Radiolabeling of MAG3-morpholino oligomers with 188Re at high labeling efficiency and specific radioactivity for tumor pretargeting

We are investigating a novel pretargeting approach involving an initial IV injection of antitumor antibody conjugated with a phosphorodiamidate morpholino oligomer (MORF, a DNA analog) and the subsequent IV injection of the radiolabeled complement oligomer (cMORF). In this paper, the cMORF was labeled with 188Re using MAG3 as chelator for therapeutic applications. Since (c)MORFs are unstable in acidic condition, an optimal labeling pH was first selected and the other labeling factors were then examined. A labeling efficiency of greater than 90% can be achieved even at a concentration of MAG3–cMORF as low as 0.8 μM. The labeled cMORF is stable and capable of hybridizing to its complement.