No-carrier-added meta-[123I]iodobenzylguanidine: synthesis and preliminary evaluation.

No-carrier-added [123I]MIBG was prepared from 3-(trimethylsilyl)benzylguanidine in 80-90% yield. Binding of this tracer to SK-N-SH human neuroblastoma cells maintained a constant level of > 50% over 2-3 log activity range. In comparison, the binding of [123I]MIBG prepared by isotopic exchange steadily decreased with dose. Biodistribution studies in normal mice demonstrated maximal concentrations in heart and adrenals for both preparations. In heart, significant 1.5-3.0 times higher levels (P < 0.05) were seen for the no-carrier-added preparation. Radiation dosimetry calculations suggest that the no-carrier-added preparation would increase the dose received by several tissues, most notably the heart where a 91% increase in dose is predicted.