In vivo 212Pb/212Bi generator using indium-DTPA-tagged liposomes

International audienceIndium-DTPA-tagged liposomes were studied in the present work as carriers of in vivo 212Pb / 212Bi generator to be used in targeted alpha therapy. The liposomal uptake of 212Pb, into preformed liposomes, was investigated using different lipophilic chelate (DCP, 2,3-dimercapto-1-propanol (BAL), sodium acetate, and A23187), as a function of various parameters (temperature, concentrations of lipids, Pb, DTPA,...) with 212Pb as a tracer. Different formulations of liposomes were tested to evaluate the radiolabeling efficiency. No complexing agent was necessary for the passage of Pb2+ through the membrane. It occurs naturally via a partial permeability of the lipid bilayer which increases with the temperature. A complexing agent (DTPA) appears necessary to concentrate Pb in the internal compartment of the liposomes. Conditions were found (T = 65°C, internal DTPA concentration of 0.025 M, pH 7.4, ...) yielding a high and rapid uptake of 212Pb in liposomes. The protocol established provides a novel method for the efficient entrapment of about 2-3 Pb atoms per liposome with a yield of 75% in conditions relevant for nuclear medicine