ErbB and Nrg: Potential molecular targets for vestibular schwannoma pharmacotherapy

Objective: Identify molecular targets for development of tumor-specific pharmacotherapeutics aimed at treating vestibular schwannomas (VSs). Activated epidermal growth factor receptor B (ErbB) 2 and ErbB3 are abundantly expressed in VS. ErbB2 signaling is essential for Schwann cell differentiation, survival, and proliferation. VS arise after loss of functional merlin, a putative tumor suppressor. Merlin internalizes ErbB2 receptors in rodent Schwann cells. Unregulated ErbB signaling may contribute to VS tumorigenesis. Study Design: Molecular analyses, retrospective clinical correlation. Setting: Tertiary referral center. Patients: Thirty-eight specimens from patients operated for sporadic (n = 21) and neurofibromatosis (NF) 2-related (n 17) VS. Intervention(s): VS analyses via real-time polymerase chain reaction, immunohistochemistry, and correlation with patient clinical data. Main Outcome Measure(s): ErbB signaling molecule expression, tumor size, age, and NF2 status. Results: VS upregulated epidermal growth factor (EGF) receptor in 68% (62% sporadic and 75% NF2-associated VS) and ErbB2 in 84% (76% sporadic and 94% NF2-related VS). ErbB3 was upregulated in 34%, and ErbB4 is downregulated in NF2-related VS. Of EGF receptor (EGFR) ligands, EGF was upregulated in all NF2-related VS, but none of the sporadic VS (p < 0.01), and transforming growth factor alpha and beta-cellulin showed upregulation in 67% of NF2-related VS but not sporadic VS (p = 0.02 and p = 0.01, respectively). Neuregulin (Nrg) was upregulated in 86% of sporadic VS versus 19% of NF2-related VS (p < 0.01). EGFR expression levels correlated directly with VS tumor size and inversely with patient age, whereas Nrg expression correlated directly With age (p = 0.0005). EGF expression predicts NF2 status, whereas Nrg predicts non-NF2 status (p < 0.01). Conclusion: These findings implicate the ErbB pathway in VS growth and as potential molecular targets for VS pharmacotherapy.