Carbonic Anhydrase Inhibitors, Interaction of Boron Derivatives with Isozymes I and II: A New Binding Site for Hydrophobic Inhibitors at the Entrance of the Active Site as shown by Docking Studies

The interaction of human carbonic anhydrase (hCA) isozymes I and II with boron derivatives was investigated by kinetic and spectroscopic studies. These derivatives, tested as new inhibitors of carbonic anhydrase, are sulfonamide and non-sulfonamide boron derivatives and some of them proved to be moderately efficient inhibitors of hCA I and hCA II, their activities being comparable to those of the un-substituted sulfonamides, the classical inhibitors of these zinc enzymes. Ph2BOH, one of the compounds with the highest affinity for hCA II in the present study, has been docked within the active site. After minimisation it was found situated at 7.9 Å from zinc, within the hydrophobic half of the active site, in Van der Waals contacts with the amino acid residues: Val 121, Phe 130, Val 135, Leu 141, Val 143, Val 207 and Pro 201. This is the first time that a CA inhibitor has been found to bind at the edge of the active site cavity, similarly to the CA activator histamine, which binds on the hydrophilic half. This finding may be of importance also for the design of novel types of inhibitors with increased affinity for the different CA isozymes.