Chlorogenic Acid and Its Microbial Metabolites Exert Anti -Proliferative Effects, S-Phase Cell-Cycle Arrest and Apoptosis in Human Colon Cancer Caco-2 Cells

Chlorogenic acid (CGA) decreases colon cancer-cell proliferation but the combined anti-cancer effects of CGA with its major colonic microbial metabolites, caffeic acid (CA), 3-phenylpropionic acid (3-PPA) and benzoic acid (BA), needs elucidation as they occur together in colonic digesta. Caco-2 cancer cells were treated for 24 h with the four compounds individually (50-1000 mu M) and as an equimolar ratio (1:1:1:1; MIX). The effective concentration to decrease cell proliferation by 50% (EC50) was lower for MIX (431 +/- 51.84 mu M) and CA (460 +/- 21.88) versus CGA (758 +/- 19.09 mu M). The EC50 for cytotoxicity measured by lactate dehydrogenase release in MIX (527 75.34 mu M) showed more potency than CA (740 +/- 38.68 mu M). Cell proliferation was decreased by 3-PPA and BA at 1000 mu M with no cytotoxicity. Cell-cycle arrest was induced at the S-phase by CA (100 mu M), MIX (100 mu M), CGA (250 mu M) and 3-PPA (500 mu M) with activation of caspase-3 by CGA, CA, MIX (500 and 1000 PM). Mitochondrial DNA content was reduced by 3-PPA (1000 mu M). The anti-cancer effects occurred at markedly lower concentrations of each compound within MIX than when provided singly, indicating that they function together to enhance anti-colon cancer activities.