Synthetic organotelluride compounds induce the reversal of Pdr5p mediated fluconazole resistance in Saccharomyces cerevisiae

Antifungal activity of β-lapachone against a fluconazole-resistant Candida auris strain

Candida spp. can be found in the human microbiome. However, immunocompromised patients are likely to develop invasive Candida infections, with mortality rates higher than 50%. The discovery of C. auris, a species that rapidly acquire antifungal resistance, increased the concern about Candida infections. The limited number of antifungal agents and the high incidence of resistance to them make imperative the development of new antifungal drugs. β-lapachone is a biological active naphthoquinone that displays antifungal activity against C. albicans and C. glabrata. The aim of this study was to evaluate if this substance affects C. auris growth and elucidate its mechanism of action. A fluconazole-resistant C. auris isolate was used in this study. The antifungal activity of β-lapachone was determined through microbroth dilution assays, and its mechanism of action was evaluated using fluorescent probes. Interaction with fluconazole and amphotericin B was assessed by disk diffusion assay and checkerboard. β-lapachone inhibited planktonic C. auris cell growth by 92.7%, biofilm formation by 84.9%, and decrease the metabolism of preformed biofilms by 87.1% at 100 µg/ml. At 100 µg/ml, reductions of 30% and 59% of Calcofluor White and Nile red fluorescences were observed, indicating that β-lapachone affects cell wall chitin and neutral lipids content, respectively. Also, the ratio 590 nm/529 nm of JC-1 decreased 52%, showing that the compound affects mitochondria. No synergism was observed between β-lapachone and fluconazole or amphotericin B. Data show that β-lapachone may be a promising candidate to be used as monotherapy to treat C. auris resistant infections.

Antimicrobial Properties of New Polyamines Conjugated with Oxygen-Containing Aromatic Functional Groups

Antibiotic resistance is now a first-order health problem, which makes the development of new families of antimicrobials imperative. These compounds should ideally be inexpensive, readily available, highly active, and non-toxic. Here, we present the results of our investigation regarding the antimicrobial activity of a series of natural and synthetic polyamines with different architectures (linear, tripodal, and macrocyclic) and their derivatives with the oxygen-containing aromatic functional groups 1,3-benzodioxol, ortho/para phenol, or 2,3-dihydrobenzofuran. The new compounds were prepared through an inexpensive process, and their activity was tested against selected strains of yeast, as well as Gram-positive and Gram-negative bacteria. In all cases, the conjugated derivatives showed antimicrobial activity higher than the unsubstituted polyamines. Several factors, such as the overall charge at physiological pH, lipophilicity, and the topology of the polyamine scaffold were relevant to their activity. The nature of the lipophilic moiety was also a determinant of human cell toxicity. The lead compounds were found to be bactericidal and fungistatic, and they were synergic with the commercial antifungals fluconazole, cycloheximide, and amphotericin B against the yeast strains tested.

Structural and Functional Alterations Caused by Aureobasidin A in Clinical Resistant Strains of Candida spp

Candida species are one of the most concerning causative agents of fungal infections in humans. The treatment of invasive Candida infections is based on the use of fluconazole, but the emergence of resistant isolates has been an increasing concern which has led to the study of alternative drugs with antifungal activity. Sphingolipids have been considered a promising target due to their roles in fungal growth and virulence. Inhibitors of the sphingolipid biosynthetic pathway have been described to display antifungal properties, such as myriocin and aureobasidin A, which are active against resistant Candida isolates. In the present study, aureobasidin A did not display antibiofilm activity nor synergism with amphotericin B, but its combination with fluconazole was effective against Candida biofilms and protected the host in an in vivo infection model. Alterations in treated cells revealed increased oxidative stress, reduced mitochondrial membrane potential and chitin content, as well as altered morphology, enhanced DNA leakage and a greater susceptibility to sodium dodecyl sulphate (SDS). In addition, it seems to inhibit the efflux pump CaCdr2p. All these data contribute to elucidating the role of aureobasidin A on fungal cells, especially evidencing its promising use in clinical resistant isolates of Candida species.

Digoxin Derivatives Sensitize a Saccharomyces cerevisiae Mutant Strain to Fluconazole by Inhibiting Pdr5p

The poor outcome of treatments for fungal infections is a consequence of the increasing incidence of resistance to antifungal agents, mainly due to the overexpression of efflux pumps. To surpass this mechanism of resistance, a substance able to inhibit these pumps could be administered in association with antifungals. Saccharomyces cerevisiae possesses an efflux pump (Pdr5p) homologue to those found in pathogenic yeast. Digoxin is a natural product that inhibits Na⁺, K⁺-ATPase. The aim of this study was to evaluate whether digoxin and its derivatives (i.e., DGB, digoxin benzylidene) can inhibit Pdr5p, reversing the resistance to fluconazole in yeasts. An S. cerevisiae mutant strain that overexpresses Pdr5p was used in the assays. The effects of the compounds on yeast growth, efflux activity, and Pdr5p ATPase activity were measured. All derivatives enhanced the antifungal activity of fluconazole against S. cerevisiae, in comparison to fluconazole alone, with FICI values ranging from 0.031 to 0.500. DGB 1 and DGB 3 presented combined effects with fluconazole against a Candida albicans strain, with fractional inhibitory concentration index (FICI) values of 0.625 and 0.281, respectively The compounds also inhibited the efflux of rhodamine 6G and Pdr5p ATPase activity, with IC₅₀ values ranging from 0.41 μM to 3.72 μM. The results suggest that digoxin derivatives impair Pdr5p activity. Considering the homology between Pdr5p and efflux pumps from pathogenic fungi, these compounds are potential candidates to be used in association with fluconazole to treat resistant fungal infections.

Effects of β-lapachone and β-nor-lapachone on multidrug efflux transporters and biofilms of Candida glabrata

Infections caused particularly by Candida glabrata are hard to treat due to the development of antifungal resistance that occurs mainly through the production of efflux pumps and biofilm. Thus, a promising strategy to overcome infections caused by C. glabrata could be to use a substance able to inhibit efflux pumps and eradicate biofilms. Lapachones are natural naphthoquinones that possess a variety of pharmacological properties. Previous studies show that these substances inhibit the growth, virulence factors and efflux pumps of C. albicans. The aim of the present study was to evaluate whether lapachones are able to inhibit efflux pumps related to antifungal resistance in C. glabrata and either prevent biofilm formation or affect mature biofilms. Assays were performed with Saccharomyces cerevisiae strains that overexpress C. glabrata transporters (CgCdr1p and CgCdr2p). One C. glabrata clinical isolate that overexpresses CgCdr1p was also used. Both β-lapachone and β-nor-lapachone affected the growth of S. cerevisiae and C. glabrata when combined to fluconazole, and this action was inhibited by ascorbic acid. Both lapachones stimulated ROS production, inhibited efflux activity, adhesion, biofilm formation and the metabolism of mature biofilms of C. glabrata. Data obtained on the present study point to the potential use of β-lapachone and β-nor-lapachone as antibiofilm agents and adjuvants on the antifungal therapy related to resistant infections caused by C. glabrata.

Sphingolipid Inhibitors as an Alternative to Treat Candidiasis Caused by Fluconazole-Resistant Strains

Candida species are fungal pathogens known to cause a wide spectrum of diseases, and Candida albicans and Candida glabrata are the most common associated with invasive infections. A concerning aspect of invasive candidiasis is the emergence of resistant isolates, especially those highly resistant to fluconazole, the first choice of treatment for these infections. Fungal sphingolipids have been considered a potential target for new therapeutic approaches and some inhibitors have already been tested against pathogenic fungi. The present study therefore aimed to evaluate the action of two sphingolipid synthesis inhibitors, aureobasidin A and myriocin, against different C. albicans and C. glabrata strains, including clinical isolates resistant to fluconazole. Susceptibility tests of aureobasidin A and myriocin were performed using CLSI protocols, and their interaction with fluconazole was evaluated by a checkerboard protocol. All Candida strains tested were sensitive to both inhibitors. Regarding the evaluation of drug interaction, both aureobasidin A and myriocin were synergic with fluconazole, demonstrating that sphingolipid synthesis inhibition could enhance the effect of fluconazole. Thus, these results suggest that sphingolipid inhibitors in conjunction with fluconazole could be useful for treating candidiasis cases, especially those caused by fluconazole resistant isolates.

Mechanisms of Candida Resistance to Antimycotics and Promising Ways to Overcome It: The Role of Probiotics

Pathogenic Candida and infections caused by those species are now considered as a serious threat to public health. The treatment of candidiasis is significantly complicated by the increasing resistance of pathogenic strains to current treatments and the stagnant development of new antimycotic drugs. Many species, such as Candida auris, have a wide range of resistance mechanisms. Among the currently used synthetic and semi-synthetic antifungal drugs, the most effective are azoles, echinocandins, polyenes, nucleotide analogs, and their combinations. However, the use of probiotic microorganisms and/or the compounds they produce is quite promising, although underestimated by modern pharmacology, to control the spread of pathogenic Candida species.

Casearia sylvestris essential oil and its fractions inhibit Candida albicans ABC transporters related to multidrug resistance (MDR)

Abstract ABC transporters constitute a superfamily of transmembrane proteins that act mediating the translocation of several substrates across the membrane, using the energy of ATP hydrolysis. This mechanism of unrelated substrates efflux (multidrug resistance) has been associated with several diseases and it is a problem in chemotherapy efficacy. Nowadays, approximately 25% of the prescription drugs in the world are derived from plants. Casearia sylvestris is commonly found in the Americas and different parts of this plant are popularly used to treat several diseases. Previous studies have also confirmed the biological activities of C. sylvestris, such as anti-tumor, anti-leishmania, and antifungal properties. Then, the propose of this study was demonstrate that fraction 1-6 of C. sylvestris, essential oil, was able to reverse the fluconazole resistance phenotype in the Saccharomyces cerevisiae model mediated by the heterologous protein CaCdr2p from Candida albicans. The MIC value of fraction 1-6 combined with fluconazole in the checkerboard assay decreased approximately 4-fold, suggesting a synergistic effect. In addition, fraction 1-6 increased intracellular rhodamine 6G accumulation from 17% to 49% in the presence of glucose. Data indicate that C. sylvestris fraction 1-6 is a potential reverser of the fluconazole resistance phenotype.

Batzelladine D and norbatzelladine L purified from marine sponge Monanchora arbuscula induce the reversal of fluconazole

ATP-Binding Cassette (ABC) transporters are the main class of transmembrane transporters involved in pathogenic fungal resistance against chemotherapeutic agents. Herein we report results which show that batzelladine D (1) and norbatzelladine L (2) reverse the fluconazole resistance phenotype mediated by Pdr5p transporter on Saccharomyces cerevisiae. Both alkaloids were able to chemosensitize the Pdr5p-overexpressing strain by synergistic interaction with fluconazole. Both compounds also showed an inhibitory effect on the catalytic activity and on the intracellular accumulation of rhodamine 6G, and did not show significant in vitro mammalian cells toxicity.

β-Lapachone enhances the antifungal activity of fluconazole against a Pdr5p-mediated resistant Saccharomyces cerevisiae strain

OBJECTIVES

The aim of this study was to evaluate the ability of lapachones in disrupting the fungal multidrug resistance (MDR) phenotype, using a model of study which an azole-resistant Saccharomyces cerevisiae mutant strain that overexpresses the ATP-binding cassette (ABC) transporter Pdr5p.

METHODS

The evaluation of the antifungal activity of lapachones and their possible synergism with fluconazole against the mutant S. cerevisiae strain was performed through broth microdilution and spot assays. Reactive oxygen species (ROS) and efflux pump activity were assessed by fluorometry. ATPase activity was evaluated by the Fiske and Subbarow method. The effect of β-lapachone on PDR5 mRNA expression was assessed by RT-PCR. The release of hemoglobin was measured to evaluate the hemolytic activity of β-lapachone.

RESULTS

α-nor-Lapachone and β-lapachone inhibited S. cerevisiae growth at 100 μg/ml. Only β-lapachone enhanced the antifungal activity of fluconazole, and this combined action was inhibited by ascorbic acid. β-Lapachone induced the production of ROS, inhibited Pdr5p-mediated efflux, and impaired Pdr5p ATPase activity. Also, β-lapachone neither affected the expression of PDR5 nor exerted hemolytic activity.

CONCLUSIONS

Data obtained indicate that β-lapachone is able to inhibit the S. cerevisiae efflux pump Pdr5p. Since this transporter is homologous to fungal ABC transporters, further studies employing clinical isolates that overexpress these proteins will be conducted to evaluate the effect of β-lapachone on pathogenic fungi.

Synthesis and Antimicrobial Evaluation of Some New Organic Tellurium Compounds Based on Pyrazole Derivatives

A novel series of organic tellurium compounds based on pyrazole derivatives with a general formula of ArTeBr₃ and Ar₂TeBr₂ [Ar = 2-(3-(4-substituted phenyl) -5-(2-chlorophenyl)-1H-pyrazol-1-yl)-3,5-dinitrophenyl] were obtained by the refluxing of corresponding aryl mercuric chlorides with TeBr₄ in two different mole ratio of 1:1 and 2:1, respectively, in free-moisture dioxane solvent under an argon atmosphere. Compounds of ArTeBr₃ and Ar₂TeBr₂ were reduced by the action of ethanolic solution of hydrazine hydrate obtained Ar₂Te₂ and Ar₂Te, respectively. Reaction of Ar₂Te₂ with excess thionyl chloride or iodine gave the corresponding trihalides ArTeCl₃ and ArTeI₃, respectively while the reaction of Ar₂Te with thionyl chloride or iodine gave the corresponding Ar₂TeCl₃ and Ar₂TeI₃, respectively. The structures were elucidated according to their elemental analysis of carbon, hydrogen and nitrogen (CHN) and some of the spectroscopic techniques such as infrared IR and nuclear magnetic resonance for ¹H and ¹³C. The antimicrobial activity for all the synthetic compounds were assayed against both Gram-negative and Gram-positive bacteria by using the agar diffusion method. The tellurated pyrazole derivatives showed a good degree against bacteria growth. In some cases, the antimicrobial activities of the synthetic compounds were better than amoxicillin.

Characterisation of an ABC transporter of a resistant Candida glabrata clinical isolate

BACKGROUND

Candida glabrata ranks second in epidemiological surveillance studies, and is considered one of the main human yeast pathogens. Treatment of Candida infections represents a contemporary public health problem due to the limited availability of an antifungal arsenal, toxicity effects and increasing cases of resistance. C. glabrata presents intrinsic fluconazole resistance and is a significant concern in clinical practice and in hospital environments.

OBJECTIVE

The aim of this study was to characterise the azole resistance mechanism presented by a C. glabrata clinical isolate from a Brazilian university hospital.

METHODS

Azole susceptibility assays, chemosensitisation, flow cytometry and mass spectrometry were performed.

FINDINGS

Our study demonstrated extremely high resistance to all azoles tested: fluconazole, voriconazole, posaconazole and itraconazole. This isolate was chemosensitised by FK506, a classical inhibitor of ABC transporters related to azole resistance, and Rhodamine 6G extrusion was observed. A mass spectrometry assay confirmed the ABC protein identification suggesting the probable role of efflux pumps in this resistance phenotype.

MAIN CONCLUSIONS

This study emphasizes the importance of ABC proteins and their relation to the resistance mechanism in hospital environments and they may be an important target for the development of compounds able to unsettle drug extrusion.

Synthetic Organotellurium Compounds Sensitize Drug-Resistant Candida albicans Clinical Isolates to Fluconazole

Invasive Candida albicans infections are a serious health threat for immunocompromised individuals. Fluconazole is most commonly used to treat these infections, but resistance due to the overexpression of multidrug efflux pumps is of grave concern. This study evaluated the ability of five synthetic organotellurium compounds to reverse the fluconazole resistance of C. albicans clinical isolates. Compounds 1 to 4, at <10 μg/ml, ameliorated the fluconazole resistance of Saccharomyces cerevisiae strains overexpressing the major C. albicans multidrug efflux pumps Cdr1p and Mdr1p, whereas compound 5 only sensitized Mdr1p-overexpressing strains to fluconazole. Compounds 1 to 4 also inhibited efflux of the fluorescent substrate rhodamine 6G and the ATPase activity of Cdr1p, whereas all five of compounds 1 to 5 inhibited Nile red efflux by Mdr1p. Interestingly, all five compounds demonstrated synergy with fluconazole against efflux pump-overexpressing fluconazole-resistant C. albicans clinical isolates, isolate 95-142 overexpressing CDR1 and CDR2, isolate 96-25 overexpressing MDR1 and ERG11, and isolate 12-99 overexpressing CDR1, CDR2, MDR1, and ERG11 Overall, organotellurium compounds 1 and 2 were the most promising fluconazole chemosensitizers of fluconazole-resistant C. albicans isolates. Our data suggest that these novel organotellurium compounds inhibit pump efflux by two very important and distinct families of fungal multidrug efflux pumps: the ATP-binding cassette transporter Cdr1p and the major facilitator superfamily transporter Mdr1p.

Prevalence and Fluconazole Susceptibility Profile of Candida spp. Clinical Isolates in a Brazilian Tertiary Hospital in Minas Gerais, Brazil

Candidiasis has become an important concern for clinical practice, especially with the increasing incidence of immunocompromised patients. In this scenario, the development resistance to fluconazole presents a challenge for treating these opportunistic infections. The aim of this study was to evaluate some epidemiology features of Candidainfections in a Brazilian University Hospital using data, previously unavailable. We observed that 44% of the 93 clinical isolates tested, belonged to Candida albicansspecies and 56% belonged to non-Candida albicansspecies (mainly Candida tropicalis and Candida glabrata). Most strains were isolated from urine samples where C. albicans was predominantly detected. 29 strains presented a fluconazole resistance phenotype and of these, 22 were chemosensitised by FK506, a classical inhibitor of ABC transporters related to azoles resistance. These data suggest the probable role of efflux pumps in this resistance phenotype. Our study highlights the need for developing effective control measures for fungal infections, rational use of antifungal drugs and development of new molecules able to abrogate the active transport of antifungals.