Advances in neurofibromatosis 2 (NF2): a workshop report

The efficacy of lapatinib and nilotinib in combination with radiation therapy in a model of NF2 associated peripheral schwannoma

Neurofibromatosis type 2 (NF2), a neurogenetic condition manifest by peripheral nerve sheath tumors (PNST) throughout the neuroaxis for which there are no approved therapies. In vitro and in vivo studies presented here examine agents targeting signaling pathways, angiogenesis, and DNA repair mechanisms. In vitro dose response assays demonstrated potent activity of lapatinib and nilotinib against the mouse schwannoma SC4 (Nf2 ^-/-) cell line. We then examined the efficacy of everolimus, nilotinib, lapatinib, bevacizumab and radiation (RT) as mono- and combination therapies in flank and sciatic nerve in vivo NF2-PNST models. Data were analyzed using generalized linear models, two sample T-tests and paired T-tests, and linear regression models. SC4(Nf2 ^-/-) cells implanted in the flank or sciatic nerve showed similar rates of growth (p = 0.9748). Lapatinib, nilotinib and RT significantly reduced tumor growth rate versus controls in the in vivo flank model (p = 0.0025, 0.0062, and 0.009, respectively) whereas bevacizumab and everolimus did not. The best performers were tested in the in vivo sciatic nerve model of NF2 associated PNST, where chemoradiation outperformed nilotinib or lapatinib as single agents (nilotinib vs. nilotinib + RT, p = 0.0001; lapatinib versus lapatinib + RT, p < 0.0001) with no observed toxicity. There was no re-growth of tumors even 14 days after treatment was stopped. The combination of either lapatinib or nilotinib with RT resulted in greater delays in tumor growth rate than any modality alone. This data suggest that concurrent low dose RT and targeted therapy may have a role in addressing progressive PNST in patients with NF2.

Biologic and genetic characterization of the novel amyloidogenic lambda light chain-secreting human cell lines, ALMC-1 and ALMC-2

Primary systemic amyloidosis (AL) is a rare monoclonal plasma cell (PC) disorder characterized by the deposition of misfolded immunoglobulin (Ig) light chains (LC) in vital organs throughout the body. To our knowledge, no cell lines have ever been established from AL patients. Here we describe the establishment of the ALMC-1 and ALMC-2 cell lines from an AL patient. Both cell lines exhibit a PC phenotype and display cytokine-dependent growth. Using a comprehensive genetic approach, we established the genetic relationship between the cell lines and the primary patient cells, and we were also able to identify new genetic changes accompanying tumor progression that may explain the natural history of this patient's disease. Importantly, we demonstrate that free lambda LC secreted by both cell lines contained a beta structure and formed amyloid fibrils. Despite absolute Ig LC variable gene sequence identity, the proteins show differences in amyloid formation kinetics that are abolished by the presence of Na(2)SO(4). The formation of amyloid fibrils from these naturally secreting human LC cell lines is unprecedented. Moreover, these cell lines will provide an invaluable tool to better understand AL, from the combined perspectives of amyloidogenic protein structure and amyloid formation, genetics, and cell biology.

Distribution of nonvestibular cranial nerve schwannomas in neurofibromatosis 2

OBJECTIVE

To describe the prevalence and location of cranial nerve schwannomas, other than bilateral vestibular schwannoma, in patients with neurofibromatosis 2 (NF2). The NF2 Natural History Consortium prospectively gathered cranial magnetic resonance imaging for 83 patients across 3 annual evaluations. The time between the first and last evaluation was approximately 3 years.

RESULTS

Forty-two patients (51%) had nonvestibular cranial nerve schwannomas (NVSs). Of these, 25 (60%) also had cranial meningiomas. Twenty-one of those without NVS (25% of 83) had at least 1 meningioma. The average size of the NVS was 0.4 cubic centimeters. Overall, there was no significant change in NVS size from Year 1 to Year 3 or from Year 1 to Year 2. The most common locations of the NVS were occulomotor and trigeminal. A family history of NF2 did not predict NVS location or growth.

CONCLUSION

Nonvestibular cranial nerve schwannoma usually affect cranial nerves III and V, as was the case in our NF2 sample. Fortunately, neuropathies associated with these tumors are rare. In contrast, lower cranial nerve schwannomas, although also rare, are associated with swallowing difficulty, aspiration, and other sequelae.

Hearing preservation surgery for neurofibromatosis Type 2–related vestibular schwannoma in pediatric patients

OBJECT

The authors reviewed the proportion of pediatric patients with neurofibromatosis Type 2 (NF2) in whom hearing was preserved after middle fossa resection of vestibular schwannoma (VS).

METHODS

In this retrospective chart review the authors examined the cases of 35 children with NF2 who had undergone middle fossa resection (47 surgeries) between 1992 and 2004 in a neurotological tertiary care center. Surgical outcome was assessed using pure-tone average (PTA) thresholds obtained before and immediately after resection. Speech discrimination scores (SDSs) and pre- and postfacial nerve grades were also recorded. In 55% of surgeries, hearing of less than or equal to 70 dB PTA was maintained postoperatively. The American Academy of Otolaryngology-Head and Neck Surgery Class A hearing (PTA < or = 30 dB and SDS > or = 70%) was preserved in 47.7%. Facial nerve function was good (House-Brackmann Grades I or II) in 81% of the patients. Twelve patients had bilateral middle fossa resections; in nine (75%) of these patients hearing was maintained postoperatively in both ears.

CONCLUSIONS

More than half of the children with NF2 in the authors' cohort experienced hearing preservation after middle fossa resection was performed for VS. The authors recommend this approach for preserving hearing in children with NF2.

Purification of the NF2 tumor suppressor protein from human erythrocytes

BACKGROUND

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease predisposing individuals to the risk of developing tumors of cranial and spinal nerves. The NF2 tumor suppressor protein, known as Merlin/Schwanomin, is a member of the protein 4.1 superfamily that function as links between the cytoskeleton and the plasma membrane.

METHODS

Upon selective extraction of membrane-associated proteins from erythrocyte plasma membrane (ghosts) using low ionic strength solution, the bulk of NF2 protein remains associated with the spectrin-actin depleted inside-out-vesicles. Western blot analysis showed a approximately 70 kDa polypeptide in the erythrocyte plasma membrane. Furthermore, quantitative removal of NF2 protein from the inside-out-vesicles was achieved using 1.0 M potassium iodide, a treatment known to remove tightly-bound peripheral membrane proteins.

RESULTS

These results suggest a novel mode of NF2 protein association with the erythrocyte membrane that is distinct from the known membrane interactions of protein 4.1. Based on these biochemical properties, several purification strategies were devised to isolate native NF2 protein from human erythrocyte ghosts. Using purified and recombinant NF2 protein as internal standards, we quantified approximately 41-65,000 molecules of NF2 protein per erythrocyte.

CONCLUSION

We provide evidence for the presence of NF2 protein in the human erythrocyte membrane. The identification of NF2 protein in the human erythrocyte membrane will make it feasible to discover novel interactions of NF2 protein utilizing powerful techniques of erythrocyte biochemistry and genetics in mammalian cells.

Tumors of the peripheral nerves and plexuses

Peripheral nerve tumors are a diverse group of lesions histologically and in their clinical behavior. The genetic disorders neurofibromatosis type 1 and 2 and schwannomatosis are significant risk factors for the development of peripheral nerve tumors. An understanding of these disorders is important in allowing appropriate management. Active treatment of peripheral nerve tumors is reserved for lesions that are malignant or causing neurologic dysfunction, pain, compressive symptomatology, or cosmetic concern. The mainstay of treatment is surgical intervention, the nature of which will vary with the type of tumor and anatomical location. In the case of malignant tumors, adjuvant chemotherapy and radiotherapy are commonly used. Developments in the understanding of the genetics and molecular biology of peripheral nerve tumors are opening up potentially exciting new avenues of treatment. The prognosis of benign peripheral nerve tumors is excellent, with a recurrence rate of just 5% or less after successful surgery. Malignant tumors have proven to be more challenging, with a much higher recurrence rate and a 5-year survival rate of 64%.

Merlin/NF-2 mediates contact inhibition of growth by suppressing recruitment of Rac to the plasma membrane

Introduction of activated p21-activated kinase (PAK) is sufficient to release primary endothelial cells from contact inhibition of growth. Confluent cells display deficient activation of PAK and translocation of Rac to the plasma membrane at matrix adhesions. Targeting Rac to the plasma membrane rescues these cells from contact inhibition. PAK's ability to release human umbilical vein endothelial cells from contact inhibition is blocked by an unphosphorylatable form of its target Merlin, suggesting that PAK promotes mitogenesis by phosphorylating, and thus inactivating, Merlin. Merlin mutants, which are presumed to exert a dominant-negative effect, enable recruitment of Rac to matrix adhesions and promote mitogenesis in confluent cells. Small interference RNA–mediated knockdown of Merlin exerts the same effects. Dominant-negative Rac blocks PAK-mediated release from contact inhibition, implying that PAK functions upstream of Rac in this signaling pathway. These results provide a framework for understanding the tumor suppressor function of Merlin and indicate that Merlin mediates contact inhibition of growth by suppressing recruitment of Rac to matrix adhesions.

Vestibular schwannoma growth rates in neurofibromatosis type 2 natural history consortium subjects

OBJECTIVE

To determine the amount of growth in vestibular schwannomas in Neurofibromatosis type 2 (NF2) patients from diagnosis through short-term (up to 2 yr) and long-term (up to 4 yr) follow-up.

STUDY DESIGN

Retrospective magnetic resonance imaging (MRI) films were obtained on subjects enrolled in the NF2 Natural History study and examined for changes in vestibular schwannoma size over time.

SETTING

Data were collected from nine foreign and domestic NF2 centers, including hospital-based, academic, and tertiary care centers.

SUBJECTS

NF2 patients with MRI data and at least one follow-up examination within 9 months to 2 years of diagnosis were included; n=56 patients with 84 lesions for evaluation of growth.

INTERVENTION

Routine, clinically obtained, magnetic resonance images were digitized and measured using image management software. Short-term follow-up was defined as up to 2 years (n=84 lesions), and long-term follow-up was defined as 3 to 4 years (n=29 lesions).

OUTCOME MEASURES

Vestibular schwannoma size was assessed using anterior-posterior, medial-lateral, and greatest diameter linear measurements.

RESULTS

Vestibular schwannomas increased in size (at least 5 mm) in 8% of the vestibular schwannomas across short-term follow-up. At long-term follow-up, 13% of the tumors had increased in size. On average, schwannomas increased in greatest diameter 1.3 mm per year across short-term follow-up.

CONCLUSION

Slightly greater than 1 in 10 diagnosed NF2-related vestibular schwannomas increased in size by at least 5 mm by 4 years of follow-up, if still untreated at that time.

The neurofibromatoses: hereditary predisposition to multiple peripheral nerve tumors

Neurosurgeons must be aware of the neuro-fibromatoses because they frequently present with nervous system tumors. Such patients develop numerous peripheral nerve sheath tumors; fortunately, only a few of these tumors are symptomatic or malignant. The tumor burden in individual patients can be remarkable, however, producing significant morbidity and requiring extensive or repeated care by a skilled neurosurgeon. Because it is impossible to predict which of the deep neurofibromas will undergo malignant transformation, it behooves clinicians and patients to be aware of any change in symptoms or growth of tumors, because early resection of MPNST offers the only chance for cure. Neurosurgical professionals should be familiar with the diagnostic criteria of the neurofibromatoses, because the patient who presents with an initial neurofibroma or schwannoma immediately falls into a category in which those disorders must be ruled out. In this regard, a family history of nerve sheath tumors is revealing and should prompt referral for a clinical genetics evaluation. Cutaneous manifestations of NFI can confirm the diagnosis at initial presentation. Missing the initial presentation of a patient with NF2 can lead to marked morbidity, such as deafness,because surveillance for subsequent tumors was inadequate. Tumorigenesis in all neurofibromatoses involves loss of tumor suppressor genes. These disorders illustrate that the two-hit loss of tumor suppressor gene model, which applies best for NF2, is oversimplified. As with most cancers,a theory of multistep progressive acquisition of genetic changes that promote unregulated grow this emerging in schwannomatosis. In addition, the hyperpigmentation and learning disability of NF 1 highlight that loss of one copy of the gene is sufficient to cause nontumoral manifestations of the disorder. Genetic counseling and testing have an important role in the diagnosis of NFI and NF2 as well as in the management of all the neurofibromatoses.