Induction of apoptosis by γ-humulene in HT29 human colorectal carcinoma cell lines

The present study was designed to investigate whether γ-humulene exerts cytotoxic activity against colorectal cancer cells by inducing apoptosis and to examine the possible mechanism in the phenomenon. Inhibition of proliferation of γ-humulene on HT29 colorectal cancer cells was determined by the MTT assay. Apoptosis of γ-humulene-treated cells was determined by morphological analysis and quantities by flow cytometry after staining with propidium iodide (PI). Cell cycle and the cell surface expression of the CD95/CD95 ligand were evaluated by flow cytometry. Caspase activities were also analyzed. Results: Treatment with γ-humulene of colorectal cancer cells not only inhibited cell proliferation, but also induced apoptosis. Treatment with γ-humulene resulted in an up-regulation of the CD95 receptor and CD95L on the cell surface. γ-humulene-treated cells showed the activation of caspase-8 and caspase-3. Both zVAD-FMK (a broad range caspase inhibitor) and IETD-FMK (a caspase-8 inhibitor) showed apparent inhibition of the apoptosis-inducing effect. Our results suggest that γ-humulene triggers apoptosis in colorectal cancer cell lines via the activation of the CD95 receptor/ligand system, and that this agent may be useful for developing new therapeutic regimens for the treatment of colorectal carcinoma.