title: Selective abstraction of 2H from C-1' of the C residue in AGC.ICT by the radical center at C-2 of activated neocarzinostatin chromophore: structure of the drug/DNA complex responsible for bistranded lesion formation.
abstract: Glutathione-activated neocarzinostatin chromophore (NCS-Chrom) generates bistranded lesions at AGC.GCT sequences in DNA, consisting of an abasic site at the C residue and a strand break at the T residue on the complementary strand, due to hydrogen atom abstraction from C-1' and C-5', respectively. Earlier work showed that 2H from C-5' of T was selectively abstracted by the radical center at C-6 of activated NCS-Chrom, supporting a proposed model of the active-drug/DNA complex. However, since under the conditions used breaks at the T exceeded their inclusion in bistranded lesions, it was not clear what fraction of the hydrogen transfer represented bistranded lesions. Since virtually all abasic sites at the C are part of a bistranded lesions, hydrogen transfer from C-1' of C into the drug should reflect only the bistranded reaction. Accordingly, a self-complementary oligodeoxynucleotide 5'-GCAGCICTGC-3' was synthesized in which the C contained 2H at the C-1' position. In order to eliminate an 2H isotope effect on the transfer and to increase the extent of the bistranded reaction, an I residue was substituted for the G opposite the C residue. Sequencing gel electrophoretic analysis revealed that under one-hit kinetics, 37% of the damage reaction was associated with abasic site (alkali-labile break) formation at the C residue and 48% with direct strand breaks at the T residue. Thus, 74% of the damage involved a bistranded lesion. 1H NMR spectroscopic analysis of the reacted chromophore showed that 2H had been selectively transferred into the C-2 position to the extent of approximately 22%.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: S M
authors.initials: SM
authors.lastname: Meschwitz
authors.forename: R G
authors.initials: RG
authors.lastname: Schultz
authors.forename: G W
authors.initials: GW
authors.lastname: Ashley
authors.forename: I H
authors.initials: IH
authors.lastname: Goldberg
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D004249:DNA Damage; D003903:Deuterium; D053281:Enediynes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D009353:Zinostatin / Q000031:analogs & derivatives*
chemical_list: D053281:Enediynes; D009838:Oligodeoxyribonucleotides; C032372:neocarzinostatin chromophore; D004247:DNA; D009353:Zinostatin; D003903:Deuterium