Toxicological Effects of Thymoquinone in Combination With Celecoxib and Irinotecan on DNA Damage, Oxidative Stress, G2/M Arrest, Apoptosis, and Inflammatory Response in SW620 Cells

Although the effect of thymoquinone (TQ), the biologically active component of black cumin seeds, has been investigated in many types of cancer, its effects on molecular pathways of cancer cells further need to be elucidated. This study aimed to investigate the effects of TQ on genotoxicity, oxidative stress, apoptosis, and inflammatory pathways in SW620 cells treated with irinotecan (IR), celecoxib (Clx), individually or both. DNA damage, oxidative stress/inflammatory response, cell cycle, apoptosis, and expression of carcinogenesis-related genes were determined using the Comet assay, ELISA assay, flow cytometry, and RT-PCR techniques, respectively. TQ (8 µM) combination with IR (8 µM) + Clx (4 µM) significantly increased cytotoxicity and genotoxicity of IR with/without Clx, while decreasing oxidative stress and inflammatory responses. TQ upregulated p21 and Bax, while downregulating Bcl-2 and Bcl-XL, increasing Bax/Bcl-2 ratio, which indicates an induction of apoptotic pathways. TQ also increased the percentage of cells in G2/M phase and decreased those in G0/G1 phase, thereby affecting cell cycle checkpoints in IR-treated cells with or without Clx. In conclusion, this study shows that the combination of TQ with IR, Clx, or both exerts significant effects on SW620 colon cancer cells, such that by enhancing DNA damage, TQ may induce G2/M cell cycle arrest and apoptosis, while reducing inflammatory responses, oxidative stress, and G0/G1 cell cycle arrest. These in vitro findings indicate that TQ may enhance the chemotherapeutic effects of IR and act as a potential adjuvant therapy; however, further in vivo studies are required to verify its suggested effects.