The reaction of platinum(II) complexes with DNA. Kinetics of intrastrand crosslink formation in vitro.

The kinetics of the formation of bifunctional DNA platinum(II) adducts (DNA-crosslinks) have been investigated by endonuclease digestion and subsequent HPLC analysis of the soluble nucleotides and nucleotide platinum(II) adducts. The results indicate two waves of crosslinking [rate constants (0.2-0.3) min-1 and (0.015-0.025) min-1] that correlate with changes in ultra violet absorbance and ethidium bromide dependent fluorescence intensity, previously interpreted in terms of two consecutive, local conformational rearrangements of platinum-DNA (Schaller, W., Reisner, H., and Holler, E. (1987) Biochemistry 26, 943-950). The formation of crosslinks at sequences d(GpG) and d(GpNpG) follows identical kinetics. A minimal reaction mechanism is proposed for the binding of cis-diamminedichloroplatinum(II) to DNA under in vitro conditions. The approximately 3-fold higher rate for meso-[1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine]diaquaplatinum(II) in comparison to the rate for cis-diamminediaquaplatinum(II) indicates that crosslink formation is affected by the nature of the non-leaving platinum ligand(s).