title: Natural proteasome inhibitor celastrol suppresses androgen-independent prostate cancer progression by modulating apoptotic proteins and NF-kappaB.
abstract: BACKGROUND
  Celastrol is a natural proteasome inhibitor that exhibits promising anti-tumor effects in human malignancies, especially the androgen-independent prostate cancer (AIPC) with constitutive NF-κB activation. Celastrol induces apoptosis by means of proteasome inhibition and suppresses prostate tumor growth. However, the detailed mechanism of action remains elusive. In the current study, we aim to test the hypothesis that celastrol suppresses AIPC progression via inhibiting the constitutive NF-κB activity as well as modulating the Bcl-2 family proteins.
  
  
  RESULTS
  We examined the efficacy of celastrol both in vitro and in vivo, and evaluated the role of NF-κB in celastrol-mediated AIPC regression. We found that celastrol inhibited cell proliferation in all three AIPC cell lines (PC-3, DU145 and CL1), with IC₅₀ in the range of 1-2 µM. Celastrol also suppressed cell migration and invasion. Celastrol significantly induced apoptosis as evidenced by increased sub-G1 population, caspase activation and PARP cleavage. Moreover, celastrol promoted cleavage of the anti-apoptotic protein Mcl-1 and activated the pro-apoptotic protein Noxa. In addition, celastrol rapidly blocked cytosolic IκBα degradation and nuclear translocation of RelA. Likewise, celastrol inhibited the expression of multiple NF-κB target genes that are involved in proliferation, invasion and anti-apoptosis. Celastrol suppressed AIPC tumor progression by inhibiting proliferation, increasing apoptosis and decreasing angiogenesis, in PC-3 xenograft model in nude mouse. Furthermore, increased cellular IκBα and inhibited expression of various NF-κB target genes were observed in tumor tissues.
  
  
  CONCLUSIONS
  Our data suggest that, via targeting the proteasome, celastrol suppresses proliferation, invasion and angiogenesis by inducing the apoptotic machinery and attenuating constitutive NF-κB activity in AIPC both in vitro and in vivo. Celastrol as an active ingredient of traditional herbal medicine could thus be developed as a new therapeutic agent for hormone-refractory prostate cancer.
authors.affiliation: Department of Radiation Oncology, Division of Radiation and Cancer Biology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
authors.forename: Yao
authors.initials: Y
authors.lastname: Dai
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Desano
authors.forename: Wenhua
authors.initials: W
authors.lastname: Tang
authors.forename: Xiaojie
authors.initials: X
authors.lastname: Meng
authors.forename: Yang
authors.initials: Y
authors.lastname: Meng
authors.forename: Ezra
authors.initials: E
authors.lastname: Burstein
authors.forename: Theodore S
authors.initials: TS
authors.lastname: Lawrence
authors.forename: Liang
authors.initials: L
authors.lastname: Xu
mesh_terms: D000728:Androgens / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D045744:Cell Line, Tumor; D018450:Disease Progression; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006801:Humans; D020128:Inhibitory Concentration 50; D008297:Male; D051379:Mice; D008819:Mice, Nude; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D016328:NF-kappa B / Q000494:pharmacology*; D053978:Pentacyclic Triterpenes; D011471:Prostatic Neoplasms / Q000188:drug therapy*; D011480:Protease Inhibitors / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014315:Triterpenes / Q000494:pharmacology
chemical_list: D000728:Androgens; D004791:Enzyme Inhibitors; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D016328:NF-kappa B; D053978:Pentacyclic Triterpenes; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D014315:Triterpenes; C050414:celastrol