title: Topoisomerase II - drug interaction domains: identification of substituents on etoposide that interact with the enzyme.
abstract: Etoposide is one of the most successful chemotherapeutic agents used for the treatment of human cancers. The drug kills cells by inhibiting the ability of topoisomerase II to ligate nucleic acids that it cleaves during the double-stranded DNA passage reaction. Etoposide is composed of a polycyclic ring system (rings A-D), a glycosidic moiety at the C4 position, and a pendent ring (E-ring) at the C1 position. Although drug-enzyme contacts, as opposed to drug-DNA interactions, mediate the entry of etoposide into the topoisomerase II-drug-DNA complex, the substituents on etoposide that interact with the enzyme have not been identified. Therefore, saturation transfer difference [1H]-nuclear magnetic resonance spectroscopy and protein-drug competition binding assays were employed to define the groups on etoposide that associate with yeast topoisomerase II and human topoisomerase IIalpha. Results indicate that the geminal protons of the A-ring, the H5 and H8 protons of the B-ring, and the H2' and H6' protons and the 3'- and 5'-methoxyl protons of the pendent E-ring interact with both enzymes in the binary protein-ligand complexes. In contrast, no significant nuclear Overhauser enhancement signals arising from the C-ring, the D-ring, or the C4 glycosidic moiety were observed with either enzyme, suggesting that there is limited or no contact between these portions of etoposide and topoisomerase II in the binary complex. The functional importance of E-ring substituents was confirmed by topoisomerase II-mediated DNA cleavage assays.
authors.affiliation: Departments of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Wilstermann
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Bender
authors.forename: Murrell
authors.initials: M
authors.lastname: Godfrey
authors.forename: Sungjo
authors.initials: S
authors.lastname: Choi
authors.forename: Clemens
authors.initials: C
authors.lastname: Anklin
authors.forename: David B
authors.initials: DB
authors.lastname: Berkowitz
authors.forename: Neil
authors.initials: N
authors.lastname: Osheroff
authors.forename: David E
authors.initials: DE
authors.lastname: Graves
mesh_terms: D000951:Antigens, Neoplasm / Q000737:chemistry; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry*; D001667:Binding, Competitive; D004250:DNA Topoisomerases, Type II / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry; D005047:Etoposide / Q000737:chemistry*; D006801:Humans; D019906:Nuclear Magnetic Resonance, Biomolecular; D017434:Protein Structure, Tertiary
chemical_list: D000951:Antigens, Neoplasm; D000972:Antineoplastic Agents, Phytogenic; D004268:DNA-Binding Proteins; D005047:Etoposide; D004250:DNA Topoisomerases, Type II