Frequent promoter hypermethylation and low expression of the MGMT gene in oligodendroglial tumors

A MDR1 (ABCB1) gene single nucleotide polymorphism predicts outcome of temozolomide treatment in glioblastoma patients

BACKGROUND

Some patients with glioblastoma multiform do not respond to temozolomide even though they have aberrant promoter methylation of the DNA repair enzyme O(6)-methylguanine methyltransferase (MGMT). This suggests that additional factors hamper temozolomide cytotoxicity. We aimed to confirm first that temozolomide is a target for the multidrug resistance transporter MDR1/ABCB1 and second to investigate whether genetic variants of the MDR1 gene are associated with the survival of glioblastoma patients treated with temozolomide.

MATERIALS AND METHODS

Temozolomide-mediated cytotoxicity was determined by the colorimetric methyl-thiazol-tetrazolium assay in MDR-expressing and MDR-nonexpressing cell lines. Genotypes of three single nucleotide polymorphisms (SNPs) of the MDR1 gene (C1236T, G2677T, and C3435T), MDR1 mRNA expression levels, and the MGMT promoter methylation status were analyzed in 112 glioblastoma patients who had been treated either by surgery plus radiotherapy alone or by additional temozolomide chemotherapy.

RESULTS

In vitro analysis revealed that temozolomide-mediated cytotoxicity is dependent on MDR1 expression. Multivariate analysis of MDR1 genotypes showed that the C/C variant of the exon12 C1236T SNP is predictive for survival of patients treated with temozolomide. This effect was independent of the MGMT methylation status. Patients with the C/C genotype had a 2-year overall survival of 37% compared with 8% and 10% for patients with C/T and T/T genotypes, respectively (P=0.02). No influence was seen in the group of patients with radiotherapy only.

CONCLUSION

The genotype of the MDR1 exon12 C1236T SNP is a novel independent predictive factor for outcome of temozolomide treatment in glioblastoma patients.

Temozolomide preferentially depletes cancer stem cells in glioblastoma

The prognosis of patients suffering from glioblastoma (GBM) is dismal despite multimodal therapy. Although chemotherapy with temozolomide may contain tumor growth for some months, invariable tumor recurrence suggests that cancer stem cells (CSC) maintaining these tumors persist. We have therefore investigated the effect of temozolomide on CD133(+) and CD133(-) GBM CSC lines. Although differentiated tumor cells constituting the bulk of all tumor cells were resistant to the cytotoxic effects of the substance, temozolomide induced a dose- and time-dependent decline of the stem cell subpopulation. Incubation with sublethal concentrations of temozolomide for 2 days completely depleted clonogenic tumor cells in vitro and substantially reduced tumorigenicity in vivo. In O(6)-methylguanine-DNA-methyltransferase (MGMT)-expressing CSC lines, this effect occurred at 10-fold higher doses compared with MGMT-negative CSC lines. Thus, temozolomide concentrations that are reached in patients were only sufficient to completely eliminate CSC in vitro from MGMT-negative but not from MGMT-positive tumors. Accordingly, our data strongly suggest that optimized temozolomide-based chemotherapeutic protocols might substantially improve the elimination of GBM stem cells and consequently prolong the survival of patients.

[Diagnostic and prognostic values of 1p and 19q deletions in adult gliomas: critical review of the literature and implications in daily clinical practice]

Losses of chromosomes 1p and 19q are deemed correlated with diagnosis of oligodendroglioma, higher chemosensitivity and better prognosis. We reviewed the literature to evaluate the usefulness of these correlations in daily clinical practice. The rates of deletions relative to histology (WHO classifications) were extracted from 33 studies, including 2666 patients. The 1p deletions and 1p19q codeletion mean rates were respectively 65.4 and 63.3% in oligodendrogliomas, 28.7 and 21.6% in oligoastrocytomas, 13.2 and 7.5% in astrocytomas, 11.6 and 2.9% in glioblastomas. The presence of 1p deletion and 1p19q codeletion were strongly correlated with the histological diagnosis corresponding to oligodendroglioma. Calculation of specificity, sensitivity, predictive positive values and false negative rates suggests that presence of deletion 1p or codeletion represents a strong argument in favor of the diagnosis of oligodendroglioma. However, considering the high false negative rate, absence of such deletions does not rule out the diagnosis. In grade 3 oligodendroglial tumors, the probability of responding to chemotherapy, and the duration of response, were higher when codeletions were present. This suggests that, in these tumors, the presence of codeletion is a strong argument in favor of adjuvant chemotherapy. However, chemotherapy should not be systematically excluded when codeletions are absent, as the chances of response are about 33% in this situation. Data concerning low-grade gliomas were more controversial. Oligodendroglial tumors with 1p deletion or 1p19q codeletion seemed to have a better prognosis, as five-year survival rates were 50% higher than in tumors without deletion. This might be explained by the correlation between 1p deletion and other identified prognosis factors: (1) higher chemosensitivity, (2) tumor location more frequently in the frontal lobe, leading to better resection and lower risk of neurological deficit, (3) slower growth rate, (4) higher risk of epilepsy, leading to an early detection.

Predictive and prognostic markers in neuro-oncology

Over the past few years molecular assays have been introduced to aid in typing and grading of gliomas. This is the result of improved understanding of these tumors at the molecular level. In particular, the presence or absence of combined 1p/19 loss in oligodendroglial tumors, epidermal growth factor receptor amplification, epidermal growth factor receptor vIII mutations in grade III tumors and glioblastoma multiforme, and MGMT promoter gene methylation in glioblastoma multiforme are now being used to tailor treatment decisions in patients. However, the application of these tests is far from straightforward, and certain standards are required before any test can be introduced in the daily management of patients. Some of these requirements concern inter- and intratest variability, including whether a test gives the same results if repeated in the same or in another laboratory or when different methodologies are used (e.g. loss of heterozygosity vs fluorescence in situ hybridization and a polymerase chain reaction-based test vs immunohistochemistry). The sensitivity and specificity of a test (or negative and positive predictive value) indicate the likelihood that the test results are positive if the disease is present and the likelihood that the disease is present if the test results are positive. Studies on these test characteristics usually require the presence of a gold standard to which new tests should be compared. Last but not least there is the question of what added value the test has; this criterion determines the clinical usefulness of the assay and why some recently introduced molecular assays need to be scrutinized.

MGMT immunohistochemical expression and promoter methylation in human glioblastoma

O6-methylguanine-DNA methyltransferase (MGMT) expression has been recently proposed as a useful prognostic and/or predictive marker in glioblastoma patients receiving adjuvant therapy after the surgery. We studied samples from 50 patients with histologically confirmed GBM to evaluate MGMT expression by immunohistochemistry and its relation to promoter methylation status. Genomic DNA was extracted from scrapings of formalin-fixed, paraffin-embedded tissue corresponding to hematoxylin and eosin sections. Using the mouse monoclonal antibody MT3.1, MGMT expression was assessed and scored in tumor cells: (1=negative or limited to <10% positive tumor cells, 2=10% to 50%, 3=>50%). Methylation-specific polymerase chain reaction was performed after bisulfite treatment. Assessment of MGMT expression in neoplastic tissue required careful scrutiny because of its expression in a variety of non-neoplastic cells. MGMT expression was present in tumor cells with a score of 1, 2, and 3, respectively in 36 (72%), 13 (26%), and 1 (2%) cases. Methylation-specific polymerase chain reaction yielded interpretable results in 39 cases (78%). MGMT promoter methylation was detected in 15 cases (38.5%), whereas 24 (61.5%) were unmethylated. Among the methylated samples, 14 (of 15) had a score of 1, and 1 had a score of 3 by immunohistochemistry. Of the 24 unmethylated samples, 18 had a score of 1, and 6 of 2. There was no significant correlation between MGMT expression and methylation, and no significant survival difference was observed between patients whose tumors were negative versus positive for MGMT protein by immunohistochemistry. This study underscores some of the difficulties in applying immunohistochemistry to assess MGMT expression.

Intratumoral homogeneity of MGMT promoter hypermethylation as demonstrated in serial stereotactic specimens from anaplastic astrocytomas and glioblastomas

Hypermethylation of the DNA repair gene O(6)-methyl-guanine DNA methyltransferase (MGMT) has been linked to prolonged survival in glioblastoma patients treated with alkylating agents. It was aimed to analyze prospectively whether the MGMT status of malignant gliomas could be determined from small-sized stereotactic biopsies (maximum volume: 1 mm(3)). Special attention was directed towards the intratumoral distribution of the MGMT promoter methylation, the MGMT protein expression and potential correlations between both. Twenty-five adult patients were included (20 patients with primary World Health Organisation (WHO) Grade III or IV malignant gliomas, 5 patients with secondary malignant gliomas). About 2-4 biopsy specimens per tumor were collected from different sites within the tumor. Promoter methylation of the MGMT gene was assessed by methylation-specific PCR (MSP) and sodium bisulfite sequencing in each of the collected specimens (overall number of specimens: 69). Both methods were validated for application in small-sized tissue samples (1 mm(3)). The MGMT protein expression was analyzed by immunohistochemistry. The overall MGMT promoter methylation rate was 30% in the de novo group and 80% in the tumor progression group. The success rates of MSP and sequencing were 100% and 80%, respectively. Sequence analysis and MSP exhibited 100% concordant findings. No differences in MGMT promoter methylation were detected between the different samples of each individual tumor in 24 of 25 patients. One false negative result was obtained due to the contamination of the biopsy specimen by necrotic tissue. Tissue samples taken from different sites of each individual tumor (13 tumors investigated) exhibited equal or highly similar MGMT protein expression. No correlation between MGMT protein expression and MGMT promoter methylation was observed. The MGMT promoter methylation status of malignant gliomas can be reliably determined from small-sized stereotactic biopsies. The methylation profile, as defined by MSP and sodium bisulfite sequencing, constitutes a homogeneous marker throughout malignant gliomas. The lack of correlation between MGMT status and MGMT protein expression needs further evaluation.

Variation of O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation in serial samples in glioblastoma

Methylation of the promoter region of the O ( 6 ) -methylguanine-DNA methyltransferase (MGMT) gene is known to be predictive of response to temozolomide treatment in patients with glioblastoma. Contrastingly, little is known about variation in the methylation status of the MGMT promoter after treatment or across different regions of the same tumor. About 22 samples from 10 patients who had undergone multiple resections of a glioblastoma were examined with promoter sequencing. Of these, 20 were also analyzed using Methylation Specific PCR (MSP). The methylation status of the MGMT promoter was altered in the specimens obtained pre and post treatment in 2 of 9 samples as assessed by MSP and 7 out of 10 patients as assessed by promoter sequencing. In four patients, the MGMT promoter was unmethylated at primary surgery, but displayed some methylation (32, 44, 12, and 4%) on post-treatment sampling. Alteration in MSP status from unmethylated to methylated was also observed in 2 of these 4 patients. In another patient, methylation increased from 40% on initial sampling to 68% on the second sample. The remaining two patients initially demonstrated some degree of methylation (72% and 12%); subsequent sampling showed no methylation of the MGMT promoter. To ensure variable methylation status was not due to intra-tumoral variability, three to four specimens were sampled from different regions of large glioblastomas (n = 7). Promoter sequencing revealed minimal variation in methylation in all but two sites examined. Immunohistochemistry also demonstrated minimal change in MGMT expression across the tumors. This suggests that variation in MGMT promoter methylation can occur within the same tumor after treatment, necessitating caution in clinical decision-making based on this analysis.

Molecular targeted therapies and chemotherapy in malignant gliomas

PURPOSE OF REVIEW

To review current developments in the field of chemotherapy and targeted treatment of high-grade glioma.

RECENT FINDINGS

Two independent large phase III trials on adjuvant procarbazine, lomustine and vincristine chemotherapy in anaplastic oligodendroglial tumors have shown this improves progression-free survival, but not overall survival, regardless of 1p/19q status. If given sequentially, the timing of procarbazine, lomustine and vincristine chemotherapy has no clear effect on the survival of anaplastic oligodendroglioma. Virtually none of the many new targeted agents directed against pathways that are upregulated in high-grade gliomas has shown significant clinical activity as single agent in phase II studies. The exception are trials with the vascular endothelial growth factor signaling system inhibiting agents bevacizumab and AZD2171 (cediranib) that showed high response rates (which might be due to vessel normalization similar to the effects of steroid treatment) and promising 6-month progression-free survival rates in glioblastoma multiforme.

SUMMARY

Further research to define the role of vascular endothelial growth factor inhibition in the management is indicated. For the many other targeted agents, a critical review of the pathological role of their targets in glioblastoma multiforme is required, especially if combination regimens are investigated. The role of combined chemo-irradiation for non-glioblastoma multiforme high-grade glioma remains to be identified.

Molecular genetic markers as predictors of response to chemotherapy in gliomas

PURPOSE OF REVIEW

This review summarizes recent studies on applications of molecular markers such as chromosome 1p/19q codeletion and MGMT status in the treatment of glioma.

RECENT FINDINGS

Prospective trials confirmed that 1p/19q codeletion represents a strong and independent favourable prognostic factor in anaplastic oligodendroglial tumours. Other retrospective studies have suggested that 1p/19q loss is also predictive of chemosensitivity to alkylating agents (nitrosoureas and temozolomide) in low-grade gliomas. Recent reports have provided evidence that 1p and 19q deletions are mediated by unbalanced translocation. The targeted genes remain to be identified, however. Promoter methylation of MGMT gene silencing has been shown to predict benefit from chemotherapy in glioblastoma. MGMT promoter methylation and low expression of MGMT-encoded protein are frequently observed in low-grade gliomas and anaplastic oligodendroglial tumours. In such tumours, however, preliminary studies have yielded contradictory results on the predictive value of MGMT status regarding objective response to chemotherapy and correlation with 1p/19q deletion.

SUMMARY

There is mounting evidence that 1p/19q deletion and MGMT inactivation are relevant prognostic markers and predictors of chemosensitivity in gliomas. Although such markers remain to be formally validated by ongoing and planned prospective trials, it is likely that they will soon become essential for optimizing treatment decisions.

MS-MLPA: an attractive alternative laboratory assay for robust, reliable, and semiquantitative detection of MGMT promoter hypermethylation in gliomas

Expression of the DNA repair protein O6-alkylguanine-DNA-alkyltransferase (AGT), encoded by the O6-methylguanine (O6-mG) -DNA-methyltransferase (MGMT) DNA repair gene, results in resistance to alkylating agents, and hypermethylation of the MGMT promoter is associated with chemosensitivity as it prevents AGT expression. As the interpretation of the results of immunohistochemistry to evaluate AGT expression proved to be difficult, the aim of our present study is to establish a feasible, reliable, and robust method for MGMT promoter hypermethylation testing that can be easily implemented in a diagnostic setting and is applicable to routinely processed tissue. MGMT hypermethylation analysis using methylation-specific (MS-) multiplex ligation-dependent probe amplification (MLPA) was performed on 62 glioma samples of 55 individual tumors (including 12 cell lines) and compared to the more conventionally used, but improved, MS-polymerase chain reaction (PCR). In contrast to MS-PCR, MS-MLPA (i) is not based on bisulfite conversion of unmethylated cytosines (a somewhat troublesome step in MS-PCR), (ii) provided methylation status of all samples, (iii) proved to be semiquantitative, (iv) can be used to evaluate methylation status of multiple sequences (CpG dinucleotides) simultaneously, and (v) allows for a combined copy number detection and methylation specific analysis. The potential therapeutic value of MGMT hypermethylation evaluation using MS-MLPA was shown in a group of 20 glioblastoma patients receiving temozolomide chemotherapy. We conclude that MS-MLPA is a robust and reliable method that can be easily applied to differently processed tissues, including those fixed in formalin and embedded in paraffin. The semiquantitative aspect of MS-MLPA may prove to be of great value, especially in predicting response to alkylating agents, not only for gliomas as evaluated in this study but also for tumors in general.

Chemoradiotherapy in Malignant Glioma: Standard of Care and Future Directions

Glioma has been considered resistant to chemotherapy and radiation. Recently, concomitant and adjuvant chemoradiotherapy with temozolomide has become the standard treatment for newly diagnosed glioblastoma. Conversely (neo-)adjuvant PCV (procarbazine, lomustine, vincristine) failed to improve survival in the more chemoresponsive tumor entities of anaplastic oligoastrocytoma and oligodendroglioma. Preclinical investigations suggest synergism or additivity of radiotherapy and temozolomide in glioma cell lines. Although the relative contribution of the concomitant and the adjuvant chemotherapy, respectively, cannot be assessed, the early introduction of chemotherapy and the simultaneous administration with radiotherapy appear to be key for the improvement of outcome. Epigenetic inactivation of the DNA repair enzyme methylguanine methyltransferase (MGMT) seems to be the strongest predictive marker for outcome in patients treated with alkylating agent chemotherapy. Patients whose tumors do not have MGMT promoter methylation are less likely to benefit from the addition of temozolomide chemotherapy and require alternative treatment strategies. The predictive value of MGMT gene promoter methylation is being validated in ongoing trials aiming at overcoming this resistance by a dose-dense continuous temozolomide administration or in combination with MGMT inhibitors. Understanding of molecular mechanisms allows for rational targeting of specific pathways of repair, signaling, and angiogenesis. The addition of tyrosine kinase inhibitors vatalanib (PTK787) and vandetinib (ZD6474), the integrin inhibitor cilengitide, the monoclonal antibodies bevacizumab and cetuximab, the mammalian target of rapamycin inhibitors temsirolimus and everolimus, and the protein kinase C inhibitor enzastaurin, among other agents, are in clinical investigation, building on the established chemoradiotherapy regimen for newly diagnosed glioblastoma.

Efficacy and Tolerability of Temozolomide in an Alternating Weekly Regimen in Patients With Recurrent Glioma

Purpose

Evaluation of toxicity and efficacy of an alternating weekly regimen of temozolomide administered 1 week on and 1 week off in patients with recurrent glioma.

Patients and Methods

Ninety adult patients with recurrent gliomas accrued in one center received chemotherapy with temozolomide at 150 mg/m2/d (days 1 through 7 and 15 through 21 every 4 weeks) with individual dose adjustments according to hematologic toxicity.

Results

A total of 906 treatment weeks were delivered. Grade 4 hematotoxicity according to the Common Terminology Criteria for Adverse Events (CTCAE; version 3.0) was observed in 24 treatment weeks (2.6%). CTCAE grade 4 lymphopenia eventually developed in 11 patients (12%). There were neither cumulative lymphopenias nor opportunistic infections. The progression-free survival (PFS) rate at 6 months for glioblastoma patients was 43.8%. The median PFS in these patients was 24 weeks (95% CI, 17 to 26 weeks), the median survival time from diagnosis of progression was 38 weeks (95% CI, 30 to 46 weeks), and the 1-year survival rate from progression was 23%. O6-methylguanine DNA methyltransferase (MGMT) gene promoter methylation in the tumor tissue was not associated with longer PFS (log-rank P = .37).

Conclusion

These data imply that the alternating weekly schedule is feasible, safe, and effective and clearly warrants investigation in randomized studies. Compared with more protracted low-dose temozolomide schedules, the 1-week-on/1-week-off schedule may be less toxic. We provide preliminary evidence that this dose-dense schedule is also active in patients with tumors lacking MGMT gene promoter methylation.

DNA hypermethylation and aberrant expression of the EMP3 gene at 19q13.3 in Human Gliomas

Allelic losses on 19q are found in the majority of oligodendroglial tumors and approximately one-third of diffuse astrocytomas. However, the tumor suppressor genes (TSG) on 19q are still elusive. Using cDNA microarray expression profiling, EMP3 at 19q13.3 was among those genes showing the most pronounced expression differences. In line with this, other authors reported EMP3 as being epigenetically silenced in neuroblastomas and astrocytomas. To further investigate EMP3 as a TSG candidate on 19q13.3, we performed molecular analysis of this gene in 162 human gliomas. Mutation analysis did not reveal EMP3 alteration in 132 gliomas. In oligodendroglial tumors, we found that aberrant methylation in the 5'-region of EMP3 was significantly associated with reduced mRNA expression and LOH 19q. In astrocytomas, EMP3 hypermethylation was also paralleled by reduced expression but was independent of the 19q status. EMP3 hypermethylation was detected in more than 80% of diffuse, anaplastic astrocytomas and secondary glioblastomas. Primary glioblastomas, however, mostly lacked EMP3 hypermethylation and frequently overexpressed EMP3. Our data corroborate that oligodendroglial and astrocytic gliomas often show EMP3 hypermethylation and aberrant expression. Furthermore, our findings suggest that primary and secondary glioblastomas are not only characterized by distinct genetic profiles but also differ in their epigenetic aberrations.

Genetic and epigenetic biomarkers in cancer : improving diagnosis, risk assessment, and disease stratification

Gene expression patterns change during the initiation, progression, and development of cancer, as a result of both genetic and epigenetic mechanisms. Genetic changes arise due to irreversible changes in the nucleotide sequence, whereas epigenetic changes occur due to changes in chromatin conformation, histone acetylation, and methylation of the CpG islands located primarily in the promoter region of a gene. Both genetic and epigenetic markers can potentially be utilized to identify different stages of tumor development. Several such markers exhibit high sensitivity and specificity for different tumor types and can be assayed in biofluids and other specimens collected by noninvasive technologies. In spite of the availability of large numbers of diagnostic markers, only a few have been clinically validated so far. The current status and the challenges in the field of genetic and epigenetic markers in cancer diagnosis, risk assessment, and disease stratification are discussed.

Mechanisms of disease: genetic predictors of response to treatment in brain tumors

Brain tumors are currently diagnosed on the basis of their histology. The most common types in adults are astrocytomas, oligodendrogliomas and oligoastrocytomas or mixed tumors, which almost invariably lead to death. Improvements in outcome have been elusive despite intensive research. Recent findings indicate that response to conventional therapy, at least in some cases, correlates better with genetic characteristics than histopathology. An understanding of the molecular mechanisms that underlie the malignant phenotype of gliomas also provides the possibility of rational design of molecularly targeted therapies. This approach has proved successful in other areas of oncology. As many tumors have the same types of molecular abnormalities, molecular targeted therapies developed for nonbrain tumor types might be adapted for the treatment of brain tumors. There are a number of unique problems involved in treating tumors in the brain that must be overcome. The genetic predictors of response to conventional therapies, the genes and cellular mechanisms involved in glioma development, and potential therapeutic targets are reviewed. The possibility of designing tailored molecular therapy based on the molecular characteristics of the tumors is also explored.

Methylation profiling using degenerated oligonucleotide primer-PCR specific for genome-wide amplification of bisulfite-modified DNA

DNA methylation is one of the essential epigenetic processes that play a role in regulating gene expression. Aberrant methylation of CpG-rich promoter regions has been associated with many forms of human cancers. The current method for determining the methylation status relies mainly on bisulfite treatment of genomic DNA, followed by methylation-specific PCR (MSP). The difficulty in acquiring a methylation profiling often is limited by the amount of genomic DNA that can be recovered from a given sample, whereas complex procedures of bisulfite treatment further compromise the effective template for PCR analysis. To circumvent these obstacles, we developed degenerated oligonucleotide primer (DOP)-PCR to enable amplification of bisulfite-modified genomic DNA at a genome-wide scale. A DOP pair was specially designed as follows: first 3' DOP, CTCGAGCTGHHHHHAACTAC, where H is a mixture of base consisting of 50% A, 25% T, and 25% C; and second 5' DOP, CTCGAGCTGDDDDDGTTTAG, where D is a mixture of base consisting of 50% T, 25% G, and 25% A. Our results showed that bisulfite-modified DNAs from a cell line, cord blood cells, or cells obtained by laser capture microdissection were amplified by up to 1000-fold using this method. Subsequent MSP analysis using these amplified DNAs on nine randomly selected cancer-related genes revealed that the methylation status of these genes remained identical to that derived from the original unamplified template.

Expression of O6-methylguanine-deoxyribose nucleic acid methyltransferase and temozolomide response in a patient with a malignant spinal cord astrocytoma. Case report

The authors report the case of a 28-year-old woman with a high-grade spinal cord astrocytoma. Treatment using surgery, radiation, and temozolomide (TMZ) led to functional recovery and regression of the residual tumor as demonstrated on serial magnetic resonance images. Genetic testing revealed that this tumor did not express the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT). This is the first report in the literature correlating MGMT expression with the clinical response of a high-grade spinal cord astrocytoma treated using TMZ.

Epigenetic Inactivation of the hMLH1 Gene in Progression of Gliomas

Gliomas (GLs) are characterized by highly variable biologic behavior. After surgical resection and postoperative therapy, they frequently recur with the same or higher-grade histology. Although a number of genetic aberrations have been described in different histologic types of GLs, the molecular mechanisms of histologic and clinical progression are poorly understood. In this study, we have performed longitudinal mismatch repair gene polymerase chain reaction-single strand conformation polymorphism and methylation analysis in paired samples of primary and recurrent GLs to reveal whether the inactivation of the normal DNA repair mechanism is associated with tumor progression. Polymerase chain reaction-single strand conformation polymorphism analysis of the hMLH1 gene was performed in 24 cases, in each case the samples of the first and second biopsies being evaluated simultaneously, but no alterations in the hMLH1 gene were found. Methylation analysis of the CpG sites in the hMLH1 promoter revealed a total of 4 (16.6%) hypermethylations in recurrent GLs. These results suggest that hMLH1 promoter hypermethylation may occur in low-grade GLs, associated with the development and progression of moderate malignant GL, but not with structural alterations in the hMLH1 gene. It seems that hMLH1 promoter hypermethylation is an early event in the development and progression or the clonal evolution of GLs, this gene inactivation proving stable even on tumor recurrence.

Longitudinal assessment of genetic and epigenetic markers in oligodendrogliomas

PURPOSE

Because little is known about the evolution of genetic and epigenetic changes that occur during tumor progression in oligodendrogliomas, we evaluated these changes in paired early and progressive oligodendrogliomas.

EXPERIMENTAL DESIGN

1p36, 19q13, 10q22-26, and O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation status were assessed in 46 paired early and progressive oligodendrogliomas from 23 patients.

RESULTS

In early tumors, 60.8% were of low grade compared with only 17% low-grade tumors at recurrence. Of 17 early tumors described as pure oligodendrogliomas, 76.5% remained in this lineage, regardless of their grade, whereas others changed to astrocytic tumors. Oligoastrocytic tumors had a significantly higher tendency to transform to astrocytic tumors. All pure oligodendrogliomas with 1p/19q codeletions remained phenotypically unchanged, unlike mixed tumors with codeletions, of which 83% changed their cell lineage. Of tumors with early 1p deletion, 80% remained oligodendroglial at progression, whereas 75% of tumors with an intact 1p changed to astrocytic phenotype. 10q loss was uncommon in both early and progressive tumors. The proportional gain in methylation at progression was 31% for tumors with early 1p deletion, unlike tumors with an intact 1p, which had an 87.5% gain of methylation at progression.

CONCLUSIONS

Pure oligodendrogliomas with 1p/19q deletion tend to retain their cell phenotype and genetic profile unlike tumors with no deletions or mixed histology. MGMT promoter methylation is more pronounced at tumor progression, particularly in tumors with an intact 1p. These observations suggest that MGMT promoter methylation is a late event in progressive oligodendrogliomas, and therefore, their chemosensitivity is not necessarily related to MGMT methylation status.

Methylation of Ras association domain family protein 1, isoform A correlated with proliferation and drug resistance in hepatocellular carcinoma cell line SMMC-7721

BACKGROUND

It has been proposed that aberrant DNA methylation can alter cancer's response to therapeutic agents. The purpose of the present study was to investigate the relationship between Ras association domain family protein 1, isoform A (RASSF1A) and drug resistance or growth of hepatocellular carcinoma cell line SMMC-7721.

METHODS

Methylation status of RASSF1A from genomic gene of SMMC-7721 was determined with methylation-specific polymerase chain reaction and was further verified by demethylation treatment with 5-aza-2'-deoxycytidine. Wild-type RASSF1A cDNA was introduced into SMMC-7721; chemosensitivity to cisplatin, mitomycin and fluorouracil were analyzed using 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide assay. Growth of cells was detected by colony formation assay and xenograft model.

RESULTS

RASSF1A was inactivated in SMMC-7721 cell line through epigenetic hypermethylation, and reintroduction of RASSF1A was markedly able to reduce the resistance to some anticancer drugs and inhibit the growth of cancer cells either in vitro or in vivo.

CONCLUSION

These results correlate methylation status of RASSF1A with biological profiles of SMMC-7721 and thus, associate methylation with cancer therapy. RASSF1A may be useful to predict treatment response and help to develop novel treatment strategies for clinical treatment of hepatocellular carcinoma.

Correlation Between O6-Methylguanine-DNA Methyltransferase and Survival in Inoperable Newly Diagnosed Glioblastoma Patients Treated With Neoadjuvant Temozolomide

Purpose

This phase II study evaluated the efficacy and safety of a 7-day on/7-day off regimen of temozolomide before radiotherapy (RT) in patients with inoperable newly diagnosed glioblastoma.

Patients and Methods

Patients received temozolomide (150 mg/m2/d on days 1 to 7 and days 15 to 21 every 28 days; 7 days on/7 days off) for up to four cycles before conventional RT (2-Gy fractions to a total of 60 Gy) and for four cycles thereafter or until disease progression. The primary end point was tumor response. Tumor tissue from 25 patients was analyzed for O6-methylguanine-DNA methyltransferase (MGMT) expression.

Results

Twenty-nine patients with a median age of 60 years were treated, and 28 were assessable for response. Seven (24%) of 29 patients had a partial response, nine patients (31%) had stable disease, and 12 patients (41%) had progressive disease. Median progression-free survival (PFS) time was 3.8 months, and median overall survival (OS) time was 6.1 months. Patients with low MGMT expression, compared with patients with high MGMT expression, had a significantly higher response rate (55% v 7%, respectively; P = .004) and improved PFS (median, 5.5 v 1.9 months, respectively; P = .009) and OS (median, 16 v 5 months, respectively; P = .003). The most common grade 3 and 4 toxicities were thrombocytopenia (20%) and neutropenia (17%).

Conclusion

This dose-dense temozolomide regimen resulted in modest antitumor activity with an acceptable safety profile in the neoadjuvant setting, and expression of MGMT correlated with response to temozolomide. However, this treatment approach seems to be inferior to standard concomitant RT plus temozolomide.

Chromosome arm 1q gain associated with good response to chemotherapy in a malignant glioma. Case report

The authors describe the case of a patient with a glioblastoma multiforme who showed remarkably good response to chemotherapy. A genetic analysis using comparative genomic hybridization (CGH) revealed that the tumor had a gain on the q arm of chromosome 1 (1q). Using CGH for a series of genetic analyses of more than 180 patients with gliomas, six were found to have a demonstrated 1q gain. Although the tumors in all six of these cases were histopathologically diagnosed as high-grade gliomas, compared with other malignant gliomas they demonstrated a good prognosis because of their favorable chemotherapeutic sensitivity. In immunohistochemical tests, most of the tumor cells in these cases were negative for O6-methylguanine-DNA methyltransferase, which antagonizes the effect of DNA-alkylating chemotherapeutic agents. The authors believed that a gain of 1q could be produced through the genetic events that cause loss of 1p, because these chromosomal aberrations have an imbalance of DNA copy number in common (1p < 1q). A gain of 1q is an infrequent chromosomal aberration and its clinical importance should be investigated in a larger study; however, patients with malignant gliomas demonstrating a 1q gain possibly show longer survival and good response to chemotherapy similar to patients with tumors demonstrating 1p loss. The importance of using genetic analysis for gliomas is emphasized in this report because it may help in selecting cases responsive to chemotherapy and because appropriate treatment for these patients will lead to progress in the treatment of malignant gliomas.

A simplified laboratory validated assay for MGMT promoter hypermethylation analysis of glioma specimens from formalin-fixed paraffin-embedded tissue

Glioma, and in particular high-grade astrocytoma termed glioblastoma multiforme (GBM), is the most common primary tumor of the brain. Epigenetic silencing of the MGMT (O(6)-methylguanine-DNA Methyl transferase) DNA repair gene by promoter methylation compromises DNA repair and has been associated with longer survival in patients with GBM who receive alkylating agents. The methylation status of the MGMT promoter is determined by methylation-specific polymerase chain reaction analysis (MSP). This protocol is often challenging with GBM specimens, because of extensive necrosis and scarcity of malignant cells. The objective of this study was to develop a reliable, clinically validated assay for detection of epigenetic silencing of the MGMT gene using formalin-fixed, paraffin-embedded brain tumor resections and methylation-specific PCR.

S-alkylthiolation of O6-methylguanine-DNA-methyltransferase (MGMT) to sensitize cancer cells to anticancer therapy

O6-methylguanine DNA methyltransferase/O6-alkylguanine DNA alkyltransferase (MGMT/AGT) removes alkyl adducts from the O6-position of guanine in DNA. Expression of MGMT in human cancers has been associated with resistance to therapies using alkylating agents. MGMT promoter methylation regulates its expression and response to alkylating agents. A combination of O6-benzylguanine-based inhibitors of MGMT with alkylating agents improved the efficacy. However, this is associated with enhanced cytotoxicity and the induction of GC to AT transition mutations presumably also in progenitor/stem cells. A few recent studies have described analogs of O6-benzylguanine targeting defined pathways of cancer cells that can be used to improve the selectivity of O6-benzylguanine-based inhibitors for cancer cells. Therefore, MGMT inhibitor targeting represents a reliable strategy for improving cancer therapy with alkylating agents.

Clinicopathologic aspects of 1p/19q loss and the diagnosis of oligodendroglioma

CONTEXT

Significant interobserver variability exists with respect to the diagnosis of oligodendroglial neoplasms, especially their distinction from astrocytoma and mixed oligoastrocytoma. Combined loss of the short arm of chromosome 1 and the long arm of chromosome 19 has been shown to be both relatively specific to oligodendroglioma and, when present, a marker of improved prognosis in patients with these tumors. In addition, 1p/19q loss has been shown to be a marker of "classic" oligodendroglial histology. These findings raise questions as to the role of 1p/19q testing in clinical practice, both as a prognostic marker and as a potential diagnostic marker among infiltrating glial neoplasms.

OBJECTIVE

This review discusses the issues raised above and tries to clarify the current status of 1p/19q evaluation in the diagnosis of oligodendroglioma.

DATA SOURCES

Sources for this review include recent literature as well as the experience of 3 practicing neuropathologists.

CONCLUSIONS

1p/19q status is an important marker in oligodendroglioma. Loss of 1p/19q is associated with classic oligodendroglioma histology as well as improved prognosis. The combined 1p/19q marker will continue to be a clinically useful marker of prognosis and could potentially be incorporated into diagnostic criteria in the future.

MGMT methylation: a marker of response to temozolomide in low-grade gliomas

The methylation status of the O6-methylguanine-methyltransferase promoter (MGMTP) was evaluated in 68 low-grade gliomas treated by neoadjuvant temozolomide. Methylated MGMTP was detected in 63 of 68 (92.6 %) patients and was a favorable predictor of progression-free survival as compared with unmethylated MGMTP tumors (p < 0.0001). Assessment of MGMTP status could help identifying low-grade gliomas patients more likely to respond to chemotherapy or to benefit from MGMT depletion strategies.

Hypermethylation and transcriptional downregulation of the CITED4 gene at 1p34.2 in oligodendroglial tumours with allelic losses on 1p and 19q

Deletions of chromosomal arms 1p and 19q are frequent in oligodendroglial tumours and have been associated with sensitivity to radio- and chemotherapy as well as favourable prognosis. By using microarray-based expression profiling, we found that oligodendroglial tumours with 1p and 19q losses showed significantly lower expression of the CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 4 gene (CITED4) at 1p34.2 as compared to tumours without 1p and 19q losses. Mutational analysis showed no CITED4 mutations in gliomas. However, 1p and 19q losses as well as low expression of CITED4 transcripts were significantly associated with hypermethylation of the CITED4-associated CpG island. In line with the latter finding, treatment of CITED4 hypermethylated glioma cell lines with 5-aza-2'-deoxycytidine and trichostatine A resulted in a marked increase of the CITED4 transcript levels. Furthermore, CITED4 hypermethylation was significantly associated with longer recurrence-free and overall survival of patients with oligodendroglial tumours. Taken together, our results indicate that CITED4 is epigenetically silenced in the vast majority of oligodendroglial tumours with 1p and 19q deletions and suggest CITED4 hypermethylation as a novel prognostic marker in oligodendroglioma patients.

Subtypes of oligodendroglioma defined by 1p,19q deletions, differ in the proportion of apoptotic cells but not in replication-licensed non-proliferating cells

Oligodendrogliomas may be divided into those with deletion of chromosomes 1p and 19q (Del+), and those without (Del−). Del+ tumours show better survival and chemoresponsiveness but the reason for this difference is unknown. We have investigated whether these subgroups differ in (a) apoptotic index, (b) the proportion of cells licensed for DNA replication but not in-cycle, and (c) the relative length of G₁-phase. Fluorescence in situ hybridisation with probes to 1p and 19q was used to determine the deletion status of 54 oligodendrogliomas, including WHO grades II and III. The apoptotic index was determined using counts of apoptotic bodies. Replication-licensed non-proliferating cells were determined from the Mcm2 minus Ki67 labelling index, whilst the geminin to Ki67 ratio was used as a measure of the relative length of G₁. Del+ oligodendrogliomas showed a higher apoptotic index than Del− tumours (P = 0.037); this was not accounted for by differences in tumour grade or in proliferation. There were no differences in the Mcm2 − Ki67 index or in the geminin/Ki67 ratio between the subgroups, but grade III tumours showed a higher proportion of licensed non-proliferating cells than grade II tumours (P = 0.001). An increased susceptibility to apoptosis in oligodendrogliomas with 1p ± 19q deletion may be important in their improved clinical outcome compared to Del− tumours.

Expression analyses of 27 DNA repair genes in astrocytoma by TaqMan low-density array

DNA repair systems act to maintain genome integrity in the face of replication errors, environmental insults, and the cumulative effects of age. The mRNA expressions of 27 genes of the DNA repair system as well as their correlation with the clinical characteristics were studied in human astrocytoma. We applied TaqMan low-density array to investigate the mRNA expressions of 27 DNA repair genes in 40 astrocytoma tissues (10 of grade II, 10 of grade III, and 20 of grade IV, according to the WHO Grading System). And the normal brain tissues from 10 non-astrocytoma patients were collected as the control. In addition, correlation of their mRNA levels with clinical characteristics was also analyzed. We found that the expression of the 13 genes were significantly (P<0.01) down-regulated in grade II, III, IV of astrocytoma compared to normal brain tissues, including ERCC1, ERCC2, ERCC3, ERCC4, MGMT, MLH1, MLH3, NTHL1, OGG1, RAD50, SMUG1, XRCC4 and XRCC5. Meanwhile, we found that the expression of MSH2, MSH6, NUDT1 and XRCC3 were only significantly lower in grade II and III of astrocytoma, and the expression of MRE11A and MUS81 were only significantly lower in grade III and IV. But the expression of MPG, MSH3, MUTHY and RAD51 were not changed in any grade of astrocytoma. Furthermore, we found that the decrease expression of eight genes was significantly (P<0.05) associated with a poor prognosis, including ERCC3, ERCC4, MLH3, MRE11A, NTHL1, RAD50, XRCC4 and XRCC5. We suggest that TaqMan low-density array is an effective multivariate technique to examine the expression of DNA repair genes in astrocytomas, which can be applied to identify tumor-specific genes. We also suggest that the down-regulation of some DNA repair genes may be associated with pathogenesis and poor prognosis of astrocytoma.

Recent advances in the medical therapy of high-grade gliomas

Malignant glial neoplasms, including glioblastoma, are amongst the most devastating and intractable of solid tumors. Until recently the standard of care for newly diagnosed glioblastoma was surgical resection to the extent feasible followed by conventional fractionated radiotherapy. When administered for disease progression, chemotherapy had modest benefit and its use in the adjuvant setting was controversial. Temozolomide, an oral alkylating chemotherapeutic agent, has now been demonstrated to increase survival time in patients with newly diagnosed glioblastoma when used concurrently with radiotherapy and as adjuvant or maintenance treatment for six cycles thereafter. Correlative molecular studies suggested that the benefit of temozolomide is largely restricted to patients whose tumor has silenced the gene for methylguanine methyltransferase, a repair enzyme implicated in resistance to alkylator chemotherapy. Use of temozolomide chemotherapy upfront in the management of glioblastoma is now considered the standard of care. This significant advance has also stimulated development of therapeutic strategies that incorporate temozolomide, and other agents, in the initial management of most high-grade gliomas. Furthermore, our increased understanding of the molecular derangements that underlie gliomagenesis has identified a number of putative molecular targets against which novel therapeutics have been tested with encouraging preliminary results. Finally, the challenges presented by the blood–brain barrier to adequate drug delivery have stimulated the development of unique locoregional delivery techniques that are currently undergoing clinical evaluation. This review summarizes these recent advances, and speculates on how the field is likely to evolve in the near future.

Should concomitant and adjuvant treatment with temozolomide be used as standard therapy in patients with anaplastic glioma?

Malignant gliomas are devastating tumors associated with poor prognosis. Standard treatment has been surgery followed by radiotherapy while the role of chemotherapy has remained controversial. Concomitant and adjuvant treatment with temozolomide has recently been shown to improve survival in patients with glioblastoma. While it seems intuitive to apply this regimen to patients with anaplastic gliomas which have traditionally been considered more chemosensitive, chemotherapy has not been shown to prolong life in patients with anaplastic gliomas. Despite promising preclinical and early clinical results, there is currently not enough level 1 evidence to justify concomitant and adjuvant temozolomide as standard therapy for patients with newly diagnosed anaplastic gliomas. Further investigation is needed to better define the role of chemotherapy in patients with anaplastic gliomas. Trials evaluating chemoradiotherapy as well as targeted therapeutic agents are the subject of further research.

Correlations Between O6-Methylguanine DNA Methyltransferase Promoter Methylation Status, 1p and 19q Deletions, and Response to Temozolomide in Anaplastic and Recurrent Oligodendroglioma: A Prospective GICNO Study

Purpose

To date, no data are available on the relationship between 1p/19q deletions and the response to temozolomide (TMZ) in primary anaplastic oligodendroglioma (AO) and anaplastic oligoastrocytoma (AOA) recurrent after surgery and standard radiotherapy. The aim of this study was to evaluate correlations between 1p/19q deletions, O6-methylguanine DNA methyltransferase (MGMT) promoter methylation, and response rate to TMZ in this setting.

Patients and Methods

From June 2000 to February 2005, 67 patients were enrolled; 39 patients (58%) had AO and 28 patients (42%) had AOA. All patients received 150 to 200 mg/m2 of TMZ every 28 days. Chromosome 1p and 19q deletions were detected by fluorescence in situ hybridization and MGMT promoter methylation was analyzed using methylation specific polymerase chain reaction.

Results

The overall response rate was 46.3% (17 complete responses and 14 partial responses). The response rate was higher in patients with AO than in those with AOA (61.5% v 25%, P = .003). Combined 1p/19q allelic loss was found in 32 patients (47.8%), while MGMT methylation occurred in 37 (68.5%) of 54 assessable patients. 1p/19q loss was significantly correlated with response rate (P = .04), time-to-progression (P = .003), and overall survival (P = .0001). Despite the significant concordance found between MGMT promoter methylation and 1p/19q deletions (P = .02), MGMT promoter methylation showed only a borderline correlation with overall survival (P = .09).

Conclusion

TMZ is active in anaplastic oligodendroglial tumors treated at first recurrence. In this setting, 1p/19q allelic loss is an important predictive and prognostic factor. Further studies on MGMT promoter methylation should be performed in randomized trials to test its correlation with survival.

DNA methylation and allelic losses on chromosome arm 14q in oligodendroglial tumours

Cytogenetic and molecular genetic studies have shown frequent losses on the long arm of chromosome 14 in different types of human gliomas. Using differential methylation hybridization as a genome-wide screening approach to determine DNA methylation patterns in gliomas, we recently identified two DNA fragments in 14q23.1 (CGI-clone musical sharp396) and 14q32.12 (CGI-clone musical sharp519) that were differentially methylated between astrocytic gliomas and mixed oligoastrocytomas. To validate this observation, we examined these 14q32.12 locus for methylation in an extended series of 43 astrocytic and oligodendroglial gliomas. All tumours were additionally investigated for loss of heterozygosity (LOH). Microsatellite analysis showed LOH in seven of 28 (25%) oligodendroglial tumours and three of 15 (20%) astrocytic tumours. Seven tumours demonstrated LOH at all informative 14q loci whereas three tumours carried partial deletions defining a commonly deleted region at 14q22.3-q32.1 between the microsatellite markers D14S282 and D14S995. Methylation-specific PCR analysis of the 14q32.12 locus revealed hypermethylation in 12 of 43 gliomas (28%). Hypermethylation was restricted to tumours with oligodendroglial differentiation (12 of 28 tumours, 43%). However, none of the hypermethylated tumours demonstrated LOH on 14q and vice versa. In total, 19 of 28 oligodendroglial tumours (68%) showed either hypermethylation at the 14q32.12 locus or LOH at 14q22.3-q32.2. Taken together, our data lend further support for the location of one or more yet to be identified glioma-associated tumour suppressor gene(s) on 14q. In addition, the restriction of 14q32.12 methylation to oligodendroglial tumours suggests a role for epigenetic DNA modifications in these particular gliomas.

Phase II trial of lomustine plus temozolomide chemotherapy in addition to radiotherapy in newly diagnosed glioblastoma: UKT-03

PURPOSE

To evaluate toxicity and efficacy of the combination of lomustine, temozolomide (TMZ) and involved-field radiotherapy in patients with newly diagnosed glioblastoma (GBM).

PATIENTS AND METHODS

Thirty-one adult patients (median Karnofsky performance score 90; median age, 51 years) accrued in two centers received involved-field radiotherapy (60 Gy in 2-Gy fractions) and chemotherapy with lomustine 100 mg/m2 (day 1) and TMZ 100 mg/m2/d (days 2 to 6) with individual dose adjustments according to hematologic toxicity.

RESULTS

A median of five courses (range, one to six courses) were delivered. WHO grade 4 hematotoxicity was observed in five patients (16%) and one of these patients died as a result of septicemia. Nonhematologic toxicity included one patient with WHO grade 4 drug-induced hepatitis (leading to discontinuation of lomustine and TMZ) and one patient with WHO grade 2 lung fibrosis (leading to discontinuation of lomustine). The progression-free survival (PFS) rate at 6 months was 61.3%. The median PFS was 9 months (95% CI, 5.3 to 11.7 months), the median overall survival time (MST) was 22.6 months (95% CI, 12.5 to not assessable), the 2-year survival rate was 44.7%. O6-methylguanine-DNA methyltransferase (MGMT) gene-promoter methylation in the tumor tissue was associated with longer PFS (P = .014, log-rank test) and MST (P = .037).

CONCLUSION

The combination of lomustine, TMZ, and radiotherapy had acceptable toxicity and yielded promising survival data in patients with newly diagnosed GBM. MGMT gene-promoter methylation was a strong predictor of survival.

Temozolomide: a milestone in neuro-oncology and beyond?

Temozolomide (Temodal, Temodar), an imidazol derivative, is a second-generation alkylating agent. The orally available prodrug with the capacity of crossing the blood-brain barrier received accelerated US FDA approval in 1999. Three pivotal Phase II trials showed modest activity in the treatment of recurrent anaplastic astrocytoma glioblastoma. In 2005, the FDA and the European Agency for the Evaluation of Medicinal Products approved temozolomide for use in newly diagnosed glioblastoma, in conjunction with radiotherapy, based on an European Organisation for Research and Treatment of Cancer/National Cancer Institute of Canada Phase III trial. The adverse events associated with temozolomide are mild-to-moderate and generally predictable; the most serious are noncumulative and reversible myelosuppression and, in particular, thrombocytopenia, which occurs in less than 5% of patients. Continuous temozolomide administration is associated with profound CD4-selective lymphocytopenia. Molecular studies have suggested that the benefit of temozolomide chemotherapy is restricted to patients whose tumors have a methylated methylguanine methyltransferase gene promotor and are thus unable to repair some of the chemotherapy-induced DNA damage. Temozolomide is under investigation for other disease entities, in particular lower-grade glioma, brain metastases and melanoma.

Frequent loss of chromosome 9, homozygous CDKN2A/p14ARF/CDKN2B deletion and low TSC1 mRNA expression in pleomorphic xanthoastrocytomas

The molecular pathogenesis of pleomorphic xanthoastrocytoma (PXA), a rare astrocytic brain tumor with a relatively favorable prognosis, is still poorly understood. We characterized 50 PXAs by comparative genomic hybridization (CGH) and found the most common imbalance to be loss on chromosome 9 in 50% of tumors. Other recurrent losses affected chromosomes 17 (10%), 8, 18, 22 (4% each). Recurrent gains were identified on chromosomes X (16%), 7, 9q, 20 (8% each), 4, 5, 19 (4% each). Two tumors demonstrated amplifications mapping to 2p23-p25, 4p15, 12q13, 12q21, 21q21 and 21q22. Analysis of 10 PXAs with available high molecular weight DNA by high-resolution array-based CGH indicated homozygous 9p21.3 deletions involving the CDKN2A/p14(ARF)/CDKN2B loci in six tumors (60%). Interphase fluorescence in situ hybridization to tissue sections confirmed the presence of tumor cells with homozygous 9p21.3 deletions. Mutational analysis of candidate genes on 9q, PTCH and TSC1, revealed no mutations in PXAs with 9q loss and no evidence of TSC1 promoter methylation. However, PXAs consistently showed low TSC1 transcript levels. Taken together, our study identifies loss of chromosome 9 as the most common chromosomal imbalance in PXAs and suggests important roles for homozygous CDKN2A/p14(ARF)/CDKN2B deletion as well as low TSC1 mRNA expression in these tumors.

Oligodendroglial tumors

Oligodendroglial tumors represent approximately 4-7% of all gliomas; however, in some series the incidence has been reported to be as high as 10-20% because of improved histological appreciation and recently recognized molecular signatures. Oligodendroglial tumors are classified as being low-grade oligodendroglial tumors, high-grade anaplastic oligodendroglial tumors or mixed oligo-astrocytic tumors. The mixed tumors can again be low-grade or high-grade. The recent European Organization for Research and Treatment of Cancer and Radiation Therapy Oncology Group randomized trials have provided level 1 evidence regarding the best management of these tumors. This review provides an overview of oligodendroglial tumors and discusses contemporary and evolving treatment strategies.

Reclassification of oligoastrocytomas by loss of heterozygosity studies

Oligoastrocytomas (OAs) are WHO grade II or III tumors composed of a mixture of 2 neoplastic cell types morphologically resembling the cells in oligodendrogliomas and diffuse astrocytomas. Investigations on the genetic profile of OAs may yield important information for their classification and help for their clinical management. We have studied, in 94 OAs (46 WHO grade II and 48 WHO grade III), the patterns of loss of heterozygosity (LOH) of 4 genomic regions: 1p, 19q, 17p and 10q. Results were as follows: LOH 1p was present in 46% of the tumors; LOH 19q in 45%; LOH 17p in 22%; LOH 10q in 16%. LOH 1p and 19q were associated in 32%, other LOH associations were rare (<3%). Patients had a median follow-up of 30 months. Patients without LOH on 1p had shorter progression free survival than patients with LOH on 1p: 30 vs. 132 months, p < 0.0001. MRI indicated that tumors without LOH on 1p were often temporal (p < 0.02), and showed signal inhomogeneity on T1 and T2 images (p < 0.02) and contrast enhancement (p < 0.04). Thus, LOH on 1p identifies two subgroups of OAs. OAs without LOH on 1p behave like WHO grade II or III diffuse astrocytomas: they have shorter survival, MRI characteristics implying malignancy and genetic alterations associated with tumor progression. OAs with LOH on 1p, on the other hand, behave like WHO grade II or III oligodendrogliomas with 1p loss: they are associated with longer survival and do not have MRI or genetic alterations associated with malignancy. These findings suggest that the definition of OAs or mixed gliomas could be reshaped in agreement with the genetic information.

Malignant glioma: Neuropathology and Neurobiology

Malignant gliomas may manifest at any age including congenital and childhood cases. Peak incidence is, however, in adults older than 40 years. Males are more frequently affected than females. The sole unequivocal risk factor is therapeutic ionizing irradiation. Malignant gliomas comprise a spectrum of different tumor subtypes. Within this spectrum, glioblastoma, anaplastic astrocytoma and anaplastic oligodendroglioma share as basic features preferential location in cerebral hemispheres, diffuse infiltration of brain tissue, fast tumor growth with fatal outcome within months or years. Invasion is regarded as one of the main reasons for poor therapeutic success, because it makes complete surgical removal of gliomas impossible. Invasion of glioma cells requires interaction with the extracellular matrix and with surrounding cells of the healthy brain tissue. Vascular proliferates and tissue necrosis are characteristic features of malignant gliomas, in particular glioblastoma. These features are most likely the consequence of rapidly increasing tumor mass that is inadequately oxygenized by the preexisting vasculature. In malignant glioma, distinct molecular pathways including the p53 pathway, the RB pathway and the EGFR pathway show frequent alterations that seem to be pathogenetically relevant. Methylguanine-methyltransferase (MGMT) promoter methylation status in glioblastoma and 1p19q deletion status in anaplastic oligodendroglioma are associated with response to chemotherapy. The role of neuropathology and neurobiology in neurooncology is 1. to provide a clinically meaningful classification of brain tumors on basis of pathobiological factors, 2. to clarify etiology and pathogenesis of brain tumors as rational basis for development of new diagnostic tests and therapies, and 3. to translate testing for new clinically relevant molecular parameters into clinical application.

Progressive low-grade oligodendrogliomas: response to temozolomide and correlation between genetic profile and O6-methylguanine DNA methyltransferase protein expression

BACKGROUND

Loss of heterozygosity (LOH) on chromosomes 1p and 19q has been associated with chemosensitivity and improved prognosis in patients with oligodendrogliomas. The DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT) may induce resistance to DNA-alkylating agents. Recent studies demonstrated that temozolomide (TMZ), an oral alkylating agent, has efficacy in the treatment of patients with progressive, low-grade oligodendroglioma (LGO). However, to the authors' knowledge, limited data are available regarding the 1p/19q profile and its correlation with MGMT protein expression and response to treatment with DNA-alkylating drugs.

METHODS

Adult patients with magnetic resonance imaging (MRI) findings and/or clinical deterioration compatible with progressive LGO were eligible for the study if they were radiotherapy-naive. TMZ cycles were repeated every 28 days at a dose of 200 mg/m2 daily for 5 consecutive days. Clinical and MRI data were used to evaluate outcomes, and Kaplan-Meier estimates were used to assess the median time to tumor progression (TTP). The 1p/19q status was analyzed from paired tumor-blood DNA samples using polymerase chain reaction-based microsatellite analysis. MGMT protein expression was estimated semiquantitatively by immunohistochemistry using paraffin embedded tumor sections.

RESULTS

There were 28 patients who received treatment, and the median time from diagnosis to tumor progression was 33.5 months. The median number of TMZ cycles per patient was 12.5. Marked clinical improvements were recorded in 15 patients (54%), and objective responses were recorded in 17 patients (61%). The median TTP was 31 months, and the progression-free survival rate was 70% at 24 months. Loss of chromosome 1p and low MGMT protein expression were associated with objective response (P < .003 and P < .04, respectively).

CONCLUSIONS

TMZ was active in patients with progressive LGO, and their response to treatment was associated with 1p deletion and low MGMT protein expression. The authors suggest the possible use of MGMT immunostaining as a surrogate marker for predicting tumor chemosensitivity.

Age at diagnosis and loss of heterozygosity on chromosome 1p and 19q in oligodendroglial tumors

The age distribution and incidence of loss of heterozygosity (LOH) of 1p and 19q was analyzed in 85 oligodendroglial tumors WHO II and III. The peak of tumor manifestation was in the age group of 35 to 55 years. There was no association between age at diagnosis and LOH incidence. We conclude that the prognostic effect of age on survival is not mediated by LOH 1p/19q.

Recent advances in the treatment of oligodendrogliomas

The optimal treatment for patients with oligodendrogliomas is unknown, and current management strategies remain controversial. This past year, further exploration of the molecular genetics of the tumors and its prognostic implications for outcome, evaluation of the utility of positron emission tomography imaging, and the role of radiation and chemotherapy in the treatment of oligodendrogliomas have been reported. It is becoming increasingly apparent that oligodendrogliomas are several distinct diseases on a molecular level, and that key genetic derangements can signify a response to treatment and favorable outcome. The added contributions of recent publications consolidates these emerging impressions. Ultimately, the combination of improved imaging techniques, molecular profiling, and new therapies should result in improved outcome with reduced treatment-related toxicity for patients with newly diagnosed, progressive, and recurrent oligodendrogliomas.