Efficacy of Caffeic Acid Phenethyl Ester (CAPE) in skin B16-F0 melanoma tumor bearing C57BL/6 mice

Caffeic acid phenethyl ester: A review on its pharmacological importance, and its association with free radicals, COVID-19, and radiotherapy

Caffeic acid phenethyl ester (CAPE), a main active component of propolis and a flavonoid, is one of the natural products that has attracted attention in recent years. CAPE, which has many properties such as anti-cancer, anti-inflammatory, antioxidant, antibacterial and anti-fungal, has shown many pharmacological potentials, including protective effects on multiple organs. Interestingly, molecular docking studies showed the possibility of binding of CAPE with replication enzyme. In addition, it was seen that in order to increase the binding security of the replication enzyme and CAPE, modifications can be made at three sites on the CAPE molecule, which leads to the possibility of the compound working more powerfully and usefully to prevent the proliferation of cancer cells and reduce its rate. Also, it was found that CAPE has an inhibitory effect against the main protease enzyme and may be effective in the treatment of SARS-CoV-2. This review covers in detail the importance of CAPE in alternative medicine, its pharmacological value, its potential as a cancer anti-proliferative agent, its dual role in radioprotection and radiosensitization, and its use against coronavirus disease 2019 (COVID-19).

Paradoxical Radiosensitizing Effect of Carnosic Acid on B16F10 Metastatic Melanoma Cells: A New Treatment Strategy

Carnosic acid (CA) is a phenolic diterpene characterized by its high antioxidant activity; it is used in industrial, cosmetic, and nutritional applications. We evaluated the radioprotective capacity of CA on cells directly exposed to X-rays and non-irradiated cells that received signals from X-ray treated cells (radiation induced bystander effect, RIBE). The genoprotective capacity was studied by in vivo and in vitro micronucleus assays. Radioprotective capacity was evaluated by clonogenic cell survival, MTT, apoptosis and intracellular glutathione assays comparing radiosensitive cells (human prostate epithelium, PNT2) with radioresistant cells (murine metastatic melanoma, B16F10). CA was found to exhibit a genoprotective capacity in cells exposed to radiation (p < 0.001) and in RIBE (p < 0.01). In PNT2 cells, considered as normal cells in our study, CA achieved 97% cell survival after exposure to 20 Gy of X-rays, eliminating 67% of radiation-induced cell death (p < 0.001), decreasing apoptosis (p < 0.001), and increasing the GSH/GSSH ratio (p < 0.01). However, the administration of CA to B16F10 cells decreased cell survival by 32%, increased cell death by 200% (p < 0.001) compared to irradiated cells, and increased cell death by 100% (p < 0.001) in RIBE bystander cells (p < 0.01). Furthermore, it increased apoptosis (p < 0.001) and decreased the GSH/GSSG ratio (p < 0.01), expressing a paradoxical radiosensitizing effect in these cells. Knowing the potential mechanisms of action of substances such as CA could help to create new applications that would protect healthy cells and exclusively damage neoplastic cells, thus presenting a new desirable strategy for cancer patients in need of radiotherapy.

Dietary Phenolic Compounds as Anticancer Natural Drugs: Recent Update on Molecular Mechanisms and Clinical Trials

Given the stochastic complexity of cancer diseases, the development of chemotherapeutic drugs is almost limited by problems of selectivity and side effects. Furthermore, an increasing number of protective approaches have been recently considered as the main way to limit these pathologies. Natural bioactive compounds, and particularly dietary phenolic compounds, showed major protective and therapeutic effects against different types of human cancers. Indeed, phenolic substances have functional groups that allow them to exert several anti-cancer mechanisms, such as the induction of apoptosis, autophagy, cell cycle arrest at different stages, and the inhibition of telomerase. In addition, in vivo studies show that these phenolic compounds also have anti-angiogenic effects via the inhibition of invasion and angiogenesis. Moreover, clinical studies have already highlighted certain phenolic compounds producing clinical effects alone, or in combination with drugs used in chemotherapy. In the present work, we present a major advance in research concerning the mechanisms of action of the different phenolic compounds that are contained in food medicinal plants, as well as evidence from the clinical trials that focus on them.

Inhibitory effect of polyphenols (phenolic acids, lignans, and stilbenes) on cancer by regulating signal transduction pathways: a review

Natural products, especially polyphenols (phenolic acids, lignans, and stilbenes) are suggested to be more potent anticancer drugs because of their no or less adverse effects, excess availability, high accuracy, and secure mode of action. In the present review, potential anticancer mechanisms of action of some polyphenols including phenolic acids, lignans, and stilbenes are discussed based on clinical, epidemiological, in vivo, and in vitro studies. The emerging evidence revealed that phenolic acids, lignans, and stilbenes induced apoptosis in the treatment of breast (MCF-7), colon (Caco-2), lung (SKLU-1), prostate (DU-145 and LNCaP), hepatocellular (hepG-2), and cervical (A-431) cancer cells, cell cycle arrest (S/G₂/M/G₁-phases) in gastric (MKN-45 and MKN-74), colorectal (HCT-116), bladder (T-24 and 5637), oral (H-400), leukemic (HL-60 and MOLT-4) and colon (Caco-2) cancer cells, and inhibit cell proliferation against the prostate (PC-3), liver (LI-90), breast (T47D and MDA-MB-231), colon (HT-29 and Caco-2), cervical (HTB-35), and MIC-1 cancer cells through caspase-3, MAPK, AMPK, Akt, NF-κB, Wnt, CD95, and SIRT1 pathways. Based on accumulated data, we suggested that polyphenols could be considered as a viable therapeutic option in the treatment of cancer cells in the near future.

The Antitumor Effect of Caffeic Acid Phenethyl Ester by Downregulating Mucosa-Associated Lymphoid Tissue 1 via AR/p53/NF-κB Signaling in Prostate Carcinoma Cells

Caffeic acid phenethyl ester (CAPE), a honeybee propolis-derived bioactive ingredient, has not been extensively elucidated regarding its effect on prostate cancer and associated mechanisms. The mucosa-associated lymphoid tissue 1 gene (MALT1) modulates NF-κB signal transduction in lymphoma and non-lymphoma cells. We investigated the functions and regulatory mechanisms of CAPE in relation to MALT1 in prostate carcinoma cells. In p53- and androgen receptor (AR)-positive prostate carcinoma cells, CAPE downregulated AR and MALT1 expression but enhanced that of p53, thus decreasing androgen-induced activation of MALT1 and prostate-specific antigen expressions. p53 downregulated the expression of MALT in prostate carcinoma cells through the putative consensus and nonconsensus p53 response elements. CAPE downregulated MALT1 expression and thus inhibited NF-κB activity in p53- and AR-negative prostate carcinoma PC-3 cells, eventually reducing cell proliferation, invasion, and tumor growth in vitro and in vivo. CAPE induced the ERK/JNK/p38/AMPKα1/2 signaling pathways; however, pretreatment with the corresponding inhibitors of MAPK or AMPK1/2 did not inhibit the CAPE effect on MALT1 blocking in PC-3 cells. Our findings verify that CAPE is an effective antitumor agent for human androgen-dependent and -independent prostate carcinoma cells in vitro and in vivo through the inhibition of MALT1 expression via the AR/p53/NF-κB signaling pathways.

Design cytotoxicity: The effect of silver nanoparticles stabilized by selected antioxidants on melanoma cells

Silver nanoparticles (AgNPs) prepared and stabilized by diverse biologically active substances seem to be especially useful in diverse biological and medical applications. The combination of AgNPs with bioactive substances, such as antioxidants, can lead to the development of new systems of desired anticancer properties. In this research, AgNPs were prepared with the use of diverse antioxidant combinations including gallic acid (GA), (-)-epicatechin-3-gallate (EGCG), and caffeine (CAF). The insightful physicochemical characteristic revealed that each type of AgNPs exhibited spherical shape, comparable size distribution and negative surface charge. Surface-enhanced Raman spectroscopy (SERS) delivered the information about the chemistry of AgNP stabilizing layers, which turned out to be a crucial factor tuning toxicity of AgNPs toward murine B16 melanoma cells (B16-F0) and human skin melanoma (COLO 679) cells. EGCGAgNPs were the most cytotoxic among all the investigated AgNPs. They strongly reduced the activity of mitochondria, damaged cell membrane integrity, and penetrated inside the cells causing DNA damage. In turn, the toxicity of GAAgNPs strongly manifested via the induction of oxidative stress in the cells. It was found that CAFGAAgNPs exhibited the lowest toxicity toward the melanoma cells, which proved that a proper combination of antioxidants enable to prepare AgNPs of differentiated toxicity. It was established that human skin melanoma cells were significantly more sensitive to AgNPs than the murine melanoma cells.

Recent progresses in the pharmacological activities of caffeic acid phenethyl ester

The past decades have seen a growing interest in natural products. Caffeic acid phenethyl ester (CAPE), a flavonoid isolated from honeybee propolis, has shown multiple pharmacological potentials, including anti-cancer, anti-inflammatory, antioxidant, antibacterial, antifungal, and protective effects on nervous systems and multiple organs, since it was found as a potent nuclear factor κB (NF-κB) inhibitor. This review summarizes the advances in these beneficial effects of CAPE, as well as the underlying mechanisms, and proposes that CAPE offers an opportunity for developing therapeutics in multiple diseases. However, clinical trials on CAPE are necessary and encouraged to obtain certain clinically relevant conclusions.

Medicinal Plants Towards Modeling Skin Cancer

Skin cancer remains a major cause of mortality worldwide. It can be divided into melanoma and non-melanoma cancer, which comprise mainly squamous cell carcinoma and basal cell carcinoma. Although conventional therapies have ameliorated the management of skin cancer, the search for chemopreventive compounds is still the most effective and safer strategy to treat cancer. Nowadays, chemoprevention is recognized as a novel approach to prevent or inhibit carcinogenesis steps with the use of natural products. Crude extracts of plants and isolated phytocompounds are considered chemopreventive agents since they harbor anti-inflammatory, antioxidant and anti-oncogenic properties against many types of diseases and cancers. In this review, we will discuss the therapeutic effect and preventive potential of selected medicinal plants used as crude extracts or as phytocompounds against melanoma and non-melanoma cutaneous cancers.

Effect of Rosmarinic Acid and Ionizing Radiation on Glutathione in Melanoma B16F10 Cells: A Translational Opportunity

To explain a paradoxical radiosensitizing effect of rosmarinic acid (RA) on the melanoma B16F10 cells, we analyzed the glutathione (GSH) intracellular production on this cell (traditionally considered radioresistant) in comparison with human prostate epithelial cells (PNT2) (considered to be radiosensitive). In PNT2 cells, the administration of RA increased the total GSH content during the first 3 h (p < 0.01) as well as increased the GSH/oxidized glutathione (GSSG) ratio in all irradiated cultures during all periods studied (1h and 3h) (p < 0.001), portraying an increase in the radioprotective capacity. However, in B16F10 cells, administration of RA had no effect on the total intracellular GSH levels, decreasing the GSH/GSSG ratio (p < 0.01); in addition, it caused a significant reduction in the GSH/GSSG ratio in irradiated cells (p < 0.001), an expression of radioinduced cell damage. In B16F10 cells, the administration of RA possibly activates the metabolic pathway of eumelanin synthesis that would consume intracellular GSH, thereby reducing its possible use as a protector against oxidative stress. The administration of this type of substance during radiotherapy could potentially protect healthy cells for which RA is a powerful radioprotector, and at the same time, cause significant damage to melanoma cells for which it could act as a radiosensitive agent.

An Update on the Role of Dietary Phytochemicals in Human Skin Cancer: New Insights into Molecular Mechanisms

Human skin is continuously subjected to environmental stresses, as well as extrinsic and intrinsic noxious agents. Although skin adopts various molecular mechanisms to maintain homeostasis, excessive and repeated stresses can overwhelm these systems, leading to serious cutaneous damage, including both melanoma and non-melanoma skin cancers. Phytochemicals present in the diet possess the desirable effects of protecting the skin from damaging free radicals as well as other benefits. Dietary phytochemicals appear to be effective in preventing skin cancer and are inexpensive, widely available, and well tolerated. Multiple in vitro and in vivo studies have demonstrated the significant anti-inflammatory, antioxidant, and anti-angiogenic characteristics of dietary phytochemicals against skin malignancy. Moreover, dietary phytochemicals affect multiple important cellular processes including cell cycle, angiogenesis, and metastasis to control skin cancer progression. Herein, we discuss the advantages of key dietary phytochemicals in whole fruits and vegetables, their bioavailability, and underlying molecular mechanisms for preventing skin cancer. Current challenges and future prospects for research are also reviewed. To date, most of the chemoprevention investigations have been conducted preclinically, and additional clinical trials are required to conform and validate the preclinical results in humans.

Caffeic Acid Phenethyl Ester Assisted by Reversible Electroporation-In Vitro Study on Human Melanoma Cells

Melanoma is one of the most serious skin cancers. The incidence of this malignant skin lesion is continuing to increase worldwide. Melanoma is resistant to chemotherapeutic drugs and highly metastatic. Surgical resection can only be used to treat melanoma in the early stages, while chemotherapy is limited due to melanoma multi-drug resistance. The overexpression of glutathione S-transferase (GST) may have a critical role in this resistance. Caffeic acid phenethyl ester (CAPE) is a natural phenolic compound, which occurs in many plants. Previous studies demonstrated that CAPE suppresses the growth of melanoma cells and induces reactive oxygen species generation. It is also known that bioactivation of CAPE to its corresponding quinone metabolite by tyrosinase would lead to GST inhibition and selective melanoma cell death. We investigated the biochemical toxicity of CAPE in combination with microsecond electropermeabilization in two human melanoma cell lines. Our results indicate that electroporation of melanoma cells in the presence of CAPE induced high oxidative stress, which correlates with high cytotoxicity. Moreover, it can disrupt the metabolism of cancer cells by inducing apoptotic cell death. Electroporation of melanoma cells may be an efficient CAPE delivery system, enabling the application of this compound, while reducing its dose and exposure time.

Caffeic Acid Phenethyl Ester Inhibits UV-Induced MMP-1 Expression by Targeting Histone Acetyltransferases in Human Skin

Caffeic acid phenethyl ester (CAPE), a naturally occurring bioactive compound, displays anti-inflammatory, anti-carcinogenic, and anti-microbial effects. However, the effect of CAPE on skin photoaging is unknown. Herein, we investigated the inhibitory effect of CAPE against ultraviolet (UV) irradiation-mediated matrix metalloproteinase (MMP)-1 expression and its underlying molecular mechanism. CAPE treatment suppressed UV-induced MMP-1 levels in both human dermal fibroblasts (HDF) and human skin tissues. While CAPE did not display any significant effects against the upstream regulatory pathways of MMP-1, CAPE was capable of reversing UV-mediated epigenetic modifications. CAPE suppressed UV-induced acetyl-histone H3 (Lys9) as well as total lysine acetylation in HDF cells. Similarly, CAPE also attenuated UV-induced lysine acetylations in human skin tissues, suggesting that the CAPE-mediated epigenetic alterations can be recapitulated in ex vivo conditions. CAPE was found to attenuate UV-induced histone acetyltransferase (HAT) activity in HDF. Notably, CAPE was able to directly inhibit the activity of several HATs including p300, CREP-binding protein (CBP), and p300/CBP-associated factor (PCAF), further confirming that CAPE can function as an epigenetic modulator. Thus, our study suggests that CAPE maybe a promising agent for the prevention of skin photoaging via targeting HATs.

Unraveling the molecular mechanisms and the potential chemopreventive/therapeutic properties of natural compounds in melanoma

Melanoma is the most fatal form of skin cancer. Current therapeutic approaches include surgical resection, chemotherapy, targeted therapy and immunotherapy. However, these treatment strategies are associated with development of drug resistance and severe side effects. In recent years, natural compounds have also been extensively studied for their anti-melanoma effects, including tumor growth inhibition, apoptosis induction, angiogenesis and metastasis suppression and cancer stem cell elimination. Moreover, a considerable number of studies reported the synergistic activity of phytochemicals and standard anti-melanoma agents, as well as the enhanced effectiveness of their synthetic derivatives and novel formulations. However, clinical data confirming these promising effects in patients are still scanty. This review emphasizes the anti-tumor mechanisms and potential application of the most studied natural products for melanoma prevention and treatment.

Antiproliferative and apoptotic effects of caffeic acid on SK-Mel-28 human melanoma cancer cells

Cutaneous melanoma (CM) is an extremely aggressive cancer presenting low survival and high mortality. The vast majority of patients affected by this disease does not respond or show resistance to the chemotherapeutic drugs, which makes the treatment ineffective. In this sense, the necessity for the development of new agents to assist in CM therapy is extremely important. One of the sources of great interest in this search are compounds of natural origin. Among these compounds, caffeic acid has demonstrated a broad spectrum of pharmacological activities as well as antitumor effects in some types of cancer. Therefore, the objective of this work was to investigate the possible antitumor effect of caffeic acid on the SK-Mel-28 cell line, human CM cells. Cells were cultured in flasks with culture medium containing fetal bovine serum, antibiotic, and antifungal, and maintained in ideal conditions. Cells were treated with 25 µM, 50 µM, 100 µM, 150 µM and 200 µM of caffeic acid and dacarbazine at 1 mg/mL. We verified the effect on cell viability and cell death, apoptosis, cell cycle, colony formation and gene expression of caspases. Results showed a decrease in cell viability, cell death induction by apoptosis, inhibition of colony formation, modulation of cell cycle and alterations in gene expression of caspases after caffeic acid treatment. These results suggest an antitumor effect of the compound on SK-Mel-28 cells. This study provides original information on mechanisms by which caffeic acid may play a key role in preventing tumor progression in human melanoma cells.

The role of ginsenoside Rb1, a potential natural glutathione reductase agonist, in preventing oxidative stress-induced apoptosis of H9C2 cells

Background

Oxidative stress-induced cardiomyocytes apoptosis is a key pathological process in ischemic heart disease. Glutathione reductase (GR) reduces glutathione disulfide to glutathione (GSH) to alleviate oxidative stress. Ginsenoside Rb1 (GRb1) prevents the apoptosis of cardiomyocytes; however, the role of GR in this process is unclear. Therefore, the effects of GRb1 on GR were investigated in this study.

Methods

The antiapoptotic effects of GRb1 were evaluated in H9C2 cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, annexin V/propidium iodide staining, and Western blotting. The antioxidative effects were measured by a reactive oxygen species assay, and GSH levels and GR activity were examined in the presence and absence of the GR inhibitor 1,3-bis-(2-chloroethyl)-1-nitrosourea. Molecular docking and molecular dynamics simulations were used to investigate the binding of GRb1 to GR. The direct influence of GRb1 on GR was confirmed by recombinant human GR protein.

Results

GRb1 pretreatment caused dose-dependent inhibition of tert-butyl hydroperoxide-induced cell apoptosis, at a level comparable to that of the positive control N-acetyl-L-cysteine. The binding energy between GRb1 and GR was positive (−6.426 kcal/mol), and the binding was stable. GRb1 significantly reduced reactive oxygen species production and increased GSH level and GR activity without altering GR protein expression in H9C2 cells. Moreover, GRb1 enhanced the recombinant human GR protein activity in vitro, with a half-maximal effective concentration of ≈2.317 μM. Conversely, 1,3-bis-(2-chloroethyl)-1-nitrosourea co-treatment significantly abolished the GRb1's apoptotic and antioxidative effects of GRb1 in H9C2 cells.

Conclusion

GRb1 is a potential natural GR agonist that protects against oxidative stress–induced apoptosis of H9C2 cells.

Phytochemicals in Skin Cancer Prevention and Treatment: An Updated Review

Skin is the largest human organ, our protection against various environmental assaults and noxious agents. Accumulation of these stress events may lead to the formation of skin cancers, including both melanoma and non-melanoma skin cancers. Although modern targeted therapies have ameliorated the management of cutaneous malignancies, a safer, more affordable, and more effective strategy for chemoprevention and treatment is clearly needed for the improvement of skin cancer care. Phytochemicals are biologically active compounds derived from plants and herbal products. These agents appear to be beneficial in the battle against cancer as they exert anti-carcinogenic effects and are widely available, highly tolerated, and cost-effective. Evidence has indicated that the anti-carcinogenic properties of phytochemicals are due to their anti-oxidative, anti-inflammatory, anti-proliferative, and anti-angiogenic effects. In this review, we discuss the preventive potential, therapeutic effects, bioavailability, and structure–activity relationship of these selected phytochemicals for the management of skin cancers. The knowledge compiled here will provide clues for future investigations on novel oncostatic phytochemicals and additional anti-skin cancer mechanisms.

Migration Rate Inhibition of Breast Cancer Cells Treated by Caffeic Acid and Caffeic Acid Phenethyl Ester: An In Vitro Comparison Study

One of the deadliest cancers among women is a breast cancer. Research has shown that two natural substances occurring in propolis, caffeic acid (CA) and caffeic acid phenethyl ester (CAPE), have significant anticancer effects. The purpose of our in vitro study was to compare cytotoxic activity and migration rate inhibition using CA and CAPE (doses of 50 and 100 µm) against triple-negative, MDA-MB-231 breast adenocarcinoma line cells, drawn from Caucasian women. Viability was measured by XTT-NR-SRB assay (Tetrazolium hydroxide-Neutral Red-Sulforhodamine B) for 24 h and 48 h periods. Cell migration for wound healing assay was taken for 0 h, 8 h, 16 h, and 24 h periods. CAPE displayed more than two times higher cytotoxicity against MDA-MB-231 cells. IC₅₀ values for the XTT assay were as follows: CA for 24 h and 48 h were 150.94 µM and 108.42 µM, respectively, while CAPE was 68.82 µM for 24 h and 55.79 µM for 48 h. For the NR assay: CA was 135.85 µM at 24 h and 103.23 µM at 48 h, while CAPE was 64.04 µM at 24 h and 53.25 µM at 48 h. For the SRB assay: CA at 24 h was 139.80 µM and at 48 h 103.98 µM, while CAPE was 66.86 µM at 24 h and 47.73 µM at 48 h. Both agents suspended the migration rate; however, CAPE displayed better activity. Notably, for the 100 µM CAPE dose, motility of the tested breast carcinoma cells was halted.

Prdx6 Deficiency Ameliorates DSS Colitis: Relevance of Compensatory Antioxidant Mechanisms

BACKGROUND AND AIMS

An imbalance between cellular antioxidant defence system[s] and reactive oxygen species [ROS]-driven oxidative stress has been implicated in the pathogenesis of inflammatory bowel disease. Peroxiredoxin [PRDX] 6 contributes to an appropriate redox balance by clearing ROS and reducing peroxidized membrane phospholipids. We here studied the role of PRDX6 in acute and chronic dextran sodium sulphate [DSS]-induced colitis.

METHODS

To investigate the impact of PRDX6 on intestinal inflammation, we used wild type [WT], Prdx6 knock-out mice [Prdx6-/-] and transgenic mice [Prdx6tg/tg], overexpressing Prdx6. Acute and chronic colitis was induced by DSS in WT, Prdx6-/- and Prdx6tg/tg mice. Colitis was evaluated by endoscopy, colon length, histopathological assessment and myeloperoxidase [MPO] activity. Changes in mRNA and protein expression of pro-inflammatory cytokines and antioxidant enzymes were evaluated by real-time quantitative polymerase chain reaction [RT-qPCR] and western blot. Total glutathione [GSH] levels in colon samples were determined.

RESULTS

Prdx6-/- mice exposed to acute and chronic DSS showed a significant decrease in the clinical parameters and in colonic expression of pro-inflammatory cytokines compared with WT mice. mRNA expression of antioxidant enzymes in colon samples was significantly increased in Prdx6-/- compared with WT mice exposed to acute and chronic DSS. In addition, total GSH levels were increased in Prdx6-/- mice treated with DSS in comparison with WT. Overexpression of Prdx6 did not significantly influence acute and chronic colitis.

CONCLUSIONS

Our data indicate that a lack of the antioxidant enzyme PRDX6 protects against the development of acute and chronic experimental colitis and is associated with increased expression and function of other antioxidant enzymes, suggesting effective compensatory mechanisms.

Galangin Activates the ERK/AKT-Driven Nrf2 Signaling Pathway to Increase the Level of Reduced Glutathione in Human Keratinocytes

Previously, we demonstrated that galangin (3,5,7-trihydroxyflavone) protects human keratinocytes against ultraviolet B (UVB)-induced oxidative damage. In this study, we investigated the effect of galangin on induction of antioxidant enzymes involved in synthesis of reduced glutathione (GSH), and investigated the associated upstream signaling cascades. By activating nuclear factor-erythroid 2-related factor (Nrf2), galangin treatment significantly increased expression of glutamate-cysteine ligase catalytic subunit (GCLC) and glutathione synthetase (GSS). This activation of Nrf2 depended on extracellular signal-regulated kinases (ERKs) and protein kinase B (AKT) signaling. Inhibition of GSH in galangin-treated cells attenuated the protective effect of galangin against the deleterious effects of UVB. Our results reveal that galangin protects human keratinocytes by activating ERK/AKT-Nrf2, leading to elevated expression of GSH-synthesizing enzymes.

Antioxidative Theranostic Iron Oxide Nanoparticles toward Brain Tumors Imaging and ROS Production

Gliomas are the most common primary brain tumor in humans. To date, the only treatment of care consists of surgical removal of the tumor bulk, irradiation, and chemotherapy, finally resulting in a very poor prognosis due to the lack of efficiency in diagnostics. In this context, nanomedicine combining both diagnostic and magnetic resonance imaging (MRI) and therapeutic applications is a relevant strategy referred to theranostic. Magnetic nanoparticles (NP) are excellent MRI contrast agents because of their large magnetic moment, which induces high transverse relaxivity (r₂) characteristic and increased susceptibility effect (T₂*). NP can be also used for drug delivery by coating their surface with therapeutic molecules. Preliminary in vitro studies show the high potential of caffeic acid (CA), a natural polyphenol, as a promising anticancer drug due to its antioxidant, anti-inflammatory, and antimetastatic properties. In this study, the antioxidative properties of iron oxide NP functionalized with caffeic acid (γFe₂O₃@CA NP) are investigated in vitro on U87-MG brain cancer cell lines. After intravenous injection of these NP in mice bearing a U87 glioblastoma, a negative contrast enhancement was specifically observed on 11.7 T MRI images in cancerous tissue, demonstrating a passive targeting of the tumor with these nanoplatforms.

Caffeic acid phenethyl ester induced cell cycle arrest and growth inhibition in androgen-independent prostate cancer cells via regulation of Skp2, p53, p21Cip1 and p27Kip1

Prostate cancer (PCa) patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant prostate cancer (CRPC) within 1–3 years. Treatment with caffeic acid phenethyl ester (CAPE) suppressed cell survival and proliferation via induction of G1 or G2/M cell cycle arrest in LNCaP 104-R1, DU-145, 22Rv1, and C4–2 CRPC cells. CAPE treatment also inhibited soft agar colony formation and retarded nude mice xenograft growth of LNCaP 104-R1 cells. We identified that CAPE treatment significantly reduced protein abundance of Skp2, Cdk2, Cdk4, Cdk7, Rb, phospho-Rb S807/811, cyclin A, cyclin D1, cyclin H, E2F1, c-Myc, SGK, phospho-p70S6kinase T421/S424, phospho-mTOR Ser2481, phospho-GSK3α Ser21, but induced p21^Cip1, p27^Kip1, ATF4, cyclin E, p53, TRIB3, phospho-p53 (Ser6, Ser33, Ser46, Ser392), phospho-p38 MAPK Thr180/Tyr182, Chk1, Chk2, phospho-ATM S1981, phospho-ATR S428, and phospho-p90RSK Ser380. CAPE treatment decreased Skp2 and Akt1 protein expression in LNCaP 104-R1 tumors as compared to control group. Overexpression of Skp2, or siRNA knockdown of p21^Cip1, p27^Kip1, or p53 blocked suppressive effect of CAPE treatment. Co-treatment of CAPE with PI3K inhibitor LY294002 or Bcl-2 inhibitor ABT737 showed synergistic suppressive effects. Our finding suggested that CAPE treatment induced cell cycle arrest and growth inhibition in CRPC cells via regulation of Skp2, p53, p21^Cip1, and p27^Kip1.

Bioactivation of luteolin by tyrosinase selectively inhibits glutathione S-transferase

Glutathione S-transferase (GST) plays a significant role in the metabolism and detoxification of drugs used in treatment of melanoma, resulting in a decrease in drug efficacy. Tyrosinase is an abundant enzyme found in melanoma. In this study, we used a tyrosinase targeted approach to selectively inhibit GST. In the presence of tyrosinase, luteolin (10 μM) showed 87% GST inhibition; whereas in the absence of tyrosinase, luteolin led to negligible GST inhibition. With respect to GSH, both luteolin-SG conjugate and luteolin-quinone inhibited ≥90% of GST activity via competitive reversible and irreversible mixed mechanisms with Ki of 0.74 μM and 0.02 μM, respectively. With respect to CDNB, the luteolin-SG conjugate inhibited GST activity via competitive reversible mechanism and competitively with Ki of 0.58 μM, whereas luteolin-quinone showed irreversible mixed inhibition of GST activity with Ki of 0.039 μM. Luteolin (100 μM) inhibited GST in mixed manner with Ki of 53 μM with respect to GSH and non-competitively with respect to CDNB with Ki of 38 μM. Luteolin, at a concentration range of 5-80 μM, exhibited 78-99% GST inhibition in human SK-MEL-28 cell homogenate. Among the 3 species of intact luteolin, luteolin-SG conjugate, and luteoline-quinone, only the latter two have potential as drugs with Ki < 1 μM, which is potentially achievable in-vivo as therapeutic agents. The order of GST inhibition was luteolin-quinone >> luteolin-SG conjugate >>> luteolin. In summary, our results suggest that luteolin was bioactivated by tyrosinase to form a luteolin-quinone and luteolin-glutathione conjugate, which inhibited GST. For the first time, in addition to intracellular GSH depletion, we demonstrate that luteolin acts as a selective inhibitor of GST in the presence of tyrosinase. Such strategy could potentially be used to selectively inhibit GST, a drug detoxifying enzyme, in melanoma cells.

Caffeic Acid phenethyl ester and ethanol extract of propolis induce the complementary cytotoxic effect on triple-negative breast cancer cell lines

Chemotherapy of breast cancer could be improved by bioactive natural substances, which may potentially sensitize the carcinoma cells’ susceptibility to drugs. Numerous phytochemicals, including propolis, have been reported to interfere with the viability of carcinoma cells. We evaluated the in vitro cytotoxic activity of ethanol extract of propolis (EEP) and its derivative caffeic acid phenethyl ester (CAPE) towards two triple-negative breast cancer (TNBC) cell lines, MDA-MB-231 and Hs578T, by implementation of the MTT and lactate dehydrogenase (LDH) assays. The morphological changes of breast carcinoma cells were observed following exposure to EEP and CAPE. The IC₅₀ of EEP was 48.35 µg∙mL⁻¹ for MDA-MB-23 cells and 33.68 µg∙mL⁻¹ for Hs578T cells, whereas the CAPE IC₅₀ was 14.08 µM and 8.01 µM for the MDA-MB-231 and Hs578T cell line, respectively. Here, we report that propolis and CAPE inhibited the growth of the MDA-MB-231 and Hs578T lines in a dose-dependent and exposure time-dependent manner. EEP showed less cytotoxic activity against both types of TNBC cells. EEP and, particularly, CAPE may markedly affect the viability of breast cancer cells, suggesting the potential role of bioactive compounds in chemoprevention/chemotherapy by potentiating the action of standard anti-cancer drugs.

Caffeic Acid phenethyl ester is a potential therapeutic agent for oral cancer

Head and neck cancers, which affect 650,000 people and cause 350,000 deaths per year, is the sixth leading cancer by cancer incidence and eighth by cancer-related death worldwide. Oral cancer is the most common type of head and neck cancer. More than 90% of oral cancers are oral and oropharyngeal squamous cell carcinoma (OSCC). The overall five-year survival rate of OSCC patients is approximately 63%, which is due to the low response rate to current therapeutic drugs. In this review we discuss the possibility of using caffeic acid phenethyl ester (CAPE) as an alternative treatment for oral cancer. CAPE is a strong antioxidant extracted from honeybee hive propolis. Recent studies indicate that CAPE treatment can effectively suppress the proliferation, survival, and metastasis of oral cancer cells. CAPE treatment inhibits Akt signaling, cell cycle regulatory proteins, NF-κB function, as well as activity of matrix metalloproteinase (MMPs), epidermal growth factor receptor (EGFR), and Cyclooxygenase-2 (COX-2). Therefore, CAPE treatment induces cell cycle arrest and apoptosis in oral cancer cells. According to the evidence that aberrations in the EGFR/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling, NF-κB function, COX-2 activity, and MMPs activity are frequently found in oral cancers, and that the phosphorylation of Akt, EGFR, and COX-2 correlates to oral cancer patient survival and clinical progression, we believe that CAPE treatment will be useful for treatment of advanced oral cancer patients.

Possible molecular targets for therapeutic applications of caffeic acid phenethyl ester in inflammation and cancer

Of the various derivatives of caffeic acid, caffeic acid phenethyl ester (CAPE) is a hydrophobic, bioactive polyphenolic ester obtained from propolis extract. The objective in writing this review article was to summarize all published studies on therapeutics of CAPE in inflammation and cancer to extract direction for future research. The possible molecular targets for the action of CAPE, include various transcription factors such as nuclear factor-κB, tissue necrosis factor-α, interleukin-6, cyclooxygenase-2, Nrf2, inducible nitric oxide synthase, nuclear factor of activated T cells, hypoxia-inducible factor-1α, and signal transducers and activators of transcription. Based on the valuable data on its therapeutics in inflammation and cancer, clinical studies of CAPE should also be conducted to explore its toxicities, if any.

Fucoxanthin enhances the level of reduced glutathione via the Nrf2-mediated pathway in human keratinocytes

Fucoxanthin, a natural carotenoid, is abundant in seaweed with antioxidant properties. This study investigated the role of fucoxanthin in the induction of antioxidant enzymes involved in the synthesis of reduced glutathione (GSH), synthesized by glutamate-cysteine ligase catalytic subunit (GCLC) and glutathione synthetase (GSS), via Akt/nuclear factor-erythroid 2-related (Nrf2) pathway in human keratinocytes (HaCaT) and elucidated the underlying mechanism. Fucoxanthin treatment increased the mRNA and protein levels of GCLC and GSS in HaCaT cells. In addition, fucoxanthin treatment promoted the nuclear translocation and phosphorylation of Nrf2, a transcription factor for the genes encoding GCLC and GSS. Chromatin immune-precipitation and luciferase reporter gene assays revealed that fucoxanthin treatment increased the binding of Nrf2 to the antioxidant response element (ARE) sequence and transcriptional activity of Nrf2. Fucoxanthin treatment increased phosphorylation of Akt (active form), an up-regulator of Nrf2 and exposure to LY294002, a phosphoinositide 3-kinase (PI3K)/Akt inhibitor, suppressed the fucoxanthin-induced activation of Akt, Nrf2, resulting in decreased GCLC and GSS expression. In accordance with the effects on GCLC and GSS expression, fucoxanthin induced the level of GSH. In addition, fucoxanthin treatment recovered the level of GSH reduced by ultraviolet B irradiation. Taken together, these findings suggest that fucoxanthin treatment augments cellular antioxidant defense by inducing Nrf2-driven expression of enzymes involved in GSH synthesis via PI3K/Akt signaling.

Caffeic acid phenethyl ester as a protective agent against nephrotoxicity and/or oxidative kidney damage: a detailed systematic review

Caffeic acid phenethyl ester (CAPE), an active component of propolis, has been attracting the attention of different medical and pharmaceutical disciplines in recent years because of its antioxidant, anti-inflammatory, antiproliferative, cytotoxic, antiviral, antifungal, and antineoplastic properties. One of the most studied organs for the effects of CAPE is the kidney, particularly in the capacity of this ester to decrease the nephrotoxicity induced by several drugs and the oxidative injury after ischemia/reperfusion (I/R). In this review, we summarized and critically evaluated the current knowledge regarding the protective effect of CAPE in nephrotoxicity induced by several special medicines such as cisplatin, doxorubicin, cyclosporine, gentamycin, methotrexate, and other causes leading to oxidative renal injury, namely, I/R models and senility.

Caffeic acid phenethyl ester and therapeutic potentials

Caffeic acid phenethyl ester (CAPE) is a bioactive compound of propolis extract. The literature search elaborates that CAPE possesses antimicrobial, antioxidant, anti-inflammatory, and cytotoxic properties. The principal objective of this review article is to sum up and critically assess the existing data about therapeutic effects of CAPE in different disorders. The findings elaborate that CAPE is a versatile therapeutically active polyphenol and an effective adjuvant of chemotherapy for enhancing therapeutic efficacy and diminishing chemotherapy-induced toxicities.

Caffeic acid phenethyl ester suppresses melanoma tumor growth by inhibiting PI3K/AKT/XIAP pathway

Melanoma is highly metastatic and resistant to chemotherapeutic drugs. Our previous studies have demonstrated that caffeic acid phenethyl ester (CAPE) suppresses the growth of melanoma cells and induces reactive oxygen species generation. However, the exact mechanism of the growth suppressive effects of CAPE was not clear. Here, we determined the potential mechanism of CAPE against melanoma in vivo and in vitro. Administration of 10 mg/kg/day CAPE substantially suppressed the growth of B16F0 tumor xenografts in C57BL/6 mice. Tumors from CAPE-treated mice showed reduced phosphorylation of phosphoinositide 3-kinase, AKT, mammalian target of rapamycin and protein level of X-linked inhibitor of apoptosis protein (XIAP) and enhanced the cleavage of caspase-3 and poly (ADP ribose) polymerase. In order to confirm the in vivo observations, melanoma cells were treated with CAPE. CAPE treatment suppressed the activating phosphorylation of phosphoinositide 3-kinase at Tyr 458, phosphoinositide-dependent kinase-1 at Ser 241, mammalian target of rapamycin at Ser 2448 and AKT at Ser 473 in B16F0 and SK-MEL-28 cells in a concentration and time-dependent study. Furthermore, the expression of XIAP, survivin and BCL-2 was downregulated by CAPE treatment in both cell lines. Significant apoptosis was observed by CAPE treatment as indicated by cleavage of caspase-3 and poly (ADP ribose) polymerase. AKT kinase activity was inhibited by CAPE in a concentration-dependent manner. CAPE treatment increased the nuclear translocation of XIAP, indicating increased apoptosis in melanoma cells. To confirm the involvement of reactive oxygen species in the inhibition of AKT/XIAP pathway, cells were treated with antioxidant N-acetyl-cysteine (NAC) prior to CAPE treatment. Our results indicate that NAC blocked CAPE-mediated AKT/XIAP inhibition and protected the cells from apoptosis. Because AKT regulates XIAP, their interaction was examined by immunoprecipitation studies. Our results show that CAPE treatment decreased the interaction of AKT with XIAP. To establish the involvement of AKT in the apoptosis-inducing effects of CAPE, cells were transfected with AKT. Our results revealed that AKT overexpression attenuated the decrease in XIAP and significantly blocked CAPE-mediated apoptosis. Similarly, overexpression of XIAP further decreased CAPE-induced apoptosis. Taken together, our results suggest that CAPE suppresses phosphoinositide 3-kinase/AKT/XIAP pathway leading to apoptosis in melanoma tumor cells in vitro and in vivo.

Caffeic Acid phenethyl ester as a potential treatment for advanced prostate cancer targeting akt signaling

Prostate cancer is the fifth most common cancer overall in the world. Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, most prostate cancer patients receiving the androgen ablation therapy ultimately develop recurrent castration-resistant tumors within 1–3 years after treatment. The median overall survival time is 1–2 years after tumor relapse. Chemotherapy shows little effect on prolonging survival for patients with metastatic hormone-refractory prostate cancer. More than 80% of prostate tumors acquire mutation or deletion of tumor suppressor phosphatase and tensin homolog (PTEN), a negative regulator of PI3K/Akt signaling, indicating that inhibition of PI3K/Akt might be a potential therapy for advanced prostate tumors. Caffeic acid phenethyl ester (CAPE) is a strong antioxidant extracted from honeybee hive propolis. CAPE is a well-known NF-κB inhibitor. CAPE has been used in folk medicine as a potent anti-inflammatory agent. Recent studies indicate that CAPE treatment suppresses tumor growth and Akt signaling in human prostate cancer cells. We discuss the potential of using CAPE as a treatment for patients with advanced prostate cancer targeting Akt signaling pathway in this review article.

Caffeic acid phenylethyl ester and MG132, two novel nonconventional chemotherapeutic agents, induce apoptosis of human leukemic cells by disrupting mitochondrial function

The ability to modulate balance between cell survival and death is recognized for its great therapeutic potential. Therefore, research continues to focus on elucidation of cell machinery and signaling pathways that control cell proliferation and apoptosis. Conventional chemotherapeutic agents often have a cytostatic effect over tumor cells. New natural or synthetic chemotherapeutic agents have a wider spectrum of interesting antitumor activities that merit in-depth studies. In the present work, we aimed at characterizing the molecular mechanism leading to induction of cell death upon treatment of the lymphoblastoid cell line PL104 with caffeic acid phenylethyl ester (CAPE), MG132 and two conventional chemotherapeutic agents, doxorubicine (DOX) and vincristine (VCR). Our results showed several apoptotic hallmarks such as phosphatidylserine (PS) exposure on the outer leaflet of the cell membrane, nuclear fragmentation, and increase sub-G1 DNA content after all treatments. In addition, all four drugs downregulated survivin expression. CAPE and both chemotherapeutic agents reduced Bcl-2, while only CAPE and MG132 significantly increased Bax level. CAPE and VCR treatment induced the collapse of mitochondrial membrane potential (∆ψm). All compounds induced cytochrome c release from mitochondrial compartment to cytosol. However, only MG132 caused the translocation of Smac/DIABLO. Except for VCR treatment, all other drugs increased reactive oxygen species (ROS) production level. All treatments induced activation of caspases 3/7, but only CAPE and MG132 led to the activation of caspase 9. In conclusion, our results indicate that CAPE and MG132 treatment of PL104 cells induced apoptosis through the mitochondrial intrinsic pathway, whereas the apoptotic mechanism induced by DOX and VCR may proceed through the extrinsic pathway.

CAPE suppresses VEGFR-2 activation, and tumor neovascularization and growth

The growth and metastasis of human solid tumors and the development of conditions such as diabetic retinopathy, rheumatoid arthritis, inflammatory psoriasis, and others are regulated by the balance between angiogenic stimulators and inhibitors released in the angiogenic-pathological microenvironment. Vascular endothelial growth factor (VEGF), an angiogenic factor, is a potent endothelial-specific mitogen that activates endothelial cells in pathological angiogenesis. Recently, we demonstrated that caffeic acid phenethyl ester (CAPE) inhibits tumor growth, invasion, and metastasis. However, the precise molecular mechanism underlying the inhibitory effect of CAPE on VEGF-mediated angiogenesis remains unknown. Here, we show that CAPE suppressed VEGF-induced proliferation, tube formation, migration, the formation of actin stress fibers and loss of VE-cadherin at cell-cell contacts in endothelial cells, indicating the inhibition of VEGF-mediated VEGF receptor-2 (VEGFR-2) and its downstream signal activation in vitro. CAPE blocked VEGF-stimulated neovascularization in the Matrigel plugs assay, and reduced vascular permeability in mouse skin capillaries in vivo. CAPE inhibited the growth and neovascularization of primary tumor cells in C57BL/6 and BALB/c mice inoculated with Lewis lung carcinoma, colon carcinoma, and melanoma cells. These results suggest that CAPE negatively modulates VEGF-induced angiogenesis by suppressing VEGFR-2 activation, and might be a therapeutic avenue for anti-angiogenesis.

Caffeic acid phenethyl ester (CAPE), derived from a honeybee product propolis, exhibits a diversity of anti-tumor effects in pre-clinical models of human breast cancer

Breast cancer (BC) patients use alternative and natural remedies more than patients with other malignancies. Specifically, 63-83% use at least one type of alternative medicine and 25-63% use herbals and vitamins. Propolis is a naturopathic honeybee product, and CAPE (caffeic acid phenethyl ester), is a major medicinal component of propolis. CAPE, in a concentration dependent fashion, inhibits MCF-7 (hormone receptor positive, HR+) and MDA-231 (a model of triple negative BC (TNBC) tumor growth, both in vitro and in vivo without much effect on normal mammary cells and strongly influences gene and protein expression. It induces cell cycle arrest, apoptosis and reduces expression of growth and transcription factors, including NF-κB. Notably, CAPE down-regulates mdr-1 gene, considered responsible for the resistance of cancer cells to chemotherapeutic agents. Further, CAPE dose-dependently suppresses VEGF formation by MDA-231 cells and formation of capillary-like tubes by endothelial cells, implicating inhibitory effects on angiogenesis. In conclusion, our results strongly suggest that CAPE inhibits MDA-231 and MCF-7 human breast cancer growth via its apoptotic effects, and modulation of NF-κB, the cell cycle, and angiogenesis.

The metabolic bioactivation of caffeic acid phenethyl ester (CAPE) mediated by tyrosinase selectively inhibits glutathione S-transferase

Glutathione S-transferase (GST) and multidrug resistance-associated proteins (MRPs) play major roles in drug resistance in melanoma. In this study, we investigated caffeic acid phenethyl ester (CAPE) as a selective GST inhibitor in the presence of tyrosinase, which is abundant in melanoma cells. Tyrosinase bioactivates CAPE to an o-quinone, which reacts with glutathione to form CAPE-SG conjugate. Our findings indicate that 90% CAPE was metabolized by tyrosinase after a 60-min incubation. LC-MS/MS analyses identified a CAPE-SG conjugate as a major metabolite. In the presence of tyrosinase, CAPE (10-25μM) showed 70-84% GST inhibition; whereas in the absence of tyrosinase, CAPE did not inhibit GST. CAPE-SG conjugate and CAPE-quinone (25μM) demonstrated ⩾85% GST inhibition via reversible and irreversible mechanisms, respectively. Comparing with CDNB and GSH, the non-substrate CAPE acted as a weak, reversible GST inhibitor at concentrations >50μM. Furthermore, MK-571, a selective MRP inhibitor, and probenecid, a non-selective MRP inhibitor, decrease the IC(50) of CAPE (15μM) by 13% and 21%, apoptotic cell death by 3% and 13%, and mitochondrial membrane potential in human SK-MEL-28 melanoma cells by 10% and 56%, respectively. Moreover, computational docking analyses suggest that CAPE binds to the GST catalytic active site. Caffeic acid, a hydrolyzed product of CAPE, showed a similar GST inhibition in the presence of tyrosinase. Although, as controls, 4-hydroxyanisole and L-tyrosine were metabolized by tyrosinase to form quinones and glutathione conjugates, they exhibited no GST inhibition in the absence and presence of tyrosinase. In conclusion, both CAPE and caffeic acid selectively inhibited GST in the presence of tyrosinase. Our results suggest that intracellularly formed quinones and glutathione conjugates of caffeic acid and CAPE may play major roles in the selective inhibition of GST in SK-MEL-28 melanoma cells. Moreover, the inhibition of MRP enhances CAPE-induced toxicity in the SK-MEL-28 melanoma cells.

Biochemical mechanism of caffeic acid phenylethyl ester (CAPE) selective toxicity towards melanoma cell lines

In the current work, we investigated the in vitro biochemical mechanism of Caffeic Acid Phenylethyl Ester (CAPE) toxicity and eight hydroxycinnamic/caffeic acid derivatives in vitro, using tyrosinase enzyme as a molecular target in human SK-MEL-28 melanoma cells. Enzymatic reaction models using tyrosinase/O(2) and HRP/H(2)O(2) were used to delineate the role of one- and two-electron oxidation. Ascorbic acid (AA), NADH and GSH depletion were used as markers of quinone formation and oxidative stress in CAPE induced toxicity in melanoma cells. Ethylenediamine, an o-quinone trap, prevented the formation of o-quinone and oxidations of AA and NADH mediated by tyrosinase bioactivation of CAPE. The IC(50) of CAPE towards SK-MEL-28 melanoma cells was 15muM. Dicoumarol, a diaphorase inhibitor, and 1-bromoheptane, a GSH depleting agent, increased CAPE's toxicity towards SK-MEL-28 cells indicating quinone formation played an important role in CAPE induced cell toxicity. Cyclosporin-A and trifluoperazine, inhibitors of the mitochondrial membrane permeability transition pore (PTP), prevented CAPE toxicity towards melanoma cells. We further investigated the role of tyrosinase in CAPE toxicity in the presence of a shRNA plasmid, targeting tyrosinase mRNA. Results from tyrosinase shRNA experiments showed that CAPE led to negligible anti-proliferative effect, apoptotic cell death and ROS formation in shRNA plasmid treated cells. Furthermore, it was also found that CAPE selectively caused escalation in the ROS formation and intracellular GSH (ICG) depletion in melanocytic human SK-MEL-28 cells which express functional tyrosinase. In contrast, CAPE did not lead to ROS formation and ICG depletion in amelanotic C32 melanoma cells, which do not express functional tyrosinase. These findings suggest that tyrosinase plays a major role in CAPE's selective toxicity towards melanocytic melanoma cell lines. Our findings suggest that the mechanisms of CAPE toxicity in SK-MEL-28 melanoma cells mediated by tyrosinase bioactivation of CAPE included quinone formation, ROS formation, intracellular GSH depletion and induced mitochondrial toxicity.