A multi-modality assay platform for ultra-high throughput screening

Kinetic considerations on the development of binding assays in single-addition mode: application to the search for α2δ1 modulators

The development of assays in single-addition mode is of great interest for screening purposes given the multiple advantages of minimizing the number of intervention steps. Binding assays seem to be more prone to this attractive format because no functional biological activity is taking place but instead a biophysical process, whose dynamics seem easier to control without introducing significant alterations, is happening. Therefore, single-addition assays based on the displacement of prebound labeled ligands can be conceived, but careful kinetic considerations must still be taken to maximize the sensitivity of the assay and to avoid jeopardizing the identification of compounds with slow-binding kinetics. This article shows the development of a single-addition, displacement-based binding assay intended to identify modulators that act by binding to the gabapentin site of the ion channel regulatory protein α2δ1. After studying the kinetics of gabapentin binding and the influence they might have on the assay sensitivity, the best conditions were identified, and the sensitivity was compared with that of the more classical two-additions competition-based assay. Although the present study focuses on α2δ1 and its interaction with gabapentin, the rationale and the methodology followed are of broad purpose and can be applied to virtually every binding assay.

Cellular imaging in drug discovery

Traditional screening paradigms often focus on single targets. To facilitate drug discovery in the more complex physiological environment of a cell or organism, powerful cellular imaging systems have been developed. The emergence of these detection technologies allows the quantitative analysis of cellular events and visualization of relevant cellular phenotypes. Cellular imaging facilitates the integration of complex biology into the screening process, and addresses both high-content and high-throughput needs. This review describes how cellular imaging technologies contribute to the drug discovery process.

Development of an Assay Suitable for High-Throughput Screening to Measure Matrix Metalloprotease Activity

MMPs, part of a family of enzymes with >35 known members, play an important role in tissue remodeling and repair, in the biology of neoplasia, and during development. Hydroxamic and carboxylic acid inhibitors of these proteases have long been available, but their specificities are poor and there still exists a desire to find novel chemical structures, which could be modified to optimize specificity and biocompatibility. Established methods for measuring MMP activity are based on the cleavage of MCA-PLGL-A2pr(DNP)-AR, which provides a prompt fluorescent signal when cleaved; however, its absorption/emission properties (325/400 nm) are not best suited for HTS assays. We describe an HTS-compatible method using the peptide substrate PLGLAARK, labeled at N- and C-termini with CyDye fluors Cy3 and Cy5Q, respectively, which is cleavable by MMP-1, -2, -3, -7, -9, and -13. HTS assays for MMP-13 and MMP-9 inhibitors were set up in approximately 20 microl in 384-well plates as a prompt fluorescence readout (excitation/emission = 540/570 nm) using the LEADseeker homogenous imaging system. These assays yielded IC(50) values comparable to standard methods, but with a faster, very sensitive, and normalized readout, thus conserving compound, enzyme (approximately 1.5 ng/well), and time (20 s read/plate). Data quality (Z' approximately 0.9) was such that hit-picking to -25% change in primary screening could be performed with confidence, and the subsequent rate of confirmation and validation in IC(50) determinations of the picked compounds was >60%. Parallel screening of related proteases also permitted immediate specificity comparisons, including evaluation of inactive or weakly active compounds.