Effects of adducts of [PtCl(NH3)3]Cl or chlorodiethylenetriamineplatinum(II) on DNA stability were studied with emphasis on thermodynamic origins of that stability. Oligodeoxyribonucleotide duplexes (15-bp) containing the single, site-specific monofunctional adduct at G-residues of the central sequences TGT/ACA or 5'-AGT/5'-ACT were prepared and analyzed by differential scanning calorimetry, temperature-dependent ultraviolet absorption and circular dichroism. The unfolding of the platinated duplexes was accompanied by relatively small unfavorable free energy terms. This destabilization was enthalpic in origin. On the other hand, a relatively large reduction of melting temperature (T(m)) was observed as a consequence of the monofunctional adduct in the TGT sequence, whereas T(m) due to the adduct in the AGT sequence was reduced only slightly. We also examined the efficiency of the mammalian nucleotide excision repair system to remove from DNA the monofunctional adducts and found that these lesions were not recognized by this repair system. Thus, rather thermodynamic than thermal characterization of DNA adducts of monofunctional platinum compounds is a property implicated in the modulation of downstream effects such as protein recognition and repair.

• MeSH
• DNA Adducts analysis   chemistry   MeSH
• Nucleic Acid Denaturation MeSH
• DNA analysis   chemistry   MeSH
• Kinetics MeSH
• DNA Repair * MeSH
• Platinum analysis   chemistry   MeSH
• Energy Transfer MeSH
• Temperature MeSH
• Thermodynamics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• DNA MeSH
• Platinum MeSH

The structure-pharmacological activity relationships generally accepted for antitumor platinum compounds stressed the necessity for the cis-[PtX(2)(amine)(2)] structure while the trans-[PtX(2)(amine)(2)] structure was considered inactive. However, more recently, several trans-platinum complexes have been identified which are potently toxic, antitumor-active and demonstrate activity distinct from that of conventional cisplatin (cis-[PtCl(2)(NH(3))(2)]). We have shown in the previous report that the replacement of ammine ligands by iminoether in transplatin (trans-[PtCl(2)(NH(3))(2)]) results in a marked enhancement of its cytotoxicity so that it is more cytotoxic than its cis congener and exhibits significant antitumor activity, including activity in cisplatin-resistant tumor cells. In addition, we have also shown previously that this new trans compound (trans-[PtCl(2)(E-iminoether)(2)]) forms mainly monofunctional adducts at guanine residues on DNA, which is generally accepted to be the cellular target of platinum drugs. In order to shed light on the mechanism underlying the antitumor activity of trans-[PtCl(2)(E-iminoether)(2)] we examined oligodeoxyribonucleotide duplexes containing a single, site-specific, monofunctional adduct of this transplatin analog by the methods of molecular biophysics. The results indicate that major monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] locally distort DNA, bend the DNA axis by 21 degrees toward the minor groove, are not recognized by HMGB1 proteins and are readily removed from DNA by nucleotide excision repair (NER). In addition, the monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] readily cross-link proteins, which markedly enhances the efficiency of this adduct to terminate DNA polymerization by DNA polymerases in vitro and to inhibit removal of this adduct from DNA by NER. It is suggested that DNA-protein ternary cross-links produced by trans-[PtCl(2)(E-iminoether)(2)] could persist considerably longer than the non-cross-linked monofunctional adducts, which would potentiate toxicity of this antitumor platinum compound toward tumor cells sensitive to this drug. Thus, trans-[PtCl(2)(E-iminoether)(2)] represents a quite new class of platinum antitumor drugs in which activation of trans geometry is associated with an increased efficiency to form DNA-protein ternary cross-links thereby acting by a different mechanism from 'classical' cisplatin and its analogs.

• MeSH
• DNA Adducts chemistry   metabolism   MeSH
• CHO Cells MeSH
• Cisplatin analogs & derivatives   chemistry   pharmacology   MeSH
• DNA-Directed DNA Polymerase metabolism   MeSH
• DNA chemistry   drug effects   metabolism   MeSH
• HMG-Box Domains MeSH
• HeLa Cells MeSH
• Nucleic Acid Conformation drug effects   MeSH
• Cricetinae MeSH
• Rats MeSH
• Humans MeSH
• Macromolecular Substances MeSH
• Oligonucleotides chemistry   metabolism   MeSH
• HMGB1 Protein chemistry   metabolism   MeSH
• Cross-Linking Reagents chemistry   pharmacology   MeSH
• Protein Binding MeSH
• Binding Sites MeSH
• Animals MeSH
• Check Tag
• Cricetinae MeSH
• Rats MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA Adducts MeSH
• Cisplatin MeSH
• DNA-Directed DNA Polymerase MeSH
• DNA MeSH
• Macromolecular Substances MeSH
• Oligonucleotides MeSH
• HMGB1 Protein MeSH
• Cross-Linking Reagents MeSH