Abstract 647: In situ detection of human and mouse species-specific molecules in patient derived xenograft mouse models
Authors: Li Na , Ye Xin K. , He Ming-Xiao , Zhang Zhifu , Sun Hongzhe , Wang Xin , Luo Yuling , Ma Xiao-Jun , Gu Zhenyu , Park Emily 
Published: July 2016

Patient derived xenograft (PDX) mouse models are widely used in targeted cancer therapy study and cancer drug development. With human cancer tissues embedded into mouse microenvironment, both human and mouse derived molecules contribute to the proliferation and invasion of the implanted tumor cells. In order to explore the working mechanisms of targeted therapy and evaluate its anti-cancer effects, it is important to uncover the expression and spatial relation of targeted molecules in situ. Although profiling methods such as microarray and RNAseq can address the origin of relevant gene transcripts, they lose tissue spatial and cell morphology information by using tissue lysates. Immunohistochemistry (IHC) can preserve tissue and cell morphology information, however good antibodies are not readily available for every target molecule. In addition, IHC cannot detect long non-coding RNA targets. It is therefore crucial to find a broadly applicable method to separately detect human and mouse derived genes in PDX tissue samples.

Species-specific probes targeting on seven cancer related genes, EGFR, ERBB2, FGFR1, FGFR2, FGFR4, PECAM1 and TGFB1, were designed for RNAscope in situ hybridization assays. The assays were performed in colorectal cancer (CRC) PDX sections and liver cancer PDX TMAs. The RNA expression results were categorized into 5 grades according to manufacturer's scoring guidelines.

Probe species-specificity of human probes and mouse probes was tested in human colon cancers and mouse colons. Both tissues passed quality control by hybridizions with probe-Hs-PPIB/probe-Mm-Ppib and probe-dapB. All human species-specific probes produced negative results in mouse colons, whereas mouse species-specific probes generated signals for Egfr, Erbb2, Fgfr2, Pecam1 and Tgfb1 (score 2 or more than 2) in mouse colons. No mouse species-specific probe signals were observed in human colon cancers. In CRC PDX sections, human species-specific probes detected signals of ERBB2 and FGFR4 (score 3) in colorectal tumor cells whereas mouse species-specific probes detected signals for Fgfr1, Pecam1 and Tgfb1 (score 2 or more than 2) in stroma areas. In liver cancer PDX TMAs, human EGFR, ERBB2, FGFR1, FGFR2, FGFR4 and TGFB1 (score 2 or more than 2) were identified by species-specific probes in liver cancer cells; mouse Egfr, Fgfr1, Pecam1 and Tgfb1 signals (score 2 or more than 2) were observed in the stroma regions. RNAscope duplex assays identified both human FGFR1 and mouse Fgfr1 probe signals in the same sections with different colors.

RNAscope technology using species-specific probes can detect in situ human and mouse genes, respectively, which provides a powerful method to uncover the location of targeted cancer therapy related genes, their expression levels and the spatial correlation of positive cells with surrounding cells. This method will facilitate targeted therapy studies and cancer drug development in PDX mouse models.

Citation Format: Na Li, Xin K. Ye, Ming-Xiao He, Zhifu Zhang, Hongzhe Sun, Xin Wang, Yuling Luo, Xiao-Jun Ma, Zhenyu Gu, Emily Park. In situ detection of human and mouse species-specific molecules in patient derived xenograft mouse models. [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 647.