Fragment-based screening for enzyme inhibitors using enthalpy arrays

Fragment-based screening has typically relied on X-ray or NMR methods to identify low affinity ligands that bind to therapeutic targets. These techniques are expensive in terms of material and time, so it useful to have a higher-throughput method to reliably pre-screen a fragment library to identify a subset of compounds for structural analysis. Calorimetry provides a label-free method to assay binding and enzymatic activity that is unaffected by the spectroscopic properties of the sample. Conventional microcalorimetry is hampered by requiring large quantities of reagents and long measurement times. Nanocalorimeters can overcome these limitations of conventional ITC. Here we have used enthalpy arrays, which are arrays of nanocalorimeters, to perform an enzyme activity based fragment screen for competitive inhibitors of phosphodiesterases. Several inhibitors with KI<2 mM were identified and moved to X-ray crystallization trials, yielding high-resolution data. This talk will describe how we use array calorimetry as a pre-screening method for fragment-based lead discovery with enzyme targets.