TC-99m(Sn)-N-pyridoxylaminates: a new series of hepatobiliary imaging agents

Three derivatives of N-pyridoxylamino acid were synthesized: Tc-99m(Sn)-N-pyridoxylphenylalanine, -N-pyridoxyltryptophan, and -N-pyridoxyl-5-methyltryptophan. The chemical and biologic properties of each complex was found to be quite analogous to those of the corresponding Tc-99m(Sn)pyridoxylideneaminate. In rats, Tc-99m(Sn)-N-pyridoxyl-5-methyltryptophan [Tc-99m(Sn)PHMT] showed rapid blood clearance, fast hepatobiliary transit, low urinary excretion, and no intestinal reabsorption. Over 90% of the dose arrived in the intestine through the liver at 30 min after i.v. administration, whereas only 2% of the dose escaped through the kidneys. In rabbits the gallbladder was clearly visualized within 5 min of injection and no renal or bladder images were noted on any scintiphotos. The BSP (sulfobromophthalein) intervention study revealed that the biliary excretion of Tc-99m(Sn)PHMT is much more resistant than that of TC-99m(Sn) diethyl-IDA to the intervention of BSP and hence to serum bilirubin. Toxicity studies on PHMT and Sn-PHMT indicated a wide margin of safety for the proposed human dose.