Poly(glycoamidoamine)s: Understanding their Structure and Structure-Bioactivity Relationships
Taori, Vijay P.
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In order to achieve efficient therapeutic effect, it is important to understand the structure of biomaterials that are used in the therapeutic delivery system. This dissertation is dedicated towards understanding the hydrolysis pattern of plasmid DNA (pDNA) delivery vehicles comprised of poly(glycoamidoamine)s (PGAAs) under physiological conditions and effects of subtle changes in the chemical structure of the PGAAs on its biological performance. The unusual hydrolysis of the tartarate and galactarate based PGAAs was investigated by studying the hydrolysis of small model molecules which mimic the repeat unit of the respective polymers. In the case of galactarate and tartarate based molecules with terminal amines showed faster hydrolysis of the amide bonds. In addition for the tartarate based compounds, it was also found that it is necessary to have terminal amine functionality for the intramolecular hydrolysis to occur. The model compounds consists of two amide bonds and were designed symmetric, however amide bond on only one side of the tartarate moiety show underwent hydrolysis. Further studies show that one side of the amine assists the hydrolysis of the amide bond on the other side of the tartarate moiety. The degradation of poly(L-tartaramidopentaethylenetetramine) (T4) was also used to study the sustained release of pDNA from the layer-by-layer constructs of T4/pDNA. The thickness of the constructs was characterized by ellipsometry while the UV-visible spectroscopy was used to characterize the loading capacity of the constructs for pDNA. The indirect sustained release of pDNA under the physiological conditions with respect to time was characterized by the cellular uptake studies in HeLa cells. The increase in the uptake of the Cy5 labeled pDNA was seen at extended period of eleven days. The integrity of the sustained released pDNA for the transgene expression was characterized with an assay to see the expression of the green fluorescent protein (GFP) from the T4/GFP-pDNA layer-by-layer constructs. PGAAs show a very efficient delivery of the pDNA in a non-toxic manner. The chemical structure of the polymer can dictate the binding with pDNA and also the release of the pDNA form the polymer-pDNA complexes. In order to better understand the fundamentals of the nucleic acid delivery and to better design the nucleic acid delivery vehicles, subtle changes in the chemical structure of the PGAAs were designed and studied for the biological activity. The effect of charge type was investigated by designing and synthesizing guanidine based polymer series analogues to galactarate and tartarate based PGAAs (G1 and T1) which incorporate secondary amines as the charge type on the polymer backbone. The guanidine based polymer series, poly(glycoamidoguanidine)s (PGAGs), show very non toxic behavior in HeLa cells at all the different polymer to pDNA ratio (N/P ratio) studied. Interestingly PGAGs are the only non-toxic guanidine containing polymers which are reported in the literature to the date. The cellular uptake of pDNA assisted from the PGAGs is a little higher than PGAAs compared although both the series of polymers show similar transgene expression. The transgene expression in case of PGAGs also imply the release of the polymer-pDNA complexes from the endosome. In another study of structure-bioactivity relationship based on the degree of polymerization (DP) of poly(galactaramidopentaethylenetetramine) (G4), it was found that the increase in the DP of G4 increases the toxicity of the polymers in the HeLa cells.
- Doctoral Dissertations