Production of Mass-Separated Erbium-169 Towards the First Preclinical in vitro Investigations

The $\beta^-$-particle-emitting erbium-169 is a potential radionuclide toward therapy of metastasized cancer diseases. It can be produced in nuclear research reactors, irradiating isotopically-enriched $^{168}$Er$_2$O$_3$. This path, however, is not suitable for receptor-targeted radionuclide therapy, where high specific molar activities are required. In this study, an electromagnetic isotope separation technique was applied after neutron irradiation to boost the specific activity by separating $^{169}$Er from $^{168}$Er targets. The separation efficiency increased up to 0.5% using resonant laser ionization. A subsequent chemical purification process was developed as well as activity standardization of the radionuclidically pure $^{169}$Er. The quality of the $^{169}$Er product permitted radiolabeling and pre-clinical studies. A preliminary in vitro experiment was accomplished, using a $^{169}$Er-PSMA-617, to show the potential of $^{169}$Er to reduce tumor cell viability