Effect of siRNA pre-Exposure on Subsequent Response to siRNA Therapy

An alternative cancer therapy based on RNA interference (RNAi) has shown considerable promise but the possibility of resistance development is not known. This study explored the possibility of therapeutic resistance against siRNA nanoparticles in human cancer cells. Two approaches to siRNA treatment were undertaken using lipid-modified polyethylenimines, a single high concentration (shock) and repeated increasing concentrations (gradual). The targets were Mcl-1, RPS6KA5 and KSP in MDA-MB-435 cells. There was no evidence of resistance development in shock-treated cells, while the decrease in mRNA levels of targeted proteins was not as robust in na < ve cells in gradual treatment. However, silencing efficiency was restored after a 7-day recovery period when expression of suppressed proteins returned to normal levels. Cellular uptake of siRNA was not affected by pre-treatments. Other mediators involved in cell survival and proliferation were altered in siRNA-treated cells, but only JUN silencing led to a heightened loss of viability. In vivo experiments demonstrated similar silencing efficiency at mRNA level after repeat doses. Human cancer cells responded to repeat siRNA nanoparticles in a similar fashion after a temporary initial alteration and little, if any, resistance was evident against repeated siRNA treatments.