Coumarin-Thiourea Hybrids: Structural Features Governing CA Inhibition and Antiproliferative Effects

Selective inhibition of the tumour-associated carbonic anhydrase (CA) isoforms IX and XII, which are overexpressed in hypoxic tumours, has emerged as a promising strategy for the development of novel anticancer agents. Among the diverse CA inhibitors reported to date, coumarins have attracted particular attention. These chromenone derivatives, widely distributed in phytochemicals, display a broad range of biological activities and are known to act as suicide inhibitors of CAs. Following the tail approach, we designed a series of hybrid compounds combining a coumarin core with an N-arylthioureido scaffold located at the C-7 position and investigated how structural variations-including substituents on the coumarin and aromatic moieties, tether length, and urea/thiourea isosterism-influence their biological properties (CA inhibition and antiproliferative activity). Substituted coumarins at C-3 and C-4 were efficiently prepared via Pechmann condensation, while the thioureido motif was introduced using various aryl isothiocyanates as key synthetic intermediates. The lead compound, featuring a dimethylated coumarin, a pentyl linker, and an N-(p-tolyl)thioureido residue, inhibited the target enzymes in the low- to mid-nanomolar range (K_i = 6.0 and 49.9 nM, respectively), displaying selectivity indexes (S.I.s) surpassing those of the reference drug acetazolamide (AAZ). Moreover, it exhibited potent antiproliferative activity, with GI₅₀ values in the low micromolar range (1.9-3.5 µM) against both drug-sensitive and multidrug-resistant cancer cell lines. Label-free three-dimensional holotomographic microscopy revealed that this compound triggers slow apoptosis, leading to cell death after approximately 20 h of exposure.