P2-004 - Autophagy inhibition improves CD47-blocking immunotherapy in laryngeal squamous cell carcinoma

Abstract

Background: CD47 blocking immunotherapy, an effective treatment strategy that triggers phagocytosis of tumor cells by macrophage in diverse cancers. Here, we investigated the synergistic antitumor effect of simultaneously targeting CD47 and autophagy in Laryngeal squamous cell carcinoma (LSCC) cells. Methods: Cell vitality was detected by MTT assay. Autophagic flux was analyzed by laser scanning confocal microscope. Protein expression was examined by western blotting. In vivo anti-tumor activity was assessed using LSCC xenograft established in nude mice. Results: We demonstrated that blocking CD47-SIRPα by SIRPα-Fc could significantly induce cytotoxicity and phagocytosis of LSCC cells. Meanwhile, we found that autophagy was activated by SIRPα-Fc, inducing the activity of LC3 which was converted from LC3-I to LC3-II, while Akt/mTOR signaling pathway was involved in autophagic process. Furthermore, inhibiting SIRPα-Fc-induced autophagy by pharmacological inhibitors or small interfering RNA significantly enhanced SIRPα-Fc-triggered macrophage phagocytosis and cytotoxicity, revealing autophagy played a cytoprotective role in CD47-targeted therapy of LSCC. Moreover, xenograft experiment showed that combination of autophagy inhibitor potentiated the anti-tumor efficacy of SIRPα-Fc, with recruitment of macrophages and apoptosis of tumor cells. Conclusion: These findings demonstrated that CD47-blocking therapies alone and in combination with autophagy inhibitor could potently kill LSCC cells, highlighting potential therapeutic strategies for cancer immunotherapy.