Galectin-3 inhibition with belapectin combined with anti-OX40 therapy reprograms the tumor microenvironment to favor anti-tumor immunity
Elizabeth R. Sturgill, Annah S. Rolig, Stefanie N. Linch, Courtney Mick, Melissa J. Kasiewicz, Zhaoyu Sun, Peter G. Traber, Harold Shlevin, William L. Redmond
Abstract
Treatment with an agonist anti-OX40 antibody (aOX40) boosts anti-tumor immunity by providing costimulation and driving effector T cell responses. However, tumor-induced immune suppression contributes significantly to poor response rates to aOX40 therapy, thus combining aOX40 with other agents that relieve tumor-mediated immune suppression may significantly improve outcomes. Once such target is galectin-3 (Gal-3), which drives tumor-induced immunosuppression by increasing macrophage infiltration and M2 polarization, restricting TCR signaling, and inducing T cell apoptosis. A wide-variety of tumors also upregulate Gal-3, which is associated with poor prognosis. Tumor-bearing (MCA-205 sarcoma, 4T1 mammary carcinoma, TRAMP-C1 prostate adenocarcinoma) mice were treated with a Gal-3 inhibitor (belapectin; GR-MD-02), aOX40, or combination therapy and the extent of tumor growth was determined. The phenotype and function of tumor-infiltrating lymphocytes was determined by flow cytometry, multiplex cytokine assay, and multiplex immunohistochemistry. Gal-3 inhibition synergized with aOX40 to promote tumor regression and increase survival. Specifically, aOX40/belapectin therapy significantly improved survival of tumor-bearing mice through a CD8+ T cell-dependent mechanism. Combination aOX40/belapectin therapy enhanced CD8+ T cell density within the tumor and reduced the frequency and proliferation of regulatory Foxp3+CD4+ T cells. Further, aOX40/belapectin therapy significantly reduced monocytic MDSC (M-MDSCs) and MHC-IIhi macrophage populations, both of which displayed reduced arginase 1 and increased iNOS. Combination aOX40/belapectin therapy alleviated M-MDSC-specific functional suppression compared to M-MDSCs isolated from untreated tumors. Our data suggests that Gal-3 inhibition plus aOX40 therapy reduces M-MDSC-meditated immune suppression thereby increasing CD8+ T cell recruitment leading to increased tumor regression and survival.