iv. Need for in vivo evaluation of brain drug pharmacokinetics.
v. Need to understand of the role(s) of extracellular matrix within the
microvascular permeability barrier on component cell function.
vi. Need to identify new brain drug targeting systems.
vii. Need to speed development and application of molecular imaging
probes and targeted contrast agents. ANUSHA NADIKATLA

68. BARRIERS TO FUTURE PROGRESS IN BRAIN DRUG
TARGETING
i. Lack of training programs for scientists specializing in brain drug
targeting.
ii. Lack of NIH funding opportunities targeted to BBB drug delivery
research.
iii. Lack of BBB and CNS drug targeting emphasis in the
pharmaceutical industry.
iv. Lack of detailed understanding of BBB transport biology.
v. Lack of in vivo validation of in vitro BBB studies.
vi. Lack of controlled clinical trials addressing CNS drug delivery.
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69. IMPORTANT FUTURE RESEARCH AREAS IN BRAIN DRUG
TARGETING
An overall goal of future research in brain drug targeting is to expand the
CNS drug space from lipid-soluble small molecules to the much larger
space of pharmaceutics that include molecules that do not normally cross
the BBB. The following specific areas have been identified:
 Identify new BBB transporters that could be portals of entry for brain
drug targeting systems.
 Develop brain drug targeting systems that enable the brain delivery of
recombinant protein neurotherapeutics.
 Validate new drug targeting systems using in vivo models.
 Optimize pharmacokinetics of in vivo brain drug targeting systems.
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70.  Develop genomic and proteomic discovery platforms that enable the
identification of new BBB transporters.
 Apply protein-based therapeutics in specific brain diseases, including
stroke, neurogenesis, e.g., as an adjuvant to stem cell therapy.Greater
understanding of the function of active efflux transporters at the BBB.
 Improve understanding of the regulation of BBB transport by
astrocyte foot processes.
 Improve understanding of the interaction of the neuronal and
microvascular (endothelial cell-astrocyte endfoot) components of the
neurovascular unit, their participation in the permeability barrier, in
transport receptor expression, and their facilitation of the passage of
agents into the neuropil.
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71. CONCLUSION
The treatment of CNS diseases is particularly challenging
because the delivery of drug molecules to the brain is often precluded by
a variety of physiological, metabolic and biochemical obstacles that
collectively comprise the BBB, BCB and BTB. The techniques used to
this day involve direct injection or infusion of therapeutic compounds
into the brain, the cerebro-ventricles or the CSF, but all these approaches
are severely limited by poor distribution into brain parenchyma.
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72. Only the use of technologies able to transport molecules through
the endothelial cells of the BBB will allow a homogenous distribution of
therapeutics in the brain and thus provide a uniform and rapid exposure
to brain cells. Drug delivery directly to the brain interstitium has recently
been markedly enhanced through the rational design of polymer-based
drug delivery systems. Substantial progress will only come about,
however, if continued vigorous research efforts to develop more
therapeutic and less toxic drug molecules are paralleled by the aggressive
pursuit of more effective mechanisms for delivering those drugs to their
CNS targets.
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