Abstract PD2-07: Tumor CD73 regulates zoledronate induced TIL accumulation into triple negative breast cancer

Abstract Background: CD73 is a membrane-bound protein that by extracellular adenosine production, regulates immune cell function. Low CD73 expression is associated with better prognosis among triple-negative breast cancer (TNBC) patients. Adjuvant bisphosphonates (BPs, such as zoledronate) improve survival among post-menopausal breast cancer patients, but the mechanism for this is unknown. Since BPs also affect immune cells, we studied 1) whether zoledronate-treatment has an effect on tumor infiltrating lymphocytes (TILs) and 2) whether tumor CD73 expression affects these responses in TNBC tumors. Methods: 4T1 mouse mammary cells, stably expressing non-targeting shRNA (sh-NT, control cells) or sh-CD73 were inoculated into the mammary fat pads of Balb/c mice. The mice were treated with i.p. vehicle or zoledronate (ZOL) each 4th day for total of six times. Additionally, to deplete B-cells, the mice were treated with an anti-CD20 or control IgG antibody. Tumor sizes were assessed with a caliper, TILs were studied with immunostainings. Blood lymphocytes were analyzed with Flow cytometry. Results: Sh-CD73 cells formed significantly smaller tumors, than sh-NT cells. ZOL significantly inhibited the growth of both sh-CD73 and sh-NT tumors, but at sacrifice, this effect of ZOL was more significant against sh-CD73 tumors. ZOL increased the % of CD19+/CD21+ and CD19+/23+ in blood of both mice groups, and this effect was inhibited by anti-CD20 antibody. Although neither treatment alone had an effect, the % of CD3+/CD8+ cells in blood were increased in both mice groups by the combination of ZOL and anti-CD20-antibody. ZOL induced accumulation of B220+, CD4+ and CD8+ TILs into both tumor groups. These TIL effects were reduced with anti-CD20 antibody treatment. Anti-CD20 antibody alone inhibited significantly sh-CD73 tumor growth. Anti-CD20 antibody did not interfere with ZOL inhibition of tumor growth in either group. Conclusions: ZOL has inflammatory effects on blood lymphocytes and TILs, which may be affected by tumor expression of immune system regulating proteins, such as CD73. B cell depletion may further prevent tumor growth, in the context of CD73 inhibition. Further studies are needed to investigate whether B-cell inhibition affects ZOL-induced tumor growth inhibition. Citation Format: Nataliia Petruk, Arafat Siddiqui, Sina Tadayon, Arja Jukkola, Jorma Määttä, Pieta Mattila, Jouko Sandholm, Katri S. Selander. Tumor CD73 regulates zoledronate induced TIL accumulation into triple negative breast cancer. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD2-07.