In Vivo Characterization of 123/125I-2-Iodo-L- Phenylalanine in an R1M Rhabdomyosarcoma Athymic Mouse Model as a Potential Tumor

The application of 123I-3-iodo--methyltyrosine is limited to di-agnosis of brain tumors due to its marked long-term uptake in kidneys. In vitro evaluation of 125I-2-iodo-L-phenylalanine showed high uptake in R1M cells by L-type amino acid trans-port system 1 (LAT1). This study evaluates 123I-2-iodo-L-phenyl-alanine as a new specific tumor tracer for SPECT. Methods: 123/125I-2-Iodo-L-phenylalanine is prepared as a one-pot kit using the Cu1-assisted isotopic exchange method. The characteris-tics of 125I-2-iodo-L-phenylalanine were examined in vivo in R1M tumor–bearing athymic mice and in acute inflammation–bear-ing NMRI mice. The uptake of 123/125I-2-iodo-L-phenylalanine in tumor and other organs of interest was measured by dynamic planar imaging (DPI) and -counting after dissection. Displace-ment of 123I-2-iodo-L-phenylalanine radioactivity by L-phenylal-anine, L-methionine, and L-cysteine was measured. 123I-Iodo