Abstract B03: Dissecting molecular pathways in human tumor vs. mouse stromal environment in patient-derived cancer models
Authors: Park Emily , Li Na , Ye Katherine , He Mingxiao , He Mingxiao , Zhang Zhifu , Sun Hongzhe , Wang Xin , Anderson Courtney , Luo Yuling , Gu Zhenyu , Ma Xiao-Jun 
Published: March 2017

Abstract
The tumor microenvironment plays multiple roles in tumor cell proliferation, differentiation, vascularity, and metastasis through tumor cell-stromal cell interactions. The molecular responses of tumor cells to drug treatment can modify or be modified by the molecular signaling in stromal cells. Therefore, understanding the molecular features of both tumor cells and the tumor microenvironment is crucial for understanding cancer biology and the discovery of targeted therapy. Patient-derived xenograft (PDX) tumor models contain human tumor cells growing in a mouse stromal environment and are widely used models for cancer research and drug discovery.
In this study we have applied in situ hybridization to visualize gene expression in human tumor and mouse stroma by developing species-specific probes based on the RNAscope technology. Eight genes were selected for this study based on their roles in a wide range of human cancers: EGFR, ERBB2, FGF19, FGFR1, FGFR4, MET, PECAM1 and TGFB1. We designed human and mouse species-specific probes by targeting the most divergent regions (&lt;80% homology) between orthologous sequences. PDX tumors of two types of human cancers were used: human colorectal cancer (CRC) and human liver cancer.
In both CRC and liver cancer PDX tumors, human-specific probes detected strong expression of ERBB2, FGFR4, and MET in human tumor cells but no signals in mouse stromal cells. Conversely, the mouse-specific probes only detected expression of Erbb2, Fgfr4, and Met genes in mouse stromal cells. Notably, strong expression of several mouse genes, including Tgfb1, Fgfr1, Egfr, and Pecam1, were detected in the stroma surrounding the human tumor by mouse-specific probes while no human probe signals were detected in the same region. Human TGFB1, FGFR1, EGFR, and PECAM1 probes detected varied levels of gene expression in the human tumor cells from the same sample without cross-detection of the mouse ortholog sequences in the stromal region.
We also observed extensive gene expression heterogeneity, both within the same tumor and between tumors. Heterogeneity of FGFR4 and FGF19 expression in the liver cancer model was particularly notable. Our results indicate that RNAscope, a single molecule RNA detection method can robustly detect the expression patterns of FGFR4-FGF19 in PDX tumors and can be utilized for selecting PDX models for mouse trials with therapeutic agents targeting FGFR4 signaling pathway.
Overall the findings in this study demonstrate the successful use of RNAscope based in-situ hybridization to examine human tumor specific gene expression in mouse stromal environment in PDX animal models by visualizing gene expression in both the human tumor and mouse stroma with species-specific probes. As human tumor engrafts acquire mouse stromal cells during growth in the murine host, the method presented here will further enable the molecular dissection in PDX tumor models of tumor-host interactions involved in tumor growth, progression, and metastasis as well as responses to cancer drugs and development of drug resistance.
Citation Format: Emily Park, Na Li, Katherine Ye, Mingxiao He, Mingxiao He, Zhifu Zhang, Hongzhe Sun, Xin Wang, Courtney Anderson, Yuling Luo, Zhenyu Gu, Xiao-Jun Ma. Dissecting molecular pathways in human tumor vs. mouse stromal environment in patient-derived cancer models. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B03.