TAK-243 (MLN7243) is a potent, mechanism-based small-molecule inhibitor of the ubiquitin activating enzyme (UAE) with an IC50 of 1 ± 0.2 nM in the UBCH10 E2 thioester assay. It has minimal inhibitory activity in a panel of kinase and receptor assays, as well as on human carbonic anhydrase type I and type II. TAK-243 (MLN7243) induces ER stress, abrogates NFκB pathway activation and promotes apoptosis.