Isoniazid metal complex reactivity and insights for a novel anti-tuberculosis drug design

Recent advances in the role of dissolved organic matter during antibiotics photodegradation in the aquatic environment

The presence of residual antibiotics in the environment is a prominent issue. Photodegradation behavior is an important way of antibiotics reduction, which is closely related to dissolved organic matter (DOM) in water. The review provides an overview of the latest advancements in the field. Classification, characterization of DOM, and the dominant mechanisms for antibiotic photodegradation were discussed. Furthermore, it summarized and compared the effects of DOM on different antibiotics photodegradation. Moreover, the review comprehensively considered the factors influencing the photodegradation of antibiotics in the aquatic environment, including the characteristics of light, temperature, dosage of DOM, concentration of antibiotics, solution pH, and the presence of coexisting ions. Finally, potential directions were proposed for the development of predictive models for the photodegradation of antibiotics. Based on the review of existing literature, this paper also considered several pathways for the future study of antibiotic photodegradation. This study allows for a better understanding of the DOM's environmental role and provides important new insights into the photochemical fate of antibiotics in the aquatic environment.

A bioinorganic chemistry perspective on the roles of metals as drugs and targets against Mycobacterium tuberculosis - a journey of opportunities

Medicinal inorganic chemists have provided many strategies to tackle a myriad of diseases, pushing forward the frontiers of pharmacology. As an example, the fight against tuberculosis (TB), an infectious bacterial disease, has led to the development of metal-based compounds as potential drugs. This disease remains a current health issue causing over 1.4 million of deaths per year. The emergence of multi- (MDR) and extensively-drug resistant (XDR) Mycobacterium tuberculosis (Mtb) strains along with a long dormancy process, place major challenges in developing new therapeutic compounds. Isoniazid is a front-line prodrug used against TB with appealing features for coordination chemists, which have been explored in a series of cases reported here. An isoniazid iron-based compound, called IQG-607, has caught our attention, whose in vitro and in vivo studies are advanced and thoroughly discussed, along with other metal complexes. Isoniazid is inactive against dormant Mtb, a hard to eliminate state of this bacillus, found in one-fourth of the world's population and directly implicated in the lengthy treatment of TB (ca. 6 months). Thus, our understanding of this phenomenon may lead to a rational design of new drugs. Along these lines, we describe how metals as targets can cross paths with metals used as selective therapeutics, where we mainly review heme-based sensors, DevS and DosT, as a key system in the Mtb dormancy process and a current drug target. Overall, we report new opportunities for bioinorganic chemists to tackle this longstanding and current threat.

Recent advances in drug discovery against Mycobacterium tuberculosis: Metal-based complexes

Metal-based drugs are privileged motifs that act as primary pharmacophores in bioactive compounds for various diseases, including tuberculosis (TB). This potentially life-threatening and extremely contagious infectious disease is caused by Mycobacterium tuberculosis (Mtb). In 2018, TB infected about 10 million people and caused 1.2 million deaths worldwide. A large number of ligands are promising scaffolds in drug design, including heterocyclic, phosphines, schiff bases, thio and semicarbazones, aliphatic amines, cyclopalladated, cyanometallates and miscellaneous. Moreover, several metal-based complexes have been studied for the treatment of numerous illnesses, including infectious diseases. To contribute to drug design, we identified the metal-based organometallic complexes against Mtb. Thus, in this review article, we analysed the recent contributions of metal-based scaffolds for design of new anti-Mtb drugs in the last decade (2011-2020). Besides, metal-based approaches will be presented in order to find out new antitubercular agents.

Transbuccal delivery of metal complexes of isoniazid as an alternative to overcome antimicrobial resistance problems

In isolated isoniazid (INH)-resistant strains, deletion or mutations in thekatGgene have been identified, which result in loss of catalase-peroxidase activity. This enzyme plays a key role in the activation of this prodrug. As an alternative, the coordination of the INH to metal complexes has been purposed to activate it regardless of enzyme functionality. Although pentacyanido(isoniazid)ferrate(II) complexes have shown to be effective against resistant strains of Mycobacterium tuberculosis, low oral bioavailability was found. In this context, buccal mucosa was selected as an alternative route to the metal complex delivery. Moreover, oral manifestations of tuberculosis(TB) have been observed in some patients, particularly when resistant strains are present, and no therapeutic options are currently available on the market. Pentacyanidoferrate (PCF-INH) and Prussian-blue (PB-INH) complexes were initially prepared and characterized, followed by buccal permeability studies in Franz-type diffusion cells. The electrochemical potential of the complexes demonstrated their ability to self-activate. Job's method suggested the presence of structural defects in PB-INH complexes, which was correlated with permeability results. In fact, PB-INH showed a higher dissociation rate in salt-rich aqueous medium and thus a high transport rate of INH through the buccal mucosa. Its passage through the tissue would not be possible due to the high molecular size. PCF-INH, in turn, presented a lower dissociation rate in the salt-rich aqueous medium, justifying its slower transport rate through the tissue. Taken together, these results suggest that INH-based metal complexes may be efficiently administered through the buccal route, impacting on both oral bioavailability and microbial resistance.

Organic Salts Based on Isoniazid Drug: Synthesis, Bioavailability and Cytotoxicity Studies

Tuberculosis is one of the ten causes of morbidity and mortality worldwide caused by Mycobacterium tuberculosis complex. Some of the anti-tuberculosis drugs used in clinic studies, despite being effective for the treatment of tuberculosis, present serious adverse effects as well as poor bioavailability, stability, and drug-resistance problems. Thus, it is important to develop approaches that could provide shorter drug regimens, preventing drug resistance, toxicity of the antibiotics, and improve their bioavailability. Herein, we reported the use of organic salts based on the isoniazid drug, which can act as an organic cation combined with suitable organic anions such as alkylsulfonate-based (mesylate, R or S-Camphorsulfonate), carboxylate-based (glycolate, vanylate) and sacharinate. The synthesis, characterization, and cytotoxicity studies comparing with the original isoniazid drug have been performed. The possibility to explore dicationic salts seems promising in order to improve original bioavailability, and promote the elimination of polymorphic forms as well as higher stability, which are relevant characteristics that the pharmaceutical industry pursues.

Metal Complexes as Promising Agents for Biomedical Applications

Background::

In this review article, a brief overview of novel metallotherapeutic agents (with an emphasis on the complexes of essential biometals) promising for medical application is presented. We have also focused on the recent work carried out by our research team, specifically the development of redox-active antimicrobial complexes of sterically hindered diphenols with some essential biometals (copper, zinc, nickel).

Results::

The complexes of essential metals (manganese, iron, cobalt, nickel, copper, zinc) described in the review show diverse in vitro biological activities, ranging from antimicrobial and antiinflammatory to antiproliferative and enzyme inhibitory. It is necessary to emphasize that the type of organic ligands in these metal complexes seems to be responsible for their pharmacological activities. In the last decades, there has been a significant interest in synthesis and biological evaluation of metal complexes with redox-active ligands. A substantial step in the development of these redox-active agents is the study of their physicochemical and biological properties, including investigations in vitro of model enzyme systems, which can provide evidence on a plausible mechanism underlying the pharmacological activity. When considering the peculiarities of the pharmacological activity of the sterically hindered diphenol derivatives and their nickel(II), copper(II) and zinc(II) complexes synthesized, we took into account the following: (i) all these compounds are potential antioxidants and (ii) their antimicrobial activity possibly results from their ability to affect the electron-transport chain.

Conclusion::

We obtained novel data demonstrating that the level of antibacterial and antifungal activity in the series of the above-mentioned metal-based antimicrobials depends not only on the nature of the phenolic ligands and complexing metal ions, but also on the lipophilicity and reducing ability of the ligands and metal complexes, specifically regarding the potential biotargets of their antimicrobial action – ferricytochrome c and the superoxide anion radical. The combination of antibacterial, antifungal and antioxidant activity allows one to consider these compounds as promising substances for developing therapeutic agents with a broad spectrum of activities.

Pentacyanoferrate(II) complex of pyridine-4- and pyrazine-2-hydroxamic acid as source of HNO: investigation of anti-tubercular and vasodilation activities

A pharmacophore design approach, based on the coordination chemistry of an intimate molecular hybrid of active metabolites of pro-drugs, known to release active species upon enzymatic oxidative activation, is devised. This is exemplified by combining two anti-mycobacterial drugs: pyrazinamide (first line) and delamanid (third line) whose active metabolites are pyrazinoic acid (PyzCOOH) and likely nitroxyl (HNO (or NO^.)), respectively. Aiming to generate those active species, a hybrid compound was envisaged by coordination of pyrazine-2-hydroxamic acid (PyzCONHOH) with a Na₃[Fe^II(CN)₅] moiety. The corresponding pentacyanoferrate(II) complex Na₄[Fe^II(CN)₅(PyzCONHO^-)] was synthesized and characterized by several spectroscopic techniques, cyclic voltammetry, and DFT calculations. Chemical oxidation of this complex with H₂O₂ was shown to induce the release of the metabolite PyzCOOH, without the need of the Mycobacterium tuberculosis (Mtb) pyrazinamidase enzyme (PncA). Control experiments show that both H₂O₂- and N-coordinated pyrazine Fe^II species are required, ruling out a direct hydrolysis of the hydroxamic acid or an alternative oxidative route through chelation of a metal center by a hydroxamic group. The release of HNO was observed using EPR spectroscopy in the presence of a spin trapping agent. The devised iron metal complex of pyrazine-2-hydroxamic acid was found inactive against an actively growing/non-resistant Mtb strain; however, it showed a strong dose-dependent and reversible vasodilatory activity with mostly lesser toxic effects than the reference drug sodium nitroprussiate, unveiling thus a potential indication for acute or chronic cardiovascular pathology. This is a priori a further indirect evidence of HNO release from this metal complex, standing as a possible pharmacophore model for an alternative vasodilator drug.

Light-induced disruption of an acyl hydrazone link as a novel strategy for drug release and activation: isoniazid as a proof-of-concept case

Photocleavage of an acyl hydrazone bridge was achieved by conjugating isoniazid to a ruthenium(ii) metal complex through the generation of singlet oxygen, which released and activated the anti-tuberculosis pro-drug isoniazid.

An anthracene-pendant ruthenium(ii) complex conjugated to a biotin anchor, an essential handle for photo-induced anti-cancer activity

Efficient avidin binding and selective cancer cell response upon light irradiation of an enhanced ROS photogenerator biotinylated ruthenium complex.

Is IQG-607 a Potential Metallodrug or Metallopro-Drug With a Defined Molecular Target in Mycobacterium tuberculosis?

The emergence of strains of Mycobacterium tuberculosis resistant to isoniazid (INH) has underscored the need for the development of new anti-tuberculosis agents. INH is activated by the mycobacterial katG-encoded catalase-peroxidase, forming an acylpyridine fragment that is covalently attached to the C4 of NADH. This isonicotinyl-NAD adduct inhibits the activity of 2-trans-enoyl-ACP(CoA) reductase (InhA), which plays a role in mycolic acid biosynthesis. A metal-based INH analog, Na₃[Fe^II(CN)₅(INH)]·4H₂O, IQG-607, was designed to have an electronic redistribution on INH moiety that would lead to an intramolecular electron transfer to bypass KatG activation. HPLC and EPR studies showed that the INH moiety can be oxidized by superoxide or peroxide yielding similar metabolites and isonicotinoyl radical only when associated to IQG-607, thereby supporting redox-mediated drug activation as a possible mechanism of action. However, IQG-607 was shown to inhibit the in vitro activity of both wild-type and INH-resistant mutant InhA enzymes in the absence of KatG activation. IQG-607 given by the oral route to M. tuberculosis-infected mice reduced lung lesions. Experiments using early and late controls of infection revealed a bactericidal activity for IQG-607. HPLC and voltammetric methods were developed to quantify IQG-607. Pharmacokinetic studies showed short half-life, high clearance, moderate volume of distribution, and low oral bioavailability, which was not altered by feeding. Safety and toxic effects of IQG-607 after acute and 90-day repeated oral administrations in both rats and minipigs showed occurrence of mild to moderate toxic events. Eight multidrug-resistant strains (MDR-TB) were resistant to IQG-607, suggesting an association between katG mutation and increasing MIC values. Whole genome sequencing of three spontaneous IQG-607-resistant strains harbored katG gene mutations. MIC measurements and macrophage infection experiments with a laboratorial strain showed that katG mutation is sufficient to confer resistance to IQG-607 and that the macrophage intracellular environment cannot trigger the self-activation mechanism. Reduced activity of IQG-607 against an M. tuberculosis strain overexpressing S94A InhA mutant protein suggested both the need for KatG activation and InhA as its target. Further efforts are suggested to be pursued toward attempting to translate IQG-607 into a chemotherapeutic agent to treat tuberculosis.

Revisiting Activation of and Mechanism of Resistance to Compound IQG-607 in Mycobacterium tuberculosis

IQG-607 is a metal complex previously reported as a promising anti-tuberculosis (TB) drug against isoniazid (INH)-resistant strains of Mycobacterium tuberculosis Unexpectedly, we found that INH-resistant clinical isolates were resistant to IQG-607. Spontaneous mutants resistant to IQG-607 were subjected to whole-genome sequencing, and all sequenced colonies carried alterations in the katG gene. The katG(S315T) mutation was sufficient to confer resistance to IQG-607 in both MIC assays and inside macrophages. Moreover, overexpression of the InhA(S94A) protein caused IQG-607's resistance.

Inhibitory activity of pentacyano(isoniazid)ferrate(II), IQG-607, against promastigotes and amastigotes forms of Leishmania braziliensis

M. tuberculosis and parasites of the genus Leishmania present the type II fatty acid biosynthesis system (FASII). The pentacyano(isoniazid)ferrate(II) compound, named IQG-607, inhibits the enzyme 2-trans-enoyl-ACP(CoA) reductase from M. tuberculosis, a key component in the FASII system. Here, we aimed to evaluate the inhibitory activity of IQG-607 against promastigote and amastigote forms of Leishmania (Viannia) braziliensis isolated from patients with different clinical forms of L. braziliensis infection, including cutaneous, mucosal and disseminated leishmaniasis. Importantly, IQG-607 inhibited the proliferation of three different isolates of L. braziliensis promastigotes associated with cutaneous, mucosal and disseminated leishmaniasis. The IC₅₀ values for IQG-607 ranged from 32 to 75 μM, for these forms. Additionally, IQG-607 treatment decreased the proliferation of intracellular amastigotes in infected macrophages, after an analysis of the percentage of infected cells and the number of intracellular parasites/100 cells. IQG-607 reduced from 58% to 98% the proliferation of L. braziliensis from cutaneous, mucosal and disseminated strains. Moreover, IQG-607 was also evaluated regarding its potential toxic profile, by using different cell lines. Cell viability of the lineages Vero, HaCat and HepG2 was significantly reduced after incubation with concentrations of IQG-607 higher than 2 mM. Importantly, IQG-607, in a concentration of 1 mM, did not induce DNA damage in HepG2 cells, when compared to the untreated control group. Future studies will confirm the mechanism of action of IQG-607 against L. braziliensis.

Paulo T, de França Lopes LG, Sousa EHS. A biphosphinic ruthenium complex with potent anti-bacterial and anti-cancer activity

Photorelease of CO and moderate binding to DNA did not seem to be essential features for potent biological activities.

Anti-mycobacterial activities of copper(II) complexes. Part II. Lipophilic hydroxypyridinones derived from maltol

Eight lipophilic 3-hydroxy-4-pyridinones have been prepared from a microwave-mediated reaction along with the corresponding copper(II) complexes. All complexes have been obtained elementally pure and X-ray diffraction studies on two of the copper complexes have confirmed the structure of these compounds. Some of these complexes showed a promising degree of anti-mycobacterial activity against Mycobacterium tuberculosis, where activity seemed to vary by substitution at the pyridinone nitrogen atom.