Diminution of phosphorylated MET and associ ated decreases in ERK1/2 and AKT phosphorylation has been shown to be important in growth, migration and cell survival pathways for other cancer cell types. Amuvatinib proved to be effective in inducing cell death not only in a MET dependent myeloma cell line but also in primary CD138 malignant plasma cells obtained from patients with myeloma. In contrast, amuvatinib did not cause cell death in normal CD138 cells obtained from the same individuals. These data provide evidence of the selectivity of amuvatinib, suggesting that it may be used specifically for myeloma treatment without impairing other normal hematological cells in the bone marrow. In line with this selective cytotoxic effect on CD138 plasma cells, MET phosphorylation was reduced by amuvatinib treat ment in primary plasma cells but not CD138 cells.

The effects of amuvatinib described here provide proof of concept that MET is important for the survival of myeloma cells and that reduction of its kinase activity may prove to be an effective targeted therapy. The 25 uM dose of amuvatinib needed to robustly induce apoptosis in cell lines and plasma cells under full serum conditions may not be achievable in vivo. Pharmacokinetic studies of amuvatinib during a phase I trial indicated that plasma levels reached between 1 and 2 uM. Hence, newer generation and more potent MET tyrosine kinase inhibi tors are needed. ARQ 197 is a small molecule, non ATP competitive inhibitor which is highly specific for MET. This drug is well tolerated in clinical trials and has shown efficacy in solid tumors.

Pharmacodynamic studies from a phase I trial in dicated that at an oral dosing of 360 mg, twice daily, ARQ 197 reached steady state plasma concentrations of 6 7 uM. This correlated with decreases in total MET and phospho FAK and increases in TUNEL positive cells in patients tumors. Our results with amuvatinib provided the impetus to pursue testing of ARQ 197 in myeloma cells. Our preclin ical studies indicated that treatment with ARQ 197 for 48 hours was cytotoxic to myeloma cell lines at clinically achiev able doses. Moreover, these studies provided the foundation for a Cancer Therapy Evaluation Program, National Cancer Institute sponsored phase 2 clinical trial of ARQ 197 in myeloma patients, which is currently un derway at MD Anderson Cancer Center.

Conclusions Our finding provides proof of principle that MET is im portant for the survival of myeloma cells and using a MET inhibitor such as amuvatinib may prove to be an effective Dacomitinib strategy for treatment of MM. Amuvatinib ex hibited tumoricidal activity in myeloma cells which was associated with inhibition of MET signaling. Amuvatinibs lack of effect on CD138 cells from the same patients fur ther establishes the selectivity of this agent.