Surface Modification of Nanoparticles forBiomedical Applications 1 1
• Consequently a multi-component nanomedical system can be constructed in reverse order of controlling events, namely from the inside out. The outer components are the first to be used. The inner components are the last.
lipids, polimers (biocompatible-biodegradablematerials)Also water is available (liposomes)
Aptamers are oligonucleic acid molecules that bind aspecific target molecule. Aptamers are usually createdby selecting them from a large random sequence pool, but natural aptamers also exist in riboswitches. Aptamers can be used for both basic research and clinical purposes as macromolecular drugs.
• aptamers offer advantages over antibodies as they can be engineered completely in a test tube, are readily produced by chemical synthesis, possess desirable storage properties, and elicit little or no immunogenicity in therapeutic applications.
Aptamer target protein or molecule ApplicationPSMA Prostate cancer diagnosis and therapyWT1 Understanding Wilms tumor pathogenesis4,4′-methylenedianiline Detecting DNA-damaging compoundsVEGF Inhibiting angiogenesisRET Inhibition of pro-growth signalingHER-3 Reducing drug resistance in HER-2+ cancersTCF-1 Colon cancer growth inhibitionTenascin-C Glioblastoma (brain cancer) detectionMUC1 Breast, pancreatic, ovarian cancers; targeting demonstratedPDGF/PDGFR Improving transport to tumors and targeting brain cancersNF-κB Targeting a transcription factor implicated in many diseasesPhosphatidylcholine:cholesterol liposomes Triggering liposome degradationRaf-1 Inhibiting pro-growth signalingαvβ3 integrin Targeting tumor-associated vasculatureHuman keratinocyte growth factor Inhibiting pro-growth signali
Properties of aptamers versus antibodiesAptamers AntibodiesBinding affinity nanomolar to picomolar Binding affinity nanomolar to picomolarSelection is a chemical process carried out Selection requires a biological system,in vitro and can therefore target any thus it is difficult to raise antibodiesprotein to toxins (not tolerated by animal) or non-Can select for ligands under a variety of immunogenic targets.conditions for in vitro diagnostics Limited to physiologic conditions for diagnosticsUniform activity regardless of batch Screening monoclonal antibodies timesynthesis consuming and expensivePK parameters can be changed on demand Activity of antibodies vary from batch toInvestigator determines target site of batchprotein Difficult to modify PK parametersWide variety of chemical modifications to Immune system determines target site ofmolecule for diverse functions of molecule proteinReturn to original conformation after Temperature sensitive and undergotemperature insult irreversible denaturation Limited shelf-lifeUnlimited shelf-life Significant immunogenicityNo evidence of immunogenicity
PEPTIDES• Peptide sequences recognized by receptors responsible of binding can be identified and synthesized.• Examples are peptide sequences derived from ApoE apolipoprotein that are recognized by LDL receptor on cell membranes
Peptides aptamers• Peptide aptamers consist of a variable peptide loop attached at both ends to a protein scaffold. This double structural constraint greatly increases the binding affinity of the peptide aptamer to levels comparable to an antibodys (nanomolar range).The variable loop length is typically comprised of 10 to 20 amino acids, and the scaffold may be any protein which has good solubility and compacity properties. Currently, the bacterial protein Thioredoxin-A is the most used scaffold protein, the variable loop being inserted within the reducing active site, which is a -Cys-Gly-Pro-Cys- loop in the wild protein, the two Cysteines lateral chains being able to form a disulfide bridge.Peptide aptamer selection can be made using different systems, but the most used is currently the yeast two- hybrid system.
OTHER LIGANDS• Natural ligands for receptors can be employed.Examples:FolateApoETrasferrin
LNA• A locked nucleic acid (LNA), often referred to as inaccessible RNA, is a modified RNA nucleotide. The ribose moiety is modified with an extra bridge connecting the 2 oxygen and 4 carbon. LNA nucleotides can be mixed with DNA or RNA residues in the oligonucleotide whenever desired. Such oligomers are commercially available. The locked ribose conformation enhances base stacking and backbone pre- organization. This significantly increases the hybridization properties (melting temperature) of oligonucleotides.