Abstract 4123: Rhus verniciflua Stokes (RVS) inhibits PD-1 expression and induces anticancer effects via enhancing T-cell function

Abstract Rhus verniciflua Stokes (RVS) has traditionally been used for centuries as a therapeutic herb and food supplement in East Asian countries. Over the last decade, the anticancer effects of RVS have been demonstrated in various preclinical and clinical studies. RVS contains major flavonoids such as fustin, fisetin, and sulfuretin, which were known to have apoptotic or anti-proliferative activities in various cancer cell lines. In clinical retrospective studies, RVS administration exclusively suggested more favorable outcomes with prolonged overall survival in solid cancer patients. However, the effect of RVS on immuno-oncology, especially the functional properties of T cells and their phenotypes remain unclear. Dried RVS grown in Wonju (Korea) was extracted with sterile distilled water after removing the allergen (urushiol). Peripheral blood mononuclear cells (PBMCs) from breast cancer patients with HLA-A*02:01 were isolated using a vacutainer tube and cultured for T cell expansion in the presence of interleukin (IL)-2 for 14 days. Cells were enriched above 90% CD3+ T cells after 14 days of expansion. Red fluorescent protein (RFP)-expressing HLA-A*02:01-matched breast cancer cell lines (MCF7 and MDA-MB-231), were used to determine the anticancer activity of T cells in the presence or absence of RVS. For in vitro killing assays, MCF7 and MDA-MB-231 cell lines expressing RFP were co-cultured with T cells with or without RVS treatment for 48 h, and cell viability was measured by the MTT assay. The phenotypic characteristics of the T cells were profiled by staining with various T cell surface markers, including CD3, CD4, CD8, PD-1, and CTLA4. RVS toxicity in the target cells (MCF7 and MDA-MB-231) was not observed at RVS concentrations up to 250 ug/mL. The anticancer activity of T cells against breast cancer cells was significantly increased by adding both 10 ug/mL and 100ug/mL of RVS. T cells co-cultured with MCF7 and MDA-MB-231 cells in the presence of 100 ug/mL of RVS showed 20.6% increases in cytotoxicity in MCF7 cells and 36.2% in MDA-MB-231 cells compared to no RVS treatment. Interestingly, relative reductions in programmed death-1 (PD-1) were found in T cells co-cultured with target cells by adding RVS, even though there was no significant difference in the other markers observed. Our findings showed that RVS could improve the function of T cells against cancer cells in the tumor microenvironment, as interpreted by reduced PD-1 expression in T cells after RVS treatment. Therefore, the components of RVS are candidates for restoring T cells exhausted against cancer. Active compounds should be identified for clinical efficacy, and further studies are necessary for combination strategies with conventional cancer treatments, such as chemotherapy and radiotherapy. Citation Format: Seoyoung Kim, Young-Kwan Lee, Hyoun Jong Moon, Sunki Lim, Yujeong Gho, Wang Jun Lee, Sanghun Lee, Excelsisbio Inc.. Rhus verniciflua Stokes (RVS) inhibits PD-1 expression and induces anticancer effects via enhancing T-cell function. [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 4123.