OR22-6 Ovarian Cancer Cell Glucocorticoid Receptor Activity Is Associated With Cytokine Secretion Promoting Infiltration of Immunosuppressive Cells Into the Tumor Microenvironment

Immunosuppressive cells abundantly infiltrate tumors during cancer progression. Notably, immunosuppressive myeloid-derived suppressor cells (MDSCs) have recently been identified as a heterogeneous cell population that expand during tumor-associated inflammation and are significantly increased in the tumor, peripheral blood, as well as ascites of ovarian cancer patients. MDSCs contribute to tumor immune tolerance via inhibition of T-cell proliferation and activation. Signals from the tumor microenvironment in the form of soluble cytokines are proposed to lead to MDSC infiltration. It is also known that high tumor cell glucocorticoid receptor (GR) expression is associated with a relatively poor prognosis in ovarian cancer patients. We hypothesized that ovarian cancer cell GR expression and activity may modulate tumor cell cytokine secretion thereby leading to increased MDSC generation and recruitment to the tumor, thereby creating an immunosuppressive environment. Our preliminary data confirm that GR activation in two high-grade ovarian cancer cell lines (HeyA8 and SKOV3) modulates the cytokine secretome. Our results demonstrate GR-mediated secretion of several pro-tumorigenic and immunosuppressive proteins including G-CSF, M-CSF, TGF-b, and MCP-1 in those ovarian cancer models. We also observed downregulation of potent cytotoxic T-cell activating cytokines required for anti-tumor T-cell function including IL-2, IFN-g and MIP1 upon GR activation. Importantly, treatment of cells with a selective GR modulator (SGRM) reverses this immunosuppressive secretome effect. Furthermore, upon culturing healthy peripheral blood mononuclear cells (PBMCs) with tumor conditioned media from GR activated ovarian cancer cells, we show that secreted immunomodulatory factors have the capacity to promote differentiation of human MDSCs from progenitor myeloid cells. The resulting MDSC population was characterized via expression of activation markers including Arginase-1, iNOS, VEGF and TGF-b. Most importantly, the suppressive function of these MDSCs is being evaluated by determining their inhibitory potential on cytotoxic T-cell proliferation and/or activation. Based on the insight provided by these data, we propose to determine whether ovarian tumor cell-intrinsic GR activation and resulting MDSC generation contributes to earlier relapse of GR-positive ovarian cancers, and eventually whether this mechanism may be targeted to improve patient outcomes in this subset of ovarian cancers. Presentation: Monday, June 13, 2022 12:15 p.m. - 12:30 p.m.