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 1alpha (HIF-1alpha) and Akt. Deguelin is a rotenoid with antitumor activities. We investigated whether the antitumor activities of deguelin involve the functional inhibition of Hsp90.


METHODS
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 examined by docking analysis and by competition binding experiments with ATP-Sepharose beads. The proteasome inhibitor MG132 was used to investigate deguelin's effect on the induction of ubiquitin-mediated proteasomal degradation of HIF-1alpha. 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-1alpha. Administration of deguelin to xenograft-bearing mice statistically significantly decreased tumor growth by inducing apoptosis and decreasing the expression of Hsp90 client proteins, without detectable toxic effects. For example, at 15 days after the start of deguelin treatment, the volume of untreated control H1299 xenograft tumors was 798 mm3 and that of xenograft tumors treated with deguelin at 4 mg/kg was 115.9 mm3 (difference = 682.1 mm3, 95% confidence interval = 480.4 to 883.9 mm3; P<.001).


CONCLUSIONS
The antitumor activities of deguelin appear to involve its binding to the ATP-binding pocket of Hsp90, which suppresses Hsp90 function.
Oh
Seung Hyun
SH
Department of Thoracic/Head and Neck Medical Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA.
Woo
Jong Kyu
JK
Yazici
Yasemin Dakak
YD
Myers
Jeffrey N
JN
Kim
Woo-Young
WY
Jin
Quanri
Q
Hong
Soon Sun
SS
Park
Hyun-Ju
HJ
Suh
Young-Ger
YG
Kim
Kyu-Won
KW
Hong
Waun Ki
WK
Lee
Ho-Young
HY
D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001665:Binding Sites; D001667:Binding, Competitive; D048708:Cell Growth Processes / Q000187:drug effects; D005260:Female; D005634:Fructose-Bisphosphate Aldolase / Q000096:biosynthesis; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D008819:Mice, Nude; D008958:Models, Molecular; D009369:Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism; D012402:Rotenone / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis; D023041:Xenograft Model Antitumor Assays
C497442:HIF1A protein, human; D018841:HSP90 Heat-Shock Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017382:Reactive Oxygen Species; D042461:Vascular Endothelial Growth Factor A; D012402:Rotenone; D000255:Adenosine Triphosphate; D005634:Fructose-Bisphosphate Aldolase; C107676:deguelin