Abstract LB276: Exposing a vulnerability to mTOR inhibition in triple negative breast cancer by targeting NIMA related kinase 2 (NEK2)

Abstract Triple Negative Breast Cancer (TNBC) conveys poor patient outcomes due to limited effective therapeutic strategies. While inhibiting mTOR (mammalian Target of Rapamycin) is effective in patients with other subtypes of breast cancer, TNBC is intrinsically resistant to mTOR-targeted agents. mTOR promotes survival of mitotic arrest, thus we proposed that inducing mitotic defects may induce a vulnerability to mTOR inhibition, particularly in genomically unstable cancers such as TNBC. We tested this possibility by co-targeting NIMA-related Kinase 2 (NEK2) and mTOR. NEK2 is the most differentially expressed mitotic kinase gene in basal-like breast cancer, a molecular subtype that highly overlaps with TNBC. High expression of NEK2 is also associated with patient outcomes from this disease. Consistent with its roles in promoting mitotic progression and fidelity, suppressing NEK2 activity induces G2/M arrest and mitotic catastrophe in TNBC cells. Moreover, inhibiting mTOR in combination with NEK2 (genetically and pharmacologically) induces a delay in mitosis and profound apoptotic cell death in multiple TNBC cell lines to a greater extent than suppressing either alone. These data indicate that mTOR is essential for progression and survival of mitotic arrest that is induced by NEK2 disruption. This effect was translated to in vivo models where we found that combined NEK2/mTOR inhibition effectively reduces tumor volume in 3 human TNBC mouse models including a patient derived xenograft to a greater extent than either drug alone. No concomitant changes occurred in mouse weight, indicating efficacy without overt toxicity. Mechanistically, short term NEK2/mTOR inhibition induces mitotic checkpoint activation, as indicated by concurrent Cyclin B1 (CCNB1, a marker of the spindle assembly checkpoint) and pHH3 accumulation. However, longer treatment results in CCNB1 loss in G2/M cells, indicating that mTOR is essential for sustaining CCNB1 expression and suppressing G2/M progression during mitotic dysfunction. Despite diminished mTOR activity in mitosis, mTOR is the primary driver of translation in interphase cells. We hypothesize that mTOR-driven interphase translation primes cells to survive mitotic arrest. Current studies are evaluating how mTOR mediated translation of CCNB1 promotes mitotic fidelity and survival, while assessing toxicity in non-transformed cells. These data propose a novel role for mTOR in promoting mitotic fidelity through the spindle assembly checkpoint and lay the foundation for investigating the clinical utility of combining mTOR inhibitors with mitosis-targeting agents, such as those blocking activity of NEK2. Citation Format: Mary Vincent, Kristen Weber-Bonk, Daniella Obidi, Ananya Jain, Darcie Seachrist, Ruth Keri. Exposing a vulnerability to mTOR inhibition in triple negative breast cancer by targeting NIMA related kinase 2 (NEK2) abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86 (8Suppl): Abstract nr LB276.