A loop-mimetic inhibitor of the HCV-NS3 protease derived from a minibody

We have been interested for some time in establishing a strategy for derivi ng lead compounds from macromolecule ligands such as minibody variants. A m inibody is a minimized antibody variable domain whose two loops are amenabl e to combinatorial mutagenesis, This approach can be especially useful when dealing with 'difficult' targets, One such target is the NS3 protease of h epatitis C virus (HCV), a human pathogen that is believed to infect about 1 00 million individuals worldwide and for which an effective therapy is not yet available. Based on known inhibitor specificity (residues P6-P1) of NS3 protease, we screened a number of minibodies from our collection and we we re able to identify a competitive inhibitor of this enzyme. We thus validat ed an aspect of recognition by HCV NS3 protease, namely that an acid anchor is necessary for inhibitor activity, In addition, the characterization of the minibody inhibitor led to the synthesis of a constrained hexapeptide mi micking the bioactive loop of the parent macromolecule, The cyclic peptide is a lead compound prone to rapid optimization through solid phase combinat orial chemistry. We therefore confirmed that the potential of turning a pro tein ligand into a low molecular weight active compound for lead discovery is achievable and can complement more traditional drug discovery approaches .