SDX-105 (Treanda™), Active in Non-Hodgkin’s Lymphoma Cells, Induces the Mitotic Catastrophe Death Pathway.

SDX-105 (Treanda™) is an alkylating agent with a distinct mechanism of action that has been shown to be active in clinical trials in NHL and CLL patients refractory to traditional DNA-damaging agents. SDX-105 induces unique changes in gene expression in NHL cells and displays a lack of cross resistance with other 2-chloroethylamine alkylating agents. Quantitative PCR analysis confirmed that the G²/M checkpoint regulators Polo-like kinase 1 (PLK-1) and Aurora A kinase (AurkA) are down-regulated in the NHL cell line SU-DHL-1 after 8 hours of exposure to clinically relevant concentrations of SDX-105. No changes in these same genes were observed when cells were exposed to equi-toxic doses of chlorambucil or an active metabolite of cyclophosphamide. Because our previous studies demonstrated that SDX-105 treatment can activate apoptotic cell death pathways, we examined the ability of SDX-105 to induce cytotoxicity in cells unable to undergo ‘classical’ caspase-mediated apoptosis. Multi-drug resistant MCF-7/ADR cells and p53 deficient RKO-E6 colon adenocarcinoma cells were exposed for two or three days to either 50 μM SDX-105 alone or 50 μM SDX-105 and 20 μM pan-caspase inhibitor zVAD-fmk. Although zVAD-fmk was able to inhibit SDX-105 induced increases in Annexin-V-positive cells, microscopic analysis of nuclear morphology using the DNA stain DAPI in cells treated with either SDX-105 alone or in combination with zVAD-fmk showed increased incidence of micronucleation. Multi/micro-nucleation and abnormal chromatin condensation are both hallmarks of mitotic catastrophe and have been observed in tumor cells exposed to microtubule-binding drugs such as the vinca alkaloids and taxanes. Activation of mitotic catastrophe may amplify the cytotoxicity of SDX-105 and its activity in tumor cells where classical apoptotic pathways are inhibited. This may explain, at least in part, the potent anti-tumor activity of SDX-105 in tumor cells refractory to conventional 2-chloroethylamine DNA-damaging agents. Additional studies are ongoing to further elaborate the role of mitotic catastrophe in SDX-105’s mechanism of action. The capacity to induce mitotic catastrophe may explain the anti-tumor activity of SDX-105 in chemotherapy relapsed and resistant patients.