Maria Letizia Di Pietro

Electrochemical biosensor evaluation of the interaction between DNA and metallo-drugs

Electrochemical techniques were used to study the interaction between a panel of antiproliferative metallo-drugs and double-stranded DNA immobilized on screen-printed electrodes as a model of the analogous interaction occurring in solution. The propensity of a given metal drug to interact with DNA was measured as a function of the decrease of guanine oxidation signal, which was detected by square wave voltammetry. Estimates of variations in experimental parameters, such as the concentration of complexes, time following dissolution (ageing time) and the presence of chloride, are provided.

Characterization of the cell growth inhibitory effects of a novel DNA-intercalating bipyridyl-thiourea-Pt(II) complex in cisplatin-sensitive and—resistant human ovarian cancer cells

SummaryThe cellular effects of a novel DNA-intercalating agent, the bipyridyl complex of platinum(II) with diphenyl thiourea, [Pt(bipy)(Ph2-tu)2]Cl2, has been analyzed in the cisplatin (cDDP)—sensitive human ovarian carcinoma cell line, 2008, and its—resistant variant, C13* cells, in which the highest accumulation and cytotoxicity was found among six related bipyridyl thiourea complexes. We also show here that this complex causes reactive oxygen species to form and inhibits topoisomerase II activity to a greater extent in the sensitive than in the resistant line. The impairment of this enzyme led to DNA damage, as shown by the comet assay. As a consequence, cell cycle distribution has also been greatly perturbed in both lines. Morphological analysis revealed deep cellular derangement with the presence of cellular masses, together with increased membrane permeability and depolarization of the mitochondrial membrane. Some of these effects, sometimes differentially evident between the two cell lines, might also be related to the decrease of total cell magnesium content caused by this thiourea complex both in sensitive and resistant cells, though the basal content of this ion was higher in the cDDP-resistant line. Altogether these results suggest that this compound exerts its cytotoxicity by mechanisms partly mediated by the resistance phenotype. In particular, cDDP-sensitive cells were affected mostly by impairing topoisomerase II activity and by increasing membrane permeability and the formation of reactive oxygen species; conversely, mitochondrial impairment appeared to play the most important role in the action of complex F in resistant cells.

Luminescence of a Pt(II) complex in the presence of DNA. Dependence of luminescence changes on the interaction binding mode

Luminescence intensity changes of a Pt(II) complex which is known to bind externally to DNA at low [DNA]/[complex] ratio and to intercalate at high [DNA]/[complex] ratio are studied in the presence of calf thymus DNA. External binding is demonstrated to induce luminescence enhancement whereas intercalation leads to luminescence quenching. The reasons for this behaviour are discussed.

Relationship between binding affinity for calf-thymus DNA of [Pt(2,2′-bpy)(n-Rpy)2]2+(n= 2,4) and basicity of coordinated pyridine

The binding affinity for DNA of the complexes [Pt(2,2′-bpy)(n-Rpy)2]2+(n= 2,4) systematically increases on increasing pKa of the coordinated pyridine, with the exception of the 2-methyl-substituted derivative.

Luminescent Ir(III) Complex Exclusively Made of Polypyridine Ligands Capable of Intercalating into Calf-Thymus DNA

Efficient intercalation of a luminescent Ir(III) complex exclusively made of polypyridine ligands in natural and synthetic biopolymers is reported for the first time. The emission of the complex is largely enhanced in the presence of [poly(dA-dT)(2)] and strongly quenched in the presence of [poly(dG-dC)(2)]. By comparing the emission decays in DNA and in synthetic polynucleotides, it is proposed that the emission quenching of the title compound by guanine residues in DNA is no longer effective over a distance of four dA-dT base pairs.

Luminescence properties of Pt(II) complexes containing polypyridine ligands with extended aromatic moieties

The luminescence properties of eleven Pt(II) complexes containing polypyridine ligands with extended aromatic moieties have been studied, both in acetonitrile fluid solution at 298 K and in butyronitrile rigid matrix at 77 K. For comparison purposes, also the phosphorescence properties of three free ligands at 77 K in butyronitrile have been investigated. The absorption spectra of all the compounds exhibit intense bands (epsilon in the range 10(4)-10(5) M(-1) cm(-1)) in the UV region, which are attributed to spin-allowed ligand-centered (LC) transitions, and moderately intense bands (epsilon in the range 10(3)-10(4) M(-1) cm(-1)) in the visible region, which receive contribution from both spin-allowed LC transitions and spin-allowed metal-to-ligand charge-transfer (MLCT) transitions. At low energy, less intense spin-forbidden MLCT bands are also present. At 77 K in rigid matrix, all the studied compounds exhibit structured and long-lived (lifetimes from 840 micros on the millisecond timescale) luminescence, which is attributed to triplet LC states in all cases. At room temperature in fluid solution the luminescence lifetime of all the compounds is largely shortened (nanosecond timescale), and most of the emission spectra are unstructured and red-shifted. For species exhibiting structured emission spectra even at room temperature, low luminescence quantum yields are always obtained (Phi < 10(4)), and their emission is assigned to triplet LC states, which mainly deactivate to the ground state by thermal-activated surface crossing to a closely-lying metal-centered (MC) triplet state. Compounds exhibiting unstructured emission show relatively high emission quantum yields (about 0.1) and their emission is assigned to a mixed LC/MLCT state.

Photophysics of transition metal complexes

This chapter deals with studies on the photophysical properties of selected metal complexes and their polynuclear supramolecular assemblies reported in literature in the period January 2011 to December 2012. The transition metal species considered here belong to families of complexes featuring largely studied optical properties. The complexes are from the following metal centres: d6 Ru(II), Os(II), Re(I), Ir(III) and Rh(III), d8 Pt(II) and Pd(II), d10 Cu(I) and Au(I), d3 Cr(III); finally some example is given of lanthanide (Ln) complexes or supramolecular arrays.

Carbohydrates and Charges on Oligo(phenylenethynylenes): Towards the Design of Cancer Bullets

Two new tetralkylammonium-OPEs, bearing one or two positively charged groups directly linked to the aromatic residues and two β-d-glucopyranose terminations, were synthesized. Their peculiar structural features, joining the biologically relevant sugar moieties, flat aromatic cores and positive charges, make these luminescent dyes soluble in aqueous media and able to strongly interact with DNA. As a result of UV/Vis spectral variations, DNA melting temperature measures, viscometric titrations and induced CD, we propose a partial insertion of the OPEs aromatic core into the helix, stabilized by glucose H-bonding with the groups accessible from the grooves. This interaction leads to the quenching of the OPE luminescence due to guanine reduction. The biocompatibility of the monocationic OPE with healthy and cancer cells, and the reduction of proliferation in HEp-2 cancer cells induced by the dicationic one, make this class of compounds promising for future biological applications.

Electrochemical biosensor for PCR free nucleic acids detection: A novel biosensor containing three planar microelectrodes for melocular diagnostic applications

An effective electrode modification strategy, integrated in a miniaturized silicon biosensor, was investigated for the rapid and sensitive electrochemical detection of low amount of DNA without PCR step. The miniaturized biosensor here presented is composed of three planar microelectrodes for electrochemical transduction of hybridized DNA target on working electrode, the hybridization is probed by the intercalation of Osmium redox probe.

Opposite influence of calf thymus DNA on the rate of substitution of ethylenediamine, by thiourea, in the complex cations [Pd(bpy)(en)]2+ and [Pd(bromazepam)(en)]2+ (bromazepam = 7-bromo-1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepin-2-one)

Calf thymus DNA inhibits the substitution of ethylenediamine, by thiourea, in [Pd(bpy)(en)]2+ and catalyses the same reaction in [Pd(bromazepam)(en)]2+ (bromazepam = 7-bromo-1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepin-2-one); this kinetic effect can be related to the different binding modes of the two complexes to the biopolymer.