DNA-DNA interstrand cross-linking by 2,5-bis(1-aziridinyl)-3,6-bis(carbethoxyamino)-1,4-benzoquinone: covalent structure of the dG-to-dG cross-links in calf thymus DNA and a synthetic DNA duplex.

The products of the alkylation reaction of reduced 2,5-bis(1-aziridinyl)-3,6-bis(carbethoxyamino)-1,4-benzoquinone (AZQ, 1a) with duplex DNA were studied using calf thymus DNA and a synthetic oligodeoxynucleotide. Reaction of calf thymus DNA with a mixture of AZQ and ascorbic acid followed by enzymatic digestion of the sugar phosphate backbone afforded numerous AZQ-derived products including substances identified as monoadducts of AZQ with both dG and dA (with the former in greater abundance) and two diadducts, as would be expected for intrastrand or interstrand cross-links, with one containing two dG residues per AZQ and the other one each of dG and dA (with the former adduct in greater abundance). The nucleotide connectivity and covalent structure of the dG-to-dG interstrand cross-links were studied in greater detail using a synthetic DNA duplex containing the nucleotide sequence 5'-d(GGGCCC), where it appeared that the predominant interstrand cross-links bridged dG residues on opposite strands and were separated by two intervening base pairs [5'-d(GNNC)]. The covalent structure of this lesion was tentatively identified as 2b, in which the N7 atoms of two dG residues have been alkylated by the aziridine functions of AZQ, based upon the results of piperidine fragmentation and characterization of the enzymatic and acidic hydrolysates of the cross-linked DNA.