Photolysis and Thermolysis of Platinum(IV) 2,2′-Bipyridine Complexes Lead to Identical Platinum(II) DNA Adducts

Two Pt-IV and two Pt-II complexes containing a 2,2'-bipyridine ligand were treated with a short DNA oligonucleotide under light irradiation at 37 degrees C or in the dark at 37 and 50 degrees C. Photolysis and thermolysis of the Pt-IV complexes led to spontaneous reduction of the Pt-IV to the corresponding Pt-II complexes and to binding of Pt-II 2,2'-bipyridine complexes to N7 of guanine. When the reduction product was [Pt(bpy)Cl-2], formation of bis-oligonucleotide adducts was observed, whereas [Pt(bpy)(MeNH2)Cl](+) gave monoadducts, with chloride ligands substituted in both cases. Neither in the dark nor under light irradiation was the reductive elimination process of these Pt-IV complexes accompanied by oxidative DNA damage. This work raises the question of the stability of photoactivatable Pt-IV complexes toward moderate heating conditions.