Structural, kinetic, and pharmacodynamic mechanisms of D-amino acid oxidase inhibition by small molecules.

We characterized the mechanism and pharmacodynamics of five structurally distinct inhibitors of d-amino acid oxidase. All inhibitors bound the oxidized form of human enzyme with affinity slightly higher than that of benzoate (Kd ≈ 2-4 µM). Stopped-flow experiments showed that pyrrole-based inhibitors possessed high affinity (Kd ≈ 100-200 nM) and slow release kinetics (k < 0.01 s(-1)) in the presence of substrate, while inhibitors with pendent aromatic groups altered conformations of the active site lid, as evidenced by X-ray crystallography, and showed slower kinetics of association. Rigid bioisosteres of benzoic acid induced a closed-lid conformation, had slower release in the presence of substrate, and were more potent than benzoate. Steady-state d-serine concentrations were described in a PK/PD model, and competition for d-serine sites on NMDA receptors was demonstrated in vivo. DAAO inhibition increased the spatiotemporal influence of glial-derived d-serine, suggesting localized effects on neuronal circuits where DAAO can exert a neuromodulatory role.

Synthesis and pharmacological evaluation of 4-(3,4-dichlorophenyl)-N-methyl-1,2,3,4-tetrahydronaphthalenyl amines as triple reuptake inhibitors.

The present work describes a series of novel chiral amines that potently inhibit the in vitro reuptake of serotonin, norepinephrine and dopamine (triple reuptake inhibitors) and were active in vivo in a mouse model predictive of antidepressant like activity. The detailed synthesis and in vitro activity and ADME profile of compounds is described, which represent a previously undisclosed triple reuptake inhibitor chemotype.

Evidence for an interaction between the SH3 domain and the N-terminal extension of the essential light chain in class II myosins.

The function of the src-homology 3 (SH3) domain in class II myosins, a distinct beta-barrel structure, remains unknown. Here, we provide evidence, using electron cryomicroscopy, in conjunction with light-scattering, fluorescence and kinetic analyses, that the SH3 domain facilitates the binding of the N-terminal extension of the essential light chain isoform (ELC-1) to actin. The 41 residue extension contains four conserved lysine residues followed by a repeating sequence of seven Pro/Ala residues. It is widely believed that the highly charged region interacts with actin, while the Pro/Ala-rich sequence forms a rigid tether that bridges the approximately 9 nm distance between the myosin lever arm and the thin filament. In order to localize the N terminus of ELC in the actomyosin complex, an engineered Cys was reacted with undecagold-maleimide, and the labeled ELC was exchanged into myosin subfragment-1 (S1). Electron cryomicroscopy of S1-bound actin filaments, together with computer-based docking of the skeletal S1 crystal structure into 3D reconstructions, showed a well-defined peak for the gold cluster near the SH3 domain. Given that SH3 domains are known to bind proline-rich ligands, we suggest that the N-terminal extension of ELC interacts with actin and modulates myosin kinetics by binding to the SH3 domain during the ATPase cycle.

Affinity ligand selection from a library of small molecules: assay development, screening, and application.

A facile and cost-effective process for screening synthetic libraries for an affinity ligand is described. A high throughput 96-well plate filtration method was designed to screen both discrete compounds and mixtures of compounds attached to a solid support. Human serum albumin (HSA) was used as a target protein to demonstrate the proof of concept. Detection and quantitation by fluorescence was accomplished with the use of fluorescamine to conjugate the protein in the filtrate. It is found that mixtures demonstrating low average binding reflect an overall lower hit rate of the components, whereas deconvolution of mixtures with high protein binding consistently provides a high hit rate. This differs from many of the previous experiences screening solid-phase mixtures in which high false positive rates are noted to occur. A total of 100K compounds were tested: 25K as discrete samples and 75K as mixtures. An overall hit rate of 8% was observed. Secondary screening of compounds measured specificity, recovery, and dynamic binding capacity. The effectiveness of the method is illustrated using an affinity column made with a representative lead compound. A similar purity was achieved in a single-step purification of HSA from serum as compared to that obtained by two steps of ion-exchange chromatography. The process for primary screening of a large number of compounds is simple, inexpensive, and applicable to any soluble target protein of known or unknown function from crude mixtures and may have additional utility as a generic chemical affinity tool for the functional characterization of novel proteins emerging from proteomics work.

A high-throughput method for enzyme kinetic studies.

A simple and flexible setup for conducting drug metabolism studies is described in this report. A heating block was designed for the Multimek liquid handler platform for incubation of multiple samples at 37 degrees C in a 96-well format. This setup enables the rapid performance of drug metabolism experiments on a large number of samples. In this report, the authors present the validation of the system by 1) showing reproducible and consistent determination of the in vitro half-life of midazolam in every well across the entire plate and 2) determination of metabolic parameter values of midazolam, testosterone, diclofenac, warfarin, and dextromethorphan and inhibition parameter values of quinidine and ketoconazole, all comparable to literature values. In addition, the authors demonstrate the application of the setup to determining the metabolic stability of a set of proprietary compounds, the inhibition of activity of cytochrome P450 (CYP) enzymes, and the conduct of a single combination experiment that can simultaneously determine the metabolic stability and CYP inhibition activity. Overall, the system represents a simple, high-throughput and useful tool for drug metabolism screening in drug discovery.