68GaTHM2BED: a potential generator-produced tracer of myocardial perfusion for positron emission tomography

THM2BED [N,N,N',N'-tetrakis-(2-hydroxy-3,5-dimethylbenzyl)ethylenediamine] is a new hexadentate ligand which has been synthesized and complexed with gallium isotopes. A conditional stability constant of 22.3 and a pM value of 20.7 have been determined for GaTHM2BED at physiological pH. Hexachelated and pentachelated complexes of GaTHM2BED have been isolated via preparatory HPLC and evaluated individually. The hexachelated isomer of 68GaTHM2BED clears slowly from the myocardium of rats and at 1 h post-injection the heart-to-blood ratio is 1.65. The data ratio indicates that this radiotracer may be capable of measuring blood flow in the heart. The ability of 68GaTHM2BED to delineate myocardial tissue in a dog has been evaluated and good images were obtained using hexachelated 68GaTHM2BED. There is evidence that this complex penetrates the blood-brain barrier.