DNA interactions of a novel platinum drug, cis-[PtCl(NH3)2(N7-acyclovir)]+

We synthesized a novel platinum drug, cis-[PtCl(NH3)2(N7-ACV)]+, in which ACV is the antiviral drug acyclovir [a deoxyriboguanosine analogue, 9-(2-hydroxyethoxymethyl)guanine]. This new compound exhibits antiviral efficacy in vitro and exhibits an antitumor activity profile different from that of cisplatin [Metal-Based Drugs 2:249-256 (1995)]. To contribute to understanding the mechanisms underlying biological activity of this new compound, we studied modifications of natural and synthetic DNAs in cell-free media by cis-[PtCl(NH3)2(N7-ACV)]+ by various biochemical and biophysical methods. The results indicated that the major DNA adduct of cis-[PtCl(NH3)2(N7-ACV)]+ was a stable monofunctional adduct at guanine residues. In contrast to DNA adducts of other monodentate and clinically ineffective platinum(II) compounds, the adducts of cis-[PtCl(NH3)2(N7-ACV)]+ terminated in vitro DNA and RNA synthesis. In addition, although DNA adducts of cis-[PtCl(NH3)2(N7-ACV)]+ and cisplatin were different, some properties of DNA modified by either compound were qualitatively similar. Such similarities were not noticed if DNA modifications by other ineffective monofunctional platinum(II) complexes were investigated. Thus, the DNA binding mode of monofunctional cis-[PtCl(NH3)2(N7-ACV)]+ was different from that of other monofunctional but ineffective platinum(II) complexes. It has been suggested that the unique capability of cis-[PtCl(NH3)2(N7-ACV)]+ to modify DNA may be relevant to a distinct antitumor efficiency of this novel drug in comparison with cisplatin. It also has been suggested that at least some aspects of DNA interactions of cis-[PtCl(NH3)2(ACV)]+ revealed in the current study could be exploited in the search for and development of new antiviral platinum complexes containing, as a part of the coordination sphere, antiviral nucleosides.