The 4th International Protein Kinases in Drug Discovery & Development meeting (October 20–22, 2003, Philadelphia, USA) organized by SRI (http://www.srinstitute.com) integrated sessions that aimed to address the key issues for kinase drug discovery. With over 500 kinases in the human kinome [1] and the costs of drug development approaching the billion dollar mark, the meeting focused on strategies to move kinase drug discovery forward in a more rapid and efficient manner, including protein kinase target validation, selectivity and drugability. Topics included kinase assay technology and profiling, novel strategies for kinase inhibitor generation and associated technologies for target identification and validation, including RNAi applications. Biochemical, cell-based assays and screening methods Owing to enormous efforts made within the pharmaceutical industry, there are now numerous biochemical and cell-based screening methods for the thorough profiling of kinase inhibitors. Numerous factors such as cost, data quality, throughput and screening-library size need to be taken into consideration and different assays can therefore yield different screening results. Over 13 novel assay formats were outlined during the course of the meeting for tyrosine and serine/threonine kinases, all with the aim of resolving assay development bottlenecks. Gregory Moore (Upstate Discovery; http://www.upstate.com) described assay formats for a range of serine/threonine kinases using monoclonal antibodies based on a small collection of substrates and generic fluorescent polarization assays for tyrosine kinases based on Upstate’s anti-phosphotyrosine antibody, 4G10. Upstate currently has the capacity to screen over 120 human protein kinases. Michael Curtin (Promega Corporation; http://www.promega.com) described the development of two novel homogeneous, non-radioactive high- throughput assays to determine the activity of many protein kinases These assays can be readily optimized and data were presented to demonstrate that these formats can produce comparable IC50s to those in the literature for known inhibitors of protein kinase A (PKA) and src family tyrosine kinases. Phosphorylation of serine, threonine and tyrosine residues is recognised as a key mode of signal transduction and amplification in eukaryotic cells. Pierre Thibault (Caprion Pharmaceuticals; http://www.caprion.com) described how, with protein expression profiling as a principle focus in proteomic research for cancer therapies and biomarkers, Caprion has pioneered a novel mass spectrometry–bioinformatics approach to measure relative protein abundance from purified protein extracts of patient- matched disease and normal specimens. Steven Pelech (Kinexus Bioinformatics; http://www.kinexus.ca) gave an insightful overview of Kinexus’s antibody- based detection method (Kinetworks™), used to track >100 protein kinases simultaneously in diverse cell and tissue types. The multi-immunoblotting services provided by Kinexus allows researchers to accurately measure protein expression, phosphorylation and interactions with many other proteins through the direct capture and quantification of proteins by immobilized peptide probes. Brian Holaway (Roche Protein Expression Group; http://www.roche.com) described the expression of p38 alpha in inactive or activated forms using a continuous-exchange cell-free (CECF) protein expression system, which potentially overcomes the limitations of current cell-based methods. Rigorous biophysical characterization, including 2D-NMR approaches, also identified a number of conformational differences between the activation states that could potentially be exploited by small-molecule inhibitors. Structure-based design strategies and applications Structure-based drug design (SBDD) facilitates rapid compound potency optimization against protein targets. Kinases are readily amenable to SBDD and with >40 novel kinase structures deposited in the Protein Data Bank, there is a growing understanding of how to achieve selectivity. Kumkum Saxena (Vertex Pharmaceuticals; http://www.vpharm.com) discussed how rapid structure determination of kinase target crystal structures is a key tool in the drug discovery process at Vertex. Many hundreds of constructs for each kinase are designed, expressed and purified by high-throughput methods and, following rigorous protein analysis, this approach produces a large increase in crystallization success rates of these update conference DDT Vol. 9, No. 1 January 2004 1359-6446/04/$ – see front matter ©2004 Elsevier Ltd. All rights reserved. PII: S1359-6446(03)02932-5 16 www.drugdiscoverytoday.com Protein kinases in drug discovery and development Adrian Gill, Department of Medicinal Chemistry, Astex Technology, 436 Cambridge Science Park, Milton Road, Cambridge, CB4 0WE, e-mail: a.gill@astex-technology.com