Inhibition of Tumor Growth and Sensitization to Sunitinib by RNA Interference Targeting Programmed Death-ligand 1 in Mouse Renal Cell Carcinoma RenCa Model

Background/Aim: There are several unresolved issues regarding the combined treatment with an immune checkpoint inhibitor and anti-angiogenic agent for renal cell carcinoma (RCC) patients. The purpose of this study was to address the inhibitory effects of programmed death-ligand 1 (PD-L1) expression on growth and sensitivity to sunitinib in the mouse RCC RenCa model. Materials and Methods: We established RenCa/sh-PD-L1 by transfecting RenCa cells with a plasmid carrying a short hairpin RNA targeted against PD-L1. The growth pattern of RenCa/sh-PD-L1 with or without sunitinib was compared to that of RenCa cells transfected with control plasmid alone (RenCa/Co). Results: No significant difference in growth or sensitivity to sinitinib was noted between RenCa/sh-PD-L1 and RenCa/Co cells in vitro. The tumor volume in mice subcutaneously injected with RenCa/sh-PD-L1 was significantly smaller than that with RenCa/Co. Treatment of mice bearing each tumor with sunitinib resulted in a significant reduction of the RenCa/sh-PD-L1 tumor compared to the RenCa/Co tumor. Moreover, infiltration by CD8(+) T cells of RenCa/sh-PD-L1 tumors was significantly higher than that of RenCa/Co tumors, irrespective of treatment with sunitinib. Conclusion: Suppressed expression of PD-L1 could increase tumor-infiltrating CD8(+) T cells and result in growth inhibition as well as enhanced sensitivity to sunitinib in the RenCa model.