Abstract 4149: Direct immune cell contact to basal-like triple negative breast cancer cells evokes downregulation of EGFR and PD-L1

Abstract

Abstract BACKGROUND: We previously reported that direct co-culture of triple negative breast cancer cell line MDA-MB-231 and immune cells results in reduction of EGFR expression on cell surface of MDA-MB-231 (AACR 2015 #2349). However, a role of reduction of EGFR on MDA-MB-231 via co-culture with immune cells still remains unclear. Therefore, we evaluated a role of reduction of EGFR on MDA-MB-231 at the immunological point of view by testing expression of immune related genes including PD-L1. METHODS: In order to verify the importance of direct immune cell contact to breast cancer cell, MDA-MB-231 cells were co-cultured directly or indirectly with THP-1 cells (human monocytic cell line) at 1:50 cellular ratios. In order to study indirect co-culture assay, we used cell culture insert to avoid direct cancer cell-immune cell contact. We analyzed gene expression by quantitative real time PCR and membrane protein expression by flow cytometry of EGFR, also other HER family on MDA-MB-231 which is directly or indirectly co-cultured with THP-1. We also evaluated the expression of immune related genes including PD-L1. RESULTS: Both mRNA and protein level of EGFR on MDA-MB-231 cells directly co-cultured with THP-1 were significantly decreased as compared to those with indirectly co-cultured MDA-MB-231 cells. There are no significant differences in EGFR expression between indirectly co-cultured MDA-MB-231 cells and control MDA-MB-231 cells. Importantly, PD-L1 expression on MDA-MB-231 cells directly co-cultured with THP-1 was significantly decreased as compared to that with indirectly co-cultured MDA-MB-231 cells. CONCLUSION: It has been reported that PD-L1 expression in cancers is regulated by phosphatidylinositol 3-kinase (PI3K) and Akt signaling. Thus, our findings may give a novel insight on regulation of PD-L1 expression on cancer cells in tumor microenvironment that tumor infiltrated immune cell directly contact with cancer cells and EGFR down-regulation leads to reduction of PD-L1 expression on cancer cells. Further investigation is needed to elucidate the mechanism of reduction of EGFR by direct immune cell contact to cancer cells and its interaction with modulation of PD-L1 expression. This will provide novel aspects for immune therapy of breast cancer patients. Citation Format: Ayane Yamaguchi, Eiji Suzuki, Kosuke Kawaguchi, Mariko Nishie, Moe Tsuda, Masakazu Toi. Direct immune cell contact to basal-like triple negative breast cancer cells evokes downregulation of EGFR and PD-L1. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4149.