Expression of insulin-like growth factors I and II and their receptor mRNAs in primary human astrocytomas and meningiomas;in vivo studies usingin situ hybridization and immunocytochemistry

The effects of insulin-like growth factors on tumorigenesis and neoplastic growth

Several decades of basic and clinical research have demonstrated that there is an association between the insulin-like growth factors (IGFs) and neoplasia. We begin with a brief discussion of the function and regulation of expression of the IGFs, their receptors and the IGF-binding proteins (IGFBPs). A number of investigational interventional strategies targeting the GH or IGFs are then reviewed. Finally, we have assembled the available scientific knowledge about this relationship for each of the major tumor types. The tumors have been grouped together by organ system and for each of the major tumors, various key elements of the relationship between IGFs and tumor growth are discussed. Specifically these include the presence or absence of autocrine IGF-I and IGF-II production; presence or absence of IGF-I and IGF-II receptor expression; the expression and functions of the IGFBPs; in vitro and in vivo experiments involving therapeutic interventions; and available results from clinical trials evaluating the effect of GH/IGF axis down-regulation in various malignancies.

Combined activation of Ras and Akt in neural progenitors induces glioblastoma formation in mice

Gliomas are the most common primary malignant brain tumours and are classified into four clinical grades, with the most aggressive tumours being grade 4 astrocytomas (also known as glioblastoma multiforme; GBM). Frequent genetic alterations in GBMs (refs 2-5) result in stimulation of common signal transduction pathways involving Ras, Akt and other proteins. It is not known which of these pathways, if any, are sufficient to induce GBM formation. Here we transfer, in a tissue-specific manner, genes encoding activated forms of Ras and Akt to astrocytes and neural progenitors in mice. We found that although neither activated Ras nor Akt alone is sufficient to induce GBM formation, the combination of activated Ras and Akt induces high-grade gliomas with the histological features of human GBMs. These tumours appear to arise after gene transfer to neural progenitors, but not after transfer to differentiated astrocytes. Increased activity of RAS is found in many human GBMs (ref. 11), and we show here that Akt activity is increased in most of these tumours, implying that combined activation of these two pathways accurately models the biology of this disease.

Antagonists of growth hormone-releasing hormone inhibit the growth of U-87MG human glioblastoma in nude mice

Antagonists of growth hormone-releasing hormone(GH-RH)inhibit the growth of various cancers by mechanisms that involve the suppression of the insulin-like growth factor (IGF)-I and/or IGF-II. In view of the importance of the IGF system in glioma tumorigenesis, the effects of GH-RH antagonists MZ-5-156 and JV-1-36 were investigated in nude mice bearing subcutaneous and orthotopic xenografts of U-87MG human glioblastomas. After 4 weeks of therapy with MZ-5-156 or JV-1 -36 at the dose of 20 microg/day per animal, the final volume of subcutaneous U-87MG tumors was significantly (P < .01) decreased by 84% and 76%, respectively, as compared with controls. Treatment with GH-RH antagonists also reduced tumor weight and the levels of mRNA for IGF receptor type I (IGFR-I). A reduction in the mRNA levels for IGF-II was found in tumors of mice treated with MZ-5-156. Treatment with MZ-5-156 or JV-1 -36 also extended the survival of nude mice implanted orthotopically with U-87MG glioblastomas by 81% (P < .005) and 18%, respectively, as compared with the controls. Exposure in vitro to GH-RH antagonists MZ-5-156 or JV-1 -36 at 1 microM concentration for 24 hours decreased the tumorigenicity of U-87MG cells in nude mice by 10% to 30% and extended the latency period for the development of subcutaneous palpable tumors by 31% to 56%, as compared with the controls. Exposure of U-87MG cells to GH-RH antagonists in vitro also resulted in a time-dependent increase in the mRNA levels of IGFR-II or a decrease in the mRNA levels of IGFR-I. mRNA for GH-RH was detected in U-87MG cells and xenografts implying that GH-RH may play a role in the pathogenesis of this tumor. Our results suggest that GH-RH antagonists MZ-5-156 and JV-1-36 inhibit the growth of U-87MG human glioblastoma by mechanisms that involve the suppression of IGF system. Antagonistic analogs of GH-RH merit further development for the treatment of malignant glioblastoma.

Long-term follow up of progesterone receptor status in benign meningioma: a prognostic indicator of recurrence?

OBJECT

A long-term prospective analysis of patients with benign meningioma was undertaken to determine whether progesterone receptor (PR) status of the excised tumor has any influence on recurrence.

METHODS

Between 1983 and 1985, a total of 62 meningiomas in 53 patients (age range 19-79 years, mean age 55.6 years) were studied for clinical, histological, and pathological characteristics, including hormone receptor status and DNA features. Progesterone receptor status was quantified by cryostat section assay, and then factors affecting recurrence were analyzed. During 1997 all case records were reviewed to determine whether tumor had recurred in any patient, and PR status was correlated with tumor recurrence. Of the 62 tumors, 60 were benign, and of the benign tumors 29 (48%) were PR positive. Patients harboring 14 of the 60 benign tumors were lost to follow up. Of the 46 tumors included in the final analysis, 13 were recurrent (all within 5 years) and 33 were nonrecurrent. Of the 33 nonrecurrent tumors, 14 had not recurred 5 to 10 years postresection and 19 had not recurred after more than 10 years. Chi-square analysis of the results did not show an association between recurrence and patient's sex, extent of resection, histological subtype, or tumor site but did show an association between recurrence and PR negativity (p = 0.013).

CONCLUSIONS

The results indicate that benign meningiomas that are PR positive are less likely to recur, a finding that has prognostic and therapeutic implications.

Genomic imprinting of IGF2 and H19 in human meningiomas

A number of genes, including IGF2 and H19, are normally imprinted with preferential expression of the paternal or maternal allele, respectively. Loss of imprinting (LOI) of IGF2 and H19 is found in a number of tumours, suggesting that LOI of IGF2 and/or H19 may play an important role in tumorigenesis. The IGF2 gene codes for a fetal growth factor and the H19 gene is likely to act as an RNA with an antitumour effect. We investigated the imprinting status of IGF2 and H19 in human meningiomas. The normally imprinted IGF2 gene lacks imprint in the leptomeninges and choroid plexus of the brain. To examine the imprinting status of IGF2 and H19 in human meningiomas we used the ApaI polymorphism in exon 9 for the IGF2 gene and the AluI polymorphism in exon 5 for the H19 gene. In total, 24 meningiomas of WHO grade I, II and III were analysed. 15 meningiomas (63%) were informative for the ApaI polymorphism in the IGF2 gene. Monoallelic expression (MAE) for IGF2 was found in 11 out of 15 tumours (73%) which is in contrast to the lack of imprinting status of IGF2 in leptomeninges. Ten cases (42%) were heterozygous for the H19 gene and biallelic expression was found in 3 out of 10 meningiomas (30%). These results indicate that modulation of the imprinting status of IGF2 and H19 may play an important role for the development of meningiomas.

Intracranial malignant meningioma with abdominal metastases associated with hypoglycemic shock: a case report

A thirty-year-old male with an intracranial malignant meningioma, first diagnosed 9 years ago, with three recurrences was admitted with a hypoglycemic shock. The blood glucose level was 17 mg/dl, requiring treatment with high doses of intravenous and oral dextrose for improvement. A large metastatic tumor in the liver was noted. All hormones and peptides influencing blood glucose levels were in their normal levels. Chemo-embolization and injection of anti-cancer drugs was employed in the management of the metastatic tumor. Positron emission tomography was performed to measure the glucose metabolism of the abdominal tumor and it indicated that glucose consumption within the tumor was much elevated than the surrounding abdominal organs. Hypoglycemia secondary to primary hepatoma or islet-cell cancer has been frequently described, but a complication of metastatic meningioma is an exceedingly rare event. Elevated glucose consumption within the tumor might be addressed as one of the reasons for hypoglycemia, not due to the elevated serum levels of insulin or IGF, but due to the closely related blood glucose level.

Current perspectives in immunotherapy

Since the declaration of the war on cancer in 1971, our ability to effectively treat cancer has been less successful than anticipated. Surgery and radiation therapy remain our most effective treatment modalities, with chemotherapy proving beneficial in only a limited number of tumor types. The reality of this poor response to conventional therapy has prompted a search for other potentially beneficial therapies. The idea of using the immune system to eradicate tumor is not new. Over 100 years ago, William Coley (in 1893) first reported on the ability to induce tumor regressions by nonspecific activation of the immune system in response to bacterial toxins. Despite this early beginning, efforts to reliably manipulate the immune system to promote tumor regression has been universally disappointing. With recent advances in our understanding of the immune system, and the identification and availability of numerous growth promoting and growth-suppression cytokines, the concept of immunotherapy being a useful therapeutic intervention for the treatment of cancer is becoming a reality. Immunology in general, and tumor immunology specifically, are fields foreign to the practicing tumor surgeon. As progress in these fields are made, it will become important for the surgical oncologist to have a better understanding of tumor immunology as it relates to therapy. This paper reviews our current understanding of the immune system as it relates to cancer immunotherapy (using primary intracranial glioma as the tumor model), and then relates this knowledge to recent work in the development of tumor-specific vaccines.

Growth hormone receptor expression and function in meningiomas: effect of a specific receptor antagonist

OBJECT

This study was undertaken to explore the effects of growth hormone (GH) and the GH-stimulated peptide insulin-like growth factor-1 (IGF-1) on the growth rate of meningiomas.

METHODS

Polymerase chain reaction and ribonuclease protection assays were used to demonstrate that GH receptor messenger RNA was present in all 14 meningioma specimens studied, regardless of tumor grade. Both wild type (GHRwt) and a previously described exon 3 deletion isoform (GHRd3) of the GH receptor were identified in individual tumor specimens. The importance of the GH receptor was assessed using a GH receptor antagonist (B2036). Blockade of the GH receptor with B2036 reduced serum-induced DNA synthesis, as measured by thymidine incorporation, by 8 to 33% (mean 20%) in primary meningioma cultures. Tumors that expressed the GHRwt and GHRd3 isoforms, or a combination of the two, were all responsive to antagonist treatment. The importance of IGF- in stimulating meningioma cell growth was also assessed. It was found that IGF-1 increased thymidine incorporation in primary meningioma cultures in a dose-dependent manner: 1 ng/ml, 5 ng/ml, and 10 ng/ml resulted in increases in thymidine incorporation of 21%, 43%, and 176%, respectively, over baseline values.

CONCLUSIONS

In these studies the authors demonstrate that activation of the GH/IGF-1 axis significantly increases the growth rate of meningiomas. Blockade of the GH receptor on tumor cells inhibited tumor growth. If these findings are confirmed in animal studies, agents that downregulate the GH/IGF-1 axis might represent a potential adjuvant therapy in the management of patients with meningioma.

Formation of autocrine loops in human cerebral meningioma tissue by leukemia inhibitor factor, interleukin-6, and oncostatin M: inhibition of meningioma cell growth in vitro by recombinant oncostatin M

OBJECT

It has been demonstrated that growth of cerebral meningiomas found in humans is controlled by a variety of factors, including growth factors, aminergic agents, neuropeptides, and steroids. To further our knowledge of this process, the authors investigated the presence and function of the cytokines leukemia inhibitory factor (LIF), interleukin-6 (IL-6), and oncostatin M (OSM) on meningioma cell proliferation.

METHODS

Active transcription of LIF, IL-6, and OSM, their related receptors (LIF-R, IL-6-R, and gp130), and the consecutive signal-transducing molecules (STAT 1, STAT 3, and STAT 5a) were analyzed in reverse transcriptase-polymerase chain reaction experiments. The presence of endogenous LIF, IL-6, and OSM proteins was demonstrated in the supernatant of cultured meningioma cells using the enzyme-linked immunosorbent assay and Western blot experiments, thus indicating an autocrine signaling pathway for all three cytokines. The biological function of all three cytokines was evaluated by studying their effects on meningioma cell growth. Recombinant LIF and IL-6 showed no significant growth modulating effects; however, recombinant OSM decreased meningioma cell growth by 66%. The antiproliferative potency of OSM was demonstrated by cell count experiments, the [3H]thymidine incorporation assay, and cell cycle analysis.

CONCLUSIONS

These in vitro data support the concept that growth of meningioma cells may be modulated by cytokines, and they also indicate that recombinant OSM may be one future candidate for use in the adjuvant treatment of inoperable and recurrent meningiomas.

Familial meningioma: analysis of expression of neurofibromatosis 2 protein Merlin. Report of two cases

Meningiomas are primarily benign brain tumors thought to arise through multistep tumorigenesis, involving both the activation of oncogenes and the loss of tumor suppressor genes. The recently isolated neurofibromatosis 2 (NF2) tumor suppressor gene has been found to be mutated in a large proportion of meningiomas. Almost all cases of familial meningioma occur in association with NF2. Familial meningioma in isolation from NF2 (sporadic) is exceedingly rare, with only 14 reports since 1959. The authors report the existence of a family lacking any stigmata of NF2, in which two members had spinal meningiomas. Tumor specimens were subjected to immunocytochemical analysis for the NF2 protein product Merlin, which has been implicated in the tumorigenesis of meningioma. Merlin immunoreactivity was present in both tumor specimens, implying that the NF2 tumor suppressor gene was not deleted in these tumors. This supports the hypothesis that a second tumor suppressor gene locus, other than NF2, acts in the formation of familial sporadic meningioma. The results are discussed in the context of putative oncogenic mechanisms of familial meningiomas.

Visual improvement during octreotide therapy in a case of episellar meningioma

Meningiomas of the tuberculum sellae can induce compression of the optic tract. We report the case of a 54-year-old female patient affected by a suspected pituitary macroadenoma with severe visual field defects, who experienced a significant clinical and visual improvement during short-term octreotide therapy, contrasting with the lack of neuroradiological evidence for tumor shrinkage. The patient subsequently underwent transcranial surgery with a final diagnosis of meningioma. The putative mechanisms of visual improvement during octreotide therapy are discussed.

Insulin-like growth factors in central nervous system tumors

Insulin-like growth factors (IGFs) appear to play a role in the development of tumors in general and brain tumors in particular. Specific receptors for IGFs have been identified in normal human and rat brain, and evidence suggests that components of the IGF signal transduction system may play a role in the transformation process. Secretion of IGFs by a variety of human brain tumors has been confirmed, and these growth factors appear to have an autocrine stimulatory effect on these tumors. IGFs circulate in the blood stream bound to at least six distinct binding proteins which may modulate the effects of these growth factors on target tissues. Sex steroids may also regulate the behavior of certain brain tumors such as meningiomas at least in part through their effects on the expression of IGFs and their binding proteins. Recently, antisense gene technology against certain IGFs or their receptors have resulted in potent antitumor effects in the case of several gliomas, although the mechanism for this remains unclear.

Insulin-like growth factors (IGF) enhance three-dimensional (3D) growth of human glioblastomas

Human glioblastomas (gliomas) are characterized as rapidly growing brain tumors which are highly invasive but rarely metastatic. Human gliomas synthesize and secrete increased levels of insulin-like growth factors (IGFs) as well as expressing increased numbers of IGF receptors when compared to normal brain tissue. These observations suggest the existence of an IGF-mediated autocrine mechanism for glioma growth regulation. The purpose of this study was to examine the effect of human recombinant IGF (hrIGF) treatment on the in vitro growth of human glioma monolayer and three-dimensional (3D) multicellular spheroid cultures. The data demonstrate that hrIGF-I treatment of glioma cell lines slightly enhanced tumor monolayer proliferation as measured by [(3)H]thymidine incorporation. In contrast, treatment of glioma spheroids with hrIGF-I or hrDes(1-3)IGF-I, the truncated brain form of IGF-I, dramatically enhanced 3D tumor growth with a 1.5-2-fold reduction in spheroid doubling time (FRSDT). In addition, IGF-treated glioma spheroids were more densely packed than spheroids grown in media alone with no observed necrosis. These data suggest that IGFs will dramatically enhance glioma proliferation when 3D cell-cell contact occurs. This observed enhancement suggests that IGFs both synthesized in the brain and systemically support rapid proliferation of gliomas in vivo.

Formation of autocrine loops in human cerebral meningioma tissue by leukemia inhibitor factor, interleukin-6, and oncostatin M: inhibition of meningioma cell growth in vitro by recombinant oncostatin M

It has been demonstrated that growth of cerebral meningiomas found in humans is controlled by a variety of factors, including growth factors, aminergic agents, neuropeptides, and steroids. The authors investigated the presence and function of the cytokines leukemia inhibitory factor (LIF), interleukin-6 (IL-6), and oncostatin M (OSM) on meningioma cell proliferation.

Active transcription of LIF, IL-6, OSM, their related receptors (LIF-R, IL-6-R, gp130), and the consecutive signal-transducing molecules (STAT 1, STAT 3, and STAT 5a) were analyzed in reverse transcriptase-polymerase chain reaction experiments.

The presence of endogenous LIF, IL-6, and OSM proteins was demonstrated in the supernatant of cultured meningioma cells using enzyme-linked immunosorbent assay and Western blot experiments, thus indicating an autocrine signaling pathway for all three cytokines.

The biological function of all three cytokines was evaluated by studying their effects on meningioma cell growth. Recombinant LIF and IL-6 showed no significant growth modulating effects; however, recombinant OSM decreased meningioma cell growth by 66%. The antiproliferative potency of OSM was demonstrated by cell count experiments, [3H]thymidine incorporation assay, and cell cycle analysis. These in vitro data support the concept that growth of meningioma cells may be modulated by cytokines and also indicates that recombinant OSM may be one of the future candidates for use in the adjuvant treatment of inoperable and recurrent meningiomas.

Histamine-stimulated expression of insulin-like growth factors in human glioma cells

Glioma tumour growth is associated with the expression of insulin-like growth factors I and II (IGFs) and of both type I and type II IGF receptors. It has also been shown that IGFs can stimulate proliferation of cultured glioma cells. We previously reported that histamine too can stimulate the growth of glioma cells in vitro. In this report, we study whether the histamine-induced growth of G47 glioma cells is mediated by the IGFs. We found that histamine stimulates the expression of both IGF-I and IGF-II mRNAs, as determined by a semiquantitative in situ hybridization analysis. Furthermore, incubation of G47 cells with histamine also induced cellular immunostaining for IGF-II. It could be shown that IGF-I-stimulated proliferation is inhibited by IGFBP-3, which decreases the availability of IGFs for binding to the IGF receptors, and by beta-galactosidase, which may decrease IGF binding to the type II IGF receptor, but is not inhibited by the anti-type I IGF receptor monoclonal antibody alphaIR3. However, neither IGFBP-3 nor beta-galactosidase nor alphaIR3 inhibited the histamine-induced proliferation. These results show that the growth-stimulatory effect of histamine is accompanied by the induction of IGFs. This histamine-induced growth stimulation is not mediated by activation of cell surface IGF receptors, although intracrine activation of type II IGF receptors may be involved.

Expression of insulin-like growth factors (IGFs), their receptors and IGF binding protein-3 in normal, benign and malignant smooth muscle tissues

To assess the role of insulin-like growth factors (IGFs) in growth and transformation of normal (myometrium) and tumorous smooth muscle cell (SMC) tissues, in situ hybridization (ISH) analysis for insulin-like growth factor I and II (IGF-I and IGF-II) mRNAs was combined with detection of IGF peptides, their receptors and IGF binding protein-3 (IGFBP-3). mRNAs for both IGFs were detected in smooth muscle cells in normal, benign and malignant SMC tissues, together with the IGF peptides, both IGF receptors and IGFBP-3. This suggests an autocrine role for both IGFs. Leiomyomas had higher IGF-I peptide levels and higher levels of type I IGF receptors than myometrium, supporting the idea that IGFs play a role in the growth and transformation of these tumours. Low-grade leiomyosarcomas contained more IGF-II mRNAs than myometrium and leiomyoma, fewer type II IGF/mannose 6-phosphate receptors and less IGFBP-3 than myometrium and, in addition, fewer IGF-I mRNAs and type I IGF receptors than leiomyoma. Intermediate- and high-grade leiomyosarcomas had intermediate levels of IGF-II mRNAs and peptide, ranging between those in myometrium and low-grade leiomyosarcomas. Thus, growth and transformation of leiomyosarcomas may be regulated by IGF-II, although more markedly in low-grade than in high-grade leiomyosarcomas. In conclusion, the various categories of SMC tissues are associated with a distinct expression pattern of the IGF system. This suggests that each category of SMC tumours arises as a distinct entity and that there is no progression of transformation in these tissues.

Autocrine growth stimulation of human meningioma cells by platelet-derived growth factor

The authors have previously shown that meningioma-derived conditioned medium profoundly stimulates the in vitro proliferation of meningioma cells. In this paper, self mitogenic agents found in the conditioned medium-autocrine growth-stimulatory factors actually secreted by human meningioma cells-are characterized as proteins related to the B chain of platelet-derived growth factor (PDGF) and possibly to the A chain of PDGF as well. The addition to conditioned medium of a neutralizing antibody against PDGF-BB caused a significant inhibition of the conditioned medium-stimulated DNA synthesis in all three meningioma cultures studied. A similar neutralizing effect was observed with an anti-PDGF-AA antibody in one meningioma culture studied. Gel filtration chromatography of concentrated conditioned medium from two different meningiomas using a Sephadex G-100 column revealed similar profiles from both conditioned media with a major peak of mitogenic activity against meningioma cells at a molecular weight (M(r)) of approximately 32 to 36 kD, accompanied by a minor peak at approximately 22 kD. The major peak mitogenic activity was significantly reduced by addition of an anti-PDGF-BB antibody. Western blot analysis of protein extracts from five meningioma specimens was performed using a monoclonal antibody against the B chain of PGDF, and a major band of PDGF-B immunoreactivity was detected at an M(r) of approximately 19 kD in all five meningiomas under both reducing and nonreducing conditions. Exogenous human and porcine PDGFs both exhibited a significant dose-dependent stimulation of DNA synthesis in two of three and three of five meningioma cultures examined, respectively. Although not all meningiomas investigated proved to share the biological activity associated with PDGF and these results may be preliminary, it seems that the autocrine growth-stimulatory loop established by PDGF-B-related molecules plays an important functional role in meningioma cell proliferation.

Hormonal dependency of cerebral meningiomas

Though meningiomas are benign intracranial tumors, a minor group invades the skull base and the connective tissue of the sinus cavernous inducing neurological deficits. These patients can not be cured by surgical treatment. Therefore, the development of an adjuvant medical therapy has been the goal during the last decade. We report here on different medical concepts which are based on steroids, amines, growth factor antagonists and cytokines. In addition, our data give evidence that the growth of intracranial meningiomas is under multifactorial proliferative control.

Inhibition of in vitro meningioma proliferation after growth factor stimulation by calcium channel antagonists: Part II--Additional growth factors, growth factor receptor immunohistochemistry, and intracellular calcium measurements

We have previously reported that calcium channel antagonists can block both the growth of meningiomas in culture and the potent growth stimulation of meningioma cells by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). This study further defines the nature of this growth inhibition. Primary meningioma cultures were established, and cells were characterized. Fibroblast growth factor or insulin-like growth factor-I growth stimulation in the presence of calcium channel antagonists was examined. In addition, the effects of ethylene glycol-bis-(aminoethylether) N,N,N',N"-tetraacetic acid and Bay K 8644, a calcium channel agonist, on the growth factors were analyzed. Growth factor receptor immunohistochemistry was performed on the original tumors and the in vitro meningioma cells. Twelve of 17 (71%) meningiomas in this study were positive for the EGF receptor, and 14 of 17 (82%) were positive for the PDGF receptor. Five of six (83%) of the culture cells were positive for the EGF receptor, and four of five (80%) were positive for the PDGF receptor. Intracellular calcium changes were quantified using the intracellular calcium-chelating, fluorescent dye, Fura-2. The growth stimulation of fibroblast growth factor and insulin-like growth factor-I on meningioma cells in culture was decreased in a dose-dependent manner by calcium channel antagonists. The growth stimulation of fibroblast growth factor and insulin-like growth factor-I was not affected by a reduction of extracellular calcium, whereas the growth stimulation of EGF and PDGF was. Interestingly, intracellular calcium was not increased after exposure to growth factors but was increased after serum stimulation. This increase could be blocked by preincubation with verapamil. Calcium channel antagonists can inhibit proliferation of meningioma cells in culture after stimulation with a number of growth factors. These drugs might disrupt intracellular calcium homeostasis or interfere with key elements of the growth factor signal transduction pathways. These mechanisms as well as the potential clinical relevance of these findings are discussed.

Expression and localization of endothelin-1 and endothelin receptors in human meningiomas. Evidence for a role in tumoral growth

In addition to its well-known homoeostatic actions in the cardiovascular system, ET-1 has been shown to constitute a potent growth regulatory peptide in various tissues. We have studied the expression of ET-1 and its receptors (ET-Ar and ET-Br) in human meningiomas (n = 35) as well as their involvement in cellular growth. By PCR of reverse-transcribed RNA we detected ET-1 mRNA in 91% (32 of 35), ET-Ar mRNA in 82% (29 of 35), and ET-Br mRNA in 42% (15 of 35) of human meningiomas examined. The localization of ET-1 mRNA, ET-Ar mRNA, and ET-1 peptide in tumoral cells was observed by in situ hybridization and immunohistochemistry, whereas ET-Br mRNA was expressed at low level only in cells belonging to blood vessels. In addition, we found that ET-1 stimulated [3H] thymidine incorporation in primary cell cultures of 20 meningiomas and that this effect could be blocked by BQ-123, a specific antagonist for ET-Ar. In contrast, RES-701-3, an antagonist of ET-Br, did not block the proliferative effect of ET-1. In conclusion, our data provide evidence that ET-1 constitutes an important growth factor for meningiomas acting via ET-Ar. We can hypothesize that ET-1, acting in concert with other growth factors and cytokines, is involved in the meningioma tumorigenesis.

Insulin- and insulin-like growth-factor-I receptor tyrosine-kinase activities in human renal carcinoma

We studied expression and functional characteristics of the insulin- and insulin-like-growth-factor-I (IGF-I) receptors in human renal carcinoma. Ligand-binding properties and tyrosine-kinase activity of both receptors, as well as the expression of the 2 isoforms of the human insulin receptor (HIR-A and -B) were analyzed in renal carcinoma and normal adjacent kidney tissue of 8 adult patients. Partially purified insulin- and IGF-I receptors from normal and renal cell carcinoma tissue possessed identical affinities for their ligands. Renal cell carcinoma, however, contained 3- to 4-fold more specific insulin-binding sites and 2-fold more IGF-I binding sites than adjacent normal kidney tissue. In addition, we determined the relative content of insulin/IGF-I receptor hybrids in both tissues. Renal cell carcinoma and adjacent normal tissue revealed similar amounts of insulin/IGF-I receptor hybrids, i.e., 44 +/- 8.2% of tracer IGF-I binding in normal tissue and 46 +/- 12.0% in renal cell carcinoma. When equal amounts of insulin- and IGF-I receptor protein were studied, we found significantly increased receptor autophosphorylation and elevated substrate phosphorylation in carcinoma tissue. To assess whether the differences in insulin-receptor tyrosine-kinase activity were caused by an altered pattern of insulin receptor isoform expression, we determined mRNA levels for HIR-A and -B. The 2 insulin receptor isoforms were, however, expressed in highly variable ratios in both normal and tumor tissue. Our experiments show that renal carcinoma expresses an elevated amount of insulin- and IGF-I receptor protein with increased specific autophosphorylation and tyrosine-kinase activity each. The increase of insulin-receptor tyrosine-kinase activity in renal carcinoma cannot be explained by an altered expression pattern of insulin receptor isoforms.

The role of growth factor receptors in central nervous system development and neoplasia

Future advances in neuro-oncology will increasingly rely on an understanding of the molecular biology of brain tumors. Recent laboratory work, including the identification of oncogenes and tumor suppressor genes, has elucidated many of the molecular events contributing to oncogenesis. In particular, the signaling pathways for the growth factors have been implicated in the genesis and the maintenance of several human tumors, including neoplasms of the central nervous system (CNS). Growth factor autocrine and paracrine stimulatory loops promote tumor proliferation and angiogenesis. A family of structurally related growth factor receptors, the receptor tyrosine kinases, are particularly relevant to tumors of the CNS. This large family includes the receptors for the epidermal growth factor, the platelet-derived growth factor, the fibroblast growth factor, the insulin-like growth factor, the neurotrophins related to the nerve growth factor, and the vascular endothelial growth factor, as well as several receptors for which no growth factor ligand has been identified. Several of these receptor molecules and their growth factor ligands are preferentially expressed in the embryonic brain and are thought to play a central role in regulating the determination of the cell fate during the development of the CNS. Moreover, the overexpression or the mutation of genes encoding these receptors can be oncogenic. Researchers think that some receptors in this family (i.e., those that have been shown to be overexpressed or mutated in human brain tumors) contribute to brain tumor oncogenesis. This article will focus on recent experimental work and will discuss the classification and the biology of the receptor tyrosine kinases, as well as their roles in the development of the CNS and in tumorigenesis.

Case report: hypoglycemia secondary to a meningioma

Hypoglycemia secondary to a meningioma that has not metastasized to the liver has not been reported previously. A 41-year-old woman with a spinal cord meningioma first diagnosed 5 years previously with 3 recurrences in the spinal cord resulting in 4 neurosurgical procedures was admitted with a serum glucose of 23 mg/dL. Six months before the current admission, the patient was noted to have an abdominal mass of 10 cm not present on previous computed tomography. Three months later, the mass was 15.2 cm, and on the current admission, had increased to 23 cm and encased both the aorta and inferior vena cava. A needle biopsy of this mass before referral to the authors' hospital with hypoglycemia revealed that it was a meningioma. Evaluation of the etiology of the hypoglycemia, which required continuous intravenous glucose therapy, revealed that circulating insulin, C-peptide (i.e., connecting peptide), insulin-like growth factor-I (i.e., somatomedin-C) and insulin-like growth factor-II were all normal or low. Serum cortisol also was not low. Based on her endocrine evaluation, the hypoglycemia was secondary to the large mass of tumor cells, requiring a large glucose uptake to sustain its growth. After radiation therapy of 3,770 CGy to the meningioma, the patient became euglycemic without glucose supplementation.

The insulin-like growth factor system in regulation of normal and malignant hematopoiesis

The published data available on the insulin-like growth factor (IGF) family of peptides, its receptors and binding proteins in connection with normal and neoplastic hematopoietic processes are reviewed. It is found that nearly all the different hematopoietic cells, either normal or neoplastic, express IGF receptors. The IGFs are involved in normal erythropoiesis, granulopoiesis and lymphopoiesis. IGFs, especially IGF-1, are mitogenic for cell lines of myeloid and lymphoid leukemias and Burkitt's lymphoma. Differentiation of certain immature malignant cell lines is associated with a decrease in the number and affinity of IGF receptors. It might be concluded that the IGFs have an important role in the physiologic and neoplastic processes of the hematopoietic system, and the expanding knowledge of this issue will contribute to the understanding of proliferation and differentiation processes in specific hematologic disorders.

Inhibition of proliferation of human cerebral meningioma cells by suramin: effects on cell growth, cell cycle phases, extracellular growth factors, and PDGF-BB autocrine growth loop

The growth of human cerebral meningiomas depends on various growth factors, including epidermal growth factor (EGF), transforming growth factor (TGF)-alpha and TGF-beta, platelet-derived growth factor (PDGF)-BB, insulin-like growth factor (IGF)-I and IGF-II, and acidic and basic fibroblast growth factors. The latter three have been shown to form autocrine loops that are thought to be a major component of uncontrolled growth in meningioma tissue. Suramin is known to prevent binding of a variety of growth factors to their receptors in mammalian tissue, thus abolishing para- and/or autocrine-mediated cell growth. The authors therefore tested the effect of suramin on the proliferation of cultured human meningioma cells. Suramin (10(-5) to 10(-4) M) significantly inhibited the growth of meningioma cells in culture. The maximum effect observed was with the higher dose (10(-4) M), which resulted in a 40% to 70% reduction in cellular proliferation. This effect was observed in all 15 tumor samples studied and was confirmed by [3H]thymidine uptake. In studies using DNA flow cytometry, suramin inhibited meningioma cell proliferation in five tumor samples by arresting cells in the S and G2/M phases of the cell cycle. Growth factor (EGF, IGF-I, and PDGF-BB)-induced cell proliferation was completely abolished in five tumor samples when 10(-4) M suramin was applied to meningioma cells. Western blot analysis of three tumor samples showed that the intracellular PDGF-BB content of meningioma cells was significantly reduced after treating the cells with 10(-4) M suramin. Binding of iodinated growth factors (that is, [125I]EGF, [125I]IGF-I, and [125I]PDGF-BB) to their receptor sites was prevented by suramin in a dose-dependent manner in 10 meningioma membrane fractions. Lowering of the intracellular PDGF content and prevention of extracellular growth factor receptor binding demonstrates that suramin disrupts autocrine loops and paracrine growth stimulation in meningioma tissue. These data provide evidence that growth of cerebral meningiomas in culture is strongly inhibited by suramin at a concentration of 10(-4) M. Suramin acts as a scavenger neutralizing exogenous growth factors; thus it can interrupt autocrine loops and paracrine stimulation of human meningioma cell growth. The evidence favors suramin as a therapeutic option for controlling meningioma proliferation in patients with inoperable and recurrent high-grade meningiomas.

Radioimmunoassay of insulin-like growth factors I and II in the cerebrospinal fluid of patients with pituitary and other central nervous system tumors

Tumor cells are characterized by abnormalities in growth and metabolism, including the autocrine secretion of certain growth factors. On the basis of our previous demonstration of the production of insulin-like growth factors (IGFs) and their binding proteins by central nervous system (CNS) tumors, we asked whether the levels of IGFs in the CSF may be altered in patients with pituitary and other CNS tumors and may reflect autocrine secretion. We used specific radioimmuoassays for IGF-I and -II and measured these growth factors in the cerebrospinal fluid (CSF) from 26 patients with tumors located adjacent to the ventricular system. The tumors included were eight pituitary tumors (five nonsecreting, three growth hormone secreting), five gliomas, two meningiomas, five medulloblastomas, three metastases, and three other tumors. CSF from patients without tumors served as controls. For radioimmunoassay, CSF was treated with acetic acid overnight and IGF-binding proteins were separated from IGFs by C-2 solid phase cartridge extraction. The pituitary tumors were characterized by significantly elevated levels of IGFs in the CSF. In nonseceting pituitary tumors, the levels of IGF-I in the CSF were similar to normal levels, whereas IGF-II levels were significantly elevated. In acromegalic patients, levels of both IGF-I and -II in the CSF were significantly elevated compared with normal levels and compared with levels in patients with nonsecreting tumors. In contrast, the levels of IGFs in the CSF from most of the primary and metastatic CNS CNS tumors did not significantly differ from normal values. In summary, although IGFs may contribute to the regulation of cell growth in primary CNS tumors, CSF levels are not elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Gene therapy of murine teratocarcinoma: separate functions for insulin-like growth factors I and II in immunogenicity and differentiation

Teratocarcinoma is a germ-line carcinoma giving rise to an embryoid tumor with structures derived from the three embryonic layers: mesoderm, endoderm, and ectoderm. Teratocarcinoma is widely used as an in vitro model system to study regulation of cell determination and differentiation during mammalian embryogenesis. Murine embryonic carcinoma (EC) PCC3 cells express insulin-like growth factor I(IGF-I) and its receptor, while all derivative tumor structures express IGF-I and IGF-II and their receptors. Therefore the system lends itself to dissect the role of these two growth factors during EC differentiation. With an episomal antisense strategy, we define a role for IGF-I in tumorigenicity and evasion of immune surveillance. Antisense IGF-I EC transfectants are shown to elicit a curative anti-tumor immune response with tumor regression at distal sites. In contrast, IGF-II is shown to drive determination and differentiation in EC cells. Since IGF-I and IGF-II bind to type I receptor and antisense sequence used for IGF-II cannot form duplex with endogenous IGF-I transcripts, it follows that this receptor is not involved in determination and differentiation.

Growth regulation of human glioblastoma T98G cells by insulin-like growth factor-1 and its receptor

The interaction of insulin-like growth factors (IGFs) with the IGF-1 receptor is an important step in the control of cell proliferation and development. In particular, IGF-1 and IGF-2 are key regulators of central nervous system development, and may modulate the growth of glial tumors. We have investigated the growth factor regulation of the human glioblastoma cell line T98G. These cells growth arrested in serum-free medium at 34 degrees C, despite their secretion of substantial amounts of bioactive IGF-1. To be stimulated to divide, growth-arrested cells required the addition of platelet-derived growth factor (PDGF) or its equivalent, 1% serum. Cell proliferation in serum-free medium could also be obtained by shifting the cells to a temperature of 39.6 degrees C. Treatment of growth-arrested cells with PDGF or temperature shift was accompanied by a transient increase in the expression of the mRNA for the IGF-1 receptor. Transfection with a plasmid constitutively expressing the full cDNA for the human IGF-1 receptor allowed autonomous growth in serum-free medium at 34 degrees C. By contrast, growth induction by growth factors or temperature shift was abrogated by transfection of the cells with a plasmid expressing a 300 bp segment of mRNA antisense to the IGF-1 receptor mRNA. Cloning in soft agar was also inhibited by expression of antisense IGF-1 receptor mRNA. These results demonstrate that the IGF-1 receptor is strictly required for the growth of T98G glioblastoma cells. Moreover, the autocrine interaction of IGF-1 with its receptor regulates both autonomous and anchorage-independent growth of these cells.

Characterization of the influence of anti-hormone and/or anti-growth factor neutralizing antibodies on cell clone architecture and the growth of human neoplastic astrocytic cell lines

The influence of five anti-hormone and/or anti-growth factor neutralizing antibodies on the in vitro proliferation of four human astrocytic tumor cell lines (U87, U138, U373, H4) is quantitatively described by means of a new tool which makes it possible to evaluate cell growth and cell clone architecture concomitantly. This tool relies upon the combined use of the digital cell image analyses of Feulgen-stained nuclei and the Delaunay and Voronoi mathematical triangulation and paving techniques. Of the five anti-hormone and/or anti-growth factors tested here, the anti-luteinizing hormone-releasing hormone (LHRH) antibody induced the most marked perturbation in the U138 and U373 cell lines, whereas this role was played by the anti-epidermal growth factor (EGF) antibody in the U87 and H4 cell lines. The anti-gastrin (G) antibody significantly modified the growth and/or cell clone architecture of the U138, U87 and H4 cell lines, as did the anti-transforming growth factor alpha (TGFalpha) antibody. The anti-transforming growth factor beta (TGFbeta) antibody modified the growth and/or cell clone architecture of the four cell lines under study. If the five antibodies are taken into consideration, the results strongly suggest that four (the anti-G, the anti-EGF, the anti-LHRH and the anti-TGFalpha) act as inhibitory agents on some glioma cell line proliferation, while the fifth one, i.e. the anti-TGFbeta, act as a stimulator of cell proliferation, perhaps by abrogating the inhibitory effects of TGFbeta on proliferation. A comparison of cell growth data with cell clone architecture characteristics provided further evidence of some specific influence exercised by a given hormone and/or growth factor on glioma cell proliferation. Indeed, the anti-LHRH antibody caused the most pronounced perturbations in the U138 and U373 cell clone architecture; this feature was observed in the H4 cell line and, to a lesser extent in the U87 one after the anti-EGF antibody had been used.

Correlation of proto-oncogene expression and proliferation and meningiomas

Proliferation and proto-oncogene expression in 19 meningiomas of typical and atypical histology were analyzed in an attempt to understand the mechanism of growth that characterizes the neoplastic process in these tumors. Proliferation was estimated as the proliferative index by the enumeration of S-phase cells in imprints of tumor tissue exposed to bromodeoxyuridine in vitro, and the gene expression of c-myc, c-fos, c-src, c-H-ras, N-myc, acidic and basic fibroblast growth factor, insulin-like growth factors I and II, platelet-derived growth factor-alpha, and epidermal growth factor was quantified by messenger ribonucleic acid dot-blot hybridization assay. Atypical and malignant tumors had significantly higher proliferative indexes than did their nonmalignant counterparts. Levels of c-myc and c-fos messenger ribonucleic acid were elevated more than fivefold in 72 and 78% of the tumors, respectively, relative to the lowest levels detected in the series. Levels of growth factor messenger ribonucleic acid were sporadically elevated; 37 to 44% of tumors had more than fivefold enhanced levels of acidic and basic fibroblast growth factor. Positive correlations between proliferation and proto-oncogene/growth factor expression were found for c-myc in atypical/malignant tumors and for epidermal growth factor in fibroblastic meningiomas. Deregulated expression of c-myc and c-fos common to both typical and atypical tumors suggests that these are early events in the meningioma tumor process that may disturb the control of cell differentiation and together with fibroblast growth factors are likely to endow the transformed cell with a selective growth advantage by reducing the requirement for exogenous mitogens and by providing a niche for the growth of the tumor clone. Positive correlation of c-myc levels with proliferation in atypical/malignant meningiomas implies that this is a feature of malignancy and indicates continued disruption of the negative regulation of proto-oncogene expression, perhaps by tumor suppressor gene losses, during the course of tumor progression.

Identification of insulin-like growth factor (IGF) and glucose transporter-1 and -3 mRNA in CNS tumors

Glucose metabolism is increased in CNS tumors and correlates with malignant grade. We have previously investigated the role of IGFs in regulating CNS tumor growth and metabolism. In the present study we examined total cellular RNA from human CNS tumors for the presence for glucose transporter (Glut) and IGF mRNA. Human meningiomas and gliomas were frozen in liquid nitrogen at the time of surgery and then stored at -80 degrees C. Total cellular RNA was prepared by acid-guanidinium phenol-chloroform extraction and 20 micrograms of RNA was loaded for agarose-formaldehyde gel electrophoresis and transfer. RNA integrity in 5 meningiomas and 2 gliomas was confirmed by ethidium bromide staining of 28S and 18S ribosomal RNA and hybridization with a cDNA probe for beta-actin. For analysis, membranes were hybridized to radioactively labeled human Glut-1, Glut-3, IGF-I, and IGF-II cDNA probes, and mRNA transcripts were identified by autoradiography. All 7 tumors expressed Glut-1 and Glut-3 mRNA and Glut-3 appeared to be more abundant in meningiomas. IGF-II mRNA was detected in 2 of 6 meningiomas and in both gliomas. IGFs may play an important role in the regulation of glucose metabolism in CNS tumors. IGFs and specific glucose transporters may prove useful as markers of malignancy and potential targets for future therapy.

Expression of insulin-like growth factors and their receptors in human meningiomas

Meningiomas have previously been shown to highly express the gene for insulin-like growth factor-II (IGF-II), and receptors for IGF-I have been demonstrated by binding studies in membranes prepared for meningiomas. The co-expression of insulin and the insulin-like growth factors with their corresponding receptors in meningiomas has not been explored. Immunofluorescence microscopy was carried out on twelve meningotheliomatous meningiomas using antibodies directed against insulin, IGF-I, IGF-II, insulin receptor and IGF-I receptor. In addition, these results were contrasted with similar studies using antibodies against desmoplakin and basic fibroblast growth factor. Although insulin immunoreactivity was detected in only one tumor, IGF-I and IGF-II immunoreactivity was present in six and eight of the tumors, respectively. In addition, the IGF-I receptor was expressed in four of the tumors while the insulin receptor was expressed in 10 out of 12 meningiomas. The pattern of distribution of IGF-II and the insulin receptor was especially regional. The insulin-like growth factors and their receptors are expressed in meningiomas in a pattern of distribution suggestive of a paracrine mechanism.

Treatment and prevention of rat glioblastoma by immunogenic C6 cells expressing antisense insulin-like growth factor I RNA

Rat C6 glioma cells express insulin-like growth factor I (IGF-I) and form rapidly growing tumors in syngeneic animals. When transfected with an episome-based vector encoding antisense IGF-I complementary DNA, these cells lost tumorigenicity. Subcutaneous injection of IGF-I antisense-transfected C6 cells into rats prevented formation of both subcutaneous tumors and brain tumors induced by nontransfected C6 cells. The antisense-transfected cells also caused regression of established brain glioblastomas when injected at a point distal to the tumor. These antitumor effects result from a glioma-specific immune response involving CD8+ lymphocytes. Antisense blocking of IGF-I expression may reverse a phenotype that allows C6 glioma cells to evade the immune system.