Celastrol (NSC 70931)

Celastrol at 5 μM inhibits the chymotrypsin-like, PGPH-like, and trypsin-like activities of the purified 20S proteasome by 80%, 5%, and <1%, respectively, whereas at 10 μM, it inhibits these three proteasomal activities by ∼90%, 15%, and <1%, respectively. Celastrol significantly inhibits the proteasomal chymotrypsin activity in PC-3 cells in a concentration-dependent manner. Celastrol at 2.5 μM to 5 μM induces caspase-3 activity by 4.7-fold to 5.5-fold in PC-3 cells. Celastrol (5 μM) treated cells, the levels of the proteasome target proteins, IκB-α and Bax, are increased after 1 hour and further increased to its peak for 4 hours to 12 hours. Celastrol (2.5 μM) treatment induces proteasome inhibition by 40%, as shown by the decreased levels of chymotrypsin-like activity and increased accumulation of ubiquitinated proteins in LNCaP cells. Celastrol (2.5 μM) induces apoptosis in the Celastrol-treated LNCaP cells, as shown by increased levels of caspase-3 activity (up to 3.5-fold), PARP cleavage, and apoptotic morphology. ^[1] Celastrol (300 nM) is found to suppress LPS-induced production of TNF-alpha and IL-1beta by human monocytes and macrophages. Celastrol (100 nM) also decreases LPS-induced expression of class II MHC molecules by microglia. Celastrol strongly inhibits LPS and IFN-y-induced NO production with IC50 of 200 nM in macrophage lineage cells. Celastrol strongly inhibits TNF-α and IFN-γ-induced NO production with IC50 of 200 nM in endothelial cells. ^[2] Celastrol (2.5 μM) potentiates the apoptosis induced by TNF and chemotherapeutic agents and inhibits invasion, both regulated by NF-kappaB activation, in KBM-5 cells. Celastrol (2.5 μM) suppresses the expression of TNF induced the expression of gene products involved in antiapoptosis (IAP1, IAP2, Bcl-2, Bcl-XL, c-FLIP, and survivin), proliferation (cyclin D1 and COX-2), invasion (MMP-9), and angiogenesis (VEGF) in KBM-5 cells. Celastrol (5 μM) is found to inhibit the TNF-induced activation of IkappaBalpha kinase, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 nuclear translocation and phosphorylation, and NF-kappaB-mediated reporter gene expression. ^[3] Celastrol inhibits proliferating of RPMI 8226, KATOIII, UM-SCC1, U251MG and MDA-MB-231 cells with IC50 of 0.52 μM, 0.54 μM, 0.76 μM, 0.69 μM and 0.67 μM, respectively. Celastrol (1 μM) inhibits growth of RPMI 8226 with a decrease in the levels of cyclin D1 and cyclin E, but concomitant increase in the levels of p21 and p27. Celastrol induces apoptosis in RPMI-8226 cells indicated by the activation of caspase-8, bid cleavage, caspase-9 activation, caspase-3 activation, PARP cleavage and through the down regulation of anti-apoptototic proteins. Celastrol (1 μM) suppresses Akt pathway and activates JNK kinase in RPMI-8226 cells. ^[4]