Sulforaphane induces DNA single strand breaks in cultured human cells

Iberverin exhibits antineoplastic activities against human hepatocellular carcinoma via DNA damage-mediated cell cycle arrest and mitochondrial-related apoptosis

Hepatocellular carcinoma (HCC) is one of the malignant tumors with high incidence and mortality rates in the world. Isothiocyanates (ITCs), bioactive substances present primarily in the plant order Brassicales, have been proved to be promising candidates for novel anti-HCC drugs with chemopreventive and anticancer activities. Iberverin, a predominant ITC isolated from the seeds of oxheart cabbage, has been discovered with anticancer property in lung cancer cells. However, the roles of iberverin in HCC remain elusive. In the present study, the effect and potential mechanisms of iberverin against human HCC were dissected. We demonstrated that low concentrations of iberverin inhibited cell proliferation, suppressed migration and induced mitochondrial-related apoptosis in vitro, and hampered tumorigenicity in vivo, with no obvious toxicity. Furthermore, we found that iberverin treatment induced DNA damage and G2/M phase arrest. Iberverin treatment also caused increased intracellular reactive oxygen species formation and glutathione depletion. Taken together, these results suggest that iberverin promotes mitochondrial-mediated apoptosis and induces DNA damage and G2/M cell cycle arrest in HCC by enhancing oxidative stress. Our findings provide better understanding of the anti-HCC mechanisms of ITCs and the potential for the natural product iberverin as a promising new anti-HCC biotherapeutic.

Sulforaphane and bladder cancer: a potential novel antitumor compound

Bladder cancer (BC) is a common form of urinary tract tumor, and its incidence is increasing annually. Unfortunately, an increasing number of newly diagnosed BC patients are found to have advanced or metastatic BC. Although current treatment options for BC are diverse and standardized, it is still challenging to achieve ideal curative results. However, Sulforaphane, an isothiocyanate present in cruciferous plants, has emerged as a promising anticancer agent that has shown significant efficacy against various cancers, including bladder cancer. Recent studies have demonstrated that Sulforaphane not only induces apoptosis and cell cycle arrest in BC cells, but also inhibits the growth, invasion, and metastasis of BC cells. Additionally, it can inhibit BC gluconeogenesis and demonstrate definite effects when combined with chemotherapeutic drugs/carcinogens. Sulforaphane has also been found to exert anticancer activity and inhibit bladder cancer stem cells by mediating multiple pathways in BC, including phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK), nuclear factor kappa-B (NF-κB), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), zonula occludens-1 (ZO-1)/beta-catenin (β-Catenin), miR-124/cytokines interleukin-6 receptor (IL-6R)/transcription 3 (STAT3). This article provides a comprehensive review of the current evidence and molecular mechanisms of Sulforaphane against BC. Furthermore, we explore the effects of Sulforaphane on potential risk factors for BC, such as bladder outlet obstruction, and investigate the possible targets of Sulforaphane against BC using network pharmacological analysis. This review is expected to provide a new theoretical basis for future research and the development of new drugs to treat BC.

Reviewing the Prospective Pharmacological Potential of Isothiocyanates in Fight against Female-Specific Cancers

Gynecological cancers are the most commonly diagnosed malignancies in females worldwide. Despite the advancement of diagnostic tools as well as the availability of various therapeutic interventions, the incidence and mortality of female-specific cancers is still a life-threatening issue, prevailing as one of the major health problems worldwide. Lately, alternative medicines have garnered immense attention as a therapeutic intervention against various types of cancers, seemingly because of their safety profiles and enhanced effectiveness. Isothiocyanates (ITCs), specifically sulforaphane, benzyl isothiocyanate, and phenethyl isothiocyanate, have shown an intriguing potential to actively contribute to cancer cell growth inhibition, apoptosis induction, epigenetic alterations, and modulation of autophagy and cancer stem cells in female-specific cancers. Additionally, it has been shown that ITCs plausibly enhance the chemo-sensitization of many chemotherapeutic drugs. To this end, evidence has shown enhanced efficacy in combinatorial regimens with conventional chemotherapeutic drugs and/or other phytochemicals. Reckoning with these, herein, we discuss the advances in the knowledge regarding the aspects highlighting the molecular intricacies of ITCs in female-specific cancers. In addition, we have also argued regarding the potential of ITCs either as solitary treatment or in a combinatorial therapeutic regimen for the prevention and/or treatment of female-specific cancers. Hopefully, this review will open new horizons for consideration of ITCs in therapeutic interventions that would undoubtedly improve the prognosis of the female-specific cancer clientele. Considering all these, it is reasonable to state that a better understanding of these molecular intricacies will plausibly provide a facile opportunity for treating these female-specific cancers.

In Silico and In Vitro Analysis of Sulforaphane Anti-Candida Activity

Oropharyngeal candidiasis/candidosis is a common and recurrent opportunistic fungal infection. Fluconazole (FLZ), one of the most used and effective antifungal agents, has been associated with a rise of resistant Candida species in immunocompromised patients undergoing prophylactic therapy. Sulforaphane (SFN), a compound from cruciferous vegetables, is an antimicrobial with yet controversial activities and mechanisms on fungi. Herein, the in silico and antifungal activities of SFN against C. albicans were investigated. In silico analyzes for the prediction of the biological activities and oral bioavailability of SFN, its possible toxicity and pharmacokinetic parameters, as well as the estimates of its gastrointestinal absorption, permeability to the blood-brain barrier and skin, and similarities to drugs, were performed by using different software. SFN in vitro anti-Candida activities alone and in combination with fluconazole (FLZ) were determined by the broth microdilution method and the checkerboard, biofilm and hyphae formation tests. Amongst the identified probable biological activities of SFN, nine indicated an antimicrobial potential. SFN was predicted to be highly absorbable by the gastrointestinal tract, to present good oral availability, and not to be irritant and/or hepatotoxic. SFN presented antifungal activity against C. albicans and prevented both biofilm and hyphae formation by this microorganism. SFN was additive/synergistic to FLZ. Overall, the data highlights the anti-Candida activity of SFN and its potential to be used as an adjuvant therapy to FLZ in clinical settings.

Discovery of Sulforaphane as an Inducer of Ferroptosis in U-937 Leukemia Cells: Expanding Its Anticancer Potential

In recent years, natural compounds have emerged as inducers of non-canonical cell death. The isothiocyanate sulforaphane (SFN) is a well-known natural anticancer compound with remarkable pro-apoptotic activity. Its ability to promote non-apoptotic cell-death mechanisms remains poorly investigated. This work aimed to explore the capacity of SFN to induce non-apoptotic cell death modalities. SFN was tested on different acute myeloid leukemia cell lines. The mechanism of cell death was investigated using a multi-parametric approach including fluorescence microscopy, western blotting, and flow cytometry. SFN triggered different cell-death modalities in a dose-dependent manner. At 25 μM, SFN induced caspase-dependent apoptosis and at 50 μM ferroptosis was induced through depletion of glutathione (GSH), decreased GSH peroxidase 4 protein expression, and lipid peroxidation. In contrast, necroptosis was not involved in SFN-induced cell death, as demonstrated by the non-significant increase in phosphorylation of receptor-interacting protein kinase 3 and phosphorylation of the necroptotic effector mixed lineage kinase domain-like pseudokinase. Taken together, our results suggest that the antileukemic activity of SFN can be mediated via both ferroptotic and apoptotic cell death modalities.

GSH Levels Serve As a Biological Redox Switch Regulating Sulforaphane-Induced Cell Fate in Human Lens Cells

Purpose

Sulforaphane (SFN) is a therapeutic phytochemical agent for many health conditions. SFN-induced cytotoxicity is shown to have promise in preventing posterior capsule opacification (PCO). In the current study, we aimed to elucidate key processes and mechanisms linking SFN treatment to lens cell death.

Methods

The human lens epithelial cell line FHL124 and central anterior epithelium were used as experimental models. Cell death was assessed by microscopic observation and cell damage/viability assays. Gene or protein levels were assessed by TaqMan RT-PCR or immunoblotting. Mitochondrial networks and DNA damage were assessed by immunofluorescence. Mitochondrial membrane potential, activating transcription factor 6 (ATF6) activity, ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), and glutathione reductase (GR) activity were measured using different light reporter assays. SFN metabolites were analyzed by LC-MS/MS.

Results

Treatment with N-acetylcysteine (NAC), a reactive oxygen species scavenger, prevented SFN-induced cell death in both models. NAC also significantly protected FHL124 cells from SFN-induced mitochondrial dysfunctions, endoplasmic reticulum stress (ERS), DNA damage and autophagy. SFN significantly depleted GSH, the major antioxidant in the eye, and reduced GR activity, despite doubling its protein levels. The most abundant SFN conjugate detected in lens cells following SFN application was SFN–GSH. The addition of GSH protected lens cells from all SFN-induced cellular events.

Conclusions

SFN depletes GSH levels in lens cells through conjugation and inhibition of GR activity. This leads to increased reactive oxygen species and oxidative stress that trigger mitochondrial dysfunction, ERS, autophagy, and DNA damage, leading to cell death. In summary, the work presented provides a mechanistic understanding to support the therapeutic application of SFN for PCO and other disorders.

Effects of in vivo treatment of mice with sulforaphane on repair of DNA pyridyloxylbutylation

The phytochemical sulforaphane (SF) has gained interest for its apparent association with reduced cancer risk and other cytoprotective properties, at least some of which are attributed to activation of the transcription factor Nrf2. Repair of bulky DNA adducts is important for mitigating carcinogenesis from exogenous DNA damaging agents, but it is unknown whether in vivo treatment with SF affects adduct repair. At 12 h following a single oral dose of 100 mg/kg SF, an almost doubling in activity for repair of pyridyloxobutylated DNA was observed in CD-1 mouse liver nuclear extracts, but not in lung extracts. This change at 12 h in repair activity was preceded by the induction of Nrf2-regulated genes but not accompanied by changes in levels of the specific nucleotide excision repair (NER) proteins XPC, XPA, XPB and p53 or in binding of hepatic XPC, XPA and XPB to damaged DNA. SF also did not significantly alter histone deacetylase activity as measured by acetylated histone H3 levels, or stimulate formation of γ-H2A.X, a marker of DNA damage. A significant reduction in oxidative DNA damage, as measured by 8-OHdG (a biomarker of oxidative DNA damage), was observed only in DNA from the lungs of SF-treated mice 3 h post-dosing. These results suggest that the ability of SF to increase bulky adduct repair activity is organ-selective and is consistent with activation of the Nrf2 signaling pathway.

The phytoprotective agent sulforaphane prevents inflammatory degenerative diseases and age-related pathologies via Nrf2-mediated hormesis

In numerous experimental models, sulforaphane (SFN) is shown herein to induce hormetic dose responses that are not only common but display endpoints of biomedical and clinical relevance. These hormetic responses are mediated via the activation of nuclear factor erythroid- derived 2 (Nrf2) antioxidant response elements (AREs) and, as such, are characteristically biphasic, well integrated, concentration/dose dependent, and specific with regard to the targeted cell type and the temporal profile of response. In experimental disease models, the SFN-induced hormetic activation of Nrf2 was shown to effectively reduce the occurrence and severity of a wide range of human-related pathologies, including Parkinson's disease, Alzheimer's disease, stroke, age-related ocular damage, chemically induced brain damage, and renal nephropathy, amongst others, while also enhancing stem cell proliferation. Although SFN was broadly chemoprotective within an hormetic dose-response context, it also enhanced cell proliferation/cell viability at low concentrations in multiple tumor cell lines. Although the implications of the findings in tumor cells are largely uncertain at this time and warrant further consideration, the potential utility of SFN in cancer treatment has not been precluded. This assessment of SFN complements recent reports of similar hormesis-based chemoprotections by other widely used dietary supplements, such as curcumin, ginkgo biloba, ginseng, green tea, and resveratrol. Interestingly, the mechanistic profile of SFN is similar to that of numerous other hormetic agents, indicating that activation of the Nrf2/ARE pathway is probably a central, integrative, and underlying mechanism of hormesis itself. The Nrf2/ARE pathway provides an explanation for how large numbers of agents that both display hormetic dose responses and activate Nrf2 can function to limit age-related damage, the progression of numerous disease processes, and chemical- and radiation- induced toxicities. These findings extend the generality of the hormetic dose response to include SFN and many other chemical activators of Nrf2 that are cited in the biomedical literature and therefore have potentially important public health and clinical implications.

Effects of sulforaphane on the oxidative response, apoptosis, and the transcriptional profile of human stomach mucosa cells in vitro

Oxidative stress is a critical factor in the pathogenesis of several gastrointestinal diseases. Sulforaphane (SFN), a bioactive compound found in cruciferous vegetables, activates the redox-sensitive nuclear erythroid 2-related factor 2 (NRF2). In addition to its protective role, SFN exerts cytotoxic effects on cancer cells. However, there is a lack of information concerning the toxicity of SFN in normal cells. We investigated the effects of SFN on cell viability, antioxidant defenses, and gene expression in human stomach mucosa cells (MNP01). SFN reduced ROS formation and protected the cells against induced oxidative stress but high concentrations increased apoptosis. An intermediate SFN concentration (8 μM) was chosen for RNA sequencing studies. We observed upregulation of genes of the NRF2 (antioxidant) pathway, the DNA damage response, and apoptosis signaling; whereas SFN downregulated cell cycle and DNA repair pathway genes. SFN may be cytoprotective at low concentrations and cytotoxic at high concentrations.

Molecular targets in cancer prevention by 4-(methylthio)butyl isothiocyanate - A comprehensive review

The consumption of cruciferous vegetables rich in isothiocyanates has long been associated with a reduced risk of various types of cancer. 4-(methylthio)butyl isothiocyanate also called erucin is an isothiocyanate present in appreciable quantity in the seeds of Eruca sativa Mill. plant. Although the literature has revealed its protective effects via inducing phase II enzymes and inhibiting carcinogen activating phase I enzymes, recent studies also suggest that, it inhibits the proliferation of cancer cells by altering the telomerase activity, dynamics of microtubules, expression of histone deacetylases, and other molecular pathways. With this in mind, the emphasis has been made to review the molecular targets involved in cancer prevention by 4-(methylthio)butyl isothiocyanate.

Mechanism of selective anticancer activity of isothiocyanates relies on differences in DNA damage repair between cancer and healthy cells

Purpose

Isothiocyanates (ITCs) are compounds derived from Brassica plants with documented anticancer activity. Molecular mechanisms of their selective activity against cancer cells are still underexplored. In this work, the impact of ITC on DNA replication and damage was compared between PC-3 prostate cancer cells and HDFa normal fibroblasts as well as PNT2 prostate epithelial cells.

Methods

Cells were treated with sulforaphane or phenethyl isothiocyanate. [³H]thymidine incorporation and the level of histone γH2A.X were estimated as indicators of DNA replication and double-strand breaks (DSB), respectively. Levels of HDAC3, CtIP, and p-RPA were investigated by immunoblotting. Comet assay was performed to visualize DNA damage.

Results

ITCs inhibited DNA replication in all tested cell lines, and this activity was independent of reactive oxygen species of mitochondrial origin. It was followed by DSB which were more pronounced in cancer than noncancerous cells. This difference was independent of HDAC activity which was decreased in both cell lines when treated with ITCs. On the other hand, it correlated with faster removal of DSB, and thus, transient activation of repair proteins in normal cells, while in PC-3 prostate cancer, cell DNA repair was significantly less effective.

Conclusion

DNA damage induced by ITCs is a consequence of the block in DNA replication which is observed in both, cancer and normal cells. Selective antiproliferative activity of ITCs towards cancer cells results from less efficient DNA repair in cancer cells relative to normal cells.

Antioxidant effects of sulforaphane in human HepG2 cells and immortalised hepatocytes

Sulforaphane (SFN) has shown anti-cancer effects in cellular and animal studies but its effectiveness has been limited in human studies. Here, the effects of SFN were measured in both human hepatocytes (HHL5) and hepatoma (HepG2) cells. Results showed that SFN inhibited cell viability and induced DNA strand breaks at high doses (≥20 μM). It also activated the nuclear factor (erythroid-derived 2)-like 2 (Nrf2), and increased intracellular glutathione (GSH) levels at 24 h. Pre-treatment with a low dose SFN (≤5 μM) protected against hydrogen peroxide (H₂O₂)-induced cell damage. High doses of SFN were more toxic towards HHL5 compared to HepG2 cells; the difference is likely due to the disparity in the responses of Nrf2-driven enzymes and -GSH levels between the two cell lines. In addition, HepG2 cells hijacked the cytoprotective effect of SFN over a wider dose range (1.25-20 μM) compared to HHL5. Manipulation of levels of GSH and Nrf2 in HepG2 cells confirmed that both molecules mediate the protective effects of SFN against H₂O₂. The non-specific nature of SFN in the regulation of cell death and survival could present undesirable risks, i.e. be more toxic to normal cells, and cause chemo-resistance in tumor cells. These issues should be addressed in the context for cancer prevention and treatment before large scale clinical trials are undertaken.

Sulforaphane enriched transcriptome of lung mitochondrial energy metabolism and provided pulmonary injury protection via Nrf2 in mice

Nrf2 is essential to antioxidant response element (ARE)-mediated host defense. Sulforaphane (SFN) is a phytochemical antioxidant known to affect multiple cellular targets including Nrf2-ARE pathway in chemoprevention. However, the role of SFN in non-malignant airway disorders remain unclear. To test if pre-activation of Nrf2-ARE signaling protects lungs from oxidant-induced acute injury, wild-type (Nrf2^+/+) and Nrf2-deficient (Nrf2^-/-) mice were given SFN orally or as standardized broccoli sprout extract diet (SBE) before hyperoxia or air exposure. Hyperoxia-induced pulmonary injury and oxidation indices were significantly reduced by SFN or SBE in Nrf2^+/+ mice but not in Nrf2^-/- mice. SFN upregulated a large cluster of basal lung genes that are involved in mitochondrial oxidative phosphorylation, energy metabolism, and cardiovascular protection only in Nrf2^+/+ mice. Bioinformatic analysis elucidated ARE-like motifs on these genes. Transcript abundance of the mitochondrial machinery genes remained significantly higher after hyperoxia exposure in SFN-treated Nrf2^+/+ mice than in SFN-treated Nrf2^-/- mice. Nuclear factor-κB was suggested to be a central molecule in transcriptome networks affected by SFN. Minor improvement of hyperoxia-caused lung histopathology and neutrophilia by SFN in Nrf2^-/- mice implies Nrf2-independent or alternate effector mechanisms. In conclusion, SFN is suggested to be as a preventive intervention in a preclinical model of acute lung injury by linking mitochondria and Nrf2. Administration of SFN alleviated acute lung injury-like pathogenesis in a Nrf2-dependent manner. Potential AREs in the SFN-inducible transcriptome for mitochondria bioenergetics provided a new insight into the downstream mechanisms of Nrf2-mediated pulmonary protection.

Sulforaphane from Cruciferous Vegetables: Recent Advances to Improve Glioblastoma Treatment

Sulforaphane (SFN), an isothiocyanate (ITC) derived from cruciferous vegetables, particularly broccoli and broccoli sprouts, has been widely investigated due to its promising health-promoting properties in disease, and low toxicity in normal tissue. Although not yet fully understood, many mechanisms of anticancer activity at each step of cancer development have been attributed to this ITC. Given the promising data available regarding SFN, this review aimed to provide an overview on the potential activities of SFN related to the cellular mechanisms involved in glioblastoma (GBM) progression. GBM is the most frequent malignant brain tumor among adults and is currently an incurable disease due mostly to its highly invasive phenotype, and the poor efficacy of the available therapies. Despite all efforts, the median overall survival of GBM patients remains approximately 1.5 years under therapy. Therefore, there is an urgent need to provide support for translating the progress in understanding the molecular background of GBM into more complex, but promising therapeutic strategies, in which SFN may find a leading role.

Chemopreventive Activities of Sulforaphane and Its Metabolites in Human Hepatoma HepG2 Cells

Sulforaphane (SFN) exhibits chemopreventive effects through various mechanisms. However, few studies have focused on the bioactivities of its metabolites. Here, three metabolites derived from SFN were studied, known as sulforaphane glutathione, sulforaphane cysteine and sulforaphane-N-acetylcysteine. Their effects on cell viability, DNA damage, tumorigenicity, cell migration and adhesion were measured in human hepatoma HepG2 cells, and their anti-angiogenetic effects were determined in a 3D co-culture model of human umbilical vein endothelial cells (HUVECs) and pericytes. Results indicated that these metabolites at high doses decreased cancer cell viability, induced DNA damage and inhibited motility, and impaired endothelial cell migration and tube formation. Additionally, pre-treatment with low doses of SFN metabolites protected against H₂O₂ challenge. The activation of the nuclear factor E2-related factor 2 (Nrf2)-antioxidant response element (ARE) pathway and the induction of intracellular glutathione (GSH) played an important role in the cytoprotective effects of SFN metabolites. In conclusion, SFN metabolites exhibited similar cytotoxic and cytoprotective effects to SFN, which proves the necessity to study the mechanisms of action of not only SFN but also of its metabolites. Based on the different tissue distribution profiles of these metabolites, the most relevant chemical forms can be selected for targeted chemoprevention.

Food as Pharma? The Case of Glucosinolates

BACKGROUND

Glucosinolates (GLSs) are dietary plant secondary metabolites occurring in the order Brassicales with potential health effects, in particular as anti-carcinogenic compounds. GLSs are converted into a variety of breakdown products (BPs) upon plant tissue damage and by the gut microbiota. GLS biological activity is related to BPs rather than to GLSs themselves.

METHODS

we have reviewed the most recent scientific literature on the metabolic fate and the biological effect of GLSs with particular emphasis on the epidemiological evidence for health effect and evidence from clinical trials. An overview of potential molecular mechanisms underlying GLS biological effect is provided. The potential toxic or anti-nutritional effect has also been discussed.

RESULTS

Epidemiological and human in vivo evidence point towards a potential anti-cancer effect for sulforaphane, indole-3-carbinol and 3,3-diindolylmethane. A number of new human clinical trials are on-going and will likely shed further light on GLS protective effect towards cancer as well as other diseases. BPs biological effect is the results of a plurality of molecular mechanisms acting simultaneously which include modulation of xenobiotic metabolism, modulation of inflammation, regulation of apoptosis, cell cycle arrest, angiogenesis and metastasis and regulation of epigenetic events. BPs have been extensively investigated for their protective effect towards cancer but in recent years the interest also includes other diseases.

CONCLUSION

It appears that certain BPs may protect against and may even represent a therapeutic strategy against several forms of cancer. Whether this latter effect can be achieved through diet or supplements should be investigated more thoroughly.

The Role of MicroRNAs in the Chemopreventive Activity of Sulforaphane from Cruciferous Vegetables

Colorectal cancer is an increasingly significant cause of mortality whose risk is linked to diet and inversely correlated with cruciferous vegetable consumption. This is likely to be partly attributable to the isothiocyanates derived from eating these vegetables, such as sulforaphane, which is extensively characterised for cytoprotective and tumour-suppressing activities. However, its bioactivities are likely to extend in complexity beyond those currently known; further insight into these bioactivities could aid the development of sulforaphane-based chemopreventive or chemotherapeutic strategies. Evidence suggests that sulforaphane modulates the expression of microRNAs, many of which are known to regulate genes involved at various stages of colorectal carcinogenesis. Based upon existing knowledge, there exist many plausible mechanisms by which sulforaphane may regulate microRNAs. Thus, there is a strong case for the further investigation of the roles of microRNAs in the anti-cancer effects of sulforaphane. There are several different types of approach to the wide-scale profiling of microRNA differential expression. Array-based methods may involve the use of RT-qPCR or complementary hybridisation probe chips, and tend to be relatively fast and economical. Cloning and deep sequencing approaches are more expensive and labour-intensive, but are worth considering where viable, for their greater sensitivity and ability to detect novel microRNAs.

Sulforaphane suppresses the growth of glioblastoma cells, glioblastoma stem cell-like spheroids, and tumor xenografts through multiple cell signaling pathways

OBJECTIVE Defects in the apoptotic machinery and augmented survival signals contribute to drug resistance in glioblastoma (GBM). Moreover, another complexity related to GBM treatment is the concept that GBM development and recurrence may arise from the expression of GBM stem cells (GSCs). Therefore, the use of a multifaceted approach or multitargeted agents that affect specific tumor cell characteristics will likely be necessary to successfully eradicate GBM. The objective of this study was to investigate the usefulness of sulforaphane (SFN)-a constituent of cruciferous vegetables with a multitargeted effect-as a therapeutic agent for GBM. METHODS The inhibitory effects of SFN on established cell lines, early primary cultures, CD133-positive GSCs, GSC-derived spheroids, and GBM xenografts were evaluated using various methods, including GSC isolation and the sphere-forming assay, analysis of reactive oxygen species (ROS) and apoptosis, cell growth inhibition assay, comet assays for assessing SFN-triggered DNA damage, confocal microscopy, Western blot analysis, and the determination of in vivo efficacy as assessed in human GBM xenograft models. RESULTS SFN triggered the significant inhibition of cell survival and induced apoptotic cell death, which was associated with caspase 3 and caspase 7 activation. Moreover, SFN triggered the formation of mitochondrial ROS, and SFN-triggered cell death was ROS dependent. Comet assays revealed that SFN increased single- and double-strand DNA breaks in GBM. Compared with the vehicle control cells, a significantly higher amount of γ-H2AX foci correlated with an increase in DNA double-strand breaks in the SFN-treated samples. Furthermore, SFN robustly inhibited the growth of GBM cell-induced cell death in established cell cultures and early-passage primary cultures and, most importantly, was effective in eliminating GSCs, which play a major role in drug resistance and disease recurrence. In vivo studies revealed that SFN administration at 100 mg/kg for 5-day cycles repeated for 3 weeks significantly decreased the growth of ectopic xenografts that were established from the early passage of primary cultures of GBM10. CONCLUSIONS These results suggest that SFN is a potent anti-GBM agent that targets several apoptosis and cell survival pathways and further preclinical and clinical studies may prove that SFN alone or in combination with other therapies may be potentially useful for GBM therapy.

The Fast-Halo Assay for the Detection of DNA Damage

The need for express screening of the DNA damaging potential of chemicals has progressively increased over the past 20 years due to the wide number of new synthetic molecules to be evaluated, as well as the adoption of more stringent chemical regulations such as the EU REACH and risk reduction politics. In this regard, DNA diffusion assays such as the microelectrophoretic comet assay paved the way for rapid genotoxicity testing. A more significant simplification and speeding up of the experimental processes was achieved with the fast halo assay (FHA) described in the present chapter. FHA operates at the single cell level and relies on radial dispersion of the fragments of damaged DNA from intact nuclear DNA. The fragmented DNA is separated by diffusion in an alkaline solvent and is stained, visualized, and finally quantified using computer-assisted image analysis programs. This permits the rapid assessment of the extent of DNA breakage caused by different types of DNA lesions. FHA has proven to be sensitive, reliable, and flexible. This is currently one of the simplest, cheapest, and quickest assays for studying DNA damage and repair in living cells. It does not need expensive reagents or electrophoretic equipment and requires only 40 min to prepare samples for computer-based quantification. This technique can be particularly useful in rapid genotoxicity assessments and in high-throughput genotoxicity screenings.

Sulforaphane inhibits damage-induced poly (ADP-ribosyl)ation via direct interaction of its cellular metabolites with PARP-1

SCOPE

The isothiocyanate sulforaphane, a major breakdown product of the broccoli glucosinolate glucoraphanin, has frequently been proposed to exert anticarcinogenic properties. Potential underlying mechanisms include a zinc release from Kelch-like ECH-associated protein 1 followed by the induction of detoxifying enzymes. This suggests that sulforaphane may also interfere with other zinc-binding proteins, e.g. those essential for DNA repair. Therefore, we explored the impact of sulforaphane on poly (ADP-ribose)polymerase-1 (PARP-1), poly (ADP-ribosyl)ation (PARylation), and DNA single-strand break repair (SSBR) in cell culture.

METHODS AND RESULTS

Immunofluorescence analyses showed that sulforaphane diminished H2 O2 -induced PARylation in HeLa S3 cells starting from 15 μM despite increased lesion induction under these conditions. Subcellular experiments quantifying the damage-induced incorporation of (32) P-ADP-ribose by PARP-1 displayed no direct impact of sulforaphane itself, but cellular metabolites, namely the glutathione conjugates of sulforaphane and its interconversion product erucin, reduced PARP-1 activity concentration dependently. Interestingly, this sulforaphane metabolite-induced PARP-1 inhibition was prevented by thiol compounds. PARP-1 is a stimulating factor for DNA SSBR-rate and we further demonstrated that 25 μM sulforaphane also delayed the rejoining of H2 O2 -induced DNA strand breaks, although this might be partly due to increased lesion frequencies.

CONCLUSION

Sulforaphane interferes with damage-induced PARylation and SSBR, which implies a sulforaphane-dependent impairment of genomic stability.

Cytotoxic and Antitumor Activity of Sulforaphane: The Role of Reactive Oxygen Species

According to recent estimates, cancer continues to remain the second leading cause of death and is becoming the leading one in old age. Failure and high systemic toxicity of conventional cancer therapies have accelerated the identification and development of innovative preventive as well as therapeutic strategies to contrast cancer-associated morbidity and mortality. In recent years, increasing body of in vitro and in vivo studies has underscored the cancer preventive and therapeutic efficacy of the isothiocyanate sulforaphane. In this review article, we highlight that sulforaphane cytotoxicity derives from complex, concurring, and multiple mechanisms, among which the generation of reactive oxygen species has been identified as playing a central role in promoting apoptosis and autophagy of target cells. We also discuss the site and the mechanism of reactive oxygen species' formation by sulforaphane, the toxicological relevance of sulforaphane-formed reactive oxygen species, and the death pathways triggered by sulforaphane-derived reactive oxygen species.

Sulforaphane enhances temozolomide-induced apoptosis because of down-regulation of miR-21 via Wnt/β-catenin signaling in glioblastoma

Temozolomide (TMZ) has been widely used in the treatment of glioblastoma (GBM), although inherent or acquired resistance restricts the application. This study was aimed to evaluate the efficacy of sulforaphane (SFN) to TMZ-induced apoptosis in GBM cells and the potential mechanism. Biochemical assays and subcutaneous tumor establishment were used to characterize the function of SFN in TMZ-induced apoptosis. Our results revealed that β-catenin and miR-21 were concordantly expressed in GBM cell lines, and SFN significantly reduced miR-21 expression through inhibiting the Wnt/β-catenin/TCF4 pathway. Furthermore, down-regulation of miR-21 enhanced the pro-apoptotic efficacy of TMZ in GBM cells. Finally, we observed that SFN strengthened TMZ-mediated apoptosis in a miR-21-dependent manner. In conclusion, SFN effectively enhances TMZ-induced apoptosis by inhibiting miR-21 via Wnt/β-catenin signaling in GBM cells. These findings support the use of SFN for potential therapeutic approach to overcome TMZ resistance in GBM treatment. Our studies indicate that sulforaphane (SFN) enhances temozolomide (TMZ)-induced apoptosis because of down-regulation of miR-21 through Wnt/β-catenin signaling in glioblastoma (GBM) cells. These findings demonstrate SFN could be considered as a potential adjuvant therapeutic agent in treating GBM patients combined with TMZ in the future to affect resistance emergence. The further explorations are essential for the clinical application of SFN in GBM patients, and our results reveal an important mechanism of SFN chemopreventive and chemotherapeutic activity. Chr17, chromosome 17.

Sulforaphane-induced apoptosis involves p53 and p38 in melanoma cells

In malignant melanoma complex reprogramming of cell death and survival pathways leads to increased chemoresistance and poor longer-term survival. Sulforaphane (SF) is a promising isothiocyanate compound occurring in cruciferous plants with reported antiproliferative and proapoptotic activity in several tumor cell lines including melanoma. In this work we investigated the effects of SF in several melanoma cell lines and fresh melanoma cultivates. We found that SF is cytotoxic and induces mitochondrial, caspase-dependent apoptosis in our study model, however with lower efficiency in fresh melanoma cultivates. Moreover, our results indicate that in melanoma cell lines and fresh melanoma cultivates SF induces multiple signaling including oxidative stress-mediated activation of DNA-damage response pathway, changes in p38 kinase activity and enhanced expression of Bax and Puma proapoptotic proteins. In addition, in SF-exposed p53-mutant melanoma cells Puma expression seem to be under p38 control and acts as a compensatory proapoptotic mechanism. Conversely, decreased apoptosis in SF-exposed melanoma cultivates might be attributed to Akt-mediated suppression of p38 as well as p53 activity. Together, our results suggest that SF inhibits growth and proliferation and induces mitochondrial apoptosis both in melanoma cell lines as well as in fresh melanoma cultivates. This proapoptotic effect might be enhanced in combination with Akt inhibitors, in particular in melanoma samples. SF is thus commendable for further preclinical testing, both as a single agent as well as in combination regimens.

Effect of antioxidants on the genotoxicity of phenethyl isothiocyanate

Isothiocyanates are plant-derived compounds that may be beneficial in the prevention of certain chronic diseases. Yet, by stimulating the production of reactive oxygen species (ROS), isothiocyanates can be genotoxic. Whether antioxidants influence isothiocyanate-induced genotoxicity is unclear, but this situation was clarified appreciably herein. In HCT116 cells, phenethyl isothiocyanate (PEITC) increased ROS production, which was inhibited by N-acetylcysteine (NAC) and deferoxamine (DFO) but not by ascorbic acid (ASC) and trolox (TRX) that were found to be more potent radical scavengers. Surprisingly, ASC and TRX each intensified the DNA damage that was caused by PEITC, but neither ASC nor TRX by themselves caused any DNA damage. In contrast, NAC and DFO each not only attenuated PEITC-induced DNA damage but also attenuated the antioxidant-intensified, PEITC-induced DNA damage. To determine if the DNA damage could be related to possible changes in the major antioxidant defence system, glutathione (GSH) was investigated. PEITC lowered GSH levels, which was prevented by NAC, whereas ASC, TRX and DFO neither inhibited nor enhanced the GSH-lowering effect of PEITC. The GSH synthesis inhibitor, buthionine sulphoxime, intensified PEITC-induced DNA damage, although by itself buthionine sulphoxime did not directly cause DNA damage. The principal findings suggest that ASC and TRX make PEITC more genotoxic, which might be exploited in killing cancer cells as one approach in killing cancer cells is to extensively damage their DNA so as to initiate apoptosis.

Study of the cytotoxic effects of the new synthetic Isothiocyanate CM9 and its fullerene derivative on human T-leukemia cells

One important strategy to develop effective anticancer agents is based on natural products. Many active phytochemicals are in human clinical trials and have been used for a long time, alone and in association with conventional anticancer drugs, for the treatment of various types of cancers. A great number of in vitro, in vivo and clinical reports document the multi-target anticancer activities of isothiocyanates and of compounds characterized by a naphthalenetetracarboxylic diimide scaffold. In order to search for new anticancer agents with a better pharmaco-toxicological profile, we investigated hybrid compounds obtained by inserting isothiocyanate group(s) on a naphthalenetetracarboxylic diimide scaffold. Moreover, since water-soluble fullerene derivatives can cross cell membranes thus favoring the delivery of anticancer therapeutics, we explored the cytostatic and cytotoxic activity of hybrid compounds conjugated with fullerene. We studied their cytostatic and cytotoxic effects on a human T-lymphoblastoid cell line by using different flow cytometric assays. In order to better understand their pharmaco-toxicological potential, we also analyzed their genotoxicity. Our global results show that the synthesized compounds reduced significantly the viability of leukemia cells. However, the conjugation with a non-toxic vector did not increase their anticancer potential. This opens an interesting research pattern for certain fullerene properties.

Benefits and risks of the hormetic effects of dietary isothiocyanates on cancer prevention

The isothiocyanate (ITC) sulforaphane (SFN) was shown at low levels (1–5 µM) to promote cell proliferation to 120–143% of the controls in a number of human cell lines, whilst at high levels (10–40 µM) it inhibited such cell proliferation. Similar dose responses were observed for cell migration, i.e. SFN at 2.5 µM increased cell migration in bladder cancer T24 cells to 128% whilst high levels inhibited cell migration. This hormetic action was also found in an angiogenesis assay where SFN at 2.5 µM promoted endothelial tube formation (118% of the control), whereas at 10–20 µM it caused significant inhibition. The precise mechanism by which SFN influences promotion of cell growth and migration is not known, but probably involves activation of autophagy since an autophagy inhibitor, 3-methyladenine, abolished the effect of SFN on cell migration. Moreover, low doses of SFN offered a protective effect against free-radical mediated cell death, an effect that was enhanced by co-treatment with selenium. These results suggest that SFN may either prevent or promote tumour cell growth depending on the dose and the nature of the target cells. In normal cells, the promotion of cell growth may be of benefit, but in transformed or cancer cells it may be an undesirable risk factor. In summary, ITCs have a biphasic effect on cell growth and migration. The benefits and risks of ITCs are not only determined by the doses, but are affected by interactions with Se and the measured endpoint.

Natural compounds to overcome cancer chemoresistance: toxicological and clinical issues

INTRODUCTION

Defects in initiating or executing cell death programs are responsible for cancer chemoresistance. The growing understanding of apoptotic programs suggests that compounds simultaneously inhibiting multiple signaling pathways might provide a better therapeutic outcome than that of individual inhibitors.

AREAS COVERED

Natural compounds can modulate different survival pathways, thus enhancing the therapeutic effects of anticancer treatments. This review provides an overview of the preclinical and clinical relevance of chemosensitization, giving special reference to curcumin (CUR) and sulforaphane (SFN) as agents to overcome apoptosis resistance against chemotherapy.

EXPERT OPINION

Even if CUR and SFN are common dietary constituents, they are characterized by several problems still unresolved and hampering their development as anticancer drugs. For a drug to be safe, it must be devoid of toxicity, and some studies conducted to date raises concern about CUR and SFN safety. Moreover, the efficacy of a drug, alone or in association, is usually determined by randomized, placebo-controlled, double-blind clinical trials. No such trials have shown CUR and SFN to be effective so far. Thus, caution should be exercised when suggesting the use of CUR or SFN for cancer-related therapeutic purpose, especially for very early stage of malignancy, or in patients who are undergoing chemotherapy.

Antileukemic activity of sulforaphane in primary blasts from patients affected by myelo- and lympho-proliferative disorders and in hypoxic conditions

Sulforaphane is a dietary isothiocyanate found in cruciferous vegetables showing antileukemic activity. With the purpose of extending the potential clinical impact of sulforaphane in the oncological field, we investigated the antileukemic effect of sulforaphane on blasts from patients affected by different types of leukemia and, taking into account the intrinsically hypoxic nature of bone marrow, on a leukemia cell line (REH) maintained in hypoxic conditions. In particular, we tested sulforaphane on patients with chronic lymphocytic leukemia, acute myeloid leukemia, T-cell acute lymphoblastic leukemia, B-cell acute lymphoblastic leukemia, and blastic NK cell leukemia. Sulforaphane caused a dose-dependent induction of apoptosis in blasts from patients diagnosed with acute lymphoblastic or myeloid leukemia. Moreover, it was able to cause apoptosis and to inhibit proliferation in hypoxic conditions on REH cells. As to its cytotoxic mechanism, we found that sulforaphane creates an oxidative cellular environment that induces DNA damage and Bax and p53 gene activation, which in turn helps trigger apoptosis. On the whole, our results raise hopes that sulforaphane might set the stage for a novel therapeutic principle complementing our growing armature against malignancies and advocate the exploration of sulforaphane in a broader population of leukemic patients.

Sulforaphane induces oxidative stress and death by p53-independent mechanism: implication of impaired glutathione recycling

Sulforaphane (SFN) is a naturally-occurring isothiocyanate best known for its role as an indirect antioxidant. Notwithstanding, in different cancer cell lines, SFN may promote the accumulation of reactive oxygen species (ROS) and cause cell death e.g. by apoptosis. Osteosarcoma often becomes chemoresistant, and new molecular targets to prevent drug resistance are needed. Here, we aimed to determine the effect of SFN on ROS levels and to identify key biomarkers leading to ROS unbalance and apoptosis in the p53-null MG-63 osteosarcoma cell line. MG-63 cells were exposed to SFN for up to 48 h. At 10 μM concentration or higher, SFN decreased cell viability, increased the%early apoptotic cells and increased caspase 3 activity. At these higher doses, SFN increased ROS levels, which correlated with apoptotic endpoints and cell viability decline. In exposed cells, gene expression analysis revealed only partial induction of phase-2 detoxification genes. More importantly, SFN inhibited ROS-scavenging enzymes and impaired glutathione recycling, as evidenced by inhibition of glutathione reductase (GR) activity and combined inhibition of glutathione peroxidase (GPx) gene expression and enzyme activity. In conclusion, SFN induced oxidative stress and apoptosis via a p53-independent mechanism. GPx expression and activity were found associated with ROS accumulation in MG-63 cells and are potential biomarkers for the efficacy of ROS-inducing agents e.g. as co-adjuvant drugs in osteosarcoma.

Alkaline nuclear dispersion assays for the determination of DNA damage at the single cell level

Over the past three decades the development of methods for visualizing at the cell level the extent of DNA breakage significantly contributed to genotoxicity testing: their availability greatly improved the knowledge in the field of genetic toxicology. These procedures are based on the separation and visualization of DNA fragments resulting from cleavage of nuclear DNA. The separation process can be obtained either electrically (comet assay, linear migration of DNA fragments) or chemically (alkaline dispersion assays, radial diffusion of DNA fragments). Once separated and stained, intact and fragmented DNA can be observed with fluorescence or light microscope. Appropriate computer-assisted image analysis allows quantitative determination of the extent of DNA breakage. These procedures have been proven to be sensitive, flexible, and reliable, and, as compared to former methods, they are simpler, are less time and money consuming, and have the unique capability of detecting DNA damage at the single cell level. This last feature has the additional advantage of allowing the identification of cellular subpopulations characterized by different sensitivity to the damaging agent. The fast halo assay (FHA) is currently the simplest and quickest nuclear dispersion assay; recent modifications of FHA have further improved the assay and pave the way to a full exploitation of its analytical potential. In this chapter the development, procedures, applications, and limits of these dispersion assays, with a particular focus on FHA, will be illustrated.

Assessment of DNA damage and repair in adults consuming allyl isothiocyanate or Brassica vegetables

Allyl isothiocyanate (AITC) is a dietary component with possible anticancer effects, though much information about AITC and cancer has been obtained from cell studies. To investigate the effect of AITC on DNA integrity in vivo, a crossover study was conducted. Adults (n=46) consumed AITC, AITC-rich vegetables [mustard and cabbage (M/C)] or a control treatment with a controlled diet for 10 days each. On day 11, volunteers provided blood and urine before and after consuming treatments. Volunteers were characterized for genotype for GSTM1 and GSTT1 (glutathione S-transferases) and XPD (DNA repair). DNA integrity in peripheral blood mononuclear cells was assessed by single-cell gel electrophoresis. Urine was analyzed for 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and creatinine. Ten-day intake of neither AITC nor M/C resulted in statistically significant differences in DNA strand breaks [least squares mean (LSmean) % DNA in tail±S.E.M.: 4.8±0.6 for control, 5.7±0.7 for AITC, 5.3±0.6 for M/C] or urinary 8-oxodG (LSmean μg 8-oxodG/g creatinine±S.E.M.: 2.95±0.09 for control, 2.88±0.09 for AITC, 3.06±0.09 for M/C). Both AITC and M/C increased DNA strand breaks 3 h postconsumption (LSmean % DNA in tail±S.E.M.: 3.2±0.7 for control, 8.3±1.7 for AITC, 8.0±1.7 for M/C), and this difference disappeared at 6 h (4.2±0.9 for control, 5.7±1.2 for AITC, 5.5±1.2 for M/C). Genotypes for GSTM1, GSTT1 and XPD were not associated with treatment effects. In summary, DNA damage appeared to be induced in the short term by AITC and AITC-rich products, but that damage disappeared quickly, and neither AITC nor AITC-rich products affected DNA base excision repair.

Epigallocatechin gallate and sulforaphane combination treatment induce apoptosis in paclitaxel-resistant ovarian cancer cells through hTERT and Bcl-2 down-regulation

The cellular development of resistance to chemotherapy contributes to the high mortality noted in patients affected by ovarian cancer. Novel compounds that specifically target cellular drug resistance in ovarian cancer are therefore highly desired. Previous epidemiological studies indicate that consumption of green tea and cruciferous vegetables is inversely associated with occurrence of ovarian cancer. Therefore revealing the effects and mechanisms of major components of green tea (epigallocatechin gallate, EGCG) and cruciferous vegetables (sulforaphane, SFN) on ovarian cancer cells will provide necessary knowledge for developing potential novel treatments for the disease. In this study, EGCG or SFN was used to treat both paclitaxel-sensitive (SKOV3-ip1) and -resistant (SKOV3TR-ip2) ovarian cancer cell lines alone or in combination. We found that SFN inhibits cell viability of both ovarian cancer cell lines time- and dose-dependently and that EGCG potentiates the inhibiting effect of SFN on ovarian cancer cells. Cell cycle analysis indicates SFN can arrest ovarian cancer cells in G2/M phase, while EGCG and SFN co-treatment can arrest cells in both G2/M and S phase. Combined EGCG and SFN treatment increases apoptosis significantly in paclitaxel-resistant SKOV3TR-ip2 cells after 6 days of treatment, while reducing the expression of hTERT, the main regulatory subunit of telomerase. Western blotting also indicates that SFN can down-regulate Bcl-2 (a gene involved in anti-apoptosis) protein levels in both cell types. Cleaved poly(ADP-ribose) polymerase (PARP) becomes up-regulated by 6 days of treatment with SFN and this is more pronounced for combination treatment indicating induction of apoptosis. Furthermore, phosphorylated H2AX is up-regulated after 6 days of treatment with SFN alone, and EGCG can potentiate this effect, suggesting that DNA damage is a potential cellular mechanism contributing to the inhibiting effect of EGCG and SFN combination treatment. Taken together, these results indicate that EGCG and SFN combination treatment can induce apoptosis by down-regulating of hTERT and Bcl-2 and promote DNA damage response specifically in paclitaxel-resistant ovarian cancer cell lines and suggest the use of these compounds for overcoming paclitaxel resistance in ovarian cancer treatment.

Inhibition of Epstein-Barr virus reactivation in nasopharyngeal carcinoma cells by dietary sulforaphane

Epstein-Barr virus (EBV) has been associated with several human malignancies including nasopharyngeal carcinoma (NPC). Reactivation of latent EBV has been considered to contribute to the carcinogenesis of NPC. Blocking the EBV lytic cycle has been shown effective in the treatment of EBV-associated diseases. We have searched for natural dietary compounds inhibiting EBV reactivation in NPC cells. Among them, sulforaphane (SFN) was found to be effective in the inhibition of EBV reactivation in latent EBV-positive NPC cells, NA and HA. SFN is a histone deacetylase (HDAC) inhibitor and has been recognized as an antioxidant and antitumor compound for chemoprevention. However, its antiviral effect is less well elucidated. In this study, after determination of the cytotoxicity of SFN on various epithelial cells, we showed that SFN treatment inhibits EBV reactivation, rather than induction, by detection of EBV lytic gene expression in EBV-positive NPC cells. We also determined that the number of cells supporting the EBV lytic cycle is decreased using immunofluorescence and flow cytometric analysis. Moreover, we have found that this inhibitory effect decreases virus production. To elucidate the inhibitory mechanism of SFN on the EBV lytic cycle, luciferase reporter assays were carried out on the Zta and Rta promoters. The results show that SFN inhibits transactivation activity of the EBV immediate-early gene Rta but not Zta. Together, our results suggest that SFN has the capability to inhibit EBV lytic cycle and the potential to be taken as a dietary compound for prevention of EBV reactivation.

Sulforaphane potentiates RNA damage induced by different xenobiotics

Background

The isothiocyanate sulforaphane (SFN) possesses interesting anticancer activities. However, recent studies reported that SFN promotes the formation of reactive oxygen species (ROS) as well as DNA breakage.

Methodology/Principal Findings

We investigated whether SFN is able to damage RNA, whose loss of integrity was demonstrated in different chronic diseases. Considering the ability of SFN to protect from genotoxicity, we also examined whether SFN is able to protect from RNA damage induced by different chemicals (doxorubicin, spermine, S-nitroso-N-acetylpenicillamine, H₂O₂). We observed that SFN was devoid of either RNA damaging and RNA protective activity in human leukemic cells. It was able to potentiate the RNA damage by doxorubicin and spermine. In the first case, the effect was attributable to its ability of modulating the bioreductive activation of doxorubicin. For spermine, the effects were mainly due to its modulation of ROS levels produced by spermine metabolism. As to the cytotoxic relevance of the RNA damage, we found that the treatment of cells with a mixture of spermine or doxorubicin plus SFN increased their proapoptotic potential. Thus it is conceivable that the presence of RNA damage might concur to the overall toxic response induced by a chemical agent in targeted cells.

Conclusions/Significance

Since RNA is emerging as a potential target for anticancer drugs, its ability to enhance spermine- and doxorubicin-induced RNA damage and cytotoxicity could represent an additional mechanism for the potentiating effects of SFN associated with anticancer drugs.

Synergy between sulforaphane and selenium in the up-regulation of thioredoxin reductase and protection against hydrogen peroxide-induced cell death in human hepatocytes

Dietary isothiocyanates and selenium are chemopreventive agents and potent inducers of antioxidant enzymes. It has been previously shown that sulforaphane and selenium have a synergistic effect on the upregulation of thioredoxin reductase-1 (TrxR-1) in human hepatoma HepG2 cells. In this paper, further evidence is presented to show that sulforaphane and selenium synergistically induce TrxR-1 expression in immortalised human hepatocytes. Sulforaphane was found to be more toxic toward hepatocytes than HepG2 cells with IC50=25.1 and 56.4 μM, respectively. Sulforaphane can protect against hydrogen peroxide-induced cell death and this protection was enhanced by co-treatment with selenium. Using siRNA to knock down TrxR-1 or Nrf2, sulforaphane (5 μM)-protected cell viability was reduced from 73% to 46% and 34%, respectively, suggesting that TrxR-1 is an important enzyme in protection against hydrogen peroxide-induced cell death. Sulforaphane-induced TrxR-1 expression was positively associated with significant levels of Nrf2 translocation into the nucleus, but co-treatment with selenium showed no significant increase in Nrf2 translocation. Moreover, MAPK (ERK, JNK and p38) and PI3K/Akt signalling pathways were found to play no significant role in sulforaphane-induced Nrf2 translocation into the nucleus. However, blocking ERK and JNK signalling pathways decreased sulforaphane-induced TrxR-1 mRNA by about 20%; whereas blocking p38 and PI3K/AKT increased TrxR-1 transcription. In summary, a combination of sulforaphane and selenium resulted in a synergistic upregulation of TrxR-1 that contributed to the enhanced protection against free radical-mediated oxidative damage in human hepatocytes.

Targeting DNA damage and repair: embracing the pharmacological era for successful cancer therapy

DNA is under constant assault from genotoxic agents which creates different kinds of DNA damage. The precise replication of the genome and the continuous surveillance of its integrity are critical for survival and the avoidance of carcinogenesis. Cells have evolved an arsenal of repair pathways and cell cycle checkpoints to detect and repair DNA damage. When repair fails, typically cell cycle progression is halted and apoptosis is initiated. Here, we review the different sources and types of DNA damage including DNA replication stress and oxidative stress, the repair pathways that cells utilize to repair damaged DNA, and discuss their biological significance, especially with reference to cancer induction and cancer therapy. We also describe the main methodologies currently used for the detection of DNA damage with their strengths and limitations. We conclude with an outline as to how this information can be used to identify novel pharmacological targets for DNA repair pathways or enhancers of DNA damage to develop improved treatment strategies that will benefit cancer patients.

Natural isothiocyanates: genotoxic potential versus chemoprevention

Isothiocyanates, occurring in many dietary cruciferous vegetables, show interesting chemopreventive activities against several chronic-degenerative diseases, including cancer, cardiovascular diseases, neurodegeneration, diabetes. The electrophilic carbon residue in the isothiocyanate moiety reacts with biological nucleophiles and modification of proteins is recognized as a key mechanism underlying the biological activity of isothiocyanates. The nuclear factor-erythroid-2-related factor 2 system, which orchestrates the expression of a wide array of antioxidant genes, plays a role in the protective effect of isothiocyanates against almost all the pathological conditions reported above. Recent emerging findings suggest a further common mechanism. Chronic inflammation plays a central role in many human diseases and isothiocyanates inhibit the activity of many inflammation components, suppress cyclooxygenase 2, and irreversibly inactivate the macrophage migration inhibitory factor. Due to their electrophilic reactivity, some isothiocyanates are able to form adducts with DNA and induce gene mutations and chromosomal aberrations. DNA damage has been demonstrated to be involved in the pathogenesis of various chronic-degenerative diseases of epidemiological relevance. Thus, the genotoxicity of the isothiocyanates should be carefully considered. In addition, the dose-response relationship for genotoxic compounds does not suggest evidence of a threshold. Thus, chemicals that are genotoxic pose a greater potential risk to humans than non-genotoxic compounds. Dietary consumption levels of isothiocyanates appear to be several orders of magnitude lower than the doses used in the genotoxicity studies and thus it is highly unlikely that such toxicities would occur in humans. However, the beneficial properties of isothiocyanates stimulated an increase of dietary supplements and functional foods with highly enriched isothiocyanate concentrations on the market. Whether such concentrations may exert a potential health risk cannot be excluded with certainty and an accurate evaluation of the toxicological profile of isothiocyanates should be prompted before any major increase in their consumption be recommended or their clinical use suggested.

Design, synthesis and biological evaluation of new naphtalene diimides bearing isothiocyanate functionality

The synthesis and the biological activities of new derivatives 1-3, characterized by the isothiocyanate (ITC) functionalities coming from sulforaphane (SFN), a well-known anticancer natural product, were reported. The most interesting compound of the series was 2. It was chemically characterized by two ITC functionalities mounted on the 1,4,5,8-naphthalentetracarboxylic diimide (NDI) scaffold through two polymethylene chains, each constituted by three carbon units. It demonstrated an IC(50) value in the submicromolar range, more potent than SFN, displaying also the ability to trigger apoptotic induction in the same range by eliciting both extrinsic and intrinsic apoptotic pathways. Finally, it was observed that 2 inhibited the cell growth by blocking the cell cycle in G1 phase.

Dietary phytochemicals, HDAC inhibition, and DNA damage/repair defects in cancer cells

Genomic instability is a common feature of cancer etiology. This provides an avenue for therapeutic intervention, since cancer cells are more susceptible than normal cells to DNA damaging agents. However, there is growing evidence that the epigenetic mechanisms that impact DNA methylation and histone status also contribute to genomic instability. The DNA damage response, for example, is modulated by the acetylation status of histone and non-histone proteins, and by the opposing activities of histone acetyltransferase and histone deacetylase (HDAC) enzymes. Many HDACs overexpressed in cancer cells have been implicated in protecting such cells from genotoxic insults. Thus, HDAC inhibitors, in addition to unsilencing tumor suppressor genes, also can silence DNA repair pathways, inactivate non-histone proteins that are required for DNA stability, and induce reactive oxygen species and DNA double-strand breaks. This review summarizes how dietary phytochemicals that affect the epigenome also can trigger DNA damage and repair mechanisms. Where such data is available, examples are cited from studies in vitro and in vivo of polyphenols, organosulfur/organoselenium compounds, indoles, sesquiterpene lactones, and miscellaneous agents such as anacardic acid. Finally, by virtue of their genetic and epigenetic mechanisms, cancer chemopreventive agents are being redefined as chemo- or radio-sensitizers. A sustained DNA damage response coupled with insufficient repair may be a pivotal mechanism for apoptosis induction in cancer cells exposed to dietary phytochemicals. Future research, including appropriate clinical investigation, should clarify these emerging concepts in the context of both genetic and epigenetic mechanisms dysregulated in cancer, and the pros and cons of specific dietary intervention strategies.

Sulforaphane induces cytotoxicity and lysosome- and mitochondria-dependent cell death in colon cancer cells with deleted p53

Mechanisms and pathways responsible for cytotoxicity of sulforaphane (SF) in colon cancer cells with deleted p53 were investigated during 48 h of exposure. SF showed dose-dependent cytotoxicity and proapoptotic activity in the present model. In addition, in HCT-116 p53KO cells SF induced DNA damage with the subsequent cellular response and signaling not including p53 and caspase-2 pathways. Conversely, in SF-treated cells JNK was activated which led to an early lysosomal membrane permeabilization, release of cathepsin B and D and activation of Bid by specific cleavage. Concomitantly, the expression of Bax increased in the presence of JNK-mediated Bcl-2 inhibition which was followed by mitochondrial release of cytochrome c and activation of apoptosis. These results suggest that SF may be useful as a chemopreventive agent in colon cancer with inactivated or lost p53.

Phytochemicals: cancer chemoprevention and suppression of tumor onset and metastasis

Carcinogenesis is a multi-step process which could be prevented by phytochemicals. Phytochemicals from dietary plants and other plant sources such as herbs are becoming increasingly important sources of anticancer drugs or compounds for cancer chemoprevention or adjuvant chemotherapy. Phytochemicals can prevent cancer initiation, promotion, and progression by exerting anti-inflammatory and anti-oxidative stress effects which are mediated by integrated Nrf2, NF-kappaB, and AP-1 signaling pathways. In addition, phytochemicals from herbal medicinal plants and/or some dietary plants developed in recent years have been shown to induce apoptosis in cancer cells and inhibition of tumor growth in vivo. In advanced tumors, a series of changes involving critical signaling molecules that would drive tumor cells undergoing epithelial-mesenchymal transition and becoming invasive. In this review, we will discuss the potential molecular targets and signaling pathways that mediate tumor onset and metastasis. In addition, we will shed light on some of the phytochemicals that are capable of targeting these signaling pathways which would make them potentially applicable to cancer chemoprevention, treatment and control of cancer progression.