Abstract 5026: B7-H1 confers tumor chemoresistance by regulating MAPK/ERK activation

Abstract Development of resistance to chemotherapy and immunotherapy is a major obstacle in extending the survival of cancer patients. Although several molecular mechanisms have been identified that can contribute to chemoresistance, the role of immune checkpoint molecules in tumor chemoresistance has received little consideration. Elevated expression of B7-H1 (also named PD-L1) is predictive of an aggressive disease course, including increases in disease progression and cancer-related mortality in a variety of cancers (ovary, breast, liver, pancreas, esophagus, colon and lung). Although the aggressiveness of B7-H1 positive tumors has been attributed to B7-H1's immune-suppressive function, B7-H1 itself may be directly altering tumor cell intracellular signaling pathways promoting acquisition of drug resistance. It has been reported that overexpression of B7-H1 confers chemoresistance in human cancers. However, the mechanisms by which B7-H1 contributes to tumor chemoresistance have yet to be defined. We show that B7-H1 transfected tumor cells are resistant to chemotherapy. This resistance is due to increased activation of MAPK/ERK pathway in tumor cells with B7-H1 overexpression. Inhibition of ERK activation restored drug sensitivity of B7-H1 positive tumor cells. We further analyzed the downstream elements of B7-H1 signaling pathway and identified a new B7-H1 associated protein that is involved in DNA damage repair and MAPK/ERK activation mechanisms. We conclude that B7-H1 mediates tumor chemoresistance by enhancing the activation of MAPK/ERK pathway via its intracellular signaling pathway. Our studies may identify a novel pharmaceutical target for treatment of B7-H1 positive refractory tumor cells. Citation Format: Amanda Orzechowski, Haidong Dong. B7-H1 confers tumor chemoresistance by regulating MAPK/ERK activation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5026. doi:10.1158/1538-7445.AM2014-5026