Cationic polymers for nuclaic acid delivery to tumors

Abstract

In the field of cancer gene therapy, the use of gene carrier systems is considered indispensable. Cationic polymers are able to effectively condense plasmid DNA to nano-sized particles, further referred to as polyplexes. Compared to free DNA, polyplexes have shown improved nuclease-resistance, a more efficient uptake by the target cells, and enhanced transfection activity. However, clinical introduction of polyplex-systems is hampered by concerns regarding toxicity and the extent and duration of gene expression mediated by the systems. Biodegradable cationic polymers show promise in non-viral gene delivery as they are likely to limit the long-term toxicity of polyplexes. Additionally, biodegradable polymers might also positively affect the gene expression profile mediated by polyplexes. So far, polyplexes based on biodegradable polymers have demonstrated low cytotoxicity and considerable in vitro transfection activity. Few studies reported on the in vivo transfection and toxicity characteristics of biodegradable polymers for gene delivery. In this thesis different biodegradable polymers were investigated for their in vivo tumor transfection properties in mice, after local as well as systemic administration. Different intravenously administered non-degradable cationic carriers were assessed for their capability to deliver nucleic acids to a distant tumor site. In addition, further optimization was explored by addressing the effect of polymer molecular weight and the bacterial motifs present in plasmid DNA on the tumor transfection activity of polyplexes. The in vivo evaluation of biodegradable polymers in this study has led to the identification of two gene delivery systems with considerable in vivo tumor transfection activities, i.e. p(DMAEA)-ppz and pHPMA-DMAE. Interestingly, the i.v. administration of p(DMAEA)-ppz yielded a tumor selective gene expression. The benefits of several advanced non-degradable carrier systems to deliver nucleic acids to a distant tumor site could not be attributed to benefits relevant during the transport phase. Rather, the benefits might be attributed to carrier-induced changes in the intratumoral processing of the nucleic acids. Finally, major improvements in the in vivo transfection efficiency/toxicity ratio of polyplex systems could be established by controlling the molecular weight of the polymeric vehicle and by the replacement of CpG motifs within the plasmid of the polyplexes.