SA-49, a novel aloperine derivative, induces MITF-dependent lysosomal degradation of PD-L1Research in context

• Main Authors: Na Zhang, Yueying Dou, Lu Liu, Xin Zhang, Xiaojia Liu, Qingxuan Zeng, Yang Liu, Mingxiao Yin, Xiujun Liu, Hongbin Deng, Danqing Song
• Format: Article
• Language: English
• Published: Elsevier 2019-02-01
• Series: EBioMedicine
• Online Access: http://www.sciencedirect.com/science/article/pii/S235239641930060X

Background: Programmed death-ligand 1 (PD-L1) is a T-cell inhibitory checkpoint molecule that suppresses antitumor immunity. Anti-PD-L1 antibodies have shown remarkable promise in treating tumors, but the patient response rate is low. Therefore, small-molecule checkpoint inhibitors blocking PD-L1 function are urgently needed. Methods: Changes of protein expression and phosphorylation levels were determined by immunoblotting. The level of Membrane PD-L1 was examined by flow cytometer. Cytotoxicity of T cells and NK cells toward tumor cells were detected using LDH and cell index assays. Lysosome function was investigated by NAG assay. Changes in lysosomal-related genes were measured by RT-PCR. In vivo anti-NSCLC cancer effects were assessed using C57BL/6 mice bearing Lewis tumor xenografts. Findings: We identified SA-49 as a new regulator of PD-L1 expression from a series of novel aloperine derivatives. SA-49 decreased the expression of PD-L1 in NSCLC cells and enhanced the cytotoxicity of co-cultured T and NK cells toward tumor cells. Importantly, lysosomal pathway contributed to SA-49-mediated down-regulation of PD-L1. SA-49 increased the biogenesis of lysosome and promoted translocation of PD-L1 to lysosome for proteolysis, which was associated with nuclear translocation of MITF. SA-49-induced MITF translocation acted through activation of PKCα and subsequently suppression of GSK3β activity. Furthermore, SA-49 suppressed Lewis tumor xenograft growth by activating immune microenvironment in C57BL/6 mice. Interpretation: Our data demonstrate that SA-49 can be used to regulate PD-L1 in cancer cells and trigger its degradation by activating lysosome function. Keywords: Aloperine, PD-L1, Lysosome, MITF, Checkpoint inhibitors