University of Colorado, School of Pharmacy,
Keywords: nanoparticles, cholesterol, genes
Summary:Previous work has shown that cholesterol can be incorporated into lipid-based carriers to impart stability in the blood. While many studies on serum stability of nanoparticles have been conducted by our laboratory and others, very few studies have considered potential interactions with blood cells. Our most recent results suggest that gene delivery vehicles preferentially interact with blood cells, and thus do not perform as predicted for particles that are capable of free diffusion. Such results raise questions regarding conventional models involving extended circulation, targeting and enhanced permeation into tumors. The resulting conclusions are consistent with the very low tumor accumulation that is typically observed, and emphasis is therefore shifted toward maximizing the effectiveness of the delivered cargo. In this context, we have demonstrated that cationic agents traditionally used for nucleic acid delivery cause cellular toxicity that results in progressive cell death over many days; an effect that ultimately limits expression in vivo. By combining an endogenous cationic amphiphile with other naturally-occurring lipids, we have developed a delivery system that exhibits greatly reduced toxicity. By combining this less-toxic delivery vehicle with compatible plasmid alterations, we are able to achieve prolonged expression in vivo. When miRNA sequences that silence tumor-specific genes are encoded in our plasmid, we are able to achieve unprecedented gene silencing (> 99.99%) throughout the tumor. Because it is unlikely that any particulate gene delivery system is able to efficiently penetrate tumors in order to access cells in the tumor interior, we suggest that the exosomal pathway serves to distribute expressed miRNAs throughout the tumor.