Structure-Activity Relationships in Self-Assembled Heparin-Binding Nanostructures

Heparin sulfate finds itself widely used as an anticoagulant within medicine. However, only one rescue agent for it exists, protamine sulfate. Protamine sulfate is an arginine-rich cationic peptide, and its use within medicine is fraught with issues and a substantial proportion of patients will experience side effects from its use. Gene therapy has the potential to cure a variety of genetic disorders including Cystic Fibrosis. Viral DNA vectors work well, but there are significant safety concerns, hence the interest in the development of an effective non-viral vector method. The work in this thesis synthesised a stereoisomeric family of novel palmitic acid based cationic binders using a self-assembled multivalency (SAMul) approach. This family of novel binders comprises of two enantiomeric pairs, which were synthesised using a previously reported TBTU-mediated peptide coupling strategy and repeated Boc-(de)protection steps to afford control over the regioselectivity of the synthesis. Through the use of 1H, 13C and DEPT-135 NMR alongside Infrared spectroscopy and Mass Spectrometry analysis, it has been shown that the target compounds have successfully been synthesised. Significant analysis of the behaviour of these SAMul systems has been performed via a series of binding assays, as well as Transmission Electron Microscopy, Dynamic Light Scattering and Isothermal Titration Calorimetry. It has been determined that all four novel binders undergo self-assembly in solution, and this self-assembly is a prerequisite for successful heparin sulfate and/or DNA binding. All four systems bind both heparin sulfate and DNA at micromolar effective concentrations, much lower than the CAC obtained by Nile Red, which implies the presence of the biological polyanion enhances binding affinity. It has also been noted that there is a preference for D-lysine on binding DNA, but for heparin, the preference is much less pronounced. Finally, the binder:DNA aggregates imaged by TEM are small enough that they may successfully undergo endocytosis into mammalian cells and hence could be useful DNA transfection agents.