CBK006377 (CBK77) is a small molecule inhibitor of the ubiquitin-proteasome system (UPS) with EC50 of 4.3 uM in MelJuSo Ub-YFP cells (6h treatment).CBK77 (16h treatment, 10 uM) causes an irreversible, global impairment of the UPS collapse, accompanied by a general accumulation of ubiquitylated proteins and caspase-dependent cell death.CBK77 causes a global impairment of ubiquitin-dependent proteasomal degradation without global inhibition of proteasome or DUB activity.NAD(P)H:quinone oxidoreductase 1 (NQO1) is a critical factor for CBK77-mediated UPS impairment, CBK77 is an NQO1 substrate, efficiently metabolized by NQO1.CBK77 reduces growth of NQO1-proficient human cancer cells and xenograft tumors in mice without overt signs of toxicity.
