hCAIX/XII-IN-6 is an orally active carbonic anhydrase ( CA ) inhibitor. hCAIX/XII-IN-6 inhibits human CA isoforms hCA I, II,IV, IX, and XII with K i values of 6697 nM, 2950 nM, 4093 nM, 4.1 nM and 7.7 nM, respectively. hCAIX/XII-IN-6 can be used for the research of rheumatoid arthritis (RA).