DNA binding and alkylation by the "left half" of azinomycin B

Azinomycin B (also known as carzinophilin A) contains two electrophilic fun ctional groups-an epoxide and an aziridine residue-that react with nucleoph ilic sites in duplex DNA to form cross-links at 5'-dGNT and 5'-dGNC sequenc es. Although the aziridine residue of azinomycin is undoubtedly required fo r cross-link formation, analogues containing an intact epoxide group but no aziridine residue retain significant biological activity. Azinomycin epoxi de analogues (e.g., 5 and 6) are of interest due to their potent biological activity and because there is evidence that azinomycin may decompose in vi vo to yield such compounds. To investigate the chemical events underlying t he toxicity of azinomycin epoxides, DNA binding and alkylation by synthetic analogues of azinomycin B (6, 8, and 9) that comprise the naphthalene-cont aining "left half" of the antibiotic have been investigated, The epoxide-co ntaining analogue of azinomycin (6) efficiently alkylates guanosine residue s in duplex DNA. DNA alkylation by 6 is facilitated by noncovalent binding of the compound to the double helix. The results of UV-vis absorbance, fluo rescence spectroscopy, DNA winding, viscometry. and equilibrium dialysis ex periments indicate that the naphthalene group of azinomycin binds to DNA vi a intercalation. Equilibrium dialysis experiments provide an estimated bind ing constant of (1.3 +/- 0.3) x 10(3) M-1 for the association of a nonalkyl ating azinomycin analogue (9) with duplex DNA. The DNA-binding and alkylati ng properties of the azinomycin epoxide 6 provide a basis for understanding the cytotoxicity of azinomycin analogues which contain an epoxide residue but no aziridine group and may provide insight into the mechanisms by which azinomycin forms interstrand DNA cross-links.