Sequence-dependent termination of in vitro DNA synthesis by cis- and trans-diamminedichloroplatinum(II)

Abstract

Inhibition of DNA replication by the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP) has been proposed to be responsible for its cytotoxicity. Treatment of primed phage M13 mp8 viral DNA templates with the drug followed by second-strand synthesis using large fragment DNA polymerase I reveals that cis-DDP forms an adduct with DNA that inhibits DNA synthesis in vitro. This inhibition occurs at all [dG](n) (n ≥ 2) sequences in the template strand, confirming that these regions are the major cis-DDP binding sites on DNA. trans-Diamminedichloroplatinum(II), which is inactive as a drug, also forms adducts that inhibit DNA synthesis. Although considerably lower specificity is observed with the trans isomer, there appears to be a preference for d(GpNpG) sequences, where N is any intervening nucleotide. The monofunctional adduct formed between chlorodiethylenetriamineplatinum(II) chloride and DNA does not inhibit DNA synthesis in this system.