Cellular metabolism is an important determinant of 99mTc uptake by the sodium-iodide symporter

1774 Objectives Stem cell therapy in the heart is plagued by low engraftment. SPECT imaging of human sodium-iodide symporter (hNIS)-labeled rat cardiosphere-derived cells (CDCs) is useful for longitudinal assessment and optimization of engraftment. An in-depth understanding of the determinants of the NIS cell-derived signal is needed to improve understanding of in vivo stem cell biology and correctly interpret SPECT imaging results. Methods CDCs were trypsinized and used for in vitro studies of glucose (18FDG) uptake, ATP levels and 99mTc uptake or injected (3x106 CDCs) into infarcted/normal myocardium in a syngeneic, gender-mismatched rat transplantation model. Dual isotope SPECT-CT imaging was performed at 1 & 24hrs following cell transplantation after intravenous injection of 99mTc-pertechnetate and 201Tl-chloride. Quantification of 99mTc uptake by engrafted cells was performed using a phantom. Quantitative polymerase chain reaction (qPCR) for the male-specific rat SRY gene was used to quantify engraftment at 1 & 24hrs following transplantation. Results Trypsinization followed by cell suspension for 1 hr in glucose-containing medium resulted in decreased glucose uptake, cellular ATP and 99mTc uptake by 90%, 47% & 42% respectively, when compared to adherent cells. Absence of glucose in the medium decreased 99mTc uptake by an additional 63% in suspended cells. In vivo 99mTc uptake was significantly lower at 1 hr, when compared to 24 hrs following cell transplantation in the non-infarct (63±2.5 kBq at 1 hr vs. 148±16 kBq at 24 hrs, p Conclusions Trypsinization and cell suspension which are essential first steps in clinical and experimental studies of cell transplantation impair CDC bioenergetics and 99mTc uptake by hNIS-CDCs, resulting in reduced cell-derived SPECT signal at 1 hr following cell transplantation. Research Support This work is supported by NIH/NHLBI grant RO1 HL092985