Radiolabeling of Human Serum Albumin With Terbium-161 Using Mild Conditions and Evaluation of in vivo Stability

Abstract

Targeted radionuclide therapy (TRNT) is a promising approach for cancer therapy. Terbium has four medically interesting isotopes (149Tb, 152Tb, 155Tb and 161Tb) which span the entire radiopharmaceutical space (TRNT, PET and SPECT imaging). Since the same element is used, accessing the various diagnostic or therapeutic properties without changing radiochemical procedures and pharmacokinetic properties is advantageous. The use of (heat-sensitive) biomolecules as vector molecule with high affinity and selectivity for a certain molecular target is promising. However, mild radiolabeling conditions are required to prevent thermal degradation of the biomolecule. Herein, we report the evaluation of potential bifunctional chelators for Tb-labeling of heat-sensitive biomolecules using human serum albumin (HSA) to assess the in vivo stability of the constructs. p-SCN-Bn-CHX-A”-DTPA, p-SCN-Bn-DOTA, p-NCS-Bz-DOTA-GA and p-SCN-3p-C-NETA were conjugated to HSA via a lysine coupling method. All HSA-constructs were labeled with [161Tb]TbCl3 at 40°C with radiochemical yields higher than 98%. The radiolabeled constructs were stable in human serum up to 24 h at 37°C. 161Tb-HSA-constructs were injected in mice to evaluate their in vivo stability. Increasing bone accumulation as a function of time was observed for [161Tb]TbCl3 and [161Tb]Tb-DTPA-CHX-A”-Bn-HSA, while negligible bone uptake was observed with the DOTA, DOTA-GA and NETA variants over a 7-day period. The results indicate that the p-SCN-Bn-DOTA, p-NCS-Bz-DOTA-GA and p-SCN-3p-C-NETA are suitable bifunctional ligands for Tb-based radiopharmaceuticals, allowing for high yield radiolabeling in mild conditions.

A simple and automated method for 161Tb purification and ICP-MS analysis of 161Tb

“…This material was dissolved in 1 M HNO 3 and split into two portions. One portion was purified using the HPIC method (Cassells et al 2021 ) at the Belgian Nuclear Research Center (SCK CEN). The other portion was added to H 2 O (final HNO 3 concentration 0.08 M) and left unpurified.…”

“…Several methods have been developed including those by Lehenberger et al and Gracheva et al, typically involving a large cation exchange column for purification and a small secondary solid phase extraction (SPE) column for concentration of the final product (Lehenberger et al 2011 ) (Gracheva et al 2019 ). Although such methods achieve a high radionuclidic purity, to accommodate the complex elution systems, they require custom made modules and acid-resistent high performance ion chromatography (HPIC) systems that are not easily adaptable to different laboratories (Cassells et al 2021 ). This paper reports a new method involving three small SPE columns with simple and predictable elution conditions, practical for smaller centres and lab settings.…”

Comparative Study of a Decadentate Acyclic Chelate, HOPO-O10, and Its Octadentate Analogue, HOPO-O8, for Radiopharmaceutical Applications

“…Spectra were analyzed using the Genie 2000 software package (Version X, Canberra Industries) using the 464. 55 International, 4 MPa), 210−220 mg of natural barium was pressed into a pellet of 10 mm diameter using a 10 mm die set and then pressed into an aluminum backing (4 MPa). The aluminum backing (6082 alloy) used to hold the barium was 1.6 mm thick and of 28 mm diameter with a centered 10 mm indent (0.55 mm depth).…”

Gamma counting protocols for the accurate quantification of 225Ac and 213Bi without the need for a secular equilibrium between parent and gamma-emitting daughter

“…225 Ac-constructs were synthesized by adding [ 225 Ac]Ac(NO 3 ) 3 (1–2 MBq, 100 μL, 0.05 M) to a Tris–HCl buffer (0.37 M, pH 8.5, chelex treated) solution containing DEPA or DOTA (50 µM) and reacting in a glass vial for 60 min at 95 °C. 225 Ac-constructs were purified using a C 18 Plus Sep-Pak cartridge (Waters Co., Milford, MA, USA) by loading the reaction mixture, rinsing with water (5 mL) to remove unreacted [ 225 Ac]Ac(NO3) 3 , and eluting the purified complex with absolute ethanol (0.5 mL) as described by Cassells et al ( 2021 ). After purification, radiolabeled aliquots were applied immediately to the test media.…”

“…The RCY of each reaction mixture was determined by instant thin-layer liquid chromatography (iTLC-SG, Varian, Diegem, Belgium) with an elution chamber using acetonitrile/water (75%/25% v/v) such that bound 225 Ac and bound daughter radionuclides will migrate with the solvent front to the upper part of the iTLC strip, while unbound radionuclides will remain at the lower part where the mixture was originally spotted (Fig. 2 ) (Cassells et al 2021 ). Once the solvent front reached the 1-cm mark of the iTLC strip at time t i (cfr solvent front Fig.…”