Systemic oxygenation weakens the hypoxia and hypoxia inducible factor 1α-dependent and extracellular adenosine-mediated tumor protection

Intratumoral hypoxia and hypoxia inducible factor-1 alpha (HIF-1-alpha)-dependent CD39/CD73 ectoenzymes may govern the accumulation of tumor-protecting extracellular adenosine and signaling through A2A adenosine receptors (A2AR) in tumor microenvironments (TME). Here, we explored the conceptually novel motivation to use supplemental oxygen as a treatment to inhibit the hypoxia/HIF-1 alpha-CD39/CD73-driven accumulation of extracellular adenosine in the TME in order to weaken the tumor protection. We report that hyperoxic breathing (60 % O-2) decreased the TME hypoxia, as well as levels of HIF-1 alpha and downstream target proteins of HIF-1 alpha in the TME according to proteomic studies in mice. Importantly, oxygenation also downregulated the expression of adenosine-generating ectoenzymes and significantly lowered levels of tumor-protecting extracellular adenosine in the TME. Using supplemental oxygen as a tool in studies of the TME, we also identified FHL-1 as a potentially useful marker for the conversion of hypoxic into normoxic TME. Hyperoxic breathing resulted in the upregulation of antigen-presenting MHC class I molecules on tumor cells and in the better recognition and increased susceptibility to killing by tumor-reactive cytotoxic T cells. Therapeutic breathing of 60 % oxygen resulted in the significant inhibition of growth of established B16.F10 melanoma tumors and prolonged survival of mice. Taken together, the data presented here provide proof-of principle for the therapeutic potential of systemic oxygenation to convert the hypoxic, adenosine-rich and tumor-protecting TME into a normoxic and extracellular adenosine-poor TME that, in turn, may facilitate tumor regression. We propose to explore the combination of supplemental oxygen with existing immunotherapies of cancer.