Synthesis and Optimization of the Labeling Procedure of Tc-99m-Hynic-Interleukin-2 for In vivo Imaging of Activated T lymphocytes

We have previously described the labeling of interleukin-2 (IL2) with I-123 and Tc-99m-N3S. Both radiopharmaceuticals were successfully applied in humans to image several inflammatory lesions and autoimmune diseases characterized by tissue infiltrating lymphocytes expressing the IL2 receptor (CD25). However, both radiopharmaceuticals had some specific disadvantages, such as cost and time of synthesis.Here, we describe a new improved method for labeling interleukin-2 with Tc-99m using HYNIC-NHS and tricine as coligand. Several optimizations of reagent concentrations and labeling conditions were performed in order to standardize the procedure. After labeling, IL2 was purified by tC2 reverse-phase chromatography and tested in vitro and in vivo, in mice and in a normal volunteer. Results showed that this labeling procedure is cheap, fast, reliable, and reproducible, leading to a product with high specific activity (153 A mu Ci/A mu g), high stability and capable of binding in vitro to CD25 positive cells. In vivo biodistribution in mice and human volunteer did not show any significant different from Tc-99m-N3S-IL2.In conclusion, the optimization of Tc-99m-HYNIC-IL2 has a great advantage in terms of cost and time of production and a simple kit formulation can be considered for routine application to study patients affected by autoimmune diseases, graft rejection, or other chronic inflammatory disorders.