Structure-Thermodynamics Correlations of Fluorinated Benzensulfonamides as Inhibitors of Human Carbonic Anhydrases

Abstract

The carbonic anhydrases (CA) are established as therapeutic targets [1]. There are 12 catalytically active CA isozymes in human body. At least 30 CA sulfonamide inhibitors have been used as drugs to treat glaucoma, epileptic seizures, altitude sickness, and as diuretics. However, most of them exhibit poor selectivity towards target isozymes and result in various side effects. In this work, a class of 4-substituted-2,3,5,6-tetrafluorobenzensulfonamides as inhibitors of CA is reported. Crystal structures of CAII, CAXII and CAXIII bound with the fluorinated compounds were solved and provided structural details of inhibitor binding. The binding affinity to carbonic anhydrases I, II, VII, XII and XIII was measured by isothermal titration calorimetry and the fluorescent thermal shift assay, and inhibition was determined by stopped-flow CO2 hydration assay. The combined use of these methods has provided a detailed picture of protein-ligand interactions. Experimentally obtained binding data usually depends on various factors including temperature, pH, buffer, etc. In this study, we present intrinsic parameters of binding that are independent of experimental conditions. Structure-thermodynamics correlations were studied using intrinsic parameters. All used biophysical methods have confirmed that fluorinated sulfonamides bound stronger to CA than non-fluorinated, because of the presence of electronegative substituents that decrease the pKa of sulfonamide group and this correlates with an increase in the CA inhibitory properties [2]. A large group of fluorinated compounds possessed nanomolar affinity for selected CAs and several of them were selective towards CAI.