Aromatic sulfonamides including a sulfonic acid tail: New membrane impermeant carbonic anhydrase inhibitors for targeting selectively the cancer‐associated isoforms

We report here a new drug design strategy for producing membrane‐impermeant carbonic anhydrase (CA; EC 4.2.1.1) inhibitors selectively targeting the tumor‐associated, membrane‐bound human CAs IX and XII over off‐target cytosolic isoforms. To date, this approach has only been pursued by including permanent positively charged pyridinium type or highly hydrophilic glycosidic moieties into the structure of aromatic sulfonamide CA inhibitors (CAIs). Aliphatic (propyl and butyl) sulfonic acid tails, deprotonated at physiological pH, were thus incorporated onto a benzenesulfonamide scaffold by a common 1,2,3‐triazole linker and different types of spacers. Twenty such derivatives were synthesized and tested for their inhibition of target (hCAs IV, IX, and XII) and off‐target CAs (hCAs I and II). Most sulfonate CAIs induced a potent inhibition of hCAs II, IX, and XII up to a low nanomolar KI range (0.9–459.4 nM) with a limited target/off‐target CA selectivity of action. According to the drug design schedule, a subset of representative derivatives was assessed for their cell membrane permeability using Caco‐2 cells and a developed FIA‐MS/MS method. The complete membrane impermeability of the sulfonate tailed CAIs (≥98%) validated these negatively charged moieties as being suitable for achieving, in vivo, the selective targeting of the tumor‐associated CAs over off‐target ones.