Preparation of 68 Ga-Mg-Ca-phytate colloid and its evaluation as a liver imaging agent.

Abstract

The objective of this study was to investigate the radiosynthesis of 68 Ga-Mg-Ca-phytate colloid and then characterise the formulation for radiochemical purity (RCP), radioactive particle size distribution, and biodistribution in normal rats. This radiocolloid was prepared by mixing an aqueous solution of phytic acid, 68 Ga3+ ions, a dispersant, Mg2+ and Ca2+ ions, and then heating the contents at 100°C for 5minutes. After cooling the vial to 5°C, the solution was basified to pH5 and stored in the cold. The resulting product contained 92±3% RCP 68 Ga-colloidal particles and a low level (8±3%) of soluble 68 Ga-Mg-Ca-phytate. Particle size experiments defined the radioactive particle population was 6±4% <20nm, 90±6% 20 to 200nm, and 4% were >200nm in diameter. Intravenous injection of the 68 Ga-colloid dispersion to rats resulted in 93% uptake by the liver plus spleen, 1% lungs, 1% total blood, and 6% in the carcass after 20minutes. This optimal formulation remained stable at 5°C for 1½hours in vitro, and it resulted in the same biodistribution as the formulation prepared at t=0hours. The preclinical data so far indicate that 68 Ga-Mg-Ca-colloid has excellent potential as a liver imaging agent.