DNA Content and Chromosomal Composition of Malignant Human Gliomas

CD163, a novel therapeutic target, regulates the proliferation and stemness of glioma cells via casein kinase 2

Glioma is a devastating cancer with a dismal prognosis and there is an urgent need to discover novel glioma-specific antigens for glioma therapy. Previous studies have identified CD163-positive tumour cells in certain solid tumours, but CD163 expression in glioma remains unknown. In this study, via an analysis of public datasets, we demonstrated that CD163 overexpression in glioma specimens correlated with an unfavourable patient prognosis. CD163 expression was increased in glioma cells, especially primary glioma cells. The loss of CD163 expression inhibited both cell cycle progression and the proliferation of glioblastoma multiforme (GBM) cell lines and primary glioma cells. CD163 interacted directly with casein kinase 2 (CK2) and CD163 silencing reduced AKT/GSK3β/β-catenin/cyclin D1 pathway activity via CK2. Moreover, CD163 was upregulated in CD133-positive glioma stem cells (GSCs), and CD163 downregulation decreased the expression of GSC markers, including CD133, ALDH1A1, NANOG and OCT4. The knockdown of CD163 impaired GSC stemness by inhibiting the CK2/AKT/GSK3β/β-catenin pathway. Finally, a CD163 antibody successfully induced complement-dependent cytotoxicity against glioma cells. Our findings indicate that CD163 contributes to gliomagenesis via CK2 and provides preclinical evidence that CD163 and the CD163 pathway might serve as a therapeutic target for glioma.

Glioblastomas are composed of genetically divergent clones with distinct tumourigenic potential and variable stem cell-associated phenotypes

Glioblastoma (GBM) is known to be a heterogeneous disease; however, the genetic composition of the cells within a given tumour is only poorly explored. In the advent of personalised medicine the understanding of intra-tumoural heterogeneity at the cellular and the genetic level is mandatory to improve treatment and clinical outcome. By combining ploidy-based flow sorting with array-comparative genomic hybridization we show that primary GBMs present as either mono- or polygenomic tumours (64 versus 36 %, respectively). Monogenomic tumours were limited to a pseudodiploid tumour clone admixed with normal stromal cells, whereas polygenomic tumours contained multiple tumour clones, yet always including a pseudodiploid population. Interestingly, pseudodiploid and aneuploid fractions carried the same aberrations as defined by identical chromosomal breakpoints, suggesting that evolution towards aneuploidy is a late event in GBM development. Interestingly, while clonal heterogeneity could be recapitulated in spheroid-based xenografts, we find that genetically distinct clones displayed different tumourigenic potential. Moreover, we show that putative cancer stem cell markers including CD133, CD15, A2B5 and CD44 were present on genetically distinct tumour cell populations. These data reveal the clonal heterogeneity of GBMs at the level of DNA content, tumourigenic potential and stem cell marker expression, which is likely to impact glioma progression and treatment response. The combined knowledge of intra-tumour heterogeneity at the genetic, cellular and functional level is crucial to assess treatment responses and to design personalized treatment strategies for primary GBM.

Recent advances in the molecular understanding of glioblastoma

Glioblastoma is the most common and most aggressive primary brain tumor. Despite maximum treatment, patients only have a median survival time of 15 months, because of the tumor’s resistance to current therapeutic approaches. Thus far, methylation of the O⁶-methylguanine-DNA methyltransferase (MGMT) promoter has been the only confirmed molecular predictive factor in glioblastoma. Novel “genome-wide” techniques have identified additional important molecular alterations as mutations in isocitrate dehydrogenase 1 (IDH1) and its prognostic importance. This review summarizes findings and techniques of genetic, epigenetic, transcriptional, and proteomic studies of glioblastoma. It provides the clinician with an up-to-date overview of current identified molecular alterations that should ultimately lead to new therapeutic targets and more individualized treatment approaches in glioblastoma.

Molecular cytogenetic analysis in the study of brain tumors: findings and applications

Classic cytogenetics has evolved from black and white to technicolor images of chromosomes as a result of advances in fluorescence in situ hybridization (FISH) techniques, and is now called molecular cytogenetics. Improvements in the quality and diversity of probes suitable for FISH, coupled with advances in computerized image analysis, now permit the genome or tissue of interest to be analyzed in detail on a glass slide. It is evident that the growing list of options for cytogenetic analysis has improved the understanding of chromosomal changes in disease initiation, progression, and response to treatment. The contributions of classic and molecular cytogenetics to the study of brain tumors have provided scientists and clinicians alike with new avenues for investigation. In this review the authors summarize the contributions of molecular cytogenetics to the study of brain tumors, encompassing the findings of classic cytogenetics, interphase- and metaphase-based FISH studies, spectral karyotyping, and metaphase- and array-based comparative genomic hybridization. In addition, this review also details the role of molecular cytogenetic techniques in other aspects of understanding the pathogenesis of brain tumors, including xenograft, cancer stem cell, and telomere length studies.

Cytogenetic abnormalities related to histopathologic grade of astrocytic tumors

Cytogenetic analysis was performed on 7 low-grade astrocytomas, 10 anaplastic astrocytomas, and 14 glioblastomas. Abnormal chromosome numbers were noted in all cases of high-grade astrocytomas but were rarely noted in low-grade astrocytomas (28%). The most consistent changes in high-grade astrocytomas were complete loss of chromosome 10 (61%), gain of chromosome 7 (56%), and loss of chromosome 17 (28%). Certain structural abnormalities, such as marker chromosomes and double minutes (33%), and the deletion and translocation of chromosomes 1 (33%) and 17 (17%), were also noted. These results indicate that changes in the number and/or structure of chromosomes with related inactivation of tumor suppressor gene or oncogene activation might play a critical role in the formation and anaplastic progression of astrocytic tumors.

Nuclear morphometry and DNA densitometry of human gliomas by image analysis

In 48 patients with gliomas in whom complete clinical follow-up was obtained, DNA ploidy was evaluated by using formalin-fixed paraffin-embedded tissues and by means of image analysis. The mean DNA indices, determined by averaging DNA indices of all tumor cells in a tumor, were mainly affected by mean DNA indices of the nuclei of SG2M phase tumor cell (including S phase and G2M phase cells) (SG2M DNA indices) and that mean DNA indices correlated with the SG2M phase fraction. The SG2M DNA indices and the percentage of tumor cells with S phase and G2M phase were higher in high grade gliomas including anaplastic glioma and glioblastoma multiforme than in low grade gliomas. Patients with G2M-hypertetraploid tumors demonstrated a shorter time to tumor progression than those with G2M-tetraploid in high grade glioma. Morphometrically, the nuclei of SG2M phase glioma cells were larger and more deformity than those of G0G1 phase (including G0 phase and G1 phase cells) cells. The G2M-hypertetraploid tumors were highly malignant and demonstrated large nuclei, greater nuclear deformity, and a higher proliferative potential. The G2M-tetraploid gliomas demonstrated a shorter time to tumor progression in cases whose the SG2M fraction was large. In contrast, G2M-hypotetraploid gliomas revealed an insignificant trend towards a longer time to tumor progression than those associated with tetraploid and hypertetraploid gliomas. We emphasize herein the prognostic importance of the SG2M phase cell, as well as other proliferation indices.

Familial glioblastoma

The authors describe a family with three members affected by glioblastoma. The proband patient, a 7 year-old girl, developed a rare complication, a pulmonary metastasis. Chromosomal analysis of her peripheral blood lymphocytes showed a normal karyotype (46, XX), without structural abnormalities. Cytogenetic study of the tumor cells disclosed several abnormalities: 46, XX, 7q-/46, XX, -2, 4p-, 7p-, +15/46, XX. Some aspects about genetics of glial neoplasms are discussed.

Relationship between DNA ploidy level and tumor sociology behavior in 12 nervous cell lines

Cell population sociology was studied in two medulloblastomas and 10 astrocytic human tumor cell lines by means of the characterization of the structure of neoplastic cell colonies growing on histological slides. This was carried out via digital cell image analysis of Feulgen-stained nuclei, to which the Delaunay triangulation and Voronoi paving mathematical techniques were applied. Such assessments were compared to the DNA polidy level (assessed by means of DNA histogram typing). The results show that the cell colony architecture characteristics differed markedly according to whether the cell lines were euploid (diploid or tetraploid) or aneuploid (hyperdiploid, triploid, hypertriploid, or polymorphic). In fact, the cell colonies from the euploid cell nuclei populations were larger and more dense than those from the aneuploid ones. Furthermore, for an identical period of culture, the cell lines from high-grade malignant astrocytic tumors (glioblastomas) exhibited cell colonies that were larger and more dense than those in cell lines from low-grade astrocytic tumors (astrocytomas). In each of these two groups, the diploid cell nuclei populations exhibited cell colonies larger and more dense than the nondiploid colonies. The present methodology is now being applied in vivo to histological sections of surgically removed human brain tumors in order to distinguish between high-risk clinical subgroups and medium-risk subgroups in clearly circumscribed histopathological groups.

Chromosome number and carmustine sensitivity in human gliomas

BACKGROUND

Although some patients with malignant gliomas respond to treatment with chemotherapeutic agents like BCNU, tumor recurrence inevitably occurs, heralding the development of chemoresistance. Treating and/or preventing chemoresistance requires distinguishing newly developed resistance from the presence of intrinsically resistant cells in the primary tumor population. This study relates the chromosomal complements of freshly resected astrocytomas to the cells' chemosensitivity and ultimately to the patients' response to treatment.

METHODS

The authors dissociated 31 freshly resected human gliomas (5 astrocytomas, 10 anaplastic astrocytomas, 16 glioblastomas multiforme) into single cells, and performed cytogenetic analysis and BCNU sensitivity testing using the colony-forming assay (CFA) on first division cells from these tumors.

RESULTS

The major cytogenetic abnormalities involved the loss of a sex chromosome in all three classes of gliomas and the gain of chromosome 7 in anaplastic astrocytoma and glioblastoma multiforme; clonal marker chromosomes were observed in only anaplastic astrocytoma and glioblastoma multiforme with no common rearrangement observed among the tumors. The five astrocytomas were near-diploid (2n+/-, 35-57 chromosomes/cell), and all were resistant to BCNU. Seven of ten anaplastic astrocytomas were composed primarily of 2n+/- cells and were BCNU resistant. Three other anaplastic astrocytomas had a 39% or greater representation of 4n+/- cells (88-101 chromosomes/cell), and these tumors were sensitive to BCNU. Ten of 16 glioblastomas multiforme were composed predominantly of 2n+/- cells and were resistant to carmustine. Six other glioblastomas multiforme had at least 41% 3n+/- (58-87 chromosomes/metaphase) and 4n+/- cell populations and were sensitive to carmustine. Thus, gliomas demonstrating BCNU sensitivity were more than 60% hyperdiploid (60 or more chromosomes/metaphase) with 1 to 8 clonal marker chromosomes and multiple clonal populations involving complex karyotypic deviations. In contrast, all 22 resistant tumors were composed primarily of near-diploid cells. Only 4 of 22 tumors had a clonal marker, and the chromosome ploidy changes were less extensive.

CONCLUSIONS

In freshly resected untreated human gliomas, BCNU is most effective against hyperdiploid cells that have extensive ploidy changes and chromosome rearrangement, whereas resistance to carmustine is characteristic of near-diploid populations with few ploidy changes and rearranged chromosomes. This observation was consistent for all three classes of gliomas.

Relationship between proliferative activity and ploidy level in a series of 530 human brain tumors, including astrocytomas, meningiomas, schwannomas, and metastases

By identifying six DNA histogram types (diploid, hyperdiploid, triploid, hypertriploid, tetraploid, and polymorphic) in a series of 206 astrocytic tumors, we showed recently that patients with hypertriploid astrocytic tumors have a better possibility of survival than patients with other DNA histogram-type related tumors. In the present work DNA histogram type and proliferation index (S-phase fraction) are characterized in a series of 530 adult tumors from the central and peripheral nervous systems. Of these 530 tumors, there were 79 nerve sheath tumors, 181 meningiomas, 221 astrocytic tumors, and 49 metastases. Analysis was performed by means of digital cell image examination of Feulgen-stained nuclei from formalin-fixed, paraffin-embedded tumors. The data reveal that there was a majority of diploid tumors (66%) in the primary tumor group (nerve sheath tumors, meningiomas, and astrocytic tumors), while aneuploid tumors were in a marked majority (90%) in the secondary (metastatic) brain tumor group, with a predominance (47%) of the polymorphic tumor type. Independently of tumor histopathologic group, the hypertriploid-type tumors proliferated less actively than the five other types. Such a feature might partly explain the better prognosis associated with hypertriploid astrocytic tumors as compared with what occurs with respect to the other DNA histogram-type related tumors.

Histopathologic grading and DNA ploidy in relation to survival among 206 adult astrocytic tumor patients

BACKGROUND

The authors studied the benefit of performing histopathologic grading and DNA ploidy characterization with respect to patient survival in a series of 206 astrocytomas (AST) for which they obtained 134 complete clinical follow-ups.

METHODS

The material analyzed came from archival material, i.e., formalin-fixed paraffin-embedded tissues. DNA ploidy was assessed by means of a cell image processor computing the integrated optical density (IOD) on Feulgen-stained nuclei.

RESULTS

Results showed that histopathologic diagnosis in three grades, i.e., AST, anaplastic astrocytoma (ANA), and glioblastoma multiforme (GBM), had a significant prognostic value. Patients with AST showed a mean survival time (between histopathologic diagnosis and death) of more than 36 +/- 6 months (AST versus ANA or GBM) (P less than 0.001). Patients with ANA and GBM showed a mean survival time of 15 +/- 2 and 10 +/- 1 months, respectively, (ANA versus GBM) (P less than 0.05). Patient age strongly correlated with survival. Patients younger than 40 years of age had a mean survival time of 20 +/- 4 months. Patients between 41 and 60 years of age had a mean survival time of 12 +/- 2 months, and patients older than 60 years of age had a mean survival time of 11 +/- 1 months.

CONCLUSIONS

Considering DNA ploidy characterization, the authors noticed that aneuploid ANA (DNA index [DI] more than 1.30) were associated with a significantly higher mean patient survival time compared with that associated with euploid ANA. In contrast, the authors did not find this in either of the groups with AST and GBM. Recognizing six DNA histogram types (diploid, triploid, tetraploid, hyperdiploid, hypertriploid, and polymorphic), the authors observed that hypertriploid tumors were associated with greater patient survival compared with what happened in the cases of the five other DNA histogram types. This was true with respect to the three AST histopathologic types. Thus, DNA ploidy determination seemed helpful in characterizing aggressiveness in adult AST.

Cytophotometry in tumor pathology. A critical review of methods and applications, and some results of DNA analysis

In tumor pathology the quantitation of cellular substances can be of diagnostic value. Microscope cytophotometry and digital image analysis and, on the other hand, flow cytometry are supplementary methods for measuring, each with a typical spectrum of application. The methods are predominantly used for DNA analysis: Static and image cytophotometry are applicable to cytologic and histologic slides preferably for identifying stem lines in tumors of heterogenous morphology and in merely circumscribed lesions (e.g., precancerous lesions). On the other hand, sampling errors due to preselection, and the often low number of cells actually measured, may preclude the possibility of exact cell cycle analysis. This is, in fact, an important additional option of flow cytometry resulting from the high resolution of DNA histograms, which is explained by the large number of cells that can be measured in a short period. Sampling errors in flow cytometry may result from the preparation of single cell suspensions which in certain tumor entities may suppress a varying amount of particularly fragile cells or nuclei. The prognostic significance of DNA ploidy, stem line heterogeneity and S-phase fraction is clearly described in quite a number of tumor entities. Independent of its prognostic value, the cytometric identification of stem lines might be particularly useful in the follow-up of tumor patients, where it may indicate the effectivity of systemic therapy. The development of therapeutic concepts is aptly supported by flow cytometric cell cycle analysis which helps to assess the in vitro effect of combined cytostatics on the proliferative process. Moreover, multiparameter analysis of biopsy samples may provide greater accuracy in characterising individual tumor stem lines and may furthermore help to develop improved protocols for the therapy of solid tumors.

DNA in human glioblastomas. A flow-fluorescence cytometrical examination of 96 tumors

The Flow-Fluorescence Cytometric Method (FCM) was applied to investigate the DNA content and the ploidy outlines of each of 96 glioblastomas. No specific DNA pattern was detected, possibly because of the tangle morphology of these variable tumors. Due to their capricious growth the DNA distribution proved to fluctuate greatly. Thus, the series, arranged according to increased PI (proliferation index) values, exhibited a wide spread within a total range from 7.1-97.15% (mean 39.3%) PI. A threefold subdivision of main types (I-III) appears to be of practical use for clinical prognostic assessment: "diploid" tumors with a PI range up to 10% (N = 7) are followed by "abnormal" chiefly tetra- and hyper-tetraploid tumors up to PI values about 30% (N = 21). The third category includes cases showing excessive "aneuploidy" combined more and more with polyploidy and valid stemlines, up to the PI maximum of about 97 rel.% (N = 68). Thus, in 89 tumors clear pathological changes of DNA content can be decoded; of these 68 (76.4%) express a considerable aneuploidy and polyploidy respectively.

Major structural alterations of the c-sis gene are not observed in a series of tumors of the human central nervous system

Expression of the c-sis oncogene, the gene encoding the B chain of platelet-derived growth factor (PDGF), may be related to initiation and/or progression of glial cell tumorigenesis by PDGF-mediated autocrine growth stimulation. As the mechanism for activation of expression of the c-sis gene in gliomas is not known, we searched for possible structural alterations of c-sis DNA in these tumors. Genomic Southern blots of DNA from 7 different cultured human glioblastoma cell lines and 15 different solid human brain tumors revealed no significant change in either the gross structure or the copy number of the c-sis gene in tumor cells vs. control cells. Activation of glioma c-sis gene expression is therefore not the result of a gross rearrangement or amplification of the c-sis gene. Expression of c-sis mRNA was detected in all of 12 different solid human brain tumors, 11 of which were of glial cell origin. However, in tissue adjacent to 5 different tumors, approximately the same level of c-sis mRNA was seen.

Proto-oncogene abnormalities and their relationship to tumorigenicity in some human glioblastomas

Human glioblastomas are highly malignant intracranial tumors, some of which demonstrate amplification of the epidermal growth factor-receptor (EGF-R) gene. Overexpression of this gene is seen in the majority of primary tumors; however, the role of the EGF-R gene in glial tumorigenesis is unknown. The authors explored the relationship between EGF-R gene expression and glioblastoma cell growth in vitro and in vivo and found that this level of EGF-R gene expression did not correlate with tumor cell growth either in soft agar or in the nude mouse. This suggests that the EGF-R gene is not involved in effecting direct growth stimulation in glial oncogenesis. Tumorigenesis involves differentiation arrest; therefore, the expression of several proto-oncogenes in neuroectodermal tumors was investigated to evaluate the potential involvement of the EGF-R gene in glial differentiation. A nonoverlapping expression of the N-myc and EGF-R genes was found in neuronal-derived and glial-derived tumors, respectively. This suggests that the EGF-R gene may be involved in differentiation or its arrest in glia.

Oncogenes and neuro-oncology

The application of molecular biological techniques to the study of lympho-erythroid neoplasms, colo-rectal carcinoma and neuroblastoma has led to fundamental insights into the nature of cellular proliferation, transformation and immortalisation as well as providing prognostic information about the biological behaviour of certain tumours. The study of the molecular genetics of central nervous system tumours with particular reference to oncogenes is however in its infancy. Most of the current literature concerns studies of small numbers of glial tumours or of glial tumour cell lines. In this review the results of these studies are analysed and compared with relevant oncogene findings in experimental cerebral neoplasia, extracranial tumours and postulated mechanisms of oncogene activation. The role of proto-oncogenes in the development of the brain, and the clinical relevance of advances in molecular biology to central nervous system neoplasia are discussed.

DNA content and marker expression in human glioma explants

Immunohistochemical studies of astrocytoma tissue have predominantly shown fibronectin (FN) positivity restricted to vessels and glial fibrillary acidic protein (GFAP) positivity in the parenchyma. Cultured glioma cell lines, however, express both FN and GFAP. We measured the DNA content of explants of gliomas to determine if the ploidy of the FN-positive and GFAP-positive cells differed. Thirty-three explants from four high grade gliomas were cultured on slides. FN and GFAP markers were determined by double immunofluorescence. The slides were stained by the Feulgen method, the explants relocated and the DNA content measured by microdensitometry using the CAS-100 instrument. Human leukocytes applied to the slides were used as a diploid standard. Eleven GFAP-positive explants were hyperdiploid and one hypodiploid. Five FN-positive explants were diploid, three hypodiploid and ten hyperdiploid. One FN-positive explant was biclonal with aneuploid subpopulations. Two hyperdiploid explants, each of which had monoclonal histogram patterns, expressed both FN and GFAP. We conclude that most FN-positive cells, in addition to GFAP-positive cells, from cultured gliomas represent neoplastic cells. These may be present in the tumor in low numbers or may result from marker switching in culture.