Pharmacologic inhibition of the catalytic immunoproteasome subunit PSMB8 also synergizes with MI-503 to more significantly reduce leukemia cell proliferation and gene expression in MLLr and NPM1 mutant AML cell lines and patient-derived MLLr xenograft models through increased expression of the tumor suppressive transcription factor BASP1 [204]. This evidence concerns the gene NPM1 and acute myeloid leukemia.