New research suggests that a drug originally designed to treat the sexually transmitted infection gonorrhoea may provide a new and unexpected form of cancer treatments.
Acriflavine, which was used in the 1930s, appears to stop the growth of new blood vessels, which are required by tumours to provide oxygen for cell division.
Laboratory tests have revealed that cancer-prone mice which were treated with daily injections of acriflavine showed no signs of cancer growth.
Dr Jun Liu, professor of pharmacology and molecular sciences at Johns Hopkins University School of Medicine, commented: "Oftentimes we are surprised that a drug known to do something else has another hidden property.
"Mechanistically, this is the first drug of its kind."
The drug appears to work by blocking a protein called hypoxia-inducible factor (HIF)-1, which turns on genes for building new blood vessels when it senses that oxygen levels are low.
The researchers, whose findings are published in the Proceedings of the National Academy of Sciences, hope that acriflavine may one day be combined with chemotherapy drugs to provide a more potent form of cancer treatment.
Acriflavine was used during the first world war to treat sleeping sickness and is also used to treat fungal infections in aquarium fish.