Comparative analysis of polymers for short interfering RNA delivery in vascular smooth muscle cells

The use of short interfering RNA (siRNA) to degrade messenger RNA in the cell cytoplasm and transiently attenuate intracellular proteins shows promise in the inhibition of vascular pathogenesis. However, a critical obstacle for therapeutic application is a safe and effective delivery system. Biodegradable polymers are promising alternative molecular carriers for genetic material. Here, we aim to perform a comparative analysis of poly(B-amino ester) (PBAE) and polyethylenimine (PEI) polymers in their efficacy for vascular smooth muscle cell transfection using siRNA against the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) housekeeping gene as our test target.

Human aortic smooth muscle cells (HASMC) were transfected in vitro with polymers conjugated to GAPDH or negative control (NC) siRNAs. Increasing siRNA:polymer ratios were tested for optimal transfection efficiency. DharmaFECT2 chemical transfection complexes were used for comparative analysis. Live/dead dual stain was used to measure cell viability, and GAPDH gene silencing was measured by quantitative polymerase chain reaction normalized to 18S.

The highest rate of PEI-mediated silencing was achieved with a 9μL polymer:220 pmol/mL siRNA conjugate (16 ± 2% expression versus NC; n = 6). Comparable PBAE-mediated silencing could be achieved with a 1.95μL polymer:100 pmol/mL siRNA conjugate (10 ± 1% expression versus NC; n = 5). Transfection using PEIs resulted in silencing equivalent to other methods but with less efficiency and increased cell toxicity at 24h polymer exposure. Decreasing PEI exposure time to 4 h resulted in similar silencing efficacy (21 ± 9% expression versus NC, n = 6) with an improved toxicity profile.

Polymeric bioconjugates transfected HASMCs in a manner similar to chemical complexes, with comparable cell toxicity and silencing efficiency. PEI bioconjugates demonstrated silencing equivalent to PBAE bioconjugates, although less efficient in terms of required polymer concentrations. Given the cost-to-benefit difference between the assayed polymers, and PEI's ability to transfect HASMCs within a short duration of exposure with an improved toxicity profile, this study shows that PEI bioconjugates are a potential transfection agent for vascular tissue. Future studies will expand on this method of gene therapy to validate delivery of gene-specific inhibitors aimed at attenuating smooth muscle cell proliferation, adhesion, and migration. These studies will lay the framework for our future experimental plans to expand on this method of gene therapy for in vivo transfection in animal models of vascular disease.