Actinium-225 ion (Ac-225)

Actinium-225 ion (Ac-225) is a radioactive isotope of actinium that exists as a trivalent cation (Ac^3+^) in chemical processes[9]. It emits alpha particles during its decay, making it highly cytotoxic at a micro-environmental level[2][3][4]. Actinium-225 is synthetically produced in cyclotrons or nuclear reactors, with a half-life of about 9.92 days[4][7][8]. It is used as a radionuclide component rather than as a molecular therapeutic target: in radiopharmaceutical applications, acts as a payload for tumor-targeted alpha particle therapy (TAT), attached to targeting molecules (such as antibodies against tumor antigens) via chelators[1][2][3][4]. Upon localization to a tumor, the decay chain of Ac-225 releases four alpha particles, leading to potent double-stranded DNA breaks in nearby cells and resulting in cell death[1][3][4][5][8]. It has shown preclinical and clinical efficacy in solid and hematologic malignancies such as prostate cancer, leukemia, neuroendocrine tumors, and brain tumors[2][4][6]. However, it is not itself a receptor, transporter, enzyme, or similar therapeutic target class, but rather a radioactive ion used for delivery of cytotoxic radiation. Safety concerns include systemic radiotoxicity when progeny escape the target site, as well as challenges in chelation chemistry to ensure all decay products remain localized[1][4][5]. Key clarifications: - Actinium-225 ion is not a classical therapeutic target (e.g., not a receptor, transporter, or enzyme), but a radionuclide payload for targeted radiotherapy[2][3][4][8][9]. - Often, radiolabeled drug constructs (e.g., [^225Ac]Ac-PSMA, [^225Ac]Ac-J591) are the therapeutics, with the biological targeting conferred by the molecule, while Ac-225 provides the cytotoxic effect[1][3][4]. If you require information on a specific molecular target (receptor, transporter, etc.) against which Actinium-225-labeled agents are directed (e.g., “Prostate-specific membrane antigen receptor,” “CD33 antigen”), please clarify.

Other names

^225AcAc-225Actinium-225