This review analyses other plausible mechanisms of pomegranate in preventing the progression of breast cancer and how it can possibly be a therapeutic agent by acting at various steps of carcinogenesis including proliferation, invasion, migration, metastasis, angiogenesis, and inflammation via various molecular mechanisms.
Therapeutic pomegranate on breast carcinogenesis
CONDUCTED BY: Cancer Research Programme, Rajiv Gandhi Centre for Biotechnology, Trivandrum, India
PUBLISHED ON: Bio Factors
Punica granatum has a vast ethnomedical history and represents a reservoir of phytochemicals with high medicinal values.
The different anatomical compartments of the tree, that is, fruit, seed, juice, peel, leaf, flower, bark, and roots, are known to have varied pharmacological activities and extracts of these parts are known to target a wide range of diseases including cardiovascular disorders, diabetes, male infertility, Alzheimer’s disease, and AIDS.
Studies have shown that the extracts of the parts of the fruit also possess anticancer activity. The mechanisms of action are diverse and include interference with tumor cell proliferation, cell cycle, invasion, and inhibition of angiogenesis. Pomegranate is a fruit abundant in polyphenols, hydrolysable tannins punicalagin, pedinculgin, punicallin gallic and ellagic acids, esters of glucose anthocyanins and other polyphenols, and anthocynidins such as delphinidin, cyanidin, and pelargonidin.
The concentration of polyphenols in pomegranate (3.8 mg/mL gallic acid equivalents) is observed to be higher than in any other fruit juice, for example, grape, blueberry, black cherry, apple, cranberry, or orange (0.46–2.6 mg/mL of gallic acid equivalents). Therapeutically significant constituents of pomegranate include ellagic acid, ellagitannins (including punicalagins), punicic acid, flavanoids, anthocyanidins, anthocyanins, and estrogenic flavonols and flavones.
Evidences suggest that pomegranate extracts act against multiple human carcinoma, one of which is breast cancer, a highly heterogeneous disease and the fifth cause of death from cancer worldwide (globocan). Breast cancer is classified into different molecular subtypes. Studies have clearly shown that these cancer cells respond differently to the treatments depending on the molecular subtypes, pathways, and genomic aberrations when subjected to pathway-targeted therapy.
Current targets for breast cancer depend on its subtypes and the molecular targets of targeted therapy include tyrosine kinases, which encompass receptors like HER1, HER2, HER3, IGF receptor (IGFR), C-MET, FGF receptor (FGFR); molecules relevant to intracellular signaling pathways, such as PI3K, AKT, mammalian target of rapamycin (mTOR), and ERK; those that are involved in angiogenesis molecules associated with DNA repair and evading death by chemotherapeutic drugs; and enzymes such as aromatase.
The chemotherapeutic drugs currently in use have several side effects. Volumes of research have demonstrated that phytochemicals present in fruit and vegetables can also act as potent chemopreventive agent. Hence, dietary modification could potentially be one of the ways to combat the disease.
Also, many plant parts, which are not otherwise consumed, for example, the peel or the pericarp of certain fruits, have similar potent phytochemicals which can possibly be isolated and translated into marketable drugs. A few of the studies have pointed to relevance of these phytochemicals in overcoming multidrug resistance, which is a limiting factor in drug-based cancer treatments.
A great deal of research, therefore, is currently focused on finding alternatives that have minimal side effects but lend themselves for use in the much-effective targeted or combinatorial therapies. Punica granatum or pomegranate is one such potential candidate. The plant has been shown, in several studies, to contain phytochemicals that target multiple molecules involved in various steps of carcinogenesis, making them potential candidates for use in targeted breast cancer therapies. The potent anticancer phytochemicals include tannins such as ellagic acid, gallic acid, punicalagin; flavanoids including flavones, flavanol, anthocynanidins, flavan-3-ols; alkaloids such as piperidines and pyrrolidines and organic acids like punicic acid and linoleic acid .
Many of these components, individually, or in combination as well as in the form of extract have been demonstrated to be effective against breast cancer. The major component of the juice and pericarp of Punica are polyphenols like anthocyanins such as delphinidin, cyanidin, and pelargonidin, which give the juice its red color , besides hydrolyzable tannins, such as punicalagin and gallagic acid [8, 9]. Other polyphenolic components of potential interest include kaempferol, quercetin, and luteolin [10, 11]. The seed oil, which comprises 65–80% conjugated fatty acids, also contains many compounds of interest with known anticancer activities. The predominant among these fatty acids is punicic acid [12, 13], which has been proven to be effective against breast cancer.
This review focuses mainly on the potential of Punica extracts in fighting breast cancer, its ability to inhibit and interfere with steps that are of paramount importance to breast tumor progression from proliferation of the tumor to its migration, invasion, metastasis, angiogenesis, and inflammation as Fig.1indicates.
Breast Cancer Phytochemicals are one of the most important class of compounds in the human diet which have gained traction in the therapeutic field because of their pivotal role in human health, their abundance, and lack of toxicity. Phytochemicals encompass tannins, flavanoids, organic acids, and alkaloids. Ample epidemiological data show that phytochemicals confer protection against different cancers including breast cancer[14-16].
Also few of these, such as soy phytochemicals, are understood since long to have preventive action in breast cancer. Many phytochemicals like genistein, curcumin, resveratol, and epigallocatechin gallate are reported to act against breast cancer by interrupting or targeting intracellular signaling pathways. Some of them are known to act as inhibitors of enzymes involved in estrogen biosynthesis, while others act as inhibitors of proliferation, migration, invasion, or angiogenesis. Few phytochemicals are reported to act as phytoestrogens and are known to modulate signal transduction via estrogen receptors (alpha and beta), aryl hydrocarbon receptor, the pregnane X-receptor, the constitutive androstane receptor, and the peroxisome proliferator-activated receptors (alpha and gamma) and also are reported to influence transport proteins, kinases, and enzymes like 11 beta-hydroxysteroid dehydrogenase, 1,17 beta-hydroxysteroid dehydrogenases, sulfatase, and sulfotransferaseThey are also known to inhibit aromatasesand estrone sulfatase.
Reports also suggest that phytochemicals can inhibit CYP1B1, an enzyme responsible for metabolizing E2 to toxic substances like 4-OHE. It has been demonstrated that few flavanoids, a class of phytochemicals, can also help in overcoming one of the primary obstacles that limit the therapeutic efficacy of anticancer agents that is the outcome of producing apoptotic defects in cancer cells by targeting novel noncanonical cell death pathways[24, 25]. A few of this category of phytochemicals are also found to affect epigenetic factors like HDACand thus disrupt chromatin remodeling in breast tumor cells. They are understood to suppress triple negative breast cancer cells, a class of cell line which has emerged as a challenge because of its poor prognosis [28-30]. Among the phytochemicals, studies have identified some which can enhance the efficacy of chemotherapeutic drugs by inhibiting ATP-binding cassette (ABC) transporters like P-gp [31, 32], ABCG2 [33-35], and MRP-1 , which are relevant to multidrug resistance. Another interesting study showed that flavanoids can suppress breast cancer stem cells which are highly tumorigenic and possess the capacity to self-renew by inhibiting NANOG, a gene associated with regulating cancer stem cells and enhanced tumorigenicity .
Similarly, studies pointing to the inhibition of ABCG2, which are also proposed markers of stemness, is an indicator that phytochemicals may effectively reduce stem cell population in breast cancer. Thus, these different classes of phytochemicals, by different mechanisms, are known to combat breast cancer. But several phytochemicals have been shown to have biphasic effect on cell survival, that is, they can aid inhibition as well as proliferation of breast cancer cells, depending on the concentration . A major caveat for the effective action of phytochemicals is their bioavailability and distribution to tissues and organs which varies according to their category and might depend on molecular size, polarity, and solubility . For these reasons, the effect of the treatment with flavanoids in cultured cells might vary greatly when extended to in vivo level. Hence, at the clinical level, further detailed studies on the bioavailability and metabolism of flavanoids might be required.
Punica granatum, a Plant with Potential for Breast Cancer Prevention and Treatment
Pomegranate extracts and their constituents are known to exert their activity by diverse mechanisms and are known to inhibit angiogenesis, proliferation, invasiveness, growth, and also to induce apoptosis . These extracts (juice, seed oil, peel) individually and upon combinatorial treatment are reported to inhibit tumor growth. Interestingly, the combinatorial treatment was found to be more effective than treatment with single extract . Several in vivo studies have also elucidated the potential anticancer mechanism of the extracts [8, 39]. This review mainly emphasizes on the action of pomegranate extracts against breast tumor and its progression.
Taken together, these studies connote the potential of pomegranate extract in fighting breast cancer and underpin the ability of the extract to act in various steps of breast cancer, from initial growth to proliferation, metastasis to angiogenesis and escape of immune surveillances, and its ability to target many levels of regulation of cell growth and apoptosis. Thus, it can possibly act as an adjuvant in chemotherapy. A plethora of action of P. granatum have been reported against breast cancer and many of these have targets coinciding with the current targeted therapies of breast cancer mentioned earlier in this review, pointing to its relevance in breast cancer treatment and prevention. Researchers have also attempted to understand the bioavailability and metabolism of different components in pomegranate juice. A good many researches have focused on the phytoestrogenic potential of pomegranate extract, which has been found to inhibit enzymes like 17-β-hydroxysteroid dehydrogenase type 1 and aromatase which are relevant to estrogen biosynthesis. It is also found to compete with estrogen to bind to its receptor. The extracts have also been reported to downregulate estrogen-responsive genes at specific concentrations.
The antioxidant potential of the fruit has been extensively studied. One of the implications of the studies with regard to breast cancer is its possible ability to inhibit the enzyme COX, a relevant enzyme in breast cancer growth and metastasis.Punica extracts have also been demonstrated to inhibit angiogenesis via VEGF and MIF and survivin. Extracts of the fruit have been found to reduce invasiveness, migration, and the metastatic potential of breast cancer by acting via different molecular mechanisms, including enhancing the expression of adhesion proteins, reducing migratory proteins, decreasing response to chemokines responsible for metastasis, and downregulating/upregulating transcription factors involved in migration and metastasis. Pomegranate extract can also downregulate molecules like NF κb, a transcription factor involved in tumor progression, survival, and angiogenesis. A handful of investigations have demonstrated the antiproliferative activity of the extract. Many investigations have also brought to light the role of these extracts in inducing apoptosis and arresting cell cycle. Very recent research brought to attention the mechanisms and molecular targets by which it targets DNA repair pathway. Researches also demonstrate that pomegranate extract can reduce inflammatory responses that help in tumor survival. The components responsible for these actions are mainly punicic acid, ellagitannins, and luteolin. It also has possible contributions with respect to overcoming MDR resistance and thus has a plausible role in aiding chemotherapy by a combinatorial treatment.
Studies claim that Punica extracts can induce cytotoxicity and reduce proliferation in mammary cancer stem cells. Few of the active ingredients include ursolic acid, ellagic acid, luteolin, and punicic acid. Few others luteolin γ-tocopherol and quericitin are components present in Punica that are already reported to have anti-breast cancer activity when isolated from other plants. Bioavailability studies point out that the in vivoeffect of pomegranate extracts is predominantly due to the presence of colon microflora that metabolize the components, especially compounds like ellagitannins and bring health benefits associated with the same. Understanding the bioavailability of the relevant components of the extract might further help in bypassing their limitations.
Collectively, the findings indicate that Punica can be considered a promising candidate for preventing and inhibiting the progress of breast cancer. However, investigations at a clinical level have not gained the required spotlight of research. More studies at clinical level are warranted to measure and evaluate the actual potential of these extracts and their specific components, both individually and in combination.
Chemotherapy has always been associated with number of side effects. Targeted therapy approach in treating different cancer is reducing the side effects associated with generic drugs. Suitable adjuvants might make chemotherapy more effective. Punica granatum might serve to be one such ideal adjuvant for breast cancer therapy.
RESEARCH SUMMARY: Punica granatum has a recorded history of pharmacological properties which can be attributed to its rich reservoir of phytochemicals. Investigations in recent years have established its tremendous potential as an antitumorogenic agent against various cancers including breast cancer, which is the second leading cause of cancer-related deaths in women. The plausible role of Punica as a therapeutic agent, as an adjuvant in chemotherapy, and its dietary implications as chemopreventive agent in breast cancer have been explored. Mechanistic studies have revealed that Punica extracts and its components, individually or in combination, can modulate and target key proteins and genes involved in breast cancer. Our earlier finding also demonstrated the role of methanolic extract of pomegranate pericarp in reducing proliferation in breast cancer by binding to estrogen receptor at the same time not affecting uterine weight unlike estradiol or tamoxifen. This review analyses other plausible mechanisms of Punica in preventing the progression of breast cancer and how it can possibly be a therapeutic agent by acting at various steps of carcinogenesis including proliferation, invasion, migration, metastasis, angiogenesis, and inflammation via various molecular mechanisms.