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Title: Different architectural polymers used in drug gene delivery
Author: Renuka Nilmini, A. H. L.
ISNI:       0000 0004 2748 0702
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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Synthetic polycations have shown promise as gene delivery vehicles but suffer from unacceptable toxicity and low transfection efficiency. In this thesis novel architectures are being explored to increase transfection efficiency, including hydrophobically modified poly(ethylene imine) (PEI), copolymers with thermoresponsive characters and bioresponsive polymers designed to promote cytosolic delivery. The physical properties of weak poryelectrolytes may be tailored via hydrophobic modification to exhibit useful properties under appropriate pH and ionic strength conditions as a sequence of the often inherently competing effects of electrostatics and hydrophobicity. Pulsed-gradient spin-echo NMR (PGSE-NMR), electron paramagnetic resonance (EPR), and small-angle neutron scattering (SANS) have been used to examine the solution conformation and aggregation behavior of a series of hydrophobically modified hyperbranched PEI polymers in aqueous solution, an their interaction with sodium dodecylsulfate (SDS). According PGSE-NMR, branched PEI2K is monodispersed compare to PEI25K, PEI50K and PEI750K samples. Analysis of the SANS data showed that the propensity to form highly elliptical or rod-like aggregated at higher pHs, reflecting both the changes in protonation behavior induced by the hydrophobic modification and an hydrophobic interaction, but that these structures were disrupted with decreasing pH (increasing charge). The physicochemical characterization of a family of copolymers comprising a core of the cationic polymer PEI with differing thermoresponsive poly (N-isopropylacrylamide) (PNIPAM) grafts has been carried out using PGSE-NMR and SANS. Copolymers with longer chain PNIPAM grafts displayed clear picture for the collapse of grafts with increasing temperature and the associated emergence of an attractive interpolymer interaction. These aspects depend on the number of PNIPAM grafts attached to the PEI core. Even though a collapse in the smaller PNIPAM grafts is observed for the third polymer, could not observe any interpolymer interaction. These facts provide further insight into the association behavior of these copolymers, which is fundamental to developing a full understanding of how they interact with nucleic acids. Bioresponsive polymers designed to promote cytosolic delivery of macromolecular drugs (including proteins and genes) are so far unsuccessful to exhibit their potential in clinical applications. The physicochemical properties of rx)ly(arnidoamine) (PAA) ISA23.HC1 have been studied as a model polymer, in order to understand the mechanism of endosomolyitc polymers with biologically relevant surfaces over the pH range the polymer would encounter during membrane trafficking. Previous work has demonstrated that ISA23.HC1 interacted very strongly with the anionic surface of small globular micelles (SDS), but weak interaction with biologically relevant phospholipid-lyso-PC. This surprising conclusion is elaborated in this thesis for a series of simple membrane mimics studied via EPR using spin-probes dissolved into vesicle and a spin-labelled polymer. Vesicles have been prepared from mixtures of the three most common lipids found in membranes - l,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), l,2-dipalmitoyl-sn-glycero-3-phosphor-L-serine (sodium salt) (DPPS) and l,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) - in ratios that reflect the composition of plasma, endosomal and lysosoaml membranes. The spectrum arising from the nitroxide spin-probe present in the lipid bilayer provided a measure of the dynamics and polarity of the bilayer. The nitroxide spin- label covalently attached to the polymer gave a complementary measure of the polymer flexibility in the presence of the vesicles. No interaction between the polymer and vesicle surface was detected for any of these membrane mimics, across the entire pH range studied (pH 7.4 to 4.0).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available