Michel Kalamarides

Merlin regulates transmembrane receptor accumulation and signaling at the plasma membrane in primary mouse Schwann cells and in human schwannomas.

The NF2 gene product, merlin/schwannomin, is a cytoskeleton organizer with unique growth-inhibiting activity in specific cell types. A narrow spectrum of tumors is associated with NF2 deficiency, mainly schwannomas and meningiomas, suggesting cell-specific mechanisms of growth control. We have investigated merlin function in mouse Schwann cells (SCs). We found that merlin regulates contact inhibition of proliferation by limiting the delivery of several growth factor receptors at the plasma membrane of primary SCs. Notably, upon cell-to-cell contact, merlin downregulates the membrane levels of ErbB2 and ErbB3, thus inhibiting the activity of the downstream mitogenic signaling pathways protein kinase B and mitogen-activated protein kinase. Consequently, loss of merlin activity is associated with elevated levels of ErbB receptors in primary SCs. We also observed accumulation of growth factor receptors such as ErbB2 and 3, insulin-like growth factor 1 receptor and platelet-derived growth factor receptor in peripheral nerves of Nf2-mutant mice and in human NF2 schwannomas, suggesting that this mechanism could play an important role in tumorigenesis.

High incidence of activating TERT promoter mutations in meningiomas undergoing malignant progression.

Meningiomas are common central nervous system tumors. The World Health Organization (WHO) defines three grades, predictive of the risk of recurrence. These tumors can relapse frequently and sometimes undergo malignant transformation. Maintenance of telomere length is a key process in malignant progression, and mutations in TERT promoter have recently been identified in various types of cancer. We sequenced the TERT promoter in 85 meningiomas from 73 patients. We found a high incidence of TERT promoter mutations in patients with meningiomas undergoing malignant histological progression (28%, n = 5/18 patients). In this subset of patients with histological progression, TERT promoter mutations were found in both the lowest and the highest grade tumors, and in both NF2‐mutated and nonmutated samples. In contrast, one mutation was identified in 35 meningiomas without recurrence or progression, belonging to various histological grades. This sample was an aggressive meningioma in a patient who died shortly after surgery. Interestingly, tumors showing relapse without histological progression were not mutated for TERT promoter (n = 20). Finally, TERT promoter mutations were associated with a marked increase in TERT expression. Thus, TERT promoter mutations are pivotal genetic alterations involved in malignant progression of meningiomas and could be used as a biomarker to identify meningiomas at risk of malignant transformation.

Comparative Pathology of Nerve Sheath Tumors in Mouse Models and Humans

Despite the progress made in our understanding of the biology of neurofibromatosis (NF), the long-term clinical outcome for affected patients has not changed significantly in the past decades, and both NF1 and NF2 are still associated with a significant morbidity and a decreased life span. A number of NF1 and NF2 murine models have been generated to aid in the study of NF tumor biology and in the development of targeted therapies for NF patients. A single, universal pathological classification of the lesions generated in these murine models is essential for the validation of the models, for their analysis and comparison with other models, and for their future effective use in preclinical treatment trials. For the formulation of a pathological classification of these lesions, the WHO classification of human tumors was used as a reference. However, it was not adopted for the classification of the GEM lesions because of some important differences between the human and murine lesions. A novel classification scheme for peripheral nerve sheath tumors in murine models was therefore devised.

Consensus Recommendations for Current Treatments and Accelerating Clinical Trials for Patients with Neurofibromatosis Type 2

Neurofibromatosis type 2 (NF2) is a tumor suppressor syndrome characterized by bilateral vestibular schwannomas (VS) which often result in deafness despite aggressive management. Meningiomas, ependymomas, and other cranial nerve and peripheral schwannomas are also commonly found in NF2 and collectively lead to major neurologic morbidity and mortality. Traditionally, the overall survival rate in patients with NF2 is estimated to be 38% at 20 years from diagnosis. Hence, there is a desperate need for new, effective therapies. Recent progress in understanding the molecular basis of NF2 related tumors has aided in the identification of potential therapeutic targets and emerging clinical therapies. In June 2010, representatives of the international NF2 research and clinical community convened under the leadership of Drs. D. Gareth Evans (University of Manchester) and Marco Giovannini (House Research Institute) to review the state of NF2 treatment and clinical trials. This manuscript summarizes the expert opinions about current treatments for NF2 associated tumors and recommendations for advancing therapies emerging from that meeting. The development of effective therapies for NF2 associated tumors has the potential for significant clinical advancement not only for patients with NF2 but for thousands of neuro‐oncology patients afflicted with these tumors.

Identification of a progenitor cell of origin capable of generating diverse meningioma histological subtypes

Meningiomas are among the most common primary central nervous system tumours in adults. Studies focused on the molecular basis for meningioma development are hampered by a lack of information with regard to the cell of origin for these brain tumours. Herein, we identify a prostaglandin D synthase-positive meningeal precursor as the cell of origin for murine meningioma, and show that neurofibromatosis type 2 (Nf2) inactivation in prostaglandin D2 synthase (PGDS) (+) primordial meningeal cells, before the formation of the three meningeal layers, accounts for the heterogeneity of meningioma histological subtypes. Using a unique PGDSCre strain, we define a critical embryonic and early postnatal developmental window in which biallelic Nf2 inactivation in PGDS (+) progenitor cells results in meningioma formation. Moreover, we identify differentially expressed markers that characterize the two major histological meningioma subtypes both in human and mouse tumours. Collectively, these findings establish the cell of origin for these common brain tumours as well as a susceptible developmental period in which signature genetic mutations culminate in meningioma formation.

Auditory brainstem implant in neurofibromatosis type 2 and non-neurofibromatosis type 2 patients.

Objective: To evaluate the auditory brainstem implant (ABI) performances in neurofibromatosis type 2 (NF2) and non-NF2 patients. Study Design: Retrospective cohort study. Setting: Tertiary referral center. Patients: Between 1996 and 2006, 31 adult patients (mean age, 41 yr; range, 17-65 yr) were implanted with a 21-electrode Nucleus device (Cochlear Inc., Lane Cove, Australia). The population comprised 23 NF2, 3 postmeningitis bilateral ossified cochleas, 3 solitary vestibular schwannomas on the only hearing ear, 1 inner ear malformation, and 1 bilateral cochlear destruction by otosclerosis. Intervention: Auditory brainstem implant was placed through a translabyrinthine or a retrosigmoid approach. Main Outcome Measures: Auditory brainstem implant was evaluated by open-set words and sentences in sound, vision, and sound-plus-vision modes. Results: In NF2 patients, 16 (70%) were daily users of their implants. In these patients, the open-set dissyllabic word recognition was 36 ± 6.0 % for vision-only mode, 33 ± 6.5 % for sound-only mode, and 65 ± 8.0 % in vision-plus-sound mode with a high interindividual variation. Negative prognostic factors were long duration of total hearing loss (>10 yr), low number of active electrodes (<10), and local complications (meningitis, hematoma). Six non-NF2 patients (75%) were daily ABI users. The performances of patients with ossified cochleas were similar to best NF2 cases. Conclusion: A clear benefit of ABI could be evidenced in NF2 patients, especially in case of small tumor and short duration of hearing loss. Auditory brainstem implant may also be indicated in patients with bilateral profound hearing loss and a predictable failure of cochlear implantation.

Meningiomas and neurofibromatosis

Neurofibromatosis type 2 (NF2) is a rare genetic disorder predisposing to multiple benign tumors of the nervous system. Meningiomas occur in about half of NF2 patients, and are often multiple. Patients harboring seemingly isolated multiple meningiomas should be investigated to diagnose NF2 by careful familial history collection, detailed clinical examination (skin lesions and slit lamp examination of the lens), audiovestibular testing, and fine cranio-spinal Magnetic Resonance Imaging. Somatic mosaicism is frequent in NF2 and may explain a mild phenotype as, e.g. isolated multiple meningiomas. Neurofibromatosis type 1 is not associated with an increased risk of meningioma. Whether meningiomas are part of the schwannomatosis tumor phenotype or not remains debated. Meningiomas in NF2 patients are associated with a higher risk of mortality, and their treatment is challenging, but data about natural history of meningiomas in NF2 patients in the literature are sparse. Thus, knowledge of tumor behavior is essential in slow growing tumors like meningiomas, to balance the risk of treatment against the natural history of the disease, and to evaluate the efficiency of alternative therapeutics (radiation therapy or new drugs).

Evaluation of the Management of Postoperative Aseptic Meningitis

BACKGROUND A consensus conference recommended empirical antibiotic therapy for all patients with postoperative meningitis and treatment withdrawal after 48 or 72 h if cerebrospinal fluid culture results are negative. However, this approach is not universally accepted and has not been assessed in clinical trials. METHODS We performed a cohort study of all patients who received a diagnosis of postoperative meningitis from January 1998 through May 2005 in a teaching hospital. From January 1998 through September 2003 (control period), guidelines were lacking or were not implemented. From October 2003 through May 2005 (interventional period), all patients received a predefined intravenous antibiotic therapy that was discontinued on the third day if the meningitis was considered aseptic. Clinical outcome and duration of antibiotic therapy were analyzed for each patient. RESULTS Seventy-five episodes of postoperative meningitis (21 cases of bacterial meningitis and 54 cases of aseptic meningitis) were investigated. Patients with aseptic meningitis received antibiotic treatment for a mean +/- standard deviation duration of 11+/-5 days during the control period and 3.5+/-2 days during the intervention period (P=.001). The duration of antibiotic treatment for bacterial meningitis was not significantly different between the 2 periods. All episodes of bacterial and aseptic meningitis were cured, and complications were rare during both periods. CONCLUSIONS Stopping antibiotic treatment after 3 days is effective and safe for patients with postoperative meningitis whose cerebrospinal fluid culture results are negative.

Conservative management versus surgery for small vestibular schwannomas

Conclusion A high rate of deterioration in hearing function and the loss of patient compliance during conservative management should be taken into account when considering hearing preservation strategies for patients with vestibular schwannoma (VS). Objective To compare conservative management with surgery for solitary small VS. Material and methods Among 693 patients followed up for VS between 1991 and 2002, 114 (16%) intracanalicular VSs (stage 1) and 302 (44%) VSs measuring <15 mm in the cerebellopontine angle (stage 2) were included in this study. Initially, surgery was performed in 305 (73%) cases (50 stage 1, 255 stage 2) and 111 (27%) were managed conservatively (64 stage 1, 54 stage 2) by means of annual MRI scans and audiometry. Conservative management was chosen in patients aged >60 years and in those who refused surgery. In this subgroup, the mean follow-up period was 33 months (range 6–111 months). Results In the conservative management group, 47% of VSs showed significant growth, 47% were stable and 6% showed regression. Seventeen patients (15%) were operated on secondarily for tumour growth and 1 (1%) was irradiated for tumour growth and because surgery was contraindicated. Deterioration of hearing function by ≥1 class was observed in 56% of cases, 34% of patients were initially in hearing class D and only 10% showed stable hearing function. Of the conservative management group, 17% were lost during follow-up. After surgery, grade 1 or 2 facial function was obtained in 86% of cases. Following hearing preservation attempts (n=137), 54% of patients were in hearing classes A–C.

Consensus Recommendations to Accelerate Clinical Trials for Neurofibromatosis Type 2

Purpose: Neurofibromatosis type 2 (NF2) is a rare autosomal dominant disorder associated primarily with bilateral schwannomas seen on the superior vestibular branches of the eighth cranial nerves. Significant morbidity can result from surgical treatment of these tumors. Meningiomas, ependymomas, and other benign central nervous system tumors are also common in NF2. The lack of effective treatments for NF2 marks an unmet medical need. Experimental Design: Here, we provide recommendations from a workshop, cochaired by Drs. D. Gareth Evans and Marco Giovannini, of 36 international researchers, physicians, representatives of the biotechnology industry, and patient advocates on how to accelerate progress toward NF2 clinical trials. Results: Workshop participants reached a consensus that, based on current knowledge, the time is right to plan and implement NF2 clinical trials. Obstacles impeding NF2 clinical trials and how to address them were discussed, as well as the candidate therapeutic pipeline for NF2. Conclusions: Both phase 0 and phase II NF2 trials are near-term options for NF2 clinical trials. The number of NF2 patients in the population remains limited, and successful recruitment will require ongoing collaboration efforts between NF2 clinics. (Clin Cancer Res 2009;15(16):5032–9)