Comparative molecular genetic profiles of anaplastic astrocytomas/glioblastomas multiforme and their subsequent recurrences

The effects of alternating electric fields in glioblastoma: current evidence on therapeutic mechanisms and clinical outcomes

Glioblastoma is both the most common and most lethal primary CNS malignancy in adults, accounting for 45.6% of all malignant CNS tumors, with a 5-year survival rate of only 5.0%, despite the utilization of multimodal therapy including resection, chemotherapy, and radiation. Currently available treatment options for glioblastoma often remain limited, offering brief periods of improved survival, but with substantial side effects. As such, improvements in current treatment strategies or, more likely, the implementation of novel strategies altogether are warranted. In this topic review, the authors provide a comprehensive review on the potential of alternating electric fields (AEFs) in the treatment of glioblastoma. Alternating electric fields-also known as tumor-treating fields (TTFs)-represent an entirely original therapeutic modality with preliminary studies suggesting comparable, and at times improved, efficacy to standard chemotherapeutic agents in the treatment of recurrent glioblastoma. A recent multicenter, Phase III, randomized clinical trial comparing NovoTTF-100A monotherapy to physician's best choice chemotherapy in patients with recurrent glioblastoma revealed that AEFs have similar efficacy to standard chemotherapeutic agents with a more favorable side-effects profile and improved quality of life. In particular, AEFs were shown to have limited systemic adverse effects, with the most common side effect being contact dermatitis on the scalp at the sites of transducer placement. This study prompted FDA approval of the NovoTTF-100A system in April 2011 as a standalone therapy for treatment of recurrent glioblastoma refractory to surgical and radiation treatment. In addition to discussing the available clinical evidence regarding the utilization of AEFs in glioblastoma, this article provides essential information regarding the supposed therapeutic mechanism as well as modes of potential tumor resistance to such novel therapy, delineating future perspectives regarding basic science research on the issue.

Molecular characterizations of glioblastoma, targeted therapy, and clinical results to date

During the last decade, extensive multiplatform genome-wide analysis has yielded a wealth of knowledge regarding the genetic and molecular makeup of glioblastoma multiforme (GBM). These profiling studies support the emerging view that GBM comprises a group of highly heterogeneous tumor types, each with its own distinct molecular and genetic signatures. This heterogeneity complicates the process of defining reliable intertumor/intratumor biological states, which will ultimately be needed for classifying tumors and for designing effective customized therapies that target resultant disease pathways. The increased understanding of the molecular pathogenesis of GBM has brought the hope and expectation that such knowledge will lead to better and more rational therapies directed toward specific molecular targets. To date, however, these expectations have largely been unrealized. This review discusses some of the principal genetic and epigenetic aberrations found in GBM that appear promising for targeted therapies now and in the near future, and it offers suggestions for future directions concerning the rather disappointing results of clinical trials to date.

ADAR2 editing activity in newly diagnosed versus relapsed pediatric high-grade astrocytomas

Background

High-grade (WHO grade III and IV) astrocytomas are aggressive malignant brain tumors affecting humans with a high risk of recurrence in both children and adults. To date, limited information is available on the genetic and molecular alterations important in the onset and progression of pediatric high-grade astrocytomas and, even less, on the prognostic factors that influence long-term outcome in children with recurrence. A-to-I RNA editing is an essential post-transcriptional mechanism that can alter the nucleotide sequence of several RNAs and is mediated by the ADAR enzymes. ADAR2 editing activity is particularly important in mammalian brain and is impaired in both adult and pediatric high-grade astrocytomas. Moreover, we have recently shown that the recovered ADAR2 activity in high-grade astrocytomas inhibits in vivo tumor growth. The aim of the present study is to investigate whether changes may occur in ADAR2-mediated RNA editing profiles of relapsed high-grade astrocytomas compared to their respective specimens collected at diagnosis, in four pediatric patients.

Methods

Total RNAs extracted from all tumor samples and controls were tested for RNA editing levels (by direct sequencing on cDNA pools) and for ADAR2 mRNA expression (by qRT-PCR).

Results

A significant loss of ADAR2-editing activity was observed in the newly diagnosed and recurrent astrocytomas in comparison to normal brain. Surprisingly, we found a substantial rescue of ADAR2 editing activity in the relapsed tumor of the only patient showing prolonged survival.

Conclusions

High-grade astrocytomas display a generalized loss of ADAR2-mediated RNA editing at both diagnosis and relapse. However, a peculiar Case, in complete remission of disease, displayed a total rescue of RNA editing at relapse, intriguingly suggesting ADAR2 activity/expression as a possible marker for long-term survival of patients with high-grade astrocytomas.

Characterization and response of newly developed high-grade glioma cultures to the tyrosine kinase inhibitors, erlotinib, gefitinib and imatinib

High-grade gliomas (HGG), are the most common aggressive brain tumours in adults. Inhibitors targeting growth factor signalling pathways in glioma have shown a low clinical response rate. To accurately evaluate response to targeted therapies further in vitro studies are necessary. Growth factor pathway expression using epidermal growth factor receptor (EGFR), mutant EGFR (EGFRvIII), platelet derived growth factor receptor (PDGFR), C-Kit and C-Abl together with phosphatase and tensin homolog (PTEN) expression and downstream activation of AKT and phosphorylated ribosomal protein S6 (P70S6K) was analysed in 26 primary glioma cultures treated with the tyrosine kinase inhibitors (TKIs) erlotinib, gefitinib and imatinib. Response to TKIs was assessed using 50% inhibitory concentrations (IC(50)). Response for each culture was compared with the EGFR/PDGFR immunocytochemical pathway profile using hierarchical cluster analysis (HCA) and principal component analysis (PCA). Erlotinib response was not strongly associated with high expression of the growth factor pathway components. PTEN expression did not correlate with response to any of the three TKIs. Increased EGFR expression was associated with gefitinib response; increased PDGFR-α expression was associated with imatinib response. The results of this in vitro study suggest gefitinib and imatinib may have therapeutic potential in HGG tumours with a corresponding growth factor receptor expression profile.

Amplicons on chromosome 12q13-21 in glioblastoma recurrences

There is limited knowledge on the in vivo behavior of amplified regions in human tumors. First evidence indicates that amplicon structures are largely maintained in recurrent tumors. Here, we investigated the fate of amplified regions in several independent cases of recurrent glioblastoma and the possible association of 12q13-21 amplifications and survival. We analyzed 12q13-21 amplicon numbers and sizes in glioblastoma and their recurrences by array-CGH. The majority of the 12q13-21 amplicons found in the original tumor are lost in the subsequent recurrence. Likewise, the majority of the amplicons found in the first recurrence are lost in the second recurrence. The remaining amplicons of recurrences often expanded or were maintained in size. Because of re-emergences and de novo appearances of amplicons, however, the overall number of amplicons did not decrease in the recurrences. Understanding genetic changes including gene amplifications in the development of tumor recurrences will contribute to rational therapeutic strategies for an improved patient survival. We recognized a significant longer survival time in glioblastoma patients that lack amplifications of either CDK4, CYP27B1, XRCC6BP1 (KUB3), or MDM2.

Different molecular patterns in glioblastoma multiforme subtypes upon recurrence

One of the hallmarks of glioblastoma is its inherent tendency to recur. At this point patients with relapsed GBM show a survival time of only few months. The molecular basis of the recurrence process in GBM is still poorly understood. The aim of the present study was to investigate the genetic profile of relapsed GBM compared to their respective primary tumors. We have included 20 paired GBMs. In all tumor samples, we have analyzed p53 and PTEN status by sequencing analysis, EGFR amplification by semiquantitative PCR and a wide-genome fingerprinting was performed by microsatellite analysis. Among primary GBM, we observed twelve type 2 GBM, four type 1 GBM and four further GBM showing neither p53 mutations nor EGFR amplification (non-type 1-non-type 2 GBM). Upon recurrence, we have detected two molecular patterns of tumor progression: GBM initially showing either type 1 or type 2 profiles conserved them at the time of relapse. In contrast, non-type 1-non-type 2 GBM acquired the typical pattern of type 2 GBM and harbor EGFR amplification without p53 mutation. New PTEN mutations upon relapse were only detected in type 2 GBM. Additional LOH were more frequently identified in relapses of type 2 GBM than in those showing the type 1 signature. Taken together, our results strongly suggest that recurrences of GBM may display two distinct pattern of accumulation of molecular alterations depending on the profile of the original tumor.

Advances in the genetics of glioblastoma: are we reaching critical mass?

Glioblastoma is the most common and highest-grade brain tumor, causing over 10,000 deaths each year in the US alone. Given the resistance of this tumor to standard surgery, radiation and chemotherapy, an understanding of the underlying genetic lesions is vital. Recent efforts to comprehensively profile glioblastomas using the latest technologies, both by The Cancer Genome Atlas (TCGA) project and by other groups, are addressing this need. Some genetic aberrations in glioblastoma have been known for decades, but early output from the new profiling initiatives has further illuminated the relevant genetics in this disease. Some genetic lesions, such as TP53 mutation, NF1 deletion or mutation, and ERBB2 amplification, have been found to be more common than was previously reported. New and unexpected discoveries have also been made, such as frequent mutations of the IDH1 and IDH2 genes in secondary glioblastoma. We might be tempted to speculate that we are approaching a comprehensive knowledge of the genetic lesions involved in glioblastoma, although other major discoveries doubtless remain to be made. In addition, the complex task of incorporating our updated knowledge into new--and possibly personalized--therapies for patients with glioblastoma still lies ahead.

Potent synergy of dual antitumor peptides for growth suppression of human glioblastoma cell lines

Molecular targeting agents have become formidable anticancer weapons, which show much promise against the refractory tumors. Functional peptides are among the more desirable of these nanobio-tools. Intracellular delivery of multiple functional peptides forms a basis for potent, non-invasive mode of delivery, providing distinctive therapeutic advantages. Here, we examine growth suppression efficiency of human glioblastomas by dual-peptide targeting. We did simultaneous introduction of two tumor suppressor peptides (p14(ARF) and p16(INK4a) or p16(INK4a) and p21(CIP1) functional peptides) compared with single-peptide introduction using Wr-T-mediated peptide delivery. Wr-T-mediated transport of both p14(ARF) and p16(INK4a) functional peptides (p14-1C and p16-MIS, respectively) into human glioblastoma cell line, U87DeltaEGFR, reversed specific loss of p14 and p16 function, thereby drastically inhibiting tumor growth by >95% within the first 72 h, whereas the growth inhibition was approximately 40% by p14 or p16 single-peptide introduction. Additionally, the combination of p16 and p21(CIP1) (p21-S154A) peptides dramatically suppressed the growth of glioblastoma line Gli36DeltaEGFR, which carries a missense mutation in p53, by >97% after 120 h. Significantly, our murine brain tumor model for dual-peptide delivery showed a substantial average survival enhancement (P < 0.0001) for peptide-treated mice. Wr-T-mediated dual molecular targeting using antitumor peptides is highly effective against growth of aggressive glioblastoma cells in comparison with single molecule targeting. Thus, jointly restoring multiple tumor suppressor functions by Wr-T-peptide delivery represents a powerful approach, with mechanistic implications for development of efficacious molecular targeting therapeutics against intractable human malignancies.

Indomethacin stimulates activity and expression of ecto-5'-nucleotidase/CD73 in glioma cell lines

Gliomas are the most common and devastating primary tumors of the central nervous system. Ecto-NTPDases and ecto-5'-nucleotidase/CD73 can control extracellular ATP/adenosine levels, which have been described as proliferation factors. Here, we investigate the influence of indomethacin on the enzyme cascade that catalyses the interconversion of purine nucleotides in U138-MG and C6 glioma cell lines. Exposure of glioma cells to 100 microM indomethacin for 48 h caused increases of 52% (P < 0.05) and 62% (P < 0.05) in the AMP hydrolysis rate in C6 and U138-MG cell lines, respectively. Indomethacin treatments also increased ATP hydrolysis. Significant increase in ecto-5'-nucleotidase/CD73 mRNA and protein levels were observed after treatment with indomethacin. Pretreatment of glioma cells with a specific antagonist of the adenosine A(3) receptor, MRS1220 (1 microM; 9-Chloro-2-(2-furanyl)-5-((phenylacetyl)amino)-[1,2,4]triazolo[1,5-c]quinazoline), significantly reduced the inhibition of cell proliferation induced by indomethacin. In addition, a significant increase in mRNA levels of the adenosine A(3) receptor was observed after treatment with indomethacin. In conclusion, our data indicate that adenosine A(3) receptors and the enzyme, ecto-5'-nucleotidase/CD73, are involved in the anti-proliferative effect of indomethacin in glioma cells.

Dynamics of chemosensitivity and chromosomal instability in recurrent glioblastoma

Glioblastoma multiforme is characterised by invasive growth and frequent recurrence. Here, we have analysed chromosomal changes in comparison to tumour cell aggressiveness and chemosensitivity of three cell lines established from a primary tumour and consecutive recurrences (BTL1 to BTL3) of a long-term surviving glioblastoma patient together with paraffin-embedded materials of five further cases with recurrent disease. Following surgery, the BTL patient progressed under irradiation/ lomustine but responded to temozolomide after re-operation to temozolomide. The primary tumour -derived BTL1 cells showed chromosomal imbalances typical of highly aggressive glioblastomas. Interestingly, BTL2 cells established from the first recurrence developed under therapy showed signs of enhanced chromosomal instability. In contrast, BTL3 cells from the second recurrence resembled a less aggressive subclone of the primary tumour. Although BTL2 cells exhibited a highly aggressive phenotype, BTL3 cells were characterised by reduced proliferative and migratory potential. Despite persistent methylation of the O6-methylguanine-DNA methyltransferase promoter, BTL3 cells exhibited the highest temozolomide sensitivity. A comparable situation was found in two out of five glioblastoma patients, both characterised by enhanced survival time, who also relapsed after surgery/chemotherapy with less aggressive recurrences. Taken together, our data suggest that pretreated glioblastoma patients may relapse with highly chemosensitive tumours confirming the feasibility of temozolomide treatment even in case of repeated recurrence.

Loss of p16 in recurrent malignant mixed müllerian tumors of the uterus

Uterine malignant mixed müllerian tumors (MMMTs) are rare and highly aggressive malignancies with poor clinical prognoses. We examined for differences in the oncoprotein profiles of primary versus recurrent MMMTs. Five cases of recurrent uterine MMMT were examined by paraffin immunohistochemistry for the expression of p53, p16, P-cadherin, and Cerb-B2. P16, p53, and P-cadherin were each expressed in 100%, 80%, and 60% of the primary cases, respectively. Three cases expressed all three oncoproteins. All five cases were negative for Cerb-B2. No difference in antigen expression was seen in the epithelial versus sarcomatous components. Primary and recurrent tumors were concordant for p53, P-cadherin, and Cerb-B2. However, three cases of recurrent tumors were negative for p16 expression. P53, p16, and P-cadherin are common tumor suppressor genes expressed in uterine MMMT. Interestingly, p16 protein expression was lost in some cases of MMMTs when they recurred. This suggests that the oncoprotein and possibly genetic profile of p16 changes over time. We did not observe any difference in antigen expression between areas of epithelial or sarcomatous differentiation, which would support a single pluripotential malignant clone in the histogenesis of these tumors.

CpG island promoter hypermethylation of the pro-apoptotic gene caspase-8 is a common hallmark of relapsed glioblastoma multiforme

Glioblastoma multiforme (GBM) is an incurable malignancy with inherent tendency to recur. In this study, we have comparatively analyzed the epigenetic profile of 32 paired tumor samples of relapsed GBM and their corresponding primary neoplasms with special attention to genes involved in the mitochondria-independent apoptotic pathway. The CpG island promoter hypermethylation status was assessed by methylation-specific polymerase chain reaction and selected samples were double checked by bisulfite genomic sequencing. Thirteen genes were analyzed for DNA methylation: the pro-apoptotic CASP8, CASP3, CASP9, DcR1, DR4, DR5 and TMS1; the cell adherence CDH1 and CDH13; the candidate tumor suppressor RASSF1A and BLU; the cell cycle regulator CHFR and the DNA repair MGMT. The CpG island promoter hypermethylation profile of relapsed GBM in comparison with their corresponding primary tumors was identical in 37.5% of the cases, whereas in 62.5% of patients, differences in the DNA methylation patterns of the 13 genes were observed. The most prominent distinction was the presence of previously undetected CASP8 hypermethylation in the GBM relapses (P = 0.031). This finding was also linked to the observation that an unmethylated CASP8 CpG island together with methylated BLU promoter in the primary GBM was associated with prolonged time to tumor progression (P = 0.0035). Our data strongly suggest that hypermethylation of the pro-apoptotic CASP8 is a differential feature of GBM relapses. These remarkable findings may foster the development of therapeutic approaches using DNA demethylating drugs and activators of the extrinsic apoptotic pathway to improve the dismal prognosis of GBM.

Cellular DNA content parameters as prognostic indicators in human astrocytomas

OBJECTIVE

Clinical parameters such as grade, size and/or location of the tumor are good predictors of outcome in patients with astrocytoma. The objective of this study was to determine whether DNA content parameters have a prognostic significance for this group of tumors.

METHODS

Following optimization and validation of methodology for evaluating cellular DNA content parameters (CDCP), tumor DNA ploidy and percent S phase fraction (SPF) were determined from 64 patients using formalin fixed, paraffin embedded specimens (mean coefficient of variation=4.94) obtained over a 10-year period. Median survival times correlated with grade (I/II=1154 vs. III/IV=483days, P=0.0317). Fifty-five percent of the specimens contained DNA aneuploid (DNA-A) components (average SPF=18.3%) and 45% were DNA diploid (DNA-D) (average SPF=9.6%). Survival did not correlate with overall differences in DNA ploidy (DNA-D=181 vs. DNA-A=206days, P=0.6314) when treated and untreated tumors were analyzed. However, a trend for prolonged median survival was observed in patients whose tumors were untreated with respect to cytotoxic therapy based on DNA ploidy status (DNA-D=275 vs. DNA-A=15days, P=0.3408). Survival for all patients did not correlate with median SPF (<13.5% av.=121 vs. >13.5% av.=154days, P=0.6534).

CONCLUSION

DNA content parameters may correlate with the natural history and treatment outcome of newly diagnosed untreated patients with astrocytomas.

Independent molecular development of metachronous glioblastomas with extended intervening recurrence-free interval

Two metachronous glioblastomas with different cerebral locations in a 53-year-old long-term survival patient were analyzed by multiple genetic approaches. Using comparative genomic hybridization a different pattern of chromosomal aberrations was observed, with 19 imbalances in the first tumor and only 2 imbalances in the second. Sequence analysis revealed a distinct mutation profile in each tumor, with amino acid substitutions in the p53 and PTEN genes only in the first tumor, ie, p53 in codon 273 (CGT-->TGT, Arg-->Cys) and PTEN in codon 336 (TAC-->TTC, Tyr-->Phe). A splicing acceptor site PTEN mutation (IVS8-2A>G) was observed only in the second GBM. EGFR amplification, mutations of p16INK4a/CDKN2A or p14ARF were not observed. According to the results of p53 mutational analysis and EGFR amplification studies, the first tumor is classified as a type 1 GBM, whereas the alterations in the second one are different from those typically encountered in type 1 or type 2 tumors. In conclusion, our data strongly suggest that the metachronous tumors in this patient are exceptional in that they developed independently from each other. Whether the molecular features of the first glioblastoma are associated with the notably extended recurrence-free period of 5 years remains to be elucidated.

Expression of platelet-derived growth factor-AA is associated with tumor progression in osteosarcoma

Platelet-derived growth factors are secreted by mesenchymal cells. The homodimer platelet-derived growth factor-AA especially stimulates bone cells through interaction with the platelet-derived growth factor-alpha receptor homodimer. In this study we wanted to determine the expression of the receptor and its ligand in human osteosarcomas and to correlate the expression of platelet-derived growth factor-AA and -alpha receptor with clinicopathological parameters. Fifty-seven osteosarcomas were immunohistochemically analyzed for expression of platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor. Spearman's correlation coefficient revealed a strong correlation between the expression of platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor (r = 0.867). No differences were observed relative to gender, age, tumor stage, tumor location, and response to neoadjuvant chemotherapy between high or low platelet-derived growth factor-AA and platelet-derived growth factor-alpha receptor expression. High platelet-derived growth factor-AA expression correlated with tumor progression in univariate analysis (P = .0415; log-rank test), whereas platelet-derived growth factor-alpha receptor expression showed a trend toward a shorter disease-free survival, which failed to reach significance (P = .0627, log-rank test). In multivariate analysis, platelet-derived growth factor-AA expression remained a significant independent predictor of tumor progression (P = .021, Cox regression). Immunohistochemical analysis of platelet-derived growth factor-AA expression in osteosarcoma may be a useful marker of prognosis and may be considered as a possible target for novel therapeutic strategies.

Chemosensitivity of glioblastoma cells during treatment with the organo-tin compound triethyltin(IV)lupinylsulfide hydrochloride

Malignant gliomas are the most common primary brain tumors in humans. However, poor response to conventional therapeutic approaches, including chemotherapy, leads invariably to disease recurrence and progression. The organo-tin derivative triethyltin(IV)lupinylsulfide hydrochloride (IST-FS 29) was identified and developed as potential antiproliferative agent in human cancer cell lines. However, for its peculiar chemical structure and good lipophilicity, this compound also appeared an eligible candidate for the treatment of gliobastoma cells. The present experiments were designed to explore the in vitro effects of IST-FS 29 on four human glioblastoma cell lines: A-172, DBTRG.05MG, U-87MG and CAS-1. The average IC50 values were obtained by MTT assay and ranged between 3 and 10 microM. Time-course assays with cell recovery after drug withdrawal, demonstrated marked cytotoxicity following exposure to IST-FS 29 for 8, 24 and 72 h. Cultures treated for 8 h were able to partially re-grow by 144 h; on the contrary, longer times of exposure did not allow surviving cells to recover from the damage and actively proliferate. Cell morphology of cultures exposed to IST-FS 29 was assessed by inverted light microscopy after 24 and 72 h and was more consistent with cell death by necrosis which included cell size reduction, vacuolation of cytoplasm, round dying cells. The present results and our previous data, in vitro and in vivo, indicate the relevant cytotoxic activity of this organo-tin compound and suggest that IST-FS 29 might be a promising novel agent to be developed for the treatment of malignant brain neoplasms.

A novel member of the WD-repeat gene family, WDR11, maps to the 10q26 region and is disrupted by a chromosome translocation in human glioblastoma cells

Allelic deletions of 10q25-26 and 19q13.3-13.4 are the most common genetic alterations in glial tumors. We have identified a balanced t(10;19) reciprocal translocation in the A172 glioblastoma cell line which involves both critical regions on chromosomes 10 and 19. In addition, loss of an entire copy of chromosome 10 has occurred in this cell line suggesting that the translocation event may provide a highly specific critical inactivating event in a gene responsible for tumorigenesis. Positional cloning of this translocation breakpoint resulted in the identification of a novel chromosome 10 gene, WDR11, which is a member of the WD-repeat gene family. The WDR11 gene is ubiquitously expressed, including normal brain and glial tumors. WDR11 is composed of 29 exons distributed over 58 kilobases and oriented towards the telomere. The translocation resulted in deletion of exon 5 and consequently fusion of intron 4 of WDR11 to the 3' untranslated region of a novel member, ZNF320, of the Krüppel-like zinc finger gene family. Since ZNF320 is oriented toward the centromere of chromosome 19, both genes appeared on the same derivative chromosome der(10). The chimeric transcript encodes the WDR11 polypeptide, which is truncated after the second of six WD-repeats. ZNF320 is also expressed in A172 cells, although it is not clear if the translocation affects the expression of the altered gene because of the presence of another unrearranged gene on chromosome 19. We suggest that, because of its localization in a region frequently showing LOH and the observation of inactivation of this gene in glioblastoma cells, WDR11 is a candidate gene for the frequently proposed tumor suppressor gene in 10q25-26 which is involved in tumorigenesis of glial and other tumors showing frequent alterations in the distal 10q region.