CN128: A New Orally Active Hydroxypyridinone Iron Chelator

A guide to ferroptosis, the biological rust of cellular membranes

Unprotected iron can rust due to oxygen exposure. Similarly, in our body, oxidative stress can kill cells in an iron-dependent manner, which can give rise to devastating diseases. This type of cell death is referred to as ferroptosis. Generally, ferroptosis is defined as an iron-catalyzed form of regulated necrosis that occurs through excessive peroxidation of polyunsaturated fatty acids within cellular membranes. This review summarizes how ferroptosis is executed by a rather primitive biochemical process, under tight regulation of lipid, iron, and redox metabolic processes. An overview is given of major classes of ferroptosis inducers and inhibitors, and how to detect ferroptosis. Finally, its detrimental role in disease is briefly discussed.

Ferroptosis inhibitors: past, present and future

Ferroptosis is a non-apoptotic mode of programmed cell death characterized by iron dependence and lipid peroxidation. Since the ferroptosis was proposed, researchers have revealed the mechanisms of its formation and continue to explore effective inhibitors of ferroptosis in disease. Recent studies have shown a correlation between ferroptosis and the pathological mechanisms of neurodegenerative diseases, as well as diseases involving tissue or organ damage. Acting on ferroptosis-related targets may provide new strategies for the treatment of ferroptosis-mediated diseases. This article specifically describes the metabolic pathways of ferroptosis and summarizes the reported mechanisms of action of natural and synthetic small molecule inhibitors of ferroptosis and their efficacy in disease. The paper also describes ferroptosis treatments such as gene therapy, cell therapy, and nanotechnology, and summarises the challenges encountered in the clinical translation of ferroptosis inhibitors. Finally, the relationship between ferroptosis and other modes of cell death is discussed, hopefully paving the way for future drug design and discovery.

Synthesis and structure-activity optimization of hydroxypyridinones against rhabdomyolysis-induced acute kidney injury

The important role of accumulated iron is well recognized in the pathophysiology of rhabdomyolysis-induced acute kidney injury (RM-AKI). Our previous work further confirmed the labile iron triggered iron-dependent ferroptosis thus leading to the renal failure. In view of this, a series of hydroxypyridinones (HOPOs) with excellent iron chelation capability have been designed and synthesized in this study. A lead compound 6k was identified with good ferroptosis inhibition (EC50 = 20 μM) and no obvious cytotoxicity (CC50 > 100 μM), indicating a good therapeutic window (safety index = CC50/EC50 > 5.00). Moreover, intraperitoneal treatment of 6k (10 mg/kg) displayed a superior protective effect than deferiprone (50 mg/kg) in glycerol-induced RM-AKI mice with alleviating kidney dysfunction and pathological injury, decreasing the renal iron level as well as downregulating the mRNA level of ferroptosis associated genes (Acls4 and Ptgs2). Also, 6k exhibited a good in vivo safety profile, even at single high dose up to 1 g/kg without inducing mortality or toxic symptoms. Importantly, 6k could significantly upregulate the protein hypoxia-inducible factor 1α, possibly involving HIF pathway against the ferroptosis. These results collectively highlighted that the strategy of iron chelation and downstream ferroptosis inhibition has a therapeutic potential against RM-AKI.

Targeting ferroptosis opens new avenues for the development of novel therapeutics

Ferroptosis is an iron-dependent form of regulated cell death with distinct characteristics, including altered iron homeostasis, reduced defense against oxidative stress, and abnormal lipid peroxidation. Recent studies have provided compelling evidence supporting the notion that ferroptosis plays a key pathogenic role in many diseases such as various cancer types, neurodegenerative disease, diseases involving tissue and/or organ injury, and inflammatory and infectious diseases. Although the precise regulatory networks that underlie ferroptosis are largely unknown, particularly with respect to the initiation and progression of various diseases, ferroptosis is recognized as a bona fide target for the further development of treatment and prevention strategies. Over the past decade, considerable progress has been made in developing pharmacological agonists and antagonists for the treatment of these ferroptosis-related conditions. Here, we provide a detailed overview of our current knowledge regarding ferroptosis, its pathological roles, and its regulation during disease progression. Focusing on the use of chemical tools that target ferroptosis in preclinical studies, we also summarize recent advances in targeting ferroptosis across the growing spectrum of ferroptosis-associated pathogenic conditions. Finally, we discuss new challenges and opportunities for targeting ferroptosis as a potential strategy for treating ferroptosis-related diseases.

Targeting Labile Iron-Mediated Ferroptosis Provides a Potential Therapeutic Strategy for Rhabdomyolysis-Induced Acute Kidney Injury

Acute kidney injury (AKI) is a global health problem that occurs in a variety of clinical settings. Despite some advances in supportive clinical care, no medicinal intervention has been demonstrated to reliably prevent AKI thus far. Therefore, it is highly necessary to investigate the pathophysiology and mechanisms involved in AKI for the discovery of therapeutics. In the current study, a robust change in the level of renal malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) and elevated renal iron levels were observed in murine rhabdomyolysis-induced AKI (RM-AKI), which supports a pathogenic role of labile iron-mediated ferroptosis and provides a chance to utilize iron chelation for RM-AKI prevention. Given that the existing small molecule-based iron chelators did not show promising preventative effects against RM-AKI, we further designed and synthesized a new hydroxypyridinone-based iron chelator to potently inhibit labile iron-mediated ferroptosis. Lead compound AKI-02 was identified, which remarkably protected renal proximal tubular epithelial cells from ferroptosis as well as showed excellent iron chelation ability. Moreover, administration of AKI-02 led to renal function recovery, a result that was substantiated by the decreased contents of BUN and creatinine, as well as the reduced labile iron level and improved histopathology. Thus, our studies highlighted that targeting labile iron-mediated ferroptosis could provide therapeutic benefits against RM-AKI.

Mitochondrial Iron Metabolism: The Crucial Actors in Diseases

Iron is a trace element necessary for cell growth, development, and cellular homeostasis, but insufficient or excessive level of iron is toxic. Intracellularly, sufficient amounts of iron are required for mitochondria (the center of iron utilization) to maintain their normal physiologic function. Iron deficiency impairs mitochondrial metabolism and respiratory activity, while mitochondrial iron overload promotes ROS production during mitochondrial electron transport, thus promoting potential disease development. This review provides an overview of iron homeostasis, mitochondrial iron metabolism, and how mitochondrial iron imbalances-induced mitochondrial dysfunction contribute to diseases.

An iron-deficient diet prevents alcohol- or diethylnitrosamine-induced acute hepatotoxicity in mice by inhibiting ferroptosis

The liver is easily injured by exogenous chemicals through reactive oxygen species (ROS), which lead to ferroptosis, a ROS-dependent programmed cell death characterized by iron accumulation and lipid peroxidation. However, whether iron restriction has a positive role in chemicals-induced liver injuries is unknown. The present study investigated the effects of an iron-deficient diet on liver injuries induced by alcohol or diethylnitrosamine (DEN). Mice were fed an iron-deficient diet for four weeks, then treated with three doses of alcohol (5 g/kg, 24 h interval, gavage) to mimic mild liver injury or five doses of DEN (50 mg/kg, 24 h interval, i. p.) to mimic severe liver failure. The results showed that mice were iron-deficient after four weeks of feeding. Interestingly, as evaluated by H&E staining of liver slices, liver/body weight ratio, serum ALT and AST, iron deficiency significantly alleviated liver injuries triggered by alcohol or DEN. The activities of alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH), and the expression of CYP2E1 were increased by iron deficiency. Mechanistically, iron deficiency prevented the decrease of glutathione peroxidase 4 (GPX4), which eliminated malondialdehyde (MDA) by utilizing glutathione (GSH). In summary, alcohol- or DEN-induced liver injuries were mitigated by the iron-deficient diet by inhibiting ferroptosis, which might be a promising measure for preventing liver injuries induced by alcohol, DEN, or other exogenous chemicals.

New Deferric Amine Compounds Efficiently Chelate Excess Iron to Treat Iron Overload Disorders and to Prevent Ferroptosis

Excess iron accumulation occurs in organs of patients with certain genetic disorders or after repeated transfusions. No physiological mechanism is available to excrete excess iron and iron overload to promote lipid peroxidation to induce ferroptosis, thus iron chelation becomes critical for preventing ion toxicity in these patients. To date, several iron chelators have been approved for iron chelation therapy, such as deferiprone and deferoxamine, but the current iron chelators suffer from significant limitations. In this context, new agents are continuously sought. Here, a library of new deferric amine compounds (DFAs) with adjustable skeleton and flexibility is synthesized by adopting the beneficial properties of conventional chelators. After careful evaluations, compound DFA1 is found to have greater efficacy in binding iron through two molecular oxygens in the phenolic hydroxyl group and the nitrogen atom in the amine with a 2:1 stoichiometry. This compound remarkably ameliorates iron overload in diverse murine models through both oral and intravenous administration, including hemochromatosis, high iron diet-induced, and iron dextran-stimulated iron accumulation. Strikingly, this compound is found to suppress iron-induced ferroptosis by modulating the intracellular signaling that drives lipid peroxidation. This study opens a new approach for the development of iron chelators to treat iron overload.

Intracellular Iron Binding and Antioxidant Activity of Phytochelators

Phytochelators have been studied as templates for designing new drugs for chelation therapy. This work evaluated key chemical and biological properties of five candidate phytochelators for iron overload diseases: maltol, mimosine, morin, tropolone, and esculetin. Intra- and extracellular iron affinity and antioxidant activity, as well as the ability to scavenge iron from holo-transferrin, were studied in physiologically relevant settings. Tropolone and mimosine (and, to a lesser extent, maltol) presented good binding capacity for iron, removing it from calcein, a high-affinity fluorescent probe. Tropolone and mimosine arrested iron-mediated oxidation of ascorbate with the same efficiency as the standard iron chelator DFO. Also, both were cell permeant and able to access labile pools of iron in HeLa and HepG2 cells. Mimosine was an effective antioxidant in cells stressed by iron and peroxide, being as efficient as the cell-permeant iron chelator deferiprone. These results reinforce the potential of those molecules, especially mimosine, as adjuvants in treatments for iron overload.

Iron Chelators in Treatment of Iron Overload

Patients suffering from iron overload can experience serious complications. In such patients, various organs, such as endocrine glands and liver, can be damaged. Although iron is a crucial element for life, iron overload can be potentially toxic for human cells due to its role in generating free radicals. In the past few decades, there has been a major improvement in the survival of patients who suffer from iron overload due to the application of iron chelation therapy in clinical practice. In clinical use, deferoxamine, deferiprone, and deferasirox are the three United States Food and Drug Administration-approved iron chelators. Each of these iron chelators is well known for the treatment of iron overload in various clinical conditions. Based on several up-to-date studies, this study explained iron overload and its clinical symptoms, introduced each of the above-mentioned iron chelators, and evaluated their advantages and disadvantages with an emphasis on combination therapy, which in recent studies seems a promising approach. In numerous clinical conditions, due to the lack of accurate indicators, choosing a standard approach for iron chelation therapy can be difficult; therefore, further studies on the issue are still required. This study aimed to introduce each of these iron chelators, combination therapy, usage doses, specific clinical applications, and their advantages, toxicity, and side effects.

Group-Assisted-Purification Chemistry Strategy for the Efficient Assembly of Cyclic Fused Pyridinones

A group-assisted-purification (GAP) chemistry strategy-based Ugi four-center three-component reaction (Ugi-4C-3CR) was explored. The reaction proceeded well to deliver the cyclic fused pyridinones selectively. Moreover, the reaction conditions were mild and avoided additional chromatography or recrystallization workup. Also, wide variations in substrates, such as anilines and aliphatic amines as well as amino alcohols and amino acid esters were all tolerated and pyridinones are achieved in good to excellent yields. Importantly, ladder-type cyclic fused pyridinones can be further constructed in excellent yield of 91%.

Discovery of benzamide-hydroxypyridinone hybrids as potent multi-targeting agents for the treatment of Alzheimer's disease

A novel class of benzamide-hydroxypyridinone (HPO) derivatives were innovatively designed, synthesised, and biologically evaluated as potential multitargeting candidates for the treatment of Alzheimer's disease (AD) through pharmacophores-merged approaches based on lead compounds 18d, benzyloxy phenyl analogs, and deferiprone (DFP). These hybrids possessed potent Monoamine oxidase B (MAO-B) inhibition as well as excellent iron chelation, with pFe³⁺ values ranging from 18.13 to 19.39. Among all the compounds, 8g exhibited the most potent selective MAO-B inhibitor (IC₅₀ = 68.4 nM, SI = 213). Moreover, 8g showed favourable pharmacokinetic properties and had great potential to penetrate the BBB in silico and PAMPA-BBB assay. Molecular modelling showed that 8g could adopt an extended conformation and have more enhanced interactions with MAO-B than 18d. In vitro and in vivo assays demonstrated that 8g remarkably resisted Aβ-induced oxidation and ameliorated cognitive impairment induced by scopolamine. Taken collectively, these results suggest that compound 8g is a potential multifunctional candidate for anti-AD treatment.

Identifying a Deferiprone-Resveratrol Hybrid as an Effective Lipophilic Anti-Plasmodial Agent

Malaria i a serious health problem caused by Plasmodium spp. that can be treated by an anti-folate pyrimethamine (PYR) drug. Deferiprone (DFP) is an oral iron chelator used for the treatment of iron overload and has been recognized for its potential anti-malarial activity. Deferiprone-resveratrol hybrids (DFP-RVT) have been synthesized to present therapeutic efficacy at a level which is superior to DFP. We have focused on determining the lipophilicity, toxicity and inhibitory effects on P. falciparum growth and the iron-chelating activity of labile iron pools (LIPs) by DFP-RVT. According to our findings, DFP-RVT was more lipophilic than DFP (p < 0.05) and nontoxic to blood mononuclear cells. Potency for the inhibition of P. falciparum was PYR > DFP-RVT > DFP in the 3D7 strain (IC₅₀ = 0.05, 16.82 and 47.67 µM, respectively) and DFP-RVT > DFP > PYR in the K1 strain (IC₅₀ = 13.38, 42.02 and 105.61 µM, respectively). The combined treatment of DFP-RVT with PYR additionally enhanced the PYR activity in both strains. DFP-RVT dose-dependently lowered LIP levels in PRBCs and was observed to be more effective than DFP at equal concentrations. Thus, the DFP-RVT hybrid should be considered a candidate as an adjuvant anti-malarial drug through the deprivation of cellular iron.

N-Propargylamine-hydroxypyridinone hybrids as multitarget agents for the treatment of Alzheimer's disease

AD is a progressive brain disorder. Because of the lack of remarkable single-target drugs against neurodegenerative disorders, the multitarget-directed ligand strategy has received attention as a promising therapeutic approach. Herein, we rationally designed twenty-nine hybrids of N-propargylamine-hydroxypyridinone. The designed hybrids possessed excellent iron-chelating activity (pFe³⁺ = 17.09-22.02) and potent monoamine oxidase B inhibitory effects. Various biological evaluations of the optimal compound 6b were performed step by step, including inhibition screening of monoamine oxidase (hMAO-B IC₅₀ = 0.083 ± 0.001 µM, hMAO-A IC₅₀ = 6.11 ± 0.08 µM; SI = 73.5), prediction of blood-brain barrier permeability and mouse behavioral research. All of these favorable results proved that the N-propargylamine-hydroxypyridinone scaffold is a promising structure for the discovery of multitargeted ligands for AD therapy.

Is Chelation Therapy a Potential Treatment for Parkinson's Disease?

Iron loading in some brain regions occurs in Parkinson’s Disease (PD), and it has been considered that its removal by iron chelators could be an appropriate therapeutic approach. Since neuroinflammation with microgliosis is also a common feature of PD, it is possible that iron is sequestered within cells as a result of the “anaemia of chronic disease” and remains unavailable to the chelator. In this review, the extent of neuroinflammation in PD is discussed together with the role played by glia cells, specifically microglia and astrocytes, in controlling iron metabolism during inflammation, together with the results of MRI studies. The current use of chelators in clinical medicine is presented together with a discussion of two clinical trials of PD patients where an iron chelator was administered and showed encouraging results. It is proposed that the use of anti-inflammatory drugs combined with an iron chelator might be a better approach to increase chelator efficacy.

Effectiveness of the Iron Chelator CN128 in Mitigating the Formation of Dopamine Oxidation Products Associated with the Progression of Parkinson's Disease

The occurrence and progression of Parkinson's disease (PD) has been associated with the observation of elevated iron concentrations in the substantia nigra pars compacta (SNpc). While the reasons for the impact of elevated iron concentrations remain unclear, one hypothesis is that the presence of labile iron induces the oxidation of dopamine (DA) to toxic quinones such as aminochrome (DAC) and reactive oxygen species (ROS). As such, one of the proposed therapeutic strategies has been the use of iron chelators such as deferiprone (DFP) (which is recognized to have limitations related to its rapid degradation in the liver) to reduce the concentration of labile iron. In this study, a detailed investigation regarding the novel iron chelator, CN128, was conducted and a kinetic model developed to elucidate the fundamental behavior of this chelator. The results in this work reveal that CN128 is effective in alleviating the toxicity induced by iron and DA to neurons when DA is present at moderate concentrations. When all the iron is chelated by CN128, the formation of DAC and the oxidation of DA can be reduced to levels identical to that in the absence of iron. The production of H₂O₂ is lower than that generated via the autoxidation of the same amount of DA. However, when severe leakage of DA occurs, the application of CN128 is insufficient to alleviate the associated toxicity. This is attibuted to the less important role of iron in the production of toxic intermediates at high concentrations of DA. CN128 is superior to DFP with regard to the reduction in formation of DAC and elevation in DA concentration. In summary, the results of this study suggest that prodromal application of the chelator CN128 could be effective in preventing the onset and slowing the early stage development of PD symptoms associated with oxidants and toxic intermediates resulting from the iron-mediated oxidation of the neurotransmitter dopamine with CN128 likely to be superior to DFP in view of its greater in vivo availability and less problematic side effects.

Hydroxypyridinone-Based Iron Chelators with Broad-Ranging Biological Activities

Iron plays an essential role in all living cells because of its unique chemical properties. It is also the most abundant trace element in mammals. However, when iron is present in excess or inappropriately located, it becomes toxic. Excess iron can become involved in free radical formation, resulting in oxidative stress and cellular damage. Iron chelators are used to treat serious pathological disorders associated with systemic iron overload. Hydroxypyridinones stand out for their outstanding chelation properties, including high selectivity for Fe³⁺ in the biological environment, ease of derivatization, and good biocompatibility. Herein, we overview the potential for multifunctional hydroxypyridinone-based chelators to be used as therapeutic agents against a wide range of diseases associated either with systemic or local elevated iron levels.