Studies on molecular mechanisms of growth inhibitory effects of thymoquinone against prostate cancer cells: role of reactive oxygen species.
Thymoquinone (TQ), an active ingredient of black seed oil (Nigella Sativa), has been shown to possess antineoplastic activity against a variety of experimental tumors. However, the precise mechanism of action of TQ is not known. We investigated the mechanism of action of TQ in androgen receptor (AR)-independent (C4-2B) and AR naïve (PC-3) prostate cancer cells, as models of aggressive prostate cancers. Exposure (24-48 h) to TQ (25-150 micromol/L) inhibited the growth of both C4-2B and PC-3 cells, with IC(50) values of approximately 50 and 80 micromol/L, respectively. Within one hour, TQ increased reactive oxygen species (ROS) levels (3-fold) and decreased glutathione (GSH) levels (60%) in both cell types. Pretreatment with N-acetylcysteine (NAC) inhibited both TQ-induced ROS generation and growth inhibition. TQ did not increase the activity of caspases and the caspase inhibitor, z-VAD-FMK did not decrease TQ-induced apoptosis. Furthermore, although TQ treatment resulted in the activation of Jun kinase (JNK), pretreatment with the JNK inhibitor, SP600125, did not protect cells from TQ. However, TQ significantly up-regulated the expressions of growth arrest and DNA damage inducible gene (GADD45alpha) and apoptosis-inducing factor-1 and down-regulated the expressions of several Bc12-related proteins, such as BAG-1, Bcl2, Bcl2A1, Bcl2L1 and BID. In C4-2B cells, TQ dose dependently inhibited both total and nuclear AR levels (4-5 fold) and AR-directed transcriptional activity (10-12 fold). Interestingly, this suppressive effect on AR was not prevented by NAC, which clearly suggested that TQ-induced cytotoxicity is not due to changes in AR regulation. These data suggest that TQ-induced cell death is primarily due to increased ROS generation and decreased GSH levels, and is independent of AR activity.
Department of Pharmacology, Tulane University School of Medicine, New Orleans, LA 70112, USA.
Padma Sandeep
PS
Koka
Debasis
D
Mondal
Michelle
M
Schultz
Asim B
AB
Abdel-Mageed
Krishna C
KC
Agrawal
D000970:Antineoplastic Agents / Q000494:pharmacology*; D016227:Benzoquinones / Q000302:isolation & purification / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D020869:Gene Expression Profiling; D006801:Humans; D020128:Inhibitory Concentration 50; D008297:Male; D031881:Nigella sativa / Q000737:chemistry; D011471:Prostatic Neoplasms / Q000517:prevention & control*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction
D000970:Antineoplastic Agents; D016227:Benzoquinones; D017382:Reactive Oxygen Species; C003466:thymoquinone