No-carrier-added iodine-131-FIBG: evaluation of an MIBG analog.
The purpose of this study was to evaluate the properties of 4-fluoro-3-[131I]iodobenzylguanidine ([131I]FIBG), a potential neuroendocrine tumor and myocardial imaging radiopharmaceutical.


METHODS
The binding of [131I]FIBG and [125I]MIBG was compared in vitro using the SK-N-SH human neuroblastoma cell line. The role of the active uptake-1 mechanism was investigated by determining the effect on cell binding of desipramine (DMI), ouabain, norepinephrine (NE), unlabeled MIBG and FIBG and by incubation at 4 degrees C. Finally, the tissue distributions of [131I]FIBG and [125I]MIBG were compared in normal mice.


RESULTS
The specific binding of [131I]FIBG remained fairly constant (45%-60%) over a 2-3-log activity range and consistently was 11%-14% higher (p < 0.05) than that of [125I]MIBG. The uptake of [131I]FIBG was reduced to 13% of control values by 1.5 microM DMI, to 31% by 1 mM ouabain, to 8% by lower temperature, to 8% by 50 microM NE and to 6% and 5% by 10 microM each of unlabeled MIBG and FIBG, respectively. The amount of [131I]FIBG retained by SK-N-SH cells was significantly higher than that of [125I]MIBG with the maximum difference observed at 72 hr. In mice, the uptake of [131I]FIBG was higher than that of [125I]MIBG not only in target tissues (heart and adrenals) but also in many other normal tissues; conversely, thyroidal uptake of [131I]FIBG was 2-3-fold lower than that of [125I]MIBG. The uptake of [131I]FIBG in the heart and adrenals was reduced by DMI.


CONCLUSIONS
Iodine-131-FIBG is an analog of MIBG with prolonged binding to neuroblastoma cells in vitro and retention in the myocardium in vivo.
Vaidyanathan
G
G
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Zhao
X G
XG
Strickland
D K
DK
Zalutsky
M R
MR
D019797:3-Iodobenzylguanidine; D000818:Animals; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics* / Q000627:therapeutic use; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics* / Q000627:therapeutic use; D007462:Iodobenzenes / Q000493:pharmacokinetics* / Q000627:therapeutic use; D051379:Mice; D008807:Mice, Inbred BALB C; D009447:Neuroblastoma / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000532:radiotherapy; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics* / Q000627:therapeutic use; D014018:Tissue Distribution; D014055:Tomography, Emission-Computed; D014407:Tumor Cells, Cultured
D005462:Fluorine Radioisotopes; D007457:Iodine Radioisotopes; D007462:Iodobenzenes; D019275:Radiopharmaceuticals; C090053:(4-fluoro-3-iodobenzyl)guanidine; D019797:3-Iodobenzylguanidine