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MPC-6827: A Small-Molecule Inhibitor of Microtubule Formation That Is Not a Substrate for Multidrug Resistance Pumps

¹ Epicept Corporation, San Diego, California; ² Myriad Pharmaceuticals, Inc., Salt Lake City, Utah; and Departments of ³ Therapeutic Radiology and Oncology and ⁴ Internal Medicine, Innsbruck Medical University, Innsbruck, Austria

Requests for reprints: Christopher M. Pleiman, Myriad Pharmaceuticals, 320 Wakara Way, Salt Lake City, UT 84108. Phone: 801-584-1154; Fax: 801-883-3213; E-mail: cpleiman{at}myriad.com.

A novel series of 4-arylaminoquinazolines were identified from a cell-based screening assay as potent apoptosis inducers. Through structure-activity relationship studies, MPC-6827 and its close structural analogue, MPI-0441138, were discovered as proapoptotic molecules and mitotic inhibitors with potencies at low nanomolar concentrations in multiple tumor cell lines. Photoaffinity and radiolabeled analogues of MPC-6827 were found to bind a 55-kDa protein, and this binding was competed by MPC-6827, paclitaxel, and colchicine, but not vinblastine. MPC-6827 effectively inhibited the polymerization of tubulin in vitro, competed with colchicine binding, and disrupted the formation of microtubules in a variety of tumor cell lines, which together showed the molecular target as tubulin. Treatment of MCF-7 breast carcinoma or Jurkat leukemia cells with MPC-6827 led to pronounced G₂-M cell cycle arrest followed by apoptosis. Apoptosis, as determined by terminal deoxyribonucleotidyl transferase–mediated dUTP nick end labeling assay, was preceded by loss of mitochondrial membrane potential, cytochrome c translocation from mitochondria to nuclei, activation of caspase-3, and cleavage of poly(ADP-ribose) polymerase. MPC-6827 was equipotent in an in vitro growth inhibition assay in several cancer cell lines regardless of the expression levels of the multidrug resistance ABC transporters MDR-1 (Pgp-1), MRP-1, and BCRP-1. In B16-F1 allografts and in OVCAR-3, MIAPaCa-2, MCF-7, HT-29, MDA-MB-435, and MX-1 xenografts, statistically significant tumor growth inhibition was observed with MPC-6827. These studies show that MPC-6827 is a microtubule-disrupting agent with potent and broad-spectrum in vitro and in vivo cytotoxic activities and, therefore, MPC-6827 is a promising candidate for development as a novel therapeutic for multiple cancer types. [Cancer Res 2007;67(12):5865–71]