Targeting heat shock protein 90 with non-quinone inhibitors: a novel chemotherapeutic approach in human hepatocellular carcinoma.
The inhibition of heat shock protein 90 (Hsp90) has emerged as a promising antineoplastic strategy in diverse human malignancies. Hsp90 has been predicted to be involved in hepatocellular carcinoma (HCC) development; however, its role in hepatocarcinogenesis remains elusive. Using chemically distinctive Hsp90 inhibitors, we show that Hsp90 capacitates the aberrant expression and activity of crucial hepatocarcinogenesis-driving factors (e.g., insulin-like growth factor receptor 1, hepatocyte growth factor receptor, protein kinase B, v-raf-1 murine leukemia viral oncogene homolog 1, and cyclin-dependent kinase 4). In vitro, Hsp90 inhibition with both geldanamycin analogs (17-allylamino-17-desmethoxygeldanamycin (17-AAG) and 17-dimethylaminoethylamino-17-desmethoxygeldanamycin (17-DMAG)) and the non-quinone compound 8-(6-iodobenzo[d][1,3]dioxol-5-ylthio)-9-(3-(isopropylamino)propyl)-9H-purin-6-amine (PU-H71) reduced the viability of various HCC cell lines, induced the simultaneous degradation of numerous hepatocarcinogenic factors, and caused substantial cell cycle arrest and apoptosis. In contrast, nontumorigenic hepatocytes were less susceptible to Hsp90 inhibition. Because conventional geldanamycin-derivate Hsp90 inhibitors induce dose-limiting liver toxicity, we tested whether novel Hsp90 inhibitors lacking the benzoquinone moiety, which has been deemed responsible for hepatotoxicity, can elicit antineoplastic activity without causing significant liver damage. In HCC xenograft mouse models, PU-H71 was retained in tumors at pharmacologically relevant concentrations while being rapidly cleared from nontumorous liver. PU-H71 showed potent and prolonged in vivo Hsp90 inhibitory activity and reduced tumor growth without causing toxicity.


CONCLUSIONS
Hsp90 constitutes a promising therapeutic target in HCC. Non-quinone Hsp90 inhibitors exhibit tumor-specific accumulation and exert potent antineoplastic activity without causing significant hepatotoxicity.
Breinig
Marco
M
Department of General Pathology, University Hospital Heidelberg, Heidelberg, Germany.
Caldas-Lopes
Eloisi
E
Goeppert
Benjamin
B
Malz
Mona
M
Rieker
Ralf
R
Bergmann
Frank
F
Schirmacher
Peter
P
Mayer
Matthias
M
Chiosis
Gabriela
G
Kern
Michael André
MA
D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy*; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy*; D051379:Mice; D011809:Quinones; D014407:Tumor Cells, Cultured
D018841:HSP90 Heat-Shock Proteins; D011809:Quinones