Immunoproteasomeinhibitor 1 is a highly potent and reversible inhibitor of both immunoproteasome and proteasome activity. It exhibits time-independent inhibitory effects on immunoproteasome subunits β5c, β1i, and β5i, with respective Ki values of 1.18 μM, 0.27 μM, and 1.91 μM. This compound shows promising potential for the treatment of select neoplastic diseases [1].