Technetium-99m-MRP20, a potential brain perfusion agent: in vivo biodistribution and SPECT studies in non-primate animals.

MRP20 (N-(2(1H pyrolylmethyl]N'-(4-pentene-3-one-2] ethane-1,2-diamine) complexes with technetium-99m, yielding a neutral, lipophilic species. This compound has been characterized as [TcO(MRP20)]. Biologic investigation of [99mTc][TcO(MRP20)] in female rats showed 2.35% ID in the brain 30 min p.i. with no significant wash-out over 3 hr. A single-photon emission computed tomography (SPECT) study in a dog demonstrated rapid tracer uptake in the brain, reaching a maximum within 1 min, with 2.24% i.d. 15 min p.i., decreasing to 1.7% after 4 hr. The complex undergoes hydrolysis in vitro forming a cationic species. This is possibly the trapping mechanism in the brain in vivo. The main excretory route of [99mTc][TcO(MRP20)] is via the hepatobiliary tract. There is evidence of some "in vivo" cell labeling and soft-tissue uptake.