Abstract 6964: Dual inhibition of PKMYT1 and WEE1 kinases as a targeted therapy for ATIP3-deficient breast cancers

Abstract ATIP3, a microtubule-associated protein with tumor suppressor functions, is frequently lost in aggressive breast cancers, particularly in 60-80% of triple-negative breast cancer (TNBC), where its absence correlates with poor prognosis. ATIP3 deficiency is associated with heightened aneuploidy, presenting a vulnerability exploitable by targeted therapies. WEE1 kinase, a critical regulator of the G2/M checkpoint, has demonstrated therapeutic promise in this context. Inhibiting WEE1 with AZD1775 selectively compromises ATIP3-deficient cells by exacerbating DNA damage, mitotic abnormalities and chromosome pulverization, ultimately leading to cell death. However, the clinical application of WEE1 inhibitors is constrained by dose-dependent toxicities, necessitating combination strategies to enhance efficacy while reducing toxicity. To address these challenges, we explored the complementary targeting of PKMYT1, another G2/M checkpoint kinase with distinct yet overlapping functions to WEE1. Using 3D cultures of breast cancer cell lines, we compared the responses of ATIP3-deficient and ATIP3-expressing cells to three PKMYT1 inhibitors—RP-6306, GSK1520489A, and MYT1-IN-I. ATIP3-deficient cells exhibited heightened sensitivity to all three inhibitors, particularly RP-6306, which achieved significantly lower IC50 values. To maximize therapeutic impact, we combined RP-6306 with AZD1775, resulting in a synergistic reduction in cell viability in ATIP3-deficient cells. Dual inhibition of WEE1 and PKMYT1 intensified replication stress, DNA damage, and abnormal mitoses, exceeding the effects observed with either inhibitor alone. Importantly, the dual-targeting approach enables the use of lower doses of WEE1 inhibitors, potentially mitigating the toxicities associated with high-dose monotherapies. Our findings establish PKMYT1 as a complementary target to WEE1 in ATIP3-deficient breast cancers. The synergistic effects of their combined inhibition not only enhance therapeutic efficacy but also address key limitations of current WEE1-based therapies. This dual-targeting strategy holds promise for improving outcomes in aggressive breast cancer subtypes. Furthermore, our work highlights the potential of ATIP3 as a predictive biomarker for patient stratification and the rational development of personalized therapies. Citation Format: Maria M. Haykal, Marie Varin de Lapeyriere, Alexis Denis, Sylvie Rodrigues-Ferreira, Clara Nahmias. Dual inhibition of PKMYT1 and WEE1 kinases as a targeted therapy for ATIP3-deficient breast cancers [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 6964.