Abstract 5730: Targeting the cell cycle with AZD8421, a potent and highly selective CDK2 inhibitor

Abstract Cyclin-dependent Kinase 2 (CDK2) is a Ser/Thr kinase activated via interaction with its cyclin partners CCNE and CCNA, driving G1/S progression of the cell cycle. CDK2 inhibition has the potential to address multiple resistance mechanisms to CDK4/6 inhibitors in breast cancer. In addition, CCNE1 is frequently amplified and over-expressed in cancers including ovarian, uterine, breast, gastric and others, with pre-clinical data linking CDK2 inhibition sensitivity to high CCNE1. The CDK2 inhibitor field has historically suffered from high attrition in Phase I due to off-target toxicity. AZD8421 is a uniquely selective CDK2 inhibitor, that offers potential to show improved therapeutic index and combinability. As well as achieving CDK family selectivity in cells versus key off-targets (CDK1, CDK4/6, CDK9), AZD8421 had no significant kinase inhibition outside the CDK family. Only 7 distinct targets showed greater than 50% inhibition in a panel of 403 kinases when screened with 1µM of AZD8421. In nanoBRET assays measuring cellular target engagement, AZD8421 had an IC50 against CDK2 of 9nM with selectivity over CDK1, CDK4 and CDK6. In vitro cellular assays demonstrated that AZD8421 inhibits endogenous phospho-substrate at 58nM with >327-fold selectivity over CDK9 phospho-substrate pSer2 of RNAPII (>19.2 µM). In a CCNE1 amplified cell line, AZD8421 potently inhibited cell proliferation (69nM, OVCAR3), correlated with inhibition of pRB, arrest in G1/S phase of the cell cycle and induction of senescence, compared to a CCNE1 non-amplified cell line (SKOV3) with IC50 of 2.05 µM. In vitro combination assays in CDK4/6 inhibitor resistant breast cancer cell lines showed combination benefit with AZD8421 plus approved CDK4/6 inhibitors. In vivo, AZD8421 potently suppressed phosphorylation of Rb, and demonstrated robust monotherapy and CDK4/6i combination activity in breast and ovarian in vivo models. In vivo PD marker suppression and efficacy was demonstrated in CDK4/6 inhibitor resistant breast PDXs in combination with palbociclib (CDK4/6i). AZD8421 showed robust monotherapy activity in a CCNE1 amplified ovarian model OVCAR3 with regressions seen with monotherapy and in combination with palbociclib. Monotherapy activity and combination benefit in vivo with standard of care agents was also observed in ovarian PDX models with elevated levels of CCNE1. AZD8421 is a potent and highly selective CDK2 inhibitor, with double digit nM potency in cells, as well as suitable physical and pharmacokinetic properties for progression into the clinic. Citation Format: Christopher R. Denz, Michael Grondine, Jun Fan, Jessie Hao-Ru Hsu, Anne Jackson, James Robinson, Grace Guo, Wen Li, Yanjun Wang, Maryann San Martin, Laura Prickett, Jeffrey Johannes, Avipsa Ghosh, Dhivya Sudhan, Christina Vasalou, Ryan Richards, Kevin Beaumont, Matt Peters, Lisa Drew, Stephen Fawell, Frederick W. Goldberg. Targeting the cell cycle with AZD8421, a potent and highly selective CDK2 inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5730.