In vivo anti-V-ATPase antibody treatment delays ovarian tumor growth by increasing anti-tumor immune responses.

Tumor acidity is the key metabolic feature promoting cancer progression and is modulated by pH regulators on a cancer cell's surface that pump out excess protons/lactic acid for cancer cell survival. Neutralizing tumor acidity improves the therapeutic efficacy of current treatments including immunotherapies. Vacuolar-ATPase (V-ATPase) proton pumps encompass unique plasma membrane-associated subunit isoforms, making this molecule an important target for anticancer therapy. Here, we examined thein vivotherapeutic efficacy of an antibody (a2v-mAB) targeting specific V-ATPase-'V0a2' surface isoform in controlling ovarian tumor growth.In vitroa2v-mAb treatment inhibited the proton pump activity in ovarian cancer (OVCA) cells.In vivointraperitoneal a2v-mAb treatment drastically delayed ovarian tumor growth with no measurablein vivotoxicity in a transplant tumor model. To explore the possible mechanism causing delayed tumor growth, histochemical analysis of the a2v-mAb-treated tumor tissues displayed high immune cell infiltration (M1-macrophages, neutrophils, CD103(+)cells, and NK cells) and an enhanced antitumor response (iNOS, IFN-y, IL-1 alpha) compared to control. There was marked decrease in CA-125-positive cancer cells and an enhanced active caspase-3 expression in a2v-mAb-treated tumors. RNA-seq analysis of a2v-mAb tumor tissues further revealed upregulation of apoptosis-related and toll-like receptor pathway-related genes. Indirect coculture of a2v-mAb-treated OVCA cells with human PBMCs in an unbuffered medium led to an enhanced gene expression of antitumor molecules IFN-y, IL-17, and IL-12-A in PBMCs, further validating thein vivoantitumor responses. In conclusion, V-ATPase inhibition using a monoclonal antibody directed against the V0a2 isoform increases antitumor immune responses and could therefore constitute an effective treatment strategy in OVCA.