Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. New perspectives of curcumin in cancer prevention Wungki Park, A.R.M Ruhul Amin, Zhuo Georgia Chen, and Dong M. Shin Department of Hematology and Medical Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia, 30322, U.S.A. Running Title: Curcumin in Cancer Prevention Key Words: Chemoprevention, Curcumin, Natural compound, Molecular target, Bioavailability Financial Support: This work was supported, in whole or in part, by National Institutes of Health Grants P50 CA128613 (DMS) and R03 CA159369 (ARA) and Robbins Scholar Award (ARA) Conflict of Interest: None Address for Correspondence: Dong M. Shin, Department of Hematology and Medical Oncology, Winship Cancer Institute of Emory University, School of Medicine, Atlanta, GA, 30322, U.S.A. Phone: 1-404-778-2980; Fax: 1-404-778-5520; E-mail: [email protected] 1 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Abstract: Numerous natural compounds have been extensively investigated for their potential for cancer prevention over 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. Nevertheless, 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 action mechanisms. Finally, we suggest specific recommendations to improve its efficacy and bioavailability for clinical applications. 2 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Introduction Cancer is a major health problem that can debilitate and destroy human lives. One out of every four deaths in the U.S. is caused by cancer. Over $124.6 billion was spent in direct medical costs for the 13.7 million cancer survivors and 1.5 million newly diagnosed cancer patients in the U.S. in 2010. Increasing human life expectancy will inevitably raise cancer prevalence and the related costs. Consequently, the development of effective cancer prevention strategies is increasingly important. Histologically, the development of cancer involves multiple steps, which occur over several years after the initial carcinogen exposure from normal to hyperplasia, mild, moderate, and severe dysplasia, and carcinoma in situ, before finally progressing to invasive cancer (1). Throughout this long, multi-step developmental course, there is a wide scope of possible preventive approaches that can delay or prevent the development of cancer. Different cancer prevention strategies such as behavioral modification, vaccines, surgical manipulation, and chemoprevention have evolved with tremendous research efforts (2). Many investigations have proven that healthy lifestyles involving balanced diets, regular exercise, smoking cessation, alcohol reduction, weight control, and stress management are beneficial for decreasing cancer risk and can never be overemphasized (3-7). One particular milestone in cancer prevention was the approval by the U.S. Food and Drug Administration (FDA) of the human papilloma virus (HPV) cervical cancer vaccine in 2009 as a result of positive randomized controlled clinical trials. The term chemoprevention was first coined by M. B. Sporn in 1976 who defined it as a 3 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. preventive modality in which natural or synthetic agents can be employed to slow, stop, reverse, or prevent the development of cancer. Since then, researchers have investigated numerous agents for the purpose with few successes. The first important translational study of a potentially chemopreventive agent was conducted with 13-cis retinoic acid (13-cRA), which resulted in successful size reduction of the premalignant lesion oral leukoplakia, albeit with some notable toxicities (8). In an attempt to reduce the toxicity, this study was followed by another trial using high dose isotretinoin induction and maintenance with isotretinoin or beta carotene, which suggested that isotretinoin is significantly more effective than beta carotene against leukoplakia (9). Another follow up study using low dose isotretinoin and a large cohort of patients resulted in a negative outcome (10). In contrast, the field of breast cancer chemoprevention research gained considerable momentum after positive large-scale clinical trials of Tamoxifen, a selective estrogen receptor modulator (SERM), led to its FDA approval (11). However, not all cancer types have successful chemoprevention stories. In colorectal cancer, despite positive secondary clinical trials of sulindac, celecoxib, and aspirin, primary prevention using cyclooxygenase-2 (COX-2) inhibitors was shown to have no benefit in the general population and the study was terminated early due to cardiovascular toxicity (12-14). Another disappointment was the recently conducted selenium and vitamin E cancer prevention trial (SELECT), which gave negative results in patients with lung and prostate cancers (15). After several large negative clinical trials were reported, the focus of the new era in chemoprevention has shifted toward molecularly targeted agents and less toxic natural compounds. 4 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. In chemoprevention, safety of the participants is the first priority and should be considered of the utmost importance since essentially healthy people will receive the chemopreventive treatment for a long period of time. Moreover, the toxicity of the agents could impact patient accrual in larger scale studies in real clinical practice. To this end, unlike synthetic compounds, the safety of natural compounds present in fruits, vegetables, and spices are well established through their long-term consumption in human history (16). Therefore, taking natural compounds for cancer prevention can be a well justified and effective strategy for people with increased risk for cancer development – such as those with premalignant lesions of intraepithelial neoplasia. Among many such natural compounds, curcumin has drawn special attention for its chemoprevention potential because of its safety, multi-targeted anticancer effects, and easy accessibility (16). The following sections will discuss different aspects of curcumin as a chemopreventive agent, including its safety, efficacy, and mechanism of action. Curcumin in Chemoprevention Since 1987, the National Cancer Institute (NCI) has tested over 1,000 different potential agents for chemoprevention activity, of which only about 40 promising agents were moved to clinical trials (17). Curcumin, present in the Indian spice “haldi”, is one such agent that is currently under clinical investigation for cancer chemoprevention. Three polyphenols (Figure 1) were isolated from Curcuma longa, of which curcumin (bis-α,β- unsaturated β-diketone) is the most abundant, potent and extensively investigated (16). Curcumin has been used empirically as a remedy for many illnesses in different cultures. It is only in the last few decades that curcumin’s effects against cancer and cancer 5 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. therapy-related complications have emerged, through much investigation. The first clinical report of the anticancer properties of curcumin was from Kuttan and coworkers, who used 1% curcumin ointment on skin cancerous lesions with a reduction in smell in 90% of patients (18). 10% patients experienced a reduction in pain and lesion size. In an experimental model of mammary cancer induced by 7,12-dimethylbenz-[a]-anthracene (DMBA) in female rats, the initiation of DMBA-induced mammary adenocarcinoma was significantly decreased by intraperitoneal infusion of curcumin 4 days before DMBA administration (19). In a study of esophageal cancer prevention in curcumin-fed F344 rats, the chemopreventive activity of curcumin was observed not only in the initiation phase but also in post-initiation phases (20). Also, in a familial adenomatous polyposis (FAP)- simulated study in which the APC gene of C57Bl/6J Min/+ mice was mutated to result in the development of numerous adenomas by 15 weeks of age, an oral curcumin diet prevented adenoma development in the intestinal tract, suggesting the chemopreventive effect of curcumin in colorectal cancer with APC mutation (21). Moreover, in a rat model of N-nitrosodiethylamine and phenobarbital-induced hepatic cancer, curcumin reduced lipid peroxidation and salvaged hepatic glutathione antioxidant defense, which eventually may have contributed to hepatic cancer prevention (22). Several studies of cancer prevention at different stages have demonstrated the multi-targeted anticancer and chemopreventive effects of curcumin and have suggested it as a very favorable agent for chemoprevention. Mechanisms of Anticancer Effects According to their mode of action, chemopreventive agents are classified into different 6 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. subgroups: antiproliferatives, antioxidants, or carcinogen blocking agents. Curcumin belongs to all three subgroups, given its multiple mechanisms of action. The anticancer effects of curcumin mainly result from multiple biochemical mechanisms that are involved in the regulation of programmed cell death and survival signals. The curcumin targets that are involved in signaling pathways include transcription factors, growth factors, inflammatory cytokines, receptors, and enzymes (Figure 2). In different types of cancers, curcumin exhibits anticancer actions through a combination of different mechanisms including; survival signal reduction, proapoptotic promotion, anti- inflammatory actions, and reactive oxygen stress (ROS) scavenging to different degrees. The effects of curcumin on these signaling pathways are expected to be more complicated in the real setting, and the mechanisms of curcumin’s chemopreventive, chemosensitizing, and radiosensitizing effects are more vigorously being studied now. Survival signals - nuclear factor-κB (NF–κB) The survival signals in cancer cells are upregulated to support proliferation and survival against anticancer treatment. The central role players in this process are nuclear factor-κB (NF-κB), Akt, and their downstream cascades that can lead to the upregulation of anti- apoptotic Bcl-2 proteins. Curcumin can modulate these signals by inhibiting the NF-κB pathways at multiple levels (23, 24). Curcumin significantly inhibited the growth of squamous cell carcinoma of head and neck (SCCHN) xenograft tumors in nude mice. Inhibition of nuclear and cytoplasmic IκB-β kinase (IKKβ) in the xenograft tumors decreased NF-κB activity (25). Curcumin was also shown to enhance chemosensitivity in 5-fluorouracil and cisplatin treated esophageal adenocarcinoma as well as in paclitaxel 7 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. treated breast cancer cells by inhibiting compensatorily upregulated NF-κB (26). Likewise in a colon cancer cell line during radiotherapy, curcumin blocked NF-κB and reduced radioresistance (27). Apoptotic signals – intrinsic and extrinsic Curcumin induces programmed cell death (apoptosis) in many cancer cell types. Both the intrinsic and extrinsic apoptotic pathways are activated by curcumin. In the intrinsic pathway, various cell stresses – irreversible DNA damage, defective cell cycle, or loss of growth factors – can generate death signals and ultimately pass them down to mitochondria. Then, depending on the balance of Bcl-2 family members, the destiny of the cell is driven into apoptosis. Curcumin upregulates the p53 modulator of apoptosis (PUMA) and Noxa, which, in turn, activates the proapoptotic multi-domain Bcl-2 family members Bax, Bim, and Bak and downregulates Bcl-2 and Bcl-xl. Loss of balance between pro- and anti-apoptotic Bcl-2 proteins causes calcium influx into mitochondria and decrease in mitochondrial outer membrane permeability (MOMP) which allows cytochrome C and Smac release into the cytoplasm, eventually leading to the activation of a cascade of caspases and formation of the apoptosome, causing apoptosis (28). In the extrinsic pathway, death signals are initiated from the exterior environment of the cells via Fas, tumor necrosis factor (TNF), and death receptors (DR) 3-6. When the signal is received, conformational change in the receptors allows Fas-associated death domain (FADD) binding and recruits the death-induced signaling complex (DISC), which activates the formation of initiator caspases 8 and 10. Curcumin was shown to upregulate 8 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. extrinsic apoptosis pathway signals via the Fas pathway. In TNF-related apoptosis inducing ligand (TRAIL)-resistant cell lines, curcumin also enhanced apoptosis by upregulating the expression of DR 4 and 5 (29). After DISC recruitment, activation of the initiator caspases is regulated by FLICE-like inhibitory protein (FLIP) and curcumin was shown to downregulate c-FLIP in natural killer/T-cell lymphoma (30). Afterwards, the initiator caspase cleaves Bid and the truncated Bid (tBid) provides crosstalk between the intrinsic and extrinsic pathways by delivering death signals from initiator caspases directly to the mitochondrial pathway. In SKOV3 and OVCA429 ovarian carcinoma cells, curcumin showed induction of both intrinsic and extrinsic apoptosis by cleavage of pro- caspase 3, 8, 9 and cytochrome C release followed by tBid formation (31). p53 plays a major role in tumor development and treatment, however, more than 50% of all cancers have p53 mutations. p53 proofreads DNA and recognizes uncorrectable mutations, at which point it arrests the cell cycle and steers the cell toward programmed cell death. Curcumin was shown to upregulate p53 expression followed by an increase in p21 (WAF-1/CIP-1), resulting in cell cycle arrest at G0/G1 and/or G2/M phases. This is eventually followed by the upregulation of Bax expression, which induces apoptosis (32). On the other hand, curcumin has also showed its p53-independent anticancer effect as an inhibitor of the proteasome pathway by inhibiting ubiquitin isopeptidase (33). In a prostate cancer cell line, curcumin downregulated MDM2, the ubiquitous ligase of p53, and displayed enhanced anticancer effect via PI3K/mTOR/ETS2 pathways in PC3 xenografts in nude mice receiving gemcitabine and radiation therapy (34). In p53 mutant or knockout ovarian cancer cell lines, curcumin induced p53-independent apoptosis 9 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research. Author Manuscript Published OnlineFirst on March 6, 2013; DOI: 10.1158/1940-6207.CAPR-12-0410 Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. which involved p38 mitogen-activated protein kinase (MAPK) activation and inhibited Akt, resulting in decreased expression of Bcl-2 and survivin (31). Taken together, cancers with both deleted/mutant and wild-type p53 can benefit from curcumin treatment to achieve an anticancer effect. Trophic signals – growth factors and cytokines Different kinds of trophic factors including growth factors and cytokines can contribute to growth signals in cancer cells. Curcumin inhibits epidermal growth factor receptor (EGFR) kinase phosphorylation and strongly degrades Her2/neu protein, which ultimately inhibits cancer growth (35). In SCCHN, curcumin targets both EGFR and vascular endothelial growth factor (VEGF) to inhibit cell growth (36). Therefore, the multi-targeted activity of curcumin may be potentially more effective. In an estrogen receptor negative breast cancer cell line, curcumin inhibited angiogenesis factors such as VEGF and basic fibroblast growth factor (b-FGF) at the transcriptional level (37). Curcumin was also shown to inhibit expression of pro-inflammatory cytokines such as IL-1β and -6 and exhibited growth inhibitory effects through inhibition of the NF-κB and MAPK pathways (38). In a breast cancer cell line, curcumin was shown to inhibit phosphorylation of Akt within the MAPK/PI3K pathway, which led to proapoptosis (39). Roles of reactive oxidative stress (ROS) ROS has opposing effects on cancers: it can be an insult causing DNA mutations in carcinogenesis, and it can also drive mitochondrial apoptosis. Minimizing DNA insult by scavenging ROS is important for the prevention of cancer, whereas generating ROS to 10 Downloaded from cancerpreventionresearch.aacrjournals.org on April 5, 2019. © 2013 American Association for Cancer Research.