Carbonic anhydrase inhibitors. Inhibition of the human cytosolic isozyme VII with aromatic and heterocyclic sulfonamides

The inhibition of a newly cloned human carbonic anhydrase (CA, EC 4.2.1.1), isozyme VII (hCA VII), has been investigated with a series of aromatic and heterocyclic sulfonamides, including some of the clinically used derivatives (acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, brinzolamide and benzolamide), as well as the sulfamate antiepileptic drug topiramate. Inhibition data for the the other physiologically relevant cytosolic isoforms hCA I, hCA II and mCA XIII are also provided for comparison. hCA VII shows a high catalytic activity for the CO2 hydration reaction, with a kcat of 9.5 × 105 s−1 and kcat/Km of 8.3 × 107 M−1 s−1 at pH 7.5 and 20 °C. A very interesting inhibition profile against hCA VII with this series of 32 sulfonamides/sulfamates was observed. hCA VII shows high affinity for all the investigated compounds, with inhibition constants in the range of 0.45–210 nM. Topiramate, ethoxzolamide and benzolamide showed subnanomolar hCA VII inhibitory activity, whereas acetazolamide, methazolamide, dorzolamide and brinzolamide showed KI-s in the range of 2.1–3.5 nM. Dichlorophenamide was slightly less active (KI of 26.5 nM). A number of heterocyclic or bicyclic aromatic sulfonamides also showed excellent hCA VII inhibitory properties (KI-s in the range of 4.3–7.0 nM) whereas many monosubstituted or disubstituted benzenesulfonamides were less active (KI-s in the range of 45–89 nM). The least active hCA VII inhibitors were some substituted benzene-1,3-disulfonamides as well as some halogenated sulfanilamides (KI-s in the range of 100–210 nM). The inhibition profile of hCA VII is rather different of that of the other cytosolic isozymes, providing thus a possibility for the design of more selective, hCA VII-specific inhibitors. In addition, these data furnish further evidence that hCA VII is the isozyme responsible for the anticonvulsant/antiepileptic activity of sulfonamides and sulfamates.