Epigenetic cancer prevention mechanisms in skin cancer

Epigenetics of Dietary Phytochemicals in Cancer Prevention: Fact or Fiction

ABSTRACT

Cancer development takes 10 to 50 years, and epigenetics plays an important role. Recent evidence suggests that ~80% of human cancers are linked to environmental factors impinging upon genetics/epigenetics. Because advanced metastasized cancers are resistant to radiation/chemotherapeutic drugs, cancer prevention by relatively nontoxic "epigenetic modifiers" will be logical. Many dietary phytochemicals possess powerful antioxidant and anti-inflammatory properties that are hallmarks of cancer prevention. Dietary phytochemicals can regulate gene expression of the cellular genome via epigenetic mechanisms. In this review, we will summarize preclinical studies that demonstrate epigenetic mechanisms of dietary phytochemicals in skin, colorectal, and prostate cancer prevention. Key examples of the importance of epigenetic regulation in carcinogenesis include hypermethylation of the NRF2 promoter region in cancer cells, resulting in inhibition of NRF2-ARE signaling. Many dietary phytochemicals demethylate NRF2 promoter region and restore NRF2 signaling. Phytochemicals can also inhibit inflammatory responses via hypermethylation of inflammation-relevant genes to block gene expression. Altogether, dietary phytochemicals are excellent candidates for cancer prevention due to their low toxicity, potent antioxidant and anti-inflammatory properties, and powerful epigenetic effects in reversing procarcinogenic events.

Natural Compounds in Non-Melanoma Skin Cancer: Prevention and Treatment

The elevated occurrence of non-melanoma skin cancer (NMSC) and the adverse effects associated with available treatments adversely impact the quality of life in multiple dimensions. In connection with this, there is a necessity for alternative approaches characterized by increased tolerance and lower side effects. Natural compounds could be employed due to their safety profile and effectiveness for inflammatory and neoplastic skin diseases. These anti-cancer drugs are often derived from natural sources such as marine, zoonotic, and botanical origins. Natural compounds should exhibit anti-carcinogenic actions through various pathways, influencing apoptosis potentiation, cell proliferation inhibition, and metastasis suppression. This review provides an overview of natural compounds used in cancer chemotherapies, chemoprevention, and promotion of skin regeneration, including polyphenolic compounds, flavonoids, vitamins, alkaloids, terpenoids, isothiocyanates, cannabinoids, carotenoids, and ceramides.

Interventions for preventing keratinocytic cancer in patients with a history of a previous keratinocytic carcinoma: A systematic review

Keratinocyte cancer (KC) is the most common cancer worldwide. It is important to analyze the actual interventions that are available for the prevention of patients with a previous history of a KC. We aim to review the existent literature to assess the efficacy and safety of interventions to prevent KC in patients with a history of previous KC. We searched clinical trials in which the main outcome was the prevention of KC in patients with a previous history of KC using the strategy published in the International Prospective Register of Systematic Reviews (PROSPERO registry), CRD42016045981. We analyzed 18 clinical trials from which eight reported a benefit with their respective intervention but had methodological flaws and a variable risk of bias. Two clinical trials (regarding celecoxib and oral supplementation with nicotinamide) seemed to have the most beneficial results reducing the incidence of KC in treated groups. However, all of the studies are highly heterogeneous, which does not allow a meta-analysis to be performed. New studies with greater epidemiological value should be conducted.

Sulforaphane inhibits CD44v6/YAP1/TEAD signaling to suppress the cancer phenotype

Sulforaphane (SFN) is a promising cancer prevention and treatment agent that strongly suppresses the cutaneous squamous cell carcinoma (CSCC) cell cancer phenotype. We previously showed that yes-associated protein 1 (YAP1)/TEAD signaling is a key procancer stimulator of the aggressive CSCC cell cancer phenotype. However, SFN-responsive upstream regulators of YAP1/TEAD signaling are not well characterized and so there is a pressing need to identify these factors. We show that CD44v6 knockdown reduces YAP1/TEAD-dependent transcription and target gene expression, and that this is associated with reduced spheroid formation, invasion and migration. CD44v6 knockout cell lines also display reduced YAP1/TEAD activity and target gene expression and attenuated spheroid formation, invasion, migration and tumor formation. An important finding is that SFN treatment suppresses CD44v6 level leading to a reduction in YAP1/TEAD signaling and marker gene expression. Sox2 level and epithelial-mesenchymal transition (EMT) are also reduced. Forced expression of constitutive active YAP1 in CD44v6 knockdown cells partially restores the aggressive cancer phenotype. These important findings suggest that CD44v6 drives YAP1/TEAD signaling to enhance the CSCC cell cancer phenotype and that SFN treatment reduces CD44v6 level/function which, in turn, reduces YAP1/TEAD signaling leading to reduced stemness, EMT and tumor growth.

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.

DNA Methylome and Transcriptome Study of Triterpenoid CDDO in TPA-Mediated Skin Carcinogenesis Model

Overexposure to ultraviolet radiation and environmental carcinogens drive skin cancer development through redox imbalance and gene mutation. Antioxidants such as triterpenoids have exhibited anti-oxidative and anti-inflammatory potentials to alleviate skin carcinogenesis. This study investigated the methylome and transcriptome altered by tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) or TPA with 2-cyano 2,3-dioxoolean-1,9-dien-28-oic acid (CDDO). The results show that CDDO blocks TPA-induced transformation dose dependently. Several differential expressed genes (DEGs) involved in skin cell transformation, while counteracted by CDDO, were revealed by differential expression analysis including Lyl1, Lad1, and Dennd2d. In CpG methylomic profiles, the differentially methylated regions (DMRs) in the promoter region altered by TPA while showing the opposite methylation status in the CDDO treatment group were identified. The correlation between DNA methylation and RNA expression has been established and DMRs showing inverse correlation were further studied as potential therapeutic targets. From the CpG methylome and transcriptome results, CDDO significantly restored gene expression of NAD(P)H:quinone oxidoreductase 1 (Nqo1) inhibited by TPA by decreasing their promoter CpG methylation. Ingenuity Pathways Analysis (IPA) shows that CDDO neutralized the effect of TPA through modulating cell cycles, cell migration, and inflammatory and immune response regulatory pathways. Notably, Tumor Necrosis Factor Receptor 2 (TNFR2) signaling was significantly downregulated by CDDO potentially contributing to prevention of TPA-induced cell transformation. Overall, incorporating the transcriptome, CpG methylome, and signaling pathway network, we reveal potential therapeutic targets and pathways by which CDDO could reverse TPA-induced carcinogenesis. The results could be useful for future human study and targets development for skin cancer.

Epigenetics/epigenomics of triterpenoids in cancer prevention and in health

Triterpenoids are a powerful group of phytochemicals derived from plant foods and herbs. Many reports have shown that they possess chemopreventive and chemotherapeutic effects not only in cell lines and animal models but also in clinical trials. Because epigenetic changes could potentially occur in the early stages of carcinogenesis preceding genetic mutations, epigenetics are considered promising targets in early interventions against cancer using epigenetic bioactive substances. The biological properties of triterpenoids in cancer prevention and in health have multiple mechanisms, including antioxidant and anti-inflammatory activities, cell cycle regulation, as well as epigenetic/epigenomic regulation. In this review, we will discuss and summarize the latest advances in the study of the pharmacological effects of triterpenoids in cancer chemoprevention and in health, including the epigenetic machinery.

Fasting and Its Impact on Skin Anatomy, Physiology, and Physiopathology: A Comprehensive Review of the Literature

Skin serves as the first protective line and barrier of the body. Like many other organs, skin can be affected by several disorders in response to external factors such as pathogens, ultraviolet light, and pollution, as well as endogenous alterations related to aging and/or oxidative stress disturbance. Researchers have reported new insights into how skin cells are altered in response to caloric restriction diets in mammals. One of the most well-known caloric restriction diets is the Ramadan intermittent fasting, which is a radical change in the diet plan of practitioners for the period of one lunar month. Ramadan fasting represents the fourth of the five pillars of the Islamic creed. Even though infirm individuals are waived to take part in this religious duty, patients with various health problems, including those with different skin disorders, might choose to share this event with peers and family members. No standardized protocols or guidelines exist, however, to advise their physicians on the proper management of their patients' condition during fasting. With an increasing Muslim population living in Western countries, this topic has started to draw substantial attention, not only of Middle-Eastern physicians, but also of clinicians in the West. For this purpose, we carried out a comprehensive overview on the topic. Our main findings are that: (1) there is a strong need for evidence-based suggestions and guidance. Literature on the impact of the Ramadan fasting, as well as of other kinds of fasting, on skin diseases is scarce and of poor quality, as well as the information available from the Internet; (2) patients willing to fast should be advised about the importance of taking proper treatments or consider alternative options including administration of trans-dermal/topical drugs, as they are permitted during daylight hours. Further, non-compliance has important, clinical and economic implications for an effective patient management.

Antitumor activity of sulforaphane in mice model of skin cancer via blocking sulfatase-2

Although there are many treatment options for skin cancer, the chemotherapeutic agents for skin cancer are linked with many adverse effects as well as the development of multidrug resistance. Sulforaphane is an isothiocyanate, which is found in cruciferous vegetables. Consumption of sulforaphane-rich diet has been linked to inhibition of UV-exposed skin carcinogenesis. Therefore, the goal of this study was to determine the ability of sulforaphane to reduce skin cancer in mice through inhibition of sulfatase-2 enzyme. Epicutaneous application of 7,12-dimethylbenz (a) anthracene was performed on the shaved dorsal skin of mice followed by croton oil. Sulforaphane (9 μmol/mouse/day) was administered to mice orally. Skin was removed from the dorsal area for assessment of sulfatase-2, glypican-3, heparan sulphate proteoglycans (HSPGs), nuclear factor (NF)κB, nuclear factor E2-related factor 2 (Nrf2), tumor necrosis factor (TNF)-α, IL-1β and caspase-3. In addition, skin sections were stained with haematoxylin/eosin, Mallory and cytokeratin immunostaining. We found that, sulforaphane blocked sulfatase-2 activity, leading to significant elevation in HSPGs as well as significant reduction in glypican-3. In addition, sulforaphane significantly activated Nrf2 and reduced both the gene and protein expression of NFκB, TNF-α, IL-1β and caspase-3. In parallel, stained sections obtained from skin cancer mice treated with sulforaphane showed significant reduction in hyperkeratosis, acanthosis and epithelial dysplasia. The collective results indicate that sulforaphane suppresses skin cancer via blocking sulfatase-2 with subsequent elevation in HSPGs and reduction in glypican-3. Moreover, sulforaphane attenuated skin cancer-induced activation of inflammatory and apoptotic pathways.

Chemopreventive activity of sulforaphane

Cancer is one of the major causes of morbidity and mortality in the world. Carcinogenesis is a multistep process induced by genetic and epigenetic changes that disrupt pathways controlling cell proliferation, apoptosis, differentiation, and senescence. In this context, many bioactive dietary compounds from vegetables and fruits have been demonstrated to be effective in cancer prevention and intervention. Over the years, sulforaphane (SFN), found in cruciferous vegetables, has been shown to have chemopreventive activity in vitro and in vivo. SFN protects cells from environmental carcinogens and also induces growth arrest and/or apoptosis in various cancer cells. In this review, we will discuss several potential mechanisms of the chemopreventive activity of SFN, including regulation of Phase I and Phase II drug-metabolizing enzymes, cell cycle arrest, and induction of apoptosis, especially via regulation of signaling pathways such as Nrf2-Keap1 and NF-κB. Recent studies suggest that SFN can also affect the epigenetic control of key genes and greatly influence the initiation and progression of cancer. This research may provide a basis for the clinical use of SFN for cancer chemoprevention and enable us to design preventive strategies for cancer management, reduce cancer development and recurrence, and thus improve patient survival.

Anticancer Natural Compounds as Epigenetic Modulators of Gene Expression

Accumulating evidence shows that hallmarks of cancer include: "genetic and epigenetic alterations leading to inactivation of cancer suppressors, overexpression of oncogenes, deregulation of intracellular signaling cascades, alterations of cancer cell metabolism, failure to undergo cancer cell death, induction of epithelial to mesenchymal transition, invasiveness, metastasis, deregulation of immune response and changes in cancer microenvironment, which underpin cancer development". Natural compounds as bioactive ingredients isolated from natural sources (plants, fungi, marine life forms) have revolutionized the field of anticancer therapeutics and rapid developments in preclinical studies are encouraging. Natural compounds could affect the epigenetic molecular mechanisms that modulate gene expression, as well as DNA damage and repair mechanisms. The current review will describe the latest achievements in using naturally produced compounds targeting epigenetic regulators and modulators of gene transcription in vitro and in vivo to generate novel anticancer therapeutics.

Epigenetic modifications of triterpenoid ursolic acid in activating Nrf2 and blocking cellular transformation of mouse epidermal cells

Ursolic acid (UA), a well-known natural triterpenoid found in abundance in blueberries, cranberries and apple peels, has been reported to possess many beneficial health effects. These effects include anticancer activity in various cancers, such as skin cancer. Skin cancer is the most common cancer in the world. Nuclear factor E2-related factor 2 (Nrf2) is a master regulator of antioxidative stress response with anticarcinogenic activity against UV- and chemical-induced tumor formation in the skin. Recent studies show that epigenetic modifications of Nrf2 play an important role in cancer prevention. However, the epigenetic impact of UA on Nrf2 signaling remains poorly understood in skin cancer. In this study, we investigated the epigenetic effects of UA on mouse epidermal JB6 P+ cells. UA inhibited cellular transformation by 12-O-tetradecanoylphorbol-13-acetate at a concentration at which the cytotoxicity was no more than 25%. Under this condition, UA induced the expression of the Nrf2-mediated detoxifying/antioxidant enzymes heme oxygenase-1, NAD(P)H:quinone oxidoreductase 1 and UDP-glucuronosyltransferase 1A1. DNA methylation analysis revealed that UA demethylated the first 15 CpG sites of the Nrf2 promoter region, which correlated with the reexpression of Nrf2. Furthermore, UA reduced the expression of epigenetic modifying enzymes, including the DNA methyltransferases DNMT1 and DNMT3a and the histone deacetylases (HDACs) HDAC1, HDAC2, HDAC3 and HDAC8 (Class I) and HDAC6 and HDAC7 (Class II), and HDAC activity. Taken together, these results suggest that the epigenetic effects of the triterpenoid UA could potentially contribute to its beneficial effects, including the prevention of skin cancer.

MEP50/PRMT5 Reduces Gene Expression by Histone Arginine Methylation and this Is Reversed by PKCδ/p38δ Signaling

PKCδ and p38δ are key proteins in a cascade that stimulates keratinocyte differentiation. This cascade activates transcription of involucrin (hINV) and other genes associated with differentiation. Protein arginine methyltransferase 5 (PRMT5) is an arginine methyltransferase that symmetrically dimethylates arginine residues. This protein interacts with a cofactor, MEP50, and symmetrically dimethylates arginine eight of histone 3 (H3R8me2s) and arginine three of histone 4 (H4R3me2s) to silence gene expression. We use the involucrin gene as a tool to understand the relationship between PKCδ/p38δ and PRMT5/MEP50 signaling. MEP50 suppresses hINV mRNA level and promoter activity. This is associated with increased arginine dimethylation of hINV gene-associated H3/H4. We further show that the PKCδ/p38δ keratinocyte differentiation cascade reduces PRMT5 and MEP50 expression, association with the hINV gene promoter, and H3R8me2s and H4R2me2s formation. We propose that PRMT5/MEP50-dependent methylation is an epigenetic mechanism that assists in silencing of hINV expression, and that PKCδ signaling activates gene expression by directly activating transcription and by suppressing PRMT5/MEP50 dependent arginine dimethylation of promoter associated histones. This is an example of crosstalk between PKCδ/p38δ signaling and PRMT5/MEP50 epigenetic silencing.

Fatty acid synthase methylation levels in adipose tissue: effects of an obesogenic diet and phenol compounds

DNA methylation is an epigenetic mechanism that can inhibit gene transcription. The aim of this study was to assess changes induced by an obesogenic diet in the methylation profile of genes involved in adipose tissue triacylglycerol metabolism, and to determine whether this methylation pattern can be altered by resveratrol and pterostilbene. Rats were divided into four groups. The control group was fed a commercial standard diet, and the other three groups were fed a commercial high-fat, high-sucrose diet (6 weeks): the high-fat, high-sucrose group, the resveratrol-treated group (RSV; 30 mg/kg/day), and the pterostilbene-treated group (PT; 30 mg/kg/day). Gene expression was measured by RT-PCR and gene methylation by pyrosequencing. The obesogenic diet induced a significant increase in adipose tissue weight. Resveratrol and pterostilbene partially prevented this effect. Methylation pattern of ppnla2 and pparg genes was similar among the experimental groups. In fasn, significant hypomethylation in -90-bp position and significant hypermethylation in -62-bp position were induced by obesogenic feeding. Only pterostilbene reversed the changes induced by the obesogenic diet in fasn methylation pattern. By contrast, the addition of resveratrol to the diet did not induce changes. Both phenolic compounds averted fasn up-regulation. These results demonstrate that the up-regulation of fasn gene induced by an obesogenic feeding, based on a high-fat, high-sucrose diet, is related to hypomethylation of this gene in position -90 bp. Under our experimental conditions, both molecules prevent fasn up-regulation, but this change in gene expression seems to be mediated by changes in methylation status only in the case of pterostilbene.