Abstract 358: INK4A/B as predictive biomarkers for enhanced efficacy of dual WEE1 and PKMYT1 inhibition in CDK4/6 inhibitor-resistant breast cancer

Purpose: Although CDK4/6 inhibitors combined with endocrine therapy represent the standard of care for ER+/HER2- advanced breast cancer, resistance inevitably develops in a significant subset of patients, limiting effective treatment options. Similarly, patients with triple-negative breast cancer (TNBC) lacking BRCA mutations face an absence of targeted therapeutic strategies. These challenges underscore the urgent need for biomarker-driven targeted therapies in approximately 30% of breast cancer patients. Both CDK4/6 inhibitor-resistant (CDK4/6i-R) breast cancer and TNBC exhibit increased replication stress and cell cycle dysregulation, suggesting potential sensitivity to interventions targeting G2/M transition regulation by kinases like WEE1 and PKMYT1. Prior findings show that WEE1 and PKMYT1 inhibition disrupts TNBC cell survival by forcing cell cycle progression without adequate DNA repair and chromosome segregation. Our findings further indicate that WEE1 or PKMYT1 inhibition can effectively suppress CDK4/6i-R tumor growth. Additionally, PKMYT1 upregulation mediates resistance to WEE1 inhibition, suggesting that dual WEE1/PKMYT1 inhibition may provide synergistic tumor suppression in CDK4/6i-R and TNBC contexts. This study aimed to identify predictive biomarkers of response to WEE1/PKMYT1 dual inhibition while maintaining manageable toxicity. Results: Evaluating WEE1 inhibitors (adavosertib or azenosertib) in combination with the PKMYT1 inhibitor (lunresertib) across CDK4/6i-R and TNBC models, including patient-derived xenografts (PDXs) and organoids, demonstrated significant tumor suppression, with the novel dual WEE1/PKMYT1 inhibitor SGR-3515 showing comparable efficacy. RNA sequencing analysis revealed a positive association between high INK4B (p15) expression and robust treatment response, while baseline expression data from the Cancer Cell Line Encyclopedia indicated a positive correlation between both INK4A (p16) and INK4B expression and responsiveness to dual WEE1/PKMYT1 inhibition across ER-positive and TNBC subtypes. Notably, forced overexpression of INK4B sensitized cells to dual inhibition, whereas INK4B knockdown increased resistance, underscoring its pivotal role in therapeutic response. Higher baseline levels of INK4A and INK4B in CDK4/6i-R and TNBC PDX models further correlated with improved treatment outcomes. Conclusion: Dual inhibition of WEE1 and PKMYT1 presents a compelling therapeutic strategy for CDK4/6i-R breast cancer and TNBC. Elevated baseline levels of INK4A and INK4B are strongly associated with enhanced treatment responses, highlighting their potential as predictive biomarkers for selecting patients likely to benefit from WEE1/PKMYT1 dual inhibition therapy. Citation Format: Mei-Kuang Chen,Xiaoting Jiang,Xiayu Rao,Tuyen Bui,Yan Wang,Jing Wang,Grace DeAlessandro,Nicole L. Massoumi,Rachel Y. Kim,Roanna A. Debler,Serena Kim,Kelly K. Hunt,Felicia Gray,Shaoxian Sun,Khandan Keyomarsi. INK4A/B as predictive biomarkers for enhanced efficacy of dual WEE1 and PKMYT1 inhibition in CDK4/6 inhibitor-resistant breast 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 358.