NPI-0052 (also known as marizomab) is a second generation proteasome inhibitor being developed as an anticancer agent. Proteasomes are responsible for degrading substrates such as damaged and aged proteins, tumor suppressors, and cell cycle regulators, and for regulating NF-κB activation by degrading its inhibitor, IκB. Blocking the proteasome pathway results in accumulation of proteins, which can cause cell death, particularly in tumor cells (Kisselev, 2001).