Boosting the apoptotic response of high-grade serous ovarian cancers with CCNE1 amplification to paclitaxel in vitro by targeting APC/C and the pro-survival protein MCL-1

Ovarian cancer exhibits the highest mortality rate among gynecological malignancies. Antimitotic agents, such as paclitaxel, are frontline drugs for the treatment of ovarian cancer. They inhibit microtubule dynamics and their efficiency relies on a prolonged mitotic arrest and the strong activation of the spindle assembly checkpoint (SAC). Although ovarian cancers respond well to paclitaxel, the clinical efficacy is limited due to an early onset of drug resistance, which may rely on a compromised mitosis exit associated with weakend intrinsic apoptosis. Accordingly, we aimed at overcoming SAC silencing that occurs rapidly during paclitaxel-induced mitotic arrest. To do this, we used a specific anaphase-promoting complex/cyclosome (APC/C) inhibitor to prevent a premature mitotic exit upon paclitaxel treatment. Furthermore, we investigated the role of the antiapoptotic BCL-2 family member MCL-1 in determining the fate of ovarian cancer cells lines with CCNE1 amplification that are challenged with clinically relevant dose of paclitaxel. Using time-laps microscopy, we demonstrated that APC/C and MCL-1 inhibition under paclitaxel prevents mitotic slippage in ovarian cancer cell lines and restores death in mitosis. Consistent with this, the combinatorial treatment reduced the survival of ovarian cancer cells in 2D and 3D cell models. Since a therapeutic ceiling has been reached with taxanes, it is of utmost importance to develop alternative strategies to improve the patient's survival. Thus, our study provides not only elements to understand the causes of taxane resistance in CCNE1-amplified ovarian cancers but also suggests a new combinatorial strategy that may improve paclitaxel-based efficacy in this highly lethal gynecological disease.