In Vitro Antiproliferative Effects of Sulforaphane on Human Colon Cancer Cell Line SW620

Sulforaphane: A Broccoli Bioactive Phytocompound with Cancer Preventive Potential

Simple Summary

As of the past decade, phytochemicals have become a major target of interest in cancer chemopreventive and chemotherapeutic research. Sulforaphane (SFN) is a metabolite of the phytochemical glucoraphanin, which is found in high abundance in cruciferous vegetables, such as broccoli, watercress, Brussels sprouts, and cabbage. In both distant and recent research, SFN has been shown to have a multitude of anticancer effects, increasing the need for a comprehensive review of the literature. In this review, we critically evaluate SFN as an anticancer agent and its mechanisms of action based on an impressive number of in vitro, in vivo, and clinical studies.

Abstract

There is substantial and promising evidence on the health benefits of consuming broccoli and other cruciferous vegetables. The most important compound in broccoli, glucoraphanin, is metabolized to SFN by the thioglucosidase enzyme myrosinase. SFN is the major mediator of the health benefits that have been recognized for broccoli consumption. SFN represents a phytochemical of high interest as it may be useful in preventing the occurrence and/or mitigating the progression of cancer. Although several prior publications provide an excellent overview of the effect of SFN in cancer, these reports represent narrative reviews that focused mainly on SFN’s source, biosynthesis, and mechanisms of action in modulating specific pathways involved in cancer without a comprehensive review of SFN’s role or value for prevention of various human malignancies. This review evaluates the most recent state of knowledge concerning SFN’s efficacy in preventing or reversing a variety of neoplasms. In this work, we have analyzed published reports based on in vitro, in vivo, and clinical studies to determine SFN’s potential as a chemopreventive agent. Furthermore, we have discussed the current limitations and challenges associated with SFN research and suggested future research directions before broccoli-derived products, especially SFN, can be used for human cancer prevention and intervention.

Synergistic Combinations of Curcumin, Sulforaphane, and Dihydrocaffeic Acid against Human Colon Cancer Cells

Nutraceutical combinations that act synergistically could be a powerful solution against colon cancer, which is the second deadliest malignancy worldwide. In this study, curcumin (C), sulforaphane (S), and dihydrocaffeic acid (D, a chlorogenic acid metabolite) were evaluated, individually and in different combinations, over the viability of HT-29 and Caco-2 colon cancer cells, and compared against healthy fetal human colon (FHC) cells. The cytotoxic concentrations to kill 50%, 75%, and 90% of the cells (CC₅₀, CC₇₅, and CC₉₀) were obtained, using the MTS assay. Synergistic, additive, and antagonistic effects were determined by using the combination index (CI) method. The 1:1 combination of S and D exerted synergistic effects against HT-29 at 90% cytotoxicity level (doses 90:90 µM), whereas CD(1:4) was synergistic at all cytotoxicity levels (9:36–34:136 µM) and CD(9:2) at 90% (108:24 µM) against Caco-2 cells. SD(1:1) was significantly more cytotoxic for cancer cells than healthy cells, while CD(1:4) and CD(9:2) were similarly or more cytotoxic for healthy cells. Therefore, the SD(1:1) combination was chosen as the best. A model explaining SD(1:1) synergy is proposed. SD(1:1) can be used as a basis to develop advanced food products for the prevention/co-treatment of colon cancer.

Targeting Colorectal Cancer Proliferation, Stemness and Metastatic Potential Using Brassicaceae Extracts Enriched in Isothiocyanates: A 3D Cell Model-Based Study

Colorectal cancer (CRC) recurrence is often attributable to circulating tumor cells and/or cancer stem cells (CSCs) that resist to conventional therapies and foster tumor progression. Isothiocyanates (ITCs) derived from Brassicaceae vegetables have demonstrated anticancer effects in CRC, however little is known about their effect in CSCs and tumor initiation properties. Here we examined the effect of ITCs-enriched Brassicaceae extracts derived from watercress and broccoli in cell proliferation, CSC phenotype and metastasis using a previously developed three-dimensional HT29 cell model with CSC-like traits. Both extracts were phytochemically characterized and their antiproliferative effect in HT29 monolayers was explored. Next, we performed cell proliferation assays and flow cytometry analysis in HT29 spheroids treated with watercress and broccoli extracts and respective main ITCs, phenethyl isothiocyanate (PEITC) and sulforaphane (SFN). Soft agar assays and relative quantitative expression analysis of stemness markers and Wnt/β-catenin signaling players were performed to evaluate the effect of these phytochemicals in stemness and metastasis. Our results showed that both Brassicaceae extracts and ITCs exert antiproliferative effects in HT29 spheroids, arresting cell cycle at G₂/M, possibly due to ITC-induced DNA damage. Colony formation and expression of LGR5 and CD133 cancer stemness markers were significantly reduced. Only watercress extract and PEITC decreased ALDH1 activity in a dose-dependent manner, as well as β-catenin expression. Our research provides new insights on CRC therapy using ITC-enriched Brassicaceae extracts, specially watercress extract, to target CSCs and circulating tumor cells by impairing cell proliferation, ALDH1-mediated chemo-resistance, anoikis evasion, self-renewal and metastatic potential.

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.

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.

Chemoprevention in colorectal cancer--where we stand and what we have learned from twenty year's experience

INTRODUCTION

Colorectal chemoprevention is a strategy aimed at preventing tumour progression before irreversible changes to the proteome are in full progress. Chemoprevention is not a new concept. In fact, medical practitioners since the early 19th century have tried various herbal and medicinal products as methods that could prevent tumours. The current understanding of tumourigenesis and cellular signalling focuses on a more targeted approach and paves the way for better understanding of colorectal chemoprevention.

METHODS

The online databases PubMed, Medline, Medscape Oncology and Scirrus were searched for articles of relevance. The Keyword involved the following words: "Colorectal Cancer Chemoprevention", "Colorectal Cancer", "Chemoprevention", "Adenoma-Carcinoma Sequence" and "Colorectal Polyps". The search was started from the period of June 1995 until September 2010 inclusive.

RESULTS

More than 50 natural and synthetic compounds have been shown to have chemotherapeutic effect but the majority of these agents are still in their early experimental stages and hence far from our subject of discussion. Our discussion will focus on large scale randomised trials on human subjects or established compounds. Within the context of chemoprevention, Non-steroidal anti-inflammatory agents have undergone extensive research and have shown promising results with large scale randomised trials. Additionally, metformin, resveratrol, Histone deacetylase inhibitors, Src kinases as well monoclonal antibodies have shown promising results as well.

CONCLUSION

Colorectal cancer is the fourth most common cancer in the world. In the UK alone the number of cases reported in 2008 was almost 40,000 which make it the third most common tumour nationwide. Curative intent surgery or Colectomy is the treatment of choice for most cases of bowel cancer; however, in a select subpopulation of patients who have been colonoscopically diagnosed to harbour pre-malignant lesions, have a family history of colorectal cancer, or have been genetically diagnosed and treated surgically for colorectal tumours; chemoprevention might play a crucial role in deterring further tumour progression. The very latest studies that are in publication or are just accruing results are giving us encouraging data that might suggest whether mass scale ingestion of a specific medication might deter colorectal tumour progression.

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.

Anticancer activity of a broccoli derivative, sulforaphane, in barrett adenocarcinoma: potential use in chemoprevention and as adjuvant in chemotherapy

INTRODUCTION

The incidence of Barrett esophageal adenocarcinoma (BEAC) has been increasing at an alarming rate in western countries. In this study, we have evaluated the therapeutic potential of sulforaphane (SFN), an antioxidant derived from broccoli, in BEAC.

METHODS

BEAC cells were treated with SFN, alone or in combination with chemotherapeutic, paclitaxel, or telomerase-inhibiting agents (MST-312, GRN163L), and live cell number determined at various time points. The effect on drug resistance/chemosensitivity was evaluated by rhodamine efflux assay. Apoptosis was detected by annexin V labeling and Western blot analysis of poly(ADP-ribose) polymerase cleavage. Effects on genes implicated in cell cycle and apoptosis were determined by Western blot analyses. To evaluate the efficacy in vivo, BEAC cells were injected subcutaneously in severe combined immunodeficient mice, and after the appearance of palpable tumors, mice were treated with SFN.

RESULTS

SFN induced both time- and dose-dependent decline in cell survival, cell cycle arrest, and apoptosis. The treatment with SFN also suppressed the expression of multidrug resistance protein, reduced drug efflux, and increased anticancer activity of other antiproliferative agents including paclitaxel. A significant reduction in tumor volume was also observed by SFN in a subcutaneous tumor model of BEAC. Anticancer activity could be attributed to the induction of caspase 8 and p21 and down-regulation of hsp90, a molecular chaperon required for activity of several proliferation-associated proteins.

CONCLUSIONS

These data indicate that a natural product with antioxidant properties from broccoli has great potential to be used in chemoprevention and treatment of BEAC.

Activation of several concurrent proapoptic pathways by sulforaphane in human colon cancer cells SW620

Despite the reported cytotoxicity and apoptosis-inducing properties of sulforaphane (SF) in colon cancer cells, the details concerning individual mechanisms and signaling cascades underlying SF-mediated apoptosis remain unclear. To understand different aspects of SF-induced proapoptic signaling in advanced colon carcinoma, we investigated its mechanisms in metastatic SW620 cell line. Our results indicate that in SW620 cells SF acts to induce multivariate cascades including DNA-damage response pathway whose proapoptotic signaling is nevertheless reduced owing to the mutant status of p53 and caspase-2-JNK pathway which seems to complement and enhance p53-dependent signaling, however only in wild-type p53. Furthermore, both pathways require the active role of mitochondria and do not depend on generation of ROS, making SF an attractive chemopreventive agent whose antitumor properties should be further investigated in colon cancer.

Binding to protein by isothiocyanates: a potential mechanism for apoptosis induction in human non small lung cancer cells

The upstream events by which isothiocyanates (ITCs) induce apoptosis have not been fully investigated. Numerous studies have reported that the apoptosis was induced by ITCs through generation of reactive oxygen species (ROS) as a result of conjugating with and, consequently, depleting cellular glutathione. As electrophiles, ITCs could potentially trigger apoptosis by binding to macromolecules including DNA and proteins. The results showed that DNA damage may not be an important early event for the apoptosis induction by ITCs. Phenethyl isothiocyanate (PEITC) is a more potent inducer of apoptosis than sulforaphane (SFN) in A549 cells, but SFN induces more ROS generation and oxidative damages than PEITC, suggesting that oxidative stress again is probably not a trigger for apoptosis in these cells. In contrast, we found that PEITC binds more to intracellular proteins than SFN. We identified tubulin as 1 of the protein targets of ITCs through proteomics approach. We showed that the relative tubulin binding affinity of ITCs correlates well with their potency of cell growth inhibition and apoptosis induction. These results collectively suggest that the covalent binding to protein targets, such as tubulin, by ITCs is an important chemical event in apoptosis induction by ITCs in human lung A549 cells.