The effect of exogenous gangliosides on matrix metalloproteinase secretion by human glioma cells in vitro

GD3 ganglioside is a promising therapeutic target for glioma patients

Glioblastoma is the most frequent and aggressive primary brain tumor in adults. Currently, no curative treatment is available. Despite first-line treatment composed by the association of surgery, radiotherapy, and chemotherapy, relapse remains inevitable in a median delay of 6 to 10 months. Improving patient management and developing new therapeutic strategies are therefore a critical medical need in neuro-oncology. Gangliosides are sialic acid-containing glycosphingolipids, the most abundant in the nervous system, representing attractive therapeutic targets. The ganglioside GD3 is highly expressed in neuroectoderm-derived tumors such as melanoma and neuroblastoma, but also in gliomas. Moreover, interesting results, including our own, have reported the involvement of GD3 in the stemness of glioblastoma cells. In this review, we will first describe the characteristics of the ganglioside GD3 and its enzyme, the GD3 synthase (GD3S), including their biosynthesis and metabolism. Then, we will detail their expression and role in gliomas. Finally, we will summarize the current knowledge regarding the therapeutic development opportunities against GD3 and GD3S.

Ganglioside GD3 synthase (GD3S), a novel cancer drug target

Gangliosides are a class of important glycosphingolipids containing sialic acid that are widely distributed on the outer surface of cells and are abundantly distributed in brain tissue. Disialoganglioside with three glycosyl groups (GD3) and disialoganglioside with two glycosyl groups (GD2) are markedly increased in pathological conditions such as cancers and neurodegenerative diseases. GD3 and GD2 were found to play important roles in cancers by mediating cell proliferation, migration, invasion, adhesion, angiogenesis and in preventing immunosuppression of tumors. GD3 synthase (GD3S) is the regulatory enzyme of GD3 and GD2 synthesis, and is important in tumorigenesis and the development of cancers. The study of GD3S as a drug target may be of great significance for the discovery of new drugs for cancer treatment. This review will describe the gangliosides and their roles in physiological and pathological conditions; the roles of GD3 and GD2 in cancers; the expression, functions and mechanisms of GD3S, and its potential as a drug target in cancers.

Approaches to mitochondrially mediated cancer therapy

For some malignant cancers even combined surgical, radiotherapeutic and chemotherapeutic approaches are not curative, indeed, in certain tumour types even a modest survival benefit is difficult to achieve. There are various biological reasons which underlie this profound resistance but the propensity of cancer cells to repair breaks caused by DNA-damaging radiation and cytotoxic drugs is of major significance in this context. Such highly resistant tumours include the malignant gliomas which are intrinsic to and directly affect the brain and spinal cord. In evaluating approaches which do not elicit tumour cell death directly by DNA damage, it is intriguing to consider mitochondrially mediated apoptosis as a potentially effective alternative. Since the mitochondrial membrane potentials in cancer cells are frequently reduced in comparison with those of non-neoplastic cells this allows a window of opportunity for small molecule agents to enter the tumour cell mitochondria and reduce oxygen consumption with subsequent release of cytochrome c and activation of a caspase pathway to apoptosis which is cancer cell specific. In the quest for agents which can selectively destroy neoplastic cells in this manner, whilst leaving normal adjacent cells intact, various tricyclic drugs have come under scrutiny. In a range of laboratory assays we, and others, have established that certain cancers and, in particular, malignant glioma, are intrinsically sensitive to this approach. We have also established the cellular, molecular and biochemical mechanisms underlying this process. While such archival tricyclics as the antidepressants, clomipramine and amitriptyline, have been used in these experiments their commercial development in cancer therapy has not been forthcoming and their clinical use in glioma has been confined to anecdotal cases. In addition, the dose-dependant role of agents such as anticonvulsants and steroids commonly used in glioma patients in modulating efficacy of the tricyclics is a matter for continued investigation. Other ways of targeting the mitochondrion for cancer therapy include exploitation of the 18kDa translocator protein (peripheral-type benzodiazepine receptor) within the mitochondrial permeability transition pore and enzymatic or molecular modification of a species of ganglioside (GD3/GD3(A)) expressed on the surface of neoplastic cells which are determinants of mitochondrially mediated apoptosis. It is hoped that such approaches may lead to clinical programmes which will improve the prognosis for patients suffering from highly resistant neoplasms.

RETRACTED ARTICLE: Hepatocyte growth factor production is stimulated by gangliosides and TGF-β isoforms in human glioma cells

Hepatocyte growth factor (HGF) is a pleiotrophic cytokine that stimulates motility and invasion of several cancer cell types and induces angiogenesis, which is known to be expressed in several malignancies including glioma. The effect of transforming growth factor-beta (TGF-beta) isoforrns as well as gangliosides on HGF production was investigated in human glioma cell lines. TGF-beta isoforms and gangliosides were found to differentially stimulate HGF production by these cells. The ganglioside GD3 enhanced this release to the greatest extent and the stimulation was more marked in a glioblastoma cell line than in the two other anaplastic astrocytoma cell lines. These results suggest that both TGF-betas and gangliosides may act as indirect angiogenic factors by stimulating HGF secretion.

Ganglioside GD1a negatively regulates matrix metalloproteinase-9 expression in mouse FBJ cell lines at the transcriptional level

Mouse FBJ virus-induced osteosarcoma FBJ-S1 cells rich in GD1a are not readily metastatic, whereas FBJ-LL cells with low levels of GD1a are highly metastatic. GD1a was previously shown to suppress metastasis of mouse FBJ cells and to upregulate caveolin-1 and stromal interaction molecule 1 expression. The present study demonstrates that matrix metalloproteinase-9 (MMP-9) expression renders FBJ-LL cells invasive. MMP-9 is inversely regulated by GD1a, based upon four observations: MMP-9 mRNA content was 5 times higher in FBJ-LL cells than FBJ-S1 cells; a GD1a-re-expressing FBJ-LL cell variant produced through beta1,4GalNAcT-1 cDNA transfection expressed lower levels of MMP-9; exogenous addition of GD1a to FBJ-LL cells decreased MMP-9 production in a dose- and time-dependent manner; and treatment of GD1a-rich cells with D-PDMP or siRNA targeting St3gal2 decreased GD1a expression, but augmented MMP-9 expression. This is the first report demonstrating that GD1a negatively regulates expression of MMP-9 at the transcriptional level.

Cancer stem cells in the mammalian central nervous system

Malignant tumours intrinsic to the central nervous system (CNS) are among the most difficult of neoplasms to treat effectively. The major biological features of these tumours that preclude successful therapy include their cellular heterogeneity, which renders them highly resistant to both chemotherapy and radiotherapy, and the propensity of the component tumour cells to invade, diffusely, the contiguous nervous tissues. The tumours are classified according to perceived cell of origin, gliomas being the most common generic group. In the 1970s transplacental administration of the potent neurocarcinogen, N-ethyl-N-nitrosourea (ENU), enabled investigation of the sequential development of brain and spinal neoplasms by electron microscopy and immunohistochemistry. The significance of the primitive cells of the subependymal plate in cellular origin and evolution of a variety of glial tumours was thereby established. Since then, the development of new cell culture methods, including the in vitro growth of neurospheres and multicellular tumour spheroids, and new antigenic markers of stem cells and glial/neuronal cell precursor cells, including nestin, Mushashi-1 and CD133, have led to a reappraisal of the histological classification and origins of CNS tumours. Moreover, neural stem cells may also provide new vectors in exciting novel therapeutic strategies for these tumours. In addition to the gliomas, stem cells may have been identified in paediatric tumours including cerebellar medulloblastoma, thought to be of external granule cell neuronal derivation. Interestingly, while the stem cell marker CD133 is expressed in these primitive neuroectodermal tumours (PNETs), the chondroitin sulphate proteoglycan neuronal/glial 2 (NG2), which appears to denote increased proliferative, but reduced migratory activity in adult gliomas, is rarely expressed. This is in contrast to the situation in the histologically similar supratentorial PNETs. A possible functional 'switch' between proliferation and migration in developing neural tumour cells may exist between NG2 and ganglioside GD3. The divergent pathways of differentiation of CNS tumours and the possibility of stem cell origin, for some, if not all, such neoplasms remain a matter for debate and continued research, but the presence of self-renewing neural stem cells in the CNS of both children and adults strongly suggests a role for these cells in tumour initiation and resistance to current therapeutic strategies.

Cathepsin L in glioma progression: Comparison with cathepsin B

OBJECTIVE

Lysosomal cysteine cathepsins have been implicated in tumor progression. This study is aimed to reveal differential expression and compare the prognostic significance of cathepsins B and L in glioma patients.

METHODS

The histological slides of 82 patients with primary astrocytic tumors were reviewed. We evaluated the immunostaining of the cathepsins in tumor and endothelial cells.

RESULTS

Cathepsins B and L stained positive in 98 and 88% of cases, respectively. The total score was significantly higher in malignant than in benign tumors, both for cathepsin B (p<0.001) and for cathepsin L (p<0.01). The IHC score in endothelial cells in the malignant group was significantly higher only for cathepsin B (p<0.0001). Survival analysis indicated that in contrast to the prognostic significance of total cathepsin B and endothelial cells associated cathepsin B for shorter patients' survival, the prognostic role of cathepsin L was not confirmed.

CONCLUSION

Cathepsin L is preferentially expressed in tumor cells, increasing with glioma progression, but is not significantly associated with new vasculature of glioblastoma. In contrast to cathepsin B, cathepsin L has no prognostic impact, suggesting different roles of the two cathepsins in glioma progression.

Medulloblastoma displays distinct regional matrix metalloprotease expression

Matrix metalloproteases (MMPs) play an important role in tissue remodeling and neoangiogenesis during tumor progression. Little is known about the presence and regional distribution of MMPs in medulloblastomas. Based on immunohistochemical, immunocytochemical and zymographical analysis is the present study illustrates the differential pattern of MMP expression for the medulloblastoma compared to that of glioma and ependymoma. In 10 examined medulloblastoma tumors gelatinase-A was strongly expressed by clusters of tumor cells. Gelatinase-B was, similar to glioma and ependymoma, predominantly found around endothelial cells. The DAB signal for macrophage metalloelastase was seen around macrophages and matrilysin was expressed by single tumor cells. Stromelysin-1 protein was detected in medulloblastoma but not in glioma or ependymoma. From the presented data it follows that each tumor entity might display its own characteristic MMP expression pattern.

Gangliosides GD1b, GT1b, and GQ1b suppress the growth of human melanoma by inhibiting interleukin-8 production: the inhibition of adenylate cyclase

We studied the effects of various gangliosides on in vitro growth of human metastatic melanoma WM266-4. GD1b, GT1b, and GQ1b inhibited 3H-thymidine uptake and growth rate of WM266-4 whereas the other gangliosides were ineffective. The growth inhibition by GD1b, GT1b, and GQ1b was counteracted by interleukin-8 but not by the other growth factors. The growth inhibition by gangliosides was not detected in the presence of anti-interleukin-8 antibody. GD1b, GT1b, and GQ1b reduced the constitutive interleukin-8 secretion and mRNA levels in WM266-4. Transient transfection showed that GD1b, GT1b, and GQ1b inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in WM266-4. Transfection with a series of 5'-deleted mutants demonstrated that the sequences between -98 and -62 bp on interleukin-8 promoter may be involved in the transcriptional repression by these gangliosides. Cyclic AMP analog dibutyryl cAMP counteracted GD1b, GT1b, and GQ1b-induced inhibition of interleukin-8 production at the levels of protein secretion, mRNA expression, and promoter activity. GD1b, GT1b, and GQ1b reduced cAMP level and protein kinase A activity in WM266-4. These gangliosides suppressed adenylate cyclase activity without altering that of cyclic nucleotide phosphodiesterase in WM266-4. The data indicate that GD1b, GT1b, and GQ1b may suppress the growth of melanoma by inhibiting interleukin-8 production via the inhibition of adenylate cyclase.

Medulloblastoma displays distinct regional matrix metalloprotease expression

Matrix metalloproteases (MMPs) play an important role in tissue remodeling and neoangiogenesis during tumor progression. Little is known about the presence and regional distribution of MMPs in medulloblastomas. Based on immunohistochemical, immunocytochemical and zymographical analysis is the present study illustrates the differential pattern of MMP expression for the medulloblastoma compared to that of glioma and ependymoma. In 10 examined medulloblastoma tumors gelatinase-A was strongly expressed by clusters of tumor cells. Gelatinase-B was, similar to glioma and ependymoma, predominantly found around endothelial cells. The DAB signal for macrophage metalloelastase was seen around macrophages and matrilysin was expressed by single tumor cells. Stromelysin-1 protein was detected in medulloblastoma but not in glioma or ependymoma. From the presented data it follows that each tumor entity might display its own characteristic MMP expression pattern.

Migration and invasion in brain neoplasms

Local invasion of the brain by neoplastic glial cells is a major obstacle to effective treatment of intrinsic brain tumors. Invasion is directly related to histologic malignancy, but occurs to some extent irrespective of tumor grade. Because the brain-to-tumor interface is not well demarcated, total surgical removal is rarely possible; moreover, as invading cells transiently arrest from cell division they are refractory to radiotherapeutic intervention. Invading cells may also be protected from the action of cytotoxic drugs by the presence of an intact blood-brain barrier. The invading cells, having migrated several millimeters or even centimeters from the main focus of the tumor, return to cycle phase under the control of some as yet unknown microenvironmental cue to form a recurrent tumor adjacent to the original site of presentation. Recent cellular and genetic information concerning factors underlying invasion may not only yield suitable targets for adaptation of existing therapies, but may also lead to novel approaches in glioma management.

The effects of exogenous growth factors on matrix metalloproteinase secretion by human brain tumour cells

Matrix metalloproteinases (MMPs) are a growing family of zinc-dependent endopeptidases that are capable of degrading various components of the extracellular matrix. These enzymes have been implicated in a variety of physiological and pathological conditions including embryogenesis and tumour invasion. The synthesis of many MMPs is thought to be regulated by growth factors, cytokines and hormones. In this study, we investigated the effects of five exogenous growth factors known to be expressed by gliomas [epidermal growth factor (EGF), basic growth factor (bFGF), transforming growth factor beta (TGF-beta1,2) and vascular endothelial growth factor (VEGF)].on MMP-2 and MMP-9 expression in an ependymoma, two grade III astrocytomas, a grade III oligoastrocytoma and a benign meningioma. Zymogram analysis revealed that the effects of the growth factors depended upon the cell lines used in the study. Growth factors generally up-regulated MMP-2 and MMP-9 expression in the gliomas but were least effective in the meningioma; the effect being most prominent with TGF-beta1 and TGF-beta2 in all the cell lines. It is hypothesized that paracrine growth factor interplay may be crucial in the regulation of MMP expression by glioma invasion of the normal brain.

Heterogeneous regional expression patterns of matrix metalloproteinases in human malignant gliomas

The aim of the study was to assess the differential intra- and intertumoral heterogeneity and patterns of matrix metalloproteinase expression in human glioblastomas in vivo. 12 glioblastoma samples were analyzed for MMP expression by semi-quantitative RT-PCR. A total of 56 samples (8 adjoining regions of 6 glioblastoma tumors) were immunohistochemically examined for the expression and regional distribution of gelatinase-A (MMP-2), gelatinase-B (MMP-9), matrilysin (MMP-7) and stromelysin-1 (MMP-3). Gelatinase-A mRNA was detected in all samples, gelatinase-B was found in numerous samples. Correspondingly, strong expression levels of both gelatinase protein was seen in immunohistochemistry. Gelatinase-A was expressed by both tumor cells and endothelium while gelatinase-B was found to be restricted to endothelial cells. Stromelysin-1 protein was not detected in any of the samples. Matrilysin was found around tumor cells of three samples from one patient only. The strong immunoreactivity seen for gelatinase-A around tumor cells and blood vessels suggests a role in both tissue degradation and tumor neoangiogenesis which is in accordance with previously published in vitro data. The marked localization of gelatinase-B to the endothelium and its presence in non-infiltrative benign lesions, however, makes a direct proteolytic role of gelatinase-B on ECM components during glioma invasion appear unlikely. Its close association with vascular structures, however, might indicate a link to neoangiogenesis. The significance of matrilysin which was only seen in tumor cells in three samples remains unclear. Stromelysin-1, though strongly expressed in cell lines, does not appear to play a role in glioblastoma tumors in vivo.

The NG2 chondroitin sulfate proteoglycan: role in malignant progression of human brain tumours

The expression and function of NG2, a transmembrane chondroitin sulfate proteoglycan was studied in human gliomas of various histological types in culture using immunocytochemistry and flow cytometry. NG2 was differentially expressed in the neoplasms, with higher expression in high compared to low-grade gliomas. In acutely isolated cells from human biopsies, NG2 +ve and NG2 -ve populations were morphologically distinct from each other, and NG2 +ve cells were more proliferative than NG2 -ve cells. The mitogens platelet derived growth factor (PDGF-AA) and basic fibroblast growth factor (bFGF) added in combination to serum-free medium (SFM) upregulated NG2 expression on glioblastoma multiforme cells in culture but had little effect on NG2 expression on the anaplastic astrocytoma cells. Furthermore, NG2 was colocalised with the platelet derived growth factor alpha receptor (PDGFalphaR) and antibody blockade of the PDGF-alphaR ablated NG2 expression on the glioblastoma multiforme cells, suggesting that increased NG2 expression in the presence of PDGF-AA is mediated via the PDGF-alphaR. Assays of migration and invasion indicate that NG2 +ve glioma cells migrated more efficiently on collagen IV and that NG2 -ve cells were more invasive than their NG2 +ve counterparts. The results indicate that NG2 may be, respectively, positively and negatively related to the proliferative and invasive capacity of glioma cells. Thus, expression of the NG2 proteoglycan may have major implications for malignant progression in glial neoplasms and may prove a useful target for future therapeutic regimens.

Vascular and perivascular GD3 expression in human glioma

A major hallmark of gliomas is their intense neovascularisation. Ganglioside GD3, is one of the major gangliosides which has been implicated in tumour angiogenesis. Recently we reported that GD3 was a potent stimulator of vascular endothelial growth factor release in human glioma cell lines. In the present study we were able to detect GD3-immunoreactivity in 10 out of 10 cases of glioblastoma multiforme and 7 out of 10 cases of anaplastic astrocytoma while low grade tumours were negative. Interestingly, GD3 was intensively expressed in hypervascularised areas of high grade gliomas. These data support the involvement of this ganglioside in brain tumour angiogenesis.

Vascular endothelial growth factor production is stimulated by gangliosides and TGF-beta isoforms in human glioma cells in vitro

Vascular endothelial growth factor (VEGF) is an angiogenic factor which is known to be expressed in several malignancies including glioma. The effect of transforming growth factor-beta (TGF-beta) isoforms as well as gangliosides on VEGF production was investigated in human glioma cell lines. TGF-beta isoforms and gangliosides were found to differentially stimulate VEGF production by these cells. The ganglioside GD3 enhanced this release to the greatest extent and the stimulation was more marked in a glioblastoma cell line than in the two other anaplastic astrocytoma cell lines. These results suggest that both TGF-betas and gangliosides may act as indirect angiogenic factors by stimulating VEGF secretion.