Comparison of the Accumulation Kinetics of L-(Methyl-11C)-Methionine and D-(Methyl-11C)-Methionine in Brain Tumors Studied with Positron Emission Tomography

Stereotactic image-based histological analysis reveals a correlation between 11C-methionine uptake and MGMT promoter methylation in non-enhancing gliomas

Gliomas are genetically and histopathologically heterogeneous. Intratumoral heterogeneity in the MGMT promoter methylation status is an important clinical biomarker of glioblastoma. A higher uptake of ¹¹C-methionine in positron-emission tomography (PET) reportedly reflects increased MGMT promoter methylation; however, non-stereotactic comparison of MGMT methylation and ¹¹C-methionine PET images may not be accurate. The present study examined the correlation between ¹¹C-methionine uptake and MGMT promoter methylation in non-enhancing gliomas using stereotactic image-based histological analysis. Data were collected from 9 patients with newly diagnosed non-enhancing glioma who underwent magnetic resonance imaging and ¹¹C-methionine PET during pre-surgical examination. Clinical data were also collected from 3 patients during repeat surgery. The correlation between ¹¹C-methionine uptake and MGMT methylation or cell density was analyzed using histological specimens obtained by multiple stereotactic sampling and an exact local comparison of ¹¹C-methionine PET images and histological specimens was made. A total of 31 stereotactic sample sites were identified. In newly diagnosed cases, the tumor to normal uptake (T/N) ratio revealed a significant positive correlation with MGMT methylation (R=0.54, P=0.009) and a marginal correlation with cell density (R=0.42, P=0.05). In recurrent cases, the T/N ratio demonstrated no correlation with MGMT methylation (R=0.01, P=0.97) or cell density (R=0.15, P=0.70). An increased uptake of ¹¹C-methionine in PET may reflect increased MGMT promoter methylation according to stereotactic image-based histological analysis. ¹¹C-methionine PET could therefore be a useful tool for detecting regional MGMT promoter methylation in non-enhancing primary glioma.

(11)C-methinine uptake correlates with MGMT promoter methylation in nonenhancing gliomas

OBJECTIVES

Several studies have aimed to detect biomarkers in glioma using noninvasive imaging techniques. However, few studies have been able to image 1p/19q deletion by (11)C-methionine positron emission tomography ((11)C-methionine PET) or 2-hydroxyglutarate (2HG) by proton magnetic resonance spectroscopy (MRS). This study examines the correlation between (11)C-methionine uptake and MGMT promoter methylation in grade II and grade III nonenhancing gliomas.

PATIENTS AND METHODS

Data was collected from 20 patients with grade II and III nonenhancing gliomas who underwent both MRI and (11)C-methionine PET as part of their pre-surgical examination. We examined MGMT promoter methylation by quantitative methylation-specific PCR.

RESULTS

The mean MGMT promoter methylation for tumors with T/N ratios ≥1.6 was 28.0±26.3, and that for tumors with T/N ratios <1.6 was 0.68±0.89. The MGMT promoter methylation for tumors with T/N ratios ≥1.6 was significantly higher than that for tumors with T/N ratios <1.6 (P<0.05).

CONCLUSIONS

A higher uptake in (11)C-methionine PET may reflect increased MGMT promoter methylation. (11)C-methionine PET could be a useful tool to detect MGMT promoter methylation in nonenhancing glioma.

Specific biomarkers of receptors, pathways of inhibition and targeted therapies: clinical applications

A deeper understanding of the role of specific genes, proteins, pathways and networks in health and disease, coupled with the development of technologies to assay these molecules and pathways in patients, promises to revolutionise the practice of clinical medicine. In particular, the discovery and development of novel drugs targeted to disease-specific alterations could benefit significantly from non-invasive imaging techniques assessing the dynamics of specific disease-related parameters. Here we review the application of imaging biomarkers in the management of patients with brain tumours, especially malignant glioma. This first part of the review focuses on imaging biomarkers of general biochemical and physiological processes related to tumour growth such as energy, protein, DNA and membrane metabolism, vascular function, hypoxia and cell death. These imaging biomarkers are an integral part of current clinical practice in the management of primary brain tumours. The second article of the review discusses the use of imaging biomarkers of specific disease-related molecular genetic alterations such as apoptosis, angiogenesis, cell membrane receptors and signalling pathways. Current applications of these biomarkers are mostly confined to experimental small animal research to develop and validate these novel imaging strategies with future extrapolation in the clinical setting as the primary objective.

Principles and Application of PET in Brain Tumors

For tumors of the central nervous system (CNS), the ability to accurately delineate the extent of tumor has implications for diagnosis, prognosis, and treatment. PET, mainly with (18)F-fluorodeoxyglucose (FDG), has become commonplace in the work-up of many extracranial tumors. However, the relative high background of FDG-PET activity of normal brain tissue has limited the applicability of this modality in CNS tumors to date. More recently, novel PET tracers for imaging of CNS tumors have been developed. This article outlines recent advances in PET as a complementary imaging modality with implications for diagnosis, prognosis, surgical and radiation treatment planning, and post-therapy surveillance in malignancies of the CNS. Pharmacokinetic properties of the radiotracers and the influence of blood-brain-barrier integrity are also incorporated into the discussion.

(11)C-methionine uptake correlates with tumor cell density rather than with microvessel density in glioma: A stereotactic image-histology comparison

(11)C-methionine positron emission tomography ((11)C-methionine PET) provides accurate detection of brain tumors. Several reports have analyzed the correlation between uptake of (11)C-methionine and Ki-67 index or microvessel density non-stereotactically and suggested that (11)C-methionine uptake reflects both proliferation potential and angiogenic capability in gliomas. As gliomas possess heterogeneous histological architecture, non-stereotactic comparison of the histology and (11)C-methionine PET image may not be accurate. In the present study, the correlation between (11)C-methionine uptake and cell or microvessel density was analyzed using histological specimens obtained by stereotactic biopsy, and an exact local comparison of (11)C-methionine PET image and histological specimens was conducted. The tumor/normal tissue (T/N) ratio of (11)C-methionine positron emission tomography was found to correlate better with cell density (R=0.747, p=0.000042) and Ki-67 index (R=0.675, p=0.00041) than with microvessel density (R=0.467, p=0.025) in a histological comparison using a stereotactic image. Furthermore, multiple linear regression analysis revealed that cell density was the key determinant for predicting (11)C-methionine level while microvessel density was not. These results suggest that cell density contributes more to (11)C-methionine uptake than microvessel density in glioma tissues and that the previously reported correlation of (11)C-methionine uptake and microvessel density in glioma patients requires reevaluation.

Positron emission tomography of the brain

Positron emission tomography (PTE) is a technique that allows imaging of the temporal and spatial distribution of positron-emitting radionuclides. The purpose of this article is to outline the current clinical use for PET imaging in the brain and other radiopharmaceutical used for assessing various physiologic parameters pertaining to tumor metabolism.

Positron Emission Tomography of the Brain

Positron emission tomography (PET) is a technique that allows imaging of the temporal and spatial distribution of positron-emitting radionuclides. The purpose of this article is to outline the current clinical use for PET imaging in the brain and other radiopharmaceuticals used for assessing various physiologic parameters pertaining to tumor metabolism.

Nuclear medicine techniques in breast imaging

Progress has been made in anatomic imaging with mammography, ultrasound, and MRI, but the noninvasive differentiation of malignant from benign breast masses is an unmet goal. Most breast biopsies still are performed in patients with benign disease. Improved nuclear medicine imaging devices, better radiopharmaceutical agents, and new methods of guiding biopsies and surgery are being developed, signaling a growing role for nuclear medicine techniques. The use of dual-photon positron emission tomography and single-photon imaging are discussed as a means of imaging both primary and regionally metastatic breast cancers.

Functional characterization of brain tumors: an overview of the potential clinical value

Early detection and characterization are still challenging issues in the diagnostic approach to brain tumors. Among functional imaging techniques, a clinical role for positron emission tomography studies with [18F]-fluorodeoxyglucose and for single photon emission computed tomography studies with [201Tl]-thallium-chloride has emerged. The clinical role of magnetic resonance spectroscopy is still being defined, whereas functional magnetic resonance imaging seems able to provide useful data for presurgical localization of critical cortical areas. Integration of morphostructural information provided by computed tomography and magnetic resonance imaging, with functional characterization and cyto-histologic evaluation of biologic markers, may assist in answering the open diagnostic questions concerning brain tumors.

The normal pituitary examined with positron emission tomography and (methyl-11C)-L-methionine and (methyl-11C)-D-methionine

Four patients with radiologically normal pituitary gland were examined with positron emission tomography after the administration of (methyl-11C)-L-methionine. On a following day the examination was repeated with (methyl-11C)-D-methionine. The accumulation rate of L-methionine in the pituitary was measured, giving a value that was about twice that of normal brain tissue. The accumulation rate of D-methionine in the pituitary was almost a factor of 10 lower than that of L-methionine. In the normal brain tissue that ratio was 2.3. The study clearly indicates that the methionine uptake in the pituitary is stereospecific. 11C-D-methionine is freely distributed in the tissue without entrapment, whereas 11C-L-methionine is irreversibly bound. It is concluded that PET with 11C-L-methionine can be used to study amino acid utilization in the pituitary.