A bifunctional chelating agent (BFC) such as 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) is often used to link a radionuclide with a monoclonal antibody (mAb) for the targeted imaging or radioimmunotherapy of cancers (1). However, a major limitation of using BFCs is that harsh reaction conditions such as high temperatures are required to facilitate the formation of the radionuclide-BFC complex (2). In addition, these complexes are not very stable in vivo. Ferreira et al. developed two BFCs, 1-oxa-4,7,10-triazacyclododecane-S-5-(4-nitrobenzyl)-4,7,10-triacetic acid (p-NO(2)-Bn-Oxo-DO3A) and 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-S-4-(4-nitrobenzyl)-3,6,9-triacetic acid (p-NO(2)-Bn-PCTA), and showed that these chelators produced stable radiolabeled complexes with 64Cu under mild conditions ([64Cu]-Oxo-DO3A and [64Cu]-PCTA) (3). A preliminary ex vivo biodistribution study in mice showed that, compared with [64Cu]-DOTA, there was a lower accumulation of radioactivity in the liver with [64Cu]-Oxo-DO3A and [64Cu]-PCTA. It was also observed that clearance of the label from the kidneys of the animals was faster with [64Cu]-PCTA than with either [64Cu]-Oxo-DO3A or [64Cu]-DOTA (3).