Celastrol is a pentacyclic triterpenoid that is 24,25,26-trinoroleana-1(10),3,5,7-tetraen-29-oic acid bearing an oxo substituent at position 2, a hydroxy substituent at position 3 and two methyl groups at positions 9 and 13. An antioxidant and anti-inflammatory agent. Potently inhibits lipid peroxidation in mitochondria and inhibits TNF-alpha-induced NFB activation. Also shown to inhibit topoisomerase II activity in vitro (IC50 = 7.41 M). Celastrol is a potent proteasome inhibitor for the chymotrypsin-like activity of a purified 20S proteasome with IC50 of 2.5 μM. Celastrol is also a novel HSP90 inhibitor, it has anti-proliferative, anti-inflammatory, anti-tumor , antiangiogenesis, and antioxidant activities. Celastrol inhibits Plasmodium falciparum enoyl-acyl carrier protein reductase and inhibits VEGF receptors expression.