Sulfocoumarin-, Coumarin-, 4-Sulfamoylphenyl-Bearing Indazole-3-carboxamide Hybrids: Synthesis and Selective Inhibition of Tumor-Associated Carbonic Anhydrase Isozymes IX and XII

A series of sulfocoumarin-, coumarin-, and 4-sulfamoylphenyl-bearing indazole-3-carboxamide hybrids were synthesized and investigated as inhibitors of the human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms I and II (cytosolic isozymes), as well as hCA IX and XII (transmembrane, tumor-associated enzymes). Compounds 6 a-g (amide derivatives) and 7 a-h (triazoles) act as "prodrugs", and their hydrolysis products are the de facto CA inhibitors. These compounds displayed sub-micromolar to high-nanomolar inhibitory activity against hCA isoforms IX and XII, which were recently validated as antitumor drug targets. Moreover, no inhibition of the off-target hCA I and II isoforms was observed. Compounds 8 a-f (another set of triazoles) exhibited nanomolar inhibition against hCA isoforms I, II, IX and XII, among which compounds 8 c, 8 d, and 8 f were found to inhibit the tumor-associated hypoxia-induced hCA isoform IX with Ki values of 1.8, 2.3, and 2.0 nm respectively. Further exploration of these compounds could be useful for the development of novel antitumor agents with selective mechanisms of CA inhibitory action.