Combination of bifunctional alkylating agent and arsenic trioxide synergistically suppresses the growth of drug-resistant tumor cells.

Drug resistance is a crucial factor in the failure of cancer chemotherapy. In this study, we explored the effect of combining alkylating agents and arsenic trioxide (ATO) on the suppression of tumor cells with inherited or acquired resistance to therapeutic agents. Our results showed that combining ATO and a synthetic derivative of 3a-aza-cyclopenta[a]indenes (BO-1012), a bifunctional alkylating agent causing DNA interstrand cross-links, was more effective in killing human cancer cell lines (H460, H1299, and PC3) than combining ATO and melphalan or thiotepa. We further demonstrated that the combination treatment of H460 cells with BO-1012 and ATO resulted in severe G(2)/M arrest and apoptosis. In a xenograft mouse model, the combination treatment with BO-1012 and ATO synergistically reduced tumor volumes in nude mice inoculated with H460 cells. Similarly, the combination of BO-1012 and ATO effectively reduced the growth of cisplatin-resistant NTUB1/P human bladder carcinoma cells. Furthermore, the repair of BO-1012-induced DNA interstrand cross-links was significantly inhibited by ATO, and consequently, gammaH2AX was remarkably increased and formed nuclear foci in H460 cells treated with this drug combination. In addition, Rad51 was activated by translocating and forming foci in nuclei on treatment with BO-1012, whereas its activation was significantly suppressed by ATO. We further revealed that ATO might mediate through the suppression of AKT activity to inactivate Rad51. Taken together, the present study reveals that a combination of bifunctional alkylating agents and ATO may be a rational strategy for treating cancers with inherited or acquired drug resistance.