Sesquiterpene lactones-enriched fraction of Inula helenium L. induces apoptosis through inhibition of signal transducers and activators of transcription 3 signaling pathway in MDA-MB-231 breast cancer cells.

Inula helenium L., commonly known as Elecampane, has been extensively used for many countries in the folk medicine. Its root is a rich source of sesquiterpene lactones, which possess various pharmacological activities. To develop the phytomedicine including sesquiterpene lactones, we prepared hexane fraction from I. helenium (HFIH) and examined the inhibitory effect of HFIH on signal transducers and activators of transcription 3 (STAT3) activation in human breast cancer MDA-MB-231 cells. Additionally, detailed chemical investigation was done to pinpoint the most active sesquiterpene lactones responsible for its anticancer activity. HFIH selectively suppressed STAT3 phosphorylation at tyrosine 705, not affecting its upstream kinases. HFIH downregulated the expression of STAT3 target genes including cyclin D1 , c-myc, and bcl-2 and induced caspase-mediated apoptosis. Moreover, sesquiterpene lactones of HFIH clearly suppressed STAT3 activation. The in vivo results further supported that HFIH inhibits the growth of human breast xenograft tumors. Our results suggest that HFIH possesses potential anticancer activity, which is mainly mediated through STAT3 signaling pathway. These findings provide the potential of HFIH as a promising phytomedicine for the treatment and prevention of triple-negative breast cancer.