Carbonic Anhydrase Inhibitors. Comparison of Aliphatic Sulfamate/Bis-sulfamate Adducts with Isozymes II and IX as a Platform for Designing Tight-Binding, More Isoform-Selective Inhibitors

Two approaches were used to design inhibitors of the metalloenzyme carbonic anhydrase (CA, EC4.2.1.1): the tail and the ring approaches. Aliphatic sulfamates constitute a class ofCAinhibitors (CAIs)that cannot be classified in either one of these categories. Wereport here the detailed inhibition profile offour such compounds against isoforms CAs I-XIV, the first crystallographic structures of thesecompounds in adduct with isoform II, and molecular modeling studies for their interaction with hCAIX. Aliphatic monosulfamates/bis-sulfamates were nanomolar inhibitors of hCAs II, IX, and XII,unlike aromatic/heterocyclic sulfonamides that promiscuously inhibit most CA isozymes with lownanomolar affinity. The bis-sulfamates incorporating 8 or 10 carbon atoms showed higher affinity forthe tumor-associated hCA IX compared to hCA II, whereas the opposite was true for the monosulfamates.The explanation for their interaction with CA active site furnishes insights for obtainingcompounds with increased affinity/selectivity for various isozymes.IntroductionA paradigm in carbonic anhydrase (CA,a EC 4.2.1.1) drugdesign was that aliphatic sulfonamidesRSO2NH2 (R=aliphaticgroup) are inactive as inhibitors, unlike the aromatic/heterocyclicones of the type ArSO2NH2.1 This view was subsequentlychallenged, being shown that aliphatic sulfonamidesincorporating perhaloalkyl moieties of the type CnX2nþ1SO2-NH2 (n=1-4, X=F, Cl),2 as well as various aliphaticsulfamates/bis-sulfamates3-5 potently inhibit several CA isozymesinvolved in fundamental physiologic/pathologic states.Indeed, this family of metalloenzymes comprises 16 differentisoforms, of which several are cytosolic (CAs I-III, CA VII,and CAXIII), five are membrane-bound (CA IV, CAIX, CAXII, CA XIV, and CA XV), two are mitochondrial (CAs VAand VB), and one (CA VI) is secreted into saliva/milk.6-13Three acatalytic forms are also known, i.e., CA VIII, CA X,and CA XI.9 These enzymes are involved in crucial physiologicalprocesses connected with respiration and transport ofCO2/bicarbonate betweenmetabolizing tissues and lungs, pHand CO2 homeostasis, electrolyte secretion in a variety oftissues/organs, biosynthetic reactions (such as gluconeogenesis,lipogenesis, and ureagenesis), bone resorption, calcification,tumorigenicity, and