A COMPARATIVE-STUDY ON PROTEIN INCORPORATION OF L-[METHYL-H-3]METHIONINE, L-[1-C-14]LEUCINE AND L-2-[F-18]FLUOROTYROSINE IN TUMOR-BEARING MICE

Brain and tumor uptake of L-[methyl-H-3]methionine (H-3-Met), L-[1-C-1 4]leucine (C-14-Leu) and L-2-[F-18]fluorotyrosine (F-18-Tyr) and their incorporation into the acid-precipitable fraction (APF) were investig ated in mice bearing FM3A-PO and the higher metastatic FM3A-P15A mamma ry carcinomas in order to compare the potential of positron emitting a nalogs for measuring protein synthesis rates (PSR) in brain and tumors by positron emission tomography (PET). The total uptake of the H-3-Me t by the brain was higher than those of two other amino acids. On the other hand, the incorporation rates into the APF in the brain and tumo rs were significantly faster with C-14-Leu compared to the others. Mos t of the C-14 in the APF was identified in labeled proteins; however, considerable amounts of H-3 were recovered in the lipid and RNA fracti ons, and F-18 was also detected in the lipids. Among the positron emit ting analogs of three amino acids, C-11-labeled Leu could be the most suitable for measuring PSR by PET. For all the amino acids, the total uptake and the APF both expressed as the % injected dose seemed slight ly higher in the FM3A-P15A than in the FM3A-PO, although the differenc es did not reach statistical significance.