LAUSR

Immunotherapy targeting the programmed cell death ligand 1/programmed cell death protein 1 (PD-L1/PD-1) pathway using antibodies is clinically effective in treating a spectrum of cancers. Acetaminophen (AAP) has shown antitumor and/or chemo-enhancing effects in human cancer cells in vitro and in vivo. We investigated the effects of AAP exposure on cancer cells’ immune checkpoint PD-L1 expression in vitro and their in vivo tumorigenic ability. Acetaminophen (10 mM) alone for 2 hr has no effect on cell viability and no effect on PD-L1 level of A2058 melanoma and H460 non-small cell lung carcinoma in vitro. However, AAP treatment for 2 hr followed by interferon-γ (20 ng/ml) stimulated PD-L1 protein expression. The stimulatory effect of AAP pretreatment was not replicated with other glutathione-depleting reagents, including hydrogen peroxide (100 μM; 2hr) or buthionine sulfoximine (50 μM; 24hr). For the in vivo tumorigenesis study, cancer cells (2.5x107) pretreated with AAP developed significantly (p=0.0028 in A2058 and p=0.002 in H460) smaller tumor size after being subcutaneously implanted into athymic rats. Compared to vehicle control, AAP also showed more tumor CD68+ macrophage infiltration by immunohistochemistry. Our results demonstrate for the first time the short-time exposure of AAP inhibited tumor growth by enhancing CD68+ macrophage infiltration. We conclude that high-dose AAP may be immune modulatory, a cell marker regulator and it could be potentially used as a single agent or in combination with other immunotherapy drugs to facilitate therapeutic efficacy. Citation Format: Jeffrey Wu, Alexander J. Neuwelt, Leslie L. Muldoon, Edward A. Neuwelt. Acetaminophen pretreatment stimulated interferon γ-induced PD-L1 protein expression in vitro and CD68 positive macrophage infiltration in tumor xenograft [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A87.