Natural Sesquiterpene Lactones Induce Apoptotic Cell Death in Prostate Cancer Cells In Vitro and In Vivo

Sesquiterpene lactones are natural compounds, usually derived from oleogum resins, which have been frequently used in traditional medicine to mitigate inflammatory diseases. Besides, putative anticancer activities of sesquiterpene lactones have been described. We isolated and characterized sesquiterpene lactones from Artemisia glabella and aimed to investigate their efficacy against prostate cancer cells. We used a variety of biological tests to characterize cell death in vitro and in vivo . Whereas all tested prostate cancer cell lines were sensitive to the selected sesquiterpene lactones, non‐tumorous prostate epithelial cells remained unaffected indicating cancer cell selectivity. Flow cytometric measurements revealed that exposure to sesquiterpene lactones triggered apoptosis as indicated by the activation of caspase‐3 and the binding of annexin‐V to phosphatidylserine on the outer leaflet of the cell membrane. These findings were translated into a preclinical in vivo model: Prostate cancer cells were xenotransplanted onto chorioallantoic membranes (CAMs) of fertilized chick eggs and solid tumors were treated with sesquiterpene lactones at different concentrations. To assess the therapeutic response, tumor xenografts were collected and analyzed histologically by using Ki‐67 as a marker of proliferative cells and TUNEL staining to detect DNA fragmentation indicative of cancer cell apoptosis. After repeated administration of sesquiterpene lactones, prostate cancer xenografts contained a significantly lower fraction of Ki‐67 positive proliferative cells and a higher proportion of apoptotic TdT positive cells. To address how sesquiterpene lactones exert their cytotoxic activity on the molecular level, we performed Western immunoblotting showing changes in oncologically relevant signalling pathways. In particular, we observed interference of sesquiterpene lactones with the mTOR pathway already after a short incubation time. The mTOR pathway is regulated by different cytokines, e.g. by TNF‐α. Although the primary role of TNF‐α is in the regulation of immune cells, available evidence suggests that it also promotes the proliferation of cancer cells. TNF‐α mediates its biological activity by distinct signaling pathways, e.g. the by the transcription factor nuclear factor κB (NF‐κB), which protects cancer cells from apoptosis. We used NF‐κB reporter cells and observed that sesquiterpene lactones from Artemisia glabella are able to suppress NF‐κB expression in prostate cancer cells. Our data suggest that sesquiterpene lactones from Artemisia glabella mediate cancer cell‐selective apoptosis by inhibition of TNF‐α‐dependent NF‐κB und mTOR. Thus, these natural compounds warrant further investigation for their potential application in the clinical treatment of cancer diseases. Support or Funding Information This work was supported by the Academic Center for Complementary and Integrative Medicine (AZKIM), State Ministry of Baden‐Württemberg for Sciences, Research and Arts. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .