Radioiodinated meta-iodobenzylguanidine (MIBG) is used routinely for imagin
g and targeted radiotherapy of tumours derived from the neural crest. Since
active uptake of MIBG by the noradrenaline transporter (NAT) makes a great
er contribution to total drug accumulation than passive uptake when MIBG is
present at low concentrations, tumour-specific uptake should be enhanced b
y the administration of lower molar amounts of MIBG. This could be achieved
through the use of MIBG with a high specific activity. Commercially availa
ble preparations of I-123-MIBG have specific activities of approximately 20
0 MBq.mg(-1). We have synthesized and used no-carrier-added (n.c.a.) I-123-
MIBG produced by an iododesilylation reaction (specific activity 0.7 TBq.mg
(-1)). We report here the first clinical studies comparing the commercially
available and n.c.a. MIBG diagnostic preparations. Five patients with know
n phaeochromocytoma were studied. Unlike studies in animal models, no consi
stent improvement in tumour uptake was observed with the n.c.a. material. A
larger patient group is required to determine whether there are significan
t differences between the two preparations, before proceeding to studies at
therapeutic activity levels of n.c.a. I-131-MIBG. Even with no improvement
in tumour uptake, n.c.a. MIBG may be the favoured formulation for therapeu
tic applications to reduce the molar amount of drug injected. ((C) 2000 Lip
pincott Williams & Wilkins).