Aberrant MGMT (O6-methylguanine-DNA methyltransferase) promoter methylation in choroid plexus tumors

Choroid Plexus Tumors: Experience of 10 Cases with Special References to Adult Cases

Choroid plexus tumors (CPTs) are rare intraventricular neoplasms accounting for about 0.3–0.6% of all intracranial tumors. This retrospective study on CPTs presents clinico-pathological features and management strategies based on a 20-year single-institutional experience. This series included 10 consecutive patients with pathologically proven CPTs; 5 choroid plexus papillomas (CPPs), 3 atypical CPPs (ACPPs), and 2 choroid plexus carcinomas (CPCs). Their clinical, radiological, and histopathological features as well as management including follow-up studies were reviewed. The patients included five males and five females, aging from 0 years to 61 years with median of 28 years. The affected site was lateral ventricle in two adults and fourth ventricle in eight patients; four children and four adults. The most common symptoms were gait disturbance and memory disturbance. All the patients underwent craniotomy with total, subtotal, and partial removals achieved in 50%, 40%, and 10% of the patients, respectively. The occurrence of the high grade subtypes was 50% in both the adult and pediatric groups. The Ki-67/MIB-1 index increased across the three histological subtypes, from CPP to ACPP and then to CPC. Adjuvant therapy was administered in three patients. The two patients (one adult and one child) with CPC died of whole central nervous system dissemination. At a median of 62-month follow-up, the other eight patients were alive, with only one patient having recurrence and reoperation. The results demonstrate that gross total resection is usually curative for CPP and ACPP, and adjuvant chemoradiotherapy would be required for CPC and incompletely resected ACPP.

Quantitative analysis of DNA methylation in the promoter region of the methylguanine-O(6) -DNA-methyltransferase gene by COBRA and subsequent native capillary gel electrophoresis

Along with histone modifications, RNA interference and delayed replication timing, DNA methylation belongs to the key processes in epigenetic regulation of gene expression. Therefore, reliable information about the methylation level of particular DNA fragments is of major interest. Herein the methylation level at two positions of the promoter region of the gene methylguanine-O(6) -DNA-Methyltransferase (MGMT) was investigated. Previously, it was demonstrated that the epigenetic status of this DNA region correlates with response to alkylating anticancer agents. An automated CGE method with LIF detection was established to separate the six DNA fragments resulting from combined bisulfite restriction analysis of the methylated and non-methylated MGMT promoter. In COBRA, the DNA was treated with bisulfite converting cytosine into uracil. During PCR uracil pairs with adenine, which changes the original recognition site of the restriction enzyme Taql. Artificial probes generated by mixing appropriate amounts of DNA after bisulfite treatment and PCR amplification were used for validation of the method. The methylation levels of these samples could be determined with high accuracy and precision. DNA samples prepared by mixing the corresponding clones first and then performing PCR amplification led to non-linear correlation between the corrected peak areas and the methylation levels. This effect is explained by slightly different PCR amplification of DNA with different sequences present in the mixture. The superiority of CGE over PAGE was clearly demonstrated. Finally, the established method was used to analyze the methylation levels of human brain tumor tissue samples.

Epigenetic repression of the dopamine receptor D4 in pediatric tumors of the central nervous system

Epigenetic alterations are common events in cancer. Using a genome wide methylation screen (Restriction Landmark Genomic Scanning-RLGS) we identified the gene for the dopamine receptor D4 (DRD4) as tumor-specific methylated. As DRD4 is involved in early brain development and may thus be involved in developmentally dependent tumors of the CNS in children epigenetic deregulation of DRD4 and its functional consequences were analyzed in vitro. CpG methylation of DRD4 was detected in 18/24 medulloblastomas, 23/29 ependymomas, 6/6 high-grade gliomas, 7/10 CNS PNET and 8/8 cell lines by qCOBRA and bisulfite sequencing. Real-time RT-PCR demonstrated a significantly inferior expression of DRD4 in primary tumors compared to cell lines and non-malignant control tissues. Epigenetic deregulation of DRD4 was analyzed in reexpression experiments and restoration of DRD4 was observed in medulloblastoma (MB) cells treated with 5-Aza-CdR. Reexpression was not accompanied by demethylation of the DRD4 promoter but by a significant decrease of H3K27me3 and of bound enhancer of zeste homologue 2 (EZH2). Knockdown of EZH2 demonstrated DRD4 as a direct target for inhibition by EZH2. Stimulation of reexpressed DRD4 resulted in an activation of ERK1/2. Our analyses thus disclose that DRD4 is epigenetically repressed in CNS tumors of childhood. DRD4 is a direct target of EZH2 in MB cell lines. EZH2 appears to dominate over aberrant DNA methylation in the epigenetic inhibition of DRD4, which eventually leads to inhibition of a DRD4-mediated stimulation of the ERK1/2 kinase pathway.

Current management of choroid plexus carcinomas

Choroid plexus carcinoma (CPC) is a World Health Organization (WHO) grade III brain tumor with a poor prognosis that occurs mainly in children. Gross total resection of CPC is highly recommended and is associated with improved overall survival, although it is often associated with increased morbidity. The use of adjuvant therapies has yet to be standardized, although evidence suggests that for patients with incompletely resected CPCs, a combination of chemotherapy and radiation therapy may be beneficial. The use of radiation therapy for younger children (<3 years old) with CPC, however, is not recommended, due to the potential negative neurological sequelae associated with radiation to the developing brain. Given that the majority of CPC patients are young children, questions regarding optimal radiation dose, chemotherapy agents, and how to combine these two adjuvant treatment modalities to achieve the best outcomes remain unanswered. In this paper we summarize the current management of CPC in the literature. Further studies are needed to standardize the treatment paradigm for this malignant brain tumor.

MGMT promoter methylation and temozolomide response in choroid plexus carcinoma

Choroid plexus carcinoma (CPC) is a malignant tumor with a strong tendency to spread along the cerebrospinal fluid pathway. There is no standardized chemotherapy protocol for this rare tumor. We report a 38-year-old man with CPC in the lateral ventricle with obstructive hydrocephalus. Because of the poor demarcation between thalamus and fornix, subtotal tumor resection was performed. Postoperative spine magnetic resonance (MR) image revealed whole spinal axis dissemination. After diagnosis of CPC, the patient was treated with whole ventricular and spine radiation concomitant with temozolomide chemotherapy, although the O(6)-methylguanine-DNA methyltransferase (MGMT) promoter was found to be unmethylated. Although MR images revealed transient stable disease during adjuvant therapy, tumor progression was depicted after four cycles of temozolomide therapy. We discuss the ineffectiveness of adjuvant temozolomide therapy for CPC in connection with O(6)-methylguanine-DNA methyltransferase promoter methylation.

MGMT as a potential stratification marker in relapsed high-grade glioma of children: the HIT-GBM experience

BACKGROUND

Studies in adults with malignant glioma suggest MGMT methylation as a stratification marker. Similar data for children are sparse. We investigated the impact of MGMT methylation and expression on survival of children with high-grade glioma (HGG) registered into the German HIT-GBM database receiving temozolomide (TMZ) as part of their treatment (n = 21 relapsed, n = 4 primary).

PROCEDURE

Twenty-four patients were included retrospectively. Methylation specific PCR (MSP), calibrated combined bisulfite restriction analysis (COBRA), and immunohistochemistry (IHC) were applied. Survival analyses were performed by Kaplan-Meier and Cox proportional-hazards models.

RESULTS

MSP demonstrated DNA methylation in 77%. Patients with a methylated MGMT promoter had a sixfold longer median EFS (P = 0.015; 5.5 months vs. 0.9 months). Considering the results of calibrated COBRA, MGMT methylation was again associated with an elevated EFS (P = 0.05; 10.2 months vs. 2.6 months) and OS (P = 0.06; 18.7 months vs. 7.2 months) only if methylation was >14%. No difference in EFS and OS at all was noted between unmethylated and tumors methylated at low level (n = 9). Twenty-two tumors were positive by IHC, 10 showed low MGMT expression (IHC score 0-4). We did not detect any difference in EFS and OS between moderate/high-expressing tumors (IHC score 6-12) and those with low or no expression (IHC score 0-4).

CONCLUSION

DNA methylation, but not protein expression of MGMT was associated with an increased median EFS and OS of children with relapsed HGG. MGMT methylation status warrants prospective evaluation as a stratification marker for children with HGG.

Choroid plexus: biology and pathology

The choroid plexus is an epithelial-endothelial vascular convolute within the ventricular system of the vertebrate brain. It consists of epithelial cells, fenestrated blood vessels, and the stroma, dependent on various physiological or pathological conditions, which may contain fibroblasts, mast cells, macrophages, granulocytes or other infiltrates, and a rich extracellular matrix. The choroid plexus is mainly involved in the production of cerebrospinal fluid (CSF) by using the free access to the blood compartment of the leaky vessels. In order to separate blood and CSF compartments, choroid plexus epithelial cells and tanycytes of circumventricular organs constitute the blood-CSF-brain barrier. As non-neuronal cells in the brain and derived from neuroectoderm, choroid plexus epithelia are defined as a subtype of macroglia. The choroid plexus is involved in a variety of neurological disorders, including neurodegenerative, inflammatory, infectious, traumatic, neoplastic, and systemic diseases. Abeta and Biondi ring tangles accumulate in the Alzheimer's disease choroid plexus. In multiple sclerosis, the choroid plexus could represent a site for lymphocyte entry in the CSF and brain, and for presentation of antigens. Recent studies have provided new diagnostic markers and potential molecular targets for choroid plexus papilloma and carcinoma, which represent the most common brain tumors in the first year of life. We here revive some of the classical studies and review recent insight into the biology and pathology of the choroid plexus.