99mTc(CO)3-Nitrilotriacetic Acid: A New Renal Radiopharmaceutical Showing Pharmacokinetic Properties in Rats Comparable to Those of 131I-OIH

To develop a 99mTc renal tracer with a capacity tomeasure effec-tive renal plasma flow comparable to that of the clinical gold standard 131I-o-iodohippurate (131I-OIH) and superior to that of 99mTcO-mercaptoacetyltriglycine, which has a clearance only 50%260 % that of 131I-OIH, we investigated 99mTc-tricarbonyl nitrilotriacetic acid (Na2[99mTc(CO)3(NTA)]). This radiopharma-ceutical, which is based on an aminopolycarboxylate ligand, is formed as a single species and has a dangling carboxylate group favoring tubular transport.Methods: Na2[99mTc(CO)3(NTA)] was prepared by using commercially available NTA and an IsoLink kit and isolated by high-performance liquid chromatography. The stability of Na2[99mTc(CO)3(NTA)] in isotonic saline was assessed for 24 h andwas further evaluated by incubation in 0.1Mcysteine and histidine for 4 h at 37C. The biodistribution of Na2[99mTc (CO)3(NTA)], coinjected with 131I-OIH as an internal control