Insights into the effect of elaborating coumarin-based aryl enaminones with sulfonamide or carboxylic acid functionality on carbonic anhydrase inhibitory potency and selectivity

Recently, different mechanisms for inhibition of carbonic anhydrases (CAs) have been reported, such as the classical zinc-binding (exerted by sulfonamides and carboxylic acids) as well as occluding the entrance of the CA active site (exerted by coumarins). In this manuscript, we studied the effect of combining the pharmacopheric parts responsible for these two mechanisms on CA inhibitory potency and selectivity through the design and synthesis of novel coumarins tethered with the zinc-binding sulfonamide (5a-f, 11a-b and 13a-b) or carboxylic acid (7a-f) groups. In addition, another set of coumarin derivatives (9a-b) with no zinc-binding group (ZBG) was designed to act as non-classical CA inhibitors. The synthesized coumarins were examined for their inhibitory activities towards four hCA isoforms I, II, IX and XII. Coumarin sulfonamides (5a-f, 11a-b and 13a-b) effectively inhibited both tumor-associated hCA IX (KIs: 8.9-133.5 nM) and hCA XII (KIs: 3.4-42.9 nM) isoforms, whereas coumarin carboxylic acids (7a-f) weakly affected hCA IX (KIs: 0.49-11.2 μM) and hCA XII (KIs: 0.51-10.1 μM) isoforms. The coumarin based inhibitors featuring zinc-binding sulfonamide or carboxylic acid group achieved low to moderate hCA IX/XII selectivity. Interestingly, the ZBG-free coumarin derivatives (9a-b) emerged not only as effective hCA IX (KIs = 93.3 and 63.8 nM, respectively) and hCA XII (KIs = 85.7 and 72.1 nM, respectively) inhibitors, but also as a highly hCA IX/XII selective inhibitors over the off-target hCA I/II isoforms (SIs > 1000). Coumarin 9a was further evaluated for its anti-proliferative effect on MCF-7 and PANC-1 cancer cell lines, as well as its effect on the cell cycle and apoptosis towards MCF-7 cell line.