Radioactive protein ferries against prostate cancer

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If you fight cancer cells with chemotherapy, the healthy cells of the body are also damaged. The result: severe side effects. Scientists have now discovered a protein on prostate cancer cells that could help transport weapons against the cancer directly into the tumor without causing damage elsewhere.

PSMA is the key to the new prostate cancer therapy that is currently being tested in a phase II clinical trial. The abbreviation stands for “prostate specific membrane antigen”. This molecule is found in large numbers on prostate cancer cells and is rarely found on other cells.

Key to the lock

Scientists from the German Cancer Research Center in Heidelberg have developed a so-called “small molecule” that fits PSMA like the key to a lock: PSMA-617. If it is equipped with a highly radioactive substance, it destroys the cancer cells.

In an initial test, doctors administered PSMA-617 to 145 patients via an intravenous infusion. The result: the therapy worked in almost half of the patients (45 percent). The tumor shrank, or at least grew more slowly.

Minor side effects

These and other new methods that target tumor-specific surface molecules are summarized under the umbrella term immunotherapy. "Based on the experience that we have so far, the therapy is safe and effective with relatively few pronounced side effects," says Professor Bernd Joachim Krause, President of the German Society for Nuclear Medicine, to Because unlike chemotherapy, for example, it ideally leaves the healthy body cells on which this antigen does not sit undisturbed.

Metastases found

He also emphasizes another possible application of PSMA-617: "It enables the tumor disease to be made visible throughout the body." To do this, the PSA-617 is marked as weakly radioactive and then a computed tomography (CT) is performed. Doctors already use the procedure when the tumor marker PSA in a cancer patient's blood rises again and it is not known where the cancer has spread again.

Currently only for study patients

Further clinical studies are pending before every patient can receive PSMA-617 as a cancer therapy. For this reason, the procedure can currently only be used if all other therapeutic measures such as hormone therapy and chemotherapy have failed. Incidentally, specific surface proteins have also been discovered in thyroid cancer and so-called neuroendocrine tumors. In the future, these could also be treated with specific radioactive radiation.

Source: Press release of the German Society for Nuclear Medicine: "Prostate Cancer: Worldwide Response to New Forms of Diagnosis and Therapy", 23.01.2017.

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