piperidines and Neurilemmoma

Neurofibromatosis Type II (NF2) is an autosomal dominant cancer predisposition syndrome in which germline haploinsufficiency at the NF2 gene confers a greatly increased propensity for tumor development arising from tissues of neural crest derived origin. NF2 encodes the tumor suppressor, Merlin, and its biochemical function is incompletely understood. One well-established function of Merlin is as a negative regulator of group A serine/threonine p21-activated kinases (PAKs). In these studies we explore the role of PAK1 and its closely related paralog, PAK2, both pharmacologically and genetically, in Merlin-deficient Schwann cells and in a genetically engineered mouse model (GEMM) that develops spontaneous vestibular and spinal schwannomas. We demonstrate that PAK1 and PAK2 are both hyper activated in Merlin-deficient murine schwannomas. In preclinical trials, a pan Group A PAK inhibitor, FRAX-1036, transiently reduced PAK1 and PAK2 phosphorylation in vitro, but had insignificant efficacy in vivo. NVS-PAK1-1, a PAK1 selective inhibitor, had a greater but still minimal effect on our GEMM phenotype. However, genetic ablation of Pak1 but not Pak2 reduced tumor formation in our NF2 GEMM. Moreover, germline genetic deletion of Pak1 was well tolerated, while conditional deletion of Pak2 in Schwann cells resulted in significant morbidity and mortality. These data support the further development of PAK1-specific small molecule inhibitors and the therapeutic targeting of PAK1 in vestibular schwannomas and argue against PAK1 and PAK2 existing as functionally redundant protein isoforms in Schwann cells.

Topics: Animals; Cell Proliferation; Cell Survival; Disease Models, Animal; Genes, Tumor Suppressor; Indoles; Longevity; Mice; Neurilemmoma; Neurofibromatosis 2; Neurofibromin 2; p21-Activated Kinases; Phosphorylation; Piperidines; Pyrimidines; Schwann Cells

Patients with bilateral vestibular schwannomas associated with neurofibromatosis type 2 (NF2) experience significant morbidity such as complete hearing loss. We have recently shown that treatment with bevacizumab provided tumor stabilization and hearing recovery in a subset of NF2 patients with progressive disease. In the current study, we used two animal models to identify the mechanism of action of anti-vascular endothelial growth factor (VEGF) therapy in schwannomas. The human HEI193 and murine Nf2(-/-) cell lines were implanted between the pia and arachnoid meninges as well as in the sciatic nerve to mimic central and peripheral schwannomas. Mice were treated with bevacizumab (10 mg/kg/wk i.v.) or vandetanib (50 mg/kg/d orally) to block the VEGF pathway. Using intravital and confocal microscopy, together with whole-body imaging, we measured tumor growth delay, survival rate, as well as blood vessel structure and function at regular intervals. In both models, tumor vessel diameter, length/surface area density, and permeability were significantly reduced after treatment. After 2 weeks of treatment, necrosis in HEI193 tumors and apoptosis in Nf2(-/-) tumors were significantly increased, and the tumor growth rate decreased by an average of 50%. The survival of mice bearing intracranial schwannomas was extended by at least 50%. This study shows that anti-VEGF therapy normalizes the vasculature of schwannoma xenografts in nude mice and successfully controls the tumor growth, probably by reestablishing a natural balance between VEGF and semaphorin 3 signaling.

Topics: Angiogenesis Inhibitors; Animals; Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Bevacizumab; Brain Neoplasms; Cell Growth Processes; Cell Line, Tumor; Humans; Mice; Mice, Nude; Neovascularization, Pathologic; Neurilemmoma; Neurofibromatosis 2; Neurofibromin 2; Piperidines; Quinazolines; Vascular Endothelial Growth Factor A

Topics: Adult; Amides; Analgesia, Epidural; Anesthesia, Epidural; Anesthesia, Inhalation; Atracurium; Brachial Plexus; Brachial Plexus Neuropathies; Desflurane; Female; Fentanyl; Humans; Isoflurane; Magnetic Resonance Imaging; Midazolam; Neurilemmoma; Neuromuscular Nondepolarizing Agents; Peripheral Nervous System Neoplasms; Piperidines; Propofol; Remifentanil; Ropivacaine