Cationic [Tc-99m(III)(DIARS)(2)(SR)(2)](+) complexes as potential myocardial perfusion imaging agents (DIARS equals o-phenylenebis(dimethylarsine); SR(-) equals thiolate)

Reduction-substitution reactions on [(TcO4)-Tc-99m](-) with both o-phenylenebis(dimethylarsine) (DIARS) and various thiols produce a series of monocationic [Tc-99m(DIARS)(2)(SR)(2)](+) complexes. Addition of [(TcO4)-Tc-99g](-) to the above reaction mixtures allows the characterization of the ''carrier-added'' complexes by means of reverse-phase high-performance liquid chromatography with radiometric and optical detection systems. The identity of the [Tc-99g(DIARS)(2)(SR)(2)](+) complexes is confirmed by fast atom bombardment mass spectroscopy; equivalence of the [Tc-99g(DIARS)(2)(SR)(2)](+) and [Tc-99m(DIARS)(2)(SR)(2)](+) species is demonstrated by identical HPLC retention times. All the [Tc-99m(DIARS)(2)(SR)(2)](+) complexes tested accumulate in the myocardium of Sprague-Dawley rats with an average uptake of 1.5-2.0% of injected dose/g at 30 min. Thus, as designed, these nonreducible Tc(III) complexes do not exhibit the rapid myocardial washout observed for reducible Tc(III) complexes. These [Tc-99m(DIARS)(2)(SR)(2)](+) complexes also exhibit an initially high liver uptake, but the presence of ether groups within the thiolate ligands causes this liver uptake to decrease over time without affecting the heart uptake, thereby improving the heart/liver ratio.