Cytotoxic activity of Thymus capitatus collected from Hail region in Saudi Arabia with mechanistic study via induction of caspase-dependent apoptosis and S-phase arrest

Thymus capitatus is a plant grows in Mediterranean area and some Arab countries such as Saudi Arabia. It possesses numerous medicinal values. Its common name is Zaatar and it belongs to family Lamiaceae Thymus capitatus leaves and stem were collected from Hail region, Saudi Arabia. Then both leaves and stem were extracted with ethanol. This study was performed to evaluate cytotoxic activity of Thymus capitatus leaves and stem ethanolic extract in details. Doxorubicin was used as a standard and the relevant half maximal inhibitory concentration (IC50) values were computed for each cell line by 3-(4,5- diemthylthiazole-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. In addition, further mechanistic study was carried out by using Apoptosis assay to explore cytotoxic activity of plant extract. Both leaves and stems extracts were screened against HepG2, A-549, HCT-116 and   MCF-7 cancer cell lines. It was found that leaves’ extract shows high and moderate cytotoxic activity against both A-549 and HepG2 cancer cell lines, respectively (with IC50 = 13.6 and 21.5 μg/ml, respectively), while stem’s extract exerted moderate cytotoxic activity against A-549 cancer cell lines (with IC50 = 21.38 μg/ml).  Further mechanistic study was carried out on A-549 cells by using apoptosis assay. It showed that leaves’ extract resulted in arrest of S-phase and caused apoptosis through activation of caspase-3, p53 and Bax, in addition to down regulation of Bcl-2.