Production and purification of radiolabeling-ready <sup>132/135</sup>La from the irradiation of metallic <sup>nat</sup>Ba targets with low energy protons.

Abstract

<h4>Introduction</h4>Radiolanthanides ¹³²La and ¹³⁵La form a promising chemically matched theranostic pair. With a half-life of 18.95 h, ¹³⁵La acts as the therapeutic isotope as it releases approximately 11 Auger electrons per decay, making it compatible with targeted Auger electron therapy (TAET), whereas ¹³²La with half-life of 4.58 h undergoes positron emission making it compatible with imaging via positron emission tomography (PET).<h4>Methods</h4>^132/135La were produced via irradiation of natural barium targets (99.9 %) with 12.8 MeV protons. A two-step separation scheme using extraction chromatographic resin TK200 (50-100 μm) and cation exchange resin Dowex 50Wx4 (200-400 mesh) was designed. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify non-radioactive impurities in each fraction of the separation method. The distribution coefficients of La³⁺ in HNO₃ on the TK200 resin and on both Dowex 50Wx8 (200-400 mesh) and Dowex 50Wx4 resins in ammonium α-hydroxyisobutyrate (pH 4.8) were determined, respectively.<h4>Results</h4>This novel separation scheme allowed for reliable separation of [^132/135La]La³⁺ from the Ba²⁺ target material, resulting in a high radiochemical yield of 98.3 ± 2.1 % (n = 3) with the final elute being directly compatible with subsequent radiolabeling due to the use of ammonium α-hydroxyisobutyrate to eliminate steps in the radiopharmaceutical synthetic process.