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

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Abstract
Inhibition of DNA replication by the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP) may be responsible for its cytotoxicity. Treatment of primed phage M13mp8 viral DNA templates with the drug followed by 2nd-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 .gtoreq. 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 chlorodiethylenetriamineplantinum(II) chloride and DNA does not inhibit DNA synthesis in this system.