Cytotoxic effects of polyacetylenes from E. pallida on human cancer cell lines and their bioavailability through Caco-2 cell monolayers

In previous studies, root hexanic extracts from the three medicinal Echinacea species (E. purpurea, E. pallida and E. angustifolia) exhibited a cytotoxic activity on human cancer cell lines and E. pallida was found to be the most cytotoxic one. Moreover, E. pallida root hexanic extract contains polyacetylenes, which are almost absent in the other two species of Echinacea where alkylamides are the main constituents. In the present study the cytotoxic effects of polyacetylenes single compounds isolated by a bio-guided assay fractionation from an E. pallida hexanic extract and their potential bioavailability were investigated. Antitumoral effects were assessed on human pancreatic MIA PaCa-2 and colonic COLO320 cancer cell lines. Cell viability was evaluated by the colorimetric WST-1 assay and apoptotic cell death was evaluated by an immunoenzimatic analysis of the cytosolic internucleosomal DNA enrichment and by the caspase 3/7 activity test. Bioavailability was studied using the Caco-2 cell monolayer, an in vitro model of intestinal permeability. All the isolated compounds exhibited a concentration- and time-dependent cytotoxicity (1-100 µM; 24-72h) in both cell types and a greater potency on colonic cancer cells was observed. Apoptotic cell death was demonstrated to be involved in the cytotoxic effect of the most active polyacetylene, as revealed by both the assays used. Finally, polyacetylenes were found to cross the Caco-2 monolayer suggesting a likely bioavailability when taken orally. In conclusion, our data demonstrate, for the first time, an anticancer activity of constituents from E. pallida root hexanic extract and suggest their potential in vivo bioavailability.