[Amino acid uptake in brain tumors using positron emission tomography as an indicator for evaluating metabolic activity and malignancy]. / Die Aufnahme von Aminosäuren in Hirntumoren mit der Positronen-Emissionstomographie als Indikator für die Beurteilung von Stoffwechselaktivität und Malignität.

Diagnosis and post-therapeutic follow-up of tumour patients necessitates morphological and particularly functional imaging methods. For the latter approach positron emission tomography has proven a valid tool for the measurement of perfusion, of energy consumption parameters such as oxygen extraction, glucose metabolism and amino acid uptake. However, neither perfusion nor energy consumption parameters have yielded unambiguous information on the clinical status of various tumours in respect of their malignancy and their growth status. It is shown in this paper that amino acid uptake seems to be a valid measure for the functional activity of tumour tissue for a broad range of neoplasms. The uptake of 11C-L-Methionine was measured in 33 patients having various brain tumours, and was compared with 6 patients who had an infarction, and with 8 patients suffering from arachnoidal cysts. The amino acid uptake correlated well with the histological grading of the tumours and the clinical status of the patient. The uptake was well differentiated against metabolically inactive lesions. Parallel investigations on the uptake mechanisms of amino acids in an animal model have shown that transport phenomena regulate the uptake rather than protein synthesis rates. However, protein synthesis may nevertheless exercise a control function on the transport process.

Non selective transport of [11C-methyl]-L-and D-methionine into a malignant glioma.

Images obtained by X-ray CT, brain scintigraphy (99mTc-DTPA) and positron emission tomography (PET) with [11C-methyl]-L- and D-methionine in a case of malignant glioma are presented, showing good agreement of PET and CT findings, in particular nearly identical localization of L- and D-methionine accumulation, whereas the blood brain barrier is only slightly disturbed. In a greater number of patients the amount of accumulated stereoisomers do not differ on a significant level, indicating that a raised transport rate mediated by a carrier of low stereospecifity seems to contribute substantially to the increased uptake of [11C-methyl]-L-methionine in human brain tumors. Several cerebral functions and diseases have been studied with positron emission tomography (PET), which represents a clinical tool for visualizing metabolic activities rather than morphologic lesions (Reivich et al. 1985; Mazziotta et al. 1986). With regard to the malignancy of brain tumors DiChiro et al. (1982, 1984, 1985a, b) showed a correlation between tumor grade and its glucose metabolism measured with 18F-fluorodeoxyglucose. An increased uptake of [11C-methyl]-L-methionine into tumor tissue has also been described (Hübner et al. 1980; Bergström et al. 1983; Kubota et al. 1984; Meyer et al. 1985; Schober et al. 1986b). Bustany et al. (1981, 1983, 1985a, b, 1986) developed a model for quantitative determination of protein synthesis, postulating that methionine incorporation into protein in brain tumors correlates with grade of malignancy. We do not believe that the uptake of [11C-methyl]-L-methionine mainly reflects protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)