Mouse Skin Tumorigenesis Research Articles

Norathyriol Suppresses Skin Cancers Induced by Solar Ultraviolet Radiation by Targeting ERK Kinases

Ultraviolet (UV) irradiation is the leading factor in the development of skin cancer, prompting great interest in chemopreventive agents for this disease. In this study, we report the discovery of norathyriol, a plant-derived chemopreventive compound identified through an in silico virtual screening of the Chinese Medicine Library. Norathyriol is a metabolite of mangiferin found in mango, Hypericum elegans, and Tripterospermum lanceolatum and is known to have anticancer activity. Mechanistic investigations determined that norathyriol acted as an inhibitor of extracellular signal-regulated kinase (ERK)1/2 activity to attenuate UVB-induced phosphorylation in mitogen-activated protein kinases signaling cascades. We confirmed the direct and specific binding of norathyriol with ERK2 through a cocrystal structural analysis. The xanthone moiety in norathyriol acted as an adenine mimetic to anchor the compound by hydrogen bonds to the hinge region of the protein ATP-binding site on ERK2. Norathyriol inhibited in vitro cell growth in mouse skin epidermal JB6 P+ cells at the level of G(2)-M phase arrest. In mouse skin tumorigenesis assays, norathyriol significantly suppressed solar UV-induced skin carcinogenesis. Further analysis indicated that norathyriol mediates its chemopreventive activity by inhibiting the ERK-dependent activity of transcriptional factors AP-1 and NF-κB during UV-induced skin carcinogenesis. Taken together, our results identify norathyriol as a safe new chemopreventive agent that is highly effective against development of UV-induced skin cancer.

Chk1 is essential for chemical carcinogen-induced mouse skin tumorigenesis

Chk1 is a key regulator of DNA damage checkpoint responses and genome stability in eukaryotes. To better understand how checkpoint proficiency relates to cancer development, we investigated the effects of genetic ablation of Chk1 in the mouse skin on tumors induced by chemical carcinogens. We found that homozygous deletion of Chk1 immediately before carcinogen exposure strongly suppressed benign tumor (papilloma) formation, and that the few, small lesions that formed in the ablated skin always retained Chk1 expression. Remarkably, Chk1 deletion rapidly triggered spontaneous cell proliferation, γ-H2AX staining and apoptosis within the hair follicle, a principal site of origin for carcinogen-induced tumors. At later times, the ablated skin was progressively repopulated by non-recombined Chk1-expressing cells and ultimately normal sensitivity to tumor induction was restored when carcinogen treatment was delayed. In marked contrast, papillomas formed normally in Chk1 hemizygous skin but showed an increased propensity to progress to carcinoma. Thus, complete loss of Chk1 is incompatible with epithelial tumorigenesis, whereas partial loss of function (haploinsufficiency) fosters benign malignant tumor progression.

Myricetin is a potent chemopreventive phytochemical in skin carcinogenesis

Myricetin is a widely distributed flavonol that is found in many plants, including tea, berries, fruits, vegetables, and medicinal herbs. Abundant sources provide interesting insights into the multiple mechanisms by which myricetin mediates chemopreventive effects on skin cancer. Myricetin strongly inhibited tumor promoter-induced neoplastic cell transformation by inhibiting MEK, JAK1, Akt, and MKK4 kinase activity directly. In a mouse skin model, myricetin attenuated the ultraviolet B (UVB)-induced COX-2 expression and skin tumor formation by regulating Fyn. Myricetin-mediated inactivation of Akt in the UVB response plays a role in regulating UVB-induced carcinogenesis. Recently, myricetin was found to inhibit UVB-induced angiogenesis by targeting PI3-K in an SKH-1 hairless mouse skin tumorigenesis model. Raf kinase is a critical target for myricetin in inhibiting the UVB-induced formation of wrinkles and suppression of type I procollagen and collagen levels in mouse skin. Accumulated data suggest that myricetin acts as a promising agent for the chemoprevention of skin cancer.

7,3′,4′-Trihydroxyisoflavone, a Metabolite of the Soy Isoflavone Daidzein, Suppresses Ultraviolet B-induced Skin Cancer by Targeting Cot and MKK4

Nonmelanoma skin cancer is one of the most frequently occurring cancers in the United States. Chronic exposure to UVB irradiation is a major cause of this cancer. Daidzein, along with genistein, is a major isoflavone found in soybeans; however, little is known about the chemopreventive effects of daidzein and its metabolites in UVB-induced skin cancer. Here, we found that 7,3',4'-trihydroxyisoflavone (THIF), a major metabolite of daidzein, effectively inhibits UVB-induced cyclooxygenase 2 (COX-2) expression through the inhibition of NF-κB transcription activity in mouse skin epidermal JB6 P+ cells. In contrast, daidzein had no effect on COX-2 expression levels. Data from Western blot and kinase assays showed that 7,3',4'-THIF inhibited Cot and MKK4 activity, thereby suppressing UVB-induced phosphorylation of mitogen-activated protein kinases. Pull-down assays indicated that 7,3',4'-THIF competed with ATP to inhibit Cot or MKK4 activity. Topical application of 7,3',4'-THIF clearly suppressed the incidence and multiplicity of UVB-induced tumors in hairless mouse skin. Hairless mouse skin results also showed that 7,3',4'-THIF inhibits Cot or MKK4 kinase activity directly, resulting in suppressed UVB-induced COX-2 expression. A docking study revealed that 7,3',4'-THIF, but not daidzein, easily docked to the ATP binding site of Cot and MKK4, which is located between the N- and C-lobes of the kinase domain. Collectively, these results provide insight into the biological actions of 7,3',4'-THIF, a potential skin cancer chemopreventive agent.

Synergistic growth inhibition of mouse skin tumors by pomegranate fruit extract and diallyl sulfide: Evidence for inhibition of activated MAPKs/NF-κB and reduced cell proliferation

Limited outcomes from earlier chemopreventive studies have necessitated that some modifications be made to get better efficacy. It is proposed that cancer prevention is more feasible than treatment, and this could be achieved effortlessly with use of multiple agents competent of targeting multiple targets. This study was initiated to examine the chemopreventive efficacy of pomegranate fruit extract (PFE) and diallyl sulfide (DAS), alone and in combination, using 2-stage mouse skin tumorigenesis model. PFE and DAS alone delayed onset and tumor incidence by ∼55% and ∼45%, respectively, while their combination at low doses synergistically decreased tumor incidence more potentially (∼84%, p<0.01). In addition, regression in tumor volume was seen with continuous combinatorial treatment (p<0.01). Mechanistic studies revealed that this inhibition was associated with decreased expression of phosphorylated ERK1/2, JNK1 and activated NF-κB/p65, IKKα, IκBα phosphorylation and degradation in skin tissue/tumor. Histological and cell death analysis also confirmed that combined PFE and DAS inhibit cellular proliferation and markedly induce apoptosis than the single agents. Altogether, our results suggest that PFE and DAS in combination impart better suppressive activity than either of these agents alone and provide support that development of novel combination therapies/chemoprevention using dietary agents will be more beneficial against cancer.

TRPV1-antagonist AMG9810 promotes mouse skin tumorigenesis through EGFR/Akt signaling

In addition to capsaicin, a transient receptor potential channel vanilloid subfamily 1 (TRPV1) agonist, two kinds of antagonists against this receptor are used as therapeutic drugs for pain relief. Indeed, a number of small molecule TRPV1 antagonists are currently undergoing Phase I/II clinical trials to determine their effect on relieving chronic inflammatory pain and migraine headache pain. However, we previously reported that the absence of TRPV1 in mice results in a striking increase in skin carcinogenesis, suggesting that chronic blockade of TRPV1 might increase the risk of tumor development. In this study, we found that a typical TRPV1 antagonist, AMG9810, promotes mouse skin tumor development. The topical application of AMG9810 resulted in a significant increase in the expression level of the epidermal growth factor receptor (EGFR) and its downstream Akt/mammalian target of rapamycin (mTOR)-signaling pathway. This increase was not only observed in AMG9810-treated tumor tissue but was also found in skin tissue treated with AMG9810. In telomerase-immortalized primary human keratinocytes, AMG9810 promoted proliferation that was mediated through the EGFR/Akt/mTOR-signaling pathway. In summary, our data suggest that the TRPV1 antagonist, AMG9810, promotes mouse skin tumorigenesis mediated through EGFR/Akt/mTOR signaling. Thus, the application of this compound for pain relief might increase the risk of skin cancer.

Chemically Induced Skin Carcinogenesis in Mice and Its Prevention by Aegle marmelos (an Indian Medicinal Plant) Fruit Extract

This study assessed the chemopreventive potential of the Aegle marmelos plant on mouse skin tumorigenesis initiated by 7,12-dimethylbenz(a)anthracene (DMBA) and promoted by croton oil. A significant reduction in tumor incidence, tumor burden, tumor multiplicity, and the cumulative number of papillomas, along with a significant increase in the average latent period, was recorded in mice treated orally with A. marmelos extract (AME) at peri - and post-initiation phases (i.e., 7 days before DMBA application and continued until the end of the experiment) of papillomagenesis as compared with the carcinogen-treated controls. Furthermore, a significant increase in catalase activity, reduced glutathione and total proteins, and a depleted level of lipid peroxidation were observed in liver and skin of AME-treated animals as compared with the carcinogen-treated controls. Thus, the oral administration of AME, at a dose of 50 mg/kg body wt per day per animal, was found to be significantly effective in reducing skin tumors against chemical carcinogenesis in mice.

Enhanced human papillomavirus type 8 oncogene expression levels are crucial for skin tumorigenesis in transgenic mice

Human papillomavirus 8 (HPV8) is involved in skin cancer development in epidermodysplasia verruciformis patients. Transgenic mice expressing HPV8 early genes (HPV8-CER) developed papillomas, dysplasias and squamous cell carcinomas. UVA/B-irradiation and mechanical wounding of HPV8-CER mouse skin led to prompt papilloma induction in about 3 weeks. The aim of this study was to analyze the kinetics and level of transgene expression in response to skin irritations. Transgene expression was already enhanced 1 to 2 days after UVA/B-irradiation or tape-stripping and maintained during papilloma development. The enhanced transgene expression could be assigned to UVB and not to UVA. Papilloma development was thus always paralleled by an increased transgene expression irrespective of the type of skin irritation. A knock-down of E6 mRNA by tattooing HPV8-E6-specific siRNA led to a delay and a lower incidence of papilloma development. This indicates that the early increase of viral oncogene expression is crucial for induction of papillomatosis.

Runx1 Directly Promotes Proliferation of Hair Follicle Stem Cells and Epithelial Tumor Formation in Mouse Skin

Runx1/AML1 is a transcription factor implicated in tissue stem cell regulation and belongs to the small Runx family of cancer genes. In the hair follicle (HF), Runx1 epithelial deletion in morphogenesis impairs normal adult hair homeostasis (cycle) and blocks adult hair follicle stem cells (HFSCs) in quiescence. Here, we show that these effects are overcome later in adulthood. By deleting Runx1 after the end of morphogenesis, we demonstrate its direct role in promoting anagen onset and HFSC proliferation. Runx1 deletion resulted in cyclin-dependent kinase inhibitor Cdkn1a (p21) upregulation. Interfering with Runx1 function in cultured HFSCs impaired their proliferation and normal G(0)/G1 and G(1)/S cell cycle progression. The proliferation defect could be rescued by Runx1 readdition or by p21 deletion. Chemically induced skin tumorigenesis in mice turned on broad Runx1 expression in regions of the skin epithelium, papillomas, and squamous cell carcinomas. In addition, it revealed reduced rates of tumor formation in the absence of Runx1 that were accompanied by decreased epithelial levels of phospho-Stat3. Runx1 protein expression was similar in normal human and mouse hair cycles. We propose that Runx1 may act as a skin oncogene by directly promoting proliferation of the epithelial cells.

Abstract 1871: Honokiol, a natural plant product, inhibits ultraviolet radiation-induced skin tumorigenesis in mice through inhibition of inflammation and inflammatory mediators

Abstract Chronic exposure of solar ultraviolet (UV) radiation is the major etiologic agent for over one million new cases of non-melanoma skin cancers in the US each year. These cutaneous malignancies thus have a tremendous impact on public health and healthcare expenditures. The use of natural plant products has received considerable interest to protect skin from adverse biological effects of UV radiation since the protective clothing and use of sunscreens are not adequate for skin photoprotection. The photoprotective effect of honokiol, a plant product from Magnolia species, therefore assessed using SKH-1 hairless mouse model. To determine the skin cancer chemopreventive effect and associated mechanism of honokiol, a hydrophilic cream based topical formulation was developed. Different groups of mice (n=20) treated with or without honokiol were subjected to photocarcinogenesis protocol. Mice were irradiated to UVB (180 mJ/cm2) three times a week. At the termination of the experiment at 24th week, we found that topical application of honokiol (1mg &amp; 3mg/mouse) inhibited UVB-induced skin tumor development in terms of tumor incidence (10-20%), tumor multiplicity (40-60%) and tumor size (50-75%). Since UV-induced inflammation plays a crucial role in the development of skin tumors, we examined the effect of honokiol on UVB-induced biomarkers of inflammation, such as the expression levels of cyclooxygenase-2 (COX-2), prostaglandins (PG), proliferating cell nuclear antigen (PCNA), infiltration of inflammatory leukocytes, development of edema and epidermal hyperplastic response using immunostaining, western blotting and RT-PCR. Our data revealed that topical application of honokiol before each exposure of UVB radiation resulted in a dose-dependent inhibition of UVB-induced expression of COX-2, PGE2, developments of edema and infiltration of leukocytes at the UVB-irradiated skin sites. Honokiol also inhibited the levels of PCNA (hyperplastic potential) in epidermal keratinocytes of UVB-exposed skin. The inhibitory effects of honokiol on inflammatory mediators were also found in skin tumor samples. The results of this study suggest that honokiol has the ability to inhibit UVB radiation-induced skin tumor development in mice and it is associated with the inhibition of UVB-induced inflammation and inflammatory mediators in mouse skin and skin tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1871.

Abstract 3891: Reduced tumor formation by forced expression of cyclin-dependent kinase 6 in mouse epidermis

Abstract The Cyclin-Dependent kinases (CDKs) are a family of essential serine-threonine kinases that are cell cycle regulated by association with cyclins at specific time-points during the cell cycle. Specifically, D-type cyclins form complexes and activate CDK4 and CDK6. We have previously determined that overexpression of CDK4 in mouse epidermis increases malignant progression in chemically induced skin tumors. In order to study the role of CDK6 in squamous epithelial tissues, we generated transgenic mice overexpressing CDK6, driven by the regulatory sequence of the keratin 5 promoter (K5CDK6). Keratinocytes from K5CDK6 mice have similar levels of proliferation compared to wild type mice, however, contrary to the role of CDK4 in mouse skin tumorigenesis, forced expression of CDK6 results in strong reduction of the multiplicity (papillomas per mouse) and incidence of skin tumors. Tumors derived from K5CDK6 or the wild type sibling show no histological differences nor changes in the rate of malignant progression, suggesting that CDK6 expression affects early stages of skin carcinogenesis. Our previous results have also shown that CDK6 preferentially binds to cyclin D3, which overexpression also decreases tumor development in mouse epidermis. Interestingly, lack of Cyclin D1 produces similar phenotype upon chemical carcinogenesis treatment. Thus, we hypothesize that overexpression of Cyclin D3 or CDK6 in a Cyclin D1-null background should synergize with the reduced tumor development previously observed in cyclin D1-null mice. As expected, a lower number of tumors were found in K5-cyclin D3/cyclin D1−/− compound mice compared to cyclin D1−/− siblings. Thus, we hypothesized that the reduced tumor development observed in these mice is a result of the CDK6/Cyclin D3 complex activity. Consequently, K5-CDK6/cyclin D3−/− compound mice are being generated to investigate whether CDK6-associated tumor inhibition depends on cyclin D3 expression. Only in few cases, CDK6 has been associated with tumorigenesis as compared to CDK4 and CDK2, in particular, no association of CDK6 with epidermal tumors has been reported so far. We propose that CDK6/cyclin D3 complexes play an important role in maintaining normal epidermal homeostasis. Therefore we speculate that upregulation of one or both of its components will block tumor development which could be use as a therapeutic approach. Supported by NIH grant CA116328. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3891.

5-Deoxykaempferol Plays a Potential Therapeutic Role by Targeting Multiple Signaling Pathways in Skin Cancer

Nontoxic small molecules with multitargeting effects are believed to have potential in cancer prevention. Dietary phytochemicals were shown to exhibit cancer-preventive effects attributed to their antioxidant capacities. In this report, we show that the natural compound 5-deoxykaempferol (5-DK) exerts a chemopreventive effect on UVB-induced skin carcinogenesis by targeting multiple signaling molecules. 5-DK suppressed the UVB-induced expression of cyclooxygenase-2 (COX-2) and vascular endothelial growth factor in mouse skin epidermal JB6 P+ cells. Moreover, 5-DK inhibited phosphorylation of MKK3/6, MKK4, and Akt, but had no effect on phosphorylation of Src, extracellular signal-regulated kinases, or ribosomal S6 kinase (RSK). However, 5-DK affected multiple targets by reducing Src, phosphoinositide 3-kinase (PI3K), and RSK2 activities. In particular, pull-down assays revealed that 5-DK specifically bound to and competed with ATP for binding with Src, PI3K, and RSK2. Exposure to 5-DK significantly suppressed UVB-induced tumorigenesis in mouse skin in a dose-dependent manner, and it inhibited the UVB-induced expression of COX-2, proliferating cell nuclear antigen, vascular endothelial growth factor, and matrix metalloproteinase-9. Our data suggest that 5-DK docks at the ATP-binding site of Src, PI3K, and RSK2. For RSK2, the ATP-binding site is located between the N- and C-lobes of the kinase domain. Taken together, our results indicate that 5-DK holds promise for the treatment of UVB-induced skin cancer by targeting Src, PI3K, and RSK2 signaling.

Myricetin inhibits UVB-induced angiogenesis by regulating PI-3 kinase in vivo

Myricetin is one of the principal phytochemicals in onions, berries and red wine. Previous studies showed that myricetin exhibits potent anticancer and chemopreventive effects. The present study examined the effect of myricetin on ultraviolet (UV) B-induced angiogenesis in an SKH-1 hairless mouse skin tumorigenesis model. Topical treatment with myricetin inhibited repetitive UVB-induced neovascularization in SKH-1 hairless mouse skin. The induction of vascular endothelial growth factor, matrix metalloproteinase (MMP)-9 and MMP-13 expression by chronic UVB irradiation was significantly suppressed by myricetin treatment. Immunohistochemical and western blot analyses revealed that myricetin inhibited UVB-induced hypoxia inducible factor-1alpha expression in mouse skin. Western blot analysis and kinase assay data revealed that myricetin suppressed UVB-induced phosphatidylinositol-3 (PI-3) kinase activity and subsequently attenuated the UVB-induced phosphorylation of Akt/p70(S6K) in mouse skin lysates. A pull-down assay revealed the direct binding of PI-3 kinase and myricetin in mouse skin lysates. Our results indicate that myricetin suppresses UVB-induced angiogenesis by regulating PI-3 kinase activity in vivo in mouse skin.

Anticancer Activity of an Indian Medicinal Plant, Alstonia scholaris, on Skin Carcinogenesis in Mice

Alstonia scholaris, commonly known as sapthaparna, has been used for centuries in Ayurvedic medicine for treatment of various disorders. The objective of this study was to investigate the possible chemopreventive and anti-oxidative properties of this medicinal plant on two-stage process of skin carcinogenesis induced by a single application of 7, 12-dimethyabenz(a)anthrecene (100 lg/100 ll acetone), and two weeks later, promoted by repeated application of croton oil (1% in acetone/thrice a week) till the end of the experiment (16 weeks) in Swiss albino mice.The tumor incidence, tumor yield, tumor burden and cumulative number of papillomas were found to be higher in the carcinogen treated control (without ASE treatment) as compared to experimental animals (ASE treated). Furthermore, a significant increase in reduced glutathione, superoxide dismutase and catalase but decrease in lipid peroxidation was measured in ASE administered experimental groups than the carcinogen treated control. The present study demonstrates the chemopreventive potential of Alstonia scholaris bark extract in DMBA-induced skin tumorigenesis in Swiss albino mice.

Induction of apoptosis by [6]-gingerol associated with the modulation of p53 and involvement of mitochondrial signaling pathway in B[a]P-induced mouse skin tumorigenesis.

To unravel the molecular mechanisms underlying the chemopreventive potential of [6]-gingerol, a pungent ingredient of ginger rhizome (Zingiber officinale Roscoe, Zingiberaceae), against benzo[a]pyrene (B[a]P)-induced mouse skin tumorigenesis. Topical treatment of [6]-gingerol (2.5 muM/animal) was given to the animals 30 min prior and post to B[a]P (5 mug/animal) for 32 weeks. At the end of the study period, the skin tumors/tissues were dissected out and examined histopathologically. Flow cytometry was employed for cell cycle analysis. Further immunohistochemical localization of p53 and regulation of related apoptogenic proteins were determined by Western blotting. Chemopreventive properties of [6]-gingerol were reflected by delay in onset of tumorigenesis, reduced cumulative number of tumors, and reduction in tumor volume. Cell cycle analysis revealed that the appearance of sub-G1 peak was significantly elevated in [6]-gingerol treated animals with post treatment showing higher efficacy in preventing tumorigenesis induced by B[a]P. Moreover, elevated apoptotic propensity was observed in tumor tissues than the corresponding non-tumor tissues. Western blot analysis also showed the same pattern of chemoprevention with [6]-gingerol treatment increasing the B[a]P suppressed p53 levels, also evident by immunohistochemistry, and Bax while decreasing the expression of Bcl-2 and Survivin. Further, [6]-gingerol treatment resulted in release of Cytochrome c, Caspases activation, increase in apoptotic protease-activating factor-1 (Apaf-1) as mechanism of apoptosis induction. On the basis of the results we conclude that [6]-gingerol possesses apoptotic potential in mouse skin tumors as mechanism of chemoprevention hence deserves further investigation.

Erbb2 Suppresses DNA Damage-Induced Checkpoint Activation and UV-Induced Mouse Skin Tumorigenesis

The Erbb2 receptor is activated by UV irradiation, the primary cause of non-melanoma skin cancer. We hypothesized that Erbb2 activation contributes to UV-induced skin tumorigenesis by suppressing cell cycle arrest. Consistent with this hypothesis, inhibition of Erbb2 in v-ras(Ha) transgenic mice before UV exposure resulted in both 56% fewer skin tumors and tumors that were 70% smaller. Inhibition of the UV-induced activation of Erbb2 also resulted in milder epidermal hyperplasia, S-phase accumulation, and decreased levels of the cell cycle regulator Cdc25a, suggesting altered cell cycle regulation on inhibition of Erbb2. Further investigation using inhibition or genetic deletion of Erbb2 in vitro revealed reduced Cdc25a levels and increased S-phase arrest in UV-irradiated cells lacking Erbb2 activity. Ectopic expression of Cdc25a prevented UV-induced S-phase arrest in keratinocytes lacking Erbb2 activity, demonstrating that maintenance of Cdc25a by Erbb2 suppresses cell cycle arrest. Examination of checkpoint pathway activation upstream of Cdc25a revealed Erbb2 activation did not alter Ataxia Telangiectasia and Rad3-related/Ataxia Telangiectasia Mutated activity but increased inhibitory phosphorylation of Chk1-Ser(280). Since Akt phosphorylates Chk1-Ser(280), the effect of Erbb2 on phosphatidyl inositol-3-kinase (PI3K)/Akt signaling during UV-induced cell cycle arrest was determined. Erbb2 ablation reduced the UV-induced activation of PI3K while inhibition of PI3K/Akt increased UV-induced S-phase arrest. Thus, UV-induced Erbb2 activation increases skin tumorigenesis through inhibitory phosphorylation of Chk1, Cdc25a maintenance, and suppression of S-phase arrest via a PI3K/Akt-dependent mechanism.

Chemopreventive effect of farnesol on DMBA/TPA-induced skin tumorigenesis: Involvement of inflammation, Ras-ERK pathway and apoptosis

Aims Naturally-derived farnesol has been reported for its chemopreventive and chemotherapeutic efficacy in various cancers. However, the mechanism of action of farnesol is still to be elucidated. The present study demonstrates the chemopreventive potential of farnesol on 9,10-dimethylbenz(a)anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted skin tumorigenesis in Swiss albino mice. Main methods Farnesol at three different doses 25, 50 and 100 mg/kg body weight was topically applied to the mouse skin, 30 min prior to TPA (2 µg/200 µl acetone) to evaluate edema, hyperplasia, expression of cyclooxygenase-2 (COX-2), oxidative stress response and hyperproliferation, and expression of Ras, Raf, p-ERK1/2, Bax and Bcl-2 in DMBA/TPA-induced tumors. Key findings Farnesol at both the low doses significantly reduced the TPA-induced skin edema, hyperplasia, expression of COX-2 and oxidative stress response. Interestingly, higher dose of farnesol did not show any significant response. Pretreatment of farnesol significantly decreased TPA-induced ornithine decarboxylase (ODC) activity and [ 3H]thymidine incorporation in dose-dependent manner. During promotion phase, farnesol with higher dose significantly regressed tumor incidence and tumor burden with an extension of latency period of 4–8 weeks. More importantly, low doses of farnesol significantly inhibited Ras/Raf/ERK1/2 signaling pathway in mouse skin tumors whereas higher dose of farnesol induced the pathway. Moreover, farnesol at all doses altered Bax/Bcl-2 ratio which leads to induction of apoptosis as confirmed by DNA fragmentation. Significance These findings revealed that oxidative stress, inflammation, Ras/Raf/ERK1/2 pathway and apoptosis collectively played a crucial role in the chemopreventive activity of farnesol to inhibit the murine skin tumorigenesis.

Bromelain inhibits COX-2 expression by blocking the activation of MAPK regulated NF-kappa B against skin tumor-initiation triggering mitochondrial death pathway

Chemoprevention impels the pursuit for either single targeted or cocktail of multi-targeted agents. Bromelain, potential agent in this regard, is a pharmacologically active compound, present in stems and fruits of pineapple ( Ananas cosmosus), endowed with anti-inflammatory, anti-invasive and anti-metastatic properties. Herein, we report the anti tumor-initiating effects of bromelain in 2-stage mouse skin tumorigenesis model. Pre-treatment of bromelain resulted in reduction in cumulative number of tumors (CNT) and average number of tumors per mouse. Preventive effect was also comprehended in terms of reduction in tumor volume up to a tune of ∼65%. Components of the cell signaling pathways, connecting proteins involved in cell death were targeted. Bromelain treatment resulted in upregulation of p53 and Bax and subsequent activation of caspase 3 and caspase 9 with concomitant decrease in Bcl-2. A marked inhibition in cyclooxygenase-2 (Cox-2) expression and inactivation of nuclear factor-kappa B (NF-κB) was recorded, as phosphorylation and consequent degradation of Iκ Bα was blocked by bromelain. Also, bromelain treatment curtailed extracellular signal regulated protein kinase (ERK1/2), p38 mitogen-activated protein kinase (MAPK) and Akt activity. The basis of anti tumor-initiating activity of bromelain was revealed by its time dependent reduction in DNA nick formation and increase in percentage prevention. Thus, modulation of inappropriate cell signaling cascades driven by bromelain is a coherent approach in achieving chemoprevention.

Effect of phosphodiesterase antagonists on glucocorticoid mediated growth inhibition in murine skin cell lines

The effects of two cyclic nucleotide phosphodiesterase type 4 (PDE4) inhibitors on proliferation of cell lines representing different stages of mouse skin tumorigenesis were studied. Skin papillomas and carcinomas become resistant to the growth inhibition by glucocorticoids. Their control of cellular functions is mediated by a well-known transcription factor, glucocorticoid receptor. The primary aim of the present study was to determine whether the PDE4 inhibitors, that raise intracellular cAMP levels, can increase the sensitivity of mouse skin papillomas and carcinomas to the glucocorticoids. We sought to establish the effect of cAMP signaling on the glucocorticoid receptor function using well-known model representing non-tumorigenic keratinocyte cell line (3PC), papilloma (MT1/2) and squamous cell carcinoma cell line (Ca3/7). These cells were treated with the glucocorticoid fluocinolone acetonide (FA) alone or in concert with PDE4 inhibitors – rolipram or YM976. Results of our study revealed that both PDE4 inhibitors may increase the sensitivity of transformed cell lines to the growth inhibitory effect of FA. In the transformed cell lines, changes in the viability of cells were accompanied by an increase in mRNA level of two negative regulators of the cell cycle – p21 and p27 proteins. Co-treatment with PDE4 inhibitors and FA caused inhibition of an endogenous glucocorticoid-responsive gene (MT-1) expression. Thus, the PDE4 inhibitors exerted a differential effect on non-transformed and transformed keratinocytes and on glucocorticoid receptor signal transduction. These findings warrant further studies to clarify the mechanism by which PDE4 inhibitors modulate glucocorticoid receptor signal transduction in transformed cells.

Inhibitory effects of oligonol on phorbol ester-induced tumor promotion and COX-2 expression in mouse skin: NF-κB and C/EBP as potential targets

Plant polyphenols possess anti-oxidant and anti-inflammatory activities and are hence potential candidates for preventing cancer. The present study was aimed at evaluating the anti-inflammatory and anti-tumor promoting activity of oligonol, a formulation of catechin-type oligomers, in mouse skin stimulated with a proto-type tumor promoter 12- O-tetradecanoylphorbol-13-acetate (TPA). Pretreatment of mouse skin with oligonol significantly inhibited TPA-induced expression of cyclooxygenase-2 (COX-2). Oligonol diminished nuclear translocation and DNA binding of nuclear factor-kappaB (NF-κB) via blockade of phosphorylation and subsequent degradation of IκBα in TPA-treated mouse skin. Moreover, oligonol suppressed TPA-induced DNA binding of CCAAT/enhancer-binding protein (C/EBP) in mouse skin. Oligonol pretreatment also attenuated the phosphorylation and/or catalytic activities of extracellular signal-regulated protein kinase-1/2 (ERK1/2) and p38 mitogen-activated protein (MAP) kinase. Moreover, p38 MAP kinase inhibitor SB203580, but not the MEK inhibitor U0126, negated TPA-induced DNA binding of C/EBP. In addition, oligonol reduced the incidence and the multiplicity of papillomas and squamous cell carcinomas in 7,12-dimethylbenz[ a]anthracene (DMBA)-initiated and TPA-promoted mouse skin, and prolonged the survival of tumor-bearing mice. Pretreatment with oligonol diminished the levels of proliferating cell nuclear antigen and expression of COX-2 in papillomas and carcinomas, respectively, as compared to DMBA plus TPA treatment alone. Taken together, the above findings suggest that oligonol inhibits TPA-induced COX-2 expression by blocking the activation of NF-κB and C/EBP via modulation of MAP kinases and suppresses chemically induced mouse skin tumorigenesis.