15O - Targeting CCNE1-amplified ovarian and endometrial cancers by combined inhibition of PKYMT1 and ATR

Background

Ovarian cancers (OVCAs) and endometrial cancers (EMCAs) with CCNE1-amplification are often resistant to standard of care treatment and represent an unmet clinical need. Previously, synthetic lethal screening identified loss of the CDK1 regulator, PKMYT1, as synthetically lethal with CCNE1-amplification. We hypothesized that CCNE1-amplification associated replication stress will be more effectively targeted by combining the PKMYT1 inhibitor, RP-6306 (lunresertib), with the ATR inhibitor, RP-3500 (camonsertib).

Methods

The inhibition efficacy of PKMYT1 and ATR inhibitors (RP-6306, RP-3500) were evaluated by cell viability and colony formation assays in CCNE1 amplified, copy gain or copy number low gynecological cancer cells. Mechanism studies utilized western blot, flow cytometry, immunohistochemistry, high content imaging and quantitative image-based cytometry (QIBC). In vivo tumor suppression effect of monotherapies and drug combinations were tested in orthotopic ovarian cancer patient-derived xenograft (PDX) models.

Results

Low dose combination RP-6306 with RP-3500 synergistically increased cytotoxicity more in CCNE1 amplified compared to non-amplified cells. Combination treatment produced durable antitumor activity and an increase in survival in CCNE1 amplified patient-derived and cell line-derived xenografts. Mechanistically, low doses of RP-6306 withRP-3500 increase CDK1 activation more so than monotherapy, triggering rapid and robust induction of premature mitosis, DNA damage and apoptosis in a CCNE1-dependent manner.

Conclusions

These findings suggest that targeting CDK1 activity by combining RP-6306 with RP-3500 is a novel therapeutic approach to treat CCNE1-amplifed OVCAs and EMCAs.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

F. Simpkins.

Funding

Repare Therapeutics.

Disclosure

F. Simpkins: Other, Institutional, Research Grant: Repare Therapeutics; Non-Financial Interests, Institutional, Principal Investigator: Repare Therapeutics. D. Gallo, R. Kryczka, M. Hyer, J. Fourtounis, R. Stocco, E. Aguado-Fraile, A. Petrone, S.Y. Yin, A. Shiwram, G. Marshall: Financial Interests, Personal, Stocks/Shares: Repare Therapeutics. All other authors have declared no conflicts of interest.