title: Initial Evaluation of (99m)Tc(CO)3(ASMA) as a Renal Tracer in Healthy Human Volunteers.
abstract: OBJECTIVE
  Preclinical studies in rats showed that two of (99m)Tc(CO)3(ASMA) isomers (rac- and L-ASMA) had pharmacokinetic properties equivalent to that of (131)I-OIH, the radiopharmaceutical standard for the measurement of effective renal plasma flow. The aim of this study was to evaluate the pharmacokinetics of (99m)Tc(CO)3(ASMA) isomers in healthy human subjects.
  
  
  METHODS
  Three ASMA ligands (rac-, L- and D-ASMA) were labeled with (99m)Tc(CO)3 using an IsoLink kit (Covidien), and each formed (99m)Tc(CO)3(ASMA) tracer was co-injected with (131)I-OIH into healthy human subjects followed by sequential imaging, plasma clearance measurements and timed urine collection. Plasma protein binding, red cell uptake and percent injected dose in the urine were determined. Urine from each group of volunteers was analyzed for metabolites by HPLC.
  
  
  RESULTS
  Image quality was excellent with all three agents. Each (99m)Tc(CO)3(ASMA) preparation was excreted unchanged in the urine. The plasma clearance ratio ((99m)Tc(CO)3(ASMA)/(131)I-OIH) was 81 ± 3 % for D-ASMA compared to only 20 ± 4 % for L-ASMA and 37 ± 7 % for rac-ASMA; the 81 % clearance ratio for D-ASMA isomer is still ∼ 30 % higher than the (99m)Tc-MAG3/(131)I-OIH clearance ratio (∼50-60 %). Red cell uptake was similar for all three tracers (6-9 %), and all tracers had a relatively rapid renal excretion; at 3 h, the (99m)Tc(CO)3(ASMA)/(131)I-OIH urine ratio was 100 ± 3 % for D-ASMA, 80 ± 2 % for L-ASMA and 88 ± 1 % for rac-ASMA.
  
  
  CONCLUSIONS
  The renal excretion characteristics of (99m)Tc(CO)3(D-ASMA) in humans are superior to those of the other two (99m)Tc(CO)3(ASMA) isomers studied, but are still inferior to (131)I-OIH, even though there was no difference in the clearance of two of (99m)Tc(CO)3(ASMA) isomers and (131)I-OIH in rats. The work described here demonstrates the sensitivity in in vivo biological behavior of (99m)Tc(CO)3(ASMA) isomers to their subtle structural differences.
authors.affiliation: Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Road, NE, Atlanta, GA 30322 USA.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Lipowska
authors.affiliation: Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Road, NE, Atlanta, GA 30322 USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Klenc
authors.affiliation: Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Road, NE, Atlanta, GA 30322 USA.
authors.forename: Russell D
authors.initials: RD
authors.lastname: Folks
authors.affiliation: Department of Radiology and Imaging Sciences, Emory University, 1364 Clifton Road, NE, Atlanta, GA 30322 USA.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Taylor
keywords: 131I-o-iodohippurate; 99mTc(CO)3(ASMA); Imaging; Kidney; Renal radiopharmaceuticals; Technetium