The eta-carbonic anhydrases (CAs, EC 4.2.1.1) were recently discovered as the sixth genetic class of this metalloenzyme superfamily, and are so far known only in protozoa, including various Plasmodium species, the causative agents of malaria. We report here an inhibition study of the eta-CA from Plasmodium falciparum (PfCA) against a panel of sulfonamides and one sulfamate compound, some of which are clinically used. The strongest inhibitors identified were ethoxzolamide and sulthiame, with K(I)s of 131-132 nM, followed by acetazolamide, methazolamide and hydrochlorothiazide (K(I)s of 153-198 nM). Brinzolamide, topiramate, zonisamide, indisulam, valdecoxib and celecoxib also showed significant inhibitory action against PfCA, with KIs ranging from 217 to 308 nM. An interesting observation was that the more efficient PfCA inhibitors are representative of several scaffolds and chemical classes, including benzene sulfonamides, monocyclic/bicyclic heterocyclic sulfonamides and compounds with a more complex scaffold (i.e., the sugar sulfamate derivative, topiramate, and the coxibs, celecoxib and valdecoxib). A comprehensive inhibition study of small molecules for eta-CAs is needed as a first step towards assessing PfCA as a druggable target. The present work identifies the first known eta-CA inhibitors and provides a platform for the development of next generation novel PfCA inhibitors. (C) 2014 Elsevier Ltd. All rights reserved.
