Prothioconazole and prothioconazole-desthio activities against Candida albicans sterol 14-α-demethylase

Genetic interaction analysis of Candida glabrata transcription factors CST6 and UPC2A in the regulation of respiration and fluconazole susceptibility

Candida glabrata is the second most common cause of invasive candidiasis and is widely known to have reduced susceptibility to fluconazole relative to many other Candida spp. Upc2A is a transcription factor that regulates ergosterol biosynthesis gene expression under conditions of sterol stress such as azole drug treatment or hypoxia. Through an in vitro microevolution experiment, we found that loss-of-function mutants of the ATF/CREB transcription factor CST6 suppresses the fluconazole hyper-susceptibility of the upc2A∆ mutant. Here, we confirm that the cst6∆ upc2A∆ mutants are resistant to fluconazole but not to hypoxia relative to the upc2A∆ mutant. Sterol analysis of these mutants indicates that this suppression phenotype is not due to restoration of ergosterol levels in the cst6∆ upc2A∆ mutant. Furthermore, increased expression of CDR1, the efflux pump implicated in the vast majority of azole-resistant C. glabrata strains, does not account for the suppression phenotype. Instead, our data suggest that this effect is due in part to increased expression of the adhesin EPA3, which has been shown by others to reduce fluconazole susceptibility in C. glabrata. In addition, we find that loss of both UPC2A and CST6 reduces the expression of mitochondrial and respiratory genes and that this also contributes to the suppression phenotype as well as to the resistance of cst6∆ to fluconazole. These latter data further emphasize the connection between mitochondrial function and azole susceptibility.

Multiple routes to fungicide resistance: Interaction of Cyp51 gene sequences, copy number and expression

We examined the molecular basis of triazole resistance in Blumeria graminis f. sp. tritici (wheat mildew, Bgt), a model organism among powdery mildews. Four genetic models for responses to triazole fungicides were identified among US and UK isolates, involving multiple genetic mechanisms. Firstly, only two amino acid substitutions in CYP51B lanosterol demethylase, the target of triazoles, were associated with resistance, Y136F and S509T (homologous to Y137F and S524T in the reference fungus Zymoseptoria tritici). As sequence variation did not explain the wide range of resistance, we also investigated Cyp51B copy number and expression, the latter using both reverse transcription-quantitative PCR and RNA-seq. The second model for resistance involved higher copy number and expression in isolates with a resistance allele; thirdly, however, moderate resistance was associated with higher copy number of wild-type Cyp51B in some US isolates. A fourth mechanism was heteroallelism with multiple alleles of Cyp51B. UK isolates, with significantly higher mean resistance than their US counterparts, had higher mean copy number, a high frequency of the S509T substitution, which was absent from the United States, and in the most resistant isolates, heteroallelism involving both sensitivity residues Y136+S509 and resistance residues F136+T509. Some US isolates were heteroallelic for Y136+S509 and F136+S509, but this was not associated with higher resistance. The obligate biotrophy of Bgt may constrain the tertiary structure and thus the sequence of CYP51B, so other variation that increases resistance may have a selective advantage. We describe a process by which heteroallelism may be adaptive when Bgt is intermittently exposed to triazoles.

Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within the Mucor species complex

Mucormycoses are emerging fungal infections caused by a variety of heterogeneous species within the Mucorales order. Among the Mucor species complex, Mucor circinelloides is the most frequently isolated pathogen in mucormycosis patients and despite its clinical significance, there is an absence of established genome manipulation techniques to conduct molecular pathogenesis studies. In this study, we generated a spontaneous uracil auxotrophic strain and developed a genetic transformation procedure to analyze molecular mechanisms conferring antifungal drug resistance. With this new model, phenotypic analyses of gene deletion mutants were conducted to define Erg3 and Erg6a as key biosynthetic enzymes in the M. circinelloides ergosterol pathway. Erg3 is a C-5 sterol desaturase involved in growth, sporulation, virulence, and azole susceptibility. In other fungal pathogens, erg3 mutations confer azole resistance because Erg3 catalyzes the production of a toxic diol upon azole exposure. Surprisingly, M. circinelloides produces only trace amounts of this toxic diol and yet, it is still susceptible to posaconazole and isavuconazole due to alterations in membrane sterol composition. These alterations are severely aggravated by erg3Δ mutations, resulting in ergosterol depletion and, consequently, hypersusceptibility to azoles. We also identified Erg6a as the main C-24 sterol methyltransferase, whose activity may be partially rescued by the paralogs Erg6b and Erg6c. Loss of Erg6a function diverts ergosterol synthesis to the production of cholesta-type sterols, resulting in resistance to amphotericin B. Our findings suggest that mutations or epimutations causing loss of Erg6 function may arise during human infections, resulting in antifungal drug resistance to first-line treatments against mucormycosis.

IMPORTANCE

The Mucor species complex comprises a variety of opportunistic pathogens known to cause mucormycosis, a potentially lethal fungal infection with limited therapeutic options. The only effective first-line treatments against mucormycosis consist of liposomal formulations of amphotericin B and the triazoles posaconazole and isavuconazole, all of which target components within the ergosterol biosynthetic pathway. This study uncovered M. circinelloides Erg3 and Erg6a as key enzymes to produce ergosterol, a vital constituent of fungal membranes. Absence of any of those enzymes leads to decreased ergosterol and consequently, resistance to ergosterol-binding polyenes such as amphotericin B. Particularly, losing Erg6a function poses a higher threat as the ergosterol pathway is channeled into alternative sterols similar to cholesterol, which maintain membrane permeability. As a result, erg6a mutants survive within the host and disseminate the infection, indicating that Erg6a deficiency may arise during human infections and confer resistance to the most effective treatment against mucormycoses.

Alternative ergosterol biosynthetic pathways confer antifungal drug resistance in the human pathogens within the Mucor species complex

Mucormycoses are emerging fungal infections caused by a variety of heterogeneous species within the Mucorales order. Among the Mucor species complex, Mucor circinelloides is the most frequently isolated pathogen in mucormycosis patients and despite its clinical significance, there is an absence of established genome manipulation techniques to conduct molecular pathogenesis studies. In this study, we generated a spontaneous uracil auxotrophic strain and developed a genetic transformation procedure to analyze molecular mechanisms conferring antifungal drug resistance. With this new model, phenotypic analyses of gene deletion mutants were conducted to define Erg3 and Erg6a as key biosynthetic enzymes in the M. circinelloides ergosterol pathway. Erg3 is a C-5 sterol desaturase involved in growth, sporulation, virulence, and azole susceptibility. In other fungal pathogens, erg3 mutations confer azole resistance because Erg3 catalyzes the production of a toxic diol upon azole exposure. Surprisingly, M. circinelloides produces only trace amounts of this toxic diol and yet, it is still susceptible to posaconazole and isavuconazole due to alterations in membrane sterol composition. These alterations are severely aggravated by erg3Δ mutations, resulting in ergosterol depletion and consequently, hypersusceptibility to azoles. We also identified Erg6a as the main C-24 sterol methyltransferase, whose activity may be partially rescued by the paralogs Erg6b and Erg6c. Loss of Erg6a function diverts ergosterol synthesis to the production of cholesta-type sterols, resulting in resistance to amphotericin B. Our findings suggest that mutations or epimutations causing loss of Erg6 function may arise during human infections, resulting in antifungal drug resistance to first-line treatments against mucormycosis.

Azole fungicide sensitivity and molecular mechanisms of reduced sensitivity in Irish Pyrenopeziza brassicae populations

BACKGROUND

Light leaf spot, caused by Pyrenopeziza brassicae, is amongst the most damaging diseases of winter oilseed rape (Brassica napus), and currently the sterol 14α-demethylase (CYP51) inhibitors (azoles) represent the main class of fungicides used to control light leaf spot development. However, a shift in sensitivity to azole fungicides in P. brassicae populations has been observed in different European countries, including Ireland.

RESULTS

To assess the sensitivity status of Irish P. brassicae populations to azole fungicides, three collections of P. brassicae from 2018-2020 were tested in vitro against tebuconazole and prothioconazole-desthio, and the PbCYP51 gene targeted by this class of fungicides was genotyped in different isolates. A change in sensitivity to azole fungicides was observed and differences in sensitivity to tebuconazole between Irish populations were present. There were two substitutions within PbCYP51 (G460S and S508T) and inserts of different sizes in its promoter region. The presence of the G460S/S508T double mutant was reported for the first time, and the diversity in insert size was greater than previously known. Compared to wild type isolates, those carrying G460S or S508T were less sensitive to both fungicides and, where inserts were also identified, they further reduced sensitivity to azole fungicides.

CONCLUSIONS

The results of this study suggest that azole fungicides are still very effective in controlling light leaf spot in Ireland. However, using azole fungicides in mixtures of fungicides with different modes of action is recommended. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Photoredox-Driven Three-Component Coupling of Aryl Halides, Olefins, and O2

Modern organic synthesis requires methodologies that bring together abundant feedstock chemicals in a mild and efficient manner. To aid in this effort, we have developed a multicomponent radical hydroxyarylation reaction that utilizes aryl halides, olefins, and O2 as the reaction components. Crucial to this advance was an oxidative, rather than a reductive, approach to aryl radical generation, which enables reaction tolerance to O2. This methodology displays a broad functional group tolerance with a variety of functionalized aryl halides and a broad array of olefins. Development of this methodology enables rapid access to biologically relevant hydroxyaryl products from simple, commercially available starting materials.

Survey of prothioconazole sensitivity in Fusarium pseudograminearum isolates from Henan Province, China, and characterization of resistant laboratory mutants

BACKGROUND

Fusarium crown rot (FCR) is one of the most significant diseases limiting crop production in the Huanghuai wheat-growing region of China. Prothioconazole, a triazole sterol 14α-demethylation inhibitor (DMI) fungicide developed by the Bayer Crop Protection Company, is mainly registered for the prevention and control of wheat powdery mildew and stripe rust (China Pesticide Information Network). It is known to exhibit high activity against F. pseudograminearum, but further research, particularly regarding the potential for fungicide resistance, is required before it can be registered for the control of FCR in China.

RESULTS

The current study found that the baseline sensitivity of 67 field isolates of F. pseudograminearum collected between 2019 and 2021 ranged between 0.016-2.974 μg/mL, with an average EC50 value of 1.191 ± 0.720 μg/mL (mean ± SD). Although none of the field isolates exhibited signs of resistance, three highly resistant mutants were produced by repeated exposure to prothioconazole under laboratory conditions. All of the mutants were found to exhibit significantly reduced growth rates on potato dextrose agar (PDA), as well as reduced levels of sporulation, which indicated that there was a fitness cost associated with the resistance. However, inoculation of wounded wheat coleoptiles revealed that the pathogenicity of the resistant mutants was little affected or actually increased. Molecular analysis of the genes corresponding to the prothioconazole target protein, FpCYP51 (FpCYP51A, FpCYP51B, and FpCYP51C), indicated that the resistant mutants contained three conserved substitutions (M63I, A205S, and I246V) that were present in the FpCYP51C sequence of all three mutants, as well as several non-conserved substations in their FpCYP51A and FpCYP51B sequences. Expression analysis revealed that the presence of prothioconazole (0.1 μg/mL) generally resulted in reduced expression of the three FpCYP51 genes, but that the three mutants exhibited more complex patterns of expression that differed in comparison to their parental isolates. The study found no evidence of cross-resistance between prothioconazole and any of the fungicides tested including three DMI fungicides tebuconazole, prochloraz, and flutriafol.

CONCLUSIONS

Taken together these results not only provide new insight into the resistant mechanism and biological characteristics associated with prothioconazole resistance in F. pseudograminearum, but also strong evidence that prothioconazole could provide effective and sustained control of FCR, especially when applied in combination with other fungicides.

Establishing the extent of pesticide contamination in Irish agricultural soils

To establish meaningful and sustainable policy directives for sustainable pesticide use in agriculture, baseline knowledge of pesticide levels in soils is required. To address this, five pesticides and one metabolite widely used in Irish agriculture and five neonicotinoid compounds pesticides were screened from soils from 25 fields. These sites represented a diversity of soil and land use types. Prothioconazole was detected in 16 of the 18 sites where it had been recently applied, with the highest maximum concentration quantified of 46 μg/kg. However, a week after application only four fields had prothioconazole concentrations above the limit of quantification (LOQ). Fluroxypyr was applied in 11 sites but was not detected above LOQ. Glyphosate and AMPA were not detected. Interestingly, neonicotinoids were detected in 96% of all sampling sites, even though they were not reported as recently applied. Excluding neonicotinoids, 60% of sites were found to contain pesticide residues of compounds that were not previously applied, with boscalid and azoxystrobin detected in 15 of the 25 sites sampled. The total number of pesticides detected in Irish soils were significantly negatively correlated with clay fraction, while average pesticide concentrations were significantly positively correlated with log Kow values. 17 fields were found to have total pesticide concentrations in excess of 0.5 μg/kg, even when recently applied pesticides were removed from calculations. Theoretical consideration of quantified pesticides determined that azoxystrobin has high leaching risk, while boscalid, which was detected but not applied, has an accumulation risk. This information provides insight into the current level of pesticide contamination in Irish agricultural soil and contributes to the European-level effort to understand potential impacts of pesticide contamination in soil.

Structural modeling of cytochrome P450 51 from a deep-sea fish points to a novel structural feature in other CYP51s

Cytochromes P450 (CYP), enzymes involved in the metabolism of endogenous and xenobiotic substrates, provide an excellent model system to study how membrane proteins with unique functions have catalytically adapted through evolution. Molecular adaptation of deep-sea proteins to high hydrostatic pressure remains poorly understood. Herein, we have characterized recombinant cytochrome P450 sterol 14α-demethylase (CYP51), an essential enzyme of cholesterol biosynthesis, from an abyssal fish species, Coryphaenoides armatus. C. armatus CYP51 was heterologously expressed in Escherichia coli following N-terminal truncation and purified to homogeneity. Recombinant C. armatus CYP51 bound its sterol substrate lanosterol giving a Type I binding spectra (KD 15 μM) and catalyzed lanosterol 14α-demethylation turnover at 5.8 nmol/min/nmol P450. C. armatus CYP51 also bound the azole antifungals ketoconazole (KD 0.12 μM) and propiconazole (KD 0.54 μM) as determined by Type II absorbance spectra. Comparison of C. armatus CYP51 primary sequence and modeled structures with other CYP51s identified amino acid substitutions that may confer an ability to function under pressures of the deep sea and revealed heretofore undescribed internal cavities in human and other non-deep sea CYP51s. The functional significance of these cavities is not known. PROLOGUE: This paper is dedicated in memory of Michael Waterman and Tsuneo Omura, who as good friends and colleagues enriched our lives. They continue to inspire us.

Toxicokinetic and toxicodynamic mixture effects of plant protection products: A case study

Authorisation of ready to use plant protection products (PPPs) usually relies on the testing of acute and local toxicity only. This is in stark contrast to the situation for active substances where the mandatory data set comprises a most comprehensive set of studies. While the combination of certain active ingredients and co-formulants may nevertheless result in increased toxicity of the final product such combinations have never been evaluated systematically for complex and long-term toxicological endpoints. We therefore investigated the effect of three frequently used co-formulants on the toxicokinetic and toxicodynamic of the representative active substance combination of tebuconazol (Teb) and prothioconazol (Pro) or of cypermethrin (Cpm) and piperonyl butoxide (Pip), respectively. With all four active substances being potential liver steatogens, cytotoxicity and triglyceride accumulation in HepaRG were used as primary endpoints. Concomitantly transcriptomics and biochemical studies were applied to interrogate for effects on gene expression or inhibition of CYP3A4 as key enzyme for functionalization. Some of the tested combinations clearly showed more than additive effects, partly due to CYP3A4 enzyme inhibition. Other effects comprised the modulation of the expression and activity of steatosis-related nuclear key receptors. Altogether, the findings highlight the need for a more systematic consideration of toxicodynamic and toxicokinetic mixture effects during assessment of PPPs.

Mechanism and Kinetics of Prothioconazole Photodegradation in Aqueous Solution

This study investigated the effects of light source, pH value, and NO₃^- concentration on the photodegradation of prothioconazole in aqueous solution. The half-life (t_1/2) of prothioconazole was 173.29, 21.66, and 11.18 min under xenon, ultraviolet, and high-pressure mercury lamps, respectively. At pH values of 4.0, 7.0, and 9.0 under a xenon lamp light source, the t_1/2 values were 693.15, 231.05, and 99.02 min, respectively. Inorganic substance NO₃^- clearly promoted the photodegradation of prothioconazole, with t_1/2 values of 115.53, 77.02, and 69.32 min at NO₃^- concentrations of 1.0, 2.0, and 5.0 mg L^-1, respectively. The photodegradation products were identified as C₁₄H₁₅Cl₂N₃O, C₁₄H₁₆ClN₃OS, C₁₄H₁₅Cl₂N₃O₂S, and C₁₄H₁₃Cl₂N₃ based on calculations and the Waters compound library. Furthermore, density functional theory (DFT) calculations showed that the C-S, C-Cl, C-N, and C-O bonds of prothioconazole were the reaction sites with high absolute charge values and greater bond lengths. Finally, the photodegradation pathway of prothioconazole was concluded, and the variation in energy of the photodegradation process was attributed to the decrease in activation energy caused by light excitation. This work provides new insight into the structural modification and photochemical stability improvement of prothioconazole, which plays an important role in decreasing safety risk during application that will reduce the exposure risk in field environment.

Bioactivity, Uptake, and Distribution of Prothioconazole Loaded on Fluorescent Double-Hollow Shelled Mesoporous Silica in Soybean Plants

Prothioconazole (PTC) has been widely utilized for plant fungal disease control, but its metabolite prothioconazole-desthio (PTC-d) exhibits reproductive toxicity. In the present study, carbon quantum dot (CQD)-modified fluorescent double-hollow shelled mesoporous silica nanoparticles (FL-MSNs) loaded with PTC, referred to as PTC@FL-MSNs, were constructed with an average size of 369 nm and a loading capacity of 28.1 wt %, which could increase the antifungal efficiency of PTC. In addition, upright fluorescence microscope and UPLC-MS/MS studies showed that PTC@FL-MSNs could be effectively transported via root uptake and foliar spray in soybean plants. Compared to a 30% PTC dispersible oil suspension agent, the PTC@FL-MSN treatment group showed higher concentrations (leaves: 0.50 > 0.48 mg/kg), longer half-lives for degradation (leaves: 3.62 > 3.21 d; roots: 3.39 > 2.82 d), and fewer metabolites. These findings suggest that sustained pesticide release and toxicity reduction are potential applications for PTC nanofungicide delivery technology.

Environmental fate and metabolism of the systemic triazolinthione fungicide prothioconazole in different aerobic soils

As a best-selling triazolinthione fungicide, prothioconazole (PTZ) has been widely used worldwide and has aroused concern about its environmental effect. This study used phenyl-UL-¹⁴C-labeled PTZ and an improved fate model to investigate the fate and metabolism of this fungicide in aerobic soil. During 120 d of incubation, PTZ rapidly transformed into metabolites and bound residues, with a half-life (DT₅₀) of less than 1 d. After 120 d, approximately 45-55% of PTZ formed bound residues, and the extractable metabolite residues were gradually degraded over time. Approximately 19%, 44% and 27% of phenyl-UL-¹⁴C-PTZ was mineralized in red soil, fluvo-aquic soil and cinnamon soil, respectively, but only approximately 3% was mineralized in black soil. Five metabolites were identified and confirmed, and a possible metabolic pathway for phenyl-UL-¹⁴C-PTZ in soil was proposed. Based on the correlation analysis between soil properties and model rate constants, soil properties exerted important effects on PTZ transformation. These results will provide basic data for environmental risk assessments and removal of the PTZ pollutant and suggest that the soil type should be considered in the selection and application of pesticides.

Efficient selective targeting of Candida CYP51 by oxadiazole derivatives designed from plant cuminaldehyde

Candida infection represents a global threat with associated high resistance and mortality rate. Azoles such as the triazole drug fluconazole are the frontline therapy against invasive fungal infections; however, the emerging multidrug-resistant strains limit their use. Therefore, a series of novel azole UOSO1-15 derivatives were developed based on a modified natural scaffold to combat the evolved resistance mechanism and to provide improved safety and target selectivity. The antifungal screening against C. albicans and C. auris showed that UOSO10 and 12-14 compounds were the most potent derivatives. Among them, UOSO13 exhibited superior potent activity with MIC50 values of 0.5 and 0.8 μg mL-1 against C. albicans and C. auris compared to 25 and 600 μg mL-1 for fluconazole, respectively. UOSO13 displayed significant CaCYP51 enzyme inhibition activity in a concentration-dependent manner with an IC50 10-fold that of fluconazole, while exhibiting no activity against human CYP50 enzyme or toxicity to human cells. Furthermore, UOSO13 caused a significant reduction of Candida ergosterol content by 70.3% compared to a 35.6% reduction by fluconazole. Homology modeling, molecular docking, and molecular dynamics simulations of C. auris CYP51 enzyme indicated the stability and superiority of UOSO13. ADME prediction indicated that UOSO13 fulfils the drug-likeness criteria with good physicochemical properties.

Anti-Candida albicans Activity of Ononin and Other Secondary Metabolites from Platonia Insignis MART

Candida albicans is a human pathogen that is part of the healthy microbiome. However, it is often associated with opportunistic fungal infections. The treatment of these infections is challenging because prolonged exposure to antifungal drugs can culminate in fungal resistance during therapy, and there is a limited number of available drugs. Therefore, this study investigated the antifungal activity of ononin by in silico and in vitro assays, and in Tenebrio molitor as an alternative in vivo model of infection caused by C. albicans. Ononin is an isoflavone glycoside derived from formononetin that has various biological activities. According in silico evaluation, ononin showed the best electron affinity in molecular docking with CaCYP51, with a binding free energy of -10.89 kcal/mol, superior to that of the antifungal drugs fluconazole and posaconazole. The ononin + CaCYP51 complex formed hydrogen bonds with Tyr132, Ser378, Phe380, and Met508, as well as hydrophobic connections with Tyr118, Leu121, Phe126, Leu131, Ile304, and Leu309, and interactions with the heme group. Ononin exerted anti-Candida albicans activity, with MIC between 3.9 and 7.8 µg/mL, and inhibited young and mature biofilms, with a reduction in cell density and metabolic activity of 50 to 80%. The compound was not cytotoxic to sheep red blood cells at concentrations up to 1000 µg/mL. Larvae of the mealworm T. molitor were used as an alternative in vivo model of C. albicans infection. Ononin was able to prolong larval survival at concentrations of 0.5, 1, and 5 mg/kg, and was not toxic up to a concentration of 20 mg/kg. Moreover, ononin reduced the fungal charge in treated animals. In conclusion, our results suggest that ononin has anti-Candida albicans activity and is a potential candidate for the development of new therapeutic alternatives.

Enantioselective effect of chiral fungicide prothioconazole on Fusarium graminearum: Fungicidal activity and DON biosynthesis

Prothioconazole, a chiral triazole fungicide, is widely used to control Fusarium head blight (FHB) of wheat. Fusarium graminearum (F. graminearum), as the main pathogen of FHB, can produce many secondary metabolites including deoxynivalenol (DON), which threatens the health of humans and animals. However, some fungicides may stimulate F. graminearum to synthesize more DON under certain conditions. Until now, the fungicidal activity and enantioselective effect of prothioconazole enantiomers on DON production, transcriptome and metabolome of F. graminearum were unclear. The fungicidal activity of R-(-)-prothioconazole against F. graminearum was 9.12-17.73 times higher than that of S-(+)-prothioconazole under all conditions. Prothioconazole enantiomers can induce F. graminearum to synthesize more DON under 0.99 water activity (a_w) and 30 °C, especially R-(-)-prothioconazole. The expression levels of TRI6, TRI10 and TRI101 under R-(-)-prothioconazole treatment were significantly higher than those under S-(+)-prothioconazole treatment. Most genes in glycolysis, pyruvate metabolism, the target of rapamycin (TOR) signaling transduction pathway and the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling transduction pathway showed higher expression levels under R-(-)-prothioconazole treatment than uner S-(+)-prothioconazole treatment and the control. The peroxisome pathway displayed higher transcriptional activity under S-(+)-prothioconazole treatment compared with R-(-)-prothioconazole and the control. Based on metabolomic data, R-(-)-prothioconazole can significantly influence phenylalanine metabolism, and no significantly enriched pathway was found under S-(+)-prothioconazole treatment. These results are helpful to understand the risk of prothioconazole enantiomers on DON production of F. graminearum and uncover the relevant underlying mechanisms of prothioconazole enantiomers.

Sensitivity and Resistance Risk Assessment of Fusarium graminearum from Wheat to Prothioconazole

Fusarium head blight (FHB), caused mainly by Fusarium graminearum, is one of the most devastating diseases of wheat. Prothioconazole is a broad-spectrum demethylation inhibitor fungicide with excellent efficacy against FHB. In this study, 235 strains of F. graminearum collected from different regions of Henan Province of China in 2016, 2017, and 2018 were randomly selected. The sensitivity of F. graminearum to prothioconazole was determined by the mycelial growth inhibition method. The results showed that the half maximal effective concentration (EC₅₀) values of F. graminearum to prothioconazole ranged from 0.4742 to 3.4403 μg/ml, and the average EC₅₀ value was 1.7758 ± 0.6667 μg/ml. The sensitivity frequency distribution presented a consequent unimodal curve, and thus the average EC₅₀ value can be established as the baseline sensitivity of F. graminearum to prothioconazole. Ten strains of prothioconazole-resistant mutants were obtained by fungicide taming, and the resistance factor of the mutants ranged from 5.71 to 12.32. The genetic stability assay showed that resistance can be inherited stably for 10 generations. All mutants displayed different degrees of defects in vegetative growth, conidia formation, and pathogenicity compared with the parental strain. These results indicated that F. graminearum has a low risk of resistance to prothioconazole. Cross-resistance assay showed that no cross-resistance was found between prothioconazole and carbendazim, tebuconazole, phenamacril, and pydiflumetofen. Among all mutants, sequence analysis showed that no mutation site was found in cyp51A and cyp51B. Real-time PCR assays showed that the expression levels of cyp51A and cyp51B of the mutants were significantly increased after prothioconazole treatment for 24 h. In summary, our study provided a theoretical basis for the resistance risk assessment of F. graminearum to prothioconazole and scientific application of prothioconazole in controlling FHB.

Toxification metabolism and treatment strategy of the chiral triazole fungicide prothioconazole in water

Toxification metabolism of the chiral triazole fungicide prothioconazole in the environment has attracted an increasing amount of attention. To better understand the fate of prothioconazole in aquatic ecosystems and develop a treatment strategy, the stereoselective toxicity, degradation and bioconcentration of prothioconazole were investigated in water with algae at the enantiomer level. There was remarkable enantioselectivity against Chlorella pyrenoidosa, and the highly toxic S-prothioconazole was preferentially degraded with enantiomer fraction values ranging from 0.5 to 0.74. Metabolism experiment results showed that the parent compound was quickly eliminated driven by biodegradation and abiotic degradation (hydrolysis, photolysis). Fourteen phase I and two phase II metabolites involved in the reactions of hydroxylation, methylation, dechlorinating, desulfuration, dehydration and conjugation were identified, where prothioconazole-desthio was the major metabolite. The highly toxic metabolite prothioconazole-desthio persisted in water and hardly degraded with or without C. pyrenoidosa. Furthermore, the reaction system including 1 mg of cobalt coated in nitrogen doped carbon nanotubes and 0.156 g of peroxymonosulfate was used to eliminate prothioconazole-desthio. Approximately 96% prothioconazole-desthio was eliminated and transformed to low toxicity metabolites. This work provides a strategy for the risk evaluation of prothioconazole in aquatic ecosystems and proposes a workable plan for the elimination of pesticide residues in water.

Toxicological effects of acute prothioconazole and prothioconazole-desthio administration on liver in male Chinese lizards (Eremias argus)

Prothioconazole (PTC) is a high effective systemic fungicide, and one of its major metabolites is prothioconazole-desthio (PTC-d). Because of its wildly use in the farmland of China, the local eco-toxicological effects of PTC as well as PTC-d are needed to be concerned. This study investigated hepatoxicity of Chinese lizards (Eremias argus), a local non-target organism, after single dose oral treated (100 mg kg^-1 BW) through pathological, enzyme activity and gene expression analysis. PTC treatment caused ballooning and PTC-d treatment led to macrovesicular steatosis of hepatocyte. The elevation of serum indexes, including the activities of aspartate aminotransferase (AST), alkaline phosphatase (ALP) and alanine aminotransferase (ALT), further confirmed the hepatic injury. PTC and PTC-d treatments altered oxidative status reflected by the inhibition of superoxide dismutase (SOD) activity , meanwhile, the stimulation of catalase (CAT) activity, glutathione peroxidase (GPx) activity and malondialdehyde (MDA) content. The mRNA expression changes of apoptosis-related factors and cytokines genes, including Bax, Bcl-2, TNF-α, NF-κB, Caspase-3 and Nrf2, deeply uncovered the potential mechanism of hepatotoxicity caused by PTC and PTC-d. In brief, the results indicated that both of these two compounds altered oxidative status, then were likely to trigger caspase-3 by affecting the ratio of pro- and anti-apoptotic factors which belong to intrinsic apoptosis pathway. Specifically, more serious impacts were induced by PTC-d than its parent compound. This study is the first to provide specific insight into potential hepatotoxicity resulted from PTC and PTC-d in male Chinese lizards.

Loss-of-Function ROX1 Mutations Suppress the Fluconazole Susceptibility of upc2AΔ Mutation in Candida glabrata, Implicating Additional Positive Regulators of Ergosterol Biosynthesis

Two of the major classes of antifungal drugs in clinical use target ergosterol biosynthesis. Despite its importance, our understanding of the transcriptional regulation of ergosterol biosynthesis genes in pathogenic fungi is essentially limited to the role of hypoxia and sterol-stress-induced transcription factors such as Upc2 and Upc2A as well as homologs of sterol response element binding (SREB) factors. To identify additional regulators of ergosterol biosynthesis in Candida glabrata, an important human fungal pathogen with reduced susceptibility to ergosterol biosynthesis inhibitors relative to other Candida spp., we used a serial passaging strategy to isolate suppressors of the fluconazole hypersusceptibility of a upc2AΔ deletion mutant. This led to the identification of loss-of-function mutations in two genes: ROX1, the homolog of a hypoxia gene transcriptional suppressor in Saccharomyces cerevisiae, and CST6, a transcription factor that is involved in the regulation of carbon dioxide response in C. glabrata. Here, we describe a detailed analysis of the genetic interaction of ROX1 and UPC2A. In the presence of fluconazole, loss of Rox1 function restores ERG11 expression to the upc2AΔ mutant and inhibits the expression of ERG3 and ERG6, leading to increased levels of ergosterol and decreased levels of the toxic sterol 14α methyl-ergosta-8,24(28)-dien-3β, 6α-diol, relative to the upc2AΔ mutant. Our observations establish that Rox1 is a negative regulator of ERG gene biosynthesis and indicate that a least one additional positive transcriptional regulator of ERG gene biosynthesis must be present in C. glabrata.

IMPORTANCECandida glabrata is one of the most important human fungal pathogens and has reduced susceptibility to azole-class inhibitors of ergosterol biosynthesis. Although ergosterol is the target of two of the three classes of antifungal drugs, relatively little is known about the regulation of this critical cellular pathway. Sterols are both essential components of the eukaryotic plasma membrane and potential toxins; therefore, sterol homeostasis is critical for cell function. Here, we identified two new negative regulators in C. glabrata of ergosterol (ERG) biosynthesis gene expression. Our results also indicate that in addition to Upc2A, the only known activator of ERG genes, additional positive regulators of this pathway must exist.

A Typical Fungicide and Its Main Metabolite Promote Liver Damage in Mice through Impacting Gut Microbiota and Intestinal Barrier Function

The environmental risks of prothioconazole (PTC), a popular agricultural fungicide, and its main metabolite, prothioconazole-desthio (PTCd), have attracted more and more attention recently. In this study, the adverse effects of PTC and PTCd on liver function in mice and their underlying mechanisms have been systematically studied from the perspective of gut microbiota. Combining the results of physiological, biochemical, and histopathological analysis showed that PTC and PTCd exposure could cause lipid accumulation and inflammation in the liver of mice. In addition, exposure to PTC and PTCd could also significantly affect the transcriptome of liver tissue, leading to disorders of lipid metabolism of the liver. Particularly, the abundances of bacteria in liver tissues were significantly increased with PTC and PTCd exposure. Further results show that PTC and PTCd could affect the expression of genes related to inflammation and the barrier function in colon tissue, leading to intestinal dysfunction in mice. Last but not least, the results based on 16S rRNA gene sequencing and ¹H NMR metabolomics analysis showed that exposure to PTC and PTCd could cause gut microbiota imbalances and cecal content metabolic profile disorders. In short, this study found that PTC and PTCd exposure could cause liver damage in mice by changing the gut microbiota, disrupting the intestinal barrier function and promoting bacterial translocation. These results clarified the key role of gut microbiota in liver damage induced by PTC and PTCd in mice and proposed a new insight into the mechanisms of liver toxicity induced by pesticides through the dialogue of the gut-liver axis.

Effect of Fungicide Application on Lowbush Blueberries Soil Microbiome

Lowbush blueberries (Vaccinium sp.) are perennial crops produced throughout eastern Canada and Maine through management of wild populations. Given the constraints of this cropping system, the application of fungicides is critical to reducing disease pressure and ensuring consistent yields. However, as plant health is intertwined with soil health, it is important to consider the impact of fungicides on microbial communities. To understand the effects of fungicides in this context, bacterial and fungal microbial communities from fungicide-treated plots, as well as untreated control plots (UTG) were analyzed using amplicon sequencing. The fungicides, considered collectively as a combined treatment group (CTG), lead to a loss in fungal richness. One family, Clavariaceae, had an increased abundance under prothioconazole relative to UTG. This finding may be significant as taxa in Clavariaceae have been thought to potentially form ericoid mycorrhizae with Vaccinium. Five functional pathways and 74 enzymes differed significantly in relative abundance between CTG and UTG including enzymes associated with soil nutrient cycles. Most notably, enzymes corresponding to the breakdown of halogen-organic compounds had an increased abundance in CTG, suggesting bacterial fungicide degradation. Some enzymes associated with soil nutrient cycles differed significantly, possibly implying changes to nutrient pathways due to fungicide treatment.

Insights in the molecular mechanisms of an azole stress adapted laboratory-generated Aspergillus fumigatus strain

Aspergillus fumigatus is the main cause of invasive aspergillosis, for which azole drugs are the first-line therapy. Emergence of pan-azole resistance among A. fumigatus is concerning and has been mainly attributed to mutations in the target gene (cyp51A). However, azole resistance may also result from other mutations (hmg1, hapE) or other adaptive mechanisms. We performed microevolution experiment exposing an A. fumigatus azole-susceptible strain (Ku80) to sub-minimal inhibitory concentration of voriconazole to analyze emergence of azole resistance. We obtained a strain with pan-azole resistance (Ku80R), which was partially reversible after drug relief, and without mutations in cyp51A, hmg1, and hapE. Transcriptomic analyses revealed overexpression of the transcription factor asg1, several ATP-binding cassette (ABC) and major facilitator superfamily transporters and genes of the ergosterol biosynthesis pathway in Ku80R. Sterol analysis showed a significant decrease of the ergosterol mass under voriconazole exposure in Ku80, but not in Ku80R. However, the proportion of the sterol compounds was similar between both strains. To further assess the role of transporters, we used the ABC transporter inhibitor milbemycine oxime (MLB). MLB inhibited transporter activity in both Ku80 and Ku80R and demonstrated some potentiating effect on azole activity. Criteria for synergism were reached for MLB and posaconazole against Ku80. Finally, deletion of asg1 revealed some role of this transcription factor in controlling drug transporter expression, but had no impact on azole susceptibility.This work provides further insight in mechanisms of azole stress adaptation and suggests that drug transporters inhibition may represent a novel therapeutic target.

LAY SUMMARY

A pan-azole-resistant strain was generated in vitro, in which drug transporter overexpression was a major trait. Analyses suggested a role of the transporter inhibitor milbemycin oxime in inhibiting drug transporters and potentiating azole activity.

Electron donor cytochrome b5 is required for hyphal tip accumulation of sterol-rich plasma membrane domains and membrane fluidity in Aspergillus fumigatus

The electron donor cytochrome b5 (CybE/Cyb5) fuels the activity of the ergosterol biosynthesis-related P450 enzymes/P450s by providing electrons to P450s to promote ergosterol biosynthesis. Previous studies reported that lack of Aspergillus fumigatus (A. fumigatus) CybE reduces the proportion of ergosterol in total sterols and induces severe growth defects. However, the molecular characteristics of CybE and the underlying mechanism for CybE maintaining A. fumigatus growth remain poorly understood. Here, we found that CybE locates at the endoplasmic reticulum by its C-terminus with two transmembrane regions. Therefore, lack of the C-terminus of CybE is able to phenocopy a cybE deletion. Notably, cybE deletion reduced the accumulation of the sterol-rich plasma membrane domains (SRDs, the assembly platform of polarity factors/cell end markers and growth machinery) in hyphal tips and decreased membrane fluidity, which correspond to tardiness of hyphal extension and hypersensitivity to low temperature in cybE deletion mutant. Additionally, overexpressing another electron donor-heme-independent P450 reductase (CPR) significantly rescued growth defects and recovered SRD accumulation in deletion of cybE almost to the wild-type level, suggesting CybE maintaining the growth and deposition of SRDs in hyphal tips attributes to its nature as an electron donor. Protein pull-down assays revealed that CybE probably participates in metabolism and transfer of lipids, construction of cytoskeleton and mitochondria-associated energy metabolism to maintain the SRD accumulation in hyphal tips, membrane fluidity and hyphal extension. Findings in this study give a hint that inhibition of CybE may be an effective strategy for resisting the infection of the human pathogen A. fumigatus Importance Investigating the knowledge of the growth regulation in the human opportunistic pathogen A. fumigatus is conducive to design new antifungal approach. The electron donor cytochrome b5 (CybE) plays a crucial role in maintaining the normal growth of A. fumigatus, however, the potential mechanism remains elusive. Herein, we characterized the molecular features of CybE and found the C-terminus with two transmembrane domains are required for its ER localization and functions. In addition, we demonstrated that CprA, an electron donor-heme-independent P450 reductase, provides a reciprocal function for the missing cytochrome b5 protein-CybE in A. fumigatus CybE maintains the normal growth probably via supporting two crucial physiological processes, the SRD accumulation in hyphal tips and membrane fluidity. Therefore, our finding reveals the mechanisms underlying the regulatory effect of CybE on A. fumigatus growth and indicates that inhibition of CybE might be an effective approach for alleviating A. fumigatus infection.

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.

Effects of exposure to prothioconazole and its metabolite prothioconazole-desthio on oxidative stress and metabolic profiles of liver and kidney tissues in male mice

Prothioconazole (PTC), a popular agricultural fungicide, and its main metabolite prothioconazole-desthio (PTCd) are receiving great attention due to their toxicological effects in the non-target organisms. This study investigated their dosage-dependent (1 and 5 mg/kg BW/day) toxicological effects on oxidative stress and metabolic profiles of liver and kidney tissues using male mice. PTC and PTCd significantly inhibited the growth phenotype including body weights gain, liver and kidney indices. Furthermore, these effects were deeply investigated using the biomarkers of oxidative stress, and metabolomics. Notably, these effects were dose and tissue-dependent. Specifically, the more serious impacts involving oxidative stress and metabolic disorders were observed in the high concentration treatment groups. Also, the liver tissue was more severely affected than the kidney tissue. Lastly, the change in oxidative stress biomarkers and metabolomics profile revealed that PTCd induced more severe toxic effects than the parent compound PTC. In brief, these results indicate that exposure to PTC and PTCd could cause potential health risks in mammals.

Effect of application method and formulation on prothioconazole residue behavior and mycotoxin contamination in wheat

In this study, efficient and sensitive analytical methods based on liquid chromatography-tandem mass spectrometry were established to evaluate the degradation behavior of prothioconazole and prothioconazole-desthio along with mycotoxin contamination in wheat samples. The mean recoveries of prothioconazole and prothioconazole-desthio ranged from 76.05% to 96.17% with intraday relative standard deviations (RSDs) of 0.84%-14.38%. Mean recoveries of the five mycotoxins were 85.82%-103.24% with RSDs of 1.82%-7.03%. The residue and degradation behavior of prothioconazole was studied in wheat plant and grain under field conditions with different spraying equipment and prothioconazole formulations. Both application method and formulation affected prothioconazole degradation, and the content of all mycotoxin was lower than the national standards. The proposed analytic methods can be used to systematically evaluate prothioconazole and prothioconazole-desthio along with mycotoxin contamination in food. These results suggest that prothioconazole is safe for the control Fusarium head blight in wheat.

Small-Molecule Inhibitors Targeting Sterol 14α-Demethylase (CYP51): Synthesis, Molecular Modelling and Evaluation Against Candida albicans

Fungal infections are a global issue affecting over 150 million people worldwide annually, with 750 000 of these caused by invasive Candida infections. Azole drugs are the frontline treatment against fungal infections; however, resistance to current azole antifungals in C. albicans poses a threat to public health. Two series of novel azole derivatives, short and extended derivatives, have been designed, synthesised and investigated for CYP51 inhibitory activity, binding affinity and minimum inhibitory concentration (MIC) against C. albicans strains. The short derivatives were more potent against the C. albicans strains (e. g., MIC 2-(4-chlorophenyl)-N-(2,4-dichlorobenzyl)-3-(1H-imidazol-1-yl)propanamide (5 f) <0.03 μg/mL, N-(4-((4-chlorophenyl)sulfonamido)benzyl)-2-phenyl-3-(1H-1,2,4-triazol-1-yl)propanamide (12 c), 1 μg/mL, fluconazole 0.125 μg/mL) but both displayed comparable enzyme binding and inhibition (5 f Kd 62±17 nM, IC50 0.46 μM; 12 c Kd 43±18 nM, IC50 0.33 μM, fluconazole Kd 41±13 nM, IC50 0.31 μM, posaconazole Kd 43±11 nM, IC50 0.2 μM). The short series had poor selectivity for CaCYP51 over the human homologue, whereas the selectivity of the extended series, for example, compound 12 c, was higher (21.5-fold) than posaconazole (4.7-fold) based on Kd values, although posaconazole was more selective (615-fold) than 12 c (461-fold) based on IC50 values. Based on inhibitory activity and selectivity profile, the extended series are the better of the two series for further development.

A binding mode hypothesis for prothioconazole binding to CYP51 derived from first principles quantum chemistry

In order to assess safety and efficacy of small molecule drugs as well as agrochemicals, it is key to understanding the nature of protein-ligand interaction on an atomistic level. Prothioconazole (PTZ), although commonly considered to be an azole-like inhibitor of sterol 14-α demethylase (CYP51), differs from classical azoles with respect to how it binds its target. The available evidence is only indirect, as crystallographic elucidation of CYP51 complexed with PTZ have not yet been successful. We derive a binding mode hypothesis for PTZ binding its target, compare to DPZ, a triazole-type metabolite of PTZ, and set our findings into context of its biochemistry and spectroscopy. Quantum Theory of Atoms in Molecules (QTAIM) analysis of computed DFT electron densities is used to qualitatively understand the topology of binding, revealing significant differences of how R- and S-enantiomers are binding and, in particular, how the thiozolinthione head of PTZ binds to heme compared to DPZ's triazole head. The difference of binding enthalpy is calculated at coupled cluster (DLPNO-CCSD(T)) level of theory, and we find that DPZ binds stronger to CYP51 than PTZ by more than ΔH ~ 11 kcal/mol.

Combined Machine Learning and Molecular Modelling Workflow for the Recognition of Potentially Novel Fungicides

Novel machine learning and molecular modelling filtering procedures for drug repurposing have been carried out for the recognition of the novel fungicide targets of Cyp51 and Erg2. Classification and regression approaches on molecular descriptors have been performed using stepwise multilinear regression (FS-MLR), uninformative-variable elimination partial-least square regression, and a non-linear method called Forward Stepwise Limited Correlation Random Forest (FS-LM-RF). Altogether, 112 prediction models from two different approaches have been built for the descriptor recognition of fungicide hit compounds. Aiming at the fungal targets of sterol biosynthesis in membranes, antifungal hit compounds have been selected for docking experiments from the Drugbank database using the Autodock4 molecular docking program. The results were verified by Gold Protein-Ligand Docking Software. The best-docked conformation, for each high-scored ligand considered, was submitted to quantum mechanics/molecular mechanics (QM/MM) gradient optimization with final single point calculations taking into account both the basis set superposition error and thermal corrections (with frequency calculations). Finally, seven Drugbank lead compounds were selected based on their high QM/MM scores for the Cyp51 target, and three were selected for the Erg2 target. These lead compounds could be recommended for further in vitro studies.

Analysis of mutations in West Australian populations of Blumeria graminis f. sp. hordei CYP51 conferring resistance to DMI fungicides

BACKGROUND

Powdery mildew caused by Blumeria graminis f. sp. hordei (Bgh) is a constant threat to barley production but is generally well controlled through combinations of host genetics and fungicides. An epidemic of barley powdery mildew was observed from 2007 to 2013 in the West Australian grain belt.

RESULTS

We collected isolates across Australia, examined their sensitivity to demethylation inhibitor (DMI) fungicides and sequenced the Cyp51B target gene. Five amino acid substitutions were found, of which four were novel. The most resistant haplotypes increased in prevalence from 0% in 2009 to 16% in 2010 and 90% in 2011. Yeast strains expressing the Bgh Cyp51 haplotypes replicated the altered sensitivity to various DMIs and these results were complemented by in silico protein docking studies.

CONCLUSIONS

The planting of very susceptible cultivars and the use of a single fungicide mode of action was followed by the emergence of a major epidemic of barley powdery mildew. Widespread use of DMI fungicides led to the selection of Bgh isolates carrying both the Y137F and S524T mutations, which, as in Zymoseptoria tritici, account for resistance factors varying from 3.4 for propiconazole to 18 for tebuconazole, the major azoles used at that time in WA. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The negative cofactor 2 complex is a key regulator of drug resistance in Aspergillus fumigatus

The frequency of antifungal resistance, particularly to the azole class of ergosterol biosynthetic inhibitors, is a growing global health problem. Survival rates for those infected with resistant isolates are exceptionally low. Beyond modification of the drug target, our understanding of the molecular basis of azole resistance in the fungal pathogen Aspergillus fumigatus is limited. We reasoned that clinically relevant antifungal resistance could derive from transcriptional rewiring, promoting drug resistance without concomitant reductions in pathogenicity. Here we report a genome-wide annotation of transcriptional regulators in A. fumigatus and construction of a library of 484 transcription factor null mutants. We identify 12 regulators that have a demonstrable role in itraconazole susceptibility and show that loss of the negative cofactor 2 complex leads to resistance, not only to the azoles but also the salvage therapeutics amphotericin B and terbinafine without significantly affecting pathogenicity.

Resistance to primary treatments of invasive aspergillosis is growing. Here, the authors generate a knockout library for 484 transcription factors in Aspergillus fumigatus, and show that loss of the NCT complex leads to cross-resistance to all primary and some salvage therapeutics without affecting pathogenicity.

Comparative Genomics for the Elucidation of Multidrug Resistance in Candida lusitaniae

Antifungal resistance is an inevitable phenomenon when fungal pathogens are exposed to antifungal drugs. These drugs can be grouped in four distinct classes (azoles, candins, polyenes, and pyrimidine analogs) and are used in different clinical settings. Failures in therapy implicate the sequential or combined use of these different drug classes, which can result in some cases in the development of multidrug resistance (MDR). MDR is particularly challenging in the clinic since it drastically reduces possible treatment alternatives. In this study, we report the rapid development of MDR in Candida lusitaniae in a patient, which became resistant to all known antifungal agents used until now in medicine. To understand how MDR developed in C. lusitaniae, whole-genome sequencing followed by comparative genome analysis was undertaken in sequential MDR isolates. This helped to detect all specific mutations linked to drug resistance and explained the different MDR patterns exhibited by the clinical isolates.

Multidrug resistance (MDR) has emerged in hospitals due to the use of several agents administered in combination or sequentially to the same individual. We reported earlier MDR in Candida lusitaniae during therapy with amphotericin B (AmB), azoles, and candins. Here, we used comparative genomic approaches between the initial susceptible isolate and 4 other isolates with different MDR profiles. From a total of 18 nonsynonymous single nucleotide polymorphisms (NSS) in genome comparisons with the initial isolate, six could be associated with MDR. One of the single nucleotide polymorphisms (SNPs) occurred in a putative transcriptional activator (MRR1) resulting in a V668G substitution in isolates resistant to azoles and 5-fluorocytosine (5-FC). We demonstrated by genome editing that MRR1 acted by upregulation of MFS7 (a multidrug transporter) in the presence of the V668G substitution. MFS7 itself mediated not only azole resistance but also 5-FC resistance, which represents a novel resistance mechanism for this drug class. Three other distinct NSS occurred in FKS1 (a glucan synthase gene that is targeted by candins) in three candin-resistant isolates. Last, two other NSS in ERG3 and ERG4 (ergosterol biosynthesis) resulting in nonsense mutations were revealed in AmB-resistant isolates, one of which accumulated the two ERG NSS. AmB-resistant isolates lacked ergosterol and exhibited sterol profiles, consistent with ERG3 and ERG4 defects. In conclusion, this genome analysis combined with genetics and metabolomics helped decipher the resistance profiles identified in this clinical case. MDR isolates accumulated six different mutations conferring resistance to all antifungal agents used in medicine. This case study illustrates the capacity of C. lusitaniae to rapidly adapt under drug pressure within the host.

Sensitivity of the U.S. Blumeria graminis f. sp. tritici Population to Demethylation Inhibitor Fungicides

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed in the United States with cultivar resistance and foliar fungicides. Despite high levels of fungicide sensitivity in other cereal mildew populations, fungicide sensitivity of U.S. B. graminis f. sp. tritici has never been evaluated. Almost 400 B. graminis f. sp. tritici isolates were collected from 15 U.S. states over 2 years and phenotyped for sensitivity to two widely used demethylation inhibitor (DMI) fungicides, tebuconazole and prothioconazole. A large range of sensitivity to both DMIs was observed, with more insensitive isolates originating from the eastern United States (Great Lakes, Mid-Atlantic, and Southeast regions) and more sensitive isolates from central states (Plains region, Arkansas, and Missouri). Cross-resistance was indicated by a positive although weak association between tebuconazole and prothioconazole sensitivities at all levels of analysis (EC₅₀ values, P < 0.0001). A possible fitness cost was also associated with prothioconazole insensitivity (P = 0.0307) when analyzed at the state population level. This is the first assessment of fungicide sensitivity in the U.S. B. graminis f. sp. tritici population, and it produced evidence of regional selection for reduced DMI efficacy. The observation of reduced sensitivity to DMI fungicides in the eastern United States underlines the importance of rotating between chemistry classes to maintain the effectiveness of DMIs in U.S. wheat production. Although cross-resistance was demonstrated, variability in the relationship of EC₅₀ values for tebuconazole and prothioconazole also suggests that multiple mechanisms influence B. graminis f. sp. tritici isolate responses to these two DMI fungicides.

Gonadal disruption after single dose exposure of prothioconazole and prothioconazole-desthio in male lizards (Eremias argus)

Prothioconazole (PTC) is a widely used triazole fungicide with low toxicity, and its desulfurization metabolite, prothioconazole-desthio (PTC-d), is reported to have higher reproductive toxicity to mammals. However, little is known about the reproductive toxicity, much less endocrine disrupting effect, of these two chemicals on reptiles. In this study, we investigated the effects of single dose of PTC/PTC-d (100 mg kg^-1 body weight) exposure on the pathomorphism of testes and epididymides, serum sex steroid hormones (testosterone and 17β-estradiol) and transcription of steroidogenic-related genes (STARD, cyp11A, cyp17, cyp19A, 17β-HSD, 3β-HSD, AR and ER-α) in gonads of male lizards (Eremias argus). Although structural disorder existed in PTC-d exposure group, severe gonadal disruption, especially suppression of spermatogenesis was only observed in testis after PTC treatment, which consequently led to the lack of spermatozoa in epididymal ducts. Consistent with this result, T/E₂ value in PTC exposure was elevated to a significant higher level compared with control and continually increased over time, while T/E₂ value in the PTC-d exposure group slightly increased only at 12 h. These results demonstrated a more serious disruption of PTC on male lizard gonads than PTC-d. In addition, the expression of cyp17 gene was inhibited at 6 h, however, was induced at 12 h, and exhibited negative correlations with STARD, cyp11A and 3β-HSD after PTC exposure at each timepoint. In PTC-d group, the expression of STARD and 3β-HSD were significantly down-regulated, in contrast, cyp11A and cyp17 were up-regulated, and each gene showed consistent changes over time. For 17β-HSD, no significance was observed in both treated groups. This study was the first to compare the gonadal disruption of PTC and PTC-d in male lizards and elucidated that these two chemicals influenced the physiological function of male gonads through differential transcriptional modulation.

Isavuconazole and voriconazole inhibition of sterol 14α-demethylases (CYP51) from Aspergillus fumigatus and Homo sapiens

Here we report the first evaluation of isavuconazole inhibition of Aspergillus fumigatus CYP51 and thus sterol biosynthesis in the fungus. Voriconazole and isavuconazole both bound tightly to recombinant A. fumigatus CYP51 isoenzymes A and B (AfCYP51A and AfCYP51B) isolated in Escherichia coli membranes. CYP51 reconstitution assays confirmed that AfCYP51A and AfCYP51B as well as three AfCYP51A mutants known to confer azole resistance (G54W, L98H and M220K) were strongly inhibited by both triazoles. Voriconazole bound relatively weakly to purified Homo sapiens CYP51 (HsCYP51), unlike isavuconazole that bound tightly. However, isavuconazole was a relatively poor inhibitor of HsCYP51 activity, with an IC₅₀ value (half-maximal inhibitory concentration) of 25 µM, which was 55- to 120-fold greater than those observed for the A. fumigatus CYP51 enzymes, albeit not as poor an inhibitor of HsCYP51 as voriconazole with an IC₅₀ value of 112 µM. Sterol analysis of triazole-treated A. fumigatus Af293 cells confirmed that isavuconazole and voriconazole both inhibited cellular CYP51 activity with the accumulation of 14-methylated sterol substrates and depletion of ergosterol levels. Isavuconazole elicited a stronger perturbation of the sterol composition in A. fumigatus Af293 than voriconazole at 0.0125 µg/mL, indicating increased potency. However, complementation studies in Saccharomyces cerevisiae using strains containing AfCYP51A and AfCYP51B showed isavuconazole to be equally as effective at inhibiting CYP51 activity as voriconazole. These in vitro studies suggest that isavuconazole is an effective alternative to voriconazole as an antifungal agent against the target CYP51 in A. fumigatus.

Dissipation of Prothioconazole and Its Metabolite Prothioconazole-Desthio in Rice Fields and Risk Assessment of Its Dietary Intake

Rice is an important food crop, with a long history of cultivation in China, and is one of the important staple foods for Chinese today. However, the occurrence of rice diseases has had a substantial impact on its yield. At present, chemical control is the main means of prevention and control of rice diseases. As a high-efficacy and broad-spectrum fungicide, prothioconazole shows an ideal effect on the prevention and control of common rice diseases, but the residuals that remain after its use may have an impact on human health. In this paper, ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to develop a residue analysis method and explore the dissipation of prothioconazole and its metabolite prothioconazole-desthio in rice grain, rice husk, and rice plants, and the risks of chronic and acute dietary intake of prothioconazole in different Chinese populations were evaluated. The results showed that at a concentration range of 0.005-5.0 μg/mL, prothioconazole and its metabolites showed good linear correlations, and the correlation coefficients were all above 0.9992. The average recoveries of prothioconazole in three matrixes ranged from 80.0% to 99.7%, the RSD was between 1.54% and 11.0%, and the limit of quantitation was less than 0.01 μg/g. The sensitivity, accuracy, and precision of the established method all met the measurement requirements. The dissipation experimental results showed that the parent compound prothioconazole was rapidly metabolized to prothioconazole-desthio in the rice field environment, and the dissipation half-life in rice plants after application was 2.5-10.1 d. According to the results of dietary risk assessment, under the standardized residue test conditions, the residual level of rice at the sampling interval of 7 days was within the acceptable range for the chronic and acute dietary risks of different populations in China. Our research is important for directing the scientific application of pesticides in China.

The Evolution of Azole Resistance in Candida albicans Sterol 14α-Demethylase (CYP51) through Incremental Amino Acid Substitutions

Recombinant Candida albicans CYP51 (CaCYP51) proteins containing 23 single and 5 double amino acid substitutions found in clinical strains and the wild-type enzyme were expressed in Escherichia coli and purified by Ni²⁺-nitrilotriacetic acid agarose chromatography. Catalytic tolerance to azole antifungals was assessed by determination of the concentration causing 50% enzyme inhibition (IC₅₀) using CYP51 reconstitution assays. The greatest increase in the IC₅₀ compared to that of the wild-type enzyme was observed with the five double substitutions Y132F+K143R (15.3-fold), Y132H+K143R (22.1-fold), Y132F+F145L (10.1-fold), G307S+G450E (13-fold), and D278N+G464S (3.3-fold). The single substitutions K143R, D278N, S279F, S405F, G448E, and G450E conferred at least 2-fold increases in the fluconazole IC₅₀, and the Y132F, F145L, Y257H, Y447H, V456I, G464S, R467K, and I471T substitutions conferred increased residual CYP51 activity at high fluconazole concentrations. In vitro testing of select CaCYP51 mutations in C. albicans showed that the Y132F, Y132H, K143R, F145L, S405F, G448E, G450E, G464S, Y132F+K143R, Y132F+F145L, and D278N+G464S substitutions conferred at least a 2-fold increase in the fluconazole MIC. The catalytic tolerance of the purified proteins to voriconazole, itraconazole, and posaconazole was far lower and limited to increased residual activities at high triazole concentrations for certain mutations rather than large increases in IC₅₀ values. Itraconazole was the most effective at inhibiting CaCYP51. However, when tested against CaCYP51 mutant strains, posaconazole seemed to be the most resistant to changes in MIC as a result of CYP51 mutation compared to itraconazole, voriconazole, or fluconazole.

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.

The influence of chosen fungicides on the activity of aminopeptidases in winter oilseed rape during pods development

Cultivation of oilseed rape requires application of specific fungicides. Besides their protective role, they can potentially influence the expression and activity of crucial enzymes in the plant. Among the large number of enzymes expressed in plants, aminopeptidases play a key role in all crucial physiological processes during the whole life cycle (e.g. storage protein mobilization and thus supplying plant with needed amino acids, as well as plant aging, protection and defense responses). In the present paper, we evaluate for the first time, the influence of the treatment of winter oilseed rape with commercially available fungicides (Pictor 400 SC, Propulse 250 SE and Symetra 325 SC), on the activity of aminopeptidases expressed in each plant organ (flowers, leaves, stems and pods separately). Fungicides were applied once, at one of the three stages of oilseed rape development (BBCH 59-61, BBCH 63-65 and BBCH 67-69). The aminopeptidase activity was determined using six different amino acid p-nitroanilides as substrates. The results have shown, that in control plants, at the beginning of intensive pods development and seeds production, hydrophobic amino acids with bulky side chains (Phe, Leu) were preferentially hydrolysed. In control plants, the activity was ~3.5 times higher in stems and pods, compared to leaves. The treatment with all pesticides caused significant increase in aminopeptidases hydrolytic activity toward small amino acids Gly, Ala as well as proline, mostly in flowers and leaves. These amino acids are proven to be crucial in the mechanisms of delaying of plant aging, development of better resistance to stress and plant defense. It can be suggested, that studied fungicides enhance such mechanisms, by activating the expression of genes coding for aminopeptidases, which are active in hydrolysis of N-terminal amino acids such as Gly, Ala, Pro from storage peptides and proteins. Depending on fungicide, the major increase of aminopeptidase activity was observed after application at BBCH 67-69 (Pictor 400 SC and Symetra 325 SC) and BBCH 63-65 (Propulse 250 SE) stages of development. Our study revealed, that agrochemical treatment and time of application, influenced the expression and activity of aminopeptidases, even though they were not molecular targets of applied fungicides. Since aminopeptidases are widely distributed throughout all organisms and are crucial in many key physiological processes, it can be expected, that factors influencing their expression and activity in plants, can also influence these enzymes in other organisms, especially humans and other mammals.

Crystal structure of 2-(2-(1-Chlorocyclopropyl)-3-(2-chlorophenyl)-2-hydroxypropyl)-1H-1,2,4-triazole-3(2H)-thione, C14H15Cl2N3OS

C14H14Cl2N3OS, monoclinic, P21/n (no. 14), a = 9.9215(8) Å, b = 9.5992(7) Å, c = 16.5801(13) Å, β = 92.702(1)°, V = 1577.3(2) Å3, Z = 4, R gt(F) = 0.0323, wR ref(F 2) = 0.0918, T = 296 K.

In Vitro and In Vivo Efficacy of a Novel and Long-Acting Fungicidal Azole, PC1244, on Aspergillus fumigatus Infection

The antifungal effects of the novel triazole PC1244, designed for topical or inhaled administration, against Aspergillus fumigatus were tested in a range of in vitro and in vivo studies. PC1244 demonstrated potent antifungal activities against clinical A. fumigatus isolates (n = 96) with a MIC range of 0.016 to 0.25 μg/ml, whereas the MIC range for voriconazole was 0.25 to 0.5 μg/ml. PC1244 was a strong tight-binding inhibitor of recombinant A. fumigatus CYP51A and CYP51B (sterol 14α-demethylase) enzymes and strongly inhibited ergosterol synthesis in A. fumigatus with a 50% inhibitory concentration of 8 nM. PC1244 was effective against a broad spectrum of pathogenic fungi (MIC range, <0.0078 to 2 μg/ml), especially Aspergillus terreus, Trichophyton rubrum, Candida albicans, Candida glabrata, Candida krusei, Cryptococcus gattii, Cryptococcus neoformans, and Rhizopus oryzae. PC1244 also proved to be quickly absorbed into both A. fumigatus hyphae and bronchial epithelial cells, producing persistent antifungal effects. In addition, PC1244 showed fungicidal activity (minimum fungicidal concentration, 2 μg/ml) which indicated that it was 8-fold more potent than voriconazole. In vivo, once-daily intranasal administration of PC1244 (3.2 to 80 μg/ml) to temporarily neutropenic, immunocompromised mice 24 h after inoculation with itraconazole-susceptible A. fumigatus substantially reduced the fungal load in the lung, the galactomannan concentration in serum, and circulating inflammatory cytokine levels. Furthermore, 7 days of extended prophylaxis with PC1244 showed in vivo effects superior to those of 1 day of prophylactic treatment, suggesting accumulation of the effects of PC1244. Thus, PC1244 has the potential to be a novel therapy for the treatment of A. fumigatus infection in the lungs of humans.

Changes in field dose-response curves for demethylation inhibitor (DMI) and quinone outside inhibitor (QoI) fungicides against Zymoseptoria tritici, related to laboratory sensitivity phenotyping and genotyping assays

BACKGROUND

Insensitivity of Zymoseptoria tritici to demethylation inhibitor (DMI) and quinone outside inhibitor (QoI) fungicides has been widely reported from laboratory studies, but the relationships between laboratory sensitivity phenotype or target site genotype and field efficacy remain uncertain. This article reports field experiments quantifying dose-response curves, and investigates the relationships between field performance and in vitro half maximal effective concentration (EC₅₀ ) values for DMIs, and the frequency of the G143A substitution conferring QoI resistance.

RESULTS

Data were analysed from 83 field experiments over 21 years. Response curves were fitted, expressed as percentage control, rising towards an asymptote with increasing dose. Decline in DMI efficacy over years was associated with a decrease in the asymptote, and reduced curvature. Field ED₅₀ values were positively related to in vitro EC₅₀ values for isolates of Z. tritici collected over a 14-year period. Loss of QoI efficacy was expressed through a change in asymptote. Increasing frequency of G143A was associated with changes in field dose-response asymptotes.

CONCLUSION

New resistant strains are often detected by resistance monitoring and laboratory phenotyped/genotyped before changes in field performance are detected. The relationships demonstrated here between laboratory tests and field performance could aid translation between laboratory and field for other fungicide groups. © 2017 Society of Chemical Industry.

Azole sensitivity in Leptosphaeria pathogens of oilseed rape: the role of lanosterol 14α-demethylase

Lanosterol 14-α demethylase is a key enzyme intermediating the biosynthesis of ergosterol in fungi, and the target of azole fungicides. Studies have suggested that Leptosphaeria maculans and L. biglobosa, the causal agents of phoma stem canker on oilseed rape, differ in their sensitivity to some azoles, which could be driving pathogen frequency change in crops. Here we used CYP51 protein modelling and heterologous expression to determine whether there are interspecific differences at the target-site level. Moreover, we provide an example of intrinsic sensitivity differences exhibited by both Leptosphaeria spp. in vitro and in planta. Comparison of homologous protein models identified highly conserved residues, particularly at the azole binding site, and heterologous expression of LmCYP51B and LbCYP51B, with fungicide sensitivity testing of the transformants, suggests that both proteins are similarly sensitive to azole fungicides flusilazole, prothioconazole-desthio and tebuconazole. Fungicide sensitivity testing on isolates shows that they sometimes have a minor difference in sensitivity in vitro and in planta. These results suggest that azole fungicides remain a useful component of integrated phoma stem canker control in the UK due to their effectiveness on both Leptosphaeria spp. Other factors, such as varietal resistance or climate, may be driving observed frequency changes between species.

Target Abundance-Based Fitness Screening (TAFiS) Facilitates Rapid Identification of Target-Specific and Physiologically Active Chemical Probes

Conventional drug screening typically employs either target-based or cell-based approaches. The first group rely on biochemical assays to detect modulators of a purified target. However, hits frequently lack drug-like characteristics such as membrane permeability and target specificity. Cell-based screens identify compounds that induce a desired phenotype, but the target is unknown, which severely restricts further development and optimization. To address these issues, we have developed a second-generation target-based whole-cell screening approach that incorporates the principles of both chemical genetics and competitive fitness, which enables the identification of target-specific and physiologically active compounds from a single screen. We have chosen to validate this approach using the important human fungal pathogen Candida albicans with the intention of pursuing novel antifungal targets. However, this approach is broadly applicable and is expected to dramatically reduce the time and resources required to progress from screening hit to lead compound.

Traditional approaches to drug discovery are frustratingly inefficient and have several key limitations that severely constrain our capacity to rapidly identify and develop novel experimental therapeutics. To address this, we have devised a second-generation target-based whole-cell screening assay based on the principles of competitive fitness, which can rapidly identify target-specific and physiologically active compounds. Briefly, strains expressing high, intermediate, and low levels of a preselected target protein are constructed, tagged with spectrally distinct fluorescent proteins (FPs), and pooled. The pooled strains are then grown in the presence of various small molecules, and the relative growth of each strain within the mixed culture is compared by measuring the intensity of the corresponding FP tags. Chemical-induced population shifts indicate that the bioactivity of a small molecule is dependent upon the target protein’s abundance and thus establish a specific functional interaction. Here, we describe the molecular tools required to apply this technique in the prevalent human fungal pathogen Candida albicans and validate the approach using two well-characterized drug targets—lanosterol demethylase and dihydrofolate reductase. However, our approach, which we have termed target abundance-based fitness screening (TAFiS), should be applicable to a wide array of molecular targets and in essentially any genetically tractable microbe.

IMPORTANCE Conventional drug screening typically employs either target-based or cell-based approaches. The first group relies on biochemical assays to detect modulators of a purified target. However, hits frequently lack drug-like characteristics such as membrane permeability and target specificity. Cell-based screens identify compounds that induce a desired phenotype, but the target is unknown, which severely restricts further development and optimization. To address these issues, we have developed a second-generation target-based whole-cell screening approach that incorporates the principles of both chemical genetics and competitive fitness, which enables the identification of target-specific and physiologically active compounds from a single screen. We have chosen to validate this approach using the important human fungal pathogen Candida albicans with the intention of pursuing novel antifungal targets. However, this approach is broadly applicable and is expected to dramatically reduce the time and resources required to progress from screening hit to lead compound.

Accumulation of Azole Drugs in the Fungal Plant Pathogen Magnaporthe oryzae Is the Result of Facilitated Diffusion Influx

Magnaporthe oryzae is an agricultural mold that causes disease in rice, resulting in devastating crop losses. Since rice is a world-wide staple food crop, infection by M. oryzae poses a serious global food security threat. Fungicides, including azole antifungals, are used to prevent and combat M. oryzae plant infections. The target of azoles is CYP51, an enzyme localized on the endoplasmic reticulum (ER) and required for fungal ergosterol biosynthesis. However, many basic drug-pathogen interactions, such as how the azole gets past the fungal cell wall and plasma membrane, and is transported to the ER, are not understood. In addition, reduced intracellular accumulation of antifungals has consistently been observed as a drug resistance mechanism in many fungal species. Studying the basic biology of drug-pathogen interactions may elucidate uncharacterized mechanisms of drug resistance and susceptibility in M. oryzae and potentially other related fungal pathogens. We characterized intracellular accumulation of azole drugs in M. oryzae using a radioactively labeled fluconazole uptake assay to gain insight on whether azoles enter the cell by passive diffusion, active transport, or facilitated diffusion. We show that azole accumulation is not ATP-dependent, nor does it rely on a pH-dependent process. Instead there is evidence for azole drug uptake in M. oryzae by a facilitated diffusion mechanism. The uptake system is specific for azole or azole-like compounds and can be modulated depending on cell phase and growth media. In addition, we found that co-treatment of M. oryzae with ‘repurposed’ clorgyline and radio-labeled fluconazole prevented energy-dependent efflux of fluconazole, resulting in an increased intracellular concentration of fluconazole in the fungal cell.

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.

Residue and intake risk assessment of prothioconazole and its metabolite prothioconazole-desthio in wheat field

In the environment, plants and animals in vivo, pesticides can be degraded or metabolized to form transformation products (TPs) or metabolites, which are even more toxic than parent pesticides. Hence, it was necessary to evaluate residue and risk of pesticides and their TPs (or metabolites). Here, a rapid, simple, and reliable method using QuEChERS and LC-MS/MS had been developed for simultaneous analysis of prothioconazole and its toxic metabolite, prothioconazole-desthio, in soil, wheat plant, straw, and grain. The average recoveries of prothioconazole and prothioconazole-desthio in four matrices ranged from 86 to 108% with relative standard deviations (RSDs) of 0.53-11.87% at three spiking levels. The method was successfully applied to investigate the dissipation and terminal residues of the two compounds in wheat field. It was shown that prothioconazole was rapidly degraded to prothioconazole-desthio, with half-lives below 5.82 days. Prothioconazole-desthio was slowly dissipated in soil and plant. The terminal residues of prothioconazole in wheat grain with a pre-harvest interval (PHI) of 21 or 28 days were below the maximum residue limits (MRLs) (0.1 mg/kg, Codex Alimentarius Commission (CAC)). We also evaluated the intake risk of prothioconazole-desthio residues in wheat grain in China. For long-term intake assessment, the hazard quotients (HQ) ranged from 1.30 to 5.95%. For short-term intake assessment, the acute hazard indexes (aHI) ranged from 1.94 to 18.2%. It indicated that the intake risk of prothioconazole-desthio in wheat consumption was acceptable. Thus, the prothioconazole application on wheat with the scientific practices would not pose public health risk.

In Vitro and In Vivo Antifungal Profile of a Novel and Long-Acting Inhaled Azole, PC945, on Aspergillus fumigatus Infection

The profile of PC945, a novel triazole antifungal designed for administration via inhalation, was assessed in a range of in vitro and in vivo studies. PC945 was characterized as a potent, tightly binding inhibitor of Aspergillus fumigatus sterol 14α-demethylase (CYP51A and CYP51B) activity (50% inhibitory concentrations [IC₅₀s], 0.23 μM and 0.22 μM, respectively) with characteristic type II azole binding spectra. Against 96 clinically isolated A. fumigatus strains, the MIC values of PC945 ranged from 0.032 to >8 μg/ml, while those of voriconazole ranged from 0.064 to 4 μg/ml. Spectrophotometric analysis of the effects of PC945 against itraconazole-susceptible and -resistant A. fumigatus growth yielded IC₅₀ (determined based on optical density [OD]) values of 0.0012 to 0.034 μg/ml, whereas voriconazole (0.019 to >1 μg/ml) was less effective than PC945. PC945 was effective against a broad spectrum of pathogenic fungi (with MICs ranging from 0.0078 to 2 μg/ml), including Aspergillus terreus, Trichophyton rubrum, Candida albicans, Candida glabrata, Candida krusei, Cryptococcus gattii, Cryptococcus neoformans, and Rhizopus oryzae (1 or 2 isolates each). In addition, when A. fumigatus hyphae or human bronchial cells were treated with PC945 and then washed, PC945 was found to be absorbed quickly into both target and nontarget cells and to produce persistent antifungal effects. Among temporarily neutropenic immunocompromised mice infected with A. fumigatus intranasally, 50% of the animals survived until day 7 when treated intranasally with PC945 at 0.56 μg/mouse, while posaconazole showed similar effects (44%) at 14 μg/mouse. This profile affirms that topical treatment with PC945 should provide potent antifungal activity in the lung.