Synthesis, separation and biodistribution of ^99mTc-CO-MIBI complex

^99mTc-CO-MIBI was prepared by a two-step procedure involving the convenient preparation of the [^99mTc(CO)₃(OH ₂)₃]⁺ precursor and followed by the substitution of the water molecules by the MIBI (2-methoxyisobutylisonitrile) ligands. In a second step, the reaction solution was adjusted to different pH values, and then the product, ^99mTc-CO-MIBI, was confirmed to be a mixture of two complexes: complex A and complex B, whose labeling yields could be over 90%. The ratio of complex B to the sum of A and B could increase gradually from 0 to 1 when pH was shifted from 3.0 to 9.0. These changes were monitored by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The two complexes were stable within 8h at room temperature in vitro. The partition coefficient of the two complexes indicated that there was distinct difference between them. Biodistribution in mice demonstrated that complex B showed better myocardial imaging properties than that of complex A. The heart/liver ratios of complex A, the mixture, and complex B were 1.57, 1.93, and 2.33, respectively, for 30 min post-injection. The discovery of chemical and biological properties of ^99mTc-CO-MIBI would certainly promote the research on a new promising myocardial perfusion-imaging agent.