RT Journal Article SR Electronic T1 Comparative Biodistribution of Iodinated Amino Acids in Rats: Selection of the Optimal Analog for Oncologic Imaging Outside the Brain JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1489 OP 1494 VO 44 IS 9 A1 Tony Lahoutte A1 John Mertens A1 Vicky Caveliers A1 Philippe R. Franken A1 Hendrik Everaert A1 Axel Bossuyt YR 2003 UL http://jnm.snmjournals.org/content/44/9/1489.abstract AB 3-123I-Iodo-α-methyltyrosine (123I-3-IMT) is used for the detection of residual and recurrent brain tumors. The application of 123I-3-IMT for the study of extracerebral malignancies is limited by its marked and rapid renal uptake. In this study, we compared the tumor uptake, biodistribution, and specificity of 5 structurally related iodinated amino acids with those of 123I-3-IMT. The aim was to select the optimal analog for oncologic imaging outside the brain. Methods: We studied 3-123I-iodotyrosine (123I-3-IT), 2-123I-iodotyrosine (123I-2-IT), 123I-iodo-azatyrosine (123I-IAzaT), 2-123I-iodophenylalanine (123I-2-IPhe), and 4-123I-iodophenylalanine (123I-4-IPhe). Tumor uptake and renal uptake in sarcoma-bearing rats were measured by use of in vivo dynamic imaging. The differential uptake ratio (average counts per pixel of the region of interest divided by the average counts per pixel inside the total body) and rates of tracer accumulation (K1 values) were calculated. Results were compared with the values obtained for 123I-3-IMT in the same rat. Tracers that demonstrated high tumor uptake were labeled with 125I and coinjected with 18F-FDG in rats with turpentine-induced acute inflammation. After 30 min, the rats were sacrificed and dissected. Amino acid tracer uptake in organs and tissues was measured, and the increase in uptake in the inflamed muscle was expressed relative to the increase in 18F-FDG uptake. Results: Tumor uptake and K1 values for 123I-2-IT and 123I-2-IPhe were comparable to those for 123I-3-IMT. 123I-4-IPhe showed high tumor uptake but a reduced K1 value because of high blood-pool activity. 123I-3-IT and 123I-IAzaT did not accumulate markedly in tumor tissue. Renal accumulation of 123I-2-IT, 123I-2-IPhe, and 123I-4-IPhe was at least 6 times lower than that of 123I-3-IMT. 18F-FDG uptake was markedly increased in areas of acute inflammation (215%). The increases for 125I-3-IMT and 125I-4-IPhe were 35.5% and 22.2%, respectively, of the increase for 18F-FDG. Almost no increase was found for 125I-2-IT (3.3%) and 125I-2-IPhe (2.8%). Conclusion: 123I-2-IT and 123I-2-IPhe are promising tracers for oncologic imaging outside the brain. 123I-2-IT has the advantage of an established kit for radiosynthesis.