Click-tailed coumarins with potent and selective inhibitory action against the tumor-associated carbonic anhydrases IX and XII

Coumarins behave as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) with a mechanism of inhibition distinct from other classes of inhibitors. A series of 7-substituted coumarins incorporating aryl-triazole moieties were prepared by click chemistry procedures starting from 7-hydroxycoumarin or 4-methyl-7-aminocoumarin. The panel of new compounds was assayed for the inhibition of the cytosolic, widespread human (h) isoforms hCA I and II, and the transmembrane, tumor-associated ones hCA IX and XII. Most of the coumarins were weak inhibitors or did not inhibit significantly hCA I and II, but showed low nanomolar inhibitory action against the transmembrane isoforms (K(I) of 14.3-34.4 nM against hCA IX and of 4.7-37.8 nM against hCA XII). Since many hypoxic tumors overexpress hCA IX/XII, and as these targets were recently validated for obtaining antitumor/antimetastatic agents, with one inhibitor in Phase I clinical trials, the present findings constitute an interesting extension to the knowledge of non-sulfonamide, selective inhibitors of CA isoforms involved in serious pathologies.