CO-releasing properties and anticancer activities of manganese complexes with imidazole/benzimidazole ligands

Metal-based carbon monoxide releasing molecules with promising cytotoxic properties

Carbon monoxide, the "silent killer" gas, is increasingly recognised as an important signalling molecule in human physiology, which has beneficial biological properties. A particular way of achieving controlled CO administration is based on the use of biocompatible molecules that only release CO when triggered by internal or external factors. These approaches include the development of pharmacologically effective prodrugs known as CO releasing molecules (CORMs), which can supply biological systems with CO in well-regulated doses. An overview of transition metal-based CORMs with cytotoxic properties is here reported. The mechanisms at the basis of the biological activities of these molecules and their potential therapeutical applications with respect to their stability and CO releasing properties have been discussed. The activation of metal-based CORMs is determined by the type of metal and by the nature and features of the auxiliary ligands, which affect the metal core electronic density and therefore the prodrug resistance towards oxidation and CO release ability. A major role in regulating the cytotoxic properties of these CORMs is played by CO and/or CO-depleted species. However, several mysteries concerning the cytotoxicity of CORMs remain as intriguing questions for scientists.

Synthesis, antimicrobial activity and molecular docking study of benzyl functionalized benzimidazole silver(I) complexes

In this study, a series of N-functionalized benzimidazole silver(I) complexes were prepared and characterized by FT-IR, 1H, 13C{1H} NMR spectroscopy, and elemental analysis. Synthesized N-benzylbenzimidazole silver(I) complexes were evaluated for their antimicrobial activities against bacteria Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and the fungal strains Candida albicans and Candida glabrata. The results indicated that N-alkylbenzimidazole silver(I) complexes exhibited good antimicrobial activity compared to N-alkylbenzimidazole derivatives. Especially, complex 2e presented perfect antimicrobial activity than the other complexes. The characterized molecules were optimized by DFT-based calculation methods and the optimized molecules were analyzed in detail by molecular docking methods against bacterial DNA-gyrase and CYP51. The amino acid residues detected for both target molecules are consistent with expectations, and the calculated binding affinities and inhibition constants are promising for further studies. A series of N-alkylbenzimidazole silver(I) complexes were synthesized and fully characterized by means of 1H NMR, 13C NMR, and FT-IR spectroscopies. Synthesized N-alkylbenzimidazole silver(I) complexes were investigated for their antimicrobial activities against bacteria Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and the fungal strains Candida albicans and Candida glabrata. All complexes showed better activity according to Ampicilin against Pseudomonas aeruginosa. The molecules which were firstly optimized by DFT-based calculation methods were also analyzed by molecular docking methods against DNA gyrase of E. Coli and CYP51. 338 × 190 mm (96 × 96 DPI).

Comprehensive Insights into Medicinal Research on Imidazole-Based Supramolecular Complexes

The electron-rich five-membered aromatic aza-heterocyclic imidazole, which contains two nitrogen atoms, is an important functional fragment widely present in a large number of biomolecules and medicinal drugs; its unique structure is beneficial to easily bind with various inorganic or organic ions and molecules through noncovalent interactions to form a variety of supramolecular complexes with broad medicinal potential, which is being paid an increasing amount of attention regarding more and more contributions to imidazole-based supramolecular complexes for possible medicinal application. This work gives systematical and comprehensive insights into medicinal research on imidazole-based supramolecular complexes, including anticancer, antibacterial, antifungal, antiparasitic, antidiabetic, antihypertensive, and anti-inflammatory aspects as well as ion receptors, imaging agents, and pathologic probes. The new trend of the foreseeable research in the near future toward imidazole-based supramolecular medicinal chemistry is also prospected. It is hoped that this work provides beneficial help for the rational design of imidazole-based drug molecules and supramolecular medicinal agents and more effective diagnostic agents and pathological probes.

Molybdenum Carbonyl Complexes with Benzimidazole Derivatives Against SARS-CoV-2 by Molecular Docking and DFT/TDDFT Methods

Benzimidazole derivative molecules attract attention of scientists due to their bioactivities. The dramatic changes in recorded activities according to the type and position of the substituents motivate synthesis and analysis of new molecules. Commercial benzimidazole-based molecules have been used in therapeutic procedures. It is known that the activities of metal complexes with benzimidazole derivative ligands have different activities when compared to the benzimidazole main structure. Nowadays, one of the most important health problems is COVID-19, which caused the pandemic that we are still experiencing. Although vaccine studies are important to overcome acute problems, regarding the possible post-vaccination adverse effects, the need for new drugs against the virus is obvious. Considering the urgency and the limited facilities during the pandemic, preliminary in silico studies of candidate molecules are essential. In this study, {[bis-(N-benzylbenzimidazole)] tetracarbonylmolybdenum}, {[bis-(N-4-chlorobenzylbenzimidazole)] tetracarbonylmolybdenum} and {[bis-(N-4-methoxybenzylbenzimidazole)] tetracarbonylmolybdenum} were synthesized and characterized. The optimization and the structural analysis of these molecules were performed by DFT/TDDFT methods. The molecules were docked into SARS coronavirus main peptidase (PDB ID: 2gtb), COVID-19 main protease in complex with Z219104216 (PDB ID: 5r82), COVID-19 main protease in complex with an inhibitor N3 (PDB ID: 6lu7) and Papain-like protease of SARS-CoV-2 (PDB ID: 6w9c) crystal structures for evaluation of their anti-viral activity.

Synthesis, characterization, antimicrobial and antibiofilm activity, and molecular docking analysis of NHC precursors and their Ag-NHC complexes

Microorganisms attach to surfaces and interfaces and form biofilms which create a sheltered area for host cell response. Therefore, biofilms provide troubles in fields such as medicine, food, and pharmaceuticals. Inhibition of formation of biofilms through hindering of quorum sensing could be a method for the production of new generation antibiotics. In this study, four new benzimidazole type NHC precursors (1-allyl-3-benzyl-5,6-dimethylbenzimidazolium chloride, 1-allyl-3-(2,4,6-trimethylbenzyl)-5,6-dimethylbenzimidazolium chloride, 1-allyl-3-(2,3,5,6-tetramethylbenzyl)-5,6-dimethylbenzimidazolium chloride, and 1-allyl-3-(2,3,4,5,6-pentamethylbenzyl)-5,6-dimethylbenzimidazolium chloride and Ag-NHC complexes of these molecules were synthesized and characterized by elemental analysis, FT-IR spectroscopy, ¹H, and ¹³C{¹H} NMR spectroscopy, LC-MS, and single crystal crystallography. Antimicrobial and biofilm formation inhibition activities of the molecules were evaluated. In addition, the activities of the molecules were examined in detail by molecular docking analysis. According to the results obtained, higher activity was achieved with the complex molecules when compared with the benzimidazole derivative ligands.

Light-activated cytotoxicity of dicarbonyl Ru(II) complexes with a benzimidazole coligand towards breast cancer

Reaction between [RuCl₂(CO)₂]_n and 1H-benzimidazol-2-ylmethyl-(N-phenyl)amine ligands (L^R) functionalized with various electron-donating and electron-withdrawing substituents on the phenyl ring (R = H, 4-CH₃, 4-Cl, 4-COOCH₃, and 3-COOCH₃) afforded the dark-stable photoactivatable carbon monoxide prodrugs of the general formula [RuCl₂(CO)₂L^R]. Release of the CO molecules from the Ru(II) compounds was examined by monitoring the electronic and IR spectra upon illumination at 365 nm. A noticeable decrease in the intensities of the two characteristic ν(CO) modes for Ru(CO)II2 species, and the growth of two new bands for the mono-carbonyl species and free CO, were the main features of the photolysis profiles. The cytotoxicity of the complexes towards breast cancer (MCF-7) cells was assessed with and without illumination at 365 nm. All the complexes except that with a 4-COOCH₃ group (IC₅₀ = 45.08 ± 3.5 μM) are nontoxic under dark conditions. Upon illumination, all the compounds acquired cytotoxicity in the following order: H > 4-COOCH₃ > 4-CH₃ > 4-Cl > 3-COOCH₃. Investigation of the cytotoxicity of the CO-depleted fragments showed that the light-induced cytotoxicity can be attributed to the liberated CO and CO-depleted metal fragments, including the liberated benzimidazole ligands.

Manganese(I) tricarbonyl complexes as potential anticancer agents

The antiproliferative activity of [Mn(CO)₃(N^N)Br] (N^N = phendione 1, bipy 3) and of the two newly synthesized Mn complexes [Mn(CO)₃(acridine)(phendione)]OTf (2) and [Mn(CO)₃(di-triazole)Br] (4) has been evaluated by MTS against three tumor cell lines A2780 (ovarian carcinoma), HCT116 (colorectal carcinoma), HCT116doxR (colorectal carcinoma resistant to doxorubicin), and in human dermal fibroblasts. The antiproliferative assay showed a dose-dependent effect higher in complex 1 and 2 with a selectivity toward ovarian carcinoma cell line 21 times higher than in human fibroblasts. Exposure of A2780 cells to IC₅₀ concentrations of complex 1 and 2 led to an increase of reactive oxygen species that led to the activation of cell death mechanisms, namely via intrinsic apoptosis for 2 and autophagy and extrinsic apoptosis for 1. Both complexes do not target DNA or interfere with cell cycle progression but are able to potentiate cell migration and neovascularization (for 2) an indicative that their application might be directed for initial tumor stages to avoid tumor invasion and metastization and opening a new avenue for complex 2 application in regenerative medicine. Interestingly, both complexes do not show toxicity in both in vivo models (CAM and zebrafish).

The potentials of carbon monoxide-releasing molecules in cancer treatment: An outlook from ROS biology and medicine

Carbon monoxide (CO) is now well recognized a pivotal endogenous signaling molecule in mammalian lives. The proof-of-concept employing chemical carriers of exogenous CO as prodrugs for CO release, also known as CO-releasing molecules (CO-RMs), has been appreciated. The major advantage of CO-RMs is that they are able to deliver CO to the target sites in a controlled manner. There is an increasing body of experimental studies suggesting the therapeutic potentials of CO and CO-RMs in different cancer models. This review firstly presents a short but crucial view concerning the characteristics of CO and CO-RMs. Then, the anticancer activities of CO-RMs that target many cancer hallmarks, mainly proliferation, apoptosis, angiogenesis, and invasion and metastasis, are discussed. However, their anticancer activities are varying and cell-type specific. The aerobic metabolism of molecular oxygen inevitably generates various oxygen-containing reactive metabolites termed reactive oxygen species (ROS) which play important roles in both physiology and pathophysiology. Although ROS act as a double-edged sword in cancer, both sides of which may potentially have been exploited for therapeutic benefits. The main focus of the present review is thus to identify the possible signaling network by which CO-RMs can exert their anticancer actions, where ROS play the central role. Another important issue concerning the potential effect of CO-RMs on the aerobic glycolysis (the Warburg effect) which is a feature of cancer metabolic reprogramming is given before the conclusion with future prospects on the challenges of developing CO-RMs into clinically pharmaceutical candidates in cancer therapy.

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CO-RMs as pro-drugs for controlled CO delivery are potentially beneficial in cancer treatment.

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Anticancer activities of CO-RMs are varying and cell-type specific.

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Anti-proliferative, pro-apoptotic, and anti-angiogenic effects are major niches.

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ROS may play a central role in the molecular pathways underlying anticancer activities of CO-RMs.

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CO-RMs can act against Warburg effect, a feature of cancer metabolic reprogramming.

Metal-Free Synthesis of Benzimidazoles via Oxidative Cyclization of d-Glucose with o-Phenylenediamines in Water

d-Glucose has been identified as an efficient C1 synthon in the synthesis of benzimidazoles from o-phenylenediamines via an oxidative cyclization strategy. Isotopic studies with ¹³C₆-d-glucose and D₂O unambiguously confirmed the source of methine. The notable features of this method include the following: broad functional group tolerance, a biorenewable methine source, excellent reaction yields, a short reaction time, water as an environmentally benign solvent, and the synthesis of vitamin B₁₂ component on the gram scale.

Cytotoxicity of Mn-based photoCORMs of ethynyl-α-diimine ligands against different cancer cell lines: The key role of CO-depleted metal fragments

A series of tricarbonyl manganese complexes bearing 4-ethynyl-2,2'-bipyridine and 5-ethynyl-1,10-phenanthroline α-diimine ligands were synthetized, characterized and conjugated to vitamin B₁₂, previously used as a vector for drug delivery, to take advantage of its water solubility and specificity toward cancer cells. The compounds act as photoactivatable carbon monoxide-releasing molecules rapidly liberating on average ca. 2.3 equivalents of CO upon photo-irradiation. Complexes and conjugates were tested for their anticancer effects, both in the dark and following photo-activation, against breast cancer MCF-7, lung carcinoma A549 and colon adenocarcinoma HT29 cell lines as well as immortalized human bronchial epithelial cells 16HBE14o- as the non-carcinogenic control. Our results indicate that the light-induced cytotoxicity these molecules can be attributed to both their released CO and to their CO-depleted metal fragments including liberated ligands.

Photoactivated [Mn(CO)3Br(μ-bpcpd)]2 induces apoptosis in cancer cells via intrinsic pathway

Carbon monoxide releasing molecules (CORMs) are organometallic/organic compounds that release carbon monoxide (CO) spontaneously or upon activation. PhotoCORMs are capable of releasing CO on light based activation. This group of molecules is used in photodynamic therapy due to their ability to release CO in a controlled manner. In the present investigation, the release of CO from [Mn(CO)₃Br(μ-bpcpd)]₂ (MnCORM) upon irradiation at λ_max 365 nm was assessed spectrophotometrically using myoglobin assay and confirmed by liquid FT-IR spectroscopic analysis. Further, the cytotoxic potential of MnCORM on normal cells (HEK 293) and cancer cell lines such as lung (A549), cervical (HeLa), breast (MDA MB-231) and colon (HCT-15) was evaluated. The IC₅₀ values of MnCORM were found to be 21.37 ± 1.72, 24.12 ± 1.03, 21.89 ± 0.59 and 13.69 ± 0.91 μM on cervical (HeLa), lung (A549), colon (HCT-15) and breast (MDA MB-231) cancer cells respectively. An inquest into the nature of cell death was confirmed based on the nuclear and cytological examinations, flow cytometric analyses and protein expression studies. The AO/EB dual staining and cytological evaluation of the treated cells revealed that the cell death might be due to apoptosis. The flow cytometric analysis of propidium iodide (PI) stained cells showed a significant amount of sub-G1 hypodiploid cells due to MnCORM treatment. The MnCORM-induced apoptosis was mediated through the generation of reactive oxygen species (ROS), specifically superoxide radicals leading to loss of mitochondrial membrane potential. The intrinsic pathway of apoptosis was elucidated based on the expression studies of pro-apoptotic and apoptotic proteins such as bcl-2, bax, cyt c, cleaved caspase-3, cleaved caspase-9 and cleaved PARP. Due to its innate potential to release CO upon photoactivation and its ability to induce apoptosis via intrinsic pathway, the MnCORM molecule could be exploited for controlled release and photodynamic cancer therapy.

Visible-Light-Activated Quinolone Carbon-Monoxide-Releasing Molecule: Prodrug and Albumin-Assisted Delivery Enables Anticancer and Potent Anti-Inflammatory Effects

The delivery of controlled amounts of carbon monoxide (CO) to biological targets is of significant current interest. Very few CO-releasing compounds are currently known that can be rigorously controlled in terms of the location and amount of CO released. To address this deficiency, we report herein a new metal-free, visible-light-induced CO-releasing molecule (photoCORM) and its prodrug oxidized form, which offer new approaches to controlled, localized CO delivery. The new photoCORM, based on a 3-hydroxybenzo[ g]quinolone framework, releases 1 equiv of CO upon visible-light illumination under a variety of biologically relevant conditions. This nontoxic compound can be tracked prior to CO release using fluorescence microscopy and produces a nontoxic byproduct following CO release. An oxidized prodrug form of the photoCORM is reduced by cellular thiols, providing an approach toward activation in the reducing environment of cancer cells. Strong noncovalent affinity of the nonmetal photoCORM to albumin enables use of an albumin:photoCORM complex for targeted CO delivery to cancer cells. This approach produced cytotoxicity IC₅₀ values among the lowest reported to date for CO delivery to cancer cells by a photoCORM. This albumin:photoCORM complex is also the first CO delivery system to produce significant anti-inflammatory effects when introduced at nanomolar photoCORM concentration.

Photoactivated in Vitro Anticancer Activity of Rhenium(I) Tricarbonyl Complexes Bearing Water-Soluble Phosphines

Fifteen water-soluble rhenium compounds of the general formula [Re(CO)3(NN)(PR3)]+, where NN is a diimine ligand and PR3 is 1,3,5-triaza-7-phosphaadamantane (PTA), tris(hydroxymethyl)phosphine (THP), or 1,4-diacetyl-1,3,7-triaza-5-phosphabicylco[3.3.1]nonane (DAPTA), were synthesized and characterized by multinuclear NMR spectroscopy, IR spectroscopy, and X-ray crystallography. The complexes bearing the THP and DAPTA ligands exhibit triplet-based luminescence in air-equilibrated aqueous solutions with quantum yields ranging from 3.4 to 11.5%. Furthermore, the THP and DAPTA complexes undergo photosubstitution of a CO ligand upon irradiation with 365 nm light with quantum yields ranging from 1.1 to 5.5% and sensitize the formation of 1O2 with quantum yields as high as 70%. In contrast, all of the complexes bearing the PTA ligand are nonemissive and do not undergo photosubstitution upon irradiation with 365 nm light. These compounds were evaluated as photoactivated anticancer agents in human cervical (HeLa), ovarian (A2780), and cisplatin-resistant ovarian (A2780CP70) cancer cell lines. All of the complexes bearing THP and DAPTA exhibited a cytotoxic response upon irradiation with minimal toxicity in the absence of light. Notably, the complex with DAPTA and 1,10-phenanthroline gave rise to an IC50 value of 6 μM in HeLa cells upon irradiation, rendering it the most phototoxic compound in this library. The nature of the photoinduced cytotoxicity of this compound was explored in further detail. These data indicate that the phototoxic response may result from the release of both CO and the rhenium-containing photoproduct, as well as the production of 1O2.

Aspects of Carbon Monoxide in Form of CO-Releasing Molecules Used in Cancer Treatment: More Light on the Way

Carbon monoxide (CO) has always been recognised as a toxic gas, due to its higher affinity for haemoglobin than oxygen. However, biological studies have revealed an intriguing role for CO as an endogenous signalling molecule, a gasotransmitter. CO is demonstrated to exert many cellular activities including anti-inflammatory, antiapoptotic, and antiproliferative activities. In animal studies, CO gas administration can prevent tissues from hypoxia or ischemic-reperfusion injury. As a result, there are a plethora of reports dealing with the biological applications of CO and CO-releasing molecules (CORMs) in inflammatory and vascular diseases. CORMs have already been tested as a therapeutic agent in clinical trials. More recently, an increased interest has been drawn to CO's potential use as an anticancer agent. In this review, we will aim to give an overview of the research focused on the role of CO and CORMs in different types of cancer and expand to the recent development of the next generation CORMs for clinical application in cancer treatment.