Development of gene therapy for schwannomas associated with neurofibromatosis type 2

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Schwannomas associated with neurofibromatosis type 2 (NF2) are difficult to treat because they are multiple and tend to recur. We performed basic researches to develop gene therapy for schwannomas with NF2.Surgically resected sporadic or NF2-associated schwannomas were primarily cultured. Cultured cells were positive for S-100 immunostaining. B- galactosidase gene was transfected into cultured cells using adenovirus vector. More than 50% cells expressed the gene at MOI = 1, and almost 100% cells at MOI = 10.Vascular endothelial growth factor (VEGF) has been reported to act as a survival factor for Schwann cells. We therefore investigated VEGF expression. VEGF immunostaining was present in sporadic and NF2-associated schwannomas. VEGF mRNA was detected in all 4 schwannomas tested from the NF2 group and in 1 of 4 sporadic schwannomas. MIB-1 labeling index and microvascular density were higher in the NF2 than the sporadic group. VEGF was also detected in the culture medium of schwannoma cells at the concentration of 100〜1180 pg/ml.These results suggested that VEGF might be a factor affecting proliferative potential of schwannomas. Then, gene therapy to bloc the function of VEGF was planned. Adenovirus vector expressing excess extracellular domain of Flt-1 (soluble VEGF receptor) was prepared.Expression of peroxisome proliferatior-activated receptorγ(PPARγ) was confirmed in gliomas. Administration of its ligand suppressed the growth of glioma cell lines. New mechanism to inhibit the tumor growth was suggested.For injection of gene into multiple cranial or spinal schwannomas in NF2 patients, neuroendoscope must be utilized. We performed preliminary research using dogs. After suboccipital craniotomy or lumber laminectomy, spinal subarachnoid space was investigated using a fine neuroendoscope. Although spinal nerves were observed, injection was difficult. Further slender neuroendoscope with a channel for drug injection needs to be designed.