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At least 19 recordsLinked to original sources
PubMed2000

Azoles for allergic bronchopulmonary aspergillosis.

BACKGROUND: Allergic Broncho-pulmonary Aspergillosis (ABPA) is hypersensitivity to the fungus Aspergillus Fumigatus that complicates patients with asthma and cystic fibrosis. The condition usually results in an increase in symptoms, a greater reliance on corticosteroids to control the disease process and may lead to a progressive decline in lung function. The mainstay of treatment for ABPA remains oral corticosteroids, though this does not completely prevent exacerbations and may not prevent the decline in lung function. OBJECTIVES: The purpose of this review is to determine the efficacy of azoles in the treatment of ABPA SEARCH STRATEGY: An initial search was carried out using the Cochrane Airways Group Asthma RCT register. The register was searched using the following terms: (asthma or wheeze) and (allergic bronchopulmonary aspergillosis or aspergillosis or allergic pulmonary aspergillosis or allergic fungal and disease or allergic mycotic and disease) and (azole or triazole or itraconazole or ketoconazole). SELECTION CRITERIA: All controlled trials that assessed the effect of azole antifungal agents compared to placebo or other standard, for any duration or dose regimen in subjects with ABPA of any age or severity were reviewed. Studies in languages other than English were included. DATA COLLECTION AND ANALYSIS: All identified trials were independently reviewed by both reviewers & all data collected. Trial quality was scored by the Cochrane assessment of allocation concealment & the Jadad scale of methodological quality. MAIN RESULTS: A total of 11 trials were identified concerning the use of azoles in ABPA. Only two prospective controlled trials were identified. The first trial examined the use of Ketoconazole 400 mg daily for 12 months and demonstrated a reduction in immunological markers of disease activity and symptom scores, there was no significant improvement in lung function. The other trial examined the use of itraconazole for 16 weeks. This demonstrated a reduction in corticosteroid usage, an improvement in immunological markers, an improvement in pulmonary function and exercise tolerance. This study was only available as an abstract and limited details were available. REVIEWER'S CONCLUSIONS: There is insufficient information available to recommend the use of azole anti-fungal agents in the routine treatment of patients with ABPA.

Antifungal Agents↗
PubMed1998

Amino acid substitutions in the cytochrome P-450 lanosterol 14alpha-demethylase (CYP51A1) from azole-resistant Candida albicans clinical isolates contribute to resistance to azole antifungal agents.

The cytochrome P-450 lanosterol 14alpha-demethylase (CYP51A1) of yeasts is involved in an important step in the biosynthesis of ergosterol. Since CYP51A1 is the target of azole antifungal agents, this enzyme is potentially prone to alterations leading to resistance to these agents. Among them, a decrease in the affinity of CYP51A1 for these agents is possible. We showed in a group of Candida albicans isolates from AIDS patients that multidrug efflux transporters were playing an important role in the resistance of C. albicans to azole antifungal agents, but without excluding the involvement of other factors (D. Sanglard, K. Kuchler, F. Ischer, J.-L. Pagani, M. Monod, and J. Bille, Antimicrob. Agents Chemother. 39:2378-2386, 1995). We therefore analyzed in closer detail changes in the affinity of CYP51A1 for azole antifungal agents. A strategy consisting of functional expression in Saccharomyces cerevisiae of the C. albicans CYP51A1 genes of sequential clinical isolates from patients was designed. This selection, which was coupled with a test of susceptibility to the azole derivatives fluconazole, ketoconazole, and itraconazole, enabled the detection of mutations in different cloned CYP51A1 genes, whose products are potentially affected in their affinity for azole derivatives. This selection enabled the detection of five different mutations in the cloned CYP51A1 genes which correlated with the occurrence of azole resistance in clinical C. albicans isolates. These mutations were as follows: replacement of the glycine at position 129 with alanine (G129A), Y132H, S405F, G464S, and R467K. While the S405F mutation was found as a single amino acid substitution in a CYP51A1 gene from an azole-resistant yeast, other mutations were found simultaneously in individual CYP51A1 genes, i.e., R467K with G464S, S405F with Y132H, G129A with G464S, and R467K with G464S and Y132H. Site-directed mutagenesis of a wild-type CYP51A1 gene was performed to estimate the effect of each of these mutations on resistance to azole derivatives. Each single mutation, with the exception of G129A, had a measurable effect on the affinity of the target enzyme for specific azole derivatives. We speculate that these specific mutations could combine with the effect of multidrug efflux transporters in the clinical isolates and contribute to different patterns and stepwise increases in resistance to azole derivatives.

Amino Acid Sequence↗
PubMed1995

Antagonistic interactions between azoles and amphotericin B with yeasts depend on azole lipophilia for special test conditions in vitro.

The interactions of the azole antifungal agents fluconazole, itraconazole, ketoconazole, or miconazole with amphotericin B (AmB) in their effect on Candida albicans were investigated. These four azoles antagonized the fungistatic activity of AmB at sub-MICs if both substances acted simultaneously. This coincubation test was primarily developed to observe the azole-mediated demethylase inhibition quantitatively by bioassay. Interestingly, the occurrence of azole-AmB antagonism depended on azole lipophilia if specially selected test conditions were applied. By a consecutive incubation regimen, preincubation at high azole concentrations (1 to 50 micrograms/ml) and then subsequent incubation with AmB (1 microgram/ml), only preincubation with the three lipophilic azoles decreased the fungicidal activity of AmB but not that of FCZ. It was shown that yeasts absorb only lipophilic azoles to a remarkable extent. This fact might be responsible for the absence of antagonism of FCZ to AmB when yeasts were incubated consecutively. It can be concluded with caution that consecutive treatment of candidiasis with FCZ and AmB does not necessarily result in a clinically relevant antagonism.

Amphotericin B↗
PubMed1998

Synergic effects of tactolimus and azole antifungal agents against azole-resistant Candida albican strains.

We investigated the effects of combining tacrolimus and azole antifungal agents in azole-resistant strains of Candida albicans by comparing the accumulation of [3H]itraconazole. The CDR1-expressing resistant strain C26 accumulated less itraconazole than the CaMDR-expressing resistant strain C40 or the azole-sensitive strain B2630. A CDR1-expressing Saccharomyces cerevisiae mutant, DSY415, showed a marked reduction in the accumulation of both fluconazole and itraconazole. A CaMDR-expressing S. cerevisiae mutant, DSY416, also showed lower accumulation of fluconazole, but not of itraconazole. The addition of sodium azide, an electron-transport chain inhibitor, increased the intracellular accumulation of itraconazole only in the C26 strain, and not in the C40 or B2630 strains. Addition of tacrolimus, an inhibitor of multidrug resistance proteins, resulted in the highest increase in itraconazole accumulation in the C26 strain. The combination of itraconazole and tacrolimus was synergic in azole-resistant C. albicans strains. In the C26 strain, the MIC of itraconazole decreased from >8 to 0.5 mg/L when combined with tacrolimus. Our results showed that two multidrug resistance phenotypes (encoded by the CDR1 and CaMDR genes) in C. albicans have different substrate specificity for azole antifungal agents and that a combination of tacrolimus and azole antifungal agents is effective against azole-resistant strains of C. albicans.

AIDS-Related Opportunistic Infections↗
PubMed1986

The lipid composition of azole-sensitive and azole-resistant strains of Candida albicans.

The lipid compositions of two azole-sensitive (A and B2630) and two azole-resistant (AD and KB) strains of the opportunistic fungal pathogen Candida albicans were studied by using several lipid extraction procedures: no differences were observed between the lipid content or total phospholipid/neutral lipid ratios of the four strains. All contained phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol and phosphatidylserine as major phospholipids, with smaller amounts of phosphatidylglycerol and diphosphatidylglycerol; the relative proportions of these lipids differed between all four strains. The fatty acid composition of each major phospholipid within each strain differed, and there were also interstrain differences. A marked effect of culture growth phase in batch culture on lipid composition was observed. The major neutral lipids in each strain were triacylglycerol, non-esterified sterol and non-esterified fatty acid. The fatty acid compositions of the three fatty-acid-containing neutral lipids were distinct from each other and the phospholipids, and there were also interstrain differences. All strains possessed (lyso)phospholipase activity, which was non-specific. The proportions of triacylglycerol and non-esterified fatty acid did not vary between strains, but the azole-resistant strains AD and KB contained more non-esterified sterol, giving them a phospholipid/sterol ratio approximately half that of azole-sensitive strains. There appeared to be a relationship between the phospholipid/sterol ratio of exponentially growing sensitive strains and their ability to take up azole; this did not extend to the resistant strains, which either did not take up azole (AD and KB) or took it up at a faster rate (Darlington) than sensitive strains.

Candida albicans↗
PubMed1989

Defective sterol C5-6 desaturation and azole resistance: a new hypothesis for the mode of action of azole antifungals.

Two azole resistant isolates of Saccharomyces cerevisiae carried mutations allelic to erg 3 and were blocked to differing degrees at the C5-6 desaturation step of ergosterol biosynthesis. When treated with the sterol 14 alpha-demethylation inhibitor fluconazole the wild-type sensitive strain accumulated lanosterol and 14 alpha-methyl-erogosta-8,24(28)-dien-3 beta, 6 alpha-diol (14-methyl-3,6 diol). The stringent desaturase mutant, A2, accumulated 14 alpha-methyl-8,24(28)-dien-3 beta-ol (14-methyl fecosterol) and lanosterol as the major sterol components when treated with fluconazole. Resistant isolate A3 accumulated 14-methyl-3,6-diol, 14-methyl fecosterol, and lanosterol and was only partially blocked at sterol C5-6 desaturation. We conclude that functional sterol C5-6 desaturase is required for the synthesis of 14-methyl-3,6-diol under conditions of azole inhibition. We present a new hypothesis for the mode of action of azole antifungals based on the inability of 14-methyl-3,6-diol to support growth, and suggest that growth can occur through utilisation of 14-methyl fecosterol, produced by a combination of azole inhibition and defective sterol C5-6 desaturation.

Antifungal Agents↗
PubMed1994

Disposition of azole antifungal agents. III. Binding of fluconazole and other azoles in rat liver.

It has been shown for the azole antifungal agents, ketoconazole and DTP, that hepatic binding, is a major determinant of their volume of distribution and this observation is of particular interest in view of the well-documented avid binding of azoles to cytochromes P450. Whilst the hepatic binding characteristics of these two compounds are similar, their hepatic clearance differs markedly in terms of the rate of metabolism and the number and nature of metabolites produced. Fluconazole is a bis-triazole drug similar in structure to DTP but not subject to metabolism in rat. We have demonstrated by means of steady-state infusion studies the clearance of this azole (1.85ml/min/kg) to be independent of blood concentration over a 0.01-50mg/L range. Also fluconazole plasma protein binding is minimal (9.5%) and its blood:plasma ratio unity over a similar concentration range. Liver:blood partition coefficients for fluconazole are concentration dependent ranging from 30 to 2. The volume of distribution term is also nonlinear with concentration and can be correlated with the liver:blood partition coefficient. These findings are discussed together with earlier documented data on ketoconazole and DTP in terms of a tissue binding role for hepatic cytochromes P450. The similarity in behaviour of the hepatic partitioning of the three azoles contrasts markedly with the nature of (or lack of) hepatic metabolism.

Adrenal Glands↗
PubMed1996

Naturally azole-resistant Leishmania braziliensis promastigotes are rendered susceptible in the presence of terbinafine: comparative study with azole-susceptible Leishmania mexicana promastigotes.

Leishmania braziliensis (isolate 2903) was naturally resistant to ketoconazole or the bis-triazole D0870, inhibitors of sterol C-14 demethylase, which produced only moderate effects on the proliferation of promastigotes at 10 microM. In contrast, Leishmania mexicana (isolate NR) was extremely susceptible to the azoles, as complete growth arrest and cell lysis were induced by incubation of the parasites with 0.05 microM concentrations of the drugs for 72 h. The opposite response was observed with terbinafine, an inhibitor of squalene epoxidase: L. braziliensis 2903 was three times more susceptible to the drug than L. mexicana NR (MICs of 5 and 15 microM, respectively). However, when the L. braziliensis stock was grown in the presence of 1 microM terbinafine, which by itself produced only marginal (< 10%) effects on growth, it became highly susceptible to the azoles, with an MIC of 0.03 microM. Analysis of cellular free sterols by high-resolution capillary gas chromatography coupled to mass spectrometry showed that 14-methyl sterols can support normal growth of L. braziliensis 2903 but not of L. mexicana NR. On the other hand, the higher susceptibility of the L. braziliensis isolate to terbinafine was correlated with a massive accumulation of squalene in the presence of the allylamine while no significant effects on L. mexicana sterol composition were observed at drug concentrations up to 1 microM. Thus, the > 300-fold increase in the susceptibility of L. braziliensis promastigotes to azoles in the presence of terbinafine was attributed to the combined effect of squalene and the methylated sterol precursors on the physical properties of the cell's membranes, leading to the loss of cell viability. Combination therapy with azoles and terbinafine in the treatment of human L. braziliensis infections deserves further study.

Animals↗
PubMed1987

The lipid composition and permeability to azole of an azole- and polyene-resistant mutant of Candida albicans.

Candida albicans 6.4, which is resistant to both polyene and azole groups of antifungal antibiotics, has a larger lipid content and lower polar lipid to neutral lipid ratio compared with other strains that are sensitive or resistant only to azoles. C. albicans 6.4 contains a relatively greater proportion of triacylglycerol in its neutral lipid in the exponential phase of batch culture compared with other strains, but, unlike them, does not accumulate triacylglycerols or any other stored lipid in the stationary phase. Like other strains, in C. albicans 6.4 the major phospholipids are phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, but sphingomyelin is absent; the major fatty acids are palmitic, palmitoleic, oleic and linoleic acids. In common with other C. albicans strains, strain 6.4 contains non-specific (lyso)phospholipase activity. The main distinctive feature of the lipid composition of C. albicans 6.4 is the absence of ergosterol, which is replaced by methylated sterol; mainly lanosterol, 24-methylene-24,25-dihydrolanosterol and 4-methylergostadiene-3-ol. It is suggested that the altered membrane sterol pattern provides a common basis for the double resistance by preventing polyene binding and reducing azole permeability.

Antifungal Agents↗
PubMed1991

Restriction fragment length polymorphism analysis of azole-resistant and azole-susceptible Candida albicans strains.

Restriction fragment length polymorphism analysis was performed with the endonucleases EcoRI, BglII, and HinfI on a collection of Candida albicans strains comprising eight strains randomly selected from clinical microbiology laboratory specimens, three reported azole-resistant strains from treatment failures, and several subcultures of the azole-resistant strain NCPF 3310 (also known as the Darlington strain) received from different laboratories. The results demonstrated a diversity of the restriction fragment length polymorphism patterns that were obtained and revealed that two of the proposed Darlington subcultures had patterns distinct from each other and from those of the other Darlington isolates; both were also found to have lost their azole resistance.

Azoles↗
PubMed1999

The ATP binding cassette transporter gene CgCDR1 from Candida glabrata is involved in the resistance of clinical isolates to azole antifungal agents.

The resistance mechanisms to azole antifungal agents were investigated in this study with two pairs of Candida glabrata clinical isolates recovered from two separate AIDS patients. The two pairs each contained a fluconazole-susceptible isolate and a fluconazole-resistant isolate, the latter with cross-resistance to itraconazole and ketoconazole. Since the accumulation of fluconazole and of another unrelated substance, rhodamine 6G, was reduced in the azole-resistant isolates, enhanced drug efflux was considered as a possible resistance mechanism. The expression of multidrug efflux transporter genes was therefore examined in the azole-susceptible and azole-resistant yeast isolates. For this purpose, C. glabrata genes conferring resistance to azole antifungals were cloned in a Saccharomyces cerevisiae strain in which the ATP binding cassette (ABC) transporter gene PDR5 was deleted. Three different genes were recovered, and among them, only C. glabrata CDR1 (CgCDR1), a gene similar to the Candida albicans ABC transporter CDR genes, was upregulated by a factor of 5 to 8 in the azole-resistant isolates. A correlation between upregulation of this gene and azole resistance was thus established. The deletion of CgCDR1 in an azole-resistant C. glabrata clinical isolate rendered the resulting mutant (DSY1041) susceptible to azole derivatives as the azole-susceptible clinical parent, thus providing genetic evidence that a specific mechanism was involved in the azole resistance of a clinical isolate. When CgCDR1 obtained from an azole-susceptible isolate was reintroduced with the help of a centromeric vector in DSY1041, azole resistance was restored and thus suggested that a trans-acting mutation(s) could be made responsible for the increased expression of this ABC transporter gene in the azole-resistant strain. This study demonstrates for the first time the determinant role of an ABC transporter gene in the acquisition of resistance to azole antifungals by C. glabrata clinical isolates.

ATP-Binding Cassette Transporters↗
PubMed2003

Tacrolimus dosage requirements after initiation of azole antifungal therapy in pediatric thoracic organ transplantation.

Azole antifungals inhibit the metabolism of tacrolimus mediated by CYP3A4. Upon initiation of azole therapy, the required dose reduction of tacrolimus is unknown. We reviewed our experience with azole antifungals in our pediatric thoracic transplant population receiving tacrolimus. Tacrolimus levels and dosage requirements were compared before and during azole therapy. Thirty-one patients received both tacrolimus and an azole antifungal (fluconazole = 9, itraconazole = 22). The tacrolimus dose was empirically reduced by approximately one-third when azole therapy was initiated. Mean tacrolimus dose requirements decreased by 68% within the first month of therapy (pre-azole: 0.27 +/- 0.14 mg/kg/day; 30 day post-azole: 0.087 +/- 0.069 mg/kg/day; p < 0.001). Despite a mean decrease in tacrolimus dose from baseline of 33, 42, and 55% on day 1, 2, and 4 of azole therapy, respectively, there was still an unintended 38% increase in tacrolimus levels during the first month of azole therapy. A calculated dose-reduction protocol of 50% on day of azole initiation, 70% on day 3, and 75% on day 14 should result in minimal mean changes in the tacrolimus levels. There was no difference in tacrolimus dose reduction between fluconazole and itraconazole groups. Azole antifungals markedly decrease tacrolimus requirements within the first few days of therapy. An initial reduction in tacrolimus dose by one-third is insufficient, and dose reduction of at least 50% upon azole initiation seems warranted. Once azole antifungal therapy is initiated, frequent therapeutic drug monitoring is required.

Analysis of Variance↗
PubMed2003

Multiple mechanisms account for variation in base-line sensitivity to azole fungicides in field isolates of Mycosphaerella graminicola.

Molecular mechanisms that account for variation in base-line sensitivity to azole fungicides were examined in a collection of twenty field isolates, collected in France and Germany, of the wheat pathogen Mycosphaerella graminicola (Fuckel) Schroeter. The isolates tested represent the wide baseline sensitivity to the azole fungicide tebuconazole described previously. The isolates were cross-sensitive to other azoles tested, such as cyproconazole and ketoconazole, but not to unrelated chemicals like cycloheximide, kresoxim-methyl or rhodamine 6G. Progenies from a genetic cross between an isolate with an intermediate and a high sensitivity to azoles displayed a continuous range of phenotypes with respect to cyproconazole sensitivity, indicating that variation in azole sensitivity in this haploid organism is polygenic. The basal level of expression of the ATP-binding cassette transporter genes MgAtr1-MgAtr5 from Mgraminicola significantly varied amongst the isolates tested, but no clear increase in the transcript level of a particular MgAtr gene was found in the less sensitive isolates. Cyproconazole strongly induced expression of MgAtr4, but no correlation between expression levels of this gene and azole sensitivity was observed. One isolate with intermediate sensitivity to azoles over-expressed CYP51, encoding cytochrome P450 sterol 14alpha-demethylase from M graminicola. Isolates with a low or high sensitivity to azoles were tested for accumulation of cyproconazole, but no clear correlation between reduced accumulation of the fungicide in mycelium and sensitivity to azoles was observed. Therefore, differences in accumulation cannot account exclusively for the variation in base-line sensitivity of the isolates to azoles. The results indicate that multiple mechanisms account for differences in base-line sensitivity to azoles in field isolates of M graminicola.

ATP-Binding Cassette Transporters↗
PubMed1995

Mechanisms of resistance to azole antifungals.

Until the late eighties, clinical resistance to azole antifungals was a rare phenomenon. Only a few cases of resistance to ketoconazole were found in patients with chronic mucocutaneous candidiasis (CMC). The spread of AIDS and the widespread prophylactic and therapeutic use of the hydrophilic azole compound fluconazole resulted both in the selection and induction of resistant strains and in a shift in the nature of the infecting organisms. Most azole antifungals such as itraconazole, ketoconazole and fluconazole are active against a variety of fungal diseases. However, the concentration needed to inhibit growth is dependent on the nature of the infecting species. Mucor spp., e.g., are almost insensitive to present available azole compounds and can be regarded as intrinsically resistant to azole treatment. Physiochemical features, such as the hydrophobicity and pKa, of a given azole, define whether or not it will be active or cross-resistant against a given species. Fluconazole is almost inactive against Candida krusei and Aspergillus fumigatus, whereas the lipophilic itraconazole is active against these species. A third type of resistance is acquired or induced resistance. This is the most controversial type because, even within a given species, organisms may differ in their response to the same azole. For these strains, convincing evidence can only be obtained when there is a genotypically related strain, which does not show resistance. In a limited number of biochemical or molecular biological studies the mechanisms of resistance have been investigated at the molecular level. These studies show that resistance can occur when there is an insufficient intracellular content of the azole. This can be due to impermeability problems, inactivated uptake systems or, and more likely, the presence of active multidrug resistance gene products of the P-glycoprotein type. Alteration or overexpression of the target for azole antifungals, the cytochrome P450-dependent 14 alpha-demethylase, also induces resistance. The nature and amount of the accumulating sterols also are of great importance for azole-induced growth inhibition. This may explain why mutations in other enzymes of the ergosterol biosynthesis pathway, e.g. the delta 5-6 desaturase, can contribute to azole resistance.

Antifungal Agents↗
PubMed2026

Identification and characterization of non-canonical azole antifungal resistance pathways in Aspergillus fumigatus.

UNLABELLED: Human fungal infections, especially those caused by Aspergillus fumigatus, pose a significant global health threat, particularly in immunocompromised individuals. Azole antifungals are the primary treatment for this pathogen; however, the prevalence of azole-resistant A. fumigatus strains is steadily increasing. Mutations in cyp51A, which encodes an enzyme involved in ergosterol biosynthesis and the molecular target of the azoles, are well established to confer resistance in this fungal species. However, additional mechanisms governing resistance to this antifungal class remain understudied and poorly characterized, despite growing recognition of their importance in clinical resistance. In this study, we investigated the genetic basis of azole resistance in A. fumigatus isolates from clinical settings worldwide, with a particular focus on mechanisms independent of cyp51A (non-canonical). Using a combination of genomic and functional approaches, including whole-genome sequencing and transcriptomic analysis, we identified novel genetic variants and characterized population structure, advancing our understanding of the genetic diversity and evolutionary dynamics of resistance in A. fumigatus. By expanding our understanding of the complex genetic and molecular factors underlying azole resistance in this important human fungal pathogen, this research is poised to inform the development of novel antifungal strategies and contribute to global efforts to combat fungal infections. IMPORTANCE: Azole antifungals are the frontline therapy for infections caused by the opportunistic mold Aspergillus fumigatus, yet resistance to these drugs is rapidly increasing worldwide. Most studies have focused on mutations in cyp51A, the canonical target of azoles; however, a growing proportion of resistant clinical isolates lack these mutations, indicating that alternative resistance mechanisms are emerging. Here, we integrate population genomics, transcriptomics, and functional analyses across a global collection of isolates to define the architecture of cyp51-independent (non-canonical) azole resistance. We show that this resistance phenotype is strongly associated with a distinct population lineage and is driven by a highly polygenic network of metabolic, mitochondrial, and regulatory adaptations rather than single target site mutations. These isolates exhibit extensive transcriptional rewiring and metabolic remodeling under azole stress, suggesting distinct survival strategies beyond canonical resistance. Our findings reveal that azole resistance in A. fumigatus can evolve through diverse evolutionary routes and emphasize the need to monitor and therapeutically target non-canonical pathways that may increasingly contribute to antifungal treatment failure.

Aspergillus fumigatus↗
PubMed2002

Azole antifungals are potent inhibitors of cytochrome P450 mono-oxygenases and bacterial growth in mycobacteria and streptomycetes.

The genome sequence of Mycobacterium tuberculosis has revealed the presence of 20 different cytochrome P450 mono-oxygenases (P450s) within this organism, and subsequent genome sequences of other mycobacteria and of Streptomyces coelicolor have indicated that these actinomycetes also have large complements of P450s, pointing to important physiological roles for these enzymes. The actinomycete P450s include homologues of 14alpha-sterol demethylases, the targets for the azole class of drugs in yeast and fungi. Previously, this type of P450 was considered to be absent from bacteria. When present at low concentrations in growth medium, azole antifungal drugs were shown to be potent inhibitors of the growth of Mycobacterium smegmatis and of Streptomyces strains, indicating that one or more of the P450s in these bacteria were viable drug targets. The drugs econazole and clotrimazole were most effective against M. smegmatis (MIC values of <0.2 and 0.3 micro M, respectively) and were superior inhibitors of mycobacterial growth compared to rifampicin and isoniazid (which had MIC values of 1.2 and 36.5 micro M, respectively). In contrast to their effects on the actinomycetes, the azoles showed minimal effects on the growth of Escherichia coli, which is devoid of P450s. Azole drugs coordinated tightly to the haem iron in M. tuberculosis H37Rv P450s encoded by genes Rv0764c (the sterol demethylase CYP51) and Rv2276 (CYP121). However, the azoles had a higher affinity for M. tuberculosis CYP121, with K(d) values broadly in line with the MIC values for M. smegmatis. This suggested that CYP121 may be a more realistic target enzyme for the azole drugs than CYP51, particularly in light of the fact that an S. coelicolor DeltaCYP51 strain was viable and showed little difference in its sensitivity to azole drugs compared to the wild-type. If the azole drugs prove to inhibit a number of important P450s in M. smegmatis and S. coelicolor, then the likelihood of drug resistance developing in these species should be minimal. This suggests that azole drug therapy may provide a novel antibiotic strategy against strains of M. tuberculosis that have already developed resistance to isoniazid and other front-line drugs.

Antifungal Agents↗
PubMed1996

In vitro interaction between amphotericin B and azoles in Candida albicans.

The use of azole prophylaxis as a measure to prevent invasive fungal infections in high-risk patients is increasing and is now the standard of care in many institutions. Previous studies disagree on whether preexposure of Candida albicans to azoles affects their subsequent susceptibility to amphotericin B (AmB). The present in vitro study indicates that azole exposure generates a subpopulation of cells that are not affected by subsequent exposure to AmB. These cells that are phenotypically resistant to AmB tolerated by most cells not exposed to azole. The percentage of cells that convert to phenotypic resistance to AmB varies with the concentration and the azole. Itraconazole is more effective than fluconazole in generating cells that are phenotypically resistant to AmB and that tolerate an otherwise lethal transient exposure to AmB. Until cells that are not exposed to fluconazole are simultaneously challenged with AmB, they are not protected to a significant extent from killing by AmB. Cells that are challenged with continuous exposure to AmB also acquire phenotypic resistance to AmB at increased frequencies by azole preexposure, but this requires that the azole be continuously present during incubation with AmB. In addition, Candida cells taken from mature colonies that are not actively growing are not susceptible to the short-term killing effects of AmB without azole preexposure. The adaptive responses of C. albicans to AmB and potentially other antifungal agents that may result from prior exposure to azoles in vitro or potentially in microenvironments in vivo that induce physiological changes may have major clinical implications.

Amphotericin B↗