Abstract 4686: Omx a Hypoxia Modulator Reverses the Immunosuppressive Glioblastoma Microenvironment by Stimulating T Cell Infiltration and Activation That Results in Increased Number of Long-Term Survivors

Abstract Oxygen is one of the key modulators of tumor microenvironment whereby low oxygen or hypoxia is associated with resistance to chemo- and radio- therapies and poor patient outcomes. Hypoxia favors an immunosuppressive tumor microenvironment by promoting Treg recruitment and activation and suppressing T cell and NK cell proliferation and effector function and pro-inflammatory cytokine secretion. Therefore, reversing tumor hypoxia could create an immunopermissive microenvironment and improve the efficacy of several immunotherapies. Omniox has developed an oxygen carrier OMX that can specifically deliver oxygen to hypoxic tumor regions without affecting oxygenation of tissues within physiologic oxygen levels. Due to its biochemical features, OMX is well tolerated in small (rats and mice) and large (sheep and dogs) animals. Following intravenous administration, OMX extravasates through leaky tumor vasculature and accumulates within immunocompetent rodent orthotopic glioblastoma models as well as spontaneous canine brain tumors. Consequently, OMX decreases hypoxia levels in the tumor tissue measured directly using oxygen sensor probes and indirectly with exogenous hypoxia markers using ELISA, immunohistochemistry and flow cytometry methods. Here we evaluated OMX’ activity in reversing the immunosupressive tumor microenvironment using a combination of immunohistochemistry, flow cytometry and Luminex methods. Moreover, we investigated the efficacy of OMX in improving mouse survival and effectiveness of checkpoint inhibitors (CPI). Similar to previously published findings, we demonstrated that T lymphocytes are mostly excluded from hypoxic tumor areas in the GL261 model. A single OMX treatment in GL261 tumor-bearing mice reduces tumor hypoxia, enhances T cell localization in previously hypoxic tumor areas, and increases CD8 accumulation by ~4-fold. Specifically, OMX treatment increased the activated cytotoxic T lymphocytes (CTLs) fraction by ~2 fold and reduced the immunosuppressive Treg fraction by 2-fold, resulting in a 3-fold increase of Teff/Treg ratio, which indicates a switch from an immunosupressive to an immunopermissive microenvironment. When combined with CPI, OMX reverses the immunosuppressive tumor microenvironment by increasing CD8 T cell infiltration, proliferation and cytotoxic activity, and modulating IFNg and IFNg-inducible cytokines that may polarize T cells towards a Th1 phenotype. Furthermore, treatment of late-stage GL261 tumor-bearing mice with the combination of OMX-CPI increases mouse survival by 80%. By delivering oxygen specifically to the hypoxic tumor microenvironment, OMX may restore anti-cancer immune responses in glioblastoma patients and synergize with radiotherapy and immunotherapy to enhance tumor control and improve patient outcomes. Citation Format: Natacha Le Moan, Philberta Leung, Sarah Ng, Tina Davis, Carol Liang, Jonathan W. Winger, Stephen P. Cary, Nicolas Butowski, Ana Krtolica. Omx a hypoxia modulator reverses the immunosuppressive glioblastoma microenvironment by stimulating T cell infiltration and activation that results in increased number of long-term survivors [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 4686. doi:10.1158/1538-7445.AM2017-4686