Interstrand cross-linking by Adriamycin in nuclear and mitochondrial DNA of MCF-7 cells

Activation of Adriamycin by formaldehyde leads to the formation of drug-DNA adducts in vitro and these adducts stabilise the DNA to such a degree that they function as virtual interstrand cross-links. The formation of these v irtual interstrand cross-links by Adriamycin was investigated in MCF-7 cell s using a gene-specific interstrand cross-linking assay. Crosslinking was m easured in both the nuclear-encoded DHFR gene and in mitochondrial DNA (mtD NA), Cross-link formation increased linearly with adriamycin concentration following a 4 h exposure to the drug. The rate of formation of adriamycin c ross-links in each of the genomes was similar, reaching maximal levels: of 0.55 and 0.4 cross-links/10 kb in the DHFR gene and mtDNA respectively, fol lowing exposure to 20 mu M Adriamycin for 8 h. The interstrand cross-link w as short lived in both DNA compartments, with a half-life of 4.5 and 3.3 h in the DHFR gene and mtDNa respectively. The kinetics of total Adriamycin a dduct formation,:detected using [C-14]Adriamycin, was similar to that of cr oss-link formation. Maximal adduct levels (30 lesions/10 kb) were observed following incubation at 20 mu M drug for 8 h. The formation of such high le vels of adducts and cross-links could therefore be expected to contribute t o the mechanism of action of Adriamycin.