Deferiprone protects against doxorubicin-induced myocyte cytotoxicity

The Vital Role Played by Deferiprone in the Transition of Thalassaemia from a Fatal to a Chronic Disease and Challenges in Its Repurposing for Use in Non-Iron-Loaded Diseases

The iron chelating orphan drug deferiprone (L1), discovered over 40 years ago, has been used daily by patients across the world at high doses (75-100 mg/kg) for more than 30 years with no serious toxicity. The level of safety and the simple, inexpensive synthesis are some of the many unique properties of L1, which played a major role in the contribution of the drug in the transition of thalassaemia from a fatal to a chronic disease. Other unique and valuable clinical properties of L1 in relation to pharmacology and metabolism include: oral effectiveness, which improved compliance compared to the prototype therapy with subcutaneous deferoxamine; highly effective iron removal from all iron-loaded organs, particularly the heart, which is the major target organ of iron toxicity and the cause of mortality in thalassaemic patients; an ability to achieve negative iron balance, completely remove all excess iron, and maintain normal iron stores in thalassaemic patients; rapid absorption from the stomach and rapid clearance from the body, allowing a greater frequency of repeated administration and overall increased efficacy of iron excretion, which is dependent on the dose used and also the concentration achieved at the site of drug action; and its ability to cross the blood-brain barrier and treat malignant, neurological, and microbial diseases affecting the brain. Some differential pharmacological activity by L1 among patients has been generally shown in relation to the absorption, distribution, metabolism, elimination, and toxicity (ADMET) of the drug. Unique properties exhibited by L1 in comparison to other drugs include specific protein interactions and antioxidant effects, such as iron removal from transferrin and lactoferrin; inhibition of iron and copper catalytic production of free radicals, ferroptosis, and cuproptosis; and inhibition of iron-containing proteins associated with different pathological conditions. The unique properties of L1 have attracted the interest of many investigators for drug repurposing and use in many pathological conditions, including cancer, neurodegenerative conditions, microbial conditions, renal conditions, free radical pathology, metal intoxication in relation to Fe, Cu, Al, Zn, Ga, In, U, and Pu, and other diseases. Similarly, the properties of L1 increase the prospects of its wider use in optimizing therapeutic efforts in many other fields of medicine, including synergies with other drugs.

Nature-Inspired Bioactive Compounds: A Promising Approach for Ferroptosis-Linked Human Diseases?

Ferroptosis is a type of cell death driven by iron overload and lipid peroxidation. It is considered a key mechanism in the development of various diseases such as atherosclerosis, Alzheimer, diabetes, cancer, and renal failure. The redox status of cells, such as the balance between intracellular oxidants (lipid peroxides, reactive oxygen species, free iron ions) and antioxidants (glutathione, glutathione Peroxidase 4), plays a major role in ferroptosis regulation and constitutes its principal biomarkers. Therefore, the induction and inhibition of ferroptosis are promising strategies for disease treatments such as cancer or neurodegenerative and cardiovascular diseases, respectively. Many drugs have been developed to exert ferroptosis-inducing and/or inhibiting reactions, such as erastin and iron-chelating compounds, respectively. In addition, many natural bioactive compounds have significantly contributed to regulating ferroptosis and ferroptosis-induced oxidative stress. Natural bioactive compounds are largely abundant in food and plants and have been for a long time, inspiring the development of various low-toxic therapeutic drugs. Currently, functional bioactive peptides are widely reported for their antioxidant properties and application in human disease treatment. The scientific evidence from biochemical and in vitro tests of these peptides strongly supports the existence of a relationship between their antioxidant properties (such as iron chelation) and ferroptosis regulation. In this review, we answer questions concerning ferroptosis milestones, its importance in physiopathology mechanisms, and its downstream regulatory mechanisms. We also address ferroptosis regulatory natural compounds as well as provide promising thoughts about bioactive peptides.

New Iron Metabolic Pathways and Chelation Targeting Strategies Affecting the Treatment of All Types and Stages of Cancer

There is new and increasing evidence from in vitro, in vivo and clinical studies implicating the pivotal role of iron and associated metabolic pathways in the initiation, progression and development of cancer and in cancer metastasis. New metabolic and toxicity mechanisms and pathways, as well as genomic, transcription and other factors, have been linked to cancer and many are related to iron. Accordingly, a number of new targets for iron chelators have been identified and characterized in new anticancer strategies, in addition to the classical restriction of/reduction in iron supply, the inhibition of transferrin iron delivery, the inhibition of ribonucleotide reductase in DNA synthesis and high antioxidant potential. The new targets include the removal of excess iron from iron-laden macrophages, which affects anticancer activity; the modulation of ferroptosis; ferritin iron removal and the control of hyperferritinemia; the inhibition of hypoxia related to the role of hypoxia-inducible factor (HIF); modulation of the function of new molecular species such as STEAP4 metalloreductase and the metastasis suppressor N-MYC downstream-regulated gene-1 (NDRG1); modulation of the metabolic pathways of oxidative stress damage affecting mitochondrial function, etc. Many of these new, but also previously known associated iron metabolic pathways appear to affect all stages of cancer, as well as metastasis and drug resistance. Iron-chelating drugs and especially deferiprone (L1), has been shown in many recent studies to fulfill the role of multi-target anticancer drug linked to the above and also other iron targets, and has been proposed for phase II trials in cancer patients. In contrast, lipophilic chelators and their iron complexes are proposed for the induction of ferroptosis in some refractory or recurring tumors in drug resistance and metastasis where effective treatments are absent. There is a need to readdress cancer therapy and include therapeutic strategies targeting multifactorial processes, including the application of multi-targeting drugs involving iron chelators and iron-chelator complexes. New therapeutic protocols including drug combinations with L1 and other chelating drugs could increase anticancer activity, decrease drug resistance and metastasis, improve treatments, reduce toxicity and increase overall survival in cancer patients.

Iron: Key player in cancer and cell cycle?

BACKGROUND

Iron is an essential element for growth and metabolic activities of all living organisms but remains in its oxyhydroxide ferric ion form in the surrounding. Unavailability of iron in soluble ferrous form led to development of specific pathways and machinery in different organisms to make it available for use and maintain its homeostasis. Iron homeostasis is essential as under different circumstances iron in excess as well as deprivation leads to different pathological conditions in human.

OBJECTIVE

This review highlights the current findings related to iron excess as well as deprivation with regards to cellular proliferation.

CONCLUSIONS

Iron excess is extensively associated with different types of cancers viz. colorectal cancer, breast cancer etc. by producing an oxidative stressed condition and alteration of immune system. Ironically its deprivation also results in anaemic conditions and leads to cell cycle arrest at different phases with mechanism yet to be explored. Iron deprivation arrests cell cycle at G1/S and in some cases at G2/M checkpoints resulting in growth arrest. However, in some cases iron overload arrests cell cycle at G1 phase by blocking certain signalling pathways. Certain natural and synthetic iron chelators are being explored from few decades to combat diseases caused by alteration in iron homeostasis.

A QSAR study that compares the ability of bisdioxopiperazine analogs of the doxorubicin cardioprotective agent dexrazoxane (ICRF-187) to protect myocytes with DNA topoisomerase II inhibition

The cardiotoxicity caused by doxorubicin and extravasation injury caused by anthracyclines is reduced by the clinically approved bisdioxopiperazine drug dexrazoxane. Dexrazoxane is a rings-closed analog of EDTA and is hydrolyzed in vivo to a form that strongly binds iron. Its protective effects were originally thought to be due to the ability of its metabolite to remove iron from the iron-doxorubicin complex, thereby preventing oxygen radical damage to cellular components. More recently it has been suggested that dexrazoxane may exert its protective effects by inhibiting topoisomerase IIβ in the heart and inducing a reduction in its protein levels through induction of proteasomal degradation. The ability of dexrazoxane, other bisdioxopiperazines, and mitindomide to protect against doxorubicin-induced damage was determined in primary neonatal rat myocytes. This QSAR study showed that the protection that a series of bisdioxopiperazine analogs of dexrazoxane and the bisimide mitindomide offered against doxorubicin-induced myocyte damage was highly correlated with the ability of these compounds to catalytically inhibit the decatenation activity of topoisomerase II. The structural features of the dexrazoxane analogs that contribute to the binding and inhibition of topoisomerase II have been identified. These results suggest that the inhibition of topoisomerase II in myocytes by dexrazoxane is central to its role in its activity as an anthracycline cardioprotective agent. Additionally, sequence identity analysis of the amino acids surrounding the dexrazoxane binding site showed extremely high identity, not only between both invertebrate topoisomerase II isoforms, but also with yeast topoisomerase II as well.

Advances on Chelation and Chelator Metal Complexes in Medicine

Metal ions such as iron, copper and zinc are essential for life. Chelators (Chele, greek χειλή-claw of a crab) are organic molecules possessing specific ligands which have high affinity and can bind/carry metal ions and play very important roles in living systems e.g., haemoglobin, transferrin, phytochelators and microbial siderophores [...].

The History of Deferiprone (L1) and the Paradigm of the Complete Treatment of Iron Overload in Thalassaemia

Deferiprone (L1) was originally designed, synthesised and screened in vitro and in vivo in 1981 by Kontoghiorghes G. J. following his discovery of the novel alpha-ketohydroxypyridine class of iron chelators (1978–1981), which were intended for clinical use. The journey through the years for the treatment of thalassaemia with L1 has been a very difficult one with an intriguing turn of events, which continue until today. Despite many complications, such as the extensive use of L1 suboptimal dose protocols, the aim of chelation therapy-namely, the complete removal of excess iron in thalassaemia major patients, has been achieved in most cases following the introduction of specific L1 and L1/deferoxamine combinations. Many such patients continue to maintain normal iron stores. Thalassemia has changed from a fatal to chronic disease; also thanks to L1 therapy and thalassaemia patients are active professional members in all sectors of society, have their own families with children and grandchildren and their lifespan is approaching that of normal individuals. No changes in the low toxicity profile of L1 have been observed in more than 30 years of clinical use and prophylaxis against the low incidence of agranulocytosis is maintained using mandatory monitoring of weekly white blood cells’ count. Thousands of thalassaemia patients are still denied the cardioprotective and other beneficial effects of L1 therapy. The safety of L1 in thalassaemia and other non-iron loaded diseases resulted in its selection as one of the leading therapeutics for the treatment of Friedreich’s ataxia, pantothenate kinase-associated neurodegeneration and other similar cases. There are also increasing prospects for the application of L1 as a main, alternative or adjuvant therapy in many pathological conditions including cancer, infectious diseases and as a general antioxidant for diseases related to free radical pathology.

Bacterial magnetosomes loaded with doxorubicin and transferrin improve targeted therapy of hepatocellular carcinoma

High metastatic rate and recurrence of tumor because of tumor circulating cells are seriously hinders for clinical tumor therapy. Herein, we develop a novel, active-targeting nanotherapeutic by simultaneously loading doxorubicin (DOX) and transferrin (Tf) onto bacterial magnetosomes (Tf-BMs-DOX) and investigate its antitumor efficacy in vitro and in vivo. Drug release profiles indicated that Tf-BMs/BMs loaded with DOX were capable of sustained drug release, suggesting that reduce drugs required frequency of administration and enhance their therapeutic effect. The results of cellular uptake revealed that Tf-BMs-DOX recognized hepatocellular carcinoma HepG2 cells more specifically compared to HL-7702 normal hepatocytes because of high expression of transferrin receptor (TfR) on the surface of HepG2 cells. Tf-BMs-DOX increased tumor cytotoxicity and apoptosis more significantly than free DOX or BMs-DOX by regulating the expression of tumor-related and apoptosis-related genes. Following intravenous injection in HepG2 cell-bearing mice, Tf-BMs-DOX displayed tumor suppression rate of 56.78%, significantly higher than that of the BMs-DOX (41.53%) and free DOX (31.26%) groups. These results suggest that Tf-BMs-DOX have the potential to actively target to tumor sites, as well as the ability to kill circulating tumor cells via intravenous injection. Our findings provide a promising candidate for the clinical treatment of metastatic cancer.

Oral deferiprone administration ameliorates cisplatin-induced nephrotoxicity in rats

OBJECTIVES

Cisplatin is one of the widely used antitumour agents with major clinical side effect, nephrotoxicity. We showed the role of iron in cisplatin-induced nephrotoxicity that entrance to the cell via transferrin receptor (TfR) as a gatekeeper for iron uptake. We also examined the effect of iron chelator deferiprone against this toxicity.

METHODS

Thirty male Wistar rats were randomly divided into six groups. Group I (saline orally for 10 days); group II (saline orally for 10 days plus single injection of cisplatin 7 mg/kg, intraperitoneally on 5^th day); groups III, IV and V (deferiprone 50, 100 and 200 mg/kg orally for 10 days, respectively, plus cisplatin on 5th day). Group VI (deferiprone, orally).

RESULTS

Deferiprone provided functional and significant histological-proven protection in group IV. Deferiprone attenuated the increased creatinine, BUN, malondialdehyde and iron concentrations in cisplatin-injected animals. The increased amounts of TfR and decreased levels of HIF-1α and related anti-apoptotic genes expression in cisplatin-treated animals were improved by deferiprone.

CONCLUSIONS

The results supported a role for iron in cisplatin-induced nephrotoxicity and TfR may serve as an important source of iron. Based on these findings, deferiprone pretreatment may play a role in preventing cisplatin-induced nephropathy in cancer patient.

Creatine Supplementation and Doxorubicin-Induced Skeletal Muscle Dysfunction: An Ex Vivo Investigation

Supplementing the diet with creatine (Cr) to manage chemotherapy-induced skeletal muscle weakness and fatigue has potential, but little has been done exploring it as an intervention. This study examined the effects of Cr on skeletal muscle dysfunction induced by the chemotherapy drug doxorubicin (Dox). Soleus and extensor digitorum longus (EDL) from male Sprague-Dawley rats maintained in an organ bath were incubated in Krebs-Henseleit (KH) buffer with or without creatine monohydrate (25 mM) for 30 min. Skeletal muscle was then incubated in KH buffer with or without Dox (24 μM) for an additional 30 min. Baths were then refreshed with KH buffer, and a 100-s fatigue protocol was administered. At baseline (0 s time point), no significant differences in force production were observed in the slow, type I soleus, but the Dox-treated soleus fatigued quicker than the non-Dox-treated soleus; however, pretreatment with Cr extended the time to fatigue in the Dox-treated soleus. In the fast, type II EDL, Dox treatment decreased force production at baseline and increased fatigue, and Cr treatment prior to Dox attenuated this dysfunction. Creatine pretreatment mitigated Dox-induced skeletal muscle dysfunction ex vivo suggesting that Cr may play a role in managing Dox-induced skeletal muscle side effects.

Efficacy of doxorubicin-transferrin conjugate in apoptosis induction in human leukemia cells through reactive oxygen species generation

Background

Doxorubicin (DOX) is a small molecular cytotoxic agent that can be transferred efficiently to cancer cells by nanocarriers. This anthracycline antibiotic serves as an effective anti-neoplastic drug against both hematological and solid malignancies. Here, we set out to assess the capacity of a novel doxorubicin - transferrin conjugate (DOX-TRF) to provoke apoptosis in human normal and leukemia cells through free radicals produced via a redox cycle of doxorubicin (DOX) when released from its conjugate.

Methods

After DOX-TRF exposure, we determined the time-course of apoptotic and necrotic events, the generation of reactive oxygen species (ROS), changes in mitochondrial membrane potential, as well as alterations in cytochrome c levels and intracellular calcium concentrations in human leukemia-derived cell lines (CCRF-CEM, K562 and its doxorubicin-resistant derivative K562/DOX) and normal peripheral blood-derived mononuclear cells (PBMC).

Results

We found that DOX-TRF can induce apoptosis in all leukemia-derived cell lines tested, which was associated with morphological changes and decreases in mitochondrial membrane potential. In comparison to free DOX treated cells, we observed a time-dependency between a higher level of ROS generation and a higher drop in mitochondrial membrane potential, particularly in the doxorubicin-resistant cell line. In addition, we found that the apoptotic cell death induced by DOX-TRF was directly associated with a release of cytochrome c from the mitochondria and an increase in intracellular calcium level in all human leukemia-derived cell lines tested.

Conclusions

Our data indicate that DOX-TRF is considerably more cytotoxic to human leukemia cells than free DOX. In addition, we show that DOX-TRF can effectively produce free radicals, which are directly involved in apoptosis induction.

JAK2/STAT3 Pathway Mediates Protection of Metallothionein Against Doxorubicin-Induced Cytotoxicity in Mouse Cardiomyocytes

Doxorubicin (Dox) is one of the most important anticancer agents; however, its clinical application is limited by its severe cardiotoxicity. In our previous study, we found that the gene expression levels of the Janus-activated kinase/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway were different between MT(-/-) cardiomyocytes and MT(+/+) cardiomyocytes when they were treated with Dox. Thus, this study was intended to investigate the role of JAK2/STAT3 pathway in metallothionein (MT) protection of Dox-induced cardiotoxicity. Tyrphostin AG490 (α-cyano-(3,4-dihydroxy)-N-benzylcinnamide) is a synthetic protein tyrosine kinase inhibitor which at first has been considered as a specific JAK2 inhibitor and can inhibit the JAK2/STAT3 signaling pathway. In the present study, AG490 was used to assess the role of JAK2/STAT3 in MT protection against Dox-induced cardiotoxicity. The AG490 can attenuate the MT protection by increasing lactate dehydrogenase and the number of apoptotic cells. Interestingly, pretreated with AG490, MT(-/-) cardiomyocytes were more sensitive than MT(+/+) to Dox-induced cytotoxicity as measured by reactive oxygen species generation, lipid peroxidation, and protein carbonylation. Metallothionein 1 and MT-2 messenger RNA were upregulated by Dox, and AG490 decreased the protein expression of MT-1 and MT-2. After Dox treatment, the protein expression of p-Jak2 and p-Stat3 levels was significantly increased in MT(+/+) cardiomyocytes, suggesting that the JAK2/STAT3 pathway was partially involved in MT protection against Dox-induced cardiotoxicity.

A systematic review of the pathophysiology of 5-fluorouracil-induced cardiotoxicity

Background

Cardiotoxicity is a serious side effect to treatment with 5-fluorouracil (5-FU), but the underlying mechanisms are not fully understood. The objective of this systematic review was to evaluate the pathophysiology of 5-FU- induced cardiotoxicity.

Methods

We systematically searched PubMed for articles in English using the search terms: 5-FU OR 5-fluorouracil OR capecitabine AND cardiotoxicity. Papers evaluating the pathophysiology of this cardiotoxicity were included.

Results

We identified 27 articles of 26 studies concerning the pathophysiology of 5-FU-induced cardiotoxicity. The studies demonstrated 5-FU-induced: hemorrhagic infarction, interstitial fibrosis and inflammatory reaction in the myocardium; damage of the arterial endothelium followed by platelet aggregation; increased myocardial energy metabolism and depletion of high energy phosphate compounds; increased superoxide anion levels and a reduced antioxidant capacity; vasoconstriction of arteries; changes in red blood cell (RBC) structure, function and metabolism; alterations in plasma levels of substances involved in coagulation and fibrinolysis and increased endothelin-1 levels and N-terminal-pro brain natriuretic peptide levels. Based on these findings the proposed mechanisms are: endothelial injury followed by thrombosis, increased metabolism leading to energy depletion and ischemia, oxidative stress causing cellular damage, coronary artery spasm leading to myocardial ischemia and diminished ability of RBCs to transfer oxygen resulting in myocardial ischemia.

Conclusions

There is no evidence for a single mechanism responsible for 5-FU-induced cardiotoxicity, and the underlying mechanisms might be multifactorial. Further research is needed to elucidate the pathogenesis of this side effect.

Iron chelators with topoisomerase-inhibitory activity and their anticancer applications

SIGNIFICANCE

Iron and topoisomerases are abundant and essential cellular components. Iron is required for several key processes such as DNA synthesis, mitochondrial electron transport, synthesis of heme, and as a co-factor for many redox enzymes. Topoisomerases serve as critical enzymes that resolve topological problems during DNA synthesis, transcription, and repair. Neoplastic cells have higher uptake and utilization of iron, as well as elevated levels of topoisomerase family members. Separately, the chelation of iron and the cytotoxic inhibition of topoisomerase have yielded potent anticancer agents.

RECENT ADVANCES

The chemotherapeutic drugs doxorubicin and dexrazoxane both chelate iron and target topoisomerase 2 alpha (top2α). Newer chelators such as di-2-pyridylketone-4,4,-dimethyl-3-thiosemicarbazone and thiosemicarbazone -24 have recently been identified as top2α inhibitors. The growing list of agents that appear to chelate iron and inhibit topoisomerases prompts the question of whether and how these two distinct mechanisms might interplay for a cytotoxic chemotherapeutic outcome.

CRITICAL ISSUES

While iron chelation and topoisomerase inhibition each represent mechanistically advantageous anticancer therapeutic strategies, dual targeting agents present an attractive multi-modal opportunity for enhanced anticancer tumor killing and overcoming drug resistance. The commonalities and caveats of dual inhibition are presented in this review.

FUTURE DIRECTIONS

Gaps in knowledge, relevant biomarkers, and strategies for future in vivo studies with dual inhibitors are discussed.

Oxidative stress, redox signaling, and metal chelation in anthracycline cardiotoxicity and pharmacological cardioprotection

SIGNIFICANCE

Anthracyclines (doxorubicin, daunorubicin, or epirubicin) rank among the most effective anticancer drugs, but their clinical usefulness is hampered by the risk of cardiotoxicity. The most feared are the chronic forms of cardiotoxicity, characterized by irreversible cardiac damage and congestive heart failure. Although the pathogenesis of anthracycline cardiotoxicity seems to be complex, the pivotal role has been traditionally attributed to the iron-mediated formation of reactive oxygen species (ROS). In clinics, the bisdioxopiperazine agent dexrazoxane (ICRF-187) reduces the risk of anthracycline cardiotoxicity without a significant effect on response to chemotherapy. The prevailing concept describes dexrazoxane as a prodrug undergoing bioactivation to an iron-chelating agent ADR-925, which may inhibit anthracycline-induced ROS formation and oxidative damage to cardiomyocytes.

RECENT ADVANCES

A considerable body of evidence points to mitochondria as the key targets for anthracycline cardiotoxicity, and therefore it could be also crucial for effective cardioprotection. Numerous antioxidants and several iron chelators have been tested in vitro and in vivo with variable outcomes. None of these compounds have matched or even surpassed the effectiveness of dexrazoxane in chronic anthracycline cardiotoxicity settings, despite being stronger chelators and/or antioxidants.

CRITICAL ISSUES

The interpretation of many findings is complicated by the heterogeneity of experimental models and frequent employment of acute high-dose treatments with limited translatability to clinical practice.

FUTURE DIRECTIONS

Dexrazoxane may be the key to the enigma of anthracycline cardiotoxicity, and therefore it warrants further investigation, including the search for alternative/complementary modes of cardioprotective action beyond simple iron chelation.

Inhibition of doxorubicin-induced senescence by PPARδ activation agonists in cardiac muscle cells: cooperation between PPARδ and Bcl6

Senescence and apoptosis are two distinct cellular programs that are activated in response to a variety of stresses. Low or high doses of the same stressor, i.e., the anticancer drug doxorubicin, may either induce apoptosis or senescence, respectively, in cardiac muscle cells. We have demonstrated that PPARδ, a ligand-activated transcriptional factor that controls lipid metabolism, insulin sensitivity and inflammation, is also involved in the doxorubicin-induced senescence program. This occurs through its interference with the transcriptional repressor protein B cell lymphoma-6 (Bcl6). Low doses of doxorubicin increase the expression of PPARδ that sequesters Bcl6, thus preventing it from exerting its anti-senescent effects. We also found that L-165041, a specific PPARδ activator, is highly effective in protecting cardiomyocytes from doxorubicin-induced senescence through a Bcl6 related mechanism. In fact, L-165041 increases Bcl6 expression via p38, JNK and Akt activation, and at the same time it induces the release of Bcl6 from PPARδ, thereby enabling Bcl6 to bind to its target genes. L-165041 also prevented apoptosis induced by higher doses of doxorubicin. However, while experiments performed with siRNA analysis techniques very clearly showed the weight of Bcl6 in the cellular senescence program, no role was found for Bcl6 in the anti-apoptotic effects of L-165041, thus confirming that senescence and apoptosis are two very distinct stress response cellular programs. This study increases our understanding of the molecular mechanism of anthracycline cardiotoxicity and suggests a potential role for PPARδ agonists as cardioprotective agents.

A multifaceted evaluation of imatinib-induced cardiotoxicity in the rat

Cardiotoxicity was an unanticipated side effect elicited by the clinical use of imatinib (Imb). This toxicity has been examined in only a limited number of experimental studies. The present study sought, by a variety of approaches, to identify important characteristics of Imb-induced cardiac alterations. Male spontaneously hypertensive rats (SHRs) received oral doses of 10, 30, or 50 mg/kg Imb or water daily for 10 d. Cardiac lesions, detected at all doses, were characterized by cytoplasmic vacuolization and myofibrillar loss. In a second experiment, cardiac lesions were found in Sprague Dawley (SD) and SHR rats given 50 or 100 mg/kg Imb for 14 d. Mean cardiac lesion scores and serum levels of cardiac troponin I were higher in SHRs than in SD rats. Imb induced myocyte death by necrosis, autophagy, and apoptosis. Dose-related increases in cardiac expression were observed for several genes associated with endoplasmic reticulum stress response, protein folding, and vascular development and remodeling. Imb caused alterations in isolated myocytes (myofibrillar loss, highly disrupted and disorganized sarcomeric α-actinin, apoptosis, and increased lactate dehydrogenase release) at low concentrations (5 mM). The authors conclude that Imb exerts cardiotoxic effects that are manifest through a complex pattern of cellular alterations, the severity of which can be influenced by arterial blood pressure.

Comparison of various iron chelators used in clinical practice as protecting agents against catecholamine-induced oxidative injury and cardiotoxicity

Catecholamines are stress hormones and sympathetic neurotransmitters essential for control of cardiac function and metabolism. However, pathologically increased catecholamine levels may be cardiotoxic by mechanism that includes iron-catalyzed formation of reactive oxygen species. In this study, five iron chelators used in clinical practice were examined for their potential to protect cardiomyoblast-derived cell line H9c2 from the oxidative stress and toxicity induced by catecholamines epinephrine and isoprenaline and their oxidation products. Hydroxamate iron chelator desferrioxamine (DFO) significantly reduced oxidation of catecholamines to more toxic products and abolished redox activity of the catecholamine-iron complex at pH 7.4. However, due to its hydrophilicity and large molecule, DFO was able to protects cells only at very high and clinically unachievable concentrations. Two newer chelators, deferiprone (L1) and deferasirox (ICL670A), showed much better protective potential and were effective at one or two orders of magnitude lower concentrations as compared to DFO that were within their clinically relevant plasma levels. Ethylenediaminetetraacetic acid (EDTA), dexrazoxane (ICRF-187, clinically approved cardioprotective agent against anthracycline-induced cardiotoxicity) as well as selected beta adrenoreceptor antagonists and calcium channel blockers exerted no effect. Hence, results of the present study indicate that small, lipophilic and iron-specific chelators L1 and ICL670A can provide significant protection against the oxidative stress and cardiomyocyte damage exerted by catecholamines and/or their reactive oxidation intermediates. This potential new application of the clinically approved drugs L1 and ICL670A warrants further investigation, preferably using more complex in vivo animal models.

Amelioration of doxorubicin-induced cardiotoxicity by deferiprone in rats

The therapeutic usefulness of doxorubicin (Dox), an anthracycline antibiotic used as an anticancer agent, is limited by its cardiotoxicity. Dox-induced cardiotoxicity is mainly attributed to accumulation of reactive oxygen species and interaction of Dox with cellular iron metabolism. The present study investigated the effects of the iron chelator deferiprone (Def) against Dox-induced cardiotoxicity in rats. Dox (15 mg/kg) was injected intraperitoneally as a single dose, and Def (10 mg/kg) was administered orally for 10 days. Dox showed cardiotoxicity as evidenced by increased heart rate, elevated ST segment, prolonged QTc interval, and increased T wave amplitude. In addition, Dox enhanced aconitine cardiotoxicity by decreasing its dose, producing ventricular tachycardia. Administration of Def significantly attenuated Dox-induced electrocardiographic changes. Cardiotoxicity of Dox was confirmed biochemically by a significant elevation in serum creatine kinase-MB and lactate dehydrogenase activities as well as by myocardial malondialdehyde and reduced glutathione contents. Moreover, Dox caused a significant decrease in myocardial superoxide dismutase activity. Administration of Def significantly attenuated the biochemical changes. These results suggest that Def might be a potential cardioprotective agent against Dox-induced cardiotoxicity.

Advances in iron chelation: an update

INTRODUCTION

Oxidative stress (caused by excess iron) can result in tissue damage, organ failure and finally death, unless treated by iron chelators. The causative factor in the etiology of a variety of disease states is the presence of iron-generated reactive oxygen species (ROS), which can result in cell damage or which can affect the signaling pathways involved in cell necrosis-apoptosis or organ fibrosis, cancer, neurodegeneration and cardiovascular, hepatic or renal dysfunctions. Iron chelators can reduce oxidative stress by the removal of iron from target tissues. Equally as important, removal of iron from the active site of enzymes that play key roles in various diseases can be of considerable benefit to the patients.

AREAS COVERED

This review focuses on iron chelators used as therapeutic agents. The importance of iron in oxidative damage is discussed, along with the three clinically approved iron chelators.

EXPERT OPINION

A number of iron chelators are used as approved therapeutic agents in the treatment of thalassemia major, asthma, fungal infections and cancer. However, as our knowledge about the biochemistry of iron and its role in etiologies of seemingly unrelated diseases increases, new applications of the approved iron chelators, as well as the development of new iron chelators, present challenging opportunities in the areas of drug discovery and development.

Mechanisms of myocyte cytotoxicity induced by the multikinase inhibitor sorafenib

The use of the anticancer multikinase inhibitor sorafenib is associated with cardiac ischemia or infarction and an increase in hypertension. We investigated various mechanisms that might be responsible for its cardiotoxicity in a neonatal rat myocyte model. As measured by lactate dehydrogenase release, sorafenib treatment of myocytes caused dose-dependent damage at therapeutically relevant concentrations. It had been hypothesized that inhibition of RAF1 and BRAF kinases may be responsible for sorafenib induced cardiotoxicity. However, because sorafenib treatment did not inhibit phosphorylation of ERK (extracellular signal-regulated kinase), it was concluded that sorafenib did not exert its damaging effects through RAF inhibition of the RAF/MEK/ERK kinase cascade. The clinically approved doxorubicin cardioprotective agent dexrazoxane did not protect myocytes from damage. At lower sorafenib concentrations, at least, these results are consistent with sorafenib not being able to induce significant oxidative damage. In conclusion, given the extreme lack of kinase selectivity that sorafenib exhibits, it is likely that inhibition of kinases other than RAF, or combinations of kinases, contributes to the cardiotoxic effects of sorafenib.

Kinamycin F downregulates cyclin D3 in human leukemia K562 cells

The bacterial metabolite kinamycin F, which contains an unusual and potentially reactive diazo group, is being investigated as an antitumor agent with a potentially novel target. Treatment of K562 cells with kinamycin F induced erythroid differentiation, a rapid apoptotic response, induction of caspase-3/7 activities and a delayed cell cycle progression through the S and G(2)/M phases. Kinamycin F caused a selective reduction of cyclin D3 protein, which appeared to be mediated at the level of transcription, rather than by affecting the stability of either cyclin D3 protein or mRNA. Thus cyclin D3 is a potential target of kinamycin F.

Anthracycline-induced cardiotoxicity: overview of studies examining the roles of oxidative stress and free cellular iron

The risk of cardiotoxicity is the most serious drawback to the clinical usefulness of anthracycline antineoplastic antibiotics, which include doxorubicin (adriamycin), daunorubicin or epirubicin. Nevertheless, these compounds remain among the most widely used anticancer drugs. The molecular pathogenesis of anthracycline cardiotoxicity remains highly controversial, although the oxidative stress-based hypothesis involving intramyocardial production of reactive oxygen species (ROS) has gained the widest acceptance. Anthracyclines may promote the formation of ROS through redox cycling of their aglycones as well as their anthracycline-iron complexes. This proposed mechanism has become particularly popular in light of the high cardioprotective efficacy of dexrazoxane (ICRF-187). The mechanism of action of this drug has been attributed to its hydrolytic transformation into the iron-chelating metabolite ADR-925, which may act by displacing iron from anthracycline-iron complexes or by chelating free or loosely bound cellular iron, thus preventing site-specific iron-catalyzed ROS damage. However, during the last decade, calls for the critical reassessment of this "ROS and iron" hypothesis have emerged. Numerous antioxidants, although efficient in cellular or acute animal experiments, have failed to alleviate anthracycline cardiotoxicity in clinically relevant chronic animal models or clinical trials. In addition, studies with chelators that are stronger and more selective for iron than ADR-925 have also yielded negative or, at best, mixed outcomes. Hence, several lines of evidence suggest that mechanisms other than the traditionally emphasized "ROS and iron" hypothesis are involved in anthracycline-induced cardiotoxicity and that these alternative mechanisms may be better bases for designing approaches to achieve efficient and safe cardioprotection.

Post-acute pathological changes in the thalamus and internal capsule in aged mice following controlled cortical impact injury: a magnetic resonance imaging, iron histochemical, and glial immunohistochemical study

Traumatic brain injury (TBI) is a major cause of neurological disability across all ages, but the elderly are particularly vulnerable and have a worse prognosis than younger individuals. To advance the understanding of long-term pathogenesis induced by TBI in the elderly, aged mice (21 -- 24 months) were given a controlled cortical impact (CCI) injury to the sensorimotor cortex, and their brains were analyzed by MRI and histopathology at 1 and 2 months after CCI injury, a post-acute period. A T2 hypointensity was observed in the ipsilateral thalamus but not in the contralateral thalamus or in the thalamus of sham operated, control mice. The hypointensity was co-localized with increased histochemical staining of iron, a paramagnetic substance that causes a shortening of the T2 relaxation time. Since iron catalyzes reactions that lead to toxic free radicals, the deposition of iron in the thalamus raises the possibility that it promotes pathogenesis following TBI. Astrocyte gliosis and microgliosis were also observed in the ipsilateral thalamus in the post-acute period. The ipsilateral internal capsule displayed a trend for a T2 hypointensity, however, unlike the thalamus it did not have an increase of iron or GFAP staining, but it did have evidence of microgliosis. In summary, areas of T2 hypointensity were revealed in both the thalamus and internal capsule during the post-acute period following CCI injury, but the underlying pathology appeared to be distinct between these regions.

Anthracycline toxicity to cardiomyocytes or cancer cells is differently affected by iron chelation with salicylaldehyde isonicotinoyl hydrazone

BACKGROUND AND PURPOSE

The clinical utility of anthracycline antineoplastic drugs is limited by the risk of cardiotoxicity, which has been traditionally attributed to iron-mediated production of reactive oxygen species (ROS).

EXPERIMENTAL APPROACH

The aims of this study were to examine the strongly lipophilic iron chelator, salicylaldehyde isonicotinoyl hydrazone (SIH), for its ability to protect rat isolated cardiomyocytes against the toxicity of daunorubicin (DAU) and to investigate the effects of SIH on DAU-induced inhibition of proliferation in a leukaemic cell line. Cell toxicity was measured by release of lactate dehydrogenase and staining with Hoechst 33342 or propidium iodide and lipid peroxidation by malonaldehyde formation.

KEY RESULTS

SIH fully protected cardiomyocytes against model oxidative injury induced by hydrogen peroxide exposure. SIH also significantly but only partially and with no apparent dose-dependency, reduced DAU-induced cardiomyocyte death. However, the observed protection was not accompanied by decreased lipid peroxidation. In the HL-60 acute promyelocytic leukaemia cell line, SIH did not blunt the antiproliferative efficacy of DAU. Instead, at concentrations that reduced DAU toxicity to cardiomyocytes, SIH enhanced the tumoricidal action of DAU.

CONCLUSIONS AND IMPLICATIONS

This study demonstrates that iron is most likely involved in anthracycline cardiotoxicity and that iron chelation has protective potential, but apparently through mechanism(s) other than by inhibition of ROS-induced injury. In addition to cardioprotection, iron chelation may have considerable potential to improve the therapeutic action of anthracyclines by enhancing their anticancer efficiency and this potential warrants further investigation.

Deferiprone does not protect against chronic anthracycline cardiotoxicity in vivo

Anthracycline cardiotoxicity ranks among the most severe complications of cancer chemotherapy. Although its pathogenesis is only incompletely understood, "reactive oxygen species (ROS) and iron" hypothesis has gained the widest acceptance. Besides dexrazoxane, novel oral iron chelator deferiprone has been recently reported to afford significant cardioprotection in both in vitro and ex vivo conditions. Therefore, the aim of this study was to assess whether deferiprone 1) has any effect on the anticancer action of daunorubicin and 2) whether it can overcome or significantly reduce the chronic anthracycline cardiotoxicity in the in vivo rabbit model (daunorubicin, 3 mg/kg i.v., weekly for 10 weeks). First, using the leukemic cell line, deferiprone (1-300 microM) was shown not to blunt the antiproliferative effect of daunorubicin. Instead, in clinically relevant concentrations (>10 microM), deferiprone augmented the antiproliferative action of daunorubicin. However, deferiprone (10 or 50 mg/kg administered p.o. before each daunorubicin dose) failed to afford significant protection against daunorubicin-induced mortality, left ventricular lipoperoxidation, cardiac dysfunction, and morphological cardiac deteriorations, as well as an increase in plasma cardiac troponin T. Hence, this first in vivo study changes the current view on deferiprone as a potential cardioprotectant against anthracycline cardiotoxicity. In addition, these results, together with our previous findings, further suggest that the role of iron and its chelation in anthracycline cardiotoxicity is not as trivial as originally believed and/or other mechanisms unrelated to iron-catalyzed ROS production are involved.

The use of dexrazoxane for the prevention of anthracycline extravasation injury

BACKGROUND

The use of the anthracycline anticancer drugs doxorubicin, daunorubicin, epirubicin and idarubicin sometimes results in accidental extravasation injury and can be a serious complication of their use.

OBJECTIVE

The object of this review was to evaluate the preclinical and clinical literature on the use of dexrazoxane in preventing anthracycline-induced extravasation injury.

METHODS

A review of the literature was carried out using PubMed.

RESULTS/CONCLUSIONS

Dexrazoxane, which is clinically used to reduce doxorubicin-induced cardiotoxicity, has been shown in two clinical studies and in several case reports to be highly efficacious in preventing anthracycline-induced extravasation injury. Dexrazoxane is a prodrug analog of the metal chelator EDTA that likely acts by removing iron from the iron-anthracycline complex, thus preventing formation of damaging reactive oxygen species.

Doxorubicin generates a proapoptotic phenotype by phosphorylation of elongation factor 2

We have previously shown that doxorubicin sensitizes prostate cancer cells to tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL). Sensitization correlated with decreased expression of the antiapoptotic cellular FLICE-like inhibitor protein (cFLIP(S)). The decrease in cFLIP(S) could not be explained by transcriptional regulation or increased degradation, leading us to focus on translational mechanisms. In this study, we found that doxorubicin caused strong and sustained phosphorylation of elongation factor 2 (EF-2), which interferes with protein elongation. Phosphorylation of EF-2 appeared to occur in a kinase-independent manner. Treatment with hydrogen peroxide recapitulated the events observed after doxorubicin treatment. In addition, cells treated with hydrogen peroxide expressed less X-linked inhibitor of apoptosis protein (XIAP) and survivin which, like cFLIP(S), are short-half-life proteins with an antiapoptotic function while expression levels of DR5, caspases-8, -9, -3, and Bax are maintained. The doxorubicin-mediated decrease in cFLIP(S) and XIAP and the TRAIL-induced apoptosis were prevented by pretreatment with an iron chelator, indicating that expression of these proteins was affected by free radical generation upon interaction of iron with doxorubicin. In conclusion, our data suggest that free radicals can affect the phosphorylation of EF-2 resulting in a net loss of short-half-life proteins such as cFLIP(S) and XIAP, leaving a cell more vulnerable to apoptotic stimuli.

Mechanism of the cytotoxicity of the diazoparaquinone antitumor antibiotic kinamycin F

The bacterial metabolite kinamycin F, which is being investigated as a potent antitumor agent, contains an unusual and potentially reactive diazo group, a paraquinone, and a phenol functional group. Kinamycin F reacted with glutathione (GSH) in a complex series of reactions which suggested that kinamycin F may have its cytotoxicity modulated by GSH. Consistent with this idea, 2-oxo-4-thiazolidinecarboxylic acid treatment to increase cellular GSH levels and buthionine sulfoximine treatment to decrease GSH levels resulted in decreased and increased kinamycin F cytotoxicity, respectively, in K562 leukemia cells. Kinamycin F weakly bound to DNA and induced DNA damage in K562 cells that was independent of GSH levels. The GSH-promoted DNA nicking induced by kinamycin F in vitro was attenuated by deferoxamine, dimethyl sulfoxide, and catalase, which indicated that DNA damage initiated by this agent occurred in an iron-, hydrogen-peroxide-, and hydroxyl-radical-dependent manner. Electron paramagnetic resonance spectroscopy experiments showed that the GSH/kinamycin F system produced a semiquinone free radical and that the hydrogen peroxide/peroxidase/kinamycin F system generated a phenoxyl free radical. In conclusion, the results indicated that kinamycin F cytotoxicity may be due to reductive and/or peroxidative activation to produce DNA-and protein-damaging species.

Iron chelation-afforded cardioprotection against chronic anthracycline cardiotoxicity: A study of salicylaldehyde isonicotinoyl hydrazone (SIH)

Pyridoxal-derived aroylhydrazone iron chelators have been previously shown as effective cardioprotectants against chronic anthracycline cardiotoxicity. In this study we focused on a novel salicylaldehyde analogue (salicylaldehyde isonicotinoyl hydrazone, SIH), which has been recently demonstrated to possess marked and dose-dependent protective effects against oxidative injury of cardiomyocytes. Therefore, in the present study the cardioprotective potential of SIH against daunorubicin (DAU) cardiotoxicity was assessed in vitro (isolated rat ventricular cardiomyocytes; DAU 10 microM, 48 h exposure) as well as in vivo (chronic DAU-induced cardiomyopathy in rabbits; DAU 3mg/kg, i.v. weekly, 10 weeks). In vitro, SIH (3-100 microM) was able to partially, but significantly decrease the LDH leakage from cardiomyocytes. In vivo, SIH co-administration was capable to reduce (SIH dose of 0.5mg/kg, i.v.) or even to completely prevent (1.0mg/kg, i.v.) the DAU-induced mortality. Moreover, the latter dose of the chelator significantly improved the left ventricular function (LV dP/dt(max)=1185+/-80 kPa/s versus 783+/-53 kPa/s in the DAU group; P<0.05) and decreased the severity of the myocardial morphological changes as well as the plasma levels of cardiac troponin T. Unfortunately, further escalation of the SIH dose (to 2.5mg/kg) resulted in a nearly complete reversal of the protective effects as judged by the overall mortality, functional, morphological as well as biochemical examinations. Hence, this study points out that aroylhydrazone iron chelators can induce a significant cardioprotection against anthracycline cardiotoxicity; however, they share the curious dose-response relationship which is unrelated to the chemical structure or the route of the administration of the chelator.

Toxic effects of Fusarium mycotoxin butenolide on rat myocardium and primary culture of cardiac myocytes

Mycotoxin toxicosis has been implicated in the etiopathogenesis of Keshan disease (KD), an endemic cardiomyopathy prevailing in some regions of China. Butenolide (4-acetamido-4-hydroxy-2-butenoic acid gamma-lactone, CAS No. 16275-44-8), a mycotoxin produced by several Fusarium species such as Fusarium tricinctum and Fusarium graminearum, is frequently detected from the cereals in the endemic areas of KD. The present study is undertaken to investigate whether this mycotoxin can induce myocardial damage. Exposure of primary culture of cardiac myocytes to butenolide resulted in significant cytotoxicity, manifested by changes in cell morphology and decreases in cell viability. Consistent with the in vitro findings, distinct myocardial toxicity in vivo was observed after administration of rats by gavage with butenolide (10 and 20 mg/kg/day) for 2 months, and the myocardial injuries were characterized by focal necrosis of myocardium and fragmentation of myofiber. Butenolide also induced significant oxidative damage to the myocardium in vitro evidenced by a concentration-dependent lipid peroxidation in the myocardial homogenates, whereas antioxidants superoxide dismutase (SOD), N-acetylcysteine (NAC) and glutathione (GSH) provided significant protections against this oxidative effect. Taken together, these results clearly reveal that butenolide possesses the potential to induce myocardial toxicity. The present findings may reinforce the hypothesis that toxicosis by mycotoxins is one of the etiological factors for KD.

Deferiprone, an orally deliverable iron chelator, ameliorates experimental autoimmune encephalomyelitis

The iron chelator, Desferal, suppressed disease activity of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), and it has been tested in pilot trials for MS. The administration regimen of Desferal is cumbersome and prone to complications. Orally-deliverable, iron chelators have been developed that circumvent these difficulties, and the objective of this study was to test an oral chelator in EAE. SJL mice with active EAE were randomly assigned to receive deferiprone (150 mg/kg) or vehicle (water) 2×/day via gavage. EAE mice given deferiprone had significantly less disease activity and lower levels of inflammatory cell infiltrates (revealed by H&E staining) than EAE mice administered vehicle. T-cell infiltration, assessed by anti-CD3 immunohistochemical staining, also was reduced, although not significantly. Splenocytes cultured from naïve SJL mice were stimulated with anti-CD3 and anti-CD28 with or without 250 μM deferiprone. While ~39% of costimulated splenocytes without deferiprone underwent division, only ~2.8% of costimulated splenocytes with deferiprone divided and the latter cells were only 53% as viable as the former. Deferiprone had no effect on proliferation or viability of cells that were not costimulated. In summary, deferiprone effectively suppressed active EAE disease and it inhibited T-cell function. Multiple Sclerosis 2007; 13: 1118—1126. http://msj.sagepub.com

New iron chelators in anthracycline-induced cardiotoxicity

The use of anthracycline anticancer drugs is limited by a cumulative, dose-dependent cardiac toxicity. Iron chelation has long been considered as a promising strategy to limit this unfavorable side effect, either by restoring the disturbed cellular iron homeostasis or by removing redox-active iron, which may promote anthracycline-induced oxidative stress. Aroylhydrazone lipophilic iron chelators have shown promising results in the rabbit model of daunorubicin-induced cardiomyopathy as well as in cellular models. The lack of interference with the antiproliferative effects of the anthracyclines also favors their use in clinical settings. The dose, however, should be carefully titrated to prevent iron depletion, which apparently also applies for other strong iron chelators. We have shown that a mere ability of a compound to chelate iron is not the sole determinant of a good cardioprotector and the protective potential does not directly correlate with the ability of the chelators to prevent hydroxyl radical formation. These findings, however, do not weaken the role of iron in doxorubicin cardiotoxicity as such, they rather appeal for further investigations into the molecular mechanisms how anthracyclines interact with iron and how iron chelation may interfere with these processes.

Role of NADPH cytochrome P450 reductase in activation of RH1

PURPOSE

RH1 is a new bioreductive agent that is an excellent substrate for the two-electron reducing enzyme, NAD(P)H quinone oxidoreductase 1 (NQO1). RH1 may be an effective NQO1-directed antitumor agent for treatment of cancer cells having elevated NQO1 activity. As some studies have indicated that RH1 may also be a substrate for the one-electron reducing enzyme, NADPH cytochrome P450 reductase (P450 Red), P450 Red may contribute to the activation of RH1 where NQO1 activities are low and P450 Red activities are high. The mean P450 Red activity in the human tumor cell line panel used by NCI for evaluation of new anticancer agents is 14.8 nmol min(-1) mg prot(-1), while the mean NQO1 activity in these cell lines is 199.5 nmol min(-1) mg prot(-1). Thus, we investigated whether P450 Red could play a role in activating RH1.

METHODS

Reduction of RH1 by purified human P450 Red was investigated using electron paramagnetic resonance and spectroscopic assays. The ability of RH1 to produce DNA damage following reduction by P450 Red was studied using gel assays. To determine the role of P450 Red in activation of RH1 in cells, cell growth inhibition studies with inhibitors of P450 Red and NQO1 were carried out in T47D human breast cancer cells and T47D cells transfected with the human P450 Red gene (T47D-P450) that have P450 Red activities of 11.5 and 311.8 nmol min(-1) mg prot(-1), respectively.

RESULTS

Reduction studies using purified P450 Red and NQO1 confirmed that RH1 can be reduced by both enzymes, but redox cycling was slower following reduction by NQO1. RH1 produced DNA strand breaks and crosslinks in isolated DNA after reduction by either P450 Red or NQO1. DPIC, an inhibitor of P450 Red, had no effect on cell growth inhibition by RH1 in T47D cells, and had only a small effect on cell growth inhibition by RH1 in the presence of the NQO1 inhibitor, dicoumarol, in T47D-P450 cells.

CONCLUSIONS

These results demonstrated that P450 Red does not contribute to the activation of RH1 in cells with normal P450 Red activity and plays only a minor role in activating this agent in cells with high levels of this enzyme. These studies confirmed that P450 Red could activate RH1 and provided the first direct evidence that RH1 could produce both DNA strand breaks and DNA crosslinks after reduction by P450 Red. However, the results strongly suggest that P450 Red does not play a significant role in activating RH1 in cells with normal P450 Red activity.

Ceruloplasmin expression and its role in iron transport in C6 cells

Ceruloplasmin (CP) is essential for brain iron homeostasis. However, little is known about the effect of iron on CP expression in the brain. Also, the role of CP in brain iron transport has not been well determined. In this study, we investigated the effects of iron on CP expression and the role of CP in iron transport in the C6 rat glioma cells. Our data showed that treatment of the cells with iron (cell iron overload) or iron chelators (cell iron deficiency) did not induce a significant change in the expression of CP mRNA. However, western blotting analysis demonstrated that cell iron overload induced a significant decrease in CP protein content in the cells and that treatment with iron chelators led to a significant increase in CP protein level in the cells. These findings suggest a translational regulation of CP expression by iron in the cells. We also examined the effects of CP on iron transport in the cells. We found that glycosylphosphatidylinositol-anchored CP did not have any impact on iron uptake by normal iron or iron-deficient cells nor on iron release from normal iron or iron-sufficient cells. However, low concentrations of soluble CP (2-8 microg/ml) increased iron uptake by iron-deficient C6 glioma cells, while the same concentrations of CP had no effect on iron uptake by normal iron cells and iron release from normal iron and iron-sufficient cells. The possible reason for the difference between our results in vitro and those obtained from in vivo studies was discussed.

The reductive activation of the antitumor drug RH1 to its semiquinone free radical by NADPH cytochrome P450 reductase and by HCT116 human colon cancer cells

RH1 (2,5-diaziridinyl-3-(hydroxymethyl)-6-methyl-1,4-benzoquinone), which is currently in clinical trials, is a diaziridinyl benzoquinone bioreductive anticancer drug that was designed to be activated by the obligate two-electron reductive enzyme NAD(P)H quinone oxidoreductase 1 (NQO1). In this electron paramagnetic resonance (EPR) study we showed that RH1 was reductively activated by the one-electron reductive enzyme NADPH cytochrome P450 reductase and by a suspension of HCT116 human colon cancer cells to yield a semiquinone free radical. As shown by EPR spin trapping experiments RH1 was reductively activated by cytochrome P450 reductase and underwent redox cycling to produce damaging hydroxyl radicals in reactions that were both H2O2- and iron-dependent. Thus, reductive activation by cytochrome P450 reductase or other reductases to produce a semiquinone that can redox cycle to produce damaging hydroxyl radicals and/or DNA-reactive alkylating species may contribute to the potent cell growth inhibitory effects of RH1. These results also suggest that selection of patients for treatment with RH1 based on their expression levels of NQO1 may be problematic.

Cytochrome P450 destruction by benzene metabolites 1,4-benzoquinone and 1,4-hydroquinone and the formation of hydroxyl radicals in minipig liver microsomes

Reactive metabolites of benzene 1,4-benzoquinone and 1,4-hydroquinone exert their toxic effects through covalent and/or oxidative damage to DNA and proteins. Since minipigs have been proposed as a suitable model species in toxicological and pharmacological research, the aim of this study was to explore mechanisms by which catechol, 1,4-hydroquinone and 1,4-benzoquinone destroy cytochrome P450 (P450) and induce oxidative stress in minipig liver microsomes. Our second goal was to assess the usefulness of minipig liver microsomes as a model system for the testing of the production of oxidative stress by clinically relevant quinone-containing compounds, e.g. anthracyclines. Of the three benzene metabolites tested, the highest P450 destruction was caused by 1,4-benzoquinone. This destructive effect did not correlate with the production of hydroxyl radicals as measured by ESR spin trapping which was the highest in samples containing 1,4-hydroquinone. Our results confirm previous findings that 1,4-benzoquinone exerts its effect mainly by direct attack on macromolecules while 1,4-hydroquinone rather stimulates the production of reactive oxygen species. Doxorubicin stimulated the production of hydroxyl radicals and the destruction of P450 similarly as 1,4-hydroquinone. Minipig liver microsomes should be further tested as a possibly suitable model system for the testing of potential modulators of the toxicity of doxorubicin.

Deferiprone protects the isolated atria from cardiotoxicity induced by doxorubicin

AIM

To investigate the effects of deferiprone on doxorubicin-induced cardiotoxicity and determine its protection on cardiac contractility in vivo at tissue level.

METHODS

Spontaneously-beating isolated atria from rats were pretreated with deferiprone for 10 min at 1.2 mmol/L or 0.3 mmol/L, respectively before co-incubation with doxorubicin (DOX) at 0.03 mmol/L for 60 min. Contractility (dF/dt) was assessed every 10 min during the incubation. After that, the tissues around the sinuatrial nodes were fixed for ultrastructural study; succinate dehydrogenase (SDH) and Cu, Zn superoxide dismutase (Cu, Zn-SOD) activity, as well as malondialdehyde (MDA) level of the atria were assayed.

RESULTS

Treatment with DOX alone resulted in a 49.34% reduction of the contractility, mitochondria swelling, disruption of mitochondrial crista and decreased electron density of the matrices. Conversely, with the presence of deferiprone, the negative inotropic effect and lesions in the cardiac mitochondria structure induced by DOX were attenuated. Cu, Zn-SOD activity increased by 12.97%-12.11%, the MDA level decreased by 29.12%-39.82% and succinate dehydrogenase (SDH) activity was ameliorated by 25.15%-34.76%.

CONCLUSION

Deferiprone can efficiently preserve cardiac contractility. Moreover, the results of this study indicate that deferiprone is able to protect mitochondrial function and structure form damage induced by DOX. This cardiac protective potential of deferiprone could be due to its defense capability against oxidative damage.

Therapeutic potential of iron chelators in diseases associated with iron mismanagement

A considerable array of diseases are now recognized to be associated with misplacement of iron. Excessive deposits of the metal in sensitive tissue sites can result in formation of destructive hydroxyl radicals as well as in stimulation of growth of neoplastic and microbial cell invaders. To counteract potential iron damage, hosts employ the iron chelators, transferrin and lactoferrin. These proteins have been recently developed into pharmaceutical products. Additionally, a variety of low molecular mass iron chelators are being used/tested to treat whole body iron loading, and specific diseases for which the metal is a known or suspected risk factor.

Cardioprotective Effects of a Novel Iron Chelator, Pyridoxal 2-Chlorobenzoyl Hydrazone, in the Rabbit Model of Daunorubicin-Induced Cardiotoxicity

Iron chelation is the only pharmacological intervention against anthracycline cardiotoxicity whose effectiveness has been well documented both experimentally and clinically. In this study, we aimed to assess whether pyridoxal 2-chlorobenzoyl hydrazone (o-108, a strong iron chelator) can provide effective protection against daunorubicin (DAU)-induced chronic cardiotoxicity in rabbits. First, using the HL-60 leukemic cell line, it was shown that o-108 has no potential to blunt the antiproliferative efficacy of DAU. Instead, o-108 itself moderately inhibited cell proliferation. In vivo, chronic DAU treatment (3 mg/kg weekly for 10 weeks) induced mortality (33%), left ventricular (LV) dysfunction, a troponin T rise, and typical morphological LV damage. In contrast, all animals treated with 10 mg/kg o-108 before DAU survived without a significant drop in the LV ejection fraction (63.2 +/- 0.5 versus 59.2 +/- 1.0%, beginning versus end, not significant), and their cardiac contractility (dP/dt(max)) was significantly higher than in the DAU-only group (1131 +/- 125 versus 783 +/- 53 kPa/s, p < 0.05), which corresponded with histologically assessed lower extent and intensity of myocardial damage. Although higher o-108 dose (25 mg/kg) was well tolerated when administered alone, in combination with DAU it led to rather paradoxical and mostly negative results regarding both cardioprotection and overall mortality. In conclusion, we show that shielding of free intracellular iron using a potent lipophilic iron chelator is able to offer a meaningful protection against chronic anthracycline cardiotoxicity. However, this approach lost its potential with the higher chelator dose, which suggests that iron might play more complex role in the pathogenesis of this disease than previously assumed.