[I-125 I-127/I-131] IODORHODAMINE - SYNTHESIS, CELLULAR-LOCALIZATION,AND BIODISTRIBUTION IN ATHYMIC MICE BEARING HUMAN TUMOR XENOGRAFTS AND COMPARISON WITH [TC-99M]HEXAKIS(2-METHOXYISOBUTYLISONITRILE)/

The synthesis of halogenated rhodamine (Rh) derivatives was carried ou t by controlling the stoichiometry of the halogenating agents, bromine and iodine monochloride. In the no-carrier-added synthesis of radioio dinated rhodamine 123, direct labeling of rhodamine 123 (Rh 123) with (NaI)-I-125/(NaI)-I-131 required the presence of the oxidant peracetic acid. I-125/I-131-Rh 123 was synthesized in modest yields (40-45%). H PLC purification separated Rh 123 from its mono-and diiodo derivatives . Monohalogenation of Rh 123 did not alter the compound's ability to p ermeate viable cells and localize in mitochondria. I-125/I-131-Rh 123 was stable in serum in vitro but rapidly metabolized after intravenous injection into mice. Consequently, scintigraphy and biodistribution d ata reveal poor targeting of subcutaneously growing human tumor xenogr afts. The results are compared to those obtained following the adminis tration of [Tc-98m]hexakis(2-methoxyisobutylisonitrile) which also did not image human tumor xenografts in nude mice.