Carbonic anhydrase inhibitors: Inhibition of the transmembrane isozyme XIV with sulfonamides

Abstract

The inhibition of the last human carbonic anhydrase (CA, EC 4.2.1.1) isozyme (hCA XIV) discovered has been investigated with a series of sulfonamides, including some clinically used derivatives (acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide, benzolamide, and zonisamide), as well as the sulfamate antiepileptic drug topiramate. The full-length hCA XIV is an enzyme showing a medium-low catalytic activity, quite similar to that of hCA XII, with the following kinetic parameters at 20 °C and pH 7.5, for the CO 2 hydration reaction: k cat = 3.12 × 10 5 s −1 and k cat/ K M = 3.9 × 10 7 M −1 s −1. All types of activities have been detected for the investigated compounds, with several micromolar inhibitors, including zonisamide, topiramate, and simple sulfanilamide derivatives ( K I-s in the range of 1.46–6.50 μM). In addition, topiramate and zonisamide were observed to behave as weak hCA XII inhibitors, while zonisamide was an effective hCA IX inhibitor ( K I of 5.1 nM). Some benzene-1,3-disulfonamide derivatives or simple five-membered heteroaromatic sulfonamides showed K I-s in the range of 180–680 nM against hCA XIV, whereas the most effective of such inhibitors, including 3-chloro-/bromo-sulfanilamide, benzolamide-like, ethoxzolamide-like, and acetazolamide/methazolamide-like derivatives, showed inhibition constant in the range of 13–48 nM. The best hCA XIV inhibitor was aminobenzolamide ( K I of 13 nM), but no CA XIV-selective derivatives were evidenced. There are important differences of affinity of these sulfonamides/sulfamates for the three transmembrane CA isozymes, with CA XII showing the highest affinity, followed by CA IX, whereas CA XIV usually showed the lowest affinity for these inhibitors.