Abstract A42: Evaluation of HGF and MET protein expression in NSCLC tumor specimens from patients previously treated with targeted or chemotherapies.
Authors: Sankar Sabita , Wright Jennifer , Galderisi Chad 
Published: August 2014

Background: Although epidermal growth factor receptor (EGFR) T790M mutation accounts for majority of the resistance to the first generation EGFR tyrosine kinase inhibitors (TKIs), activation of the MET pathway through increased expression of hepatocyte growth factor (HGF) or amplification of MET (the HGF receptor) has also been identified as a resistance mechanism in patients. Effective treatment of patients that have progressed on first-generation TKIs requires diagnostic assays that detect the major resistance mechanisms and direct therapy selection. We have developed immunohistochemistry (IHC) assays to detect both HGF and MET protein expression in formalin-fixed paraffin-embedded (FFPE) tissues, and evaluated expression levels in patients previously treated with EGFR TKIs or chemotherapy.

Methods: The IHC assays were developed using the Ventana Benchmark automated staining system. The MET antibody (SP44) was obtained from Ventana. Five different HGF antibodies from several vendors were evaluated. The assay was established using cell pellets generated from cell lines overexpressing HGF as well as a FFPE metastatic cancer tissue array. In addition, tissue specimens obtained from remnant material from surgery or autopsy were used for the assay optimization.

Results: The MET (SP44) assay was validated using the recommended protocol supplied by Ventana. Robust staining was observed in multiple FFPE samples, and both cytoplasmic and membranous staining were defined as positive. The expression was scored on the basis of intensity and fraction of positive cells. In contrast, among the 5 HGF antibodies tested for specificity, only the IBL antibody demonstrated HGF-specific staining in cell lines and the metastatic tissue array. The selected MET and HGF antibodies were used to evaluate a set of 25 NSCLC patient FFPE tissues. 19/25 specimens tested showed positive MET expression. Of these, 13 were 3+ whereas 6 were 2+ in terms of staining intensity. Additionally, 2 of the specimens with 2+ score exhibited predominantly cytoplasmic staining. In contrast, HGF expression was more variable with 5/24 with strong, 9/24 with weak and 10/24 with negative staining (one specimen was not evaluable for HGF). There was no clear correlation between MET and HGF staining patterns. In this sample set, there was not a clear correlation between MET or HGF expression and patient status as relapsed versus newly diagnosed.

Conclusions: We have developed robust assays for evaluation of MET and HGF expression in FFPE sections and applied these assays in analyzing 25 NSCLC patient specimens, documenting a higher than expected proportion of the samples as MET or HGF positive. A more expansive dataset, potentially evaluating factors beyond protein expression levels, will be needed to elucidate a relationship between MET pathway activation and response to EGFR TKIs.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A42.

Citation Format: Sabita Sankar, Jennifer Wright, Chad Galderisi. Evaluation of HGF and MET protein expression in NSCLC tumor specimens from patients previously treated with targeted or chemotherapies. [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 A42.