PS-341 is a specific and selective inhibitor of the 26S proteasome.

NF-κB is activated when the proteasome degrades the inhibitor protein 1κBa resulting in downregulation of multiple gene products. NF-κB plays a role in maintaining cell viability through the transcription of inhibitors of apoptosis. PS-341 can block activation of NF-κB, which may induce apoptosis and also make cells more sensitive to a variety of chemotherapy agents.