Esters of iopanoic acid as liver-specific CT contrast agents: biodistribution and CT evaluation

The synthesis and preliminary biodistribution data for a series of sterol-like esters of iopanoic acid having potential value as liver-specific CT contrast agents are described. Structural modification of the sterol portion of the iopanoate ester afforded a group of compounds that displayed tissue specificity similar to cholesteryl iopanoate, the prototype ester of this series, but were rapidly cleared from the target tissues after hydrolysis. From the biodistribution data, the most promising of these agents, pregnenolone iopanoate (PI), was evaluated by CT in rabbits receiving a radiologic dose equivalent to 30 mg I/kg. The hepatic parenchyma was enhanced within 2 h of infusion to a maximal level of 31 HU above precontrast values. Hepatic CT attenuation returned to normal within 24 h. However, CT performed after PI infusion into Vx2 tumor-bearing rabbits failed to provide superior images compared with those acquired following bolus administration of urographic contrast.