Novel cell-based therapies currently represent a significant focus in cancer immunotherapies. Despite recent successes, the full potential of these treatments has yet to be discovered. The continued development of these therapies requires highly sensitive methods to follow the migration and activity of the immune cells after administration. Current imaging techniques for cell-based immunotherapies are limited in information and lack targeted imaging of the immune system. Therefore, we propose to develop a noninvasive tracking method that reveals the migration and distribution of immune cells to help explain the mechanisms behind novel cell-based immunotherapies.

We utilize a pre-targeted approach, which involves directly labeling the cell surface with a bioorthogonal functional group, such as an alkyne, and then reacting that functional group with a radiolabeled imaging probe, allowing for visualization via PET/CT. We used a metabolic labeling method to attach an alkyne to the cell surface, which can later be reacted with an azide by a Cu-catalyzed click reaction to track alkyne-labeled cells selectively. 

To further develop this method, we synthesized a Cu-chelating azide to enhance the click reaction speed and reduce cytotoxicity introduced by the use of Cu(I). An in vitro assay was developed this summer to test the reactivity of Cu-chelating azides with cell surface alkynes and a kinetic assay to analyze the reaction rate of different Cu-chelating azides. The most recently synthesized Cu-chelating azide in the Farwell lab was determined to have a pseudo first-order rate constant k=112.7 M-1s-1, enhancing the reaction rate by more than ten times compared to Cu-catalyzed click reactions without Cu-chelation. With the development of the kinetic assay, we can further test the kinetics of different Cu-chelating azides in vitro.