When Millennium Pharmaceuticals Inc. began working on the first proteasome inhibitor to reach the market, Velcade bortezomib, one of the potential issues was that the presence of proteasomes in all cells and the proteasome's broad housekeeping functions might result in too many side effects. That turned out not to be the case. Nevertheless, MLNM has spent the last several years working on a proteasome inhibitor more specific to cancer cells.

The resulting molecule, MLN4924, regulates a particular subset of the pathway whose client proteins are specific to the growth and proliferation of cancer cells of several types.