**2.2 Radiolabeled C2A**

C2A domain of synaptotagmin I also binds PS with nanomolar affinity in a calciumdependent manner. The C2A is labeled in the form of C2A-GST (GST: glutathione Stransferase) fusion protein. The fusion protein can be stably labeled with 99mTc at a reasonably high radiochemical yield and purity through thiolation using 2-iminothiolane (Zhao, et al., 2006). 99mTc-C2A-GST accumulates well in the area at risk in a rat model of acute myocardial infarction in both in-vivo imaging and autoradiography. Recently, 18F-C2A-GST was synthesized and significant uptake in the VX2 rabbit lung cancer with paclitaxel induced apoptosis was observed in small animal PET/CT (Wang, et al., 2011). Radiochemical purity of 18F-C2A-GST was more than 95% and stable for 4 h after formulation. Biodistribution in mice was favorable with major excretion from the kidneys and rapid clearance from blood and nonspecific organs.
