As a single agent, melphalan is used as a preparative treatment prior to autologous stem cell transplant (ASCT) in patients with multiple myeloma (MM) given its myelosuppressive and anti-myeloma effects. While most patients achieve complete remission following ASCT, a majority will develop recurrent disease. Therefore, novel combinations that improve the anti-myeloma activity of melphalan may improve post-transplant outcomes. The first-in-class agent Filanesib (Fil) is a kinesin spindle protein inhibitor which induces mitotic arrest/apoptosis in proliferating cells and has demonstrated anti-myeloma activity in vitro and in vivo. In this study, we tested the effects of combination treatment with filanesib and melphalan in the human myeloma cell lines (HMCLs), U266, MM1S and NCI-H929. As single agents, melphalan and filanesib both inhibit myeloma cell proliferation as assessed by the MTS assay. However, when HMCLs were treated simultaneously with both drugs an antagonistic interaction was observed. This antagonism was in part due to cell cycle arrest in the S-phase, which prevented filanesib from downregulating the anti-apoptotic proteins, BCL-2 and MCL-1 and exerting its cytotoxic effect in the G2/M-phase.. To elucidate whether sequential treatment could enhance cytotoxicity, HMCLs were treated with either melphalan (1 hour) followed by filanesib (MelFil) for 48 hours or filanesib for 48 hours followed by 1 hour melphalan treatment (FilMel). Compared to the apoptosis observed with individual drugs, the MelFil sequence led to significantly lower apoptosis, whereas the the FilMel treatment led to enhanced apoptosis following 48 hours after drug washout. Furthermore examination of recovery of cell proliferation following seven days of recovery after drug removal revealed an increase in cell proliferation for the MelFil treatment compared to a decline in the number of viable cells for FilMel treatment. Taken together, our findings suggest that filanesib pretreatment prior to melphalan may be a clinically relevant therapeutic combination strategy. Moreover, our data underscore the importance of testing sequencing strategies for optimizing therapeutic efficacy of combination treatment.

Citation Format: Darla Destephanis, Eric J. Norris, Brian Turnquist, Saad Usmani, Mahrukh Ganapathi, Ram Ganapathi. Enhanced cytotoxicity following sequential treatment with filanesib and melphalan in human myeloma cell lines. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4828.