Clioquinol induces DNA double-strand breaks, activation of ATM, and subsequent activation of p53 signaling

Clioquinol induces mitochondrial toxicity in SH-SY5Y neuroblastoma cells by affecting the respiratory chain complex IV and OPA1 dynamin-like GTPase

Clioquinol has been thought of as the causative drug of subacute myelo-optic neuropathy (SMON). The underlying mechanisms of clioquinol toxicity, however, have not been elucidated in detail. Here, we revealed that clioquinol (20 μm) suppressed the expression of SCO1 and SCO2 copper chaperones for mitochondrial respiratory chain Complex IV (cytochrome c oxidase) in SH-SY5Y neuroblastoma cells. The assembly of Complex IV components and Complex IV activity were suppressed in clioquinol-treated cells. Clioquinol (10-50 μm) decreased cellular ATP levels in glucose-free media. Clioquinol (10-50 μm) induced OMA1 mitochondrial protease-dependent degradation of the dynamin-related GTPase OPA1 and suppressed the expression of CHCHD10 and CHCHD2 involved in the maintenance of cristae structure. These results suggest that mitochondrial toxicity is one of the mechanisms of clioquinol-induced neuronal cell death.

Loss-of-function polymorphisms in NQO1 are not associated with the development of subacute myelo-optico-neuropathy

BACKGROUND

Subacute myelo-optico-neuropathy (SMON) is a neurological disorder associated with the administration of clioquinol, particularly at very high doses. Although clioquinol has been used worldwide, there was an outbreak of SMON in the 1950s-1970s in which the majority of cases were in Japan, prompting speculation that the unique genetic background of the Japanese population may have contributed to the development of SMON. Recently, a possible association between loss-of-function polymorphisms in NQO1 and the development of SMON has been reported. In this study, we analyzed the relationship between NQO1 polymorphisms and SMON in Japan.

METHODS

We analyzed 125 Japanese patients with SMON. NQO1 loss-of-function polymorphisms (rs1800566, rs10517, rs689452, and rs689456) were evaluated. The allele frequency distribution of each polymorphism was compared between the patients and the healthy Japanese individuals (Human Genomic Variation Database and Integrative Japanese Genome Variation Database), as well as our in-house healthy controls.

RESULTS

The frequencies of the loss-of-function NQO1 alleles in patients with SMON and the normal control group did not differ significantly.

CONCLUSION

We conclude that known NQO1 polymorphisms are not associated with the development of SMON.

[Toward the complete understanding of the pathogenic mechanism of clioquinol-induced subacute myelo-optic neuropathy (SMON)]

Clioquinol was extensively used as an amebicide to treat indigestion and diarrhea in the mid-1900s. However, it was withdrawn from the market in Japan because its use was epidemiologically linked to an increase in the incidence of subacute myelo-optic neuropathy (SMON). SMON is characterized by the subacute onset of sensory and motor disturbances in the lower extremities with occasional visual impairments, which are preceded by abdominal symptoms. Although pathological studies demonstrated axonopathy of the spinal cord and optic nerves, the underlying mechanisms of clioquinol toxicity have not been elucidated in detail. We previously performed a global analysis of human neuroblastoma cells using DNA chips and demonstrated that clioquinol induced 1) DNA double-strand breaks and subsequent activation of ATM/p53 signaling; 2) the expression of VGF, the precursor of neuropeptides involved in pain reactions, by inducing c-Fos; 3) the expression of interleukin-8, which is reported to be involved in intestinal inflammation, optic neuropathy, and neuropathic pain, by down-regulating GATA-2 and GATA-3. We also demonstrated that clioquinol induced zinc influx and oxidation of the copper chaperone ATOX1, leading to the impairment of the functional maturation of a copper-dependent enzyme dopamine-β-hydroxylase and the inhibition of noradrenaline biosynthesis. Thus, clioquinol-induced neurotoxicity in SMON seems to be mediated by multiple pathways.

Paeoniflorin suppresses neuronal ferroptosis to improve the cognitive behaviors in Alzheimer's disease mice

Aim of this research was to examine the impact of paeoniflorin (Pae) in suppressing the occurrence of ferroptosis in individuals with Alzheimer's disease (AD). The study utilized APP/PS1 mice with AD as the experimental subjects. Following the administration of Pae, the cognitive behaviors of mice were evaluated and the key indexes of ferroptosis were measured, as well as levels of oxidative stress (OS). For in-vitro experiments, Erastin was adopted for inducing the ferroptosis of PC12 cells, and the level of cell ferroptosis was detected after Pae treatment. Pae improved the cognitive ability of AD mice, reduced the level of ferroptosis, decreased the iron ion and MAD levels in brain tissues, and increased SOD expression. In PC12 cells, Pae suppressed the Erastin-induced ferroptosis, mitigated oxidative damage, and reduced the level of ROS. Based on the findings from our research, it was observed that Pae exhibited a specific binding affinity to P53, leading to the suppression of ferroptosis. This mechanism ultimately resulted in the improvement of nerve injury in mice with AD.

NQO1 protects against clioquinol toxicity

Clioquinol (CQ) was widely used as oral antibiotic before being taken off the market in many countries in 1970, after it was linked to subacute myelo-optic neuropathy (SMON) in Japan, leading to vision loss with many patients left wheelchair-bound. The common pathology of CQ-associated SMON was reproduced in animals but none of the proposed modes of toxicity explained the restriction of CQ-induced SMON to Japan. Given a re-emergence of CQ and related analogues as neuroprotectants, it is crucial to understand the underlying mechanism of CQ-induced toxicity to prevent any potential CQ-associated risks to future patients. A small molecule screen to find drugs that induce mitochondrial dysfunction in vitro identified CQ and the structurally related 8-hydroxyquinoline (8-OHQ). Their mitochondrial liability, pro-oxidative and cytotoxic activity was subsequently confirmed in some cell lines but surprisingly not in others. Subsequent studies in isogenic cell lines demonstrated that the antioxidant protein NQO1 is differentially expressed in the cell lines tested and potently protects against CQ toxicity. CQ-induced reduction of cellular ATP levels, increased lipid peroxidation and elevated cell death was also attenuated by antioxidants, implicating oxidative stress as the core mechanism of CQ-induced toxicity. These in-vitro findings were replicated in zebrafish. Visual acuity in zebrafish larvae that do not express NQO1, was reduced by CQ in a dose-dependent manner, while CQ did not affect visual function in the adult zebrafish that express NQO1. Similarly, pharmacological inhibition of NQO1 activity resulted in CQ-induced oxidative stress in the retina and severe acute systemic toxicity in the adult fish. Given the much higher prevalence of the inactivating C609T NQO1 polymorphism in the Japanese population compared to the European population, the results of this study could for the first time indicate how the geographic restriction of SMON cases to Japan could be explained. Importantly, if CQ or its derivatives are to be used safely for the treatment of neurodegenerative diseases, it seems imperative that NQO1 levels and activity of prospective patients should be ascertained.

Founder genetic variants of ABCC4 and ABCC11 in the Japanese population are not associated with the development of subacute myelo-optico-neuropathy (SMON)

BACKGROUND

Subacute myelo-optico-neuropathy (SMON) is a severe neurological disorder associated with clioquinol administration, which frequently occurred in Japan during the 1950s and 1960s. The unique genetic background of the Japanese population is considered to be strongly involved in the development of this neurological disease. Recently, genetic variants of ABCC4 (OMIM: 605250) and ABCC11 (OMIM: 607040), which are particularly common in the Japanese population, were suggested as possible genetic susceptibility factors for the development of SMON.

METHODS

We analyzed 125 Japanese SMON patients who provided consent for this study. Patient DNA was collected from peripheral blood, and genetic analysis was performed for ABCC4 rs3765534 (c.2268G>A, p.Glu857Lys) and ABCC11 rs17822931 (c.538G>A, p.Gly180Arg) polymorphisms using the Sanger sequencing method and/or TaqMan PCR method. The frequency distribution of each polymorphism was compared with that in healthy Japanese people recorded in two genomic databases (Human Genomic Variation Database and Integrative Japanese Genome Variation Database), and each genotype was compared with the clinical features of patients.

RESULTS

The frequencies of ABCC4 rs3765334 and ABCC11 rs17822931 polymorphisms in SMON patients and healthy Japanese people were not significantly different in the multifaceted analysis.

CONCLUSION

We conclude that the ABCC4 rs3765334 and ABCC11 rs17822931 polymorphisms are not associated with the development of SMON.

Chloroxine overrides DNA damage tolerance to restore platinum sensitivity in high-grade serous ovarian cancer

High-grade serous cancer (HGSC) accounts for ~67% of all ovarian cancer deaths. Although initially sensitive to platinum chemotherapy, resistance is inevitable and there is an unmet clinical need for novel therapies that can circumvent this event. We performed a drug screen with 1177 FDA-approved drugs and identified the hydroxyquinoline drug, chloroxine. In extensive validation experiments, chloroxine restored sensitivity to both cisplatin and carboplatin, demonstrating broad synergy in our range of experimental models of platinum-resistant HGSC. Synergy was independent of chloroxine's predicted ionophore activity and did not relate to platinum uptake as measured by atomic absorption spectroscopy. Further mechanistic investigation revealed that chloroxine overrides DNA damage tolerance in platinum-resistant HGSC. Co-treatment with carboplatin and chloroxine (but not either drug alone) caused an increase in γH2AX expression, followed by a reduction in platinum-induced RAD51 foci. Moreover, this unrepaired DNA damage was associated with p53 stabilisation, cell cycle re-entry and triggering of caspase 3/7-mediated cell death. Finally, in our platinum-resistant, intraperitoneal in vivo model, treatment with carboplatin alone resulted in a transient tumour response followed by tumour regrowth. In contrast, treatment with chloroxine and carboplatin combined, was able to maintain tumour volume at baseline for over 4 months. In conclusion, our novel results show that chloroxine facilitates platinum-induced DNA damage to restore platinum sensitivity in HGSC. Since chloroxine is already licensed, this exciting combination therapy could now be rapidly translated for patient benefit.

[Fifity years after the identification of the cause of SMON]

SMON (subacute myelo-optico-neuropathy) is toxic neurological disease which had a profound impact on the population in Japan in 1960's. The clinical characteristics of SMON includes an ascending sensory disturbance, spasticity, and visual impairment typically following abdominal symptoms. Infection was first suspected as an underlying cause of this epidemic. The disorder was ultimately attributed to the overuse of clioquinol, based on the analysis of green urine from affected patients and confirmed by the epidemiological surveys and experimental animal studies. The factors that contributed to the prevalence of SMON which remains the worst example of drug-associated toxicity in Japan to date include the conversion of clioquinol from a purely topical agent to an orally-administered drug, dogma associated with drug safety, relatively limited regulation of drug use, an increase in the number of prescriptions due to the availability of universal insurance, as well as the complexity of the associated abdominal symptoms. Periodical examination of the patients diagnosed with SMON continues to this day. As such, it is important to have a better understanding of clioquinol-induced neurotoxicity together with the mechanisms underlying drug susceptibility; we should not permit the memory of this severe and prominent drug-associated toxicity fade from view.

Feasibility of Repurposing Clioquinol for Cancer Therapy

BACKGROUND

Cancer is a prevalent disease in the world and is becoming more widespread as time goes on. Advanced and more effective chemotherapeutics need to be developed for the treatment of cancer to keep up with this prevalence. Repurposing drugs is an alternative to discover new chemotherapeutics. Clioquinol is currently being studied for reposition as an anti-cancer drug.

OBJECTIVE

This study aimed to summarize the anti-cancer effects of clioquinol and its derivatives through a detailed literature and patent review and to review their potential re-uses in cancer treatment.

METHODS

Research articles were collected through a PubMed database search using the keywords "Clioquinol" and "Cancer." The keywords "Clioquinol Derivatives" and "Clioquinol Analogues" were also used on a PubMed database search to gather research articles on clioquinol derivatives. Patents were gathered through a Google Patents database search using the keywords "Clioquinol" and "Cancer."

RESULTS

Clioquinol acts as a copper and zinc ionophore, a proteasome inhibitor, an anti-angiogenesis agent, and is an inhibitor of key signal transduction pathways responsible for its growth-inhibitory activity and cytotoxicity in cancer cells preclinically. A clinical trial conducted by Schimmer et al., resulted in poor outcomes that prompted studies on alternative clioquinol-based applications, such as new combinations, new delivery methods, or new clioquinol-derived analogues. In addition, numerous patents claim alternative uses of clioquinol for cancer therapy.

CONCLUSION

Clioquinol exhibits anti-cancer activities in many cancer types, preclinically. Low therapeutic efficacy in a clinical trial has prompted new studies that aim to discover more effective clioquinol- based cancer therapies.

Clioquinol inhibits cell growth in a SERCA2-dependent manner

Clioquinol has been reported to act as a potential therapy for neurodegenerative diseases and cancer. However, the underlying mechanism is unclear. We have previously reported that clioquinol induces S-phase cell cycle arrest through the elevation of calcium levels in human neurotypic SH-SY5Y cells. In this study, different types of cells were observed to detect if the effect of clioquinol on intracellular calcium levels is cell type-specific. The Cell Counting Kit-8 assay showed that clioquinol exhibited varying degrees of concentration-dependent cytotoxicity in different cell lines, and that the growth inhibition caused by it was not related to cell source or carcinogenesis. In addition, the inhibition of cell growth by clioquinol was positively associated with its effect on intracellular calcium content ([Ca²⁺ ]_i ). Furthermore, the elevation of [Ca²⁺ ]_i induced by clioquinol led to S-phase cell cycle arrest. Similar to our previous studies, the increase in [Ca²⁺ ]_i was attributed to changes in the expression levels of the calcium pump SERCA2. Comparison of expression levels of SERCA2 between cell lines showed that cells with high levels of SERCA2 were more sensitive to clioquinol. In addition, analysis using UALCAN and the Human Protein Atlas also showed that the expression of SERCA2 in the corresponding human tissues was similar to that of the cells tested in this study, suggesting potential in the application of clioquinol in the future. In summary, our results expand the understanding of the molecular mechanism of clioquinol and provide an important strategy for the rational use of clioquinol.

PBT2 acts through a different mechanism of action than other 8-hydroxyquinolines: an X-ray fluorescence imaging study

8-Hydroxyquinolines (8HQs) comprise a family of metal-binding compounds that have been used or tested for use in numerous medicinal applications, including as treatments for bacterial infection, Alzheimer's disease, and cancer. Two key 8HQs, CQ (5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (2-(dimethylamino)methyl-5,7-dichloro-8-hydroxyquinoline), have drawn considerable interest and have been the focus of many studies investigating their in vivo properties. These drugs have been described as copper and zinc ionophores because they do not cause metal depletion, as would be expected for a chelation mechanism, but rather cellular accumulation of these ions. In studies of their anti-cancer properties, CQ has been proposed to elicit toxic intracellular copper accumulation and to trigger apoptotic cancer cell death through several possible pathways. In this study we used synchrotron X-ray fluorescence imaging, in combination with biochemical assays and light microscopy, to investigate 8HQ-induced alterations to metal ion homeostasis, as well as cytotoxicity and cell death. We used the bromine fluorescence from a bromine labelled CQ congener (5,7-dibromo-8-hydroxyquinoline; B2Q) to trace the intracellular localization of B2Q following treatment and found that B2Q crosses the cell membrane. We also found that 8HQ co-treatment with Cu(ii) results in significantly increased intracellular copper and significant cytotoxicity compared with 8HQ treatments alone. PBT2 was found to be more cytotoxic, but a weaker Cu(ii) ionophore than other 8HQs. Moreover, treatment of cells with copper in the presence of CQ or B2Q resulted in copper accumulation in the nuclei, while PBT2-guided copper was distributed near to the cell membrane. These results suggest that PBT2 may be acting through a different mechanism than that of other 8HQs to cause the observed cytotoxicity.

Clioquinol kills astrocyte-derived KT-5 cells by the impairment of the autophagy-lysosome pathway

Clioquinol has been implicated as a causative agent for subacute myelo-optico-neuropathy (SMON) in humans, although the mechanism remains to be elucidated. In this study, we utilized astrocyte-derived cell line, KT-5 cells to explore its potential cytotoxicity on glial cells. KT-5 cells were exposed in vitro to a maximum of 50 μM clioquinol for up to 24 h. 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenylte trazolium bromide (MTT) assay of the cells revealed that clioquinol induced significant cell damage and death. We also found that clioquinol caused accumulation of microtubule-associated protein light chain-3 (LC3)-II and sequestosome-1 (p62) in a dose- and time-dependent manner, suggesting the abnormality of autophagy-lysosome pathway. Consistent with these findings, an exposure of 20 μM clioquinol induced the accumulation of cellular autophagic vacuoles. Moreover, an exposure of 20 μM clioquinol provoked a statistically significant reduction of intracellular lysosomal acid hydrolases activities but no change in lysosomal pH. It also resulted in a significant decline of intracellular ATP levels, enhanced cellular levels of reactive oxygen species, and eventually cell death. This cell death at least did not appear to occur via apoptosis. 10 μM Chloroquine, lysosomal inhibitor, blocked the autophagic degradation and augmented clioquinol-cytotoxicity, whereas rapamycin, an inducer of autophagy, rescued clioquinol-induced cytotoxicity. Thus, our present results strongly suggest clioquinol acts as a potentially cytotoxic agent to glial cells. For future clinical application of clioquinol on the treatment of neurological and cancer disorders, we should take account of this type of cell death mechanism.

Clioquinol inhibits dopamine-β-hydroxylase secretion and noradrenaline synthesis by affecting the redox status of ATOX1 and copper transport in human neuroblastoma SH-SY5Y cells

Clioquinol (5-chloro-7-indo-8-quinolinol), a chelator and ionophore of copper/zinc, was extensively used as an amebicide to treat indigestion and diarrhea in the mid-1900s. However, it was withdrawn from the market in Japan because its use was epidemiologically linked to an increase in the incidence of subacute myelo-optic neuropathy (SMON). SMON is characterized by the subacute onset of sensory and motor disturbances in the lower extremities with occasional visual impairments, which are preceded by abdominal symptoms. Although pathological studies demonstrated axonopathy of the spinal cord and optic nerves, the underlying mechanisms of clioquinol toxicity have not been elucidated in detail. In the present study, a reporter assay revealed that clioquinol (20-50 µM) activated metal response element-dependent transcription in human neuroblastoma SH-SY5Y cells. Clioquinol significantly increased the cellular level of zinc within 1 h, suggesting zinc influx due to its ionophore effects. On the other hand, clioquinol (20-50 µM) significantly increased the cellular level of copper within 24 h. Clioquinol (50 µM) induced the oxidation of the copper chaperone antioxidant 1 (ATOX1), suggesting its inactivation and inhibition of copper transport. The secretion of dopamine-β-hydroxylase (DBH) and lysyl oxidase, both of which are copper-dependent enzymes, was altered by clioquinol (20-50 µM). Noradrenaline levels were reduced by clioquinol (20-50 µM). Disruption of the ATOX1 gene suppressed the secretion of DBH. This study suggested that the disturbance of cellular copper transport by the inactivation of ATOX1 is one of the mechanisms involved in clioquinol-induced neurotoxicity in SMON.

Iron-sulfur cluster biosynthesis and trafficking - impact on human disease conditions

Iron-sulfur clusters (Fe-S) are one of the most ancient, ubiquitous and versatile classes of metal cofactors found in nature. Proteins that contain Fe-S clusters constitute one of the largest families of proteins, with varied functions that include electron transport, regulation of gene expression, substrate binding and activation, radical generation, and, more recently discovered, DNA repair. Research during the past two decades has shown that mitochondria are central to the biogenesis of Fe-S clusters in eukaryotic cells via a conserved cluster assembly machinery (ISC assembly machinery) that also controls the synthesis of Fe-S clusters of cytosolic and nuclear proteins. Several key steps for synthesis and trafficking have been determined for mitochondrial Fe-S clusters, as well as the cytosol (CIA - cytosolic iron-sulfur protein assembly), but detailed mechanisms of cluster biosynthesis, transport, and exchange are not well established. Genetic mutations and the instability of certain steps in the biosynthesis and maturation of mitochondrial, cytosolic and nuclear Fe-S cluster proteins affects overall cellular iron homeostasis and can lead to severe metabolic, systemic, neurological and hematological diseases, often resulting in fatality. In this review we briefly summarize the current molecular understanding of both mitochondrial ISC and CIA assembly machineries, and present a comprehensive overview of various associated inborn human disease states.

The ATM kinase inhibitor KU-55933 provides neuroprotection against hydrogen peroxide-induced cell damage via a γH2AX/p-p53/caspase-3-independent mechanism: Inhibition of calpain and cathepsin D

The role of the kinase ataxia-telangiectasia mutated (ATM), a well-known protein engaged in DNA damage repair, in the regulation of neuronal responses to oxidative stress remains unexplored. Thus, the neuroprotective efficacy of KU-55933, a potent inhibitor of ATM, against cell damage evoked by oxidative stress (hydrogen peroxide, H₂O₂) has been studied in human neuroblastoma SH-SY5Y cells and compared with the efficacy of this agent in models of doxorubicin (Dox)- and staurosporine (St)-evoked cell death. KU-55933 inhibited the cell death induced by H₂O₂ or Dox but not by St in undifferentiated (UN-) and retinoic acid-differentiated (RA)-SH-SY5Y cells, with a more pronounced effect in the latter cell phenotype. Furthermore, this ATM inhibitor attenuated the Dox- but not H₂O₂-induced caspase-3 activity in both UN- and RA-SH-SY5Y cells. Although KU-55933 inhibited the H₂O₂- and Dox-induced activation of ATM, it attenuated the toxin-induced phosphorylation of the proteins H2AX and p53 only in the latter model of cell damage. Moreover, the ATM inhibitor prevented the H₂O₂-evoked increases in calpain and cathepsin D activity and attenuated cell damage to a similar degree as inhibitors of calpain (MDL28170) and cathepsin D (pepstatin A). Finally, we confirmed the neuroprotective potential of KU-55933 against the H₂O₂- and Dox-evoked cell damage in primary mouse cerebellar granule cells and in the mouse hippocampal HT-22 cell line. Altogether, our results extend the neuroprotective portfolio of KU-55933 to a model of oxidative stress, with this effect not involving inhibition of the γH2AX/p-p53/caspase-3 pathway and instead associated with the attenuation of calpain and cathepsin D activity.

Parkinson's Disease: The Mitochondria-Iron Link

Mitochondrial dysfunction, iron accumulation, and oxidative damage are conditions often found in damaged brain areas of Parkinson's disease. We propose that a causal link exists between these three events. Mitochondrial dysfunction results not only in increased reactive oxygen species production but also in decreased iron-sulfur cluster synthesis and unorthodox activation of Iron Regulatory Protein 1 (IRP1), a key regulator of cell iron homeostasis. In turn, IRP1 activation results in iron accumulation and hydroxyl radical-mediated damage. These three occurrences-mitochondrial dysfunction, iron accumulation, and oxidative damage-generate a positive feedback loop of increased iron accumulation and oxidative stress. Here, we review the evidence that points to a link between mitochondrial dysfunction and iron accumulation as early events in the development of sporadic and genetic cases of Parkinson's disease. Finally, an attempt is done to contextualize the possible relationship between mitochondria dysfunction and iron dyshomeostasis. Based on published evidence, we propose that iron chelation-by decreasing iron-associated oxidative damage and by inducing cell survival and cell-rescue pathways-is a viable therapy for retarding this cycle.

Histone deacetylase inhibitor attenuates neurotoxicity of clioquinol in PC12 cells

Clioquinol is considered to be a causative agent of subacute myelo-optico neuropathy (SMON), although the pathogenesis of SMON is yet to be elucidated. We have previously shown that clioquinol inhibits nerve growth factor (NGF)-induced Trk autophosphorylation in PC12 cells transformed with human Trk cDNA. To explore the further mechanism of neuronal damage by clioquinol, we evaluated the acetylation status of histones in PC12 cells. Clioquinol reduced the level of histone acetylation, and the histone deacetylase (HDAC) inhibitor Trichostatin A upregulated acetylated histones and prevented the neuronal cell damage caused by clioquinol. In addition, treatment with HDAC inhibitor decreased neurite retraction and restored the inhibition of NGF-induced Trk autophosphorylation by clioquinol. Thus, clioquinol induced neuronal cell death via deacetylation of histones, and HDAC inhibitor alleviates the neurotoxicity of clioquinol. Clioquinol is now used as a potential medicine for malignancies and neurodegenerative diseases. Therefore, HDAC inhibitors can be used as a candidate medicine for the prevention of its side effects on neuronal cells.