Combinatorial Chemistry & High Throughput Screening - Volume 12, Issue 3, 2009

The phenolic compounds produced by in vitro shoots of Brassica oleracea L. var. costata DC were screened by HPLC-DAD-MS/MS. Thirty seven compounds were characterized, which included chlorogenic acids, flavonoids (the majority of them were hydroxycinnamic acid esters of kaempferol and quercetin glycosides) and hydroxycinnamic acyl glycosides (with predominance of synapoyl gentiobiosides). The antioxidant capacity of the shoots was assessed against DPPH radical and two reactive oxygen species (superoxide radical and hypochlorous acid). A strong concentrationdependent antioxidative capacity was verified in the DPPH and superoxide radicals assays, but a reduced effect was noticed against hypochlorous acid. The results obtained indicate that the in vitro production of B. oleracea var. costata shoots can become important in the obtention of a noticeable dietary source of compounds with health protective potential.

The neurotransmission mediated by γ-aminobutyric acid (GABA) in the mammalian brain is terminated by a family of four GABA transporters (GATs). Inhibition of GATs is currently used in the treatment of epilepsy and these proteins are generally considered as important drug targets. In this study, we perform the first elaborate pharmacological characterization of all four human GAT subtypes. We conduct the experiments in parallel in a [3H]GABA uptake assay using 14 standard GAT substrates and inhibitors. This setup enables direct comparison of the absolute values of inhibitory activities of the compounds between the different GAT subtypes. The results are overall in agreement with data reported by other groups for the orthologous murine GATs. However, there do seem to be some minor variations among species. In contrast to the several subtype selective ligands identified for the GAT-1 subtype, no subtype selective ligands have been reported for the three remaining GATs. Given the potential therapeutic relevance of the individual GAT subtypes, a search for novel structures displaying selectivities for specific GAT subtypes is important. In this study, we validate our [3H]GABA uptake assay for use in high throughput screening. We find that the assay is categorized by high Z'-factors (Z' > 0.5) for all four GAT subtypes, demonstrating that the assay is excellent for a high throughput screen. This [3H]GABA uptake assay therefore enables future high throughput screening of compound libraries at the four human GATs.

For years, the physicochemical properties of drug candidates have been used to predict their in vivo pharmacokinetic behaviors. Several theories and empirical correlations have been established by various researchers with the overall goal of expediting the drug candidate selection process, with greater confidence and faster turnaround. This study describes a 96-well reverse phase HPLC method, simultaneously determining LogD, LogP, and pKa values of drugs in a throughput mode. The LogD and LogP values of each compound were determined, based on the octanol-aqueous partitioning behavior of the charged and non-charged species under different pH values. The pKa value was determined by using the Polynomial fit between LogP and LogD and the equation LogD (pKa) ≈ LogP - 0.301. The advantages of this method are: low sample consumption, suitability for low solubility compounds, less restriction on compound purity, potential for higher throughput, precise data, and multiple determinations in one assay.

RNA triphosphatases are attractive and mostly unexplored therapeutic targets for the development of broad spectrum antiprotozoal, antiviral and antifungal agents. The use of malachite green as a readout for phosphatases is well characterized and widely employed. However, the reaction depends on high quantities of inorganic phosphate to be generated, which makes this assay not easily amenable to screening in 1536-well format. The overly long reading times required also prohibit its use to screen large chemical libraries. To overcome these limitations, we sought to develop a fluorescence polarization (FP) -based assay for triphosphatases, compatible with miniaturization and fast readouts. For this purpose, we took advantage of the nucleoside triphosphatase activity of this class of enzyme to successfully adapt the Transcreener™ ADP assay based on the detection of generated ADP by immunocompetition fluorescence polarization to the RNA triphosphatase TbCet1 in 1536-well format. We also tested the performance of this newly developed assay in a pilot screen of 3,000 compounds and we confirmed the activity of the obtained hits. We present and discuss our findings and their importance for the discovery of novel drugs by high throughput screening.

The laccase CotA from Bacillus subtilis was converted from a generalist, an enzyme with broad specificity, to a specialist, an enzyme with narrowed specificity. Laccases are members of the multicopper oxidase family and have many applications in biotechnology. To date, it has not been demonstrated that substrate specificity can be tapered for a laccase. Wild-type CotA oxidizes ABTS (ABTS = diammonium 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) and SGZ (SGZ = 4-hydroxy-3,5- dimethoxy-benzaldehyde azine), and it was engineered for increased specificity for ABTS by combining rational and directed evolution approaches. The wild-type was evolved by simultaneously randomizing 19 amino acids found in the substrate-binding pocket. A mutant was identified that had a catalytic efficiency, (kcat/KM)ATBS / (kcat/KM)SGZ, 7.0 times greater when compared to the wild-type after one round of screening. This illustrates that the substrate-binding pocket is highly evolvable for specificity.

An effective parallel solid phase route to methylenesulfonamides and amides bearing a wide variety of substituents is described. The three key reaction steps were reductive amination of a haloheteroaromatic aldehyde onto a benzhydrylamine type polystyrene resin, sulfonamide or amide formation and palladium catalysed transformation of the remaining heteroaromatic halogen. A process of virtual library design and filtering, together with solution and solid phase optimisations, aided the preparation of several novel drug-like product classes in high purities and should allow access to a variety of further useful analogues.

A multi-step NMR based screening assay is described for identifying and evaluating chemical leads for their ability to bind a target protein. The multi-step NMR assay provides structure-related information while being an integral part of a structure based drug discovery and design program. The fundamental principle of the multi-step NMR assay is to combine distinct 1D and 2D NMR techniques, in such a manner, that the inherent strengths and weakness associated with each technique is complementary to each other in the screen. By taking advantage of the combined strengths of 1D and 2D NMR experiments, it is possible to minimize protein requirements and experiment time and differentiate between nonspecific and stoichiometric binders while being able to verify ligand binding, determine a semi-quantitative dissociation constant, identify the ligand binding site and rapidly determine a protein-ligand co-structure. Furthermore, the quality and physical behavior of the ligand is readily evaluated to determine its appropriateness as a chemical lead. The utility of the multi-step NMR assay is demonstrated with the use of PrgI from Salmonella typhimurium and human serum albumin (HSA) as target proteins.

Whole-cell patch-clamp-based electrophysiological techniques are powerful tools for examining the biophysical and pharmacological properties of ion channels. However, the recent validation of ion channels as novel drug targets necessitates the development of a faster screening method for ion channels. Therefore, we have developed a rapid, reliable, and sensitive cell-based high throughput screening (HTS) assay for T-type Ca2+ channels. We had previously constructed HEK293/α1G/Kir2.1 cell lines that stably expressed α1G and Kir2.1 subunits [1] and found that α1G T-type channel- sensitive Ca2+ signals were detected by the application of high concentrations of KCl under fura-2-based single cell measurements of intracellular Ca2+ concentration ([Ca2+]i). In the present study, we applied HEK293/??1G/Kir2.1 cells to the FDSS6000 (Functional Drug Screening System) to develop a fast and reliable cell-based HTS method for α1G T-type Ca2+ channels. After detecting 70 mM KCl-induced [Ca2+]i increases using the FDSS6000 system, we verified this new α1G channel HTS system by examining two T-type Ca2+ channel blockers, Ni2+ and mibefradil, and measuring the Z'- factor (Z' factor = 0.66) in 96-well plates. Furthermore, we assayed selected 3,4-dihydroquinazolin derivatives using this FDSS6000-based α1G channel HTS system at the level of IC50 values and compared the results with those obtained from whole-cell patch-clamp recordings. Taken together, our results suggest that the FDSS6000-based α1G channel HTS system is a fast and feasible assay for α1G T-type Ca2+ channels. This assay can be utilized as a primary screening method for Ttype Ca2+ channel-targeted chemicals and for the development of HTS systems for other types of ion channels.

Virtual (database) screening (VS) of molecules promises to accelerate the discovery of new drugs and reduce costs by identifying molecules with high probabilities of binding to a target receptor. The large amount of available protein X-ray crystal structures, together with the development of more effective homology modelling techniques, has led recently to a steep increase in docking-based VS studies. This approach needs computational fitting of molecules into a receptor active site using advanced algorithms, followed by the scoring and ranking of these molecules to identify potential leads. In this review, the main published docking-based VS studies developed over the last eight years are investigated, and details are provided about the software used, the results achieved and the novel methods employed.

Current advances of new technologies with robotic automated assays combined with highly selective and sensitive LC-MS enable high-speed screening of lead series libraries in many in vitro assays. In this review, we summarize state of the art high throughput assays for screening of key physicochemical properties such as solubility, lipophilicity, pKa, drug-plasma protein binding and brain tissue binding as well as in vitro ADME profiling. We discuss two primary approaches for high throughput screening of solubility, i.e. an automated 96-well plate assay integrated with LC-MS and a rapid multi-wavelength UV plate reader. We address the advantages of newly developed miniaturized techniques for high throughput pKa screening by capillary electrophoresis combined with mass spectrometry (CE-MS) with automated data analysis flow. Several new lipophilicity approaches other than octanol-water partitioning are critically reviewed, including rapid liquid chromatographic retention based approach, immobilized artificial membrane (IAM) partitioning and liposome, and potential microemulsion electrokinetic chromatography (MEEKC) for accurate screening of LogP. We highlight the sample pooling (namely cassette dosing, all-in-one, cocktail) as an efficient approach for high throughput screening of physicochemical properties and in vitro ADME profiling with emphasis on the benefit of on-line quality control. This cassette dosing approach has been widely adapted in drug discovery for rapid screening of in vivo pharmacokinetic parameters with significantly increased capacity and dramatically reduced animal usage.