Evaluation of liquid handling conditions in microplates

Liquid handling in higher density microplates (e.g., 1536-well microplates) for more efficient drug screening necessitates carefully selected and optimized parameters. The quality of a liquid handling procedure is dependent on the carryover rate of residual liquids during the pipetting process, the mixing behavior in the wells, foam and bubble formation, and evaporation. We compared and optimized these parameters in 96-, 384-, and 1536-well microplates, and herein we critically evaluate the performance of the CyBi-Well 96/384/1536 automated micropipetting device, which formed the basis of our evaluation studies.

Dragon's Blood incense: misbranded as a drug of abuse?

An unknown red substance was being sold and used with other drugs of abuse in Virginia (often being used in conjunction with marihuana). The red substance was identified as Dragon's Blood incense from Daemonorops draco. In bioassays, Dragon's Blood incense exhibited a low, but measurable cytotoxicity in in vitro cell lines. Dragon's Blood incense or Volatilized Dragon's Blood had no adverse effect on mouse motor performance based on the inclined screen and rotorod tests. delta(9)-Tetrahydrocannibinol (THC) produced a dose-related decline in mouse performance on the rotorod test. The combination of Dragon's Blood incense or Volatilized Dragon's Blood with delta(9)-THC did not contribute further to the impairment of the mice on the rotorod. This data suggests that the abuse potential for Dragon's Blood incense alone or in combination with marihuana is minimal.

Feigrisolides A, B, C and D, new lactones with antibacterial activities from Streptomyces griseus

Four new lactone compounds, named feigrisolides A to D (1 to 4), have been isolated from Streptomyces griseus. The chemical structures were determined by detail analysis of their spectroscopic data and chemical transformations. Structurally, the feigrisolides A (1) and B (2) are hepta-lactones, feigrisolide C (3) and D (4) are 16-membered macrodiolides. Biological studies showed that feigrisolide B (2) exhibited strong antibacterial, as well as medium cyctotoxic, and antiviral activities. Feigrisolides A (1), C (3) and D (4) are medium inhibitors of 3alpha-hydroxysteroid-dehydrogenase (3alpha-HSD) inhibiting activity.

New 1-O-acyl alpha-L-rhamnopyranosides and rhamnosylated lactones from Streptomyces sp., inhibitors of 3 alpha-hydroxysteroid-dehydrogenase (3alpha-HSD)

Chemical screening with extracts of Streptomyces sp. (strain GT 61150) resulted in the detection, isolation, and structure elucidation of two new acyl alpha-L-rhamnopyranosides (1 and 2) and three new rhamnosyllactones A, B1 and B2 (3 approximately 5). Rhamnosyllactones B1 and B2 were obtained as a 5:1 mixture. The structures were confirmed by spectroscopic analysis, especially 2D-NMR techniques. The rhamnosyltransferase of our strain is able to connect the sugar moiety to heteroaromatic carboxylic acids and enols. The metabolites 1 and 4/5 as well as previously reported acylrhamnosides 6 approximately 11 inhibit the enzyme 3alpha-hydroxysteroid-dehydrogenase (3alpha-HSD).

Natural Products in High Throughput Screening: Automated High-Quality Sample Preparation

At present, compound libraries from combinatorial chemistry are the major source for high throughput screening (HTS) programs in drug discovery. On the other hand, nature has been proven to be an outstanding source for new and innovative drugs. Secondary metabolites from plants, animals, and microorganisms show a striking structural diversity that supplements chemically synthesized compounds or libraries in drug discovery programs. Unfortunately, extracts from natural sources are usually complex mixtures of compounds, often generated in time-consuming and, for the most part, manual processes. Because quality and quantity of the provided samples play a pivotal role in the success of HTS programs, this poses serious problems. In order to make samples of natural origin competitive with synthetic compound libraries, we devised a novel, automated sample preparation procedure based on solid-phase extraction (SPE). By making use of modified Zymark (Hopkinton, MA) RapidTrace® SPE workstations, we developed an easy-to-handle and effective fractionation method that generates high-quality samples from natural origin, fulfilling the requirements for an integration in high throughput drug discovery programs.

Miniaturization of a functional transcription assay in yeast (human progesterone receptor) in the 384- and 1536-well plate format

Miniaturization of high throughput screening assays to high-density microplate formats (384 or 1536 wells) is currently the focus of research activity in modern drug discovery facilities. In this article, we describe the adaptation of a fluorescence-based functional transcription assay in yeast for assessing modulators of human progesterone receptor to the 384- and 1536-well microplate format, comparing the experimental results to those obtained in the well-established 96-well format. The experiences gained from the optimization of the liquid-handling procedures and the miniaturization of an enzyme assay (beta-galactosidase) were implemented. Thus optimized pipetting protocols were developed to perform a reporter gene assay in yeast in microplate formats of higher density. In the functional transcription assay in yeast, the reporter gene expression showed the expected dependence on the ligand's dose and affinity in principle in all three microplate formats. For the first time, this assay system has been established in the 1536-well microplate format using CyBi-Well 96/384/1536 as the liquid-handling unit. The comparison of the signal:background ratios showed a lower sensitivity of the assay in the microplate formats of higher density. This study is an example of a successful miniaturization of a yeast cell-based assay to high-density plate formats on the basis of a careful adaptation procedure and optimized liquid-handling conditions.

Biomolecular-chemical screening: a novel screening approach for the discovery of biologically active secondary metabolites. III. New DNA-binding metabolites

Based on the chemical screening technique, biomolecular-chemical screening has been developed which makes use of two-dimensional TLC analysis of microbial extracts and combines thin-layer chromatography (RP-18) with binding studies towards DNA. In the first dimension the metabolites of the crude microbial extract are separated, and in the second dimension binding properties towards DNA are analysed. An initial screening program with 500 microbial extracts prepared by solid-phase extraction with XAD-16 resin resulted in 17 samples which contained metabolites with significant DNA-binding behavior. Fermentation, isolation and structural characterization led to already known metabolites [phenazine-1,6-dicarboxylate (1), phencomycin (2), 11-carboxy-menoxymycin B (3), soyasaponine I (4), and (8S)-3-(2-hydroxypropyl)-cyclohexanone (5)], as well as to new secondary metabolites. Fermentation of the producing organisms of the new DNA-binding metabolites, ent-8,8adihydro-ramulosin (6). (2R,4R)-4-hydroxy-2-(1,3-pentadienyl)-piperidine (7), (5R)-dihydro-5-pentyl-4'-methyl-4'-hydroxy-2(3H)-furanone (8), and seco-4,23-hydroxyoleane-12-en-22-one-3-carboxylic acid (9), as well as isolation, structural characterization, and physico-chemical properties are reported.

Biomolecular-chemical screening: a novel screening approach for the discovery of biologically active secondary metabolites. II. Application studies with pure metabolites

The novel screening strategy called "biomolecular-chemical screening" combines the advantages of the chemical screening approach--the analysis of the chromatographic and chemical behaviour of secondary metabolites on TLC plates--with binding studies of these molecules with bio-macromolecules like DNA. This approach was advantageously used to detect the interaction of pure compounds with DNA. In order to prove the reliability of the biomolecular-chemical screening and to examine DNA-binding properties, 470 pure secondary metabolites were analysed by this method. Besides the confirmation of already known binders with the TLC-based method, for a number of natural products DNA-binding properties were discovered for the first time. In consequence, binding of pure compounds can be measured by 1D TLC in a reliable and easy manner, in which DNA is applied together with the test compound at the starting spot. Analysis is performed via differences in Rf-values in comparison to a reference chromatogram without DNA.

Biomolecular-chemical screening: a novel screening approach for the discovery of biologically active secondary metabolites. I. Screening strategy and validation

Chemical screening using thin-layer chromatography and various staining reagents offers the opportunity to visualize an almost complete picture of a microbial secondary metabolite pattern (metabolic finger-print). A thorough application of this strategy resulted in a number of biologically active new secondary metabolites, although the screening strategy is per se not correlated to any biological activity. In the present paper we report on a novel approach called biomolecular-chemical screening which combines the chemical screening strategy with binding studies of biological relevance. Making use of thin-layer chromatography (TLC) and subsequent staining, biomolecular-chemical screening allows to examine binding properties of low molecular weight metabolites to certain bio-macromolecules. The screening strategy itself, as well as independent validation of the results using DNA as selected bio-macromolecule are presented. The biomolecular-chemical screening method is useful to screen binding behaviour towards DNA of both, pure metabolites by one-dimensional TLC, and crude extracts by two-dimensional TLC. Investigation of pure secondary metabolites as well as screening of crude microbial extracts and new secondary metabolites obtained with this screening strategy are presented in accompanying papers.

Synthesis and cytotoxic evaluation of cycloheximide derivatives as potential inhibitors of FKBP12 with neuroregenerative properties

On the basis of the new finding that the protein synthesis inhibitor cycloheximide (1, 4-[2-(3, 5-dimethyl-2-oxocyclohexyl)-2-hydroxyethyl]-2,6-piperidinedione) is able to competitively inhibit hFKBP12 (K(i) = 3.4 microM) and homologous enzymes, a series of derivatives has been synthesized. The effect of the compounds on the activity of hFKBP12 and their cytotoxicity against eukaryotic cell lines (mouse L-929 fibroblasts, K-562 leukemic cells) were determined. As a result, several less toxic or nontoxic cycloheximide derivatives were identified by N-substitution of the glutarimide moiety and exhibit IC(50) values in the range of 22.0-4.4 microM for inhibition of hFKBP12. Among these compounds cycloheximide-N-(ethyl ethanoate) (10, K(i) = 4.1 microM), which exerted FKBP12 inhibition to an extent comparable to that of cycloheximide (1), was found to cause an approximately 1000-fold weaker inhibitory effect on eukaryotic protein synthesis (IC(50) = 115 microM). Cycloheximide-N-(ethyl ethanoate) (10) was able to significantly speed nerve regeneration in a rat sciatic nerve neurotomy model at dosages of 30 mg/kg.

Strep-tag II for one-step affinity purification of active bHLHzip domain of human c-Myc

The c-Myc protein, the product of the c-myc protooncogene, is a nuclear phosphoprotein with DNA-binding properties when heterodimerized with the Max protein. It contains an amino-terminal transcriptional activation domain and a carboxy-terminal basic helix-loop-helix leucine zipper (bHLHzip) domain that directs heterodimerization and promotes DNA binding. Here, we describe the isolation of the bHLHzip domain of human c-Myc with a technique for efficient single-step purification. Using a C-terminal Strep-tag II affinity peptide and a novel Streptactin-Sepharose matrix, elution is performed under mild conditions by competition with the biotin analog desthiobiotin. No significant influence of the affinity tag on the activity of the bHLHzip domain was observed when the fusion protein was subjected to glutathione S-transferase (GST) pull-down assays for investigating its in vitro-binding properties with GST-Max. The use of the C-terminal Strep-tag II was shown to be more suitable for obtaining pure product fractions than use of the N-terminal GST affinity tag.

Dual reporter systems in yeast and mammalian cells for assessing progesterone receptor modulators

In the present study we describe the set-up of a new one-hybrid reporter gene assay in Saccharomyces cerevisiae composed of the human progesterone receptor fused to the DNA-binding domain of the yeast transcriptional activator Gal4. This assay allows the convenient estimation of receptor mediated progestogenic as well as antiprogestogenic actions of compounds. The induction of the beta-galactosidase reporter gene expression correlated well with the progesterone receptor affinity and the concentration of the progestins tested. The results corresponded to those obtained from a reporter gene assay in the cancer cell line CV-1 and in vitro binding experiments using rabbit uterus cytosol. In both the yeast and CV-1 cells the activity of antiprogestins was detectable by inhibition of the progestin-induced reporter gene expression. Secondary reporter genes under the transcriptional control of receptor unrelated promoters have been introduced into yeast and mammalian test strains to distinguish between specific receptor mediated antihormone actions and nonspecific effects on cellular metabolism.

Bioactive agents from natural sources: trends in discovery and application

About 30% of the worldwide sales of drugs are based on natural products. Though recombinant proteins and peptides account for increasing sales rates, the superiority of low-molecular mass compounds in human diseases therapy remains undisputed mainly due to more favorable compliance and bioavailability properties. In the past, new therapeutic approaches often derived from natural products. Numerous examples from medicine impressively demonstrate the innovative potential of natural compounds and their impact on progress in drug discovery and development. However, natural products are currently undergoing a phase of reduced attention in drug discovery because of the enormous effort which is necessary to isolate the active principles and to elucidate their structures. To meet the demand of several hundred thousands of test samples that have to be submitted to high-throughput screening (HTS) new strategies in natural product chemistry are necessary in order to compete successfully with combinatorial chemistry. Today, pharmaceutical companies have to spend approximately US $350 million to develop a new drug. Currently, approaches to improve and accelerate the joint drug discovery and development process are expected to arise mainly from innovation in drug target elucidation and lead finding. Breakthroughs in molecular biology, cell biology, and genetic engineering in the 1980 s gave access to understanding diseases on the molecular or on the gene level. Subsequently, constructing novel target directed screening assay systems of promising therapeutic significance, automation, and miniaturization resulted in HTS approaches changing the industrial drug discovery process drastically. Furthermore, elucidation of the human genome will provide access to a dramatically increased number of new potential drug targets that have to be evaluated for drug discovery. HTS enables the testing of an increasing number of samples. Therefore, new concepts to generate large compound collections with improved structural diversity are desirable.

Label-free monitoring of DNA-ligand interactions

We report on the label- and isotope-free monitoring of DNA interactions with low-molecular-weight ligands. An optical technique based on interference at thin layers was used to monitor in real time binding of ligands at DNA which was immobilized by Coulomb interactions at a positively charged surface. Approximately 2 ng DNA/m2 was irreversibly bound to the surface, which remained stable over several days. This result was confirmed by characterization of the layer using spectroscopic ellipsometry. During incubation of immobilized DNA with a variety of intercalators and other DNA-binding compounds in a flow system, interactions were monitored by reflectometric interference spectroscopy. Binding effects between 10 and 400 pg/ mm2 were detected unambiguously. Nonspecific binding effects were excluded by using a negatively charged reference surface. Variation of intercalator concentration allowed the characterization of interaction with respect to kinetics and thermodynamics by the evaluation of binding rate and equilibrium coverage. The affinity constants were determined in the range between 10(5) and 10(6) M-1, in good agreement to those obtained by homogeneous phase assays. Association rate constants between 10(3) and 10(5) M-1 s-1 and dissociation rate constants between 10(-1) and 10(-2) s-1 were determined by evaluation of the binding curves. Both the fast and simple test format and a universal applicability make the new technique described attractive for detecting and characterizing interaction of low-molecular-weight molecules with DNA.

New cineromycins and musacins obtained by metabolite pattern analysis of Streptomyces griseoviridis (FH-S 1832). II. Structure elucidation

A detailed analysis of the secondary metabolite pattern produced by Streptomyces griseoviridis (strain FH-S 1832) using a chemical screening method resulted in the detection, isolation and structure elucidation of new 14-membered lactones of the cineromycin B-type [dehydrocineromycin B (5), oxycineromycin B (7), and 2,3-dihydrocineromycin B (8)], as well as new gamma-lactones related to nigrosporalactone and 4,5-dihydroxy-octa-2,6-dienoic acid esters named musacins A to F (10, 13 approximately 15, 17, 18 and 21). The constitution of these metabolites were deduced from spectroscopic data as well as chemical transformations. The configuration of musacin D (10) was determined by derivatization with chiral acids (Helmchen's method).

New cineromycins and musacins obtained by metabolite pattern analysis of Streptomyces griseoviridis (FH-S 1832). I. Taxonomy, fermentation, isolation and biological activity

Chemical screening using thin layer chromatography and various staining reagents offers the opportunity to visualize a nearly complete picture of a microbial secondary metabolite pattern (metabolic finger-print). This approach can be used advantageously for both, the detection of so-called "talented" strains, and for qualifying microbial strain collections, especially as a fundamental step of efficiently applied biological high-throughput assays. Based on their metabolic finger-print, microbial isolates can be classified in: (i) non-producing organisms, which gave no indication of the formation of secondary metabolites up to a defined detection limit, (ii) organisms of narrow productivity, which produce one or two secondary metabolites as main products with a restricted dependence to alteration of the culture conditions, and (iii) talented organisms, which are able to synthesize an array of structurally different secondary metabolites. As an example, the talented strain, Streptomyces griseoviridis (FH-S 1832), was studied in detail. Investigations in its taxonomical characterization, fermentation, as well as the isolation and purification procedures leading to 14-membered macrocyclic lactones of the cineromycin-type (cineromycin B and three new congeners) and to the musacins A to F are reported. Musacin C exhibits anthelminthic and weak antiviral activities.

Secondary metabolites by chemical screening, 26.1 7-O-beta-D-galactosyl-brefeldin A via transglycosylation with Penicillium brefeldianum

A lactose-containing fermentation medium initiated the formation of 7-O-beta-D-galactosyl-brefeldin A [1] in the brefeldin A-producing organism, Penicillium brefeldianum. The detection, isolation, and physicochemical properties of 1, which has been produced by biological derivatization via transglycosylation, are described. Compound 1 is the first glycosylated brefeldin A derivative to have been prepared.

A non-enzymatic reaction in the late biosynthesis of the decarestrictine family

In the late biosynthesis of the decarestrictines, inhibitors of the de novo formation of cholesterol isolated from the culture broth of Penicillium simplicissimum (FH-A 6090), a common pentaketide precursor undergoes post-polyketide modifications leading to the different members of the decarestrictine family. Besides subsequent enzymatically catalyzed reactions an unexpected non-enzymatic conversion was found to be the key step in the biosynthetic sequence. Under acidic conditions during fermentation the decarestrictines A1 and A2 (3 and 4) are converted into the main product decarestrictine D (2) and the new decarestrictines N (5) and O (6), whose physico-chemical data are reported. Mechanistic aspects of the non-enzymatic reaction as well as a more detailed picture of the biosynthetic relationships of the decarestrictine family are described. By the application of pH-static fermentations these results were successfully used to manipulate the secondary metabolite pattern of strain FH-A 6090 directing the fermentation process to produce desired members of the decarestrictine family.

Secondary metabolites by chemical screening. 9. Decarestrictines, a new family of inhibitors of cholesterol biosynthesis from Penicillium. II. Structure elucidation of the decarestrictines A to D

The structures of the novel 10-membered lactones, named decarestrictines A1/A2 (1/2), B (3), C1/C2 (5/6) and D (7), are presented. The structures of these secondary metabolites, isolated from different Penicillium species, were established by spectroscopic analysis and confirmed by X-ray analysis of 7 and a derivative of 3 leading to the stereochemical information. The decarestrictines vary in the oxygenation pattern between C-3 and C-7 and show structural similarities to known lactones from other fungi.

Secondary metabolites by chemical screening. 8. Decarestrictines, a new family of inhibitors of cholesterol biosynthesis from Penicillium. I. Strain description, fermentation, isolation and properties

A family of new 10-membered lactones was detected by chemical screening. Taxonomic studies and fermentation conditions of the producing organisms, which belong to the species Penicillium simplicissimum and Penicillium corylophilum, are presented. The isolation as well as physico-chemical data of the new compounds named decarestrictines A to D are reported. In vitro testing using the HEP-G2 cell assay showed the decarestrictines to be inhibitors of cholesterol biosynthesis, which could be confirmed in vivo. In addition to the decarestrictines from P. corylophilum epoxyagroclavine-I (1) was isolated.

The structure of manumycin. II. Derivatives

Derivatives of manumycin (1) were obtained by acetylation and reduction, respectively, and characterized by their spectroscopic data. Structure-activity relationships of the antibiotic were discussed.

The structure of manumycin. III. Absolute configuration and conformational studies

Chromic acid oxidation of manumycin (1), an antibiotic produced by Streptomyces parvulus (strain Tü 64), led to the isolation of 2-(2-methyl-4-oxo-2-pentenoylamino)-5,6-epoxy-1,4-benzoquinone (3) and (-)-(R)-2-methylhexanoic acid (4). From the absolute configuration of 4, determined by comparing its optical rotation with published data, follows the absolute configuration at the center of chirality in the diene side chain of manumycin (1) to be (6'R). Based on the direct comparison of the CD spectra of the two chromic acid oxidation products 2 and 3 with those of the antibiotic G7063-2 (5) and (-)-terreic acid (6) the stereochemistry at C-5 and C-6 of 1 was determined as (5R, 6S). From the negative CD-couplet of manumycin (1) its stereochemistry at C-4 was assigned as (4R).

The structure of manumycin. I. Characterization, structure elucidation and biological activity

Manumycin (1), produced by Streptomyces parvulus (strain Tü 64), was isolated from the mycelium by extraction with acetone and could easily be purified chromatographically. Chemical degradation of 1 (C31H38N2O7) gave 2-acetamino-3-hydroxycyclopent-2-enone (2) by acetolysis, 2,4,6-trimethyl-2,4-decadienoic acid (3) by alkaline hydrolysis, and 2-(2,4,6-trimethyl-2,4-decadienoylamino)-5,6-epoxy-1,4-benzoquinon e (5) by chromic acid oxidation. In connection with a detailed spectroscopic analysis, the structure of 1 could be elucidated and the (E)-configuration of the double bonds in the triene and diene chain was established. Manumycin exhibits biological activity against Gram-positive bacteria and fungi and furthermore, an inhibition of the developmental processes of some insects.