Protease Activity, Inhibition and Ligand Interaction Analysis Developments and Applications for Drug Discovery

Abstract: The present study has focused on characterising protease-ligand interactions in the context of drug discovery. The proteases that have been studied are human matrix metallopeptidase 12 (MMP-12), HIV-protease and Hepatitis C virus (HCV) NS3/NS4A protease. These studies have involved kinetic characterisation of protease-inhibitor interactions using biosensor technology, as well as determination of inhibition and activity regulation by using activity assays.The regulation of MMP-12 activity by calcium was proposed, based on the study of the calcium dependence of MMP-12 activity. Furthermore, it was shown that the high affinity of hydroxamate-based inhibitors of MMP-12 were due to slow dissociation of the enzyme-inhibitor complex by using a new biosensor assay for the study of interactions between MMP-12 and ligands.A study of the pH-dependency of protease-inhibitor interactions revealed that the interaction kinetics of HIV-protease inhibitors differed with pH in a way that could be related to the inhibitor structures. This suggested that the forces of interaction are different in the association and dissociation phases of an interaction. Furthermore, it demonstrated the usefulness of pH as a variable in characterising protein-ligand interactions.Results applicable in the discovery of drugs against Hepatitis C were obtained, with the analysis of structure-activity relationships of novel inhibitors. Furthermore, the mode of binding imposed by key functional groups of the inhibitors was explored by investigating the effect of pH on the interactions with NS3.The results show the importance of using appropriate model systems for drug discovery by selecting relevant targets and assay conditions. Furthermore, the usefulness of kinetic rate information in drug discovery is demonstrated. Thus, by contributing to the knowledge of protease-ligand interactions, applicable to both protease inhibitor interactions and protease activity regulation, this thesis is expected to have an impact on the field of protease inhibitor development and drug discovery in general.