The use of a patient derived tumor xenograft collection to assess different Met and HGF detection methods and their predictive values for therapy response.

Aims: Met inhibitors are targeted drugs which hold promise for the treatment of tumors with HGF/Met pathway activation. To accurately identify such tumors, relevant and well validated predictive biomarkers are needed. In the present study, we used our large collection of tumor models to investigate the value of Met and HGF as determined by multiple methods for predicting sensitivity to Met-inhibitors. Materials and Methods: HGF and Met were assessed at DNA, RNA and protein levels in a panel of 292 tumor models covering 15 different histotypes. The tumors were analyzed for Met amplification and protein expression in a tissue microarray analysis using standard FISH and IHC assays. Met and HGF were also assessed for gene copy number variations, mutations, mRNA and protein expression levels and phosphorylation. For relevant tumors, sensitivity to the Met inhibitors PF-04217903 and/or JNJ-38877605 was evaluated by Tumor Clonogeneic Assays (TCA) and/or in vivo testing. Results: Regarding Met and HGF expression, results obtained at the DNA, RNA and protein level were highly consistent. Affymetrix analyses showed expression of Met mRNA in a large proportion of the models, with a good correlation to protein levels detected by IHC or Western blot. Western blot analyses revealed that most tumors which overexpressed Met showed a high phosphorylation level of the receptor. The FISH and SNP6 analyses allowed identification of a subset of tumors with Met gene amplification, associated with overexpression of Met mRNA, protein and receptor phosphorylation. These models were sensitive to Met-inhibitors in both TCA and in vivo assays. In addition, a subset of tumor xenografts displayed very high Met expression levels and sensitivity to Met-inhibitors, although they did not carry an amplified Met gene. IHC analyses revealed that Met was diversely expressed in some tumors, indicative of intra tumoral heterogeneity that could impact on response to Met inhibitors. HGF, both at mRNA and protein level, was detectable in a subset of tumors, including tumors which did not overexpress Met. Some of these tumors were strongly sensitive to Met inhibitors, suggesting a predictive value of HGF expression. Of interest, these tumors had different topography, such as the liver, the kidney and the lung as well as sarcomas. Conclusion: This study reveals Met overexpression as one of the major determinants of tumor sensitivity to Met-inhibitors. Accurate assessment of Met levels by mRNA array, western blot and IHC analyses showed that Met overexpression was not only due to gene amplification, demonstrating the importance of gene expression assessment complementary to gene copy number evaluation. The in situ analysis also demonstrated that intra-tumoral heterogeneity in Met expression levels can be of importance. Furthermore, HGF levels may be a good predictor for response to Met inhibitors in tumors. Taken together, out data show that in addition to the well-established ex vivo 3D assay with PDX, Met and HGF expression emerges as a powerful parameter to predict tumor response to cMet-directed therapies in vivo. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C25. Citation Format: Vincent Vuaroqueaux, Torsten Giesemann, Luigi Tornillo, Armin Maier, Rebekka Krumbach, Anne-Lise Peille, Tim Kees, Jianing Guo, Frederic Foucault, Zakia Amalou, Serenella Eppenberger, Luigi Terracciano, Heinz-Herbert Fiebig. The use of a patient derived tumor xenograft collection to assess different Met and HGF detection methods and their predictive values for therapy response. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C25.