Synthesis, interaction with double-helical DNA and biological activity of the water soluble complex cis-dichloro-1,2-propylenediamine-N,N,N′,N′-tetraacetato ruthenium (III) (RAP)

The effects exerted by the new complex cis-dichloro-1,2-propylenediaminetetraacetato ruthenium (III), H[RuCl(2)(PDTA-H(2))] [1, RAP], on DNA and cultured tumor cells (ovarian carcinoma TG cell line) were studied. The comparative study of circular dichroism (CD) spectra obtained from DNA and RAP-DNA system evidences the interaction of the complex with DNA. Compound 1 also interacted with tumor TG cells to slow their proliferation rate. BrdU incorporation was enhanced in cells treated with compound 1, as evidenced by a single-cell electrophoresis method (comet assay), in accordance with RAP-induced DNA damage. DNA migration of compound 1-treated cells was similar to that induced by noxious agents other than cross-linking chemicals. The stability of [RuCl(2)(PDTA-H(2))]-DNA binding is suggested by the high degree of damage that persisted after removal of compound 1 from the culture medium.

Synthesis, structure and biological activity of a new and efficient Cd(II)–uracil derivative complex system for cleavage of DNA

The new complex formed by Cd(II) and the 1:2 Schiff-base-type ligand 2,6-bis[1-(4-amino-1,2,3,6-tetrahydro-1,3-dimethyl-2,6-dioxopyrimidin-5-yl)imino]ethylpyridine (DAPDAAU) has been chemically and structurally characterized by X-ray diffraction: the ion Cd(II) is surrounded by six nitrogen atoms from two DAPDAAU ligands which coordinates each one in a tridentate fashion through the pyridine ring (N1) and both azomethine nitrogen atoms (N5). The interaction of the Cd(II) complex (compound I) with calf-thymus DNA as observed by circular dichroism spectroscopy suggests the initial unwinding of the DNA double helix strongly depends on increasing incubation times and metal-to-nucleic acid molar ratios. Electrophoretic experiments indicate that the cadmium complex induces cleavage of the plasmid pBR322 DNA to give ulterior nicking and shortening of this molecule, as a result of the complex binding to DNA, resulting in the conclusion that compound I behaves as a chemical nuclease. Cytotoxic activity of the Cd(II) complex against selected different human cancer cell lines is specific and increases with increasing concentration of the metal compound; this fact indicates the potential antitumor character of the complex. When the culture medium is supplemented with compound I, a remarkable inhibition of the growing cell is observed, important cell degeneration appears before 48 h and abundant precipitates are formed that correspond to cell residues and denatured proteins.

Effects of Tris and Hepes buffers on the interaction of palladium–diaminopropane complexes with DNA

The Pd(II) complexes, [PdCl(2)(1,2-pn)] and [PdCl(2)(1,3-pn)] (pn is diaminopropane), were synthesized and characterized by analytical and spectroscopic (FT-IR, (1)H NMR and (13)C NMR) techniques. UV difference spectral study performed on Pd-pn/DNA systems, indicate a pronounced interaction of palladium complexes with DNA in cell-free media; comparison of lambda(max), Abs(max) and %H values observed for the two compounds might be attributed to structural differences of the chelated ligand rings. Results obtained from electrophoretic analysis of Pd complexes in presence of pBR322 plasmid DNA show a clear decreasing of the supercoiled (SC) DNA form mobility, that could be attributed to unwinding of the double helix; a parallel increasing of the open-circular (OC) DNA form mobility is also noted, this fact implying that the binding of complexes either shortens or condenses the DNA helix. Interaction studies of Pd complexes with plasmid DNA in different buffer systems indicate that DNA binding efficiency capable of modifying the tertiary structure of pBR322 decreased from NaClO(4) to Hepes 2, Hepes 1 [Hepes=4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid], and Tris [(hydroxymethyl)aminomethane] buffers, in this order. Moreover, the level of DNA modifications produced by palladium complexes in 10 mM NaClO(4) remains unchanged after transferring the samples into the medium required for subsequent biophysical or biochemical analyses.

Quantification of isomeric equilibria formed by metal ion complexes of 8-[2-(phosphonomethoxy)ethyl]-8-azaadenine (8,8aPMEA) and 9-[2-(phosphonomethoxy)ethyl]-8-azaadenine (9,8aPMEA). Derivatives of the antiviral nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA)

The acidity constants of the two-fold protonated acyclic 9-[2-(phosphonomethoxy)ethyl]-8-azaadenine, H2(9,8aPMEA)(+)(-), and its 8-isomer, 8-[2-(phosphonomethoxy)ethyl]-8-azaadenine, H2(8,8aPMEA)(+)(-), both abbreviated as H2(PA)(+)(-), as well as the stability constants of their M(H;PA)+ and M(PA) complexes with the metal ions M2+=Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ or Cd2+, have been determined by potentiometric pH titrations in aqueous solution at I=0.1 M (NaNO3) and 25 degrees C. Application of previously determined straight-line plots of log K(M)M(R-PO3) versus pK(H)H(R-PO3)for simple phosph(on)ate ligands, R-PO3(2-), where R represents a residue without an affinity for metal ions, proves that for all M(PA) complexes a larger stability is observed than is expected for a sole phosphonate coordination of the metal ion. This increased stability is attributed to the formation of five-membered chelates involving the ether oxygen present in the aliphatic residue (-CH2-O-CH2-PO3(2-)) of the ligands. The formation degrees of these chelates were calculated; they vary between about 13% for Ca(8,8aPMEA) and 71% for Cu(8,8aPMEA). The adenine residue has no influence on complex stability except in the Cu(9,8aPMEA) and Zn(9,8aPMEA) systems, where an additional stability increase attributable to the adenine residue is observed and equilibria between four different isomers exist. This means (1) an open isomer with a sole phosphonate coordination, M(PA)op, where PA(2-)=9,8aPMEA2-, (2) an isomer with a five-membered chelate involving the ether oxygen, M(PA)cl/O, (3) an isomer which contains five- and seven-membered chelates formed by coordination of the phosphonate group, the ether oxygen and the N3 site of the adenine residue, M(PA)cl/O/N3, and finally (4) a macrochelated isomer involving N7, M(PA)cl/N7. For Cu(9,8aPMEA) the formation degrees are 15, 30, 48 and 7% for Cu(PA)op, Cu(PA)cl/O, Cu(PA)cl/O/N3 and Cu(PA)cl/N7, respectively; this proves that the macrochelate involving N7 is a minority species. The situation for the Cu(PMEA) system, where PMEA2- represents the parent compound, i.e. the dianion of 9-[2-(phosphonomethoxy)ethyl]adenine, is quite similar. The relationship between the antiviral activity of acyclic nucleoside phosphonates and the structures of the various complexes is discussed and an explanation is offered why 9,8aPMEA is biologically active but 8,8aPMEA is not.

Synthesis, characterization, interaction with DNA and cytotoxicity of the new potential antitumour drug cis-K[Ru(eddp)Cl2]

The new potential antitumour soluble drug K[Ru(eddp)Cl(2)].3H(2)O, (eddp=ethylenediamine-N,N'-di-3-propionate) has been isolated and characterized. The analysis of the interaction of this complex with pBR322 plasmid DNA by circular dichroism spectroscopy shows that the ruthenium complex initially induces alteration of both CD positive and negative features resembling those previously observed for monofunctional platinum complexes. Further addition of drug at r(i) higher than 0.50 suggests appreciable conformational alterations of typical secondary structure of B-type DNA, implying loss of DNA helicity and unwinding of the double helix. The results reported herein about the binding of K[Ru(eddp)Cl(2)] to the named plasmid performed by electrophoresis indicate that the Ru(III) center preferentially forms initial monofunctional adducts with this plasmid. In addition, the DNA binding data suggest that the plasmid is cleaved by K[Ru(eddp)Cl(2)] in the presence of physiological concentrations of ascorbate. These results support the hypothesis that reactive Ru(II) species may be formed from Ru(III) upon incubation with a reductant agent such as ascorbate. The testing of the cytotoxic activity of this complex against several human cancer cell lines evidenced that K[Ru(eddp)Cl(2)] complex had a remarkable and selective antiproliferative effect against the cervix carcinoma HeLa and colon adenocarcinoma HT-29, behaving in these two cases as an antineoplastic drug.

Study of the biological effects and DNA damage exerted by a new dipalladium-Hmtpo complex on human cancer cells

The new dipalladium complex [Pd(2)(mu-mtpo-N(3),N(4))(2)(phen)(2)](NO(3))(2) (where phen=1,10-phenantroline; Hmtpo=5,7-dihydro-7-oxo-5-methyl[1,2,4]triazolopyrimidine), (Pd(2)-Hmtpo, or complex I), interacts effectively with DNA plasmid (pBS), as studied by circular dichroism spectroscopy (CD), causing large helix distortions, altering the direction of the main DNA helix axis and producing unwinding of the DNA double helix. DNA damage induced by complex I was highly significant at 2.81 microM (ovarian carcinoma TG cell line), as assessed by comet assay, a dose at which all treated nuclei showed more than 30% DNA migration to the comet tail. DNA damage effect is a consequence of genotoxicity and not a false positive response caused by cytotoxicity. In vitro cytotoxic assay on the two human tumor cell lines TG and BT-20 (breast carcinoma), shows that doses of 0.47, 1.41 and 2.81 microM produce significant antiproliferative effects after 4 days of treatment compared with control. Complex I was highly cytotoxic at 2.81 microM causing an inhibition of viable cells of 65.5%. Cisplatin (cis-DDP) exhibits lower cytotoxic activity in TG cells than dipalladium complex (a cisplatin dose of 6.67 microM inhibits 30.3%) and does not cause migration of DNA to comet tail.

Intramolecular stacking interactions in ternary copper(II) complexes formed with 2,2'-bipyridine or 1,10-phenanthroline and 9-(4-phosphonobutyl)adenine (dPMEA), the carba relative of the antiviral nucleotide analogue 9

The stability constants of the mixed ligand complexes formed between Cu(Arm)2+, where Arm=2,2'-bipyridine (Bpy) or 1,10-phenanthroline (Phen), and the monoanion or the dianion of 9-(4-phosphonobutyl)adenine (dPMEA=3'-deoxa-PMEA), which is the carba analogue of the antivirally active 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), were determined by potentiometric pH titrations in aqueous solution at 25 degrees C and I=0.1 M (NaNO3). Detailed stability constant comparisons reveal that in the monoprotonated ternary Cu(Arm)(H;dPMEA)+ complexes the proton is at the phosphonate group and that stacking between Cu(Arm)2+ and H(dPMEA)- plays a significant role. For the Cu(Arm)(dPMEA) complexes a large increase in complex stability (compared to the stability expected on the basis of the basicity of the phosphonate group) is observed, which is due to intramolecular stack formation between the aromatic ring systems of Phen or Bpy and the purine moiety of dPMEA2-. The formation degree of the stacked isomer in the Cu(Arm)(dPMEA) systems is on the order of 90%, though it is somewhat more pronounced with Phen than with Bpy. Comparisons of the Cu(Arm)(N) systems, where N=dPMEA2- and PMEA2- or adenosine 5'-monophosphate (AMP2-), reveal that the stacking properties of dPMEA2- and PMEA2-resemble closely those of their parent nucleotide AMP2-.