Terpenoids Isolated From the Shoot of Plectranthus hadiensis Induces Apoptosis in Human Colon Cancer Cells Via the Mitochondria-Dependent Pathway

The plant Plectranthus hadiensis is a rich source of many bioactive phytochemicals, especially terpenoids. The terpenoid fraction was isolated and phytochemical characterization was done using GC-MS. The aim of the present study was to find out the antiproliferative activity and the mechanism of cell death induction by the terpenoid fraction on human colon cancer cells (HCT-15). MTT assay was performed with different concentrations of the fraction (10, 20, and 50 µg/mL) to obtain IC50 value for 24 h to induce cell death. The induction of apoptosis were studied by Hoechst staining, acridine orange/ethidium bromide staining, Comet assay, DNA fragmentation, and caspase-3 activity assays. The mechanism of apoptosis induction was studied by expression analysis of antiapoptotic Bcl-2 and proapoptotic Bax using RT-PCR and also by Western blot analysis of proteins involved in the apoptotic pathway. The terpenoid fraction induced significant morphological changes and DNA fragmentation in the cells. Positive Hoechst staining and acridine orange/ethidium bromide staining indicated apoptosis induction by the fraction. DNA fragmentation, which is a characteristic feature of apoptosis, was also observed. Upregulation of caspase-3 activity and proapoptotic Bax, and the downregulation of antiapoptotic Bcl-2 and COX-2 confirmed that the apoptosis induction was via the mitochondria-dependent pathway.