2-aminoethylphosphonic acid: biodistribution of a naturally occurring phosphonate after labelling with technetium-99m

Phosphonic acid derivatives (P-C-P bond) are thought to be devoid of a mammalian synthetic pathway. Nevertheless, a natural phosphonate derivative, 2-aminoethylphosphonic acid (2-AEP), has been detected in animal and human tissue. After labelling with 99Tcm, biodistribution studies were performed in normal and tumour-bearing rats. A scintigraphic rabbit investigation was also completed. When expressed as percent injected dose per gram, the lung, liver, kidney and bone concentrated > 1% of the 99Tcm-2-AEP at 5 min. By 6 h, the liver, bone, marrow and kidney dominated. The 2 h rabbit scintigraphic image coincided with the rat data. Tumour-to-organ ratios showed values intermediate with those obtained with 99Tcm-diphosphonate and 99Tcm-pertechnetate. 99Tcm-2-AEP may show promise as a soft tumour scintigraphic agent because of its unique structure and low gastrointestinal uptake, provided the relatively short t1/2p of 99Tcm proves to be suitable.