2-[18F]fluoroputrescine: preparation, biodistribution, and mechanism of defluorination

A new radiolabeled analog of putrescine, 18F labeled 2-fluoroputrescine, has been prepared as a potential in vivo imaging agent for prostate and prostate derived tumors. The radiosynthesis yielded 1.5-4.5 mCi amounts of the 18F labeled putrescine analog (1-3% yields at end-of-synthesis), with specific activities ranging from 0.85-4.3 Ci/mmol, in a synthesis time of 2 h. The in vivo biodistribution in mature male rats showed considerable uptake by the bone, indicating defluorination of the compound. In animals pretreated with aminoguanidine, an inhibitor of diamine oxidase, the enzyme important in the metabolism of putrescine, defluorination was markedly reduced, but uptake by the prostate did not improve. These results suggest the need for development of a 18F labeled analog of putrescine which does not defluorinate in vivo, and which has biological properties similar to putrescine.