Abstract 1279: Development of a selective CDK2-E inhibitor in CCNE driven cancers

Background: Cyclin dependent kinases (CDK) comprise a family of proteins which are activated upon cyclin binding to promote cell cycle progression. Historically, CDK family inhibitors have had limited utility in the clinic due to 1) toxicities associated with broad spectrum CDK inhibition; and 2) varied and unpredictable efficacy due to lack of a patient selection strategy. The recent approval of three selective CDK4/6 drugs (palbociclib, ribociclib and abemaciclib) has revived the pursuit of therapies against a related interphase kinase, CDK2. Cyclin E gene (CCNE) alterations are prevalent in cancers with high unmet medical need and are emerging as a potential mechanism of clinical resistance to targeted therapies (e.g. CDK4/6 therapies). Methods: Here we report preclinical validation leading to the development of a selective CDK2 inhibitor for the treatment of cancers harboring CCNE alterations. We highlight advanced, orally bioavailable compounds exhibiting single-digit low nanomolar biochemical and cellular potency (pRB), exquisite CDK family selectivity (CDK1, 4, 6, 7 and 9), and whole kinome selectivity. We have characterized the phenotypic and mechanistic consequences of targeting CDK2, employing both genetic and pharmacologic methods across cell lines and xenograft models (e.g. OVCAR-3, MKN-1, HCC1569). Results: In a panel of cell lines, CCNE1-amplified lines exhibited profound sensitivity to selective CDK2 inhibition by halting cells at the G1/S phase of the cell cycle. Upon further inspection, CDK2 inhibition induced multiple markers of senescence, e.g. SA-b-gal and IL-6, in CCNE1-amplified but not in CCNE non-amplified cell lines. Consistent with this, these compounds exhibit robust anti-tumor activity in multiple CCNE1-amplified xenograft models, which was sustained after removal of treatment with these compounds. Conclusions: These data provide a strong rationale for advancing this class of compounds toward clinical development in CCNE-altered cancers. Citation Format: Yoon J. Choi, Steve Wenglowsky, Victoria Brown, Neil Bifulco, Yeon S. Choi, Jian Guo, Megan Hatlen, Joseph Kim, Tim LaBranche, Riadh Lobbardi, Emanuele Perola, Emily Rozsahegyi, Michelle Maynard, Phil Ramsden, Grace Silva, Faith Stevison, Richard Vargas, Ruduan Wang, Doug Wilson, Rich Woessner, Dean Zhang, Rob Meissner, Klaus Hoeflich, Marion Dorsch. Development of a selective CDK2-E inhibitor in CCNE driven cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1279.