Isabel Gugel

Gene-expression profiling elucidates molecular signaling networks that can be therapeutically targeted in vestibular schwannoma.

OBJECT Vestibular schwannomas (VS) are common benign tumors of the vestibular nerve that cause significant morbidity. The current treatment strategies for VS include surgery or radiation, with each treatment option having associated complications and side effects. The transcriptional landscape of schwannoma remains largely unknown. METHODS In this study the authors performed gene-expression profiling of 49 schwannomas and 7 normal control vestibular nerves to identify tumor-specific gene-expression patterns. They also interrogated whether schwannomas comprise several molecular subtypes using several transcription-based clustering strategies. The authors also performed in vitro experiments testing therapeutic inhibitors of over-activated pathways in a schwannoma cell line, namely the PI3K/AKT/mTOR pathway. RESULTS The authors identified over 4000 differentially expressed genes between controls and schwannomas with network analysis, uncovering proliferation and anti-apoptotic pathways previously not implicated in VS. Furthermore, using several distinct clustering technologies, they could not reproducibly identify distinct VS subtypes or significant differences between sporadic and germline NF2-associated schwannomas, suggesting that they are highly similar entities. The authors identified overexpression of PI3K/AKT/mTOR signaling networks in their gene-expression study and evaluated this pathway for therapeutic targeting. Testing the compounds BEZ235 and PKI-587, both novel dual inhibitors of PI3K and mTOR, attenuated tumor growth in a preclinical cell line model of schwannoma (HEI-293). In vitro findings demonstrated that pharmacological inhibition of the PI3K/AKT/mTOR pathway with next-generation compounds led to decreased cell viability and increased cell death. CONCLUSIONS These findings implicate aberrant activation of the PI3K/AKT/mTOR pathway as a molecular mechanism of pathogenesis in VS and suggest inhibition of this pathway as a potential treatment strategy.

Ultrasound assessment of peripheral nerve pathology in neurofibromatosis type 1 and 2

OBJECTIVE The neurofibromatoses (NF) type 1 and 2 are hereditary tumor predisposition syndromes caused by germline mutations in the NF1 and NF2 tumor suppressor genes. In NF1 and 2, peripheral nerve tumors occur regularly. For further characterizing nerve ultrasound was performed in patients with NF1 and 2. METHODS Patients with established diagnosis of NF1 (n=27) and NF2 (n=10) were included. Ultrasound of peripheral nerves and cervical roots was performed during routine follow-up visits. Healthy volunteers were studied for comparison. RESULTS In patients with NF1, median cross-sectional area (CSA) of most nerves was significantly increased compared to controls and to NF2 due to generalized plexiform tumors, which arose out of multiple fascicles in 23 of 27 patients (85%). These were often accompanied by cutaneous or subcutaneous neurofibromas. In NF2, the overall aspect of peripheral nerves consisted of localized schwannomas (80%) and, apart from that, normal nerve segments. CONCLUSION Nerve ultrasound is able to visualize different nerve pathologies in NF1 and NF2. It is a precise and inexpensive screening method for peripheral nerve manifestation in neurofibromatosis and should be considered as the first choice screening imaging modality for all peripheral nerves within reach of non-invasive ultrasound techniques. SIGNIFICANCE Ultrasound patterns of peripheral nerve pathologies are described for the first time in a large cohort of patients with NF1 and NF2. It is a suitable screening tool and enables targeted MRI analysis.

Implications of Vestibular Schwannoma Consistency: Analysis of 140 Cases Regarding Radiologic and Clinical Features

OBJECTIVE To evaluate the effects of vestibular schwannoma (VS) consistency on internal auditory canal (IAC) widening, magnetic resonance imaging appearance, presenting symptoms, and facial nerve outcome. MATERIAL AND METHODS We performed a retrospective analysis of 140 consecutive patients presenting with unilateral VS who underwent surgical treatment at the Department of Neurosurgery, Tuebingen University, Germany. Operative videos were analyzed, and the tumors were classified into soft and firm according to resectability with an ultrasonic aspirator at 40% power. IAC opening was measured in preoperative bone-window computed tomography on the pathologic and healthy sides, and the percentage of widening between both sides was calculated. Tumor signal intensity was assessed on T2-weighted magnetic resonance imaging scans. Preoperative and postoperative findings in the patient reports were documented. RESULTS Widening of the IAC due to presence of the VS occurred in 118 patients (84.3%). The degree of IAC widening on the tumor side compared to the other side ranged from 0.1 to 10.1 mm (mean 2.6 mm). The mean widening of the IAC in relation to the healthy side was 1.9 mm in soft tumors and 3.6 mm in firm tumors. A significant correlation was found between tumor consistency and degree of widening of the IAC (P < 0.0001). No significant correlation was found between tumor intensity (on T2-weighted imaging) and tumor consistency. In the early postoperative course, patients with soft tumors had better facial nerve function than those having firm tumors. However, at the last examination no difference between both groups was found. CONCLUSION The consistency of VS has an impact on the immediate postoperative outcome. Widening on bony computed tomography scan, but not T2 intensity on magnetic resonance imaging, predicts whether the tumor is soft or firm.

Phenotypic and genotypic overlap between mosaic NF2 and schwannomatosis in patients with multiple non-intradermal schwannomas

Schwannomatosis and neurofibromatosis type 2 (NF2) are both characterized by the development of multiple schwannomas but represent different genetic entities. Whereas NF2 is caused by mutations of the NF2 gene, schwannomatosis is associated with germline mutations of SMARCB1 or LZTR1. Here, we studied 15 sporadic patients with multiple non-intradermal schwannomas, but lacking vestibular schwannomas and ophthalmological abnormalities, who fulfilled the clinical diagnostic criteria for schwannomatosis. None of them harboured germline NF2 or SMARCB1 mutations as determined by the analysis of blood samples but seven had germline LZTR1 variants predicted to be pathogenic. At least two independent schwannomas from each patient were subjected to NF2 mutation testing. In five of the 15 patients, identical somatic NF2 mutations were identified (33%). If only those patients without germline LZTR1 variants are considered (n = 8), three of them (37.5%) had mosaic NF2 as concluded from identical NF2 mutations identified in independent schwannomas from the same patient. These findings imply that a sizeable proportion of patients who fulfil the diagnostic criteria for schwannomatosis, are actually examples of mosaic NF2. Hence, the molecular characterization of tumours in patients with a clinical diagnosis of schwannomatosis is very important. Remarkably, two of the patients with germline LZTR1 variants also had identical NF2 mutations in independent schwannomas from each patient which renders differential diagnosis of LZTR1-associated schwannomatosis versus mosaic NF2 in these patients very difficult.

Dorsal root ganglia volume differentiates schwannomatosis and neurofibromatosis 2: DRG, Schwannomatosis, and NF2

Schwannomatosis and neurofibromatosis type 2 are hereditary tumor syndromes, and peripheral neuropathy has been reported in both. We prospectively applied in vivo morphometric measurement of dorsal root ganglia volume in 16 schwannomatosis patients, 14 neurofibromatosis type 2 patients, and 26 healthy controls by magnetic resonance neurography. Compared to healthy controls, dorsal root ganglia hypertrophy was a consistent finding in neurofibromatosis type 2 (L3, + 267%; L4, + 235%; L5, + 241%; S1, + 300%; S2, + 242%; Bonferroni‐adjusted p < 0.001) but not in schwannomatosis. Dorsal root ganglia may be a vulnerable site in origination of areflexia and sensory loss and a useful diagnostic marker in neurofibromatosis type 2. Ann Neurol 2018;83:854–857

NFAT and T-Cell Response Play Major Roles in the Formation of Sporadic Vestibular Schwannomas

Introduction: Even though clinical and morphological differences of vestibular schwannomas are well documented, the knowledge on molecular mechanisms of development is limited. In this study, we examined differences in gene expression between tumor and control tissue in search of underlying disease-causing deregulated pathways. Material and Methods: We performed whole genome microarray expression profiling (HG-U219 Array Plate, Affymetrix) and pathway analysis of tissue samples from 36 patients with sporadic vestibular schwannomas versus 7 postmortem samples of the vestibulocochlear nerve. Results: We identified 2,694 genes that were deregulated over twofold: 1,471 were upregulated and 1,223 were downregulated. The most significantly deregulated pathways in vestibular schwannomas include the role of nuclear factor of activated T-cells (NFAT) in immune response, phospholipase C signaling and antigen presentation. Conclusion: An important role in vestibular schwannoma formation is attributed to nuclear factors of activated T-cells and their transcriptional partners, whose combined interactions result in a deranged T-cell response and may thereby lead to an imbalance between tumorigenesis and immune response.