Minimal Functionalization of Ruthenium Compounds with Enhanced Photoreactivity against Hard-to-Treat Cancer Cells and Resistant Bacteria.

Metallocompounds have emerged as promising new anticancer agents, which can also exhibit properties to be used in photodynamic therapy. Here, we prepared two ruthenium-based compounds with a 2,2'-bipyridine ligand conjugated to an anthracenyl moiety. These compounds coded GRBA and GRPA contain 2,2'-bipyridine or 1,10-phenathroline as auxiliary ligands, respectively, which provide quite a distinct behavior. Notably, compound GRPA exhibited remarkably high photoproduction of singlet oxygen even in water (Ï•Δ = 0.96), almost twice that of GRBA (Ï•Δ = 0.52). On the other hand, this latter produced twice more superoxide and hydroxyl radical species than GRPA, which may be due to the modulation of their excited state. Interestingly, GRPA exhibited a modest binding to DNA (Kb = 4.51 × 104), while GRBA did not show a measurable interaction only noticed by circular dichroism measurements. Studies with bacteria showed a great antimicrobial effect, including a synergistic effect in combination with commercial antibiotics. Besides that, GRBA showed very low or no cytotoxicity against four mammalian cells, including a hard-to-treat MDA-MB-231, triple-negative human breast cancer. Potent activities were measured for GRBA upon blue light irradiation, where IC50 of 43 and 13 nmol L-1 were seen against hard-to-treat triple-negative human breast cancer (MDA-MB-231) and ovarian cancer cells (A2780), respectively. These promising results are an interesting case of a simple modification with expressive enhancement of biological activity that deserves further biological studies.

New nitrosyl ruthenium complexes with combined activities for multiple cardiovascular disorders.

Nitrosyl ruthenium complexes are promising platforms for nitric oxide (NO) and nitroxyl (HNO) release, which exert their therapeutic application. In this context, we developed two polypyridinic compounds with the general formula cis-[Ru(NO)(bpy)2(L)]n+, where L is an imidazole derivative. These species were characterized by spectroscopic and electrochemical techniques, including XANES/EXAFS experiments, and further supported by DFT calculations. Interestingly, assays using selective probes evidenced that both complexes can release HNO on reaction with thiols. This finding was biologically validated by HIF-1α detection. The latter protein is related to angiogenesis and inflammation processes under hypoxic conditions, which is selectively destabilized by nitroxyl. These metal complexes also presented vasodilating properties using isolated rat aorta rings and demonstrated antioxidant properties in free radical scavenging experiments. Based on these results, the new nitrosyl ruthenium compounds showed promising characteristics as potential therapeutic agents for the treatment of cardiovascular conditions such as atherosclerosis, deserving further investigation.

Nitroprusside─Expanding the Potential Use of an Old Drug Using Nanoparticles.

For more than 70 years, sodium nitroprusside (SNP) has been used to treat severe hypertension in hospital emergency settings. During this time, a few other clinical uses have also emerged such as in the treatment of acute heart failure as well as improving mitral incompetence and in the intra- and perioperative management during heart surgery. This drug functions by releasing nitric oxide (NO), which modulates several biological processes with many potential therapeutic applications. However, this small molecule has a short lifetime, and it has been administered through the use of NO donor molecules such as SNP. On the other hand, SNP also has some setbacks such as the release of cyanide ions, high water solubility, and very fast NO release kinetics. Currently, there are many drug delivery strategies that can be applied to overcome many of these limitations, providing novel opportunities for the use of old drugs, including SNP. This Perspective describes some nitroprusside properties and highlights new potential therapeutic uses arising from the use of drug delivery systems, mainly silica-based nanoparticles. There is a series of great opportunities to further explore SNP in many medical issues as reviewed, which deserves a closer look by the scientific community.

Anti-asthmatic effect of nitric oxide metallo-donor FOR811A [cis-[Ru(bpy)2(2-MIM)(NO)](PF6)3] in the respiratory mechanics of Swiss mice.

We aimed at evaluating the anti-asthmatic effect of cis-[Ru(bpy)2(2-MIM)(NO)](PF6)3 (FOR811A), a nitrosyl-ruthenium compound, in a murine model of allergic asthma. The anti-asthmatic effects were analyzed by measuring the mechanical lung and morphometrical parameters in female Swiss mice allocated in the following groups: untreated control (Ctl+Sal) and control treated with FOR811A (Ctl+FOR), along asthmatic groups untreated (Ast+Sal) and treated with FOR811A (Ast+FOR). The drug-protein interaction was evaluated by in-silico assay using molecular docking. The results showed that the use of FOR811A in experimental asthma (Ast+FOR) decreased the pressure-volume curve, hysteresis, tissue elastance, tissue resistance, and airway resistance, similar to the control groups (Ctl+Sal; Ctl+FOR). However, it differed from the untreated asthmatic group (Ast+Sal, p<0.05), indicating that FOR811A corrected the lung parenchyma and relaxed the smooth muscles of the bronchi. Similar to control groups (Ctl+Sal; Ctl+FOR), FOR811A increased the inspiratory capacity and static compliance in asthmatic animals (Ast+Sal, p<0.05), showing that this metallodrug improved the capacity of inspiration during asthma. The morphometric parameters showed that FOR811A decreased the alveolar collapse and kept the bronchoconstriction during asthma. Beyond that, the molecular docking using FOR811A showed a strong interaction in the distal portion of the heme group of the soluble guanylate cyclase, particularly with cysteine residue (Cys141). In summary, FOR811A relaxed bronchial smooth muscles and improved respiratory mechanics during asthma, providing a protective effect and promising use for the development of an anti-asthmatic drug.

A divergent mode of activation of a nitrosyl iron complex with unusual antiangiogenic activity.

Nitric oxide (NO) and nitroxyl (HNO) have gained broad attention due to their roles in several physiological and pathophysiological processes. Remarkably, these sibling species can exhibit opposing effects including the promotion of angiogenic activity by NO compared to HNO, which blocks neovascularization. While many NO donors have been developed over the years, interest in HNO has led to the recent emergence of new donors. However, in both cases there is an expressive lack of iron-based compounds. Herein, we explored the novel chemical reactivity and stability of the trans-[Fe(cyclam)(NO)Cl]Cl2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) complex. Interestingly, the half-life (t1/2) for NO release was 1.8 min upon light irradiation, vs 5.4 h upon thermal activation at 37 °C. Importantly, spectroscopic evidence supported the generation of HNO rather than NO induced by glutathione. Moreover, we observed significant inhibition of NO donor- or hypoxia-induced HIF-1α (hypoxia-inducible factor 1α) accumulation in breast cancer cells, as well as reduced vascular tube formation by endothelial cells pretreated with the trans-[Fe(cyclam)(NO)Cl]Cl2 complex. Together, these studies provide the first example of an iron-nitrosyl complex with anti-angiogenic activity as well as the potential dual activity of this compound as a NO/HNO releasing agent, which warrants further pharmacological investigation.

Nitro-imidazole-based ruthenium complexes with antioxidant and anti-inflammatory activities.

Inflammation is a physiological process triggered in response to tissue damage, and involves events related to cell recruitment, cytokines release and reactive oxygen species (ROS) production. Failing to control the process duration lead to chronification and may be associated with the development of various pathologies, including autoimmune diseases and cancer. Considering the pharmacological potential of metal-based compounds, two new ruthenium complexes were synthesized: cis-[Ru(NO2)(bpy)2(5NIM)]PF6 (1) and cis-[RuCl(bpy)2(MTZ)]PF6 (2), where bpy = 2,2'-bipyridine, 5NIM = 5-nitroimidazole and MTZ = metronidazole. Both products were characterized by spectroscopic techniques, followed by Density Functional Theory (DFT) calculations in order to support experimental findings. Afterwards, their in vitro cytotoxic, antioxidant and anti-inflammatory activities were investigated. Compounds 1 and 2 presented expressive in vitro antioxidant activity, reducing lipid peroxidation and decreasing intracellular ROS levels with comparable effectiveness to the standard steroidal drug dexamethasone or α-tocopherol. These complexes showed no noticeable cytotoxicity on the tested cancer cell lines. Bactericidal assay against metronidazole-resistant Helicobacter pylori, a microorganism able to disrupt oxidative balance, unraveled compound 1 moderate activity over that strain. Besides this, it was able to inhibit interleukin-6 (IL-6) and tumor necrosis factor-α (TNF- α) production as well as interleukin-1ß (IL-1ß) and cyclooxygenase-2 (COX-2) expression in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. This latter activity is remarkable, which has not been reported for other ruthenium-based complexes. Altogether, these results suggest cis-[Ru(NO2)(bpy)2(5NIM)]PF6 complex has potential pharmacological application as an anti-inflammatory agent that deserve further biological investigation.

Antihypertensive potential of cis-[Ru(bpy)2(ImN)(NO)]3+, a ruthenium-based nitric oxide donor.

The aim of this study was to investigate the antihypertensive properties of cis-[Ru(bpy)2ImN(NO)]3+ (FOR0811) in normotensive and in Nω-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. Vasorelaxant effects were analyzed by performing concentration response curve to FOR0811 in rat aortic rings in the absence or presence of 1H-[1,2,4]-oxadiazolo-[4,3,-a]quinoxalin-1-one (ODQ), L-cysteine or hydroxocobalamin. Normotensive and L-NAME-hypertensive rats were treated with FOR0811 and the effects in blood pressure and heart rate variability in the frequency domain (HRV) were followed. FOR0811 induced relaxation in rat aortic rings. Neither endothelium removal nor L-cysteine altered the FOR0811 effects. However, the incubation with ODQ and hydroxocobalamin completely blunted FOR0811 effects. FOR0811 administered intravenously by bolus infusion (0.01-1 mg/bolus) or chronically by using subcutaneous implanted osmotic pumps significantly reduced the mean arterial blood pressure. The effect was long lasting and did not induce reflex tachycardia. FOR0811 prevented both LF and VLF increases in L-NAME hypertensive rats and has antihypertensive properties. This new ruthenium complex compound might be a promising nitric oxide donor to treat cardiovascular diseases.

Synthesis and mechanistic investigation of iron(II) complexes of isoniazid and derivatives as a redox-mediated activation strategy for anti-tuberculosis therapy.

The emergence of multidrug-resistant strains of Mycobacterium tuberculosis (MTB) represents a major threat to global health. Isoniazid (INH) is a prodrug used in the first-line treatment of tuberculosis. It undergoes oxidation by a catalase-peroxidase KatG, leading to generation of an isonicotinoyl radical that reacts with NAD(H) forming the INH-NADH adduct as the active metabolite. A redox-mediated activation of isoniazid using an iron metal complex was previously proposed as a strategy to overcome isoniazid resistance due to KatG mutations. Here, we have prepared a series of iron metal complexes with isoniazid and analogues, containing alkyl substituents at the hydrazide moiety, and also with pyrazinamide derivatives. These complexes were activated by H2O2 and studied by ESR and LC-MS. For the first time, the formation of the oxidized INH-NAD adduct from the pentacyano(isoniazid)ferrate(II) complex was detected by LC-MS, supporting a redox-mediated activation, for which a mechanistic proposition is reported. ESR data showed all alkylated hydrazides, in contrast to non-substituted hydrazides, only generated alkyl-based radicals. The structural modifications did not improve minimal inhibitory concentration (MIC) against MTB in comparison to isoniazid iron complex, providing support to isonicotinoyl radical formation as a requirement for activity. Nonetheless, the pyrazinoic acid hydrazide iron complex showed redox-mediated activation using H2O2 with generation of a pyrazinoyl radical intermediate and production of pyrazinoic acid, which is in fact the active metabolite of pyrazinamide prodrug. Thereby, this strategy can also unveil new opportunities for activation of this type of drug.

Aryl-Substituted Ruthenium(II) Complexes: A Strategy for Enhanced Photocleavage and Efficient DNA Binding.

Ruthenium polypyridine complexes have shown promise as agents for photodynamic therapy (PDT) and tools for molecular biology (chromophore-assisted light inactivation). To accomplish these tasks, it is important to have at least target selectivity and great reactive oxygen species (ROS) photogeneration: two properties that are not easily found in the same molecule. To prepare such new agents, we synthesized two new ruthenium complexes that combine an efficient DNA binding moiety (dppz ligand) together with naphthyl-modified (1) and anthracenyl-modified (2) bipyridine as a strong ROS generator bound to a ruthenium complex. The compounds were fully characterized and their photophysical and photochemical properties investigated. Compound 2 showed one of the highest quantum yields for singlet oxygen production ever reported (ΦΔ= 0.96), along with very high DNA binding (log Kb = 6.78). Such photochemical behavior could be ascribed to the lower triplet state involving the anthracenyl-modified bipyridine, which is associated with easier oxygen quenching. In addition, the compounds exhibited moderate selectivity toward G-quadruplex DNA and binding to the minor groove of DNA, most likely driven by the pendant ligands. Interestingly, they also showed DNA photocleavage activity even upon exposure to a yellow light-emitting diode (LED). Regarding their biological activity, the compounds exhibited an exciting antibacterial action, particularly against Gram-positive bacteria, which was enhanced upon blue LED irradiation. Altogether, these results showed that our strategy succeeded in producing light-triggered DNA binding agents with pharmacological and biotechnological potential.

[Fe(CN)5(isoniazid)](3-): an iron isoniazid complex with redox behavior implicated in tuberculosis therapy.

Tuberculosis has re-emerged as a worldwide threat, which has motivated the development of new drugs. The antituberculosis complex Na3[Fe(CN)5(isoniazid)] (IQG607) in particular is of interest on account of its ability to overcome resistance. IQG607 has the potential for redox-mediated-activation, in which an acylpyridine (isonicotinoyl) radical could be generated without assistance from the mycobacterial KatG enzyme. Here, we have investigated the reactivity of IQG607 toward hydrogen peroxide and superoxide, well-known intracellular oxidizing agents that could play a key role in the redox-mediated-activation of this compound. HPLC, NMR and electronic spectroscopy studies showed a very fast oxidation rate for bound isoniazid, over 460-fold faster than free isoniazid oxidation. A series of EPR spin traps were used for detection of isonicotinoyl and derived radicals bound to iron. This is the first report for an isonicotinoyl radical bound to a metal complex, supported by (14)N and (1)H hyperfine splittings for the POBN and PBN trapped radicals. POBN and PBN exhibited average hyperfine coupling constants of aN=15.6, aH=2.8 and aN=15.4, aH=4.7, respectively, which are in close agreement to the isonicotinoyl radical. Radical generation is thought to play a major role in the mechanism of action of isoniazid and this work provides strong evidence for its production within IQG607, which, along with biological and chemical oxidation data, support a redox-mediated activation mechanism. More generally the concept of redox activation of metallo prodrugs could be applied more widely for the design of therapeutic agents with novel mechanisms of action.

DosT and DevS are oxygen-switched kinases in Mycobacterium tuberculosis.

Exposure of Mycobacterium tuberculosis to hypoxia is known to alter the expression of many genes, including ones thought to be involved in latency, via the transcription factor DevR (also called DosR). Two sensory kinases, DosT and DevS (also called DosS), control the activity of DevR. We show that, like DevS, DosT contains a heme cofactor within an N-terminal GAF domain. For full-length DosT and DevS, we determined the ligand-binding parameters and the rates of ATP reaction with the liganded and unliganded states. In both proteins, the heme state was coupled to the kinase such that the unliganded, CO-bound, and NO-bound forms were active, but the O(2)-bound form was inactive. Oxygen-bound DosT was unusually inert to oxidation to the ferric state (half life in air >60 h). Though the kinase activity of DosT was unaffected by NO, this ligand bound 5000 times more avidly than O(2) to DosT (K(d) [NO] approximately 5 nM versus K(d) [O(2)] = 26 microM). These results demonstrate direct and specific O(2) sensing by proteins in M. tuberculosis and identify for the first time a signal ligand for a sensory kinase from this organism. They also explain why exposure of M. tuberculosis to NO donors under aerobic conditions can give results identical to hypoxia, i.e., NO saturates DosT, preventing O(2) binding and yielding an active kinase.

Oxygen blocks the reaction of the FixL-FixJ complex with ATP but does not influence binding of FixJ or ATP to FixL.

The RmFixL-RmFixJ oxygen signal transduction system ensures that a cascade of the Sinorhizobium meliloti nitrogen fixation genes is induced as the concentration of O2 drops below 50 microM in symbiotic nodules. Deoxy-RmFixL is a histidine protein kinase that catalyzes a phosphoryl transfer from ATP to the aspartate 54 residue of RmFixJ; RmFixJ is a response regulator that becomes activated as a transcription factor by phosphorylation. Association of O2 with a heme-binding domain in RmFixL triggers a conformational change that inhibits its kinase activity. Here we consider whether this inhibition is achieved by disrupting binding of either of the substrates, i.e., RmFixJ or ATP, to the RmFixL kinase. The ATP affinities of the oxy and deoxy states were compared via competition of ATP against TNP-nucleotide fluorophores. The influence of O2 on formation of the RmFixL-RmFixJ complex was investigated by fluorescence polarization. Oxygen dramatically inhibited the reaction of the RmFixL-RmFixJ complex with ATP but affected neither ATP binding (Kd approximately 100 microM) nor RmFixL-RmFixJ complex formation (Kd approximately 4 microM), indicating that inhibition of the kinase by the oxy-heme in RmFixL is achieved by inactivating the catalytic site, rather than by blocking the association of this enzyme with either of its substrates. An 8-fold enhancement of the rate of reaction of RmFixL with ATP in a deoxy-RmFixL-D54N RmFixJ complex, compared to that in isolated deoxy-RmFixL, exposes the strength of the allosteric effect of RmFixJ on the reaction. These results clarify the mechanistic roles of the signal and regulatory partner in this signal transduction system.