Bufadienolides from Helleborus foetidus and their cytotoxic properties on MCF-7 breast cancer cells

Twelve bufadienolides and six 19-norbufadienolides were isolated from the aerial parts of Helleborus foetidus. They consist of aglycons and glucosides and include nine previously undescribed compounds and a compound reported for the first time as a genuine natural product. Their structures were established by extensive spectroscopic analysis and the structure and absolute configuration of two previously unreported 3,4-epoxy derivatives were confirmed by single crystal X-ray diffraction analysis. The compounds were tested for their cytotoxicity on MCF-7 human breast cancer cells. They show differential cytotoxic activity with IC₅₀ values in the range of 2.4 nM - >10 μM. The potency of the activity strongly correlates with the presence of a C-19 aldehyde group. The data complement the scientific basis underpinning the use of H. foetidus in anthroposophic medicine for the integrative treatment of cancer.