Preparation and evaluation of [201Tl](III)-DTPA complex for cell labeling

Due to interesting physical properties and wide availability of 201 Tl as a SPECT radionuclide, the incorporation of this nuclide into DTPA for cell labeling was targeted. Thallium-201 ( T 1/2 = 3.04 d) in Tl + form was converted to Tl 3+ cation in the presence of O 3 /6M HCl and di-isopropyl ether, controlled by RTLC/gel electrophoresis methods. The final evaporated activity reacted with cDTPA in normal saline to yield [ 201 Tl](III)DTPA at room temperature after 0.5 hour, followed by solid phase extraction purification using C 18 Sep-Pak column (radiochemical yield >95%). Radiochemical purity of more than 99% was obtained using RTLC with specific activity of about 260 GBq/mmol. The stability of the tracer was checked in the final product in the presence of human serum at 37 °C up to 3 days. The partition coefficient was also measured. The labeled compound was used in red blood cell (RBC) labeling. The cell uptake ratio was determined at 4, 25 and 37 °C up to 3 hours.