EVALUATION OF RADIOIODINATED IODOCLORGYLINE AS A SPECT RADIOPHARMACEUTICAL FOR MAO-A IN THE BRAIN

An in vivo estimation of the newly synthesized MAO-A specific inhibitor, [I-125]-labeled N-[3(2,4-dichloro-6-iodophenoxy)propyl]-N-methyl-2-propynylamine ([I-125]-iodoclorgyline), was performed. Retention of the radioactivity of this radioligand was observed in the brain from 1 h post-injection. Pretreatments with clorgyline and I-deprenyl showed selective binding of [I-125]-iodoclorgyline to MAO-A in the brain at 24 h post-injection. Moreover, a good correlation (r = 0.907) between the uptake of [I-125]-iodoclorgyline and MAO-A enzyme activity in the cortex was observed in the pretreatment study with several doses of clorgyline. Although improvement to increase the brain/blood ratio is desirable because of slow blood clearance of the radioactivity, radioiodinated iodoclorgyline may serve as a useful SPECT radiopharmaceutical for quantitative analysis of MAO-A in the brain.