hCAIX-IN-11 (Compound 5d) is a selective carbonic anhydrase IX and XII inhibitor with K i s of 32.7 and 623.5 nM for hCA IX and hCA XII, respectively. hCA IX and hCA XII are transmembrane isoforms which have been characterized as biomarkers for several types of tumors. The hCA XII assists in maintenance of acid-base homoeostasis in normal as well as tumor cells.