Anthrax toxins have attracted considerable attention as potential anticancer agents due to their ability to specifically target and kill tumor cells. However, the clinical development of these toxins has been limited because the mechanisms underlying their antitumor effects have been unclear, and because their long-term use is precluded by the body’s strong immune response against these foreign proteins.

Researchers examined the antitumor effects of anthrax toxins, and found that combined treatment with immunosuppressive drugs enables multiple cycles of therapy and reduction in tumor growth.

Using genetic mouse models, the authors found that anthrax toxins reduce tumor growth by binding to capillary morphogenesis protein-2 on tumor endothelial cells, thereby inhibiting the formation of new blood vessels.

Moreover, the antitumor effects of anthrax toxins in mice with an aggressive form of lung cancer were enhanced by combined treatment with immunosuppressants called pentostatin and cyclophosphamide. These two clinically approved drugs selectively depleted B-cell populations and eliminated toxin-neutralizing antibodies, enabling five cycles of therapy over the course of 42 days.

According to the authors, combined treatment with anthrax toxins and immunosuppressive drugs could lead to strong, long-term reductions in tumor growth and may warrant further investigation in clinical trials for a broad spectrum of cancers.

http://www.pnas.org/content/early/2016/06/28/1600982113