New99mTc-diiodine substituted IDA derivative (DIIODIDA) for hepatobiliary imaging

The effect of lipophilicity on the hepatobiliary properties of iminodiacetic acid derivatives in the conditions of hyperbilirubinemia

The partition coefficients (log P) of theoretically possible alkyliodinated iminodiacetic acid (IDA) derivatives and commercial IDA derivatives were calculated using two computer programs: ChemSketch Log P and ChemOffice Ultra. Newly synthesized ligands (DIETHYLIODIDA and DIISOPROPYLIODIDA) with the highest calculated log P were labeled with technetium-99m. The biodistribution and the influence of bilirubin on their biokinetics were investigated in rats and compared to corresponding results for commercial (99m)Tc-BROMIDA. Log P of (99m)Tc-complexes of synthesized ligands were determined experimentally as well as the protein binding. In comparison to (99m)Tc-BROMIDA, (99m)Tc-DIETHYLIODIDA has: (a) better biliary excretion (2.76±0.15%ID/g versus 1.83±0.10%ID/g); (b) faster hepatic clearance (2.90±0.21%ID/g versus 7.47±0.70%ID/g) and decreased biliary excretion (for 14% versus 22%) in conditions of hyperbilirubinemia after 15min. It is proved that (99m)Tc-DIISOPROPYLIODIDA has a prolonged hepatic transit time and decreased biliary excretion.

Acid-base equilibria of 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid and its labeling with technetium-99m

The acid-base equilibria of a novel hepatobiliary imaging agent, 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid (DIIODIDA) were studied. The potentiometrically determined acidity constants of the second carboxylic group, amino and amide groups were pK2 = 2.52 ? 0.02; pK3 = 5.86 ? 0.06 and pK4 = 10.9 ? 0.1. The determinations were performed at 25 ?C and an ionic strength of 0.1 mol/dm3 (NaCl). The acidity constants (pK1 = 1.3 ? 0.4) corresponding to the first carboxylic group was determined indirectly, on the basis of equilibrium constants obtained in a heterogeneous system, at 25 ?C and an ionic strength 1 mol/dm3 (HCl, NaCl). DIIODIDA was labeled with technetium-99m, and the influence of pH on the yield of labeling was investigated. It was found that labeling within the pH range from 5.5 to 6.5 provided a radiopharmaceutical of high radiochemical purity (>98 %).