First evaluation of a 99mTc-tricarbonyl complex, 99mTc(CO)3(LAN), as a new renal radiopharmaceutical in humans.
(99m)Tc-Mercaptoacetyltriglycine ((99m)Tc-MAG3), (99m)Tc-dd- and ll-ethylene-dicysteine ((99m)Tc-EC), and (99m)Tc-mercaptoacetamide-ethylene-cysteine ((99m)Tc-MAEC) contain N(3)S or N(2)S(2) ligands designed to accommodate the 4 ligating sites of the ((99m)TcO)(3+) core; they are all excellent renal imaging agents but have renal clearances lower than that of (131)I-orthoiodohippurate ((131)I-OIH). To explore the potential of the newly accessible but less polar [(99m)Tc(CO)(3)](+) core with 3 ligating sites, we decided to build on the success of (99m)Tc-EC, with its N(2)S(2) ligand and 2 dangling carboxylate groups; we chose an N(2)S ligand that also has 2 dangling carboxylate groups, lanthionine, to form (99m)Tc(CO)(3)(LAN), a new renal radiopharmaceutical.


METHODS
Biodistribution studies were performed on Sprague-Dawley rats with (99m)Tc(CO)(3)(LAN) isomers, meso-LAN and dd,ll-LAN (an enantiomeric mixture), coinjected with (131)I-OIH. Human studies also were performed by coinjecting each (99m)Tc-labeled product ( approximately 74 MBq [ approximately 2 mCi]) and (131)I-OIH ( approximately 7.4 MBq [ approximately 0.2 mCi]) into 3 healthy volunteers and then performing dual-isotope imaging by use of a camera system fitted with a high-energy collimator. Blood samples were obtained from 3 to 90 min after injection, and urine samples were obtained at 30, 90, and 180 min.


RESULTS
Biodistribution studies in rats revealed rapid blood clearance as well as rapid renal extraction for both preparations, with the dose in urine at 60 min averaging 88% that of (131)I-OIH. In humans, both agents provided excellent renal images, with the plasma clearance averaging 228 mL/min for (99m)Tc(CO)(3)(meso-LAN) and 176 mL/min for (99m)Tc(CO)(3)(dd,ll-LAN). At 3 h, both (99m)Tc(CO)(3)(meso-LAN) and (99m)Tc(CO)(3)(dd,ll-LAN) showed good renal excretion, averaging 85% and 77% that of (131)I-OIH, respectively. Plasma protein binding was minimal (10% and 2%, respectively), and erythrocyte uptake was similar (24% and 21%, respectively) for (99m)Tc(CO)(3)(meso-LAN) and (99m)Tc(CO)(3)(dd,ll-LAN).


CONCLUSIONS
Although the plasma clearance and the rate of renal excretion of the (99m)Tc(CO)(3)(LAN) complexes were still lower than those of (131)I-OIH, the results of this first application of a (99m)Tc-tricarbonyl complex as a renal radiopharmaceutical in humans demonstrate that (99m)Tc(CO)(3)(LAN) complexes are excellent renal imaging agents and support continued renal radiopharmaceutical development based on the (99m)Tc-tricarbonyl core.
Lipowska
Malgorzata
M
Department of Radiology, Emory University School of Medicine, Atlanta, Georgia, USA.
He
Haiyang
H
Malveaux
Eugene
E
Xu
Xiaolong
X
Marzilli
Luigi G
LG
Taylor
Andrew
A
D000328:Adult; D000818:Animals; D005260:Female; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging* / Q000378:metabolism*; D008297:Male; D008657:Metabolic Clearance Rate; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D014018:Tissue Distribution
C511834:99mTc(CO)3(LAN); D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals