Potential in vivo generator for alpha-particle therapy with 212Bi: presentation of a system to minimize escape of daughter nuclide after decay of 212Pb to 212Bi

Radiopharmaceuticals based on 212Pb (t1/2 = 10.6 h) are of interest for use as an in vivo generator of α-particle emitting 212Bi (t1/2 = 60.6 min). Sterically stabilized liposomes were evaluated as carriers of 212Pb/212Bi radionuclides in the reported study. 212Pb/212Bi-containing vesicles were prepared by ionophore mediated loading of 212Pb into preformed liposomes. The liposomal uptake of 212Pb with or without various concentrations of lead carrier was investigated. The retention of 212Pb and 212Bi in liposomes incubated in serum was studied. Conditions were found yielding a high and rapid uptake of 212Pb in liposomes. 90 ± 2% of 212Pb was incorporated after 30 min. The retention of radionuclides was high, 95% of 212Pb and 212Bi were retained in liposomes after incubating for 20 h at 37 C in serum. The results from the present work indicate that an effective retention of 212Bi after the β;--decay of 212Pb is achievable. This technology could be the basis of α-emitting radiopharmaceuticals built upon 212Pb. (orig.)