title: Thymoquinone inhibits growth of human medulloblastoma cells by inducing oxidative stress and caspase-dependent apoptosis while suppressing NF-κB signaling and IL-8 expression.
abstract: Medulloblastoma (MB) is the most common malignant brain tumor of childhood. The transcription factor NF-κB is overexpressed in human MB and is a critical factor for MB tumor growth. NF-κB is known to regulate the expression of interleukin-8 (IL-8), the chemokine that enhances cancer cell growth and resistance to chemotherapy. We have recently shown that thymoquinone (TQ) suppresses growth of hepatocellular carcinoma cells in part by inhibiting NF-κB signaling. Here we sought to extend these studies in MB cells and show that TQ suppresses growth of MB cells in a dose- and time-dependent manner, causes G2M cell cycle arrest, and induces apoptosis. TQ significantly increased generation of reactive oxygen species (ROS), while pretreatment of MB cells with the ROS scavenger N-acetylcysteine (NAC) abrogated TQ-induced cell death and apoptosis, suggesting that TQ-induced cell death and apoptosis are oxidative stress-mediated. TQ inhibitory effects were associated with inhibition of NF-κB and altered expression of its downstream effectors IL-8 and its receptors, the anti-apoptotic Bcl-2, Bcl-xL, X-IAP, and FLIP, as well as the pro-apoptotic TRAIL-R1, caspase-8, caspase-9, Bcl-xS, and cytochrome c. TQ-triggered apoptosis was substantiated by up-regulation of the executioner caspase-3 and caspase-7, as well as cleavage of the death substrate poly(ADP-ribose)polymerase. Interestingly, pretreatment of MB cells with NAC or the pan-caspase inhibitor zVAD-fmk abrogated TQ-induced apoptosis, loss of cyclin B1 and NF-κB activity, suggesting that these TQ-mediated effects are oxidative stress- and caspase-dependent. These findings reveal that TQ induces both extrinsic and intrinsic pathways of apoptosis in MB cells, and suggest its potential usefulness in the treatment of MB.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh, 11451, Kingdom of Saudi Arabia. aeashour@yahoo.com.
authors.forename: Abdelkader E
authors.initials: AE
authors.lastname: Ashour
authors.affiliation: Department of Pharmacognosy, College of Pharmacy, King Saud University, Riyadh, Kingdom of Saudi Arabia.
authors.forename: Atallah F
authors.initials: AF
authors.lastname: Ahmed
authors.affiliation: Vitiligo Research Chair, College of Medicine, King Saud University, Riyadh, Kingdom of Saudi Arabia.
authors.forename: Ashok
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh, 11451, Kingdom of Saudi Arabia.|Cell Biology Department, National Research Centre, Cairo, Egypt.
authors.forename: Khairy M A
authors.initials: KM
authors.lastname: Zoheir
authors.affiliation: Medical and Molecular Genetics Research Chair, Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, King Saud University, Riyadh, Kingdom of Saudi Arabia.|Biochemistry Department, Faculty of Agriculture, Cairo University, Giza, Egypt.
authors.forename: Mourad A
authors.initials: MA
authors.lastname: Aboul-Soud
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh, 11451, Kingdom of Saudi Arabia.
authors.forename: Sheikh F
authors.initials: SF
authors.lastname: Ahmad
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, King Saud University, P.O. Box 2457, Riyadh, 11451, Kingdom of Saudi Arabia.|Department of Pharmacology and Toxicology, College of Pharmacy, Al-Azhar University, Cairo, Egypt.
authors.forename: Sabry M
authors.initials: SM
authors.lastname: Attia
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, Al-Azhar University, Cairo, Egypt.
authors.forename: Adel R A
authors.initials: AR
authors.lastname: Abd-Allah
authors.affiliation: Department of Oncology, Karmanos Cancer Institute, Wayne State University, Detroit, MI, USA.
authors.forename: Vino T
authors.initials: VT
authors.lastname: Cheryan
authors.affiliation: Department of Oncology, Karmanos Cancer Institute, Wayne State University, Detroit, MI, USA.|John D. Dingell Veterans Affairs Medical Center, Detroit, MI, USA.
authors.forename: Arun K
authors.initials: AK
authors.lastname: Rishi
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones / Q000494:pharmacology*; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics; D008527:Medulloblastoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics
chemical_list: D016227:Benzoquinones; C508606:CXCL8 protein, human; D016209:Interleukin-8; D016328:NF-kappa B; D009363:Neoplasm Proteins; D020169:Caspases; C003466:thymoquinone
keywords: Apoptosis; Cancer; Daoy cells; Medulloblastoma; NF-κB; Thymoquinone