Caffeic Acid Phenethyl Ester (CAPE) inhibits growth of head and neck squamous cancer stem cells

Purpose: Cancer stem cells are resistant to chemotherapy and radiotherapy and are implicated in tumor relapse and high patient mortality. Substances impairing cancer stem cell activity could be very useful as novel cancer therapeutics. Caffeic acid phenethyl ester (CAPE), a component of propolis, whose antitumor activity has been confirmed in several tumor types in vitro, has recently been shown to inhibit the growth of some cancer stem cell types. Methods: An ALDH1-positive fraction was isolated from UT-SCC-74A cells as cancer stem cells by magnetic-activated cell sorting. The isolated cells were characterized by sphere formation assay and biomarkers of cancer stem cells were analyzed by quantitative RT-PCR. To demonstrate the effect of CAPE on head and neck squamous cancer stem cells, XTT cell viability assays were performed. Results: Increasing concentrations of CAPE decrease the viability of head and neck squamous cancer stem cells. IC50 value was calculated from XTT results as 50.29 mu g/ml. Conclusion: CAPE has a growth inhibitory effect on head and neck squamous cancer stem cells in vitro.