RETRACTED ARTICLE: Quinoxaline 1,4-dioxides induce G2/M cell cycle arrest and apoptosis in human colon cancer cells

Quinoxaline 1,4-Dioxides: Advances in Chemistry and Chemotherapeutic Drug Development

N-Oxides of heterocyclic compounds are the focus of medical chemistry due to their diverse biological properties. The high reactivity and tendency to undergo various rearrangements have piqued the interest of synthetic chemists in heterocycles with N-oxide fragments. Quinoxaline 1,4-dioxides are an example of an important class of heterocyclic N-oxides, whose wide range of biological activity determines the prospects of their practical use in the development of drugs of various pharmaceutical groups. Derivatives from this series have found application in the clinic as antibacterial drugs and are used in agriculture. Quinoxaline 1,4-dioxides present a promising class for the development of new drugs targeting bacterial infections, oncological diseases, malaria, trypanosomiasis, leishmaniasis, and amoebiasis. The review considers the most important methods for the synthesis and key directions in the chemical modification of quinoxaline 1,4-dioxide derivatives, analyzes their biological properties, and evaluates the prospects for the practical application of the most interesting compounds.

Revision of the Regioselectivity of the Beirut Reaction of Monosubstituted Benzofuroxans with Benzoylacetonitrile. 6-Substituted quinoxaline-2-carbonitrile 1,4- dioxides: Structural Characterization and Estimation of Anticancer Activity and Hypoxia Selectivity

BACKGROUND

Quinoxaline 1,4-dioxides have a broad range of biological activity that causes a growing interest in their derivatives for drug discovery. Recent studies demonstrated that quinoxaline 1,4- dioxides have a promising anticancer activity and good hypoxia-selectivity.

OBJECTIVE

The preparation, isolation, structure characterization, and screening for anticancer activity of the first representatives of 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides have been described.

MATERIALS AND METHODS

A series of 7- and 6-halogeno-3-phenylquinoxaline-2-carbonitrile 1,4-dioxides was synthesized by the Beirut reaction. The cytotoxicity was assessed by MTT test (72 h incubation) in normoxia (21% O2) and hypoxia (1% O2) conditions.

RESULTS

We found that during the Beirut reaction between a benzofuroxan bearing an electron withdrawing group and benzoylacetonitrile in the presence of triethylamine, in addition to well-known 7-substituted quinoxaline-2-carbonitrile 1,4-dioxides 7-11a, the 6-isomers 7-11b are formed. Moreover, the yield of the 6- isomers increased with the increase in the electron-withdrawing character of the substituent. For benzofuroxans with CO2Me and CF3 groups, 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides 10-11b were the major products. Despite similarities in physicochemical and spectroscopic properties, the obtained isomers exhibit considerable differences in their anticancer activity and hypoxia selectivity.

CONCLUSION

Substituents and their electronic effects play a key role in the formation of 7- and 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides in the Beirut reaction and in the cytotoxicity properties of the obtained isomers.

Sevoflurane inhibits the progression of ovarian cancer through down-regulating stanniocalcin 1 (STC1)

Background

Ovarian cancer is one of the leading causes of female death worldwide, with a poor prognosis of advanced patients. Sevoflurane, a volatile anesthetic commonly used in clinical operations, has been reported to have anti-cancer activity against some tumors. In the present study, we aimed to investigate the effects of sevoflurane on the progression of ovarian cancer and its potential mechanism.

Methods

The effects of sevoflurane on ovarian cancer cell viability, proliferation, migration, invasion, cell cycle, and apoptosis were determined by functional experiments in vitro. Gelatin zymography assay was performed to examine MMP9 activity. In vivo, sevoflurane was injected into mice of transplantation tumor with SKOV3 cells or with pcDNA-STC1 treated SKOV3 cells.

Results

We found that sevoflurane inhibited the viability of SKOV3 and OVCAR3 cells in a dose-dependent manner, and colony formation assay revealed that sevoflurane inhibited ovarian cancer cell colony-formation abilities. Additionally, sevoflurane could induce cell cycle arrest and promote cell apoptosis in SKOV3 and OVCAR3 cells. Moreover, sevoflurane reduced the migration and invasion abilities of SKOV3 and OVCAR3 cells, as well as the MMP-9 activity. Furthermore, sevoflurane down-regulated the expression of stanniocalcin 1 (STC1), and up-regulation of STC1 could reverse the inhibitory effects of sevoflurane on cell proliferation and invasion. In vivo, sevoflurane significantly inhibited the tumor growth, which was be reversed by STC1 overexpression.

Conclusion

These data reveal an anti-cancer activity of sevoflurane on the growth and invasion of ovarian cancer, which may be through down-regulating STC1. Sevoflurane may serve as a potential anti-cancer agent in ovarian cancer therapy.

Novel Quinoxaline-2-Carbonitrile-1,4-Dioxide Derivatives Suppress HIF1α Activity and Circumvent MDR in Cancer Cells

A series of 3-aryl/hetarylquinoxaline-2-carbonitrile-1,4-dioxides was synthesized and evaluated against breast cancer cell lines in normoxia and hypoxia. Selected compounds in this series demonstrated better cytotoxicity and comparable hypoxia selectivity than tirapazamine. In contrast to Dox, quinoxaline-1,4-dioxides showed potent cytotoxicity against different MDR cells. Compound 2g inhibits of cancer cell growth through p53-independent mechanisms. Our results showed that compound 2g sensitized MCF-7 cells to metformin in hypoxia. Treatment with 2g results in the increase of ROS accumulation in cancer cells. Compound 2g can be considered as the lead compound for further anticancer drug design, evaluation, and development of new potent antitumor agents.

Retraction Note to: Quinoxaline 1,4-dioxides induce G2/M cell cycle arrest and apoptosis in human colon cancer cells

The authors have retracted this article because of overlap in images within the publication and with another previously published article. It was brought to our attention that there are inconsistencies in Figs. 3, 5 and 6. The left middle panel in Fig. 3, labeled "Ctrl", is the same as the left panel in Fig. 6, labeled "PD98059", except that the latter is flipped upside down and right-left. In Fig. 5, the gel in the middle left panel labeled TGF-β2 has been cropped in two different ways and used in Figs. 2 and 3 of Harakeh et al. This has been investigated by the Internal Research Integrity panel of the American University of Beirut who recommended retraction of the article as the original data are not available. *All authors agree to this retraction.

Curcumin attenuates quinocetone-induced oxidative stress and genotoxicity in human hepatocyte L02 cells

Quinocetone (QCT), a new quinoxaline 1,4-dioxides, has been used as antimicrobial feed additive in China. Potential genotoxicity of QCT was concerned as a public health problem. This study aimed to investigate the protective effect of curcumin on QCT-induced oxidative stress and genotoxicity in human hepatocyte L02 cells. Cell viability and intracellular reactive oxygen species (ROS), biomarkers of oxidative stress including superoxide dismutase (SOD) activity and glutathione (GSH) level were measured. Meanwhile, comet assay and micronucleus assay were carried out to evaluate genotoxicity. The results showed that, compared to the control group, QCT at the concentration ranges of 2-16 μg/mL significantly decreased L02 cell viability, which was significantly attenuated with curcumin pretreatment (2.5 and 5 μM). In addition, QCT significantly increased cell oxidative stress, characterized by increases of intracellular ROS level, while decreased endogenous antioxidant biomarkers GSH level and SOD activity (all p < 0.05 or 0.01). Curcumin pretreatment significantly attenuated ROS formation, inhibited the decreases of SOD activity and GSH level. Furthermore, curcumin significantly reduced QCT-induced DNA fragments and micronuclei formation. These data suggest that curcumin could attenuate QCT-induced cytotoxicity and genotoxicity in L02 cells, which may be attributed to ROS scavenging and anti-oxidative ability of curcumin. Importantly, consumption of curcumin may be a plausible way to prevent quinoxaline 1,4-dioxides-mediated oxidative stress and genotoxicity in human or animals.

In vitro and in vivo anti-glioma activity of a chalcone-quinoxaline hybrid

Chalcones are important compounds that exhibit multiple biological activities, including anti-inflammatory, antimitotic and antibacterial properties. In the present study, we have analyzed the potential anti-cancer activity of a chalcone named N9 (a hybrid chalcone-quinoxaline compound) using in vitro and in vivo experimental glioma models. Here, we report N9-induced inhibition of cell proliferation and also N9-induced cell death in a concentration-dependent manner in U87-MG glioma cells. These effects of N9 appear to be associated with its ability to inhibit the expression of cell cycle-associated proteins, and also the augmentation in the expression of the p21 (p21/Cip1) protein, a cyclin-dependent kinase inhibitor. Additionally, N9 also potentiates the production of the pro-apoptotic markers Bax and p53 via inhibition of MDM2. Moreover, our results show that N9 also significantly enhanced apoptosis of U87-MG cells with disruption of mitochondrial membrane potential, generation of ROS and caspase-9 activation. In vivo experiments carried out in a murine xenograft model of U87-MG revealed that N9 produced a significant reduction of tumors volume when compared to vehicle treated mice. Collectively, data demonstrate that N9 possess in vitro and in vivo anti-cancer activity, an effect that seems to involve the induction of p53 and p21 proteins, as well as, the activation of mitochondrial apoptosis pathway associated with the inhibition of protein MDM2. Overall, this study suggests N9 is affecting a variety of intracellular pathways related to tumor apoptosis. Perhaps N9 or derivate molecules could represent new potential drugs for cancer therapeutics.

Olaquindox induces apoptosis through the mitochondrial pathway in HepG2 cells

Olaquindox is used in China as feed additive for growth promotion in pigs. Recently, we have demonstrated that olaquindox induced genome DNA damage and oxidative stress in HepG2 cells. The aim of this study was to explore the molecular mechanism of cell cycle arrest and apoptosis induced by olaquindox in HepG2 cells. In the present study olaquindox induced cell cycle arrest to the S phase and dose-dependent apoptotic cell death in HepG2 cells, indicated by accumulation of sub-G1 cell population, nuclear condenstion, DNA fragmentation, caspases activation and PARP cleavage. Meanwhile, the data showed that olaquindox triggered ROS-mediated apoptosis in HepG2 cells correlated with both the mitochondrial DNA damage and nuclear DNA damage, collapse of Δψ(m), opening of mPTP, down-regulation of Bcl-2 and up-regulation of Bax. Furthermore, we also found that olaquindox increased the expression of p53 protein and induced the release of cytochrome C from mitochondria to cytosol. In conclusion, olaquindox induced apoptosis of HepG2 cells through a caspase-9 and -3 dependent mitochondrial pathway, involving p53, Bcl-2 family protein expression, Δψ(m) disruption and mPTP opening.

Cell death by the quinoxaline dioxide DCQ in human colon cancer cells is enhanced under hypoxia and is independent of p53 and p21

INTRODUCTION

We have shown that the radio sensitizer DCQ enhances sensitivity of HCT116 human colon cancer cells to hypoxia. However, it is not known whether the p53 or p21 genes influence cellular response to DCQ. In this study, we used HCT116 that are either wildtype for p53 and p21, null for p53 or null for p21 to understand the role of these genes in DCQ toxicity.

METHODS

HCT116 cells were exposed to DCQ and incubated under normoxia or hypoxia and the viability, colony forming ability, DNA damage and apoptotic responses of these cells was determined, in addition to the modulation of HIF-1α and of p53, p21, caspase-2, and of the ataxia telangiectasia mutated (ATM) target PIDD-C.

RESULTS

DCQ decreased colony forming ability and viability of all HCT116 cells to a greater extent under hypoxia than normoxia and the p21-/-cell line was most sensitive. Cells had different HIF-1α responses to hypoxia and/or drug treatment. In p53+/+, DCQ significantly inhibited the hypoxia-induced increases in HIF-1α protein, in contrast to the absence of a significant HIF-1α increase or modulation by DCQ in p21-/- cells. In p53-/- cells, 10 μM DCQ significantly reduced HIF-1α expression, especially under hypoxia, despite the constitutive expression of this protein in control cells. Higher DCQ doses induced PreG1-phase increase and apoptosis, however, lower doses caused mitotic catastrophe. In p53+/+ cells, apoptosis correlated with the increased expression of the pro-apoptotic caspase-2 and inhibition of the pro-survival protein PIDD-C. Exposure of p53+/+ cells to DCQ induced single strand breaks and triggered the activation of the nuclear kinase ATM by phosphorylation at Ser-1981 in all cell cycle phases. On the other hand, no drug toxicity to normal FHs74 Int human intestinal cell line was observed.

CONCLUSIONS

Collectively, our findings indicate that DCQ reduces the colony survival of HCT116 and induces apoptosis even in cells that are null for p53 or p21, which makes it a molecule of clinical significance, since many resistant colon tumors harbor mutations in p53.

Structure and vibrational frequencies of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione based on density functional theory calculations: The role of pi-electron conjugation and back-donation

This work deals with the vibrational spectroscopy of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione by means of quantum chemical calculations. The mid and far FT-IR and FT-Raman spectra are recorded in the condensed State. The fundamental vibrational frequencies and intensity of vibrational bands are evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* method and basis set combination and is scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectrum is interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations are applied to simulate infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The infrared unscaled frequencies and intensities are used to disentangle the role played by back-donation in the title compound. For this purpose five other molecules are considered as references: ethane, dimethyl ether, anisole, p-nitro-anisole, and p-hydroxyanisole, in which back-donation has already been ascertained also experimentally. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group.

Radiosensitization of EMT6 mammary carcinoma cells by 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide

BACKGROUND AND PURPOSE

Previously, we have reported that 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide (DCQ) is a radiosensitizer. Here, we investigate the mechanism of radiosensitization.

MATERIALS AND METHODS

EMT6 cells were treated with DCQ for 4h prior to ionizing radiation (IR). Flow cytometry, clonogenic assay, TUNEL, and Western blotting were performed to assess the effect of treatment on cells.

RESULTS

Propidium iodide staining of EMT6 cells treated with IR+/-DCQ revealed high numbers of cells with decreased DNA, consistent with an apoptotic response. TUNEL assay revealed apoptosis was 4%, 38%, and 49% 24h after treatment with IR alone, DCQ alone, and DCQ+IR, respectively. Clonogenic assays revealed that the survival of irradiated EMT6 cells was significantly reduced by DCQ treatment. DCQ treatment abrogated the radiation-induced expression of p21 and p53. The increased apoptosis observed in DCQ+IR-treated cells was correlated to suppression of radiation-induced phosphorylation of Akt and the expression of Bcl-X(L). DCQ also caused the phosphorylation of mitogen-activated protein kinases Erk and Jnk.

CONCLUSIONS

The radiosensitization effect of DCQ occurs through enhancement of radiation-induced apoptosis, which correlates to the inhibition of p-Akt kinase and Bcl-X(L) and the activation of Erk and Jnk kinases, but appears independent of p53 induction or modulation of Bax/Bcl-2 gene expression. These data suggest DCQ should be tested as a radiosensitizer in vivo and has potential in the treatment of human solid tumors.

(2α,3β)-2,3-Dihydroxyolean-12-en-28-oic acid, a new natural triterpene fromOlea europea, induces caspase dependent apoptosis selectively in colon adenocarcinoma cells

Triterpenoids are known to induce apoptosis and to be anti-tumoural. Maslinic acid, a pentacyclic triterpene, is present in high concentrations in olive pomace. This study examines the response of HT29 and Caco-2 colon-cancer cell lines to maslinic-acid treatment. At concentrations inhibiting cell growth by 50-80% (IC50HT29=61+/-1 microM, IC80HT29=76+/-1 microM and IC50Caco-2=85+/-5 microM, IC80Caco-2=116+/-5 microM), maslinic acid induced strong G0/G1 cell-cycle arrest and DNA fragmentation, and increased caspase-3 activity. However, maslinic acid did not alter the cell cycle or induce apoptosis in the non-tumoural intestine cell lines IEC-6 and IEC-18. Moreover, maslinic acid induced cell differentiation in colon adenocarcinoma cells. These findings support a role for maslinic acid as a tumour suppressant and as a possible new therapeutic tool for aberrant cell proliferation in the colon. In this report, we demonstrate for the first time that, in tumoural cancer cells, maslinic acid exerts a significant anti-proliferation effect by inducing an apoptotic process characterized by caspase-3 activation by a p53-independent mechanism, which occurs via mitochondrial disturbances and cytochrome c release.