LXR activation radiosensitizes non-small cell lung cancer by restricting myeloid-derived suppressor cells

Radiotherapy (RT) is an important radical treatment for locally advanced non-small cell lung cancer (NSCLC). However, radioresistance greatly impairs the efficacy of this therapy in the clinic. Radioresistance can be caused by radiation-induced myeloid-derived suppressor cell (MDSC) infiltration. Liver-X nuclear receptor (LXR) agonists have demonstrated potent antitumor activity in preclinic animal models. Here, we report for the first time that LXR agonists, GW3965 and RGX-104, radiosensitized NSCLC in a subcutaneous homograft murine model. LXR activation significantly reduced MDSC abundance in the tumor microenvironment (TME). Treatment with RGX-104 greatly promoted MDSC apoptosis in vitro. Depleting MDSC activated cytotoxic T lymphocyte (CTL) and T-helper 1 (Th1) responses in the TME. In conclusion, the immunosuppressive effects of radiotherapy can be abrogated partly with an LXR agonist by depleting MDSC, which sensitizes NSCLC to RT.