A NOVEL SPIN-PROBE WITH LONG-LIFE IN-VIVO FOR ESR IMAGING

A dextran-bonded nitroxide radical (TEMPO-DX) was synthesized to obtai n a radical with long life in vivo for ESR imaging. TEMPO-DX was injec ted intravenously into a rat tail vein and the decrease in ESR intensi ty in the collected, circulating blood was followed. The result showed that the half life of TEMPO-DX in vivo was 30 min, the longest value reported so far and more than 30 times longer than the corresponding r adicals of the six-membered piperidine ring, which means that the bond ing of a radical to the polymer greatly prolonged life. The stabilitie s of TEMPO-DX against the reduction with L-ascorbic acid and the rat l iver homogenate were also examined and compared with those of the 3-ca rbamoyl-2,2,5,5-tetramethylpyrolidin-1-yloxy (CPROXYL) known as a radi cal stable in vivo. TEMPO-DX was shown not to be as stable as CPROXYL, thus in vivo stability of TEMPO-DX arises from the fact that it is sl owly absorbed into the tissues where the radicals are quenched. An ESR image of the mouse head domain was obtained only by an intravenous in jection of TEMPO-DX solution into the tail vein.