Ixazomib- 13 C 2 , 15 N is 13 C and 15 N labeled Ixazomib. Ixazomib (MLN2238) is a selective, potent, and reversible proteasome inhibitor, which inhibits the chymotrypsin-like proteolytic (β5) site of the 20S proteasome with an IC 50 of 3.4 nM ( K i of 0.93 nM).