Separation of 90Nb from zirconium target for application in immuno-PET

Fast progressing immuno- PET asks to explore new radionuclides. One of the promising candidates is Nb-90. It has a half-life of 14.6 h that allows visualizing and quantifying biological processes with medium and slow kinetics, such as tumor accumulation of antibodies and antibodies fragments or drug delivery systems and nanoparticles. Nb-90 exhibits a positron branching of 53% and an average kinetic energy of emitted positrons of.. mean = 0.35MeV. Currently, radionuclide production routes and Nb V labeling techniques are explored to turn this radionuclide into a useful imaging probe. However, efficient separation of Nb-90 from irradiated targets remains in challenge. Ion exchange based separation of Nb-90 from zirconium targets was investigated in systems AG 1 x 8 - HCl/H2O2 and UTEVA-HCl. Nb-95 (t(1/2) = 35.0 d), Zr-95 (t(1/2) = 64.0 d) and (92m) Nb (t(1/2) = 10.15 d) were chosen for studies on distribution coefficients. Separation after AG 1 x 8 anion exchange yields 99% of Nb-90/95. Subsequent use of a solid-phase extraction step on UTEVA resin further decontaminates Nb-90/95 from traces of zirconium with yields 95% of Nb-90/95. A semi-automated separation takes one hour to obtain an overall recovery of Nb-90/95 of 90%. The amount of Zr was reduced by factor of 10(8). The selected separation provides rapid preparation (< 1h) of high purity Nb-90 appropriate for the synthesis of Nb-90-radiopharmaceuticals, relevant for purposes of immuno-PET. Applying the radioniobium obtained, Nb-90/95-labeling of a monoclonal antibody (rituximab) modified with desferrioxamine achieved labeling yields of> 90% after 1 h incubation at room temperature.