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Addressing the Needs of Drug Discovery with the MicroCal PEAQ-ITC Instruments

Measurements and characterization of binding interactions between proteins and low-molecular weight ligands are fundamental for drug discovery. Among the most recognized challenges in characterizing binding interactions are (1) the need to accurately assess a wide span of binding affinities (KD) and (2) accurately rank and characterize low-molecular weight (LMW) ligands based on affinity, mechanism of action, and energetics of interaction.

Reliable interpretation of binding data can be complicated by the presence of inactive protein fraction or inaccurate assessment of protein concentration. Assessment of this data can be further hampered by inherent uncertainty in concentration of compound stocks. This uncertainty results from inaccurate measurement, limited solubility, or potential chemical heterogeneity of the compounds such as presence of enantiomers and isomers.

Isothermal titration calorimetry (ITC) directly measures heat released or absorbed in a binding event, providing means for studying protein-small molecule interactions in solution without the need for labeling or immobilization. A highly sensitive ITC instrument and properly designed experimental conditions make it possible to account for inaccurately assessed protein concentration or inactive protein fraction, and to account for imprecise concentration of compound solutions. From quality control (QC) to assay development and lead optimization, ITC has a role in improving our understanding of biochemical data. Normalizing for protein or compound concentrations and accounting for inactive populations of protein can improve decisionmaking processes, one example being a more careful assessment of changes in enthalpic contributions to binding, which are critical in many best-in-class drug studies.

This white paper highlights the advantages of the new ITC instruments—MicroCal PEAQ-ITC and MicroCal PEAQ-ITC Automated systems and MicroCal PEAQ-ITC Analysis Software. The software allows analysis of binding interactions complicated by the presence of inactive protein material, incorrect protein concentration, and/or inaccurate concentration or heterogeneity of compound solutions.