The Tie2 antagonist rebastinib reduces ovarian cancer growth in a syngeneic murine model

Background The receptor tyrosine kinase TIE2 and its ligands, angiopoietins (ANGPTs), promote angiogenesis. In addition to expression on vascular endothelial cells, TIE2 is expressed on M2-like pro-tumorigenic macrophages. Thus, the TIE2 inhibitor rebastinib was developed as a potential therapy to address multiple cancers. The objective of this study was to determine the effects of rebastinib alone and combined with chemotherapy in a syngeneic murine model of ovarian cancer. Methods Female C57Bl6J mice were intraperitoneally injected with syngeneic ID8 ovarian cancer cells. Once tumors were established, mice were untreated (control) or treated with rebastinib, carboplatin plus paclitaxel (chemotherapy), or rebastinib plus chemotherapy. In one set of experiments, survival was followed for 140 days. In other experiments, ascites was harvested 24 h after the last treatment and analyzed by flow cytometry. In in vitro experiments, RNA sequencing was performed on ID8 cells and murine peritoneal macrophage cells (PMJ2R) after treatment with rebastinib, chemotherapy, or rebastinib plus chemotherapy. Results Tumor-bearing mice treated with rebastinib plus chemotherapy had longer median survival than mice treated with chemotherapy (132.5 vs. 127 days, P < 0.01). Ascites from mice treated with rebastinib had more CD45 + macrophages (P < 0.03) and cytotoxic T cells (P < 0.0001) than ascites from mice treated with chemotherapy. Rebastinib had no significant effect on the numbers of regulatory T cells, Tie2 + macrophages, or Tie2 + M2 macrophages. In ID8 cells, in vitro, rebastinib treatment upregulated 1528 genes and downregulated 3115 genes. In macrophages, in vitro, rebastinib treatment upregulated 2302 genes and downregulated 2970 genes. Rebastinib differentially regulated ANGPT-like proteins in both types of cells, including several ANGPT-like genes involved in tumorigenesis, angiogenesis, and proliferation. ANGPTL1, an anti-angiogenic and anti-apoptotic gene, was increased tenfold in ID8 cells treated with rebastinib (P < 0.001) but was not altered in macrophages. Conclusions Rebastinib plus chemotherapy extends survival in a syngeneic murine model of ovarian cancer. Rebastinib alters proportions of immune cell subsets, increases cytotoxic T cells in ascites, and alters gene expression in tumor cells and macrophages.