Abstract B157: Effect of HGF concentration on c-Met phosphorylation and inhibition in paracrine-activated tumor cells

Abstract

Abstract c-Met is a receptor tyrosine kinase critical for embryogenesis and liver repair. In tumors, including breast, prostate, glioblastoma, and thyroid cancer, Met protein levels are often elevated and associated with disease progression and metastasis. The c-Met pathway is activated by the endogenous ligand hepatocyte growth factor (HGF). HGF is produced by mesenchymal cells and binds to the c-Met protein, leading to phosphorylation and upregulation of a variety of downstream signaling pathways that result in increased tumor cell migration, proliferation, survival, and induction of angiogenesis. Consequently, there has been significant interest in the development of c-Met inhibitors as anticancer therapeutics. The efficacy of such agents usually initially are determined in vitro utilizing HGF concentrations of 25-50 ng/mL. However, HGF serum levels in humans typically range from 0.4-0.8 ng/mL. To examine the impact of exogenous HGF levels on c-Met inhibitor activity, human prostate (PC-3, DU145) and lung (A549) cancer cell lines were utilized in this study. These cell lines have been previously characterized as paracrine-activated: cell lines that express the c-Met receptor, but not HGF. In the presence of 25-50 ng/mL HGF, these cell lines demonstrated a reduction in migration, invasion, and phosphorylation of Met after treatment with the small-molecule c-Met inhibitor BMS-777607. However, such antitumor efficacy was absent when these paracrine-activated cell lines were treated with BMS-777607 in the presence of physiologically normal concentrations of HGF (0.4-0.8 ng/mL). A human HGF-expressing mouse model has been developed for xenograft studies of human c-Met inhibition, on the basis that mouse HGF does not activate human c-Met. However, we found that mouse HGF was able to induce phosphorylation of Met in the human DU145 cell line. In vivo, DU145 xenografts in NSG mice treated with BMS-777607 showed no reduction in c-Met phosphorylation unless the mice were administered exogenous HGF during tumor growth. Taken together, these findings indicate that the utilization of nonphysiologic concentrations of HGF in tissue culture evaluations of c-Met targeting agents may result in an overestimation of agent activity not likely to be observed in the tumor microenvironment. Citation Format: Veronica S. Hughes, Dietmar W. Siemann. Effect of HGF concentration on c-Met phosphorylation and inhibition in paracrine-activated tumor cells [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B157.