New 64Cu PET imaging agents for personalised medicine and drug development using the hexa-aza cage, SarAr

The success of positron emission tomography (PET) in personalised medicine and drug development requires radioisotopes that provide high quality images and flexible chemistry for a broad application. 64Cu is arguably one of the most suitable PET isotopes for imaging with the evolving target agents, but there are not many appropriate chelating agents for 64Cu and this has limited its wider application. The bi-functional chelator, SarAr is known to bind 64Cu2+ quantitatively (i.e. one metal per ligand present) and rapidly (<2 min) at 10(-6) M over a range of pH (4-9). In this paper the conjugation of SarAr to the whole and fragmented antibody is described. Conjugation of the SarAr to the protein does not impair its coordination of the 64Cu. It complexes the 64Cu2+ rapidly, quantitatively and essentially irreversibly at pH 5. Animal studies show that the 64Cu-SarAr-immunoconjugates maintain their specificity for the target and are stable in vivo. Also, SarAr is a platform technology, is easy to use in a kit formulation and is readily adaptable for the wider application in 64Cu PET imaging.