The structure and characterization of human cytochrome P450 8B1 supports future drug design for nonalcoholic fatty liver disease and diabetes.

Human cytochrome P450 8B1 (CYP8B1) is involved in conversion of cholesterol to bile acids. It hydroxylates the steroid ring at C12 to ultimately produce the bile acid cholic acid. Studies implicated this enzyme as a good drug target for nonalcoholic fatty liver disease and type 2 diabetes, but there are no selective inhibitors known for this enzyme and no structures to guide inhibitor development. Herein, the human CYP8B1 protein was generated and used to identify and characterize interactions with a series of azole inhibitors, which tend to be poorly selective P450 inhibitors. Structurally related miconazole, econazole, and tioconazole bound with submicromolar dissociation constants and were effective inhibitors of the native reaction. CYP8B was cocrystallized with S-tioconazole to yield the first X-ray structure. This inhibitor bound in the active site with its azole nitrogen coordinating the heme iron, consistent with inhibitor binding and inhibition assay data. Additionally, the CYP8B1 active site was compared with similar P450 enzymes to identify features that may facilitate the design of more selective inhibitors. Selective inhibitors should promote a better understanding of the role of CYP8B1 inhibition in normal physiology and disease states and provide a possible treatment for nonalcoholic fatty liver disease and type 2 diabetes.

Fabrication of a drug delivery system that enhances antifungal drug corneal penetration.

Fungal keratitis (FK) remains a severe eye disease, and effective therapies are limited by drug shortages and critical ocular barriers. Despite the high antifungal potency and broad spectrum of econazole, its strong irritant and insolubility in water hinder its ocular application. We designed and fabricated a new drug delivery system based on a polymeric vector for the ocular antifungal application of econazole. This novel system integrates the advantages of its constituent units and exhibits superior comprehensive performance. Using the new system, drug content was significantly increased more than 600 folds. The results of in vivo and in vitro experiments demonstrated that the econazole-loaded formulation exhibited significantly enhanced corneal penetration after a single topical ocular administration, excellent antifungal activity, and good tolerance in rabbits. Drug concentrations and ocular relative bioavailability in the cornea were 59- and 29-time greater than those in the control group, respectively. Following the topical administration of one eye drop (50 µL of 0.3% w/v econazole) in fungus-infected rabbits, a high concentration of antimycotic drugs in the cornea and aqueous humor was sustained and effective for 4 h. The mechanism of corneal penetration was also explored using dual fluorescent labeling. This novel drug delivery system is a promising therapeutic approach for oculomycosis and could serve as a candidate strategy for use with various hydrophobic drugs to overcome barriers in the treatment of many other ocular diseases.

Improvement of the Ocular Bioavailability of Econazole Nitrate upon Complexation with Cyclodextrins.

Econazole nitrate (EC) is an active, imidazole antifungal agent. However, low aqueous solubility and dissolution rate of EC has discouraged its usage for the treatment of ophthalmic fungal infection. In this study, inclusion complexes of EC with cyclodextrins were prepared to enhance its solubility, dissolution, and ocular bioavailability. To achieve this goal, EC was complexed with ß-CyD/HP-ß-CyD using kneading, co-precipitation, and freeze-drying techniques. Phase-solubility studies were performed to investigate the complexes in the liquid form. Additionally, the complexes in the solid form were characterized with Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and transmission electron microscopy (TEM). Furthermore, different eye drops containing EC-CyD complexes were prepared using different polymers and then characterized regarding their drug contents, pH, viscosity, mucoadhesive strength, and in vitro release characteristics. The results showed that stable EC-CyD complexes were formed in 1:1 molar ratio as designated by BS-type diagram. Econazole nitrate water solubility was significantly increased in about three- and fourfold for ß-CyD and HP-ß-CyD, respectively. The results showed that the prepared complexes were spherical in shape having an average particle diameter from 110 to 288.33 nm with entrapment efficiency ranging from 64.24 to 95.27%. DSC investigations showed the formation of real inclusion complexes obtained with co-precipitation technique. From the in vitro studies, all eye drops containing co-precipitate complexes exhibited higher release rate than that of other complexes and followed the diffusion-controlled mechanism. In vivo study proved that eye drops containing EC-CyD complexes showed higher ocular bioavailability than EC alone which indicated by higher AUC, Cmax, and relative bioavailability values.

Percutaneous delivery of econazole using microemulsion as vehicle: formulation, evaluation and vesicle-skin interaction.

This project was carried out to exploit the feasibility of using microemulsion (ME) as an alternative carrier for percutaneous delivery econazole nitrate (ECN) and elucidate the underlying mechanism of permeation enhancement. The ME was developed based on Labrafil M 1944 Cs as oil phase, Solutol HS15 and Span 80 as surfactants, Transcutol P as cosurfactant and water as aqueous phase. The solubility of ECN was firstly determined for screening the ingredients of the system. Pseudo-ternary phase diagrams were constructed to formulate ME and select surfactant and cosurfactant. Central composite design-response surface methodology (CCD-RSM) was utilized to optimize the formulation of ME. The ECN loaded ME was characterized in terms of morphology, particle size and size distribution, pH value, refractive index, viscosity and conductivity, and storage stability of the ECN loaded ME was assayed. Percutaneous permeation of ECN from ME in vitro through rat skin was investigated in comparison with PBS aqueous suspension (1%, w/w), and results showed that ME enhanced drug retention in the skin and permeation through the skin, the enhancement of ME on skin deposition was further visualized through fluorescent-labeled ME by confocal laser scanning microscope (CLSM). The action mechanism of ME on improving percutaneous delivery was studied by performing a pretreatment test. It can speculate that ME does not simply behave as enhancer but it also acts as drug carrier. Furthermore, ME-skin interaction was elucidated through transmission electron microscope (TEM), and attenuated total reflectance fourier-transform infrared (ATR-FTIR). TEM was performed to visualize the micro morphological change of skin. ATR-FTIR was carried out to investigate the molecular vibrations of the components of stratum corneum (SC). The results indicate that the ME system may be a promising vehicle for percutaneous delivery of ECN.

Binding free energies of inhibitors to iron porphyrin complex as a model for Cytochrome P450.

The binding free energies of the inhibitor-heme model complexes are calculated using the density functional methods and the implicit solvation models in water, where the 16 structurally diverse compounds with a spectrum of IC(50) values from 0.05 (clotrimazole) to 1000 (piroxicam) µM are chosen as inhibitors for Cytochrome P450 3A4 (CYP3A4). CYP3A4 is the most predominant constituent of the human hepatic CYP enzymes that play a role in metabolizing structurally diverse xenobiotics. The observed free energy change for each inhibitory binding, ΔG inh0, is obtained from its IC(50) value. The total binding free energy (ΔG b0) of each inhibitor-heme model complex is calculated by the sum of its relative free energy (ΔG(0) ) in the gas phase and solvation free energy to the water-heme model complex. The UB3LYP/LanL2DZ level of theory provides the correct relative stabilities of the high- and low-spin states for the penta- and hexa-coordinated ferric complexes, respectively. The optimized distances of the inhibitor nitrogen (or water oxygen) and the methyl mercaptide S to the ferric iron of the inhibitor-heme model complexes at the same level of theory are consistent with the values of the corresponding X-ray structures, except for the econazole complex. The correlation coefficient r(2) values of 0.91 and 0.75 are obtained from the ΔG b0-ΔG inh0 and ΔG(0) -ΔG inh0 plots, respectively, at the UM06/LanL2DZ:CPCM_UB3LYP/LanL2DZ//UB3LYP/LanL2DZ level of theory in water. This indicates that the total binding free energies calculated for the inhibitor-heme model complexes can be a good descriptor in interpreting the inhibitor binding to CYP3A4 and the relative free energies in the gas phase are mainly responsible for the total binding free energies in water, although the desolvation can be a factor to affect the binding affinity of the inhibitors to CYP3A4. From the theozyme analysis of the X-ray structures for ketoconazole- and metyrapone-CYP3A4 complexes, the interaction free energy of the neighboring residues with each inhibitor in the active site is calculated to be about -3 kcal mol(-1) in water, whose the interaction energy and the desolvation free energy change are about -5 and 2 kcal mol(-1) , respectively.

An enlarged, adaptable active site in CYP164 family P450 enzymes, the sole P450 in Mycobacterium leprae.

CYP164 family P450 enzymes are found in only a subset of mycobacteria and include CYP164A1, which is the sole P450 found in Mycobacterium leprae, the causative agent of leprosy. This has previously led to interest in this enzyme as a potential drug target. Here we describe the first crystal structure of a CYP164 enzyme, CYP164A2 from Mycobacterium smegmatis. CYP164A2 has a distinctive, enlarged hydrophobic active site that extends above the porphyrin ring toward the access channels. Unusually, we find that CYP164A2 can simultaneously bind two econazole molecules in different regions of the enlarged active site and is accompanied by the rearrangement and ordering of the BC loop. The primary location is through a classic interaction of the azole group with the porphyrin iron. The second econazole molecule is bound to a unique site and is linked to a tetracoordinated metal ion complexed to one of the heme carboxylates and to the side chains of His 105 and His 364. All of these features are preserved in the closely homologous M. leprae CYP164A1. The computational docking of azole compounds to a homology model of CYP164A1 suggests that these compounds will form effective inhibitors and is supported by the correlation of parallel docking with experimental binding studies of CYP164A2. The binding of econazole to CYP164A2 occurs primarily through the high-spin "open" conformation of the enzyme (K(d) [dissociation constant] of 0.1 µM), with binding to the low-spin "closed" form being significantly hindered (K(d) of 338 µM). These studies support previous suggestions that azole derivatives may provide an effective strategy to improve the treatment of leprosy.

Expression and characterization of Mycobacterium tuberculosis CYP144: common themes and lessons learned in the M. tuberculosis P450 enzyme family.

CYP144 from Mycobacterium tuberculosis was expressed and purified. CYP144 demonstrates heme thiolate coordination in its ferric form, but the cysteinate is protonated to thiol in both the carbon monoxide-bound and ligand-free ferrous forms (forming P420 in the former). Tight binding of various azole drugs was shown, with affinity for miconazole (K(d)=0.98 µM), clotrimazole (0.37 µM) and econazole (0.78 µM) being highest. These azoles are also the trio with the highest affinity for the essential CYP121 and for the cholesterol oxidase CYP125 (essential for host infection), and have high potency as anti-mycobacterial drugs. Construction of a Mtb gene knockout strain demonstrated that CYP144 is not essential for growth in vitro. However the deletion strain was more sensitive to azole inhibition in culture suggesting an important role for CYP144 in cell physiology and/or in mediating azole resistance. The biophysical and genetic features of CYP144 are compared to those of other characterized Mtb P450s, identifying both commonality in properties (including thiolate protonation in ferrous P450s) and intriguing differences in thermodynamic and spectroscopic features. Our developing knowledge of the Mtb P450s has revealed unusual biochemistry and gene essentiality, highlighting their potential as drug targets in this human pathogen.

Azole binding properties of Candida albicans sterol 14-alpha demethylase (CaCYP51).

Purified Candida albicans sterol 14-α demethylase (CaCYP51) bound the CYP51 substrates lanosterol and eburicol, producing type I binding spectra with K(s) values of 11 and 25 µM, respectively, and a K(m) value of 6 µM for lanosterol. Azole binding to CaCYP51 was "tight" with both the type II spectral intensity (ΔA(max)) and the azole concentration required to obtain a half-ΔA(max) being proportional to the CaCYP51 concentration. Tight binding of fluconazole and itraconazole was confirmed by 50% inhibitory concentration determinations from CYP51 reconstitution assays. CaCYP51 had similar affinities for clotrimazole, econazole, itraconazole, ketoconazole, miconazole, and voriconazole, with K(d) values of 10 to 26 µM under oxidative conditions, compared with 47 µM for fluconazole. The affinities of CaCYP51 for fluconazole and itraconazole appeared to be 4- and 2-fold lower based on CO displacement studies than those when using direct ligand binding under oxidative conditions. Econazole and miconazole were most readily displaced by carbon monoxide, followed by clotrimazole, ketoconazole, and fluconazole, and then voriconazole (7.8 pmol min(-1)), but itraconzole could not be displaced by carbon monoxide. This work reports in depth the characterization of the azole binding properties of wild-type C. albicans CYP51, including that of voriconazole, and will contribute to effective screening of new therapeutic azole antifungal agents. Preliminary comparative studies with the I471T CaCYP51 protein suggested that fluconazole resistance conferred by this mutation was through a combination of increased turnover, increased affinity for substrate, and a reduced affinity for fluconazole in the presence of substrate, allowing the enzyme to remain functionally active, albeit at reduced velocity, at higher fluconazole concentrations.

Structural basis of human CYP51 inhibition by antifungal azoles.

The obligatory step in sterol biosynthesis in eukaryotes is demethylation of sterol precursors at the C14-position, which is catalyzed by CYP51 (sterol 14-alpha demethylase) in three sequential reactions. In mammals, the final product of the pathway is cholesterol, while important intermediates, meiosis-activating sterols, are produced by CYP51. Three crystal structures of human CYP51, ligand-free and complexed with antifungal drugs ketoconazole and econazole, were determined, allowing analysis of the molecular basis for functional conservation within the CYP51 family. Azole binding occurs mostly through hydrophobic interactions with conservative residues of the active site. The substantial conformational changes in the B' helix and F-G loop regions are induced upon ligand binding, consistent with the membrane nature of the protein and its substrate. The access channel is typical for mammalian sterol-metabolizing P450 enzymes, but is different from that observed in Mycobacterium tuberculosis CYP51. Comparison of the azole-bound structures provides insight into the relative binding affinities of human and bacterial P450 enzymes to ketoconazole and fluconazole, which can be useful for the rational design of antifungal compounds and specific modulators of human CYP51.

Azole resistance in Mycobacterium tuberculosis is mediated by the MmpS5-MmpL5 efflux system.

Tuberculosis (TB) remains the leading cause of mortality due to a bacterial pathogen, Mycobacterium tuberculosis. Moreover, the recent isolation of M. tuberculosis strains resistant to both first- and second-line antitubercular drugs (XDR-TB) threatens to make the treatment of this disease extremely difficult and becoming a threat to public health worldwide. Recently, it has been shown that azoles are potent inhibitors of mycobacterial cell growth and have antitubercular activity in mice, thus favoring the hypothesis that these drugs may constitute a novel strategy against tuberculosis disease. To investigate the mechanisms of resistance to azoles in mycobacteria, we isolated and characterized several spontaneous azoles resistant mutants from M. tuberculosis and Mycobacterium bovis BCG. All the analyzed resistant mutants exhibited both increased econazole efflux and increased transcription of mmpS5-mmpL5 genes, encoding a hypothetical efflux system belonging to the resistance-nodulation-division (RND) family of transporters. We found that the up-regulation of mmpS5-mmpL5 genes was linked to mutations either in the Rv0678 gene, hypothesized to be involved in the transcriptional regulation of this efflux system, or in its putative promoter/operator region.

Mycobacterium tuberculosis CYP130: crystal structure, biophysical characterization, and interactions with antifungal azole drugs.

CYP130 is one of the 20 Mycobacterium tuberculosis cytochrome P450 enzymes, only two of which, CYP51 and CYP121, have so far been studied as individually expressed proteins. Here we characterize a third heterologously expressed M. tuberculosis cytochrome P450, CYP130, by UV-visible spectroscopy, isothermal titration calorimetry, and x-ray crystallography, including determination of the crystal structures of ligand-free and econazole-bound CYP130 at a resolution of 1.46 and 3.0A(,) respectively. Ligand-free CYP130 crystallizes in an "open" conformation as a monomer, whereas the econazole-bound form crystallizes in a "closed" conformation as a dimer. Conformational changes enabling the "open-closed" transition involve repositioning of the BC-loop and the F and G helices that envelop the inhibitor in the binding site and reshape the protein surface. Crystal structure analysis shows that the portion of the BC-loop relocates as much as 18A between the open and closed conformations. Binding of econazole to CYP130 involves a conformational change and is mediated by both a set of hydrophobic interactions with amino acid residues in the active site and coordination of the heme iron. CYP130 also binds miconazole with virtually the same binding affinity as econazole and clotrimazole and ketoconazole with somewhat lower affinities, which makes it a plausible target for this class of therapeutic drugs. Overall, binding of the azole inhibitors is a sequential two-step, entropy-driven endothermic process. Binding of econazole and clotrimazole exhibits positive cooperativity that may reflect a propensity of CYP130 to associate into a dimeric structure.

Activity of the Kluyveromyces lactis Pdr5 multidrug transporter is modulated by the Sit4 protein phosphatase.

A possible role for posttranslational modifications in regulating the activity of ATP-binding cassette (ABC) transporters has not been well established. In this study, the drug efflux ABC transporter gene KlPDR5 was isolated from the budding yeast Kluyveromyces lactis, and it was found that the encoded KlPdr5 drug pump is posttranslationally regulated by the type 2A-related Ser/Thr protein phosphatase, Sit4p. The KlPdr5 transporter is a protein of 1,525 amino acids sharing 63.8% sequence identity with its Saccharomyces cerevisiae counterpart, ScPdr5p. Overexpression of the KlPDR5 gene confers resistance to oligomycin, antimycin, econazole, and ketoconazole, whereas cells with a disrupted allele of KlPDR5 are hypersensitive to the drugs and have a decreased capacity to carry out efflux of the anionic fluorescent dye rhodamine 123. It was found that a chromosomal disruption of KlPDR5 abolishes the drug-resistant phenotype associated with sit4 mutations and that a synergistic hyperresistance to the drugs can be created by overexpressing KlPDR5 in sit4 mutants. These data strongly indicate that the multidrug-resistant phenotype of sit4 mutants is mediated by negatively modulating the activity of KlPdr5p. As the transcriptional level of KlPDR5 and the steady-state level of KlPdr5p are not significantly affected by mutations in SIT4, the regulation by Sit4p appears to be a posttranslational process.

Influence of the corneal epithelium on the efficacy of topical antifungal agents.

A model of deep stromal Candida albicans infection was established by injecting 25 microliters of a suspension containing 5 X 10(9) colony forming units/ml of the yeast into corneas of pigmented rabbits. In this model, the infection lasts for more than 8 days. Using quantitative techniques, the authors compared the efficacy of six topical antifungal agents in the presence of an intact epithelium and in corneas debrided of epithelium. In corneas debrided on a daily basis, the polyenes (amphotericin B 0.15% and 0.075% and natamycin 5%) exhibited a significant antifungal effect. When the epithelium was left intact, 5% natamycin and 0.075% amphotericin B were without effect, while the efficacy of the 0.15% preparation of amphotericin B was much reduced. Removal of the epithelium appeared to affect adversely the efficacy of flucytosine. The imidazoles were not efficacious in this model.

Effects of econazole nitrate on yeast cells and mitochondria.

The inhibitory effect of econazole nitrate on the growth of yeast Saccharomyces cerevisiae is proportional to the concentration of the product. It depends on the phase of culture and on the number of cells present at the moment of econazole addition into the medium. The most important inhibition is obtained in the exponential phase of growth with a low concentration of cells. It is enhanced with cells which were previously in contact with the product. There is no adaptation of the yeast toward increased concentrations of econazole. The product penetrates the cells and attaches first to particular fractions, later to soluble fractions. The highest concentration of econazole nitrate in cells lies in the mitochondria. No product of econazole metabolism by S. cerevisiae was uncovered. Econazole nitrate does not slow down the in vivo activities of mitochondrial enzymes (cytochrome c oxidase, succinate dehydrogenase and phenylalanyl-tRNA synthetase), but inhibits the biosynthesis of mitochondrial membrane enzymes without affecting that of the synthetase, a matrix enzyme.

The metabolic fate of 3[H]econazole in man.

1. Following single oral doses of 3[H]econazole base (500 mg) to two human subjects, excretion of radioactivity was prolonged, and incomplete after five days (means of 40% and 27% dose in urine and faeces respectively). 2. Plasma concn. of unchanged econazole and total radioactivity attained peak values at approx. the same for each subject (1.5 - 3h), but the former declined much faster than the latter. Most of the 3H in early plasma samples was present as unchanged drug and extractable metabolites, but after 24h concn. of econazole were close to the limit of detection (0.04 ug/ml) and very little plasma 3H was extractable, whereas total 3H concn. were still measurable after five days (mean 1.54 ug/ml). Thus, plasma contained metabolites with much longer half-lives than econazole. 3. The main route of biotransformation of econazole in man involved multiple oxidation of the imidazole ring carbons followed by O-dealkylation and conjugation of the resulting alcohols, probably with glucuronic acid.

Pharmacokinetics of imidazole antimycotics.

According to data on the imidazole antimycotics at present on the market, none of these products satisfactorily fills the gaps which exist in the treatment for mycoses of internal organs, although they have brought considerable progress in the topical treatment of mycoses. On the basis of their very broad spectrum and high intensity of activity under suitable test conditions, and the comparatively tolerable amount of side effects in man, the present imidazole antimycotics are considered to be an encouraging start for future development of derivatives which will lead to products with considerably better pharmacokinetic, and therefore better therapeutic, properties.

[Vaginal absorption of econazole]. / Untersuchungen zur vaginalen Resorption von Econazol.

After vaginal application econazol is absorbed to a high degree. Plasma levels are maintained for a relatively long period. Metabolism occurs in the vagina already. As there are no objections concerning toxicology the fact of absorption is considered positive from the therapeutical view-point because this drug does exert its effect not only in the vaginal cavity but also in the epithelium. It is suggested that vaginal absorption is influenced by cervical mucus.

Econazole: a review of its antifungal activity and therapeutic efficacy.

Econazole1 is a recently introduced imidazole antifungal agent which is very closely related structurally to another imidazole derivative, miconazole. For local application the nitrate salt of econazole is used, while in preliminary investigations of systemic use in a few patients econazole base has been administered orally or intravenously. In uncontrolled studies in large numbers of patients, econazole nitrate has been administered topically in the treatment of dermatomycoses due to a wide variety of fungi, and vaginally in the treatment of vaginal candidosis; but it has not been compared with any other antifungal drug in controlled therapeutic trials in mycoses of the skin and has only been compared with nystatin in a few patients with vaginal candidosis. Until adequate comparative studies are done the relative place of econazole in the treatment of dermatomycoses and vaginal condidosis, compared with traditional antifungal agents and with other imidazole derivatives such as miconazole or clotrimazole, cannot be clearly stated. Nevertheless, econazole nitrate is an effective antifungal drug. In dermatological studies about 90% of a large number of patients were cured, often after a relatively short treatment period (2 to 6 weeks, as occurs with other imidazole antifungal agents). The cure rate was only slightly lower (about 85%) in patients with severe mycoses of many years' duration than in those whose infections were of more recent onset. In vaginal candidosis a 3-day treatment regimen using a 150mg suppository once daily was only slightly less effective (85% mycological cure rate) than a 15-day regimen using a 50mg dose (suppository or cream) once daily (90% cure rate). A 3 to 5 day 'higher' dose regimen was slightly more effective than a standard 15-day regimen of nystatin vaginal inserts in a small group of patients with vaginal candidosis. The convenience of the higher-dose shorter term regimen would likely be an important advantage to most patients. Whether other agents useful in vaginal candidosis would be as effective as econazole were they to be used in this way, has not been determined. Topical or intravaginal econazole nitrate has usually been well tolerated, side effects being limited to local irritation in about 1 to 4% of patients in most studies.