Fisetin inhibits growth, induces G₂ /M arrest and apoptosis of human epidermoid carcinoma A431 cells: role of mitochondrial membrane potential disruption and consequent caspases activation

Assessment of antioxidant, anticancer and antimicrobial activity of two vegetable species of Amaranthus in Bangladesh

BACKGROUND

Amaranthus (Amaranthaceae) has previously been reported to possess different bioactive phytochemicals including phenols, tannins and flavonoids. The current study was designed to evaluate the antioxidant, anti-proliferative and antimicrobial activity of stem and seed extracts of Amaranthus lividus (AL) and Amaranthus hybridus (AH), respectively.

METHODS

Antioxidant activity of methanol extract was assessed by DPPH radical scavenging assay. Determination of lectin activity of Amaranthus extract was carried out using hemagglutination assay on mouse blood. A total of thirty six Swiss albino mice containing Ehrlich's ascites carcinoma (EAC) cells were treated with AL and AH extract at 25, 50 and 100 μg/ml/day/mouse for six days. Growth inhibitory activity was determined by haemocytometer counting of EAC cells using trypan blue dye and DAPI (4΄,6-diamidino-2-phenylindole) staining was used to assess apoptotic cells. Gene amplification study was conducted to observe the expression pattern of p53, Bax, Bcl-2 and caspase-3 mRNA using PCR (polymer chain reaction) technique. In vitro susceptibility of five pathogenic bacteria including Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Salmonella typhi and Staphylococcus aureus was detected using disk diffusion assay.

RESULTS

The radical scavenging assay indicated that AH and AL possesses potent antioxidant potential, exhibiting IC50 value of 28 ± 1.5 and 93 ± 3.23 μg/ml, respectively. Hemagglutination assay revealed that AH and AL agglutinated mice blood at 1.565 and 3.125 μg/wall, respectively. Administration of AH and AL extract led to 45 and 43 % growth inhibition of EAC cells, respectively at 100 μg/ml with marked features of apoptosis including cell shrinkage, condensation of cytoplasm and aggregation of apoptotic bodies etc. Up-regulation of p53, Bax and caspase-3 and down-regulation of Bcl-2 mRNA in Amaranthus treated mice indicated mitochondria mediated apoptosis of EAC cells in comparison with control. None of the bacterial species showed susceptibility to the extract of both the Amaranthus species.

CONCLUSION

Our current findings suggest that both of the Amaranthus species have strong antioxidant, lectin and anti-proliferative activity on EAC cells. The current anticancer potential was observed due mainly to the mitochondria mediated apoptosis of EAC cells.

Dietary flavonoid fisetin for cancer prevention and treatment

Cancer remains a major public health concern and a significant cause of death worldwide. Identification of bioactive molecules that have the potential to inhibit carcinogenesis continues to garner interest among the scientific community. In particular, flavonoids from dietary sources are the most sought after because of their safety, cost-effectiveness, and feasibility of oral administration. Emerging data have provided newer insights into understanding the molecular mechanisms that are essential to identify novel mechanism-based strategies for cancer prevention and treatment. Dietary flavonoid fisetin (3,3',4',7-tetrahydroxyflavone) found in many fruits and vegetables has been shown in preclinical studies to inhibit cancer growth through alteration of cell cycle, inducing apoptosis, angiogenesis, invasion, and metastasis without causing any toxicity to normal cells. Although data from in-vitro and in-vivo studies look convincing, well-designed clinical trials in humans are needed to conclusively determine the efficacy across various cancers. This review highlights the chemopreventive and therapeutic effects, molecular targets, and mechanisms that contribute to the observed anticancer activity of fisetin against various cancers.

Exploring the molecular targets of dietary flavonoid fisetin in cancer

The last few decades have seen a resurgence of interest among the scientific community in exploring the efficacy of natural compounds against various human cancers. Compounds of plant origin belonging to different groups such as alkaloids, flavonoids and polyphenols evaluated for their cancer preventive effects have yielded promising data, thereby offering a potential therapeutic alternative against this deadly disease. The flavonol fisetin (3,3',4',7-tetrahydroxyflavone), present in fruits and vegetables such as strawberries, apple, cucumber, persimmon, grape and onion, was shown to possess anti-microbial, anti-inflammatory, anti-oxidant and more significantly anti-carcinogenic activity when assessed in diverse cell culture and animal model systems. The purpose of this review is to update and discuss key findings obtained till date from in vitro and in vivo studies on fisetin, with special focus on its anti-cancer role. The molecular mechanism(s) described in the observed growth inhibitory effects of fisetin in different cancer cell types is also summarized. Moreover, an attempt is made to delineate the direction of future studies that could lead to the development of fisetin as a potent chemopreventive/chemotherapeutic agent against cancer.

5-Hydroxy-7-Methoxyflavone Triggers Mitochondrial-Associated Cell Death via Reactive Oxygen Species Signaling in Human Colon Carcinoma Cells

Plant-derived compounds are an important source of clinically useful anti-cancer agents. Chrysin, a biologically active flavone found in many plants, has limited usage for cancer chemotherapeutics due to its poor oral bioavailability. 5-Hydroxy-7-methoxyflavone (HMF), an active natural chrysin derivative found in various plant sources, is known to modulate several biological activities. However, the mechanism underlying HMF-induced apoptotic cell death in human colorectal carcinoma cells in vitro is still unknown. Herein, HMF was shown to be capable of inducing cytotoxicity in HCT-116 cells and induced cell death in a dose-dependent manner. Treatment of HCT-116 cells with HMF caused DNA damage and triggered mitochondrial membrane perturbation accompanied by Cyt c release, down-regulation of Bcl-2, activation of BID and Bax, and caspase-3-mediated apoptosis. These results show that ROS generation by HMF was the crucial mediator behind ER stress induction, resulting in intracellular Ca²⁺ release, JNK phosphorylation, and activation of the mitochondrial apoptosis pathway. Furthermore, time course study also reveals that HMF treatment leads to increase in mitochondrial and cytosolic ROS generation and decrease in antioxidant enzymes expression. Temporal upregulation of IRE1-α expression and JNK phosphorylation was noticed after HMF treatment. These results were further confirmed by pre-treatment with the ROS scavenger N-acetyl-l-cysteine (NAC), which completely reversed the effects of HMF treatment by preventing lipid peroxidation, followed by abolishment of JNK phosphorylation and attenuation of apoptogenic marker proteins. These results emphasize that ROS generation by HMF treatment regulates the mitochondrial-mediated apoptotic signaling pathway in HCT-116 cells, demonstrating HMF as a promising pro-oxidant therapeutic candidate for targeting colorectal cancer.

The Dietary Flavonoid Fisetin Causes Cell Cycle Arrest, Caspase-Dependent Apoptosis, and Enhanced Cytotoxicity of Chemotherapeutic Drugs in Triple-Negative Breast Cancer Cells

Fisetin (3,3',4',7-tetrahydroxyflavone), a flavonoid found in a number of fruits and vegetables, has diverse biological activities, including cytotoxic effects on cancer cells. In this study, we investigated the effect of fisetin on triple-negative breast cancer (TNBC) cells. TNBC has a poorer prognosis than other types of breast cancer and treatment options for this disease are limited. Fisetin inhibited the growth of MDA-MB-468 and MDA-MB-231 TNBC cells, as well as their ability to form colonies, without substantially affecting the growth of non-malignant cells. In addition, fisetin inhibited the growth of estrogen receptor-bearing MCF-7 breast cancer cells and human epidermal growth factor receptor 2-overexpressing SK-BR-3 breast cancer cells. Fisetin inhibited TNBC cell division and induced apoptosis, which was associated with mitochondrial membrane permeabilization and the activation of caspase-9 and caspase-8, as well as the cleavage of poly(ADP-ribose) polymerase-1. Induction of caspase-dependent apoptosis by fisetin was confirmed by reduced killing of TNBC cells in the presence of the pan-caspase inhibitors Z-VAD-FMK and BOC-D-FMK. Decreased phosphorylation of histone H3 at serine 10 in fisetin-treated TNBC cells at G2/M phase of the cell cycle suggested that fisetin-induced apoptosis was the result of Aurora B kinase inhibition. Interestingly, the cytotoxic effect of cisplatin, 5-fluorouracil, and 4-hydroxycyclophosphamide metabolite of cyclophosphamide on TNBC cells was increased in the presence of fisetin. These findings suggest that further investigation of fisetin is warranted for possible use in the management of TNBC. J. Cell. Biochem. 117: 1913-1925, 2016. © 2016 Wiley Periodicals, Inc.

Phytochemicals for the Management of Melanoma

Melanoma claims approximately 80% of skin cancer-related deaths. Its life-threatening nature is primarily due to a propensity to metastasize. The prognosis for melanoma patients with distal metastasis is bleak, with median survival of six months even with the latest available treatments. The most commonly mutated oncogenes in melanoma are BRAF and NRAS accounting approximately 60% and 20% of cases, respectively. In malignant melanoma, accumulating evidence suggests that multiple signaling pathways are constitutively activated and play an important role in cell proliferation, cell survival, epithelial to mesenchymal transition, metastasis and resistance to therapeutic regimens. Phytochemicals are gaining considerable attention because of their low toxicity, low cost, and public acceptance as dietary supplements. Cell culture and animals studies have elucidated several cellular and molecular mechanisms by which phytochemicals act in the prevention and treatment of metastatic melanoma. Several promising phytochemicals, such as, fisetin, epigallocatechin-3-gallate, resveratrol, curcumin, proanthocyanidins, silymarin, apigenin, capsaicin, genistein, indole-3-carbinol, and luteolin are gaining considerable attention and found in a variety of fresh fruits, vegetables, roots, and herbs. In this review, we will discuss the preventive potential, therapeutic effects, bioavailability and structure activity relationship of these selected phytochemicals for the management of melanoma.

Fisetin inhibits TNF-α-induced inflammatory action and hydrogen peroxide-induced oxidative damage in human keratinocyte HaCaT cells through PI3K/AKT/Nrf-2-mediated heme oxygenase-1 expression

Oxidative skin damage and skin inflammation play key roles in the pathogenesis of skin-related diseases. Fisetin is a naturally occurring flavonoid abundantly found in several vegetables and fruits. Fisetin has been shown to exert various positive biological effects, such as anti-cancer, anti-proliferative, neuroprotective and anti-oxidative effects. In this study, we investigate the skin protective effects and anti-inflammatory properties of fisetin in hydrogen peroxide- and TNF-α-challenged human keratinocyte HaCaT cells. When HaCaT cells were treated with non-cytotoxic concentrations of fisetin (1-20μM), heme oxygenase (HO)-1 mRNA and protein expression increased in a dose-dependent manner. Furthermore, fisetin dose-dependently increased cell viability and reduced ROS production in hydrogen peroxide-treated HaCaT cells. Fisetin also inhibited the production of NO, PGE2 IL-1β, IL-6, expression of iNOS and COX-2, and activation of NF-κB in HaCaT cells treated with TNF-α. Fisetin induced Nrf2 translocation to the nuclei. HO-1 siRNA transient transfection reversed the effects of fisetin on cytoprotection, ROS reduction, NO, PGE2, IL-1β, IL-6, and TNF-α production, and NF-κB DNA-binding activity. Moreover, fisetin increased Akt phosphorylation and a PI3K pathway inhibitor (LY294002) abolished fisetin-induced cytoprotection and NO inhibition. Taken together, these results provide evidence for a beneficial role of fisetin in skin therapy.

Curculigoside regulates proliferation, differentiation, and pro-inflammatory cytokines levels in dexamethasone-induced rat calvarial osteoblasts

BACKGROUND

Curculigoside (CCG), one of the main bioactive phenolic compounds isolated from the rhizome of Curculigo orchioides Gaertn., is reported to prevent bone loss in ovariectomized rats. However, the underlying molecular mechanisms are largely unknown. Therefore, we investigated the effects of CCG on proliferation and differentiation of calvarial osteoblasts and discussed the related mechanisms.

MATERIALS AND METHODS

Osteoblasts were incubated with dexamethasone (DEX) in the absence or presence of CCG concentrations for 24-72 h. Cell proliferation was evaluated by Cell Counting Kit-8 assay. Mitochondria membrane potential (MMP) and reactive oxygen species (ROS) were assessed by flow cytometry. We assessed the anti-inflammatory responses of CCG on DEX-induced osteoblasts by an enzyme-linked immunosorbent assay (ELISA). Relative protein expression of BMP-2, b-catenin, RANKL, OPG and RANK was measured using Western blotting.

RESULTS

It was found that osteoblasts proliferation decreased significantly after treated with 1 μM of dexamethasone (DEX), compared with untreated osteoblasts and the cytotoxic effect of DEX was reversed remarkably when pretreatment with 25-100 μg/ml of CCG. Pretreatment with 25-100 μg/ml of CCG increased MMP level and decreased ROS production in osteoblasts induced by DEX. In addition, DEX-induced inhibition of differentiation markers such as alkaline phosphatase (ALP), OPG, BMP-2, β-catenin, IGF-1 and M-CSF level, and promotion of differentiation markers such as RANKL and RANK was significantly reversed in the presence of CCG. CCG also reversed DEX-induced production of pro-inflammatory cytokines.

CONCLUSIONS

These results provide new insights into the osteoblast-protective mechanisms of CCG through inducing proliferation and differentiation and reducing the inflammatory responses, indicating that CCG may be developed as an agent for the prevention and treatment of osteoporosis.

Fisetin Ameliorated Photodamage by Suppressing the Mitogen-Activated Protein Kinase/Matrix Metalloproteinase Pathway and Nuclear Factor-κB Pathways

Ultraviolet (UV) irradiation is one of the most important extrinsic factors contributing to skin photodamage. After UV irradiation, a series of signal transductions in the skin will be activated, leading to inflammatory response and photoaged skin. In this study, fisetin, a flavonol that exists in fruits and vegetables, was investigated for its photoprotective effects. The results revealed that 5-25 μM fisetin inhibits cyclooxygenase-2 (COX-2) and matrix metalloproteinase (MMP)-1, MMP-3, MMP-9 expression induced by ultraviolet B (UVB) irradiation in human skin fibroblasts. In addition, fisetin suppressed UVB-induced collagen degradation. With regard to its effect on upper-stream signal transduction, we found that fisetin reduced the expression of ultraviolet (UV)-induced ERK, JNK, and p38 phosphorylation in the mitogen-activated protein kinase (MAP kinase) pathway. Furthermore, fisetin reduced inhibitor κB (IκB) degradation and increased the amount of p65, which is a major subunit of nuclear factor-κB (NF-κB), in cytoplasm. It also suppressed NF-κB translocated to the nucleus and inhibited cAMP response element-binding protein (CREB) Ser-133 phosphorylation level in the phosphoinositide 3-kinase/protein kinase B/CREB (PI3K/AKT/CREB) pathway. Finally, fisetin inhibited UV-induced intracellular reactive oxygen species (ROS), prostaglandin E2 (PGE2), and nitric oxide (NO) generation. The mentioned effects and mechanisms suggest that fisetin can be used in the development of photoprotective agents.

Knockdown of Bcl-xL enhances growth-inhibiting and apoptosis-inducing effects of resveratrol and clofarabine in malignant mesothelioma H-2452 cells

Mcl-1 and Bcl-xL, key anti-apoptotic proteins of the Bcl-2 family, have attracted attention as important molecules in the cell survival and drug resistance. In this study, we investigated whether inhibition of Bcl-xL influences cell growth and apoptosis against simultaneous treatment of resveratrol and clofarabine in the human malignant mesothelioma H-2452 cells. Resveratrol and clofarabine decreased Mcl-1 protein levels but had little effect on Bcl-xL levels. In the presence of two compounds, any detectable change in the Mcl-1 mRNA levels was not observed in RT-PCR analysis, whereas pretreatment with the proteasome inhibitor MG132 led to its accumulation to levels far above basal levels. The knockdown of Bcl-xL inhibited cell proliferation with cell accumulation at G2/M phase and the appearance of sub-G0/G1 peak in DNA flow cytometric assay. The suppression of cell growth was accompanied by an increase in the caspase-3/7 activity with the resultant cleavages of procaspase-3 and its substrate poly (ADP-ribose) polymerase, and increased percentage of apoptotic propensities in annexin V binding assay. Collectively, our data represent that the efficacy of resveratrol and clofarabine for apoptosis induction was substantially enhanced by Bcl-xL-lowering strategy in which the simultaneous targeting of Mcl-1 and Bcl-xL could be a more effective strategy for treating malignant mesothelioma.

Fisetin inhibits UVB-induced cutaneous inflammation and activation of PI3K/AKT/NFκB signaling pathways in SKH-1 hairless mice

Solar ultraviolet B (UVB) radiation has been shown to induce inflammation, DNA damage, p53 mutations and alterations in signaling pathways eventually leading to skin cancer. In this study, we investigated whether fisetin reduces inflammatory responses and modulates PI3K/AKT/NFκB cell survival signaling pathways in UVB-exposed SKH-1 hairless mouse skin. Mice were exposed to 180 mJ cm(-2) of UVB radiation on alternate days for a total of seven exposures, and fisetin (250 and 500 nmol) was applied topically after 15 min of each UVB exposure. Fisetin treatment to UVB-exposed mice resulted in decreased hyperplasia and reduced infiltration of inflammatory cells. Fisetin treatment also reduced inflammatory mediators such as COX-2, PGE2 as well as its receptors (EP1-EP4) and MPO activity. Furthermore, fisetin reduced the level of inflammatory cytokines TNFα, IL-1β and IL-6 in UVB-exposed skin. Fisetin treatment also reduced cell proliferation markers as well as DNA damage as evidenced by increased expression of p53 and p21 proteins. Further studies revealed that fisetin inhibited UVB-induced expression of PI3K, phosphorylation of AKT and activation of the NFκB signaling pathway in mouse skin. Overall, these data suggest that fisetin may be useful against UVB-induced cutaneous inflammation and DNA damage.

Melatonin enhances the anti-tumor effect of fisetin by inhibiting COX-2/iNOS and NF-κB/p300 signaling pathways

Melatonin is a hormone identified in plants and pineal glands of mammals and possesses diverse physiological functions. Fisetin is a bio-flavonoid widely found in plants and exerts antitumor activity in several types of human cancers. However, the combinational effect of melatonin and fisetin on antitumor activity, especially in melanoma treatment, remains unclear. Here, we tested the hypothesis that melatonin could enhance the antitumor activity of fisetin in melanoma cells and identified the underlying molecular mechanisms. The combinational treatment of melanoma cells with fisetin and melatonin significantly enhanced the inhibitions of cell viability, cell migration and clone formation, and the induction of apoptosis when compared with the treatment of fisetin alone. Moreover, such enhancement of antitumor effect by melatonin was found to be mediated through the modulation of the multiply signaling pathways in melanoma cells. The combinational treatment of fisetin with melatonin increased the cleavage of PARP proteins, triggered more release of cytochrome-c from the mitochondrial inter-membrane, enhanced the inhibition of COX-2 and iNOS expression, repressed the nuclear localization of p300 and NF-κB proteins, and abrogated the binding of NF-κB on COX-2 promoter. Thus, these results demonstrated that melatonin potentiated the anti-tumor effect of fisetin in melanoma cells by activating cytochrome-c-dependent apoptotic pathway and inhibiting COX-2/iNOS and NF-κB/p300 signaling pathways, and our study suggests the potential of such a combinational treatment of natural products in melanoma therapy.

Piperlongumine, an alkaloid causes inhibition of PI3 K/Akt/mTOR signaling axis to induce caspase-dependent apoptosis in human triple-negative breast cancer cells

The phosphatidylinositol 3-kinase (PI3 K)/Akt/mammalian target of rapamycin (mTOR) signaling axis plays a central role in cell proliferation, growth and survival under physiological conditions. However, aberrant PI3 K/Akt/mTOR signaling has been implicated in many human cancers, including human triple negative breast cancer. Therefore, dual inhibitors of PI3 K/Akt and mTOR signaling could be valuable agents for treating breast cancer. The objective of this study was to investigate the effect of piperlongumine (PPLGM), a natural alkaloid on PI3 K/Akt/mTOR signaling, Akt mediated regulation of NF-kB and apoptosis evasion in human breast cancer cells. Using molecular docking studies, we found that PPLGM physically interacts with the conserved domain of PI3 K and mTOR kinases and the results were comparable with standard dual inhibitor PF04691502. Our results demonstrated that treatment of different human triple-negative breast cancer cells with PPLGM resulted in concentration- and time-dependent growth inhibition. The inhibition of cancer cell growth was associated with G1-phase cell cycle arrest and down-regulation of the NF-kB pathway leads to activation of the mitochondrial apoptotic pathway. It was also found that PPLGM significantly decreased the expression of p-Akt, p70S6K1, 4E-BP1, cyclin D1, Bcl-2, p53 and increased expression of Bax, cytochrome c in human triple-negative breast cancer cells. Although insulin treatment increased the phosphorylation of Akt (Ser473), p70S6K1, 4E-BP1, PPLGM abolished the insulin mediated phosphorylation, it clearly indicates that PPLGM acts through PI3 k/Akt/mTOR axis. Our results suggest that PPLGM may be an effective therapeutic agent for the treatment of human triple negative breast cancer.

An oxidative stress mechanism of shikonin in human glioma cells

Shikonin is a quinone-containing natural product that induces the apoptotic death of some cancer cell lines in culture through increasing intracellular reactive oxygen species (ROS). Quinone-based drugs have shown potential in the clinic, making shikonin an interesting compound to study. Our previous study found that shikonin induces apoptosis in neuroblastoma by induction of ROS, but its mechanism of action and scope of activity are unknown. In this study, we investigated the mode of oxidative stress of shikonin in human glioma cells. ROS induction by shikonin was of mitochondrial origin, as demonstrated by detection of superoxide with MitoSOX Red. Pre-incubation of shikonin with inhibitors of different complexes of the respiratory chain suggested that shikonin-induced ROS production occurred via complex II. In addition, NADPH oxidase and lipooxygenase are two other main ROS-generated sites in shikonin treatment. ROS production by shikonin resulted in the inhibition of nuclear translocation of Nrf2. Stable overexpression of Nrf2 in glioma cells inhibited ROS generation by shikonin. ROS generation from mitochondrial complex II, NADPH oxidase and lipooxygenase is likely the primary mechanism by which shikonin induces apoptosis in glioma cells. These findings also have relevance to the development of certain ROS producers as anti-cancer agents. These, along with shikonin have potential as novel chemotherapeutic agents on human glioma.

Fisetin modulates mitochondrial enzymes and apoptotic signals in benzo(a)pyrene-induced lung cancer

The present study was aimed to delineate in vivo mechanisms of orally administered fisetin with special reference to mitochondrial dysfunction in lung tissues employing benzo(a)pyrene (B(a)P) as the model lung carcinogen. The recent revival of interest in the study of mitochondria has been stimulated by the evidence that genetic and/or metabolic alterations in this organelle lead to a variety of human diseases including cancer. These alterations could be either causative or contributing factors. Hence, the activities of mitochondrial-specific enzymes of isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase and tumor marker, carcinogenic embryonic antigen were analyzed in control and experimental groups of mice. The induction of apoptotic and anti-apoptotic proteins such as Bcl-2/Bax, cytochrome c, caspase-9 and caspase-3 was confirmed by the immunohistochemistry and Western blot analyses. Furthermore, transmission electron microscopy study of lung sections of B(a)P-induced mice showed the presence of phaemorphic cells with dense granules and increased mitochondria. All the aberrations were alleviated when the mice were treated with fisetin (25 mg/kg body weight). The results proved fisetin to be a very successful drug in combating the mitochondrial dysfunction in an experimental model of lung carcinogenesis induced by B(a)P.

Fisetin inhibits human melanoma cell invasion through promotion of mesenchymal to epithelial transition and by targeting MAPK and NFκB signaling pathways

Malignant melanoma is responsible for approximately 75% of skin cancer-related deaths. BRAF plays an important role in regulating the mitogen-activated protein kinase (MAPK) signaling cascade in melanoma with activating mutations in the serine/threonine kinase BRAF occurring in 60-70% of malignant melanomas. The BRAF-MEK-ERK (MAPK) pathway is a key regulator of melanoma cell invasion. In addition, activation of NFκB via the MAPK pathway is regulated through MEK-induced activation of IKK. These pathways are potential targets for prevention and treatment of melanoma. In this study, we investigated the effect of fisetin, a phytochemical present in fruits and vegetables, on melanoma cell invasion and epithelial-mesenchymal transition, and delineated the underlying molecular mechanism. Treatment of multiple human malignant melanoma cell lines with fisetin (5-20 µM) resulted in inhibition of cell invasion. BRAF mutated melanoma cells were more sensitive to fisetin treatment, and this was associated with a decrease in the phosphorylation of MEK1/2 and ERK1/2. In addition, fisetin inhibited the activation of IKK leading to a reduction in the activation of the NFκB signaling pathway. Treatment of cells with an inhibitor of MEK1/2 (PD98059) or of NFκB (caffeic acid phenethyl ester) also reduced melanoma cell invasion. Furthermore, treatment of fisetin promoted mesenchymal to epithelial transition in melanoma cells, which was associated with a decrease in mesenchymal markers (N-cadherin, vimentin, snail and fibronectin) and an increase in epithelial markers (E-cadherin and desmoglein). Employing three dimensional skin equivalents consisting of A375 cells admixed with normal human keratinocytes embedded onto a collagen-constricted fibroblast matrix, we found that treatment of fisetin reduced the invasive potential of melanoma cells into the dermis and increased the expression of E-cadherin with a concomitant decrease in vimentin. These results indicate that fisetin inhibits melanoma cell invasion through promotion of mesenchymal to epithelial transition and by targeting MAPK and NFκB signaling pathways.