Abstract GMM-060: A NOVEL TREATMENT APPROACH FOR TARGETING CYCLIN E OVER-EXPRESSING OVARIAN CANCERS

Ovarian cancer lacks therapies that yield complete tumor regression resulting in low cure rates. Cyclin E (CCNE1) is an oncogenic driver that is amplified in 25% of high grade serous ovarian cancers (HGSOC). Cyclin E overexpression (CCNE1HIGH) is associated with poor survival and platinum resistance in these cancers. Effective therapies for CCNE1HIGH ovarian cancers yielding complete and durable responses are lacking. Aberrant expression of Cyclin E leads to unscheduled entry into S phase, premature origin firing, nucleotide depletion, and replication fork stress. The imbalances created by this abnormal progression leads to an increased reliance on cell cycle checkpoint regulators, such as WEE1 and ATR, which counter some of the untoward effects of Cyclin E overexpression. WEE1 is a dual specificity kinase that regulates cell cycle progression by inhibiting both CDK2 and CDK1, thereby inhibiting progression from G1 to S and G2 to M phases, respectively. ATR kinase protects the replication fork from collapse thereby inhibiting G2/M progression so DNA can repair. Additionally, mutations in another G1-S phase checkpoint regulator, TP53, may accentuate dependence on WEE1 and ATR by eliminating an alternative checkpoint pathway that limits CCNE1-CDK2 activity. TP53 mutations are also ubiquitous in HGSOC, further implying the promise of WEE1i and ATRi in selective killing CCNE1HIGH tumors as a rational therapeutic strategy. We tested drug effects on survival, colony formation, cell cycle and apoptosis in vitro and in patient-derived xenograft (PDX) models. Induction of Cyclin E expression in immortalized human fallopian tube secretory epithelial cells (FTSEC) upregulates pChk1, a downstream protein of ATR. Combination of WEE1i with ATRi (WEE1i-ATRi) synergistically decreases cell viability and colony formation in CCNE1HIGH HGSOC cells. Selective inhibition of ATR and WEE1 with siRNA was synergistic supporting that ATR and WEE1 are critical to survival. WEE1i-ATRi dramatically increased cell apoptosis, decreased S phase cells and arrested cells at G2/M phase. Combination inhibition of WEE1 and ATR induced gH2AX and phosphorylation of RPA32, indicating increased double strand DNA break and replication stress. Also, combination inhibition of WEE1 and ATR promoted mitotic catastrophe, as indicated by increased pHH3. Finally, combination WEE1-ATRi is tolerable and results in a 4-fold increase in survival compared to standard chemotherapy or monotherapy in a CCNE1 amplified HGSOC PDX model. In addition, sequential treatment is as effective and less toxic as concomitant WEE1i with ATRi warranting further study. Our studies developed a novel combination treatment approach for targeting Cyclin E over-expressing ovarian cancers. Citation Format: Haineng Xu, Yasuto Kinose, Hyoung Kim, Sergey Medvedev, Erin George, Ronny Drapkin, Eric Brown, Gordon Mills, Fiona Simpkins. A NOVEL TREATMENT APPROACH FOR TARGETING CYCLIN E OVER-EXPRESSING OVARIAN CANCERS [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-060.