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 ⁹⁰ Nb. 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. ⁹⁰ Nb exhibits a positron branching of 53% and an average kinetic energy of emitted positrons of E _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 ⁹⁰Nb from irradiated targets remains in challenge. Ion exchange based separation of ⁹⁰Nb from zirconium targets was investigated in systems AG 1 × 8 - HCl/H₂O₂ and UTEVA-HCl. ⁹⁵Nb (t _1/2 = 35.0 d), ⁹⁵Zr ( 1/2 = 64.0 d) and ⁹²mNb (t _1/2 = 10.15 d) were chosen for studies on distribution coefficients. Separation after AG 1 × 8 anion exchange yields 99% of ^90/95 Nb. Subsequent use of a solidphase extraction step on UTEVA resin further decontaminates ^90/95 Nb from traces of zirconium with yields 95% of ^90/95Nb. A semi-automated separation takes one hour to obtain an overall recovery of ^90/95Nb of 90%. The amount of Zr was reduced by factor of 10⁸. The selected separation provides rapid preparation (< 1h) of high purity ⁹⁰Nb appropriate for the synthesis of ⁹⁰ Nb-radiopharmaceuticals, relevant for purposes of immuno-PET. Applying the radioniobium obtained, ^90/95 Nb-labeling of a monoclonal antibody (rituximab) modified with desferrioxamine achieved labeling yields of> 90%after 1 h incubation at room temperature.