Hydroxyaldimines as potent in vitro anticryptococcal agents

A novel zinc-chelating compound has antifungal activity against a wide range of Candida species, including multidrug-resistant Candida auris

Objectives

In recent years, the incidence of invasive fungal infections has increased, resulting in considerable morbidity and mortality, particularly among immunocompromised individuals. Potential challenges in treating these infections with the few existing antifungal agents highlight the urgency of developing new ones. Here, we evaluated six alkyl polyamine compounds (APCs), not previously reported as antifungal drugs to our knowledge, that could deprive fungi of essential transition metals.

Methods

The APC with confirmed antifungal activity against Candida spp. was analysed by using transcriptomics, followed by metal-addition experiments, mass spectrometric analyses and intracellular zinc quantification with a fluorescent probe.

Results

A cyclic APC with three pyridylmethyl groups, APC6, had high antifungal activity against a wide range of Candida species, including MDR Candida auris. We conclusively demonstrated that APC6 was able to capture zinc within fungal cells. APC6 not only exhibited activity against C. auris as a single agent but also enhanced the efficacy of an azole antifungal agent, voriconazole, in vitro and in vivo. APC6 disrupted the biofilms formed by Candida species.

Conclusions

This zinc-chelating compound has potential as an antifungal agent, and the control of zinc levels in Candida species could be a powerful approach to treating drug-resistant candidiasis.

N-acetylcysteine reduces amphotericin B deoxycholate nephrotoxicity and improves the outcome of murine cryptococcosis

Cryptococcosis is a life-threatening fungal infection, and its current treatment is toxic and subject to resistance. Drug repurposing represents an interesting approach to find drugs to reduce the toxicity of antifungals. In this study, we evaluated the combination of N-acetylcysteine (NAC) with amphotericin B (AMB) for the treatment of cryptococcosis. We examined the effects of NAC on fungal morphophysiology and on the macrophage fungicidal activity 3 and 24 hours post inoculation. The therapeutic effects of NAC combination with AMB were investigated in a murine model with daily treatments regimens. NAC alone reduced the oxidative burst generated by AMB in yeast cells, but did not inhibit fungal growth. The combination NAC + AMB decreased capsule size, zeta potential, superoxide dismutase activity and lipid peroxidation. In macrophage assays, NAC + AMB did not influence the phagocytosis, but induced fungal killing with different levels of oxidative bursts when compared to AMB alone: there was an increased reactive oxygen species (ROS) after 3 hours and reduced levels after 24 hours. By contrast, ROS remained elevated when AMB was tested alone, demonstrating that NAC reduced AMB oxidative effects without influencing its antifungal activity. Uninfected mice treated with NAC + AMB had lower concentrations of serum creatinine and glutamate-pyruvate transaminase in comparison to AMB. The combination of NAC + AMB was far better than AMB alone in increasing survival and reducing morbidity in murine-induced cryptococcosis, leading to reduced fungal burden in lungs and brain and also lower concentrations of pro-inflammatory cytokines in the lungs. In conclusion, NAC + AMB may represent an alternative adjuvant for the treatment of cryptococcosis.

Effects on anti-inflammatory, DNA binding and molecular docking properties of 2-chloroquinolin-3-yl-methylene-pyridine/pyrazole derivatives and their palladium(II) complexes

Two new sets of Schiff bases 2-chloroquinolin-3-yl-methylene-pyridin-2-amine (CMPA) and 2-chloroquinolin-3-yl-methylene-pyrazole-5-amine-3-thole (CMPT) and their respective palladium (II) complexes have been synthesised and characterized with the aid of elemental analysis, IR, ¹H &¹³C NMR, UV-Vis., and electrochemical studies. The surface morphology of palladium complexes were examined by Scanning Electron Microscopic image. The binding affinities of complexes with CT-DNA were carried out by absorption spectra and cyclic voltammetric studies. The observed hypochromic (~20%) and bathochromic (~30%) shifts indicates that the complexes bind with Guanine base pair of CT-DNA via intercalation. The increasing cathodic peak potential from +0.968 eV to +1.104 eV in complexes confirm the presence of intercalation. Anti-inflammatory activities of both ligands and complexes have been studied using carrageenan induced hind paw edema in Wistar rats. The change in paw volume revealed that the maximum percentage of inhibition was observed in metal complex at 5th hour with a dose of 200 mg/kg. In order to evaluate the binding affinity of ligand and metal complex, molecular interaction analysis were performed by maestro implemented in Schrodinger.

Cinnamyl Schiff bases: synthesis, cytotoxic effects and antifungal activity of clinical interest

The aim of this study was to synthesize and investigate the in vitro antifungal properties of 23 cinnamyl Schiff bases. In addition, cytotoxic effects of such cinnamyl Schiff bases against human lung, kidney or red blood cells were also checked. The compounds were synthesized in a single-step, 2 min of reaction under microwave irradiation produced up to 97% yield. Six of the 23 cinnamyl Schiff bases possessed antifungal activities against strains of Candida, Aspergillus, Fonsecaea and, particularly, Cryptococcus species. Indeed, cinnamyl Schiff bases 1 and 23 exhibited minimum inhibitory concentration (MIC) values more than twofold lower than fluconazole (FCZ) against all the Cryptococcus neoformans strains (MIC = 1·33, 1·4 and 5·2 µg ml^-1 , respectively) and Cryptococcus gattii strains (MIC = 5·3, 2·8 and 9·2 µg ml^-1 , respectively) (12 strains of each species) while cinnamyl Schiff base 11 was as potent as FCZ against all strains from both Cryptococcus species. No significant cytotoxic effects were observed for Schiff bases against human lung, kidney or red blood cells, all presenting selective indexes higher than 10. In conclusion, this study revealed cinnamyl Schiff bases, especially 1 and 23, as new lead anticryptococcal agents for the discovery of novel antifungal drugs. SIGNIFICANCE AND IMPACT OF THE STUDY: The occurrence and severity of fungal infections have increased in recent decades due to resistance to available antifungal drugs and the appearance of new emerging pathogens. Thus, the search for new antifungal agents is mandatory. From a series of 23 cinnamyl Schiff bases, two compounds (1 and 23) were interrogated as new anticryptococcal agents without significant cytotoxicity against human lung, kidney or red blood cells. In turns, these new Schiff bases are lead compounds for the discovery of novel antifungal drugs.

Antifungal activity of extracts and purified saponins from the rhizomes of Chamaecostus cuspidatus against Candida and Trichophyton species

AIM

To evaluate the antifungal activity of extracts of Chamaecostus cuspidatus against Candida and Trichophyton species.

METHODS AND RESULTS

Crude ethanol extracts of leaves, stems and rhizomes were prepared and evaluated for antimicrobial activity. Only the rhizomes extract (RE) showed antifungal activity but had no inhibitory effect against bacteria (Staphylococcus aureus and Escherichia coli). The RE was then submitted to liquid-liquid partition with hexane (Hex), dichloromethane, chloroform, ethyl acetate and water. The Hex fraction (Hex Fr) from the RE was found to have the best antifungal effect. Three known saponins were isolated from the Hex Fr, of which two (dioscin and aferoside A) showed good antifungal activity. In addition, Hex Fr and the two bioactive compounds had no antibacterial effect, but exhibited fungicidal activity, caused significant changes in the morphology of the fungal cells and showed anti-Candida albicans biofilm activity. Finally, the bioactive plant products presented greater selectivity for fungal cells over normal human cells.

CONCLUSIONS

The rhizomes of C. cuspidatus have bioactive saponins that function as effective antifungals against Candida and Trichophyton species, and have antibiofilm activity against C. albicans.

SIGNIFICANCE AND IMPACT OF THE STUDY

Chamaecostus cuspidatus REs may have potential clinical application towards the management of superficial mycoses caused by Candida and Trichophyton species.

Incorporation of 2-amino-thiophene derivative in nanoparticles: enhancement of antifungal activity

The objective of this study was to evaluate the effects of nanoparticles (nanospheres and nanocapsules) of the promising antifungal 2-amino-thiophene (6CN10) and 6CN10 complexed with 2-hydroxypropyl-β-cyclodextrin (6CN10:HP-β-CD) in vitro and compared with free drug against Candida and Cryptococcus, using a microdilution method to measure susceptibility. The Candida and Cryptococcus clinical strains were identified using phenotypic methods and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF). To measure in vitro antifungal susceptibility, we used microdilution trials. Serial drug or nanoparticle dilutions were prepared according to the CLSI M27-A3 guidelines. Anti-biofilm activity was verified for Cryptococcus neoformans. All Candida isolates were sensitive to the free drug (MIC = 41.66-333.33 μg/mL) and were able to grow even at the higher concentration tested for all 6CN10 nanoparticles. However, the Cryptococcus neoformans strains presented MIC values of 0.32-83.33 μg/mL for 6CN10 nanoparticles, and MIC values of 0.1-0.2 μg/mL for 6CN10:HP-β-CD nanoparticles, i.e., 3333 times more active than the free drug (MIC values 166.66-333.33 μg/mL), and presenting activity greater than that of the reference drug amphotericin B (MIC = 0.5-0.125 μg/mL). 6CN10:HP-β-CD nanosphere also showed high anti-biofilm potential. The in vitro study showed that the nanoparticles allowed better drug efficiency against Cryptococcus than did the free drug. These results suggest that 6CN10-loaded nanoparticles may become a future alternative for cryptococcosis and candidiasis therapy. In vivo experiments are essential prior to clinical use.

Evaluation of in vitro Antifungal Activity of Xylosma prockia (Turcz.) Turcz. (Salicaceae) Leaves Against Cryptococcus spp

Cryptococcus species are responsible for important systemic mycosis and are estimated to cause millions of new cases annually. The available therapy is limited due to the high toxicity and the increasing rates of yeast resistance to antifungal drugs. Popularly known as “sucará,” Xylosma prockia (Turcz.) Turcz. (Salicaceae) is a native plant from Brazil with little information on its pharmacological potential. In this work, we evaluated in vitro anticryptococcal effects of the leaf ethanolic extract of X. prockia and its fractions against Cryptococcus gattii and Cryptococcus neoformans. We also evaluated phenotypic alterations caused by ethyl acetate fraction (EAF) (chosen according to its biological results). The liquid chromatography–mass spectrometry (LC-MS) analysis of EAF demonstrated the presence of phenolic metabolites that belong to three structurally related groups as majority compounds: caffeoylquinic acid, coumaroyl-glucoside, and caffeoyl-glucoside/deoxyhexosyl-caffeoyl glucoside derivatives. The minimum inhibitory concentration (MIC) values against C. gattii and C. neoformans ranged from 8 to 64 mg/L and from 0.5 to 8 mg/L, for ethanolic extract and EAF, respectively. The EAF triggered an oxidative burst and promoted lipid peroxidation. EAF also induced a reduction of ergosterol content in the pathogen cell membrane. These effects were not associated with alterations in the cell surface charge or in the thermodynamic fingerprint of the molecular interaction between EAF and the yeasts evaluated. Cytotoxic experiments with peripheral blood mononuclear cells (PBMCs) demonstrated that EAF was more selective for yeasts than was PBMCs. The results may provide evidence that X. prockia leaf extract might indeed be a potential source of antifungal agents.

From the environment to the host: How non-azole agrochemical exposure affects the antifungal susceptibility and virulence of Cryptococcus gattii

Agrochemicals such as the non-azoles, used to improve crop productivity, poses severe undesirable effects on the environment and human health. In addition, they induce cross-resistance (CR) with clinical drugs in pathogenic fungi. However, till date emphasis has been given to the role of azoles on the induction of CR. Herein, we analyzed the effect of a non-azole agrochemical, pyraclostrobin (PCT), on the antifungal susceptibility and virulence of the human and animal pathogens Cryptococcus gattii and C. neoformans. We determined the minimum inhibitory concentration (MIC) of fluconazole (FLC), itraconazole, ravuconazole, amphotericin B, and PCT on colonies: (i) that were not exposed to PCT (non-adapted-NA-cultures), (ii) were exposed at the maximum concentration of PCT (adapted-A-cultures) and (iii) the adapted colonies after cultivation 10 times in PCT-free media (10 passages-10p-cultures). Our results showed that exposure to PCT induced both temporary and permanent CR to clinical azoles in a temperature-dependent manner. With the objective to understand the mechanism of induction of CR through non-azoles, the transcriptomes of NA and 10p cells from C. gattii R265 were analyzed. The transcriptomic analysis showed that expression of the efflux-pump genes (AFR1 and MDR1) and PCT target was higher in resistant 10p cells than that in NA. Moreover, the virulence of 10p cells was reduced as compared to NA cells in mice, as observed by the differential gene expression analysis of genes related to ion-metabolism. Additionally, we observed that FLC could not increase the survival rate of mice infected with 10p cells, confirming the occurrence of permanent CR in vivo. The findings of the present study demonstrate that the non-azole agrochemical PCT can induce permanent CR to clinical antifungals through increased expression of efflux pump genes in resistant cells and that such phenomenon also manifests in vivo.

A new acridone with antifungal properties against Candida spp. and dermatophytes, and antibiofilm activity against C. albicans

AIM

The increase in the number of fungal infections worldwide, coupled with the limitations of current antifungal chemotherapy, demand the development of safe and effective new antifungals. Here, we presented the synthesis of a novel acridone (M14) and its antifungal properties against Candida and dermatophytes species.

METHODS AND RESULTS

A series of 17 acridones was designed, synthesized and tested for its antifungal activity. The minimum inhibitory concentration (MIC) was determined by the broth microdilution method. Only the acridone M14 showed growth-inhibitory activity against reference strains and clinical isolates of Candida and dermatophytes, with MIC range of 7·81-31·25 µg ml^-1 . Moreover, M14 exhibited fungicidal activity and prevented biofilm formation by C. albicans as well as reduced the viability of preformed biofilms, even at sub-MICs. The confocal laser scanning microscopy analysis revealed that C. albicans hyphal growth was completely inhibited in the presence of M14. Similarly, there was a severe inhibition on hyphal growth of Trichophyton rubrum. We also found that M14 has relatively low toxicity to human fibroblasts.

CONCLUSIONS

The new acridone M14 has antifungal properties against Candida spp. and dermatophytes, and antibiofilm activity against C. albicans. In addition, M14 is relatively selective to fungal cells compared to human normal cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Because of its in vitro antifungal activity, anti-Candida biofilm effect and moderate cytotoxicity towards normal human cell, M14 may serve as a valuable lead compound to develop a new antifungal agent.

Butenafine and analogues: An expeditious synthesis and cytotoxicity and antifungal activities

The incidence of fungal infections is considered a serious public health problem worldwide. The limited number of antimycotic drugs available to treat human and animal mycosis, the undesirable side effects and toxicities of the currently available drugs, and the emergence of fungal resistance emphasizes the urgent need for more effective antimycotic medicines. In this paper, we describe a rapid, simple, and efficient synthetic route for preparation of the antifungal agent butenafine on a multigram scale. This novel synthetic route also facilitated the preparation of 17 butenafine analogues using Schiff bases as precursors in three steps or less. All the synthesized compounds were evaluated against the yeast, Cryptococcus neoformans/C. gattii species complexes and the filamentous fungi Trichophyton rubrum and Microsporum gypseum. Amine 4bd, a demethylated analogue of butenafine, and its corresponding hydrochloride salt showed low toxicity in vitro and in vivo while maintaining inhibitory activity against filamentous fungi.

In vivo and in vitro activity of a bis-arylidenecyclo-alkanone against fluconazole-susceptible and -resistant isolates of Candida albicans

OBJECTIVES

Candida albicans is a commensal organism and opportunistic pathogen associated both with superficial (mucosal and cutaneous) and systemic infections. Extensive use of antifungal agents has led to reduced susceptibility to the few existing drugs, which has encouraged the search for novel antifungal agents. Therefore, the present study investigated the antifungal activity of 2,6-bis[(E)-(4-pyridyl)methylidene]cyclohexanone (PMC) against C. albicans.

METHODS

The in vitro activity of PMC was evaluated against C. albicans. Additionally, an invertebrate infection model in Caenorhabditis elegans as well as two infected murine models of oral and systemic candidiasis were used to determine the antifungal efficacy of PMC in vivo.

RESULTS

Minimum inhibitory concentrations (MICs) of PMC ranged from 4-32μg/mL against nine clinical and two reference C. albicans isolates. Interestingly, PMC inhibited filamentation in vitro at subinhibitory concentrations similar to fluconazole. PMC also showed low toxicity against murine macrophages and human erythrocytes. In the invertebrate infection model, PMC was efficient in prolonging survival of C. elegans infected with C. albicans SC5314. Treatment with PMC was efficient both in murine models of systemic and oral candidiasis and was similar to that observed with conventional drug treatments (nystatin and fluconazole).

CONCLUSIONS

The results of this study indicate the therapeutic potential of PMC as it was able to inhibit filamentation of C. albicans in vitro. These alterations to the fungi by PMC resulted in a reduction of oral and systemic infection in mice. In conclusion, we present promising evidence of the anticandidal activity of PMC in vitro and in vivo.

Environmental Triazole Induces Cross-Resistance to Clinical Drugs and Affects Morphophysiology and Virulence of Cryptococcus gattii and C. neoformans

Cryptococcus gattii and Cryptococcus neoformans are environmental fungi that cause cryptococcosis, which is usually treated with amphotericin B and fluconazole. However, therapeutic failure is increasing because of the emergence of resistant strains. Because these species are constantly isolated from vegetal materials and the usage of agrochemicals is growing, we postulate that pesticides could be responsible for the altered susceptibility of these fungi to clinical drugs. Therefore, we evaluated the influence of the pesticide tebuconazole on the susceptibility to clinical drugs, morphophysiology, and virulence of C. gattii and C. neoformans strains. The results showed that tebuconazole exposure caused in vitro cross-resistance (CR) between the agrochemical and clinical azoles (fluconazole, itraconazole, and ravuconazole) but not with amphotericin B. In some strains, CR was observed even after the exposure ceased. Further, tebuconazole exposure changed the morphology, including formation of pseudohyphae in C. neoformans H99, and the surface charge of the cells. Although the virulence of both species previously exposed to tebuconazole was decreased in mice, the tebuconazole-exposed colonies recovered from the lungs were more resistant to azole drugs than the nonexposed cells. This in vivo CR was confirmed when fluconazole was not able to reduce the fungal burden in the lungs of mice. The tolerance to azoles could be due to increased expression of the ERG11 gene in both species and of efflux pump genes (AFR1 and MDR1) in C. neoformans Our study data support the idea that agrochemical usage can significantly affect human pathogens present in the environment by affecting their resistance to clinical drugs.

Eugenol Induces Phenotypic Alterations and Increases the Oxidative Burst in Cryptococcus

Eugenol is a phenolic compound and the main constituent of the essential oil of clove India. Although there are reports of some pharmacological effects of eugenol, this study is the first that proposes to evaluate the antifungal effects of this phenol against both Cryptococcus gattii and C. neoformans cells. The effect of eugenol against yeast cells was analyzed for drug susceptibility, alterations in cell diameter, capsule properties, amounts of ergosterol, oxidative burst, and thermodynamics data. Data demonstrated that there is no interaction between eugenol and fluconazole and amphotericin B. Eugenol reduced the cell diameter and the capsule size, increased cell surface/volume, changed positively the cell surface charge of cryptococcal cells. We also verified increased levels of reactive oxygen species without activation of antioxidant enzymes, leading to increased lipid peroxidation, mitochondrial membrane depolarization and reduction of lysosomal integrity in cryptococcal cells. Additionally, the results showed that there is no significant molecular interaction between eugenol and C. neoformans. Morphological alterations, changes of cellular superficial charges and oxidative stress play an important role in antifungal activity of eugenol against C. gattii and C. neoformans that could be used as an auxiliary treatment to cutaneous cryptococcosis.

Cryptococcal therapies and drug targets: the old, the new and the promising

Half a century after the introduction of Amphotericin B the management of cryptococcosis remains unsatisfactory. The disease, caused primarily by the two fungal species Cryptococcus neoformans and Cryptococcus gattii, remains responsible for considerable morbidity and mortality despite standard medical care. Current therapeutic options are limited to Amphotericin B, azoles and 5-flucytosine. However, this organism has numerous well-characterized virulence mechanisms that are amenable to pharmacological interference and are thus potential therapeutic targets. Here, we discuss existing approved antifungal drugs, resistance mechanisms to these drugs and non-standard antifungal drugs that have potential in treatment of cryptococcosis, including immunomodulatory strategies that synergize with antifungal drugs, such as cytokine administration or monoclonal antibodies. Finally, we summarize attempts to target well-described virulence factors of Cryptococcus, the capsule or fungal melanin. This review emphasizes the pressing need for new therapeutic alternatives for cryptococcosis.

Thiazole compounds with activity against Cryptococcus gattii and Cryptococcus neoformans in vitro

Human cryptococcosis can occur as a primary or opportunistic infection and develop as an acute, subacute, or chronic, systemic infection involving different host organs. We evaluated the antifungal activity of thirteen compounds against Cryptococcus gattii and Cryptococcus neoformans in vitro, by assessing the toxicity of the compounds showing the greatest antifungal activity in VERO cells and murine macrophages. From these results, four compounds were considered promising for further studies because they displayed low cytotoxicity and significant antifungal activity. The heterocyclic compounds 1b, 1c, 1d, and 1m have antifungal activity levels between that of amphotericin B and fluconazole in vitro. The death curve of Cryptococcus spp. treated with these four compounds was similar to the curve obtained for amphotericin B, in that we observed a significant reduction in cell viability within the first 24 h of treatment. Additionally, we found that there was no effect when these compounds were combined with amphotericin and fluconazole, except for 1c, which antagonized the effect of amphotericin B against C. gattii, also reflected in the reduction of the post-antifungal effect (PAFE); however, this interaction did not alter the ergosterol content. The results shown in this paper reveal the discovery of novel thiazole compounds, which are easy to synthesize, and with potentially exhibit antifungal activity, and display low cytotoxicity in normal mammalian cells. These compounds can be used as prototypes for the design of new antifungal drugs against C. gattii and C. neoformans.

Antifungal Activity of Decyl Gallate against Several Species of Pathogenic Fungi

This work aims to demonstrate that the gallic acid structure modification to the decyl gallate (G14) compound contributed to increase the antifungal activity against several species of pathogenic fungi, mainly, Candida spp., Cryptococcus spp., Paracoccidioides spp., and Histoplasma capsulatum, according to standardized microdilution method described by Clinical Laboratory Standard Institute (CLSI) documents. Moreover this compound has a particularly good selectivity index value, which makes it an excellent candidate for broad-spectrum antifungal prototype and encourages the continuation of subsequent studies for the discovery of its mechanism of action.