Cyclopamine Tartrate Enhances Antitumor Immunity in Triple-Negative Breast Cancer

Introduction: Triple-negative breast cancer (TNBC) remains a clinical challenge due to limited therapeutic options and poor response to immune checkpoint inhibitors (ICIs). Tumor hypoxia and abnormal vasculature contribute to an immunosuppressive microenvironment that restricts T-cell infiltration. Cyclopamine tartrate (CycT), a heme-targeting small molecule, has been shown to inhibit tumor oxidative metabolism and improve oxygenation[1-2]. This study examined whether CycT suppresses tumor growth and modulates the immune microenvironment in TNBC. Methods: Female BALB/c mice bearing orthotopic 4T1-Luc syngeneic tumors were treated with CycT (7.5 mg/kg Retro-Orbital Injection, twice weekly) or vehicle control. Digital calipers monitored tumor growth. Tumors were harvested for histology (H&E) and analyzed by multiparameter flow cytometry to quantify CD8+ T-cell density and PD-1 expression on tumor-infiltrating lymphocytes. Statistical significance was determined using unpaired two-tailed t-tests. Results: CycT significantly inhibited 4T1 tumor growth compared with control (p < 0.001), as shown by markedly smaller resected tumors and reduced volumes over 24 days of treatment. Flow cytometric analysis demonstrated that CycT increased intratumoral CD8+ T-cell density (p < 0.05) and elevated PD-1 median fluorescence intensity on CD8+ cells (p = 0.016), indicating a more active or antigen-experienced T-cell phenotype. Conclusions: These data indicate that CycT shows significant antitumor effects in a TNBC model while promoting CD8+ T-cell infiltration and activation. The results suggest that CycT reprograms the tumor microenvironment to become immune-accessible, providing a mechanistic basis for future combination strategies with immune checkpoint blockade in TNBC. References: 1. Sohoni, S. et al, Cancer Res (2019) 79 (10): 2511-2525. 2. Ghosh, P. et al., Cancer Res (2020) 80 (17): 3542-3555. Citation Format: Tianyuan Wang, Lorena Arango, Li Liu. Cyclopamine tartrate enhances antitumor immunity and suppresses triple-negative breast cancer growth [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 399.