Coexpression of platelet-derived growth factor (PDGF) B chain and PDGF B-type receptor in human gliomas

Importance of GFAP isoform-specific analyses in astrocytoma

Gliomas are a heterogenous group of malignant primary brain tumors that arise from glia cells or their progenitors and rely on accurate diagnosis for prognosis and treatment strategies. Although recent developments in the molecular biology of glioma have improved diagnosis, classical histological methods and biomarkers are still being used. The glial fibrillary acidic protein (GFAP) is a classical marker of astrocytoma, both in clinical and experimental settings. GFAP is used to determine glial differentiation, which is associated with a less malignant tumor. However, since GFAP is not only expressed by mature astrocytes but also by radial glia during development and neural stem cells in the adult brain, we hypothesized that GFAP expression in astrocytoma might not be a direct indication of glial differentiation and a less malignant phenotype. Therefore, we here review all existing literature from 1972 up to 2018 on GFAP expression in astrocytoma patient material to revisit GFAP as a marker of lower grade, more differentiated astrocytoma. We conclude that GFAP is heterogeneously expressed in astrocytoma, which most likely masks a consistent correlation of GFAP expression to astrocytoma malignancy grade. The GFAP positive cell population contains cells with differences in morphology, function, and differentiation state showing that GFAP is not merely a marker of less malignant and more differentiated astrocytoma. We suggest that discriminating between the GFAP isoforms GFAPδ and GFAPα will improve the accuracy of assessing the differentiation state of astrocytoma in clinical and experimental settings and will benefit glioma classification.

Transcriptional co-activator TAZ sustains proliferation and tumorigenicity of neuroblastoma by targeting CTGF and PDGF-β

Neuroblastoma is a common childhood malignant tumor originated from the neural crest-derived sympathetic nervous system. A crucial event in the pathogenesis of neuroblastoma is to promote proliferation of neuroblasts, which is closely related to poor survival. However, mechanisms for regulation of cell proliferation and tumorigenicity in neuroblastoma are not well understood. Here, we report that overexpression of TAZ in neuroblastoma BE(2)-C cells causes increases in cell proliferation, self renewal and colony formation, which was restored back to its original levels by knockdown of TAZ in TAZ-overexpression cells. Inhibition of endogenous TAZ attenuated cell proliferation, colony formation and tumor development in neuroblastoma SK-N-AS cell, which could be rescued by re-introduction of TAZ into TAZ-knockdown cells. In addition, we found that overexpressing TAZ-mediated induction of CTGF and PDGF-β expression, cell proliferation and colony formation were inhibited by knocking down CTGF and PDGF-β with siRNA in TAZ-overexpressing cell. Overall, our findings suggested that TAZ plays an essential role in regulating cell proliferation and tumorigenesis in neuroblastoma cells. Thus, TAZ seems to be a novel and promising target for the treatment of neuroblastoma.

Molecular biology of unreresectable meningiomas: implications for new treatments and review of the literature

Even though meningiomas are most often benign tumors, they can be locally invasive and can develop in locations that prevent surgical treatment. The molecular and biologic factors underlying meningioma development are only now beginning to be understood. Genetic factors such as mutations in the neurofibromatosis-2 gene and in chromosomes 1, 9, and 10 play important roles in meningioma development and may be responsible for atypical tumors in some cases. Cellular factors such as telomerase activation and tyrosine kinase receptor mutations may also play an important role. Finally, autocrine and paracrine factors including epidermal growth factor receptor, platelet-derived growth factor-1, and fibroblast growth factor have been implicated in the development of some tumors. Although the relationship between the various factors implicated in tumor development is unknown, understanding these factors will be critical in the treatment of malignant or surgically inaccessible tumors.

Phase I trial of imatinib in children with newly diagnosed brainstem and recurrent malignant gliomas: a Pediatric Brain Tumor Consortium report

This study estimated the maximum tolerated dose (MTD) of imatinib with irradiation in children with newly diagnosed brainstem gliomas, and those with recurrent malignant intracranial gliomas, stratified according to use of enzyme-inducing anticonvulsant drugs (EIACDs). In the brainstem glioma stratum, imatinib was initially administered twice daily during irradiation, but because of possible association with intratumoral hemorrhage (ITH) was subsequently started two weeks after irradiation. The protocol was also amended to exclude children with prior hemorrhage. Twenty-four evaluable patients received therapy before the amendment, and three of six with a brainstem tumor experienced dose-limiting toxicity (DLT): one had asymptomatic ITH, one had grade 4 neutropenia and, one had renal insufficiency. None of 18 patients with recurrent glioma experienced DLT. After protocol amendment, 3 of 16 patients with brainstem glioma and 2 of 11 patients with recurrent glioma who were not receiving EIACDs experienced ITH DLTs, with three patients being symptomatic. In addition to the six patients with hemorrhages during the DLT monitoring period, 10 experienced ITH (eight patients were symptomatic) thereafter. The recommended phase II dose for brainstem gliomas was 265 mg/m(2). Three of 27 patients with brainstem gliomas with imaging before and after irradiation, prior to receiving imatinib, had new hemorrhage, excluding their receiving imatinib. The MTD for recurrent high-grade gliomas without EIACDs was 465 mg/m(2), but the MTD was not established with EIACDs, with no DLTs at 800 mg/m(2). In summary, recommended phase II imatinib doses were determined for children with newly diagnosed brainstem glioma and recurrent high-grade glioma who were not receiving EIACDs. Imatinib may increase the risk of ITH, although the incidence of spontaneous hemorrhages in brainstem glioma is sufficiently high that this should be considered in studies of agents in which hemorrhage is a concern.

A list of candidate cancer biomarkers for targeted proteomics

We have compiled from literature and other sources a list of 1261 proteins believed to be differentially expressed in human cancer. These proteins, only some of which have been detected in plasma to date, represent a population of candidate plasma biomarkers that could be useful in early cancer detection and monitoring given sufficiently sensitive specific assays. We have begun to prioritize these markers for future validation by frequency of literature citations, both total and as a function of time. The candidates include proteins involved in oncogenesis, angiogenesis, development, differentiation, proliferation, apoptosis, hematopoiesis, immune and hormonal responses, cell signaling, nucleotide function, hydrolysis, cellular homing, cell cycle and structure, the acute phase response and hormonal control. Many have been detected in studies of tissue or nuclear components; nevertheless we hypothesize that most if not all should be present in plasma at some level. Of the 1261 candidates only 9 have been approved as "tumor associated antigens" by the FDA. We propose that systematic collection and large-scale validation of candidate biomarkers would fill the gap currently existing between basic research and clinical use of advanced diagnostics.

State of the art chemotherapeutic management of pediatric brain tumors

CNS tumors are the most common solid tumor of childhood. This article will review current treatments for pediatric brain tumors; low-grade gliomas, high-grade gliomas, medulloblastomas and ependymomas. It will also highlight the treatments that are used for brain tumors in very young children and in children with recurrent brain tumors. The management of recurrent pediatric brain tumors unresponsive to standard therapy will be discussed. The agents used in this setting are mainly biological modifiers, which attempt to provide molecularly targeted therapy. Future directions of therapy for pediatric brain tumors are described. Future treatment paradigms will need to consider examining the use of multiple biological modifiers. Similarly, these agents will need to be examined in combination with cytotoxic chemotherapy. Finally, the future direction of pediatric neuro-oncology and the focus of the field as it battles pediatric brain tumors is discussed.

Selective kinase inhibition with daily imatinib intensifies toxicity of chemotherapy in patients with solid tumours

The aim of this study was to determine the safety and maximum-tolerated doses of imatinib combined with cytotoxic chemotherapy (either gemcitabine or doxorubicin). Patients with advanced solid tumours were enrolled separately in two different combinations of imatinib with chemotherapy (imatinib + gemcitabine or imatinib + doxorubicin). A standard modified Fibonacci inter-cohort dose escalation was planned for each combination. Sixteen patients were accrued. Seven patients received gemcitabine and imatinib. A separate cohort of nine patients received imatinib and doxorubicin. In both groups, dose-limiting toxicity (DLT) was observed at the initial dose level requiring dose reductions for subsequent cohorts. Further DLTs were observed necessitating closure of the protocol. Daily dosing of imatinib with concurrent administration of cytotoxic chemotherapy (either gemcitabine or doxorubicin) at standard doses was associated with toxicity that was clinically unacceptable. It remains unclear whether addition of growth factors might improve tolerability for imatininb in combination with cytotoxic chemotherapy.

The treatment of high grade gliomas and diffuse intrinsic pontine tumors of childhood and adolescence: a historical - and futuristic - perspective

Pediatric high grade gliomas represent a heterogeneous group of tumors with poor prognoses despite the use of multimodal treatment. Very little progress has been made over the past decades in identifying efficacious therapeutic modalities against both high grade gliomas and diffuse brainstem gliomas in children. The degree of surgical resection is the most important clinical prognostic factor for children with high grade gliomas, and a complete resection should be attempted whenever feasible. The role of radiation therapy in the treatment of older children with high grade gliomas and diffuse brain stem gliomas is undisputed; however the benefit of using radiation for patients less than 6 years of age (with high grade gliomas) might be questionable. Despite the absence of solid evidence to support its use, chemotherapy is routinely used against these tumors. Currently temozolomide is being investigated due to its activity in adult trials and based on preliminary data regarding recurrent disease. A small subgroup of patients can be successfully treated with high dose chemotherapy followed by autologous stem cell rescue. Early trials using this modality in the past had been associated with high morbidity and mortality. High dose chemotherapy with autologous stem cell rescue in selected patients with minimal residual disease, angiogenesis inhibitors, radiosensitizers and other biological modifiers are being currently investigated in phase I/II trials.

Widespread CXCR4 activation in astrocytomas revealed by phospho-CXCR4-specific antibodies

The chemokine receptor CXCR4 is expressed in many cancers where it may regulate tumor cell growth and migration. The role of CXCR4 in cancer will depend on it being in an activated, signaling state. To better define the significance of CXCR4 expression in cancer, we developed an antibody that can distinguish CXCR4 phosphorylated on serine 339, a residue previously identified as a site for ligand-induced phosphorylation. With this antibody, we investigated the mechanisms of CXCR4 phosphorylation and evaluated the phosphorylation status of CXCR4 in human astrocytomas. In vitro, phosphorylation of serine 339 occurred in response to CXCL12 or epidermal growth factor (EGF) treatment and was increased by protein kinase C activation. In all grades of astrocytomas, CXCR4 was expressed in tumor cells and some endothelial cells, whereas CXCL12 was present in endothelial cells and infiltrating microglia. We found that CXCR4 phosphorylated on serine 339 was present in tumor cells and vascular endothelial cells in all grades of astrocytoma. These data indicate that CXCR4 is expressed and activated in astrocytomas and that phosphorylation of CXCR4 can occur through ligand activation or transactivation via the EGF receptor. These studies extend the potential roles of CXCR4 in cancer to include functions associated with benign (grade 1) tumors. The ability to distinguish phosphorylated CXCR4 will be invaluable for the continued analysis of the role of CXCR4 in cancer and the development of CXCR4 antagonist therapy for patients suffering with primary tumors of the brain and other sites.

Can mouse models for brain tumors inform treatment in pediatric patients?

Brain tumors represent the most common solid tumor of childhood. Although the histology of many pediatric brain tumors is similar to that of their adult counterparts, significant differences exist with regard to tumor location and response to therapy. The biological and genetic basis for this difference is poorly understood, as tumor tissue is generally unavailable for such studies. While targeted therapies directed against specific molecules active in cancer represents a new arsenal of agents for treating these tumors, such agents are generally not being developed for pediatric cancer in particular. Therefore, new agents for treatment of pediatric glioma must be obtained from compounds being tested against tumors of comparable histology in adult patients. Compounding this problem, although brain tumors are among the most lethal tumors of childhood, their absolute number is relatively small. As a consequence, trials with new agents must be prioritized based on the likelihood that a particular agent or combination of agents will have efficacy in pediatric cancer. Mouse models for brain tumors may help to identify targeted agents, and combinations of agents, effective against these tumors. Such data can be used to prioritize therapies for clinical trials in children with these tumors.

Molecular genetic changes in a series of neuroepithelial tumors of childhood

Amplification of the EGFR, mdm2, CDK4 and PDGFR A genes has been widely demonstrated in adult malignant gliomas, almost exclusively glioblastomas. To determine the role of these mutational events in pediatric astrocytic gliomas we investigated the presence of EGFR, mdm2, CDK4 and PDGFR A gene amplification in 38 childhood brain tumor biopsies, including 24 low-grade astrocytomas and 14 malignant tumors. We used differential PCR assay on DNA extracted either from paraffin embedded or frozen tissues. EGFR gene amplification was detected in 4 out of 14 malignant tumors; no low-grade astrocytoma showed amplification. Tumors with EGFR gene amplification were negative for the presence of p53 mutations, as observed in a previous study. One glioblastoma showed PDGFR A amplification, while no amplifications were observed for mdm2 and CDK4 genes. These data are in line with those obtained from studies on gliomas of adults and suggest the existence of two different subsets of malignant gliomas also in pediatric brain tumors: one carrying EGFR gene amplification, the other showing p53 mutations.

Molecular abnormalities and correlations with tumor response and outcome in glioma patients

Molecular analysis approaches hold promise to refine the management of patients with malignant gliomas. An important step in the application of these techniques to guide clinical decision-making involves transitioning these approaches from the research setting into the clinical diagnostic arena, using methods that can be performed rapidly and reliably on surgically obtained tumor specimens. Many centers have begun this process for the detection of chromosome 1p and 19q deletions in oligodendroglial neoplasms. It is likely that the current limited portfolio of prognostic markers will be increased substantially during the next several years as innovative techniques for tumor genotyping and gene expression profiling help to identify additional correlates of tumor prognosis. An associated challenge involves demonstrating that biological stratification can support therapeutic stratification that will influence, rather than merely predict, the outcome of patients with brain tumors. The realization of this long-range goal will require the identification of novel therapeutic strategies that hold promise for improving the outcome of molecularly defined subsets of high-grade gliomas, which as a group remain largely resistant to conventional therapies.

Receptor expression, cytogenetic, and molecular analysis of six continuous human glioma cell lines

Six human glioma cell lines were established from tissues obtained from five patients diagnosed with Kernohan grade IV glioblastoma multiforme and one from a patient with a grade II astrocytoma. One line was from a recurrent patient who had received prior therapy; the other lines were derived from patients at initial diagnosis and/or before cytoreductive therapies other than surgery were given. Considerable variability in phenotypic, karyotypic, and cell surface marker expression was displayed between the six human glioma cell lines. The karyotypes ranged from apparently normal (grade II astrocytoma) to those with complex rearrangements. Trisomy of chromosome 7 was the most common abnormality. The extensive cytogenetic and molecular characterization of these lines may facilitate their utilization in cellular and molecular biologic studies.

Platelet-derived growth factor in human brain tumors

This paper initially reviews ligand and receptor systems for the PDGF family and the signalling systems they use as well as their role in neural developments. It then describes the putative role of this family in astrocytoma, meningioma, and pituitary adenoma pathogenesis. Potential therapies with receptor antagonists or dominant negative mutants are discussed in the final sections.

Growth factor PDGF-B/v-sis confers a tumorigenic phenotype to human tumor cells bearing PDGF receptors but not to cells devoid of receptors: evidence for an autocrine, but not a paracrine, mechanism

Numerous established human tumor lines co-express platelet-derived growth factor (PDGF) and cognate receptors, suggesting that an autocrine and/or paracrine growth mechanism may be a causal or contributing mechanism to their transformed phenotype. Indeed, it is known that a PDGF-autocrine system is functional in several established tumor lines, especially in human gliomas, and a model for a functional paracrine mechanism has been established in a human melanoma line. However, at least 168 human cell lines representing 26 different human tumor types have been reported to continuously express PDGF-A and/or -B chains, and 55 of these also express PDGF receptors. For the majority of these cases, the significance of co-expression and the relative roles of autocrine and paracrine mechanisms in transformation remains unclear. Here, we show that human glioblastoma T98G cells co-express PDGF-B/c-sis and moderate levels of the cognate beta-type PDGF receptor (PR-beta) but are not tumorigenic in athymic mice. In contrast, human breast carcinoma MCF-7 cells do not express PR-beta and are tumorigenic. Clonal lines of each cell type with greatly increased secretion of p16w(T98Gsis and MCF-7sis cells) were characterized. T98Gsis cells are 85% tumorigenic and occasionally develop pulmonary metastases, showing that endogenous PR-beta can mediate complete transformation upon sufficient stimulation. In contrast, MCF-7sis cells exhibit some growth slowing in vitro and an exactly proportional decrease in tumor growth rate. We conclude that a PDGF-autocrine, and not a paracrine, mechanism best accounts for the acquired tumorigenicity of T98Gsis cells, thereby emphasizing the potential significance of expression of even moderate levels of PR-beta by human tumor cells.

Control of meningioma cell growth by platelet-derived growth factor (PDGF)

We have examined the possible involvement of PDGF and PDGF receptors in the growth control of five meningiomas, analyzing the biopsy specimens and the primary cultures derived from the same tumors. Light and electron microscopy demonstrated that MAbs against PDGF beta-receptors immunodecorate meningioma cells in vivo and in vitro, while those against alpha-receptors gave negative results. The effects of PDGF isoforms AA, AB, BB and of PDGF neutralizing antibodies on meningioma cultures were examined using [3H]thymidine incorporation analysis. Only with PDGF-AB and -BB a mitogenic effect was observed, while PDGF-neutralizing antibodies produced a reduction of [3H]thymidine incorporation. The production of PDGF-like growth factors by meningioma cells was tested analyzing the effects of meningioma culture-conditioned media on the growth of Swiss 3T3 cells. In all cases meningioma conditioned media stimulated the in vitro growth of 3T3 fibroblasts and this stimulatory effect was strongly reduced by PDGF-neutralizing antibodies. Furthermore, Northern blot analysis demonstrated expression of c-sis/PDGF-B and PDGF beta-receptors mRNA in all meningioma biopsies and in all the derived cultures. Our results provide strong evidence that PDGF-B chain and PDGF beta-receptors are involved in growth control mechanisms of human meningiomas through autocrine and/or paracrine mechanisms.

Signal-transduction therapy. A novel approach to disease management

In the past decade it has become apparent that many diseases result from aberrations in signaling pathways. These include proliferative diseases such as cancers, atherosclerosis and psoriasis and inflammatory conditions such as sepsis, rheumatoid arthritis and tissue rejection. These findings refocused the research of the medical community to seek new modalities for disease management which essentially consist of designing drugs which intercept cell signaling. In this review, the emerging success in using tyrosine kinase blockers and other signal interceptors, such as protein kinase C blockers, Ras blockers, Ca2+ signaling inhibitors and estrogen antagonists which inhibit growth of cancer cells in vitro and in vivo, will be discussed. These signal interceptors, especially tyrosine-kinase blockers, are also able to block inflammatory responses and the proliferation of vascular smooth muscle cells and psoriatic keratinocytes. The utility of signal interceptors in analyzing signal-transduction pathways is also discussed.

Antisense expression of protein kinase C alpha inhibits the growth and tumorigenicity of human glioblastoma cells

To investigate the role of protein kinase C (PKC) in the growth of astrocytic brain tumors, human glioblastoma cell line U-87 was stably transfected with the antisense complementary deoxyribonucleic acid encoding PKC alpha. The effect of selectively down-regulating the alpha isoform on other PKC isoforms, as well as serum-dependent proliferation and in vivo tumorigenicity, was determined. U-87 cells expressed high levels of PKC alpha and lesser amounts of the gamma, epsilon, and zeta isoforms, and a similar PKC isoform pattern was observed in two other human glioblastoma cell lines. Expression of the antisense PKC alpha complementary deoxyribonucleic acid resulted in no detectable PKC alpha by immunoblotting and a 95% reduction in total Ca2+/phospholipid-dependent PKC activity. U-87 cells expressing antisense PKC alpha exhibited an increase in doubling time in vitro, less serum-dependent growth, and reduced sensitivity to a selective PKC inhibitor, Ro 31-8220. The transplantation of U-87 cells expressing antisense PKC alpha into nude mice resulted in no tumor formation. These observations suggest that the inhibition of PKC alpha may be an important chemotherapeutic target for arresting the growth of glioblastomas.