Natural Products for Chemoprevention of Breast Cancer.

Breast cancer is the primary cause of cancer death in women. Although current therapies have shown some promise against breast cancer, there is still no effective cure for the majority of patients in the advanced stages of breast cancer. Development of effective agents to slow, reduce, or reverse the incidence of breast cancer in high-risk women is necessary. Chemoprevention of breast cancer by natural products is advantageous, as these compounds have few side effects and low toxicity compared to synthetic compounds. In the present review, we summarize natural products which exert chemopreventive activities against breast cancer, such as curcumin, sauchinone, lycopene, denbinobin, genipin, capsaicin, and ursolic acid. This review examines the current knowledge about natural compounds and their mechanisms that underlie breast cancer chemopreventive activity both in vitro and in vivo. The present review may provide information on the use of these compounds for the prevention of breast cancer.

INTRODUCTION

Breast cancer represents an important public health problem worldwide and is the primary cause of cancer death in women.1 Early diagnosis has become possible due to improved detection techniques. However, the mortality of patients suffering from breast cancer has increased. Current treatments including surgery, radiotherapy, adjuvant chemotherapy, and/or hormone therapies are useful for treating breast cancer, but there is still no effective cure for most patients suffering from advanced breast cancer. Recent studies have identified new pathways, biomarkers, and agents that are likely to be effective in breast cancer.2 There is an unmet need for agents that can be used to reduce the incidence of breast cancer in high-risk women. Therefore, the search for novel preventive approaches is necessary. One such approach is chemoprevention.

Cancer chemoprevention is defined as the use of natural or synthetic compounds to prevent, slow, suppress, or reverse the carcinogenic processes. Given that treatment options for patients with advanced breast cancer are limited, chemoprevention may be a rational and an appealing strategy. The discovery of novel natural drugs is important for reduction of side-effects, high selectivity, low toxicity, and better killing of cancer cells.3

The present review summarizes the current understanding of natural products which exert chemopreventive activities against breast cancer. We summarize studies on the effects of curcumin, sauchinone, lycopene, denbinobin, genipin, capsaicin, and ursolic acid against breast cancer. The structure of these natural products are shown in Figure 1. These natural compounds possess anti-inflammatory,4 anti-metastatic,5 anti-proliferative,6 anti-angiogenic,7 and anti-cancer properties in breast cancer. We focus on the possible mechanisms that may underlie the anti-cancer activities of these compounds on breast cancer progression.

Figure 1.

Chemical structures of natural products: (A) Curcumin; (B) Capsaicin; (C) Lycopene; (D) Sauchinone; (E) Genipin; (F) Denbinobin; and (G) Ursolic acid.

CURCUMIN

Curcumin [1,7- bis(4-hydroxy-3-methoxyphenyl)1,6-hepta-diene- 3,5-dione] is a natural dietary pigment from the root of the plant turmeric (Curcuma Ionga Linn).8 Curcumin possesses anti-inflammatory,4 anti-carcinogenic, and anti-metastatic5 properties, and inhibits tumor formation.8,9 Curcumin significantly inhibited cancer growth and is considered a cancer chemopreventive and chemotherapeutic agent.10 Curcumin exerted in vitro anti-breast cancer activities through regulation of matrix metalloproteinase (MMP)-2, B-cell lymphoma 2 (Bcl-2), Bax, flap endonuclease 1 (Fen1), NF-E2-related factor 2 (Nrf-2) factors, and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling.11,12

There have been several studies on the chemotherapeutic effects of curcumin in breast cancer. Curcumin down-regulates MMP-2 in a dose- and time-dependent fashion and inhibits the H-Ras-induced invasive phenotype in MCF10A human breast epithelial cells (H-Ras MCF10A).8

Curcumin has a cytotoxic effect on H-Ras MCF10A cells.8 Curcumin-induced cell death involves downregulation of Bcl-2 and upregulation of Bax, two key apoptosis-linked gene products, during apoptosis in H-Ras MCF10A cells.8,13 This has also been observed in other human breast cancer cell lines such as MDA-MB-231 and MCF-7 cells.3,11 Curcumin triggers apoptosis through the PI3K/Akt signaling pathway.12 Curcumin induces Akt phosphorylation, but combination therapy with PI3K inhibitor, LY290042, synergizes the apoptotic effect.12 Blocking the PI3K/Akt survival pathway with LY290042 affects curcumin-induced apoptosis in MCF-7 cells.12

Overexpression of Fen1, which is a DNA repair-specific nuclease, is involved in the development of breast cancer, and therefore, Fen1 can be a therapeutic target in breast cancer.14 Nrf-2 is a transcription factor which regulates cellular antioxidant defense systems.15 Curcumin decreases Fen1 promoter activity and protein expression in a dose-dependent manner and induces the expression of Nrf-2 in breast cancer.15 The Nrf-2-dependent downregulation of Fen1 by curcumin inhibits the proliferation of breast cancer cells.15

Bisphenol A (BPA) affects the development of estrogen-responsive breast cancer through the proliferation of estrogen receptor (ER)-positive human breast cancer cells.16 Curcumin inhibits the proliferative effects of BPA on human breast cancer cells.16 Curcumin inhibits miR-19 which is involved in BPA-mediated MCF-7 cell proliferation.17 Thus, treatment with curcumin, a miR-19 inhibitor, leads to suppression of proliferation, growth, and invasion/metastasis of cancer cells.17

The F-box protein S-phase kinase-associated protein 2 (Skp2) is involved in breast cancer progression, especially in ER/HER2 negative breast cancers.18 Curcumin inhibits cell growth by inhibition of Skp2 and induction of p27 in MDA-MB-231 human breast cancer cells.18 Taken together, curcumin inhibits cancer cell growth, especially in ER/HER2 negative breast cancers.18

SAUCHINONE

Saururus chinensis (SC) possesses anti-tumorigenic activity in MCF-7 human breast cancer cells.19 SC suppresses angiogenetic, proliferative, and anti-apoptotic activity by reducing VEGF, cyclin D1, and Bcl-2 gene products.19 SC activates caspase-3, which plays a role in SC-induced apoptosis and can be used as a chemotherapy agent in human breast cancer cells.19 Sauchinone, a major active constituent of SC, is extracted from the root of SC.20

Sauchinone possesses anti-pyretic, diuretic, and anti-inflammatory properties.20 Sauchinone has been used for the treatment of jaundice, edema, fever, and inflammatory diseases in Korean folk medicine for centuries.20 Sauchinone has been reported to inhibit bone destruction and to decrease mortality rates.21 It exerts anti-cancer effects through control of VEGF, cyclin D1, Bcl-2, caspase-3, and the extracellular signal-regulated kinase (ERK) signaling pathway in breast cancer cells.19,21 NF-κB activity through the ERK signaling pathway leads to increased proliferation of cells and tumor growth through the transcription of anti-apoptotic proteins.21–23 Sauchinone has been used as an anti-inflammatory herbal agent that TNF-α expression, the ERK pathway, and NF-κB activation.21,24

LYCOPENE

Lycopene is the major carotenoid in fruits and vegetables including tomatoes. Lycopene is the most effective oxygen radical quenching agent among the carotenoids.25,26 It inhibits the growth of various human cancers including breast,27 prostate,28,29 endometrial,26 colorectal,30 and lung cancer.31 The anticancer activities of lycopene progress through regulation of growth factor signaling, apoptosis induction,32 and changes in phase II detoxifying/antioxidant enzymes.31 In addition, lycopene inhibits tumor cell invasion, metastasis, and angiogenesis, thereby suppressing the development and growth of cancers.32 These anti-cancer activities also reduce DNA damage due to reactive oxygen species.33 Lycopene correlates with the ERKs and Akt/mTOR signaling pathways in breast cancer.27,34

Lycopene inhibited invasion, metastasis, and proliferation of aggressive breast cancer cell lines such as H-Ras-transformed MCF10A human breast cells and MDA-MB-231 human breast cancer cells.27 Activation of ERKs and Akt was inhibited by lycopene.27 Lycopene exerts anti-proliferation, anti-invasion, and anti-migration effects through the ERKs and Akt signaling pathways in breast cancer.27 Lycopene upregulates the expression of the Bax and increases caspase-9-induced apoptosis in MCF-7 human breast cancer cells.34,35

Lycopene possesses anti-proliferative properties in triple-negative breast cancer, which is negative for expression of ER, progesterone receptor, and HER2 proteins. Lycopene induces apoptosis through Bax protein by inhibiting phosphorylation of Akt, which plays a role in apoptosis and cell survival and is downstream of mTOR. Thus, lycopene induces apoptosis by blocking the Akt/mTOR signaling pathway in triple-negative breast cancer.36

Lycopene inhibits cell proliferation by decreasing cell viability and arresting the cell cycle in different phases.37,38 Lycopene suppresses cancer cell growth by down-regulating Skp2, which plays a role in breast cancer progression, especially in ER/HER2-negative breast cancers.18 Cyclin D1 is over-expressed in breast cancer during the G1 phase. Lycopene inhibits insulin like growth factor (IGF)-1-induced cell cycle progression from G1 to S phase and reduces cyclin D1 levels, suppressing the growth of MCF-7 cells.39

GENIPIN

Genipin is a natural product of Gardenia jasminoides Ellis and is used in the treatment of several cancers due to its anti-tumor activity.6 Genipin possesses anti-inflammatory,40 anti-angiogenic,7 anti-oxidative,41 anti-proliferative,6 and apoptosis-inducing42 properties in cell lines. It can prevent a variety of cancers including breast, periodontal,40 gastric, lung, and liver cancer. In breast cancer, genipin regulates Bcl-2, Bax, caspase-3, JNK, p38MAPK, and reactive oxygen species (ROS) production.6,43

Genipin has anti-proliferative activity in MDA-MB-231 breast cancer cells.6 Genipin induces apoptosis in MDA-MB-231 cells by downregulating Bcl-2 and upregulating Bax and caspase-3, as well as the pro-apoptosis products JNK and p38 MAPK, inducing apoptosis and inhibiting invasion/metastasis.6 Genipin was shown to be a chemopreventive agent for preventing metastatic breast cancer.6

Mitochondrial uncoupling protein (UCP2), which promotes tumorigenic properties, is over-expressed in MCF7 human breast cancer cells.44 UCP2 is also associated with cell viability through regulation of ROS production, apoptosis, and autophagy.43 Inhibition of UCP2 involves an increase in ROS production, apoptosis, and autophagy, and a decrease in cell viability.43 Thus, genipin decreases cancer cell viability by inhibiting UCP2.43

DENBINOBIN

Denbinobin (5-hydroxy-3,7-dimethoxy- 1,4-phenanthraquinone) is a substance extracted from Ephemerantha lonchophylla. It is isolated from the stems of Dendrobium moniliforme (Shi-Hu in Chinese medicine).45,46 Denbinobin possesses anti-cancer, anti-inflammatory,47 anti-angiogenesis,48 and apoptosis-inducing49 properties in several types of cancer cells. These effects are particularly relevant to Src kinase, NF-κB, and IGF-1 receptor (IGF-1R) in breast cancer.45,47

Src kinase activity is increased in breast cancer, is associated with aggressive disease, and can indicate poor prognosis.46 Denbinobin suppresses metastasis by suppressing Src kinase activity in human breast cancer cells.46 Denbinobin also inhibits breast cancer metastasis by regulating Src-mediated signaling pathways and can be therapeutic factor in breast cancer treatment.45

NO synthase (iNOS) and COX-2 play important roles in various inflammatory diseases.47 Denbinobin decreases iNOS and COX-2 activity in a concentration-dependent manner by inhibiting NF-κB activation.47 Denbinobin possesses anti-inflammatory properties and can serve as a therapeutic agent in inflammatory disease.47

Anti-angiogenic and tumor inhibition activity are associated with the enhanced activity of IGF-1R.48 IGF-1R signaling leads to apoptosis and cell proliferation, which supports breast cancer development.50,51 Denbinobin prevents the activation of IGF-1R and its down-stream signaling pathway, thus inhibiting angiogenesis.48

CAPSAICIN

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is a natural pungent ingredient found in red pepper that has anticarcinogenic, antimutagenic, and chemopreventive52,53 in a variety of cancers by inducing apoptosis.54–57 It serves as an anti-metastatic58 and anti-angiogenic factor.59 In breast cancer, ROS, Rac1, caspase-3, and the epidermal growth factor receptor (EGFR)/HER-2 signaling pathway are involved in these effects.52,60,61

Capsaicin is a pro-apoptotic agent. Capsaicin is more effective for apoptosis in the presence of p53.56 In breast cancer, capsaicin-induced apoptosis is induced by ROS and Rac1 in H-Ras MCF10A cells.52 It is selectively induced by c-Jun N-terminal protein kinase -1 and p38, but not by ERKs.53 Capsaicin promoted concentration-dependent apoptosis in MCF-7 breast cancer cells.62 In addition, capsaicin decreased breast cancer stem cells in the MCF-7 cell line.62 Capsaicin also suppresses translocation of notch intracellular membrane domain to the nucleus.62 Capsaicin promotes apoptosis of breast cancer stem cells in MCF-7 cells by controlling Notch signaling.62

Capsaicin-induced apoptosis includes caspase-3, a pro-apoptotic factor expressed in MCF-7 cells.60 Caspase-3 also affects cell cycle arrest in the S phase, thereby inhibiting growth of human breast cancer cells.60 Capsaicin suppresses breast cancer cell migration and reduces the size of MDA-MB 231 breast cancer cells.61 It is associated with factors in the EGFR/HER-2 pathway, which leads to progressive tumor growth and invasion, including ERK, cyclin D1, and p27(KIP1).63,64 Capsaicin exerts anti-proliferative effects by modulating the EGFR/HER-2 pathway.61

There have been a debate regarding the anticarcinogenic and procarcinogenic effects of capsaicin. Several studies have reported that this phytochemical exerted the procarcinogenic property, particularly in skin cancer.65,66 Capsaicin act as a carcinogen or a cocarcinogen through Erk, p38, and EGFR dependent mechanisms in 12-O-tetradecanoylphorbol-13-acetate-induced skin carcinogenesis.65,66 Therefore, a cautious consideration would be required for using capsaicin as a chemopreventive agent.65,66

URSOLIC ACID

Ursolic acid (UA) is a pentacyclic triterpenoid compound extracted naturally from herbs.67 It possesses anti-cancer, anti-invasive,68 anti-metastatic,69 anti-proliferation,70,71 and anti-angiogenesis72 properties in various human cancers, and also promotes apoptosis. In addition, UA prevents the development of nonalcoholic fatty liver disease.67 Recently, ursolic acid derivatives were newly synthesized through a more efficient reaction;73 however, we have chosen to summarize only data from the natural compound here. In breast cancer, UA affects cyclin D1, CDK4, forkhead box M1 (FoxM1), Bax, Bcl-2, and MMP-2 factors and it can be used as a cancer prevention agent.74–77

UA possesses anti-cancer effects in human breast cancer cells.75 UA is related to various apoptotic factors and signaling pathways.75 UA induces apoptosis and inhibits cell proliferation.74,75 CyclinD1/CDK4 correlates with cell cycle progression and cancer progression74 and FoxM1, a transcription factor, is a key for cell proliferation and cell cycle progression.75 UA-induced apoptosis decreases cyclinD1/CDK4 expression through regulation of FoxM1 in MCF-7 human breast cancer cells.75

UA up-regulates Bax, which is a pro-apoptosis factor, and down-regulates Bcl-2, which is an anti-apoptosis factor, leading to induction of apoptosis.78 UA-induced apoptosis involves release of cytochrome c in the mitochondrial death pathway.77 UA has inhibitory effects on migration and invasion in the metastatic breast cancer cell line MDA-MB 231.76 UA reduces MMP-2 and urokinase-type plasminogen activator expression by inhibiting NF-κB and Jun N-terminal kinase.76 UA can be a chemopreventive agent for metastatic breast cancer.

OTHERS

Terpenoids include ursolic acid, lycopene, and other polyterpenes. These terpenoids are extracted from plants or animals and are often related to chemoprevention and treatment of breast cancer.79 Triterpenoids in particular are involved in anti-inflammation, cell cycle regulation, proliferation, and apoptosis through control of multiple signal transduction pathways.79

Ginsenoside 25-OCH3-PPD, a natural product, inhibits breast cancer growth and metastasis by down-regulating the mouse double minute 2, playing role in cancer development and growth, and decreases cancer cell survival through induction of apoptosis and cell cycle transition to G1 phase.80,81 Furanodiene extracted from Curcuma wenyujin inhibits breast cancer proliferation and growth by inducing cell cycle arrest at the G0/G1 phase and suppressing tumor growth.82 Furanodiene suppresses adhesion, migration, and invasion in metastatic breast cancer cells by modulating MMP-9. Furanodiene, however, does not induce apoptosis.83 Codonolactone isolated from Chloranthus henryi Hemsl inhibits breast cancer cell migration, invasion, and metastasis through downregulation of Runx2 transcriptional activity and inhibition of MMPs.84

Fangchinoline induces apoptosis through Bax, Bcl-2, caspase-3, and cytochrome c and inhibits proliferation via Akt/GSK-3beta/cyclin D1 signaling in breast cancer cell line.85 Fangchinoline is involved in the cell cycle transition to G1 phase through proliferating cell nuclear antigen and cyclin D1.85 A flavonoid morin from Moraceae possesses anti-oxidant, anti-inflammatory, and anti-carcinogenic properties, and suppresses invasion and metastasis in the breast cancer cell line MDA-MB-231 through inhibition of the Akt pathway.86

The herbal extract Nexrutine from the plant Phellodendron amurense possesses anti-cancer effects on ER-negative breast cancer. Nexrutine is associated with apoptosis and cell cycle transition to G1 phase through protein expression of Cyclin D1 and cdk2.87 Psoralen isolated from the seeds of Psoralea corylifolia L. inhibits metastasis to bone in breast cancer.88 Retinoid inhibits growth of breast cancer cells by signaling on ER and HER2.2,89 Retinoid possesses anti-proliferative and apoptotic effects in breast cancer.90

Phytoestrogens such as resveratrol, daidzein, quercetin, and genistein can affect cell signaling pathways related to proliferation, apoptosis, and inflammation.91 They possess anti-oxidant, anti-proliferative, anti-angiogenic, anti-apoptotic, and anti-cancer properties in breast cancer.92 Another dietary phytoestrogen, arctigenin, induces apoptosis in ER-negative breast cancer via the ROS/p38 MAPK pathway and regulation of Bcl-2.93 Genistein and resveratrol are able to suppress promoters I.3/II, which are the major promoters for aromatase expression; aromatase expression can lead to overproduction of estrogen, promoting breast cancer.94 In addition, resveratrol dose-dependently inhibits the growth of estrogen receptor-positive human breast cancer cells.95

A dietary chalcone-type flavonoid isoliquiritigenin (ISL) inhibits neoangiogenesis through the VEGF/VEGFR-2 signaling pathway in breast cancer. ISL suppresses VEGF/VEGFR-2 signaling and elevates apoptosis.96 A natural compound pterostilbene possesses anti-proliferative effects and induces apoptosis through Bax activation.97 Tehranolide, isolated from Artemisia diffusa, inhibits proliferation and growth of human breast cancer cells by inducing G0/G1 arrest. It is associated with the PI3K/Akt/cyclin D1 pathway and regulation of ROS, cytochrome c, Bax and Bcl-2 in breast cancer cells.98

CONCLUSIONS

This article provides information on selected natural products for chemoprevention against breast cancer. Most of these natural products involve apoptotic factors, including Bcl-2 and Bax. Many natural products affect signaling pathways such as ERKs, Akt/mTOR, and EGFR/HER2. Some of these compounds show inhibitory effects on tumor growth, angiogenesis, proliferation, invasion, and metastasis. We summarized the mechanistic basis of chemoprevention with compounds in a Table 1 and a Figure 2. These natural products can be preventive agents that can reduce side effects and improve the effect of drugs on human breast cancer, while maintaining high selectivity and low toxicity. The identification of natural products that can control or inhibit potential molecular targets will provide many opportunities for chemoprevention.

Table 1.

Effects of natural products for chemoprevention of breast cancer

Natural product	Mechanism	Related factor	Reference
Capsaicin	Apoptosis Cell cycle transition	ROS, Rac1, c-Jun, JNK-1, p38, caspase-3	52, 53, 60
	Anti-proliferation	EGFR/HER2 signaling pathway	63, 64
Chalcone	Apoptosis, anti-angiogenesis	VEGF/VEGFR-2 signaling pathway	61
Codonolactone	Anti-invasion, anti-metastasis	Runx2, MMPs	87
Curcumin	Apoptosis	MMP-2, Bcl-2, BaxPI3K/Akt signaling pathway	8, 11, 12, 14
	Anti-proliferation	Fen1, Nrf-2, BPA proliferation, Skp2, p27	13, 15, 16, 18
	Cell cycle transition	miR-19	17
Denbinobin	Anti-metastasis	Src kinase	46
	Anti-inflammation	NF-κB, iNOS, COX-2	47
	Anti-angiogenesis	IGF-1R	48
Fangchinoline	Apoptosis	Bax, Bcl-2, caspase-3, cytochrome c	85
	Anti-proliferation	Akt/GSK-3beta/cyclin D1 signaling	85
	Cell cycle transition	PCNA, cyclin D1	85
Furanodiene	Cell cycle transition, anti-invasion, anti-metastasis	MMP-9	82, 83
Genipin	Apoptosis	Bcl-2, Bax, caspase-3, JNK, p38MAPK, UCP2, ROS	6, 43
Ginsenoside	Apoptosis, cell cycle transition	MDM2	80
Lycopene	Anti-proliferation,	Skp2	18
	Anti-metastasis, anti-invasion	ERK/Akt signaling pathway
	Apoptosis	Bax, caspase-9, cyclin D1 Akt/mTOR signaling pathway	35, 37
	Cell cycle transition	IGF-1	38
Morin	Anti-invasion, anti-metastasis	Akt pathway signaling	86
Nexrutine	Apoptosis, cell cycle transition	Cyclin D1, cdk2	87
Phytoestrogens	Apoptosis, anti-angiogenesis,	ROS/p38 MAPK pathway, Bcl-2, promoters I.3/II	93, 94
Psoralen	Anti-metastasis
Pterostilbene	Apoptosis, anti-proliferation	Bax	97
Retinoid	Apoptosis, anti-proliferation	ER/HER2 signaling	92
Sauchinone	Apoptosis	VEGF, cyclin D1, Bcl-2, caspase-3	19
	Anti-inflammation	TNF-α, NF-κB ERK signaling pathway	21, 24
Tehranolide	Anti-proliferation, cell cycle transition	PI3K/Akt/cyclin D1 pathway, ROS, cytochrome c, Bax, Bcl-2	98
Ursolic acid	Apoptosis	FoxM1, cyclin D1/CDK4Bax, Bcl-2, cytochrome c	75, 77, 78
	Anti-metastasis	NF-κB, JNK, MMP2, u-PA	76

ROS, reactive oxygen species; JNK, Jun N-terminal protein kinase; MMP, matrix metalloproteinas; Bcl-2, B-cell lymphoma 2; PI3K, phosphoinositide 3-kinase; Akt, protein kinase B; Fen1, flap endonuclease 1; Nrf-2, NF-E2-related factor 2; BPA, bisphenol A; Skp2, S-phase kinase-associated protein 2; iNOS, NO synthase; IGF-1R, insulin like growth factor 1 receptor; PCNA, proliferating cell nuclear antigen; UCP2, uncoupling protein; MDM2, mouse double minute 2; ERK, extracellular signal-regulated kinase; IGF, insulin like growth factor; ER, estrogen receptor; FoxM1, forkhead box M1; u-PA, urokinase-type plasminogen activator.

Figure 2.

Chemopreventive effects of natural compounds on breast cancer.