Abstract 5590: Inhibition of the autophagy protein Vps34 induces tumor cell secretion of proinflammatory chemokines

Abstract

Abstract Autophagy is the cellular process by which cytoplasmic contents are degraded and recycled through a lysosomal pathway. In cancer, autophagy can contribute to both tumor promotion and tumor suppression, and emerging evidence supports a role in resistance to immunotherapy. We investigated whether inhibition of autophagy with a small molecule inhibitor of the class III phosphoinositide 3-kinase Vps34 could stimulate anti-tumor immune responses and potentiate the efficacy of immune checkpoint blockade (ICB). Treatment with the Vps34 inhibitor (Vps34i) inhibited autophagy and was weakly cytotoxic to B16F10, MC38, EMT6 and CT26 mouse syngeneic tumor cell lines. In certain cancers, autophagy has been linked to lysosomal degradation of MHC I proteins, thereby downregulating expression and contributing to immune evasion. Notably, we observed minimal upregulation of MHC I surface expression on a subset of mouse and human cell lines. We further explored whether autophagy inhibition would result in release of any soluble immune stimulatory factors from mouse tumor cell lines. Inhibition of Vps34 markedly increased the secretion of several proinflammatory chemokines, including CCL5 and CXCL10. Increased chemokine secretion was also observed in a panel of human cancer cell lines, including NCI-H2009 lung cancer and PC-3 prostate cancer, confirming that the response is observed in human cancer cell lines derived from different tissue origins. As the chemokines CCL5 and CXCL10 are critical to the development of robust anti-tumor immunity, we next tested whether Vps34i treatment could potentiate the anti-tumor efficacy of ICB. We explored the activity of Vps34i as a single agent and in combination with anti-PD-1 antibody in three different syngeneic tumor models, including EMT6, CT26 and MC38. No single agent activity was observed in these models, however, combination of anti-PD-1 and Vps34i significantly inhibited the growth of CT26 tumors compared to control. Anti-tumor efficacy of combination treatment was not significantly different compared to single agents, and no complete tumor regressions were observed. No significant increases in CCL5 and CXCL10 were observed in the serum of combination treated mice, potentially explaining the lack of robust efficacy. Our results suggest that inhibition of autophagy promotes the secretion of proinflammatory cytokines from mouse and human cancer cells in vitro. As the autophagy pathway exhibits cross talk with other major cell signaling pathways, the tumor contexture may be a critical determinant of the role of autophagy in anti-tumor immune responses. Future experiments will explore which tumor contexts are sensitive to combination of autophagy inhibition and ICB. Citation Format: Marie Bernardo, Yu-an Zhang, Martin Graf, Jane Cheng, Fangxian Sun, Virna Cortez-Retamozo, Sukhvinder Sidhu, Eladio Marquez, Donald Jackson, Jack Pollard, Timothy R. Wagenaar, Donald Shaffer. Inhibition of the autophagy protein Vps34 induces tumor cell secretion of proinflammatory chemokines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5590.