Development of a lyophilized kit formulation for labeling of DNA probes with Tc-99m

DNA fragments such as oligodeoxynucleotides (ODNs) are under investigation for a possible utilization in nuclear medicine. Until now, experiments on T c-99m-labeled ODNs in vitro or in vivo have required the application of tim e-consuming procedures to obtain and control the purity of the radiolabeled compound. A lyophilized labeling kit would ease and improve the reproducib ility in further investigations with this class of promising biomolecules; therefore a study was initiated to evaluate the suitability of conjugates o f ODNs and a bifunctional chelating agent to be part of lyophilized kit for mulations. We report here the development of the first kit for one-step lab eling of oligonucleotides with Tc-99m. The formulation comprises 250-500 pm ol S-benzoyl-mercaptoacetyldiglycine (MAG2)-ODN phosphorothioate conjugate, 5 mg potassium sodium tartrate tetrahydrate and 100 mu g stannous chloride dihydrate in a lyophilized kit. Labeling yields above 90% were reproducibl y achieved after addition of 0.1-1 GBq pertechnetate and subsequent heating in a boiling water bath. Once formed, the Tc-99m-MAC2-ODN complexes were s table for at least 24 h. The shelf life of the kits is at least 10 weeks wh en stored protected from light at room temperature, but even kits stored at 40 degrees C gave labeling yields above 90% after 10 weeks. (C) 1999 Publi shed by Elsevier Science B.V. All rights reserved.