452. The Enhancement of Anticancer Effect of Chemotherapy by the Delivery of Rad51 siRNA

Abstract

Top of pageAbstract Chemotherapy is one of the effective therapies to cancer, however, cancers gradually develop machineries to resist to chemotherapy. To overcome the problem of drug resistance, we tested the combination of short interfering RNA (siRNA) against Rad51, related to the homologous recombination repair, with cis-diamminedichloroplatinum (II) (CDDP; cisplatin). Moreover, to deliver siRNA into cancer cells effectively, we have developed the HVJ (hemagglutinating virus of Japan, Sendai virus) envelope vector which has the high membrane fusion ability. When synthetic Rad51 siRNA was delivered to HeLa cells using HVJ envelope vector, no Rad51 transcripts were detected on day 2, and Rad51 protein completely disappeared for 4 days after siRNA transfer. When HeLa cells were incubated with 0.02 ug/ml CDDP for 3 hours after siRNA transfer, the number of colonies decreased to approximately 10% of that with scrambled siRNA. The sensitivity to CDDP was enhanced in various human cancer cells, but not in normal human fibroblasts. The synthetic Rad51 siRNA was also introduced into subcutaneous tumor mass of HeLa cells in SCID mice with or without intraperitoneal injection of CDDP, and tumor growth was monitored. When Rad51 siRNA was delivered into tumors using HVJ envelope vector, the delivery efficiency was approximately 50%, and the Rad51 transcript level was reduced to approximately 25%. Rad51 siRNA combined with CDDP significantly inhibited the tumor growth when compared to siRNA or CDDP alone. Rad51 siRNA could enhance the sensitivity to CDDP in cancer cells both in vitro and in vivo. Rad51 siRNA also enhanced the sensitivity of cancer cells to bleomycin. Our results suggest that the combination of CDDP and Rad51 siRNA will be an effective anticancer protocol.