Microbial systems for study of the biotransformations of drugs

Identification and characterization of a bacterial cytochrome P450 for the metabolism of diclofenac

The bacterium Actinoplanes sp. ATCC 53771 is known to perform drug metabolism of several xenobiotics similarly to humans. We identified a cytochrome P450 enzyme from this strain, CYP107E4, and expressed it in Escherichia coli using the pET101 vector. The purified enzyme showed the characteristic reduced-CO difference spectra with a peak at 450 nm, indicating the protein is produced in the active form with proper heme incorporation. The CYP107E4 enzyme was found to bind the drug diclofenac. Using redox enzymes from spinach, the reconstituted system is able to produce hydroxylated metabolites of diclofenac. Production of the human 4'-hydroxydiclofenac metabolite by CYP107E4 was confirmed, and a second hydroxylated metabolite was also produced.

Biosimulation of drug metabolism--a yeast based model

Computationally predicting the metabolic fates of drugs is a very complex task which is owed not only to the huge and diverse biochemical network in the living cell, but also to the majority of in vivo transformations that occur through the action of hepatocytes and gastro-intestinal micro-flora. Thus, xenobiotics are metabolised by more than a single cell type. However, the prediction of metabolic fates is definitely a problem worth solving since it would allow facilitate the development of drugs in a way less relying on animal testing. As a first step in this direction, PharmBiosim is being developed, a biosimulation tool which is based on substantial data reduction and on attributing metabolic fates of drug molecules to functional groups and substituents. This approach works with yeast as a model organism and is restricted to drugs that are mainly transformed by enzymes of the central metabolism, especially sugar metabolism. The reason for the latter is that the qualitative functioning of the involved biochemistry is very similar in diverse cell types involved in drug metabolism. Further it allows for using glycolytic oscillations as a tool to quantify interactions of a drug with this metabolic pathway.

Synthesis and biological evaluation of galactofuranosyl alkyl thioglycosides as inhibitors of mycobacteria

As part of our research interest directed toward the development of antimycobacterial agents, we have investigated compounds based on galactofuranose (Galf), an essential cell wall component of mycobacteria. The objective of this study was to explore structure activity relationships of Galf thioglycosides with straight chain and branched aglycons. Acylated Galf 9-heptadecyl thioglycoside was prepared by Lewis acid-catalyzed thioglycosidation of 1,2,3,5,6-penta-O-acyl-D-galactofuranose with 9-heptadecanethiol, and subsequently converted to the corresponding sulfone using m-CPBA. Both Galf 9-heptadecyl thioglycoside and sulfone displayed in vitro inhibition (MIC) of the growth of Mycobacterium smegmatis below 5 microg/mL, while Galf 1-octyl thioglycoside gave no inhibition at or below 32 microg/mL.

Synthesis and evaluation of galactofuranosyl N,N-dialkyl sulfenamides and sulfonamides as antimycobacterial agents

The recent emergence of clinically oppressive superbugs, some with resistance to nearly all frontline drug therapies, has challenged our ability to combat such infectious organisms as Mycobacterium tuberculosis, the causative agent of tuberculosis (TB). Our medicinal chemistry program targeting this pathogen has identified several potent galactofuranose-based in vitro inhibitors of mycobacterial growth. The most potent compound, the Galf N,N-didecyl sulfenamide 8d, displayed anti-mycobacterial activity (MIC) of 1 microg/mL in a cell based assay against a representative strain of Mycobacterium smegmatis.

Microbial oxidation of terfenadine and ebastine into fexofenadine and carebastine

The oxidation of tert-butyl-phenyl group of title compounds by some microorganisms was studied. We have optimized the conditions of culture to increase the formation of acid metabolites and to avoid the formation of side products. We showed that an oxidative activity is induced by soybean peptones in Streptomyces platensis. The biologically active compounds, fexofenadine and carebastine, are produced in good yield (86-95%) by Absidia corymbifera.

Microbial models of drug metabolism: microbial transformations of Trimegestone (RU27987), a 3-keto-delta(4,9(10))-19-norsteroid drug

Screening microorganisms for the biotransformation of the 3-keto-delta(4,9(10))-19-norsteroid RU27987 (Trimegestone) resulted in the isolation of nine identified metabolites, some of them being selectively produced by different strains. Eight metabolites were found to be hydroxylated on various positions of the rings, and one was additionally epoxidized. These microbial metabolites could be used as chromatographic standards and two of them were found identical to the unknown major human metabolites. Moreover, most microbial metabolites were produced in sufficient amounts to be tested for their biological activities. All these features demonstrate the usefulness and versatility of microbial biotransformation systems as a tool for early identification and convenient production of potentially active mammalian and non-mammalian metabolites.

Microbial models for drug metabolism

This review describes microbial transformation studies of drugs, comparing them with the corresponding metabolism in animal systems, and providing technical methods for developing microbial models. Emphasis is laid on the potential for selected microorganisms to mimic all patterns of mammalian biotransformations and to provide preparative methods for structural identification and toxicological and pharmacological studies of drug metabolites.

Identification of a cocaine esterase in a strain of Pseudomonas maltophilia

A strain of Pseudomonas maltophilia (termed MB11L) which was capable of using cocaine as its sole carbon and energy source was isolated by selective enrichment. An inducible esterase catalyzing the hydrolysis of cocaine to ecgonine methyl ester and benzoic acid was identified and purified 22-fold. In the presence of the solubilizing agent cholate, cocaine esterase had a native Mr of 110,000 and was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to be a monomer. In the absence of cholate, cocaine esterase had a native Mr of 410,000 and probably existed as a tetramer. The pH optimum of the enzyme was 8.0, and the Km values for cocaine, ethyl benzoate, and ethyl 2-hydroxybenzoate were 0.36, 1.89, and 1.75 mM, respectively. Inhibition studies indicated that the enzyme was a serine esterase, possibly possessing a cation-binding site similar to those of mammalian acetylcholinesterase and the atropine esterase of Pseudomonas putida PMBL-1. The cocaine esterase of P. maltophilia MB11L showed no activity with atropine, despite the structural similarity of cocaine and atropine.

Use of microorganisms for the study of drug metabolism: an update

The use of microorganisms as tools in the study of drug metabolism appears to be gaining popularity. The selected examples cited here provide additional evidence of the utility of these systems as alternative in vitro models for studying drug metabolism in humans. However, as was noted earlier, this model, nor any other in vitro model system could ever replace animals in biomedical research. However, it is apparent from the numerous examples cited here and in the previous review of this area that microorganisms are a reliable, reproducible alternative to small animals as predictive models in drug metabolism studies. The continuing development of techniques that reduce the use of animals in research is encouraged and this procedure appears to be gaining more widespread acceptance for such use.

Microbial cleavage of zearalenone

1. Zearalenone, a fungal oestrogenic compound, was subjected to microbial transformation studies. Preliminary screening with 150 fungal species showed that Gliocladium roseum was capable of metabolizing zearalenone in 80-90% yields. 2. Large-scale fermentation with G. roseum produced a 1:1 mixture of 1-(3,5-dihydroxyphenyl)-10'-hydroxy-1-undecen-6'-one and 1-(3,5-dihydroxyphenyl)-6'-hydroxy-1-undecen-10'-one. The compounds were isolated and purified at -20 degrees C, and identified using spectroscopic analysis and by comparison to products obtained from alkaline hydrolysis of zearalenone.

Biotransformation of polycyclic aromatic compounds by fungi

Incubations of several polycyclic aromatic hydrocarbons (PAHs) and heteroaromatic compounds with a series of common micro-organisms have been performed. The PAHs were not metabolized by any of the fungi studied. The sulphur-containing heterocyclic aromatic compounds dibenzothiophene, thioxanthone and thiochromanone were oxidized at sulphur by C. elegans. Other fungi are capable of oxidation at the sulphur atom of dibenzothiophene and thioxanthone. C-1 and C-3 methyl substituted thioxanthones are hydroxylated at the methyl group by C. elegans.

The use of microorganisms for the study of drug metabolism

The potential for the use of microorganisms as tools in the study of drug metabolism appears to be unlimited. The selected examples cited here are only the beginning of what could develop into a widely accepted alternative in vitro model system for studying drug metabolism in humans. As with any other in vitro model system, it is not expected that microbial systems could ever replace animals in biomedical research. The acquisition of data regarding absorption, distribution, and excretion will still require whole animal systems. However, it is clear from the examples cited that microbial systems offer a reliable, reproducible alternative to small animal models for preliminary drug metabolism studies. Due to significant species variation, small animal models may, in many cases, be less reliable than microorganisms as predictive models of human metabolism. It has been estimated that approximately 70 million animals are used each year in the U.S. for biomedical research. The development of any techniques which curtail the sacrifice of such large numbers of animals is welcomed both by animal welfare groups who wish to ensure the humane treatment of laboratory animals and by researchers who additionally appreciate the more practical and economical benefits of such alternatives.

Metabolism of phencyclidine by microorganisms

A number of microorganisms were screened for their ability to metabolize phencyclidine. Two microorganisms, Beauveria sulfurescens and Cunninghamella echinulata, produced hydroxylated metabolites, which were identified as 1-(1-phenylcyclohexyl)-4-hydroxypiperidine and 4-phenyl-4-piperidinocyclohexanol by high-pressure liquid chromatographic analysis.

Metabolism of imipramine by microorganisms

The microbial metabolism of imipramine was studied using selected fungal organisms. The major microbial metabolites were isolated, and their structures were established by spectroscopic analyses (particularly 13C-NMR) and by comparison with authentic samples. The microbial metabolites identified included 2-hydroxyimipramine, 10-hydroxyimipramine, iminodibenzyl, imipramine-N-oxide, and desipramine; these metabolites also have been found in mammalian metabolism studies.

Microbial transformations and 13C-NMR analysis of colchicine

Several microorganisms were screened for their ability to biotransform colchicine, and two were selected for preparative scale fermentations. Streptomyces spectabilis and Streptomyces griseus both produced O2-demethylcolchicine and O3-demethylcolchicine but in different amounts. The 13C-NMR assignments of colchicine, O10-demethylcolchicine, and trimethylcolchicinic acid are reported and were used to help identify the structures of the metabolites.