Actinium-225 Targeted Agents: Where Are We Now?

Abstract

α-particle targeted radionuclide therapy has shown promise for optimal cancer management, an exciting new era for brachytherapy. Alpha-emitting nuclides can have significant advantages over gamma- and beta-emitters due to their high linear energy transfer (LET). While their limited path length results in more specific tumor 0kill with less damage to surrounding normal tissues, their high LET can produce substantially more lethal double strand DNA breaks per radiation track than beta particles. Over the last decade, the physical and chemical attributes of Actinium-225 (²²⁵Ac) including its half-life, decay schemes, path length, and straightforward chelation ability has peaked interest for brachytherapy agent development. However, this has been met with challenges including source availability, accurate modeling for standardized dosimetry for brachytherapy treatment planning, and laboratory space allocation in the hospital setting for on-demand radiopharmaceuticals production. Current evidence suggests that a simple empirical approach based on ²²⁵Ac administered radioactivity may lead to inconsistent outcomes and toxicity. In this review article, we highlight the recent advances in ²²⁵Ac source production, dosimetry modeling, and current clinical studies.

Keywords: (225)Ac; Chelation; Dosimetry; Imaging; Theranostics.

Figure 1.

Results from a PubMed search conducted in May 2023 using the term Actinium for the last 10 years since 2013 (pubmed.ncbi.nlm.nih.gov)

Figure 2.

Structures of commonly used chelators

Figure 3:

Structures of PSAM-11 (imaging), PSMA-616 (therapy), and PSMA-I&T (Imaging and Therapy)

Figure 4:

The structures of DOTA-TOC and DOTA-TATE