Treatment of Vestibular Schwannoma Cells With ErbB Inhibitors

Department of Otolaryngology-Head and Neck Surgery, The Ohio State University Eye and Ear Institute, Columbus, Ohio 43212, USA.
Otology & neurotology: official publication of the American Otological Society, American Neurotology Society [and] European Academy of Otology and Neurotology (Impact Factor: 1.79). 02/2012; 33(2):244-57. DOI: 10.1097/MAO.0b013e31823e287f
Source: PubMed


Aberrant phosphorylation of ErbB family receptor tyrosine kinases (RTK) in human vestibular schwannomas (VSs) renders them susceptible to growth suppression by RTK inhibitors.
Recent evidence has implicated increased ErbB family receptor tyrosine kinase signaling in VS tumorigenesis; however, the characterization of ErbB receptor activity and the chemotherapeutic potential of RTK inhibitors in VS treatment have not been fully explored.
To confirm phosphorylation of ErbB receptors in VS, protein extracts from paired VS tumor-vestibular nerve samples were examined using phospho-RTK arrays. ErbB receptor phosphorylation was similarly examined in cultured schwannoma cells, normal Schwann cells, and VS tumor tissues using Western blotting. Also, VS tumor sections were immunostained for members of the ErbB receptor family. The effects of RTK inhibitors on ErbB phosphorylation and cell proliferation were assessed in schwannoma cells after epidermal growth factor receptor (EGFR) inhibitor (Erlotinib) and EGFR/ErbB2 inhibitor (Lapatinib) treatment.
VS tumor tissues consistently demonstrated higher levels of phosphorylated ErbB3 compared with paired vestibular nerves. However, cultured VS, malignant schwannoma, and normal Schwann cells demonstrated EGFR phosphorylation. Immunohistochemistry confirmed high expression of ErbB3 in a series of VS tumor sections. Erlotinib inhibited schwannoma cell proliferation with an IC50 value of 2.5 µmol/L, whereas Lapatinib was less potent for growth inhibition. Erlotinib treatment resulted in a decrease of multiple phospho-ErbB receptors in schwannoma cells.
VS variably express activated ErbB receptors with consistently higher levels of phospho-ErbB3 expression relative to paired vestibular nerve samples. Chemotherapeutic targeting of ErbB3 may be a novel means of inhibiting VS growth.

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    • "Since over 75% of pediatric ependymomas express ErbB2 [26] and increased ErbB family receptor tyrosine kinase signaling has been reported in the hallmark NF2-associated tumor (vestibular schwannoma) [27], [28] we examined ErbB2 activation in normal human spinal cord and in two representative spinal ependymomas from individuals with a confirmed diagnosis of NF2. These tumors are not typically removed, thus limiting a more exhaustive analysis. "
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    ABSTRACT: BACKGROUND:: Radiosurgery is increasingly used to treat vestibular schwannomas (VSs). Increasing the sensitivity of VS cells to irradiation (IR) could allow for lower and/or more effective doses of IR, improving safety and efficacy. Persistent c-Jun N-terminal kinase (JNK) activity in VS cells reduces cell death by suppressing accumulation of reactive oxygen species (ROS), raising the possibility that JNK activity protects against IR-induced VS cell death, which is mediated by ROS. OBJECTIVE:: To determine the extent to which JNK signaling contributes to VS cell radiosensitivity. METHODS:: Primary human VS cultures, derived from acutely resected tumors, received single doses (5-40 Gy) of γ-irradiation. Histone 2AX phosphorylation, a marker of IR-induced DNA damage, was assayed by western blot and immunostaining. ROS levels were quantified by measuring 2',7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA) fluorescence. Cell apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling. RESULTS:: The JNK inhibitors, SP6000125 and I-JIP, reduced H2AX phosphorylation following IR. They also increased H2DCFDA fluorescence in non-irradiated cultures and significantly increased IR-induced (5-10 Gy) H2DCFDA fluorescence 72 hours, but not 2 hours, after IR. Finally, I-JIP (50 μM) significantly increased VS cell apoptosis in cultures treated with 20-40 Gy. I-JIP (20 μM), SP600125 (20 μM), and JNK1/2 siRNA knock-down each increased VS cell apoptosis in cultures treated with 30-40 Gy, but not lower doses, of IR. CONCLUSION:: Inhibition of JNK signaling decreases H2AX phosphorylation and increases ROS and apoptosis in VS cells following γ-irradiation. These results raise the possibility of using JNK inhibitors to increase the effectiveness of radiosurgery for treatment of VSs.
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