Molecular pathway for thymoquinone-induced cell-cycle arrest and apoptosis in neoplastic keratinocytes

Thymoquinone inhibits growth of human medulloblastoma cells by inducing oxidative stress and caspase-dependent apoptosis while suppressing NF-κB signaling and IL-8 expression

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.

Effect of Thymoquinone on P53 Gene Expression and Consequence Apoptosis in Breast Cancer Cell Line

Background:

Nigella sativa has been a nutritional flavoring factor and natural treatment for many ailments for so many years in medical science. Earlier studies have been reported that thymoquinone (TQ), an active compound of its seed, contains anticancer properties. Previous studies have shown that TQ induces apoptosis in breast cancer cells but it is unclear the role of P53 in the apoptotic pathway. Hereby, this study reports the potency of TQ on expression of tumor suppressor gene P53 and apoptosis induction in breast cancer cell line Michigan Cancer Foundation-7 (MCF-7).

Methods:

MCF-7 cell line was cultured and treated with TQ, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was carried out for evaluating the half-maximal inhibitory concentration (IC50) values after 24 h of treatment. The percentage of apoptotic cells was measured by flow cytometry. Real-time polymerase chain reaction (PCR) was performed to estimate the messenger RNA expression of P53 in MCF-7 cell line at different times.

Results:

The IC50 value for the TQ in MCF-7 cells was 25 μM that determined using MTT assay. The flow cytometry and real-time PCR results showed that TQ could induce apoptosis in MCF-7 cells, and the P53 gene expression was dramatically up-regulated by ascending time, respectively. Hence, there was significant difference in 48 and 72 h.

Conclusions:

Our results demonstrated that TQ could induce apoptosis in MCF-7 cells through up-regulation of P53 expression in breast cancer cell line (MCF-7) by time-dependent manner.

Thymoquinone Modulates Blood Coagulation in Vitro via Its Effects on Inflammatory and Coagulation Pathways

Thymoquinone (THQ) is a major component of black seeds. Given that both THQ and black seeds exhibit anti-cancer and anti-inflammatory activities, we hypothesized that THQ will affect cancer-associated thrombosis (CAT), which is primarily triggered by tissue factor (TF) and inflammation. The effect of both black seed-extracted and purchased (“pure”) THQ on normal blood coagulation was tested with in vitro thromboelastography (TEG) and activated partial thromboplastin time (aPTT) coagulation assays. The effect of pure THQ on CAT was tested with aPTT assay using pancreatic cancer cell lines that are either positive or negative for TF, and with TEG assay using lipopolysaccharide as an inflammatory trigger. Additionally, the direct effect of THQ on the inactivation of factors IIa and Xa was assessed. Since TNF-α facilitates crosstalk between inflammation and thrombosis by triggering the NF-κB pathway, we tested THQ’s ability to interfere with this communication with a luciferase assay. Both extracted and pure THQ had minimal effects on normal blood coagulation. Pure THQ reversed CAT initiated by both TF and inflammation to basal levels (p < 0.001). Mechanistically, while THQ had minimal to no effect on factor IIa and Xa inactivation, it strongly reduced the effects of TNF-α on NF-κB elements (p < 0.001). THQ has a minimal effect on basal coagulation and can reverse CAT in vitro, possibly by interfering with the crosstalk between inflammation and coagulation. This study suggests the utility of THQ as a preventative anticoagulant and/or as a supplement to existing chemotherapies and anticoagulant therapies.

Novel Thymohydroquinone Derivatives as Potential Anticancer Agents: Design, Synthesis, and Biological Screening

The safety and efficacy of naturally occurring anticancer agents and their derivatives such as thymoquinone (TQ) and thymohydroquinone (THQ) have gained a rapidly growing interest. In an attempt to develop novel anticancer agents with superior activity, TQ was allowed to react with hydrazine hydrate, producing hydrazino thymohydroquinone 3. This new intermediate was subsequently reacted with various isocyanates, isothiocyanates, and acyl halides, affording three series of semicarbazone, semithiocarbazone, and acyl hydrazone derivatives, respectively. Subsequently, the anticancer activity of all the newly synthesised compounds against a panel of cancer cell lines was evaluated. Initial screening of the ability of the test compounds to inhibit cancer cell viability using the 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that compounds 5d and 6 exerted better activity against breast cancer than TQ, with half-maximal inhibitory concentration (IC50) values of 9.6 and 10.0 μM, respectively. MTT results were confirmed by the ability of these compounds to elicit apoptotic cell death through the activation of caspase 3/7 enzymes. Together, the present work provided a novel class of THQ-based derivatives with potent anticancer and apoptosis properties, thereby warranting further optimisation of these derivatives as novel members in cancer treatment protocols.

Differential Cellular Effects of Plk1 Inhibitors Targeting the ATP-binding Domain or Polo-box Domain

The expression of polo-like kinase 1 (Plk1) correlates with malignancy and is thus recognized as a target for cancer therapy. In addition to the development of ATP-competitive Plk1 inhibitors, the polo-box domain (PBD), a unique functional domain of PLKs, is being targeted to develop Plk1-specific inhibitors. However, the action mechanisms of these two classes of Plk1 inhibitors have not been thoroughly evaluated. Here, we evaluate the differences in cellular effects of ATP-binding domain inhibitors (BI 2536, GSK 461364) and PBD inhibitors (poloxin, thymoquinone) to determine their mechanisms of Plk1 inhibition. Our data show that BI 2536 and GSK461364 increased the population of cells in the G2/M phase compared with controls, while treatment with poloxin and thymoquinone increased cell population in the S phase as well as in G2/M, in a p53-independent manner. The population of cells staining positively for p-Histone H3 and MPM2, mitotic index, was increased by treatment with BI 2536 or GSK461364, but not by treatment with poloxin or thymoquinone. Furthermore, treatment with BI 2536 or GSK461364 resulted in activation of the BubR1 spindle checkpoint kinase, suggesting that treatment with ATP-binding domain inhibitors induces metaphase arrest. However, the administration of poloxin and thymoquinone resulted in an increase in p21(WAF1) and S arrest, indicating that PBD inhibitors also affected interphase before mitotic entry. Taken together, these data suggest that the PDB of Plk1 plays a role in S phase progression through interaction with other proteins, while its ATP-binding domain is important for regulating mitotic progression mediated by its catalytic activity involving consumption of ATP.

The combination of thymoquinone and paclitaxel shows anti-tumor activity through the interplay with apoptosis network in triple-negative breast cancer

Thymoquinone (TQ) is the active ingredient of Nigella sativa which has a therapeutic potential in cancer therapy and prevention. In this study, TQ has been shown to induce specific cytotoxicity and apoptosis and to inhibit wound healing in triple-negative breast cancer cell line. TQ also inhibited cancer growth in a mouse tumor model. Moreover, TQ and paclitaxel (Pac) combination inhibited cancer growth in cell culture and in mice. Genes involved in TQ and TQ-Pac-mediated cytotoxicity were studied using focused real-time PCR arrays. After bioinformatic analysis, genes in apoptosis, cytokine, and p53 signaling categories were found to be modulated with a high significance in TQ-treated cells (p < 10(-28), p < 10(-8), and p < 10(-6), respectively). Important to note, TQ has been found to regulate the genes involved in the induction of apoptosis through death receptors (p = 5.5 × 10(-5)). Additionally, tumor suppressor genes such as p21, Brca1, and Hic1 were highly upregulated by TQ and TQ-Pac combination. Interestingly, when cells were treated with high dose TQ, several growth factors such as Vegf and Egf were upregulated and several pro-apoptotic factors such as caspases were downregulated possibly pointing out key pathways manipulated by cancer cells to resist against TQ. In cells treated with the combination of TQ and Pac, genes in apoptosis cascade (p < 10(-12)), p53 signaling (p = 10(-5)), and JAK-STAT signaling (p < 10(-3)) were differentially expressed. TQ has also been shown to induce protein levels of cleaved Caspase-3, Caspase-7, and Caspase-12 and PARP and to reduce phosphorylated p65 and Akt1. The in vivo therapeutic potential of TQ-Pac combination and the genetic network involved in this synergy have been shown for the first time to the best of our knowledge.

Antiproliferative and proapoptotic effects of topotecan in combination with thymoquinone on acute myelogenous leukemia

BACKGROUND

Topotecan has shown promising antineoplastic activity in solid tumors and acute leukemia. Because of the primary dose-limiting toxicity of topotecan, it is necessary to identify other agents that can work synergistically with topotecan, potentially increasing its efficacy while limiting its toxicity. Many studies showed synergism in combination of topotecan with gemcitabine and bortezomib. Other studies report the increase in growth inhibition of gemcitabine or oxaliplatin when cells were preexposed to naturally occurring drugs such as thymoquinone. The aim of this project was to study the mode of action of topotecan along with thymoquinone, on survival and apoptosis pathways in acute myelogenous leukemia (AML) cell lines, and to investigate the potential synergistic effect of thymoquinone on topotecan.

MATERIALS AND METHODS

U937 cells were incubated with different topotecan and thymoquinone concentrations for 24 and 48 hours, separately and in combination. Cell proliferation was determined using WST-1 (Roche) reagent. The effect of the compounds on protein expression of Bax, Bcl2, p53, caspase-9, -8, and -3 was determined using Western blot analysis. Cell cycle analysis was performed in addition to annexin/propidium iodide staining.

RESULTS

Thymoquinone and topotecan exhibited antiproliferative effects on U937 cells when applied separately. In combination, the reduction in proliferation was extremely significant with a major increase in the expression levels of Bax/Bcl2, p53, and caspase-3 and -9. Preexposure with thymoquinone resulted in an increase in cell growth inhibition compared with topotecan treatment.

CONCLUSION

Thymoquinone, when combined with topotecan in noncytotoxic doses, produced synergistic antiproliferative and proapoptotic effects in AML cells. Preexposure to thymoquinone seems to be more effective than simultaneous application with topotecan.

Chemopreventive and therapeutic potentials of thymoquinone in HepG2 cells: mechanistic perspectives

Liver cancer is the fifth commonest malignancy worldwide and the third leading cause of death. Identifying novel curative and preventive therapy may improve its prognosis. In this study, thymoquinone (TQ), the most active biological ingredient of Nigella sativa Linn, was investigated for its antitumor activity. Mechanistic perspectives underlying this antitumor activity were explored by testing its effect on cell cycle, apoptosis, and angiogenesis. In addition, the chemopreventive effect of TQ was carried out by measuring its effect on phase I CYP1A1 and phase II glutathione S-transferase (GST) drug-metabolizing enzymes. The results of the present study revealed the effectiveness of TQ as an antitumor agent against different types of cancer including brain, colon, cervix and liver at both a time- and concentration-dependent manner. In HepG2 cells, it induced G2/M phase cell cycle arrest and a concentration-dependent increase in the percentage of apoptotic cells with an increase in the ratio of Bax/BCL-2. Moreover, the expression of mRNA and protein level of vascular endothelial growth factor decreased as the concentration of TQ increased. Our data showed a significant inhibition of induced phase I CYP1A1 enzyme, and elevation in the content of glutathione and activity of phase II enzyme GST, in HepG2 cells. Our results provide support for the beneficial use of TQ as a therapeutic and chemopreventive agent against liver cancer.

Interaction of human telomeric G-quadruplex DNA with thymoquinone: a possible mechanism for thymoquinone anticancer effect

BACKGROUND

Thymoquinone (TQ) has been documented to possess chemo-preventive and chemotherapeutic antitumor effects. Studies reported that TQ inhibits the growth of cancer cells in animal models, culture and xenografted tumors. Molecular mechanisms underlying these anticancer effects were attributed to inductions of cell cycle arrest, apoptosis, oxidative damage of cellular macromolecules, blockade of tumor angiogenesis and inhibitions in migration, invasion and metastasis of cancer cells. On the other hand, human telomere DNA plays a role in regulating genes' transcriptions. It folds up into G-quadruplex structures that inhibit telomerase enzyme over-expressed in cancerous cells. Molecules that selectively stabilize G-quadruplex are potential anticancer agents. Therefore, this work aimed to explore the interaction of TQ with G-quadruplex DNA as a possible underlying mechanism for the anticancer effect of TQ.

METHODS

Interactions of TQ with telomeric G-quadruplex (5'-AGGG(TTAGGG)3-3') and duplex DNAs were studied using UV-vis, fluorescence, circular dichroism, liquid and solid NMR (1H and 13C), melting temperature and docking simulation.

RESULTS

Changes in UV-vis, CD, fluorescence, 1H NMR and 13C NMR, spectra as well as melting temperatures and docking simulations provided evidences for TQ's interactions with G-quadruplex. TQ was found to interact with G-quadruplex on two binding sites adjacent to the TTA loop with binding constants 1.80×10(5) and 1.12×10(7) M(-1). Melting temperatures indicated that TQ stabilized G-quadruplex by 5.6 °C and destabilized ct-DNA by 5.1 °C. Selectivity experiment indicated that TQ is preferentially binding to G-quadruplex over duplex with selectivity coefficients of 2.80-3.33×10(-3). Results suggested an intercalation binding mode based on π-π stacking.

CONCLUSION

Our results propose that TQ can possibly act as a G-quadruplex DNA stabilizer and subsequently contribute to the inhibition of telomerase enzyme and cancer's proliferation.

GENERAL SIGNIFICANCE

Our results represent a change in the paradigms reported for structural features of G-quadruplex's stabilizers and anticancer mechanisms of TQ.

Antitumor activity of monoterpenes found in essential oils

Cancer is a complex genetic disease that is a major public health problem worldwide, accounting for about 7 million deaths each year. Many anticancer drugs currently used clinically have been isolated from plant species or are based on such substances. Accumulating data has revealed anticancer activity in plant-derived monoterpenes. In this review the antitumor activity of 37 monoterpenes found in essential oils is discussed. Chemical structures, experimental models, and mechanisms of action for bioactive substances are presented.

Thymoquinone-induced conformational changes of PAK1 interrupt prosurvival MEK-ERK signaling in colorectal cancer

Background

Thymoquinone (TQ) was shown to reduce tumor growth in several cancer models both in vitro and in vivo. So far only a few targets of TQ, including protein kinases have been identified. Considering that kinases are promising candidates for targeted anticancer therapy, we studied the complex kinase network regulated by TQ.

Methods

Novel kinase targets influenced by TQ were revealed by in silico analysis of peptide array data obtained from TQ-treated HCT116wt cells. Western blotting and kinase activity assays were used to determine changes in kinase expression patterns in colorectal cancer cells (HCT116wt, DLD-1, HT29). To study the viability/apoptotic effects of combining the PAK1 inhibitor IPA-3 and TQ, crystal violet assay and AnnexinV/PI staining were employed. Interactions between PAK1 and ERK1/2 were investigated by co-immunoprecipitation and modeled by docking studies. Transfection with different PAK1 mutants unraveled the role of TQ-induced changes in PAK1 phosphorylation and TQ´s effects on PAK1 scaffold function.

Results

Of the 104 proteins identified, 50 were upregulated ≥2 fold by TQ and included molecules in the AKT-MEK-ERK1/2 pathway. Oncogenic PAK1 emerged as an interesting TQ target. Time-dependent changes in two PAK1 phosphorylation sites generated a specific kinase profile with early increase in pPAK^Thr212 followed by late increase in pPAK^Thr423. TQ induced an increase of pERK1/2 and triggered the early formation of an ERK1/2-PAK1 complex. Modeling confirmed that TQ binds in the vicinity of Thr212 accompanied by conformational changes in ERK2-PAK1 binding. Transfecting the cells with the non-phosphorylatable mutant T212A revealed an increase of pPAK^Thr423 and enhanced apoptosis. Likewise, an increase in apoptosis was observed in cells transfected with both the kinase-dead K299R mutant and PAK1 siRNA. Using structural modeling we suggest that TQ interferes also with the kinase domain consequently disturbing its interaction with pPAK^Thr423, finally inhibiting MEK-ERK1/2 signaling and disrupting its prosurvival function. pERK1/2 loss was also validated in vivo.

Conclusions

Our study shows for the first time that the small molecule TQ directly binds to PAK1 changing its conformation and scaffold function. Because TQ affects the central RAF/MEK/ERK1/2 pathway, the combination of TQ with targeted therapies is worth considering for future anticancer treatments.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-201) contains supplementary material, which is available to authorized users.

Development and validation of liquid chromatography-tandem mass spectrometry method for quantification of a potential anticancer triterpene saponin from seeds of Nigella glandulifera in rat plasma: application to a pharmacokinetic study

Nigella glandulifera Freyn et Sit is a folk medicinal plant, whose seeds show significant anticancer activities attributed to triterpene saponins and volatile oil. In this study, an in vitro cytotoxicity assay demonstrated that Nigella A, the major component of triterpene saponins extracted from N. glandulifera, exhibited growth inhibition in the human lung carcinoma A-549 cell line. Due to this potential activity, a reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to quantify Nigella A in rat plasma for a pharmacokinetic study was developed. Nigella A and pravastatin, as internal standard (IS), were extracted from rat plasma using acetonitrile to precipitate protein. Separation was performed on an Agilent Zorbax SB-Aq (3.0 × 150 mm, 3.5 μm) column using a gradient elution method with acetonitrile-0.1% formic acid in water at a flow rate of 0.35 mL/min. Detection was performed using an electrospray ionization in a negative ion multiple reaction monitoring mode. The deprotonated precursor to product ion transitions monitored for Nigella A and IS was at m/z 1352.7→882.6 and m/z 423.1→321.0, respectively. The linear range was 0.240-120 μg/mL with a square regression coefficient (r=0.9996). The intra-day and inter-day precision was less than 6.93%. The simple extraction procedure provided recovery ranged from 92.32 to 95.44% for both analyte and IS. The method was proved to be reliable, precise, and accurate, and was successfully applied to a pharmacokinetic study of Nigella A in rats after i.v. administration via the tail vein at doses of 10, 20, and 30 mg/kg.

Mechanistic perspectives on cancer chemoprevention/chemotherapeutic effects of thymoquinone

The bioactive natural products (plant secondary metabolites) are widely known to possess therapeutic value for the prevention and treatment of various chronic diseases including cancer. Thymoquinone (2-methyl-5-isopropyl-1,4-benzoquinone; TQ), a monoterpene present in black cumin seeds, exhibits pleiotropic pharmacological activities including antioxidant, anti-inflammatory, antidiabetic and antitumor effects. TQ inhibits experimental carcinogenesis in a wide range of animal models and has been shown to arrest the growth of various cancer cells in culture as well as xenograft tumors in vivo. The mechanistic basis of anticancer effects of TQ includes the inhibition of carcinogen metabolizing enzyme activity and oxidative damage of cellular macromolecules, attenuation of inflammation, induction of cell cycle arrest and apoptosis in tumor cells, blockade of tumor angiogenesis, and suppression of migration, invasion and metastasis of cancer cells. TQ shows synergistic and/or potentiating anticancer effects when combined with clinically used chemotherapeutic agents. At the molecular level, TQ targets various components of intracellular signaling pathways, particularly a variety of upstream kinases and transcription factors, which are aberrantly activated during the course of tumorigenesis.

Therapeutic Implications of Black Seed and Its Constituent Thymoquinone in the Prevention of Cancer through Inactivation and Activation of Molecular Pathways

The cancer is probably the most dreaded disease in both men and women and also major health problem worldwide. Despite its high prevalence, the exact molecular mechanisms of the development and progression are not fully understood. The current chemotherapy/radiotherapy regime used to treat cancer shows adverse side effect and may alter gene functions. Natural products are generally safe, effective, and less expensive substitutes of anticancer chemotherapeutics. Based on previous studies of their potential therapeutic uses, Nigella sativa and its constituents may be proved as good therapeutic options in the prevention of cancer. Black seeds are used as staple food in the Middle Eastern Countries for thousands of years and also in the treatment of diseases. Earlier studies have shown that N. sativa and its constituent thymoquinone (TQ) have important roles in the prevention and treatment of cancer by modulating cell signaling pathways. In this review, we summarize the role of N. sativa and its constituents TQ in the prevention of cancer through the activation or inactivation of molecular cell signaling pathways.

Molecular targeting of Akt by thymoquinone promotes G(1) arrest through translation inhibition of cyclin D1 and induces apoptosis in breast cancer cells

AIM

Thymoquinone (TQ), the predominant bioactive constituent of black seed oil (Nigella Sativa), has been shown to possess antineoplastic activity against multifarious tumors. However, the meticulous mechanism of TQ on Akt mediated survival pathway is still unrevealed in breast cancer. Here, we investigated TQ's mechanism of action against PI3K/Akt signaling and its downstream targets by modulating proteins translational machinery, leading to apoptosis in cancer cells.

MAIN METHODS

MDA-MB-468 and T-47D cells were treated with TQ and evaluated for its anticancer activity through phase distribution and western blot. Modulatory effects of TQ on Akt were affirmed through kinase and drug potential studies.

KEY FINDINGS

Studies revealed G1 phase arrest till 24h incubation with TQ while extended exposure showed phase shift to subG1 indicating apoptosis, supported by suppression of cyclin D1, cyclin E and cyclin dependent kinase inhibitor p27 expression. Immunoblot and membrane potential studies revealed mitochondrial impairment behind apoptotic process with upregulation of Bax, cytoplasmic cytochrome c and procaspase-3, PARP cleavage along with Bcl-2, Bcl-xL and survivin downregulation. Moreover, we construed the rationale behind mitochondrial dysfunction by examining the phosphorylation status of PDK1, PTEN, Akt, c-raf, GSK-3β and Bad in TQ treated cells, thus ratifying the involvement of Akt in apoptosis. Further, the consequential effect of Akt inhibition by TQ is proven by translational repression through deregulated phosphorylation of 4E-BP1, eIF4E, S6R and p70S6K.

SIGNIFICANCE

Our observations for the first time may provide a new insight for the development of novel therapies for Akt overexpressed breast cancer by TQ.

Thymoquinone inhibits cell proliferation through regulation of G1/S phase cell cycle transition in N-nitrosodiethylamine-induced experimental rat hepatocellular carcinoma

Dysregulated cell proliferation and tumorigenesis is frequently encountered in several cancers including hepatocellular carcinogenesis (HCC). Thus, agents that inhibit cell proliferation and restrain hepatic tumorigenesis through cell cycle regulation have a beneficial effect in the treatment of hepatocellular carcinogenesis. The present study was aimed to investigate the efficacy of thymoquinone (TQ), an active compound derived from the medicinal plant Nigella sativa, on N-nitrosodiethylamine (NDEA) [0.01% in drinking water for 16 weeks]-induced hepatocarcinogenesis in experimental rats. After experimental period, the hepatic nodules, liver injury markers and tumor markers levels were substantially increased in NDEA induced liver tumors in rats. However, TQ (20mg/kg body weight) treatment greatly reduced liver injury markers and decreased tumor markers and prevented hepatic nodule formation and reduced tumor multiplicity in NDEA induced hepatic cancer bearing rats and this was evident from argyrophilic nucleolar organizer region (AgNORs) staining. Moreover, the uncontrolled cell proliferation was assessed by specific cell proliferative markers [proliferating cell nuclear antigen (PCNA) and Ki67] by immunofluorescence, immunoblot and analysis of mRNA expression. Simultaneously, we assessed the activity of TQ on G1/S phase cell cycle regulation with specific cell cycle proteins (p21(WAF1/CIP1), CDK4, Cyclin D1 and Cyclin E) by immunoprecipitation in experimental rats. Treatment with TQ significantly reduced the detrimental alterations by abrogating cell proliferation, which strongly induced G1/S arrest in cell cycle transition. In conclusion, our results suggest that TQ has a potent anti proliferative activity by regulating the G1/S phase cell cycle transition and exhibit a beneficial role in the treatment of HCC.

Thymoquinone: fifty years of success in the battle against cancer models

Thymoquinone (TQ), the main active constituent of black seed essential oil, exhibits promising effects against inflammatory diseases and cancer. TQ, modulates signaling pathways that are key to cancer progression, and enhances the anticancer potential of clinical drugs while reducing their toxic side effects. Considering that TQ was isolated 50 years ago, this review focuses on TQ's chemical and pharmacological properties and the latest advances in TQ analog design and nanoformulation. We discuss our current state of knowledge of TQ's adjuvant potential and in vivo antitumor activity and highlight its ability to modulate the hallmarks of cancer.

Cellular responses with thymoquinone treatment in human breast cancer cell line MCF-7

BACKGROUND

Nigella sativa or black seed extract has been reported to show various medicinal benefits. Thymoquinone which is an active compound of its seed has been reported to contain anti-cancer properties.

OBJECTIVE

The study addressed the anti-cancer efficiency of long-term in vitro treatment with thymoquinone towards human breast cancer cell lines MCF-7.

MATERIALS AND METHODS

Cell proliferation was determined with CellTiter 96 Aqueous. Non-Radioactive Cell Proliferation Assay Kit. It was followed with trypan blue exclusion test to determine the percentage of viable cells. The study incorporated cell cycle assay to distinguish cell distribution at various cell cycle phases using Cycletest Plus DNA Reagent Kit. The apoptosis detection kit was used to determine the percentage of apoptotic and necrotic cells using flow cytometry.

RESULTS

The 50% inhibitory concentration (IC50) value determined using the proliferation assay was 25 μM thymoquinone. Late apoptotic cell percentage increased rapidly when treatment duration was increased to 24 h with 25 and 100 μM thymoquinone. Further analysis using cell cycle assay showed thymoquinone inhibition of breast cancer cell proliferation at minimal dose 25 μM and led to S phase arrest significantly at 72 h treatment (P = 0.009). It was also noted elevation sub-G1 peak following treatment with 25 μM thymoquinone for 12 h. Increase in thymoquinone to 50 μM caused G2 phase arrest at each time-point studied.

CONCLUSION

In general thymoquinone showed sustained inhibition of breast cancer cell proliferation with long-term treatment. Specificity of phase arrest was determined by thymoquinone dose.

Redox cycling of endogenous copper by thymoquinone leads to ROS-mediated DNA breakage and consequent cell death: putative anticancer mechanism of antioxidants

Plant-derived dietary antioxidants have attracted considerable interest in recent past for their chemopreventive and cancer therapeutic abilities in animal models. Thymoquinone (TQ) is the major bioactive constituent of volatile oil of Nigella sativa and has been shown to exert various pharmacological properties, such as anti-inflammatory, cardiovascular, analgesic, anti-neoplastic, anticancer and chemopreventive. Although several mechanisms have been suggested for the chemopreventive and anticancer activity of TQ, a clear mechanism of action of TQ has not been elucidated. TQ is a known antioxidant at lower concentrations and most of the studies elucidating the mechanism have centered on the antioxidant property. However, recent publications have shown that TQ may act as a prooxidant at higher concentrations. It is well known that plant-derived antioxidants can switch to prooxidants even at low concentrations in the presence of transition metal ions such as copper. It is well established that tissue, cellular and serum copper levels are considerably elevated in various malignancies. Copper is an important metal ion present in the chromatin and is closely associated with DNA bases, particularly guanine. Using human peripheral lymphocytes and comet assay, we first show that TQ is able to cause oxidative cellular DNA breakage. Such a DNA breakage can be inhibited by copper-chelating agents, neocuproine and bathocuproine, and scavengers of reactive oxygen species. Further, it is seen that TQ targets cellular copper in prostate cancer cell lines leading to a prooxidant cell death. We believe that such a prooxidant cytotoxic mechanism better explains the anticancer activity of plant-derived antioxidants.

Thymoquinone blocks pSer/pThr recognition by Plk1 Polo-box domain as a phosphate mimic

Phosphorylation-dependent protein-protein interaction has rarely been targeted in medicinal chemistry. Thymoquinone, a naturally occurring antitumor agent, disrupts prephosphorylated substrate recognition by the polo-box domain of polo-like kinase 1, a key mitotic regulator responsible for various carcinogenesis when overexpressed. Here, crystallographic studies reveal that the phosphoserine/phosphothreonine recognition site of the polo-box domain is the binding pocket for thymoquinone and its analogue poloxime. Both small molecules displace phosphopeptides bound with the polo-box domain in a slow but noncovalent binding mode. A conserved water bridge and a cation-π interaction were found as their competition strategy against the phosphate group. This mechanism sheds light on small-molecule intervention of phospho-recognition by the polo-box domain of polo-like kinase 1 and other phospho-binding proteins in general.

Thymoquinone attenuates liver fibrosis via PI3K and TLR4 signaling pathways in activated hepatic stellate cells

Thymoquinone (TQ) is the major active compound derived from the medicinal Nigella sativa. In the present study, we investigated the anti-fibrotic mechanism of TQ in lipopolysaccharide (LPS)-activated rat hepatic stellate cells line, T-HSC/Cl-6. T-HSC/Cl-6 cells were treated with TQ (3.125, 6.25 and 12.5μM) prior to LPS (1μg/ml). Our data demonstrated that TQ effectively decreased activated T-HSC/Cl-6 cell viability. TQ significantly attenuated the expression of CD14 and Toll-like receptor 4 (TLR4). TQ also significantly inhibited phosphatidylinositol 3-kinase (PI3K) and serine/threonine kinase-protein kinase B (Akt) phosphorylation. The expression of α-SMA and collagen-I were significantly decreased by TQ. Furthermore, TQ decreased X linked inhibitor of apoptosis (XIAP) and cellular FLIP (c-FLIPL) expression, which are related with the regulation of apoptosis. Furthermore, TQ significantly increased the survival against LPS challenge in d-galactosamine (d-GlaN)-sensitized mice, and decreased the levels of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which were in line with in vitro results. Our data demonstrated that TQ attenuates liver fibrosis partially via blocking TLR4 expression and PI3K phosphorylation on the activated HSCs. Therefore, TQ may be a potential candidate for the therapy of hepatic fibrosis.

Effect of thymoquinone on 1,2-dimethyl-hydrazine-induced oxidative stress during initiation and promotion of colon carcinogenesis

We evaluated pre- and post-thymoquinone (TQ) treatment on 1,2-dimethyl-hydrazine (DMH)-induced oxidative stress during initiation and promotion of colon carcinogenesis. Wistar rats were induced with DMH (20mg/kg) for 10 or 20 weeks, and treated with TQ (5mg/kg). Following sacrifice, the colons were analysed for tumour development, reactive oxygen species (ROS) generation, lipid peroxidation [conjugated diene (CD) and malondialdehyde (MDA)], antioxidants [glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD) and reduced glutathione (GSH)], and histological changes. Increased ROS levels and lipid peroxidation were seen during tumour initiation and promotion. All ROS-scavenging enzyme activities were increased upon shorter DMH treatment but not following longer treatment, while GSH amount was increased upon both treatments. Oxidative state perturbations were associated with moderate colon dysplasia and 30% tumour incidence at initiation and marked dysplasia and 100% tumour incidence at promotion. TQ pre-treatment restored completely DMH-induced oxidative stress at initiation and established histological changes and tumour development. It also abrogated oxidative status aggravation at promotion, and significantly reduced tumour incidence (67%). By comparison, TQ post-treatment corrected oxidative status and attenuated tumour development at initiation. It slightly reduced MDA and antioxidant level at promotion, with a slight reduction in tumour state and dysplasia degree. TQ is efficacious in protecting and curing DMH-induced initiation phase of colon cancer, while exerting a protective role at promotion. TQ effect seems to be related to its capacity in preventing DMH-induced oxidative stress. These in vivo results support the notion that TQ may be of value as a chemo-preventive alternative in colorectal cancer patients.

Antineoplastic and apoptotic potential of traditional medicines thymoquinone and diosgenin in squamous cell carcinoma

Thymoquinone (TQ) and diosgenin (DG), the active ingredients obtained from black cumin (Nigella sativa) and fenugreek (Trigonella foenum graecum), respectively, exert potent bioactivity, including anticancer effects. This study investigated the antineoplastic activity of these agents against squamous cell carcinoma in vitro and sarcoma 180–induced tumors in vivo. TQ and DG inhibited cell proliferation and induced cytotoxicity in A431 and Hep2 cells. These agents induced apoptosis by increasing the sub-G₁ population, LIVE/DEAD cytotoxicity, chromatin condensation, DNA laddering and TUNEL-positive cells significantly (P<0.05). Increased Bax/Bcl-2 ratio, activation of caspases and cleavage of poly ADP ribose polymerase were observed in treated cells. These drugs inhibited Akt and JNK phosphorylations, thus inhibiting cell proliferation while inducing apoptosis. In combination, TQ and DG had synergistic effects, resulting in cell viability as low as 10%. In a mouse xenograft model, a combination of TQ and DG significantly (P<0.05) reduced tumor volume, mass and increased apoptosis. TQ and DG, alone and in combination, inhibit cell proliferation and induce apoptosis in squamous cell carcinoma. The combination of TQ and DG is a potential antineoplastic therapy in this common skin cancer.

Radioprotection by Macerated Extract of Nigella sativa in Normal Tissues of Fibrosarcoma Bearing Mice

The current study was undertaken to study the effect of a macerated extract of Nigella sativa seeds in normal as well as in tumour bearing mice against gamma radiation-induced cellular damage to normal tissues. This was done to mimic the clinical setting where in, normal tissues of cancer patients undergoing radiotherapy are exposed to the deleterious effects of radiation. The protection of cellular DNA was analysed in peripheral blood leucocytes of whole body irradiated mice following pretreatment with macerated extract of Nigella sativa seeds (100 mg/kg), using alkaline comet assay, and also estimating biochemical and blood parameters such as levels of antioxidant enzymes superoxide dismutase and catalase, thiobarbituric acid reactive substances and protein oxidation in organs such as spleen, liver, brain and intestine haemoglobin and total leucocyte count, respectively. The results showed that the macerated extract of Nigella sativa seeds protected the liver, spleen, brain and intestines both in normal as well as tumour bearing mice. This study concludes that macerated extract of Nigella sativa seeds has protective effects against radiation-induced damage and biochemical alterations which could be attributed to the ability to scavenge free radicals and its antioxidant properties. Hence macerated extract of Nigella sativa seeds, could be used in combination with radiation to protect against oxidative stress in normal tissues and improving the quality of life of cancer patients by mitigating unwanted side effects of radiation in normal tissues.

Anti-cancer effects of thymoquinone in mouse neuroblastoma (Neuro-2a) cells through caspase-3 activation with down-regulation of XIAP

Thymoquinone (TQ) is a bioactive component derived from the medicinal plant Nigella sativa. Recent studies reported that TQ exhibited cytotoxic effects in several cancer cell lines. Currently, no information in the literature is found concerning its mechanisms and cytotoxicity on neuroblastoma cells. In this study, the cytotoxicity of TQ in mouse neuroblastoma cells (Neuro-2a) was investigated. Our results showed that TQ significantly reduced viability of Neuro-2a cells than normal neuronal cells. Apoptosis induction by TQ was confirmed by DAPI and AO/PI staining. TQ triggered the apoptotic pathway, which was characterized by increased Bax/Bcl-2 ratio. TQ significantly increased the expression of pro-apoptotic protein Bax, whereas decreased the expression of anti-apoptotic protein Bcl-2, which leads to the release of cytochrome c from mitochondria into the cytoplasm. Moreover, TQ treatment directs the activation of caspase-3 followed by the cleavage of poly(ADP-ribose) polymerase (PARP). Interestingly, we also observed that TQ down-regulated caspase inhibitor X-linked inhibitor of apoptosis protein (XIAP). These results indicate that TQ induces apoptosis via caspase-3 activation with down-regulation of XIAP in Neuro-2a cells.

Mitigation of obesity-promoted diseases by Nigella sativa and thymoquinone

Obesity is closely associated with increased incidence of cardiovascular diseases, cancer, insulin resistance, and immune dysfunction, and thus obesity-mitigation strategies should take into account these secondary pathologies in addition to promoting weight loss. Recent studies indicate that black cumin (Nigella sativa) has cardio-protective, anti-cancer, anti-diabetic, antioxidant, and immune-modulatory properties. While black cumin and/or its major bioactive constituent, thymoquinone have demonstrated bioactivity in a variety of disease models, the mechanisms of action are largely unknown. Given the growing interest in and the use of functional foods and nutraceuticals, as well as the increase in obesity and chronic diseases worldwide, further research into the therapeutic/preventive effects of black cumin may be beneficial.

Characterization of thymoquinone binding to human α₁-acid glycoprotein

Thymoquinone (TQ) is the main bioactive component isolated from Nigella sativa essential oil and seeds and has been used for the treatment of inflammations, liver disorders, arthritis, and is of great importance as a promising therapeutic drug for different diseases including cancer. This paper reports the first experimental evidence on binding of TQ to human α(1)-acid glycoprotein (AGP), an important drug-binding glycoprotein in human plasma, which affects pharmacokinetic properties of various therapeutic agents. The interaction of TQ with AGP has been characterized by Fourier transform infrared (FTIR) and fluorescence spectroscopy, as well as by molecular docking experiments. FTIR spectroscopy showed that the binding of TQ to AGP slightly increases its thermal stability and shifts the existence of a molten globule-like state observed in a previous study to higher temperature. The binding constants K(a); the number of binding sites n; and the corresponding thermodynamic parameters ΔG, ΔH, and ΔS at different temperatures were calculated through fluorescence spectroscopy. Fluorescence quenching experiments indicated that TQ binding involves hydrophobic interactions and to a lower extent hydrogen bonds, in agreement with molecular docking experiments. The data on binding ability of TQ to AGP represent basic information for the TQ pharmacokinetics such as drug metabolism and distribution in the body.

Thymoquinone-induced platelet apoptosis

Thymoquinone (TQ) is a nutrient with anticarcinogenic activity that stimulates suicidal death of tumor cells. Moreover, TQ triggers suicidal death of erythrocytes or eryptosis, an effect at least partially due to increase in cytosolic Ca(2+) activity and ceramide formation. The present experiments explored whether TQ influences apoptosis of blood platelets. Cell membrane scrambling was determined utilizing Annexin V binding to phosphatidylserine exposing platelets, cytosolic Ca(2+) activity utilizing Fluo 3-AM fluorescence, caspase activity utilizing immunofluorescence and Western blotting of active caspase-3 and inactive procaspase-3, mitochondrial potential utilizing DiOC(6) fluorescence and ceramide by FACS analysis of ceramide-binding antibodies. A 30 min exposure to TQ (≥5 µM) was followed by Annexin V binding, paralleled by caspase activation, increase of cytosolic Ca(2+) activity, mitochondrial depolarization, and ceramide formation. P-selectin exposure and integrin α(IIb) β(3) activation did not increase in response to TQ. Nominal absence of extracellular Ca(2+) blunted but did not fully abolish the TQ-induced activation of caspase-3. The effects of TQ on platelets are significantly abolished with phosphoinositide-3 kinase (PI3K) inhibitor wortmannin and G-protein coupled receptor (GPCR) inhibitor pertussis toxin treatment prior to TQ stimulation. In conclusion, TQ triggers suicidal death of blood platelets in a PI3K-dependent manner, possibly through a GPCR family receptor; an effect paralleled by increase of cytosolic Ca(2+) activity, ceramide formation, mitochondrial depolarization, and caspase-3 activation.

Radiosensitization in human breast carcinoma cells by thymoquinone: role of cell cycle and apoptosis

TQ (thymoquinone), the bioactive constituent of black seed (Nigella sativa), has been shown to inhibit the growth of various human cancers both in vitro and in vivo. This study reports the radiosensitizing effect of TQ on human breast carcinoma cells (MCF7 and T47D). TQ in combination with single dose of ionizing radiation (2.5 Gy) was found to exert supra-additive cytotoxic effects on both the carcinomas as measured by cell proliferation and colony-formation assays. Annexin V binding and FACS analysis revealed the role of enhanced apoptosis and cell cycle modulation in the mechanism of TQ-mediated radiosensitization, thus supporting TQ as an adjuvant for preclinical testing in cancer chemo-radiotherapy.

Greco-arab and islamic herbal-derived anticancer modalities: from tradition to molecular mechanisms

The incidence of cancer is increasing in the developed countries and even more so in developing countries parallel to the increase in life expectancy. In recent years, clinicians and researchers advocate the need to include supportive and palliative care since the establishment of the diagnosis and throughout the duration of treatment, with the goal of improving patients' quality of life. This patient-centered approach in supportive care is also shared by various traditional and complementary medicine approaches. Traditional Arab-Islamic medicine offers a variety of therapeutic modalities that include herbal, nutritional, and spiritual approaches. Physicians and scholars, such as Avicenna (980-1037), Rhazes (965-915), Al Zahrawi (936-1013), and Ibn al Nafis (1218-1288) referred to cancer etiology in various medicinal texts and suggested both preventive and therapeutic remedies to alleviate suffering. This review presents research data related to the anticancer activities of herbs used in Arab-Islamic medicine and allude to their potential role in improving the quality of life of cancer patients.

Thymoquinone: potential cure for inflammatory disorders and cancer

Thymoquinone is an active ingredient isolated from Nigella sativa and has been investigated for its anti-oxidant, anti-inflammatory and anticancer activities in both in vitro and in vivo models since its first extraction in 1960s. Its anti-oxidant/anti-inflammatory effect has been reported in various disease models, including encephalomyelitis, diabetes, asthma and carcinogenesis. Moreover, thymoquinone could act as a free radical and superoxide radical scavenger, as well as preserving the activity of various anti-oxidant enzymes such as catalase, glutathione peroxidase and glutathione-S-transferase. The anticancer effect(s) of thymoquinone are mediated through different modes of action, including anti-proliferation, apoptosis induction, cell cycle arrest, ROS generation and anti-metastasis/anti-angiogenesis. In addition, this quinone was found to exhibit anticancer activity through the modulation of multiple molecular targets, including p53, p73, PTEN, STAT3, PPAR-γ, activation of caspases and generation of ROS. The anti-tumor effects of thymoquinone have also been investigated in tumor xenograft mice models for colon, prostate, pancreatic and lung cancer. The combination of thymoquinone and conventional chemotherapeutic drugs could produce greater therapeutic effect as well as reduce the toxicity of the latter. In this review, we summarize the anti-oxidant/anti-inflammatory and anticancer effects of thymoquinone with a focus on its molecular targets, and its possible role in the treatment of inflammatory diseases and cancer.

Thymoquinone inhibits the CXCL12-induced chemotaxis of multiple myeloma cells and increases their susceptibility to Fas-mediated apoptosis

In multiple myeloma (MM), malignant plasma cells reside in the bone marrow, where they accumulate in close contact with stromal cells. The mechanisms responsible for the chemotaxis of malignant plasma cells are still poorly understood. Thus, we investigated the mechanisms involved in the chemotaxis of MDN and XG2 MM cell lines. Both cell lines strongly expressed CCR9, CXCR3 and CXCR4 chemokine receptors but only migrated toward CXCL12. Activation of CXCR4 by CXCL12 resulted in the association of CXCR4 with CD45 and activation of PLCβ3, AKT, RhoA, IκBα and ERK1/2. Using siRNA-silencing techniques, we showed CD45/CXCR4 association is essential for CXCL12-induced migration of MM cells. Thymoquinone (TQ), the major active component of the medicinal herb Nigella sativa Linn, has been described as a chemopreventive and chemotherapeutic compound. TQ treatment strongly inhibited CXCL12-mediated chemotaxis in MM cell lines as well as primary cells isolated from MM patients, but not normal PBMCs. Moreover, TQ significantly down-regulated CXCR4 expression and CXCL12-mediated CXCR4/CD45 association in MM cells. Finally, TQ also induced the relocalization of cytoplasmic Fas/CD95 to the membrane of MM cells and increased CD95-mediated apoptosis by 80%. In conclusion, we demonstrate the potent anti-myeloma activity of TQ, providing a rationale for further clinical evaluation.

Validated high-performance thin-layer chromatographic method for the quantification of thymoquinone in Nigella Sativa extracts and formulations

INTRODUCTION

The surge of interest in naturally occurring phytochemicals with anticancer potential has led to the discovery of many molecules, one of them being thymoquinone (TQ) the bioactive constituent of the volatile oil of black seed, Nigella sativa L. (NS).

OBJECTIVE

The aim of the present work was to develop and validate an HPTLC method for determination of TQ in NS extracts, commercially available marketed oils, polyherbal formulations and in lipid-based oral and parenteral formulations prepared in-house.

METHODOLOGY

Analysis of TQ was performed on TLC aluminium plates pre-coated with silica gel 60F-254. Linear ascending development was carried out in twin trough glass chamber, saturated with mobile phase consisting of toluene-cyclohexane (8 : 2, v/v) at ambient temperature. Camag TLC scanner III was used for the spectrodensitometric scanning and analysis in absorbance mode at 254 nm.

RESULTS

The method was found to give compact spots for TQ (R(f) value of 0.28 ± 0.05) and was linear over the range 100-1400 ng/spot (r(2) = 0.9921 ± 0.0020). Accuracy, precision and repeatability were all within the required limits. The mean recoveries measured at three concentrations were higher than 95% with RSD ≤ 3%.

CONCLUSION

The HPTLC method developed was found to be relatively simple, rapid and accurate for the routine analysis of TQ in extracts, marketed oils, polyherbal and in-house formulations.

Down-regulation of UHRF1, associated with re-expression of tumor suppressor genes, is a common feature of natural compounds exhibiting anti-cancer properties

Over-expressed in numerous cancers, Ubiquitin-like containing PHD Ring Finger 1 (UHRF1, also known as ICBP90 or Np95) is characterized by a SRA domain (Set and Ring Associated) which is found only in the UHRF family. UHRF1 constitutes a complex with histone deacetylase 1 (HDAC1) and DNA methyltransferase 1 (DNMT1) via its SRA domain and represses the expression of several tumour suppressor genes (TSGs) including p16INK4A, hMLH1, BRCA1 and RB1. Conversely, UHRF1 is regulated by other TSGs such as p53 and p73. UHRF1 is hypothetically involved in a macro-molecular protein complex called "ECREM" for "Epigenetic Code Replication Machinery". This complex would be able to duplicate the epigenetic code by acting at the DNA replication fork and by activating the right enzymatic activity at the right moment. There are increasing evidence that UHRF1 is the conductor of this replication process by ensuring the crosstalk between DNA methylation and histone modifications via the SRA and Tandem Tudor Domains, respectively. This cross-talk allows cancer cells to maintain the repression of TSGs during cell proliferation. Several studies showed that down-regulation of UHRF1 expression in cancer cells by natural pharmacological active compounds, favors enhanced expression or re-expression of TSGs, suppresses cell growth and induces apoptosis. This suggests that hindering UHRF1 to exert its role in the duplication of the methylation patterns (DNA + histones) is responsible for inducing apoptosis. In this review, we present UHRF1 expression as a target of several natural products and we discuss their underlying molecular mechanisms and benefits for chemoprevention and chemotherapy.

Thymoquinone inhibits proliferation, induces apoptosis and chemosensitizes human multiple myeloma cells through suppression of signal transducer and activator of transcription 3 activation pathway

BACKGROUND AND PURPOSE

Constitutive activation of the signal transducer and activator of transcription 3 (STAT3) pathway is frequently encountered in several human cancers including multiple myeloma (MM). Thus, agents that suppress STAT3 phosphorylation have a potential for treatment of MM. In the present report, we investigated whether thymoquinone (TQ), the main component isolated from the medicinal plant Nigella sativa, modulated the STAT3 signalling pathway in MM cells.

EXPERIMENTAL APPROACH

The effect of TQ on both constitutive and IL-6-induced STAT3 activation, associated protein kinases, STAT3-regulated gene products involved in proliferation, survival and angiogenesis, cellular proliferation and apoptosis in MM cells, was investigated.

KEY RESULTS

We found that TQ inhibited both constitutive and IL-6-inducible STAT3 phosphorylation which correlated with the inhibition of c-Src and JAK2 activation. Vanadate reversed the TQ-induced down-regulation of STAT3 activation, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that TQ can induce the expression of Src homology-2 phosphatase 2 that correlated with suppression of STAT3 activation. TQ also down-regulated the expression of STAT3-regulated gene products, such as cyclin D1, Bcl-2, Bcl-xL, survivin, Mcl-1 and vascular endothelial growth factor. Finally, TQ induced the accumulation of cells in sub-G1 phase, inhibited proliferation and induced apoptosis, as indicated by poly ADP ribose polymerase cleavage. TQ also significantly potentiated the apoptotic effects of thalidomide and bortezomib in MM cells.

CONCLUSIONS AND IMPLICATIONS

Our study has identified STAT3 signalling as a target of TQ and has thus raised its potential application in the prevention and treatment of MM and other cancers.

Review on molecular and therapeutic potential of thymoquinone in cancer

Thymoquinone (TQ) is the predominant bioactive constituent present in black seed oil (Nigella sativa) and has been tested for its efficacy against cancer. Here, we summarize the literature about TQ's molecular mechanism of action and its ability to induce apoptosis and inhibit tumor growth in preclinical models. TQ has anti-inflammatory effects, and it inhibits tumor cell proliferation through modulation of apoptosis signaling, inhibition of angiogenesis, and cell cycle arrest. Chemosensitization by TQ is mostly limited to in vitro studies, and it has potential in therapeutic strategy for cancer. The results favor efficacy and enhancement of therapeutic benefit against tumor cells resistant to therapy based on cellular targets that are molecular determinants for cancer cell survival and progression. There have been attempts to synthesize novel analogs of TQ directed toward superior effects in killing tumor cells with more enhanced chemosensitizing potential than parent TQ compound. Based on published reports, we believe that further in-depth studies are warranted including investigation of its bioavailability and Phase I toxicity profiling in human subjects. The results from such studies will be instrumental in advancing this field in support of initiating clinical trials for testing the effects of this ancient agent in cancer therapy.

Thymoquinone up-regulates PTEN expression and induces apoptosis in doxorubicin-resistant human breast cancer cells

The use of innocuous naturally occurring compounds to overcome drug resistance and cancer recalcitrance is now in the forefront of cancer research. Thymoquinone (TQ) is a bioactive constituent of the volatile oil derived from seeds of Nigella sativa Linn. TQ has shown promising anti-carcinogenic and anti-tumor activities through different mechanisms. However, the effect of TQ on cell signaling and survival pathways in resistant cancer cells has not been fully delineated. Here, we report that TQ greatly inhibits doxorubicin-resistant human breast cancer MCF-7/DOX cell proliferation. TQ treatment increased cellular levels of PTEN proteins, resulting in a substantial decrease of phosphorylated Akt, a known regulator of cell survival. The PTEN expression was accompanied with elevation of PTEN mRNA. TQ arrested MCF-7/DOX cells at G2/M phase and increased cellular levels of p53 and p21 proteins. Flow cytometric analysis and agarose gel electrophoresis revealed a significant increase in Sub-G1 cell population and appearance of DNA ladders following TQ treatment, indicating cellular apoptosis. TQ-induced apoptosis was associated with disrupted mitochondrial membrane potential and activation of caspases and PARP cleavage in MCF-7/DOX cells. Moreover, TQ treatment increased Bax/Bcl2 ratio via up-regulating Bax and down-regulating Bcl2 proteins. More importantly, PTEN silencing by target specific siRNA enabled the suppression of TQ-induced apoptosis resulting in increased cell survival. Our results reveal that up-regulation of the key upstream signaling factor, PTEN, in MCF-7/DOX cells inhibited Akt phosphorylation, which ultimately causes increase in their regulatory p53 levels affecting the induction of G2/M cell cycle arrest and apoptosis. Overall results provide mechanistic insights for understanding the molecular basis and utility of the anti-tumor activity of TQ.

Cancer prevention with natural compounds

Botanical and nutritional compounds have been used for the treatment of cancer throughout history. These compounds also may be useful in the prevention of cancer. Population studies suggest that a reduced risk of cancer is associated with high consumption of vegetables and fruits. Thus, the cancer chemopreventive potential of naturally occurring phytochemicals is of great interest. There are numerous reports of cancer chemopreventive activity of dietary botanicals, including cruciferous vegetables such as cabbage and broccoli, Allium vegetables such as garlic and onion, green tea, Citrus fruits, soybeans, tomatoes, berries, and ginger, as well as medicinal plants. Several lead compounds, such as genistein (from soybeans), lycopene (from tomatoes), brassinin (from cruciferous vegetables), sulforaphane (from asparagus), indole-3-carbinol (from broccoli), and resveratrol (from grapes and peanuts) are in preclinical or clinical trials for cancer chemoprevention. Phytochemicals have great potential in cancer prevention because of their safety, low cost, and oral bioavailability. In this review, we discuss potential natural cancer preventive compounds and their mechanisms of action.

Thymoquinone, a potential therapeutic agent of Nigella sativa, binds to site I of human serum albumin

Thymoquinone (TQ) is the main constituent of Nigella sativa essential oil which shows promising in vitro and in vivo antineoplastic growth inhibition against various tumor cell lines. Because of the increasing interest to test it in pre-clinical and clinical researches for assessing its health benefits, we here evaluate the interactions between TQ and human serum albumin (HSA), a possible carrier of this drug in vivo. Binding to HSA was studied using different spectroscopic techniques. Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopies suggest that the association between TQ and HSA does not affect the secondary structure of HSA. Using fluorescence spectroscopy, one mole of TQ was found to bind one mole of HSA with a binding constant of 2.39 +/- 0.2 10(4)M(-1). At 25 degrees C (pH 7.4), van't Hoff's enthalpy and entropy that accompany the binding were found to be -10.24 kJ/mol(-1) and 45 J/mol(-1)K(-1) respectively. The thermodynamic analysis of the TQ-HSA complex formation shows that the binding process is enthalpy driven and spontaneous, and that hydrophobic interactions are the predominant intermolecular forces stabilizing the complex. Furthermore, displacement experiments using warfarin and ibuprofen indicate that TQ could bind to site I of HSA, which is also in agreement with the results of the molecular modeling study.

Effects of thymoquinone on isolated and cellular proteasomes

Thymoquinone, a naturally derived agent, has been shown to possess antioxidant, antiproliferative and proapoptotic activities. In the present study, we explored thymoquinone effects on the proteasomal complex, the major system involved in the removal of damaged, oxidized and misfolded proteins. In purified 20S complexes, subunit-dependent and composition-dependent inhibition was observed, and the chymotrypsin-like and trypsin-like activities were the most susceptible to thymoquinone treatment. U87 MG and T98G malignant glioma cells were treated with thymoquinone, and 20S and 26S proteasome activity was measured. Inhibition of the complex was evident in both cell lines, but predominantly in U87 MG cells, and was accompanied by accumulation of ubiquitin conjugates. Accumulation of p53 and Bax, two proteasome substrates with proapoptotic activity, was observed in both cell lines. Our results demonstrate that thymoquinone induces selective and time-dependent proteasome inhibition, both in isolated enzymes and in glioblastoma cells, and suggest that this mechanism could be implicated in the induction of apoptosis in cancer cells.

Thymoquinone hydrazone derivatives cause cell cycle arrest in p53-competent colorectal cancer cells

Thymoquinone (TQ), the major compound of black seed oil, has been shown to induce pro-apoptotic signaling pathways in various human cancer models. Although TQ is commonly used in traditional medicine, its use in humans is limited due to its chemical properties and poor membrane penetration capacity. We therefore attached saturated and unsaturated fatty acid residues to TQ and evaluated the effect on cell proliferation, apoptosis and underlying signaling pathways in HCT116 and HCT116(p53-/-) colon cancer and HepG2 hepatoma cells in vitro. Treatment with thymoquinone-4-α-linolenoylhydrazone (TQ-H-10) or thymoquinone-4-palmitoylhydrazone (TQ-H-11) induced a cytostatic effect, particularly in p53-competent HCT116 cells, mediated by an up-regulation of p21(cip1/waf1) and a down-regulation of cyclin E, and associated with an S/G(2) arrest of the cell cycle. Cells lacking p53 (HCT116(p53-/-)) or HepG2 liver cancer cells showed only a minor response to TQ-H-10. These findings demonstrate that derivatives of TQ inhibit cell proliferation dependent on p53 status by activating the cell cycle inhibitor p21(cip1/waf1) at lower concentrations than unmodified TQ. Structural modifications can therefore contribute to the further clinical development of TQ.