Abstract 2805: DFMO and 5-azacytidine increase M1 macrophages in the tumor microenvironment of an ovarian cancer mouse model

Although ovarian cancer has a low incidence rate encompassing roughly 1% of all new cancers, it remains the most deadly gynecologic malignancy. Our lab has designed a novel combination therapy which combines a DNA methyl transferase inhibitor (DNMTi) and ornithine decarboxylase inhibitor that together, alter the tumor microenvironment to inhibit ovarian tumor growth. Previous work has demonstrated that the DNMTi 5-Azacytidine (AZA) activates type I interferon signaling (Li, 2014, Chiappinelli, 2015) to increase IFNγ+ T cells and NK cells and reduce the percentage of macrophages and myeloid derived suppressor cells (MDSCs) in the tumor microenvironment (Stone, 2017). To improve the efficacy of epigenetic therapy, we hypothesized that the addition of α-difluoromethylornithine (DFMO), an ornithine decarboxylase inhibitor may decrease activity of MDSCs through inhibition of arginase. Immunocompetent C57Bl/6 mice were injected with syngeneic mouse ovarian surface epithelial (MOSE) tumor cells (ID8-VEGF-Defensin) and subsequently treated with AZA, DFMO, or combination AZA+DFMO. After several weeks, mice developed hemorrhagic ascites that was drained, processed and stained for cell-surface markers and analyzed by flow cytometry to identify T cells, NK cells, and macrophages. We found that in vivo AZA, DFMO, and AZA+DFMO significantly increased survival in mice, decreased tumor burden, and caused recruitment of activated (IFNγ+) CD4+ T cells, CD8+ T cells, and NK Cells compared to vehicle. The combination therapy had a striking increase in survival when compared to single agent treatment; however, the difference in recruited lymphocytes was less striking. Instead, combination therapy led to the most dramatic decrease in immunosuppressive cells such as M2 polarized macrophages and increase in tumor-killing M1 macrophages. Using a CSF1R blocking antibody, we found that depleting macrophages in this model reduced the efficacy of AZA+DFMO treatment, and resulted in fewer M1 macrophages in the tumor microenvironment. We thus conclude that our novel combination therapy modifies macrophage polarization in the tumor microenvironment, recruiting M1 macrophages and prolonging survival. We hypothesize that this treatment regimen could have a widespread impact on macrophage-rich tumors in general, and plan to test this hypothesis in additional tumor models. Citation Format: Meghan Travers, Stephen Brown, Matthew Dunworth, Cassandra Holbert, Robert Casero, Cynthia Zahnow. DFMO and 5-azacytidine increase M1 macrophages in the tumor microenvironment of an ovarian cancer mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2805.