Abstract Background: WEE1 kinase maintains genomic integrity by regulating the G1/S and G2/M cell cycle transitions, allowing cells to repair damaged DNA before progressing to the next phase. Treating tumor cells with azenosertib, a highly selective oral WEE1 inhibitor (WEE1i), promotes premature cell cycle entry, accumulation of DNA damage, and ultimately cell death. While clinically meaningful activity has so far been observed in platinum-resistant ovarian cancer, we sought to explore vulnerability to WEE1 inhibition in other solid tumor types, such as breast. With over 300,000 new cases of breast cancer diagnosed each year in the United States, approximately 15-20% are triple-negative breast cancer (TNBC). TNBC is a particularly aggressive subtype with limited availability of targeted therapies for patients. Although recent approvals of immune checkpoint inhibitors and antibody-drug conjugates (ADCs) have improved outcomes in some patients with TNBC, many eventually experience disease progression, underscoring the continued need for new therapeutic strategies. Methods: Using results from four in vitro pharmacogenomic drug screens in cell lines, we analyzed breast cancer models for sensitivity to WEE1i and potential molecular correlates, including subtype classification, mutation and expression of genes associated with replication stress, and pathway enrichment. In vivo efficacy of azenosertib was evaluated in a panel of ∼10 TNBC xenograft models implanted subcutaneously in immunocompromised mice. Clinically relevant doses of azenosertib were tested as monotherapy treatments or in combination with current standard-of-care therapies for TNBC. Results: When compared to non-TNBC breast, TNBC cell lines were significantly more sensitive to WEE1i in vitro and tended to have higher Cyclin E1 protein expression, a known marker of replication stress and vulnerability to WEE1i. In vivo, single agent azenosertib demonstrated moderate to strong efficacy in a panel of TNBC xenograft models. In models that were less sensitive to single agent azenosertib, combinations with sacituzumab govitecan (SG), trastuzumab deruxtecan (T-DXd), or datopotamab deruxtecan (Dato-DXd) enhanced tumor growth inhibition and prolonged duration of response beyond what was achieved with any of the agents alone. Conclusions: We demonstrated in vitro and in vivo evidence that TNBC models are susceptible to WEE1 inhibition. Our findings suggest that azenosertib as a single agent, or in combination with standard-of-care therapies, may be a potential treatment strategy for TNBC and warrants further exploration. Citation Format: Catherine Lee, Alexandra Levy, Mona Abed, Heekyung Chung, Olivier Harismendy, Doris Kim.. WEE1 inhibition as a therapeutic strategy in triple-negative breast cancer: Evaluating single agent and combination activity of azenosertib in preclinical models abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3902.
Lee et al. (Fri,) studied this question.