Clioquinol, an alternative antimicrobial agent against common pathogenic microbe

Recent Progress in Synthetic Chemistry and Biological Activities of Pyrimido[ 4,5-b] Quinoline Derivatives (Part III)

Abstract:

Amongst heterocyclic compounds, quinoline and pyrimidine are advantaged scaffolds that appear as significant assembly motifs for the development of new drug entities. Moreover, quinolinepyrimidine- inspired hybrids have a number of biological characteristics that are known. In addition, many pyrimido[4,5-b]quinoline ring systems (PyQs4,5-b), specifically concerning medicinal chemistry, have been reported over the past decade. The synthesis of (PyQs4,5-b) using barbituric acid, thiobarbituric acid, pyrimidine, and their derivatives is presented in this review. The preparation of PyQs4,5-b was clarified through the following chemical reactions: Friedländer, Vilsmeier-Haack formylation, Hantzsch-like reaction, and one-pot three-component reaction.

Clioquinol influences cell membrane, attenuates virulence factors, induces apoptosis to inhibit Candida albicans growth

Aim: To investigate the antifungal mechanism of clioquinol and indicate that clioquinol has potential as a novel therapeutic antifungal agent.Materials & methods: Analyze differentially expressed genes of Candida albicans treated with clioquinol using RNA-sequencing. The effects on cell wall and membrane features, virulence factors, apoptosis-induced cell death were also investigated.Results: The differentially expressed genes of C. albicans after treated with clioquinol focused on cell wall and membrane synthesis, antioxidant system and energy metabolism. Clioquinol did not change cell wall components levels while it decreased squalene epoxidase activity to influence the ergosterol biosynthesis in cell membrane. It also decreased cellular surface hydrophobicity and induced β-glucan unmasking to attenuate virulence factors. Meanwhile, clioquinol influenced enzyme activities involved in antioxidant system, citrate cycle, oxidative phosphorylation and decreased the ATP levels. Clioquinol induced apoptosis in C. albicans to exert its fungicidal activity. It induced reactive oxygen species and calcium ion elevation, leading to loss of mitochondrial membrane potential, cytochrome C release, metacaspase activation, thereby triggering apoptosis.Conclusion: Clioquinol exerted anti-C. albicans activity through influencing cell membrane, attenuating virulence factors and inducing apoptosis.

Potential antifungal applications of heterometallic silica nanohybrids: A synergistic activity

An estimated 1.7 million fatalities and 150 million cases worldwide are attributed to fungal infections annually, that are in rise due to immunocompromised patient population. The challenges posed by traditional treatments can be addressed with the help of nanotechnology advancements. In this study, Co, Cu, and Ag-were doped into silica nanoparticles. Then the synthesized monometallic silica nanohybrids were combined to formulate heterometallic silica nanohybrids, characterized structurally and morphologically, compared, and evaluated for antifungal activity based on their individual and synergistic activity. The antifungal assays were conducted by using ATCC cultures of Candida albicans and QC samples of Trichophyton rubrum, Microsporum gypseum, and Aspergillus niger. The MIC (ranging from 49.00 to 1560.00 μg/mL), MFC (ranging from 197.00 to 3125.00 μg/mL), IC50 values (ranging from 31.10 to 400.80 μg/mL), and FICI of nanohybrids were determined and compared. Moreover, well diffusion assay was performed. ABTS assay and DPPH assay were conducted to investigate the radical scavenging activity (RSA) of nanohybrids. SEM analysis clearly evidenced the structural deformations of each fungal cells and spores due to the treatment with trimetallic nanohybrid. According to the results, the trimetallic silica nanohybrids exhibited the most powerful synergistic RSA and the most effective antifungal activity, compared to the bimetallic silica nanohybrids.

Discovery of Novel 8-Hydroxyquinoline Derivatives with Potent In Vitro and In Vivo Antifungal Activity

Fungal pathogens can cause life-threatening infections, yet current antifungals are inadequate at treating many of these, highlighting the importance of novel drug discovery. Here, we report hit compound L14, a novel 8-hydroxyquinoline derivative with potent and broad-spectrum antifungal activity. In vitro experiments exhibited that L14 had better activity and lower cytotoxicity than that of clioquinol and showed synergy in combination with fluconazole (FLC). In a Candida albicans-infected murine model, L14 at 2 mg/kg showed better in vivo efficacy than clioquinol at reducing fungal burden and extending the survival of C. albicans-infected mice. In addition, L14 alone or in combination with FLC had significant inhibitory activity against hypha and biofilm formation. Overall, our data indicated that 8-hydroxyquinoline derivative L14 has favorable pharmacokinetics and acceptable safety profiles and could be further investigated as a promising antifungal hit compound.

Harnessing the dual antimicrobial mode of action with a lipophilic Mn(II) complex using the principle of the Irving-Williams Series to completely eradicate Staphylococcus aurous

The judicious selection of 5,7-dibromo-2-methy-8-quinolinol (BQ) as a Mn(II) ionophore results in the synthesis of Mn(BQ)2(DMSO)2·DMSO (1), a potent metalloantibiotic with a dual antimicrobial mode of action against four different strains of Staphylococcus aurous (SA) bacteria (MIC = 0.625 μg mL-1). Additionally, 1 can overcome ciprofloxacin-resistance in methicillin-resistant SA bacteria.

Quinoline Thiourea-Based Zinc Ionophores with Antibacterial Activity

The increasing resistance of bacteria to commercially available antibiotics threatens patient safety in healthcare settings. Perturbation of ion homeostasis has emerged as a potential therapeutic strategy to fight against antibacterial resistance and other channelopathies. This study reports the development of 8-aminoquinoline (QN) derivatives and their transmembrane Zn2+ transport activities. Our findings showed that a potent QN-based Zn2+ transporter exhibits promising antibacterial properties against Gram-positive bacteria with reduced hemolytic activity and cytotoxicity to mammalian cells. Furthermore, this combination showed excellent in vivo efficacy against Staphylococcus aureus. Interestingly, this combination prevented bacterial resistance and restored susceptibility of gentamicin and methicillin-resistant S. aureus to commercially available β-lactam and other antibiotics that had lost their activity against the drug-resistant bacterial strain. Our findings suggest that the transmembrane transport of Zn2+ by QN derivatives could be a promising strategy to combat bacterial infections and restore the activity of other antibiotics.

Development of a Clioquinol Nanocarrier as a New, Promising Option for the Treatment of Dermatomycosis

Dermatomycosis is a common fungal infection, and its treatment is limited by few antifungal agents. Clioquinol (CQ) is an antiparasitic agent that has been studied for new uses, such as antifungal and antiviral applications. CQ was incorporated into a lipid-based nanocarrier as a new, promising option for dermatomycosis. This study aimed to develop a CQ-loaded lipid-based nanocarrier for cutaneous application and to evaluate its antifungal activity. CQ-loaded nanoformulation (LBN-CQ) was developed using the ultrasonication method, and the particle size, polydispersity index (PDI), pH, zeta potential, and drug content were monitored for 45 days. To evaluate antifungal activity, broth microdilution and a time-kill assay were performed. LBN-CQ presented a particle size of 91 ± 3 nm and PDI of 0.102 ± 0.009. The zeta potential and pH values were -9.7 ± 2.0 mV and 6.0 ± 0.1, respectively. The drug content was 96.4 ± 2.3%, and the encapsulation efficiency was 98.4%. LBN-CQ was able to reduce the minimum inhibitory concentration (MIC) in a 2-fold or 4-fold manner in most of the tested strains. Additionally, LBN-CQ presented stable fungistatic action that was not concentration- or time-dependent. In conclusion, the developed CQ-loaded nanocarrier is a promising treatment for skin fungal infections and a promising candidate for future randomized clinical trials.

Intra-articular injection of clioquinol ameliorates osteoarthritis in a rabbit model

Osteoarthritis (OA) is characterized by the degeneration of articular cartilage. Decreased autophagy is tightly associated with chondrocyte death, which contributes to the progression of OA. Thus, pharmacological activation of autophagy may be a promising therapeutic approach for OA. Here, we discovered that clioquinol, an antibiotic, significantly induces autophagy in OA chondrocytes from human tissue and rabbit model. Meanwhile, clioquinol can also augment the expression of extracellular matrix (ECM) components and suppress inflammatory mediators to improve OA microenvironment. Intra-articular injection of clioquinol can greatly prevent or slow down the development of this disease in a trauma-induced rabbit model of osteoarthritis. Such protective effect induced by clioquinol was at least in part explained by decreasing chondrocyte apoptosis and increasing autophagy. This study reveals the therapeutic potential of clioquinol in OA treatment.

Antimicrobial activity of clioquinol and nitroxoline: a scoping review

Clioquinol and nitroxoline, two drugs with numerous pharmacological properties fallen into disuse for many decades. The first was considered dangerous due to contraindications and the second mainly because was taken as ineffective, despite its known antibacterial activity. In the last decades, the advances in pharmaceutical chemistry, molecular biology, toxicology and genetics allowed to better understand the cellular action of these compounds, some toxicological issues and/or activity scopes. Thus, a new opportunity for these drugs to be considered as potential antimicrobial agents has arisen. This review contemplates the trajectory of clioquinol and nitroxoline from their emergence to the present day, emphasizing the new studies that indicate the possibility of reintroduction for specific cases.

Novel avenues for identification of new antifungal drugs and current challenges

INTRODUCTION

: Some of otherwise useful fungi are pathogenic to humans, and unfortunately, the number of these pathogens is increasing. In addition to common skin infections, these opportunistic pathogens are able to cause severe, often incurable, systemic mycoses.

AREAS COVERED

: The number of antifungal drugs is limited, especially drugs that can be used for systemic administration, and resistance to these drugs is very common. This review summarizes various approaches to the discovery and development of new antifungal drugs, provides an overview of the most important molecules in terms of basic (laboratory) research and compounds currently in clinical trials, and focuses on drug repurposing strategy, while providing an overview of drugs of other indications that have been tested in vitro for their antifungal activity for possible expansion of antifungal drugs and/or support of existing antimycotics.

EXPERT OPINION

: Despite the limitations of the research of new antifungal drugs by pharmaceutical manufacturers, in addition to innovated molecules based on clinically used drugs, several completely new small entities with unique mechanisms of actions have been identified. The identification of new molecular targets that offer alternatives for the development of new unique selective antifungal highly effective agents has been an important outcome of repurposing of non-antifungal drugs to antifungal drug. Also, given the advances in monoclonal antibodies and their application to immunosuppressed patients, it may seem possible to predict a more optimistic future for antifungal therapy than has been the case in recent decades.

Using Caenorhabditis elegans to Model Therapeutic Interventions of Neurodegenerative Diseases Targeting Microbe-Host Interactions

Emerging evidence from both clinical studies and animal models indicates the importance of the interaction between the gut microbiome and the brain in the pathogenesis of neurodegenerative diseases (NDs). Although how microbes modulate neurodegeneration is still mostly unclear, recent studies have started to probe into the mechanisms for the communication between microbes and hosts in NDs. In this review, we highlight the advantages of using Caenorhabditis elegans (C. elegans) to disentangle the microbe-host interaction that regulates neurodegeneration. We summarize the microbial pro- and anti-neurodegenerative factors identified using the C. elegans ND models and the effects of many are confirmed in mouse models. Specifically, we focused on the role of bacterial amyloid proteins, such as curli, in promoting proteotoxicity and neurodegeneration by cross-seeding the aggregation of endogenous ND-related proteins, such as α-synuclein. Targeting bacterial amyloid production may serve as a novel therapeutic strategy for treating NDs, and several compounds, such as epigallocatechin-3-gallate (EGCG), were shown to suppress neurodegeneration at least partly by inhibiting curli production. Because bacterial amyloid fibrils contribute to biofilm formation, inhibition of amyloid production often leads to the disruption of biofilms. Interestingly, from a list of 59 compounds that showed neuroprotective effects in C. elegans and mouse ND models, we found that about half of them are known to inhibit bacterial growth or biofilm formation, suggesting a strong correlation between the neuroprotective and antibiofilm activities. Whether these potential therapeutics indeed protect neurons from proteotoxicity by inhibiting the cross-seeding between bacterial and human amyloid proteins awaits further investigations. Finally, we propose to screen the long list of antibiofilm agents, both FDA-approved drugs and novel compounds, for their neuroprotective effects and develop new pharmaceuticals that target the gut microbiome for the treatment of NDs. To this end, the C. elegans ND models can serve as a platform for fast, high-throughput, and low-cost drug screens that target the microbe-host interaction in NDs.

Electrospun 5-Chloro-7-iodo-8-hydroxyquinoline (Clioquinol)-Containing Poly(3-hydroxybutyrate)/Polyvinylpyrrolidone Antifungal Materials Prospective as Active Dressings against Esca

Esca is a grapevine disease known for centuries which pertains to the group of so-called vine trunk diseases. Phaeomoniella chlamydospora (P. chlamydospora) and Phaeoacremonium aleophilum (P. aleophilum) are the two main fungal pathogens associated with esca. Novel fibrous materials with antifungal properties based on poly(3-hydroxybutyrate) (PHB), polyvinylpyrrolidone (PVP) and 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol, CQ) were developed. One-pot electrospinning (“in” strategy) or electrospinning in conjunction with electrospraying (“on” strategy) were applied to obtain the materials. The materials’ morphology and their surface chemical composition were examined using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). CQ incorporated in the bulk of the fibers or in PVP particles deposited on the fibers was in the amorphous phase, which was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD). The in vitro release of CQ depended on the composition of the electrospun materials and on their design. The performed microbiological screening revealed that, unlike the non-loaded mats, the fibrous mats loaded with CQ were effective in inhibiting the growth of the pathogenic P. chlamydospora and P. aleophilum fungi. Therefore, the created materials are promising as active dressings for grapevine protection against esca.

The antimicrobial and immunomodulatory effects of Ionophores for the treatment of human infection

Ionophores are a diverse class of synthetic and naturally occurring ion transporter compounds which demonstrate both direct and in-direct antimicrobial properties against a broad panel of bacterial, fungal, viral and parasitic pathogens. In addition, ionophores can regulate the host-immune response during communicable and non-communicable disease states. Although the clinical use of ionophores such as Amphotericin B, Bedaquiline and Ivermectin highlight the utility of ionophores in modern medicine, for many other ionophore compounds issues surrounding toxicity, bioavailability or lack of in vivo efficacy studies have hindered clinical development. The antimicrobial and immunomodulating properties of a range of compounds with characteristics of ionophores remain largely unexplored. As such, ionophores remain a latent therapeutic avenue to address both the global burden of antimicrobial resistance, and the unmet clinical need for new antimicrobial therapies. This review will provide an overview of the broad-spectrum antimicrobial and immunomodulatory properties of ionophores, and their potential uses in clinical medicine for combatting infection.

Discovery of Clioquinol and analogues as novel inhibitors of Severe Acute Respiratory Syndrome Coronavirus 2 infection, ACE2 and ACE2 - Spike protein interaction in vitro

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the etiological agent for coronavirus disease 2019 (COVID-19), has resulted in an ongoing pandemic. Presently, there are no clinically approved drugs for COVID-19. Hence, there is an urgent need to accelerate the development of effective antivirals. Herein, we discovered Clioquinol (5-chloro-7-iodo-8-quinolinol (CLQ)), a Food and Drug Administration (FDA) approved drug, and two of its analogues (7-bromo-5-chloro-8-hydroxyquinoline (CLBQ14); and 5, 7-Dichloro-8-hydroxyquinoline (CLCQ)) as potent inhibitors of SARS-CoV-2 infection-induced cytopathic effect in vitro. In addition, all three compounds showed potent anti-exopeptidase activity against recombinant human angiotensin-converting enzyme 2 (rhACE2) and inhibited the binding of rhACE2 with SARS-CoV-2 Spike (RBD) protein. CLQ displayed the highest potency in the low micromolar range, with its antiviral activity showing a strong correlation with inhibition of rhACE2 and rhACE2-RBD interaction. Altogether, our findings provide a new mode of action and molecular target for CLQ and validates this pharmacophore as a promising lead series for the clinical development of potential therapeutics for COVID-19.

Radical Transformations towards the Synthesis of Quinoline: A Review

Quinoline is considered one of the most ubiquitous heterocycles due to its engaging biological activities and synthetic utility over organic transformations. Over the past few decades, numerous reports have been documented in the synthesis of quinolines. The classical methods including, Skraup, Friedlander, Doebner-von-Miller, Conrad-Limpach, Pfitzinger quinoline synthesis, and so forth, these are the well-known methods to construct principal quinoline scaffold with several advantages and limitations. Recently, radical insertion or catalyzed reactions have emerged as a powerful and efficient tool to construct heterocycles with high atom efficiency and step economy. In this concern, this minireview mainly focused on the developments of Quinoline synthesis via radical reactions. In addition, a brief description of the preparation procedure, reactivity, and mechanisms is also included, where as possible. Respectively, the synthesis of quinolines is classified and summarized based on its reactivity, so it will help the researchers to grab the information in this exploration area, as Quinolines are promising pharmacophores.

Antifungal Drug Repurposing

Control of fungal pathogens is increasingly problematic due to the limited number of effective drugs available for antifungal therapy. Conventional antifungal drugs could also trigger human cytotoxicity associated with the kidneys and liver, including the generation of reactive oxygen species. Moreover, increased incidences of fungal resistance to the classes of azoles, such as fluconazole, itraconazole, voriconazole, or posaconazole, or echinocandins, including caspofungin, anidulafungin, or micafungin, have been documented. Of note, certain azole fungicides such as propiconazole or tebuconazole that are applied to agricultural fields have the same mechanism of antifungal action as clinical azole drugs. Such long-term application of azole fungicides to crop fields provides environmental selection pressure for the emergence of pan-azole-resistant fungal strains such as Aspergillus fumigatus having TR34/L98H mutations, specifically, a 34 bp insertion into the cytochrome P450 51A (CYP51A) gene promoter region and a leucine-to-histidine substitution at codon 98 of CYP51A. Altogether, the emerging resistance of pathogens to currently available antifungal drugs and insufficiency in the discovery of new therapeutics engender the urgent need for the development of new antifungals and/or alternative therapies for effective control of fungal pathogens. We discuss the current needs for the discovery of new clinical antifungal drugs and the recent drug repurposing endeavors as alternative methods for fungal pathogen control.

Multiple Drug-Induced Stress Responses Inhibit Formation of Escherichia coli Biofilms

The prevention of bacterial biofilm formation is one of the major current challenges in microbiology. Here, by systematically screening a large number of approved drugs for their ability to suppress biofilm formation by Escherichia coli, we identified a number of prospective antibiofilm compounds. We further demonstrated different mechanisms of action for individual compounds, from induction of replicative stress to disbalance of cation homeostasis to inhibition of bacterial attachment to the surface. Our work demonstrates the potential of drug repurposing for the prevention of bacterial biofilm formation and suggests that also for other bacteria, the activity spectrum of antibiofilm compounds is likely to be broad.

In most ecosystems, bacteria exist primarily as structured surface-associated biofilms that can be highly tolerant to antibiotics and thus represent an important health issue. Here, we explored drug repurposing as a strategy to identify new antibiofilm compounds, screening over 1,000 compounds from the Prestwick Chemical Library of approved drugs for specific activities that prevent biofilm formation by Escherichia coli. Most growth-inhibiting compounds, which include known antibacterial but also antiviral and other drugs, also reduced biofilm formation. However, we also identified several drugs that were biofilm inhibitory at doses where only a weak effect or no effect on planktonic growth could be observed. The activities of the most specific antibiofilm compounds were further characterized using gene expression analysis, proteomics, and microscopy. We observed that most of these drugs acted by repressing genes responsible for the production of curli, a major component of the E. coli biofilm matrix. This repression apparently occurred through the induction of several different stress responses, including DNA and cell wall damage, and homeostasis of divalent cations, demonstrating that biofilm formation can be inhibited through a variety of molecular mechanisms. One tested drug, tyloxapol, did not affect curli expression or cell growth but instead inhibited biofilm formation by suppressing bacterial attachment to the surface.

IMPORTANCE The prevention of bacterial biofilm formation is one of the major current challenges in microbiology. Here, by systematically screening a large number of approved drugs for their ability to suppress biofilm formation by Escherichia coli, we identified a number of prospective antibiofilm compounds. We further demonstrated different mechanisms of action for individual compounds, from induction of replicative stress to disbalance of cation homeostasis to inhibition of bacterial attachment to the surface. Our work demonstrates the potential of drug repurposing for the prevention of bacterial biofilm formation and suggests that also for other bacteria, the activity spectrum of antibiofilm compounds is likely to be broad.

Discovery of Clioquinol and Analogues as Novel Inhibitors of Severe Acute Respiratory Syndrome Coronavirus 2 Infection, ACE2 and ACE2 - Spike Protein Interaction In Vitro

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the etiological agent for coronavirus disease 2019 (COVID-19), has emerged as an ongoing global pandemic. Presently, there are no clinically approved vaccines nor drugs for COVID-19. Hence, there is an urgent need to accelerate the development of effective antivirals. Here in, we discovered Clioquinol (5-chloro-7-iodo-8-quinolinol (CLQ)), a FDA approved drug and two of its analogues (7-bromo-5-chloro-8-hydroxyquinoline (CLBQ14); and 5, 7-Dichloro-8-hydroxyquinoline (CLCQ)) as potent inhibitors of SARS-CoV-2 infection induced cytopathic effect in vitro . In addition, all three compounds showed potent anti-exopeptidase activity against recombinant human angiotensin converting enzyme 2 (rhACE2) and inhibited the binding of rhACE2 with SARS-CoV-2 Spike (RBD) protein. CLQ displayed the highest potency in the low micromolar range, with its antiviral activity showing strong correlation with inhibition of rhACE2 and rhACE2-RBD interaction. Altogether, our findings provide a new mode of action and molecular target for CLQ and validates this pharmacophore as a promising lead series for clinical development of potential therapeutics for COVID-19.

Synergistic association of clioquinol with antifungal drugs against biofilm forms of clinical Fusarium isolates

BACKGROUND

The influence of biofilm on the complexity of fungal diseases has been reported in recent years, especially in non-invasive mycoses such as keratitis and onychomycosis. The difficulty in treating cases of fusariosis in the human medical clinic exemplifies this situation, because when Fusarium spp. are present in the form of biofilm, the permeation of antifungal agents is compromised.

OBJECTIVES

This study proposes an association of clioquinol, an inhibitor of fungal cells with antifungal drugs prescribed to combat fusariosis in humans.

METHODS

Susceptibility was assessed by microdilution in broth. Formation of biofilm by staining with violet crystal. Inhibition and removal of biofilm using the MTT colorimetric reagent. Time-kill combination, hypoallergenicity test, cytotoxicity test and toxicity prediction by computer analysis were also performed.

RESULTS

Clioquinol associated with voriconazole and ciclopirox inhibited biofilm formation. Possibly, clioquinol acts in the germination and elongation of hyphae, while voriconazole prevents cell adhesion and ciclopirox the formation of the extracellular polymeric matrix. The CLIO-VRC association reduced the biofilm formation by more than 90%, while the CLIO-CPX association prevented over 95%. None of the association was irritating, and over 90% of the leucocytes remained viable. Computational analysis does not reveal toxicity relevant to CLIO, whereas VRC and CPX showed some risks for systemic use, but suitable for topical formulations.

CONCLUSIONS

The combination of CLIO-VRC or CLIO-CPX proved to be a promising association strategy in the medical clinic, both in combating fungal keratitis and onychomycosis, since they prevent the initial process of establishing an infection, the formation of biofilm.

The effects of clioquinol in morphogenesis, cell membrane and ion homeostasis in Candida albicans

Background

Candida albicans is the most prevalent opportunistic fungal pathogen. Development of antifungals with novel targets is necessary for limitations of current antifungal agents and the emergence of drug resistance. The antifungal activity of clioquinol was widely accepted while the precise mechanism was poorly understood. Hence, we aimed to seek for the possible mechanism of clioquinol against Candida albicans in the present study.

Results

Clioquinol could inhibit hyphae formation in a concentration-dependent manner in multiple liquid and solid media. The concentration and time-dependent anti-biofilm activities were observed in different incubation periods quantitatively and qualitatively. Further investigation found that clioquinol disrupted cell membrane directly in high concentration and induced depolarization of the membrane in low concentration. As for the influence on ion homeostasis, the antifungal effects of clioquinol could be reversed by exogenous addition of metal ions. Meanwhile, the minimum inhibitory concentration of clioquinol was increased in media supplemented with exogenous metal ions and decreased in media supplemented with exogenous metal chelators. We also found that the cellular labile ferrous iron level decreased when fungal cells were treated with clioquinol.

Conclusion

These results indicated that clioquinol could inhibit yeast-hyphae transition and biofilm formation in Candida albicans. The effect on the cell membrane was different depending on different concentrations of clioquinol. Meanwhile, clioquinol could interfere with ion homeostasis as metal chelators for zinc, copper and iron, which was quite different with current common antifungal agents. All in all, clioquinol can be a new promising antifungal agent with novel target though more studies are needed to better understand the precise antifungal mechanism.

Identification of repositionable drugs with novel antimycotic activity by screening the Prestwick Chemical Library against emerging invasive moulds

OBJECTIVES

The incidence of severe filamentous fungal infections has increased over the past decade. Some of these filamentous fungi are resistant to available antifungals; it is thus urgent to find new compounds that are active against such life-threatening pathogens.

METHODS

In this study, 1280 drugs (Prestwick Chemical Library) were tested against six multidrug-resistant (MDR) filamentous fungi, includingAspergillus, Fusarium, Scedosporium/Lomentospora, Rhizopus and Lichtheimia species.

RESULTS

Several hits were identified that induced fungal growth inhibition ≥70%. Among the non-antifungal compounds that were effective against the clinical moulds tested in this study, clioquinol, alexidine dihydrochloride, hexachlorophene and thonzonium bromide displayed a broad activity against all strains tested.

CONCLUSION

This study enriches the potential antifungal options that can be used against MDR invasive fungal diseases.

Exploiting the vulnerable active site of a copper-only superoxide dismutase to disrupt fungal pathogenesis

Copper-only superoxide dismutases (SODs) represent a new class of SOD enzymes that are exclusively extracellular and unique to fungi and oomycetes. These SODs are essential for virulence of fungal pathogens in pulmonary and disseminated infections, and we show here an additional role for copper-only SODs in promoting survival of fungal biofilms. The opportunistic fungal pathogen Candida albicans expresses three copper-only SODs, and deletion of one of them, SOD5, eradicated candidal biofilms on venous catheters in a rodent model. Fungal copper-only SODs harbor an irregular active site that, unlike their Cu,Zn-SOD counterparts, contains a copper co-factor unusually open to solvent and lacks zinc for stabilizing copper binding, making fungal copper-only SODs highly vulnerable to metal chelators. We found that unlike mammalian Cu,Zn-SOD1, C. albicans SOD5 indeed rapidly loses its copper to metal chelators such as EDTA, and binding constants for Cu(II) predict that copper-only SOD5 has a much lower affinity for copper than does Cu,Zn-SOD1. We screened compounds with a variety of indications and identified several metal-binding compounds, including the ionophore pyrithione zinc (PZ), that effectively inhibit C. albicans SOD5 but not mammalian Cu,Zn-SOD1. We observed that PZ both acts as an ionophore that promotes uptake of toxic metals and inhibits copper-only SODs. The pros and cons of a vulnerable active site for copper-only SODs and the possible exploitation of this vulnerability in antifungal drug design are discussed.