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

New synergistic benzoquinone scaffolds as inhibitors of mycobacterial cytochrome bc1 complex to treat multi-drug resistant tuberculosis

Through a comprehensive molecular docking study, a unique series of naphthoquinones clubbed azetidinone scaffolds was arrived with promising binding affinity to Mycobacterial Cytbc1 complex, a drug target chosen to kill multi-drug resistant Mycobacterium tuberculosis (MDR-Mtb). Five compounds from series-2, 2a, 2c, 2g, 2h, and 2j, showcased significant in vitro anti-tubercular activities against Mtb H37Rv and MDR clinical isolates. Further, synergistic studies of these compounds in combination with INH and RIF revealed a potent bactericidal effect of compound 2a at concentration of 0.39 μg/mL, and remaining (2c, 2g, 2h, and 2j) at 0.78 μg/mL. Exploration into the mechanism study through chemo-stress assay and proteome profiling uncovered the down-regulation of key proteins of electron-transport chain and Cytbc1 inhibition pathway. Metabolomics corroborated these proteome findings, and heightened further understanding of the underlying mechanism. Notably, in vitro and in vivo animal toxicity studies demonstrated minimal toxicity, thus underscoring the potential of these compounds as promising anti-TB agents in combination with RIF and INH. These active compounds adhered to Lipinski's Rule of Five, indicating the suitability of these compounds for drug development. Particular significance of molecules NQ02, 2a, and 2h, which have been patented (Published 202141033473).

Metabolic Comparison and Molecular Networking of Antimicrobials in Streptomyces Species

Streptomyces are well-known for producing bioactive secondary metabolites, with numerous antimicrobials essential to fight against infectious diseases. Globally, multidrug-resistant (MDR) microorganisms significantly challenge human and veterinary diseases. To tackle this issue, there is an urgent need for alternative antimicrobials. In the search for potent agents, we have isolated four Streptomyces species PC1, BT1, BT2, and BT3 from soils collected from various geographical regions of the Himalayan country Nepal, which were then identified based on morphology and 16S rRNA gene sequencing. The relationship of soil microbes with different Streptomyces species has been shown in phylogenetic trees. Antimicrobial potency of isolates was carried out against Staphylococcus aureus American Type Culture Collection (ATCC) 43300, Shigella sonnei ATCC 25931, Salmonella typhi ATCC 14028, Klebsiella pneumoniae ATCC 700603, and Escherichia coli ATCC 25922. Among them, Streptomyces species PC1 showed the highest zone of inhibition against tested pathogens. Furthermore, ethyl acetate extracts of shake flask fermentation of these Streptomyces strains were subjected to liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis for their metabolic comparison and Global Natural Products Social Molecular Networking (GNPS) web-based molecular networking. We found very similar metabolite composition in four strains, despite their geographical variation. In addition, we have identified thirty-seven metabolites using LC-MS/MS analysis, with the majority belonging to the diketopiperazine class. Among these, to the best of our knowledge, four metabolites, namely cyclo-(Ile-Ser), 2-n-hexyl-5-n-propylresorcinol, 3-[(6-methylpyrazin-2-yl) methyl]-1H-indole, and cyclo-(d-Leu-l-Trp), were detected for the first time in Streptomyces species. Besides these, other 23 metabolites including surfactin B, surfactin C, surfactin D, and valinomycin were identified with the help of GNPS-based molecular networking.

Microbial Transformation of Broussochalcones A and B by Aspergillus niger

Broussochalcones A (BCA, 1) and B (BCB, 2) are major bioactive constituents isolated from Broussonetia papyrifera, a polyphenol-rich plant belonging to the family Moraceae. Due to their low yields from natural sources, BCA (1) and BCB (2) were prepared synthetically by employing Claisen-Schmidt condensation, and these were used as substrates for microbial transformation to obtain novel derivatives. Microbial transformation of BCA (1) and BCB (2) with the endophytic fungus Aspergillus niger KCCM 60332 yielded 10 previously undescribed chalcones (1a-1e and 2a-2e). Their structures were established based on the spectroscopic methods. The cytotoxicity of BCA (1), BCB (2), and their metabolites (1a-1e and 2a-2e) was determined by human cancer cell lines A375P, A549, HT-29, MCF-7, and HepG2, with 1e shown to be most cytotoxic.

Microbial Transformations of Two Beyerane-Type Diterpenes by Cunninghamella echinulata

Microbial transformations of two tetracyclic beyerane-type diterpenes, ent-16β-oxobeyeran-19-oic acid (1) and its chemical reduction product, ent-16β-hydroxybeyeran-19-oic acid (2), by the filamentous fungus Cunninghamella echinulata ATCC 8688a yielded eight metabolites (3-10). Incubation of the substrate 2 with C. echinulata afforded three new hydroxylated ones (3-5) along with two known ones (6-7), while incubation of 1 gave three known ones (8-10). The new compounds were characterized by 1D and 2D NMR as well as HRESIMS analysis, and the stereostructures of 3 and 4 were confirmed by X-ray crystallography. The bioreactions were involved not only in stereoselective incorporation of hydroxyl groups at inert positions C-7, -9, -12, and -14 of the two beyerane diterpenes but also in glucosidation at C-19 of 2. This is the first report on the biotransformation of the diterpenes by using C. echinulata. All compounds were assayed for their α-glucosidase inhibitory, neurotrophic, anti-inflammatory, and phytotoxic activity, and only in neurotrophic assay compounds, 2 and 9 were found to display nerve growth factor-mediated neurite-outgrowth promoting effects in PC12 cells; the others were inactive.

Microbial Transformation of Prenylquercetins by Mucor hiemalis

Quercetin, one of the most widely distributed flavonoids, has been found to show various biological activities including antioxidant, anticancer, and anti-inflammatory effects. It has been reported that bioactivity enhancement of flavonoids has often been closely associated with nuclear prenylation, as shown in 8-prenylquercetin and 5'-prenylquercetin. It has also been revealed in many studies that the biological activities of flavonoids could be improved after glucosylation. Three prenylated quercetins were prepared in this study, and microbial transformation was carried out in order to identify derivatives of prenylquercetins with increased water solubility and improved bioavailability. The fungus M. hiemalis was proved to be capable of converting prenylquercetins into more polar metabolites and was selected for preparative fermentation. Six novel glucosylated metabolites were obtained and their chemical structures were elucidated by NMR and mass spectrometric analyses. All the microbial metabolites showed improvement in water solubility.

Microbial Transformation of Licochalcones

Microbial transformation of licochalcones B (1), C (2), D (3), and H (4) using the filamentous fungi Aspergillus niger and Mucor hiemalis was investigated. Fungal transformation of the licochalcones followed by chromatographic separations led to the isolation of ten new compounds 5–14, including one hydrogenated, three dihydroxylated, three expoxidized, and three glucosylated metabolites. Their structures were elucidated by combined analyses of UV, IR, MS, NMR, and CD spectroscopic data. Absolute configurations of the 2″,3″-diols in the three dihydroxylated metabolites were determined by ECD experiments according to the Snatzke’s method. The trans-cis isomerization was observed for the metabolites 7, 11, 13, and 14 as evidenced by the analysis of their ¹H-NMR spectra and HPLC chromatograms. This could be useful in better understanding of the trans-cis isomerization mechanism of retrochalcones. The fungal transformation described herein also provides an effective method to expand the structural diversity of retrochalcones for further biological studies.

Biotransformed Metabolites of the Hop Prenylflavanone Isoxanthohumol

A metabolic conversion study on microbes is known as one of the most useful tools to predict the xenobiotic metabolism of organic compounds in mammalian systems. The microbial biotransformation of isoxanthohumol (1), a major hop prenylflavanone in beer, has resulted in the production of three diastereomeric pairs of oxygenated metabolites (2–7). The microbial metabolites of 1 were formed by epoxidation or hydroxylation of the prenyl group, and HPLC, NMR, and CD analyses revealed that all of the products were diastereomeric pairs composed of (2S)- and (2R)- isomers. The structures of these metabolic compounds were elucidated to be (2S,2″S)- and (2R,2″S)-4′-hydroxy-5-methoxy-7,8-(2,2-dimethyl-3-hydroxy-2,3-dihydro-4H-pyrano)-flavanones (2 and 3), (2S)- and (2R)-7,4′-dihydroxy-5-methoxy-8-(2,3-dihydroxy-3-methylbutyl)-flavanones (4 and 5) which were new oxygenated derivatives, along with (2R)- and (2S)-4′-hydroxy-5-methoxy-2″-(1-hydroxy-1-methylethyl)dihydrofuro[2,3-h]flavanones (6 and 7) on the basis of spectroscopic data. These results could contribute to understanding the metabolic fates of the major beer prenylflavanone isoxanthohumol that occur in mammalian system.

Aspergillus niger-mediated biotransformation of methenolone enanthate, and immunomodulatory activity of its transformed products

Two fungal cultures Aspergillus niger and Cunninghamella blakesleeana were used for the biotransformation of methenolone enanthate (1). Biotransformation with A. niger led to the synthesis of three new (2-4), and three known (5-7) metabolites, while fermentation with C. blakesleeana yielded metabolite 6. Substrate 1 and the resulting metabolites were evaluated for their immunomodulatory activities. Substrate 1 was found to be inactive, while metabolites 2 and 3 showed a potent inhibition of ROS generation by whole blood (IC50=8.60 and 7.05μg/mL), as well as from isolated polymorphonuclear leukocytes (PMNs) (IC50=14.0 and 4.70μg/mL), respectively. Moreover, compound 3 (34.21%) moderately inhibited the production of TNF-α, whereas 2 (88.63%) showed a potent inhibition of TNF-α produced by the THP-1 cells. These activities indicated immunomodulatory potential of compounds 2 and 3. All products were found to be non-toxic to 3T3 mouse fibroblast cells.

Microbial ketonization of ginsenosides F1 and C-K by Lactobacillus brevis

Ginsenosides are the major pharmacological components in ginseng. We isolated lactic acid bacteria from Kimchi to identify microbial modifications of ginsenosides. Phylogenetic analysis of 16S rRNA gene sequences indicated that the strain DCY65-1 belongs to the genus Lactobacillus and is most closely related to Lactobacillus brevis. On the basis of TLC and HPLC analysis, we found two metabolic pathways: F1 → 6α,12β-dihydroxydammar-3-one-20(S)-O-β-D-glucopyranoside and C-K → 12β-hydroxydammar-3-one-20(S)-O-β-D-glucopyranoside. These results suggest that strain DCY65-1 is capable of potent ketonic decarboxylation, ketonizing the hydroxyl group at C-3. The F1 metabolite had a more potent inhibitory effect on mushroom tyrosinase than did the substrate. Therefore, the F1 and C-K derivatives may be more pharmacologically active compounds, which should be further characterized.

Microbial transformation of oleanolic acid by Trichothecium roseum

Microbial transformation of the oleanolic acid (1) using Trichothecium roseum (pers.) Link (M 95.56) has resulted in the isolation of two new hydroxylated type metabolites, characterized as 15α-hydroxy-3-oxo-olean-12-en-28-oic acid (2) and 7β,15α-dihydroxy-3-oxo-olean-12-en-28-oic acid (3). The structure elucidation of these metabolites was based primarily on HR-EIMS, 1D NMR, and 2D NMR analyses.

Microbial transformation of asiatic acid by Alternaria longipes

Asiatic acid is a major pentacyclic triterpene isolated from Centella asiatica. It shows a variety of bioactivities. In order to obtain its derivatives, potentially useful for detailed pharmacological studies, the substrate was subjected to incubations with selected micro-organisms. In this work, asiatic acid was converted into three new compounds: 2α,3β,23,30-tetrahydroxyurs-12-ene-28-oic acid (1), 2α,3β,22β,23-tetrahydroxyurs-12-ene-28-oic acid (2), and 2α,3β,22β,23,30-pentahydroxyurs-12-ene-28-oic acid (3) by the fungus Alternaria longipes AS 3.2875. The structures of the three metabolites were determined by 1D and 2D NMR spectral data.

Biotransformation of celecoxib using microbial cultures

Microbial transformation studies can be used as models to simulate mammalian drug metabolism. In the present investigation, biotransformation of celecoxib was studied in microbial cultures. Bacterial, fungal, and yeast cultures were employed in the present study to elucidate the metabolism of celecoxib. The results indicate that a number of microorganisms metabolized celecoxib to various levels to yield eight metabolites, which were identified by high-performance liquid chromatography diode array detection and liquid chromatography tandem mass spectrometry analyses. HPLC analysis of biotransformed products indicated that majority of the metabolites are more polar than the substrate celecoxib. The major metabolite was found to be hydroxymethyl metabolite of celecoxib, while the remaining metabolites were produced by carboxylation, methylation, acetylation, or combination of these reactions. The methyl hydroxylation and further conversion to carboxylic acid was known to occur in metabolism by mammals. The results further support the use of microorganisms for simulating mammalian metabolism of drugs.

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.

Biotransformation of pantoprazole by the fungusCunninghamella blakesleeana

To investigate the biotransformation of pantoprazole, a proton-pump inhibitor, by filamentous fungus and further to compare the similarities between microbial transformation and mammalian metabolism of pantoprazole, four strains of Cunninghamella (C. blakesleeana AS 3.153, C. echinulata AS 3.2004, C. elegans AS 3.156, and AS 3.2028) were screened for the ability to catalyze the biotransformation of pantoprazole. Pantoprazole was partially metabolized by four strains of Cunninghamella, and C. blakesleeana AS 3.153 was selected for further investigation. Three metabolites produced by C. blakesleeana AS 3.153 were isolated using semi-preparative HPLC, and their structures were identified by a combination analysis of LC/MS(n) and NMR spectra. Two further metabolites were confirmed with the aid of synthetic reference compounds. The structure of a glucoside was tentatively assigned by its chromatographic behavior and mass spectroscopic data. These six metabolites were separated and quantitatively assayed by liquid chromatography-ion trap mass spectrometry. After 96h of incubation with C. blakesleeana AS 3.153, approximately 92.5% of pantoprazole was metabolized to six metabolites: pantoprazole sulfone (M1, 1.7%), pantoprazole thioether (M2, 12.4%), 6-hydroxy-pantoprazole thioether (M3, 1.3%), 4'-O-demethyl-pantoprazole thioether (M4, 48.1%), pantoprazole thioether-1-N-beta-glucoside (M5, 20.6%), and a glucoside conjugate of pantoprazole thioether (M6, 8.4%). Among them, M5 and M6 are novel metabolites. Four phase I metabolites of pantoprazole produced by C. blakesleeana were essentially similar to those obtained in mammals. C. blakesleeana could be a useful tool for generating the mammalian phase I metabolites of pantoprazole.

Stereoselective analysis of thioridazine-2-sulfoxide and thioridazine-5-sulfoxide: An investigation of rac-thioridazine biotransformation by some endophytic fungi

The purpose of this study was to develop a method for the stereoselective analysis of thioridazine-2-sulfoxide (THD-2-SO) and thioridazine-5-sulfoxide (THD-5-SO) in culture medium and to study the biotransformation of rac-thioridazine (THD) by some endophytic fungi. The simultaneous resolution of THD-2-SO and THD-5-SO diastereoisomers was performed on a CHIRALPAK AS column using a mobile phase of hexane:ethanol:methanol (92:6:2, v/v/v)+0.5% diethylamine; UV detection was carried out at 262 nm. Diethyl ether was used as extractor solvent. The validated method was used to evaluate the biotransformation of THD by 12 endophytic fungi isolated from Tithonia diversifolia, Viguiera arenaria and Viguiera robusta. Among the 12 fungi evaluated, 4 of them deserve prominence for presenting an evidenced stereoselective biotransformation potential: Phomopsis sp. (TD2) presented greater mono-2-sulfoxidation to the form (S)-(SE) (12.1%); Glomerella cingulata (VA1) presented greater mono-5-sulfoxidation to the forms (S)-(SE)+(R)-(FE) (10.5%); Diaporthe phaseolorum (VR4) presented greater mono-2-sulfoxidation to the forms (S)-(SE) and (R)-(FE) (84.4% and 82.5%, respectively) and Aspergillus fumigatus (VR12) presented greater mono-2-sulfoxidation to the forms (S)-(SE) and (R)-(SE) (31.5% and 34.4%, respectively).

Microbial transformation of 20(S)-protopanaxatriol-type saponins by Absidia coerulea

Three 20(S)-protopanaxatriol-type saponins, ginsenoside-Rg1 (1), notoginsenoside-R1 (2), and ginsenoside-Re (3), were transformed by the fungus Absidia coerulea (AS 3.3389). Compound 1 was converted into five metabolites, ginsenoside-Rh4 (4), 3beta,2beta,25-trihydroxydammar-(E)-20(22)-ene-6-O-beta-D-glucopyranoside (5), 20(S)-ginsenoside-Rh1 (6), 20(R)-ginsenoside-Rh1 (7), and a mixture of 25-hydroxy-20(S)-ginsenoside-Rh1 and its C-20(R) epimer (8). Compound 2 was converted into 10 metabolites, 20(S)-notoginsenoside-R2 (9), 20(R)-notoginsenoside-R2 (10), 3beta,12beta,25-trihydroxydammar-(E)-20(22)-ene-6-O-beta-D-xylopyranosyl-(1-->2)-beta-D-glucopyranoside (11), 3beta,12beta-dihydroxydammar-(E)-20(22),24-diene-6-O-beta-D-xylopyranosyl-(1-->2)-beta-D-glucopyranoside (12), 3beta,12beta,20,25-tetrahydroxydammaran-6-O-beta-D-xylopyranosyl-(1-->2)-beta-D-glucopyranoside (13), and compounds 4-8. Compound 3 was metabolized to 20(S)-ginsenoside-Rg2 (14), 20(R)-ginsenoside-Rg2 (15), 3beta,12beta,25-trihydroxydammar-(E)-20(22)-ene-6-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranoside (16), 3beta,12beta-dihydroxydammar-(E)-20(22),24-diene-6-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranoside (17), 3beta,12beta,20,25-tetrahydroxydammaran-6-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucopyranoside (18), and compounds 4-8. The structures of five new metabolites, 10-13 and 16, were established by spectroscopic methods.

Structural determination of three new germacrane-type sesquiterpene alcohols from curdione by microbial transformation

Five germacrane-type sesquiterpene alcohols obtained from curdione (1) by microbial biotransformation were isolated. Their structures were characterized as (2R)-2beta-hydroxycurdione (2), 1alpha, 10beta-epoxy-11-hydroxycurdione (3), (2S)-2alpha, 11-dihydroxycurdione (4), 11,15-dihydroxycurdione (5) and (3R)-3alpha-hydroxycurdione (6) based on the extensive NMR studies. Among them, 4, 5 and 6 are new compounds.

Microbial transformation of dehydrocostuslactone by Mucor polymorphosporus

Biotransformation of dehydrocostuslactone (1) by Mucor polymorphosporus yielded four compounds, and their structures were identified as 11alpha,13-dihydrodehydrocostuslactone (2), 3alpha-hydroxy-11alpha,13-dihydrodehydrocostuslactone (3), 3beta-hydroxy-4beta,15,11alpha,13-tetrahydrodehydrocostuslactone (4) and 2beta-hydroxyl-11alpha,13-dihydrodehydrocostuslactone (5), respectively, on the basis of their spectral data. Among them, compound 5 is a new compound.

Microbial and enzymatic transformations of flavonoids

Flavonoids are among the most ubiquitous phenolic compounds found in nature. These compounds have diverse physiological and pharmacological activities such as estrogenic, antitumor, antimicrobial, antiallergic, and anti-inflammatory effects. They are well-known antioxidants and metal ion-chelators. In the present review, biotransformations of numerous flavonoids catalyzed mainly by microbes and few plant enzymes are described in four different flavonoid classes, viz., chalcones, isoflavones, catechins, and flavones. Both phase I (oxidative) and phase II (conjugative) biotransformations representing a variety of reactions including condensation, cyclization, hydroxylation, dehydroxylation, alkylation, O-dealkylation, halogenation, dehydrogenation, double-bond reduction, carbonyl reduction, glycosylation, sulfation, dimerization, or different types of ring degradations are elaborated here. In some cases, the observed microbial transformations mimic mammalian and/or plant metabolism. This review recognizes Norman Farnsworth, who through his fascination and hard work in pharmacognosy has fostered the excitement of discovery by numerous students and faculty far and beyond the halls of the University of Illinois at Chicago. It is with grateful thanks for these efforts that we dedicate this review to him.

Studies on Bacillus stearothermophilus. Part IV. Influence of enhancers on biotransformation of testosterone

The impact of chemical enhancers on the biotransformation of testosterone has been exploited. Application of crude cell concentrates to produce Bacillus stearothermophilus-mediated bioconversion of testosterone at 65 degrees C for 72 h has been examined. After incubation, the xenobiotic substrate was added to the concentrated whole cell suspensions. The enhancer molecules were included in the whole cell suspension. The resultant products, after extraction into an organic solvent, were purified by thin layer chromatography and identification was carried out through spectroscopic data. Five steroid metabolites 9,10-seco-4-androstene-3,9,17-trione, 5alpha-androstan-3,6,17-trione, 17beta-hydroxy-5alpha-androstan-3,6-dione, 3beta,17beta-dihydroxyandrost-4-ene-6-one and 17beta-hydroxyandrost-4,6-diene-3-one were identified as biotransformation products of testosterone. A possible biosynthetic route for these bioconversion products is postulated.

Microbial Transformation of Mesterolone

The microbial transformation of mesterolone (= (1alpha,5alpha,17beta)-17-hydroxy-1-methylandrostan-3-one; 1), by a number of fungi yielded (1alpha,5alpha)-1-methylandrostane-3,17-dione (2), (1alpha,3beta,5alpha,17beta)-1-methylandrostane-3,17-diol (3), (5alpha)-1-methylandrost-1-ene-3,17-dione (4), (1alpha,5alpha,15alpha)-15-hydroxy-1-methylandrostane-3,17-dione (5), (1alpha,5alpha,6alpha,17beta)-6,17-dihydroxy-1-methylandrostan-3-one (6), (1alpha,5alpha,7alpha,17beta)-7,17-dihydroxy-1-methylandrostan-3-one (7), (1alpha,5alpha,11alpha,17beta)-11,17-dihydroxy-1-methylandrostan-3-one (8), (1alpha,5alpha,15alpha, 17beta)15,17-dihydroxy-1-methylandrostan-3-one (9), and (5alpha,15alpha,17beta)-15,17-dihydroxy-1-methylandrost-1-en-3-one (10). Metabolites 5-10 were found to be new compounds. All metabolites, except 2, 3, 6, and 7, exhibited potent anti-inflammatory activity. The structures of these metabolites were characterized on the basis of spectroscopic studies, and the structure of 5 was also determined by single-crystal X-ray-diffraction analysis.

Specific 12 beta-hydroxylation of cinobufagin by filamentous fungi

Biotransformation of natural products has great potential for producing new drugs and could provide in vitro models of mammalian metabolism. Microbial transformation of the cytotoxic steroid cinobufagin was investigated. Cinobufagin could be specifically hydroxylated at the 12 beta-position by the fungus Alternaria alternata. Six products from a scaled-up fermentation were obtained by silica gel column chromatography and reversed-phase liquid chromatography and were identified as 12 beta-hydroxyl cinobufagin, 12 beta-hydroxyl desacetylcinobufagin, 3-oxo-12 beta-hydroxyl cinobufagin, 3-oxo-12 beta-hydroxyl desacetylcinobufagin, 12-oxo-cinobufagin, and 3-oxo-12 alpha-hydroxyl cinobufagin. The last five products are new compounds. 12 beta-Hydroxylation of cinobufagin by A. alternata is a fast catalytic reaction and was complete within 8 h of growth with the substrate. This reaction was followed by dehydrogenation of the 3-hydroxyl group and then deacetylation at C-16. Hydroxylation at C-12 beta also was the first step in the metabolism of cinobufagin by a variety of fungal strains. In vitro cytotoxicity assays suggest that 12 beta-hydroxyl cinobufagin and 3-oxo-12 alpha-hydroxyl cinobufagin exhibit somewhat decreased but still significant cytotoxic activities. The 12 beta-hydroxylated bufadienolides produced by microbial transformation are difficult to obtain by chemical synthesis.

Chemistry, biological activity, and chemotherapeutic potential of betulinic acid for the prevention and treatment of cancer and HIV infection

3beta-Hydroxy-lup-20(29)-en-28-oic acid (betulinic acid) is a pentacyclic lupane-type triterpene that is widely distributed throughout the plant kingdom. A variety of biological activities have been ascribed to betulinic acid including anti-inflammatory and in vitro antimalarial effects. However, betulinic acid is most highly regarded for its anti-HIV-1 activity and specific cytotoxicity against a variety of tumor cell lines. Interest in developing even more potent anti-HIV agents based on betulinic acid has led to the discovery of a host of highly active derivatives exhibiting greater potencies and better therapeutic indices than some current clinical anti-HIV agents. While its mechanism of action has not been fully determined, it has been shown that some betulinic acid analogs disrupt viral fusion to the cell in a post-binding step through interaction with the viral glycoprotein gp41 whereas others disrupt assembly and budding of the HIV-1 virus. With regard to its anticancer properties, betulinic acid was previously reported to exhibit selective cytotoxicity against several melanoma-derived cell lines. However, more recent work has demonstrated that betulinic acid is cytotoxic against other non-melanoma (neuroectodermal and malignant brain tumor) human tumor varieties. Betulinic acid appears to function by means of inducing apoptosis in cells irrespective of their p53 status. Because of its selective cytotoxicity against tumor cells and favorable therapeutic index, even at doses up to 500 mg/kg body weight, betulinic acid is a very promising new chemotherapeutic agent for the treatment of HIV infection and cancer.

Microbial metabolism of the environmental estrogen bisphenol A

Preliminary microbial metabolism studies of bisphenol A (BPA) (1) on twenty six microorganisms have shown that Aspergillus fumigatus is capable of metabolizing BPA. Scale-up fermentation of 1 with A. fumigatus gave a metabolite (2) and its structure was established as bisphenol A-O-beta-D-glucopyranoside (BPAG) based on spectroscopic analyses.

Biotransformation of mirtazapine by Cunninghamella elegans

The fungus Cunninghamella elegans was used as a microbial model of mammalian metabolism to biotransform the tetracyclic antidepressant drug mirtazapine, which is manufactured as a racemic mixture of R(-)- and S(+)-enantiomers. In 168 h, C. elegans transformed 91% of the drug into the following seven metabolites: 8-hydroxymirtazapine, N-desmethyl-8-hydroxymirtazapine, N-desmethylmirtazapine, 13-hydroxymirtazapine, mirtazapine N-oxide, 12-hydroxymirtazapine, and N-desmethyl-13-hydroxymirtazapine. Circular dichroism spectral analysis of unused mirtazapine indicated that it was slightly enriched with the R(-)-enantiomer. When the fungus was treated with the optically pure forms of the drug, the S(+)-enantiomer produced all seven metabolites whereas the R(-)-enantiomer produced only 8-hydroxymirtazapine, N-desmethyl-8-hydroxymirtazapine, N-desmethylmirtazapine, and mirtazapine N-oxide. C. elegans produced five mammalian and two novel metabolites and is therefore a suitable microbial model for mirtazapine metabolism.

Microbial transformations of the antimelanoma agent betulinic acid

Microbial transformation studies of the antimelanoma agent betulinic acid (1) were conducted. Screening experiments showed a number of microorganisms capable of biotransforming 1. Three of these cultures, Bacillus megaterium ATCC 14581, Cunninghamella elegans ATCC 9244, and Mucor mucedo UI-4605, were selected for preparative scale transformation. Bioconversion of 1 with resting-cell suspensions of phenobarbital-induced B. megaterium ATCC 14581 resulted in the production of the known betulonic acid (2) and two new metabolites: 3beta,7beta-dihydroxy-lup-20(29)-en-28-oic acid (3) and 3beta,6alpha, 7beta-trihydroxy-lup-20(29)-en-28-oic acid (4). Biotransformation of 1 with growing cultures of C. elegans ATCC 9244 produced one new metabolite characterized as 1beta,3beta, 7beta-trihydroxy-lup-20(29)-en-28-oic acid (5). Incubation of 1 with growing cultures of M. mucedo UI-4605 afforded metabolite 3. Structure elucidation of all metabolites was based on NMR and HRMS analyses. In addition, the antimelanoma activity of metabolites 2-5 was evaluated against two human melanoma cell lines, Mel-1 (lymph node) and Mel-2 (pleural fluid).

Microbial transformation of the eudesmane sesquiterpene plectranthone

Microbial transformation studies of plectranthone (1) have revealed that it was metabolized by a number of microorganisms. Using a standard two-stage fermentation technique, Beauvaria bassiana (ATCC 7159) produced five metabolites, 2-6. These metabolites were characterized on the basis of spectral data.

Biotransformation of the antimelanoma agent betulinic acid by Bacillus megaterium ATCC 13368

Microbial transformation of the antimelanoma agent betulinic acid was studied. The main objective of this study was to utilize microorganisms as in vitro models to predict and prepare potential mammalian metabolites of this compound. Preparative-scale biotransformation with resting-cell suspensions of Bacillus megaterium ATCC 13368 resulted in the production of four metabolites, which were identified as 3-oxo-lup-20(29)-en-28-oic acid, 3-oxo-11alpha-hydroxy-lup-20(29)-en-28-oic acid, 1beta-hydroxy-3-oxo-lup-20(29)-en-28-oic acid, and 3beta,7beta, 15alpha-trihydroxy-lup-20(29)-en-28-oic acid based on nuclear magnetic resonance and high-resolution mass spectral analyses. In addition, the antimelanoma activities of these metabolites were evaluated with two human melanoma cell lines, Mel-1 (lymph node) and Mel-2 (pleural fluid).

Transformation of amoxapine by Cunninghamella elegans

We examined Cunninghamella elegans to determine its ability to transform amoxapine, a tricyclic antidepressant belonging to the dibenzoxazepine class of drugs. Approximately 57% of the exogenous amoxapine was metabolized to three metabolites that were isolated by high-performance liquid chromatography and were identified by nuclear magnetic resonance and mass spectrometry as 7-hydroxyamoxapine (48%), N-formyl-7-hydroxyamoxapine (31%), and N-formylamoxapine (21%). 7-Hydroxyamoxapine, a mammalian metabolite with biological activity, now can be produced in milligram quantities for toxicological evaluation.

Biotransformation of testosterone and pregnenolone catalyzed by the fungus Botrytis cinerea

Testosterone (1), a male sex hormone, and pregnenolone (2), a precursor of many steroidal hormones, were oxidized by fermentation with the fungus Botrytis cinerea. The fermentation of 1 yielded 7beta,17beta-dihydroxyandrostan-3-one (3) (73%) in a yield comparable to chemical transformations. Fermentation of 2 by the same fungus afforded a major metabolite 3beta,11alpha, 16beta-trihydroxypregn-5-en-20-one (4) (39%) along with a minor metabolite 11alpha,16beta-dihydroxypregn-4-ene-3,20-dione (5) (6%). The metabolites are characterized by detailed physical and spectroscopic studies.

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.

Biotransformation of protriptyline by filamentous fungi and yeasts

1. The potential of various fungi to metabolize protriptyline (an extensively used antidepressant) was studied to investigate similarities between mammalian and microbial metabolism. 2. Metabolites produced by each organism were isolated by high-pressure liquid chromatography and identified by nuclear magnetic resonance and mass spectrometry. The metabolites identified in one or more fungi were 2-hydroxyprotriptyline, N-desmethylprotriptyline, N-acetylprotriptyline, N-acetoxyprotriptyline, 14-oxo-N-desmethylprotriptyline, 2-hydroxy-acetoxyprotriptyline and 3-(5-hydrodibenzo[bf][7]annulen-5-yl)propanoic acid. 3. Among 27 filamentous fungi and yeast species screened, Fusarium oxysporum f. sp. pini 2380 metabolized 97% of the protriptyline added. Several other fungi screened gave significant metabolism of protriptyline, including Cunninghamella echinulata ATCC 42616 (67%), C. elegans ATCC 9245 (17%), C. elegans ATCC 36112 (22%), C. phaeospora ATCC 22110 (50%), F. moniliforme MRC-826 (33%) and F. solani 3179 (12%). 4. F. oxysporum f. sp. pini produced phase I and phase II metabolites and thus is a suitable microbial model for protriptyline metabolism.

Microbial transformation of sampangine

Microbial transformation studies of the antifungal alkaloid sampangine (2) have revealed that it is metabolized by a number of microorganisms. Using a standard two-stage fermentation technique, Beauvaria bassiana (ATCC 7159), Doratomyces microsporus (ATCC 16225), and Filobasidiella neoformans (ATCC 10226) produced the 4'-O-methyl-beta-glucopyranose conjugate (3), while Absidia glauca (ATCC 22752), Cunninghamella elegans (ATCC 9245), Cunninghamella species (NRRL 5695), and Rhizopus arrhizus (ATCC 11145) produced the beta-glucopyranose conjugate (4). Metabolites 3 and 4 have been characterized on the basis of spectral data. Both 3 and 4 had significant in vitro activity against Cryptococcus neoformans but were inactive against Candida albicans. Metabolite 4 was inactive in vivo in a mouse model of cryptococcosis.

Glucosidation of betulinic acid by Cunninghamella species

Microbial transformation of the antimelanoma agent betulinic acid (1) was studied. Preparative scale biotransformation with resting-cell suspensions of Cunninghamella species NRRL 5695 resulted in the production of a fungal metabolite of 1, which has been characterized as 28-O-beta-D-glucopyranosyl 3beta-hydroxy-lup-20(29)-en-28-oate (2) based on spectral and enzymic data. The in vitro cytotoxicity assay of metabolite 2 revealed no activity against several human melanoma cell lines.

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.

Fungal transformations of antihistamines: metabolism of cyproheptadine hydrochloride by Cunninghamella elegans

1. Metabolites formed during incubation of the antihistamine cyproheptadine hydrochloride with the zygomycete fungus Cunninghamella elegans in liquid culture were determined. The metabolites were isolated by hple and identified by mass spectrometric and proton nmr spectroscopic analysis. Two C elegans strains, ATCC 9245 and ATCC 36112, were screened and both produced essentially identical metabolites. 2. Within 72 h cyproheptadine was extensively biotransformed to at least eight oxidative phase-I metabolites primarily via aromatic hydroxylation metabolic pathways. Cyproheptadine was biotransformed predominantly to 2-hydroxycyproheptadine. Other metabolites identified were 1- and 3-hydroxycyproheptadine, cyproheptadine 10,11-epoxide, N-desmethylcyproheptadine, N-desmethyl-2-hydroxycyproheptadine, cyproheptadine N-oxide, and 2-hydroxycyproheptadine N-oxide. Although a minor fungal metabolite, cyproheptadine 10,11-epoxide represents the first stable epoxide isolated from the microbial biotransformation of drugs. 3. The enzymatic mechanism for the formation of the major fungal metabolite, 2-hydroxycyproheptadine, was investigated. The oxygen atom was derived from molecular oxygen as determined from 18O-labelling experiments. The formation of 2-hydroxycyproheptadine was inhibited 35, 70 and 97% by cytochrome P450 inhibitors metyrapone, proadifen and 1-aminobenzotriazole respectively. Cytochrome P450 was detected in the microsomal fractions of C. elegans. In addition, 2-hydroxylase activity was found in cell-free extracts of C. elegans. This activity was inhibited by proadifen and CO, and was inducible by naphthalene. These results are consistent with the fungal epoxidation and hydroxylation reactions being catalysed by cytochrome P450 monooxygenases. 4. The effects of types of media on the biotransformation of cyproheptadine were investigated. It appears that the glucose level significantly affects the biotransformation rates of cyproheptadine; however it did not change the relative ratios between metabolites produced.