We examined the role of the hepatocyte growth factor (HGF) receptor c-Met in multiple myeloma by applying a novel selective small-molecule tyrosine kinase inhibitor, PHA-665752, directed against the receptor.

Four biological sequels of HGF related to multiple myeloma were studied: (1) proliferation of myeloma cells; (2) secretion of interleukin-11 from osteogenic cells; (3) migration of myeloma cells; and (4) adhesion of myeloma cells to fibronectin. We also examined effects of the c-Met inhibitor on intracellular signaling pathways in myeloma cells.

PHA-665752 effectively blocked the biological responses to HGF in all assays, with 50 % inhibition at 5-15 nM concentration and complete inhibition at around 100 nM. PHA-665752 inhibited phosphorylation of several tyrosine residues in c-Met (Y1003, Y1230/1234/1235, and Y1349), blocked HGF-mediated activation of Akt and p44/42 Mitogen-activated protein kinase (MAPK), and prevented the adaptor molecule Gab1 from complexing with c-Met. In the HGF-producing myeloma cell line ANBL-6, PHA-665752 revealed an autocrine HGF/c-Met-mediated growth loop. The inhibitor also blocked proliferation of purified primary myeloma cells, suggesting that autocrine HGF/c-Met-driven growth loops are important for progression of multiple myeloma. Conclusions: Collectively, these findings support the role of c-Met and HGF in the proliferation, migration, and adhesion of myeloma cells and identify c-Met kinase as a therapeutic target for treatment of patients with multiple myeloma.

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