title: Potential role of imatinib mesylate (Gleevec, STI-571) in the treatment of vestibular schwannoma.
abstract: OBJECTIVE
  To determine the expression of the tyrosine kinases platelet-derived growth factor receptor (PDGFR) and c-Kit in vestibular schwannoma (VS) and to determine the potential role of imatinib mesylate (Gleevec) in regulating the growth and cell death of this tumor.
  
  
  BACKGROUND
  Protein tyrosine kinases are transmembrane tyrosine kinase receptors that transduce signals from inside and outside the cell and function as relay points for signaling pathways. They have a key role in numerous processes that affect cell proliferation, tumorigenesis, cancer invasion, metastasis, and modulation of apoptosis. A few of these kinases have been demonstrated to be overexpressed and dysregulated in many carcinomas, sarcomas, and benign tumors.
  
  
  METHODS
  Immunohistochemical staining was used to investigate the expression of PDGFR and c-Kit in archived acoustic neuroma tissue. Clinical data including size of tumors, age, sex, and symptoms were correlated with kinase expression, whereas Western blot analysis and immunofluorescence were performed to demonstrate the expression and localization of PDGFR and c-Kit in HEI193, an immortalized VS cell line. Clonogenic survival assays were performed to assess proliferation inhibition by Gleevec. Gleevec's effect on the cell cycle profile also was investigated via flow cytometry analysis.
  
  
  RESULTS
  Expression of PDGFR in the formalin-fixed VS tumor tissue was observed in 23 (67.5%) of the 34 samples. C-kit was expressed in 18 (52.9%) of the 34 samples. Western blot analysis demonstrates positive expression of c-Kit and PDGFR-Q in HEI193 and a primary VS culture. Western blot analysis showed downregulation of phospho-c-kit and phospho-PDGFR-Q with 5 and 10 uM Gleevec. Immunofluorescent staining of this cell line also reveals that PDGFR-β is localized primarily in the cytoplasm, whereas c-Kit is both nuclear and cytoplasmic. Cell cycle analysis of HEI193 96 hours after incubation with Gleevec indicates a dose-dependent increase in G1 from 61.6% to 70.7% and 74% at 5 and 10 uM of Gleevec, respectively. Colony formation assays demonstrate dose-dependent growth inhibition by Gleevec, in the HEI193 cell line as well as in a VS cell culture derived from a fresh tumor.
  
  
  CONCLUSIONS
  The expression of PDGFR-Q and c-Kit in VS tissue may indicate novel molecular targets involved in the development of this tumor. Direct inhibition of these molecules by Gleevec may have relevant therapeutic applications.
authors.affiliation: Servicio de Otorrinolaringología, Hospital Donosita, San Sebastian, Spain.
authors.forename: Xabier
authors.initials: X
authors.lastname: Altuna
authors.forename: Jay Patrick
authors.initials: JP
authors.lastname: Lopez
authors.forename: Michael Andrew
authors.initials: MA
authors.lastname: Yu
authors.forename: Maria Jesus
authors.initials: MJ
authors.lastname: Arandazi
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Harris
authors.forename: Jessica
authors.initials: J
authors.lastname: Wang-Rodriguez
authors.forename: Yi
authors.initials: Y
authors.lastname: An
authors.forename: Robert
authors.initials: R
authors.lastname: Dobrow
authors.forename: Joni K
authors.initials: JK
authors.lastname: Doherty
authors.forename: Weg M
authors.initials: WM
authors.lastname: Ongkeko
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001549:Benzamides; D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D000068877:Imatinib Mesylate; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009464:Neuroma, Acoustic / Q000188:drug therapy / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology* / Q000627:therapeutic use; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology* / Q000627:therapeutic use; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D020797:Receptor, Platelet-Derived Growth Factor beta