Tb-149: a new radiolanthanide for targeted cancer therapy

Full text: {sup 149}Tb (4.15 h) decays by the emission of both 3.9 MeV alpha particles (17% branching) and positrons (4% branch), and uniquely combines both therapeutic and PET diagnostic properties. In this paper we report the production route, systemic studies of radio-lanthanides with EDTMP ligand, and the first {sup 149}Tb phantom studies using PET. The radio-lanthanides used in this study were produced at the ISOLDE (isotope separator on-line) facility at CERN. They are produced carrier free, isotopically and chemically separated (isobaric separation using cation exchange chromatography) in a form suitable for protein labelling. Batches up to 20 mCi of {sup 149}Tb are available. We have established relationships between biokinetics, EDTMP concentration, and the ionic radius of the radiolanthanide used. The tumour to liver ratio in mice reaches a maximum value at 1 mM 10 mM and decreases from 10 by almost two decades according to the ionic radius of the lanthanide. For Tb, a tumour to liver ratio of 5 can be obtained, similar to Gd. No significant differences in the uptake in bone for all lanthanides in the EDTMP system were observed. A fast blood clearance allows clear bone images to be obtained via PET at 60-90 min postinjection, as shown with rabbits using {sup 142}Sm-EDTMP. The first phantom PET studies with {sup 149}Tb are also reported. We conclude that the fast biokinetics and the alpha decay mode open up new possibilities for a more efficient endo-radionuclide therapy using EDTMP.