Biomedical subjects

Hala Gali-Muhtasib

Publications and source records attributed to Hala Gali-Muhtasib.

11 recordsLinked to original sources

PubMed2007

Lack of p53 augments thymoquinone-induced apoptosis and caspase activation in human osteosarcoma cells.

We have recently shown that thymoquinone (TQ) is an antineoplastic drug that induces p53-dependent apoptosis in human colon cancer cells. This study evaluated the antiproliferative and pro-apoptotic effects of TQ in two human osteosarcoma cell lines with different p53 mutation status. TQ decreased cell survival dose-dependently and, more significantly, in p53-null MG63 cells (IC(50) = 17 muM) than in p53-mutant MNNG/HOS cells (IC(50) = 38 muM). Cell viability was reduced more selectively in MG63 tumor cells than in normal human osteoblasts. Flow cytometric analysis showed that TQ induced a much greater increase in the PreG(1) (apoptotic) cell population, but no cell cycle arrest in MG63. G(2)/M arrest in MNNG/HOS cells was associated with p21(WAF1) upregulation. Using three DNA damage assays, TQ was confirmed to result in a significantly greater extent of apoptosis in p53 null MG63 cells. Although the Bax/Bcl-2 ratios were not differentially modulated in both cell lines, the mitochondrial pathway appeared to be involved in TQ-induced apoptosis in MG63 by showing the cleavage of caspases-9 and -3. Oxidative stress and mitochondrial O(2)(*-) generation in isolated rat mitochondria were enhanced by TQ as measured by the dose-dependent reduction in aconitase enzyme activity and Amplex Red oxidation respectively. TQ-induced oxidative damage, reflected by an increase in gamma-H2AX foci and increased protein expression levels of gamma-H2AX and the DNA repair enzyme, NBS1, was more pronounced in MNNG/HOS than in MG63. We suggest that the resistance of MNNG/HOS cells to drug-induced apoptosis is caused by the up-regulation of p21(WAF1) by the mutant p53 (transcriptional activity was shown by p53 siRNA treatment) which induces cell cycle arrest and allows to repair DNA damage. Collectively, these findings show that TQ induces p53-independent apoptosis in human osteosarcoma cells. As the loss of p53 function is frequently observed in osteosarcoma patients, our data suggest the potential clinical usefulness of TQ for the treatment of these malignancies.

Animals↗

PubMed2007

Radiosensitization by 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide under oxia and hypoxia in human colon cancer cells.

BACKGROUND: The sensitizing effects of 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide (DCQ) and ionizing radiation (IR) were determined in four colon cancer cells and in FHs74Int normal intestinal cells. METHODS: Cell cycle modulation, TUNEL assay, clonogenic survival and DNA damage were examined under oxia or hypoxia. Effects on apoptotic molecules and on p-Akt and Cox-2 protein expression were investigated. RESULTS: The four cell lines responded differently to DCQ+IR; HT-29 cells were most resistant. Combination treatment caused significant increases in preG1 (apoptosis) in HCT-116, while G2/M arrest occurred in DLD-1. DCQ potentiated IR effects more so under hypoxia than oxia. Pre-exposure of DLD-1 to hypoxia induced 30% apoptosis, and G2/M arrest in oxia. The survival rate was 50% lower in DCQ+IR than DCQ alone and this rate further decreased under hypoxia. FHs74Int normal intestinal cells were more resistant to DCQ+IR than cancer cells.Greater ssDNA damage occurred in DLD-1 exposed to DCQ+IR under hypoxia than oxia. In oxia, p-Akt protein expression increased upon IR exposure and drug pre-treatment inhibited this increase. In contrast, in hypoxia, exposure to IR reduced p-Akt protein and DCQ restored its expression to the untreated control. Apoptosis induced in hypoxic DLD-1 cells was independent of p53-p21 modulation but was associated with an increase in Bax/Bcl-2 ratio and the inhibition of the Cox-2 protein. CONCLUSION: DCQ is a hypoxic cell radiosensitizer in DLD-1 human colon cancer cells.

Apoptosis↗

PubMed2007

Differential apoptosis by gallotannin in human colon cancer cells with distinct p53 status.

Gallotannin (GT), a plant polyphenol, has shown anticarcinogenic activities in several animal models including colon cancer. In our previous study, we showed that GT inhibits 1,2-dimethylhydrazine-induced colonic aberrant crypt foci and tumors in Balb/c mice, thus supporting a role for GT as a chemopreventive agent in colon cancer. However, at the molecular level, GT's mechanism of chemoprevention is still unclear. In this study, we aim at identifying GT's potential molecular mechanisms of action in in vitro studies. We show that GT differentially inhibits the growth of two isogenic HCT-116 (p53+/+, p53-/-) human colon cancer cells versus normal human intestinal epithelial cells (FHs 74Int). DNA flow cytometric analysis showed that GT induced S-phase arrest in both HCT-116 cell lines. Cell-cycle arrest in p53 (+/+) cells was associated with an increase in p53 protein levels and p21 transcript and protein levels. The inhibition of cell-cycle progression of HCT-116 p53 (+/+) cells by GT correlated with a reduction in the protein levels of cyclin D(1), pRb, and the Bax/Bcl-2 ratio. Although GT did not induce apoptosis in p53 (+/+) cells, a significant induction of apoptosis was observed in p53 (-/-) cells as shown by TUNEL staining and flow cytometry analysis. Apoptosis induction in p53 (-/-) cells was associated with a significant increase in Bax/Bcl-2 protein levels. Our results demonstrate that GT inhibits the growth of HCT-116 colon cancer cells in a p53-independent manner but exhibits differential sensitivity to apoptosis induction in HCT-116 cells with distinct p53 status.

Apoptosis↗

PubMed2005

Thymoquinone: a promising anti-cancer drug from natural sources.

There has been growing interest in naturally occurring compounds with anti-cancer potential. Black seed is one of the most extensively studied plants. This annual herb grows in countries bordering the Mediterranean Sea and India. Thymoquinone (TQ) is the bioactive constituent of the volatile oil of black seed. It has been shown to exert anti-neoplastic and anti-inflammatory effects. The molecular pathways of TQ action are not clear. Nevertheless, TQ is known to induce apoptosis by p53-dependent and p53-independent pathways in cancer cell lines. Growth inhibition is associated with induction of cell cycle arrest. TQ also acts on the immune system by modulating the levels of inflammatory mediators. To date, the chemotherapeutic potential of TQ in the clinic has not been tested, but numerous studies have shown its promising anti-cancer effects in animal models. The combination of TQ with clinically used anti-cancer drugs has led to improvements in their therapeutic index and prevents non-tumor tissues from sustaining chemotherapy-induced damage.

Animals↗

PubMed2005

Regulation of ultraviolet B radiation-mediated activation of AP1 signaling by retinoids in primary keratinocytes.

The main cause of skin cancer and photo-aging is chronic exposure to ultraviolet B (UVB) radiation. Such damage can be ameliorated by retinoid treatment. UVB-radiation-induced skin carcinogenesis is associated with the induction of activator protein 1 (AP1) signaling and factors, namely FOS and JUN family members. We investigated the effects of several retinoids, all-trans-retinoic acid (tRA), 9-cis-retinoic acid (cRA), and N-(4-hydroxyphenyl)-retinamide (HPR), on UVB-induced damage in primary mouse keratinocytes. In addition, the interplay between UVB radiation, retinoid receptors, and AP1 signaling was assessed using Western blot analysis and ribonuclease protection and gene reporter assays. Exposure of keratinocytes to UVB radiation caused a down-regulation of the retinoid receptor protein levels in a proteasome-mediated manner. In contrast, FOS and JUN proteins were transiently induced shortly after exposure to UVB radiation. Retinoid treatment caused a dose-dependent reduction in the levels of retinoid receptor proteins. When irradiated cells were treated with retinoids, no significant effects on AP1 protein expression were noted. Interestingly, pretreatments with tRA and cRA, but not HPR, suppressed UVB-radiation-induced AP1 activity by more than 50%, whereas post-treatment failed to produce similar effects. Our findings indicate that the inhibition of AP1 activity by retinoids explains, at least in part, the chemopreventive potential of retinoids in UV-radiation-associated epidermal damage.

Animals↗

PubMed2004

5-Aza-cytidine is a potent inhibitor of DNA methyltransferase 3a and induces apoptosis in HCT-116 colon cancer cells via Gadd45- and p53-dependent mechanisms.

Methyltransferase inhibitors commonly used in clinical trials promote tumor cell death, but their detailed cytotoxic action is not yet fully understood. A deeper knowledge about their apotosis-inducing mechanisms and their interaction with DNA methyltransferases (DNMTs) DNMT1, DNMT3a, and DNMT3b might allow the design of more effective drugs with lower cytotoxicity. 5-aza-cytidine (5-aza-CR), a potent inhibitor of DNMT1, is known to induce demethylation and reactivation of silenced genes. In this study, we investigated the p53 dependence of apoptotic, cell cycle, and growth inhibitory effects of 5-aza-CR, as well as the influence on the expression level of DNMT1, DNMT3a, and DNMT3b in the colon cancer cell line HCT-116. Exposure to 5-aza-CR induced the up-regulation of genes promoting cell cycle arrest and DNA repair (p21(WAF1) and GADD45) or apoptosis (p53, RIPK2, Bak1, caspase 5, and caspase 6). In parallel, there was a down-regulation of antiapoptotic Bcl2 protein and the G(2)/M-mediator cyclin B1. Co-incubation with pifithrin-alpha (PFT-alpha), a selective p53 inhibitor, restored GADD45, Bcl2, cyclin B1, and p21(WAF1) expression levels and almost completely reversed the growth inhibitory, cell cycle, and apoptotic effects of 5-aza-CR. 5-aza-CR treatment caused global demethylation and reactivation of p16(INK4) expression. There was a marked decrease in DNMT1 and DNMT3a mRNA expression, with PFT-alpha reversing these effects. However, 5-aza-CR treatment did not modulate DNMT3b expression. Our data demonstrate that 5-aza-CR action in HCT-116 is mediated by p53 and its downstream effectors p21(WAF1) and GADD45. This is the first report to show a link between p53 and regulation of DNMT1 and de novo methyltransferase DNMT3a.

Annexin A5↗

PubMed2004

Inhibition of proliferation and induction of apoptosis by 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide in adult T-cell leukemia cells.

Human T-cell lymphotrophic virus type-1 (HTLV-1) is a retrovirus which causes adult T-cell leukemia (ATL), an aggressive malignancy of activated T-cells. So far, there is no proven therapy for this disease. The compound 2-benzoyl-3-phenyl-6,7-dichloro quinoxaline 1,4-dioxide (DCQ) has been shown to exhibit a wide range of antibacterial activities and to induce antiproliferation and apoptosis of human colon cancer cell lines. In the present study, we investigated the in vitro effects of DCQ in HTLV-1 positive (C91-PL and HuT-102) and negative (CEM and Jurkat) malignant T-cells. The results indicate that DCQ induced growth inhibition in all four cell lines examined in a dose-dependent manner. The inhibitory effect was mainly due to the induction of apoptosis which was verified by flow cytometry analyses and ELISA-based apoptosis assays. The role of transforming growth factor (TGF) in mediating the antiproliferative and apoptotic effects of DCQ in ATL cells was investigated. Interestingly, in three of the four cell lines used, DCQ increased the TGF-beta1 transcript levels and decreased TGF-alpha mRNA, but did not induce changes in TGF-beta2 expression. DCQ treatment also induced an upregulation of p53 and p21 protein levels, key mediators of cell cycle arrest and apoptosis. The anti-apoptotic Bcl-2alpha protein level was found to be reduced. These findings indicate that DCQ inhibits the growth of ATL cell lines, at least in part, by inducing apoptosis mediated by the modulation of TGF expression, the upregulation in p53 and p21 proteins and downregulation in Bcl-2alpha expression. The present findings suggest that DCQ merits further investigation as a potential therapeutic agent for this incurable disease.

Adult↗

PubMed2004

Quinoxaline 1,4-dioxides are novel angiogenesis inhibitors that potentiate antitumor effects of ionizing radiation.

We have recently shown that quinoxaline 1,4-dioxides (QdNOs) are potent hypoxia selective cytotoxins that modulate hypoxia inducible factor-1alpha (HIF-1alpha) expression. In this study, we evaluated the cytotoxicity, anti-angiogenic, and radiosensitization activities of the two quinoxaline 1,4-dioxides (QdNOs), BPQ and DCQ. Clonogenic survival, Matrigel, and radiosensitization assays were performed in vitro and in vivo using Lewis lung carcinoma (LLC) and EMT-6 mammary adenocarcinoma cells. Transcript and protein levels of HIF-1alpha and VEGF were determined using RT-PCR and Western blotting, respectively. DCQ showed cytotoxic effects under hypoxic conditions for both cell lines. Treatment with either drug inhibited HIF-1alpha and VEGF secretion, with DCQ being more potent than BPQ. DCQ also inhibited the formation of tube-like structures of ECV-304 endothelial cells in Matrigel by 60-80% and significantly reduced neoangiogenesis in vivo. When combined with radiation (200-1000 cGy), DCQ resulted in the death of 100% of LLC or EMT-6 cells. Using the C57BL/6 mouse model, combined treatment with DCQ and radiation delayed the growth of LLC tumors for 17 days and reduced mean tumor volume by 80% at day 20. However, BPQ combined with radiation did not induce significant tumor regression. Histological analyses revealed a significant increase in tissue necrosis in tumors treated by DCQ and radiation. These results indicate a potent anti-angiogenic and radiation modification effect of two quinoxaline dioxides. These findings should stimulate further research in other tumor models as these compounds could have potential clinical applications in cancer therapy.

Adenocarcinoma↗

PubMed2004

Thymoquinone extracted from black seed triggers apoptotic cell death in human colorectal cancer cells via a p53-dependent mechanism.

For centuries, the black seed (Nigella sativa) herb and oil have been used in Asia, Middle East and Africa to promote health and fight disease. Thymoquinone (TQ), the most abundant constituent present in black seed, is a promising dietary chemopreventive agent. We investigated the effects of thymoquinone (TQ) against HCT-116 human colon cancer cells and attempted to identify its potential molecular mechanisms of action. We report that TQ inhibits the growth of colon cancer cells which was correlated with G1 phase arrest of the cell cycle. Furthermore, TUNEL staining and flow cytometry analysis indicate that TQ triggers apoptosis in a dose- and time-dependent manner. Apoptosis induction by TQ was associated with a 2.5-4.5-fold increase in mRNA expression of p53 and the downstream p53 target gene, p21WAF1. Simultaneously, we found a marked increase in p53 and p21WAF1 protein levels but a significant inhibition of anti-apoptotic Bcl-2 protein. Co-incubation with pifithrin-alpha (PFT-alpha), a specific inhibitor of p53, restored Bcl-2, p53 and p21WAF1 levels to the untreated control and suppressed TQ-induced cell cycle arrest and apoptosis. p53-null HCT-116 cells were less sensitive to TQ-induced growth arrest and apoptosis. These results indicate that TQ is antineoplastic and pro-apoptotic against colon cancer cell line HCT116. The apoptotic effects of TQ are modulated by Bcl-2 protein and are linked to and dependent on p53. Our data support the potential for using the agent TQ for the treatment of colon cancer.

Apoptosis↗

PubMed2002

Protective effect of vitamin E on ultraviolet B light-induced damage in keratinocytes.

Ultraviolet (UV) B radiation is the most common environmental factor in the pathogenesis of skin cancer. Exposure of human skin to UVB radiation leads to the depletion of cutaneous antioxidants, the activation of nuclear factor kappa B (NF-kappaB), and programmed cell death (apoptosis). Although antioxidant supplementation has been shown to prevent UVB-induced photooxidative damage, its effect on components of cell signaling pathways leading to gene expression has not been clearly established. In the present study, the effect of the antioxidant vitamin, alpha-tocopherol (alpha-T), and its acetate analog, alpha-tocopherol acetate (alpha-TAc), on UVB-induced damage in primary and neoplastic mouse keratinocytes was investigated. The ability of both vitamins to modulate UVB-induced apoptosis and activation of the transcription factor NF-kappaB were studied. Treatment of normal and neoplastic mouse epidermal keratinocytes (308 cells) with 30-60 mJ/cm(2) UVB markedly decreased viable cell number and was accompanied by DNA fragmentation. When both vitamins were applied to cells at times before and after UVB radiation, a significant increase in the percentage of viable cells and concomitant decrease in the number of apoptotic cells was noted, with vitamin pretreatment providing a better protection than posttreatment. Simultaneous posttreatment of irradiated cells with alpha-TAc abolished the cytotoxic effects of UVB and restored cell viability to control levels. In addition, simultaneous posttreatment of irradiated cells with alpha-T reduced the number of apoptotic cells by half, indicating a synergistic effect of two such treatments compared with any single one. Flow cytometry analysis indicated that vitamin treatment suppressed both an increase in pre-G0 cells and a decrease in cycling cells by UVB exposure. In addition, NF-kappaB activation was detected 2 h after UV exposure and was maintained for up to 8 h. Pretreatment with vitamins significantly inhibited NF-kappaB activation at 4 and 8 h. These results indicate that vitamin E and its acetate analog can modulate the cellular response to UVB partly through their action on NF-kappaB activation. Thus, these antioxidant vitamins are potential drugs for the protection from or the reduction of UVB-associated epidermal damage.

Animals↗

PubMed2002

Modulating cell cycle: current applications and prospects for future drug development.

The cell cycle is a highly conserved and ordered set of events, culminating in cell growth and division. It is tightly controlled by many regulatory mechanisms that either permit or restrain its progression. The main families of regulatory proteins that play key roles in controlling cell cycle progression are the cyclins, the cyclin dependent kinases (Cdks), their substrate proteins, the Cdk inhibitors (CKI) and the tumor suppressor gene products, p53 and pRb. Many cell cycle control genes, when deregulated, can cause cells that are not dividing to enter the cell cycle and begin to proliferate leading to cancer development. They do so by interfacing with the basic cell cycle regulatory machinery to activate cell cycle entry. There is at present much optimism about the possibility of finding anticancer drug treatment strategies that modulate cell cycle regulatory molecules. Candidate targets for such strategies include crucial cell cycle molecules involved in G(1) to S phase or G(2) to M phase transition. This review will outline the basic regulatory machinery responsible for catalyzing cell cycle entry and describe the latest advances made in the field of cell cycle regulation. The basis of targeting the cell cycle particularly the Cdks as an approach to developing novel, specific and perhaps more effective anticancer treatments will be discussed. Examples of novel cell cycle-targeting agents that are in, or are close to being in clinical trials will be provided.

Animals↗