Epoxomicin

Potent and Selective Proteasome Inhibitor

Epoxomicin was originally isolated from the culture medium of an Actinomycetes strain based on its in vivo antitumor activity against murine B16 melanoma [J. Antibiot., 45, 1746 (1992)].

In 1999, L. Meng et al. reported that the potent inhibitory activity of epoxomicin specifically targets the proteasome.  In contrast to peptide aldehyde proteasome inhibitors, epoxomicin does not inhibit nonproteasomal proteases such as calpain, papain, chymotrypsin, trypsin, and cathepsin B at concentrations of up to 50 mM [Proc. Natl. Acad. Sci. USA, 96, 10403 (1999)].  This specific activity of epoxomicin may be explained by the proposed inhibition mechanism based on the X-ray analysis data reported by M. Groll et al. [J. Am. Chem. Soc., 122, 1237 (2000)].  In addition, L. Meng et al.  also reported that epoxomicin shows almost equal activity with Z-Leu-Leu-Leu-H (aldehyde) in accumulation of p53 and ubiquitinated proteins in cultured cell, and its potency is much stronger than that of lactacystin.  This fact implies that epoxomicin is a cell-permeable strong inhibitor for proteasome.






Fig. 1 Inhibition Mechanism of Proteasome by Epoxomicin.

We chemically synthesized epoxomicin.  In the preliminary experiments in our laboratory, our epoxomicin showed approx. IC50 value of 9 nM against commercially available 20S proteasome.  This IC50 value is similar to that of Z-Leu-Leu-Leu-H (aldehyde), and the potency is approx. 100 fold stronger than that of lactacystin (Fig. 2).

Chemically synthesized epoxomicin, having characteristics of cell-permeable, irreversible, potent, and specific inhibitory activity for proteasome, is now available from Peptide Institute, Inc.

Inhibitor: Epoxomicin, Z-Leu-Leu-Leu-H, Lactacystin,
Substrate: Suc-Leu-Leu-Val-Tyr-MCA (4.4 mM)
Enzyme: 20S proteasome (1.1 nM), BostonBiochem lot 5799P
Buffer: 20 mM TrisHCl/0.5 mM EDTA/0.035% SDS (pH 8.0)
Temp: 25ºC
Total volume: 340 mL
Preincubation: 10 min (Inhibitor/Enzyme)
Data reading: 1 min to 50 min
Em: 450 nm, Ex: 360 nm




Fig. 2 Comparison of Proteasome Inhibitory Activity

Reagents for Ubiquitin-Proteasome System

Code	Compound	Package	Price
4381-v	Epoxomicin	0.2 mg Vial	\20,000

Inhibitor

Code	Compound	Package	Price
4368-v	Lactacystin	0.2 mg Vial	\20,000
3207-v	Ubiquitin Aldehyde	0.05mg Vial	\20,000
3169-v	Z-Ile-Glu(OBut)Ala-Leu-H (aldehyde) [PSI]	5 mg Vial	\6,000
3175-v	Z-Leu-Leu-Leu-H (aldehyde) [MG-132]	5 mg Vial	\4,000
3170-v	Z-Leu-Leu-Nva-H (aldehyde) [MG-115]	5 mg Vial	\4,000

Substrate

Code	Compound	Package	Price
3140-v	Boc-Leu-Arg-Arg-MCA	5 mg Vial	\5,400
3120-v	Suc-Leu-Leu-Val-Tyr-MCA	5 mg Vial	\6,000
3176-v	Z-Leu-Arg-Gly-Gly-MCA	5 mg Vial	\7,000
3179-v	Z-Leu-Leu-Glu-MCA	5 mg Vial	\6,000
3177-v	Z-Leu-Leu-Leu-MCA	5 mg Vial	\5,000