Small interfering RNA (siRNA) therapeutics have emerged as a means to post-transcriptionally silence gene expression and treat a wide range of genetic diseases; however, the therapeutic delivery of siRNA to cells is limited by enzymatic degradation, rapid clearance from circulation, and limited cellular uptake. To improve delivery, siRNA can be packaged into polyplexes. These polyplexes must be stable enough to deliver siRNA into targeted cells while simultaneously promoting siRNA release within these cells. To meet these contradictory demands, this effort uses photo-responsive mPEG-b-poly(5-(3-(amino)propoxy)-2-nitrobenzyl methacrylate) (mPEG-b-P(APNBMA)) diblock copolymers to create polyplexes that efficiently encapsulate siRNA, while also providing a method for modulating siRNA release via light-mediated charge reversal of the cationic polymer block. In this work, we studied two polymers consisting of identical PEG blocks but different lengths of the cationic block. The shorter polymer was shown to release siRNA more efficiently in response to the photo-stimulus; however, the longer polymer exhibited better siRNA encapsulation and stability. By formulating mixtures of the two polymers, we were able to optimize both cellular uptake and targeted gene silencing upon transfection of the polyplexes into NIH-3T3 cells. Additionally, the improved gene silencing designs coupled with mass action kinetic modeling approaches provided opportunities to predict siRNA, mRNA, and protein concentrations during the gene silencing process and thereby adjust polyplex dosing protocols to further enhance siRNA efficacy. These results demonstrate the ability to effectively tune gene silencing through small changes in polymer composition.

Optimizing gene silencing in light-responsive siRNA polyplexes by varying polymer block lengths

251st National Meeting (2016)

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