Identification of urushiols as the major active principle of the Siddha herbal medicine Semecarpus Lehyam: Anti-tumor agents for the treatment of breast cancer.

Breast cancer (BCa) is the most commonly occurring cancer in women, comprising almost one third of all malignancies. Previously we reported that the n-hexane fraction (hSL) of the Siddha herbal medicine, Semecarpus Lehyam, relatively sensitized estrogen receptor-negative (ER(-)) BCa when compared to estrogen receptor-positive (ER(+)) BCa cells. In this study we used a bioassay-guided fractionation approach leading to a simplified fraction of hSL that effectively sensitized both ER(+) (MCF-7) and ER(-) (MDA-231) BCa cells. Further bioassay-guided isolation led to the purification of three potent anti-cancer components from hSL which significantly induced apoptosis in both the BCa cell lines. Their structures were identified through NMR and mass spectroscopic analysis as (7;Z,10;Z)-3-pentadeca-7,10-dienyl-benzene-1,2-diol (1), (8;Z)-3-pentadec-10-enyl-benzene-1,2-diol (2) and 3-pentadecyl-benzene-1,2-diol (3). Compounds (1) and (2) turned out to be more active than (3). The overall results of this study suggest that these major components of hSL may be solely responsible for the anti-tumor effect of SL.