The enzyme-inhibitor approach to cell-selective labelling. III. Sulphonamide inhibitors of carbonic anhydrase as carriers for red cell labelling.

Selective radiolabelling of red blood cells via an enzyme-inhibitor approach represents a novel method in diagnostic nuclear medicine. Current problems in blood pool labelling could be overcome by using selective sulphonamide inhibitors as carriers. Red cell carbonic anhydrase is identified as an ideal target enzyme for such an approach. A brief review of the target enzyme is presented together with the screening of a series of synthesised sulphonamide inhibitors. p-Iodobenzenesulphonamide, 4-[(4-iodophenyl)thio]benzenesulphonamide and 5-(4-bromophenyl)sulphonyl]thiophene-2-sulphonamide were found to be particularly potent, reversible, lipophilic inhibitors of carbonic anhydrase, characteristics that warrant their further investigation as potential carriers. 4-Iodo-3-(iodoacetamido)benzenesulphonamide was a moderate inhibitor but caused relatively fast irreversible inactivation, making it a candidate for longer term studies.