Interaction of DNA and purine nucleosides with cis-dichlorodiammineplatinum(II) and antimitotic activity of the complexes on meristematic root cells

Effects of cis-diamminedichloroplatinum (II) loaded liposomes on mouse Ehrlich tumor cells

Cis-diamminedichloroplatinum II (cisplatin) heavily or lightly loaded (fluid, solid, negatively charged or neutral) liposomes were prepared. Cisplatin release from liposomes was observed only after long dialysis times or after liver lysosomal enzymatic disintegration in solution. Mouse Ehrlich tumor cells (ELT) cultured in vitro were treated with cisplatin, liposomes or cisplatin loaded liposomes, and the effects on the mitotic activity, the DNA content and the ultrastructure were compared. Cisplatin (1-10 micrograms/ml) had an antimitotic activity and modified the DNA content in ELT cells. Ribosome aggregation, perichromatin or interchromatin granule accumulation, and chromatin condensation or some degree of dispersion could be observed. Negatively charged fluid liposomes had an antimitotic activity and modified the DNA content in ELT cells at lower concentrations (0.3 mumoles/ml) than in the case of neutral fluid liposomes (1.5 mumoles/ml). Negatively charged solid liposomes were not toxic at these concentrations. Ultrastructural analysis of ELT cells treated in vitro with negatively charged fluid liposomes revealed their extracellular adsorption and their disintegration in phagolysosomes. A fusion between liposomes and the plasma membrane was not definitely demonstrated. Cisplatin loaded liposomes also had an antimitotic activity and modified the DNA content in ELT cells. These effects were similar to or more pronounced than those induced by free cisplatin. Ultrastructural analysis revealed some kind of electron dense material in phagolysosomes which was never observed after the treatment with free cisplatin or liposomes alone. Effects on nucleic acids were rarely observed.

Alteration in the nucleosome and chromatin structures upon interaction with platinum coordination complexes

The interaction of various platinum coordination complexes with nucleosomes and chromatin has been investigated by ultraviolet absorption spectrophotometry, circular and electric linear dichroism, and thermal denaturation, at low binding ratios (r less than 0.1-0.2). The general trend of the changes in these physicochemical properties is similar to that observed for the DNA-platinum complexes, which indicates that the same binding sites are involved in the platinum interaction with DNA and with its nucleoprotein complex. The cis-bidentate ligands, cis-dichlorodiammine, diaminocyclohexane and ethylenediamine platinum(II), showed a distinct behavior, with a more important destabilization of the DNA structure in the nucleoprotein than the trans-bidentate ligand, trans-dichlorodiammine-Pt(II), and monodentate ligand, diethylenetriamine-Pt(II). The drastic decrease of the negative electric dichroism in the 260 nm absorption band of the bases, observed with the five ligands, indicates a profound alteration of the DNA arrangement in chromatin and nucleosomes, attributed to a condensation of its superhelical structure. Some differences with previous observations on DNA complexes with the same platinum compounds indicate the possible formation of protein-DNA crosslinks in chromatin and nucleosomes. These could have some importance for the biological effects.

Denaturation level of DNA-Pt complexes evidenced by Tb3+ fluorescence enhancement and electric dichroism

The Tb3+ fluorescence is greatly enhanced, as a result of binding of various platinum coordination complexes to DNA, as compared to native DNA. The largest enhancement is observed for cis-Pt(NH3)2Cl2 but the fluorescence intensity does not however reach the level attained for thermally denatured DNA. Diethylenetriamine-Pt(II) produces very little increase of Tb3+ fluorescence. The electric dichroism in the DNA absorption band drastically decreases upon binding of the various Pt compounds investigated except diethylenetriamine-Pt. The results are discussed in terms of the various modes of binding of Pt derivatives to DNA, particularly in relation to the level of denaturation of the double helix.

Viscosity, nicking, thermal and alkaline denaturation studies on three classes of DNA-platinum complex

Viscosity, nicking, thermal denaturation and alkaline denaturation studies were used to investigate perturbations induced in the DNA secondary structure after complexation with platinum compounds. Three types of DNA-platinum complex, representative of the different modes of platinum binding, have been studied. Cis-Pt(NH3)2Cl2, which forms a cis-bidentate complex with DNA, strongly decreased the viscosity and, according to thermal and alkaline denaturations, destabilized the macromolecule. On the contrary, trans-Pt(NH3)2Cl2, a trans-bidentate complex, stabilized the DNA secondary structure and decreased the viscosity but much less than did cis-Pt(NH3)2Cl2. [Pt(dien)Cl]Cl, a monodentate complex, had no effect on the viscosity; however, addition of this compound stabilized DNA up to 0.01 platinum bound per nucleotide while further Pt binding destabilized the macromolecule. Cis- and trans-Pt(NH3)2Cl2 renatured thermally denatured DNA, which has been interpreted as evidence for the presence of interstrand crosslinks. [Pt(dien)Cl]Cl, on the other hand, did not renature DNA. If the renaturation observed for the bidentate compounds is due only to the presence of interstrand crosslinks, then one interstrand crosslink is found when 400-1000 molecules of the platinum isomer are bound per T7 DNA molecule. Electron microscopy results show that the three types of DNA-platinum complex do not nick DNA up to 0.01 bound platinum per nucleotide.

Dissociation of double-stranded poly(I) . poly(C) by cis-diammine-dichloro-Pt(II)

The covalent binding of cis-Pt(NH3)2Cl2 on the double stranded poly(I) . poly(C) induced an irreversible dissociation of the two strands. This dissociation was evidenced mainly by poly(I)-Agarose affinity chromatography which allowed to recover free strands of cis-Pt(NH3)2Cl2-poly(I) from a cis-Pt(NH3)2Cl2-poly(I) . poly(C) complex, by density equilibrium centrifugation where free poly(C) could be isolated, and by acid titrations of the metal-poly(I) . poly(C) complexes. The separation of the two strands of the polyribonucleotide upon cis-Pt(NH3)2Cl2 fixation was shown not to exceed 90--95%. A dissociation curve of the polynucleotide double helix as a function of the amount of bound cis-Pt(NH3)2Cl2 was determined and was shown to be of a characteristic cooperative effect. The fixation of the paltinum compound to poly(I) . poly(C) seemed also to be cooperative.