Abstract 1627: Enhancement of anti-cancer immunity by OMX, a novel oxygen carrier immunotherapeutic that ameliorates the hypoxic tumor microenvironment
Authors: Leong Kevin G. , Pan Yuqiong , Winger Jonathan A. , Cary Stephen P. , Moan Natacha Le , Krtolica Ana 
Published: July 2017

Abstract
Hypoxia is a hallmark of cancer and a driver of tumor progression and poor patient outcomes. By generating an immunosuppressive tumor microenvironment that limits cytotoxic T lymphocyte (CTL) infiltration and activation, hypoxia limits the effectiveness of cancer immunotherapy and thus promotes tumor cell evasion of the host immune response. Omniox has developed a first-in-class anti-cancer immunotherapeutic, OMX, specifically designed to reverse tumor hypoxia to enhance cancer immunotherapy efficacy. In preclinical models, we have demonstrated that OMX accumulates in rodent subcutaneous and orthotopic tumors, as well as spontaneous canine melanomas and brain tumors, resulting in significant tumor hypoxia reduction.Here, using multiple subcutaneous syngeneic mouse tumor models (MC38, CT26, 4T1), we assessed OMX effects on intratumoral CTLs and immunosuppressive regulatory T cells (Treg), as well as the anti-tumor potential of OMX as a single agent and in combination with established immunotherapies. Using quantitative immunohistochemistry, we confirmed reports that hypoxic tumor areas are devoid of CTLs. Accordingly, by flow cytometry we observed a negative correlation between tumor hypoxia and CTL infiltration. While OMX single agent treatment did not affect the overall CD45-positive leukocyte population, Treg cells were selectively depleted and the CTL:Treg ratio was substantially increased, suggesting that OMX induced a shift towards immunosensitization. Consistent with this finding, we observed OMX single agent anti-tumor efficacy in MC38 colon tumors. Impressively, anti-tumor effects of OMX single agent were equivalent to that of a single treatment of the checkpoint inhibitor anti-CTLA4. We next assessed whether OMX would enhance the efficacy of checkpoint inhibitors when used in combination. In CT26 colon tumors, OMX exhibited combination anti-tumor activity with anti-CTLA4, giving rise to faster cures and a greater number of complete and durable responders compared to anti-CTLA4 alone. Of note, this enhanced response was observed for both early-stage and late-stage CT26 tumors. In 4T1 breast tumors, known to be insensitive to checkpoint inhibitors, treatment of early-stage (~60mm3) tumors with combination OMX and anti-PD1 resulted in a 27% response rate, compared to a 0% response rate to anti-PD1 alone. Taken together, our data suggest that OMX, by delivering oxygen to hypoxic tumor areas, induces a microenvironmental change from an immunosuppressive to an immunopermissive state. Given that OMX is well-tolerated in both small and large animals, and that its mechanism of action is upstream of numerous major immunosuppressive pathways, OMX holds great clinical potential to synergize with multiple immunotherapeutic agents to enhance tumor control by restoring anti-cancer immune responses in cancer patients.
Citation Format: Kevin G. Leong, Yuqiong Pan, Jonathan A. Winger, Stephen P. Cary, Natacha Le Moan, Ana Krtolica. Enhancement of anti-cancer immunity by OMX, a novel oxygen carrier immunotherapeutic that ameliorates the hypoxic tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1627. doi:10.1158/1538-7445.AM2017-1627