Epoxomicin

Epoxomicin (BU 4061T) is a naturally occurring selective proteasome inhibitor with anti-inflammatory activity. Epoxomicin covalently binds to the LMP7, X, MECL1, and Z catalytic subunits of the proteasome. Epoxomicin (BU 4061T) inhibits proteasome activity in cell growth assays with an IC50 value of 4 nM and demonstrates potent cytotoxicity against B16-F10, HCT116, and Moser solid tumor cells, as well as P388 and K562 leukemia cells with IC50 values ranging from 2-44 nM. Epoxomicin also effectively inhibits NF-kappaB activation in vitro and potently blocks in vivo inflammation in the murine ear edema assay. In contrast to peptide aldehyde proteasome inhibitors, epoxomicin does not inhibit nonproteasomal proteases such trypsin, chymotrypsin, papain, calpain, and cathepsin B at concentrations of up to 50 microM. Treatment of proliferating cells with epoxomicin results in cell death through accumulation of ubiquinated proteins.