Contribution of mTOR and PTEN to Radioresistance in Sporadic and NF2-Associated Vestibular Schwannomas: A Microarray and Pathway Analysis.

The use of radiation treatment has increased for both sporadic and neurofibromatosis type 2 (NF2)-associated vestibular schwannoma (VS). However, there are a subset of radioresistant tumors and systemic treatments that are seldom used in these patients. We investigated molecular alterations after radiation in three NF2-associated and five sporadically operated recurrent VS after primary irradiation. We compared these findings with 49 non-irradiated (36 sporadic and 13 NF2-associated) VS through gene-expression profiling and pathway analysis. Furthermore, we stained the key molecules of the distinct pathway by immunohistochemistry. A total of 195 differentially expressed genes in sporadic and NF2-related comparisons showed significant differences based on the criteria of p value < 0.05 and a two-fold change. These genes were involved in pathways that are known to be altered upon irradiation (e.g., mammalian target of rapamycin (mTOR), phosphatase and tensin homolog (PTEN) and vascular endothelial growth factor (VEGF) signaling). We observed a combined downregulation of PTEN signaling and an upregulation of mTOR signaling in progressive NF2-associated VS after irradiation. Immunostainings with mTOR and PTEN antibodies confirmed the respective molecular alterations. Taken together, mTOR inhibition might be a promising therapeutic strategy in NF2-associated VS progress after irradiation. We used microdissected tumor samples of 9 recurrent irradiated VS (5 sporadic, 1 cystic and 3 NF2-associated VS), 36 sporadic, 13 NF2 associated and 9 cystic associated non-irradiated controls. There are also 7 controls of vestibular nerve tissue that were obtained post mortem.

放射治疗在散发性及2型神经纤维瘤病（neurofibromatosis type 2, NF2）相关前庭神经鞘膜瘤（vestibular schwannoma, VS）中的应用均有所增加。然而此类患者中存在一部分放射抵抗性肿瘤，且全身治疗方案在这类患者中极少应用。本研究针对经初次放射治疗后复发的3例NF2相关及5例散发性前庭神经鞘膜瘤，分析其放射治疗后的分子改变。本研究通过基因表达谱分析及通路分析，将上述结果与49例未接受放射治疗的前庭神经鞘膜瘤（其中36例为散发性、13例为NF2相关）进行对比。此外，本研究通过免疫组化染色检测了对应通路中的关键分子。基于P值<0.05且表达变化倍数≥2的筛选标准，散发性与NF2相关样本对比中共筛选出195个差异表达基因。这些基因富集于已知可被放射调控的通路，例如哺乳动物雷帕霉素靶蛋白（mammalian target of rapamycin, mTOR）、张力蛋白同源磷酸酶（phosphatase and tensin homolog, PTEN）及血管内皮生长因子（vascular endothelial growth factor, VEGF）信号通路。本研究观察到，放射治疗后进展的NF2相关前庭神经鞘膜瘤中同时存在PTEN信号通路下调与mTOR信号通路上调的改变。针对mTOR与PTEN的免疫组化染色验证了上述分子改变。综上，mTOR抑制或许可作为放射治疗后进展的NF2相关前庭神经鞘膜瘤的潜在治疗策略。本研究使用的样本包括：9例经放射治疗后复发的前庭神经鞘膜瘤（其中5例散发性、1例囊性、3例NF2相关）、36例散发性、13例NF2相关及9例囊性非放射治疗对照样本；此外还纳入7例死后获取的前庭神经组织作为对照。