Importance of metal complexes for development of potential leishmanicidal agents

Phenanthroline and Schiff Base associated Cu(II)-coordinated compounds containing N, O as donor atoms for potent anticancer activity

As an inherent metal ion, copper has been the subject of investigation for developing a novel antitumoral compound that exhibits fewer adverse effects. Copper serves as a cofactor in multiple enzymes, generates reactive oxygen species (ROS), facilitates tumour evolution, metastasis and angiogenesis and has been detected at elevated concentrations in the serum and tissues of various human cancer types. In the given setting, utilising two methodologies in developing novel Copper-based pharmaceuticals for anti-cancer applications is standard practice. These approaches involve either the sequestration of unbound Copper ions or the synthesis of Copper complexes that induce cellular apoptosis. In the past four decades, the latter system has been used, leading to numerous reviews that have examined the anticancer characteristics of a wide range of Copper complexes. These analyses have consistently demonstrated that multiple factors frequently influence the efficacy of these compounds. This review examines the possible anticancer properties of copper and Cu(II) complexes that incorporate Schiff base ligands containing 1,10-phenanthroline. The present study will comprehensively analyse the examined cell lines and mechanistic research associated with each complex.

Thiophene-Derived Schiff Base Complexes: Synthesis, Characterization, Antimicrobial Properties, and Molecular Docking

Novel thiophene-derived Schiff base ligand DE, where DE is (E)-N¹,N¹-diethyl-N²-(thiophen-2-ylmethylene)ethane-1,2-diamine, and the corresponding M(II) complexes, [M(DE)X₂] (M = Cu or Zn, X = Cl; M = Cd, X = Br), were prepared and structurally characterized. X-ray diffraction studies revealed that the geometry around the center of the M(II) complexes, [Zn(DE)Cl₂] and [Cd(DE)Br₂], could be best described as a distorted tetrahedral. In vitro antimicrobial screening of DE and its corresponding M(II) complexes, [M(DE)X₂], was performed. The complexes were more potent and showed higher activities against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, fungi Candida albicans, and protozoa Leishmania major compared to the ligand. Among the studied complexes, [Cd(DE)Br₂] exhibited the most promising antimicrobial activity against all the tested microbes compared to its analogs. These results were further supported by molecular docking studies. We believe that these complexes may significantly contribute to the efficient designing of metal-derived agents to treat microbial infections.

Antimicrobial Agents Based on Metal Complexes: Present Situation and Future Prospects

The rise in antimicrobial resistance is a cause of serious concern since the ages. Therefore, a dire need to explore new antimicrobial entities that can combat against the increasing threat of antibiotic resistance is realized. Studies have shown that the activity of the strongest antibiotics has reduced drastically against many microbes such as microfungi and bacteria (Gram-positive and Gram-negative). A ray of hope, however, was witnessed in early 1940s with the development of new drug discovery and use of metal complexes as antibiotics. Many new metal-based drugs were developed from the metal complexes which are potentially active against a number of ailments such as cancer, malaria, and neurodegenerative diseases. Therefore, this review is an attempt to describe the present scenario and future development of metal complexes as antibiotics against wide array of microbes.

New multifunctional Ru(II) organometallic compounds show activity against Trypanosoma brucei and Leishmania infantum

Human African trypanosomiasis (sleeping sickness) and leishmaniasis are prevalent zoonotic diseases caused by genomically related trypanosomatid protozoan parasites (Trypanosoma brucei and Leishmania spp). Additionally, both are co-endemic in certain regions of the world. Only a small number of old drugs exist for their treatment, with most of them sharing poor safety, efficacy, and pharmacokinetic profiles. In this work, new multifunctional Ru(II) ferrocenyl compounds were rationally designed as potential agents against these trypanosomatid parasites by including in a single molecule 1,1'-bis(diphenylphosphino)ferrocene (dppf) and two bioactive bidentate ligands: 8-hydroxyquinoline derivatives (8HQs) and polypyridyl ligands (NN). Three [Ru(8HQs)(dppf)(NN)](PF₆) compounds were synthesized and fully characterized. They showed in vitro activity on bloodstream Trypanosoma brucei (IC₅₀ 140-310 nM) and on Leishmania infantum promastigotes (IC₅₀ 3.0-4.8 μM). The compounds showed good selectivity towards T. brucei in respect to J774 murine macrophages as mammalian cell model (SI 15-38). Changing hexafluorophosphate counterion by chloride led to a three-fold increase in activity on both parasites and to a two to three-fold increase in selectivity towards the pathogens. The compounds affect in vitro at least the targets of the individual bioactive moieties included in the new chemical entities: DNA and generation of ROS. The compounds are stable in solution and are more lipophilic than the free bioactive ligands. No clear correlation between lipophilicity, interaction with DNA or generation of ROS and activity was detected, which agrees with their overall similar anti-trypanosoma potency and selectivity. These compounds are promising candidates for further drug development.

A Broad Spectrum Antiparasitic Activity of Organotin (IV) Derivatives and Its Untargeted Proteomic Profiling Using Leishmania donovani

Metals have been used in medicine since ancient times for the treatment of different ailments with various elements such as iron, gold and arsenic. Metal complexes have also been reported to show antibiotic and antiparasitic activity. In this context, we tested the antiparasitic potential of 10 organotin (IV) derivatives from 4-(4-methoxyphenylamino)-4 oxobutanoic acid (MS26) against seven eukaryotic pathogens of medical importance: Leishmania donovani, Trypanosoma cruzi, Trypanosoma brucei, Entamoeba histolytica, Giardia lamblia, Naegleria fowleri and Schistosoma mansoni. Among the compounds with and without antiparasitic activity, compound MS26Et3 stood out with a 50% effective concentration (EC₅₀) of 0.21 and 0.19 µM against promastigotes and intracellular amastigotes of L. donovani, respectively, 0.24 µM against intracellular amastigotes of T. cruzi, 0.09 µM against T. brucei, 1.4 µM against N. fowleri and impaired adult S. mansoni viability at 1.25 µM. In terms of host/pathogen selectivity, MS26Et3 demonstrated relatively mild cytotoxicity toward host cells with a 50% viability concentration of 4.87 µM against B10R cells (mouse monocyte cell line), 2.79 µM against C2C12 cells (mouse myoblast cell line) and 1.24 µM against HEK923 cells (human embryonic kidney cell line). The selectivity index supports this molecule as a therapeutic starting point for a broad spectrum antiparasitic alternative. Proteomic analysis of host cells infected with L. donovani after exposure to MS26Et3 showed a reduced expression of Rab7, which may affect the fusion of the endosome with the lysosome, and, consequently, impairing the differentiation of L. donovani to the amastigote form. Future studies to investigate the molecular target(s) and mechanism of action of MS26Et3 will support its chemical optimization.

Copper (II) complexes with N, S donor pyrazole-based ligands as anticancer agents

A group of bidentate nitrogen and sulfur donor pyrazole derivative ligands abbreviated as Na[RNCS(Pz)], Na[RNCS(Pz^Me2)], Na[RNCS(Pz^Me3)], Na[RNCS(Pz^PhMe)], Na[RNCS(Pz^Ph2)], where (R = Et, Ph), and their Cu (II) complexes were synthesized and characterized by spectroscopic and physicochemical methods. The crystal structure of [Cu(PhNCSPz^Me3)₂] was determined by X-ray crystallography analysis and the results described a distorted square planar coordination geometry for this complex. Also, the cyclic voltammetry investigations indicated that the synthesized copper complex is an electrochemically active species. Moreover, the cytotoxic activity of all of the twenty synthesized compounds was evaluated using MTT assay against the MCF-7 (human breast carcinoma) cell lines, in vitro. Cu (II) complexes indicate significant cytotoxicity against the MCF-7 cell lines as compared with the free ligands. The docking studies showed that the copper complexes have better interactions with EGFR and CDK2 proteins, compared to the free ligands, and most of the studied compounds have a higher value of binding energy relative to the studied controls. The results of QSAR analysis suggest that dipole moment is in direct correlation with the obtained IC₅₀ values, and it strongly impact the anticancer effects generated by the compounds. Our findings suggest that the developed copper complexes can be good candidates for further evaluations as chemotherapeutic agents in the treatment of cancer.

Facing Diseases Caused by Trypanosomatid Parasites: Rational Design of Pd and Pt Complexes With Bioactive Ligands

Human African Trypanosomiasis (HAT), Chagas disease or American Trypanosomiasis (CD), and leishmaniases are protozoan infections produced by trypanosomatid parasites belonging to the kinetoplastid order and they constitute an urgent global health problem. In fact, there is an urgent need of more efficient and less toxic chemotherapy for these diseases. Medicinal inorganic chemistry currently offers an attractive option for the rational design of new drugs and, in particular, antiparasitic ones. In this sense, one of the main strategies for the design of metal-based antiparasitic compounds has been the coordination of an organic ligand with known or potential biological activity, to a metal centre or an organometallic core. Classical metal coordination complexes or organometallic compounds could be designed as multifunctional agents joining, in a single molecule, different chemical species that could affect different parasitic targets. This review is focused on the rational design of palladium(II) and platinum(II) compounds with bioactive ligands as prospective drugs against trypanosomatid parasites that has been conducted by our group during the last 20 years.

Nickel (II) chloride schiff base complex: Synthesis, characterization, toxicity, antibacterial and leishmanicidal activity

The use of schiff base complex against microbial agentes a has recently received more attention as a strategy to combat infections caused by multidrug-resistant bacteria and leishmania. This study aimed to evaluate the toxicity, antibacterial and leishmanicidal activities of the nickel (II) chloride schiff base complex ([Ni(L2)] against Leishmania amazonensis promastigote, multi-resistant bacterial strains and evaluate to modulate antibiotic activity against multi-resistant bacterial. The schiff base complex was characterized by the techniques of elemental analysis, Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy and thermal analysis (TGA/DTG/DSC). The [Ni(L2)] complex presented moderate toxicity in saline artemia (LC₅₀ = 150.8 μg/mL). In leishmanicidal assay, the NiL2 complex showed values of IC₅₀ of (6.079 μg/mL ± 0.05656 at the 24 h), (0.854 μg/mL ± 0.02474, 48 h) and (1.076 μg/mL ± 0.04039, 72 h). In antibacterial assay, the [Ni(L2)] complex presented significant inhibited the bacterial growth of P. aeruginosa (MIC = 256 μg/mL). However, [Ni(L2)] complex did not present clinically relevant minimum inhibitory concentration (MIC ≥1024 μg/mL) against S. aureus and E. coli. The combination of [Ni(L2)] complex and antibacterial drugs resulted in the increased antibiotic activity of gentamicin and amikacin against S. aureus and E.coli multi-resistant strains. Thus, our results showed that [Ni(L2)] complex is a promising molecule for the development of new therapies associated with aminoglycoside antibiotics and in disease control related to resistant bacteria and leishmaniasis.

Heteroleptic Oxidovanadium(V) Complexes with Activity against Infective and Non-Infective Stages of Trypanosoma cruzi

Five heteroleptic compounds, [VVO(IN-2H)(L-H)], where L are 8-hydroxyquinoline derivatives and IN is a Schiff base ligand, were synthesized and characterized in both the solid and solution state. The compounds were evaluated on epimastigotes and trypomastigotes of Trypanosoma cruzi as well as on VERO cells, as a mammalian cell model. Compounds showed activity against trypomastigotes with IC50 values of 0.29-3.02 μM. IN ligand and the new [VVO2(IN-H)] complex showed negligible activity. The most active compound [VVO(IN-2H)(L2-H)], with L2 = 5-chloro-7-iodo-8-hydroxyquinoline, showed good selectivity towards the parasite and was selected to carry out further biological studies. Stability studies suggested a partial decomposition in solution. [VVO(IN-2H)(L2-H)] affects the infection potential of cell-derived trypomastigotes. Low total vanadium uptake by parasites and preferential accumulation in the soluble proteins fraction were determined. A trypanocide effect was observed when incubating epimastigotes with 10 × IC50 values of [VVO(IN-2H)(L2-H)] and the generation of ROS after treatments was suggested. Fluorescence competition measurements with DNA:ethidium bromide adduct showed a moderate DNA interaction of the complexes. In vivo toxicity study on C. elegans model showed no toxicity up to a 100 μM concentration of [VVO(IN-2H)(L2-H)]. This compound could be considered a prospective anti-T. cruzi agent that deserves further research.

High Throughput Approaches to Unravel the Mechanism of Action of a New Vanadium-Based Compound against Trypanosoma cruzi

Treatment for Chagas disease, a parasitosis caused by Trypanosoma cruzi, has always been based on two drugs, nifurtimox and benznidazole, despite the toxic side effects described after prolonged prescription. In this work, we study a new prospective antitrypanosomal drug based on vanadium, here named V^IVO(5Brsal)(aminophen). We found a good IC₅₀ value, (3.76 ± 0.08) μM, on CL Brener epimastigotes. The analysis of cell death mechanism allowed us to rule out the implication of a mechanism based on early apoptosis or necrosis. Recovery assays revealed a trypanostatic effect, accompanied by cell shape and motility alterations. An uptake mostly associated with the insoluble fraction of the parasites was deduced through vanadium determinations. Concordantly, no drastic changes of the parasite transcriptome were detected after 6 h of treatment. Instead, proteomic analysis uncovered the modulation of proteins involved in different processes such as energy and redox metabolism, transport systems, detoxifying pathways, ribosomal protein synthesis, and proteasome protein degradation. Overall, the results here presented lead us to propose that V^IVO(5Brsal)(aminophen) exerts a trypanostatic effect on T. cruzi affecting parasite insoluble proteins.

Synthesis, crystal structure and leishmanicidal activity of new trimethoprim Ru(III), Cu(II) and Pt(II) metal complexes

Leishmaniasis is a parasitic disease caused by protozoa of the genus Leishmania, which has very limited treatment options and affects poor and underdeveloped populations. The current treatment is plagued by many complications, such as high toxicity, high cost and resistance to parasites; therefore, novel therapeutic agents are urgently needed. Herein, the synthesis, characterization and in vitro leishmanicidal potential of new complexes with the general formula [RuCl₃(TMP)(dppb)] (1), [PtCl(TMP)(PPh₃)₂]PF₆ (2) and [Cu(CH₃COO)₂(TMP)₂]·DMF (3) (dppb = 1,4-bis(diphenylphosphino)butane, PPH₃ = triphenylphosphine and TMP = trimethoprim) were evaluated. The complexes were characterized by infrared, UV-vis, cyclic voltammetry, molar conductance measurements, elemental analysis and NMR experiments. Also, the geometry of (2) and (3) were determined by single crystal X-ray diffraction. Despite being less potent against promastigote L. amazonensis proliferation than amphotericin B reference drug (IC₅₀ = 0.09 ± 0.02 μM), complex (2) (IC₅₀ = 3.6 ± 1.5 μM) was several times less cytotoxic (CC₅₀ = 17.8 μM, SI = 4.9) in comparison with amphotericin B (CC₅₀ = 3.3 μM, SI = 36.6) and gentian violet control (CC₅₀ = 0.8 μM). Additionally, complex (2) inhibited J774 macrophage infection and amastigote number by macrophages (IC₅₀ = 6.6 and SI = 2.7). Outstandingly, complex (2) was shown to be a promising candidate for a new leishmanicidal therapeutic agent, considering its biological power combined with low toxicity.

Cu(II) and Ni(II) Complexes with New Tridentate NNS Thiosemicarbazones: Synthesis, Characterisation, DNA Interaction, and Antibacterial Activity

This paper reports the synthesis and detailed characterisation of copper(II) and nickel(II) complexes with tridentate thiosemicarbazone ligands H 2 L1 and H 2 L2 derived from 2-acetylpyrazine. The ligands and their metal complexes were characterised by different physicochemical techniques, including elemental and thermogravimetric analysis; UV-Vis, IR, 1H-NMR, and 13C-NMR spectroscopy; molar conductance measurements; and mass spectrometry. The crystal structure of the H 2 L1 ligand was determined by single crystal X-ray diffraction studies. The spectral data showed that the thiosemicarbazone behaves as an NNS tridentate ligand through the nitrogen atoms of the azomethine group and pyrazine ring and the sulphur atom of the thioamide group. Elemental and thermal analyses indicated that the obtained metal complexes had a 1 : 1 stoichiometry (metal-ligand). The interactions between these complexes and calf thymus DNA (CT-DNA) were studied by electronic absorption and viscosity measurements. The activities of these compounds against oxidative DNA cleavage were examined by agarose gel electrophoresis. Cu(II) and Ni(II) complexes can wind DNA strands through groove interactions and promote strand breakage of the plasmid pmCherry under oxidative stress conditions. Moreover, all the complexes could interact more strongly with DNA than could with the free ligands. Finally, the antibacterial activities of the ligands and their complexes were determined by in vitro tests against Gram-positive bacterial strains (S. aureus ATCC 25923, L. monocytogenes ATCC 19115, and B. cereus ATCC 10876) and Gram-negative bacterial strains (E. coli ATCC 25922, S. typhimurium ATCC 14028, and K. pneumoniae ATCC BAA-2146) using the broth microdilution method. The metal complexes showed greater antimicrobial activities than the precursor ligands against some of the microorganisms.

Exploring oxidovanadium(iv) homoleptic complexes with 8-hydroxyquinoline derivatives as prospective antitrypanosomal agents

[V^IVO(L-H)₂] and [V^VO(OCH₃)(L-H)₂] compounds of 8-hydroxyquinoline derivatives L showed activity againstTrypanosoma cruziandLeishmania infantumand high selectivities. Metallomics and interaction with BSA, apo-HTF and DNA were studied.

Synthesis, characterization, and antileishmanial activity of neutral N-heterocyclic carbenes gold(I) complexes

A series of five new mononuclear neutral gold(I) complexes containing N-heterocyclic carbenes (NHCs) was synthesized and fully characterized by spectroscopic methods. The X-ray structures of four complexes are presented. These gold(I) complexes together with four other neutral gold(I)-NHC complexes previously described were evaluated in vitro against Leishmania infantum promastigotes and axenic amastigotes. Moreover, their cytotoxicity was assessed on the murine macrophages J774A.1. Except one complex (10), eight gold(I)-NHC-Cl complexes show potent activity against the pathological relevant form of L. infantum amastigote with IC₅₀ in the low micromolar and submicromolar range and five of them exhibit a SI close to 10. The lead-complex 11 displays a very high and selective activity (IC₅₀ = 190 nM, SI = 40.29) and constitutes the best promising gold(I)-based drug of this series.

New iminodibenzyl derivatives with anti-leishmanial activity

Leishmaniasis is an infection caused by protozoa of the genus Leishmania and transmitted by sandflies. Current treatments are expensive and time-consuming, involving Sb(V)-based compounds, lipossomal amphotericin B and miltefosine. Recent studies suggest that inhibition of trypanothione reductase (TR) could be a specific target in the development of new drugs because it is essential and exclusive to trypanosomatids. This work presents the synthesis and characterization of new iminodibenzyl derivatives (dado) with ethylenediamine (ea), ethanolamine (en) and diethylenetriamine (dien) and their copper(II) complexes. Computational methods indicated that the complexes were highly lipophilic. Pro-oxidant activity assays by oxidation of the dihydrorhodamine (DHR) fluorimetric probe showed that [Cu(dado-ea)]²⁺ has the highest rate of oxidation, independent of H₂O₂ concentration. The toxicity to L. amazonensis promastigotes and RAW 264,7 macrophages was assessed, showing that dado-en was the most active new compound. Complexation to copper did not have an appreciable effect on the toxicity of the compounds.

Introducing New Antimalarial Analogues of Chloroquine and Amodiaquine: A Narrative Review

Antimalarial drugs with the 4-aminoquinoline scaffold such as the important drugs, chloroquine (CQ) and amodiaquine (AQ), have been used to prevent and treat malaria for many years. The importance of these drugs is related to their simple usage, high efficacy, affordability, and cost-effectiveness of their synthesis. In recent years, with the spread of parasite resistance to CQ and cross-resistance to its other analogues have decreased their consumption in many geographical areas. On the other hand, AQ is an effective antimalarial drug which its usage has been restricted due to hepatic and hematological toxicities. The significance of the quinoline ring at quinoline-based antimalarial drugs has prompted research centers and pharmaceutical companies to focus on the design and synthesis of new analogues of these drugs, especially CQ and AQ analogues. Accordingly, various derivatives have been synthesized and evaluated in vitro and in vivo against the resistant strains of the malaria parasite to solve the problem of drug resistance. Also, the pharmacokinetic properties of these compounds have been evaluated to augment their efficacy and diminish their toxicity. Some of these analogues are currently in clinical and preclinical development. Consequently, the recent researches showed yet 4-aminoquinoline scaffold is active moiety in new compounds with antiplasmodial activity. Hence, the aim of this review article is to introduce of the novel synthetic analogues of CQ and AQ, which may constitute the next generation of antimalarial drugs with the 4-aminoquinoline scaffold.

X-ray Structure Analysis of Indazolium trans-[Tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019) Bound to Human Serum Albumin Reveals Two Ruthenium Binding Sites and Provides Insights into the Drug Binding Mechanism

Ruthenium(III) complexes are promising candidates for anticancer drugs, especially the clinically studied indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019) and its analogue sodium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (NKP-1339). Several studies have emphasized the likely role of human serum proteins in the transportation and accumulation of ruthenium(III) complexes in tumors. Therefore, the interaction between KP1019 and human serum albumin was investigated by means of X-ray crystallography and inductively coupled plasma mass spectrometry (ICP-MS). The structural data unambiguously reveal the binding of two ruthenium atoms to histidine residues 146 and 242, which are both located within well-known hydrophobic binding pockets of albumin. The ruthenium centers are octahedrally coordinated by solvent molecules revealing the dissociation of both indazole ligands from the ruthenium-based drug. However, a binding mechanism is proposed indicating the importance of the indazole ligands for binding site recognition and thus their indispensable role for the binding of KP1019.

Exploiting the potential of aryl acetamide derived Zn(ii) complexes in medicinal chemistry: synthesis, structural analysis, assessment of biological profile and molecular docking studies

This study reports an unprecedented series of aryl acetamide derived Zn(ii) complexes as frontline enzyme inhibitors as well as anticancer and anti-parasitic agents.

Editorial of Special Issue Ruthenium Complex: The Expanding Chemistry of the Ruthenium Complexes

Recent trends in Ru complex chemistry are surveyed with emphasis on the development of anticancer drugs and applications in catalysis, polymers, materials science and nanotechnology.

Synthesis, characterization, and antileishmanial activities of gold(I) complexes involving quinoline functionalized N-heterocyclic carbenes

A series of new mononuclear cationic or neutral gold(I) complexes containing quinoline functionalized N-heterocyclic carbene(s) (NHC(s)) were synthesized and fully characterized by spectroscopic methods. The X-ray structures of two key compounds are presented. Proligands and their corresponding gold(I) complexes together with previously described silver(I) and gold(I) bis(NHC-quinoline) and gold(I) bis(NHC-methylbipyridine) complexes were evaluated in vitro towards Leishmania infantum. In parallel, the in vitro cytotoxicity of these molecules was assessed on the murine macrophages J774A.1. All gold(I) compounds show potent antileishmanial activity against L. infantum promastigotes and three of them are also efficient against L. infantum intracellular amastigotes. Structure-activity and toxicity relationships enables to evidence a lead-compound (6) displaying both a high activity and a good selectivity index.