Abstract 6955: TTK inhibition as a potential sensitizer to CDK4/6 inhibition in metastatic triple-negative breast cancer cell lines

Abstract Breast cancer (BC) is the most common and deadly malignant tumor in women worldwide.​ Triple-negative breast cancer (TNBC) is the most aggressive BC subtype since it is associated with uncontrolled cell proliferation, genetic instability, and metastasis. Advanced TNBC with distant metastasis is untreatable with anti-hormonal or anti-HER2 therapies due to the lack of hormone receptors (estrogen and progesterone) and Human Epidermal Growth Factor 2 receptor (HER2). Therefore, chemotherapy is the primary treatment for this subtype of BC. ​The main goal of treatment for advanced TNBC patients is to prolong survival while minimizing the toxicities associated with chemotherapy. TNBCs are more prevalent in Non-Hispanic Black (NHB) and Hispanic/Latinas (H/L) with TNBC, who have lower 5-year survival rates when compared to Non-Hispanic White (NHW) women with TNBC. TNBC patients with a higher percentage of African ancestry exhibit increased expression of certain mitotic kinases (e.g. Threonine tyrosine kinase, TTK), which are crucial for genomic stability, relative to NHW. TTK is a mitotic kinase that helps maintain genomic integrity by regulating the spindle assembly checkpoint. In BC, TTK overexpression mediates centrosome amplification, chromosome instability, aneuploidy and early metastasis. Cyclin-dependent kinase (CDK) 4/6 regulates DNA replication by phosphorylating Rb, which signals progression through the G1 phase of the cell cycle. The CDK4/6 inhibitor Palbociclib, which induces cellular senescence in tumors, is effective in luminal BC patients but not in TNBC patients. Preliminary data indicates that the inhibition of TTK restored levels of the G1/S regulators p21, p27, and Rb. Therefore, our objective is to evaluate if resistant TNBC cells from NHB women may be responsive/sensitive to CDK4/6 inhibition with Palbociclib treatment after inhibition of mitotic kinase TTK, compared to NHW women. We hypothesize that inhibition of mitotic kinase TTK will restore levels of G1/S regulators, therefore allowing cells to respond to Palbociclib treatment, and decreasing early metastasis and tumor growth. Inhibitor drug was added at various concentrations 24 hours after seeding MDA-MB-231 and MDA-MB-157 BC cancer cell lines in 96-well plates. After 96 hours, MTT Assay revealed IC50 values of 2.52 nM and 5.93 nM for the TTK inhibitor (BAY1217389) and 9.11 nM and 4.95 nM for Palbociclib (PD0332991) in MDA-MB-231 and MDA-MB-157, respectively. These concentrations will allow optimization for dosing in dual therapies. This will allow reducing each drug's levels and toxicity while improving safety and efficacy for clinical use. Citation Format: Gretchen M. Albarrán-Acosta, Magda N. Álvarez Rodríguez, Alexandra N. Aquino-Acevedo, Harold I. Saavedra Lugo. TTK inhibition as a potential sensitizer to CDK4/6 inhibition in metastatic triple-negative breast cancer cell lines [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 6955.