New insights into the mechanism of antifungal action of 8-hydroxyquinolines

Combinatorial effect of fluconazole, itraconazole, and terbinafine with different culture extracts of Candida parapsilosis and Trichophyton spp. against Trichophyton rubrum

Onychomycosis is a nail infection caused by dermatophytes, non-dermatophyte fungi, and yeasts, especially Candida species. The present study evaluated the combinatorial effect of different cultured extracts of Candida parapsilosis and Trichophyton mentagrophytes and Trichophyton rubrum with fluconazole, itraconazole, and terbinafine against clinical isolates of Trichophyton rubrum. In addition, investigation of the action of the extracts on the wall or membrane was performed. Pure and mixed cultures of Candida parapsilosis and dermatophytes were filtered through a 0.2-μm membrane and submitted to liquid-liquid extraction using ethyl acetate. After a checkerboard, trial with drugs was performed to evaluate the synergistic interaction with the extract. The results obtained for the minimum inhibitory concentration (MIC) of extracts against the T. rubrum strain in isolation were 500-8000 μg/mL. The MIC range for fluconazole, itraconazole, and terbinafine were 2-32 μg/mL, 0.25-0.5 μg/mL, 0.03-64 μg/mL, respectively. However, when the extract was combined with drugs, the MIC values decreased: extracts 1.9-1000 μg/mL, fluconazole 0.25-4, itraconazole 0.03-0.06 μg/mL, and terbinafine 0.001-0.02 μg/mL. The MIC values of the extracts in the Roswell Park Memorial Institute 1640 medium (RPMI) supplemented with sorbitol did not change, suggesting any action on the cell wall. However, in the presence of RPMI supplemented with ergosterol, MIC values of the extracts increased by up to 2×, indicating action on the fungal cell membrane. A synergistic action was observed between products and drugs, detecting a decrease in MIC values. There is potential and a new therapeutic perspective for fungal control.

Synergistic activity of clioquinol with voriconazole and amphotericin B against fungi of interest in eye infections

Keratoplasty represents a risk factor for fungal eye infections, despites the antibacterial actives in the corneal tissue preservation means, it does not contain active substances with antifungal action. Among the most commonly associated fungal agents are the species belonging to the genera Fusarium and Candida. These agents can trigger an infectious process characterized by swift progression associated with high rates of morbidity, causing irreversible damage. Polyene and azole antifungals are the main agents of ocular therapy, however, they demonstrate some limitations, such as their toxicity and fungal resistance. In this context, drug repositioning and the combination of antifungals may be an alternative. Hence, the goal of this study was to investigate the potential activity of clioquinol (CLQ), a derivative of 8-hydroxyquinoline with previously described antifungal activity, along with its triple and quadruple combinations with antifungal agents commonly used in ophthalmic fungal therapy, natamycin (NAT), voriconazole (VRC), and amphotericin B (AMB), against main fungal pathogens in eye infections. The MICs for CLQ ranged from 0.25 to 2.0 μg/mL, for NAT from 4.0 to 32.0 μg/mL, for AMB it ranged from 0.25 to 16.0 μg/mL and for VRC from 0.03125 to 512.0 µg/mL. Among the tested combinations, the VRC-AMB-CLQ combination stands out, which showed a synergistic effect for more than 50 % of the tested strains and did not present antagonistic results against any of them. Toxicity data were similar to those antifungals already used, even with lower potential toxicity. Therefore, both clioquinol and the triple combination VCR-AMB-CLQ exhibited promising profiles for use as active components in corneal tissue preservation medium.

Update on fungal lipid biosynthesis inhibitors as antifungal agents

Fungal diseases today represent a world-wide problem. Poor hygiene and decreased immunity are the main reasons behind the manifestation of this disease. After COVID-19, an increase in the rate of fungal infection has been observed in different countries. Different classes of antifungal agents, such as polyenes, azoles, echinocandins, and anti-metabolites, as well as their combinations, are currently employed to treat fungal diseases; these drugs are effective but can cause some side effects and toxicities. Therefore, the identification and development of newer antifungal agents is a current need. The fungal cell comprises many lipids, such as ergosterol, phospholipids, and sphingolipids. Ergosterol is a sterol lipid that is only found in fungal cells. Various pathways synthesize all these lipids, and the activities of multiple enzymes govern these pathways. Inhibiting these enzymes will ultimately impede the lipid synthesis pathway, and this phenomenon could be a potential antifungal therapy. This review will discuss various lipid synthesis pathways and multiple antifungal agents identified as having fungal lipid synthesis inhibition activity. This review will identify novel compounds that can inhibit fungal lipid synthesis, permitting researchers to direct further deep pharmacological investigation and help develop drug delivery systems for such compounds.

Increased Absorption and Inhibitory Activity against Candida spp. of Imidazole Derivatives in Synergistic Association with a Surface Active Agent

This paper's purpose was to evaluate the interaction between three imidazole derivatives, (2-methyl-1H-imidazol-1-yl)methanol (SAM3), 1,1'-methanediylbis(1H-benzimidazole (AM5) and (1H-benzo[d]imidazol-1-yl)methanol 1-hydroxymethylbenzimidazole (SAM5) on the one hand, and sodium dodecyl sulphate (SDS) on the other, as antifungal combinations against Candida spp. Inhibitory activity was assessed using the agar diffusion method and Minimal Inhibitory Concentration (MIC) and showed moderate inhibitory activity of single imidazole derivatives against Candida spp. The mean value of MIC ranged from 200 µg/mL (SAM3) to 312.5 µg/mL (SAM3), while for SDS the MIC was around 1000 µg/mL. When used in combination with SDS, the imidazole derivatives demonstrated an improvement in their antifungal activity. Their MIC decreased over five times for AM5 and over seven times for SAM3 and SAM5, respectively, and ranged from 26.56 µg/mL (SAM3) to 53.90 µg/mL (AM5). Most combinations displayed an additive effect while a clear synergistic effect was recorded in only a few cases. Thus, the FIC Index (FICI) with values between 0.311 and 0.375 showed a synergistic effect against Candida spp. when SDS was associated with SAM3 (three strains), SAM5 (two strains) and AM5 (one strain). The association of imidazole derivatives with SDS led to the increased release of cellular material as well as the intracellular influx of crystal violet (CV), which indicated an alteration of the membrane permeability of Candida spp. cells. This favored the synergistic effect via increasing the intracellular influx of imidazoles.

In silico and in vitro analysis of the mechanisms of action of nitroxoline against some medically important opportunistic fungi

The increasing resistance to antifungal agents associated with toxicity and interactions turns therapeutic management of fungal infections difficult. This scenario emphasizes the importance of drug repositioning, such as nitroxoline - a urinary antibacterial agent that has shown potential antifungal activity. The aims of this study were to discover the possible therapeutic targets of nitroxoline using an in silico approach, and to determine the in vitro antifungal activity of the drug against the fungal cell wall and cytoplasmic membrane. We explored the biological activity of nitroxoline using PASS, SwissTargetPrediction and Cortellis Drug Discovery Intelligence web tools. After confirmation, the molecule was designed and optimized in HyperChem software. GOLD 2020.1 software was used to predict the interactions between the drug and the target proteins. In vitro investigation evaluated the effect of nitroxoline on the fungal cell wall through sorbitol protection assay. Ergosterol binding assay was carried out to assess the effect of the drug on the cytoplasmic membrane. In silico investigation revealed biological activity with alkane 1-monooxygenase and methionine aminopeptidase enzymes, showing nine and five interactions in the molecular docking, respectively. In vitro results exhibited no effect on the fungal cell wall or cytoplasmic membrane. Finally, nitroxoline has potential as an antifungal agent due to the interaction with alkane 1-monooxygenase and methionine aminopeptidase enzymes, which are not the main human therapeutic targets. These results have potentially revealed a new biological target for the treatment of fungal infections. We also consider that further studies are required to confirm the biological activity of nitroxoline on fungal cells, mainly the confirmation of the alkB gene.

5-Amino-8-hydroxyquinoline-containing Electrospun Materials Based on Poly(vinyl alcohol) and Carboxymethyl Cellulose and Their Cu2+ and Fe3+ Complexes with Diverse Biological Properties: Antibacterial, Antifungal and Anticancer

Novel fibrous materials with diverse biological properties containing a model drug of the 8-hydroxyquinoline group-5-amino-8-hydroxyquinoline (5A8Q)-were fabricated using a one-pot method by electrospinning poly(vinyl alcohol) (PVA)/carboxymethyl cellulose (CMC)/5A8Q solutions. Experiments were performed to prepare Cu²⁺ (Fe³⁺) complexes of the crosslinked PVA/CMC/5A8Q materials. The formation of complexes was proven by using scanning electron microscopy (SEM), attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The release of 5A8Q and 5A8Q.Cu²⁺ (Fe³⁺) was studied and their in vitro release profiles were mostly impacted by the hydrophilic/hydrophobic properties of the materials. The performed microbiological assays revealed that fibrous materials containing 5A8Q and their complexes exhibited good antibacterial and antifungal efficacy. Their activity was stronger against bacteria S. aureus than against bacteria E. coli and fungi C. albicans. Cell viability tests using MTT showed that the presence of 5A8Q and its complexes in the fibrous materials resulted in a significant decrease in the HeLa and MCF-7 cancer cell viability for the various times of cell incubation. Moreover, the observed cytotoxicity of the mats against cancer cells was greater than that against non-cancer HaCaT keratinocytes. All these properties make the novel materials potential candidates for the design of wound healing materials and as drug delivery systems for local therapy of cervical and breast cancer.

Cu(II) and Zn(II) Complexes of New 8-Hydroxyquinoline Schiff Bases: Investigating Their Structure, Solution Speciation, and Anticancer Potential

We report the synthesis and characterization of three novel Schiff bases (L1-L3) derived from the condensation of 2-carbaldehyde-8-hydroxyquinoline with amines containing morpholine or piperidine moieties. These were reacted with CuCl₂ and ZnCl₂ yielding six new coordination compounds, with the general formula ML₂, where M = Cu(II) or Zn(II) and L = L1-L3, which were all characterized by analytical, spectroscopic (Fourier transform infrared (FTIR), UV-visible absorption, nuclear magnetic resonance (NMR), or electron paramagnetic resonance (EPR)), and mass spectrometric techniques, as well as by single-crystal X-ray diffraction. In the solid state, two Cu(II) complexes, with L1 and L2, are obtained as dinuclear compounds, with relatively short Cu-Cu distances (3.146 and 3.171 Å for Cu₂(L1)₄ and Cu₂(L2)₄, respectively). The free ligands show moderate lipophilicity, while their complexes are more lipophilic. The pK_a values of L1-L3 and formation constants of the complex (for ML and ML₂) species were determined by spectrophotometric titrations, with the Cu(II) complexes showing higher stability than the Zn(II) complexes. EPR indicated the presence of several species in solution as pH varied and binding modes were proposed. The binding of the complexes to bovine serum albumin (BSA) was evaluated by fluorescence and circular dichroism (CD) spectroscopies. All complexes bind BSA, and as demonstrated by CD, the process takes several hours to reach equilibrium. The antiproliferative activity was evaluated in malignant melanoma cells (A375) and in noncancerous keratinocytes (HaCaT). All complexes display significant cytotoxicity (IC₅₀ < 10 μM) but modest selectivity. The complexes show higher activity than the free ligands, the Cu(II) complexes being more active than the Zn(II) complexes, and approximately twice more cytotoxic than cisplatin. A Guava ViaCount assay corroborated the antiproliferative activity.

Innovative Fibrous Materials Loaded with 5-Nitro-8-hydroxyquinoline via Electrospinning/Electrospraying Demonstrate Antioxidant, Antimicrobial and Anticancer Activities

A new type of fibrous mat based on a cellulose derivative-cellulose acetate (CA) or CA and water-soluble polymers (polyvinylpyrrolidone, PVP or poly(vinyl alcohol), PVA)-loaded with the model drug 5-nitro-8-hydroxyquinoline (5N) was fabricated via electrospinning or electrospinning in conjunction with electrospraying. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), water contact angle measurements and ultraviolet-visible spectroscopy (UV-Vis) were used for the complex characterization of the obtained novel material. The decoration of CA fibers with a water-soluble polymer containing the drug resulted in the facilitation of wetting and fast drug release. The 5N-containing fibrous material showed antioxidant activity. Moreover, the proposed materials' antibacterial and antifungal properties were tested against S. aureus, E. coli, P. aeruginosa and C. albicans. Well-distinguished, sterile zones with diameters above 3.5 cm were observed around all 5N-containing mats. The mats' cytotoxicity toward HeLa carcinoma cells and normal mouse BALB/c 3T3 fibroblasts was assessed. The 5N-in-CA, PVP,5N-on-(5N-in-CA) and PVA,5N-on-(5N-in-CA) fibrous mats possessed anticancer efficacies and much lower levels of toxicity against normal cells. Therefore, the as-created novel electrospun materials, which are based on polymers loaded with the drug 5N via electrospinning/electrospraying, can potentially be applied for topical wound healing and for local cancer therapy.

A pH-Sensitive Lignin-Based Material for Sustained Release of 8-Hydroxyquinoline

The fabrication of pH-sensitive lignin-based materials has received considerable attention in various fields, such as biomass refining, pharmaceuticals, and detecting techniques. However, the pH-sensitive mechanism of these materials is usually depending on the hydroxyl or carboxyl content in the lignin structure, which hinders the further development of these smart materials. Here, a pH-sensitive lignin-based polymer with a novel pH-sensitive mechanism was constructed by establishing ester bonds between lignin and the active molecular 8-hydroxyquinoline (8HQ). The structure of the produced pH-sensitive lignin-based polymer was comprehensively characterized. The substituted degree of 8HQ was tested up to 46.6% sensitivity, and the sustained release performance of 8HQ was confirmed by the dialysis method, the sensitivity of which was found to be 60 times slower compared with the physical mixed sample. Moreover, the obtained pH-sensitive lignin-based polymer showed an excellent pH sensitivity, and the released amount of 8HQ under an alkaline condition (pH = 8) was obviously higher than that under an acidic condition (pH = 3 and 5). This work provides a new paradigm for the high-value utilization of lignin and a theory guidance for the fabrication of novel pH-sensitive lignin-based polymers.

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.

Antifungal Annona muricata L. (soursop) extract targets the cell envelope of multi-drug resistant Candida albicans

ETNOPHARMACOLOGICAL RELEVANCE

Annona muricata L. (soursop) is traditionally used in the treatment of inflammatory diseases, cancer, and infections caused by fungi. The therapeutic activity explored by its medicinal use is generally associated with its phytoconstituents, such as acetogenins and alkaloids. However, its potential antifungal bioactivity as well as its mechanism of action remains to be established.

AIM OF THE STUDY

To evaluate the antifungal activity of the ethanolic extract of A. muricata leaves against multidrug-resistant Candida albicans (ATCC® 10231).

MATERIAL AND METHODS

Phytoconstituents were detected by UFLC-QTOF-MS. The minimum inhibitory concentration was determined, followed by the determination of the minimum fungicidal concentration. For planktonic cells, the growth curve and cell density were evaluated. Studies to understand the mechanism of action on the cell envelope involved crystal violet permeability, membrane extravasation, sorbitol protection, exogenous ergosterol binding assay, metabolic activity, and cell viability. Furthermore, mitochondrial membrane potential was assessed.

RESULTS

Our analyses demonstrated a significant inhibitory effect of A. muricata, with the ability to reduce fungal growth by 58% and cell density by 65%. The extract affected both the fungal plasma membrane and cell wall integrity, with significant reduction of the cell viability. Depolarization of the fungal mitochondrial membrane was observed after treatment with A. muricata. Rutin, xi-anomuricine, kaempferol-3O-rutinoside, nornuciferine, xylopine, atherosperminine, caffeic acid, asimilobine, s-norcorydine, loliolide, annohexocin, annomuricin, annopentocin, and sucrose were identified as extract bioactive components.

CONCLUSIONS

Our findings show that the A. muricata extract is a source of chemical diversity, which acts as a potential antifungal agent with promising application to the therapy of infections caused by C. albicans.

Clioquinol and 8-hydroxyquinoline-5-sulfonamide derivatives damage the cell wall of Pythium insidiosum

AIMS

To evaluate the antimicrobial activity and to determine the pharmacodynamic characteristics of three 8-hydroxyquinoline derivatives (8-HQs) against Pythium insidiosum, the causative agent of pythiosis.

METHODS AND RESULTS

Antimicrobial activity was tested by broth microdilution and MTT assays. The antimicrobial mode of action was investigated using sorbitol protection assay, ergosterol binding assay, and scanning electron microscopy. Clioquinol, PH151, and PH153 were active against all isolates, with MIC values ranging from 0.25 to 2 µg ml-1. They also showed a time- and dose-dependent antimicrobial effect, damaging the P. insidiosum cell wall.

CONCLUSIONS

Together, these results reinforce the potential of 8-HQs for developing new drugs to treat pythiosis.

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.

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.

2-(2-(4-Methoxyphenyl)furo[3,2-h]quinolin-3-yl)acetic Acid

A simple and efficient protocol for the synthesis of the previously unknown 2-(2-(4-methoxyphenyl)furo[3,2-h]quinolin-3-yl)acetic acid was elaborated. The suggested method is based on the telescoped multicomponent reaction of 8-hydroxyquinoline, 4-methylglyoxal, and Meldrum’s acid. The studied process includes the initial interaction of the starting compounds in MeCN followed by intramolecular cyclization to the target product in refluxing acetic acid. The advantage of this approach is the application of readily available starting materials, atom economy, and a simple work-up procedure. The structure of the synthesized furylacetic acid derivative was proven by 1H, 13C, 2D-NMR, IR spectroscopy, and high-resolution mass spectrometry.

Characterization and Antidermatophyte Activity of Henna Extracts: A Promising Therapy for Humans and Animals Dermatophytoses

Dermatophytoses representing a major global health problem and dermatophyte species with reduced susceptibility to antifungals are increasingly reported. Therefore, we investigated for the first time the antidermatophyte activity and phytochemical properties of the sequential extracts of the Egyptian privet Henna (Lawsonia inermis) leaves. Total phenolic content (TPC), total flavonoids (TF), and antioxidant activity of chloroform, diethyl ether, acetone, ethanol 80%, and aqueous extracts were evaluated. The antifungal activity of henna leaves extracts (HLE) toward 30 clinical dermatophytes isolates, including Trichophyton mentagrophytes, Microsporum canis, and T. rubrum, was determined. Morphological changes in hyphae were investigated using scanning electron microscopy (SEM) analysis. Following the polarity of ethanol and acetone, they exhibited distinct efficiency for the solubility and extraction of polyphenolic polar antioxidants from henna leaves. Fraxetin, lawsone, and luteolin-3-O-glucoside were the major phenolic compounds of henna leaves, as assessed using high-performance liquid chromatography analysis. A high and significant positive correlation was found between TPC, TF, the antioxidants, and the antidermatophyte activities of HLE. Acetone and ethanol extracts exhibited the highest antifungal activity toward the tested dermatophyte species with minimum inhibitory concentration (MIC) ranges 12.5-37.5 and 25-62.5 µg/mL, respectively. Structural changes including collapsing, distortion, inflating, crushing of hyphae with corrugation of walls, and depressions on hyphal surfaces were observed in SEM analysis for dermatophyte species treated with MICs of griseofulvin, acetone, and ethanol extracts. In conclusion, acetone and ethanolic extracts of henna leaves with their major constituent fraxetin exhibited effective antifungal activity toward dermatophyte species and may be developed as an alternative for dermatophytosis treatment. These findings impart a useful insight into the development of an effective and safe antifungal agent for the treatment of superficial fungal infections caused by dermatophytes.

Novel Antimicrobial 8-Hydroxyquinoline-Based Agents: Current Development, Structure-Activity Relationships, and Perspectives

The search for new antimicrobials is imperative due to the emergent resistance of new microorganism strains. In this context, revisiting known classes like 8-hydroxyquinolines could be an interesting strategy to discover new agents. The 8-hydroxyquinoline derivatives nitroxoline and clioquinol are used to treat microbial infections; however, these drugs are underused, being available in few countries or limited to topical use. After years of few advances, in the last two decades, the potent activity of clioquinol and nitroxoline against several targets and the privileged structure of 8-hydroxyquinoline nucleus have prompted an increased interest in the design of novel antimicrobial, anticancer, and anti-Alzheimer agents based on this class. Herein, we discuss the current development and antimicrobial structure-activity relationships of this class in the perspective of using the 8-hydroxyquinoline nucleus for the search for novel antimicrobial agents. Furthermore, the most investigated molecular targets concerning 8-hydroxyquinoline derivatives are explored in the final section.

Electrospun Polymer-Fungicide Nanocomposites for Grapevine Protection

Nowadays, diseases in plants are a worldwide problem. Fungi represent the largest number of plant pathogens and are responsible for a range of serious plant diseases. Esca is a grapevine disease caused mainly by fungal pathogens Phaeomoniella chlamydospora (P. chlamydospora) and Phaeoacremonium aleophilum (P. aleophilum). The currently proposed methods to fight esca are not curative. In this study, polymer composites based on biodegradable polymer containing chemical fungicides with antifungal activity were successfully prepared by electrospinning. The obtained materials were hydrophobic with good mechanical properties. In vitro studies demonstrated that the fungicide release was higher from PLLA/K5N8Q fibrous mats (ca. 72% for 50 h) compared to the released drug amount from PLLA/5-Cl8Q materials (ca. 52% for 50 h), which is due to the better water-solubility of the salt. The antifungal activity of the fibrous materials against P. chlamydospora and P. aleophilum was studied as well. The incorporation of the fungicide in the biodegradable fibers resulted in the inhibition of fungal growth. The obtained materials are perspective candidates for the protection of vines from the penetration and growth of fungal pathogens.

Antifungal Activity of the Phenolic Compounds Ellagic Acid (EA) and Caffeic Acid Phenethyl Ester (CAPE) against Drug-Resistant Candida auris

Candida auris is an emerging healthcare-associated fungal pathogen that has become a serious global health threat. Current treatment options are limited due to drug resistance. New therapeutic strategies are required to target this organism and its pathogenicity. Plant polyphenols are structurally diverse compounds that present a vast range of biological properties. In the present study, plant-derived molecules ellagic acid (EA) and caffeic acid phenethyl ester (CAPE) were investigated for their antifungal and antivirulence activities against Candida auris. We also tested against C. albicans. The minimum inhibitory concentration (MIC) for EA ranged from 0.125 to 0.25 µg/mL and for CAPE ranged from 1 to 64 µg/mL against drug-resistant C. auris strains. Killing kinetics determined that after 4 h treatment with CAPE, there was a complete reduction of viable C. auris cells compared to fluconazole. Both compounds might act by modifying the fungal cell wall. CAPE significantly reduced the biomass and the metabolic activity of C. auris biofilm and impaired C. auris adhesion to cultured human epithelial cells. Furthermore, both compounds prolonged the survival rate of Galleria mellonella infected by C. auris (p = 0.0088 for EA at 32 mg/kg and p = 0.0028 for CAPE at 4 mg/kg). In addition, EA at 4 μg/mL prolonged the survival of C. albicans-infected Caenorhabditis elegans (p < 0.0001). CAPE was not able to prolong the survival of C. albicans-infected C. elegans. These findings highlight the antifungal and antivirulence effects of EA and CAPE against C. auris, and warrant further investigation as novel antifungal agents against drug-resistant infections.

8-Hydroxyquinoline-5-Sulfonic Acid-Containing Poly(Vinyl Alcohol)/Chitosan Electrospun Materials and Their Cu2+ and Fe3+ Complexes: Preparation, Antibacterial, Antifungal and Antitumor Activities

Novel poly(vinyl alcohol) (PVA)/chitosan (Ch)-based fibrous materials containing an ionizable model drug, 8-hydroxyquinoline-5-sulfonic acid (SQ), were successfully fabricated by electrospinning. Complexes between the components of the crosslinked PVA/Ch/SQ mats and Cu2+ and Fe3+ ions were formed. The coordination of these ions in the mats was examined by electron paramagnetic resonance spectroscopy (EPR). The microbiological screening against S. aureus and C. albicans revealed that both the incorporation of SQ in the mats and the complexation with Cu2+ and Fe3+ imparted to these materials antibacterial and antifungal activities. Moreover, the SQ-containing mats and their complexes displayed good cytotoxicity against human cervical HeLa tumor cells. The most prominent was the cytotoxicity of the Cu2+ complex of the mats. The combined antibacterial, antifungal and in vitro antitumor activities render these novel materials promising candidates for wound dressing applications and for application in the local treatment of cervical tumors.

8-hydroxyquinoline-5-(N-4-chlorophenyl) sulfonamide and fluconazole combination as a preventive strategy for Candida biofilm in haemodialysis devices

Introduction. The presence of Candida biofilms in medical devices is a concerning and important clinical issue for haemodialysis patients who require constant use of prosthetic fistulae and catheters.Hypothesis/Gap Statement. This prolonged use increases the risk of candidaemia due to biofilm formation. PH151 and clioquinol are 8-hydroxyquinoline derivatives that have been studied by our group and showed interesting anti-Candida activity.Aim. This study evaluated the biofilm formation capacity of Candida species on polytetrafluoroethylene (PTFE) and polyurethane (PUR) and investigated the synergistic effects between the compounds PH151 and clioquinol and fluconazole, amphotericin B and caspofungin against biofilm cells removed from those materials. Further, the synergistic combination was evaluated in terms of preventing biofilm formation on PTFE and PUR discs.Methodology. Susceptibility testing was performed for planktonic and biofilm cells using the broth microdilution method. The checkerboard method and the time-kill assay were used to evaluate the interactions between antifungal agents. Antibiofilm activity on PTFE and PUR materials was assessed to quantify the prevention of biofilm formation.Results. Candida albicans, Candida glabrata and Candida tropicalis showed ability to form biofilms on both materials. By contrast, Candida parapsilosis did not demonstrate this ability. Synergistic interaction was observed when PH151 was combined with fluconazole in 77.8 % of isolates and this treatment was shown to be concentration- and time-dependent. On the other hand, indifferent interactions were predominantly observed with the other combinations. A reduction in biofilm formation on PUR material of more than 50 % was observed when using PH151 combined with fluconazole.Conclusion. PH151 demonstrated potential as a local treatment for use in a combination therapy approach against Candida biofilm formation on haemodialysis devices.

Cellulose Acetate-Based Electrospun Materials with a Variety of Biological Potentials: Antibacterial, Antifungal and Anticancer

Novel eco-friendly fibrous materials with complex activities from cellulose acetate and cellulose acetate/polyethylene glycol (CA,PEG) containing 5-chloro-8-hydroxyquinoline as a model drug were obtained by electrospinning. Several methods, including scanning electron microscopy, X-ray diffraction analysis, ultraviolet-visible spectroscopy, water contact angle measurements, and mechanical tests, were utilized to characterize the obtained materials. The incorporation of PEG into the fibers facilitated the drug release. The amounts of the released drug from CA/5-Cl8Q and CA,PEG/5-Cl8Q were 78 ± 3.38% and 86 ± 3.02%, respectively (for 175 min). The antibacterial and antifungal activities of the obtained materials were studied. The measured zones of inhibition of CA/5-Cl8Q and CA,PEG/5-Cl8Q mats were 4.0 ± 0.18 and 4.5 ± 0.2 cm against S. aureus and around 4.0 ± 0.15 and 4.1 ± 0.22 cm against E. coli, respectively. The complete inhibition of the C. albicans growth was detected. The cytotoxicity of the obtained mats was tested toward HeLa cancer cells, SH-4 melanoma skin cells, and mouse BALB/c 3T3 fibroblasts as well. The CA/5-Cl8Q and CA,PEG/5-Cl8Q materials exhibited anticancer activity and low normal cell toxicity. Thus, the obtained fibrous materials can be suitable candidates for wound dressing applications and for application in local cancer treatment.

Evaluation of activity and toxicity of combining clioquinol with ciclopirox and terbinafine in alternative models of dermatophytosis

Dermatophytosis is a superficial fungal infection that affects humans and is very common in small animals. The treatment using the most commonly used antifungals is failing, and new therapeutic alternatives are required to combat the resistance of these fungal infections. Previous studies by the group have shown that clioquinol is an important therapeutic alternative in the treatment of dermatophytosis. The object was to conduct studies of antidermatophytic activity and the irritant potential from the double and triple combinations of clioquinol, terbinafine and ciclopirox in ex vivo and in vivo alternative models. To evaluate the irritant potential of antifungal combinations, the alternative HET-CAM method (chicken egg test chorioallantoic membrane) was used. Ex vivo models were used to assess the effectiveness of antifungal combinations, using pig hooves and veterinary fur. Any possible tissue damage was to assess through in histopathology of swine ears. HET-CAM results showed that all combinations can be classified as non-irritating, corroborated by the results of the histopathological evaluation of the pig's ear skin. Only the double combinations managed to remove 100% of the colony-forming units (CFU) formed on the pig's hooves. The clioquinol + terbinafine combination and the triple combination were more effective than clioquinol + ciclopirox in eradicating the preformed biofilm in fur of veterinary origin. These results show the potential of formulations of clioquinol in combination with antifungals for use in humans and in the veterinary field to combat dermatophytosis, as an important alternative therapy, for use in the near future.

Identification of Antifungal Compounds against Multidrug-Resistant Candida auris Utilizing a High-Throughput Drug-Repurposing Screen

Candida auris is an emerging fatal fungal infection that has resulted in several outbreaks in hospitals and care facilities. Current treatment options are limited by the development of drug resistance. Identification of new pharmaceuticals to combat these drug-resistant infections will thus be required to overcome this unmet medical need. We have established a bioluminescent ATP-based assay to identify new compounds and potential drug combinations showing effective growth inhibition against multiple strains of multidrug-resistant Candida auris The assay is robust and suitable for assessing large compound collections by high-throughput screening (HTS). Utilizing this assay, we conducted a screen of 4,314 approved drugs and pharmacologically active compounds that yielded 25 compounds, including 6 novel anti-Candida auris compounds and 13 sets of potential two-drug combinations. Among the drug combinations, the serine palmitoyltransferase inhibitor myriocin demonstrated a combinational effect with flucytosine against all tested isolates during screening. This combinational effect was confirmed in 13 clinical isolates of Candida auris.

The efficacy of 8-hydroxyquinoline derivatives in controlling the fungus Ilyonectria liriodendri, the causative agent of black foot disease in grapevines

AIM

The purpose of this study was to evaluate the in vitro and in vivo efficiency of derivatives of 8-Hydroxyquinoline (8HQ) in controlling the fungus Ilyonectria liriodendri.

METHODS AND RESULTS

The in vitro tests consisted of assessing its susceptibility to the minimal inhibitory concentration (MIC) and the inhibition of mycelial growth. While the in vivo tests consisted of applying and assessing the most effective products for the protection of wounds, in both preventive + curative and curative forms. The MIC values for PH 151 (6·25 µg ml^-1 ) showed better results when compared to the fungicides tebuconazole (>50 µg ml^-1 ) and mancozeb (12·5 µg ml^-1 for strain 176 and 25 µg ml^-1 for strain 1117). PH 151 significantly inhibited mycelial growth, while mancozeb did not differ from the control. In in vivo tests, PH 151 again demonstrated excellent results in vitro, especially when applied preventively.

CONCLUSIONS

The derivative of 8HQ PH 151 was effective in controlling the fungus I. liriodendri in vitro and proved to be a promising option for protecting wounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study points to the prospect of an effective and safe preventive antifungal product, which would enable the use of pesticides in vine culture to be reduced.

Insights of 8-hydroxyquinolines: A novel target in medicinal chemistry

8-Hydroxyquinoline (8-HQ) is a significant heterocyclic scaffold in organic and analytical chemistry because of the properties of chromophore and is used to detect various metal ions and anions. But from the last 2 decades, this moiety has been drawn great attention of medicinal chemists due to its significant biological activities. Synthetic modification of 8-hydroxyquinoline is under exploration on large scale to develop more potent target-based broad spectrum drug molecules for the treatment of several life-threatening diseases such as anti-cancer, HIV, neurodegenerative disorders, etc. Metal chelation properties of 8-hydroxyquinoline and its derivatives also make these potent drug candidates for the treatment of various diseases. This review comprises 8-hydroxyquinoline derivatives reported in the literature in last five years (2016-2020) and we anticipate that it will assist medicinal chemists in the synthesis of novel and pharmacologically potent agents for various therapeutic targets, mainly anti-proliferative, anti-microbial, anti-fungal and anti-viral as well as for the treatment of neurodegenerative disorders.

Combination Therapy to Treat Fungal Biofilm-Based Infections

An increasing number of people is affected by fungal biofilm-based infections, which are resistant to the majority of currently-used antifungal drugs. Such infections are often caused by species from the genera Candida, Aspergillus or Cryptococcus. Only a few antifungal drugs, including echinocandins and liposomal formulations of amphotericin B, are available to treat such biofilm-based fungal infections. This review discusses combination therapy as a novel antibiofilm strategy. More specifically, in vitro methods to discover new antibiofilm combinations will be discussed. Furthermore, an overview of the main modes of action of promising antibiofilm combination treatments will be provided as this knowledge may facilitate the optimization of existing antibiofilm combinations or the development of new ones with a similar mode of action.

Antifungal activity and toxicological parameters of 8-hydroxyquinoline-5-sulfonamides using alternative animal models

AIM

The purpose of this study was to evaluate the antifungal activity and toxicological parameters of 8-hydroxyquinoline derivatives PH151 and PH153 using alternative animal models, to understand their behaviour when subjected to in vivo experiments.

METHODS AND RESULTS

We used Toll-deficient Drosophila melanogaster to test the protective effect of compounds against Candida albicans infection. Toxicological parameters were investigated in chicken and zebrafish embryos. PH151 and PH153 showed low toxicity and the treated flies with these compounds had a significantly higher survival rate than untreated flies after 7 days of infection. The compounds did not cause interruption of chicken embryogenesis. Zebrafish embryos exposed to compounds showed dose-dependent toxicity.

CONCLUSIONS

The data supported the potential of PH151 and PH153 for the treatment of systemic candidiasis and demonstrated to be appropriate drug candidates for further studies using mammalian models.

SIGNIFICANCE AND IMPACT OF THE STUDY

The increased incidence of Candida infections resistant to antifungals currently available requires acceleration of the discovery of new agents with properties of inhibiting this fungal pathogen. In this study, we have described the antifungal potential and toxicity of two 8-hydroxyquinoline derivatives using in vivo alternative models, and the results confirm their potential to be developed as new drug candidates.

Recent update on antibacterial and antifungal activity of quinoline scaffolds

Although most of the heterocycles have been reported to possess a significant pharmacological activity, only a few of them, namely quinoline derivatives, have exhibited the finest biological activities. Despite the few medicinal properties of the plain quinoline molecule, its derivatives exhibit diverse pharmacological properties such as anticancer, anti-inflammatory, antibacterial, antiviral, antifungal, antiprotozoal activities, and so on. The potential antimicrobial properties of the quinoline derivatives are evident from the decades of research on these derivatives. Owing to limitations like drug resistance, high cost, severe side effects, and less bioavailability of previously synthesized antimicrobial agents, these drugs have become obsolete in recent years. Hence, the design of more efficient antimicrobial drugs must be given topmost priority. A breakthrough in drug discovery is a must to prevent malevolent microbial diseases. Addressing all these issues, researchers have been continuously contributing to antimicrobial drug discovery. Herein, a short description of the pharmacology of antimicrobial agents such as antibacterials and antifungals synthesized recently is provided. The versatile derivatization of the quinoline moiety leading to significant antimicrobial potencies is discussed, considering the structure-activity relationship.

Combination of Miconazole and Domiphen Bromide Is Fungicidal against Biofilms of Resistant Candida spp

The occurrence and recurrence of mucosal biofilm-related Candida infections, such as oral and vulvovaginal candidiasis, are serious clinical issues. Vaginal infections caused by Candida spp., for example, affect 70 to 75% of women at least once during their lives. Miconazole (MCZ) is the preferred topical treatment against these fungal infections, yet it has only moderate antibiofilm activity. Through screening of a drug-repurposing library, we identified the quaternary ammonium compound domiphen bromide (DB) as an MCZ potentiator against Candida biofilms. DB displayed synergistic anti-Candida albicans biofilm activity with MCZ, reducing the number of viable biofilm cells 1,000-fold. In addition, the MCZ-DB combination also resulted in significant killing of biofilm cells of azole-resistant C. albicans, C. glabrata, and C. auris isolates. In vivo, the MCZ-DB combination had significantly improved activity in a vulvovaginal candidiasis rat model compared to that of single-compound treatments. Data from an artificial evolution experiment indicated that the development of resistance against the combination did not occur, highlighting the potential of MCZ-DB combination therapy to treat Candida biofilm-related infections.

8-Hydroxyquinoline 1,2,3-triazole derivatives with promising and selective antifungal activity

Fungal infections that affect humans and plants have increased significantly in recent decades. However, these pathogens are still neglected when compared to other infectious agents. Due to the high prevalence of these infections, the need for new molecules with antifungal potential is recognized, as pathogenic species are developing resistance to the main drugs available. This work reports the design and synthesis of 1,2,3-triazole derivatives of 8-hydroxyquinoline, as well as the determination of their activities against a panel of fungal species: Candida spp., Trichosporon asahii, Magnusiomyces capitatus, Microsporum spp., Trichophyton spp. and Fusarium spp. The triazoles 5-(4-phenyl-1H-1,2,3-triazol-1-yl)quinolin-8-ol (12) and 5-(4-(cyclohex-1-en-1-yl)-1H-1,2,3-triazol-1-yl)quinolin-8-ol (16) were more promising, presenting minimum inhibitory concentration (MIC) values between 1-16 µg/ml for yeast and 2-4 µg/ml for dermatophytes. However, no relevant anti-Fusarium spp. activity was observed. In the time-kill assays with Microsporum canis, 12 and 16 presented time-dependent fungicide profile at 96 h and 120 h in all evaluated concentrations, respectively. For Candida guilliermondii, 12 was fungicidal at all concentrations at 6 h and 16 exhibited a predominantly fungistatic profile. Both 12 and 16 presented low leukocyte toxicity at 4 µg/ml and the cell viability was close to 100% after the treatment with 12 at all tested concentrations. The sorbitol assay combined with SEM suggest that damages on the fungal cell wall could be involved in the activity of these derivatives. Given the good results obtained with this series, scaffold 4-(cycloalkenyl or phenyl)-5-triazol-8-hydroxyquinoline appears to be a potential pharmacophore for exploration in the development of new antifungal agents.

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.

3-Selenocyanate-indoles as new agents for the treatment of superficial and mucocutaneous infections

The development of resistance to the current antifungal agents is an alarming problem.