Merlin is a tumour suppressor protein that is frequently mutated or downregulated in cancer. Biallelic Merlin inactivation is causative of tumour formation, including schwannoma, meningioma and ependymoma. These tumours can occur sporadically or as part of the genetic condition Neurofibromatosis type 2 (NF2) and cause significant morbidity. The current treatment options are restricted to surgery and radiotherapy, which are invasive and may cause further tumour development. The activity of both the E3 ubiquitin ligase complex Cullin 4 really interesting new gene (RING) E3 ubiquitin ligase- DNA damage binding protein (DDB1) and Cullin 4 associated factor 1 (CRL4-DCAF1) and Kinase suppressor of RAS 1 (KSR1) have been shown to be upregulated in schwannoma to drive tumour growth. KSR1 has also been shown to interact with components of the CRL4-DCAF1 complex. We investigated the expression, interaction and therapeutic potential of targeting these proteins in Merlin deficient schwannoma and meningioma using a primary human cell model and relevant cell lines. We found that DCAF1 and KSR1 protein were overexpressed in schwannoma and meningioma and confirmed that targeting both DCAF1 and KSR1 in meningioma had additive effects on proliferation. We also identified that CRL4-DCAF1 facilitates KSR1 dependent RAF/Mitogen-activated protein kinase (MAPK)/ Extracellular signal regulated kinase (ERK) kinase (MEK)/ERK pathway activity. We showed MLN3651, a neddylation inhibitor that targets ubiquitin ligase activity, reduced proliferation and activated apoptosis in Merlin-deficient tumours. We also showed that Merlin-positive tumours were less sensitive to MLN3651 than Merlin-deficient tumours; therefore, MLN3651 sensitivity may be CRL4-DCAF1-dependent. Finally, combination of MLN3651 and the MEK1/2 inhibitor AZD6244 had additive effects, particularly in meningioma. Combinatorial therapy activated the Hippo pathway, inhibited RAF/MEK/ERK pathway activity and proliferation demonstrating that targeting the activity and downstream pathways of both DCAF1 and KSR1 represents an attractive novel therapeutic strategy in Merlin-deficient tumours.

Das Ziel dieser Studie war die Analyse der Ergebnisse der mikrochirurgischen Therapie von Akustikusneurinomen (AN) über den transtemporalen Zugangsweg unter Einsatz eines flexiblen CO2-Faserlasers (Omniguide®). Zu diesem Zweck wurde eine prospektive nicht randomisierte klinische Studie durchgeführt. Bei 20 aufeinander folgenden Patienten, bei denen eine mikrochirurgische Exstirpation des Tumors über den transtemporalen Zugangsweg erfolgte, wurde die Tumorresektion mit Hilfe des flexiblen CO2-Lasers durchgeführt (Lasergruppe, LG). Als Vergleichsgruppe wurden 20 Patienten mit vergleichbarer Tumorgröße und gleichem präoperativen Hörvermögen aus einer Kohorte von 76 Patienten ausgewählt (matched pairs), die zu einem früheren Zeitpunkt vom selben Operateur ohne Zuhilfenahme des Lasers operiert worden waren (Kontrollgruppe, KG). In der frühen postoperativen Phase konnte bei jeweils sechs Patienten beider Gruppen eine Facialisschwäche nach House-Brackmann (HB) Grad 2-4 festgestellt werden. Nach drei Monaten zeigte sich lediglich bei einem Patienten der KG noch eine leichte Facialisschwäche (HB-Grad 2). Der Erhalt der Facialisfunktion (HB-Grad 1 und 2) lag bei beiden Gruppen bei 100 %. Der Hörerhalt (Gardner-Robertson-Klasse 1 und 2 prä- und postoperativ) lag in der LG bei 72 % und in der KG bei 82 % ohne statistisch signifikanten Unterschied. Die absolute Operationszeit (Schnitt-Naht-Zeit) betrug in der KG 157 min und in der LG 160 min. Die Präparationszeit des Tumors lag in der KG bei 23,2 min und bei der LG bei 36,1 min. Durch den Einsatz des CO2-Lasers konnte zwar keine Reduktion der Operationszeit erreicht werden, jedoch zeigten sich im Vergleich zur konventionellen Technik postoperativ die gleichen guten funktionellen Ergebnisse, so dass der CO2-Laser eine sinnvolle Ergänzung für spezielle Fälle sein kann (z.B. bei stark vaskularisierten Tumoren). / The aim of this study was to analyze the results of microsurgery in vestibular schwannomas (VS) with assistance of a flexible CO(2) laser fiber (Omniguide(®)) using the middle cranial fossa (MCF) approach. For that purpose we performed a prospective non-randomized clinical trial. In 20 consecutive patients suffering from VS and elected for microsurgery via the MCF approach, tumor resection was performed with the aid of the flexible CO(2) laser ("laser group", LG). Twenty patients with similar tumor volume and pre-operative hearing status out of a cohort of 76 patients previously treated by the same surgeon without laser were used as comparison group ("conventional group", CG) (matched-pair-technique). Facial weakness (House-Brackmann (HB) 2-4) was seen in early postoperative (p.o.) days in six patients in each group and all recovered completely by 3 months p.o., except one patient with HB 2 in CG. Facial nerve preservation rate (HB 1 + 2) was 100% in both groups. Hearing preservation rate (Gardner/Robertson class 1 + 2 or AAO-HNS A + B, pre- and postoperatively) was 72% in LG and 82% in CG, without significant difference. Overall time from incision to skin suture was 157 min (SD 55.9) in CG and 160 min (SD 39.7) in LG. Tumor preparation time was 23.2 min (SD 19.7) in CG and 36.1 min (SD 33.8) in LG. The use of a handheld flexible CO(2) laser fiber in VS-microsurgery is safe and subjectively facilitates tumor resection especially in "difficult" (e.g., highly vascularized) tumors. However, in this limited prospective trial the excellent functional outcome following conventional microsurgery could not be further improved, nor the surgical time reduced by means of the non-contact laser-tool. Focusing the use of the flexible CO(2) laser on "difficult" tumors may lead to different results in future.

During vestibular schwannoma surgery a large proportion of patients will lose their hearing. While there have been several papers investigating the mechanism behind this loss of auditory function, the exact pathophysiological mechanisms remain relatively elusive. The present study aimed to document the patterns of electrophysiological auditory responses during retrosigmoid vestibular schwannoma surgery. In particular, we aimed to determine whether the site of auditory impairment in individual cases was predominantly cochlea or neural. Auditory function was monitored intraoperatively in two patients who underwent unilateral vestibular schwannoma surgery via the retrosigmoid approach at St George’s Hospital in Christchurch, and Dunedin Public Hospital. A combination of electrocochleography and direct eighth nerve monitoring techniques were used to monitor the auditory evoked potentials from the cochlea and cochlear nerve during the course of the surgery. Auditory brainstem response recordings were obtained from the second participant due to the technical difficulties in the primary electrophysiological techniques. Technical difficulties faced during the surgical procedure prevented the recording of both electrocochleography and direct eighth nerve monitoring potentials from each of the participants. As a consequence of this, we were unable to draw any conclusions about the site of iatrogenic injury in each surgery. Despite the insufficient recordings of auditory function, the technical and practical knowledge acquired during the course of this pilot study has established a foundation upon which the continuing research may build.

INTRODUCTION: Asymmetrical sensorineural hearing loss [ASNHL] is a common otological complaint. Vestibular schwannoma [VS] is a rare, benign tumor that commonly presents with ASNHL. Magnetic resonance imaging [MRI] is the gold standard in diagnosing VS, but is an expensive imaging modality. Therefore, this meta-analysis evaluates the diagnostic yield of MRI scans in patients with ASNHL to rule out VS. METHODS: A systematic review was performed using a keyword search on the PubMed Database. We excluded articles based on: Non-English, case reports, wrong diagnostic test, solely pediatric subjects, inadequate/unnecessary data, repeated studies, and unclear presenting symptoms. The demographics, definition of ASNHL, and the number and results of MRIs were collected. Positive MRIs were grouped based on differences in interaural hearing loss. RESULTS: 5,783 MRIs on subjects with ASNHL were collected from fourteen studies. 296 MRI scans (5.1%) were positive for VS. 170 positive scans were grouped. In Group A (10+ dB) 11.2% had VS; in Group B (15+ dB at ≥2 frequencies or 20+ dB at 1 frequency) 6.5% had VS, Group C (20+ dB) yielded 5.1% with VS, and Group D (30+ dB) had 0.7% yield of positive VS. CONCLUSION: MRI scans to rule out VS in patients with ASNHL has an extremely low diagnostic yield when assessing subjects on the basis of ASNHL. The degree of ASNHL does not correlate with increased odds of VS diagnosis. Overall, the risk of VS diagnosis in patients with any degree of ASNHL is low.

Neurofibromatosis type 2 (NF2) is an inherited, multiple tumour disease caused by loss of the tumour suppressor protein, Merlin. There are several tumours associated with NF2 including; ependymomas, meningiomas and schwannomas. Merlin loss can also occur sporadically in all of these tumours and is associated with upregulation of various growth factor receptors and their relevant signalling pathways. At present the only treatment options for NF2 are surgery or radiosurgery, both of which incur serious morbidity and are unable to prevent recurrence of tumours. Either new drug treatments, or re-profiling of other drugs already commercially available, are urgently needed to improve outcome for NF2 patients. Cellular prion protein (PrPC), encoded by PRNP gene, is involved in tumour development by altering proliferation, adhesion, and survival in some cancers via focal adhesion kinase (FAK) /Src/ NFκB, cyclin D1 and p53 -proteins. Our group previously showed a strong elevation of PRNP gene activity in schwannoma. I hypothesise that PrPC may contribute to schwannoma development. To study the role of PrPC in schwannoma development I have used the well-established in vitro model of schwannoma that comprises primary human Schwann and schwannoma cells. I show that PrPC is upregulated in schwannoma as well as in Merlin-deficient meningiomas and human malignant mesotheliomas. In schwannoma PrPC is released both via exosomes and by α-cleavage which forms biologically active N- and C-terminal portions of the protein. PrPC contributes to pathological proliferation, adhesion and survival of schwannoma cells by activating ERK1/2, PI3K/AKT, cyclin D1, FAK, p53 pathways via the 37/67kDa non-integrin laminin receptor (LR/37/67kDa) and CD44. Furthermore, schwannoma cells appear to be intrinsically drug-resistant due to upregulation of MDR1 protein p-glycoprotein (p-gp) expression. P-gp expression is dependent on PrPC thus, inhibiting PrPC may be a good potential new therapeutic option for schwannoma patients, either alone or in combination with Sorafenib and p-gp inhibitor Valspodar (PSC833). An inhibitor of LR/37/67kDa/PrP interaction, NSC47924, or Bortezomib, a proteasome/NFκB inhibitor which has been approved for the treatment of multiple myeloma, could also be of beneficial therapeutic effect and is something to investigate in future work. I conclude that PrPC is an interesting new therapeutic target through its involvement with schwannoma patholgenesis and resistance to drug treatments PrPC may prove to be a good therapeutic target in other NF2-related tumours like meningiomas and schwannomas.

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The thesis deals with the issue of vestibular compensation in patiens after vestibular schwannoma surgery. The aim of this thesis was to objectively evaluate the dynamics of vestibular compensation in the early postoperative period and to determine whether the application of gentamicin impacts the dynamics of equilibrium functions. 32 patients participated in the study (20 women and 12 men) ranging from 28 to 73 years of age. Patients underwent a rehabilitation program with visual feedback using the interactive rehabilitation system, Homebalance. This rehabilitation program was carried out daily from the 5th postoperative day until hospital discharge. Patients were examined preoperatively, postoperatively and after rehabilitation. To assess the vestibular compensation, static posturography, the Synapsys Posturography System, and the Activities-Specific Balance Confidence Scale were used. The statistical analysis showed a significant increase in mean values of measured COP parameters (the length of the COP trajectory and COP confidence elipse area) postoperatively. After completing the rehabilitation program no significant reduction of measured COP parameters was found. The total score from the Activities- Specific Balance Confidence Scale showed a statistically significant decrease in postoperative...

OBJECTIVES: Models for the development of new treatment options in vestibular schwannoma (VS) treatment are lacking. The purpose of this study is to establish a quantifiable human VS xenograft model in mice. STUDY DESIGN AND METHODS: Both rat malignant schwannoma cells (KE-F11 and RT4) and human malignant schwannoma (HMS-97) cells were implanted near the sciatic nerve in the thigh of severe combined immunodeficiency (SCID) mice. Additionally, human benign VS specimens were implanted in another set of SCID mice. Three-dimensional tumor volumes were calculated from magnetic resonance images over the next 6 months. RESULTS: Mice implanted with malignant schwannoma cells developed visible tumors within 2 weeks. Imaging using a 4.7-tesla magnetic resonance imaging and immunohistopathologic examination identified solid tumors in all KE-F11 and HMS-97 xenografts, whereas RT4 xenografts consistently developed cystic schwannomas. VS xenografts demonstrated variability in their growth rates similar to human VS. The majority of VS xenografts did not grow but persisted throughout the study, whereas two of 15 xenografts grew significantly. Histopathologic examination and immunohistochemistry confirmed that VS xenografts retained their original microscopic and immunohistochemical characteristics after prolonged implantation. CONCLUSIONS: This study describes the first animal model for cystic schwannomas. Also, we demonstrate the use of high-field magnetic resonance imaging to quantify VS xenograft growth over time. The VS xenografts represent a model complimentary to Nf2 transgenic and knockout mice for translational VS research.