Gold-coated lanthanide phosphate nanoparticles for an ²²⁵Ac in vivo alpha generator

Retaining radioactive daughter products at a clinically relevant target site remains one of the major challenges in development of in vivo α generators with radionuclides such as ²²⁵Ac and ²²³Ra. In this work, we examine the ability of layered nanoparticle constructs to retain ²²⁵Ac and the first decay daughter, ²²¹Fr. Actinium-225 is cocrystalized in a lanthanide phosphate nanoparticle consisting of varying amounts of La and Gd. Additional lanthanide phosphate layers improve retention capability while an outer layer of gold facilitates the attachment of targeting moieties for in vivo use. Retention of ²²⁵Ac in the nanoparticles is near quantitative while the ²²¹Fr retention varies from 60-89% as a function of time, the number of layers, and nanoparticle composition. Decay corrected radiochemical yield in the multi-shell syntheses are high (76%) and comparable to or better than existing delivery approaches.