Micromechanical measurement of AChBP binding for label-free drug discovery.

A potential binding assay based on binding-driven micromechanical motion is described. Acetylcholine binding protein (AChBP) was used to modify a microcantilever. The modified microcantilever was found to bend on application of the naturally occurring agonist (acetylcholine) or the antagonist (nicotine and d-tubocurarine). Control experiments show that microcantilevers modified without AChBP do not respond to acetylcholine, nicotine, and d-tubocurarine. K(d) values obtained for acetylcholine, nicotine, and d-tubocurarine are similar to those obtained from radio-ligand binding assays. These results suggest that the microcantilever system has potential for use in label free, drug screening applications.

Direct chromatographic determination of dissociation rate constants of ligand-receptor complexes: assessment of the interaction of noncompetitive inhibitors with an immobilized nicotinic acetylcholine receptor-based liquid chromatography stationary phase.

A liquid chromatographic stationary phase containing immobilized membranes from a cell line expressing the alpha3beta4 subtype of the neuronal nicotinic acetylcholine receptor (nAChR) has been used to assess dissociation rate constants (kd) of 12 noncompetitive inhibitor-nAChR complexes. The pharmacological effects of the noncompetitive inhibitors, expressed as percent recovery of activity at 7 min and 4 h postexposure to the inhibitor, were also determined. The results demonstrate that the kd values correlated with the pharmacological effect and that this approach can be used to identify molecular structures associated with differences in kd values. The method can be adapted for use with membrane-bound receptors, ion channels, and transporters and represents a direct and facile technique for the assessment of dissociation rate constants (kd) of ligand-receptor complexes.

Pancuronium bromide (Pavulon) isolation and identification in aged autopsy tissues and fluids.

The isolation and detection of pancuronium bromide was developed for aged autopsy samples to identify and confirm this compound in questioned tissue samples. A novel protocol was optimized for the isolation of the target drug in highly decomposed tissues. Solid-phase extraction (SPE) cartridges containing styrene-divinylbenzene were investigated. This polymer retained quaternary drugs and facilitated sequential elution upon washing with commonly available solvents. The semi-purified SPE samples were prescreened by pyrolysis GC-MS. A candidate specimen was then confirmed by microbore high-performance liquid chromatography/electrospray-ionization/mass spectrometry (microHPLC-ESI-MS/MS) with a triple-quadrupole mass spectrometer. The developed procedures provided a qualitative or semiquantitative (at best) basis for the investigation of difficult cases involving overdoses of polar drugs.

Qualitative assessment of IC50 values of inhibitors of the neuronal nicotinic acetylcholine receptor using a single chromatographic experiment and multivariate cluster analysis.

It has been widely demonstrated that affinity chromatography can be used to derive binding affinities, and that these affinities can be correlated to data obtained using standard techniques such as membrane binding, ultrafiltration and equilibrium dialysis. The purpose of this study is to evaluate the use of immobilized nicotinic acetylcholine receptor stationary phase in chromatographic experiments to assess the functional activity of series of noncompetitive inhibitors (NCIs) as reflected in their IC50 values. Chromatographically determined retention values and computer generated molecular descriptors were obtained for 29 compounds and the data were analyzed by cluster analysis. The approach qualitatively ranked the test compounds as efficient NCIs (low IC50 values) or poor NCIs (high IC50 values). The data obtained with the 29 compounds used in this study demonstrate that the experimental approach had been able to place 25 of these compounds in the correct IC(50) clusters. To our knowledge, this is the first relationship established between chromatographic retention and IC50 for membrane-bound receptors. These results suggest that the chromatographic approach may be useful in development of lead drug candidates including the determination of off-target binding.

An HPLC assay for the norditerpenoid alkaloid methyllycaconitine, a potent nicotinic acetylcholine receptor antagonist.

The extremely potent and selective nicotinic acetylcholine receptor antagonist methyllycaconitine, MLA, and related norditerpene alkaloids are finding increasing use as neurochemical probes and as targets for structure-activity relationship studies. In this work, an assay procedure for MLA which utilises ion suppression reverse-phase HPLC with UV absorbance detection at 270 nm is described. The method detected 280 ng MLA on column.