Binding constants of drug-albumin complexes from DSC measurements

Abstract The DSC technique is applied for quantification of the thermodynamic binding constants in protein-ligand systems. For this purpose, the thermograms of protein denaturation are recorded at different ligand concentrations. The observed dependence of the temperature shift of denaturation peak on ligand concentration is fitted to the two-state model of denaturation. First and second sequential binding constants of drugs tolbutamide, chloropropamide, phenylbutazone, meloxicam, and ampicillin with bovine serum albumin (BSA) are determined. Ampicillin shows weak binding with BSA, while four other drugs bind quite tightly. Phenylbutazone and meloxicam bind to two different sites of BSA molecule with similar affinity, while tolbutamide and chloropropamide have higher affinities to one of the binding sites. We extensively review the available data on albumin binding of these drugs determined using different experimental methods, which are in strong disagreement with each other. DSC measurements provide reproducible denaturation curves that can be a source of data on the protein-ligand binding including the second binding constant inaccessible to some other methods.