Biological in Vitro and in Vivo Studies of a Series of New Asymmetrical Cationic [99mTc(N)(DTC-Ln)(PNP)]+ Complex (DTC-Ln = Alicyclic Dithiocarbamate and PNP = Diphosphinoamine)

Tc-99m(N)-DBODC5 is a cationic mixed compound under clinical investigation as potential myocardial imaging agent. In spite of this, analogously to the other cationic Tc-99m-agents, presents a relatively low first-pass extraction. Thus, modification of Tc-99m(N)-DBODC(5) direct to increase its first-pass extraction keeping unaltered the favorable imaging properties would be desirable. This work describes the synthesis and biological evaluation of a series of novel cationic Tc-99m-nitrido complexes, of general formula [(TcN)-Tc-99m(DTC-Ln)(PNP)](+) (DTC-Ln= alicyclic dithiocarbamates; PNP = diphosphinoamine), as potential radiotracers for myocardial perfusion imaging. The synthesis of cationic Tc-99m-(N)-complexes were accomplished in two steps. Biodistribution studies were performed in rats and compared with the distribution profiles of Tc-99m(N)-DBODC5 and Tc-99m-Sestamibi. The metabolisms of the roost promising compounds were evaluated by HPLC methods. Biological studies revealed that most of the complexes have a high initial and persistent heart uptake with rapid clearance from nontarget tissues. Among tested compounds. 2 and 12 showed improved heart uptake with respect to the gold standard Tc-99m-complexes with favorable heart-to-liver and slightly lower heart-to-lung ratios. Chromatographic profiles of Tc-99m(N)radioactivity extracted from tissues and fluids were coincident with the native compound evidencing remarkable in vivo stability of these agents. This study shows that the incorporation of alicyclic dithiocarbamate in the [Tc-99m(N)(PNP)](+) building block yields to a significant increase of the heart uptake at early injection point suggesting that the first-pass extraction fraction of these novel complexes may he increased with respect to the other cationic Tc-99m-agents keeping almost unaltered the favorable target/nontarget ratios.