Development of a lyophilized kit formulation for labeling of DNA probes with 99mTc

DNA fragments such as oligodeoxynucleotides (ODNs) are under investigation for a possible utilization in nuclear medicine. Until now, experiments on 99mTc-labeled ODNs in vitro or in vivo have required the application of time-consuming procedures to obtain and control the purity of the radiolabeled compound. A lyophilized labeling kit would ease and improve the reproducibility in further investigations with this class of promising biomolecules; therefore a study was initiated to evaluate the suitability of conjugates of ODNs and a bifunctional chelating agent to be part of lyophilized kit formulations. We report here the development of the first kit for one-step labeling of oligonucleotides with 99mTc. The formulation comprises 250-500 pmol S-benzoyl-mercaptoacetyldiglycine (MAG2)-ODN phosphorothioate conjugate, 5 mg potassium sodium tartrate tetrahydrate and 100 microg stannous chloride dihydrate in a lyophilized kit. Labeling yields above 90% were reproducibly achieved after addition of 0.1-1 GBq pertechnetate and subsequent heating in a boiling water bath. Once formed, the 99mTc-MAG2-ODN complexes were stable for at least 24 h. The shelf life of the kits is at least 10 weeks when stored protected from light at room temperature, but even kits stored at 40 degrees C gave labeling yields above 90% after 10 weeks.