Extracellular adenosine synthesis genes regulated by estrogen signaling are associated with cancer aggressiveness and poor prognosis in estrogen receptor (ER)-positive breast cancer

Abstract Background: Accumulation of extracellular adenosine regulates tumor progression. Extracellular adenosine binds to adenosine receptors, which mediates signaling to induce angiogenesis and cell proliferation, as well as functioning as an immunosuppressive agent in the tumor microenvironment (TME). CD73 and CD39 are two cell surface enzymes that catalyze the synthesis of extracellular adenosine from AMP, ADP and ATP in the TME. However, the underlying mechanisms that regulate adenosine synthesis in the TME of ER-positive breast cancer remains unknown. Methods: In order to investigate the transcriptional regulation of CD73 and CD39 in ER-positive breast cancer, we treated ER-positive breast cancer cell line, MCF7 with estrogen and tamoxifen. We also investigated the clinical significance of CD73/39 expression in ER-positive patients by bioinformatical approach using TCGA and GEO breast cancer cohorts. Results: In TCGA cohort, higher CD73 expression was associated with worse overall survival in ER-positive tumors (p=0.003), but not in ER-negative tumors. Gene set enrichment analysis revealed that estrogen response gene sets (Early; p=0.043, Late; p=0.021) were significantly enriched in CD73 low expressing ER-positive tumors, suggesting estrogen signaling may inhibit CD73 expression. To test this hypothesis, we analyzed the expression of CD73 and CD39 in MCF7 cells treated with estrogen, tamoxifen, or vehicle control. Our data revealed that estrogen treatment suppressed CD73 and CD39 expression, however tamoxifen treatment significantly enhanced expression of the genes. These findings suggest that tamoxifen treatment can induce the expression of CD73 and CD39 in ER-positive breast tumors, by removing the repressive effect of hormone signaling. Additionally, gene set enrichment analysis revealed that CD73-high ER-positive tumor was significantly associated with cancer aggressiveness characteristics, such as epithelial-mesenchymal transition (EMT) (p<0.001) and angiogenesis (p<0.001). On the other hand, CD73-high ER-positive tumor have significantly less infiltrating CD8-positive T cells, memory B cells and plasma cells in silico analysis, implying that CD73-high tumors have immunosuppressive environment. Further, we found that CD73 expression was significantly elevated post-chemotherapy as compared to the tumors prior to the treatment (p=0.007), and CD73 high expressing patients demonstrated worse relapse-free survival in the neoadjuvant chemotherapy cohort (p=0.003). Conclusion: Our molecular findings indicate that expression of CD73 and CD39 are transcriptionally repressed by estrogen signaling, however tamoxifen treatment reverses the effect. Increased expression of CD73 significantly correlates with worse outcomes in ER-positive breast cancer patients which may be due to immunosuppressive tumor microenvironment created by extracellular adenosine driving a pro-metastatic phenotype. Our data indicate an intriguing mechanism which could be therapeutically exploited by targeting CD73/39 to reverse ‘immune-cold’ microenvironment for the treatment of recurrent and metastatic ER-positive breast cancers. Citation Format: Eriko Katsuta, Tao Dai, Abhisha Sawant Dessai, Subhamoy Dasgupta. Extracellular adenosine synthesis genes regulated by estrogen signaling are associated with cancer aggressiveness and poor prognosis in estrogen receptor (ER)-positive breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-06-12.