Cytotoxic activity of polyacetylenes and polyenes isolated from roots of Echinacea pallida

Abstract

Background and purpose: The n-hexane extracts of the roots of three medicinally used Echinacea species exhibited cytotoxic activity on human cancer cell lines, with Echinacea pallida found to be the most cytotoxic. Acetylenes are present in E. pallida lipophilic extracts but essentially absent in extracts from the other two species. In the present study, the cytotoxic effects of five compounds, two polyacetylenes (namely, 8-hydroxy-pentadeca-(9E)-ene-11,13-diyn-2-one (1) and pentadeca-(9E)-ene-11,13-diyne-2,8-dione (3)) and three polyenes (namely, 8-hydroxy-pentadeca-(9E,13Z)-dien-11-yn-2-one (2), pentadeca-(9E,13Z)-dien-11-yne-2,8-dione (4) and pentadeca-(8Z,13Z)-dien-11-yn-2-one (5)), isolated from the n-hexane extract of E. pallida roots by bioassay-guided fractionation, were investigated and the potential bioavailability of these compounds in the extract was studied.

Experimental approach: Cytotoxic effects were assessed on human pancreatic MIA PaCa-2 and colonic COLO320 cancer cell lines. Cell viability was evaluated by the WST-1 assay and apoptotic cell death by the cytosolic internucleosomal DNA enrichment and the caspase 3/7 activity tests. Caco-2 cell monolayers were used to assess the potential bioavailability of the acetylenes.

Key results: The five compounds exhibited concentration-dependent cytotoxicity in both cell types, with a greater potency in the colonic cancer cells. Apoptotic cell death was found to be involved in the cytotoxic effect of the most active, compound 5. Compounds 2 and 5 were found to cross the Caco-2 monolayer with apparent permeabilities above 10 x 10(-6) cm s(-1).

Conclusions and implications: Compounds isolated from n-hexane extracts of E. pallida roots have a direct cytotoxicity on cancer cells and good potential for absorption in humans when taken orally.

Figure 1

Chemical structures of the compounds isolated from E. pallida roots.

Figure 2

Apoptotic and necrotic cell death after treatment with compound 5 for 24 h on MIA PaCa-2 (30 μM) (a) and COLO320 (2.5 μM) (b) cells. Caspase 3/7 activity (C3/7) and internucleosomal fragmentation (IF) were expressed as fold stimulation and as enrichment factor of nucleosomal fragments versus untreated cells, respectively. Data are means±s.e. from three independent experiments each run in triplicate. ^*P<0.05; ^**P<0.01, versus untreated cells.

Figure 3

Transport kinetics of acetylenes in the E. pallida root extract through Caco-2 monolayers during a 2.5 h incubation. Values are means±s.e. from three preparations each run in triplicate. Compound 2: 8-hydroxy-pentadeca-(9E,13Z)-dien-11-yn-2-one; compound 5: pentadeca-(8Z,13Z)dien-11-yn-2-one; compound 6: tetradec-(8Z)-ene-11,13-diyn-2-one.