Abstract 714: Macrophage-to-fibroblast transition promotes cancer progression in peritoneal carcinomatosis of gastrointestinal cancer patient

Proceedings: AACR 107th Annual Meeting 2016; April 16-20, 2016; New Orleans, LA [Background] Cancer stromal cell plays an important role in cancer progression. Fibroblasts localized in tumor are especially called cancer-associated fibroblasts (CAFs). CAFs and inflammatory cells form tumor microenvironment and promote cancer growth through the direct or indirect interaction between cancer cells and stromal cells. However, the origin of CAF is not fully understood. Malignant ascites contains not only cancer cells but inflammatory cells including macrophage. Accumulation of macrophages and fibrosis has close relationship. In the research field of fibrotic diseases such as renal fibrosis, some reports indicated macrophages were able to change to fibroblasts phenotypically. Peritoneal carcinomatosis also develops peritoneal fibrosis. We demonstrate that malignant ascites are abundant in macrophages and these macrophages changed to CAFs which promote cancer progression in vivo. [Material and method] Ascitic samples from 44 peritoneal carcinomatosis patients due to gastrointestinal cancer were collected at 5 institutions. This study was approved by each institutional review board. Ascites was separated into cell fraction and supernatant by centrifugation. Supernatant was stored at -20°C. Cells were sorted by FACS using anti-CD45, anti-CD14, anti-CD163 and anti-CD90 antibodies. CD45+CD14+ macrophages were cultured in RPMI medium containing fetal bovine serum (FBS) or supernatant of ascites. Human colorectal cancer cell line DLD-1 cells in combination with the cultured cells from ascites were inoculated to immunodeficient mice subcutaneously. All experiments were conducted following the guidelines of the institutional animal committee of Kyushu University. [Result] CD45+CD14+ macrophage was most frequently observed in CD45+ leukocyte fraction from ascites. Most of macrophages expressed M2 marker (CD163). Some of these macrophages changed to CD45-CD90+ fibroblast-like cells which form spindle shape after 2-3 weeks culture. These fibroblast-like cells expressed fibroblast specific genes such as COL3A1, ACTA2 and FAP. These changes were enhanced by ascites supernatant-containing medium compared with FBS-containing medium. DLD-1 cells with the fibroblast-like cells formed larger tumors in immunodeficient mice, compared with DLD-1 cells alone. [Conclusion] In peritoneal carcinomatosis, macrophage is a potential source of CAF. This macrophage-to-CAF transition is enhanced by malignant ascitic environment. As CAF induced from macrophage enhances tumor progression, inhibition of this transition could be possible therapeutic strategy. Citation Format: Mamoru Tanaka, Michitaka Nakano, Hiroshi Ariyama, Kyoko Inadomi, Risa Tanaka, Shigeo Takaishi, Hitoshi Kusaba, Eishi Baba, Koichi Akashi. Macrophage-to-fibroblast transition promotes cancer progression in peritoneal carcinomatosis of gastrointestinal cancer patient. [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 714.