Intercalation of fac-[(4,4'-bpy)ReI(CO)3(dppz)]+, dppz = dipyridyl[3,2-a:2'3'-c]phenazine, in polynucleotides. On the UV-vis photophysics of the Re(I) intercalator and the redox reactions with pulse radiolysis-generated radicals

DNA structural changes (photo)induced by tricarbonyl (pterin)rhenium(I) complex

We report on interactions of different types of DNA molecules including double-stranded and plasmid DNA as well as polynucleotides (poly[dGdC]2 and poly[dAdT]2) with fac-[ReI(CO)3(pterin)(H2O)] (or Reptr) complex. The interaction was characterized spectroscopically and changes in the plasmid structure were verified by both electrophoresis and AFM microscopy. For comparative reasons, two others related tricarbonyl rhenium(I) complexes, fac-[(4,4'-bpy)ReI(CO)3(dppz)]+ (or Redppz) and fac-[(CF3SO3)ReI(CO)3(2,2'-bpy)] (or Rebpy) were also studied to further explore the influence of the different co-ligands on the interaction and DNA (photo)damage. Data reported herein suggests that DNA molecules can be structurally modified either by direct interaction with Re(I) complexes in their ground states inducing DNA relaxation, and/or through photoinduced cross-linking processes. The chemical nature of the co-ligands modulates the extent of the damage observed.

DNA-Targeted Complexes of Tc and Re for Biomedical Applications

Due to their favorable chemical features, Re and Tc complexes have been widely used for the development of new therapeutic agents and imaging probes to solve problems of biomedical relevance. This review provides an update of the most relevant research efforts towards the development of novel cancer theranostic agents using Re and Tc-based compounds interacting with specific DNA structures. This includes a variety of homometallic complexes, namely those containing M(CO)3 (M=Re, Tc) moieties, that exhibit different modes of interaction with DNA, such as covalent binding, intercalation, groove binding or G-quadruplex DNA binding. Additionally, heterometallic complexes, designed to potentiate synergistic effects of different metal centers to improve DNA-targeting, cytotoxicity and fluorescence properties, are also reviewed. Particular attention is also given to 99m Tc- and 188 Re-labeled oligonucleotides that have been widely explored to develop imaging and therapeutic radiopharmaceuticals through the in vivo hybridization with a specific complementary DNA or RNA target sequence to provide useful molecular tools in precision medicine for cancer diagnosis and treatment. Finally, the need for further improvement of DNA-targeted Re and Tc-based compounds as potential therapeutic and diagnostic agents is highlighted, and future directions are discussed.

The rhenium(I)-diselenoether anticancer drug targets ROS, TGF-β1, VEGF-A, and IGF-1 in an in vitro experimental model of triple-negative breast cancers

The rhenium(I)-diselenoether complex (Re-diSe) is a rhenium tricarbonyl-based drug chelated by a diselenoether ligand. In this work, we compared its inhibitory effects on the hormone-independent MDA-MB231cancer line and other different cancer cell lines after an exposure time of 72 h by MTT assays. The sensitivity of MDA-MB231 was in the same range than the hormone-dependent MCF-7 breast cancer, the PC-3 prostate and HT-29 colon cancer cells, while the A549 lung and the HeLa uterine cancer cells were less sensitive. We compared the inhibitory effects of Re-diSe and of its diselenide ligand (di-Se) on MDA-MB231 and a normal HEK-293 human embryonic cell line, after 72 h and 120 h of exposure. The cytotoxicity was also studied by flow cytometry using ethidium bromide assays, as well as the effects on the ROS production by DFCA-test, while the levels of TGF-β1, VEGF-A, IGF-1 were addressed by ELISA tests. The dose required to inhibit 50% of the proliferation (IC₅₀) of MDA-MB231 breast cancer cells decreased with the time of exposure to 120 h, while the free ligand (di-Se) was found poorly active, demonstrating the important role of Re in this Re-diSe combination. The cytotoxic effects of Re-diSe were highly selective for cancer cells, with a significant increase of the number of dead cancer cells at 5 μM for an exposure time of 120 h, while normal cells were not affected. A remarkable and significant decrease of the production of ROS together with a decrease of VEGF-A, TGF-β1, and IGF-1 by the cancer cells were also observed when cancer cells were exposed to Re-diSe.

Association studies to transporting proteins of fac-ReI(CO)3(pterin)(H2O) complex

A new synthetic route to acquire the water soluble complex fac-Re^I(CO)₃(pterin)(H₂O) was carried out in aqueous solution. The complex has been obtained with success via the fac-[Re^I(CO)₃(H₂O)₃]Cl precursor complex. Re^I(CO)₃(pterin)(H₂O) has been found to bind strongly with bovine and human serum albumins (BSA and HSA) with intrinsic-binding constants, K_b, of 6.5 × 10⁵ M^-1 and 5.6 × 10⁵ M^-1 at 310 K, respectively. The interactions of serum albumins with Re^I(CO)₃(pterin)(H₂O) were evaluated employing UV-vis fluorescence and absorption spectroscopy and circular dichroism. The results suggest that the serum albumins-Re^I(CO)₃(pterin)(H₂O) interactions occurred in the domain IIA-binding pocket without loss of helical stability of the proteins. The comparison of the fluorescence quenching of BSA and HSA due to the binding to the Re(I) complex suggested that local interaction around the Trp 214 residue had taken place. The analysis of the thermodynamic parameters ΔG⁰, ΔH⁰, and ΔS⁰ indicated that the hydrophobic interactions played a major role in both HSA-Re(I) and BSA-Re(I) association processes. All these experimental results suggest that these proteins can be considered as good carriers for transportation of Re^I(CO)₃(pterin)(H₂O) complex. This is of significant importance in relation to the use of this Re(I) complex in several biomedical fields, such as photodynamic therapy and radiopharmacy.

Norharmane rhenium(i) polypyridyl complexes: synthesis, structural and spectroscopic characterization

Novel Re(i) polypyridyl complexes with norharmane as a ligand were obtained and characterized by different techniques. The nature of the electronic transitions was established by TD-DFT calculations.

Re(I) tricarbonyl complex of 1,10-phenanthroline-5,6-dione: DNA binding, cytotoxicity, anti-inflammatory and anti-coagulant effects towards platelet activating factor

The complex fac-[Re(CO)3(phendione)Cl] (1) (where phendione=1,10-phenanthroline-5,6-dione) has been synthesized and fully characterized by UV-visible, FTIR, and NMR techniques. The DNA binding properties of 1 are investigated by UV-spectrophotometric (melting curves), covalent binding assay, CV (cyclic voltammetry), circular dichroism (CD) and viscosity measurements. Experimental data indicate that 1 fits into the major groove without disrupting the helical structure of the B-DNA in contrast to the free phendione which intercalates within the base pairs of DNA. Upon irradiation, complex 1 promotes the cleavage of plasmid pBR322 DNA from supercoiled form I to nicked form II via a proton coupled electron transfer mechanism. This comes as a result of experimental data in anaerobic/aerobic conditions and in the presence of DMSO. The biological activities of 1 and its precursors [Re(CO)5Cl] and phendione are tested towards a series of cancerous cell lines as glioblastoma (T98G), prostate cancer (PC3) and breast cancer (MCF-7) as well as platelet activating factor (PAF)-aggregation. Moreover, all the aforementioned compounds are tested for their ability to modulate PAF-basic metabolic enzyme activities in preparations of rabbit leukolytes. The in vitro experiments indicate that phendione has a better antitumor effect than cisplatin whereas [Re(CO)5Cl] is a better PAF inhibitor than both the phendione ligand and 1. Moreover, for the first time it is indicated that [Re(CO)5Cl], with a IC50 of 17nM is comparable to the widely used PAF receptor antagonists, BN52021 and WEB2170 with IC50 of 30 and 20nM, respectively, whereas 1 affects PAF-catabolism.

Mass spectrometry of rhenium complexes: a comparative study by using LDI-MS, MALDI-MS, PESI-MS and ESI-MS

A group of rhenium (I) complexes including in their structure ligands such as CF(3)SO(3)-, CH(3)CO(2)-, CO, 2,2'-bipyridine, dipyridil[3,2-a:2'3'-c]phenazine, naphthalene-2-carboxylate, anthracene-9-carboxylate, pyrene-1-carboxylate and 1,10-phenanthroline have been studied for the first time by mass spectrometry. The probe electrospray ionization (PESI) is a technique based on electrospray ionization (ESI) that generates electrospray from the tip of a solid metal needle. In this work, mass spectra for organometallic complexes obtained by PESI were compared with those obtained by classical ESI and high flow rate electrospray ionization assisted by corona discharge (HF-ESI-CD), an ideal method to avoid decomposition of the complexes and to induce their oxidation to yield intact molecular cation radicals in gas state [M](+·) and to produce their reduction yielding the gas species [M](-·). It was found that both techniques showed in general the intact molecular ions of the organometallics studied and provided additional structure characteristic diagnostic fragments. As the rhenium complexes studied in the present work showed strong absorption in the UV-visible region, particularly at 355 nm, laser desorption ionization (LDI) mass spectrometry experiments could be conducted. Although intact molecular ions could be detected in a few cases, LDI mass spectra showed diagnostic fragments for characterization of the complexes structure. Furthermore, matrix-assisted laser desorption ionization (MALDI) mass spectra were obtained. Nor-harmane, a compound with basic character, was used as matrix, and the intact molecular ions were detected in two examples, in negative ion mode as the [M](-·) species. Results obtained with 2-[(2E)-3-(4-tert-buthylphenyl)-2-methylprop-2-enylidene] malononitrile (DCTB) as matrix are also described. LDI experiments provided more information about the rhenium complex structures than did the MALDI ones.

Using metal complex reduced states to monitor the oxidation of DNA

Metallointercalating photooxidants interact intimately with the base stack of double-stranded DNA and exhibit rich photophysical and electrochemical properties, making them ideal probes for the study of DNA-mediated charge transport (CT). The complexes [Rh(phi)(2)(bpy')](3+) (phi = 9,10-phenanthrenequinone diimine; bpy' = 4-methyl-4'-(butyric acid)-2,2'-bipyridine), [Ir(ppy)(2)(dppz')](+) (ppy = 2-phenylpyridine; dppz' = 6-(dipyrido[3,2-a:2',3'-c]phenazin-11-yl)hex-5-ynoic acid), and [Re(CO)(3)(dppz)(py')](+) (dppz = dipyrido[2,3-a:2',3'-c]phenazine; py' = 3-(pyridin-4-yl)-propanoic acid) were each covalently tethered to DNA to compare their photooxidation efficiencies. Biochemical studies show that upon irradiation, the three complexes oxidize guanine by long-range DNA-mediated CT with the efficiency: Rh > Re > Ir. Comparison of spectra obtained by spectroelectrochemistry after bulk reduction of the free metal complexes with those obtained by transient absorption (TA) spectroscopy of the conjugates suggests that the reduced metal states form following excitation of the conjugates at 355 nm. Electrochemical experiments and kinetic analysis of the TA decays indicate that the thermodynamic driving force for CT, variations in the efficiency of back electron transfer, and coupling to DNA are the primary factors responsible for the trend observed in the guanine oxidation yields of the three complexes.

Charge photoinjection in intercalated and covalently bound [Re(CO)3(dppz)(py)]+-DNA constructs monitored by time-resolved visible and infrared spectroscopy

The complex [Re(CO)(3)(dppz)(py'-OR)](+) (dppz = dipyrido[3,2-a:2',3'-c]phenazine; py'-OR = 4-functionalized pyridine) offers IR sensitivity and can oxidize DNA directly from the excited state, making it a promising probe for the study of DNA-mediated charge transport (CT). The behavior of several covalent and noncovalent Re-DNA constructs was monitored by time-resolved IR (TRIR) and UV/visible spectroscopies, as well as biochemical methods, confirming the long-range oxidation of DNA by the excited complex. Optical excitation of the complex leads to population of MLCT and at least two distinct intraligand states. Experimental observations that are consistent with charge injection from these excited states include similarity between long-time TRIR spectra and the reduced state spectrum observed by spectroelectrochemistry, the appearance of a guanine radical signal in TRIR spectra, and the eventual formation of permanent guanine oxidation products. The majority of reactivity occurs on the ultrafast time scale, although processes dependent on slower conformational motions of DNA, such as the accumulation of oxidative damage at guanine, are also observed. The ability to measure events on such disparate time scales, its superior selectivity in comparison to other spectroscopic techniques, and the ability to simultaneously monitor carbonyl ligand and DNA IR absorption bands make TRIR a valuable tool for the study of CT in DNA.