Design of Tc-labeled zinc-chelating imaging probe for SPECT imaging of the pancreas.

Early and sensitive diagnosis of pancreatic diseases is a contemporary clinical challenge. Zinc level in pancreatic tissue and its secretion in pancreatic juice has long been considered a surrogate marker of pancreatic function. The objective of this study was to design a Zn-chelating imaging probe (ZCIP) which could be labeled with Tc radionuclide for imaging of pancreas using single photon emission tomography (SPECT). We synthesized ZCIP as a bifunctional chelate consisting of diethylene triamine pentaacetic acid for Tc-chelation at one end and bispicolylethylamine for Zn-complexation at the other end. ZCIP was labeled with Tc by standard Sn-based reduction method. The Tc-labeled ZCIP was studied in normal mice (0.3 mCi) for SPECT imaging. We found that ZCIP consistently labeled with Tc radionuclide with over 95% efficiency. Addition of ZCIP altered the spectrum of standard dithizone-Zn complex, indicating its ability to chelate Zn. SPECT data demonstrated the ability of Tc-ZCIP to image pancreas with high sensitivity in a non-invasive manner; liver and spleen were the other major organs of Tc-ZCIP uptake. Based on these results, we conclude that Tc-ZCIP presents as a novel radiotracer for pancreas imaging for diagnosis of diseases such as pancreatitis.