Effective Results with Actinium Alpha Therapy in Stage 4 Prostate Cancer

In advanced, metastatic castration (hormone suppression)-resistant prostate cancer, treatment options for men are limited, but a new protocol emitting radioactive alpha waves, actinium therapy , offers hope. Studies whose results were published in 2017 and 2018 reported that patients with prostate-specific membrane antigen (PSMA)-positive tumors benefited more from targeted alpha therapy called actinium-225 than from beta-emitting lutetium therapy.

What is actinium?

Actinium is a radioactive element in group 3B and period 7 of the periodic table, with atomic number 89 and atomic weight 227. Actinium-225 is an isotope of actinium emitting radioactive alpha waves.

How is actinium therapy performed in prostate cancer?

Molecular applications of nuclear medicineprovide imaging and treatment by attaching radioactive substances to cell-specific receptors . Most prostate cancer cells carry prostate-specific membrane antigen (PSMA) on their surface. In actinium therapy, actinium-225, an isotope emitting short-wavelength alpha radiation with cell-killing properties, binds to the prostate cancer cell through PSMA using a carrier molecule and destroys it. This procedure is performed using a PET-BT device and is called PSMA-Actinium-225 (Ac-225) PET-BT .

"Standard" imaging, currently regarded as the best imaging method in cancer, PET-BT is not sufficiently successful at evaluating prostate cancer. This is because standard PET-BT uses glucose, meaning sugar, and prostate cancer cells use little sugar. PSMA-PET, however, uses a protein called prostate-specific membrane antigen (PSMA) on prostate cancer cells to capture and image that protein. For this new method, a molecule combining an antibody-type carrier binding to PSMA and a radioactive substance was developed. The antibody binds to PSMA, and the attached radioactive substance (for example, actinium-225) provides both imaging and destruction of the cancer cell. Theoretically, even a single cell spread throughout the body (metastasized ) can be captured with this method.

In February 2018, Journal of Clinical Oncologypublished a study showing that actinium-225 therapy may be more effective than lutetium-177, another targeted molecular radionuclide treatment. The study included patients previously treated with at least 3-4 lines of therapy: 11 patients with metastatic prostate cancer. Median overall survival with actinium therapy was 12.6 months. Of the 11 patients, 8 had a PSA response exceeding 50%. All patients experienced moderate (grade 2-3) xerostomia (dry mouth) as an adverse effect.

In conclusion, PSMA-Ac-225 therapy produced notable clinical, biochemical and radiological responses in patients with advanced metastatic prostate cancer and may be considered a promising treatment for this patient group. 

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