title: Sites in the diyne-ene bicyclic core of neocarzinostatin chromophore responsible for hydrogen abstraction from DNA.
abstract: The antitumor antibiotic neocarzinostatin exhibits its main drug action by abstracting hydrogen from DNA deoxyribose with consequent strand breakage or related lesions. All biological activities of the drug derive solely from a nonprotein chromophoric substance (NCS-chrom) consisting of a novel epoxy-bicyclo-diyne-ene system. Thiol or sodium borohydride activates NCS-chrom into a labile, reactive species that induces DNA damage but causes inactivation of the drug in the absence of the target DNA. Mass spectrometric studies indicate that the isolated thiol-activated NCS-chrom product in the presence of DNA has the same molecular weight as the thiol-inactivated NCS-chrom product in the absence of DNA. No deuterium is incorporated into the chromophore from the deuterium-labeled sulfhydryl group. Since three deuterium atoms can be incorporated into the drug by treatment with sodium borodeuteride without DNA, adding an unlabeled DNA under parallel conditions permitted the ready identification of the activated NCS-chrom product that abstracted hydrogen from the DNA. Not only does the activated NCS-chrom product have the same structure as the inactivated drug without DNA, but two of the incorporated deuterium atoms have been substituted by hydrogen. With the aid of NMR spectrometry, the two replaced hydrogen atoms are found to be incorporated into the C-2 and C-6 positions of the bicyclo-diyne-ene ring of NCS-chrom and are derived neither from borodeuteride nor from the hydroxyl functions of the solvents. In accord with current proposals, the two hydrogens incorporated into the drug may come from closely opposed sites on the complementary strands of the DNA at which the drug is bound.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: D H
authors.initials: DH
authors.lastname: Chin
authors.forename: C H
authors.initials: CH
authors.lastname: Zeng
authors.forename: C E
authors.initials: CE
authors.lastname: Costello
authors.forename: I H
authors.initials: IH
authors.lastname: Goldberg
mesh_terms: D000903:Antibiotics, Antineoplastic; D055598:Chemical Phenomena; D002621:Chemistry; D004247:DNA; D005978:Glutathione; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009353:Zinostatin
chemical_list: D000903:Antibiotics, Antineoplastic; D004247:DNA; D009353:Zinostatin; D005978:Glutathione