In pursuit of the ideal antifungal agent for Candida infections: high-throughput screening of small molecules

In vitro activity of the anthelmintic drug niclosamide against Sporothrix spp. strains with distinct genetic and antifungal susceptibility backgrounds

The drugs available to treat sporotrichosis, an important yet neglected fungal infection, are limited. Some Sporothrix spp. strains present reduced susceptibility to these antifungals. Furthermore, some patients may not be indicated to use these drugs, while others may not respond to the therapy. The anthelmintic drug niclosamide is fungicidal against the Sporothrix brasiliensis type strain. This study aimed to evaluate whether niclosamide also has antifungal activity against Sporothrix globosa, Sporothrix schenckii and other S. brasiliensis strains with distinct genotypes and antifungal susceptibility status. Minimal inhibitory and fungicidal concentrations (MIC and MFC, respectively) were determined using the microdilution method according to the CLSI protocol. The checkerboard method was employed to evaluate niclosamide synergism with drugs used in sporotrichosis treatment. Metabolic activity of the strains under niclosamide treatment was evaluated using the resazurin dye. Niclosamide was active against all S. brasiliensis strains (n = 17), but it was ineffective (MIC > 20 µM) for some strains (n = 4) of other pathogenic Sporothrix species. Niclosamide MIC values for Sporothrix spp. were similar for mycelial and yeast-like forms of the strains (P = 0.6604). Niclosamide was fungicidal (MFC/MIC ratio ≤ 2) for most strains studied (89%). Niclosamide activity against S. brasiliensis is independent of the fungal genotype or non-wild-type phenotypes for amphotericin B, itraconazole, or terbinafine. These antifungal drugs presented indifferent interactions with niclosamide. Niclosamide has demonstrated potential for repurposing as a treatment for sporotrichosis, particularly in S. brasiliensis cases, instigating in vivo studies to validate the in vitro findings.

In Vitro Evaluation of Synergistic Essential Oils Combination for Enhanced Antifungal Activity against Candida spp

In recent years, a significant number of infections have been attributed to non-albicidal Candida species (NAC), mainly due to the increasing resistance of NAC to antifungal agents. As only a few antifungal agents are available (azoles, echinocandins, polyenes, allylamines and nucleoside analogues), it is very important to look for possible alternatives to inhibit resistant fungi. One possibility could be essential oils (EOs), which have been shown to have significant antifungal and antibacterial activity. Therefore, in this study, the efficacy of 12 EOs and their combinations was evaluated against four yeasts of the genus Candida (C. albicas, C. glabrata, C. tropicalis and C. parapsilosis). GC-MS and GC-MS FID techniques were used for the chemical analysis of all EOs. VITEK-2XL was used to determine the antifungal susceptibility of the tested Candida spp. strains. The agar disc diffusion method was used for primary screening of the efficacy of the tested EOs. The broth dilution method was used to determine the minimum inhibitory concentrations (MICs) of the most potent EOs. After MIC cultivation, the minimum fungicidal concentration (MFC) was determined on Petri dishes (60 mm). The synergistic effect of combined EOs was evaluated using the checkerboard method and expressed as a fractional inhibitory concentration index (FICI). The results showed that ginger > ho-sho > absinth > dill > fennel > star anise > and cardamom were the most effective EOs. For all Candida species tested, the synergy was mainly observed in these combinations: ginger/fennel for C. albicans FICI 0.25 and C. glabrata, C. tropicalis and C. parapsilosis FICI 0.5 and absinth/fennel for C. albicans FICI 0.3125, C. tropicalis FICI 0.3125 and C. parapsilosis FICI 0.375. Our results suggest that the resistance of fungal pathogens to available antifungals could be reduced by combining appropriate EOs.

Vaginal microbiota: Potential targets for vulvovaginal candidiasis infection

Vulvovaginal candidiasis (VVC) is the second most common cause of vaginal infection globally after bacterial vaginosis (BV) and associated with adverse reproductive and obstetric outcomes, including preterm delivery, sexually transmitted infections and pelvic inflammatory disease. Although effective control of VVC is achievable with the use of traditional treatment strategies (i.e., antifungals), the possibility of drug intolerance, treatment failure and recurrence, as well as the appearance of antifungal-resistant Candida species remain critical challenges. Therefore, alternative therapeutic strategies against VVC are urgently required. In recent years, an improved understanding of the dysbiotic vaginal microbiota (VMB) during VVC has prompted the consideration of administering -biotics to restore the balance of the VMB within the context of VVC prevention and treatment. Here, we aim to summarize the current evidence of the anti-Candida effects of probiotics, postbiotics and synbiotics and their potential use as an alternative/complementary therapy against VVC. Additionally, this review discusses advantages and challenges associated with the application of -biotics in VVC to provide guidance for their later use. We also review new developments in VVC therapy, i.e., vaginal microbiota transplantation (VMT) as an emerging live biotherapeutic therapy against VVC and discuss existing shortcomings associated with this nascent field, expecting to stimulate further investigations for introduction of new therapies against VVC.

Synergistic potential of teriflunomide with fluconazole against resistant Candida albicans in vitro and in vivo

Introduction

Candida albicans is the primary cause of systemic candidiasis, which is involved in high morbidity and mortality. Drug resistance exacerbates these problems. In addition, there are limited antifungal drugs available. In order to solve these problems, combination therapy has aroused great interest. Teriflunomide is an immunosuppressant. In the present work, we aimed to identify whether teriflunomide can reverse the resistance of Candida albicans in the presence of sub-inhibitory concentrations of fluconazole in vitro and in vivo.

Methods

Seven Candida albicans isolates were used in this study. Susceptibility of Candida albicans in vitro to the drugs was determined using a checkerboard microdilution assay in accordance with the recommendations of the Clinical and Laboratory Standards Institute. The effects of drugs on biofilm biomass of Candida albicans were determined by crystal violet staining. The development ability of Candida albicans hyphae was performed using a modified broth microdilution method. Galleria mellonella was used for testing the in vivo efficacy of the combination therapies.

Results

We found that the combination of teriflunomide (64 µg/mL) and fluconazole (0.5-1 µg/mL) has a significant synergistic effect in all resistant Candida albicans isolates (n=4). Also, this drug combination could inhibit the immature biofilm biomass and hyphae formation of resistant Candida albicans. Galleria mellonella was used for testing the in vivo efficacy of this combination therapies. As for the Galleria mellonella larvae infected by resistant Candida albicans, teriflunomide (1.6 µg/larvae) combined with fluconazole (1.6 µg/larvae) significantly increased their survival rates, and reduced the fungal burden, as well as damage of tissue in comparison to that in the control group or drug monotherapy group.

Conclusion

These results expand our knowledge about the antifungal potential of teriflunomide as an adjuvant of existing antifungal drugs, and also open new perspectives in the treatment of resistant Candida albicans based on repurposing clinically available nonantifungal drugs.

Core-shell polycationic polyurea pharmadendrimers: new-generation of sustainable broad-spectrum antibiotics and antifungals

The efficacy of conventional antimicrobials is falling to critical levels and raising alarming concerns around the globe. In this scenery, engineered nanoparticles emerged as a solid strategy to fight growing deadly infections. Here, we show the in vitro and in vivo performance of pharmadendrimers, a novel class of engineered polyurea dendrimers that are synthetic mimics of antibacterial peptides, against a collection of both Gram-positive and Gram-negative bacteria and fungi. These nanobiomaterials are stable solids prepared by low-cost and green processes, display a dense positively charged core-shell, and are biocompatible and hemocompatible drugs. Mechanistic data, corroborated by coarse-grained molecular dynamics simulations, points towards a fast-killing mechanism via membrane disruption, triggered by electrostatic interactions. Altogether this study provides strong evidence and support for the future use of polyurea pharmadendrimers in antibacterial and antifungal nanotherapeutics.

Antifungal effects of alantolactone on Candida albicans: An in vitro study

The human fungal pathogen Candida albicans can cause many kinds of infections, including biofilm infections on medical devices, while the available antifungal drugs are limited to only a few. In this study, alantolactone (Ala) demonstrated antifungal activities against C. albicans, as well as other Candida species, with a MIC of 72 μg/mL. Ala could also inhibit the adhesion, yeast-to-hyphal transition, biofilm formation and development of C. albicans. The exopolysaccharide of biofilm matrix and extracellular phospholipase production could also be reduced by Ala treatment. Ala could increase permeability of C. albicans cell membrane and ROS contribute to the anti-biofilm activity of Ala. Overall, the present study suggests that Ala may provide a promising candidate for developing antifungal drugs against C. albicans infections.

Synergistic effect of thymoquinone and nystatin in the treatment of oral candidiasis; an in vitro study

The effectiveness of antifungal agents may be insufficient against resistant strains in some cases of oral candidiasis. The aim of this study was to evaluate the antifungal effect of thymoquinone against Candidaalbicans, Candidatropicalis, Candidaglabrata and Candidakrusei strains and the synergistic antifungal activity of these strains in combination with nystatin. To evaluate in vitro antifungal activity and interactions between thymoquinone and nystatin, substances were tested against Candidaalbicans ATCC 10,231, C.tropicalis ATCC 750, C.krusei ATCC 6258 and C.glabrata ATCC 2001 standard strains both individually and combinationally via microdilution method. MIC and ΣFIC index value were analysed. The Kruskal Wallis test and Bonferroni test were used for statistical evaluations. Statistical significance was set at p < 0.05. A statistically significant difference was observed between the mean ranks of all Candida species and doses of thymoquinone, nystatin, and the combination thymoquinone-nystatin (p < 0.05). MIC values for thymoquinone were determined as 15 μg/mL for C.albicans, C.tropicalis and C.krusei while it was 30 μg/mL for C.glabrata. Moreover, MIC for nystatin was found as 1.875 μg/mL for C.albicans, C.tropicalis and C.krusei, whereas it was 7.5 μg/mL in C. glabrata. Interaction assays and ΣFIC index value revealed that, TQ and nystatin have a synergistic effect against to all strains. Thymoquinone was found to have antifungal activity on Candida species and synergistic effect when combined with nystatin.

Platforms for High-Throughput Screening and Force Measurements on Fungi and Oomycetes

Pathogenic fungi and oomycetes give rise to a significant number of animal and plant diseases. While the spread of these pathogenic microorganisms is increasing globally, emerging resistance to antifungal drugs is making associated diseases more difficult to treat. High-throughput screening (HTS) and new developments in lab-on-a-chip (LOC) platforms promise to aid the discovery of urgently required new control strategies and anti-fungal/oomycete drugs. In this review, we summarize existing HTS and emergent LOC approaches in the context of infection strategies and invasive growth exhibited by these microorganisms. To aid this, we introduce key biological aspects and review existing HTS platforms based on both conventional and LOC techniques. We then provide an in-depth discussion of more specialized LOC platforms for force measurements on hyphae and to study electro- and chemotaxis in spores, approaches which have the potential to aid the discovery of alternative drug targets on future HTS platforms. Finally, we conclude with a brief discussion of the technical developments required to improve the uptake of these platforms into the general laboratory environment.

Interaction between Antifungal Isoxazolo[3,4-b]Pyridin 3(1H)-One Derivatives and Human Serum Proteins Analyzed with Biomimetic Chromatography and QSAR Approach

The development of effective, nontoxic antifungal agents is one of the most important challenges for medicinal chemistry. A series of isoxazolo [3,4-b]pyridine-3(1H)-one derivatives previously synthesized in our laboratory demonstrated promising antifungal properties. The main goal of this study was to investigate their retention behavior in a human serum proteins-high-performance liquid chromatography (HSA-HPLC) system and explore the molecular mechanism of HSA-isoxazolone interactions using a quantitative structure–retention relationship (QSRR) approach. In order to realize this goal, multiple linear regression (MLR) modeling has been performed. The proposed QSRR models presented correlation between experimentally determined lipophilicity and computational theoretical molecular descriptors derived from Dragon 7.0 (Talete, Milan, Italy) software on the affinity of isoxazolones to HSA. The calculated plasma protein binding (PreADMET software) as well as chromatographic lipophilicity (logkw) and phospholipophilicity (CHIIAM) parameters were statistically evaluated in relation to the determined experimental HAS affinities (logkHSA). The proposed model met the Tropsha et al. criteria R2 > 0.6 and Q2 > 0.5 These results indicate that the obtained model can be useful in the prediction of an affinity to HSA for isoxazolone derivatives and they can be considered as an attractive alternative to HSA-HPLC experiments.

p-Trifluoroacetophenone Oxime Ester Derivatives: Synthesis, Antimicrobial and Cytotoxic Evaluation and Molecular Modeling Studies

Background:

Azole antifungals are among the first-line drugs clinically used for the treatment of systemic candidiasis, a deadly type of fungal infection that threatens mostly immunecompromised and hospitalized patients. Some azole derivatives were also reported to have antiproliferative effects on cancer cells.

Objective:

In this study, 1-(4-trifluoromethylphenyl)-2-(1H-imidazol-1-yl)ethanone (3), its oxime (4), and a series of its novel oxime ester derivatives (5a-v) were synthesized and tested for their in vitro antimicrobial activities against certain ATCC standard strains of Candida sp. fungi and bacteria. The compounds were also tested for their cytotoxic effects against mouse fibroblast and human neuroblastoma cell lines. Molecular modeling studies were performed to provide insights into their possible mechanisms for antifungal and antibacterial actions.

Methods:

The compounds were synthesized by the reaction of various oximes with acyl chlorides. Antimicrobial activity of the compounds was determined according to the broth microdilution method. For the determination of cytotoxic effect, we used MTS assay. Molecular docking and QM/MM studies were performed to predict the binding mechanisms of the active compounds in the catalytic site of C. albicans CYP51 (CACYP51) and S. aureus flavohemoglobin (SAFH), the latter of which was created via homology modeling.

Results:

5d, 5l, and 5t showed moderate antifungal activity against C. albicans, while 3, 5c, and 5r showed significant antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa. Most of the compounds showed approximately 40-50% inhibition against the human neuroblastoma cells at 100 µM. In this line, 3 was the most potent with an IC50 value of 82.18 μM followed by 5a, 5o, and 5t. 3 and 5a were highly selective to the neuroblastoma cells. Molecular modelling results supported the hypothesis that our compounds were inhibitors of CAYP51 and SAFH.

Conclusion:

This study supports that oxime ester derivatives may be used for the development of new antimicrobial and cytotoxic agents.

Efficacy of Novel Schiff base Derivatives as Antifungal Compounds in Combination with Approved Drugs Against Candida Albicans

BACKGROUND

The increasing incidence of fungal infections, especially caused by Candida albicans, and their increasing drug resistance has drastically increased in recent years. Therefore, not only new drugs but also alternative treatment strategies are promptly required.

METHODS

We previously reported on the synergistic interaction of some azole and non-azole compounds with fluconazole for combination antifungal therapy. In this study, we synthesized some non-azole Schiff-base derivatives and evaluated their antifungal activity profile alone and in combination with the most commonly used antifungal drugs- fluconazole (FLC) and amphotericin B (AmB) against four drug susceptible, three FLC resistant and three AmB resistant clinically isolated Candida albicans strains. To further analyze the mechanism of antifungal action of these compounds, we quantified total sterol contents in FLC-susceptible and resistant C. albicans isolates.

RESULTS

A pyrimidine ring-containing derivative SB5 showed the most potent antifungal activity against all the tested strains. After combining these compounds with FLC and AmB, 76% combinations were either synergistic or additive while as the rest of the combinations were indifferent. Interestingly, none of the combinations was antagonistic, either with FLC or AmB. Results interpreted from fractional inhibitory concentration index (FICI) and isobolograms revealed 4-10-fold reduction in MIC values for synergistic combinations. These compounds also inhibit ergosterol biosynthesis in a concentration-dependent manner, supported by the results from docking studies.

CONCLUSION

The results of the studies conducted advocate the potential of these compounds as new antifungal drugs. However, further studies are required to understand the other mechanisms and in vivo efficacy and toxicity of these compounds.

Antifungal screening and in silico mechanistic studies of an in-house azole library

Systemic Candida infections pose a serious public health problem with high morbidity and mortality. C. albicans is the major pathogen identified in candidiasis; however, non-albicans Candida spp. with antifungal resistance are now more prevalent. Azoles are first-choice antifungal drugs for candidiasis; however, they are ineffective for certain infections caused by the resistant strains. Azoles block ergosterol synthesis by inhibiting fungal CYP51, which leads to disruption of fungal membrane permeability. In this study, we screened for antifungal activity of an in-house azole library of 65 compounds to identify hit matter followed by a molecular modeling study for their CYP51 inhibition mechanism. Antifungal susceptibility tests against standard Candida spp. including C. albicans revealed derivatives 12 and 13 as highly active. Furthermore, they showed potent antibiofilm activity as well as neglectable cytotoxicity in a mouse fibroblast assay. According to molecular docking studies, 12 and 13 have the necessary binding characteristics for effective inhibition of CYP51. Finally, molecular dynamics simulations of the C. albicans CYP51 (CACYP51) homology model's catalytic site complexed with 13 were stable demonstrating excellent binding.

Zinc and Iron Homeostasis: Target-Based Drug Screening as New Route for Antifungal Drug Development

The incidence of fungal diseases is on the rise and the number of fatalities is still unacceptably high. While advances into antifungal drug development have been made there remains an urgent need to develop novel antifungal agents targeting as-yet unexploited pathways, such as metal ion homeostasis. Here we report such an approach by developing a metal sensor screen in the opportunistic human fungal pathogen Candida albicans. Using this reporter strain, we screened a library of 1,200 compounds and discovered several active compounds not previously described as chemical entities with antifungal properties. Two of these, artemisinin and pyrvinium pamoate, have been further characterized and their interference with metal homeostasis and potential as novel antifungal compounds validated. Lastly, we demonstrate that the same strain can be used to report on intracellular conditions within host phagocytes, paving the way toward the development of novel screening platforms that could identify compounds with the potential to perturb ion homeostasis of the pathogen specifically within host cells.

Anadenanthera Colubrina vell Brenan: anti-Candida and antibiofilm activities, toxicity and therapeutical action

We evaluated the antifungal and antibiofilm potential of the hydroalcoholic extract of bark from Anadenanthera colubrina (vell.) Brenan, known as Angico, against Candida spp. Antifungal activity was evaluated using the microdilution technique through the Minimum Inhibitory and Fungicide Concentrations (MIC and MFC). The antibiofilm potential was tested in mature biofilms formed by Candida species and analyzed through the counting of CFU/mL and scanning electron micrograph (SEM). In vivo toxicity and therapeutic action was evaluated in the Galleria mellonella model. The treatment with the extract, in low doses, was able to reduce the growth of planktonic cells of Candida species. MIC values range between 19.5 and 39 µg/mL and MFC values range between 79 and 625 µg/mL. In addition was able to reduce the number of CFU/mL in biofilms and to cause structural alteration and cellular destruction, observed via SEM. A. colubrina showed low toxicity in the in vivo assay, having not affected the viability of the larvae at doses below 100mg/kg and high potential in the treatment of C. albicans infection. Considering its high antifungal potential, its low toxicity and potential to treatment of infections in in vivo model, A. colubrina extract is a strong candidate for development of a new agent for the treatment of oral candidiasis.

Phenotypic and genotypic variations in Candida albicans isolates from Romanian patients

Background: During the last two decades a major increase in the proportion of severe fungal infections has been noted due to the excessive use of broad-spectrum antibiotics, catheters, and a growing number of immunocompromised patients.

Objectives: This is the first investigation providing complete data regarding the phenotypic and genotypic profiles of Candida albicans (C. albicans) isolates in Romanian patients.

Methods: We investigated 301 isolates in terms of genotype determination (G), resistogram (R), phospholipase activity (Pl), haemolysis (Hl), proteinase activity (Pt), and biofilm formation (BF).

Results: The analyzed isolates of C. albicans showed low values for Pt (61.73%), Hl (95.49%), and BF (60.71%), and did not present any Pl activity (92.23%). More than half of the investigated samples were genotype A with 450 bp (52.92%) and the majority (86.19%) were resistant to sodium selenite (A), boric acid (B), sodium periodate (D) and silver nitrate (E), but sensitive to cetrimide (-). One-way ANOVA analysis revealed significant effects of the infection site on biofilm formation (p = 0.0137) and no significant correlation was found between the genotype (A, B, C) and the infection site (p =0.449).

Conclusions: Based on the obtained results it can be concluded that C. albicans isolates in Romanian patients exhibit different genotypic and phenotypic patterns, and no significant correlations between genotype and infection site could be observed.

Candida Infections and Therapeutic Strategies: Mechanisms of Action for Traditional and Alternative Agents

The Candida genus comprises opportunistic fungi that can become pathogenic when the immune system of the host fails. Candida albicans is the most important and prevalent species. Polyenes, fluoropyrimidines, echinocandins, and azoles are used as commercial antifungal agents to treat candidiasis. However, the presence of intrinsic and developed resistance against azole antifungals has been extensively documented among several Candida species. The advent of original and re-emergence of classical fungal diseases have occurred as a consequence of the development of the antifungal resistance phenomenon. In this way, the development of new satisfactory therapy for fungal diseases persists as a major challenge of present-day medicine. The design of original drugs from traditional medicines provides new promises in the modern clinic. The urgent need includes the development of alternative drugs that are more efficient and tolerant than those traditional already in use. The identification of new substances with potential antifungal effect at low concentrations or in combination is also a possibility. The present review briefly examines the infections caused by Candida species and focuses on the mechanisms of action associated with the traditional agents used to treat those infections, as well as the current understanding of the molecular basis of resistance development in these fungal species. In addition, this review describes some of the promising alternative molecules and/or substances that could be used as anticandidal agents, their mechanisms of action, and their use in combination with traditional drugs.

Synthesis, activity, and docking studies of eugenol-based glucosides as new agents against Candida sp

Seventeen new synthetic derivatives of eugenol (6, 8-15 and 8'-15') were planned following literature reports on antifungal activities of nitroeugenol and eugenol glucoside. The anti-Candida activity of these compounds was investigated by in vitro assay, and the cytotoxicity evaluation was performed with the most active compounds. The peracetylated glucosides presented better biological results than their hydroxylated analogues. The glucoside 11, a 4-nitrobenzamide, showed the best potency (MIC₅₀ range 11.0-151.84 μm), the wider spectrum of action, and overall the best selectivity indexes, especially against C. tropicalis (~30) and C. krusei (~15). To investigate its possible mechanism of action, glucoside 11 was subjected to molecular docking studies with Candida sp. enzymes involved in ergosterol biosynthesis. Results have shown that the peracetyl glucosyl moiety and the 4-nitrobenzamide group in 11 are effectively involved in its high affinity with the active site of squalene epoxidase.

Antifungal Effects of Saponin Extract from Rhizomes of Dioscorea panthaica Prain et Burk against Candida albicans

Candida albicans is the most common fungal pathogen causing serious diseases, while there are only a paucity of antifungal drugs. Therefore, the present study was performed to investigate the antifungal effects of saponin extract from rhizomes of Dioscorea panthaica Prain et Burk (Huangshanyao Saponin extract, HSE) against C. albicans. HSE inhibits the planktonic growth and biofilm formation and development of C. albicans. 16–64 μg/mL of HSE could inhibit adhesion to polystyrene surfaces, transition from yeast to filamentous growth, and production of secreted phospholipase and could also induce endogenous reactive oxygen species (ROS) production and disrupt cell membrane in planktonic cells. Inhibitory activities against extracellular exopolysaccharide (EPS) production and ROS production in preformed biofilms could be inhibited by 64–256 μg/mL of HSE. Cytotoxicity against human Chang's liver cells is low, with a half maximal inhibitory concentration (IC₅₀) of about 256 μg/mL. In sum, our study suggested that HSE might be used as a potential antifungal therapeutic against C. albicans.

Blad-containing oligomer: a novel fungicide used in crop protection as an alternative treatment for tinea pedis and tinea versicolor

PURPOSE

The lack of novel antifungal drugs and the increasing incidence and severity of fungal infections are major concerns worldwide. Herein, we tested the activity of the Blad-containing oligomer (BCO), a new antifungal molecule already in use for agriculture, on Malassezia spp. and dermatophytes, the causal agents of human tinea versicolor and tinea pedis. Given the lack of a standard method for Malassezia susceptibility testing and the plethora of published methods, we also developed an improved method for this genus.

METHODOLOGY

The efficacy of BCO was assessed in vitro and compared to that of the drugs currently utilized in the treatment of tinea versicolor (fluconazole and itraconazole) and tinea pedis (itraconazole and terbinafine). For dermatophytes, the standard microdilution broth-based method was used, with small adjustments, and several broth formulations and inocula sizes were tested to develop an improved susceptibility method for Malassezia spp.

RESULTS

We successfully developed a microdilution broth-based method with considerable advantages over other available methods, and used it for all in vitro susceptibility tests of Malassezia spp. isolates. We report that, on a molar basis, BCO was more effective than fluconazole or itraconazole on most strains of Malassezia spp. isolated from clinical samples (n=29). By contrast, BCO was less effective than itraconazole or terbinafine on the common dermatophytes Trichophyton rubrum and Trichophyton interdigitale.

CONCLUSION

These data place BCO as a promising drug for the treatment of Malassezia-associated skin diseases. Further in vivo studies are now required to ascertain its applicability in the clinical setting.

Antifungal Compounds against Candida Infections from Traditional Chinese Medicine

Infections caused by Candida albicans, often refractory and with high morbidity and mortality, cause a heavy burden on the public health while the current antifungal drugs are limited and are associated with toxicity and resistance. Many plant-derived molecules including compounds isolated from traditional Chinese medicine (TCM) are reported to have antifungal activity through different targets such as cell membrane, cell wall, mitochondria, and virulence factors. Here, we review the recent progress in the anti-Candida compounds from TCM, as well as their antifungal mechanisms. Considering the diverse targets and structures, compounds from TCM might be a potential library for antifungal drug development.

Antifungal photosensitive activity of Porophyllum obscurum (Spreng.) DC.: Correlation of the chemical composition of the hexane extract with the bioactivity

We report Porophyllum obscurum as a source of new photosensitizers with potential use in Photodynamic Therapy as an alternative for oropharyngeal candidiasis treatment. The antifungal photosensitive activity of different extracts from P. obscurum was evaluated by using microdilution and bioautographic assays. The Minimum Fungicidal Concentration for hexanic extract under UV-A irradiation was 0.98μg/mL, but it was inactive in experiments without irradiation. The bioassay-guided fractionation of this extract led to the isolation of four thiophenes responsible for the photosensitive activity: 2,2':5'2″terthiophene, 5-(3-buten-1-ynyl)-2,2'-bithiophene, 5-(4-acetoxy-1-butenyl)-2,2'- bithiophene and 5-(4-hydroxy-1-butenyl)-2,2'- bithiophene, with Minimum Fungicidal Concentrations ranging 0.24-7.81μg/mL under UV-A irradiation. The activity of the hexanic extract was evaluated against 25 clinical strains of Candida spp. isolates as etiological agents of oropharyngeal candidiasis. No differences in susceptibility were observed in strains resistant and susceptible to conventional antifungal drugs. Qualitative and quantitative chemical analyses of seven samples of P. obscurum collected in four different phenological stages were carried out showing that full flowering stage possesses the highest thiophenes content. These data also allowed us to establish a correlation between the thiophene composition of the different extracts and their antifungal photosensitive activity, according to a second order polynomial model with the equation: y=11.2603-0.6831*x+0.0108*x². The thiophenes isolated were the responsible of antifungal photosensitive activity and can be used for the future standardization of the extract. Results showed that P. obscurum hexanic extract could be potentially developed as an Herbal Medicinal Product to be applied as a photosensitizer in Photodynamic Therapy.

Synergistic antifungal effect of cyclized chalcone derivatives and fluconazole against Candida albicans

The occurrence of invasive fungal diseases, particularly in immunocompromised patients, is life-threatening and increases the economic burden. The rising problem of multi-drug resistance is becoming a major concern for clinicians. In addition, a repertoire of antifungal agents is far less in number than antibacterial drugs. To combat these problems, combination therapy has gained a lot of interest. We previously reported the synergistic interaction of some mono- and bis-dihydropyrimidinone and thione derivatives with fluconazole and amphotericin B for combination antifungal therapy. In this study we used the same approach and synthesized different azole and non-azole derivatives of mono-(M) and bis-(B) chalcones and evaluated their antifungal activity profile alone and in combination with the most commonly used antifungal drug - fluconazole (FLC) - against seven FLC susceptible and three FLC resistant clinically isolated Candida albicans strains. Based on the minimum inhibitory concentration results, the bis-derivatives showed lower MIC values compared to their mono-analogues. Both fractional inhibitory concentration index and isobologram results revealed mostly synergistic, additive or indifferent interactions between the tested compounds and FLC against different Candida isolates. None of the tested compounds showed any effect on energy dependent R6G efflux, revealing that they do not reverse the mechanism of drug efflux. However, surprisingly, these compounds profoundly decreased ergosterol biosynthesis and showed down regulation of ERG11 gene expression, which is the possible mechanism of reversal of azole drug resistance by these compounds. These results provide a platform for further research to develop pyrimidinone/thione ring containing compounds as promising new antifungal agents, which could be used in antifungal combination therapy.

Protocol for Identifying Natural Agents That Selectively Affect Adhesion, Thickness, Architecture, Cellular Phenotypes, Extracellular Matrix, and Human White Blood Cell Impenetrability of Candida albicans Biofilms

In the screening of natural plant extracts for antifungal activity, assessment of their effects on the growth of cells in suspension or in the wells of microtiter plates is expedient. However, microorganisms, including Candida albicans, grow in nature as biofilms, which are organized cellular communities with a complex architecture capable of conditioning their microenvironment, communicating, and excluding low- and high-molecular-weight molecules and white blood cells. Here, a confocal laser scanning microscopy (CLSM) protocol for testing the effects of large numbers of agents on biofilm development is described. The protocol assessed nine parameters from a single z-stack series of CLSM scans for each individual biofilm analyzed. The parameters included adhesion, thickness, formation of a basal yeast cell polylayer, hypha formation, the vertical orientation of hyphae, the hyphal bend point, pseudohypha formation, calcofluor white staining of the extracellular matrix (ECM), and human white blood cell impenetrability. The protocol was applied first to five plant extracts and derivative compounds and then to a collection of 88 previously untested plant extracts. They were found to cause a variety of phenotypic profiles, as was the case for 64 of the 88 extracts (73%). Half of the 46 extracts that did not affect biofilm thickness affected other biofilm parameters. Correlations between specific effects were revealed. The protocol will be useful not only in the screening of chemical libraries but also in the analysis of compounds with known effects and mutations.

Bridging the Gap to Non-toxic Fungal Control: Lupinus-Derived Blad-Containing Oligomer as a Novel Candidate to Combat Human Pathogenic Fungi

The lack of antifungal drugs with novel modes of action reaching the clinic is a serious concern. Recently a novel antifungal protein referred to as Blad-containing oligomer (BCO) has received regulatory approval as an agricultural antifungal agent. Interestingly its spectrum of antifungal activity includes human pathogens such as Candida albicans, however, its mode of action has yet to be elucidated. Here we demonstrate that BCO exerts its antifungal activity through inhibition of metal ion homeostasis which results in apoptotic cell death in C. albicans. HIP HOP profiling in Saccharomyces cerevisiae using a panel of signature strains that are characteristic for common modes of action identified hypersensitivity in yeast lacking the iron-dependent transcription factor Aft1 suggesting restricted iron uptake as a mode of action. Furthermore, global transcriptome profiling in C. albicans also identified disruption of metal ion homeostasis as a potential mode of action. Experiments were carried out to assess the effect of divalent metal ions on the antifungal activity of BCO revealing that BCO activity is antagonized by metal ions such as Mn²⁺, Zn²⁺, and Fe²⁺. The transcriptome profile also implicated sterol synthesis as a possible secondary mode of action which was subsequently confirmed in sterol synthesis assays in C. albicans. Animal models for toxicity showed that BCO is generally well tolerated and presents a promising safety profile as a topical applied agent. Given its potent broad spectrum antifungal activity and novel multitarget mode of action, we propose BCO as a promising new antifungal agent for the topical treatment of fungal infections.

Bioactive Compounds of Cold-pressed Thyme (Thymus vulgaris) Oil with Antioxidant and Antimicrobial Properties

Herbs rich in bioactive phytochemicals were recognized to have biological activities and possess many health-promoting effects. In this work, cold-pressed thyme (Thymus vulgaris L.) oil (TO) was studied for its lipid classes, fatty acid profile, tocols and phenolics contents. Antioxidant activity and radical scavenging potential of TO against free radicals (DPPH(・) and galvinoxyl) was determined. Antimicrobial activity (AA) of TO against food borne bacteria, food spoilage fungi and dermatophyte fungi were also evaluated. Neutral lipids accounted for the main lipid fraction in TO, followed by glycolipids and phospholipids. The major fatty acids in TO were linoleic, oleic, stearic, and palmitic. γ-Tocopherol (60.2% of total tocols) followed by α-tocotrienol (26.9%) and α-tocopherol (9.01% of total tocols) were the main tocols. TO contained high amounts of phenolic compounds (7.3 mg/g as GAE). TO had strong antiradical action wherein 65% of DPPH(・) radicals and 55% of galvinoxyl radical were quenched after 60 min of incubation. Rancimat assay showed that induction time (IT) for TO: sunflower oil blend (1:9, w/w) was 6.5 h, while TO: sunflower oil blend (2:8, w/w) recorded higher IT (9 h). TO inhibited the growth of all tested microorganisms. TO exhibited various degrees of AA against different food borne bacteria, food spoilage fungi and dermatophyte fungi, wherein the highest AA was recorded against dermatophyte fungi and yeasts including T. mentagrophytes (62 mm), T. rubrum (40 mm), and C. albicans (20 mm) followed by food spoilage fungi including A. flavus (32 mm) with minimal lethal concentrations (MLC) ranging between 80 to 320 μg/mL. Furthermore, TO exhibited broad-spectra activity against food borne bacteria including S. aureus (30 mm), E. coli (25 mm) and L. Monocytogenes (20 mm) with MLC ranging between 160 to 320 μg/mL. The results suggest that TO could be used economically as a valuable natural product with novel functional properties in food, cosmetics and pharmaceutical industries.

Flucytosine analogues obtained through Biginelli reaction as efficient combinative antifungal agents

Invasive fungal infection is a problem that continues to challenge the healthcare sector. New antifungals and new therapeutic strategies are needed to address this challenge. We previously reported that the combination of a synthetic compound with a drug with known mechanism of action is a good strategy to treat aggressive and resistant fungi. Here we revisited our approach and synthesized structural analogues of flucytosine, which is a synthetic antifungal and is being studied for its use in combination therapy with other antifungal drugs. Pyrimidin-one and -thione (often known as DHPM's) as flucytosine analogues were obtained through a Biginelli reaction of corresponding aldehydes, ethylacetoacetate and urea/thiourea. Structure was confirmed by FTIR, ¹HNMR, ¹³CNMR, COSY and MS (ESI⁺) analysis. All the newly synthesized derivatives were evaluated for the antifungal activity alone and in combination of two most commonly used antifungal drugs, amphotericin B and fluconazole against different clinically isolated Candida albicans strains. Minimum inhibitory concentration results confirmed that BG4 possess high antifungal activity against all the tested strains (MIC = 1-32 μg/ml). For all the combinations with amphotericin B and fluconazole, 37% were synergistic followed by 30% additive and 24% indifferent interactions. Interestingly, 9% antagonistic interaction was observed when BG1 and BG3 were combined with fluconazole, however, no antagonistic interaction was observed with amphotericin B. In-depth studies of all the synergies were done by constructing isobolograms with nine different ratio combinations. These results warrant the use of DHPM derivatives as chemosensitising agents which could lower down the dosages of the antifungal drugs to treat invasive fungal diseases.

Efficacy of nystatin for the treatment of oral candidiasis: a systematic review and meta-analysis

Objective

To systematically review and assess the efficacy, different treatment protocols (formulation, dosage, and duration), and safety of nystatin for treating oral candidiasis.

Methods

Four electronic databases were searched for trials published in English till July 1, 2015. Randomized controlled trials comparing nystatin with other antifungal therapies or a placebo were included. Clinical and/or mycological cure was the outcome evaluation. A meta-analysis or descriptive study on the efficacy, treatment protocols, and safety of nystatin was conducted.

Results

The meta-analysis showed that nystatin pastille was significantly superior to placebo in treating denture stomatitis. Nystatin suspension was not superior to fluconazole in treating oral candidiasis in infants, children, or HIV/AIDS patients. The descriptive investigations showed that administration of nystatin suspension and pastilles in combination for 2 weeks might achieve a higher clinical and mycological cure rate, and using the nystatin pastilles alone might have a higher mycological cure rate, when compared with using nystatin suspensions alone. Nystatin pastilles at a dose of 400,000 IU resulted in a significantly higher mycological cure rate than that administrated at a dose of 200,000 IU. Furthermore, treatment with nystatin pastilles for 4 weeks seemed to have better clinical efficacy than treatment for 2 weeks. Descriptive safety assessment showed that poor taste and gastrointestinal adverse reaction are the most common adverse effects of nystatin.

Conclusion

Nystatin pastille was significantly superior to placebo in treating denture stomatitis, while nystatin suspension was not superior to fluconazole in treating oral candidiasis in infants, children, or HIV/AIDS patients. Indirect evidence from a descriptive study demonstrated that administration of nystatin pastille alone or pastille and suspension in combination is more effective than that of suspension alone; prolonged treatment duration for up to 4 weeks can increase the efficacy of nystatin. More well designed and high quality randomized control studies are needed to confirm these findings.

Synthesis and evaluation of thiophene-based guanylhydrazones (iminoguanidines) efficient against panel of voriconazole-resistant fungal isolates

A series of new thiophene-based guanylhydrazones (iminoguanidines) were synthesized in high yields using a straightforward two-step procedure. The antifungal activity of compounds was evaluated against a wide range of medicaly important fungal strains including yeasts, molds, and dermatophytes in comparison to clinically used drug voriconazole. Cytotoxic properties of compounds were also determined using human lung fibroblast cell line and hemolysis assay. All guanylhydrazones showed significant activity against broad spectrum of clinically important species of Candida spp., Aspergillus fumigatus, Fusarium oxysporum, Microsporum canis and Trichophyton mentagrophytes, which was in some cases comparable or better than activity of voriconazole. More importantly, compounds 10, 11, 13, 14, 18 and 21 exhibited excellent activity against voriconazole-resistant Candida albicans CA5 with very low minimal inhibitory concentration (MIC) values <2 μg mL(-1). Derivative 14, bearing bromine on the phenyl ring, was the most effective compound with MICs ranging from 0.25 to 6.25 μg mL(-1). However, bis-guanylhydrazone 18 showed better selectivity in terms of therapeutic index values. In vivo embryotoxicity on zebrafish (Danio rerio) showed improved toxicity profile of 11, 14 and 18 in comparison to that of voriconazole. Most guanylhydrazones also inhibited C. albicans yeast to hyphal transition, essential for its biofilm formation, while 11 and 18 were able to disperse preformed Candida biofilms. All guanylhydrazones showed the equal potential to interact with genomic DNA of C. albicans in vitro, thus indicating a possible mechanism of their action, as well as possible mechanism of observed cytotoxic effects. Tested compounds did not have significant hemolytic effect and caused low liposome leakage, which excluded the cell membrane as a primary target. On the basis of computational docking experiments using both human and cytochrome P450 from Candida it was concluded that the most active guanylhydrazones had minimal structural prerequisites to interact with the cytochrome P450 14α-demethylase (CYP51). Promising guanylhydrazone derivatives also showed satisfactory pharmacokinetic profile based on molecular calculations.

Inclusion complexes of propiconazole nitrate with substituted β-cyclodextrins: the synthesis and in silico and in vitro assessment of their antifungal properties

Inclusion complexes with sulfobutylether-β-cyclodextrin, β-cyclodextrin sulphated sodium salt and monochlorotriazinyl-β-cyclodextrin were characterized and assessed for antifungal activity and cytotoxicity.

Potential Use of Phenolic Acids as Anti-Candida Agents: A Review

There has been a sharp rise in the occurrence of Candida infections and associated mortality over the last few years, due to the growing body of immunocompromised population. Limited number of currently available antifungal agents, undesirable side effects and toxicity, as well as emergence of resistant strains pose a considerable clinical challenge for the treatment of candidiasis. Therefore, molecules that derived from natural sources exhibiting considerable antifungal properties are a promising source for the development of novel anti-candidal therapy. Phenolic compounds isolated from natural sources possess antifungal properties of interest. Particularly, phenolic acids have shown promising in vitro and in vivo activity against Candida species. However, studies on their mechanism of action alone or in synergism with known antifungals are still scarce. This review attempts to discuss the potential use, proposed mechanisms of action and limitations of the phenolic acids in anti-candidal therapy.