Michael Aidan North

Abstract 628: A novel SND1-BRAF fusion confers resistance to the cMet inhibitor PF-04217903 in GTL16 cells

The hepatocyte growth factor receptor (HGFR/cMET) signaling pathway is a driver of tumorigenesis in a variety of tumor types, and a number of agents targeting cMet, including PF-04217903, are under investigation in clinical trials. Tumor types exhibiting an amplified MET gene locus such as gastric, NSCLC, or esophageal cancers are of particular interest for clinical development of c-Met inhibitors. While inhibition of other receptor tyrosine kinases (RTKs) such as ErbB2, EGFR, or KIT have proven to be effective treatments for cancer patients, most tumors become refractory to respective targeted therapies due to the emergence of resistance mechanisms associated with drug targets or upregulation of compensatory pathways. To identify potential mechanisms of resistance to c-Met inhibitors, a gastric carcinoma line (GTL16) was placed under selective pressure by culturing cells in increasing concentrations of PF-0421703 in vitro and resistant clones were isolated. Resistant clones were characterized for changes in signaling, gene expression, and DNA copy number variation as compared to parental GTL16 cells. These studies resulted in the identification of genomic rearrangements at the 7q32 and 7q34 loci which produce a novel SND1-BRAF fusion protein in resistant cells. The fusion protein includes the BRAF kinase domain and is both constitutively active and overexpressed relative to parent cells as determined by gene expression array, immunoblot, and mass spectrometry. In addition, phosphoproteomic analyses demonstrated enrichment of phosphopeptides associated with the MAPK pathway signaling proteins relative to wildtype cells. Cells expressing the fusion protein exhibited resistance to multiple c-Met inhibitors whereas treatment of resistant cells with a combination of c-Met and BRAF inhibitors or a MEK inhibitor (PD325901) reversed the resistance phenotype by reestablishing inhibition of MAPK signaling and restoring growth inhibition. Together, these data provide an unique example of a mechanism where MAPK activation, through BRAF amplification/rearrangement, confers resistance to a RTK/cMET inhibitor. Furthermore, the results suggest the importance of MEK/ERK signaling downstream of c-Met and that a potential combination strategy for c-Met inhibitors with BRAF or MEK inhibitors could be employed to delay onset or circumvent potential resistance mechanisms. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 628.