Mutagenic and genotoxic effects of DNA adducts formed by the anticancer drug cis-diamminedichloroplatinum(II)

The toxicity and mutagenicity of three DNA adducts formed by the anticancer drug cis-diamminedichloroplatinum(II) (cis-DDP or cisplatin) were investigated in Escherichia coli. The adducts studied were cis-[Pt(NH₃)₂{d(GpG)}] (G^*G^*),[Pt(NH₃)₂{d(ApG)}] (A^*;G^*) cis-[Pt(NH₃)₂{d(GpTpG)}] (G^*TG^*), which collectively represent ̃95% of the DNA adducts reported to form when the drug damages DNA. Oligonucleotide 24-mers containing each adduct were positioned at a known site within the viral strand of single stranded M13mp7L2 bacteriophage DNA. Following transfection into Ecoil DL7 cells, the genomes containing the G^*G^*, A^*G^* and G^*TG^* adducts had survival levels of 5.2 ± 1.2, 22 ± 2.6 and 14 ± 2.5% respectively, compared to unmodified genomes. Upon SOS induction, the survival of genomes containing the G^*G^* and A^*G^* adducts increased to 31 ± 5.4 and 32 ± 4.9% respectively. Survival of the genome containing the G^*TG^* adduct did not increase upon SOS induction. In SOS induced cells, the G^*G^* and A^*G^* adducts gave rise predominantly to G→T and A→T transversions respectively, targeted to the 5′ modified base. In addition, A′G transitions were detected for the A^*G^* adduct and low levels of tandem mutations at the 5′ modified base as well as the adjacent 5′ base were also observed for both adducts. The A^*G^* adduct was more mutagenic than the G^*G^* adduct, with a mutation frequency of 6% compared to 1.4% for the latter adduct. No cis-{Pt(NH₃)₂}²⁺ intrastrand crosslink-specific mutations were observed for the G^*TG^* adduct.