Abstract 4464: Repurposing nebivolol with CPI-613 for triple-negative breast cancer: Linking in-vitro synergy to in-vivo exposure.

Abstract Triple-negative breast cancer (TNBC) is an aggressive subtype lacking ER, PR, and HER2 expressions, making chemotherapy the default standard of care with high relapse and late-onset toxicities. Drug repurposing offers a rapid, cost-effective path to safer, mechanism-based therapies using agents with known safety. Nebivolol (NEB), an FDA-approved third-generation β1-blocker, shows anti-cancer activity in preclinical models and is believed to act in part by inhibiting oxidative phosphorylation and angiogenesis, although its precise mechanism remains incompletely defined, while CPI-613 (CPI), a lipoate analog that targets pyruvate and α-ketoglutarate dehydrogenases, disrupts mitochondrial metabolism. We hypothesized that dual metabolic targeting would suppress TNBC growth. Murine 4T1 cells were treated with NEB (0. 5-16 µM) and CPI (5-250 µM) in fixed ratios. MTT assays (72 h) and Chou-Talalay analysis identified 4-8 µM NEB + 5-50 µM CPI as the optimal synergistic ratio (90% inhibition, CI 0. 2). In vivo, orthotopic 4T1-Luc tumors were established by mammary fat-pad injection in BALB/c mice and treated with vehicle (N=5), NEB (10 mg/kg QD) (N=5), CPI (25 mg/kg BID) (N=5), or NEB + CPI (NC) (N=6), 5 days/week for 3 weeks. All treatments significantly reduced tumor growth versus vehicle on day 28 (p 0. 01-0. 001). Mean tumor volumes (mm3 ± SD) were: Vehicle 1484. 9 ± 492. 4; NEB 595. 8 ± 134. 6; CPI 634. 7 ± 116. 9; NEB + CPI 702. 5 ± 352. 0. Tumor weights showed the same pattern (p 0. 0001), with all treated groups significantly lower than vehicle but no difference among NEB, CPI, and combination. LC-MS/MS confirmed intratumoral concentrations of NEB and CPI (NEB 42. 2 ± 20. 4 ng/g; CPI 22. 7 ± 6. 6 ng/g; combo NEB 39. 3 ± 39. 8, CPI 16. 8 ± 8. 5 ng/g). Systemic PK was similar across groups, though CPI in NC showed reduced volume of distribution vs single CPI (p = 0. 0368). Tumors collected 23 h post-dose were used to calculate molar concentrations (µM = ng/g × ρₜumor (g/mL) / MW), where density (ρ = weight/volume) was derived from caliper volume. Tumor concentrations in µM were NEB 0. 093 ± 0. 051, CPI 0. 043 ± 0. 011; combo NEB 0. 067 ± 0. 080, CPI 0. 031 ± 0. 022—below the in-vitro synergistic range and not reaching the optimal ratio, which may explain the lack of combination benefit over single agents. PK/PD analyses showed moderate, non-significant trends (r = 0. 26-0. 70). NEB and CPI inhibited TNBC growth, but the combination did not outperform single agents. Sub-synergistic, ratio-mismatched tumor exposure may underlie this outcome; upcoming tumor PK studies will determine whether the synergistic ratio is reached within the dosing interval to guide dose optimization. Citation Format: Mikayla Skillman, Airong Li, Junhyoung Park, Amir Mohammad-Gholizadeh, Fatima Dagher, Meghana Trivedi, Benny Kaiparettu, Diana S-L Chow. Repurposing nebivolol with CPI-613 for triple-negative breast cancer: Linking in-vitro synergy to in-vivo exposure 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 4464.