Abstract 5419: Cyclin E1 overexpression as a predictive biomarker for PLK1 and WEE1 inhibitor efficacy in ovarian cancer

Abstract Ovarian cancer remains a lethal malignancy with limited treatment options, particularly for platinum-resistant cases. Key molecular alterations in ovarian cancer include Cyclin E1 overexpression and TP53 mutations, both of which disrupt cell cycle regulation and contribute to poor prognosis. Cyclin E1 overexpression drives unchecked G1/S progression, promoting treatment resistance. TP53 mutations, common in high-grade serous carcinoma, impair checkpoints and increase genomic instability. These features underscore the urgency for cell cycle-targeted therapies. PLK1 and WEE1 inhibitors have shown promise by disrupting cell cycle control, but predictive biomarkers remain unclear. Twelve ovarian cancer cell lines (5 high-grade serous [HGSOC], 5 clear cell [CCOC], and 2 endometrioid [EOC] ovarian carcinomas) were treated with the PLK1 inhibitor volasertib and the WEE1 inhibitor adavosertib to evaluate drug sensitivity, cell cycle effects, and apoptosis in vitro, as well as tumor growth in vivo. Cyclin E1 expression was elevated in 5 cell lines (2 HGSOC, 2 CCOC, and 1 EOC) and TP53 was mutated in 6 cell lines (5 HGSOC and 1 EOC) out of 12 cell lines by qPCR and western blotting. Drug sensitivity assays revealed a strong correlation between Cyclin E1 expression levels and sensitivity to both volasertib and adavosertib. Cell lines with high Cyclin E1 expression showed significantly lower IC50 values compared to those with low/normal expression (volasertib: 0.022-0.089 μM vs. 0.311-28.1 μM, p<0.05; adavosertib: 0.071-0.346 μM vs. 0.368-90.4 μM, p<0.01). Cyclin E1 knockdown reduced sensitivity to both inhibitors (p<0.001), supporting its role as a predictive biomarker, whereas TP53 status did not affect drug response. Flow cytometry showed distinct cell cycle effects of the inhibitors. Volasertib induced M-phase arrest and subsequent cell death, as indicated by a significant increase in the sub-G1 population in high Cyclin E1-expressing cells (p<0.001). Similarly, adavosertib dose-dependently increased sub-G1 cells and depleted G1-phase cells in high Cyclin E1-expressing cells (p<0.001). These effects were absent in low Cyclin E1-expressing cells. Both inhibitors elevated apoptosis markers and the DNA damage marker, γH2AX, in high Cyclin E1-expressing cells but not in low-expression cells. In vivo, volasertib and adavosertib significantly suppressed tumor growth in xenograft models derived from high Cyclin E1-expressing cells (p<0.001), with no significant effects observed in low-expression tumors. Both inhibitors induced cleaved PARP and γH2AX in high Cyclin E1-expressing tumors but not in low-expression models. Cyclin E1 overexpression, regardless of TP53 status, may serve as a predictive biomarker for the efficacy of these inhibitors, thereby offering potential personalized treatment strategies for ovarian cancer. Citation Format: Qian Xi, Akiko Kunita, Miho Ogawa, Mirei Ka, Saeko Nagai, Asami Matsunaga, Kousuke Watanabe, Tomohiko Fukuda, Kenbun Sone, Kei Kawana, Kazuhiro Katayama, Hidenori Kage, Katsutoshi Oda. Cyclin E1 overexpression as a predictive biomarker for PLK1 and WEE1 inhibitor efficacy in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5419.