Mitotic Exit Dysfunction through the Deregulation of APC/C Characterizes Cisplatin-Resistant State in Epithelial Ovarian Cancer.

Abstract

<b>Purpose:</b> Acquired resistance to cisplatin is a major barrier to success in treatment of various cancers, and understanding mitotic mechanisms unique to cisplatin-resistant cancer cells can provide the basis for developing novel mitotic targeted therapies aimed at eradicating these cells.<b>Experimental Design:</b> Using cisplatin-resistant models derived from primary patient epithelial ovarian cancer (EOC) cells, we have explored the status of mitotic exit mechanisms in cisplatin-resistant cells.<b>Results:</b> We have uncovered an unexpected role of long-term cisplatin treatment in inducing mitotic exit vulnerability characterized by increased spindle checkpoint activity and functional dependency on Polo-like kinase 1 (PLK1) for mitotic exit in the presence of anaphase promoting complex/cyclosome (APC/C) dysfunction in a cisplatin-resistant state. Accordingly, PLK1 inhibition decreased the survival of cisplatin-resistant cells <i>in vitro</i> and <i>in vivo</i> and exacerbated spindle checkpoint response in these cells. APC/C^CDC20 inhibition increased sensitivity to pharmacologic PLK1 inhibition, further confirming the existence of APC/C dysfunction in cisplatin-resistant cells. In addition, we uncovered that resistance to volasertib, PLK1 inhibitor, is due to maintenance of cells with low PLK1 expression. Accordingly, stable PLK1 downregulation in cisplatin-resistant cells induced tolerance to volasertib.<b>Conclusions:</b> We provide the first evidence of APC/C dysfunction in cisplatin-resistant state, suggesting that understanding APC/C functions in cisplatin-resistant state could provide a basis for developing novel mitotic exit-based therapies to eradicate cisplatin-resistant cancer cells. Our results also show that PLK1 downregulation could underlie emergence of resistance to PLK1-targeted therapies in cancers. <i>Clin Cancer Res; 24(18); 4588-601. ©2018 AACR</i>.