Abstract 6942: Targeting <i>CCNE1</i> amplification in gastric cancer

Abstract Background: Cyclin E (CCNE1) is amplified in multiple cancers including approximately 10% of esophagogastric cancers and 20% of ovarian cancers. CCNE1 amplification leads to DNA replication stress and chromosomal instability. Prior studies have found that CCNE1 amplification in gastric cancer is associated with increased liver metastasis, an “immune-cold” tumor microenvironment, and worsened clinical outcomes. At the same time, CCNE1-amplified tumors are vulnerable to loss of membrane-associated tyrosine- and threonine-specific cdc2-inhibitory kinase (PKMYT1). Lunresertib (RP-6306) is a selective, first-in-class, oral PKMYT1 inhibitor that leads to unscheduled mitotic entry and catastrophic DNA damage selectively in CCNE1-amplified cells. The purpose of this study is to evaluate the effect of PKMYT1 inhibition in CCNE1-amplified gastric cancer. Methods: Human gastric cancer cell lines derived from patient-derived organoids (PDOs) or mouse CCNE1-overexpressing gastric cancer organoids were treated with lunresertib in vitro. Cell proliferation and viability were measured by WST-1, CellTiter-Glo, and colony formation assays. Quantitative reverse-transcription PCR (qRT-PCR) was used to measure RNA expression. Mice bearing syngeneic subcutaneous CCNE1-overexpressing gastric cancer xenografts were treated with lunresertib, anti-PD1, or lunresertib plus anti-PD1. Treatment efficacy was monitored by tumor volume, and tumor-infiltrating immune cells were assessed by flow cytometry. Results: Lunresertib induced significant cytotoxicity in CCNE1-amplified gastric cancer cell lines and organoids measured through multiple cell viability and proliferation assays. Lunresertib induced DNA damage as monitored by increased γH2AX expression in CCNE1-amplified gastric cancer cells. Lunresertib also strongly induced CXCL10 expression, a downstream cytokine of the cGAS-STING cytosolic DNA sensing pathway. While lunresertib or anti-PD1 monotherapy demonstrated moderate tumor growth inhibition in vivo in a syngeneic model of CCNE1-overexpressing gastric cancer, the combination of lunresertib and anti-PD1 resulted in the strongest tumor regressions, suggesting possible synergistic activity. Flow cytometry of tumor-infiltrating immune cells identified increased CD4+ T cells and decreased neutrophils with lunresertib plus anti-PD1. Conclusion: Lunresertib demonstrated synthetic lethality in CCNE1-amplified gastric cancer across multiple in vitro and in vivo experiments. Lunresertib had synergistic effects with anti-PD1 in vivo against CCNE1-amplified gastric cancer, potentially due to induced DNA damage and inflammatory cytokine induction. Citation Format: Sung Joo Jang, Lawrence W. Wu, Sho Hangai, Cameron Shapiro, Jimyung Park, C. Gary Marshall, Ryan H. Moy. Targeting CCNE1 amplification in gastric cancer [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 6942.