Effect of siRNA pre-Exposure on Subsequent Response to siRNA Therapy
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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 naïve 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.
KEY WORDSsiRNA cancer therapy resistance polymeric carriers
Kinesin spindle protein
Myeloid leukemia cell differentiation protein
Linoleic acid-substituted polyethylenimine
RNA-induced silencing complex
Real-time polymerase chain reaction
Short interfering RNA
ACKNOWLEDGMENTS AND DISCLOSURES
The authors would like to thank Mrs. Geraldine Barron for her invaluable help with development and optimization of confocal microscopy, and Dr. Robert Clarke (Georgetown University, Washington, DC) for providing the MDA-435 cells. This project was financially supported by a Breast Cancer Research Grant from Canadian Breast Cancer Foundation (CBCF) and a NSERC Discovery Grant.
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