OA02.05 Expression of miR-223 in Mesothelioma Xenografts Originates from Stromal Cells in the Tumor Microenvironment

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive cancer caused by asbestos exposure with limited therapeutic options. Dysregulated microRNAs play an important role in MPM biology and candidate microRNAs have been investigated as diagnostic and prognostic biomarkers or as a potential treatment targets. The role of miR-223 has previously been investigated in MPM tumor cells and was shown to act as a tumor suppressor by regulating cell mobility. Previous research indicated miR-223 to be primarily expressed by myeloid progenitor derived cells during differentiation of granulocytes and monocytes. This suggests miR-223 might have a more significant role in the inflammatory response during tumorigenesis. In this study we aimed to investigate the origin of miR-223 using mesothelioma xenograft and syngraft models. Human and mouse mesothelioma cell line-derived xenograft (MSTO-H211 and H226) and syngraft (AB1) models were established. MicroRNA profiles of xenografts were compared against profiles of their corresponding in vitro cultured cells to determine candidates. RT-qPCR using TaqMan MicroRNA assays was used to validate expression levels of miR-143-3p, miR-214-3p and miR-223-3p in tumor xenografts and syngrafts with those in corresponding cell lines in vitro. Species-specific ddPCR analysis was performed on RNA from xenograft tumors to determine the expression of human and mouse pri-miR-223. MicroRNA profiles of xenograft tumors showed significant upregulation (p < 0.05) of miR-143-3p, miR-214-3p and miR-223-3p compared to corresponding in vitro mesothelioma cell lines. Only miR-223 showed significant upregulation in both xenograft and syngraft tumors compared to corresponding in vitro mesothelioma cell lines (>10000-fold increase). Other microRNAs were not significantly different between cell lines and tumors. RNA isolated from xenograft tumors contained significantly more mouse pri-miR-223 than human pri-miR-223 (p < 0.001), with only minimal expression levels of human tumor pri-miR-223 within xenograft tumors. Mature miR-223 is significantly overexpressed in xenograft tumors compared to corresponding in vitro mesothelioma cell lines suggesting stromal contribution. Species-specific pri-miRNA confirmed miR-223 is almost exclusively expressed by the mouse stromal cells in xenograft tumors. Ultimately, localizing the expression of miR-223 to specific cell types (such as myeloid derived cells) through in situ hybridization should help identify a more biologically relevant role for miR-223 in the tumor microenvironment.