Curcumin and synthetic analogs induce reactive oxygen species and decreases specificity protein (Sp) transcription factors by targeting microRNAs

Novel Evidence for Curcumin and Boswellic Acid-Induced Chemoprevention through Regulation of miR-34a and miR-27a in Colorectal Cancer

Colorectal cancer is one of the most common causes of cancer-associated mortality worldwide, but it is truly a preventable disease. Both curcumin and boswellic acids are well-established dietary botanicals with potent antitumorigenic properties that have been shown to modulate multiple oncogenic pathways. Recent data suggest that the chemopreventive effects of these botanicals may, in part, be mediated through regulation of key cancer-related microRNAs (miRNA) and their downstream gene targets. Here, we investigated the antitumorigenic effects of curcumin and 3 acetyl-11-keto-β-boswellic acid (AKBA) on modulation of specific cancer-related miRNAs in colorectal cancer cells and validated their protective effects in vivo using a xenograft mouse model. Both curcumin and AKBA inhibited cellular proliferation, induced apoptosis and cell-cycle arrest in colorectal cancer cell lines, and these effects were significantly enhanced with combined treatment. Gene-expression arrays revealed that curcumin and AKBA regulated distinct cancer signaling pathways, including key cell-cycle regulatory genes. Combined bioinformatics and in silico analysis identified apoptosis, proliferation, and cell-cycle regulatory signaling pathways as key modulators of curcumin and AKBA-induced anticancer effects. We discovered that curcumin and AKBA induced upregulation of tumor-suppressive miR-34a and downregulation of miR-27a in colorectal cancer cells. Furthermore, we demonstrated in a mouse xenograft model that both curcumin and AKBA treatments suppressed tumor growth, which corresponded with alterations in the expression of miR-34a and miR-27a, consistent with our in vitro findings. Herein, we provide novel mechanistic evidence for the chemopreventive effects of curcumin and AKBA through regulation of specific miRNAs in colorectal cancer.

Effects of Rosmarinus officinalis extract on human primary omental preadipocytes and adipocytes

The prevalence of obesity is increasing all over the world. Although it has been shown that natural substances influence fat metabolism, little is known about the effect on cellular and molecular mechanisms in human. In this in vitro study, the activity of Rosmarinus officinalis (RO) standardized extract in modulating human primary visceral preadipocytes differentiation, lipolysis, and apoptosis was investigated. Moreover, gene expression of key adipogenesis modulators and microRNAs-seq were evaluated. Preadipocytes treated with RO extract significantly reduced triglyceride incorporation during maturation in a dose-dependent manner without affecting cell viability. In addition, RO extract stimulated lipolytic activity in differentiating preadipocytes and mature adipocytes in treated cells compared to controls. Differentiating preadipocytes incubated in the presence of RO extract showed a decreased expression of cell cycle genes such as cyclin D1, cyclin-dependent kinase 4, cyclin-dependent kinase inhibitor 1A (p21, Cip1) and an increased expression of GATA binding protein 3, wingless-type MMTV integration site family, member 3A mRNA levels. Recent studies have demonstrated that some phytochemicals alter the expression of specific genes and microRNAs that play a fundamental role in the pathogenesis of obesity and related diseases. Interestingly, genes modulated in RO-treated cells were found to be validated miRNAs targets, such as let-7f-1, miR-17, and miR-143. The results indicated that RO extract modulates human adipocyte differentiation and significantly interferes with adipogenesis and lipid metabolism, supporting its interest as dietary supplement.

MicroRNA-Specificity Protein (Sp) Transcription Factor Interactions and Significance in Carcinogenesis

Specificity protein (Sp) transcription factors (TFs) such as Sp1, Sp3 and Sp4 are overexpressed in tumors and Sp1 is a negative prognostic factor for multiple tumor types. Sp TFs regulate expression of pro-oncogenic factors important for cell proliferation, survival, angiogenesis, migration/invasion and inflammation and the high expression of Sp TFs in tumors is primarily due to miRNAs. For example, expression of tumor-suppressor-like miRNAs such as miR-200b/c, miR-335, miR-22, miR-149 and others that inactivate Sp1 expression is low in many tumor types. Research in our laboratory has also demonstrated that high expression of Sp TFs is also due to miRNA-dependent inhibition of the transcriptional repressors ZBTB10 and ZBTB4 by miR-27a and miR-20a/miR-17p, respectively. Thus, miRNAs play a critical role in maintaining high levels of Sp1, Sp3, Sp4 and pro-oncogenic Sp-regulated genes in tumors and cancer cells, and there is ample evidence that anticancer agents targeting the miRNASp TF axis can be highly effective for cancer chemotherapy.

Heterocyclic cyclohexanone monocarbonyl analogs of curcumin can inhibit the activity of ATP-binding cassette transporters in cancer multidrug resistance

Curcumin (CUR) is a phytochemical that inhibits the xenobiotic ABC efflux transporters implicated in cancer multidrug resistance (MDR), such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins 1 and 5 (MRP1 and MRP5). The use of CUR in the clinic however, is complicated by its instability and poor pharmacokinetic profile. Monocarbonyl analogs of CUR (MACs) are compounds without CUR's unstable β-diketone moiety and were reported to have improved stability and in vivo disposition. Whether the MACs can be used as MDR reversal agents is less clear, as the absence of a β-diketone may negatively impact transporter inhibition. In this study, we investigated 23 heterocyclic cyclohexanone MACs for inhibitory effects against P-gp, BCRP, MRP1 and MRP5. Using flow cytometry and resistance reversal assays, we found that many of these compounds inhibited the transport activity of the ABC transporters investigated, often with much greater potency than CUR. Overall the analogs were most effective at inhibiting BCRP and we identified three compounds, A12 (2,6-bis((E)-2,5-dimethoxy-benzylidene)cyclohexanone), A13 (2,6-bis((E)-4-hydroxyl-3-methoxybenzylidene)-cyclohexanone) and B11 (3,5-bis((E)-2-fluoro-4,5-dimethoxybenzylidene)-1-methylpiperidin-4-one), as the most promising BCRP inhibitors. These compounds inhibited BCRP activity in a non-cell line, non-substrate-specific manner. Their inhibition occurred by direct transporter interaction rather than modulating protein or cell surface expression. From these results, we concluded that MACs, such as the heterocyclic cyclohexanone analogs in this study, also have potential as MDR reversal agents and may be superior alternatives to the unstable parent compound, CUR.

Improvement of pro-oxidant capacity of protocatechuic acid by esterification

Pro-oxidant effects of phenolic compounds are usually correlated to the one-electron redox potential of the phenoxyl radicals. Here we demonstrated that, besides their oxidizability, hydrophobicity can also be a decisive factor. We found that esterification of protocatechuic acid (P0) provoked a profound influence in its pro-oxidant capacity. The esters bearing alkyl chains containing two (P2), four (P4) and seven (P7) carbons, but not the acid precursor (P0), were able to exacerbate the oxidation of trolox, α-tocopherol and rifampicin. This effect was also dependent on the catechol moiety, since neither gallic acid nor butyl gallate showed any pro-oxidant effects. A comparison was also made with apocynin, which is well-characterized regarding its pro-oxidant properties. P7 was more efficient than apocynin regarding co-oxidation of trolox. However, P7 was not able to co-oxidize glutathione and NADH, which are targets of the apocynin radical. A correlation was found between pro-oxidant capacity and the stability of the radicals, as suggested by the intensity of the peak current in the differential pulse voltammetry experiments. In conclusion, taking into account that hydroquinone and related moieties are frequently found in biomolecules and quinone-based chemotherapeutics, our demonstration that esters of protocatechuic acid are specific and potent co-catalysts in their oxidations may be very relevant as a pathway to exacerbate redox cycling reactions, which are usually involved in their biological and pharmacological mechanisms of action.

Regulation of microRNAs by natural agents: new strategies in cancer therapies

MicroRNAs (miRNAs) are short noncoding RNA which regulate gene expression by messenger RNA (mRNA) degradation or translation repression. The plethora of published reports in recent years demonstrated that they play fundamental roles in many biological processes, such as carcinogenesis, angiogenesis, programmed cell death, cell proliferation, invasion, migration, and differentiation by acting as tumour suppressor or oncogene, and aberrations in their expressions have been linked to onset and progression of various cancers. Furthermore, each miRNA is capable of regulating the expression of many genes, allowing them to simultaneously regulate multiple cellular signalling pathways. Hence, miRNAs have the potential to be used as biomarkers for cancer diagnosis and prognosis as well as therapeutic targets. Recent studies have shown that natural agents such as curcumin, resveratrol, genistein, epigallocatechin-3-gallate, indole-3-carbinol, and 3,3′-diindolylmethane exert their antiproliferative and/or proapoptotic effects through the regulation of one or more miRNAs. Therefore, this review will look at the regulation of miRNAs by natural agents as a means to potentially enhance the efficacy of conventional chemotherapy through combinatorial therapies. It is hoped that this would provide new strategies in cancer therapies to improve overall response and survival outcome in cancer patients.

Curcumin inhibits the replication of enterovirus 71 in vitro

Human enterovirus 71 (EV71) is the main causative pathogen of hand, foot, and mouth disease (HFMD) in children. The epidemic of HFMD has been a public health problem in Asia-Pacific region for decades, and no vaccine and effective antiviral medicine are available. Curcumin has been used as a traditional medicine for centuries to treat a diversity of disorders including viral infections. In this study, we demonstrated that curcumin showed potent antiviral effect again EV71. In Vero cells infected with EV71, the addition of curcumin significantly suppressed the synthesis of viral RNA, the expression of viral protein, and the overall production of viral progeny. Similar with the previous reports, curcumin reduced the production of ROS induced by viral infection. However, the antioxidant property of curcumin did not contribute to its antiviral activity, since N-acetyl-l-cysteine, the potent antioxidant failed to suppress viral replication. This study also showed that extracellular signal-regulated kinase (ERK) was activated by either viral infection or curcumin treatment, but the activated ERK did not interfere with the antiviral effect of curcumin, indicating ERK is not involved in the antiviral mechanism of curcumin. Unlike the previous reports that curcumin inhibited protein degradation through ubiquitin–proteasome system (UPS), we found that curcumin had no impact on UPS in control cells. However, curcumin did reduce the activity of proteasomes which was increased by viral infection. In addition, the accumulation of the short-lived proteins, p53 and p21, was increased by the treatment of curcumin in EV71-infected cells. We further probed the antiviral mechanism of curcumin by examining the expression of GBF1 and PI4KB, both of which are required for the formation of viral replication complex. We found that curcumin significantly reduced the level of both proteins. Moreover, the decreased expression of either GBF1 or PI4KB by the application of siRNAs was sufficient to suppress viral replication. We also demonstrated that curcumin showed anti-apoptotic activity at the early stage of viral infection. The results of this study provide solid evidence that curcumin has potent anti-EV71 activity. Whether or not the down-regulated GBF1 and PI4KB by curcumin contribute to its antiviral effect needs further studies.

Curcumin loaded microsponges for colon targeting in inflammatory bowel disease: fabrication, optimization, and in vitro and pharmacodynamic evaluation

The present study was aimed to develop and optimize the microsponges of curcumin for colon specific drug delivery in a view to bypass the upper gastrointestinal tract (GIT) for enhanced therapeutic effect. Microsponges were developed by quasi emulsion solvent diffusion method using 3(2) full factorial design. Prepared microsponges were optimized in order to analyze the effects of independent variables (volume of ethanol and Eudragit L100) on the encapsulation efficiency, particle size, and drug release. The optimized formulation was subjected to in vivo study using acetic acid induced colitis model in rats. The F7 was selected as optimized formulation based on particle size of 41.63 μm, % entrapment efficiency of 78.13%, and % cumulative drug release of 84.12%, and desirability factor of 0.83. Release studies revealed that microsponges prevented the premature release of curcumin in upper GIT and specifically released the drug at colonic pH. The drug release profile of F7 formulation was subjected to different kinetic models and based upon the best correlation coefficient (r(2) = 0.9927) the release was found to follow Higuchi model, which suggested diffusion as the main mechanism of drug release. Pharmacodynamic study showed that curcumin loaded microsponges causes a significant decrease in edema, necrosis, and hemorrhage of colon as compared to free curcumin. This study proves that curcumin loaded microsponges may act as a promising drug delivery system for treatment of ulcerative colitis.

Upregulation of extrinsic apoptotic pathway in curcumin-mediated antiproliferative effect on human pancreatic carcinogenesis

Pancreatic cancer is one of the most lethal human cancers, with almost identical incidence and mortality rates. Curcumin, derived from the rhizome of Curcuma longa, has a long history of use as coloring agent and for a wide variety of disorders. Here, the antiproliferative activity of curcumin and its modulatory effect on gene expression of pancreatic cancer cell lines were investigated. The effect of curcumin on cellular proliferation and viability was monitored by sulphurhodamine B assay. Apoptotic effect was evaluated by flow cytometry and further confirmed by measuring amount of cytoplasmic histone-associated DNA fragments. Analysis of gene expression was performed with and without curcumin treatment using microarray expression profiling techniques. Array results were confirmed by real-time PCR. ingenuity pathway analysis (IPA) has been used to classify the list of differentially expressed genes and to indentify common biomarkergenes modulating the chemopreventive effect of curcumin. Results showed that curcumin induces growth arrest and apoptosis in pancreatic cancer cell lines. Its effect was more obvious on the highly COX-2 expressing cell line. Additionally, the expression of 366 and 356 cancer-related genes, involved in regulation of apoptosis, cell cycle, metastasis, was significantly altered after curcumin treatment in BxPC-3 and MiaPaCa-2 cells, respectively. Our results suggested that up-regulation of the extrinsic apoptotic pathway was among signaling pathways modulating the growth inhibitory effects of curcumin on pancreatic cancer cells. Curcumin effect was mediated through activation of TNFR, CASP 8, CASP3, BID, BAX, and down-regulation of NFκB, NDRG 1, and BCL2L10 genes.

Medicinal chemistry of the epigenetic diet and caloric restriction

The pronounced effects of the epigenetic diet (ED) and caloric restriction (CR) have on epigenetic gene regulation have been documented in many pre-clinical and clinical studies. Understanding epigenetics is of high importance because of the concept that external factors such as nutrition and diet may possess the ability to alter gene expression without modifying the DNA sequence. The ED introduces bioactive medicinal chemistry compounds such as sulforaphane (SFN), curcumin (CCM), epigallocatechin gallate (EGCG) and resveratrol (RSV) that are thought to aid in extending the human lifespan. CR, although similar to ED in the target of longevity, mildly reduces the total daily calorie intake while concurrently providing all beneficial nutrients. Both CR and ED may act as epigenetic modifiers to slow the aging process through histone modification, DNA methylation, and by modulating microRNA expression. CR and ED have been proposed as two important mechanisms that modulate and potentially slow the progression of age-related diseases such as cardiovascular disease (CVD), cancer, obesity, Alzheimer's and osteoporosis to name a few. While many investigators have examined CR and ED as separate entities, this review will primarily focus on both as they relate to age-related diseases, their epigenetic effects and their medicinal chemistry.

Involvement of miRNAs in placental alterations mediated by oxidative stress

Oxidative stress (OS) is known to be strongly involved in a large number of fetal, neonatal, and adult diseases, including placental disorders, leading to pregnancy loss and stillbirths. A growing body of research links OS to preeclampsia, gestational diabetes, obesity, spontaneous abortion, recurrent pregnancy, preterm labor, and intrauterine growth restriction. While a considerable number of miRNAs have been related to physiological functions and pathological conditions of the placenta, a direct link among these miRNAs, placental functions, and OS is still lacking. This review summarizes data describing the role of miRNAs in placental pathophysiological processes and their possible impact on OS damaging responses. As miRNAs can be found in circulation, improving our understanding on their role in the pathogenesis of pregnancy related disorders could have an important impact on the diagnosis and prognosis of these diseases.

miR181b is induced by the chemopreventive polyphenol curcumin and inhibits breast cancer metastasis via down-regulation of the inflammatory cytokines CXCL1 and -2

Chronic inflammation is a major risk factor for the development and metastatic progression of cancer. We have previously reported that the chemopreventive polyphenol Curcumin inhibits the expression of the proinflammatory cytokines CXCL1 and -2 leading to diminished formation of breast and prostate cancer metastases. In the present study, we have analyzed the effects of Curcumin on miRNA expression and its correlation to the anti-tumorigenic properties of this natural occurring polyphenol. Using microarray miRNA expression analyses, we show here that Curcumin modulates the expression of a series of miRNAs, including miR181b, in metastatic breast cancer cells. Interestingly, we found that miR181b down-modulates CXCL1 and -2 through a direct binding to their 3'-UTR. Overexpression or inhibition of miR181b in metastatic breast cancer cells has a significant impact on CXCL1 and -2 and is required for the effect of Curcumin on these two cytokines. miR181b also mediates the effects of Curcumin on inhibition of proliferation and invasion as well as induction of apoptosis. Importantly, over-expression of miR181b in metastatic breast cancer cells inhibits metastasis formation in vivo in immunodeficient mice. Finally, we demonstrated that Curcumin up-regulates miR181b and down-regulates CXCL1 and -2 in cells isolated from several primary human breast cancers. Taken together, these data show that Curcumin provides a simple bridge to bring metastamir modulation into the clinic, placing it in a primary and tertiary preventive, as well as a therapeutic, setting.

Inhibition of specificity protein 1 by dibenzylideneacetone, a curcumin analogue, induces apoptosis in mucoepidermoid carcinomas and tumor xenografts through Bim and truncated Bid

OBJECTIVES

Dibenzylideneacetone (DBA), a curcumin analogue that has anti-cancer activity in a variety of tumor cells. In this study, we investigated the apoptotic effects of DBA and its molecular mechanism in human mucoepidermoid carcinoma (MEC) cell lines and tumor xenografts.

MATERIAL AND METHODS

The apoptotic effects and related molecular mechanisms of DBA on MEC cell lines were evaluated using cell viability assay, DAPI staining, Western blot analysis, reverse transcriptase-polymerase chain reaction (RT-PCR) and Dual-luciferase Reporter Assay. The anti-tumor activity using in vivo were determined by Nude mouse xenograft assay and histopathological examination.

RESULTS

DBA decreased cell viability and induced apoptosis in MEC cells. These events were accompanied by inhibition of specificity protein 1 (Sp1). DBA did not induce major changes in Sp1 mRNA and promoter activity. Furthermore, inhibition of protein synthesis by cycloheximide demonstrated that DBA decreased Sp1 protein stability, but DBA did not attenuate phosphorylation of eIF4E. DBA also increased Bim and truncated Bid (t-Bid) via Sp1. Finally, DBA exhibited significant anti-tumor activity in athymic nude mice xenografts bearing MC-3 cells by regulating Sp1, Bim and t-Bid without any systemic toxicity.

CONCLUSION

These results elucidate a crucial apoptotic mechanism of DBA and suggest that DBA may be a potent anticancer drug candidate for MEC.

MiR-21 suppresses the anticancer activities of curcumin by targeting PTEN gene in human non-small cell lung cancer A549 cells

PURPOSE

Curcumin, a natural phytochemical, exhibits potent anticancer activities. Here, we sought to determine the molecular mechanisms underlying the cytotoxic effects of curcumin against human non-small cell lung cancer (NSCLC) cells.

METHODS

MTT assay and annexin-V/PI staining were used to analyze the effects of curcumin on the proliferation and apoptosis of A549 cells. The expression of microRNA-21 in curcumin-treated A549 cells was measured by quantitative real-time polymerase chain reaction assay. The protein level of phosphatase and tensin homolog (PTEN), a putative target of microRNA-21, was determined by Western blot analysis. Transfection of A549 cells with microRNA-21 mimic or PTEN small interfering RNA was performed to modulate the expression of microRNA-21 and PTEN under the treatment of curcumin.

RESULTS

Curcumin at 20-40 μM inhibited cell proliferation and induced apoptosis in A549 cells. Curcumin treatment produced a dose-dependent and significant (P < 0.05) suppression of microRNA-21 expression, compared to untreated A549 cells. Moreover, the protein level of PTEN, a putative target of microRNA-21, was significantly elevated in curcumin-treated A549 cells, as determined by Western blot analysis. Transfection of A549 cells with microRNA-21 mimic or PTEN small interfering RNA significantly (P < 0.05) reversed the growth suppression and apoptosis induction by curcumin, compared to corresponding controls.

CONCLUSIONS

Our data suggest a novel molecular mechanism in which inhibition of microRNA-21 and upregulation of PTEN mediate the anticancer activities of curcumin in NSCLC cells. Suppression of microRNA-21 may thus have therapeutic benefits against this malignancy.

REACTIVE OXYGEN SPECIES AND COLORECTAL CANCER

Several agents used for treatment of colon and other cancers induce reactive oxygen species (ROS) and this plays an important role in their anticancer activities. In addition to the well-known proapoptotic effects of ROS inducers, these compounds also decrease expression of specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 and several pro-oncogenic Spregulated genes important for cancer cell proliferation, survival and metastasis. The mechanism of these responses involve ROS-dependent downregulation of microRNA-27a (miR-27a) or miR-20a (and paralogs) and induction of two Sp-repressors, ZBTB10 and ZBTB4 respectively. This pathway significantly contributes to the anticancer activity of ROS inducers and should be considered in development of drug combinations for cancer chemotherapy.

Effects of dietary phytophenols on the expression of microRNAs involved in mammalian cell homeostasis

Besides synthesizing nutritive substances (proteins, fats and carbohydrates) for energy and growth, plants produce numerous non-energetic so-called secondary metabolites (mainly polyphenols) that allow them to protect themselves against infections and other types of hostile environments. Interestingly, these polyphenols often provide cells with valuable bioactive properties for the maintenance of their functions and homeostasis (signaling, gene regulation, protection against acquired or infectious diseases, etc.) both in humans and animals. Namely, from a nutritional point of view, and based on epidemiological data, it is now well accepted that the regular consumption of green vegetables, fruits and fibers has protective effects against the onset of cancer as well as of inflammatory, neurodegenerative, metabolic and cardiovascular diseases, and consequently increases the overall longevity. In particular, grapevine plants produce large amounts of a wide variety of polyphenols. The most prominent of those-resveratrol-has been shown to impair or delay cardiovascular alterations, cancer, inflammation, aging, etc. Until recently, the molecular bases of the pleiotropic effects of resveratrol remained largely unclear despite numerous studies on a variety of signaling pathways and the transcriptional networks that they control. However, it has been recently proposed that the protective properties of resveratrol may arise from its modulation of small non-coding regulatory RNAs, namely microRNAs. The aim of this review is to present up-to-date data on the control of microRNA expression by dietary phytophenols in different types of human cells, and their impact on cell differentiation, cancer development and the regulation of the inflammatory response.

miRNA as molecular target of polyphenols underlying their biological effects

Polyphenols are the most abundant antioxidants in the human diet and are widespread constituents of fruits and beverages, such as tea, coffee, and wine. Epidemiological, clinical, and animal studies support a role of polyphenols in the prevention of various chronic diseases. For a long time, their direct antioxidant effect has been reported as the mechanism responsible for the observed health properties. However, recent findings revealed that polyphenols could interact with cellular signaling cascades regulating the activity of transcription factors and consequently affecting the expression of genes. Together with this classical regulatory pathway, polyphenols have been shown to affect the expression of microRNAs (miRNA). miRNAs are small, noncoding RNAs implicated in the regulation of gene expression that control both physiological and pathological processes such as development and cancer. Furthermore, expression of miRNAs can be affected by different external stimuli including nutrients such as vitamins, lipids, and phytochemicals. In this paper, we review studies assessing modulation of miRNAs expression by dietary polyphenols that could constitute a new pathway by which these compounds may exert their health effects. Over 100 miRNAs, involved in the control of different cellular processes such as inflammation or apoptosis, were identified as modulated by polyphenols. Most of the studies were performed in vitro using different cell lines, particularly cancer cell lines, and few studies were performed in animals. From all these data, miRNAs appear as interesting mediators in regulating polyphenols' biological effects; however, further studies are needed to validate miRNA targets and particularly in physiologically relevant conditions taking into account the bioavailability of dietary polyphenols.

Reactive oxygen species mediate tolfenamic acid-induced apoptosis in human colorectal cancer cells

Several studies have shown substantial evidences that non-steroidal anti-inflammatory drugs (NSAIDs) exert anticancer effects by generating reactive oxygen species (ROS). Tolfenamic acid (TA) is one of the traditional NSAIDs widely used for treatment of migraine. TA has anti-cancer activities in several human cancer models. In this study, we report that generation of ROS by TA leads to apoptosis through modulation of several pathways in human colorectal cancer cells. TA induced rapid generation of intracellular ROS and led to an increase of phosphorylation of H2AX, a tail moment of comet and distribution of fragmented genomic DNA traces. Treatment of N-acetyl-l-cysteine (NAC) abolished TA-induced phosphorylation of H2AX and apoptosis. Treatment of TA resulted in an increase of nuclear factor-kappaB (NF-κB) transcriptional activity through inhibitor of kappa B (IκB-α) degradation and subsequent p65 nuclear translocation. In addition, TA increased apoptosis-inducing activating transcription factor 3 (ATF3) expression. However, the treatment of NAC abolished TA-mediated NF-κB activation and ATF3 expression and chemical inhibition of NF-κB or knockdown of p65 significantly attenuated TA-induced ATF3 expression. Our finding indicates that ROS-mediated DNA damage and subsequent activation of NF-κB and ATF3 expression plays a significant role in TA-induced apoptosis in human colorectal cancer cells.

New perspectives of curcumin in cancer prevention

Numerous natural compounds have been extensively investigated for their potential for cancer prevention over the decades. Curcumin, from Curcuma longa, is a highly promising natural compound that can be potentially used for chemoprevention of multiple cancers. Curcumin modulates multiple molecular pathways involved in the lengthy carcinogenesis process to exert its chemopreventive effects through several mechanisms: promoting apoptosis, inhibiting survival signals, scavenging reactive oxidative species (ROS), and reducing the inflammatory cancer microenvironment. Curcumin fulfills the characteristics for an ideal chemopreventive agent with its low toxicity, affordability, and easy accessibility. Nonetheless, the clinical application of curcumin is currently compromised by its poor bioavailability. Here, we review the potential of curcumin in cancer prevention, its molecular targets, and mechanisms of action. Finally, we suggest specific recommendations to improve its efficacy and bioavailability for clinical applications.