Species-specific gene expression profiling of patient-derived xenograft tumors by the RNAscope® in situ hybridization assay

Introduction

The tumor microenvironment plays multiple roles in tumor cell proliferation, differentiation, vascularity, and metastasis through tumor cell-stromal cell interactions¹. Patient-derived xenograft (PDX) tumor models contain human cancerous tissue growing in a mouse stromal environment (Figure 1) and are widely used for cancer research and drug discovery². Multiple gene profiling methods such as microarray and RNAseq have been applied to investigate human and murine gene expression in PDX tumor models. While these assays may identify the species of origin for the PDX transcriptome, it is difficult to reconstruct the spatial distribution and heterogeneity of the transcripts of interest. Immunohistochemistry (IHC) analysis can provide morphological insights³, however, the availability of antibodies as well as the unknown specificity and sensitivity of IHC antibodies hinder accurate interpretation of biomarker localization in the tumor microenvironment⁴. Therefore, there is a strong need to establish an accurate, specific, and widely accepted in situ method to identify speciesspecific RNAs in PDX tumor models.