Abstract 6388: High dose acetaminophen with n-acetylcysteine rescue inhibits M2 polarization of tumor associated macrophages

Abstract

Abstract Background: High dose acetaminophen (AAP) with n-acetylcysteine (NAC) rescue is among the few treatments that has shown a signal of activity in phase I trials (21% response rate, 3/14 assessable patients) without achieving dose limiting toxicity that has not progressed to evaluation in later line studies. We have previously shown that high dose AAP selectively depletes glutathione in the liver but not the tumor, suggesting that NAC, the FDA-approved antidote for AAP toxicity and a glutathione precursor, may selectively rescue the normal liver but not the tumor from high dose AAP. While the anti-tumor effects of AAP/NAC appear to not be mediated by glutathione depletion and free radical injury, the mechanism of anti-tumor effects of AAP/NAC has not been definitively characterized. Methods: In vitro the effects of Vehicle, AAP, or AAP/NAC was evaluated on bone marrow derived macrophages polarized to M2 and M1 phenotypes using IL-4 or IFN/LPS, respectively. Tumor cell viability was assessed with MTT assay. Effects of AAP on IL-4/STAT6 (M2) or IFN/LPS/STAT1 (M1) signaling, and downstream gene and protein expression was studied. In vivo, effects of AAP/NAC on tumor size and tumor associated macrophage polarization were characterized in orthotopic triple negative breast tumor models 4T1 and EF43.fgf4 using cytokine elisa of tumor lysate and flow cytometry. Results: NAC reversed AAP toxicity in the normal liver but did not reverse AAP cytotoxicity against tumor cells in vitro. AAP/NAC selectively inhibited IL-4-induced STAT6 phosphorylation but not IFN/LPS-induced STAT1 phosphorylation. Downstream, AAP/NAC inhibited IL-4 induction of M2-associated genes (such as CCL24, YM1 and arginase) and proteins (arginase, PD-L2, and CD206). However, AAP/NAC did not inhibit IFN/LPS induction of M1-associated genes (IL-6, TNF, IL-12) and proteins (INOS, PD-L1, MHC I, and CD64). In vivo, AAP/NAC inhibited tumor growth in EF43.fgf4 and 4T1 triple negative breast tumors. Flow cytometry of tumor associated macrophages revealed that AAP/NAC selectively inhibited M2 but not M1 polarization. ELISA of tumor lysate demonstrated relatively stable expression of IFN gamma but markedly suppressed expression of IL-10 in the tumor immune microenvironment. Conclusion: Our study is the first to show that at high doses AAP/NAC has profound effects on the tumor immune microenvironment that may facilitate immune-mediated inhibition of tumor growth. Citation Format: Alexander Neuwelt, Allyn Bryan, Won Lee, Pavani Pingali, Howard Li, Bhaumik Patel. High dose acetaminophen with n-acetylcysteine rescue inhibits M2 polarization of tumor associated macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6388.