Abstract PD3-09: Cd73 may influence zoledronate-induced b- and t-cell accumulation into triple-negative breast tumors

Abstract Background: CD73 is an ecto-5′-nucleotidase, which converts AMP to adenosine. In breast cancer, CD73 expression is associated with prognosis, treatment responses to anthracyclines and tumor immunity. Bisphosphonates (BP) inhibit osteoclast-mediated bone resorption. When given in the adjuvant setting, BPs increase survival among post-menopausal breast cancer patients. Since BPs also affect cells of the immune system, we hypothesized that CD73 expression may affect BP responses in triple negative breast cancer cells. Methods: Cell viability and IC50 BPs doses were determined by WST-8 kit. Apoptotic rate and cell cycle arrest were showed by FACS. The number of caspase3/7- positive cells was accessed by a red fluorescence emission via IncuCyteS3. The apoptosis-associated genes mRNA expression was determined by qPCR. To compare BP effect on TNBC tumoral responses in vivo, we used immune-competent mouse models of breast cancer. Tumors were stained by immunofluorescence and immunohistochemically.Results: Suppression of CD73 expression, but not of enzymatic activity significantly sensitized TNBC cells to nitrogen-containing BPs (n-BPs), especially to zoledronate in vitro. The stronger growth inhibitory effects of n-BPs in CD73-suppressed cells were associated with G1 cell cycle arrest and increased apoptosis, as compared with representative control cells in vitro. Zoledronate similarly inhibited both control and CD73-suppressed TNBC tumor growthin immune-competent mice. CD73 suppression in tumors led to the lower lung metastatic burden and metastases size. Zoledronate effect on increased apoptosis was similar in both groups, but significant in CD73-suppressed tumors. Impaired angiogenesis was shown by decreased CD34-positive cell number in CD73-suppressed tumors. Zoledronate significantly increased infiltration of CD45R/B220+ B cells and cytotoxic CD8+ T cells into CD73-suppressed tumors.Conclusions: Suppressed CD73 sensitizes TNBC cells to n-BP treatment, resulting inapoptosis activation and delayed proliferation in vitro. Zoledronate induces a more profound accumulation of CD45R/B220+ B cells and CD8+ T cells into TNBC tumors with the lack of CD73. Since tumor B-cell infiltration has been associated with favourable patient prognosis in breast cancer, the significance of this B-cell effect of zoledronate warrants further investigation. Citation Format: Nataliia Petruk, Arafat Siddiqui, Jorma Määttä, Jouko Sandholm, Katri Selander. Cd73 may influence zoledronate-induced b- and t-cell accumulation into triple-negative breast tumors [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 PD3-09.