CD73 in triple-negative breast cancer

Abstract

CD73 is a membrane-bound receptor that converts AMP to adenosine. Its overexpression in tumors is associated with poor outcomes in triple-negative breast cancer (TNBC) patients. TNBC patients have limited treatment options due to the lack of targeted hormonal receptors. The use of nitrogen-containing bisphosphonates (N-BPs) in the adjuvant setting has shown potential in improving overall survival, particularly among post-menopausal patients with early breast cancer (EBC). This thesis aimed to investigate the role of tumor CD73 in TNBC progression and whether tumor CD73 expression impacts treatment responses to N-BPs. Additionally, we investigated whether reformulating N-BPs enhances their immune cell targeting capabilities in the tumor microenvironment. We employed two methods to inhibit CD73: shRNA-silencing and α,β-methylene-ADP (APCP), a selective enzyme inhibitor. Our findings demonstrated that suppressing CD73 expression, rather than blocking its enzymatic activity with APCP, resulted in the inhibition of invasive properties in TNBC cells and a reduction in epithelial-mesenchymal transition. Suppressing CD73 expression attenuated the positive effects of hypoxia on cell viability and sensitized the cells to the proliferation inhibiting effects of N-BPs in vitro. In vivo experiments revealed that CD73 suppression resulted in reduced tumor growth and fewer lung metastases. In mice treated with the potent N-BP zoledronate, we observed significantly enhanced infiltration of B cells, CD8+ and CD4+ T cells into tumors with low CD73 expression. However, B cell depletion decreased CD8+ T cell infiltration into tumors with suppressed CD73 expression. These effects were not found in tumors with normal CD73 expression. Liposome-encapsulated zoledronate had reduced bone anabolic effect but significantly targeted tumor-infiltrating CD4+ T cells. This treatment also induced changes in intratumoral inflammation by shifting macrophage polarization towards the M1 phenotype. Notably, free zoledronate had only a minor impact on these events. In summary, our results provide evidence for the involvement of CD73 in the initial phases of tumor progression and the infiltration of immune cells into tumors. Furthermore, this study demonstrates that zoledronate induces immune cells infiltration into tumors. Reformulation of the drug may increase such potential.