Abstract 1849: Determining the molecular requirements for paclitaxel-induced spindle multipolarity

Abstract Paclitaxel (TaxolTM) and other microtubule poisons are standard chemotherapy agents used in the treatment of breast cancer. However, only a subset of patients experience positive therapeutic effects from these drugs, underscoring the importance of further mechanistic study. Recently we showed that paclitaxel does not accumulate in primary breast cancers at sufficient concentrations to cause mitotic arrest, as it does at typically used concentrations in cell culture. Instead, paclitaxel therapy induces multipolar spindles in breast cancers. Breast cancer cell lines treated with low nanomolar, clinically relevant doses of paclitaxel exhibit chromosome missegregation due to multipolar divisions. We have now extended this to demonstrate that low nanomolar concentrations of other clinically used microtubule poisons (including ixabepilone, vinorelbine, and eribulin) also induce multipolarity in breast cancer cells, suggesting that multipolar mitotic divisions may be a common mechanism of cytotoxicity for microtubule-targeted drugs. Importantly, supernumerary centrosomes are not required for microtubule poison-induced multipolar spindles. To gain mechanistic insight into the formation of paclitaxel-induced multipolar spindles, a variety of mitotic regulators were tested for their ability to affect spindle multipolarity in breast cancer cells treated with clinically relevant concentrations of paclitaxel. Our results demonstrate that the mitotic kinesin Eg5 and the kinase Plk1 promote both the formation and the maintenance of paclitaxel-induced spindle multipolarity, while the mitotic kinesin CENP-E and the kinase Mps1 do not. Interestingly, we found that decreasing the time to anaphase onset decreases the number of multipolar divisions in paclitaxel, resulting in reduced cytotoxicity. Previous studies have shown that Mps1 inhibition sensitizes cells to paclitaxel, and this combination therapy has entered clinical trials (NCT02138812 and NCT02366949). However, our evidence suggests that Mps1 inhibition reduces the efficacy of paclitaxel as a result of decreased time to anaphase onset and fewer multipolar divisions. Additionally, our results suggest that inhibitors of spindle pole clustering increase the number of paclitaxel-induced multipolar divisions and therefore have the potential to increase its efficacy. Identification of the cellular requirements for multipolarity induced by paclitaxel, and of agents that drive the metaphase-to-anaphase transition in the presence of multipolar spindles, may improve the clinical utility of paclitaxel and other microtubule poisons. Citation Format: Christina Scribano. Determining the molecular requirements for paclitaxel-induced spindle multipolarity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1849.