The cancer cell survival relies on the over-expression of pH regulators that pump out excess protons/lactic acid, in turn acidifying the tumor microenvironment (TME) which further promotes immune suppression and metastasis. Targeting the pH regulatory molecules can neutralize the TME acidification and inhibit cancer growth. Vacuolar ATPase (V-ATPase) proton pump is the primary pH regulator. V-ATPase ‘V0a2’ subunit, a major pH sensing unit, is over-expressed on cancer cells in a wide array of tumor types including ovarian cancer (OVCA). Here, we examined the clinical relevance of V-ATPase ‘V0a2’ subunit in OVCA patient samples and its therapeutic potential in controlling tumor growth in pre-clinical mouse model. The gene data from Cancer Genome Atlas (TCGA) showed a high frequency of V-ATPase gene alterations in OVCA patients (74%, 448/606 patients). Specifically, the V0a2 gene was highly expressed in all stages of OVCA patients indicating its importance in a centralized physiological mechanism of pH regulation. Across the different OVCA grades, the V0a2 gene expression significantly increased with the tumor grade (Grade 1< Grade2 <Grade 3). Immuno-histochemical and confocal analysis confirmed V0a2 overexpression in both Type I (IHC score= 5.8±1.6; n=46) and Type II (IHC score=7.3±1.8; n=22) OVCA patient tissues compared to non-cancer control group (IHC score=2.0±1.2; n=10). In addition to cancer cells, V0a2 was also expressed on the immune infiltrated cells recruited to TME using CD68 (macrophages) and neutrophil elastase (neutrophil) markers that co-localized with V0a2 staining. Monoclocal antibody against V0a2 (anti-V0a2; MAb) effectively inhibited the proton pump activity, MMPs activation and migration of OVCA cells in vitro. In vivo anti-V0a2 treatment (300µg in PBS; i.p) resulted in delayed tumor growth (3.8 fold, p< 0.05) compared to control, with no apparent in vivo toxicity in athymic nude mice xenograft model. Histological staining of anti-V0a2 treated tumor tissues revealed higher immune-infiltration and a marked decrease in cancer cell numbers compared to control tissues. We observed an increased total leukocyte population (CD45), macrophages (F4/80) and a higher anti-tumor response in anti-V0a2 treated tumors. These results show that V-ATPase-V0a2 is overexpressed in tumor microenvironment and its inhibition impairs ovarian cancer growth by interfering with tumor acidification and activation of anti-tumor responses. In conclusion, the study demonstrates that targeting V-ATPase pH regulators is an effective treatment strategy in ovarian cancer.

Citation Format: Arpita Kulshrestha, Gajendra K. Katara, Safaa A. Ibrahim, Alexandria N. Young, Shayna Levine, Valerie E. Riehl, Mahmood Bilal, Alice Gilman-Sachs, Kenneth Beaman. Targeting tumor associated pH regulators: Effective therapeutic strategy in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 106.