Tetraamine-derived bifunctional chelators for 99mTc labeling: synthesis, bioconjugation and evaluation as targeted SPECT imaging probes for GRPr positive tumors

Introduction: Owing to its optimal nuclear properties, ready availability, low cost and favorable dosimetry, Tc continues to be the ideal radioisotope for medical imaging applications. Most of the bifunctional chelators reported for Tc complexation, suffer from tedious labeling protocols and undesired physicochemical properties. On the other hand, bifunctional chelators based on tetraamine framework exhibit facile complexation at ambient temperature with Tc(V)O2 forming monocationic species with high in vivo stability and significant hydrophilicity leading to favorable pharmacokinetics. Although, many tetraamine based conjugates have been studied for the cell surface receptor targeted imaging of tumors, none of the reports exemplify the straightforward synthesis of tetraamine based bifunctional chelators.