Abstract 1641: Tivantinib (ARQ 197) exhibits antitumor activity by directly interacting with tubulin and overcomes ABC transporter-mediated drug resistance
Authors: Aoyama Aki , Katayama Ryohei , Okuno Yasushi , Fujita Naoya 
Published: August 2015

Abstract
The receptor tyrosine kinase c-MET is recognized as a promising therapeutic target because c-MET-addicted cancers have been shown to be highly sensitive to c-MET kinase inhibitors. Tivantinib (ARQ197) was first reported as a highly selective c-MET inhibitor and is currently being investigated in a phase 3 clinical trial. However, as recently reported by us and other groups, tivantinib showed cytotoxic activity independent of cellular c-MET status and also disrupted microtubule dynamics. To investigate if tivantinib exerts its cytotoxic activity by disrupting microtubules, we quantified polymerized tubulin in cells and xenograft tumors after tivantinib treatment. Tivantinib could reduce tubulin polymerization independent of c-MET inhibition in cells and in mouse xenograft tumors. It is well known that microtubule destabilizing agents, such as vinblastine and colchicine, directly bind to tubulins at different binding sites. To determine if tivantinib directly binds to tubulin or not, we performed an in vitro competition assay using radiolabeled agents. Tivantinib competitively inhibited colchicine binding, but not vincristine or vinblastine binding, to purified tubulin, suggesting that tivantinib directly binds to the colchicine binding site of tubulin. To predict the binding mode of tivantinib with tubulin, we performed computer simulation of the docking pose of tivantinib with tubulin using GOLD docking program. Computer simulation predicts tivantinib fit into the colchicine binding pocket of tubulin without steric hindrance.
Currently, the microtubule inhibitors are widely used for the treatment of various cancers. However the development of acquired resistance is a major obstacle for the therapy. Overexpression of the drug efflux pump (ABC transporter) is one of the major mechanisms of drug resistance. We thus tested the cytotoxic activity of tivantinib against tubulin binding agent-resistant cells that we had established by incubating cells in sublethal concentrations of drug. Tivantinib showed similar IC50 values against parental and multidrug resistant cells. In contrast, other microtubule-targeting drugs, such as vincristine, paclitaxel, and colchicine, could not suppress the growth of resistant cells. Moreover, tivantinib equally suppressed growth and survival of ABCB1-, ABCC1-, or ABCG2- transfected cells.
Our findings that tivantinib shows cytotoxic activity by disrupting tubulin polymerization, directly interacts with tubulin and overcomes ABC transporter-mediated drug resistance, suggest the possibility that tivantinib might be useful for treatment of wide variety of cancers.
Citation Format: Aki Aoyama, Ryohei Katayama, Yasushi Okuno, Naoya Fujita. Tivantinib (ARQ 197) exhibits antitumor activity by directly interacting with tubulin and overcomes ABC transporter-mediated drug resistance. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1641. doi:10.1158/1538-7445.AM2015-1641