In Vivo Evaluation and Dosimetry of 123I-2-Iodo-D-Phenylalanine, a New Potential Tumor-Specific Tracer for SPECT, in an R1M Rhabdomyosarcoma Athymic Mouse Model

Earlier reports described the preferential uptake of D-amino acids in tumor-bearing mice. Moreover, it was shown that in tumor cells in vitro the L-amino acid transporter system seemed to lack stereospecificity. Because of the successful results with 123/125I-2-iodo-L-phenylalanine, 123/125I-2-iodo-D-phenylalanine was developed, and its tumor-detecting characteristics were evaluated in vivo. Methods: 123I labeling of 2-iodo-D-phenylala-nine was performed with a kit formulation by use of Cu1-assisted nucleophilic exchange. 123I-2-Iodo-D-phenylalanine was evaluated in R1M tumor–bearing athymic mice by dynamic planar imaging (DPI) and dissection. The in vivo stability of the tracer was tested by high-performance liquid chromatography. Tumor tracer retention and tracer contrast were evaluated as a function of time. Two-compartment blood modeling from DPI results and dosimetric calculations from biodistribution result