Abstract 844: Targeting the pro-survival protein c-MET with ARQ 197 inhibits growth of multiple myeloma cells

Multiple myeloma (MM) is a B-cell disorder characterized by the accumulation of mature plasma cells in the bone marrow. Earlier studies have established that patients with MM have high plasma concentrations of hepatocyte growth factor (HGF) which is correlated with poor prognosis and advanced disease stages. HGF is the ligand for the c-MET receptor tyrosine kinase. Our group has previously shown that inactivation of the c-MET receptor by siRNA and ribozyme approaches inhibited proliferation and induced apoptosis in MM cell lines. Hence, we hypothesized that the HGF/c-MET axis plays a critical role in myeloma cell survival and targeting this pathway would be an effective strategy to treat MM. To further test our hypothesis, we used MM1.S, U266 and OPM-2 myeloma cell lines and ARQ 197 (tivantinib), a small molecule non-ATP-competitive and selective c-MET inhibitor (K i =355 nM). This drug is orally bioavailable, achieving steady-state levels of median 6-7 µM in plasma of patients with solid tumors. Cell growth was inhibited by at least 50% and annexin V/propidium iodide positive cells increased by at least 60% within 48 hours of treatment with 1 µM (U266 and OPM-2) and 3 µM (MM.1S) ARQ 197. Consistent with this biological response, downstream effectors of c-MET signaling including phospho-GAB1 and phospho-ERK1/2 were decreased. MM patients develop resistance to the current drugs such as lenalidomide and bortezomib. We tested ARQ 197 in paired MM cell lines - RPMI 8226, ANBL-6 and KAS-6/1 - that are sensitive and resistant to lenalidomide or bortezomib. In general, all the tested cell lines expressed readily detectable levels of proHGF as well as detectable albeit low levels of c-MET. Interestingly, the resistant cell lines expressed significantly higher c-MET protein levels compared to drug-naive controls, but were equally sensitive to ARQ 197 indicating that this c-MET kinase inhibitor overcomes inherent drug resistance. The bone marrow microenvironment is also a source for acquired drug resistance, yet ARQ 197 was effective in inhibiting growth of MM cell lines grown on human stromal cells (NKtert) which mimic the bone marrow microenvironment. Consistent with these data, exogenous addition of the cytokines interleukin-6 (0.5 and 1.0 ng/ml) or HGF (50 ng/ml) did not abrogate ARQ 197-mediated cell death or growth inhibition. Importantly, plasma cells from healthy donors (n = 15) showed no difference in c-MET mRNA expression compared to plasma cells from MM patients (n = 147) but showed relatively lower levels of HGF expression compared to MM patients. These results suggest that the HGF/c-MET pathway is upregulated in MM plasma cells. In conclusion, inhibition of the c-MET receptor tyrosine kinase activity with ARQ 197 is a novel-target based strategy to impact on the pathobiology of MM. Based on these data, we are initiating a clinical trial of ARQ 197 in patients with relapsed/refractory MM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 844. doi:1538-7445.AM2012-844