Polyphenols from green tea inhibit the growth of melanoma cells through inhibition of class I histone deacetylases and induction of DNA damage

Phytochemicals as Immunomodulatory Agents in Melanoma

Cutaneous melanoma is an immunogenic highly heterogenic tumor characterized by poor outcomes when it is diagnosed late. Therefore, immunotherapy in combination with other anti-proliferative approaches is among the most effective weapons to control its growth and metastatic dissemination. Recently, a large amount of published reports indicate the interest of researchers and clinicians about plant secondary metabolites as potentially useful therapeutic tools due to their lower presence of side effects coupled with their high potency and efficacy. Published evidence was reported in most cases through in vitro studies but also, with a growing body of evidence, through in vivo investigations. Our aim was, therefore, to review the published studies focused on the most interesting phytochemicals whose immunomodulatory activities and/or mechanisms of actions were demonstrated and applied to melanoma models.

Green tea polyphenols inhibit malignant melanoma progression via regulating circ_MITF/miR-30e-3p/HDAC2 axis

Green tea polyphenols (GTPs) are regarded as anticancer substances and have been revealed to play significant roles in the development of malignant melanoma. However, the mechanisms by which GTPs perform anticarcinogenic activity are not well elucidated. Cellular function assays revealed that GTPs inhibited melanoma cell proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), and promoted apoptosis in vitro. Circ_MITF expression was elevated in melanoma tissues and cells but was decreased by GTPs in cells. Functional experiments indicated circ_MITF overexpression reversed the anticancer effects of GTPs on melanoma cells. Then the underlying mechanism analysis suggested that circ_MITF served as a sponge for miR-30e-3p to upregulate the level of HDAC2. MiR-30e-3p reexpression attenuated the regulatory effects of circ_MITF on GTPs-treated melanoma cells. Silencing of miR-30e-3p promoted the malignant phenotypes in GTPs-treated melanoma cells, which were reversed by HDAC2 knockdown. Preclinically, administration of GTPs suppressed the expression of downstream target genes and repressed tumorigenesis of xenografts in nude mice. In all, GTPs suppressed melanoma progression by regulating circ_MITF/miR-30e-3p/HDAC2 axis, providing a potential therapeutic strategy for human malignant melanoma intervention.

Recent Advances in Phenolic Metabolites and Skin Cancer

Skin cancer represents any tumor development from the cutaneous structures within the epidermis, dermis or subcutaneous tissue, and is considered to be the most prevalent type of cancer. Compared to other types of cancer, skin cancer is proven to have a positive growth rate of prevalence and mortality. There are available various treatments, including chemotherapy, immunotherapy, radiotherapy and targeted therapy, but because of the multidrug resistance development, a low success has been registered. By this, the importance of studying naturally occurring compounds that are both safe and effective in the chemoprevention of skin cancer is emphasized. This review focuses on melanoma because it is the deadliest form of skin cancer, with a significantly increasing incidence in the last decades. As chemopreventive agents, we present polyphenols and their antioxidant activity, anti-inflammatory effect, their ability to balance the cell cycle and to induce apoptosis and their various other effects on skin melanoma. Besides chemoprevention, studies suggest that polyphenols can have treating abilities in some conditions. The limitations of using polyphenols are also pointed out, which are related to their poor bioavailability and stability, but as the technology is well developed, it is possible to augment the efficacy of polyphenols in the case of melanoma.

Molecular mechanisms and applications of tea polyphenols: A narrative review

Tea is a worldwide popular drink with high nutritional and medicinal values as it is rich in nutrients, such as polyphenols, amino acids, vitamins, glycosides, and so on. Among them, tea polyphenols (TPs) are the current research hotspot. TPs are known to have multiple biological activities such as anti-oxidation, anti-tumor, anti-inflammation, anti-bacteria, lowering lipid, and liver protection. By reviewing a large number of literatures, we explained the mechanism of TPs exerting biological activity and a wide range of applications. We also discussed the deficiencies and development potential of TPs, in order to provide theoretical reference and scientific basis for the subsequent development and utilization of TPs. PRACTICAL APPLICATIONS: We summarized the bioactivity mechanisms of TPs in anti-tumor, anti-oxidation, antibacterial, anti-inflammatory, lipid-lowering, and liver protection, focused on its application fields in food and medicine, and discussed the deficiency and development potential of current research on TPs, so as to provide a certain convenient way for scholars studying TPs. It is expected to contribute to the subsequent discovery of biological activity and the broadening of the field of TPs.

Another look at dietary polyphenols: challenges in cancer prevention and treatment

Cancer is a pathology that impacts in a profound manner people all over the world. The election strategy against cancer often uses chemotherapy and radiotherapy, which more often than not can present many side effects and not always reliable efficacy. By contrast, it is widely known that a diet rich in fruit and vegetables has a protective effect against cancer insurgence and development. Polyphenols are generally believed to be responsible for those beneficial actions, at least partially. In this review, we highlight the metabolic interaction between polyphenols and our metabolism and discuss their potential for anticancer prevention and therapy.

Epigenetic targeting of cancer stem cells by polyphenols (cancer stem cells targeting)

Epigenetic alterations are one of the main factors that disrupt the expression of genes and consequently, they have an important role in the carcinogenicity and the progression of different cancers. Cancer stem cells (CSCs) are accountable for the recurrence, metastasis, and therapeutic failure of cancer. The noticeable and specific pathways in CSCs can be organized by epigenetic mechanisms such as DNA methylation, chromatin remodeling, regulatory RNAs, among others. Since epigenetics modifications can be changed and reversed, it is a possible tool for cancer control and treatment. Epigenetic therapies against CSCs are emerging as a very new strategy with a good future expectation to treat cancer patients. Phenolic compounds are a vast group of substances with anticarcinogenic functions, antiinflammatory, and antioxidative activities. It seems these characteristics are related to neutralizing CSCs development, their microenvironment, and metabolism through epigenetic mechanisms. In the current work, the types of epigenetic changes known in these cells are introduced. In addition, some studies about the use of polyphenols acting through a variety of epigenetic mechanisms to counteract these cells will be reviewed. The reported results seem to indicate that the use of these phenolic compounds may be useful for CSCs defeat.

Cytotoxic and DNA-Damaging Effects of Aronia melanocarpa, Cornus mas, and Chaenomeles superba Leaf Extracts on the Human Colon Adenocarcinoma Cell Line Caco-2

Aronia melanocarpa, Cornus mas, and Chaenomeles superba leaf extracts contain large amounts of bioactive compounds-mainly polyphenols, which possess many health benefits including anti-cancer properties. Here, we investigate the biological effects of A. melanocarpa, C. mas, and C. superba leaf extracts on the human colon adenocarcinoma cell line Caco-2. The antiproliferative activity of the extracts was measured using the MTT assay. The most cytotoxic extract was C. mas (IC50 = 0.60%). The extracts caused morphological changes in the Caco-2 cells, including partial detachment of cells, necrotic cells, chromatin condensation, cytoplasmic vacuolization, cell nuclei lysis, and nucleus fragmentation. The DNA damage in the Caco-2 cells after exposure to the leaf extracts was measured using the alkaline comet assay. The extracts increased DNA damage in a concentration dependent manner. However, at lower non-cyto- and non-genotoxic (IC0) concentrations the extracts induced DNA repair in Caco-2 cells after exposure to hydrogen peroxide. In conclusion, the results of these studies suggest that A. melanocarpa, C. mas and C. superba leaf extracts can show anticancer activity. However, further research is required on the mechanisms of anti-cancer activity by these extracts, with the application of more advanced and wide-ranging techniques including in vivo experiments.

Protoflavones in melanoma therapy: Prooxidant and pro-senescence effect of protoapigenone and its synthetic alkyl derivative in A375 cells

AIMS

In our study, the anticancer effects of a semisynthetic p-quinol, protoapigenone 1'-O-butyl ether (PABut), were tested in human melanoma A375 cells also in comparison with natural congener, protoapigenone (PA).

MAIN METHODS

The cytotoxic effect of PABut and PA was determined using MTT assay. Flow cytometry analysis was used to evaluate the influence of the compounds tested on ROS generation and cell cycle distribution in A375 cells. Moreover, apoptosis was evaluated by AO/EB dual staining as well as by flow cytometry. Markers of senescence were quantified by spectrofluorimetry and by Western blot analysis.

KEY FINDINGS

Both PABut and PA showed significant cytotoxicity against melanoma A375 cells at sub-micromolar concentrations. Both protoflavones induced comparable cell cycle arrest in G2/M phase. However, a more profound upregulation of intracellular ROS levels was found following PABut treatment. An increased apoptosis in the cells following 48 h treatment with both protoflavones tested was also confirmed. Both compounds tested remarkably upregulated p21 protein levels in A375 cells. Unlike PA, PABut significantly decreased protein levels of NAD⁺-dependent deacetylase SirT1 and β-actin accompanied by mild significant upregulation of mitochondrial SOD2 and senescence markers, p16 protein and SA-β-Gal activity. However, a significant upregulation of p53 only following PA treatment was found.

SIGNIFICANCE

These results suggest that PABut and PA confer high chemotherapeutic potential in melanoma cells and are suitable for further testing. Furthermore, modification of protoapigenone with 1'-O-butyl ether moiety can be associated with improved senescence-inducing effect and, thus, enhanced chemotherapeutic potency of PABut compared to the unmodified natural protoflavone.

Neurodining: Common dietary factors may be substrates in novel biosynthetic pathways for monoaminergic neurotransmitters

It is not established that there are multiple endogenous mechanisms for synthesizing each of the three major monoamine neurotransmitters: serotonin, norepinephrine, and dopamine. Having multiple biosynthetic pathways for each of these important signaling molecules would provide greater assurance that they are available in sufficient quantities for their various physiological roles in the body. This paper puts forth the hypothesis that a number of common dietary factors-including sucrose and glucose, fats, plant components, and even ethanol-are substrates in novel biosynthetic pathways for the monoamines. A major aspect of this hypothesis is that in a range of multicellular organisms, D-glucose in particular may participate in novel biosynthetic pathways for the monoamines, where this sugar has already been linked with synthesis of the neurotransmitters acetylcholine, glutamate, and GABA through the tricarboxylic acid cycle. Another major aspect of the hypothesis is that phenol or polyphenol molecules, found in various plants, may combine with particular fats or even ethanol to form dopamine, which can then be converted to norepinephrine through the already established step involving the enzyme dopamine beta-hydroxylase. If such a biosynthetic pathway exists for converting ethanol to dopamine in humans, it could be a major factor in substance abuse, including early onset alcoholism. Further, if the above biosynthetic pathways exist in a range of organisms, they may be associated with appetitive processes regulating consumption of particular dietary factors, such as fruits and vegetables, to maintain internal "set points" of, for example, elevated noradrenergic signaling. In this scenario, exposure to psychological stress, which could eventually deplete neurotransmitters such as norepinephrine, may result in craving for sucrose, fats, or alcohol to help replenish the depleted cellular levels of this signaling molecule. An alternative to the overall biosynthetic hypothesis put forth here is that animal cells do not possess these pathways, but the animal microbiome harbors bacteria that do carry out these reactions and helps supply the body with monoamines and other signaling molecules.

Green tea polyphenols attenuate LPS-induced inflammation through upregulating microRNA-9 in murine chondrogenic ATDC5 cells

BACKGROUND

Osteoarthritis (OA), a universal chronic musculoskeletal disorder, is closely related to inflammation. More effective drugs for improving OA outcome are definitely needed. Herein, we attempted to verify the protective role of green tea polyphenols (GTP) after treatment with murine in ATDC5 cells to reveal the regulatory mechanism.

METHODS

ATDC5 cells were stimulated with lipopolysaccharide (LPS) to mimic an inflammatory response during OA. Cell activity, apoptosis, levels of relative proteins, and prophlogistic factors were tested via a Cell Counting Kit-8 experiment, a flow cytometry experiment, western blot, and RT-qPCR (ELISA and Western blot), separately. miR-9 level was detected by RT-qPCR and altered via miR-9 mimic and inhibitor transfection. We finally studied MAPK and NF-κB pathways in GTP-related modulations using western blot.

RESULTS

LPS caused inflammatory cell damage in ATDC5 cells, showing decreased cell activity, enhanced apoptosis, and increased levels of pro-inflammatory cytokines. GTP pretreatments could significantly attenuate LPS-induced alterations. In addition, LPS-induced miR-9 upregulation was further positively regulated in ATDC5 cells. The effects of GTP pretreatments in LPS-caused ATDC5 cells were enhanced via miR-9 upregulation, whereas they were reduced via miR-9 suppression. Finally, we found that GTP pretreatments could suppress the MAPK and NF-κB pathways through miR-9 regulation.

CONCLUSION

GTP pretreatments attenuated LPS-induced inflammatory response accompanied by the suppression of the MAPK and NF-κB pathways via positively regulating miR-9 in ATDC5 cells.

Anti-cancer effects of polyphenols via targeting p53 signaling pathway: updates and future directions

The anticancer effects of polyphenols are ascribed to several signaling pathways including the tumor suppressor gene tumor protein 53 (p53). Expression of endogenous p53 is silent in various types of cancers. A number of polyphenols from a wide variety of dietary sources could upregulate p53 expression in several cancer cell lines through distinct mechanisms of action. The aim of this review is to focus the significance of p53 signaling pathways and to provide molecular intuitions of dietary polyphenols in chemoprevention by monitoring p53 expression that have a prominent role in tumor suppression.

Downregulation of HDAC2 and HDAC3 via oleuropein as a potent prevention and therapeutic agent in MCF-7 breast cancer cells

Breast cancer is the most common malignancy in the world with the highest rate of morbidity and mortality. Due to the several side effects of chemotherapy and radiotherapy, recent studies have focused on the use of herbal medicines. Epidemiological reports have shown the inverse relationship between breast cancer risk and intake of olive. Oleuropein (OLE) is a polyphenolic compound in virgin olive oil with antineoplastic properties and it is well tolerated by humans. Recent reports have shown that OLE has effects on the control of cancer by modulating epigenetics, such as histone deacetylase (HDAC) inhibition. However, the epigenetic mechanisms of OLE anticancer properties are yet to be properly investigated. Therefore, this study aimed to determine the therapeutic effects of OLE through the modulation of histone deacetylase 2 (HDAC2) and histone deacetylase 3 (HDAC3) expression in breast cancer cell line. MCF-7 cells were tested with and without OLE, and also the cell viability, apoptosis, and migration were examined. HDAC2 and HDAC3 expression genes were assessed by quantitative real-time polymerase chain reaction. It was found that OLE decreased the expression of both HDAC2 and HDAC3 (P < 0.05), induced apoptosis and retarded cell migration and cell invasion in a dose-dependent manner (P < 0.05). These results showed that OLE is a potential therapeutic and preventive agent for breast cancer.

Tea polyphenols inhibit the proliferation, migration, and invasion of melanoma cells through the down-regulation of TLR4

Melanoma is the most common skin cancer and malignant melanoma which can cause skin cancer-related deaths. Toll-like receptor 4 (TLR4) had been reported to play an important role in melanoma, and tea polyphenol (TP) is regarded as an anticancer substance. However, the relationship between TP and TLR4 in melanoma is not well explored. Therefore, our aim is to figure out how TP has an influence on melanoma. Melanoma cell lines (B16F10 and A375) were treated with TP and lipopolysaccharides (LPS). Western blot assay was used to examine TLR4 expression, and MTT assay was conducted to assess proliferation. Wound healing assay was conducted to evaluate the migration of melanoma cells, and transwell assay was used to examine the melanoma cells’ invasiveness. Besides, in vivo experiments were practiced for TP function in mice with melanoma cells. TP inhibited the proliferation, migration and invasion ability of melanoma cells, which displayed a dosage and time dependence. TLR4 was highly expressed in melanoma cells compared with normal skin cells. TP could suppress TLR4 expression both in normal melanomas and in stimulated melanomas by TLR4 agonist LPS. Suppressing TLR4 in melanomas could inhibit cell function (proliferation, migration, and invasion), and blocking the expression of 67LR could abolish TP function on TLR4. TP can inhibit melanoma (B16F10) growth in vivo.

Anticancer Effects of Green Tea and the Underlying Molecular Mechanisms in Bladder Cancer

Green tea and green tea polyphenols (GTPs) are reported to inhibit carcinogenesis and malignant behavior in several diseases. Various in vivo and in vitro studies have shown that GTPs suppress the incidence and development of bladder cancer. However, at present, opinions concerning the anticancer effects and preventive role of green tea are conflicting. In addition, the detailed molecular mechanisms underlying the anticancer effects of green tea in bladder cancer remain unclear, as these effects are regulated by several cancer-related factors. A detailed understanding of the pathological roles and regulatory mechanisms at the molecular level is necessary for advancing treatment strategies based on green tea consumption for patients with bladder cancer. In this review, we discuss the anticancer effects of GTPs on the basis of data presented in in vitro studies in bladder cancer cell lines and in vivo studies using animal models, as well as new treatment strategies for patients with bladder cancer, based on green tea consumption. Finally, on the basis of the accumulated data and the main findings, we discuss the potential usefulness of green tea as an antibladder cancer agent and the future direction of green tea-based treatment strategies for these patients.

The use of natural ingredients in innovative Korean cosmeceuticals

BACKGROUND

The cosmeceutical industry is an ever-growing and in demand market, especially in Asia. Korea has been on the forefront of creating the newest generation and most innovative cosmeceuticals products including ingredients such as snail secretions, starfish powder, botanical extracts, green tea, and red ginseng. Given their increasing prevalence in the cosmeceutical industry, scientists have been conducting investigations into these extracts and their properties.

OBJECTIVE

To summarize the current literature surrounding multiple natural ingredients found in Korean cosmeceutical products.

METHODS

A review of the literature surrounding natural ingredients found in Korean cosmeceuticals was conducted using PubMed (U.S. National Library of Medicine).

RESULTS

Multiple natural extracts have been found to have antiaging, antitumor, and antimelanogenic effects making them useful additives in current cosmeceutical products.

CONCLUSION

With the public's increasing awareness of cosmeceutical products, it is important for physicians to understand the properties of these extracts in order to inform patients correctly and ensure patient safety.

Natural Agents-Mediated Targeting of Histone Deacetylases

In the past few years, basic and clinical scientists have witnessed landmark achievements in many research projects, such as those conducted by the US National Institutes of Health Roadmap Epigenomics Mapping Consortium, the International Human Epigenome Consortium, The Cancer Genome Atlas Network and the International Cancer Genome Consortium, which have provided near-complete resolution of epigenetic landscape in different diseases. Furthermore, genome sequencing of tumors has provided compelling evidence related to frequent existence of mutations in readers, erasers and writers of epigenome in different cancers. Histone acetylation is an intricate mechanism modulated by two opposing sets of enzymes and deeply studied as a key biological phenomenon in 1964 by Vincent Allfrey and colleagues. The research group suggested that this protein modification contributed substantially in transcriptional regulation. Subsequently, histone deacetylases (HDACs), histone acetyltransferases and acetyl-Lys-binding proteins were identified as transcriptional mediators, which further deepened our comprehension regarding biochemical modifications. Overwhelmingly increasing high-impact research is improving our understanding of this molecularly controlled mechanism; moreover, quantification and identification of lysine acetylation by mass spectrometry has added new layers of information. We partition this multi-component review into how both activity and expression of HDAC are targeted using natural agents. We also set spotlight on how oncogenic fusion proteins tactfully utilize HDAC-associated nano-machinery to modulate expression of different genes and how HDAC inhibitors regulate TRAIL-induced apoptosis in cancer cells. HDAC inhibitors have been reported to upregulate expression of TRAIL receptors and protect TRAIL from proteasomal degradation. Deeper understanding of HDAC biology will be useful for stratification and selection of patients who are responders, non-responders and poor-responders for HDACi therapy, and for the rational design of combination studies using HDACi.

Tumoricidal activities of pterostilbene depend upon destabilizing the MTA1-NuRD complex and enhancing P53 acetylation in hepatocellular carcinoma

The present study aimed to assess the tumoricidal effect of metastasis-associated protein 1 (MTA1) induced by pterostilbene (PTER) in hepatocellular carcinoma (HCC). The SMMC-7721 hepatoma cell line was treated with PTER. Following treatment, the mRNA transcript abundance of MTA1 was measured using quantitative polymerase chain reaction. Additionally, cell viability was determined using an MTT assay, and protein expression was measured through western blotting. Cell invasion, motility and apoptosis, as well as the cell cycle, were also investigated. Following PTER treatment, MTA1, histone deacetylase (HDAC) 1 and HDAC2 were downregulated, whereas the ratio of acetyl-p53 to total p53 was increased in HCC cells. Cell viability decreased as the PTER dose increased. MTA1 may be associated with proliferation, motility, invasion and metastasis in HCC cells. PTER appeared to repress cell proliferation, trigger apoptosis, induce cell cycle arrest, and inhibit motility and invasion via MTA1 in human liver cancer cells. The results of the present study demonstrated that PTER can downregulate the MTA1-nucleosome remodeling and deacetylase complex, and enhance p53 acetylation to inhibit the growth of tumor cells in HCC.

Cryptolepine, a Plant Alkaloid, Inhibits the Growth of Non-Melanoma Skin Cancer Cells through Inhibition of Topoisomerase and Induction of DNA Damage

Topoisomerases have been shown to have roles in cancer progression. Here, we have examined the effect of cryptolepine, a plant alkaloid, on the growth of human non-melanoma skin cancer cells (NMSCC) and underlying mechanism of action. For this purpose SCC-13 and A431 cell lines were used as an in vitro model. Our study reveals that SCC-13 and A431 cells express higher levels as well as activity of topoisomerase (Topo I and Topo II) compared with normal human epidermal keratinocytes. Treatment of NMSCC with cryptolepine (2.5, 5.0 and 7.5 µM) for 24 h resulted in marked decrease in topoisomerase activity, which was associated with substantial DNA damage as detected by the comet assay. Cryptolepine induced DNA damage resulted in: (i) an increase in the phosphorylation of ATM/ATR, BRCA1, Chk1/Chk2 and γH2AX; (ii) activation of p53 signaling cascade, including enhanced protein expressions of p16 and p21; (iii) downregulation of cyclin-dependent kinases, cyclin D1, cyclin A, cyclin E and proteins involved in cell division (e.g., Cdc25a and Cdc25b) leading to cell cycle arrest at S-phase; and (iv) mitochondrial membrane potential was disrupted and cytochrome c released. These changes in NMSCC by cryptolepine resulted in significant reduction in cell viability, colony formation and increase in apoptotic cell death.

Polyphenols and DNA Damage: A Mixed Blessing

Polyphenols are a very broad group of chemicals, widely distributed in plant foods, and endowed with antioxidant activity by virtue of their numerous phenol groups. They are widely studied as putative cancer-protective agents, potentially contributing to the cancer preventive properties of fruits and vegetables. We review recent publications relating to human trials, animal experiments and cell culture, grouping them according to whether polyphenols are investigated in whole foods and drinks, in plant extracts, or as individual compounds. A variety of assays are in use to study genetic damage endpoints. Human trials, of which there are rather few, tend to show decreases in endogenous DNA damage and protection against DNA damage induced ex vivo in blood cells. Most animal experiments have investigated the effects of polyphenols (often at high doses) in combination with known DNA-damaging agents, and generally they show protection. High concentrations can themselves induce DNA damage, as demonstrated in numerous cell culture experiments; low concentrations, on the other hand, tend to decrease DNA damage.

Emerging Phytochemicals for the Prevention and Treatment of Head and Neck Cancer

Despite the development of more advanced medical therapies, cancer management remains a problem. Head and neck squamous cell carcinoma (HNSCC) is a particularly challenging malignancy and requires more effective treatment strategies and a reduction in the debilitating morbidities associated with the therapies. Phytochemicals have long been used in ancient systems of medicine, and non-toxic phytochemicals are being considered as new options for the effective management of cancer. Here, we discuss the growth inhibitory and anti-cell migratory actions of proanthocyanidins from grape seeds (GSPs), polyphenols in green tea and honokiol, derived from the Magnolia species. Studies of these phytochemicals using human HNSCC cell lines from different sub-sites have demonstrated significant protective effects against HNSCC in both in vitro and in vivo models. Treatment of human HNSCC cell lines with GSPs, (-)-epigallocatechin-3-gallate (EGCG), a polyphenolic component of green tea or honokiol reduced cell viability and induced apoptosis. These effects have been associated with inhibitory effects of the phytochemicals on the epidermal growth factor receptor (EGFR), and cell cycle regulatory proteins, as well as other major tumor-associated pathways. Similarly, the cell migration capacity of HNSCC cell lines was inhibited. Thus, GSPs, honokiol and EGCG appear to be promising bioactive phytochemicals for the management of head and neck cancer.

Molecular mechanisms of flavonoids in melanin synthesis and the potential for the prevention and treatment of melanoma

Flavonoids are becoming popular nutraceuticals. Different flavonoids show similar or distinct biological effects on different tissues or cell types, which may limit or define their usefulness in cancer prevention and/or treatment application. This review focuses on a few selected flavonoids and discusses their functions in normal and transformed pigment cells, including cyanidin, apigenin, genistein, fisetin, EGCG, luteolin, baicalein, quercetin and kaempferol. Flavonoids exhibit melanogenic or anti-melanogenic effects mainly via transcriptional factor MiTF and/or the melanogenesis enzymes tyrosinase, DCT or TYRP-1. To identify a direct target has been a challenge as most studies were not able to discriminate whether the effect(s) of the flavonoid were from direct targeting or represented indirect effects. Flavonoids exhibit an anti-melanoma effect via inhibiting cell proliferation and invasion and inducing apoptosis. The mechanisms are also multi-fold, via ROS-scavenging, immune-modulation, cell cycle regulation and epigenetic modification including DNA methylation and histone deacetylation. In summary, although many flavonoid compounds are extremely promising nutraceuticals, their detailed molecular mechanism and their multi-target (simultaneously targeting multiple molecules) nature warrant further investigation before advancement to translational studies or clinical trials.