Po-Thur Eve General-22: 111In-Tropolone-Labeled Mesenchymal Stem Cells: In Vivo Radiotracer Kinetics

Abstract

Direct in vitro labeling of cells with 111 In ‐tropolone followed by in vivoSPECTimaging gives no information about the fate of the cells but simply tells where the 111 In has gone. It is necessary to study the kinetics of 111 In label after transplantation and determine the connection between 111 In and the presence of viable cells. Two sets (n=5) of mesenchymal stem cells (MSC) were labeled with 111 In ‐tropolone and then killed by using an ultrasound probe to rupture the cell membrane or by freezing the cells at −80°C for 60min. The resulting cell debris and supernatant were used to label two new sets of MSC. The labeling efficiency was measured and compared to a control labeled with 111 In ‐tropolone. 1.5×107 MSC labeled with 1.32MBq 111 In were killed using the ultrasound probe and then injected into the myocardium of a canine (without infarction). Whole body and SPECTimages were acquired over 13 hrs post‐injection. The animal was then sacrificed and the amount of 111 In remaining in tissue samples from the heart was measured. (0.2±0.5)% and (0.3±0.5)% labeling efficiencies were found for cells labeled with ultrasound‐killed and frozen‐killed cells, while the labeling efficiency of the control cells was found to be (53.0±2.0)% for a 30min cell culture. After 13hrs, 111 In remained in the myocardium. Analysis of the 111 In SPECTimages indicated a biological half‐life of 2.3 hours. It was concluded that 111 In leaked from dead MSC does not label other viable MSC and will be rapidly cleared from the myocardium.