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.

Design, Synthesis, and Biological Evaluation of Isothiosemicarbazones with Antimycobacterial Activity.

A series of benzaldehyde and salicylaldehyde-S-benzylisothiosemicarbazones was synthesized and tested against 12 different strains of mycobacteria, Gram-positive and Gram-negative bacteria, and the significant selectivity toward mycobacteria was proved. Twenty-eight derivatives were evaluated for the inhibition of isocitrate lyase, which is a key enzyme of the glyoxylate cycle necessary for latent tuberculosis infection, and their iron-chelating properties were investigated. Two derivatives, 5-bromosalicylaldehyde-S-(4-fluorobenzyl)-isothiosemicarbazone and salicylaldehyde-S-(4-bromobenzyl)-isothiosemicarbazone, influenced the isocitrate lyase activity and caused a better inhibition at 10 µmol/L than 3-nitropropionic acid, a standard inhibitor. The compounds were also found to act as exogenous chelators of iron, which is an obligate cofactor for many mycobacterial enzymes. Due to their low cytotoxicity, together with the activity against isocitrate lyase and the ability to sequester iron ions, the compounds belong to potential antibiotics with the main effect on mycobacteria.

Chronic anthracycline cardiotoxicity: molecular and functional analysis with focus on nuclear factor erythroid 2-related factor 2 and mitochondrial biogenesis pathways.

Anthracycline anticancer drugs (e.g., doxorubicin or daunorubicin) can induce chronic cardiotoxicity and heart failure (HF), both of which are believed to be based on oxidative injury and mitochondrial damage. In this study, molecular and functional changes induced by chronic anthracycline treatment with progression into HF in post-treatment follow-up were analyzed with special emphasis on nuclear factor erythroid 2-related factor 2 (Nrf2) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α) pathways. Chronic cardiotoxicity was induced in rabbits with daunorubicin (3 mg/kg, weekly for 10 weeks), and the animals were followed for another 10 weeks. Echocardiography revealed a significant drop in left ventricular (LV) systolic function during the treatment with marked progression to LV dilation and congestive HF in the follow-up. Although daunorubicin-induced LV lipoperoxidation was found, it was only loosely associated with cardiac performance. Furthermore, although LV oxidized glutathione content was increased, the oxidized-to-reduced glutathione ratio itself remained unchanged. Neither Nrf2, the master regulator of antioxidant response, nor the majority of its target genes showed up-regulation in the study. However, down-regulation of manganese superoxide dismutase and NAD(P)H dehydrogenase [quinone] 1 were observed together with heme oxygenase 1 up-regulation. Although marked perturbations in mitochondrial functions were found, no induction of PGC1α-controlled mitochondrial biogenesis pathway was revealed. Instead, especially in the post-treatment period, an impaired regulation of this pathway was observed along with down-regulation of the expression of mitochondrial genes. These results imply that global oxidative stress need not be a factor responsible for the development of anthracycline-induced HF, whereas suppression of mitochondrial biogenesis might be involved.

Examination of diverse iron-chelating agents for the protection of differentiated PC12 cells against oxidative injury induced by 6-hydroxydopamine and dopamine.

Labile redox-active iron ions have been implicated in various neurodegenerative disorders, including the Parkinson's disease (PD). Iron chelation has been successfully used in clinical practice to manage iron overload in diseases such as thalassemia major; however, the use of conventional iron chelators in pathological states without systemic iron overload remains at the preclinical investigative level and is complicated by the risk of adverse outcomes due to systemic iron depletion. In this study, we examined three clinically-used chelators, namely, desferrioxamine, deferiprone and deferasirox and compared them with experimental agent salicylaldehyde isonicotinoyl hydrazone (SIH) and its boronate-masked prochelator BSIH for protection of differentiated PC12 cells against the toxicity of catecholamines 6-hydroxydopamine and dopamine and their oxidation products. All the assayed chelating agents were able to significantly reduce the catecholamine toxicity in a dose-dependent manner. Whereas hydrophilic chelator desferrioxamine exerted protection only at high and clinically unachievable concentrations, deferiprone and deferasirox significantly reduced the catecholamine neurotoxicity at concentrations that are within their plasma levels following standard dosage. SIH was the most effective iron chelator to protect the cells with the lowest own toxicity of all the assayed conventional chelators. This favorable feature was even more pronounced in prochelator BSIH that does not chelate iron unless its protective group is cleaved in disease-specific oxidative stress conditions. Hence, this study demonstrated that while iron chelation may have general neuroprotective potential against catecholamine auto-oxidation and toxicity, SIH and BSIH represent promising lead molecules and warrant further studies in more complex animal models.

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

Oxidative stress is known to contribute to a number of cardiovascular pathologies. Free intracellular iron ions participate in the Fenton reaction and therefore substantially contribute to the formation of highly toxic hydroxyl radicals and cellular injury. Earlier work on the intracellular iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) has demonstrated its considerable promise as an agent to protect the heart against oxidative injury both in vitro and in vivo. However, the major limitation of SIH is represented by its labile hydrazone bond that makes it prone to plasma hydrolysis. Hence, in order to improve the hydrazone bond stability, nine compounds were prepared by a substitution of salicylaldehyde by the respective methyl- and ethylketone with various electron donors or acceptors in the phenyl ring. All the synthesized aroylhydrazones displayed significant iron-chelating activities and eight chelators showed significantly higher stability in rabbit plasma than SIH. Furthermore, some of these chelators were observed to possess higher cytoprotective activities against oxidative injury and/or lower toxicity as compared to SIH. The results of the present study therefore indicate the possible applicability of several of these novel agents in the prevention and/or treatment of cardiovascular disorders with a known (or presumed) role of oxidative stress. In particular, the methylketone HAPI and nitro group-containing NHAPI merit further in vivo investigations.

In vivo and in vitro assessment of the role of glutathione antioxidant system in anthracycline-induced cardiotoxicity.

The clinical usefulness of anthracycline antineoplastic drugs is limited by their cardiotoxicity. Its mechanisms have not been fully understood, although the induction of oxidative stress is widely believed to play the principal role. Glutathione is the dominant cellular antioxidant, while glutathione peroxidase (GPx) together with glutathione reductase (GR) constitutes the major enzymatic system protecting the cardiac cells from oxidative damage. Therefore, this study aimed to assess their roles in anthracycline cardiotoxicity. Ten-week intravenous administration of daunorubicin (DAU, 3 mg/kg weekly) to rabbits induced heart failure, which was evident from decreased left ventricular ejection fraction and release of cardiac troponins to circulation. However, no significant changes in either total or oxidized glutathione contents or GR activity were detected in left ventricular tissue of DAU-treated rabbits when compared with control animals. GPx activity in the cardiac tissue significantly increased. In H9c2 rat cardiac cells, 24-h DAU exposure (0.1-10 µM) induced significant dose-dependent toxicity. Cellular content of reduced glutathione was insignificantly decreased, oxidized glutathione and GR activity were unaffected, and GPx activity was significantly increased. Neither buthionine sulfoximine (BSO, glutathione biosynthesis inhibitor) nor 2-oxo-4-thiazolidine-carboxylic acid (OTC, glutathione biosynthetic precursor) had significant effects on DAU cytotoxicity. This contrasted with model oxidative injury induced by hydrogen peroxide, which cytotoxicity was increased by BSO and decreased by OTC. In conclusion, our results suggest that the dysfunction of glutathione antioxidant system does not play a causative role in anthracycline cardiotoxicity.

Comparison of clinically used and experimental iron chelators for protection against oxidative stress-induced cellular injury.

Iron imbalance plays an important role in oxidative stress associated with numerous pathological conditions. Therefore, iron chelation may be an effective therapeutic approach, but progress in this area is hindered by the lack of effective ligands. Also, the potential favorable effects of chelators against oxidative injury have to be balanced against their own toxicity due to iron depletion and the ability to generate redox-active iron complexes. In this study, we compared selected iron chelators (both drugs used in clinical practice as well as experimental agents) for their efficacy to protect cells against model oxidative injury induced by tert-butyl hydroperoxide (t-BHP). In addition, intracellular chelation efficiency, redox activity, and the cytotoxicity of the chelators and their iron complexes were assayed. Ethylenediaminetetraacetic acid failed to protect cells against t-BHP cytotoxicity, apparently due to the redox activity of the formed iron complex. Hydrophilic desferrioxamine exerted some protection but only at very high clinically unachievable concentrations. The smaller and more lipophilic chelators, deferiprone, deferasirox, and pyridoxal isonicotinoyl hydrazone, were markedly more effective at preventing oxidative injury of cells. The most effective chelator in terms of access to the intracellular labile iron pool was di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone. However, overall, the most favorable properties in terms of protective efficiency against t-BHP and the chelator's own inherent cytotoxicity were observed with salicylaldehyde isonicotinoyl hydrazone. This probably relates to the optimal lipophilicity of this latter agent and its ability to generate iron complexes that do not induce marked redox activity.

The novel iron chelator, 2-pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone, reduces catecholamine-mediated myocardial toxicity.

Iron (Fe) chelators are used clinically for the treatment of Fe overload disease. Iron also plays a role in the pathology of many other conditions, and these potentially include the cardiotoxicity induced by catecholamines such as isoprenaline (ISO). The current study examined the potential of Fe chelators to prevent ISO cardiotoxicity. This was done as like other catecholamines, ISO contains the classical catechol moiety that binds Fe and may form redox-active and cytotoxic Fe complexes. Studies in vitro used the cardiomyocyte cell line, H9c2, which was treated with ISO in the presence or absence of the chelator, desferrioxamine (DFO), or the lipophilic ligand, 2-pyridylcarboxaldehyde 2-thiophenecarboxyl hydrazone (PCTH). Both of these chelators were not cardiotoxic and significantly reduced ISO cardiotoxicity in vitro. However, PCTH was far more effective than DFO, with the latter showing activity only at a high, clinically unachievable concentration. Further studies in vitro showed that interaction of ISO with Fe(II)/(III) did not increase cytotoxic radical generation, suggesting that this mechanism was not involved. Studies in vivo were initiated using rats pretreated intravenously with DFO or PCTH before subcutaneous administration of ISO (100 mg/kg). DFO at a clinically used dose (50 mg/kg) failed to reduce catecholamine cardiotoxicity, while PCTH at an equimolar dose totally prevented catecholamine-induced mortality and reduced cardiotoxicity. This study demonstrates that PCTH reduced ISO-induced cardiotoxicity in vitro and in vivo, demonstrating that Fe plays a role, in part, in the pathology observed.

Direct administration of rutin does not protect against catecholamine cardiotoxicity.

High levels of catecholamines are cardiotoxic and may trigger acute myocardial infarction (AMI). Similarly, the synthetic catecholamine isoprenaline (ISO) evokes a pathological state similar to AMI. During AMI there is a marked increase of free iron and copper which are crucial catalysts of reactive oxygen species formation. Rutin, a natural flavonoid glycoside possessing free radical scavenging and iron/copper chelating activity, may therefore be potentially useful in reduction of catecholamine cardiotoxicity as was previously demonstrated after its long-term peroral administration. Male Wistar:Han rats received rutin (46 or 11.5 mg kg(-1) i.v.) alone or with necrogenic dose of ISO (100 mg kg(-1) s.c.). Haemodynamic parameters were measured 24h after drug application together with analysis of blood, myocardial content of elements and histological examination. Results were confirmed by cytotoxicity studies using cardiomyoblast cell line H9c2. Rutin in a dose of 46 mg kg(-1) aggravated ISO-cardiotoxicity while the dose of 11 mg kg(-1) had no effect. These unexpected results were in agreement with in vitro experiments, where co-incubation with larger concentrations of rutin significantly augmented ISO cytotoxicity. Our results, in contrast to previous studies in the literature, suggest that the reported positive effects of peroral administration of rutin were unlikely to have been mediated by rutin per se but probably by its metabolite(s) or by some other, at this moment, unknown adaptive mechanism(s), which merit further investigation.

HPLC-DAD and MS/MS analysis of novel drug candidates from the group of aromatic hydrazones revealing the presence of geometric isomers.

Salicylaldehyde isonicotinoyl hydrazone (SIH) is an iron-chelating aromatic hydrazone with promising pharmacological properties. However, it suffers from relatively short biological half-life. Hence, two novel derivates of SIH, HAP-INH and HPP-INH were synthesized in order to overcome this pharmacokinetic drawback. The aim of the present study was to employ HPLC-DAD and HPLC-MS/MS methods to investigate the identity of the putative impurities of these newly prepared substances, which are being formed in aqueous environment. At first, it was shown that their retention times as well as UV spectra did not correspond to any expected synthetic precursor, by-product or degradation product. HPLC-DAD analysis confirmed purity of peaks and revealed close but not identical UV spectra of putative impurities and corresponding hydrazones. The subsequent HPLC-MS/MS analyses using ESI and the ion trap mass analyzer showed the identical molecular ions (in both modes) as well as their fragmentation, which implicated presence of geometric isomers. This suggestion was further supported by the NMR analyses. Since the Z/E isomers can have different biological activities, results of this study might be of great importance for further development of the aroylhydrazones as novel drug candidates as well as from the theoretical point of view.

Intravenous rutin in rat exacerbates isoprenaline-induced cardiotoxicity likely due to intracellular oxidative stress.

OBJECTIVES: Rutin, quercetin-3-O-rutinoside, a natural flavonol glycoside, has shown various in vitro benefits with potential use treating human diseases, especially cardiovascular system disorders. Antioxidant properties are assumed to underlie the majority of these benefits. Yet rutin pro-oxidant properties have been reported as well. Our research group has recently shown aggravating effects on isoprenaline (ISO)-induced cardiotoxicity in Wistar:Han rats after 24 hours. METHODS: This study was designed to examine in more detail the reasons for the negative effects of rutin (11.5 and 46 mg/kg, i.v.) after administration of ISO (100 mg/kg, s.c.) in rats within 2 hours of continuous experiment and in the H9c2 cardiomyoblast-derived cell line. RESULTS: Like our previous findings, rutin did not (11.5 or 46 mg/kg, i.v.) reduce the ISO-induced mortality within 2 hours although the lower dose significantly reduced cardiac troponin T (cTnT) and partly improved the histological findings. In contrast, the higher dose increased the mortality in comparison with solvent (1.26% w/v sodium bicarbonate). This was not caused by any specific haemodynamic disturbances. It appears to be associated with oxidative stress as rutin enhanced intracellular reactive oxygen species formation in vitro and had the tendency to increase it in vivo. CONCLUSIONS: Rutin, likely due to its pro-oxidative effects, can exacerbate catecholamine cardiotoxicity depending on the dose used.

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)-N-(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.

Aroylhydrazone iron chelators: Tuning antioxidant and antiproliferative properties by hydrazide modifications.

Aroylhydrazones such as salicylaldehyde isonicotinoyl hydrazone (SIH) are tridentate iron chelators that may possess antioxidant and/or antineoplastic activities. Their main drawback, their low stability in plasma, has recently been partially overcome by exchanging the aldimine hydrogen for an unbranched alkyl group. In this study, ten analogs of methyl- and ethyl-substituted SIH derivatives with modified hydrazide scaffolds were synthesized to further explore their structure-activity relationships. Their iron-chelation efficiencies, anti- or pro-oxidant potentials, abilities to induce protection against model oxidative injury on the H9c2 cell line derived from rat embryonic cardiac tissue, cytotoxicities on the same H9c2 cells and antiproliferative activities on MCF-7 human breast adenocarcinoma and HL-60 human promyelotic leukemia cell lines were evaluated. Compounds derived from lipophilic naphthyl and biphenyl hydrazides displayed highly selective antiproliferative activities against both MCF-7 and HL-60 cell lines, and they showed markedly improved stabilities in plasma compared to SIH. Of particular interest is a hydrazone prepared from 2-hydroxypropiophenone and pyridazin-4-carbohydrazide that showed a considerable antiproliferative effect and protected cardiomyoblasts against oxidative stress with a five-fold higher selectivity compared to the parent compound SIH. Thus, this work highlighted new structure-activity relationships among antiproliferative and antioxidant aroylhydrazones and identified new lead compounds for further development.

Protective Effects of D-Penicillamine on Catecholamine-Induced Myocardial Injury.

Iron and copper release participates in the myocardial injury under ischemic conditions and hence protection might be achieved by iron chelators. Data on copper chelation are, however, sparse. The effect of the clinically used copper chelator D-penicillamine in the catecholamine model of acute myocardial injury was tested in cardiomyoblast cell line H9c2 and in Wistar Han rats. D-Penicillamine had a protective effect against catecholamine-induced injury both in vitro and in vivo. It protected H9c2 cells against the catecholamine-induced viability loss in a dose-dependent manner. In animals, both intravenous D-penicillamine doses of 11 (low) and 44 mg/kg (high) decreased the mortality caused by s.c. isoprenaline (100 mg/kg) from 36% to 14% and 22%, respectively. However, whereas the low D-penicillamine dose decreased the release of cardiac troponin T (specific marker of myocardial injury), the high dose resulted in an increase. Interestingly, the high dose led to a marked elevation in plasma vitamin C. This might be related to potentiation of oxidative stress, as suggested by additional in vitro experiments with D-penicillamine (iron reduction and the Fenton reaction). In conclusion, D-penicillamine has protective potential against catecholamine-induced cardiotoxicity; however the optimal dose selection seems to be crucial for further application.

Characterization of cytoprotective and toxic properties of iron chelator SIH, prochelator BSIH and their degradation products.

Free cellular iron catalyzes the formation of toxic hydroxyl radicals and therefore chelation of iron could be a promising therapeutic approach in pathological states associated with oxidative stress. Salicylaldehyde isonicotinoyl hydrazone (SIH) is a strong intracellular iron chelator with well documented potential to protect against oxidative damage both in vitro and in vivo. Due to the short biological half-life of SIH and risk of toxicity due to iron depletion, boronate prochelator BSIH has been designed. BSIH cannot bind iron until it is activated by certain reactive oxygen species to active chelator SIH. The aim of this study was to examine the toxicity and cytoprotective potential of BSIH, SIH, and their decomposition products against hydrogen peroxide-induced injury of H9c2 cardiomyoblast cells. Using HPLC, we observed that salicylaldehyde was the main decomposition products of SIH and BSIH, although a small amount of salicylic acid was also detected. In the case of BSIH, the concentration of formed salicylaldehyde consistently exceeded that of SIH. Isoniazid and salicylic acid were not toxic nor did they provide any antioxidant protective effect in H9c2 cells. In contrast, salicylaldehyde was able to chelate intracellular iron and significantly preserve cellular viability and mitochondrial inner membrane potential induced by hydrogen peroxide. However it was consistently less effective than SIH. The inherent toxicities of salicylaldehyde and SIH were similar. Hence, although SIH - the active chelating agent formed following the BSIH activation - undergoes rapid hydrolysis, its principal decomposition product salicylaldehyde accounts markedly for both cytoprotective and toxic properties.

In Vitro Characterization of the Pharmacological Properties of the Anti-Cancer Chelator, Bp4eT, and Its Phase I Metabolites.

Cancer cells have a high iron requirement and many experimental studies, as well as clinical trials, have demonstrated that iron chelators are potential anti-cancer agents. The ligand, 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone (Bp4eT), demonstrates both potent anti-neoplastic and anti-retroviral properties. In this study, Bp4eT and its recently identified amidrazone and semicarbazone metabolites were examined and compared with respect to their anti-proliferative activity towards cancer cells (HL-60 human promyelocytic leukemia, MCF-7 human breast adenocarcinoma, HCT116 human colon carcinoma and A549 human lung adenocarcinoma), non-cancerous cells (H9c2 neonatal rat-derived cardiomyoblasts and 3T3 mouse embryo fibroblasts) and their interaction with intracellular iron pools. Bp4eT was demonstrated to be a highly potent and selective anti-neoplastic agent that induces S phase cell cycle arrest, mitochondrial depolarization and apoptosis in MCF-7 cells. Both semicarbazone and amidrazone metabolites showed at least a 300-fold decrease in cytotoxic activity than Bp4eT towards both cancer and normal cell lines. The metabolites also lost the ability to: (1) promote the redox cycling of iron; (2) bind and mobilize iron from labile intracellular pools; and (3) prevent 59Fe uptake from 59Fe-labeled transferrin by MCF-7 cells. Hence, this study demonstrates that the highly active ligand, Bp4eT, is metabolized to non-toxic and pharmacologically inactive analogs, which most likely contribute to its favorable pharmacological profile. These findings are important for the further development of this drug candidate and contribute to the understanding of the structure-activity relationships of these agents.

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.

Cucurbitacin E has neuroprotective properties and autophagic modulating activities on dopaminergic neurons.

Natural molecules are under intensive study for their potential as preventive and/or adjuvant therapies for neurodegenerative disorders such as Parkinson's disease (PD). We evaluated the neuroprotective potential of cucurbitacin E (CuE), a tetracyclic triterpenoid phytosterol extracted from the Ecballium elaterium (Cucurbitaceae), using a known cellular model of PD, NGF-differentiated PC12. In our postmitotic experimental paradigm, neuronal cells were treated with the parkinsonian toxin 1-methyl-4-phenylpyridinium (MPP(+)) to provoke significant cellular damage and apoptosis or with the potent N,N-diethyldithiocarbamate (DDC) to induce superoxide (O2(•-)) production, and CuE was administered prior to and during the neurotoxic treatment. We measured cellular death and reactive oxygen species to evaluate the antioxidant and antiapoptotic properties of CuE. In addition, we analyzed cellular macroautophagy, a bulk degradation process involving the lysosomal pathway. CuE showed neuroprotective effects on MPP(+)-induced cell death. However, CuE failed to rescue neuronal cells from oxidative stress induced by MPP(+) or DDC. Microscopy and western blot data show an intriguing involvement of CuE in maintaining lysosomal distribution and decreasing autophagy flux. Altogether, these data indicate that CuE decreases neuronal death and autophagic flux in a postmitotic cellular model of PD.

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.

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.