ScienceDaily — The effective treatment of many forms of cancer continues to pose a major problem for medicine. Many tumours fail to respond to standard forms of chemotherapy or become resistant to the medication. Scientists at the Helmholtz Centre for Infection Research (HZI) in Braunschweig, the Hannover Medical School (MHH) and Leibniz-Universität (LUH) in Hanover have now discovered a chemical mechanism with which a natural substance - argyrin - destroys tumours.