Abstract 4116: Rapid imaging of tumor cell death in vivo using C2Am

Abstract

Abstract Cell death is an important target for imaging the early response of tumors to treatment. We describe here the validation of C2Am, a phosphatidylserine-binding agent based on the C2A domain of synaptotagmin-I, for detecting tumor cell death in vivo. Methods: The capability of (99m)Technetium-, (111)Indium-labelled or near- infrared fluorophore-labelled derivatives of C2Am for imaging tumor cell death was evaluated in implanted and genetically engineered [Fig.1] mouse models of lymphoma and in a human colorectal xenograft, using single photon CT (SPECT) and planar near-infrared fluorescence imaging, respectively [1,2]. Results: (99m)Tc-C2Am and (111)In-C2Am showed favorable biodistribution profiles, with predominantly renal clearance and low nonspecific retention in the spleen and liver at 24 h after probe administration. (99m)Tc-C2Am and (111In)-C2Am generated tumor-to-muscle ratios in drug-treated tumors of 4.3× and 2.2×, respectively, at 2 h and 7.3× and 4.1×, respectively, at 24 h after administration. A fluorophore-labelled C2Am derivative also showed predominantly renal clearance and high specificity and sensitivity for detecting low levels of tumor cell death (<5%). There was a significant correlation (R=0.9) between fluorescently labelled C2Am binding and histologic markers of cell death (cleaved caspase-3); no such correlation was observed with a site-directed mutant of C2Am that does not bind phosphatidylserine (iC2Am). Conclusions: Given the favorable biodistribution profile of radiolabelled C2Am derivatives, and their ability to produce rapid and cell death-specific image contrast, these agents have potential for clinical translation, particularly as PET tracers. We have initiated GMP manufacture and toxicology studies required for a Phase 1 trial.