title: Potent activity of a novel dimeric heat shock protein 90 inhibitor against head and neck squamous cell carcinoma in vitro and in vivo.
abstract: Heat shock protein 90 (Hsp90) is a molecular chaperone that promotes the conformational maturation of numerous client proteins, many of which play critical roles in tumor cell growth and survival. The ansamycin-based Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) is currently in phase I/II clinical testing. However, 17-AAG is difficult to formulate and displays weak activity against some tumors. A novel dimeric ansamycin, EC5, was evaluated for antitumor activity in eight head and neck squamous cell carcinoma (HNSCC) cell lines. Both 17-AAG and EC5 inhibited tumor cell proliferation effectively, but EC5 was more potent, with IC(50) below 200 nmol/L in most cell lines tested, including several lines that were resistant to 17-AAG. The inability of 17-AAG to kill JHU12 cells was linked to a defect in retinoblastoma signaling and could be rescued by ectopic expression of p16(INK4a). EC5 induced G(1) growth arrest of tumor cells and apoptosis, with the degradation of client proteins including epidermal growth factor receptor, c-Raf-1, Akt, and Cdk4 and inhibition of Akt phosphorylation. In vivo, EC5 dramatically reduced the growth rate of established HNSCC xenografts in nude mice and decreased expression of epidermal growth factor receptor and Akt within the xenografts. These results suggest that this novel ansamycin-based Hsp90 inhibitor affects multiple pathways involved in tumor development and progression and may represent a new strategy for the treatment of HNSCC patients.
authors.affiliation: Department of Otolaryngology/Head and Neck Surgery and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina and Conforma Therapeutics, San Diego, California, USA.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Yin
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Francis
authors.initials: F
authors.lastname: Burrows
authors.forename: Lin
authors.initials: L
authors.lastname: Zhang
authors.forename: Carol G
authors.initials: CG
authors.lastname: Shores
mesh_terms: D000818:Animals; D017209:Apoptosis; D016227:Benzoquinones; D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects*; D049109:Cell Proliferation; D020869:Gene Expression Profiling; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors; D006258:Head and Neck Neoplasms / Q000473:pathology*; D006801:Humans; D047029:Lactams, Macrocyclic; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
chemical_list: D016227:Benzoquinones; C502977:EC5 compound; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D017828:Rifabutin; C112765:tanespimycin; D017346:Protein Serine-Threonine Kinases