Advertisement
Journal of Clinical Oncology  
Search for:
Limit by:
  Browse by Subject or Issue
Home Search or Browse JCO My JCO Subscriptions Customer Service Site Map

Journal of Clinical Oncology, Vol 24, No 21 (July 20), 2006: pp. 3431-3437
© 2006 American Society of Clinical Oncology.
DOI: 10.1200/JCO.2006.05.7265
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a colleague
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Save to my personal folders
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pollack, I. F.
Right arrow Articles by Finlay, J. L.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pollack, I. F.
Right arrow Articles by Finlay, J. L.

O6-Methylguanine-DNA Methyltransferase Expression Strongly Correlates With Outcome in Childhood Malignant Gliomas: Results From the CCG-945 Cohort

Ian F. Pollack, Ronald L. Hamilton, Robert W. Sobol, Judith Burnham, Allan J. Yates, Emiko J. Holmes, Tianni Zhou, Jonathan L. Finlay

From the Departments of Neurosurgery, Pathology, and Pharmacology, University of Pittsburgh Cancer Institute, University of Pittsburgh Medical Center and the Children's Hospital of Pittsburgh, Pittsburgh, PA; Department of Pathology, Ohio State University, Columbus, OH; Department of Pediatrics, Children's Hospital Los Angeles; Department of Preventive Medicine, University of Southern California, Los Angeles; and the Children's Oncology Group, Arcadia, CA

Address reprint requests to Ian F. Pollack, MD, Department of Neurosurgery, Children's Hospital of Pittsburgh, 3705 Fifth Avenue, Pittsburgh, PA 15213; e-mail: ian.pollack{at}chp.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 Authors' Disclosures of...
 Author Contributions
 REFERENCES
 
PURPOSE: O6-Methylguanine-DNA methyltransferase (MGMT) functions to counteract the cytotoxic effects of alkylating agents, such as nitrosoureas, which play a central role in the treatment of childhood malignant gliomas. Epigenetic silencing of MGMT has been associated with prolonged survival in adults with malignant gliomas, although the association between MGMT expression status and outcome in pediatric malignant gliomas has not been defined.

METHODS: We examined the association between MGMT expression and survival duration using tumor samples from the Children's Cancer Group 945 study, the largest randomized trial for childhood malignant gliomas completed to date. All patients received alkylator-based chemotherapy as a component of adjuvant therapy. Archival histopathologic material yielded tissue of sufficient quality for immunohistochemical assessment of MGMT expression status in 109 specimens.

RESULTS: Twelve of the 109 samples demonstrated overexpression of MGMT compared with normal brain. Five-year progression-free survival was 42.1% ± 5% in the 97 patients whose tumors had low levels of MGMT expression versus 8.3% ± 8% in the 12 patients whose tumors overexpressed MGMT (P = .017, exact log-rank test). The association between MGMT overexpression and adverse outcome remained significant after stratifying for institutional histologic diagnosis (eg, anaplastic astrocytoma or glioblastoma multiforme), as well as age, amount of residual tumor, and tumor location.

CONCLUSION: Overexpression of MGMT in childhood malignant gliomas is strongly associated with an adverse outcome in children treated with alkylator-based chemotherapy, independently of a variety of clinical prognostic factors.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 Authors' Disclosures of...
 Author Contributions
 REFERENCES
 
High-grade gliomas are the most common primary CNS tumors and generally have a poor prognosis.1,2 However, many studies have found that young age is a favorable prognostic factor,1,3-6 suggesting that childhood malignant gliomas might differ biologically from similar lesions in older patients. This contention has been supported by recent molecular analyses, which have shown that childhood primary malignant gliomas rarely exhibit EGFR amplification or PTEN deletion,7-13 hallmarks of adult primary glioblastomas, but commonly exhibit p53 mutations, similar to so-called secondary adult glioblastomas that progress from lower grade lesions.14-20

Notwithstanding the biologic differences between adult and childhood malignant gliomas, both groups typically are treated with a combination of surgery, irradiation, and alkylator-based chemotherapy, using agents such as the nitrosoureas or temozolomide, which have shown activity in the treatment of malignant gliomas.21-23 In the Children's Cancer Group (CCG) 943 study, children treated with lomustine and vincristine in addition to irradiation had significantly longer survival than those treated with irradiation alone.21 Likewise, more recent studies have demonstrated a high rate of response and significantly longer survival among patients treated with temozolomide plus irradiation versus those who received irradiation alone.22,23 However, only a subset of patients responds to these agents, reflecting the substantial percentage of tumors that are intrinsically resistant.

In this regard, tumor cells can use a number of molecular mechanisms to counteract alkylation-related toxicity. O6-Methylguanine-DNA methyltransferase (MGMT) constitutes a proximal mechanism for alkylator resistance by promoting the transfer of alkyl groups from the O6 position of guanine nucleotides in DNA to an alkyl group acceptor site within MGMT.24-26 MGMT levels have been noted to be inversely associated with response to alkylating agents in brain tumor xenograft models.27 Moreover, several studies have suggested a favorable association between low MGMT levels, as defined by immunohistochemistry or gene inactivation by promoter methylation, and response to nitrosoureas or temozolomide in clinical trials for adults with malignant glioma.28-36 It is of vital clinical importance that we establish conclusively whether such a relationship exists in pediatric malignant gliomas because the vast majority of children with malignant gliomas currently receive such agents as a part of their initial therapy.

To investigate the clinical significance of MGMT expression in these tumors, we analyzed MGMT levels immunohistochemically in the multi-institutional cohort of CCG-945, a large phase III trial for children with high-grade gliomas, which incorporated alkylator-based chemotherapy as a component of adjuvant treatment.29 Our analysis demonstrated that overexpression of MGMT in these tumors was associated adversely with overall and progression-free survival, independently of a variety of clinical variables.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 Authors' Disclosures of...
 Author Contributions
 REFERENCES
 
Patients and Treatment
Tumor samples were derived from the CCG-945 clinical study, which was approved by the institutional review boards of all participating institutions. CCG-945 included 231 children with malignant gliomas arising outside the brainstem who were treated with surgery, involved-field irradiation, and one of two chemotherapy regimens. Informed consent of patients or parents/legal guardians was obtained before enrollment on the clinical trial and performance of all correlative investigations described in this report. Eligibility required an institutional histopathologic diagnosis of high-grade glioma (ie, glioblastoma multiforme [GBM], anaplastic astrocytoma, or other eligible grade 3 glioma, such as anaplastic mixed glioma). Children older than 36 months with intracranial malignant gliomas (n = 176) were randomly assigned to receive adjuvant therapy with either lomustine, vincristine, and prednisone, or the so-called eight-drugs-in-1-day regimen,21,37 which incorporated seven agents with potential activity against pediatric brain tumors: lomustine, vincristine, hydroxyurea, procarbazine, cisplatin, cytarabine, and dacarbazine, plus methylprednisolone to reduce cerebral edema. Younger children and those with malignant gliomas of the spinal cord were assigned nonrandomly to receive the eight-drug regimen. Outcome results for the overall cohort were among the best reported for these tumors, with a 5-year overall survival of 36% ± 6%, with no significant difference between treatment groups.21

Tissue accrual for the current study was coordinated by the Pediatric Branch of the Cooperative Human Tissue Network in the context of a CCG biology study, CCG-B975, which was approved by the Children's Hospital of Pittsburgh (Pittsburgh, PA) institutional review board. Patient identification was removed from all specimens by the Cooperative Human Tissue Network to mask all clinical, histologic and outcome data from investigators.

Expression of MGMT
Paraffin-embedded specimens were used for all analyses. Slides were reviewed by a neuropathologist (R.L.H.) to confirm that tumor tissue of sufficient quantity was available for the planned studies, and blocks that contained malignant glioma were sectioned at a thickness of 4 µm. Sections were stained with hematoxylin and eosin to confirm that characteristic tissue had been obtained. Adjacent sections were subjected to immunohistochemical analysis of MGMT expression. Tumor-containing sections were baked at 60°C for 30 minutes, deparaffinized in xylene, and rehydrated in graded concentrations of ethanol. Endogenous peroxidase activity was quenched by incubation in 0.3% hydrogen peroxide/methanol solution. Antigen retrieval38 was performed by heating the slides in 10 mmol citrate buffer (pH 6.0) for 20 minutes. Nonspecific antibody binding was blocked by incubation for 20 minutes in Protein Blocking Reagent (Thermo Corp, Pittsburgh, PA) for 20 minutes. Sections were then incubated with mouse anti-MGMT antibody (mT23.2, 1:100; Zymed Laboratories, San Francisco, CA)39,40 in Common Antibody Diluent (BioGenex, San Ramon, CA) at room temperature for 2 hours. Negative control sections were treated with diluent and mouse immunoglobulin G (5 µg/mL; Dako Corp, Carpinteria, CA) alone. Antibody binding was localized using a Universal Labeled Streptavidin-Biotin 2 System (LSAB 2–HRP; Dako) and visualized using 3,3'-diaminobenzidine.41 The slides were counterstained with Mayer's hematoxylin, dehydrated through graded concentrations of ethanol, cleared in xylene, mounted, and examined using a light microscope. Three positive controls (tonsil, ovary, and a glioblastoma with known MGMT overexpression) and negative controls (normal brain and tonsil treated with diluent without primary antibody) were included with each batch of sections to confirm the consistency of the analysis. Specimens had all been examined independently for immunoreactivity using an antibody against a histologically verifiable internal positive control antigen (ie, MIB1 staining of the Ki67 antigen in tumor mitotic figures), to eliminate cases in which lack of immunoreactivity for MGMT might indicate problems in tissue preservation rather than lack of protein expression. Such cases were excluded from outcome analysis.

MGMT labeling was assessed semiquantitatively by examination of stained and unstained cells in five to 10 high-power fields that incorporated the most anaplastic regions of the specimen, by an observer masked to histologic diagnoses, outcomes, or clinical features. Only cells with dense nuclear staining were graded positive. Tumors were categorized as exhibiting little or no expression (0/1) or scattered positive cells (2) comparable to normal brain, versus overexpression, in which staining was observed in most or nearly all cells (3/4).

Central Pathology Review
Although eligibility for the CCG-945 clinical study was based on the institutional histopathologic diagnosis, it was recognized subsequently that there are a number of low-grade glioma variants that may have been mistakenly classified as high-grade tumors before the adoption of contemporary classification criteria.42,43 To eliminate the possibility that prognostic associations in this study were influenced by this factor, all samples were reviewed independently in a masked fashion by a panel of five senior neuropathologists, and a consensus diagnosis was established if at least three of the five reviewers independently reached an identical histological diagnosis.42 The MGMT analyses were performed independently of this review, so that the review diagnosis of each specimen was not known during the MGMT assessment. We then examined the association between MGMT expression and outcome using the review diagnosis instead of the institutional diagnosis and excluding samples deemed to be discordant (eg, low-grade astrocytoma) or equivocal.

Statistical Analysis
For outcome analysis, tumors were classified according to the presence or absence of MGMT overexpression. The primary end point was progression-free survival, defined as the time from study entry to disease progression. Comparisons of outcome were based on the exact log-rank test; estimates and SE of survival were calculated from the product-limit estimate.44 Because it was recognized that expression of MGMT might correlate with certain clinical features, such as the histopathologic diagnosis, an analysis of the association between MGMT status and outcome was done with a stratified exact log-rank test,44 which adjusted for a variety of potential prognostic factors. Comparisons of the distribution of MGMT expression between different patient subgroups were based on two-sided Fisher's exact test and {chi}2 test, as appropriate.45 Because we observed previously that p53 expression status correlated with outcome in this cohort,12 we also examined whether MGMT expression status was associated with outcome after stratification for this factor.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 Authors' Disclosures of...
 Author Contributions
 REFERENCES
 
Patient Characteristics
One hundred nine patients had specimens that were available for analysis in the current study. Clinical and demographic details are summarized in Table 1. Twelve other patient specimens that lacked immunoreactivity for internal positive control antigens (eg, MIB1 staining of cells with mitotic figures) or had insufficient tissue for reliable assessment of immunoreactivity were excluded from analysis prospectively. Five-year progression-free survival in the assessable group of 109 tumors (38.4% ± 5%) did not differ from that of the 122 tumors for which specimens were not available or not assessable (33.2% ± 4%; P = .91, log-rank test).


View this table:
[in this window]
[in a new window]
  		Table 1. PFS as a Function of the Level of Expression of MGMT, With Stratification According to Patient Characteristics

 
Expression of MGMT and Outcome
Of 109 assessable tumors, 97 showed little or no MGMT immunoreactivity, whereas 12 showed overexpression, with dense staining in more than 25% of cells (Fig 1). A striking difference in outcome was apparent between these two groups. Five-year progression-free survival was 42.1% ± 5% in the 97 patients whose tumors had low levels of MGMT expression versus 8.3% ± 8% in the 12 patients whose tumors overexpressed MGMT (P = .017, exact log-rank test; Fig 2). A significant association between expression status and overall survival was also observed (P = .02; Fig 3).


Figure 1
View larger version (85K):
[in this window]
[in a new window]
  		Fig 1. A dramatic range of O6-methylguanine-DNA methyltransferase expression was apparent. Most tumors had (A) absent, rare, (B) or widely scattered immunoreactive cells. However, (C) a subset showed clear overexpression with dense nuclear staining in greater than 25% of cells.

 

Figure 2
View larger version (9K):
[in this window]
[in a new window]
  		Fig 2. The association of O6-methylguanine-DNA methyltransferase (MGMT) expression with progression-free survival.

 

Figure 3
View larger version (8K):
[in this window]
[in a new window]
  		Fig 3. The association of O6-methylguanine-DNA methyltransferase (MGMT) expression with overall survival.

 
The association between MGMT overexpression and adverse outcome remained significant after stratifying for age, sex, tumor location, and the amount of residual tumor (Table 1). MGMT expression was not independently associated with any of the above-described clinical variables (P > .05). The association between MGMT status and outcome was also maintained after stratification for treatment regimen (P = .016). Among patients in the lomustine, vincristine, and prednisone treatment arm, 5-year progression-free survival was 42.9% ± 9% for the 28 children whose tumors did not have MGMT overexpression, versus 0% in the five children with overexpression (P = .029). Among children in the eight-drug treatment arm, in which alkylators comprise only a portion of the agents incorporated, 5-year progression-free survival was 41.9% ± 6% in 69 patients without MGMT overexpression versus 14.3% ± 13% in the seven patients with overexpression (P = .19).

The association between MGMT overexpression and outcome was not statistically significant after stratification for p53 expression status (P = .13); however, p53 status was associated significantly with outcome after stratifying for MGMT expression (P = .006). A trend was apparent (P = .0008, test for trend) when the combination of p53 and MGMT expression status was examined; 5-year progression-free survival was 49% ± 7% in the 53 tumors without either p53 or MGMT overexpression, 33% ± 27% in the three tumors that overexpressed MGMT but not p53, 26% ± 9% in the 23 tumors that overexpressed p53 but did not overexpress MGMT, and 0% in the nine tumors that overexpressed both.

Although the association between MGMT expression and outcome was statistically significant after stratification based on the amount of residual tumor as assessed by radiologic imaging (P = .015), the association did not reach statistical significance after stratification based on the surgeon's assessment of extent of resection (P = .069). However, a significant association was observed in the subgroup of patients who did not have what was believed to be a gross total resection: 5-year progression-free survival was 25% ± 6% in the 53 patients without overexpression versus 0% in the 10 patients with overexpression (P = .042).

Analysis Based on Central Review of Histopathology
Although inclusion in the CCG-945 study was based on institutional histopathologic diagnosis, the guidelines for classifying pediatric malignant gliomas have since evolved to incorporate additional caveats for distinguishing aggressive-appearing low-grade glioma variants from high-grade gliomas.42,43 Samples from all tumors therefore were reviewed independently by a panel of senior neuropathologists using current WHO guidelines43 to ensure both consistency and stringency in tumor classification. The association between the outcome and MGMT status was significant after stratification for institutional histopathologic diagnosis (P = .013); however, the association was not significant after stratification for central review diagnosis (P = .15). For the analysis based on central review diagnosis, 36 samples for which the diagnosis was believed to be ineligible or equivocal were excluded. The association between MGMT status and outcome was not significant in the patients with review-confirmed anaplastic astrocytomas (P = .71) but was significant in patients with review-confirmed GBMs (P = .047). Among those who had review-confirmed GBMs, patients whose tumors did not have MGMT overexpression had a 5-year progression-free survival of 29% ± 9% versus 0% in those with overexpression (P = .047; Fig 4).


Figure 4
View larger version (8K):
[in this window]
[in a new window]
  		Fig 4. The association of O6-methylguanine-DNA methyltransferase (MGMT) expression with progression-free survival in centrally reviewed glioblastoma multiforme.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
Authors' Disclosures of...
 Author Contributions
 REFERENCES
 
Alkylating agents attack neoplastic cells by binding to DNA, most frequently at the O6 position of guanine.24-26 The alkylated DNA then forms cross-links with adjacent strands of DNA, which precludes DNA transcription and results in a lethal injury to the cell, or promotes abnormal base pairing.24,25 However, a number of repair mechanisms can circumvent this toxicity. The proximal repair pathway uses MGMT, a DNA-binding protein with an alkyl group acceptor site. Removal of the alkyl group from the O6 position of guanine to a cysteine residue within MGMT restores DNA to the intact state, thus abolishing the cytotoxicity of alkylating agents such as the nitrosoureas and temozolomide.24,25 MGMT has some characteristics of an enzyme, in that an energy barrier is overcome to facilitate alkyl group transfer; however, unlike a true enzyme, this acceptor site is not regenerated. Instead, the alkylated form of MGMT is unstable in mammalian cells and is degraded rapidly. Once the enzyme is depleted, additional repair by this mechanism requires de novo synthesis of the protein.46 Thus, the levels of MGMT within a given cell influence the potential for resistance to alkylator-induced DNA damage.

Tumor cell lines that lack MGMT activity are often exquisitely sensitive to alkylating agents in vitro.47 Conversely, tumor cells that express high levels of MGMT typically are resistant to alkylating agents.48-50 Thus, in vitro, tumor MGMT levels constitute a major determinant of whether or not a given cell line is sensitive to alkylators. Although endogenous MGMT levels vary widely by organ, and by cell type within a given organ, it is clear that many tumors express MGMT levels much higher than their corresponding normal tissue, suggesting that this protein provides an acquired mechanism for drug resistance. For example, normal brain tissue is known to express low to undetectable levels of the protein, whereas significant levels of expression have been observed in a substantial percentage of malignant brain tumor specimens.51,52

We found that MGMT overexpression was associated with an unfavorable prognosis after alkylator-based chemotherapy administered as a component of a multimodality treatment regimen, incorporating surgery and irradiation for children with malignant glioma. Our study was notable both for its large size and the administration of either of two alkylator-based chemotherapy regimens that yielded identical long-term survival results.37 This combination of size and consistent management optimized chances for identifying molecular features that influenced outcome. A significant association between MGMT status and progression-free survival was apparent in the treatment arm in which an alkylator was the principal active adjuvant agent (ie, lomustine, vincristine, and prednisone regimen), and a strong trend was apparent in the arm in which alkylator therapy comprised a component of a complex multiagent treatment combination (ie, eight-drug regimen). The striking association with outcome in the former regimen is consistent with the dominant contribution of an alkylating agent to the activity of this treatment arm, and the correspondingly greater sensitivity of this activity to MGMT expression status.

The observation that the association between overexpression of MGMT and prognosis was apparent in the subset of tumors classified as GBM (ie, grade 4) in analyses based on both the institutional and central review diagnoses, supports the usefulness of this marker in identifying biologically relevant subsets of the most malignant childhood gliomas. These results are consistent with recent observations in adult glioblastomas that MGMT status is an important determinant of outcome.28-30 Such studies used promoter methylation as an indirect correlate of MGMT activity, given the involvement of methylation as a mechanism for inactivating gene expression.28-30 In contrast, the current study used direct determination of MGMT expression as assessed immunohistochemically, which takes into account the observation that MGMT expression can be induced in tumors with nonmethylated MGMT promoters,53,54 and that the extent of this induction may influence response to alkylator therapy. The fact that a prognostic association between MGMT status and outcome in malignant gliomas has been observed in studies using both of these techniques supports the robustness of this marker as a predictor of alkylator response in malignant gliomas. These observations may also be relevant for other tumors in which alkylator-based therapy is a common component of adjuvant management, including a number of solid tumors and hematologic malignancies. Although this study also demonstrated an association between MGMT status and outcome in institutionally classified anaplastic astrocytomas, this association was not validated in the centrally reviewed cohort.

Our findings indicate that MGMT status is an important prognostic marker in pediatric malignant gliomas; however, it is essential to emphasize that this feature did not distinguish high-grade gliomas with a good prognosis from those with a poor prognosis. Instead, it distinguished a subgroup of children with high-grade gliomas who had an extremely unfavorable prognosis after treatment from those with a significantly better, but still suboptimal, outcome. These observations demonstrate that prognoses in children with malignant gliomas treated with conventional adjuvant chemotherapy can be adversely influenced by molecular characteristics of the tumor. In tumors with MGMT overexpression, and particularly those with concomitant overexpression of p53, alternatives to alkylator-based chemotherapy might be appropriate, and such tumors could conceivably be considered for initial management with novel, molecularly targeted agents or implementation of strategies to counteract MGMT activity, such as administration of O6-benzylguanine, which depletes MGMT.26,46,55,56 However, given the relatively low percentage of MGMT-overexpressing tumors in this series, it will be important to validate our findings in a second independent cohort before implementing therapeutic stratification based on MGMT expression status. To address this issue, we believe that molecular analyses should be included in prospective evaluations of alkylator-based adjuvant therapies for children with malignant gliomas.


   Authors' Disclosures of Potential Conflicts of Interest
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 Authors' Disclosures of...
Author Contributions
 REFERENCES
 
The authors indicated no potential conflicts of interest.


   Author Contributions
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 Authors' Disclosures of...
 Author Contributions
REFERENCES
 

Conception and design: Ian F. Pollack, Ronald L. Hamilton, Allan J. Yates, Tianni Zhou, Jonathan L. Finlay

Collection and assembly of data: Ian F. Pollack, Ronald L. Hamilton, Robert W. Sobol, Judith Burnham, Allan J. Yates, Tianni Zhou, Jonathan L. Finlay

Data analysis and interpretation: Ian F. Pollack, Ronald L. Hamilton, Robert W. Sobol, Judith Burnham, Emiko J. Holmes, Tianni Zhou

Manuscript writing: Ian F. Pollack, Ronald L. Hamilton, Tianni Zhou, Allan J. Yates

Final approval of manuscript: Ian F. Pollack, Ronald L. Hamilton, Robert W. Sobol, Allan J. Yates, Emiko J. Holmes, Tianni Zhou, Jonathan L. Finlay

 


   ACKNOWLEDGMENTS
 
The authors thank Drs Peter C. Burger, Floyd H. Gilles, Laurence E. Becker, and Richard L. Davis, who participated with Dr Allan J. Yates, MD, PhD, in the consensus pathology review for the Children’s Cancer Group study.


   NOTES
 
Supported in part by National Institute of Health Grants No. NS37704 (I.F.P.) and CA13539 to the Children's Cancer Group. A complete listing of grant support for research conducted by Children’s Oncology Group (COG) and Pediatric Oncology Group before initiation of the COG grant in 2003 is available online at http://www.childrensoncologygroup.org/admin/grantinfo.htm.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 Authors' Disclosures of...
 Author Contributions
 REFERENCES
 
1. Devaux BC, O'Fallon JR, Kelly PJ: Resection, biopsy, and survival in malignant glial neoplasms: A retrospective study of clinical parameters, therapy, and outcome. J Neurosurg 78:767-775, 1993[Medline]

2. Pollack IF: Current concepts: Brain tumors in children. N Engl J Med 331:1500-1507, 1994[Free Full Text]

3. Chandler KL, Prados MD, Malec M, et al: Long-term survival in patients with glioblastoma multiforme. Neurosurgery 32:716-720, 1993[Medline]

4. Salcman M, Scholtz H, Kaplan RS, et al: Long-term survival in patients with malignant astrocytoma. Neurosurgery 34:213-220, 1994[Medline]

5. Salford LG, Brun A, Nirfalk S: Ten-year survival among patients with supratentorial astrocytoma grade III and IV. J Neurosurg 69:506-509, 1988[Medline]

6. Duffner PK, Krischer JP, Burger PC, et al: Treatment of infants with malignant gliomas: The Pediatric Oncology Group experience. J Neurooncol 28:245-256, 1996[Medline]

7. Bredel M, Pollack IF, Hamilton RL, et al: Epidermal growth factor receptor (EGFR) expression and gene amplification in high-grade non-brainstem gliomas of childhood. Clin Cancer Res 5:1786-1792, 1999[Abstract/Free Full Text]

8. Cheng Y, Ng H-K, Zhang S-F, et al: Genetic alterations in pediatric high-grade astrocytomas. Hum Pathol 30:1284-1290, 1999[CrossRef][Medline]

9. Raffel C, Frederick L, O'Fallon JR, et al: Analysis of oncogene and tumor suppressor gene alterations in pediatric malignant astrocytomas reveals reduced survival for patients with PTEN mutations. Clin Cancer Res 5:4085-4090, 1999[Abstract/Free Full Text]

10. Sung T, Miller DC, Hayes RL, et al: Preferential inactivation of the p53 tumor suppressor pathway and lack of EGFR amplification distinguish de novo high grade pediatric astrocytomas from de novo adult astrocytomas. Brain Pathol 10:249-259, 2000[Medline]

11. Sure U, Ruedi D, Tachibana O, et al: Determination of p53 mutations, EGFR overexpression, and loss of p16 expression in pediatric glioblastomas. J Neuropathol Exp Neurol 56:782-789, 1997[Medline]

12. Pollack IF, Finkelstein SD, Woods J, et al: Expression of p53 and prognosis in malignant gliomas in children. N Engl J Med 346:420-427, 2002[Abstract/Free Full Text]

13. Pollack IF, Finkelstein SD, Burnham J, et al: The association between chromosome 1p loss and outcome in pediatric malignant gliomas: Results from the CCG-945 cohort. Pediatr Neurosurg 39:114-121, 2003[CrossRef][Medline]

14. Louis DN: A molecular genetic model of astrocytoma histopathology. Brain Pathol 7:755-764, 1997[Medline]

15. He J, Olson JJ, James CD: Lack of p16INK4 or retinoblastoma protein (pRb), or amplification-associated overexpression of cdk4 is observed in distinct subsets of malignant glial tumors and cell lines. Cancer Res 55:4833-4836, 1995[Abstract/Free Full Text]

16. von Deimling A, von Ammon K, Schoenfeld D, et al: Subsets of glioblastoma multiforme defined by molecular genetic analysis. Brain Pathol 3:19-26, 1993[Medline]

17. Galanis E, Buckner J, Kimmel D, et al: Gene amplification as a prognostic factor in primary and secondary high-grade malignant gliomas. Int J Oncol 13:717-724, 1998[Medline]

18. Watanabe K, Tachibana O, Sato K, et al: Overexpression of the EGF receptor and p53 mutations are mutually exclusive in the evolution of primary and secondary glioblastomas. Brain Pathol 6:217-224, 1996[Medline]

19. Ichimura K, Bolin MB, Goike HM, et al: Deregulation of the p14ARF/MDM2/p53 pathway is a prerequisite for human astrocytic gliomas with G1-S transition control gene abnormalities. Cancer Res 60:417-424, 2000[Abstract/Free Full Text]

20. Collins VP: Progression as exemplified by human astrocytic tumors. Semin Cancer Biol 9:267-276, 1999[CrossRef][Medline]

21. Sposto R, Ertel IJ, Jenkin RDT, et al: The effectiveness of chemotherapy for treatment of high grade astrocytoma in children: Results of a randomized trial—A report from the Children's Cancer Study Group. J Neurooncol 7:165-177, 1989[CrossRef][Medline]

22. Stupp R, Mason WP, van den Bent MJ, et al: Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med 352:987-996, 2005[Abstract/Free Full Text]

23. O'Reilly SM, Newlands ES, Glaser MG, et al: Temozolomide: A new oral cytotoxic chemotherapeutic agent with promising activity against primary brain tumours. Eur J Cancer 29A:940-942, 1993[CrossRef]

24. Gerson SL: MGMT: Its role in cancer aetiology and cancer therapeutics. Nat Rev Cancer 4:296-307, 2004[CrossRef][Medline]

25. Pegg AB: Mammalian O6-alkylguanine-DNA alkyltransferase: Regulation and importance in response to alkylating carcinogenic and therapeutic agents. Cancer Res 50:6119-6129, 1990[Free Full Text]

26. Wedge SR, Porteus JK, May BL, et al: Potentiation of temozolomide and BCNU toxicity by O(6)-benzyl-guanine: A comparative study in vitro. Br J Cancer 73:482-490, 1996[Medline]

27. Schold SC Jr, Brent TP, von Hofe E, et al: O6-alkylguanine-DNA alkyltransferase and of sensitivity to procarbazine in human brain tumor xenografts. J Neurosurg 70:573-577, 1989[Medline]

28. Esteller M, Garcia-Foncillas J, Andion E, et al: Inactivation of the DNA-repair gene MGMT and the clinical response of gliomas to alkylating agents. N Engl J Med 343:1350-1354, 2000[Abstract/Free Full Text]

29. Hegi ME, Diserens A-C, Godard S, et al: Clinical trial substantiates the predictive value of O-6-methylguanine-DNA methyltransferase promoter methylation in glioblastoma patients treated with temozolomide. Clin Cancer Res 10:1871-1874, 2004[Abstract/Free Full Text]

30. Hegi ME, Diserens A-C, Gorlia T, et al: MGMT gene silencing and benefit from temozolomide in glioblastoma. N Engl J Med 352:997-1003, 2005[Abstract/Free Full Text]

31. Belanich M, Pastor M, Randall T, et al: Retrospective study of the correlation between DNA repair protein alkyltransferase and survival of brain tumor patients treated with carmustine. Cancer Res 56:783-788, 1996[Abstract/Free Full Text]

32. Hotta T, Saito Y, Fujita H, et al: O6-alkylguanine-DNA alkyltransferase activity of human malignant glioma and its clinical implications. J Neurooncol 21:135-140, 1994[CrossRef][Medline]

33. Balana C, Ramirez JL, Taron M, et al: O6-methyl-guanine-DNA methyltransferase methylation in serum and tumor DNA predicts response to 1,3-bis(2-chloroethyl)-1-nitrosourea but not to temozolomide plus cisplatin in glioblastoma multiforme. Clin Cancer Res 9:1461-1468, 2003[Abstract/Free Full Text]

34. Jaeckle KA, Eyre HJ, Townsend JJ, et al: Correlation of tumor O6 methylguanine-DNA methyltransferase levels with survival of malignant astrocytoma patients treated with bis- chloroethylnitrosourea: A Southwest Oncology Group study. J Clin Oncol 16:3310-3315, 1998[Abstract]

35. Silber JR, Blank A, Bobola MS, et al: O6-methylguanine DNA methyltransferase-deficient phenotype in human gliomas: Frequency and time to tumor progression after alkylating agent-based chemotherapy. Clin Cancer Res 5:807-814, 1999[Abstract/Free Full Text]

36. Friedman HS, McLendon RE, Kerby T, et al: DNA mismatch repair and O6-alkylguanine-DNA alkyltransferase analysis and response to Temodal in newly diagnosed malignant glioma. J Clin Oncol 16:3851-3857, 1998[Abstract/Free Full Text]

37. Finlay JL, Boyett JM, Yates AJ, et al: Randomized phase III trial in childhood high-grade astrocytoma comparing vincristine, lomustine, and prednisone with the eight-drugs-in-1-day regimen. J Clin Oncol 13:112-123, 1995[Abstract/Free Full Text]

38. Shi SR, Key ME, Kalra KL: Antigen retrieval in formalin-fixed, paraffin embedded tissues: An enhancement method for immunohistochemical staining based on microwave oven heating of tissue sections. J Histochem Cytochem 39:741-748, 1991[Abstract]

39. Brent T, von Wronski MA, Pegram CN, et al: Immunoaffinity purification of human O6-alkylguanine-DNA alkyltransferase using newly developed monoclonal antibodies. Cancer Res 50:58-61, 1990[Abstract/Free Full Text]

40. McLendon RE, Cleveland L, Pegram C, et al: Immunohistochemical detection of DNA repair enzyme O6-methylguanine-DNA methyltransferase in formalin-fixed, paraffin-embedded astrocytomas. Lab Invest 78:643-644, 1998[Medline]

41. Hsu S, Raine L, Fanger H, et al: Use of avidin-biotin peroxidase complex (ABC) in immunoperoxidase techniques. J Histochem Cytochem 29:577-580, 1981[Abstract]

42. Pollack IF, Boyett JM, Yates AJ, et al: The influence of central review on outcome associations in childhood malignant gliomas: Results from the CCG-945 experience. Neuro-Oncol 5:197-207, 2003[Abstract]

43. Kleihues P, Burger PC, Scheithauer BW: Histological typing of tumours of the central nervous system, in Sobin LH (ed): International Histological Classification of Tumours (2nd ed). Berlin, Germany, Springer-Verlag, vol 21, 1993, pp 11-16

44. Kalbfleisch JD, Prentice RI: The Statistical Analysis of Failure Time Data. New York, NY, John Wiley and Sons, 1980, pp 163-180

45. Dixon WJ, Massey FJ: Introduction to Statistical Analysis (ed 3). New York, NY, McGraw-Hill, 1969

46. Berg SL, Gerson SL, Godwin K, et al: Plasma and cerebrospinal fluid pharmacokinetics of O6-benzylguanine and time course of peripheral blood mononuclear cell O6-methylguanine-DNA methyltransferase inhibition in the nonhuman primate. Cancer Res 55:4606-4610, 1995[Abstract/Free Full Text]

47. Fujio C, Chang HR, Tsujimura T, et al: Hypersensitivity of human tumor xenografts lacking O6-alkylguanine-DNA alkyltransferase to the anti-tumor agent 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea. Carcinogenesis (Lond) 10:351-356, 1989[Abstract/Free Full Text]

48. Bobola MS, Berger MS, Silber JR: Contribution of O6-methylguanine-DNA methyltransferase to resistance to 1,3-(2-chloroethyl)-1-nitrosourea in human brain tumor-derived cell lines. Mol Carcinog 13:81-88, 1995[Medline]

49. Brent TP, Houghton PJ, Houghton JA: O6-alkylguanine-DNA alkyltransferase activity correlates with the therapeutic response of human rhabdomyosarcoma xenografts to 1-(2-chloroethyl)-3-trans-(4-methylcyclohexyl)-1-nitrosourea. Proc Natl Acad Sci U S A 82:2985-2989, 1985[Abstract/Free Full Text]

50. Middlemas DS, Stewart CF, Kirstein MN, et al: Biochemical correlates of temozolomide sensitivity in pediatric solid tumor xenograft models. Clin Cancer Res 6:998-1007, 2000[Abstract/Free Full Text]

51. Silber JR, Mueller BA, Ewers TG, et al: Comparison of O6-methylguanine-DNA methyltransferase activity in brain tumors and adjacent normal brain. Cancer Res 53:3416-3420, 1993[Abstract/Free Full Text]

52. Hongeng S, Brent TP, Sanford RA, et al: O6-methylguanine-DNA methyltransferase protein levels in pediatric brain tumors. Clin Cancer Res 3:2459-2463, 1997[Abstract/Free Full Text]

53. Fritz G, Tano K, Mitra S, et al: Induction of the DNA repair gene encoding O6-methylguanine-DNA methyltransferase in mammalian cells by DNA-damaging treatments. Mol Cell Biol 11:4660-4668, 1991[Abstract/Free Full Text]

54. Grombacher T, Mitra S, Kaina B: Induction of the alkyltransferase (MGMT) gene by DNA damaging agents and the glucocorticoid dexamethasone and comparison with the response of base excision repair genes. Carcinogenesis 17:2329-2336, 1996[Abstract/Free Full Text]

55. Quinn JA, Pluda J, Dolan ME, et al: Phase II trial of carmustine plus O(6)-benzylguanine for patients with nitrosourea-resistant recurrent or progressive malignant glioma. J Clin Oncol 20:2277-2283, 2002[Abstract/Free Full Text]

56. Quinn JA, Desjardins A, Reardon D, et al: Phase II trial of temozolomide (Temodar) plus O6-benzylguanine (O6-BG) in the treatment of patients with Temodar-resistant malignant glioma. Neuro-Oncol 6:380, 2004 (abstr)

Submitted January 13, 2006; accepted May 11, 2006.




This article has been cited by other articles:


Home page
 Neuro OncolHome page
R. I. Jakacki, A. Yates, S. M. Blaney, T. Zhou, R. Timmerman, A. M. Ingle, L. Flom, M. D. Prados, P. C. Adamson, and I. F. Pollack
A phase I trial of temozolomide and lomustine in newly diagnosed high-grade gliomas of childhood
Neuro-oncol, August 1, 2008; 10(4): 569 - 576.
[Abstract] [Full Text] [PDF]

Home page
 JCOHome page
T. M. Horton, P. A. Thompson, S. L. Berg, P. C. Adamson, A. M. Ingle, M. E. Dolan, S. M. Delaney, M. Hedge, H. L. Weiss, M.-F. Wu, et al.
Phase I Pharmacokinetic and Pharmacodynamic Study of Temozolomide in Pediatric Patients With Refractory or Recurrent Leukemia: A Children's Oncology Group Study
J. Clin. Oncol., November 1, 2007; 25(31): 4922 - 4928.
[Abstract] [Full Text] [PDF]

Home page
 Cancer Res.Home page
I. Lavon, D. Fuchs, D. Zrihan, G. Efroni, B. Zelikovitch, Y. Fellig, and T. Siegal
Novel Mechanism whereby Nuclear Factor {kappa}B Mediates DNA Damage Repair through Regulation of O6-Methylguanine-DNA-Methyltransferase
Cancer Res., September 15, 2007; 67(18): 8952 - 8959.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a colleague
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Save to my personal folders
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pollack, I. F.
Right arrow Articles by Finlay, J. L.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pollack, I. F.
Right arrow Articles by Finlay, J. L.

About
JCO		 Editorial
Roster		 Advertising
Information		 Librarians &
Institutions		 Rights &
Permissions		 PDA Services

Copyright © 2006 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
Terms and Conditions of Use
  HighWire Press HighWire Press™ assists in the publication of JCO Online