A 2-(benzothiazol-2-yl)-phenolato platinum(II) complex as potential photosensitizer for combating bacterial infections in lung cancer chemotherapy†.

Cancer and antibiotic resistance are two global health threats that usually hamper clinical chemotherapeutic efficacy. Particularly for lung cancer, bacterial infections frequently arise thereby complicating the course of cancer treatment. In this sense, three new neutral luminescent cycloplatinated(II) photosensitizers of the type [Pt(dmba)(L)] (dmba = N,N-dimethylbenzylamine-κN,κC; L = 2-(benzo[d]oxazol-2-yl)-phenolato-κN,κO1, 2-(benzo[d]thiazol-2-yl)-phenolato-κN,κO2, and 2-(1-methyl-1H-benzo[d]imidazole-2-yl)phenolato-κN,κO3) have been characterized and developed to potentially eliminate both resistant bacteria and lung cancer cells. The phototherapeutic effects of complex 2 have been evaluated using low doses of blue light irradiation. Complex 2 exerted promising photoactivity against pathogenic Gram-positive bacteria strains of clinical interest, displaying a phototoxic index (PI) of 15 for methicillin-resistant Staphylococcus aureus, one of the major microorganisms predominating lung infections. Likewise, the anticancer activity of 2 was also increased upon light irradiation in human lung A549 cancer cells (PI = 36). Further in vitro experiments with this platinum(II) complex suggest that ROS-generating photodynamic reactions were involved upon light irradiation, thus providing a reasonable mechanism for its dual anticancer and antibacterial activities.

Combined spectroscopic and theoretical analysis of the binding of a water-soluble perylene diimide to DNA/RNA polynucleotides and G-quadruplexes.

We present here a combined spectroscopic and theoretical analysis of the binding of N,N'-bis(2-(1-piperazino)ethyl)-3,4,9,10-perylenetetracarboxylic acid diimide dichloride (PZPERY) to different biosubstrates. Absorbance titrations and circular dichroism experiments, melting studies and isothermal calorimetry (ITC) titrations reveal a picture where the binding to natural double-stranded DNA is very different from that to double and triple-stranded RNAs (poly(A)∙poly(U) and poly(U)∙poly(A)⁎poly(U)). As confirmed also by the structural and energetic details clarified by density functional theory (DFT) calculations, intercalation occurs for DNA, with a process driven by the combination of aggregates disruption and monomers intercalation. Oppositely, for RNAs, no intercalation but groove binding with the formation of supramolecular aggregates is observed. Among all the tested biosubstrates, the affinity of PZPERY towards DNA G-quadruplexes (G4) is the greatest one with a preference for human telomeric G4s. Focusing on hybrid G4 forms, either sitting-atop ("tetrad-parallel") or lateral ("groove-parallel") binding modes were considered in the discussion of the experimental results and molecular dynamics (MD) simulations. Both turned out to be possible concurrently, in agreement also with the experimental binding stoichiometries higher than 2:1.

Alcian blue pyridine variant interaction with DNA and RNA polynucleotides and G-quadruplexes: changes in the binding features for different biosubstrates.

This work concerns an analysis of the binding mechanism of a copper phthalocyanine (Alcian Blue-tetrakis(methylpyridinium) chloride, ABTP) to natural calf thymus DNA, G-quadruplexes (G4) and synthetic RNA polynucleotides in the form of double polyriboadenylic·polyribouridylic acid (poly(A)·poly(U)) or triple strands polyriboadenylic·2polyribouridylic acid (poly(A)·2poly(U)). ABTP is a well know dye that might undergo novel applications, but its interaction with DNA is scarcely studied and we lack information on possible RNA or G4 binding. This might be related to system complexity due to the presence of supramolecular dye-dye aggregates. Despite this, we show here that apparent parameters can be calculated, which provide information on the binding mechanism. Absorbance titrations in the presence of biosubstrate excess, melting and circular dichroism experiments show that ABTP binds to both RNAs and DNA. External/groove binding is the main feature for RNAs, whereas partial intercalation is the major binging mode for DNA. ABTP externally binds to both hybrid, parallel and anti-parallel G4s but seem to show a slightly different binding mode and a preference for anti-parallel structures. The thermodynamic features of the different systems are also discussed in the frame of the enthalpy-entropy compensation phenomenon.

Biological activity and photocatalytic properties of a naphthyl-imidazo phenanthroline (HNAIP) ligand and its [Ir(ppy)2(HNAIP)]Cl and [Rh(ppy)2(HNAIP)]Cl complexes.

The synthesized 2-(hydroxy-1-naphtyl)imidazo-[4,5-f][1,10]phenanthroline (HNAIP) ligand and its new iridium ([Ir(ppy)2(HNAIP)]Cl) and rhodium ([Rh(ppy)2(HNAIP)]Cl) complexes, being ppy = 2-phenylpiridinate, show cytotoxic effects in SW480 (colon adenocarcinoma) and A549 (epithelial lung adenocarcinoma) cells. They all are cytotoxic in the tested cell lines. HNAIP and [Rh(ppy)2(HNAIP)]+ are the most cytotoxic, whereas [Ir(ppy)2(HNAIP)]+ displays negligible cytotoxicity towards A549 cells and moderate activity towards SW480. The interaction of all three compounds with Bovine Serum Albumin (BSA), l-glutathione reduced (GSH), nicotinamide adenine dinucleotide (NADH) and DNA was studied to explain the differences found in terms of cytotoxicity. None of them are able to interact with BSA, thus excluding bioavailability due to plasma protein interaction as the possible differentiating factor in their biological activity. By contrast, small differences have been observed regarding DNA interaction. In addition, taking advantage of the emission properties of these molecules, they have been visualized in the cytoplasmic region of A549 cells. Inductively coupled plasma mass spectrometry (ICP-MS) experiments show, in turn, that the internalization ability follow the sequence [Rh(ppy)2(HNAIP)]+ > [Ir(ppy)2(HNAIP)]+ > cisplatin. Therefore, it seems clear that the cellular uptake by tumour cells is the key factor affecting the different cytotoxicity of the metal complexes and that this cellular uptake is influenced by the hydrophobicity of the studied complexes. On the other hand, preliminary catalytic experiments performed on the photo-oxidation of GSH and some amino acids such as l-methionine (Met), l-cysteine (Cys) and l-tryptophan (Trp) provide evidence for the photocatalytic activity of the Ir(III) complex in this type of reactions.

Thiabendazole-based Rh(III) and Ir(III) biscyclometallated complexes with mitochondria-targeted anticancer activity and metal-sensitive photodynamic activity.

Two pairs of Rh(III) and Ir(III) biscyclometallated complexes with thiabendazole (L1), named [Ir-a]Cl and [Rh-a]Cl, and N-benzyl-thiabendazole (L2), named [Ir-b]Cl and [Rh-b]Cl, have been designed and synthesized to explore the photophysical and biological effects that arise from changing both the metal center and the ancillary ligand. In the dark, the four metal complexes exhibit greater cytotoxicity than cisplatin against human colon (SW480) and human lung (A549) adenocarcinoma cell lines. Moreover, the pair of complexes bearing the ligand L2 is markedly more cytotoxic and present higher uptake values than complexes with L1, thereby their biological properties were studied further to determine their mechanism of action. Interestingly, in spite of the different metal center both the [Ir-b]Cl and [Rh-b]Cl complexes are responsible for the loss of mitochondrial functionality and the activation of apoptotic cell death pathways. Moreover, the photodynamic activity of the four complexes, [Ir-a,b]Cl and [Rh-a,b]Cl, was tested using visible blue light (460 nm) under soft irradiation conditions (20 min, 5.5 mW cm-2). While the Rh complexes are not photopotentiated, the phototoxicity index (IC50 non-irradiated/IC50 irradiated) of [Ir-a]Cl and [Ir-b]Cl complexes was 15.8 and 3.6, respectively. We also demonstrate that only the Ir derivatives are capable of photocatalyzing the oxidation of S-containing l-amino acids under blue light irradiation, [Ir-a]Cl being more active than [Ir-b]Cl, which provides a reasonable mechanism for their biological action (oxidative stress could be selectively promoted through a photocatalytic action) upon irradiation. This different PDT behaviour depending on the metal center and the ancillary substituent may be useful for future rational design of metal-based photosensitizers.

Binding Studies of Metal-Salphen and Metal-Bipyridine Complexes towards G-Quadruplex DNA.

The proposed in vivo formation of G-quadruplex DNA (G4 DNA) in promoter regions of oncogenes and in telomeres has prompted the development of small molecules with high affinity and selectivity for these structures. Herein we report the synthesis of a new di-substituted bipyridine ligand and the corresponding complexes with Ni2+ and VO2+ . Both these new complexes have been characterized spectroscopically and by X-ray crystallography. Detailed DNA binding studies of these two complexes, together with three previously reported metal salphen complexes, are presented. Using FRET melting assays, the binding affinity and selectivity of the five metal complexes against six different G4 DNA structures as well as a duplex DNA have been determined. In addition, we present detailed ITC and UV/Vis studies to characterize the interaction of the complexes with human telomeric G4 DNA. Finally, we show via a polymerase stop assay that these complexes are able to stabilize a G4 DNA structure (from the c-Myc oncogene promoter) and halt the activity of Taq polymerase.

Role of Seroalbumin in the Cytotoxicity of cis-Dichloro Pt(II) Complexes with (N

Given the potent anticancer properties of cis-diamminedichloroplatinum(II) and knowing its mode of action, we synthesized four new cis-[PtCl2(N^N)] organoplatinum complexes, two with N-substituted pbi ligands (pbiR = 1-R-2-(2-pyridyl)benzimidazole) (namely, 1 and 2) and two more with 4,4'-disubstituted bpy ligands (bpy = 2,2'-bipyridine) (namely, 3 and 4). We explored their cytotoxicity and ability to bind to deoxyguanosine monophosphate (dGMP), DNA, and albumin models. By 1H NMR and UV-vis spectroscopies, circular dichroism, agarose gel electrophoresis, differential scanning calorimetry measurements, and density functional theory calculations, we verified that only 3 can form aquacomplex species after dimethyl sulfoxide solvation; surprisingly, 1, 2, and 3 can bind covalently to DNA, whereas 4 can form a noncovalent complex. Interestingly, only complexes 1 and 4 exhibit good cytotoxicity against human ovarian carcinoma (HeLa) cell line, whereas 2 and 3 are inactive. Although lung carcinoma (A549) cells are more resistant to the four platinum complexes than HeLa cells, when the protein concentration in the extracellular media is lower, the cytotoxicity becomes substantially enhanced. By native electrophoresis of bovine seroalbumin (BSA) and inductively coupled plasma mass spectrometry uptake studies we bear out, on one hand, that 2 and 3 can interact strongly with BSA and its cellular uptake is negligible and, on the other hand, that 1 and 4 can interact with BSA only weakly, its cellular uptake being higher by several orders. These results point up the important role of the protein binding features on their biological activity and cellular uptake of cis-"PtCl2" derivatives. Our results are valuable in the future rational design of new platinum complexes with improved biological properties, as they expose the importance not only of their DNA binding abilities but also of additional factors such as protein binding.

Kinetic evidence for interaction of TMPyP4 with two different G-quadruplex conformations of human telomeric DNA.

BACKGROUND: Stabilization of G-quadruplex helices by small ligands has attracted growing attention because they inhibit the activity of the enzyme telomerase, which is overexpressed in >80% cancer cells. TMPyP4, one of the most studied G-quadruplex ligands, is used as a model to show that the ligands can exhibit different binding features with different conformations of a human telomeric specific sequence. METHODS: UV-Vis, FRET melting Assay, Isothermal Titration Calorimetry, Time-resolved Fluorescence lifetime, T-Jump and Molecular Dynamics. RESULTS: TMPyP4 yields two different complexes with two Tel22 telomeric conformations in the presence of Na+ or K+. T-Jump kinetic experiments show that the rates of formation and dissociation of these complexes in the ms time scale differ by one order of magnitude. MD simulations reveal that, in K+ buffer, "hybrid 1" conformation yields kinetic constants on interaction with TMPyP4 one order lower than "hybrid 2". The binding involves π-π stacking with external loop bases. CONCLUSIONS: For the first time we show that for a particular buffer TMPyP4 interacts in a kinetically different way with the two Tel22 conformations even if the complexes formed are thermodynamically indistinguishable. GENERAL SIGNIFICANCE: G-quadruplexes, endowed with technological applications and potential impact on regulation mechanisms, define a new research field. The possibility of building different conformations from same sequence is a complex issue that confers G-quadruplexes very interesting features. The obtaining of reliable kinetic data constitutes an efficient tool to determine reaction mechanisms between conformations and small molecules.

New insights into the mechanism of the DNA/doxorubicin interaction.

Doxorubicin (DOX) is an important anthracycline antibiotic whose intricate features of binding to DNAs, not yet fully understood, have been the object of intense debate. The dimerization equilibrium has been studied at pH = 7.0, I = 2.5 mM, and T = 25 °C. A thermodynamic and kinetic study of the binding of doxorubicin to DNA, carried out by circular dichroism, viscometry, differential scanning calorimetry, fluorescence, isothermal titration calorimetry, and T-jump relaxation measurements, has enabled us to characterize for the first time two different types of calf thymus DNA (ctDNA)/DOX complexes: PD1 for C(DOX)/C(DNA) < 0.3, and PD2 for higher drug content. The nature of the PD1 complex is described better in light of the affinity of DOX with the synthetic copolymers [poly(dA-dT)]2 and [poly(dG-dC)]2. The formation of PD1 has been categorized kinetically as a two-step mechanism in which the fast step is the groove binding in the AT region, and the slow step is the intercalation into the GC region. This bifunctional nature provides a plausible explanation for the high PD1 constant obtained (K1 = 2.3 × 10(8) M(-1)). Moreover, the formation of an external aggregate complex ctDNA/DOX (PD2) at the expense of PD1, with K2 = 9.3 × 10(5) M(-1), has been evinced.