Abstract 360: Discovery of selective and orally bioavailable PKMYT1 inhibitor: characterization of anti-tumor activities as single and dual agents

Abstract Advancing effective cancer therapies requires innovative approaches to better understand complex biological interactions. PKMYT1, a crucial regulator of the cell cycle involved in the G2/M transition through inhibitory phosphorylation of CDK1, has emerged as a promising therapeutic target. Inactivation of PKMYT1 is synthetically lethal in tumor cells with genomic alterations leading to high replication stress, such as CCNE1 amplification, which is frequently found in high-grade serous ovarian, uterine, and gastro-esophageal cancers. In this report, we present a series of potent PKMYT1 inhibitors, emphasizing their pharmacokinetic profiles and anti-tumor activities, characterized as either single agents or in combination. Furthermore, we explored the potential of combination therapy using these profiled PKMYT1 inhibitors. We hypothesized that inhibition of the DNA damage response kinase ATR and its downstream pathway may further enhance the tumor cytotoxicity of PKMYT1 inhibitors. Preclinical validation of this hypothesis demonstrated that combining PKMYT1 inhibitors with ATR inhibitors, such as prexasertib and RP-3500, resulted in enhanced antitumor activity in CCNE1-amplified cancer models. Additionally, we observed synergistic effects when combining PKMYT1 inhibitors with standard-of-care chemotherapies that induce DNA damage, such as gemcitabine and hydroxyurea. We also identified novel synergistic partners from library screening, featuring GSK3B inhibitors. These findings were confirmed in cell lines, organoid models, and in vivo CDX models, highlighting the potential of PKMYT1 inhibitors as part of combination therapy strategies. In conclusion, our study underscores the therapeutic potential of selective PKMYT1 inhibitors in CCNE1-amplified cancers and provides a strong rationale for their combination with ATR inhibitors and DNA-damaging chemotherapies. These findings support the continued development and clinical evaluation of PKMYT1 inhibitors as a novel approach to cancer treatment. Citation Format: Xiaobin Summer Wang, Sining Zhu, Haili Ding, Yang Tang, Minrui Weng, Kelly Chen, Yanna Ma, Pan Wang, Yifan Tu, Juhao Yang, Jun Wu, Dan Zhao, Xuefei Tan, Ying Ji, Xiangyu Yao, Zhipeng Yan. Discovery of selective and orally bioavailable PKMYT1 inhibitor: characterization of anti-tumor activities as single and dual agents [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 360.