Dinitrosyl iron complexes with glutathione suppress experimental endometriosis in rats

1,3,5-Triaza-7-phosphaadamantane and Cyclohexyl Groups Impart to Di-Iron(I) Complex Aqueous Solubility and Stability, and Prominent Anticancer Activity in Cellular and Animal Models

Using a multigram-scalable synthesis, we obtained nine dinuclear complexes based on nonendogenous iron(I) centers and featuring variable aminocarbyne and P-ligands. One compound from the series (FEACYP) emerged for its strong cytotoxicity in vitro against four human cancer cell lines, surpassing the activity of cisplatin by 3-6 times in three cell lines, with an average selectivity index of 6.2 compared to noncancerous HEK293 cells. FEACYP demonstrated outstanding water solubility (15 g/L) and stability in physiological-like solutions. It confirmed its superior antiproliferative activity when tested in 3D spheroids of human pancreatic cancer cells and showed a capacity to inhibit thioredoxin reductase (TrxR) similar to auranofin. In vivo treatment of murine LLC carcinoma with FEACYP (8 mg kg-1 dose) led to excellent tumor growth suppression (88%) on day 15, with no signs of systemic toxicity and only limited body weight loss.

Beneficial Effects of Dinitrosyl Iron Complexes on Wound Healing Compared to Commercial Nitric Oxide Plasma Generator

Nitric oxide (NO) is a gaseous molecule which plays a key role in wound healing. Previously, we identified the optimal conditions for wound healing strategies using NO donors and an air plasma generator. The aim of this study was to compare the wound healing effects of binuclear dinitrosyl iron complexes with glutathione (B-DNIC-GSH) and NO-containing gas flow (NO-CGF) at their optimal NO doses (0.04 mmol for B-DNIC-GSH and 1.0 mmol for NO-CGF per 1 cm²) in a rat full-thickness wound model over a 3-week period. Excised wound tissues were studied by light and transmission electron microscopy and immunohistochemical, morphometrical and statistical methods. Both treatments had an identical stimulating impact on wound healing, which indicated a higher dosage effectiveness of B-DNIC-GSH compared to the NO-CGF. B-DNIC-GSH spray application reduced inflammation and promoted fibroblast proliferation, angiogenesis and the growth of granulation tissue during the first 4 days after injury. However, prolonged NO spray effects were mild compared to NO-CGF. Future studies should determine the optimal B-DNIC-GSH solution course for a more effective wound healing stimulation.

Spray with Nitric Oxide Donor Accelerates Wound Healing: Potential Off-the-Shelf Solution for Therapy?

Background

Ditrosyl iron complexes (DNIC) are endogenous donors of nitric oxide. The possibility of their application to stimulate regeneration has been studied for more than 15 years. However, the most effective dose and form of delivery have not yet been determined.

Purpose

The aim of this research was to develop a spray form of DNIC that accelerates wound healing.

Methods

We prepared a series of DNIC sprays with spray dosages of 10, 50 and 100 μg. We modelled full-thickness skin wounds in 24 Wistar rats and treated them with distilled water (n = 6), 10 (n = 6), 50 (n = 6) and 100 μg (n = 6) for three post-operative days. On the fourth day, the excised wound tissues were studied by morphological, immunohistochemical and morphometric methods.

Results

We demonstrated that 50 μg of DNIC spray had the most beneficial effect on wound healing: the thickness of the granulation tissue layer was 140% higher, vimentin positive fibroblasts predominated and the intensity of inflammation was significantly lower than in the control. There was a dose-dependent decrease in the functional activity of mast cells in the experimental groups compared to the control.

Conclusion

DNIC spray is a potential effective dosage form for the treatment of large-area skin lesions.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.

Physico-Chemistry of Dinitrosyl Iron Complexes as a Determinant of Their Biological Activity

In this article we minutely discuss the so-called "oxidative" mechanism of mononuclear form of dinitrosyl iron complexes (M-DNICs) formations proposed by the author. M-DNICs are proposed to be formed from their building material-neutral NO molecules, Fe2+ ions and anionic non-thiol (L-) and thiol (RS-) ligands based on the disproportionation reaction of NO molecules binding with divalent ion irons in pairs. Then a protonated form of nitroxyl anion (NO-) appearing in the reaction is released from this group and a neutral NO molecule is included instead. As a result, M-DNICs are produced. Their resonance structure is described as [(L-)2Fe2+(NO)(NO+)], in which nitrosyl ligands are represented by NO molecules and nitrosonium cations in equal proportions. Binding of hydroxyl ions with the latter causes conversion of these cations into nitrite anions at neutral pH values and therefore transformation of DNICs into the corresponding high-spin mononitrosyl iron complexes (MNICs) with the resonance structure described as [(L-)2Fe2+(NO)]. In case of replacing L- by thiol-containing ligands, which are characterized by high π-donor activity, electron density transferred from sulfur atoms to iron-dinitrosyl groups neutralizes the positive charge on nitrosonium cations, which prevents their hydrolysis, ensuring relatively a high stability of the corresponding M-DNICs with the resonance structure [(RS-)2Fe2+ (NO, NO+)]. Therefore, M-DNICs with thiol-containing ligands, as well as their binuclear analogs (B-DNICs, respective resonance structure [(RS-)2Fe2+2 (NO, NO+)2]), can serve donors of both NO and NO+. Experiments with solutions of B-DNICs with glutathione or N-acetyl-L-cysteine (B-DNIC-GSH or B-DNIC-NAC) showed that these complexes release both NO and NO+ in case of decomposition in the presence of acid or after oxidation of thiol-containing ligands in them. The level of released NO was measured via optical absorption intensity of NO in the gaseous phase, while the number of released nitrosonium cations was determined based on their inclusion in S-nitrosothiols or their conversion into nitrite anions. Biomedical research showed the ability of DNICs with thiol-containing ligands to be donors of NO and NO+ and produce various biological effects on living organisms. At the same time, NO molecules released from DNICs usually have a positive and regulatory effect on organisms, while nitrosonium cations have a negative and cytotoxic effect.

Dinitrosyl iron complexes (DNICs) as inhibitors of the SARS-CoV-2 main protease

By repurposing DNICs designed for other medicinal purposes, the possibility of protease inhibition was investigated in silico using AutoDock 4.2.6 (AD4) and in vitro via a FRET protease assay. AD4 was validated as a predictive computational tool for coordinatively unsaturated DNIC binding using the only known crystal structure of a protein-bound DNIC, PDB- (calculation RMSD = 1.77). From the in silico data the dimeric DNICs TGTA-RRE, [(μ-S-TGTA)Fe(NO)₂]₂ (TGTA = 1-thio-β-d-glucose tetraacetate) and TG-RRE, [(μ-S-TG)Fe(NO)₂]₂ (TG = 1-thio-β-d-glucose) were identified as promising leads for inhibition via coordinative inhibition at Cys-145 of the SARS-CoV-2 Main Protease (SC2M^pro). In vitro studies indicate inhibition of protease activity upon DNIC treatment, with an IC₅₀ of 38 ± 2 μM for TGTA-RRE and 33 ± 2 μM for TG-RRE. This study presents a simple computational method for predicting DNIC-protein interactions; the in vitro study is consistent with in silico leads.

Role of GSH and Iron-Sulfur Glutaredoxins in Iron Metabolism-Review

Glutathione (GSH) was initially identified and characterized for its redox properties and later for its contributions to detoxification reactions. Over the past decade, however, the essential contributions of glutathione to cellular iron metabolism have come more and more into focus. GSH is indispensable in mitochondrial iron-sulfur (FeS) cluster biosynthesis, primarily by co-ligating FeS clusters as a cofactor of the CGFS-type (class II) glutaredoxins (Grxs). GSH is required for the export of the yet to be defined FeS precursor from the mitochondria to the cytosol. In the cytosol, it is an essential cofactor, again of the multi-domain CGFS-type Grxs, master players in cellular iron and FeS trafficking. In this review, we summarize the recent advances and progress in this field. The most urgent open questions are discussed, such as the role of GSH in the export of FeS precursors from mitochondria, the physiological roles of the CGFS-type Grx interactions with BolA-like proteins and the cluster transfer between Grxs and recipient proteins.

Assessment of cytotoxic and genotoxic potentials of a mononuclear Fe(II) Schiff base complex with photocatalytic activity in Trigonella

BACKGROUND

In recent times, coordination complexes of iron in various oxidation states along with variety of ligand systems have been designed and developed for effective treatment of cancer cells without adversely affecting the normal cell and tissues of various organs.

METHODS

In this study, we have evaluated the mechanism of action of a Fe(II) Schiff base complex in the crop plant Trigonella foenum-graecum L. (Fenugreek) as the screening system by using morphological, cytological, biochemical and molecular approaches. Further functional characterization was performed using MCF-7 cell line and solid tumour model for the assessment of anti-tumour activity of the complex.

RESULTS

Our results indicate efficiency of the Fe(II) Schiff base complex in the induction of double strand breaks in DNA. Complex treatment clearly induced cytotoxic and genotoxic damage in Trigonella seedlings. The Fe-complex treatment caused cell cycle arrest via the activation of ATM-ATR kinase mediated DNA damage response pathway with the compromised expression of CDK1, CDK2 and CyclinB1 protein in Trigonella seedlings. In cultured MCF-7 cells, the complex induces cytotoxicity and DNA fragmentation through intracellular ROS generation. Fe-complex treatment inhibited tumour growth in solid tumour model with no additional side effects.

CONCLUSION

The growth inhibitory and cytotoxic effects of the complex result from activation of DNA damage response along with oxidative stress and cell cycle arrest.

GENERAL SIGNIFICANCE

Overall, our results have provided comprehensive information on the mechanism of action and efficacy of a Fe(II) Schiff base complex in higher eukaryotic genomes and indicated its future implications as potential therapeutic agent.

Nitric oxide-releasing molecules at the interface of inorganic chemistry and biology: a concise overview

The useful aspects of nitric oxide (NO) are nowadays widely known. Due to the need for this molecule in the maintenance of homeostasis, NO-releasing compounds are tested every year to optimize its levels in a patient suffering from low NO production. This manuscript is an update of some important historical concerns about nitrosyl complexes having the ability to act as NO-releasing compounds under the influence of different chemically modified environments. At present, the search for efficient and less harmful NO-releasing molecules at desirable targets and concentrations has gained considerable momentum in nitrosyl chemistry. Iron, ruthenium, and manganese nitrosyls have been investigated elitely to disentangle their electronic transition (excitation) under visible light to act as NO donors without harming the healthy cells of a target. There is much evidence supporting the increase of NO lability if amino acids are used as complexing ligands, the design of a reduction center close to an NO grouping, and the development of porphyrin system-based nitrosyl complexes. From the overall survey, it may be concluded that the desirable properties of such scaffolds need to be evaluated further to complement the biological milieu.

Toward the Optimization of Dinitrosyl Iron Complexes as Therapeutics for Smooth Muscle Cells

In this study, dinitrosyl iron complexes (DNICs) are shown to deliver nitric oxide (NO) into the cytosol of vascular smooth muscle cells (SMCs), which play a major role in vascular relaxation and contraction. Malfunction of SMCs can lead to hypertension, asthma, and erectile dysfunction, among other disorders. For comparison of the five DNIC derivatives, the following protocols were examined: (a) the Griess assay to detect nitrite (derived from NO conversion) in the absence and presence of SMCs; (b) the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium (MTS) assay for cell viability; (c) an immunotoxicity assay to establish if DNICs stimulate immune response; and (d) a fluorometric assay to detect intracellular NO from treatment with DNICs. Dimeric Roussin's red ester (RRE)-type {Fe(NO)₂}⁹ complexes containing phenylthiolate bridges, [(μ-SPh)Fe(NO)₂]₂ or SPhRRE, were found to deliver NO with the lowest effect on cell toxicity (i.e., highest IC₅₀). In contrast, the RRE-DNIC with the biocompatible thioglucose moiety, [(μ-SGlu)Fe(NO)₂]₂ (SGlu = 1-thio-β-d-glucose tetraacetate) or SGluRRE, delivered a higher concentration of NO to the cytosol of SMCs with a 10-fold decrease in IC₅₀. Additionally, monomeric DNICs stabilized by a bulky N-heterocyclic carbene (NHC), namely, 1,3-bis(2,4,6-trimethylphenyl)imidazolidene (IMes), were synthesized and yielded the DNIC complexes SGluNHC, [IMes(SGlu)Fe(NO)₂], and SPhNHC, [IMes(SPh)Fe(NO)₂]. These oxidized {Fe(NO)₂}⁹ NHC DNICs have an IC₅₀ of ∼7 μM; however, the NHC-based complexes did not transfer NO into the SMC. Per contra, the reduced, mononuclear {Fe(NO)₂}¹⁰ neocuproine-based DNIC, neoDNIC, depressed the viability of the SMCs, as well as generated an increase of intracellular NO. Regardless of the coordination environment or oxidation state, all DNICs showed a dinitrosyl iron unit (DNIU)-dependent increase in viability. This study demonstrates a structure-function relationship between the DNIU coordination environment and the efficacy of the DNIC treatments.

Is it possible to combine photodynamic therapy and application of dinitrosyl iron complexes in the wound treatment?

We have studied the effect of interactions between dinitrosyl iron complexes with thiol-containing ligands (DNIC-TL) and diglucamine salt of chlorine e6 (photoditazine, PD) on the rate of photosensitized oxidation of a model organic substrate - tryptophan - in the presence and absence of an amphiphilic polymer, Pluronic F127, as well as on the DNIC-TL and PD photostability. Using EPR and UV spectroscopy, we determined the rate constants for photodegradation of mono- and dinuclear DNIC-TL and PD, respectively. The presence of the photosensitizer and Pluronic F127 has been shown to have a negligible effect on the rate of photodestruction of mono- and dinuclear DNIC-TL, taking into account the changing DNIC-TL and PD concentrations in the photoexcitation conditions. At the same time, in the DNIC-TL presence, the rate of PD photodestruction increases, however, addition of Pluronic F127 leads to a decrease in the rate constant of PD photodestruction. The latter circumstance creates an opportunity for a simultaneous application of DNIC-TL and photodynamic therapy in the wound treatment without losing the PDT efficiency. Indeed, photodynamic therapy in combination with DNIC-TL facilitated skin wound healing in laboratory rats. As shown by a morphological study, application of the DNIC-TL-PD-F127 complex with the subsequent photoactivation was beneficial in reducing inflammation and stimulating regenerative processes.

The Inhibiting Effect of Dinitrosyl Iron Complexes with Thiol-containing Ligands on the Growth of Endometrioid Tumours in Rats with Experimental Endometriosis

The possibility that binuclear dinitrosyl iron complexes with glutathione and cysteine (DNIC-GSН and B-DNIC-Cys) have a strong cytotoxic effect on the growth of endometrioid tumours (EMT) in rats with surgically induced experimental endometriosis established in our previous studies has been supported with experimental data. The increase in the DNIC-GSН or B-DNIC-Cys dose from 10 (in our previous studies) to 20 μmol/kg (after i/p administration to experimental rats) fully suppressed the growth of uterine tissues implanted onto the inner surface of the abdominal wall. At 2 μmol/kg DNIC-GSН, the median value of EMT volume increased from 0 to 15 mm³, while the mean size of EMT-from 55 to 77 mm³ (data from EMT measurements in 10 experimental rats). After treatment of animals with B-DNIC with N-acetyl-L-cysteine (10 μmol/kg) known for its ability to penetrate easily through the cell membrane, the inhibiting effect on EMT growth diminished as could be evidenced from the transformation of ~30% of the implants into large-size EMT. Possible reasons for this phenomenon are discussed.

A gentle introduction to gasotransmitters with special reference to nitric oxide: biological and chemical implications

Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are gaseous molecules of major impact in biology. Despite their toxicity, these molecules have profound effects on mammalian physiology and major implications in therapeutics. At tiny concentrations in human biology, they play key signaling and regulatory functions and hence are now labeled as “gasotransmitters.” In this literature survey, an introduction to gasotransmitters in relevance with NO, CO and H2S has been primarily focused. A special attention has been given to the conjoint physiological, pathophysiological and therapeutic aspects of NO in this work. In addition to the aforementioned elements of the investigation being reported, this report gives a detailed account of some of the recent advancements covering the NO release from both the nitro as well as nitroso compounds. The importance of the metallic center on the eve of producing the reduction center on NO and to develop photolabile properties have been elaborated within the effect of a few examples of metallic centers. Also, theoretical investigations that have been reported in the recent past and some other current theories pertaining to NO chemistry have been enlightened in this review. From the overall study, it is eminent that a number of facts are yet to be explored in context with NO for deeper mechanistic insights, model design for these molecules, other key roles and the search to find the best fit formalism in theoretical chemistry.

Recent advances in iron complexes as potential anticancer agents

The iron complexes discussed in this review highlight their promising future as anticancer agents.