Helenalin - a sesquiterpene lactone with multidirectional activity.

Sesquiterpene lactones, secondary metabolites of plants, present in a large number of species mostly from the Asteracea family, were used in the traditional medicine of many countries for the treatment of various pathological conditions. They exert a broad range of activities, including anti-inflammatory, anti-bacterial and anti-cancer properties. The best known sesquiterpene lactones which are already used as drugs or are in clinical trials are artemisinin, thapsigargin and parthenolide. Yet another sesquiterpene lactone, helenalin, an active component of Arnica montana, known for its strong anti-inflammatory activity, has been used for centuries in folk medicine to treat minor injuries. Unfortunately, helenalin's ability to cause allergic reactions and its toxicity to healthy tissues prevented so far the development of this sesquiterpene lactone as an anticancer or antiinflammatory drug. Recently, the new interest in the biological properties, as well as in the synthesis of helenalin analogs has been observed. This review describes helenalin's major biological activities, molecular mechanisms of action, its toxicity and potential for further research.