Development of a Platform to Enable Fully Automated Cross-Titration Experiments.

In the triage of hits from a high-throughput screening campaign or during the optimization of a lead compound, it is relatively routine to test compounds at multiple concentrations to determine potency and maximal effect. Additional follow-up experiments, such as agonist shift, can be quite valuable in ascertaining compound mechanism of action (MOA). However, these experiments require cross-titration of a test compound with the activating ligand of the receptor requiring 100-200 data points, severely limiting the number tested in MOA assays in a screening triage. We describe a process to enhance the throughput of such cross-titration experiments through the integration of Hewlett Packard's D300 digital dispenser onto one of our robotics platforms to enable on-the-fly cross-titration of compounds in a 1536-well plate format. The process handles all the compound management and data tracking, as well as the biological assay. The process relies heavily on in-house-built software and hardware, and uses our proprietary control software for the platform. Using this system, we were able to automate the cross-titration of compounds for both positive and negative allosteric modulators of two different G protein-coupled receptors (GPCRs) using two distinct assay detection formats, IP1 and Ca2+ detection, on nearly 100 compounds for each target.

Development of thioquinazolinones, allosteric Chk1 kinase inhibitors.

A high throughput screening campaign was designed to identify allosteric inhibitors of Chk1 kinase by testing compounds at high concentration. Activity was then observed at K(m) for ATP and at near-physiological concentrations of ATP. This strategy led to the discovery of a non-ATP competitive thioquinazolinone series which was optimized for potency and stability. An X-ray crystal structure for the complex of our best inhibitor bound to Chk1 was solved, indicating that it binds to an allosteric site approximately 13A from the ATP binding site. Preliminary data is presented for several of these compounds.

A high-precision fluorogenic cholesteryl ester transfer protein assay compatible with animal serum and 3456-well assay technology.

Cholesteryl ester transfer protein (CETP) is a serum component responsible for both cholesteryl ester and triglyceride trafficking between high-density lipoprotein (HDL) and the apolipoprotein B (apoB)-containing very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL). Several fluorescence-based assays that monitor these transfers have been reported, but to date such assays have suffered from a low signal/background (S/B) ratio and have been described for use only in relatively purified in vitro systems. We have modified the more advanced of these assays to incorporate a noninterfering, nondiffusable fluorescence quencher into previously described cosonicate particles, often referred to as microemulsions. This simple improvement resulted in particles that had an average threefold enhanced S/B window over particles without quenchers but that continued to show the essential properties of a catalytic assay, including catalysis to a single endpoint, excellent linearity with protein and particle concentration, and an appropriate sensitivity to inhibition. This reduced assay noise allowed the subsequent development of protocols for the direct measure of cholesteryl ester (CE) transfer activity resident in human and animal serum as well as the development of 384- and 3456-well screening protocols with good precision and accuracy. Thus, by expanding the dynamic response window of the assay, we have created an assay generalizable to many settings.