title: Evading Pgp activity in drug-resistant cancer cells: a structural and functional study of antitubulin furan metotica compounds.
abstract: Tumor resistance to antitubulin drugs resulting from P-glycoprotein (Pgp) drug-efflux activity, increased expression of the βIII tubulin isotype, and alterations in the drug-binding sites are major obstacles in cancer therapy. Consequently, novel antitubulin drugs that overcome these challenges are of substantial interest. Here, we study a novel chemotype named furan metotica that localizes to the colchicine-binding site in β-tubulin, inhibits tubulin polymerization, and is not antagonized by Pgp. To elucidate the structure-activity properties of this chiral chemotype, the enantiomers of its most potent member were separated and their absolute configurations determined by X-ray crystallography. Both isomers were active and inhibited all 60 primary cancer cell lines tested at the U.S. National Cancer Institute. They also efficiently killed drug-resistant cancer cells that overexpressed the Pgp drug-efflux pump 10(6)-fold. In vitro, the R-isomer inhibited tubulin polymerization at least 4-fold more potently than the S-isomer, whereas in human cells the difference was 30-fold. Molecular modeling showed that the two isomers bind to β-tubulin in distinct manners: the R-isomer binds in a colchicine-like mode and the S-isomer in a podophyllotoxin-like fashion. In addition, the dynamic binding trajectory and occupancy state of the R-isomer were energetically more favorable then those of the S-isomer, explaining the observed differences in biologic activities. The ability of a racemic drug to assume the binding modes of two prototypical colchicine-site binders represents a novel mechanistic basis for antitubulin activity and paves the way toward a comprehensive design of novel anticancer agents.
authors.affiliation: Target Structure-Based Drug Discovery Group, SAIC-Frederick, Inc., Frederick, Maryland, USA.
authors.forename: Tam Luong
authors.initials: TL
authors.lastname: Nguyen
authors.forename: Maria Rosaria
authors.initials: MR
authors.lastname: Cera
authors.forename: Andrea
authors.initials: A
authors.lastname: Pinto
authors.forename: Leonardo
authors.initials: L
authors.lastname: Lo Presti
authors.forename: Ernest
authors.initials: E
authors.lastname: Hamel
authors.forename: Paola
authors.initials: P
authors.lastname: Conti
authors.forename: Rick
authors.initials: R
authors.lastname: Gussio
authors.forename: Peter
authors.initials: P
authors.lastname: De Wulf
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005663:Furans / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D007211:Indoles / Q000737:chemistry* / Q000494:pharmacology*; D009369:Neoplasms / Q000378:metabolism; D013237:Stereoisomerism; D050257:Tubulin Modulators / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: C577609:2-(ethylthio)ethyl 6-(furan-2-yl)-3-methyl-4-oxo-4,5,6,7,tetrahydro-1H-indole-2-carboxylate; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D005663:Furans; D007211:Indoles; D050257:Tubulin Modulators