Synthesis and initial in vitro evaluations of novel antioxidant aroylhydrazone iron chelators with increased stability against plasma hydrolysis

Analysis of antiproliferative activity of new half-sandwich arene Ru(II) thiophene based aroylhydrazone complexes

Efforts in researching the efficient anti-tumor properties of three novel arene ruthenium(II) complexes incorporating thiophene-based aroylhydrazone ligands have been undertaken. The complexes' elemental composition was [(η6-p-cymene)Ru(L)Cl]. They were comprehensively characterized through elemental and spectroscopic analyses (FT-IR, UV-vis, NMR, and HR-MS). Single crystal X-ray diffraction studies revealed a pseudo-octahedral geometry with bidentate coordination of the ligands in a representative complex. The in vitro assessment of the complexes' cancer cell growth inhibition was conducted using the MTT assay against A549 (human lung carcinoma), HeLa (human cervical carcinoma), HuH-7 (hepatocellular carcinoma), and NIH-3T3 (mouse fibroblast non-cancerous cell line). Results indicated significant cytotoxicity across all cancer cell lines, with IC50 concentrations of complex 2 being 6.8 μM for A549, 11.6 μM for HeLa, and 9.4 μM for HuH-7, compared to cisplatin with IC50 values of 18.9 μM, 17.68 μM, and 24 μM respectively. Notably, complex 2 demonstrated particularly promising cytotoxicity against all tested cancerous cell lines. Fluorescent staining analysis such as acridine orange/ethidium bromide (AO-EB) and HOECHST 33342 revealed cell death mechanisms involving membrane disintegration and nuclear condensation following treatment with complex 2. Further studies were conducted to measure reactive oxygen species (ROS) levels using the dichlorodihydrofluorescein diacetate (DCFH-DA) assay, and mitochondrial membrane potential (MMP) was assessed using the JC-1 dye assay. These studies demonstrated that complex 2 increased ROS levels, decreased membrane potential, and promoted mitochondrial dysfunction-mediated cell death pathways. Additionally, flow cytometry analysis, utilizing dual staining of Annexin V-FITC and propidium iodide (PI), was employed to quantitatively study apoptosis induction.

Search for new antimicrobials: spectroscopic, spectrometric, and in vitro antimicrobial activity investigation of Ga(III) and Fe(III) complexes with aroylhydrazones

The in vitro antimicrobial activity of Fe(III) and Ga(III) complexes with N'-(2,3-dihydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (H₂L¹), N'-(2,4-dihydroxy-phenyl-methylidene)-3-pyridinecarbohydrazide (H₂L²), N'-(2,5-dihydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (H₂L³), N'-(2-hydroxy-3-methoxyphenyl-methylidene)-3-pyridine-carbohydrazide (H₂L⁴), N'-(2-hydroxy-4-methoxyphenylmethyl-idene)-3-pyridine-carbohydrazide (H₂L⁵), and N'-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbo-hydrazide (H₂L⁶) toward several Gram-positive strains of Staphylococcus aureus, a Gram-negative strain of Escherichia coli, and a yeast Candida albicans were investigated. Fe(III)-complexes do not possess antimicrobial activity against all tested strains at concentrations up to 10 mg mL^-1. Ga(III) complexes with dihydroxy derivatives showed selective activity, while the broadest range of antibacterial and antifungal activities was observed for complex with 2-hydroxy-3-methoxy-derivative, ligand H₂L⁵. In addition, the coordination properties of ligands H₂L¹-H₂L³ in solution were investigated by UV-Vis spectroscopy. The stability constants (logK) for Ga(III)-H₂L 1:1 complexes in MeOH/H₂O 1/1 at pH 2.52 were determined, and amounted to 5.8, 5.68, and 4.7, respectively. Detailed characterization of complexes was performed by high-resolution mass spectrometry. The fragmentation pathways for dimer [Fe₂(L¹)₂]²⁺, [Fe(HL)₂]⁺, [Ga(HL²)₂]⁺ and adduct ions are given. The comparison with analogue Ga(III) and Fe(III) complexes with compounds H₂L⁴-H₂L⁶ was made as well.

Prodrug strategies for targeted therapy triggered by reactive oxygen species

Increased levels of reactive oxygen species (ROS) have been associated with numerous pathophysiological conditions including cancer and inflammation and the ROS stimulus constitutes a potential trigger for drug delivery strategies. Over the past decade, a number of ROS-sensitive functionalities have been identified with the purpose of introducing disease-targeting properties into small molecule drugs - a prodrug strategy that offers a promising approach for increasing the selectivity and efficacy of treatments. This review will provide an overview of the ROS-responsive prodrugs developed to date. A discussion on the current progress and limitations is provided along with a reflection on the unanswered questions that need to be addressed in order to advance this novel approach to the clinic.

Novel tetranuclear ruthenium(II) arene complexes showing potent cytotoxic and antimetastatic activity as well as low toxicity in vivo

Ruthenium complexes have attracted a surge of interest as anticancer drug candidates because of their low toxicity, diversity in mode-of-actions and non-cross drug resistance with conventional platinum-based agents. Despite remarkable advances, only a limited number of ruthenium complexes have been demonstrated to kill cancer cells and suppress metastasis simultaneously. Here, two organometallic tetranuclear Ru(II) arene complexes (Ru-1 and Ru-2) have been synthesized and evaluated for their in vitro activity against a panel of human cancer cell lines, including a cisplatin-resistant human lung cancer A549 cell line. A superior cytotoxic activity of the ruthenium complexes compared to cisplatin across distinct cell lines was observed. Further examination of the mechanism indicated that anticancer activity was accomplished by inducing apoptosis in cancer cells. In addition, we found that such compounds exhibited promising antimetastatic activity and reduced the invasiveness of cancer cells. Importantly, choosing Ru-1 as a target compound, a significantly enhanced safety profile relative to cisplatin in animals was validated, suggesting that these complexes can be used as promising candidates for cancer therapy and deserve further investigation.

Antimicrobial assesment of aroylhydrazone derivatives in vitro

Aroylhydrazones 1-13 were screened for antimicrobial and antibiofilm activities in vitro. N'-(2-hydroxy-phenylmethylidene)-3-pyridinecarbohydrazide (2), N'-(5-chloro-2-hydroxyphenyl-methylidene)-3-pyridinecarbohydrazide (10), N'-(3,5-chloro-2-hydroxyphenylmethylidene)-3-pyridinecarbohydrazide (11), and N'-(2-hydroxy-5-nitrophenylmethylidene)-3-pyridinecarbohydrazide (12) showed antibacterial activity against Escherichia coli, with MIC values (in µmol mL-1) of 0.18-0.23, 0.11-0.20, 0.16-0.17 and 0.35-0.37, resp. Compounds 11 and 12, as well as N'-(2-hydroxy-3-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (6) and N'-(2-hydroxy-5- methoxyphenylmethylidene)-3-pyridinecarbohydrazide (8) showed antibacterial activity against Staphylococcus aureus, with the lowest MIC values of 0.005-0.2, 0.05-0.12, 0.06-0.48 and 0.17-0.99 µmol mL-1. N'-(2-hydroxy-5-methoxyphenylmethylidene)-3-pyridinecarbohydrazide (7) showed antifungal activity against both fluconazole resistant and susceptible C. albicans strains with IC90 range of 0.18-0.1 µmol mL-1. Only compound 11 showed activity against C. albicans ATCC 10231 comparable to the activity of nystatin (the lowest MIC 4.0 ×10-2 vs. 1.7 × 10-2 µmol mL-1). Good activity regarding multi-resistant clinical strains was observed for compound 12 against MRSA strain (MIC 0.02 µmol mL-1) and compounds 2, 6 and 12 against ESBL+ E. coli MFBF 12794, with the lowest MIC for compound 12 (IC50 0.16 µmol mL-1). Anti-biofilm activity was found for compounds 2 (MBFIC 0.015-0.02 µmol mL-1 against MRSA) and 12 (MBFIC 0.013 µmol mL-1 against EBSL+ E. coli). In the case of compound 2 against MRSA biofilm formation, MBFIC values were comparable to those of gentamicin sulphate, whereas in the case of compound 12 and EBSL+ E. coli even more favourable activity compared to gentamicin was observed.

Modifying aroylhydrazone prochelators for hydrolytic stability and improved cytoprotection against oxidative stress

BSIH ((E)-N'-(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylidene)isonicotinohydrazide) is a prodrug version of the metal chelator SIH ((E)-N'-(2-hydroxybenzylidene)isonicotinohydrazide) in which a boronate group prevents metal chelation until reaction with hydrogen peroxide releases SIH, which is then available for sequestering iron(III) and inhibiting iron-catalyzed oxidative damage. While BSIH has shown promise for conditionally targeting iron sequestration in cells under oxidative stress, the yield of SIH is limited by the fact that BSIH exists in cell culture media as an equilibrium mixture with its hydrolysis products isoniazid and 2-formylphenyl boronic acid. In the current study, several BSIH analogs were evaluated for their hydrolytic stability, reaction outcomes with H₂O₂, and prochelator-to-chelator conversion efficiency. Notably, the para-methoxy derivative (p-OMe)BSIH ((E)-N'-(5-methoxy-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylidene)isonicotinohydrazide) and the meta-, para-double substituted (MD)BSIH ((E)-N'-((6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzo[d][1,3]dioxol-5-yl)methylene)isonicotinohydrazide) showed 1.3- and 1.9-fold improved hydrolytic stability compared to BSIH, respectively, leading to a 22 and 50% increase in chelator released. Moreover, both prochelators were found to protect retinal pigment epithelial cells stressed with either H₂O₂ or paraquat insult.

Structure-Activity Relationships of Nitro-Substituted Aroylhydrazone Iron Chelators with Antioxidant and Antiproliferative Activities

Aroylhydrazone iron chelators such as salicylaldehyde isonicotinoyl hydrazone (SIH) protect various cells against oxidative injury and display antineoplastic activities. Previous studies have shown that a nitro-substituted hydrazone, namely, NHAPI, displayed markedly improved plasma stability, selective antitumor activity, and moderate antioxidant properties. In this study, we prepared four series of novel NHAPI derivatives and explored their iron chelation activities, anti- or pro-oxidant effects, protection against model oxidative injury in the H9c2 cell line derived from rat embryonic cardiac myoblasts, cytotoxicities to the corresponding noncancerous H9c2 cells, and antiproliferative activities against the MCF-7 human breast adenocarcinoma and HL-60 human promyelocytic leukemia cell lines. Nitro substitution had both negative and positive effects on the examined properties, and we identified new structure-activity relationships. Naphthyl and biphenyl derivatives showed selective antiproliferative action, particularly in the breast adenocarcinoma MCF-7 cell line, where they exceeded the selectivity of the parent compound NHAPI. Of particular interest is a compound prepared from 2-hydroxy-5-methyl-3-nitroacetophenone and biphenyl-4-carbohydrazide, which protected cardiomyoblasts against oxidative injury at 1.8 ± 1.2 μM with 24-fold higher selectivity than SIH. These compounds will serve as leads for further structural optimization and mechanistic studies.

Synthesis and structure of new binuclear ruthenium(ii) arene benzil bis(benzoylhydrazone) complexes: investigation on antiproliferative activity and apoptosis induction

New binuclear Ru(ii) arene benzil bis(benzoylhydrazone) complexes show excellent cytotoxicity against human cancer cell lines. The results of biochemical assays demonstrated that complexes are able to induce apoptosis.

Metal-binding hydrazone photoswitches for visible light reactivity and variable relaxation kinetics

The range of applications for photoswitching moieties is diverse, and the ability to design switches with variable photochemical and physical properties is consequently important for realizing their potential. Previously we reported on the photochromism of (E)-N'-(1-(2-hydroxyphenyl)ethylidene)isonicotinohydrazide (HAPI), an aroylhydrazone compound first developed as a transition metal chelator. Herein we report the synthesis of structurally related aroylhydrazone chelators and explore the effect of these modifications on their UVA, UVC and blue light photoreactivity, photostationary state composition, photoisomer thermal stability, and relative iron(iii) binding affinity. These findings will inform the next generation of aroylhydrazone photoswitches for metal-gated photoswitching applications.

Mfn2-Mediated Preservation of Mitochondrial Function Contributes to the Protective Effects of BHAPI in Response to Ischemia

Disturbances in intracellular iron homeostasis are associated with neuronal injury after stroke. However, exposure of cells to classical chelators may interfere with physiological iron functions. BHAPI is an iron prochelator that exerts strong iron binding capacity only under oxidative stress conditions. This study investigated the protective effects of N'-(1-(2-((4-(4,4,5,5-tetramethyl-1,2,3-dioxoborolan-2-yl)benzyl)oxy)phenyl)ethylidene (BHAPI) on an in vitro ischemia model mimicked by oxygen and glucose deprivation (OGD) in neuronal HT22 cells. The results showed that BHAPI significantly increased cell viability and decreased lactate dehydrogenase (LDH) release after OGD. BHAPI treatment also reduced apoptosis, as measured by flow cytometry, and suppressed caspase-3 activation. These protective effects were accompanied by preserved mitochondrial membrane potential (MMP), reduced mitochondrial swelling, promoted mitochondrial calcium buffering capacity, and increased mitochondrial respiration. The results of MitoTracker staining showed that BHAPI partially prevented the OGD-induced changes in mitochondrial morphology. Furthermore, BHAPI selectively increased the expression of mitochondrial dynamic protein Mfn2, with no effect on Mfn1 expression. Knockdown of Mfn2 with specific siRNA partially reversed the protective effects of BHAPI. In summary, the iron prochelator BHAPI protects HT22 cells against ischemic injury through preservation of mitochondrial function and Mfn2 signaling.

DNA and BSA binding and cytotoxic properties of copper(ii) and iron(iii) complexes with arylhydrazone of ethyl 2-cyanoacetate or formazan ligands

Copper(ii) and iron(iii) complexes with arylhydrazone of ethyl 2-cyanoacetate or formazan ligands show DNA and BSA binding and anticancer abilities.

Stimulus-Responsive Prochelators for Manipulating Cellular Metals

Metal ions are essential for a wide range of physiological processes, but they can also be toxic if not appropriately regulated by a complex network of metal trafficking proteins. Intervention in cellular metal distribution with small-molecule or peptide chelating agents has promising therapeutic potential to harness metals to fight disease. Molecular outcomes associated with forming metal-chelate interactions in situ include altering the concentration and subcellular metal distribution, inhibiting metalloenzymes, enhancing the reactivity of a metal species to elicit a favorable biological response, or passivating the reactivity of a metal species to prevent deleterious reactivity. The systemic administration of metal chelating agents, however, raises safety concerns due to the potential risks of indiscriminate extraction of metals from critical metalloproteins and inhibition of metalloenzymes. One can estimate that chelators capable of complexing metal ions with dissociation constants in the submicromolar range are thermodynamically capable of extracting metal ions from some metalloproteins and disrupting regular function. Such dissociation constants are easily attainable for multidentate chelators interacting with first-row d-block metal cations in relevant +1, + 2, and +3 oxidation states. To overcome this challenge of indiscriminate metal chelation, we have pursued a prodrug strategy for chelating agents in which the resulting "prochelator" has negligible metal binding affinity until a specific stimulus generates a favorable metal binding site. The prochelator strategy enables conditional metal chelation to occur preferentially in locations affected by disease- or therapy-associated stimuli, thereby minimizing off-target metal chelation. Our design of responsive prochelators encompasses three general approaches of activation: the "removal" approach operates by eliminating a masking group that blocks a potential metal chelation site to reveal the complete binding site under the desired conditions; the molecular "switch" approach involves a reversible conformational change between inactive and active forms of a chelator with differential metal binding affinity under specific conditions; and the "addition" approach adds a new ligand donor arm to the prochelator to constitute a complete metal chelation site. Adopting these approaches, we have created four categories of triggerable prochelators that respond to (1) reactive oxygen species, (2) light, (3) specific enzymes, and (4) biological regulatory events. This Account highlights progress from our group on building prochelators that showcase these four categories of responsive metal chelating agents for manipulating cellular metals. The creation and chemical understanding of such stimulus-responsive prochelators enables exciting applications for understanding the cell biology of metals and for developing therapies based on metal-dependent processes in a variety of diseases.

Cardioprotective effects of iron chelator HAPI and ROS-activated boronate prochelator BHAPI against catecholamine-induced oxidative cellular injury

Catecholamines may undergo iron-promoted oxidation resulting in formation of reactive intermediates (aminochromes) capable of redox cycling and reactive oxygen species (ROS) formation. Both of them induce oxidative stress resulting in cellular damage and death. Iron chelation has been recently shown as a suitable tool of cardioprotection with considerable potential to protect cardiac cells against catecholamine-induced cardiotoxicity. However, prolonged exposure of cells to classical chelators may interfere with physiological iron homeostasis. Prochelators represent a more advanced approach to decrease oxidative injury by forming a chelating agent only under the disease-specific conditions associated with oxidative stress. Novel prochelator (lacking any iron chelating properties) BHAPI [(E)-Ń-(1-(2-((4-(4,4,5,5-tetramethyl-1,2,3-dioxoborolan-2-yl)benzyl)oxy)phenyl)ethylidene) isonicotinohydrazide] is converted by ROS to active chelator HAPI with strong iron binding capacity that efficiently inhibits iron-catalyzed hydroxyl radical generation. Our results confirmed redox activity of oxidation products of catecholamines isoprenaline and epinephrine, that were able to activate BHAPI to HAPI that chelates iron ions inside H9c2 cardiomyoblasts. Both HAPI and BHAPI were able to efficiently protect the cells against intracellular ROS formation, depletion of reduced glutathione and toxicity induced by catecholamines and their oxidation products. Hence, both HAPI and BHAPI have shown considerable potential to protect cardiac cells by both inhibition of deleterious catecholamine oxidation to reactive intermediates and prevention of ROS-mediated cardiotoxicity.

Crystal structures of (E)-N'-(2-hy-droxy-5-methyl-benzyl-idene)isonicotinohydrazide and (E)-N'-(5-fluoro-2-hy-droxy-benzyl-idene)isonicotinohydrazide

Two derivatives of the well-known iron chelator, (E)-N'-(2-hy-droxy-benzyl-idene)isonicotinohydrazide (SIH), substituted in the 5-position of the 2-hy-droxy-benzene ring by a methyl and a fluorine group viz. (E)-N'-(2-hy-droxy-5-methyl-benzyl-idene)isonicotinohydrazide, C14H13N3O2, (I), and (E)-N'-(5-fluoro-2-hy-droxy-benzyl-idene)isonicotinohydrazide, C13H10FN3O2, (II), have been prepared and characterized by single-crystal X-ray diffraction, (1)H NMR and mass spectrometry. The mol-ecules of both compounds deviate slightly from planarity [r.m.s. deviations are 0.145 and 0.110 Å for (I) and (II), respectively] and adopt an E conformation with respect to the double bond of the hydrazone bridge. In each mol-ecule, there is an intra-molecular O-H⋯N hydrogen bond forming an S(6) ring motif. The dihedral angles between the mean planes of the isonicotinoyl ring and the cresol ring in (I) or the fluoro-phenol ring in (II) are 10.49 (6) and 9.43 (6)°, respectively. In the crystals of both compounds, zigzag chains are formed via N-H⋯N hydrogen bonds, in the [10-1] direction for (I) and [010] for (II). In (I), the chains are linked by weak C-H⋯π and π-π stacking inter-actions [centroid-to-centroid distances = 3.6783 (8) Å; inter-planar angle = 10.94 (5)°], leading to the formation of a three-dimensional supra-molecular architecture. In (II), adjacent chains are connected through C-H⋯O hydrogen bonds to form sheets parallel to (100), which enclose R 4 (4)(30) ring motifs. The sheets are linked by weak C-H⋯π and π-π [centroid-to-centroid distance = 3.7147 (8) Å; inter-planar angle = 10.94 (5)°] inter-actions, forming a three-dimensional supra-molecular architecture.

Prooxidant and antioxidant properties of salicylaldehyde isonicotinoyl hydrazone iron chelators in HepG2 cells

BACKGROUND

Salicylaldehyde isonicotinoyl hydrazone (SIH) is an iron chelator of the aroylhydrazone class that displays antioxidant or prooxidant effects in different mammalian cell lines. Because the liver is the major site of iron storage, elucidating the effect of SIH on hepatic oxidative metabolism is critical for designing effective hepatic antioxidant therapies.

METHODS

Hepatocyte-like HepG2 cells were exposed to SIH or to analogs showing greater stability, such as N'-[1-(2-Hydroxyphenyl)ethyliden]isonicotinoyl hydrazide (HAPI), or devoid of iron chelating properties, such as benzaldehyde isonicotinoyl hydrazone (BIH), and toxicity, oxidative stress and antioxidant (glutathione) metabolism were evaluated.

RESULTS

Autoxidation of Fe(2+)in vitro increased in the presence of SIH or HAPI (but not BIH), an effect partially blocked by Fe(2+) chelation. Incubation of HepG2 cells with SIH or HAPI (but not BIH) was non-toxic and increased reactive oxygen species (ROS) levels, activated the transcription factor Nrf2, induced the catalytic subunit of γ-glutamate cysteine ligase (Gclc), and increased glutathione concentration. Fe(2+) chelation decreased ROS and inhibited Nrf2 activation, and Nrf2 knock-down inhibited the induction of Gclc in the presence of HAPI. Inhibition of γ-glutamate cysteine ligase enzymatic activity inhibited the increase in glutathione caused by HAPI, and increased oxidative stress.

CONCLUSIONS

SIH iron chelators display both prooxidant (increasing the autoxidation rate of Fe(2+)) and antioxidant (activating Nrf2 signaling) effects.

GENERAL SIGNIFICANCE

Activation by SIH iron chelators of a hormetic antioxidant response contributes to their antioxidant properties and modulates the anti- and pro-oxidant balance.

A multifunctional, light-activated prochelator inhibits UVA-induced oxidative stress

UVA radiation can damage cells and tissues by direct photodamage of biomolecules as well as by initiating metal-catalyzed oxidative stress. In order to alleviate both concerns simultaneously, we synthesized a multifunctional prochelator PC-HAPI (2-((E)-1-(2-isonicotinoylhydrazono)ethyl)phenyl (trans)-3-(2,4-dihydroxyphenyl)acrylate) that contains a trans-(o-hydroxy)cinnamate ester photocleavable protecting group that is cleaved upon UVA exposure to release a coumarin, umbelliferone, and an aroylhydrazone metal chelator, HAPI (N'-[1-(2-hydroxyphenyl)ethyliden]isonicotinoylhydrazide). While the prochelator PC-HAPI exhibits negligible affinity for iron, it responds rapidly to UVA irradiation and converts to an iron-binding chelator that inhibits iron-catalyzed formation of reactive oxygen species and protects cells from UVA damage.

Tuning the thermotropic properties of liquid crystalline p-substituted aroylhydrazones

Lamellar smectic A to columnar mesophase crossover is observed in p-substituted aroylhydrazones by variation of the alkoxy chain density at peripherals.

Structure-activity relationships of novel salicylaldehyde isonicotinoyl hydrazone (SIH) analogs: iron chelation, anti-oxidant and cytotoxic properties

Salicylaldehyde isonicotinoyl hydrazone (SIH) is a lipophilic, tridentate iron chelator with marked anti-oxidant and modest cytotoxic activity against neoplastic cells. However, it has poor stability in an aqueous environment due to the rapid hydrolysis of its hydrazone bond. In this study, we synthesized a series of new SIH analogs (based on previously described aromatic ketones with improved hydrolytic stability). Their structure-activity relationships were assessed with respect to their stability in plasma, iron chelation efficacy, redox effects and cytotoxic activity against MCF-7 breast adenocarcinoma cells. Furthermore, studies assessed the cytotoxicity of these chelators and their ability to afford protection against hydrogen peroxide-induced oxidative injury in H9c2 cardiomyoblasts. The ligands with a reduced hydrazone bond, or the presence of bulky alkyl substituents near the hydrazone bond, showed severely limited biological activity. The introduction of a bromine substituent increased ligand-induced cytotoxicity to both cancer cells and H9c2 cardiomyoblasts. A similar effect was observed when the phenolic ring was exchanged with pyridine (i.e., changing the ligating site from O, N, O to N, N, O), which led to pro-oxidative effects. In contrast, compounds with long, flexible alkyl chains adjacent to the hydrazone bond exhibited specific cytotoxic effects against MCF-7 breast adenocarcinoma cells and low toxicity against H9c2 cardiomyoblasts. Hence, this study highlights important structure-activity relationships and provides insight into the further development of aroylhydrazone iron chelators with more potent and selective anti-neoplastic effects.

Comparison of various iron chelators and prochelators as protective agents against cardiomyocyte oxidative injury

Oxidative stress is a common denominator of numerous cardiovascular disorders. Free cellular iron catalyzes the formation of highly toxic hydroxyl radicals, and iron chelation may thus be an effective therapeutic approach. However, using classical iron chelators in diseases without iron overload poses risks that necessitate more advanced approaches, such as prochelators that are activated to chelate iron only under disease-specific oxidative stress conditions. In this study, three cell-membrane-permeable iron chelators (clinically used deferasirox and experimental SIH and HAPI) and five boronate-masked prochelator analogs were evaluated for their ability to protect cardiac cells against oxidative injury induced by hydrogen peroxide. Whereas the deferasirox-derived agents TIP and TRA-IMM displayed negligible protection and even considerable toxicity, the aroylhydrazone prochelators BHAPI and BSIH-PD provided significant cytoprotection and displayed lower toxicity after prolonged cellular exposure compared to their parent chelators HAPI and SIH, respectively. Overall, the most favorable properties in terms of protective efficiency and low inherent cytotoxicity were observed with the aroylhydrazone prochelator BSIH. BSIH efficiently protected both H9c2 rat cardiomyoblast-derived cells and isolated primary rat cardiomyocytes against hydrogen peroxide-induced mitochondrial and lysosomal dysregulation and cell death. At the same time, BSIH was nontoxic at concentrations up to its solubility limit (600 μM) and in 72-h incubation. Hence, BSIH merits further investigation for prevention and/or treatment of cardiovascular disorders associated with a known (or presumed) component of oxidative stress.

Quantitative analysis of the anti-proliferative activity of combinations of selected iron-chelating agents and clinically used anti-neoplastic drugs

Recent studies have demonstrated that several chelators possess marked potential as potent anti-neoplastic drugs and as agents that can ameliorate some of the adverse effects associated with standard chemotherapy. Anti-cancer treatment employs combinations of several drugs that have different mechanisms of action. However, data regarding the potential interactions between iron chelators and established chemotherapeutics are lacking. Using estrogen receptor-positive MCF-7 breast cancer cells, we explored the combined anti-proliferative potential of four iron chelators, namely: desferrioxamine (DFO), salicylaldehyde isonicotinoyl hydrazone (SIH), (E)-N'-[1-(2-hydroxy-5-nitrophenyl)ethyliden] isonicotinoyl hydrazone (NHAPI), and di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), plus six selected anti-neoplastic drugs. These six agents are used for breast cancer treatment and include: paclitaxel, 5-fluorouracil, doxorubicin, methotrexate, tamoxifen and 4-hydroperoxycyclophosphamide (an active metabolite of cyclophosphamide). Our quantitative chelator-drug analyses were designed according to the Chou-Talalay method for drug combination assessment. All combinations of these agents yielded concentration-dependent, anti-proliferative effects. The hydrophilic siderophore, DFO, imposed antagonism when used in combination with all six anti-tumor agents and this antagonistic effect increased with increasing dose. Conversely, synergistic interactions were observed with combinations of the lipophilic chelators, NHAPI or Dp44mT, with doxorubicin and also the combinations of SIH, NHAPI or Dp44mT with tamoxifen. The combination of Dp44mT with anti-neoplastic agents was further enhanced following formation of its redox-active iron and especially copper complexes. The most potent combinations of Dp44mT and NHAPI with tamoxifen were confirmed as synergistic using another estrogen receptor-expressing breast cancer cell line, T47D, but not estrogen receptor-negative MDA-MB-231 cells. Furthermore, the synergy of NHAPI and tamoxifen was confirmed using MCF-7 cells by electrical impedance data, a mitochondrial inner membrane potential assay and cell cycle analyses. This is the first systematic investigation to quantitatively assess interactions between Fe chelators and standard chemotherapies using breast cancer cells. These studies are vital for their future clinical development.

Characterization of a photoswitching chelator with light-modulated geometric, electronic, and metal-binding properties

Photoswitching molecules are utilized for a variety of applications where the rapid manipulation of the molecules' chemical properties and spatial orientations allows for new spatiotemporal control over molecular-scale interactions and processes. Here, we present a hydrazone-containing transition metal chelator, HAPI ((E)-N'-[1-(2-hydroxyphenyl)ethyliden]isonicotinoylhydrazide), that displays dual-wavelength photoswitching behavior. Several of its metal complexes, however, are inert to photoreaction and thereby add another layer of control over the photoswitch system. The light-induced twist in HAPI structure is accompanied by a dramatic change in electronic properties as well as chelator strength. This work introduces HAPI as the prototype for a class of molecules with properties that may be optimized for a variety of experimental applications that take advantage of phototriggered molecular changes.

Prochelator BHAPI protects cells against paraquat-induced damage by ROS-triggered iron chelation

A prochelator named BHAPI (N'-(1-(2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyloxy)phenyl)ethylidene)isonicotinohydrazide) based on the structure of experimental metal chelator HAPI (N'-[1-(2-hydroxyphenyl)ethyliden]isonicotinoylhydrazide) has been synthesized. The prochelator, which shows limited affinity for metal ions, is converted efficiently upon reaction with hydrogen peroxide into its chelator form, which binds di- and trivalent metal ions, including Zn(2+), Cu(2+) and Fe(3+). This work shows that the prochelator has a protective effect on cells under oxidative stress induced by either hydrogen peroxide or the cytotoxic herbicide paraquat. The effect of BHAPI and HAPI on cellular iron status was assessed by monitoring the mRNA level of the transferrin receptor. Whereas the chelator HAPI induces iron deficiency in cultured retinal pigment epithelial cells, the prochelator does not, providing evidence that the differential metal-binding capacity of these compounds observed in vitro is replicated in the cellular context.

Synthesis and comparison of antioxidant properties of indole-based melatonin analogue indole amino Acid derivatives

Increased levels of reactive oxygen species attributed to oxidative stress have been found to be responsible for the development of some vital diseases such as cardiovascular, neurodegenerative and autoimmune diseases. Recently, it was observed that melatonin is a highly important antioxidant, and melatonin analogues are under investigation to find out improved antioxidant activity. In this study, 14 melatonin -based analogue indole amino acid and N-protected amino acid derivatives were synthesized and elucidated spectrometrically. To investigate the antioxidant activity of the synthesized compounds and to compare with melatonin, butylhydroxytoluene and vitamin E, lipid peroxidation inhibition and 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activities were tested. The results indicated that the synthesized new indole amino acid derivatives have similar activities to melatonin in 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity assay but more potent activities in lipid peroxidation inhibition assay.

Metabolomic analysis reveals novel isoniazid metabolites and hydrazones in human urine

Isoniazid (INH) is a first-line drug for tuberculosis control; the side effects of INH are thought to be associated with its metabolism, and this study was designed to globally characterize isoniazid metabolism. Metabolomic strategies were used to profile isoniazid metabolism in humans. Eight known and seven novel INH metabolites and hydrazones were identified in human urine. The novel products included two hydroxylated INH metabolites and five hydrazones. The two novel metabolites were determined as 2-oxo-1,2-dihydro-pyridine-4-carbohydrazide and isoniazid N-oxide. Five novel hydrazones were produced by condensation of isoniazid with keto acids that are intermediates in the metabolism of essential amino acids, namely, leucine and/or isoleucine, lysine, tyrosine, tryptophan, and phenylalanine. This study enhances our knowledge of isoniazid metabolism and disposition and may offer new avenues for investigating INH-induced toxicity.