Abstract PO1-15-09: Vitamin A Metabolism Induces Ferroptosis to Enhance Immune Therapy Efficacy in HR+/HER2- Breast Cancer

Background: Immune checkpoint blockade (ICB) has substantially improved patient overall and progression-free survival in triple-negative breast cancer (TNBC), but its efficacy remains to be elucidated in the hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer, which is characterized by generally impotent lymphocytic infiltration. In the I-SPY2 trial (NCT01042379), pembrolizumab- or durvalumab-containing neoadjuvant therapy increased the pathologic complete response of HR+/HER2- patients. However, pembrolizumab-containing therapy failed to improve the survival of metastatic HR+/HER2- breast cancer patients (NCT03051659). These inconsistent results underscored the necessity of the investigation of predictive biomarkers to pinpoint potential ICB responders in HR+/HER2- breast cancer. Method: In this study, we collected pretreatment tumor samples from 16 patients in two respective clinical trials (NCT: 04215003 and 04355858) and profiled droplet-based single-cell sequencing, bulk RNA-Seq. Patients were treated with camrelizumab (PD-1 inhibitor)-containing therapy, and five of them achieved partial relief after an 8-week course. We also leveraged the bulk RNA-Seq data from the I-SPY2 trial and Fudan University Shanghai Cancer Center (FUSCC) TNBC ICB trials (NCT04418154 and NCT04613674) for external validation. Another FUSCC transcriptome dataset consisting of 933 treatment-naïve HR+/HER2- or TNBC breast cancer patients was used to detect the abundance of cell types. In vitro and in vivo experiments were used to explore mechanisms of anti-tumor immune response. Results: Based on the single-cell sequencing results, we comprehensively delineated the microenvironmental landscape of HR+/HER2- breast cancer. We discovered responders of immunotherapy showed a higher presence of CXCL9/10+ M1-like macrophages and exhibited enrichment of tumor cells with ferroptosis. We further identified the upregulation of vitamin A metabolism and the vitamin A metabolic gene CRABP1 in tumor cells with ferroptosis. We verified the vitamin A metabolism could induce ferroptosis in HR+/HER2- breast cancers rather than TNBC by CRABP1-ERK axis, which could further recruit CXCL9/10+ M1-like macrophages and promote anti-tumor immune response in HR+/HER2- breast cancer. Combining anti-PD1 with enhancing vitamin A metabolism via retinoid acid possessed greater therapeutic efficacy than monotherapy in HR+/HER2- breast cancers. Finally, we developed an immune therapy response score and validated its reliability in predicting the immunotherapy efficacy for HR+/HER2-breast cancers through both internal and external cohorts. Conclusion: Our study represents the earliest efforts to decipher the microenvironmental landscape and the mechanisms underlying the response to ICB in HR+/HER2- breast cancer at single-cell resolution. We unraveled a HR+/HER2- breast cancer-specific Vitamin A-ferroptosis axis that mediated immunotherapy response and constructed a robust immunotherapy efficacy prediction score based on this Vitamin A-ferroptosis axis. Citation Format: Yi-Fan Zhou, Hu-Yun-Long Zhang, Xi Jin, Yi-Zhou Jiang, Zhi-Ming Shao. Vitamin A Metabolism Induces Ferroptosis to Enhance Immune Therapy Efficacy in HR+/HER2- Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-15-09.