ABSTRACT
Recently it has been shown that several analogues of the clinically ineffective trans-DDP exhibit antitumor activity comparable to that of cis-DDP. The present paper describes the binding of antitumor trans-[PtCl(2)(E-iminoether)(2)] (trans-EE) to guanosinemonophosphate (GMP) and adenosinemonophosphate (AMP). We have used HPLC and (1)H and (15)N NMR to characterize the different adducts. In the case of a 1:1 mixture of trans-EE and GMP, at an early stage of the reaction, a monofunctional adduct is formed which, subsequently, is partly converted into a monosolvated monofunctional species. After about 70 hours an equilibrium is established between chloro and solvato monofunctional adducts at a ratio of 30/70. In the presence of excess GMP (4:1) the initially formed monofunctional adducts react further to give two bifunctional adducts, one with the iminoether ligands in their original E configurations and the other with the iminoether ligands having one E and the other, Z configurations. The coordination geometry obtained by energy minimization calculations is in qualitative agreement with 2D NMR data.
ABSTRACT
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.
