Abstract 4904: Developing a universal target retrieval solution and protocol for RNA in situ hybridization based on RNAscope technology

Abstract Heat induced target retrieval (HITR) is a widely adopted approach for Immunohistochemistry (IHC) and in situ hybridization (ISH) applications on formalin fixed and paraffin embedded (FFPE) tissues to facilitate target access and increase detection sensitivity. A variety of factors, such as fixative type, fixation time, tissue type, epitope abundance, antibody affinity, and probe length greatly affect the efficiency of HITR. Given such variability, over the decades, multiple HITR buffer formulations and protocols were invented to fit the needs in different experimental scenarios. We have developed a novel HITR solution that allows highly efficient target retrieval for RNA ISH application based on the RNAscope technology. When tested on 15 different tumor types, the new HITR solution resulted in significantly better sensitivity and/or tissue morphology comparing to using traditional HITR buffers, including Citrate, EDTA, and Tris based buffers with various pH. Furthermore, this new HITR solution is highly tolerant to sample variability. When used on multiple human tumor tissue microarrays (TMAs), including breast, colon, lung, and gastric cancers, the new HITR solution improved overall signal-to-noise ratio and reduced core disqualification rate, compared to traditional citrate based HITR buffer for ISH. Moreover, when tested on multiple mouse tissues fixed with different types of fixatives for varying periods of time (6 - 72 hours), a single experimental condition with the new HITR solution showed comparable results in both detection sensitivity and morphological integrity in all the samples. It also allowed detection of a target (Tbp) with extremely low abundance (<5 copies/cell). Given that all the RNAscope probes are synthetic oligonucleotide probes with length shorter than 60 bases, the new HITR solution, in combination with the RNAscope technology, will allow universal detection of any RNA targets with single molecule detection sensitivity in FFPE tissues with minimal requirement for analytical condition optimization. Citation Format: Li-chong Wang, Liuliu Pan, Kuang-Jung Chang, Daniel Kim, Xingyong Wu, Hongwei Wang, Casey Kernag, Bingqing Zhang, Mingxiao He, Nan Su, Xiao-Jun Ma, Yuling Luo. Developing a universal target retrieval solution and protocol for RNA in situ hybridization based on RNAscope technology. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4904. doi:10.1158/1538-7445.AM2015-4904