Tumor growth and metastasis involves complex crosstalk among cancer cells and immune infiltrates. The balance of pro- and antitumor infiltrating immune cells can impact the outcomes of tumor growth. Vacuolar-ATPase (V-ATPase) proton pump promotes cancer growth and metastasis by regulating the pH-associated cancer cell-signaling and the tumor microenvironment. V-ATPase is overexpressed on cancer cell surface in a wide array of tumor types including ovarian cancer (OVCA) as well as on inflammatory cells recruited to the tumor microenvironment. This makes V-ATPase an important target for anticancer therapy. We have created a monoclonal antibody that specifically recognizes the plasma membrane isoform of V-ATPase (a2v) present distinctly on malignant cells and absent on normal cells. The purpose of this study is to investigate the in vivo effect of anti-VATPase-a2v antibody (Mab; 2C1) on the growth of human ovarian cancer (OVCA). The antitumor effects were evaluated in female athymic nude mice xenograft model. Mice were injected with human OVCA cell line (A2780;0.4X106 cells; s.c in upper flank) and the tumor growth was compared to mice that were simultaneously given a single dose of MAb (2C1; 300µg in PBS) or an isotype control antibody(mouse IgG1A). The 2C1 treatment resulted in delayed tumor growth (2.4 fold, p< 0.05), with no apparent in vivo toxicity. Histologic staining of 2C1-treated tumors revealed a loose tumor matrix with higher immune-infiltration compared to control. There was a marked decrease in cancer cell numbers in 2C1-treated tumor tissues compared to control using CA125 cancer-antigen staining. In in vitro assays, there was no measurable cytotoxic effect of 2C1 on OVCA cell proliferation, indicating the role of tumor microenvironment in delayed tumor growth. We further investigated the infiltrated immune population in 2C1-treated tumors. Interestingly, we observed an overall increased total leukocyte population (CD45; p=0.028) and a higher expression of iNOS (IHC-score 2C1 treated tumor= 11.3, control =7.6; p=0.04), suggesting an antitumor response. The total F4/80 macrophage population was higher in anti-VATPase-a2v antibody treated cells (absolute numbers in 2C1 treated tumor=245.2, control tumor=193.1; p=0.04). In 2C1 treated mice, tumor-associated macrophages displayed antitumor properties with correlated iNOS expression. Further, a marked increase in the number of Ly6G positive cells (neutrophil marker) was observed in 2C1 treated tumors, further suggesting an elevated antitumor response. Studies are under way to characterize other immune infiltrated populations that may contribute to antitumor response in 2C1 treated tumor tissues. In conclusion, the study demonstrates that the anti-VATPase "a2" antibody is an effective form of treatment in ovarian cancer.

Citation Format: Arpita Kulshrestha, Gajendra K. Katara, Shayna Levine, Manoranjan Sahoo, Safaa A. Ibrahim, Alice Gilman-Sachs, Kenneth D. Beaman. Cancer growth under check: Anti-vacuolar ATPase "a2" antibody as novel therapy against ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2913.