A study published in Science Translational Medicine shows that small molecules that specifically inhibit an important selenium-containing enzyme may be useful in combating cancer. When researchers at Karolinska Institutet treated cancer in mice using these molecules, they observed rapid tumoricidal effects. Researchers now hope that this new principle for cancer treatment will eventually be developed for use in humans.

Humans need the chemical element selenium for good health. The selenium-containing enzyme thioredoxin reductase 1 (TrxR1) can be used to support the growth of various cells and to protect them from harmful forms of oxygen radicals, known as oxidative stress. Selenium intake has long been a topic of discussion in connection with cancer, although results have proved inconclusive and the correlation between selenium intake and cancer growth is extremely complex.

Raised levels of TrxR1 can be seen in several forms of cancer and are linked to worse prognoses in head and neck, lung, and breast cancers. Researchers therefore analyzed almost 400,000 different molecules in the search for new and more specific TrxR1 inhibitors than those previously available. They discovered three different molecules that met their search criteria. Sure enough, when tested, these same molecules also proved to be active as cancer medicines. It proved possible to effectively treat over 60 different types of cancer cell under laboratory conditions. Normal cells were, however, much less sensitive to these molecules.

Sensitive to oxidative stress

“This effectiveness against cancer may be a result of cancer cells’ seemingly greater sensitivity to oxidative stress when compared to normal cells, which in turn can be utilized in cancer therapy,” says Professor Elias Arnér, Department of Medical Biochemistry and Biophysics at Karolinska Institutet, who led the study.

Researchers also found rapid tumoricidal effects when treating head and neck or breast cancers in mice, without obvious side effects. The new molecules have yet to be tested on humans, but it is already known that several different cancer medicines currently in use, including cisplatin and melfalan, inhibit TrxR1. Thus far, whether or not this inhibition of the enzyme is important to the effectiveness of these medicines has remained unknown, but this study suggests that this might well be the case.

Researchers now intend to further develop the new TrxR1 inhibitors to offer a new form of cancer therapy.