Interaction of azole antifungal agents with cytochrome P-45014DM purified from Saccharomyces cerevisiae microsomes

Facile metabolic reprogramming distinguishes mycobacterial adaptation to hypoxia and starvation: ketosis drives starvation-induced persistence in M. bovis BCG

Mycobacteria adapt to infection stresses by entering a reversible non-replicating persistence (NRP) with slow or no cell growth and broad antimicrobial tolerance. Hypoxia and nutrient deprivation are two well-studied stresses commonly used to model the NRP, yet little is known about the molecular differences in mycobacterial adaptation to these distinct stresses that lead to a comparable NRP phenotype. Here we performed a multisystem interrogation of the Mycobacterium bovis BCG (BCG) starvation response, which revealed a coordinated metabolic shift away from the glycolysis of nutrient-replete growth to depletion of lipid stores, lipolysis, and fatty acid ß-oxidation in NRP. This contrasts with BCG's NRP hypoxia response involving a shift to cholesterol metabolism and triglyceride storage. Our analysis reveals cryptic metabolic vulnerabilities of the starvation-induced NRP state, such as their newfound hypersensitivity to H2O2. These observations pave the way for developing precision therapeutics against these otherwise drug refractory pathogens.

Resurgence and Repurposing of Antifungal Azoles by Transition Metal Coordination for Drug Discovery

Coordination compounds featuring one or more antifungal azole (AA) ligands constitute an interesting family of candidate molecules, given their medicinal polyvalence and the viability of drug complexation as a strategy to improve and repurpose available medications. This review reports the work performed in the field of coordination derivatives of AAs synthesized for medical purposes by discussing the corresponding publications and emphasizing the most promising compounds discovered so far. The resulting overview highlights the efficiency of AAs and their metallic species, as well as the potential still lying in this research area.

Sensitivity Baselines, Resistance Monitoring, and Molecular Mechanisms of the Rice False Smut Pathogen Ustilaginoidea virens to Prochloraz and Azoxystrobin in Four Regions of Southern China

Rice false smut caused by Ustilaginoidea virens is one of the most devastating fungal diseases of rice (Oryza sativa) worldwide. Prochloraz and azoxystrobin belong to the groups of demethylation inhibitors and quinone outside inhibitors, respectively, and are commonly used for controlling this disease. In this study, we analyzed the sensitivities of 100 U. virens isolates from Yunnan, Sichuan, Chongqing, and Zhejiang in Southern China to prochloraz and azoxystrobin. The ranges of EC50 for prochloraz and azoxystrobin were 0.004-0.536 and 0.020-0.510 μg/mL, with means and standard errors of 0.062 ± 0.008 and 0.120 ± 0.007 μg/mL, respectively. However, the sensitivity frequency distributions of U. virens to prochloraz and azoxystrobin indicated the emergence of subpopulations with decreased sensitivity. Therefore, the mean EC50 values of 74% and 68% of the isolates at the main peak, 0.031 ± 0.001 and 0.078 ± 0.004 μg/mL, were used as the sensitivity baselines of U. virens to prochloraz and azoxystrobin, respectively. We found significant sensitivity differences to azoxystrobin among different geographical populations and no correlation between the sensitivities of U. virens to prochloraz and azoxystrobin. Among 887 U. virens isolates, the isolate 5-3-1 from Zhejiang showed moderate resistance to prochloraz, with a resistance factor of 22.45, while no nucleotide variation in the 1986-bp upstream or 1827-bp gene regions of CYP51 from 5-3-1 was detected. Overexpression of CYP51 is probably responsible for its resistance to prochloraz. Finally, artificial inoculation showed that 5-3-1 was highly pathogenic to rice, suggesting that the resistance of U. virens to prochloraz must be monitored and managed in Zhejiang.

Profiling The Compendium Of Changes In Saccharomyces cerevisiae Due To Mutations That Alter Availability Of The Main Methyl Donor S-Adenosylmethionine

The SAM1 and SAM2 genes encode for S-AdenosylMethionine (AdoMet) synthetase enzymes, with AdoMet serving as the main methyl donor. We have previously shown that independent deletion of these genes alters chromosome stability and AdoMet concentrations in opposite ways in S. cerevisiae. To characterize other changes occurring in these mutants, we grew wildtype, sam1∆/sam1∆, and sam2∆/sam2∆ strains in 15 different Phenotypic Microarray plates with different components, equal to 1440 wells, and measured for growth variations. RNA-Sequencing was also carried out on these strains and differential gene expression determined for each mutant. In this study, we explore how the phenotypic growth differences are linked to the altered gene expression, and thereby predict the mechanisms by which loss of the SAM genes and subsequent AdoMet level changes, impact S. cerevisiae pathways and processes. We present six stories, discussing changes in sensitivity or resistance to azoles, cisplatin, oxidative stress, arginine biosynthesis perturbations, DNA synthesis inhibitors, and tamoxifen, to demonstrate the power of this novel methodology to broadly profile changes due to gene mutations. The large number of conditions that result in altered growth, as well as the large number of differentially expressed genes with wide-ranging functionality, speaks to the broad array of impacts that altering methyl donor abundance can impart, even when the conditions tested were not specifically selected as targeting known methyl involving pathways. Our findings demonstrate that some cellular changes are directly related to AdoMet-dependent methyltransferases and AdoMet availability, some are directly linked to the methyl cycle and its role is production of several important cellular components, and others reveal impacts of SAM gene mutations on previously unconnected pathways.

Improvement of Akanthomyces lecanii resistance to tebuconazole through UV-C radiation and selective pressure on microbial evolution and growth arenas

Tebuconazole (TEB) is a fungicide widely used in agriculture; however, its constant application has increased the emergence of resistant plant pathogenic fungal strains and reduced the effectiveness of fungi as biological control agents; for instance, the entomopathogenic and hyperparasitic fungus Akanthomyces lecanii, suitable for simultaneous biological control of insect pest and plant pathogenic fungi, is highly sensitive to fungicides. We carried out the induction of resistance to TEB in two wild type strains of A. lecanii by UV radiation and selective pressure in increasing fungicide gradients using a modified Microbial Evolution and Growth Arena (MEGA), to produce A. lecanii strains that can be used as biological control agent in the presence of tebuconazole. Nine UV-induced and three naturally adapted A. lecanii strains were resistant to TEB at the agriculturally recommended dose, and three irradiated strains were resistant to TEB concentration ten times higher; moreover, growth, sporulation rates, production of hydrolytic enzymes, and virulence against the hemipteran Coccus viridis, a major pest of coffee crops, were not affected in the TEB-resistant strains. These A. lecanii TEB-resistant strains would have a greater opportunity to develop and to establish themselves in fields where the fungicide is present and can be used in a combined biological-chemical strategy to improve insect and plant pathogenic fungal control in agriculture. Also, the selective pressure through modified MEGA plate methodology can be used for the adaptation of entomopathogenic filamentous fungi to withstand other chemical or abiotic stresses that limits its effectiveness for pest control.

Combination effects of tebuconazole with Bacillus subtilis to control rice false smut and the related synergistic mechanism

BACKGROUND

Management of rice false smut is based mainly on chemical control, which poses many safety and environmental challenges. The other option, biological control with biofungicides, does not have such problems but is not as reliable because of low systemic ability, and lower and unstable efficacy. Therefore, it is necessary to combine application of chemical fungicides and biological control agents (BCAs) and elucidate their synergistic mechanism.

RESULTS

A combination of tebuconazole and a proven BCA, Bacillus subtilis H158, was evaluated for control of rice false smut. Tebuconazole at low application rates stimulated growth of B. subtilis, prolonged the effective period of B. subtilis by enhancing its persistence on the surface of rice plants, accelerated biofilm formation of the BCA to facilitate colonization, promoted induced systemic resistance in rice by regulating defense-related enzymes and genes, and reduced the natural resistance of the pathogen by suppressing the key gene for fungal resistance to tebuconazole. However, at high application rates, tebuconazole had adverse effects on these factors and showed antagonistic combination effects with B. subtilis. The combination of B. subtilis with tebuconazole at low application rates showed great synergistic effects, but at high application rates showed only antagonistic effects in field experiments over two consecutive years.

CONCLUSION

The combination of B. subtilis with tebuconazole had significant synergistic effects at low application rates. The synergistic effects are the result of multiple mechanisms involved in BCA, rice and the fungal pathogen. © 2022 Society of Chemical Industry.

Baseline Sensitivity and Control Efficacy of Two Quinone Outside Inhibitor Fungicides, Azoxystrobin and Pyraclostrobin, Against Ustilaginoidea virens

Rice false smut caused by the filamentous fungus Ustilaginoidea virens is a devastating grain disease in rice. Fungicides have been an important measure for the control of this disease. In this study, baseline sensitivities of 179 isolates of U. virens to the quinone outside inhibitor (QoI) fungicides azoxystrobin and pyraclostrobin were established. The distribution of the 50% effective concentration (EC₅₀) values of each fungicide was unimodal. The frequency distribution of logarithmically transformed EC₅₀ values fit or fit closer to a normal distribution. The ranges of EC₅₀ values for azoxystrobin and pyraclostrobin were 0.001 to 0.864 and 0.001 to 0.569 μg/ml, with means and standard errors of the mean values of 0.203 ± 0.012 and 0.079 ± 0.006 μg/ml, respectively. There was a statistically significant and moderately positive correlation (n = 100, r = 0.469, P = 0.001) in sensitivity between these two fungicides. No cross-resistance was found between azoxystrobin, pyraclostrobin, and carbendazim or sterol demethylation inhibitor fungicides. Each fungicide had a significantly higher mean preventive efficacy compared with its curative efficacy. Field assays showed that the control efficacy of pyraclostrobin against rice false smut was greater than that of azoxystrobin. Pyraclostrobin had the best control of rice false smut in three rice varieties, with the control efficacy ranging from 81.5 to 95.5%, whereas azoxystrobin decreased the disease index by 64.1 to 69.2% under the same conditions. These results provide us a reference point in the management of U. virens and future QoI fungicide resistance monitoring programs.

Sensitivity and Resistance Risk Assessment of Puccinia striiformis f. sp. tritici to Triadimefon in China

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat that seriously threatens production safety in wheat-producing areas worldwide. In China, the disease has been largely controlled with the fungicide triadimefon. Although high levels of fungicide resistance in other fungal pathogens have been reported, failure to control Pst with any fungicides has seldomly been reported, and fungicide sensitivity of Pst has not been evaluated in China. The distribution of triadimefon-resistant Pst isolates was investigated in the present study. The baseline sensitivity of 446 Pst isolates across the country to triadimefon was determined, and the concentration for 50% of maximal effect showed a unimodal distribution curve, with a mean value of 0.19 μg ml^-1. The results indicated a wide range of sensitivity to triadimefon, with more insensitive isolates collected from Pst winter-increasing areas and northwest oversummering areas, whereas more sensitive isolates were collected from southwest oversummering areas and epidemic areas of Xinjiang and Tibet. The majority of the tested Pst isolates were sensitive to triadimefon; only 6.79% had developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in the urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. Positive cross-resistance was observed between triadimefon and tebuconazole or hexaconazole, but not between pyraclostrobin or flubeneteram. The point mutation Y134F in the 14α-demethylase enzyme (CYP51) was detected in triadimefon-resistant isolates. A molecular method (kompetitive allele-specific PCR) was established for the rapid detection of Y134F mutants in the Pst population. Two genotypes with one point mutation Y134F conferred resistance to triadimefon in Pst. The risk of resistance to triadimefon in Pst may be low to moderate. This study provided important data for establishment of high throughput molecular detection methods, fungicide resistance risk management, and the development of new target fungicides.

The fungicide Tebuconazole induces electromechanical cardiotoxicity in murine heart and human cardiomyocytes derived from induced pluripotent stem cells

Tebuconazole (TEB) is an important fungicide that belongs to the triazole family. It is widely used in agriculture and its use has experienced a tremendous increase in the last decade. The long-term exposure of humans to this pesticide is a real threat because it is stable in water and soil. The association between long-term exposure to TEB and damage of several biological systems, including hepatotoxicity and cardiotoxicity is evident, however, acute toxicological studies to reveal the toxicity of TEB are limited. This research paper addressed the acute exposure of TEB in murine hearts, cardiomyocytes, and human cardiomyocytes derived from an induced pluripotent stem cell (hiPSC-CMs), spelling out TEB's impact on electromechanical properties of the cardiac tissue. In ex vivo experiments, TEB dose dependently, caused significant electrocardiogram (ECG) remodeling with prolonged PR and QTc interval duration. The TEB was also able to change the action potential waveform in murine cardiomyocytes and hiPSC-CMs. These effects were associated with the ability of the compound to block the L-type calcium current (IC₅₀ = 33.2 ± 7.4 μmol.l^-1) and total outward potassium current (IC₅₀ = 5.7 ± 1.5 μmol.l^-1). TEB also increased the sodium/calcium exchanger current in its forward and reverse modes. Additionally, sarcomere shortening and calcium transient in isolated cardiomyocytes were enhanced when cells were exposed to TEB at 30 μmol.l^-1. Combined, our results demonstrated that acute TEB exposure affects the cardiomyocyte's electro-contractile properties and triggers the appearance of ECG abnormalities.

Roles for Structural Biology in the Discovery of Drugs and Agrochemicals Targeting Sterol 14α-Demethylases

Antifungal drugs and antifungal agrochemicals have significant limitations. These include several unintended consequences of their use including the growing importance of intrinsic and acquired resistance. These problems underpin an increasingly urgent need to improve the existing classes of antifungals and to discover novel antifungals. Structural insights into drug targets and their complexes with both substrates and inhibitory ligands increase opportunity for the discovery of more effective antifungals. Implementation of this promise, which requires multiple skill sets, is beginning to yield candidates from discovery programs that could more quickly find their place in the clinic. This review will describe how structural biology is providing information for the improvement and discovery of inhibitors targeting the essential fungal enzyme sterol 14α-demethylase.

Fungal Zn(II)2Cys6 Transcription Factor ADS-1 Regulates Drug Efflux and Ergosterol Metabolism under Antifungal Azole Stress

Antifungal azoles are the most widely used antifungal drugs in clinical and agricultural practice. Fungi can mount adaptive responses to azole stress by modifying the transcript levels of many genes, and the responsive mechanisms to azoles are the basis for fungi to develop azole resistance. In this study, we identified a new Zn(II)₂Cys₆ transcription factor, ADS-1, with a positive regulatory function in transcriptional responses to azole stress in the model filamentous fungal species Neurospora crassa Under ketoconazole (KTC) stress, the ads-1 transcript level was significantly increased in N. crassa Deletion of ads-1 increased susceptibility to different azoles, while its overexpression increased resistance to these azoles. The cdr4 gene, which encodes the key azole efflux pump, was positively regulated by ADS-1. Deletion of ads-1 reduced the transcriptional response by cdr4 to KTC stress and increased cellular KTC accumulation under KTC stress, while ads-1 overexpression had the opposite effect. ADS-1 also positively regulated the transcriptional response by erg11, which encodes the azole target lanosterol 14α-demethylase for ergosterol biosynthesis, to KTC stress. After KTC treatment, the ads-1 deletion mutant had less ergosterol but accumulated more lanosterol than the wild type, while ads-1 overexpression had the opposite effect. Homologs of ADS-1 are widely present in filamentous fungal species of Ascomycota but not in yeasts. Deletion of the gene encoding an ADS-1 homolog in Aspergillus flavus also increased susceptibility to KTC and itraconazole (ITZ). Besides, deletion of A. flavus ads-1 (Afads-1) significantly reduced the transcriptional responses by genes encoding homologs of CDR4 and ERG11 in A. flavus to KTC stress, and the deletion mutant accumulated more KTC but less ergosterol. Taken together, these findings demonstrate that the function and regulatory mechanism of ADS-1 homologs among different fungal species in azole responses and the basal resistance of azoles are highly conserved.

Chromatin Structure and Drug Resistance in Candida spp

Anti-microbial resistance (AMR) is currently one of the most serious threats to global human health and, appropriately, research to tackle AMR garnishes significant investment and extensive attention from the scientific community. However, most of this effort focuses on antibiotics, and research into anti-fungal resistance (AFR) is vastly under-represented in comparison. Given the growing number of vulnerable, immunocompromised individuals, as well as the positive impact global warming has on fungal growth, there is an immediate urgency to tackle fungal disease, and the disturbing rise in AFR. Chromatin structure and gene expression regulation play pivotal roles in the adaptation of fungal species to anti-fungal stress, suggesting a potential therapeutic avenue to tackle AFR. In this review we discuss both the genetic and epigenetic mechanisms by which chromatin structure can dictate AFR mechanisms and will present evidence of how pathogenic yeast, specifically from the Candida genus, modify chromatin structure to promote survival in the presence of anti-fungal drugs. We also discuss the mechanisms by which anti-chromatin therapy, specifically lysine deacetylase inhibitors, influence the acquisition and phenotypic expression of AFR in Candida spp. and their potential as effective adjuvants to mitigate against AFR.

Genomic Multiplication and Drug Efflux Influence Ketoconazole Resistance in Malassezia restricta

Malassezia restricta is an opportunistic fungal pathogen on human skin; it is associated with various skin diseases, including seborrheic dermatitis and dandruff, which are usually treated using ketoconazole. In this study, we clinically isolated ketoconazole-resistant M. restricta strains (KCTC 27529 and KCTC 27550) from patients with dandruff. To understand the mechanisms of ketoconazole resistance in the isolates, their genomes were sequenced and compared with the susceptible reference strain M. restricta KCTC 27527. Using comparative genome analysis, we identified tandem multiplications of the genomic loci containing ATM1 and ERG11 homologs in M. restricta KCTC 27529 and KCTC 27550, respectively. Additionally, we found that the copy number increase of ATM1 and ERG11 is reflected in the increased expression of these genes; moreover, we observed that overexpression of these homologs caused ketoconazole resistance in a genetically tractable fungal pathogen, Cryptococcus neoformans. In addition to tandem multiplications of the genomic region containing the ATM1 homolog, the PDR5 homolog, which encodes the drug efflux pump protein was upregulated in M. restricta KCTC 27529 compared to the reference strain. Biochemical analysis confirmed that drug efflux was highly activated in M. restricta KCTC 27529, implying that upregulation of the PDR5 homolog may also contribute to ketoconazole resistance in the strain. Overall, our results suggest that multiplication of the genomic loci encoding genes involved in ergosterol synthesis, mitochondrial iron metabolism, and oxidative stress response and overexpression of the drug efflux pumps are the mechanisms underlying ketoconazole resistance in M. restricta.

Searching molecular determinants of sensitivity differences towards four demethylase inhibitors in Fusarium graminearum field strains

Demethylase inhibitors (DMIs) also referred to as azoles or triazoles are currently the main fungicides used for controlling Fusarium diseases and associated toxins in cereals. DMIs also represent an important class of fungicides used in the medical domain. The level of sensitivity of a set of F. graminearum strains (n = 23), collected over the period 1994-2010 in Luxembourg, Germany, Canada, USA, Italy and Belgium against three DMIs (cyproconazole, propiconazole, tebuconazole) used in agriculture and one DMI used in medicine (tioconazole) was assessed using a microplate test. Median molar EC₅₀ values varied 113-fold among DMIs and on average 11-fold within DMIs with cyproconazole and tebuconazole being the least and the most effective ones, respectively. The EC₅₀ values of the two DMIs registered for use against Fusarium species on cereals (propiconazole and tebuconazole) were significantly correlated (r = 0.597**), while no evidence for cross-resistance was obtained for other fungicide combinations. Haplotypes for CYP51A and CYP51C were defined based on snps determining amino acid variations in the two genes. EC₅₀ values of strains with the CYP51A haplotype A0 and the CYP51C haplotype D1 varied greatly for the agricultural DMIs tebuconazole, propiconazole and cyproconazole, but not for the medical DMI tioconazole. None of the mutations and snps that were previously reported to be associated with resistance towards propiconazole was unambiguously related with resistance to tioconazole, because the mutations and snps were found in strains with low as well as with high EC₅₀ values. Our results show that (1) DMI sensitivity of F. graminearum mycelium has been largely stable between 1994 and 2010, (2) effects of snps on sensitivity towards one DMI detected in one set of strains cannot be extrapolated to other DMIs and sets of strains and (3) F. graminearum strains responded differently to DMIs used in agriculture and to a representative of a medical DMI with no evidence for cross-resistance.

Evaluating the Sensitivities and Efficacies of Fungicides with Different Modes of Action Against Phomopsis asparagi

Asparagus stem blight caused by Phomopsis asparagi is a major hindrance to asparagus production worldwide. Currently, fungicides are used to manage the disease in commercial production, but resistance to common fungicides has emerged in the wild population. In the present study, 132 isolates of P. asparagi collected from different provinces in China were tested for sensitivities to pyraclostrobin, tebuconazole, and fluazinam. We also determined the efficacies of six fungicides against P. asparagi. The frequency distributions of EC₅₀ values of the isolates tested were unimodal, but the curves for pyraclostrobin and tebuconazole had long right-hand tails. The mean EC₅₀ values for pyraclostrobin, tebuconazole, and fluazinam were 0.0426 ± 0.0029, 0.6041 ± 0.0416, and 0.0314 ± 0.0013 μg/ml, respectively. In addition, the EC₅₀ values for pyraclostrobin were very similar with or without salicylhydroxamic acid (SHAM), 20 μg/ml, indicating that SHAM is not needed to determine the sensitivity of P. asparagi to pyraclostrobin when using the mycelial growth inhibition assay. In greenhouse assays, Merivon (42.4% fluxapyroxad plus pyraclostrobin SC), Frown-cide (500 g/liter fluazinam SC), Cabrio (250 g/liter pyraclostrobin EC), and Nativo (75% trifloxystrobin plus tebuconazole WG) showed excellent preventive efficacy against P. asparagi. And these fungicides were more effective before inoculation than when they were applied after inoculation (P < 0.05). Therefore, these fungicides should be applied prior to infection to control stem blight. In field trials, Frown-cide, Merivon, Nativo, and Cabrio also performed good control effects, ranging from 75.2 to 86.0% in 2017 and 75.4 to 87.1% in 2018. We demonstrated that Frown-cide, Merivon, Nativo, and Cabrio had considerable potential to manage asparagus stem blight. In addition, rotations of these fungicides are essential for precluding or delaying the development of resistance and for controlling the disease.

Trade-Off Between Triadimefon Sensitivity and Pathogenicity in a Selfed Sexual Population of Puccinia striiformis f. sp. Tritici

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases of wheat and has been largely managed using demethylation inhibitor (DMI) fungicide triadimefon in China. To determine the sensitivity of Pst, a Chinese Pst isolate and its sexually produced progeny isolates were tested with triadimefon using the detached leaf method. The half maximal effective concentration (EC₅₀) values varied greatly among the progeny isolates, ranging from 0.06 mg L^–1 to 7.89 mg L^–1. Twenty-six of the 56 tested progeny isolates were less sensitive to triadimefon than the parental isolate. A single-nucleotide mutation at the 401 position resulting in an amino acid change from tyrosine (Y) to phenylalanine (F) in the 134th codon (Y134F) of the cytochrome P450 sterol 14a-demethylase enzyme (CYP51), the target gene of DMI fungicide, was identified in the parental isolate. The 87 tested progeny isolates segregated into 19 homozygous wild type (AA), 40 heterozygous (AT), and 28 homozygous mutant (TT) genotypes, fitting a 1:2:1 ratio (χ² = 2.43; P = 0.30). The mutant isolates had higher EC₅₀ values than the wild type isolates. Significant differences in logEC₅₀ were found between the mutant isolates and the wild type isolates (P = 2.2e^–16). However, homozygous and heterozygous mutant isolates were not significantly different (P = 0.21), indicating dominant mutation. Twenty-two progeny isolates were used to inoculate a susceptible wheat variety, and latency period and lesion growth were recorded to compare wild type and mutant isolates for the pathogenicity fitness components. A moderate but significant negative correlation was detected between lesion growth and sensitivity to triadimefon (r = −0.53; P = 0.01). No significant variation in lesion growth was found between homozygous and heterozygous mutant isolates (P = 0.83). In the case of latency period and triadimefon sensitivity, no significant correlation was found (P = 0.17). These results are useful for understanding reduced sensitivity in the pathogen population and improving stripe rust management.

Antifungal Activities of Bacillus subtilis Lipopeptides to Two Venturia inaequalis Strains Possessing Different Tebuconazole Sensitivity

Within the framework of biocontrol development, three natural substances produced by Bacillus subtilis, called lipopeptides, have been studied: fengycin (F), surfactin (S), and mycosubtilin (M). Their antifungal properties were tested in vitro, in liquid medium, on two strains of Venturia inaequalis, ascomycete fungi causing apple scab. These two strains were, respectively sensitive and less sensitive to tebuconazole, an active substance of the triazole family. These three molecules were tested on their own, in binary (FS, FM, SM) and ternary mixtures (FSM). The antifungal activities of lipopeptides were estimated by calculating an IC₅₀, compared to tebuconazole chemical substance. In tests involving the sensitive strain, all lipopeptide modalities exhibited antifungal activity. However, modalities involving fengycin and its mixtures exhibited the best antifungal activities; the activity of fengycin alone being very similar to that of tebuconazole. Interestingly, regarding the strain with reduced sensitivity to tebuconazole, surfactin and fengycin alone were not efficient while mycosubtilin and the different mixtures showed interesting antifungal activities. Specifically, the antifungal activity of FS and FSM mixture were equivalent to that of tebuconazole. For both fungal strains, microscopic observations revealed important morphological modifications in the presence of fengycin and in a less important proportion in the presence of surfactin but not in the presence of mycosubtilin. Overall, this study highlights the diversity in mode of action of lipopeptides on apple scab strains.

Genomic and transcriptome identification of fluconazole-resistant genes for Trichosporon asahii

Trichosporon asahii infection is difficult to control clinically. This study identified a case with over 15 years of T. asahii infection-related systemic dissemination disease and conducted genome and transcriptome sequencing to identify fluconazole-resistant genes in fluconazole-resistant versus susceptible strains isolated from this patient's facial skin lesions. The data revealed mutations of the ergosterol biosynthetic pathway-related genes in the T. asahii genome of the fluconazole-resistant strain, that is, there were 36 novel mutations of the ERG11 gene, three point mutations (V458L, D457V, and D334S) in the ERG3, and a missense mutation (E349D) in ERG5 in the fluconazole-resistant strain of the T. asahii genome. To ensure that ERG11 is responsible for the fluconazole resistance, we thus simultaneously cultured the strains in vitro and cloned the ERG11 CDS sequences of both fluconazole-susceptible and -resistant strains into the Saccharomyces cerevisiae. These experiments confirmed that these mutations of ERG11 gene affected fluconazole resistance (&gt; 64 μg/ml vs. &lt;8 μg/ml of the MIC value between fluconazole-resistant and -susceptible strains) in Saccharomyces cerevisiae. In addition, expression of ergosterol biosynthesis pathway genes and drug transporter was upregulated in the fluconazole-resistant strain of T. asahii. Collectively, the fluconazole resistance in this female patient was associated with mutations of ERG11, ERG3, and ERG5 and the differential expression of drug transporter and fatty acid metabolic genes.

Fungal Lanosterol 14α-demethylase: A target for next-generation antifungal design

The cytochrome P450 enzyme lanosterol 14α-demethylase (LDM) is the target of the azole antifungals used widely in medicine and agriculture as prophylaxis or treatments of infections or diseases caused by fungal pathogens. These drugs and agrochemicals contain an imidazole, triazole or tetrazole substituent, with one of the nitrogens in the azole ring coordinating as the sixth axial ligand to the LDM heme iron. Structural studies show that this membrane bound enzyme contains a relatively rigid ligand binding pocket comprised of a deeply buried heme-containing active site together with a substrate entry channel and putative product exit channel that reach to the membrane. Within the ligand binding pocket the azole antifungals have additional affinity determining interactions with hydrophobic side-chains, the polypeptide backbone and via water-mediated hydrogen bond networks. This review will describe the tools that can be used to identify and characterise the next generation of antifungals targeting LDM, with the goal of obtaining highly potent broad-spectrum fungicides that will be able to avoid target and drug efflux mediated antifungal resistance.

Can Saccharomyces cerevisiae keep up as a model system in fungal azole susceptibility research?

The difficulty of manipulation and limited availability of genetic tools for use in many pathogenic fungi hamper fast and adequate investigation of cellular metabolism and consequent possibilities for antifungal therapies. S. cerevisiae is a model organism that is used to study many eukaryotic systems. In this review, we analyse the potency and relevance of this model system in investigating fungal susceptibility to azole drugs. Although many of the concepts apply to multiple pathogenic fungi, for the sake of simplicity, we will focus on the validity of using S. cerevisiae as a model organism for two Candida species, C. albicans and C. glabrata. Apart from the general benefits, we explore how S. cerevisiae can specifically be used to improve our knowledge on azole drug resistance and enables fast and efficient screening for novel drug targets in combinatorial therapy. We consider the shortcomings of the model system, yet conclude that it is still opportune to use S. cerevisiae as a model system for pathogenic fungi in this era.

CYP51 as drug targets for fungi and protozoan parasites: past, present and future

The efficiency of treatment of human infections with the unicellular eukaryotic pathogens such as fungi and protozoa remains deeply unsatisfactory. For example, the mortality rates from nosocomial fungemia in critically ill, immunosuppressed or post-cancer patients often exceed 50%. A set of six systemic clinical azoles [sterol 14α-demethylase (CYP51) inhibitors] represents the first-line antifungal treatment. All these drugs were discovered empirically, by monitoring their effects on fungal cell growth, though it had been proven that they kill fungal cells by blocking the biosynthesis of ergosterol in fungi at the stage of 14α-demethylation of the sterol nucleus. This review briefs the history of antifungal azoles, outlines the situation with the current clinical azole-based drugs, describes the attempts of their repurposing for treatment of human infections with the protozoan parasites that, similar to fungi, also produce endogenous sterols, and discusses the most recently acquired knowledge on the CYP51 structure/function and inhibition. It is our belief that this information should be helpful in shifting from the traditional phenotypic screening to the actual target-driven drug discovery paradigm, which will rationalize and substantially accelerate the development of new, more efficient and pathogen-oriented CYP51 inhibitors.

Sterol 14α-Demethylase Structure-Based Design of VNI (( R)- N-(1-(2,4-Dichlorophenyl)-2-(1 H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide)) Derivatives To Target Fungal Infections: Synthesis, Biological Evaluation, and Crystallographic Analysis

Because of the increase in the number of immunocompromised patients, the incidence of invasive fungal infections is growing, but the treatment efficiency remains unacceptably low. The most potent clinical systemic antifungals (azoles) are the derivatives of two scaffolds: ketoconazole and fluconazole. Being the safest antifungal drugs, they still have shortcomings, mainly because of pharmacokinetics and resistance. Here, we report the successful use of the target fungal enzyme, sterol 14α-demethylase (CYP51), for structure-based design of novel antifungal drug candidates by minor modifications of VNI [( R)- N-(1-(2,4-dichlorophenyl)-2-(1 H-imidazol-1-yl)ethyl)-4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzamide)], an inhibitor of protozoan CYP51 that cures Chagas disease. The synthesis of fungi-oriented VNI derivatives, analysis of their potencies to inhibit CYP51s from two major fungal pathogens ( Aspergillus fumigatus and Candida albicans), microsomal stability, effects in fungal cells, and structural characterization of A. fumigatus CYP51 in complexes with the most potent compound are described, offering a new antifungal drug scaffold and outlining directions for its further optimization.

The Tetrazole VT-1161 Is a Potent Inhibitor of Trichophyton rubrum through Its Inhibition of T. rubrum CYP51

Prior to characterization of antifungal inhibitors that target CYP51, Trichophyton rubrum CYP51 was expressed in Escherichia coli, purified, and characterized. T. rubrum CYP51 bound lanosterol, obtusifoliol, and eburicol with similar affinities (dissociation constant [K_d ] values, 22.7, 20.3, and 20.9 μM, respectively) but displayed substrate specificity, insofar as only eburicol was demethylated in CYP51 reconstitution assays (turnover number, 1.55 min^-1; K_m value, 2 μM). The investigational agent VT-1161 bound tightly to T. rubrum CYP51 (K_d = 242 nM) with an affinity similar to that of clotrimazole, fluconazole, ketoconazole, and voriconazole (K_d values, 179, 173, 312, and 304 nM, respectively) and with an affinity lower than that of itraconazole (K_d = 53 nM). Determinations of 50% inhibitory concentrations (IC₅₀s) using 0.5 μM CYP51 showed that VT-1161 was a tight-binding inhibitor of T. rubrum CYP51 activity, yielding an IC₅₀ of 0.14 μM, whereas itraconazole, fluconazole, and ketoconazole had IC₅₀s of 0.26, 0.4, and 0.6 μM, respectively. When the activity of VT-1161 was tested against 34 clinical isolates, VT-1161 was a potent inhibitor of T. rubrum growth, with MIC₅₀, MIC₉₀, and geometric mean MIC values of ≤0.03, 0.06, and 0.033 μg ml^-1, respectively. With its selectivity versus human CYP51 and drug-metabolizing cytochrome P450s having already been established, VT-1161 should prove to be safe and effective in combating T. rubrum infections in patients.

Functional analysis of two sterol regulatory element binding proteins in Penicillium digitatum

The sterol regulatory element binding proteins (SREBPs) are key regulators for sterol homeostasis in most fungi. In the citrus postharvest pathogen Penicillium digitatum, the SREBP homolog is required for fungicide resistance and regulation of CYP51 expression. In this study, we identified another SREBP transcription factor PdSreB in P. digitatum, and the biological functions of both SREBPs were characterized and compared. Inactivation of PdsreA, PdsreB or both genes in P. digitatum reduced ergosterol contents and increased sensitivities to sterol 14-α-demethylation inhibitors (DMIs) and cobalt chloride. Fungal strains impaired at PdsreA but not PdsreB increased sensitivity to tridemorph and an iron chelator 2,2'-dipyridyl. Virulence assays on citrus fruit revealed that fungal strains impaired at PdsreA, PdsreB or both induce maceration lesions similar to those induced by wild-type. However, ΔPdsreA, ΔPdsreB or the double mutant strain rarely produce aerial mycelia on infected citrus fruit peels. RNA-Seq analysis showed the broad regulatory functions of both SREBPs in biosynthesis, transmembrane transportation and stress responses. Our results provide new insights into the conserved and differentiated regulatory functions of SREBP homologs in plant pathogenic fungi.

The Hsp90 Co-chaperones Sti1, Aha1, and P23 Regulate Adaptive Responses to Antifungal Azoles

Heat Shock Protein 90 (Hsp90) is essential for tumor progression in humans and drug resistance in fungi. However, the roles of its many co-chaperones in antifungal resistance are unknown. In this study, by susceptibility test of Neurospora crassa mutants lacking each of 18 Hsp90/Calcineurin system member genes (including 8 Hsp90 co-chaperone genes) to antifungal drugs and other stresses, we demonstrate that the Hsp90 co-chaperones Sti1 (Hop1 in yeast), Aha1, and P23 (Sba1 in yeast) were required for the basal resistance to antifungal azoles and heat stress. Deletion of any of them resulted in hypersensitivity to azoles and heat. Liquid chromatography-mass spectrometry (LC-MS) analysis showed that the toxic sterols eburicol and 14α-methyl-3,6-diol were significantly accumulated in the sti1 and p23 deletion mutants after ketoconazole treatment, which has been shown before to led to cell membrane stress. At the transcriptional level, Aha1, Sti1, and P23 positively regulate responses to ketoconazole stress by erg11 and erg6, key genes in the ergosterol biosynthetic pathway. Aha1, Sti1, and P23 are highly conserved in fungi, and sti1 and p23 deletion also increased the susceptibility to azoles in Fusarium verticillioides. These results indicate that Hsp90-cochaperones Aha1, Sti1, and P23 are critical for the basal azole resistance and could be potential targets for developing new antifungal agents.

Mitochondrial Complex I Is a Global Regulator of Secondary Metabolism, Virulence and Azole Sensitivity in Fungi

Recent estimates of the global burden of fungal disease suggest that that their incidence has been drastically underestimated and that mortality may rival that of malaria or tuberculosis. Azoles are the principal class of antifungal drug and the only available oral treatment for fungal disease. Recent occurrence and increase in azole resistance is a major concern worldwide. Known azole resistance mechanisms include over—expression of efflux pumps and mutation of the gene encoding the target protein cyp51a, however, for one of the most important fungal pathogens of humans, Aspergillus fumigatus, much of the observed azole resistance does not appear to involve such mechanisms. Here we present evidence that azole resistance in A. fumigatus can arise through mutation of components of mitochondrial complex I. Gene deletions of the 29.9KD subunit of this complex are azole resistant, less virulent and exhibit dysregulation of secondary metabolite gene clusters in a manner analogous to deletion mutants of the secondary metabolism regulator, LaeA. Additionally we observe that a mutation leading to an E180D amino acid change in the 29.9 KD subunit is strongly associated with clinical azole resistant A. fumigatus isolates. Evidence presented in this paper suggests that complex I may play a role in the hypoxic response and that one possible mechanism for cell death during azole treatment is a dysfunctional hypoxic response that may be restored by dysregulation of complex I. Both deletion of the 29.9 KD subunit of complex I and azole treatment alone profoundly change expression of gene clusters involved in secondary metabolism and immunotoxin production raising potential concerns about long term azole therapy.

The lysine biosynthetic enzyme Lys4 influences iron metabolism, mitochondrial function and virulence in Cryptococcus neoformans

The lysine biosynthesis pathway via α-aminoadipate in fungi is considered an attractive target for antifungal drugs due to its absence in mammalian hosts. The iron-sulfur cluster-containing enzyme homoaconitase converts homocitrate to homoisocitrate in the lysine biosynthetic pathway, and is encoded by LYS4 in the model yeast Saccharomyces cerevisiae. In this study, we identified the ortholog of LYS4 in the human fungal pathogen, Cryptococcus neoformans, and found that LYS4 expression is regulated by iron levels and by the iron-related transcription factors Hap3 and HapX. Deletion of the LYS4 gene resulted in lysine auxotrophy suggesting that Lys4 is essential for lysine biosynthesis. Our study also revealed that lysine uptake was mediated by two amino acid permeases, Aap2 and Aap3, and influenced by nitrogen catabolite repression (NCR). Furthermore, the lys4 mutant showed increased sensitivity to oxidative stress, agents that challenge cell wall/membrane integrity, and azole antifungal drugs. We showed that these phenotypes were due in part to impaired mitochondrial function as a result of LYS4 deletion, which we propose disrupts iron homeostasis in the organelle. The combination of defects are consistent with our observation that the lys4 mutant was attenuated virulence in a mouse inhalation model of cryptococcosis.

Triazole resistance mediated by mutations of a conserved active site tyrosine in fungal lanosterol 14α-demethylase

Emergence of fungal strains showing resistance to triazole drugs can make treatment of fungal disease problematic. Triazole resistance can arise due to single mutations in the drug target lanosterol 14α-demethylase (Erg11p/CYP51). We have determined how commonly occurring single site mutations in pathogenic fungi affect triazole binding using Saccharomyces cerevisiae Erg11p (ScErg11p) as a target surrogate. The mutations Y140F/H were introduced into full-length hexahistidine-tagged ScErg11p. Phenotypes and high-resolution X-ray crystal structures were determined for the mutant enzymes complexed with short-tailed (fluconazole and voriconazole) or long-tailed (itraconazole and posaconazole) triazoles and wild type enzyme complexed with voriconazole. The mutations disrupted a water-mediated hydrogen bond network involved in binding of short-tailed triazoles, which contain a tertiary hydroxyl not present in long-tailed triazoles. This appears to be the mechanism by which resistance to these short chain azoles occurs. Understanding how these mutations affect drug affinity will aid the design of azoles that overcome resistance.

Fragment-Based Approaches to the Development of Mycobacterium tuberculosis CYP121 Inhibitors

The essential enzyme CYP121 is a target for drug development against antibiotic resistant strains of Mycobacterium tuberculosis. A triazol-1-yl phenol fragment 1 was identified to bind to CYP121 using a cascade of biophysical assays. Synthetic merging and optimization of 1 produced a 100-fold improvement in binding affinity, yielding lead compound 2 (KD = 15 μM). Deconstruction of 2 into its component retrofragments allowed the group efficiency of structural motifs to be assessed, the identification of more LE scaffolds for optimization and highlighted binding affinity hotspots. Structure-guided addition of a metal-binding pharmacophore onto LE retrofragment scaffolds produced low nanomolar (KD = 15 nM) CYP121 ligands. Elaboration of these compounds to target binding hotspots in the distal active site afforded compounds with excellent selectivity against human drug-metabolizing P450s. Analysis of the factors governing ligand potency and selectivity using X-ray crystallography, UV-vis spectroscopy, and native mass spectrometry provides insight for subsequent drug development.

The Aspergillus fumigatus Damage Resistance Protein Family Coordinately Regulates Ergosterol Biosynthesis and Azole Susceptibility

Ergosterol is a major and specific component of the fungal plasma membrane, and thus, the cytochrome P450 enzymes (Erg proteins) that catalyze ergosterol synthesis have been selected as valuable targets of azole antifungals. However, the opportunistic pathogen Aspergillus fumigatus has developed worldwide resistance to azoles largely through mutations in the cytochrome P450 enzyme Cyp51 (Erg11). In this study, we demonstrate that a cytochrome b₅-like heme-binding damage resistance protein (Dap) family, comprised of DapA, DapB, and DapC, coordinately regulates the functionality of cytochrome P450 enzymes Erg5 and Erg11 and oppositely affects susceptibility to azoles. The expression of all three genes is induced in an azole concentration-dependent way, and the decreased susceptibility to azoles requires DapA stabilization of cytochrome P450 protein activity. In contrast, overexpression of DapB and DapC causes dysfunction of Erg5 and Erg11, resulting in abnormal accumulation of sterol intermediates and further accentuating the sensitivity of ΔdapA strains to azoles. The results of exogenous-hemin rescue and heme-binding-site mutagenesis experiments demonstrate that the heme binding of DapA contributes the decreased azole susceptibility, while DapB and -C are capable of reducing the activities of Erg5 and Erg11 through depletion of heme. In vivo data demonstrate that inactivated DapA combined with activated DapB yields an A. fumigatus mutant that is easily treatable with azoles in an immunocompromised mouse model of invasive pulmonary aspergillosis. Compared to the single Dap proteins found in Saccharomyces cerevisiae and Schizosaccharomyces pombe, we suggest that this complex Dap family regulatory system emerged during the evolution of fungi as an adaptive means to regulate ergosterol synthesis in response to environmental stimuli.

Knowledge of the ergosterol biosynthesis route in fungal pathogens is useful in the design of new antifungal drugs and could aid in the study of antifungal-drug resistance mechanisms. In this study, we demonstrate that three cytochrome b₅-like Dap proteins coordinately regulate the azole resistance and ergosterol biosynthesis catalyzed by cytochrome P450 proteins. Our new insights into the Dap regulatory system in fungal pathogens may have broad therapeutic ramifications beyond their usefulness for classic azole antifungals. Moreover, our elucidation of the molecular mechanism of Dap regulation of cytochrome P450 protein functionality through heme-binding activity may extend beyond the Kingdom Fungi with applicability toward Dap protein regulation of mammalian sterol synthesis.

Divergence of Antiangiogenic Activity and Hepatotoxicity of Different Stereoisomers of Itraconazole

PURPOSE

Itraconazole is a triazole antifungal drug that has recently been found to inhibit angiogenesis. Itraconazole is a relatively well-tolerated drug but shows hepatotoxicity in a small subset of patients. Itraconazole contains three chiral centers and the commercial itraconazole is composed of four cis-stereoisomers (named IT-A, IT-B, IT-C, and IT-D). We sought to determine whether the stereoisomers of itraconazole might differ in their antiangiogenic activity and hepatotoxicity.

EXPERIMENTAL DESIGN

We assessed in vitro antiangiogenic activity of itraconazole and each stereoisomer using human umbilical vein endothelial cell (HUVEC) proliferation and tube formation assays. We also determined their hepatotoxicity using primary human hepatocytes in vitro and a mouse model in vivo Mouse Matrigel plug and tumor xenograft models were used to evaluate in vivo antiangiogenic and antitumor activities of the stereoisomers.

RESULTS

Of the four stereoisomers contained in commercial itraconazole, we found that IT-A (2S,4R,2'R) and IT-C (2S,4R,2'S) were more potent for inhibition of angiogenesis than IT-B (2R,4S,2'R) and IT-D (2R,4S,2'S). Interestingly, IT-A and IT-B were more hepatotoxic than IT-C and IT-D. In mouse models, IT-C showed more potent antiangiogenic/antitumor activity with lower hepatotoxicity compared with itraconazole and IT-A.

CONCLUSIONS

These results demonstrate the segregation of influence of stereochemistry at different positions of itraconazole on its antiangiogenic activity and hepatotoxicity, with the 2 and 4 positions affecting the former and the 2' position affecting the latter. They also suggest that IT-C may be superior to the racemic mixture of itraconazole as an anticancer drug candidate due to its lower hepatotoxicity and improved antiangiogenic activity. Clin Cancer Res; 22(11); 2709-20. ©2016 AACR.

The Y137H mutation of VvCYP51 gene confers the reduced sensitivity to tebuconazole in Villosiclava virens

Management of rice false smut disease caused by Villosiclava virens is dependent on demethylation inhibitor (DMI) fungicides. Investigation of molecular mechanisms of resistance is therefore of upmost importance. In this study the gene encoding the target protein for DMI fungicides (VvCYP51) was cloned and investigated. The VvCYP51 gene in the resistant mutant revealed both a change from tyrosine to histidine at position 137 (Y137H) and elevated gene expression compared to the parental isolate. In order to determine which of these mechanisms was responsible for the reduced sensitivity to DMI fungicide tebuconazole, transformants expressing the mutated or the wild type VvCYP51 gene were generated. Transformants carrying the mutated gene were more resistant to tebuconazole compared to control transformants lacking the mutation, but the expression of the VvCYP51 gene was not significantly correlated with EC50 values. The wild type VvCYP51 protein exhibited stronger affinity for tebuconazole compared to the VvCYP51/Y137H in both molecular docking analysis and experimental binding assays. The UV-generated mutant as well as transformants expressing the VvCYP51/Y137H did not exhibit significant fitness penalties based on mycelial growth and spore germination, suggesting that isolates resistant to DMI fungicides based on the Y137H mutation may develop and be competitive in the field.

Application of clotrimazole via a novel controlled release device provides potent retinal protection

Age-related macular degeneration is the leading cause of legal blindness among older individuals. Therefore, the development of new therapeutic agents and optimum drug delivery systems for its treatment are crucial. In this study, we investigate whether clotrimazole (CLT) is capable of protecting retinal cells against oxidative-induced injury and the possible inhibitory effect of a sustained CLT-release device against light-induced retinal damage in rats. In vitro results indicated pretreatment of immortalized retinal pigment epithelium cells (RPE-J cells) with 10-50 µM CLT before exposure to oxygen/glucose deprivation conditions for 48 h decreased the extent of cell death, attenuated the percentage of reactive oxygen species-positive cells, and decreased the levels of cleaved caspase-3. The device consists of a separately fabricated reservoir, a CLT formulation, and a controlled release cover, which are made of poly(ethyleneglycol) dimethacrylate (PEGDM) and tri(ethyleneglycol) dimethacrylate (TEGDM). The release rate of CLT was successfully tuned by changing the ratio of PEGDM/TEGDM in the cover. In vivo results showed that use of a CLT-loaded device lessened the reduction of electroretinographic amplitudes after light exposure. These findings indicate that the application of a polymeric CLT-loaded device may be a promising method for the treatment of some retinal disorders.

Structural Insights into Binding of the Antifungal Drug Fluconazole to Saccharomyces cerevisiae Lanosterol 14α-Demethylase

Infections by fungal pathogens such as Candida albicans and Aspergillus fumigatus and their resistance to triazole drugs are major concerns. Fungal lanosterol 14α-demethylase belongs to the CYP51 class in the cytochrome P450 superfamily of enzymes. This monospanning bitopic membrane protein is involved in ergosterol biosynthesis and is the primary target of azole antifungal drugs, including fluconazole. The lack of high-resolution structural information for this drug target from fungal pathogens has been a limiting factor for the design of modified triazole drugs that will overcome resistance. Here we report the X-ray structure of full-length Saccharomyces cerevisiae lanosterol 14α-demethylase in complex with fluconazole at a resolution of 2.05 Å. This structure shows the key interactions involved in fluconazole binding and provides insight into resistance mechanisms by revealing a water-mediated hydrogen bonding network between the drug and tyrosine 140, a residue frequently found mutated to histidine or phenylalanine in resistant clinical isolates.

The A395T mutation in ERG11 gene confers fluconazole resistance in Candida tropicalis causing candidemia

The mechanism of fluconazole resistance in Candida tropicalis is still unclear. Recently, we isolated a fluconazole-resistant strain of C. tropicalis from the blood specimen of a patient with candidemia in China. In vitro antifungal susceptibility of the isolate was determined by using CLSI M27-A3 and E-test methods. The sequence of ERG11 gene was then analyzed, and the three-dimensional model of Erg11p encoded by ERG11 gene was also investigated. The sequencing of ERG11 gene revealed the mutation of A395T in this fluconazole-resistant isolate of C. tropicalis, resulting in the Y132F substitution in Erg11p. Sequence alignment and three-dimensional model comparison of Erg11ps showed high similarity between fluconazole-susceptible isolates of C. tropicalis and Candida albicans. The comparison of the three-dimensional models of Erg11ps demonstrated that the position of the Y132F substitution in this isolate of C. tropicalis is identical to the isolate of C. albicans with fluconazole resistance resulting from Y132F substitution in Erg11p. Hence, we ascertain that the Y132F substitution of Erg11p caused by A395T mutation in ERG11 gene confers the fluconazole resistance in C. tropicalis.

Improvement of experimental testing and network training conditions with genome-wide microarrays for more accurate predictions of drug gene targets

Background

Genome-wide microarrays have been useful for predicting chemical-genetic interactions at the gene level. However, interpreting genome-wide microarray results can be overwhelming due to the vast output of gene expression data combined with off-target transcriptional responses many times induced by a drug treatment. This study demonstrates how experimental and computational methods can interact with each other, to arrive at more accurate predictions of drug-induced perturbations. We present a two-stage strategy that links microarray experimental testing and network training conditions to predict gene perturbations for a drug with a known mechanism of action in a well-studied organism.

Results

S. cerevisiae cells were treated with the antifungal, fluconazole, and expression profiling was conducted under different biological conditions using Affymetrix genome-wide microarrays. Transcripts were filtered with a formal network-based method, sparse simultaneous equation models and Lasso regression (SSEM-Lasso), under different network training conditions. Gene expression results were evaluated using both gene set and single gene target analyses, and the drug’s transcriptional effects were narrowed first by pathway and then by individual genes. Variables included: (i) Testing conditions – exposure time and concentration and (ii) Network training conditions – training compendium modifications. Two analyses of SSEM-Lasso output – gene set and single gene – were conducted to gain a better understanding of how SSEM-Lasso predicts perturbation targets.

Conclusions

This study demonstrates that genome-wide microarrays can be optimized using a two-stage strategy for a more in-depth understanding of how a cell manifests biological reactions to a drug treatment at the transcription level. Additionally, a more detailed understanding of how the statistical model, SSEM-Lasso, propagates perturbations through a network of gene regulatory interactions is achieved.

Activity of imidazole compounds on Leishmania (L.) infantum chagasi: reactive oxygen species induced by econazole

Drug repositioning has been considered a promising approach to discover novel treatments against neglected diseases. Among the major protozoan diseases, leishmaniasis remains a public health threat with few therapeutic alternatives, affecting 12 million people in 98 countries. In this study, we report the in vitro antileishmanial activity of the imidazole drugs clotrimazole, and for the first time in literature, econazole and bifonazole and their potential action to affect the regulation of reactive oxygen species (ROS) of the parasites. The lethal action of the imidazoles was investigated using spectrofluorimetric techniques to detect ROS content, plasma membrane permeability, and mitochondrial membrane potential. The imidazoles showed activity against L. (L.) infantum chagasi promastigotes with IC50 values in a range of 2-8 μM; econazole was also effective against Leishmania intracellular amastigotes, with an IC50 value of 11 μM, a similar in vitro effectiveness to miltefosine. Leishmania promastigotes rapidly up-regulated the ROS release after incubation with the imidazoles, but econazole showed a marked increase in ROS content of approximately 1,900 % higher than untreated parasites. When using SYTOX(®) Green as a fluorescent probe, the imidazoles demonstrated considerable interference in plasma membrane permeability at the early time of incubation; econazole resulted in the higher influx of SYTOX(®) Green at 60 min. Despite cellular alterations, no depolarization could be observed to the mitochondrial membrane potential of Leishmania until 60 min. The lethal action of econazole involved strong permeabilization of plasma membrane of promastigotes, with an overloaded ROS content that contributed to the death of parasites. Affecting the ROS regulation of Leishmania via small molecules would be an interesting strategy for new drugs.

Identification, modeling and ligand affinity of early deuterostome CYP51s, and functional characterization of recombinant zebrafish sterol 14α-demethylase

BACKGROUND

Sterol 14α-demethylase (cytochrome P450 51, CYP51, P45014DM) is a microsomal enzyme that in eukaryotes catalyzes formation of sterols essential for cell membrane function and as precursors in biosynthesis of steroid hormones. Functional properties of CYP51s are unknown in non-mammalian deuterostomes.

METHODS

PCR-cloning and sequencing and computational analyses (homology modeling and docking) addressed CYP51 in zebrafish Danio rerio, the reef fish sergeant major Abudefduf saxatilis, and the sea urchin Strongylocentrotus purpuratus. Following N-terminal amino acid modification, zebrafish CYP51 was expressed in Escherichia coli, and lanosterol 14α-demethylase activity and azole inhibition of CYP51 activity were characterized using GC-MS.

RESULTS

Molecular phylogeny positioned S. purpuratus CYP51 at the base of the deuterostome clade. In zebrafish, CYP51 is expressed in all organs examined, most strongly in intestine. The recombinant protein bound lanosterol and catalyzed 14α-demethylase activity, at 3.2nmol/min/nmol CYP51. The binding of azoles to zebrafish CYP51 gave KS (dissociation constant) values of 0.26μM for ketoconazole and 0.64μM for propiconazole. Displacement of carbon monoxide also indicated zebrafish CYP51 has greater affinity for ketoconazole. Docking to homology models showed that lanosterol docks in fish and sea urchin CYP51s with an orientation essentially the same as in mammalian CYP51s. Docking of ketoconazole indicates it would inhibit fish and sea urchin CYP51s.

CONCLUSIONS

Biochemical and computational analyses are consistent with lanosterol being a substrate for early deuterostome CYP51s.

GENERAL SIGNIFICANCE

The results expand the phylogenetic view of animal CYP51, with evolutionary, environmental and therapeutic implications.

Photosensitizing medications and photocarcinogenesis

Photosensitivity is an exaggerated or abnormal response to ultraviolet (UV) or visible light exposure. Many current medications are known photosensitizers; however, the effects of the sensitization can be subclinical and go unnoticed by the person affected. While some of these drugs are used for short and defined periods, others are used indefinitely for the treatment of chronic disease. The question of whether either of these practices translates into an increased risk of skin cancer is an important one. Numerous medications have real, distinct and well-elucidated mechanisms that potentiate the development of skin cancer, while with some medications the mechanism for the observed carcinogenesis remains unclear. In this article we will discuss the clinical, mechanistic and epidemiological evidence supporting photochemical genotoxicity and carcinogenesis.