Induction of Apoptosis in Human Colon Cancer HCT116 Cells Treated with an Extract of the Plant Product, Chios Mastic Gum

Abstract

A hexane extract of the plant product Chios mastic gum (He-CMG) is demonstrated to kill human colon cancer cells in vitro via the process of anoikis. Specifically, the sequence of events includes He-CMG-induced G1-arrest of the cells, detachment of the cells from the substrate and subsequent apoptosis. Anoikis is dependent on the concentration and duration of treatment with He-CMG. Presence of the pan-caspase inhibitor, Z-VAD-fmk, did not prevent cell detachment, but it did prevent apoptosis of the detached cells indicating that the process of cell detachment, but not apoptosis, is independent of caspase activation. He-CMG-induced apoptosis is associated with activation of the initiator caspases-8, and -9 and the effector caspase-3. Caspases are activated in cells at a relatively long time after detachment, and caspase-3 activation may require caspase-8 or caspase-9 activation, as determined by using HCT116 isogenic clones impaired in apoptosis mechanisms that involve these two caspases. Finally, electron microscopy observations indicated a time-dependent appearance of morphological features both typical and non-typical of apoptosis in cells treated with He-CMG for various periods of time. Taken together, the results demonstrated that He-CMG induces apoptosis in HCT116 cells and, therefore, further in vivo and in vitro studies of the anticancer activities of this plant product are warranted.