Regional coupling of blood flow and methionine uptake in an experimental tumor assessed with autoradiography

(14C-methyl)-L-methionine uptake in rat brain tumors before and after treatment with the protein synthesis inhibitor cycloheximide

Autoradiographic study of (14C-methyl)-L-methionine with brain tumor bearing rats aimed at an elucidation of the mechanism of tracer accumulation in the protein synthesis of tumor. Twice as much tracer accumulated in the tumors compared as in the contralateral gray matter (nontumor region) at 90 min post intravenous injection. The protein-bound fraction of the tumors, expressed as acid-insoluble fraction (AIF), was 1.7 +/- 0.6 (mean +/- standard deviation, n = 6), significantly higher than that (0.8 +/- 0.2) of the nontumor region (p < 0.05 by the Mann-Whitney test). The tumor AIF comprised 82.3 +/- 9.2% of the total amount of the tracers accumulated in the tumors. The protein synthesis inhibitor cycloheximide reduced the tracer uptake and the AIF of the tumors to an almost same level as the nontumor region. These findings indicate that metabolic acceleration of protein synthesis may be a main reason for the high accumulation of (14C-methyl)-L-methionine in tumor.

Dose-responsive effect of radiotherapy on the tumor uptake of L-[methyl-11C]methionine; feasibility for monitoring recurrence of tumor

The L-[methyl-11C]methionine [( 11C]Met) uptake by rat AH109A tumor was decreased irradiation-dose dependently from the control to 5, 10 and 20 Gy. After 10 Gy irradiation, the [11C]Met uptake decreased earlier than the tumor volume reduction, and later, it significantly increased earlier than the recurrent growth. Double tracer autoradiography with [14C]Met and 4-[18F]fluoroantipyrine showed a decrease in the [14C]Met tumor uptake without change of blood flow after irradiation. The [11C]Met uptake representing amino acid metabolism is a sensitive indicator for monitoring radiotherapeutic effect on tumor.

Uptake of 11C-methionine in breast cancer studied by PET. An association with the size of S-phase fraction

L-[methyl-11-C]methionine (11C-methionine) uptake of seven primary breast cancers, four soft tissue metastases of breast cancer, and three other breast lesions was studied by positron emission tomography (PET). 11C-methionine accumulation was assessed by calculating the standardised uptake value (SUV). The mean SUV for breast cancer was 8.5 +/- 3.3 (s.d.), while the maximal uptake in the liver was 12.4 +/- 1.6, in the bone marrow 5.8 +/- 0.7, and in the myocardium 3.4 +/- 0.6. All eight malignant tumours larger than 30 mm in diameter accumulated clearly 11C-methionine, whereas none of the three smaller cancers (from 12 to 15 mm in diameter) were visualised. Strong uptake of 11C-methionine was associated with a large S-phase fraction (SPF) measured with flow cytometry (r = 0.77, P = 0.01), and the non-visualised cancers had all a small SPF (less than 5.5%). One benign tumour (an abscess) accumulated slightly 11C-methionine. The results indicate that both primary and metastatic breast cancer can be effectively imaged with 11C-methionine by PET, and that the accumulation of 11C-methionine may correlate with the proliferation rate of breast carcinoma.