Abstract 413: Validation of an antibody independent tool for patient selection: RNA in situ hybridization detects Met expression levels predictive for response to Met inhibition by Bay 853474

Abstract

Abstract This study was performed in order to validate RNA in situ hybridization (RNA ISH) as tool for patient selection. Met expression was analyzed in a matched sample set of FFPE versus fresh frozen tumor samples comprising 20 cases of gastric cancer. Classical immunohistochemistry using the antibody SP44 and RNA ISH (RNAscope by ACD) were used to detect c-met expression in FFPE material. The results were confirmed by sandwich-immunoassays on Met and its phosphorylation on tyrosine 1349 (MSD) as well as mass spectrometry. The level of functional relevance was determined by testing a set of cell lines comprising some with genomic amplification of the met gene as well as some non-amplified lines showing different expression levels. Among gastric cancer cell lines only those with met amplification respond to treatment with the small molecule Met inhibitor Bay 853474. The cell line result generates a responder hypothesis that can be used to define a cutoff for clinical samples. 2 of the 20 investigated clinical samples were shown to have high level Met expression by RNA ISH and IHC that could be confirmed by sandwich-immunoassays also showing high level of functional activity by phosphotyrosine 1349. Met expression in these cases was also confirmed by mass spectrometry. Expression levels and functional activity in these 2 cases were in the range that predicts response to treatment as established with gastric cancer cell lines. Determination of predictive biomarkers by immunohistochemistry can be limited due to lack of high quality antibodies of sufficient specificity. Due to its high specificity, RNA in situ hybridization is a technique that can be used to confirm the findings obtained by immunohistochemistry and may potentially even replace immunohistochemistry it if no suitable antibodies are available or not specific enough e.g. to discriminate between closely related protein isoforms. We show the biological relevance of RNA in situ hybridization on FFPE samples by correlation with immunohistochemistry, ELISA based approaches and mass spectrometry. RNA ISH is shown to be specific and sensitive enough to identify cases of functionally relevant MET overexpression levels in gastric cancers and can be used to select patients for treatment. Citation Format: Oliver von Ahsen, Thomas Krahn, Christoph Schatz. Validation of an antibody independent tool for patient selection: RNA in situ hybridization detects Met expression levels predictive for response to Met inhibition by Bay 853474. [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 413.