BACKGROUNDThymoquinone (TQ) and beta-sitosterol (BS), the bioactive constituents derived from the medicinal plant Atragene sibirica L, Ranunculus repens L, Pulsatilla Bungeana have been used for anti-cancer treatment in Traditional Mongolian Medicine. Recent studies reported that TQ, BS exhibited anti-proliferative effects on several cancer cell lines. This study was performed to investigate the antitumor effects of phytochemicals on gastric adenocarcinoma in vitro.METHODSTo this aim, we performed a cell apoptosis assay WST1 and several cancer-related gene expressions (Bcl, BIRC5, p53, BAX). NCI-N87, MKN74 cells were seeded at a density of 5×104 cells per well in 96-well culture plates. After overnight incubation, the fresh medium containing different concentrations of TQ (20, 40, 60, 80, and 100 mM/ml) and beta-sitosterol (10, 1, 0.1, 0.001, 0.001 mM/ml) were applied. Following a 24-h incubation, the cell viability was determined by WST-1 assay. We also quantified the expression levels of mRNAs of these genes through qRT-PCR experiments.RESULTSOur results showed that TQ induced a higher percentage of cell apoptosis in the human gastric adenocarcinoma cell lines compared to that of control. We observed a significant 4.8-fold change in BAX/BCL2 ratio. These increases were highly correlated with a concentration-dependent manner (p=0.00178). Moreover, the expression of p53 and BIRC5 was downregulated in MKN74 cells after treatment with TQ.CONCLUSIONSOur results demonstrate that TQ effectively inhibits cell proliferation through several gene expressions in vitro. Moreover, inhibition of the downstream molecule of these genes would explain the underlying mechanism of the antitumor activity in cancer cell lines.