Imaging of human tumors and organs with N-13-labeled L-methionine

The work described herein is the first reported use of nitrogen-13-labeled L-methionine in human subjects. Three volunteers and 14 patients with a variety of solid tumors were scanned after intravenous administration of L-(N-13) methionine. In both volunteers and cancer patients, uptake of label was seen in the liver and pancreas, with smaller amounts of label detected in the heart, urinary bladder, and salivary glands. Concentration of N-13 in tumor was seen in 12 of the 14 cancer patients. Five had repeat studies after chemotherapy; in each case, the change in tumor uptake of N-13 after N-13 methionine injection paralleled the clinical response to chemotherapy. Three patients had L-(N-13) glutamate scans the same day that they were studied with N-13 methionine. Concentration of the radiolabel in the tumor was very similar for the two compounds in each case. The systemic distribution of N-13 from methionine is similar to that from glutamate, except for a much smaller myocardial uptake and a prominent accumulation in the intestinal region. It is concluded that L-(N-13) methionine is potentially useful as a biologically significant agent for tumor visualization and assessment of therapeutic response.