Terbium-161: Radioisotope with twice the radiant power

Terbium and lutetium both belong to the lanthanides, the so-called rare earth metals. Lutetium-177 is a widely used radioisotope. It is contained, for example, in the drug Pluvicto® , which is used to treat prostate cancer. In this drug, the radionuclide is coupled to a low-molecular-weight ligand with a high affinity for prostate-specific membrane antigen (PSMA). The molecule binds to PSMA-expressing tumor cells, is taken up into the cell interior by endocytosis, and releases its radiation there. The β ^- emitter causes DNA damage and, subsequently, cell death.

In the journal "Radiochimica Acta," a team from the University of Missouri in Columbia, USA, presents the new radioisotope terbium-161 in more detail. This is also a β ^- emitter. The similar chemical properties offer advantages. The senior author of the publication, Professor Dr. Heather Hennkens, points out in a press release from the university, for example, that the similarities could enable the integration of terbium into existing treatment approaches without having to develop entirely new drugs.

What distinguishes terbium from its chemical cousin is its ability to deliver a double whammy to cancer cells with its additional low-energy electrons—Auger and conversion electrons. "These electrons travel only very short distances within the tumor, but cause significant damage to the cancer cells," explains Hennkens. This could also be used to treat smaller clusters of metastatic cells and possibly even individual circulating cells.

One Lymph node cancer could become an indication for radionuclide therapy with terbium-161, according to the Paul Scherrer Institute in Villigen, Switzerland. Promising results from experiments with a radiopharmaceutical have been published in the "Journal of Nuclear Medicine." Senior author Dr. Martin Béhé explains in a press release from the institute that terbium-161 is coupled to a CD30 antibody. This antibody binds to the CD30 receptor, which is overexpressed in almost one-third of all patients with lymph node cancer. "In this way, the radioactive terbium is delivered directly to the site of the tumor, where its radioactive radiation kills cancer cells." Healthy organs in the body, however, are spared.

The researchers in Switzerland tested the antibody-bound radioisotope on three types of tumor cells that express CD30 receptors. It was found that the drug killed cancer cells—depending on the cell type—two to 43 times more effectively than the analogous drug containing lutetium-177. Further studies showed that the terbium drug caused more severe damage to cancer cell DNA.

In later studies, cancer-stricken mice received either antibody-bound terbium-161 or lutetium-177. Animals treated with terbium-161 survived on average twice as long as their counterparts injected with the lutetium-177 drug. "Our results provide good evidence that the drug could also prove to be an effective treatment against lymphomas in humans," says lead author Elisa Rioja-Blanco, also from the Paul Scherrer Institute. Clinical trials will have to determine whether this is actually the case.