1. Preload and afterload with L-amino acids to enhance the differentiation between tumor and inflammation by labelled amino acids PET imaging Aim : Aim : Among labelled amino-acids, FET and FT are transported across the cellular membrane by the exchanger l–system. In vitro utilisation of FET and FT, after preload or prior to postload of non-radioactive L-amino-acids, was evaluated to measure the effects of intra- and extra cellular amino-acid content on the differential tracers uptake in tumor (ROS 17/2.8) and inflammatory cells (human leukocytes). Laïque Salma [1], Egrise Dominique [1], Lemaire Christian [2], Monclus Michel [1], Schmitz Frédéric [1], Luxen André [2], Goldman Serge [1] [1] PET/Biomedical Cyclotron Unit, ULB, Hopital Erasme, Route de Lennik 808, 1070 Anderlecht, BELGIUM [2] Cyclotron Research Center, ULG, B 30 Building, 4000 Liège, BELGIUM Figure 1 : principle of PET Scan imaging FET : O-(2-[ 18 F] fluoroethyl)-L-Tyrosine : not incorporated into proteins FT : 2-[ 18 F] fluoro-L-Tyrosine : incorporated into proteins Figure 2 : FDG-PET revealing, an inflammatory lesion in the mediastinum, in a patient suffering from sarcoidosis FET Chemistry (1): FT Chemistry (2) : Figure 5 : preload effect = ratio between the tracer uptake into preloaded cells and control cells Conclusions : Conclusions : L–tyrosine preload, prior to FET administration, can help in the differentiation between tumours and inflammatory lesions : see figure 6 Figure 6 : tracer uptake = % of loaded activity References : (1) Wester HJ, Herz M, Weber W, Heiss P, Senekowitsh-Schmidtke R, Schwaiger M, Stöcklin G. Synthesis and radiopharmacology of O-(2-[ 18 F]fluoroethyl)-L-tyrosine for tumor imaging. The Journal of Nuclear Medecine (1999), 40 (1) : 205-212. (2) Lemaire C, Gillet S, Guillouet S, Plenevaux A, Aerts J, Luxen A. Highly enantioselective synthesis of no-carrier-added 6-[ 18 F]fluoro-L-dopa by chiral phase transfer alkylation. European Journal of Organic Chemistry (2004), (13) : 2899-2904. (3) Ooi Takashi, Takeuchi Mifune, Kameda Minoru, Maruoka Keiji. Practical catalytic enantioselective synthesis of a  -dialkyl-  -amino acids by chiral phase-transfer catalysis. Journal of the American Chemical Society (2000), 122 (21) : 5228-5229. Table 1 : differenciation between ROS 17/2.8 and leukocytes = ratio between FET content in ROS 17/2.8 and in the inflammatory cells Figure 3 : preload effect = ratio between the tracer uptake into preloaded cells and control cells Figure 4 : preload effect = ratio between the tracer uptake into preloaded cells and control cells L-tyrosine preload prior to FET administration on ROS 17/2.8 and leukocytes : figure 3 FET Biology : L-methionine preload prior to FET administration on ROS 17/2.8 and leukocytes : figure 4 L-phenylalanine load after FET administration on ROS 17/2.8 and leukocytes : table 1 Contact :  : salma.laique@ulb.ac.be  : 0032-2-555.47.11 FT Biology : FT Biology : L-tyrosine preload prior to FT administration on ROS 17/2.8 : figure 5