Abstract 759: Sunitinib has opposite roles to regulate the myeloid-derived suppressor cells in tumors and peripheral blood

Recent studies indicate that sunitinib, a tyrosine kinase inhibitor, could decease accumulation of myeloid-derived suppressor cells (MDSC) in tumors and also in peripheral blood. This study aims to investigate the behavior and dynamic profile of myeloid-derived suppressor cells in tumor tissues and peripheral blood of sunitinib-treated mice bearing prostate adenocarcinoma TRAMP-C1 tumors. To this end, 3×106 TRAMP-C1 tumor cells were inoculated at shank muscle of C57BL6/J mouse and sunitinib was administered by intraperitoneal injection of a daily dose of 20mg/kg into mice bearing 4 mm diameter tumor. Comparing to tumors in untreated group, sunitinib administration slightly delayed tumor growth delay for 2 days, but significantly decreased micro-vascular density and induced chronic hypoxia in tumors, resulting in the specific accumulation of CD11b+Gr-1+ MDSCs at the tumor necrotic region within CA-IX positive chronic hypoxic area. Flow cytometry was used to analyze the change of CD11b+ myeloid cells within tumor tissues and peripheral blood. Results showed that sunitinib treatment decreased the percentage of CD11b+Ly6G-LyC- tumor-associated macrophages (TAMs), but increased the percentage of CD11b+Ly6G-Ly6C+ monocytic MDSCs (M-MDSCs) while had no effect on CD11b+Ly6G+Ly6C+ neutrophilic MDSCs (N-MDSCs) within tumor tissues. In contrast, both the percentage of N-MDSCs and M-MDSC were expanded in peripheral blood of sunitinib-treated mice. Multiplex immunoassay showed significant increase of CCL2, CCL3, CCL5, CXCL5, IL-17a, GM-CSF, G-CSF and VEGF-A in tumor tissues, but only CXCL5, IL-á, IL-6 and G-CSF in the peripheral blood of sunitinib-treated mice were affected. In conclusion, this study shows that sunitinib has anti-vascular effect and could disrupt the recruitment of CD11b+Ly6G-Ly6C- TAMs into tumors. We also propose that sunitinib might exert different effects on tumor microenvironment and peripheral blood. Citation Format: Fang-Hsin Chen, Sheng-Yung Fu, Chun-Chieh Wang, Chi-Shiun Chiang, Ji-Hong Hong. Sunitinib has opposite roles to regulate the myeloid-derived suppressor cells in tumors and peripheral blood. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 759.