Light-mediated activation of siRNA release in diblock copolymer assemblies for controlled gene silencing

Controllable release is particularly important for the delivery of small interfering RNA (siRNA), as siRNAs have a high susceptibility to enzymatic degradation if release is premature, yet lack silencing activity if they remain inaccessible within the cytoplasm. To overcome these hurdles, novel and tailorable mPEG-b-poly(5-(3-(amino)propoxy)-2-nitrobenzyl methacrylate) (mPEG-b-P(APNBMA)) diblock copolymers containing light-sensitive o-nitrobenzyl moieties and pendant amines are employed to provide both efficient siRNA binding, via electrostatic and hydrophobic interactions, as well as triggered charge reversal and nucleic acid release. In particular, siRNA/mPEG-b-P(APNBMA)_23.6 polyplexes show minimal aggregation in physiological salt and serum, and enhanced resistance to polyanion-induced unpackaging compared to polyethylenimine preparations. Cellular delivery of siRNA/mPEG-b-P(APNBMA)_23.6 polyplexes reveals greater than 80% cellular transfection, as well as rapid and widespread cytoplasmic distribution. Additionally, UV irradiation indicates ≈70% reduction in targeted gene expression following siRNA/mPEG-b-P(APNBMA)_23.6 polyplex treatment, as compared to 0% reduction in polyplex-treated cells without UV irradiation, and only ≈30% reduction for Lipofectamine-treated cells. The results here highlight the potential of these light-sensitive copolymers with a well-defined on/off switch for applications including cellular patterning for guided cell growth and extension, and cellular microarrays for exploring protein and drug interactions that require enhanced spatiotemporal control of gene activation.