Antitumor and immunomodulatory effects of oxygen therapy

Abstract

It is well known that ischemia and hypoxia in the tumor microenvironment promote tumor progression. Оxygen deficiency in tumor microenvironment polarizes cancer cell metabolism from oxidative phosphorylation to the aerobic mode (Warburg effect) and anaerobic glycolysis. This altered carbohydrate metabolism is characterized by low energy efficiency and excessive glucose consumption. Under hypoxic conditions, the antioxidant protection of malignant cells becomes weaker, thus causing a sufficient increase of their susceptibility to direct toxic effects of reactive oxygen species (ROS). In clinical practice, oxygen saturation of tumors is usually achieved by using water-soluble ozone or hyperbaric oxygen. The ROS are shown to be produced by oxidative burst, thus being able to enhance antitumor effects of chemoradiotherapy. The immune cell-derived ROS were shown to directly inhibit tumor growth. In addition, ROS provide additional immune stimulation through the induction of mutagenesis in the tumor cells and production of immunogenic neoantigens. ROS may also enhance antitumor immune defense by inducing synthesis of interferon-γ, tumor necrosis factor-α, IL-2 and IL-6 by immune cells. Moreover, ROS may exert a negative effect on antitumor immunity. In particular, they are able to: (I) favor the recruitment and accumulation of regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment; (II) promote accumulation of alternatively activated (M2) macrophages and (N2) neutrophils, and, (III) impair presentation of immunogenic antigens (Ag) by dendritic cells. We suggest that the maximal clinical effect of oxygen therapy could be achieved in case of its simultaneous or sequential combination with immunotherapeutic interventions.The authors conclude that:–         oxidative stress-induced reactive oxygen species may preferentially damage tumour cells without significantly affecting normal cells;–         oxygen therapy may potentiate anti-tumour effects of chemoradiotherapy;–         oxygen therapy could be effectively combined with immunotherapy to achieve maximal anticancer effects with minimal side effects.