jnci.oxfordjournals.org JNCI | Articles 949 Structural Basis for Depletion of Heat Shock Protein 90 Client Proteins by Deguelin

Background The molecular chaperone heat shock protein 90 (Hsp90) participates in preserving the expression and activity of various oncoproteins, including hypoxia-inducible factor 1 (HIF-1 ) and Akt. Deguelin is a rotenoid with antitumor activities. We investigated whether the antitumor activities of deguelin involve the functional inhibition of Hsp90. Method Human xenograft tumors were generated in mice from H1299 (n = 6 per group) and A549 (n = 4 per group) non – small-cell lung cancer cells, UMSCC38 (n = 5 per group) head and neck cancer cells, MKN45 (n = 5 per group) stomach cancer cells, and PC-3 (n = 3 per group) prostate cancer cells. Tumor-bearing mice were treated with deguelin at 4 or 8 mg/kg or with vehicle (as a control) twice a day by oral gavage for 15 – 28 days. Protein expression was assessed by western blot analysis. Akt and Hsp90 were assessed by use of adenoviral vectors expressing constitutively active Akt or Hsp90. Binding of deguelin to Hsp90 was exam-ined by docking analysis and by competition binding experiments with ATP – Sepharose beads. The protea-some inhibitor MG132 was used to investigate deguelin’s effect on the induction of ubiquitin-mediated proteasomal degradation of HIF-1 . All statistical tests were two-sided. Results Deguelin bound to the ATP-binding pocket of Hsp90 and disrupted Hsp90 function, leading to ubiquitin-mediated degradation of HIF-1 . Administration of deguelin to xenograft-bearing mice statistically signifi