Structure of DNA metal complexes in solution studied by linear and circular dichroism. [Pt(II)(ethylenediamine)(2,2′-dipyridine)]2+ binds strongly to DNA by intercalation. [Cu(II)(2,2′-dipyridine)2]2+ is not intercalated

The synthesis, characterisation and cytotoxicity of bisintercalating (2,2′:6′,2′′-terpyridine)platinum(ii) complexes

Dinuclear (2,2′:6′,2′′-terpyridine)platinum(ii) complexes were synthesised by tethering either thiol or pyridine based linkers. The cytotoxicity of the complexes was determined against human ovarian carcinoma cells (A2780) and its cisplatin-resistant sub-line A2780cis, as well as L1210 murine leukemia cells.

Ruthenium polypyridyl complexes and their modes of interaction with DNA: is there a correlation between these interactions and the antitumor activity of the compounds?

Various interaction modes between a group of six ruthenium polypyridyl complexes and DNA have been studied using a number of spectroscopic techniques. Five mononuclear species were selected with formula [Ru(tpy)L₁L₂]⁽²⁻ⁿ⁾⁺, and one closely related dinuclear cation of formula [{Ru(apy)(tpy)}₂{μ-H₂N(CH₂)₆NH₂}]⁴⁺. The ligand tpy is 2,2′:6′,2″-terpyridine and the ligand L₁ is a bidentate ligand, namely, apy (2,2′-azobispyridine), 2-phenylazopyridine, or 2-phenylpyridinylmethylene amine. The ligand L₂ is a labile monodentate ligand, being Cl⁻, H₂O, or CH₃CN. All six species containing a labile L₂ were found to be able to coordinate to the DNA model base 9-ethylguanine by ¹H NMR and mass spectrometry. The dinuclear cationic species, which has no positions available for coordination to a DNA base, was studied for comparison purposes. The interactions between a selection of four representative complexes and calf-thymus DNA were studied by circular and linear dichroism. To explore a possible relation between DNA-binding ability and toxicity, all compounds were screened for anticancer activity in a variety of cancer cell lines, showing in some cases an activity which is comparable to that of cisplatin. Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure–activity relationships that might be used to guide optimization of the activity of agents of this class of compounds.

DNA binding and cytotoxicity of ruthenium(II) and rhenium(I) complexes of 2-amino-4-phenylamino-6-(2-pyridyl)-1,3,5-triazine

[Ru(tBu2bpy)2(2-appt)](PF6)2 [1.(PF6)2, tBu2bpy = 4,4'-di-tert-butyl-2,2'-bipyridine, 2-appt = 2-amino-4-phenylamino-6-(2-pyridyl)-1,3,5-triazine] and [Re(CO)3(2-appt)Cl] (2) were prepared and characterized by X-ray crystal analysis. The binding of 1.(PF6)2 and 2 to calf thymus DNA (ct DNA) led to increases in the DNA melting temperature (Delta Tm = +12 degrees C), modest hypochromism (29% and 5% of the absorption bands at lambda max = 450 and 376 nm, respectively), and insignificant shifts in the absorption maxima. The binding constants of 1.(PF6)2 and 2 with ct DNA, as determined by absorption titration, are (8.9 +/- 0.5) x 104 and (3.6 +/- 0.1) x 104 dm3 mol-1, respectively. UV-vis absorption titration, DNA melting studies, and competition dialysis using synthetic oligonucleotides [poly(dA-dT)2 and poly(dG-dC)2] revealed that 1.(PF6)2 and 2 exhibit a binding preference for AT sequences. A modeling study on the interaction between 1 or 2 and B-DNA revealed that the minor groove is the most favored binding site and an extensive hydrogen-bonding network is formed. As determined by MTT assays, 1.(PF6)2 and 2 exhibited moderate cytotoxicities toward several human cancer cell lines (KB-3-1, HepG2, and HeLa), as well as a multi-drug-resistant cancer cell line (KB-V-1). According to confocal microscopic and flow cytometric studies, 1.(PF6)2 and 2 induced apoptosis (50-60%) in cancer cells with <5% necrosis detected.

Noncovalent Interactions of Platinum(II) Square Planar Complexes Containing Ligands Out-of-Plane with DNA

The interaction of the complexes [Pt(bipy)(4-Rpy)(2)](2+) and [Pt(4,4'-Ph(2)bipy)(4-Rpy)(2)](2+) (Ph = phenyl; bipy = 2,2'-bipyridine; R = H, CN, CH(3), NH(2)) with DNA has been studied with a series of techniques. The processes give rise to (i) lengthening of rodlike DNA and unwinding of closed circular DNA and (ii) an increase in the DNA melting temperature comparable with that observed for known intercalators. In addition, the reaction of the complexes [Pt(bipy)(py)(2)](2+) and [Pt(4,4'-Ph(2)bipy)(py)(2)](2+) is inhibited by the presence of DNA. These results have been interpreted by assuming that the substances intercalate in spite of the presence of ligands out of plane. The crystal structure determined for [Pt(4,4'-Ph(2)bipy)(3,5-Me(2)py)(2)](2+) by X-ray analysis shows that also one of the phenyl rings is twisted with respect to the square plane. Binding constants, K(B), determined spectrophotometrically at 25 degrees C and pH 7 using the McGhee-von Hippel approach, increase for both series of complexes on increasing pK(a) of coordinated pyridines and are larger for those with 4,4'-Ph(2)bipy. The increasing affinity for DNA on increasing electron density of the interacting moiety is accounted for by assuming that London dispersion forces play a major role in the processes.

Effect of platinum(II) chemotherapeutic agents on properties of DNA liquid crystals

We have investigated the X-ray and optical properties (CD spectra and polarization microscopy) of liquid-crystalline phases and dispersions formed on pretreatment of low molecular weight DNA with the platinum(II) coordination complexes, cis-diammine-dichloroplatinum(II) (DDP), 2,2'-bipyridinedichloroplatinum(II) (1) and 2,2'-bipyridineethylenediammineplatinum(II) (2). It is demonstrated that the platination of DNA leads to the ordering of neighbouring molecules of DNA in liquid-crystalline phases being diminished. The intense bands observed in the CD spectra of liquid-crystalline dispersions prepared from DNA pretreated with 1 or 2 can be used to determine the orientation of the latter compounds with respect to the helical axis of the DNA and to detect distortions in the secondary structure of DNA. The possible causes of the appearance of the intense bands in the CD spectra of liquid-crystalline phases and alterations in the manner of packing of the molecules of DNA within them are discussed.

Binding of platinum(II) intercalation reagents to deoxyribnonucleic acid. Dependence on base-pair composition, nature of the intercalator, and ionic strength

The DNA binding of three platinum(II) intercalation reagents has been studied and found to depend upon base composition, the nature of the intercalator, and the ionic strength of the solvent medium. In 0.2 M NaCl, binding data for calf thymus DNA show the association constants to be approximately 10(4) M-1. The binding constants decrease in the order [(o-phen)Pt(en)]2+ greater than or equal to [(terpy)Pt(HET)]+ greater than [(bipy)Pt(en)]2+. The number of available intercalation sites for the doubly charged intercalators is only 70% of the number expected from the nearest-neighbor exclusion model. Binding of [(o-phen)Pt(en)]2+ and [(terpy)Pt(HET)]+ to various DNAs depends linearly on G.C content. Both reagents exhibit essentially the same degree of G.C specificity. Intercalative binding is a function of ionic strength. Increasing the salt concentration minimizes the importance of metallointercalator charge, and extrapolation to 1 M salt reveals the intercalative abilities, as reflected in binding constants, to be equivalent for [(terpy)Pt(HET)]+ and [o-phen)Pt(en)]2+ and about 1 order of magnitude less than that of ethidium.