Sorafenib inhibits doxorubicin-induced PD-L1 upregulation to improve immunosuppressive microenvironment in Osteosarcoma.

PURPOSE: Although undergoing conventional chemotherapy significantly improves the prognosis of Osteosarcoma, chemoresistance and failure of therapy is still a significant challenge. Furthermore, conventional chemotherapy, like doxorubicin, would upregulate the expression of programmed death-ligand 1 (PD-L1) which caused an immunosuppressive microenvironment and unsatisfied treatment result in Osteosarcoma. Thus, it is urgent to explore a strategy to overcome this disadvantage. METHODS: Human Osteosarcoma cell line MG63 and mouse Osteosarcoma cell line K7 were included in this study. Subcutaneous tumor model was used by injection of K7 cells in BALB/C mice to test the effect of doxorubicin and sorafenib on tumor growth. PD-L1 expression was tested in vitro (flow cytometry, western blot and PCR) and in vivo (flow cytometry and immunohistochemistry). Proportion of immune cells (CD4, CD8, Tregs, and cytotoxic T lymphocytes) in vivo was analyzed with flow cytometry. RESULTS: Combination of sorafenib and doxorubicin inhibited tumor growth significantly in vivo. Doxorubicin increased PD-L1 expression in vitro and in vivo, while sorafenib inhibited doxorubicin-induced PD-L1 upregulation in vitro and in vivo. Proportion of interferon-γ-secreting CD8 + T lymphocytes in tumor tissue was increased significantly when sorafenib was combined with doxorubicin, while proportion of CD4, CD8, and Tregs was not significantly changed. Extracellular signal-regulated kinases (ERK) pathway could be one of the key mechanisms by which doxorubicin induced upregulation of PD-L1 in Osteosarcoma cells. CONCLUSION: Combination of sorafenib and conventional chemotherapeutic reagents is a potent strategy to improve treatment effectiveness by modulating tumor microenvironment in Osteosarcoma through increasing proportion of cytotoxic T lymphocytes.