Radioactive isotopes (or radioisotopes) have been employed for cancer treatment for years, with radioactive iodine being used to treat tumours of the thyroid gland since the 1950s.

However, the vast majority (90 percent) of radioisotopes used in medicine are used merely for diagnoses -- radioactive materials are injected into the body and then radiation-detecting cameras are used to build images of affected body parts or particular types of cells.

Now a new wave of radiopharmaceuticals is being used to provide targeted cancer therapies that minimise damage to other, healthy cells. Radiopharmaceuticals are comprised of a bioconjugate -- a biological "bloodhound" that targets specific cells -- and a radioactive isotope that kills the cells.  

Researchers at the Institut Laue-Langevin (ILL) have been working to create targeted, cancer-killing radioisotopes that can be attached to biological entities (the bioconjugates) that target specific cancer cells.

Traditionally, surgery and radiation therapy are often enough to treat primary stage cancers and chemotherapy that tends to be used to treat cancer when it has metastasised.

Ulli Köster, a researcher at ILL, explains: "If there is metastasis then you can't address it with surgery or radiation therapy. You have to make a systemic treatment. For a long time this has been chemotherapy."

Chemotherapy doesn't specifically attack cancer -- it destroys many cells in the hope that healthy ones recover more quickly. It can be incredibly effective in some cancers, for example testicular, where it works on 95 percent of cases, but has an over all success rate of 5-15 percent.

Köster explained: "If you have surgery and have a certain number of cancer cells, if you take it out then you have no cancer cells left. Or you use radiotherapy to irradiate those remaining cells. But chemotherapy on one cycle can push down the number by a few orders of magnitude, but then they multiply and eventually you can't repeat chemo for fear of damage to the healthy cells."

Researchers in more targeted medicine take advantage of the particular makeup of the surface of cancer cells, which distinguish themselves from other cells with special receptors. These might be antigens or peptide receptors. A huge industry worth more than $10bn a year has emerged around trying to identify suitable peptides or antibodies (both classified as bioconjugates) to target these receptors.

But it's a tough task to find an antibody that not only targets the cancer but also has a therapeutic action, either killing it or stopping it from multiplying. Köster explains: "It's a very special agent that can not only find the bad guy but also kill him, it's a kind of 007."

While many antibodies and peptides (markers) are capable of finding the cancer cells, not many are capable of killing them. But with radiopharmaceuticals, you separate the tasks of finding and killing the cancer. One would need to discover a marker that locates the cancer and then combine it with a radioisotope to kill it.

This new type of therapy means that you can check that the patient has the specific type of cancer cell that will respond to the treatment before pumping them with radioactive drugs. You would need to send in a bioconjugate filled with just an imaging isotope first to check that it's targeting the correct cells. Once this is ascertained, you can put the therapy isotope into the bioconjugate.


  1. hieeeeeee  

    Jan 28th 2013

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