Abstract 401: A novel photoimmunotherapy targeting cancer-associated fibroblasts (CAFs) overcomes therapeutic resistance in human esophageal cancer

Abstract

Abstract Cancer associated fibroblasts (CAFs) are thought to play an essential role in cancer invasion, migration, metastasis and resistance to anticancer drugs. CAFs were originally defined as fibroblasts expressing α-SMA in cancer tissue; however, fibroblast activation protein (FAP) has been recently identified as a more functional and specific surface protein of CAFs. The photoimmunotherapy (PIT) is a new molecular targeted therapy, which is based on a near-infrared (NIR) photosensitizer IR700, conjugated to monoclonal antibody (mAb) targeting particular molecules. PIT induces the selective destruction of targeted cells. The aim of this study is to analyze the influence of CAFs on human esophageal cancer and to develop a novel therapeutic strategy to eliminate CAFs by using FAP-targeting PIT. We produced the IR700-FAP antibody for this study. Human esophageal cancer cell lines (TE-4 and OE-19) and FEF3 human fibroblasts were used in this study. TE-4 and OE-19 cells stimulated with conditioned medium (CM) of CAFs exhibited malignant phenotypes confirmed by invasion assay, migration assay, and colony formation assay. Tumor cells were significantly more malignant when directly co-cultured with CAFs. We further examined whether tumor cells stimulated by CM (CAFs) could acquire the resistance to chemotherapy or radiotherapy. Cell viability assay showed that tumor cells stimulated with CAFs was more resistant to conventional chemotherapy or radiation than unstimulated tumor cells. Western blot analysis demonstrated that E-cadherin expression was decreased and that of vimentin was increased in CAF-stimulated tumor cells, indicating the epithelial mesenchymal transition (EMT) induction. Moreover, OE-19 cells stimulated with CAFs contained more CD133-positive cancer stem-like cells. In vivo experiments demonstrated that subcutaneous TE4 tumors were more refractory to chemotherapy in the presence of co-inoculated CAFs as observed in vitro. Finally, we investigated whether elimination of CAFs by FAP-targeting PIT could affect the resistance to chemotherapy in vitro and in vivo. In vivo PIT following intratumoral anti-FAP mAb-conjugated IR700 suppressed the growth of subcutaneous tumors co-inoculated with CAFs. These results demonstrated that human tumor cells became more malignant and resistant in the presence of CAFs, which could be reversed by using CAF-specific PIT. Targeting fibroblast itself is a unique strategy and can be clinically promising as combination targeting cancer cells and their fundamental microenvironment. Citation Format: Ryoichi Katsube, Kazuhiro Noma, Shinichiro Watanabe, Shinichi Urano, Takayuki Ninomiya, Toshiaki Ohara, Hiroshi Tazawa, Shunsuke Kagawa, Hisataka Kobayashi, Toshiyoshi Fujiwara. A novel photoimmunotherapy targeting cancer-associated fibroblasts (CAFs) overcomes therapeutic resistance in human esophageal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 401. doi:10.1158/1538-7445.AM2015-401