Radiolanthanide-labeled HA particles in the treatment of rheumatoid arthritis: ready-to-use cold kits for rapid formulation in hospital radiopharmacy

Hydroxyapatite (HA) Ca₁₀(PO₄)₆(OH)₂] particles radiolabeled with a variety of β^? emitting lanthanide radionuclides and also pseudolanthanide ⁹⁰Y have been proposed for the treatment of arthritis. A ready-to-use cold kit of HA particles (1–10 µm size) was developed for fast and convenient formulation of radiolanthanide-labeled HA particles at hospital radiopharmacy. Six radionuclides namely, ¹⁶⁹Er, ¹⁷⁷Lu, ¹⁵³Sm, ¹⁶⁶Ho, ¹⁴²Pr and ⁹⁰Y, having β^? emissions of a wide range of energy E_β(max) = 0.34–2.28 MeV] were identified and produced by thermal neutron activation. Clinical doses of HA particles labeled with these radionuclides were prepared in high yield (>97 %) and radiochemical purity (>99 %) using the cold kits. Pre-clinical studies of ¹⁷⁷Lu–HA carried out in Wistar rats bearing arthritis in knee joints revealed no leakage of the activity from the joints. In preliminary clinical investigation using 333 ± 46 MBq doses of the same preparation, significant improvement in the disease conditions was reported in patients with chronic rheumatoid arthritis of knee joints.