Abstract 3923: Insensitivity to c-Met inhibition at physiologic HGF concentrations in a prostate carcinoma model
Authors: Hughes Veronica S. , Rojiani Mumtaz , Siemann Dietmar 
Published: August 2018

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. C-Met is associated with disease progression and metastasis. Consequently, there has been significant interest in the development of c-Met inhibitors as anti-cancer 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. In our studies, we examined the prostate carcinoma cell line DU145, and BMS-777607. Migration and phosphorylation of c-Met increased in a dose-dependent manner with HGF treatment. Additionally, c-Met inhibition with BMS-777607 reduced migration and invasion when in the presence of 25-50 ng/mL HGF. However, at physiologically relevant HGF concentrations the drug had no effect on migration or invasion of this cell line. In vivo models of c-Met inhibition have been limited mainly to mice genetically engineered to express HGF, on the basis that mouse HGF does not stimulate human c-Met. However, in our studies, mouse HGF did stimulate c-Met in the DU145 tumor cell line. Subsequent in vivo evaluation revealed treatment with BMS-777607 had no reduction on DU145 tumor cell-induced angiogenesis in cells pretreated with the drug, nor in mice receiving oral administration of the drug. An experimental metastasis model also resulted in no significant reduction in metastasis formation, as assessed by a tail vein injection model. To characterize HGF concentration in vivo, an ELISA was used to determine an average concentration of 7.7 ng/g of DU145 tumor tissue. Further evaluations of phospho-Met are underway utilizing immunofluorescence of FFPE samples. Preliminary results indicate low levels of phospho-Met in DU145 tumor sections that can be induced by treating tumor-bearing mice with exogenous HGF. Our results suggest that in vitro evaluation of c-Met inhibitors utilizing non-physiological concentrations of HGF may produce an abnormally high phospho-Met that can subsequently be reduced by treatment with c-Met inhibition. In vitro studies performed at high HGF concentrations may not accurately predict the in vivo drug efficacy. Further characterization of HGF concentrations within the tumor is necessary to properly conduct in vitro evaluation of c-Met inhibitors.
Citation Format: Veronica S. Hughes, Mumtaz Rojiani, Dietmar Siemann. Insensitivity to c-Met inhibition at physiologic HGF concentrations in a prostate carcinoma model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3923.