Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. I. Light microscopy observations

Lucien J. Rubinstein: enduring contributions to neuro-oncology

Dr. Lucien Rubinstein is best remembered for his significant contributions to the field of neuropathology, particularly in the classification of nervous system tumors. His accomplishments in basic neuro-oncology and in the formulation of diagnostic principles reflected a unique talent for synthesizing fundamental clinicopathological concepts based on skillful diagnostic investigation and a thorough understanding of neurobiology. Dr. Rubinstein was the leader in the establishment of cell cultures from central nervous system (CNS) tumors. He meticulously analyzed both light and electron microscopic features of CNS tumors, recorded his findings, and patiently drew sketches to be shared generously with his colleagues and students. As a pioneer in neuropathology, in his work Dr. Rubinstein set the foundation for many enduring concepts in neurosurgery, neuro-oncology, neurology, and basic tumor biology.

Tumor suppressor mutations and growth factor signaling in the pathogenesis of NF1-associated peripheral nerve sheath tumors: II. The role of dysregulated growth factor signaling

Patients with neurofibromatosis type 1 (NF1), one of the most common genetic disease affecting the nervous system, develop multiple neurofibromas that can transform into aggressive sarcomas known as malignant peripheral nerve sheath tumors (MPNSTs). Studies of human tumors and newly developed transgenic mouse models indicate that Schwann cells are the primary neoplastic cell type in neurofibromas and MPNSTs and that development of these peripheral nerve sheath tumors involves mutations of multiple tumor suppressor genes. However, it is widely held that tumor suppressor mutations alone are not sufficient to induce peripheral nerve sheath tumor formation and that dysregulated growth factor signaling cooperates with these mutations to promote neurofibroma and MPNST tumorigenesis. In Part I of this review, we discussed findings demonstrating that a loss of NF1 tumor suppressor gene function in neoplastic Schwann cells is a key early step in neurofibroma formation and that progression from neurofibroma to MPNST is associated with abnormalities of additional tumor suppressor genes, including p53, INK4A, andp27(kip1). In Part II of this review, we consider evidence that dysregulated signaling by specific growth factors and growth factor receptors promotes the proliferation, migration, and survival of neoplastic Schwann cells in neurofibromas and MPNSTs.

Constitutive activation of the neuregulin-1/ErbB receptor signaling pathway is essential for the proliferation of a neoplastic Schwann cell line

Neuregulin-1 (NRG-1) proteins promote Schwann cell survival, differentiation and proliferation during development. High levels of an NRG-like activity are also present in some human peripheral nerve sheath tumors, suggesting that NRG-1 isoforms may be involved in the development of these neoplasms. We examined the expression of NRG-1 and its receptors, the erbB membrane tyrosine kinases, in JS1 cells, a rapidly proliferating line derived from a chemically induced rat malignant peripheral nerve sheath tumor (MPNST). Relative to nontransformed Schwann cells, JS1 cells overexpress the NRG-1 receptor erbB3 and its erbB2 coreceptor; JS1 erbB2 transcripts show no evidence of the activating mutation commonly found in N-ethyl-N-nitrosourea-induced neoplasms. JS1 cells do not express the epidermal growth factor receptor (EGFR), a kinase implicated in the pathogenesis of a major subset of MPNSTs. JS1 cells also express mRNAs encoding multiple alpha and beta isoforms from the glial growth factor and sensory and motor neuron-derived factor NRG-1 subfamilies. Stimulation with NRG-1beta in the presence of forskolin produces a dose-dependent increase in JS1 DNA synthesis. Even in unstimulated JS1 cells, however, erbB2 and erbB3 are constitutively tyrosine phosphorylated. Reducing this constitutive phosphorylation with the specific erbB inhibitor PD158780 markedly impairs JS1 DNA synthesis. These observations support the hypothesis that NRG-1 isoforms and erbB kinases act in an autocrine and/or paracrine fashion to promote mitogenesis in JS1 cells. The absence of EGFR expression in JS1 cells suggests that constitutive activation of the NRG-1/erbB signaling pathway is an alternative means of inducing Schwann cell neoplasia.

Immortalized rat Schwann cells produce tumours in vivo

We have recently reported the immortalization of primary Schwann cells isolated from sciatic nerves of normal neonatal rats. The cells were maintained under continuous mitogenic stimulation with glial growth factor and forskolin, achieving immortalization after 12 to 15 weeks without the use of viral infection, oncogene transformation or chemical carcinogens. The immortalized cells (1.17 cells) initially retain the capability to recognize and attach to peripheral neurons in culture as well as the ability to myelinate those neurons. The functional capacity of the cells gradually diminishes in culture, such that late passage cells can ensheath neurons but cannot form a myelin sheath. Both normal and immortalized cells secrete comparable amounts of autocrine growth factor activity in culture that can be regulated by extracellular matrix proteins. The difference between quiescent and immortalized Schwann cells seems to lie not in the production of growth factor but rather in the relative ability to respond to the factor(s). To test the potential of the immortalized Schwann cells for the ability to form tumours in vivo, we injected equal numbers of primary or immortalized Schwann cells into the sciatic nerve of adult syngenic rats and allowed them to incubate there for 6 to 13 weeks, whereupon the injected nerves were inspected for tumour formation. In every case (N = 3) the primary cells had no effect whereas every injection of immortalized cells (N = 5) resulted in a solid cellular mass surrounding the injected nerve. The tumours were encapsulated masses of actively dividing Schwann-like cells that surrounded but did not invade the nerve fascicle.(ABSTRACT TRUNCATED AT 250 WORDS)

Juxtadrenal schwannoma: verification of the diagnosis by immunohistochemical and ultrastructural studies

Solitary schwannomas arising in the juxtadrenal region are exceedingly rare. A middle-aged woman with a confusing clinical course was found to have a solid periadrenal mass, which was surgically excised. The gross and light microscopic appearance of the tumor was suggestive but not diagnostic of this entity. However, electron microscopic evaluation of the neoplasm revealed prominent basal lamina and interdigitating cellular processes characteristic of a schwannoma. The diagnosis of schwannoma was further supported by the demonstration of S-100 protein, type IV (basement membrane) collagen, and laminin immunoreactivity by immunohistochemical techniques. The use of these special studies to arrive at the diagnosis in this case and in the larger context in the diagnosis of rare adrenal and periadrenal tumors of uncertain origin is fully discussed.

Immunohistochemical recognition of human nerve sheath tumors by anti-Leu 7 (HNK-1) monoclonal antibody

Using relatively high dilutions of anti-Leu 7 monoclonal antibody and a four-step peroxidase-antiperoxidase (PAP) reaction in paraffin-embedded tissues, we tested the affinity of this antibody to the cells of 47 human nerve sheath tumors and 22 other tumors in which the differential diagnosis with nerve sheath neoplasms is known to arise. Of all the nerve sheath tumors studied 68%, including 80% of the schwannomas, contained anti-Leu 7-positive cells. All 22 non-schwannian neoplasms were entirely negative. Specimens of eight experimental malignant rat schwannomas were also negative for anti-Leu 7 antibody. Our findings suggest that anti-Leu 7 monoclonal antibody is a promising marker that may facilitate the differential diagnosis between human Schwann cell and non-Schwann cell neoplasms.

Neurogenic sarcomas of the neck in neurofibromatosis

Based on two observations and a review of the literature, the pathological and clinical findings in sarcomas of the neck in patients with neurofibromatosis are described. Histologically these neurogenic tumours show a manifold picture; in addition to spindle-cell sarcomas pleomorphic structures are to be found, which can be similar to rhabdomyo-, lipo-, chondro-, angio-, or osteogenic sarcomas so that a histological diagnosis of a neurogenic sarcoma cannot always be made without clinical details. Up to the present surgical treatment is preferred; the value of cytostatic therapy and irradiation is controversial. The results of treating these tumours are unsatisfactory. Of 29 cases reported in the literature, only two could be found in which the patient survived without a recurrence for more than five years.

Collagen synthesis in cells cultured from v. Recklinghausen's neurofibromatosis

Subcutaneous tumors of a patient with v. Recklinghausen's neurofibromatosis contained about 31% collagen calculated on the basis of lipid-free dry weight. Slices of the tumors synthesized collagen at a rate (4.7-8.5% from total protein) which was higher than that of the skin slices (2.8-5.9%). Neurofibromatosis cells were cultured from tumors of two patients. They synthesized relatively much more collagen than cultures of skin fibroblasts of the same patient or of healthy age-matched control persons. The second patient's cultures were studied in detail. The cell densities of these cultures were higher and expressed more variation than the densities of control skin fibroblasts. Ion exchange cellulose chromatograms, SDS-polyacrylamide gel electrophoresis and 3-hydroxyproline analysis of the radioactive proteins made by the cultures indicate that most of the collagenous proteins resembled type I collagen. High proliferative capacity and high collagen synthesis of selected neurofibromatosis cells explains the growth of solid tumors.

Malignant tumors of nerve sheath origin

A clinicopathologic study of malignant nerve sheath tumors diagnosed between 1962 and 1979 at the Massachusetts General Hospital was undertaken. During this 17-year period, 24 patients with such a neoplasm were seen while 607 patients were treated for schwannoma or neurofibroma. Criteria were developed for establishing the nerve sheath origin and malignancy of a given neoplasm which allowed a secure diagnosis of malignant nerve sheath tumor to be made in 11 of the 24 cases. In 7 of the remaining cases, the malignant tumors were of uncertain histogenesis and in 6 cases, a new diagnosis was made. The malignant tumors constituted 2% of all neoplasms of the nerve sheath origin diagnosed during this period. An attempt was made to grade these neoplasms, but clinical and histologic parameters were only approximately predictive of their behavior. The treatment and survival or the 11 patients with malignant nerve sheath tumors and the 7 with malignant neoplasms of uncertain histogenesis are detailed and compared. In the former group, 4 patients died within four and a half years and there were eight recurrences in 4 patients. In the latter group, 4 died within three and a half years and there were five recurrences in 3 patients.

Scanning electron microscopy of in vitro grown cells from experimentally induced neurogenic tumors

Serially transplanted neurogenic tumors of experimental origin were explanted in vitro and analyzed by scanning electron microscopy. In explants of intracerebrally transplanted gliomas, small stellate cells with branching processes were observed; in transplanted tumors of the peripheral nervous system, slender bipolar cells as well as fibroblasts emerged. The stereoscopic features were compared with the picture of conventional light microscopy. The findings are consistent with the assumption of the glial derivation of CNS-tumors induced with neurotropic alkylating carcinogens. The peripheral tumors are composed of Schwann-cell like elements and fibroblasts. The significance of the results for the cytogenetic derivation of brain tumors are discussed.

The nature of macrophages (foam cells) in neurinomas. Tissue culture study

Fourteen cases of neurinomas of variable location are studied by tissue culture technic in an attempt to typify the foam cells as primary or superimposed elements in the tumor population. Our results demonstrate that the "in vitro" behavior of the neurinomas is constant and characteristic and that three cell types are found in them: fusiform, star-shaped cells and macrophages. There appears that the macrophage is an evolutive aspect of the star-shaped cells and probably of the fusiform one. On this basis, macrophage and foam cells of neurinomas must be considered as primary.

Bovine normal peripheral nerve and nerve sheath tumour in explant culture

When bovine normal nerve and nerve sheath tumours were cultured using explant techniques, the same morphological cell types were seen:thin bipolar cells with bulging nuclei;found refractile cells; large quadrangular cells; variable polar, wide-processed cells. However, differences in the pattern of cell growth and the proportions of morphological cell types occurred between normal and tumour nerve. The bovine nerve sheath tumours cultured showed a range of histological areas which did not appear to affect the pattern of cell growth in culture or the cell types present. Antoni type A tissue was prominent in many explant blocks and probably gave rise to most cell growth. On comparison with human schwannomas maintained in explant culture, bovine nerve sheath tumours appeared to have a similar range of morphological cell types. Although suggestions for the origin of human schwannomas have been made on the basis of cell morphology, it was felt that morphology alone did not allow speculation on the origin of cells present in bovine nerve sheath tumour explant cell growth.

Central neurofibromas in two dogs

Two dogs each had a fibrous tumor of the central nervous system. One tumor involved the spinal cord and ventral nerve root, and the other involved the midbrain and posterior brain stem. Both tumors had spindle-shaped cells arranged in rhythmic patterns. There was perivascular tumor cell infiltration in the adjacent parenchyma. The tumor cells strongly resembled fibroblasts and seemed to produce collagen. Because both tumors were near nerve roots and because their histological appearances were characteristic of nerve sheath tumors they were classified as central neurofibromas.

Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. III. Melanin pigment and melanogenesis in experimental neurogenic tumors: a reappraisal of the histogenesis of pigmented nerve sheath tumors

Four melanin pigment-containing intracranial tumors were found in three Long-Evans rats in the course of experimental oncogenesis by transplacental ethylnitrosourea (ENU). One of them was a leptomeningeal melanoma. Aside from the presence of scattered melanin-pigmented cells, the other three had the typical histological features of ENU-induced malignant nerve sheath tumors. Two of the three tumors were studied by electron microscopy and in tissue and organ culture systems. One of them demonstrated progressive melanogenesis in vitro; the other failed to produce more melanin and showed increasing differentiation, with a Schwannoma-like pattern by light microscopy. Melanosomes and premelanosomes were identified in both tumors by electron microscopy; the other fine structural features were those of malignant Schwannomas. These observations are relevant to the controversy on the histogenesis of pigmented nerve sheath tumors occasionally encountered in man and on the relationship of these tumors to pigmented nevi. The findings in the present study support the view of Masson that neoplastic nerve sheath cells are capable of melanogenesis.

Studies on experimental malignant nerve sheath tumors maintained in tissue and organ culture systems. II. Electron microscopy observations

The sequential electron microscopic features of six malignant nerve sheath tumors (three cranial and three spinal) induced in rats by transplacental ethylnitrosourea and maintained in organ culture systems were compared with those of a human acoustic Schwannoma similarly cultured. After 4 weeks in vitro, the malignant tumor cells often showed progressive elongation of their processes, with the development of an interdigitating pattern resembling that seen in well-differentiated Schwannomas. This was accompanied by an increase of microtubules. Basal lamina formation, less well-developed and less complete than in the benign Schwannoma in this study, was maintained in culture. Some explants demonstrated an increase in number and width of collagen fibrils, accompanied by a relative concomitant decrease of inter-cellular basement membrane material. The malignant tumor cells also showed numerous micropinocytotic vesicles and various junctional complexes, which are characteristic of perineurial cells. Since the origin of the experimental tumors from adult Schwann cells seems well established, this apparent contradiction is best resolved by the concept that Schwann cells and perineurial fibroblasts are functional variants of the same cell type.