CA9 and neoplasm: For example, representative pyridinium sulfonamides such as 10, 11, 12, and 13, developed by our team through the conjugation of primary aromatic and heterocyclic sulfonamides with positively charged pyridinium salts, showed excellent selectivity against membrane-bound CA IV [31,32,34,46] and against tumor-associated CA IX and CA XII [35,36,47].