Photochemoprevention of ultraviolet B signaling and photocarcinogenesis

Mutation Research 571 (2005) 153–173

Review

Photochemoprevention of ultraviolet B signaling and photocarcinogenesis Farrukh Afaq, Vaqar M. Adhami, Hasan Mukhtar∗ Department of Dermatology, University of Wisconsin, Medical Sciences Center, Room #B25, 1300 University Avenue, Madison, WI 53706, USA Received 28 June 2004; accepted 8 July 2004 Available online 23 January 2005

Abstract Exposure to solar radiation, particularly its ultraviolet (UV) B component, has a variety of harmful effects on human health. Some of these effects include sunburn cell formation, basal and squamous cell cancers, melanoma, cataracts, photoaging of the skin, and immune suppression. Amongst these various adverse effects of UV radiation, skin cancer is of the greatest concern. Over the years, changes in lifestyle has led to a significant increase in the amount of UV radiation that people receive, and this consequently has led to a surge in the incidence of skin cancer. The development of skin cancer is a complex multistage phenomenon involving three distinct stages exemplified by initiation, promotion and progression stages. Each of these stages is mediated via alterations in various cellular, biochemical, and molecular changes. Initiation, the first step in the carcinogenesis process is essentially an irreversible step in which genetic alterations occur in genes that ultimately leads to DNA modification and fixation of mutation. Tumor promotion is the essential process in cancer development involving clonal expansion of initiated cells giving rise to pre-malignant and then to malignant lesions, essentially by alterations in signal transduction pathways. Tumor progression involves the conversion of pre-malignant and malignant lesions into an invasive and potentially metastatic malignant tumor. All these processes for skin cancer development involve stimulation of DNA synthesis, DNA damage and proliferation, inflammation, immunosuppression, epidermal hyperplasia, cell cycle dysregulation, depletion of antioxidant defenses, impairment of signal transduction pathways, induction of cyclooxygenase, increase in prostaglandin synthesis, and induction of ornithine decarboxylase. Photochemoprevention has been appreciated as a viable approach to reduce the occurrence of skin cancer and in recent years, the use of agents, especially botanical antioxidants, present in the common diet and beverages consumed by human population have gained considerable attention as photochemopreventive agents for human use. Many such agents have also found a place in skin care products. Although this is more common in oriental countries, its popularity is significantly growing in western countries. In this article, we have summarized the available information of laboratory studies on UVB-mediated signaling that can be exploited as targets for photochemoprevention. We suggest that the use of skin care products supplemented

∗

Corresponding author. Tel.: +1 608 263 3927; fax: +1 608 263 5223. E-mail address: [email protected] (H. Mukhtar).

0027-5107/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mrfmmm.2004.07.019

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with proven chemopreventive agents in conjunction with the use of sunscreens along with educational efforts may be an effective strategy for reducing UV-induced photodamage and skin cancer in humans. The mechanistic basis for the use of such products is discussed. © 2004 Elsevier B.V. All rights reserved. Keywords: Photochemoprevention; Ultraviolet radiation; Signal transduction; p53; PI3K/AKT; NF-␬B; AP1; MAPK; COX-2; ODC

Contents 1.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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2.

Mechanism of photochemoprevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.

Cellular signaling molecules as targets for photochemoprevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. UVB-mediated inflammation and immunosuppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1. Effect of photochemopreventive agents on UVB-mediated inflammation and immunosuppression . 3.2. Effect of UVB on apoptosis, p53 and cell cycle regulatory molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1. Modulatory effect of photochemopreventive agents on UVB-mediated apoptosis, p53 and Cell cycle regulatory molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. UVB-mediated induction of phosphotidylinositol 3-kinase/Akt pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1. Phosphotidylinositol 3-kinase/Akt pathway as a target for photochemoprevention . . . . . . . . . . . . . . . 3.4. UVB-mediated induction of nuclear factor-kappa B pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1. Nuclear factor-kappa B pathway as a target for photochemoprevention . . . . . . . . . . . . . . . . . . . . . . . . . 3.5. UVB-mediated induction of activator protein-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1. Activator protein-1 as a target for photochemoprevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6. UVB-mediated induction of mitogen-activated protein kinases pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6.1. Mitogen-activated protein kinases pathway as a target for photochemoprevention. . . . . . . . . . . . . . . . 3.7. UVB-mediated induction of cyclooxygenases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7.1. Cyclooxygenases as a target for photochemoprevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8. UVB-mediated induction of ornithine decarboxylase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8.1. Ornithine decarboxylase as a target for photochemoprevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Conclusions and future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4.

1. Introduction In the United States, alone 1.2 million new cases of skin cancer are identified each year, and this accounts for 40% of all new cancer cases that are diagnosed [1,2]. Solar ultraviolet (UV) B radiation has been implicated as the main cause for skin cancer. UV radiation in sunlight is divided into three regions depending on wavelength, short-wave UVC (200–280 nm), mid-wave UVB (280–320 nm) and long-wave UVA (320–400 nm). UVC has the highest energy and, hence, is the most biologically damaging region of UV radiation. However, UVC in solar radiation is filtered out

by ozone layer of the Earth’s atmosphere, and therefore, its role in human pathogenesis is minimal. Both UVB, and to a lesser extent, UVA radiation are responsible as a causative factor for various skin disorders including skin cancer [3–6]. Because greater than 90% of the solar radiation at the earth’s surface is UVA (320–400 nm), in recent years, the role of UVA in skin carcinogenesis has begun to be appreciated. It has become clear that UVA accounts for at least 10% of the carcinogenic dose of the sunlight. The non-melanoma skin cancers (NMSCs) comprising of basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs), are the most frequently diagnosed

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cutaneous malignancies and account for approximately 80 and 16% of all skin cancers, respectively, whereas malignant melanomas account for only 4% of all skin cancers. Both BCCs and SCCs are derived from the basal layer of the epidermis of the skin. SCCs are invasive, and more than 10% of these cancers metastasise. On the other hand, BCCs do not metastasize but can be locally invasive and destructive [7–9]. In the year 2004, 55,100 newly diagnosed cases of melanoma, resulting in ∼7910 deaths are expected to occur, while 2340 deaths are expected to occur from non-epithelial skin cancers [10]. Less common but more aggressive forms of skin cancer include Kaposi’s sarcoma and cutaneous T-cell lymphoma. Considerable body of evidence suggests that SCCs and BCCs are the most frequently diagnosed cutaneous malignancies and occur primarily on sun-exposed areas of the body and have been strongly associated with chronic sun exposure [3–5,9,11]. For primary prevention of photodamage and cutaneous disease, education about the harmful effects of UV radiation present in the sunlight, the need to avoid its excessive exposure by wearing protective clothing, and the use of sunscreen has been emphasized, but for many reasons, these primary prevention approaches have had limited success [9,11]. Therefore, additional efforts are needed to prevent skin cancers that result as a consequence of UVB exposure. Because skin cancer is a significant problem associated with mortality and morbidity concerted efforts are needed to develop novel strategies for the prevention of UV responses. One such approach to ameliorate the occurrence of skin cancer is through chemoprevention, which by definition is a means of cancer control in which the occurrence of the disease can be entirely prevented, slowed or reversed by topical or oral administration of naturally occurring or synthetic compound or their mixtures [9,11,12]. These chemopreventive compounds are known to be anti-mutagenic, anticarcinogenic and non-toxic, and have the ability to exert striking inhibitory effects on diverse cellular events associated with multistage carcinogenesis. For chemoprevention of photodamages including photocarcinogenesis, we have coined the term ‘photochemoprotection’ [11,13]. These photochemopreventive agents for human use should have the ability to ameliorate the adverse biological effects of UV radiation. The skin, situated at the interface between the body and its environment, directly suffers from the deleteri-

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ous effects of UV radiation. This UV radiation jeopardizes the integrity of the skin that is critical for cellular homeostasis. UV radiation results in an increased generation of reactive oxygen species (ROS) that overwhelms the antioxidant defense mechanisms of the target system. This condition of prooxidant/antioxidant disequilibrium is defined as ‘oxidative stress’. The epidermis is composed mainly of keratinocytes, which are rich in ROS detoxifying enzymes, such as superoxide dismutase, catalase, thioredoxin reductase, and glutathione peroxidase, and in low-molecular-mass antioxidant molecules, such as tocopherol, glutathione and ascorbic acid, and thus provides some natural protection against ROS [14–16]. Skin spontaneously responds to increased ROS levels; however, this response may not be sufficient to prevent the progression of skin cancer. Studies have shown that UV radiation to the skin results in the formation of ROS that interact with proteins, lipids and DNA [17–19]. UV radiation to mammalian skin is known to alter cellular function via DNA damage [20–22], generation of ROS [23–25], and the resultant alterations in a variety of signaling events [9,23,26–28]. The cause of these events is contingent upon the UV dose, time of exposure and the wavelength. Studies have demonstrated that oxidative stress elicited by UV irradiation activates redoxsensitive transcription factors, including nuclear factorkappa B (NF-␬B) [27–29], and members of the activator protein-1 (AP-1) complex, such as c-Fos and c-Jun [30,31]. The development of skin cancer is a complex multistage phenomenon involving three-distinct stages initiation–promotion–progression-mediated via various cellular, biochemical, and molecular changes. Initiation, the first step in the carcinogenesis process is essentially an irreversible step in which genetic alterations occur in genes that changes the response of initiated basal stem cells of the epidermis. Tumor promotion is the process that involves clonal expansion of initiated cells giving rise to pre-malignant and malignant lesions, essentially by alterations in signal transduction pathways. Tumor progression involves the conversion of pre-malignant and malignant lesions into an invasive and potentially metastatic malignant tumor. To name a few, these processes entail: (i) stimulation of DNA synthesis, DNA damage, and proliferation, (ii) inflammation, (iii) immunosuppression, (iv) epidermal hyperplasia, (v) cell cycle dysregulation, (vi) deple-

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Fig. 1. Three modes of action of photochemopreventive agents.

tion of antioxidant defenses, (vii) impairment of signal transduction pathways, (viii) induction of cyclooxygenase, (ix) increase in prostaglandin synthesis, and (x) induction of ornithine decarboxylase [9,11,32]. In this article, we have summarized the available information based on laboratory studies on the effects of UV radiation on cellular signaling (Figs. 1 and 2). We have further dealt in detail on the use of photochemopreventive agents and how they could be exploited to

target signaling molecules for photochemoprevention of UVB-mediated adverse effects.

2. Mechanism of photochemoprevention In recent years, photochemoprevention has matured into an accepted modality for controlling skin cancer. Although photochemoprevention can be achieved by

Fig. 2. UVB-induced signaling pathways and critical targets for photochemopreventive agents.

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intervention at initiation or promotion phases of skin tumorigenicity for a variety of reasons; for example, availability of sunscreens to prevent penetration of UV radiation, anti-tumor promoting agents appear to have greater likelihood for success in humans. Thus, it is important to identify mechanism-based effective novel anti-tumor-promoting agents. One of the excitements of photochemoprevention is that agents can be targeted for intervention at the initiation, promotion, or progression stage of the multistage photocarcinogenesis process. Tumor initiation is a rapid and irreversible process in which genetic alterations occur in genes that changes the response of initiated basal stem cells of the epidermis. UVB exposure initiates a cascade of events that modify gene expression profiles and alters the immune system of the skin. UVB irradiation to the skin has direct effects on biomolecules; for example, the formation of cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photodimers [33], photoisomerization of trans-to cis-urocanic acid [34], DNA strand break, DNA crosslinks, DNA-protein crosslinks and generation of reactive oxygen species [20,21,24,35]. Formation of cyclobutane pyrimidine dimers, if not repaired through nucleotide excision repair, replication leads to signature mutations. These mutations are in the form of C to T and CC to TT transition and have been observed in tumor suppressor gene p53 in large population of human SCCs, BCCs and actinic keratosis. Therefore, strategies to prevent initation process by intervention are difficult to envision. In contrast, tumor promotion is considered to be relatively lengthy process that involves clonal expansion of initiated cells giving rise to pre-malignant and malignant lesions, essentially by alterations in signal transduction pathways. Tumor progression involves the conversion of pre-malignant and malignant lesions into an invasive and potentially metastatic malignant tumor. Therefore, the intervention of cancer at the promotion stage seems to be more appropriate and practical. The major reason for this relates to the fact that tumor promotion is a reversible event at least in the early stages and requires repeated and prolonged exposure of a promoting agent [36]. In addition, the tumor promotion is an obligatory step in the carcinogenic pathway, where clonal expansion of initiated cell population occurs leading to what is termed as progress towards malignancy. Furthermore, the long latency period between the initiation and promotion stages of cancer offers large windows of

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opportunities for intervention before malignant tumors develop [37–39]. This has raised the credibility of photochemoprevention as a serious and practical approach to the control of skin cancer in the past few years.

3. Cellular signaling molecules as targets for photochemoprevention 3.1. UVB-mediated inflammation and immunosuppression Inflammation that includes the release of growth factors, proinflammatory cytokines, infiltration of inflammatory cells, and ROS production, plays an important role in skin cancer development. Chronic UVBmediated inflammation causes the induction of the Cyclooxygenase-2 (COX-2) enzyme in the skin, resulting in increased prostaglandin levels, inflammatory cell infiltration and activation, and further oxidant production [40,41]. Cyclobutane pyrimidine dimers are primarily produced in keratinocytes and Langerhans cells following UVB exposure, and also in dendritic cells in lymph nodes draining the irradiated sites [42]. The macrophages are CD1a− CD11b+ , while Langerhans cells are CD1a+ CD11b− [43]. They produce high levels of IL-10 and low levels of IL-12, and express different co-stimulatory molecules from Langerhans cells, thereby promoting suppressed immune responses in the skin. 3.1.1. Effect of photochemopreventive agents on UVB-mediated inflammation and immunosuppression UV-induced erythema in humans have been shown to be reduced following supplementation with an antioxidant combination that includes ␤-carotene, Vitamins C and E [44]. Studied have also revealed that topical application of green tea polyphenol (GTP) extracts following UV radiation also reduced erythema in humans [45]. Recent studies by Lee et al. [46] demonstrated that dietary supplementation of lutein reduces tissue swelling induced by UVB radiation and inhibits the UV-induced immunosuppressive effects. This study also suggests that lutein was found to accumulate in the skin following diet supplementation and decreases the production of ROS in skin following UVB. Oral feeding of green tea polyphenol

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to SKH-1 hairless mice, followed by irradiation with UVB, resulted in significant protection against UVB radiation-mediated cutaneous edema; depletion of the antioxidant-defense system in the epidermis; induction of epidermal ODC and COX-2 enzyme activities that play an important role in cutaneous inflammation and tumor promotion [47]. We have also demonstrated that topical application of major green tea polyphenol epigallocatechin 3-gallate (EGCG) (3 mg/mouse/3 m2 of skin area) to C3H/HeN mice, before a single dose of UVB (90 mJ/cm2 ) irradiation, decreases hydrogen peroxide and nitric oxide synthase-expressing cells and inhibits hydrogen peroxide and nitric oxide production both in the dermis and epidermis [48]. Stern and Dobson [49] have demonstrated that in human sunburn reactions can be treated successfully by nonsteroidal anti-inflammatory agents. Studies by Athar et al. [50] have shown that topical application of sulindac (1.25–5.0 mg/0.2 ml acetone) to the dorsal skin of SKH-1 hairless mice before or immediately after UVB exposure substantially inhibited inflammatory responses including erythema, edema, epidermal hyperplasia, infiltration of polymorphonuclear leukocytes in a dose-dependent manner. Oral administration of sulindac in drinking water (160 ppm) for 15 days before and during UVB irradiation similarly reduced these inflammatory responses. Studies by Wilgus et al. [40] have show that topical application of celecoxib reduced UVB-mediated inflammation, including edema, dermal myeloperoxidase activity, neutrophil infiltration, and prostaglandin E2 (PGE2 ) levels. Studies have demonstrated that blocking leukocytes using anti-CD 11b antibody or treatment with complement receptor type-1 blocked UV-induced immune suppression and tolerance induction in C3H/HeN mice [51,52]. Topical application of EGCG to the mouse skin prior to UV irradiation was found to result in inhibition of contact hypersensitivity response to contact sensitizer, reduction in the number of infiltrating macrophages and neutrophils (CD11b+ cells), downregulation in UV-induced production of interleukin-10 (IL-10) and increased production of IL-12 in the skin and draining lymph nodes [53]. Production of IL-12, the main mediator, and adjuvant of contact hypersensitivity have been shown to be increased in the draining lymph nodes to enhance T helper cell type 1 functions. EGCG was found to balance the alterations in the IL-10/IL-12 cytokines [53]. This may be mediated

by the antigen presenting cells in the skin and draining lymph nodes or by blocking the infiltration of IL10 secreting CD11b+ macrophages into the irradiated site. EGCG also inhibited the migration, depletion or death of APC’s when detected as class II MHC+ Ia+ cells and a significantly decreased dermal and epidermal H2 O2 and NO production [53]. These data, in concert with other data, suggest that application of green tea polyphenol to human skin reduces inflammation and inhibits formation of several mediators that are involved in immunosuppression that plays an important role in skin cancer development. 3.2. Effect of UVB on apoptosis, p53 and cell cycle regulatory molecules Apoptosis, a discrete way of cell death distinct from necrotic cell death, is regarded as an ideal way of elimination of damaged cells [54]. It is now well accepted that uncontrolled cellular growth, which may be a result of defects in cell cycle and apoptotic machinery, is responsible for the development of most of the cancers including skin cancer. Therefore, to maintain the integrity of the cells after DNA damage, several cellular responses are activated that include mechanisms for removal of DNA damage, delay in cell cycle, and DNA repair or apoptosis by transcriptional activation of p53-related genes, such as p21waf1/cip1 , MDM2, and Bax [55–58]. The p53 tumor suppressor gene plays a decisive role in protecting cells from DNA-damage as a consequence of UVB exposure [59–64]. It has also been suggested that p53 can play direct and indirect role in UVB-induced, transcription-coupled DNA repair [65]. An important function of p53 protein is to act as a transcription factor by binding to a p53-specific DNA consensus sequence in responsive genes [66,67]. The increased level of p53 protein after DNA damage is also associated with enhanced apoptosis, presumably in those cells that are too damaged for adequate DNA repair [66,68]. Several studies have demonstrated a transient stimulatory effect of UV light on the level of wild-type p53 in cultured cells and in mouse and human epidermis [60,61,69]. High doses of UVB has been shown to be associated with the formation of sunburn cells, initiated via a p53-dependent pathway, and causes the removal of damaged cells, thus minimizing the risk of skin cancer [70]. Lower doses of UVB allow cell survival and repair of genetic damage, but the

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cell survival response is a state of local and systemic immuno-suppression, which in itself may be deleterious and contribute to process of formation of skin cancers [71]. In addition, phosphorylation of p53 by DNA-protein kinase that is induced by ionizing radiation prevents MDM-2 from inhibiting p53-dependent transactivation [72]. These results indicate that DNAprotein kinase both activate p53 binding to DNA and block p53 inactivation by MDM2. Mutations in the p53 gene have been detected in 50% of all human cancers and in almost all skin carcinomas [73]. Studies have shown that early responses in the skin of SKH-1 mice after an acute UVB exposure include increased number of cells expressing both p21 and p53 [62]. Exposure of SKH-1 mice to chronic UVB dose resulted in modulation of the expression of cell cycle markers, with increased expression of p53 and cyclin D1 correlating with the development of skin tumors [74]. It has been suggested that increased expression of cyclin D1 in SCCs contributes to the tumor phenotype even in the presence of elevated p53 levels. Studies have also demonstrated that elevated cyclin D1 expression occurs in squamous carcinoma and papillomas [75], while decreased expression leads to reduce skin carcinogenesis [76]. SCCs developed in SKH-1 mice after chronic exposure to UVB showed increase in cyclin D1 protein levels. However, expression of dominant negative c-jun (TAM67) mutant transgene significantly reduced cyclin D1 protein expression in UVB-induced squamous cell carcinoma samples but did not modulate basal levels of cyclin D1 in the untreated transgenic mouse skin [77]. Kim et al. [74] reported that the overexpression of cyclin D1 correlates with skin tumor progression, and the onset of cyclin D1 accumulation coincides with the sudden increase in the number of tumors per animal. Because of the persistent expression of cyclin D1 during UVB-induced murine skin carcinogenesis, cyclin D1 might contribute to the neoplastic process by providing a growth advantage during the early stages of tumor promotion. This study also suggested that UVB-mediated responses observed in murine skin parallel those reported in human skin cancer development. These studies are clarifying that alterations in cyclin D1 expression are important in human skin carcinogenesis caused by chronic sun exposure. Studies have demonstrated that p53−/− murine skin has an increased sensitivity to UV radiation and fewer apoptotic cells [70]. Additionally p53−/− mice

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develop more aggressive tumors than their wild type or heterozygous counterparts [78]. Studies have shown that overexpression of P16INK4A reduces the proliferation of human and murine squamous epithelial cells [79]. Transcriptional upregulation of p16INK4A has also been shown in melanoma cells following UVB irradiation [80]. Induction of P16INK4A in human keratinocytes was reported in human epidermis and in cultured keratinocytes after UVB irradiation [81,82]. Studies have demonstrated that p16INK4A , and p14ARF−/− mice also develop epidermoid skin tumors either spontaneously or after UV radiation [83]. UV-induced mutations of p16INK4A and p14ARF genes have been reported in epithelial skin tumors from sporadic patients and from Xeroderma Pigmentosum patients, who suffer from strong UV hypersensitivity [84]. All these data suggest that the p53, p16INK4A , p21waf1/ci , p1 , and p14ARF proteins are part of parallel pathways controlling cell cycle and response to UV-DNA damage. Recent studies have demonstrated that induction of p16INK4A takes place at the posttranscriptional level in keratinocytes and participates in both the acute and adaptative response to UVB [85]. 3.2.1. Modulatory effect of photochemopreventive agents on UVB-mediated apoptosis, p53 and Cell cycle regulatory molecules Studies have demonstrated that oral administration of green tea or caffeine to SKH-1 mice enhanced UV-induced increases in the number of p53-positive cells, p21waf1/cip1 -positive cells, and apoptotic sunburn cells in the epidermis [86]. This implies that the photochemopreventive effects of tea and caffeine on UVinduced carcinogenesis may be mediated through stimulation of UV-induced increases in the number of p53positive cells, p21waf1/cip1 -positive cells, and apoptotic sunburn cells. In addition, Lu et al. [87] have also shown that oral feeding of green tea, black tea and caffeine decreases the size and the thickness of the dermal fat layer under tumors, signifying that green tea and caffeine may decrease tumor multiplicity in part by decreasing fat levels in the dermis. Apigenin treatment of mouse skin keratinocytes was also found to induce p21waf1/cip1 protein and cause stabilization of p53 protein and G2/M phase arrest [88]. More recently, McVean et al. [89] have shown that G2/M arrest induced by apigenin in these cell lines was due to inhibition of the p34cdc2 cyclin-dependent kinase protein level and activity, in-

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dependent of p21waf1/cip1 . Studies have demonstrated that treatment of HaCaT cells with silibinin prevented UVB-induced apoptosis. Consistent with its protective effect on UVB-caused apoptosis, this study further suggests silibinin also increased S phase arrest, possibly providing a prolonged time for efficient DNA repair [90]. Recently, it has been demonstrated that resveratrol imparts cancer chemopreventive effects against multiple UVB exposure-mediated modulations in the cki–cyclin–cdk network and mitogen-activated protein kinases (MAPK) pathway [91]. A study on human volunteers, showed that topical application of GTP 30 min prior to UVB exposure resulted in significantly less erythema and less production of cyclobutane pyrimidine dimer in both dermal and epidermal layers of the skin [45]. Reduction in CPD formation is likely due to protection of the DNA repair enzymes from inactivation by ROS. Collectively, from these data, it seems that GTP or EGCG have major roles to play in affording protection against UVinduced damage in human skin. Their first role is to act as antioxidants, whereby they quench ROS generated in the skin. Their second role is to modulate signal transduction pathways in a manner that results in reduced damage. Bush et al. [92] recently demonstrated that curcumin induces apoptosis in human melanoma cells through a cell membrane-mediated mechanism independent of the p53 pathway, by Fas receptor induction and caspase-8 activation. Jee et al. [93] have shown that curcumin induces apoptosis in BCC cells, by increasing p53, p21waf1/cip1 and Gadd45 protein levels in a doseand time-dependent manner. This study suggested that curcumin induction of apoptosis may be due to modulation of protein kinase-related signaling pathways. In terms of cell cycle regulators, silibinin treatment caused an induction of p21waf1/cip1 and p27kip1 together with a significant decrease in cyclin-dependent kinase CDK4, CDK-2, and cyclin D1 [94]. Ahmad et al. [95] have recently shown that treatment of human epidermoid carcinoma A431 cells with resveratrol resulted in Gl-phase cell cycle arrest and induction of apoptosis. In addition, resveratrol treatment to A431 cells leads to dose- and time-dependent (i) induction of p21waf1/cip1 ; (ii) decrease in the protein expressions of cyclin Dl, cyclin D2 and cyclin E; (iii) decrease in the expression of cdk2, cdk4, and cdk6 proteins. She et al. [96] have demonstrated that

resveratrol-induced activation of p53 and apoptosis is mediated by extracellular-signal-regulated protein kinases and p38 kinase in a mouse JB6 epidermal cell line. Experiments employing various skin tumor models found that topical or oral administration of GTP protects against UVB-induced skin carcinogenesis [24,48,97]. The polyphenol EGCG was also found to protect against UVB-induced skin damage and epidermal lipid peroxidation in guinea pig skin [98]. Topical application of apigenin prior to UV-exposure was shown to be effective in preventing UV-induced mouse skin tumorigenesis [99]. This manifested in reduction in cancer incidence and an increase in tumor free survival. 3.3. UVB-mediated induction of phosphotidylinositol 3-kinase/Akt pathway Akt, also known as protein kinase B, is a serine/threonine kinase containing a pleckstrin homology domain at its amino terminus and acts as a key protein mediator for a wide range of cellular processes [100]. Several studies have revealed that activation of Akt by various stimuli, including growth factors, insulin, and hormones, is mediated by phosphorylation of both Ser473 and Thr308 residues through a phosphatidylinositol 3-kinase (PI3K)-dependent mechanism [101,102]. PI3K is a heterodimeric lipid kinase that consists of a p85 regulatory subunit and a p110 catalytic subunit. Activation of the Akt signaling pathway reduces apoptosis in many cell types [103]. Upon phosphorylation, Akt modulates diverse downstream signaling pathways associated with cell survival, proliferation, differentiation, migration, and apoptosis. UVB radiation results in the activation of EGFR that triggers the phosphorylation of the protein kinase B (PKB/Akt) that is involved in mediating cell survival [104]. Studies have also demonstrated that UV radiation generates H2 O2 that in turn phosphorylates Akt at Ser473 and Thr308 and playd an important role in UV-induced carcinogenesis [105]. Recent studies have shown that UVB irradiation activates Akt in primary human keratinocytes, and this activation is mediated by epidermal growth factor receptor (EGFR)/phosphotidylinositol 3-kinase (PI3K). Furthermore, these studies also suggest that Akt blocks UVB-induced apoptosis by blocking mitochondrial cytochrome c release, preventing the activation of

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procaspase-3, -8, and -9 in human keratinocytes [106]. Briehl and co-workers [107] have demonstrated that two malignant variants (6M90 and 6R90) of the mouse keratinocyte 308 cell line have elevated levels of ROS that resulted in an increase in resistance to UVBinduced apoptosis. This resistance was due to basal increases of Akt phosphorylation in the malignant variants compared to the 308 cells. Modulation of ROS in the two malignant variants by catalase overexpression or antioxidant treatment has been shown to result in decreased levels of Akt phosphorylation and subsequent loss of resistance to UVB-induced apoptosis. Conversely, there results also demonstrate that treatment of 308 cells with hydrogen peroxide caused increases in Akt phosphorylation and increased apoptosis resistance.

repair mechanism more time to work [110]. Studies by Nomura et al. [111] have demonstrated that EGCG from green tea and theaflavins from black tea inhibited the activation of PI3K and also attenuated the activation of Akt and p70 S6-K, downstream effectors of PI3K, by inhibiting PI3K and extracellular signal-regulated kinases (ERK) activation in UVB signaling. Furthermore, this study also suggests that these polyphenols directly blocked UVB-induced p70 S6-K activation. EGCG was further shown to inhibit c-Fos, a key component of activator protein 1 transcription factor in cultured human epidermal keratinocyte (HaCaT) irradiated with UVB.

3.3.1. Phosphotidylinositol 3-kinase/Akt pathway as a target for photochemoprevention Studies have demonstrated that human papillomavirus type 16 (HPV16) E5 protein associated with the EGFR enhances the activation of the EGFR after stimulation by EGF in human keratinocytes. The results from this study indicate that HPV16 E5, in the presence of EGF, can act as a stress-resistant factor, which keeps the Akt levels elevated in UVB-irradiated human keratinocytes, and therefore, E5-expressing cells are protected from UVB-irradiation-induced apoptosis [108]. Studies have revealed that topical application of wortmannin to K5. Bcl-xL−/− mice sensitized the skin to apoptosis induced by UVB, although wild-type epidermis was only marginally affected by this treatment. This study suggests that the resistance to UVBinduced apoptosis largely depended on PI3K-Akt signaling in Bcl-xL-deficient mice but not in wild-type mice. Furthermore, UVB irradiation resulted in relocation of phosphorylated Akt from the basal layer to the suprabasal layer, demonstrating that Akt could spatially cooperate with Bcl-xL upon UVB exposure in the upper epidermis, where Bcl-xL is normally localized. These results further suggest that Bcl-xL and the PI3KAkt pathway form a cooperative, intercompensatory axis for the protection of epidermal keratinocytes from apoptosis in vivo [109]. Studies have shown that insulin growth factor-1 delays the onset of apoptosis through activation of the Akt signaling pathway after UVB irradiation that contributes to increased cell survival by postponing the induction of apoptosis, giving the DNA

Nuclear Factor-kappa B (NF-␬B) is a ubiquitously expressed transcription factor that belongs to the Rel family and regulates genes involved in inflammation, immunity, cell cycle progression, apoptosis, and oncogenesis [112,113]. In mammals, the Rel family comprises p50, p52, p65 (RelA), RelB, and c-Rel. The most abundant form of NF-␬B is the heterodimer of p50 and p65 that is retained in the cytoplasm as an inactive complex through association with specific inhibitory protein termed I␬B [114]. NF-␬B can be activated by a wide range of stimuli including UV light, inflammatory cytokines, phorbol esters, lipopolysaccharide, and a variety of mitogens [114]. Studies have shown that these stimuli activate I␬B kinases (IKK) either directly or indirectly and are central to NF-␬B activation [115,116]. The activated IKK phosphorylates the inhibitory ␬B proteins on either serine residues 32 and 36 of I␬B␣ or serine residues 19 and 23 of I␬B␤ for degradation by proteasomes [117,118]. The released heterodimer then moves from the cytoplasm to the nucleus, where both p50 and p65 contribute to NF-␬B DNA binding and stimulate transcription of target genes [119].

3.4. UVB-mediated induction of nuclear factor-kappa B pathway

3.4.1. Nuclear factor-kappa B pathway as a target for photochemoprevention Studies have demonstrated that EGCG inhibited constitutive expression and TNF-␣-mediated activation of NF-␬B in A431 cells more efficaciously than in normal human epidermal keratinocytes (NHEK) [120]. Recently, we have shown that EGCG protects against the adverse effects of UV radiation via modulation of

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the NF-␬B pathway. We found that the treatment of NHEK with EGCG (10–40 ␮M) for 24 h resulted in inhibition of UVB (40 mJ/cm2 )-mediated degradation and phosphorylation of I␬B␣ and activation of IKK␣ in a dose- and time-dependent manner [28]. Our data suggest that EGCG protects against the adverse effects of UV radiation via modulations in NF-␬B pathway, and provide molecular basis for the photochemopreventive effect of EGCG. To investigate, the relevance of these in vitro findings to the in vivo situations in SKH-l hairless mouse model, we found that topical application of GTP after multiple UVB exposure resulted in inhibition of UVB-induced: (i) activation of NF-␬B, (ii) activation of IKK␣, and (iii) phosphorylation and degradation of I␬B␣ [27]. In another study from our laboratory, we have shown that pre-treatment of NHEK with resveratrol inhibits UVB-mediated activation of NF␬B pathway [121]. Supplementation of antioxidants alpha-lipoic acid, N-acetyl-l-cysteine (NAC) and the flavonoid extract silymarin modulate the activation of the transcription factors NF-␬B and AP-1 in HaCaT keratinocytes after exposure to a solar UV simulator. In this study, a high concentration of NAC could achieve a complete inhibition, while low concentrations of alphalipoic acid and silymarin were shown to significantly inhibit NF-␬B activation. In contrast, in this study, AP1 activation was only partially inhibited by NAC and not at all by alpha-lipoic acid or silymarin. These results indicate that antioxidants, such as alpha-lipoic acid and silymarin can efficiently amend the cellular response to UV radiation through their selective action on NF-␬B activation [122]. Studies have demonstrated that UVinduced activation of NF-␬B-dependent gene transactivation pathways is a critical event for the subsequent development of sunburn reactions in skin. In addition, it was also shown that by using systemic, local, or topical administration of oligodeoxynucleotides (ODNs) containing the NF-␬B cis-element (NF-␬B decoy ODNs) reduced the severity of experimentally induced sunburn reactions, as assessed by ear swelling, histological changes, and the accumulation of proinflammatory cytokines [123]. Furthermore, studies by Beg et al. [124] and Klement et al. [125] revealed that deficiency in I␬B␣ gene resulted in severe dermatitis with leukocyte infiltration, signifying a pathway through which NF-␬B activation directly leads to skin inflammation. Oral supplementation of procyanidin-rich French maritime

pine bark extract pycnogenol was shown to protect human skin from solar UV simulated light-induced erythema. In addition, treatment of human keratinocyte cell line HaCaT with pycnogenol inhibited UV-induced NF-␬B-dependent gene expression in a concentrationdependent manner. However, no effect on NF-␬BDNA-binding activity was observed by PBE, suggesting that it affects the transactivation capacity of NF␬B [126]. Kim et al. [127] have shown that EGCG inhibits UVB-induced NF-␬B binding activity both under in vivo and in vitro situations. Fisher et al. [128] have demonstrated the maintenance of NF-␬B and AP1 activation for longer period (8–24 h) in human skin exposed to UVB. Topical application of glycolic acid on SKH-1 hairless mice immediately after UVB radiation inhibited UVB-induced activation of NF-kB and AP-1. Furthermore, a decreased expression of the cell-cycle regulatory proteins proliferating cell nuclear antigen (PCNA), cyclin D1, cyclin E, cdk2, and cdk4 and the signal mediators JNK, p38 kinase, and MEK was also observed that play an important role on UVBinduced skin tumor development [129]. Supplementation of the antioxidant vitamin, alpha-tocopherol, and its acetate analog, alpha-tocopherol acetate, on UVBinduced damage in primary and neoplastic mouse keratinocytes (308 cells) significantly inhibited NF-␬B activation. These results suggest that Vitamin E and its acetate analog can modulate the cellular response to UVB partly through their action on NF-␬B activation [130]. 3.5. UVB-mediated induction of activator protein-1 Activator protein-1 transcription factor is a protein dimer that consists of either heterodimers between fos and jun family gene products or homodimers of jun family gene products [9]. There are three Jun proteins (c-Jun, Jun B and Jun D) and four Fos proteins (c-Fos, Fos B, Fra-1 and Fra-2). There is growing evidence that the AP-1 family of proteins are involved in cell proliferation and survival by regulating the expression and function of a number of cell cycle regulatory proteins, such as cyclin D1, p53, p21, p19 and p16 [131]. Studies have shown that sublethal doses of UVB produce strong induction of c-jun and c-fos transcripts in several cells including human primary keratinocytes [132]. Studies have demonstrated that increased c-fos gene expression

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correlated with UVB induced AP-1 activation in HaCaT cells. This study suggested that c-fos expression might play a key role in UVB induced AP-1 activation in human keratinocytes [133,134]. 3.5.1. Activator protein-1 as a target for photochemoprevention Treatment of HaCaT cells with EGCG inhibited UVB induced c-fos gene expression and AP-1 activation [133]. From these studies, it appears that cfos could be a target gene for chemoprevention of skin cancer. Further, using the human keratinocyte cell line HaCaT, it was shown that EGCG is effective in inhibiting AP-1 activity when these cells were treated before, after or both before and after UVB irradiation [134]. UVB-induced AP-1 activation was also found to be suppressed by theaflavins and this was accompanied by suppression of ERK and JNK [135]. Studies have shown that iron-driven generation of hydroxyl radicals and lipid peroxides substantially affects JNK2 activity and c-jun transcription, two key steps of the signaling pathway, leading to matrix metalloprotinases-1 (MMP-1) and MMP-3 mRNA induction after UVB irradiation [136]. Studies have demonstrated that proteinase inhibitor I (Inh I) and proteinase inhibitor II (Inh II) from potato tubers effectively block UV irradiation-induced activation of AP-1 in mouse JB6 epidermal cells [137]. Furthermore, these investigators have shown that Inh I and Inh II up-regulated AP-1 constituent proteins, JunD and Fra-2, and suppressed c-Jun and c-Fos expression in response to UVB stimulation [138]. More recently, study by Ding et al. [139] have revealed that apple peel extract inhibited UVB-induced AP-1 activation both in vivo and in vitro, possibly by interfering with signal transduction events involving MAPK, ERKs and JNK suggesting that these pathways may be a unifying mechanism by which it inhibits carcinogenesis and tumor growth. Recently, Cooper et al. [78] have demonstrated that a dominant negative c-jun (TAM67) mutant transgene expressed in the epidermis of SKH-1 mice inhibited UVB-induced AP-1 activation and delayed and reduced UVB-induced squamous cell carcinoma incidence. Studies have also demonstrated that topical application of sodium salicylate and acetylsalicylic acid inhibited UVB-induced activation of AP-1 that correlated with inhibition of skin tumor formation [140]. In another study, deferroxamine an iron chelator

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inhibited UVB-induced AP-1 transactivation. The antioxidants trolox and NAC also inhibited UVB-induced AP-1 transactivation and trolox was able to inhibit the potentiation of UVB-induced AP-1 by FeCl3 [141]. Barthelman et al. [142] have shown that topical application of monoterpene perillyl alcohol inhibited UVBinduced AP-1 transactivation both under in vitro and in vivo situations. These studies suggest that AP-1 is an important target for the development of new photochemopreventive strategies to prevent UVB-induced skin cancer. 3.6. UVB-mediated induction of mitogen-activated protein kinases pathway Mitogen-activated protein kinases encompass a large number of serine/threonine kinases involved in regulating a wide array of cellular processes including proliferation, differentiation, stress adaptation, and apoptosis. The MAPKs are divided into three multimember subfamilies: the extracellular signal-regulated kinases, the c-Jun N-terminal kinases (JNK), and the p38 kinases. Studies have shown that ERK, JNK, and p38 subfamilies are activated in response to oxidant injury, and therefore, could potentially contribute to influence cell survival. Studies have shown that exposure of human keratinocytes to physiologic doses of ultraviolet B activates EGFR/ERK1/2 and p38 signaling pathways via ROS generation [143,144]. Studies by Assefa et al. [132] revealed that sublethal doses of UVB are potent inducers of the JNK/SAPK family of mitogen-activated protein kinases but only weak activators of ERKs. Studies have suggested that low-dose UVB irradiation of normal human skin induces rapid and reversible phosphorylation of JNK and p38. Furthermore, the expression of involucrin and skin-derived anti-leukoproteinase (SKALP)/elafin, two genes putatively under control of the c-jun and p38 pathways, were found to be increased [145]. Studies by Chen and Bowden [146] have demonstrated that both p38 and ERK were required for UVB induced c-fos expression in human keratinocytes HaCaT. Inhibition of both p38 and ERK simultaneously completely abrogated UVB induced c-fos transcription and down regulated basal transcription of the c-fos gene. These results suggest that p38 and ERK might serve as valuable molecular targets for chemoprevention of skin cancer.

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3.6.1. Mitogen-activated protein kinases pathway as a target for photochemoprevention Supplementation of antioxidant N-acetylcysteine has been shown to impair the UVB-induced activation of JNK [132]. Recently, Nomura et al. [147] showed that pre-treatment of JB6 Cl 41 cells with green tea polyphenol EGCG or black tea derived theaflavins inhibited UVB-induced phosphatidylinositol 3-kinase activation. Treatment of human epidermoid carcinoma A431 cells with silibinin was found to result in a significant decrease in ERK1/2 levels, and an up-regulation JNK1/2 and p38 MAPK activation [148]. This study suggested that an inhibition of ERK1/2 activation and an increased activation of JNK 1/2 and p38 by silibinin could be possible underlying molecular events involved in inhibition of proliferation and induction of apoptosis in epidermoid A431 cancer cells. Another study using the same cells, found that silibinin inhibits the activation of the EGF receptor and the downstream adapter protein Shc. Silibinin also showed a marked inhibition of MAPK-ERK 1/2 activation [149]. Studies have shown that trolox, a water-soluble Vitamin E analog, inhibits both basal and UVB-induced intracellular H2 O2 generation in primary keratinocytes in a concentration-dependent manner. However, trolox did not significantly affect UVB-induced phosphorylation of EGFR. Stronger inhibition was observed for ERK1/2 activation at lower, and for p38 activation at higher, concentrations of trolox added to cells before exposure to UVB. Trolox also potently suppressed UVB-induced c-jun-N-terminal kinase activation. These studies suggest that UVB-induced signaling pathway activation is differentially modulated by trolox [150]. Studies have demonstarated that both in HaCaT cells and in NHEK ascorbate was able to inhibit the AP-1-dependent transactivation of specific promoters by modulating fra-1 expression and preventing the phosphorylation of the JNK, thus inhibiting phosphorylation of the endogenous c-Jun protein. These data suggest that ascorbate mediates cellular responses by counteracting UV-mediated cell damage and cell death by interfering at multiple levels with the activity of the JNK/AP-1 pathway and modulating the expression of AP-1-regulated genes [151]. Recently, Haes et al. [152] have demonstrated that treatment of keratinocytes with 1,25-dihydroxyvitamin D3 inhibited UVB-mediated JNK activation and IL-6 production. Studies from our laboratory have shown that EGCG

and GTP inhibited UVB-induced phosphorylation of MAPK in NHEK and SKH-1 hairless mice [27,28]. 3.7. UVB-mediated induction of cyclooxygenases Cyclooxygenases are rate-limiting enzymes that catalyze the conversion of arachidonic acid to prostaglandins that are involved in many normal and pathophysiological responses [153,154]. Of the two known COX enzymes, COX-1 is constitutively expressed in nearly all cells, whereas COX-2 is primarily considered an inducible immediate-early gene product [155]. UV irradiation of epidermal cells [156], mouse skin [157], and human skin [158] has been shown to induce COX-2 protein expression. Prostaglandin production in the skin following UV irradiation occurs as a result of both an increased release of arachidonic acid by phospholipases and also by the induction of COX-2 message and protein levels [159]. While prostaglandins, such as PGE2 are necessary for a variety of normal biological processes, elevated levels of PGE2 resulting from increased expression of COX-2 have been linked with the carcinogenetic process thus contributing to the uncontrolled proliferation of damaged cells that ultimately form tumors in the skin [157,160,161]. COX-2 overexpression and elevated PGE2 levels have been demonstrated in both pre-malignant skin lesions and skin cancers, as well as skin cancer cell lines [154,160,162,163]. In addition, levels of COX-2 activity seem to increase with invasive potential and seriousness of skin tumors, with normal skin having very low levels of COX-2 and PGE2 , pre-malignant human actinic keratosis lesions having increased levels of COX-2 and PGE2 , and squamous cell carcinomas having the highest levels of detectable COX-2 and PGE2 [154,163]. 3.7.1. Cyclooxygenases as a target for photochemoprevention Cyclooxygenases are the targets for a group of drugs known as non-steroidal anti-inflammatory drugs (NSAIDs). Studies have linked the anti-cancer effects of NSAIDs with their inhibition of the COX-2 enzyme and the subsequent restoration of apoptosis, reduced tumor mitogenesis, and decreased angiogenesis [164–166]. Oral administration of the COX-2 inhibitor celecoxib has been shown to prevent the formation of skin tumors in three separate murine mod-

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els of UV-induced skin cancer [167]. Recent studies have documented the ability of oral or topical delivery of celecoxib to suppress UV-induced skin cancer formation in hairless mice [167,168]. Majority of photocarcinogenesis studies have examined the effects of COX-2 inhibition as a chemopreventive approach, and some studies have even tested COX-2 inhibitors for their therapeutic effects against skin cancers in mouse models [40]. Recent studies have demonstrated that celecoxib can prevent cancer cell growth via a COX2-independent mechanism [169], and that the structure of celecoxib can be modified chemically such that it has no anti-inflammatory properties but still induces apoptosis [170]. This activity of celecoxib may explain the PGE2 -independent decrease in PCNA seen in the skin. Since studies have shown that topical treatment with celecoxib effectively decreases cutaneous inflammation [168], it is possible that this treatment modality may, by blocking the inflammatory response, decrease the conversion of benign actinic keratotic lesions to cancerous ones. Although topical celecoxib alone does not induce regression of established skin tumors, it may prove to be an effective treatment for inhibiting progression of actinic keratotic lesions as well as in preventing the development of recurring tumors at sites of excision. Studies by Wilgus et al. [171] have demonstrated that topical treatment with chemotherapeutic agent 5-fluorouracil (5-FU) and the COX-2 inhibitor and anti-inflammatory drug celecoxib together to murine model of UVB-induced carcinogenesis was 70% more effective in reducing the number of UVBinduced skin tumors than 5-FU treatment alone. Topical application of sericin to SKH-1 hairless mice was shown to significantly suppress UVB-induced expression of COX-2 protein, and proliferating cell nuclear antigen-labeling index [172]. Studies have shown that NSAIDs can block mitogen-induced AP-1 activity and transactivation [156]. Considering the important role of AP-1 in tumoroigensis, the inhibition of AP-1 is likely to be one of the major mechanisms involved in non-steroidal antiinflammatory drugs chemopreventive effects. Piroxicam, a general COX inhibitor, and NS-398, a COX-2 selective inhibitor, effectively suppressed the activation of transcription factor AP-1 induced by UVB in mouse epidermal JB6 cells. UVB significantly increased AP-1 activity in Cox-2−/− fibroblasts transfected with an AP1 luciferase reporter gene, and this increase was found

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to be blocked by NS-389 or piroxicam. In JB6, Cox2−/− , or wild-type Cox-2+/+ cells, both NS-398 and piroxicam inhibited UVB-induced phosphorylation of c-Jun NH2-terminal kinases, the kinases that activate the AP-1–c-Jun complex. These observations do suggest that the inhibition of AP-1 activity by COX-2 inhibitors NS-398 or piroxicam may occur by a mechanism that is independent of COX-2. 3.8. UVB-mediated induction of ornithine decarboxylase ODC, the first and the rate-limiting enzyme in the biosynthesis of polyamines plays an important role in the regulation of cell proliferation and development of cancer [173]. Enzymatic decarboxylation of the dibasic amino acid, ornithine, by ODC is the first and generally regarded as the rate-limiting step in the biosynthesis of the polyamines: putrescine, spermidine, and spermine [173]. In its active form, ODC is a dimer of two identical units of 51 kDa. Even though the precise intracellular functions of the polyamines remain incompletely defined, accumulation of cellular polyamines has been shown to be essential for the growth, proliferation and differentiation of both normal and neoplastic tissue. All eukaryotic cells contain one or more of the polyamines and their concentrations vary during the cell cycle progression. Several lines of evidence indicate that aberrations in ODC regulation, and subsequent polyamine accumulation are intimately associated with neoplastic transformation [174]. Elevated levels of ODC gene products are consistently detected in transformed cell lines, virtually all-animal tumors, and in certain tissues predisposed to tumorigenesis [175]. Studies have described that overexpression of ODC dramatically increases the transforming activity of a mutated ras gene in R6 fibroblasts [176] and results in the transformation of immortalized NIH 3T3 cells [177]. Studies have also demonstrated that growth induction of normal cells is accompanied by a rapid, transient increase in ODC activity, whereas cell transformation induced by oncogenes, such as v-src [178], neu [179], and ras [180] is associated with constitutively elevated ODC activity. The up-regulation of ODC may be needed for transformation. Furthermore, overexpression of ODC by itself (under the control of strong promoters) can induce transformation of immortalized rodent fibroblasts [176] and keratinocytes [181]. Besides, targeted over-

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expression of ODC in keratinocytes of transgenic mice induces spontaneous skin tumors [182]. 3.8.1. Ornithine decarboxylase as a target for photochemoprevention Studies from our laboratory using K5/ODC expressing mice have established a definite role of ODC in photocarcinogenesis. In the same study, ODC transgenic mice were also included, which following the last UVB exposure, were given difluoromethyl ornithine (DFMO) (1%, w/v) in the drinking water. None of the ODC transgenic mice were found to develop any kind of skin tumor. Because DFMO is an irreversible inhibitor of ODC, these data further confirmed that ODC plays a key role in photocarcinogenesis [183]. Indeed, v-src-induced cell transformation can be prevented by overexpression of ODC anti-sense mRNA [175] or by treatment of the cells with DFMO, an irreversible inhibitor of ODC [175]. A recent study has shown that DFMO, a selective inhibitor of ODC possesses both preventive and therapeutic properties against the development of UV carcinogenesis in SKH-1 hairless mice [184]. This is a notable example, where ODC has been suggested as a target for inhibition of cell proliferation. Another study has shown that topical application of DFMO in humans is capable of reducing the number of actinic keratoses lesions and skin spermidine concentrations in high-risk individuals [185]. Topical application of apigenin has been shown to inhibit UVmediated induction of ODC activity in SKH-1 hairless mice [99]. Previous studies from our laboratory have shown that topical application of GTP [186], silymarin [160], and resveratrol [161] inhibits UVB-mediated activation of ODC activity and protein expression. Recent studies have shown that UVB irradiation to Ptch1+/− mice overexpressing ODC by using keratin 6 promoter that direct constitutive ODC expression accelerated induction of BCC in these mice as compared to their Ptch1+/− mice littermates. Importantly, oral administration of the suicidal ODC inhibitor DFMO was found to reduce UVB-induced BCC in these Ptch1+/− mice overexpressing ODC. These results demonstrate the crucial importance of ODC for the induction of BCC and indicate that chemopreventive strategies directed at inhibiting this enzyme may be useful in reducing BCC in human populations [187]. Collectively, these observations suggest that ODC represents a promising and rational target for photochemoprevention.

4. Conclusions and future directions Over the years, changes in lifestyle have led to a significant increase in the amount of UVB radiation that people receive, and this consequently has led to a surge in the incidence of skin cancer. For primary prevention of photodamage and cutaneous disease, education about the harmful effects of UV radiation present in the sunlight, the need to avoid its excessive exposure by wearing protective clothing, and the use of sunscreen has been emphasized, but for many reasons, these primary prevention approaches have had limited success. Therefore, additional efforts are needed to prevent skin cancers that result as a consequence of UVB exposure. Many signaling molecules and pathways have been found to play a role in UVB induced skin damages. UVB radiation to mammalian skin is known to alter cellular function via DNA damage, generation of ROS, and the resultant alterations in a variety of signaling events. Of particular has been the activation of redox-sensitive transcription factors, including NF-␬B, and members of the AP-1 complex, such as c-Fos and c-Jun. Studies have also established a role for MAPKs and the PI3K/Akt signaling in UVB-induced COX-2 expression and have demonstrated increased sensitivity to UV radiation in p53 null mice. Although many signaling events are known to be modulated by UV light, additional studies are needed to define molecules upstream of MAPKs. One approach to ameliorate the UVB light-induced photo damages is through chemoprevention. Accumulated data consistently support the view that many agents, with antioxidant properties, exert antiinflammatory and anti-carcinogenic effects in skin. This suggests the possibility that specific agents might be used to target defined and established molecular events for the prevention and treatment of a variety of human skin disorders. The use of these agents alone or in the form of a formulation could be developed for chemoprevention. Skin care products supplemented with botanicals, in conjunction with the use of sunscreens and educational efforts may be an effective approach for reducing UVB-generated ROS-mediated photodamage, inflammatory responses, and skin cancer in humans. Because of the role of UVB in cutaneous damage, the agent(s) that can protect against these radiations could be ideal photochemoprotective agent(s) for the skin.

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References [1] S.L. Parker, T. Tong, S. Bolden, P.A. Wingo, Cancer statistics, 1997, CA Cancer J. Clin. 47 (1997) 5–27. [2] T.M. Johnson, O.M. Dolan, T.A. Hamilton, M.C. Lu, N.A. Swanson, L. Lowe, Clinical and histologic trends of melanoma, J. Am. Acad. Dermatol. 38 (1998) 681–686. [3] F.R. De Gruijil, H.J.C.M. Sterenborg, P.D. Forbes, R.E. Davies, C. Cole, G. Kelfkens, H. van Weelden, H. Slaper, J.C. van der Leun, Wavelength dependence of skin cancer induction by ultraviolet irradiation of albino hairless mice, Cancer Res. 53 (1993) 53–60. [4] M. Goihman-Yahr, Skin aging and photoaging: an outlook, Clin. Dermatol. 14 (1996) 153–160. [5] A.R. Young, Cumulative effects of ultraviolet radiation on the skin: cancer and photoaging, Semin. Dermatol. 9 (1990) 25–31. [6] M.A. Bachelor, G.T. Bowden, UVA-mediated activation of signaling pathways involved in skin tumor promotion and progression, Semin. Cancer Biol. 14 (2004) 131–138. [7] R.E. Kwa, K. Campana, R.L. Moy, Biology of cutaneous squamous cell carcinoma, J. Am. Acad. Dermatol. 26 (1992) 1–26. [8] S.J. Miller, Biology of basal cell carcinoma: part I, J. Am. Acad. Dermatol. 24 (1991) 1–13. [9] G.T. Bowden, Prevention of non-melanoma skin cancer by targeting ultraviolet-B-light signaling, Nat. Rev. Cancer 4 (2004) 23–35. [10] A. Jemal, R.C. Tiwari, T. Murray, A. Ghafoor, A. Samuels, E. Ward, E.J. Feuer, M.J. Thun, American Cancer Society, Cancer statistics, 2004, CA Cancer J. Clin. 54 (2004) 8–29. [11] F. Afaq, V.M. Adhami, N. Ahmad, H. Mukhtar, Botanical antioxidants for chemoprevention of photocarcinogenesis, Front. Biosci. 7 (2002) d784–d792. [12] H. Mukhtar, N. Ahmad, Cancer chemoprevention. Future holds in multiple agents: contemporary issues in toxicology, Toxicol. Appl. Pharmacol. 158 (1999) 207–210. [13] N. Ahmad, H. Mukhtar, Cutaneous photochemoprevention by green tea: a brief review, Skin. Pharmacol. Appl. Skin Physiol. 14 (2001) 69–76. [14] F. Afaq, H. Mukhtar, Effects of solar radiation on cutaneous detoxification pathways, J. Photochem. Photobiol. B 63 (2001) 61–69. [15] M. Ichihashi, M. Ueda, A. Budiyanto, T. Bito, M. Oka, M. Fukunaga, K. Tsuru, T. Horikawa, UV-induced skin damage, Toxicology 189 (2003) 21–39. [16] S. F’guyer, F. Afaq, H. Mukhtar, Photochemoprevention of skin cancer by botanical agents, Photodermatol. Photoimmunol. Photomed. 19 (2003) 56–72. [17] T.R. Berton, D.L. Mitchell, S.M. Fischer, M.F. Locniskar, Epidermal proliferation but not the quantity of DNA photodamage is correlated with UV-induced mouse skin carcinogenesis, J. Invest. Dermatol. 109 (1997) 340–347. [18] G. Li, D.L. Mitchell, V.C. Ho, J.C. Reed, V.A. Tron, Decreased DNA repair but normal apoptosis in ultraviolet-irradiated skin of p53-transgenic mice, Am. J. Pathol. 148 (1996) 1113–1123. [19] M.J. Peak, A. Ito, C.S. Foote, J.G. Peak, Photosensitized inactivation of DNA by monochromatic 334-nm radiation in the

[20]

[21]

[22]

[23]

[24]

[25]

[26] [27]

[28]

[29]

[30]

[31]

[32]

[33]

167

presence of 2-thiouracil: genetic activity and backbone breaks, Photochem. Photobiol. 47 (1988) 809–813. H.S. Black, F.R. deGruijl, P.D. Forbes, J.E. Cleaver, H.N. Ananthaswamy, E.C. deFabo, S.E. Ullrich, R.M. Tyrrell, Photocarcinogenesis: an overview, J. Photochem. Photobiol. B 40 (1997) 29–47. H.N. Ananthaswamy, W.E. Pierceall, Molecular alterations in human skin tumors, Prog. Clin. Biol. Res. 376 (1992) 61– 84. S.K. Katiyar, A. Perez, H. Mukhtar, Green tea polyphenol treatment to human skin prevents formation of ultraviolet light B-induced pyrimidine dimers in DNA, Clin. Cancer Res. 10 (2000) 3864–3869. S.K. Katiyar, F. Afaq, K. Azizuddin, H. Mukhtar, Inhibition of UVB-induced oxidative stress-mediated phosphorylation of mitogen-activated protein kinase signaling pathways in cultured human epidermal keratinocytes by green tea polyphenol (−)-epigallocatechin-3-gallate, Toxicol. Appl. Pharmacol. 176 (2001) 110–117. S.K. Katiyar, F. Afaq, A. Perez, H. Mukhtar, Green tea polyphenol (−)-epigallocatechin-3-gallate treatment of human skin inhibits ultraviolet radiation-induced oxidative stress, Carcinogenesis 22 (2001) 287–294. C.S. Sander, H. Chang, F. Hamm, P. Elsner, J.J. Thiele, Role of oxidative stress and the antioxidant network in cutaneous carcinogenesis, Int. J. Dermatol. 43 (2004) 326–335. Y.J. Surh, Cancer chemoprevention with dietary phytochemicals, Nat. Rev. Cancer 3 (2003) 768–780. F. Afaq, N. Ahmad, H. Mukhtar, Suppression of UVB-induced phosphorylation of mitogen-activated protein kinases and nuclear factor-kappa B by green tea polyphenol in SKH-1 hairless mice, Oncogene 22 (2003) 9254–9264. F. Afaq, V.M. Adhami, N. Ahmad, H. Mukhtar, Inhibition of ultraviolet B-mediated activation of nuclear factor-kappaB in normal human epidermal keratinocytes by green tea constituent (−)-epigallocatechin-3-gallate, Oncogene 22 (2003) 1035–1044. M. Djavaheri-Mergny, M.P. Gras, J.L. Mergny, L. Dubertret, UV-A-induced decrease in nuclear factor-kappaB activity in human keratinocytes, Biochem. J. 338 (1999) 607– 613. K. Isoherranen, J. Westermarck, V.M. Kahari, C. Jansen, K. Punnonen, Differential regulation of the AP-1 family members by UV irradiation in vitro and in vivo, Cell Signal. 10 (1998) 191–195. K. Kramer-Stickland, A. Edmonds, W.B. Bair 3rd, G.T. Bowden, Inhibitory effects of deferoxamine on UVB-induced AP1 transactivation, Carcinogenesis 20 (1999) 2137–2142. Y. Matsumura, H.N. Ananthaswamy, Toxic effects of ultraviolet radiation on the skin, Toxicol. Appl. Pharmacol. 195 (2004) 298–308. G.P. Pfeifer, S.D. Steigerwald, R.S. Hansen, S.M. Gartler, A.D. Riggs, Polymerase chain reaction-aided genomic sequencing of an X chromosome-linked CpG island: methylation patterns suggest clonal inheritance, CpG site autonomy, and an explanation of activity state stability, Proc. Natl. Acad. Sci. U.S.A. 87 (1990) 8252–8256.

168

F. Afaq et al. / Mutation Research 571 (2005) 153–173

[34] F.P. Noonan, E.C. De Fabo, Immunosuppression of ultraviolet B radiation: initiation by urocanic acid, Immunol. Today 13 (1992) 250–254. [35] L.H. Kligman, F.J. Akin, A.M. Kligman, Sunscreens prevent ultraviolet photocarcinogenesis, J. Am. Acad. Dermatol. 3 (1980) 30–35. [36] S.K. Katiyar, R.R. Mohan, R. Agarwal, H. Mukhtar, Protection against induction of mouse skin papillomas with low and high risk of conversion to malignancy by green tea polyphenols, Carcinogenesis 18 (1997) 497–502. [37] F. Marks, G. Furstenberger, Cancer chemoprevention through interruption of multistage carcinogenesis: the lessons learnt by comparing mouse skin carcinogenesis and human large bowel cancer, Eur. J. Cancer 36 (2000) 314–329. [38] G.D. Stoner, M.A. Morse, G.J. Kelloff, Perspectives in cancer chemoprevention, Environ. Health Perspect. 105 (1997) 945–954. [39] H. Fujiki, M. Suganuma, A. Komori, J. Yatsunami, S. Okabe, T. Ohta, E. Sueoka, A new tumor promotion pathway and its inhibitors, Cancer Detect. Prev. 18 (1994) 1–7. [40] T.A. Wilgus, M.L. Parrett, M.S. Ross, K.L. Tober, F.M. Robertson, T.M. Oberyszyn, Inhibition of ultraviolet light B-induced cutaneous inflammation by a specific cyclooxygenase-2 inhibitor, Adv. Exp. Med. Biol. 507 (2002) 85–92. [41] M. Athar, K.P. An, K.D. Morel, A.L. Kim, M. Aszterbaum, J. Longley, E.H. Epstein Jr., D.R. Bickers, Ultraviolet B (UVB)induced cox-2 expression in murine skin: an immunohistochemical study, Biochem. Biophys. Res. Commun. 280 (2001) 1042–1047. [42] Y. Sontag, C.L.H. Guikers, A.A. Vink, F.R. de Gruijil, H. van Loveren, J. Garssen, L. Roza, M.L. Kripke, J.C. van der Leun, W.A. van Vloten, Cells with UV-specific DNA damage are present in murine lymph nodes after in vivo UV irradiation, J. Invest. Dermatol. 104 (1995) 734–738. [43] L. Meunier, Z. Csorgo, K.D. Cooper, In human dermis, ultraviolet radiation induces expansion of a CD36+ CD11b+ CD1− macrophage subset by infiltration and proliferation: CD1+ Langerhans-like antigen-presenting cells are concomitantly depleted, J. Invest. Dermatol. 105 (1995) 782– 788. [44] A.K. Greul, J.U. Grundmann, F. Heinrich, I. Pfitzner, J. Bernhardt, A. Ambach, H.K. Biesalski, H. Gollnick, Photoprotection of UV-irradiated human skin: an antioxidative combination of Vitamins E and C, carotenoids, selenium and proanthocyanidins, Skin Pharmacol. Appl. Skin. Physiol. 15 (2002) 307–315. [45] C.A. Elmets, D. Singh, K. Tubesing, M. Matsui, S. Katiyar, H. Mukhtar, Cutaneous photoprotection from ultraviolet injury by green tea polyphenols, J. Am. Acad. Dermatol. 44 (2001) 425–432. [46] H.E. Lee, D. Faulhaber, K.M. Hanson, W. Ding, S. Peters, S. Kodali, R.D. Granstein, Dietary lutein reduces ultraviolet radiation-induced inflammation and immunosuppression, J. Invest. Dermatol. 122 (2004) 510–517. [47] R. Agarwal, S.K. Katiyar, S.G. Khan, H. Mukhtar, Protection against ultraviolet B radiation-induced effects in the skin of

[48]

[49] [50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58] [59]

[60]

[61]

SKH-1 hairless mice by a polyphenolic fraction isolated from green tea, Photochem. Photobiol. 58 (1993) 695–700. S.K. Katiyar, H. Mukhtar, Green tea polyphenol (−)epigallocatechin-3-gallate treatment to mouse skin prevents UVB-induced infiltration of leukocytes, depletion of antigen presenting cells, and oxidative stress, J. Leukoc. Biol. 69 (2001) 719–726. R.S. Stern, T.B. Dobson, Ibuprofen in the treatment of UV-Binduced inflammation, Arch. Dermatol. 121 (1985) 508–512. M. Athar, K.P. An, X. Tang, K.D. Morel, A.L. Kim, L. Kopelovich, D.R. Bickers, Photoprotective effects of sulindac against ultraviolet B-induced phototoxicity in the skin of SKH-1 hairless mice, Toxicol. Appl. Pharmacol. 195 (2004) 370–378. C. Hammerberg, S.K. Katiyar, M.C. Carroll, K.D. Cooper, Activated complement component 3 (C3) is required for ultraviolet induction of immunosuppression and antigenic tolerance, J. Exp. Med. 187 (1998) 1133–1138. C. Hammerberg, N. Duraiswamy, K.D. Cooper, Temporal correlation between UV radiation locally-inducible tolerance and the sequential appearance of dermal, then epidermal, class II MHC+ CD11b+ monocytic/macrophagic cells, J. Invest. Dermatol. 107 (1996) 755–763. S.K. Katiyar, A. Challa, S. McCormick, K.D. Cooper, H. Mukhtar, Reversal of ultraviolet B-induced immunosuppression in mice by green tea polyphenol (−)-epigalloctechin-3gallate may be associated with alterations in IL-10 and IL-12 production, Carcinogenesis 20 (1999) 2117–2124. B.J. Nickoloff, J.Z. Qin, V. Chaturvedi, P. Bacon, J. Panella, M.F. Denning, Life and death signaling pathways contributing to skin cancer, J. Investig. Dermatol. Symp. Proc. 7 (2002) 27–35. J. Brugarolas, C. Chandrasekaran, J.I. Gordon, D. Beach, T. Jacks, G.T. Hannon, Radiation-induced cell cycle arrest compromised by p21 deficiency, Nature 377 (1995) 552– 557. W.S. el-Deiry, T. Tokino, V.E. Velculescu, D.B. Levy, R. Parsons, J.M. Trent, D. Lin, W.E. Mercer, K.W. Kinzler, B. Vogelstein, WAF1, a potential mediator of p53 tumor suppression, Cell 75 (1993) 817–825. T. Kamijo, J.D. Weber, G. Zambetti, F. Zindy, M.F. Roussel, C.J. Sherr, Functional and physical interactions of the ARF tumor suppressor with p53 and Mdm2, Proc. Natl. Acad. Sci. U.S.A. 95 (1998) 8292–8297. A.J. Levine, p53, the cellular gatekeeper for growth and division, Cell 88 (1997) 323–331. M.L. Smith, A.J. Fornace Jr., p53-mediated protective responses to UV irradiation, Proc. Natl. Acad. Sci. U.S.A. 94 (1997) 12255–12257. P.A. Hall, P.H. McKee, H.P. Menage, R. Dover, D.P. Lane, High levels of p53 protein in UV-irradiated normal human skin, Oncogene 8 (1993) 203–207. E. Healy, N.J. Reynolds, M.D. Smith, C. Campbell, P.M. Farr, J.L. Rees, Dissociation of erythema and p53 protein expression in human skin following UVB irradiation, and induction of p53 protein and mRNA following application of skin irritants, J. Invest. Dermatol. 103 (1994) 493–499.

F. Afaq et al. / Mutation Research 571 (2005) 153–173 [62] Y.P. Lu, Y.R. Lou, P. Yen, D. Mitchell, M.T. Huang, A.H. Conney, Time course for early adaptive responses to ultraviolet B light in the epidermis of SKH-1 mice, Cancer Res. 59 (1999) 4591–4602. [63] S.J. Kuerbitz, B.S. Plunkett, W.V. Walsh, M.B. Kastan, Wildtype p53 is a cell cycle checkpoint determinant following irradiation, Proc. Natl. Acad. Sci. U.S.A. 89 (1992) 7491–7495. [64] D.P. Lane, p53: guardian of the genome, Nature (London) 358 (1992) 15–16. [65] B.C. McKay, M.A. Francis, A.J. Rainbow, Wild type p53 is required for heat shock and ultraviolet light enhanced repair of a UV-damaged reporter gene, Carcinogenesis (London) 18 (1997) 245–249. [66] G.P. Zambetti, A.J. Levine, A comparison of the biological activities of wild-type and mutant p53, FASEB J. 7 (1993) 855–865. [67] S.E. Kern, K.W. Kinzler, A. Bruskin, D. Jarosz, P. Friedman, C. Prives, B. Vogelstein, Identification of p53 as a sequencespecific DNA-binding protein, Science (Washington DC) 252 (1991) 1708–1711. [68] E. White, Life, death, and the pursuit of apoptosis, Genes Dev. 10 (1996) 1–15. [69] R.J.W. Berg, H.J. van Kranen, H.G. Rebel, A. de Vries, W.A. van Vloten, C.F. van Kreul, J.C. van der Leun, F.R. de Gruijl, Early p53 alterations in mouse skin carcinogenesis by UVB radiation: immunohistochemical detection of mutant p53 protein in clusters of preneoplastic epidermal cells, Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 274–278. [70] A. Ziegler, A.S. Jonason, D.J. Leffell, J.A. Simon, H.W. Sharma, J. Kimmelman, L. Remington, T. Jacks, D.E. Brash, Sunburn and p53 in the onset of skin cancer, Nature 372 (1994) 773–776. [71] J.W. Streilein, J.R. Taylor, V. Vincek, I. Kurimoto, J. Richardson, C. Tie, J.P. Medema, C. Golomb, Relationship between ultraviolet radiation-induced immunosuppression and carcinogenesis, J. Invest. Dermatol. 103 (Suppl. 5) (1994) 107S–111S. [72] S.-Y. Shieh, M. Ikeda, Y. Taya, C. Prives, DNA damageinduced phosphorylation of p53 alleviates inhibition by MDM2, Cell 91 (1997) 325–334. [73] N. Basset-Seguin, J.P. Moles, V. Mils, O. Dereure, J.J. Guilhou, TP53 tumor suppressor gene and skin carcinogenesis, J. Invest. Dermatol. 103 (Suppl. 5) (1994) 102S–106S. [74] A.L. Kim, M. Athar, D.R. Bickers, J. Gautier, Stage-specific alterations of cyclin expression during UVB-induced murine skin tumor development, Photochem. Photobiol. 75 (2002) 58–67. [75] M.L. Rodriguez-Puebla, A.I. Robles, C.J. Conti, ras activity and cyclin D1 expression: an essential mechanism of mouse skin tumor development, Mol. Carcinog. 24 (1999) 1–6. [76] A.I. Robles, M.L. Rodriguez-Puebla, A.B. Glick, C. Trempus, L. Hansen, P. Sicinski, R.W. Tennant, R.A. Weinberg, S.H. Yuspa, C.J. Conti, Reduced skin tumor development in cyclin D1-deficient mice highlights the oncogenic ras pathway in vivo, Genes Dev. 12 (1998) 2469–2474. [77] S.J. Cooper, J. MacGowan, J. Ranger-Moore, M.R. Young, N.H. Colburn, G.T. Bowden, Expression of dominant negative

[78]

[79]

[80]

[81]

[82]

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

169

c-jun inhibits ultraviolet B-induced squamous cell carcinoma number and size in an SKH-1 hairless mouse model, Mol. Cancer Res. 1 (2003) 848–854. W.C. Weinberg, C.G. Azzoli, N. Kadiwar, S.H. Yuspa, p53 gene dosage modifies growth and malignant progression of keratinocytes expressing the v-rasHa oncogene, Cancer Res. 54 (1994) 5584–5592. G.H. Enders, J. Koh, C. Missero, A.K. Rustgi, E. Harlow, p16 inhibition of transformed and primary squamous epithelial cells, Oncogene 12 (1996) 1239–1245. M. Piepkorn, The expression of p16 (INK4a), the product of a tumor suppressor gene for melanoma, is upregulated in human melanocytes by UVB irradiation, J. Am. Acad. Dermatol. 42 (2000) 741–745. S. Pavey, S. Conroy, T. Russell, B. Gabrielli, Ultraviolet radiation induces p16CDKN2A expression in human skin, Cancer Res. 59 (1999) 4185–4189. N.U. Ahmed, M. Ueda, M. Ichihashi, Induced expression of p16 and p21 proteins in UVB-irradiated human epidermis and cultured keratinocytes, J. Dermatol. Sci. 19 (1999) 175– 181. M. Serrano, H. Lee, L. Chin, C. Cordon-Cardo, D. Beach, R.A. DePinho, Role of the INK4a locus in tumor suppression and cell mortality, Cell 85 (1996) 27–37. N. Soufir, L. Daya-Grosjean, P. de La Salmoniere, J.P. Moles, L. Dubertret, A. Sarasin, N. Basset-Seguin, Association between INK4a-ARF and p53 mutations in skin carcinomas of xeroderma pigmentosum patients, J. Natl. Cancer. Inst. 92 (2000) 1841–1847. M. Chazal, C. Marionnet, L. Michel, K. Mollier, J.E. Dazard, V. Della Valle, C.J. Larsen, M.P. Gras, N. Basset-Seguin, P16 (INK4A) is implicated in both the immediate and adaptative response of human keratinocytes to UVB irradiation, Oncogene 21 (2002) 2652–2661. Y.P. Lu, Y.R. Lou, X.H. Li, J.G. Xie, D. Brash, M.T. Huang, A.H. Conney, Stimulatory effect of oral administration of green tea or caffeine on ultraviolet light-induced increases in epidermal wild-type p53, p21 (WAF1/CIP1), and apoptotic sunburn cells in SKH-1 mice, Cancer Res. 60 (2000) 4785–4791. Y.P. Lu, Y.R. Lou, Y. Lin, W.J. Shih, M.T. Huang, C.S. Yang, A.H. Conney, Inhibitory effects of orally administered green tea, black tea, and caffeine on skin carcinogenesis in mice previously treated with ultraviolet B light (high-risk mice): relationship to decreased tissue fat, Cancer Res. 61 (2001) 5002–5009. M. McVean, H. Xiao, K. Isobe, J.C. Pelling, Increase in wildtype p53 stability and transactivational activity by the chemopreventive agent apigenin in keratinocytes, Carcinogenesis 21 (2000) 633–639. M. McVean, W.C. Weinberg, J.C. Pelling, A p21 (waf1)independent pathway for inhibitory phosphorylation of cyclindependent kinase p34 (cdc2) and concomitant G(2)/M arrest by the chemopreventive flavonoid apigenin, Mol. Carcinog. 33 (2002) 36–43. S. Dhanalakshmi, G.U. Mallikarjuna, R.P. Singh, R. Agarwal, Dual efficacy of silibinin in protecting or enhancing ultraviolet

170

[91]

[92]

[93]

[94]

[95]

[96]

[97]

[98]

[99]

[100] [101]

[102]

[103]

[104] [105]

F. Afaq et al. / Mutation Research 571 (2005) 153–173 B radiation-caused apoptosis in HaCaT human immortalized keratinocytes, Carcinogenesis 25 (2004) 99–106. S. Reagan-Shaw, F. Afaq, M.H. Aziz, N. Ahmad, Modulations of critical cell cycle regulatory events during chemoprevention of ultraviolet B-mediated responses by resveratrol in SKH-1 hairless mouse skin, Oncogene (May) (2004) [Epub ahead of print]. J.A. Bush, K.J. Cheung Jr., G. Li, Curcumin induces apoptosis in human melanoma cells through a Fas receptor/caspase8 pathway independent of p53, Exp. Cell Res. 271 (2001) 305–314. S.H. Jee, S.C. Shen, C.R. Tseng, H.C. Chiu, M.L. Kuo, Curcumin induces a p53-dependent apoptosis in human basal cell carcinoma cells, J. Invest. Dermatol. 111 (1998) 656–661. N. Bhatia, C. Agarwal, R. Agarwal, Differential responses of skin cancer-chemopreventive agents silibinin, quercetin, and epigallocatechin 3-gallate on mitogenic signaling and cell cycle regulators in human epidermoid carcinoma A431 cells, Nutr. Cancer 39 (2001) 292–299. N. Ahmad, V.M. Adhami, F. Afaq, D.K. Feyes, H. Mukhtar, Resveratrol causes WAF-1/p21-mediated G(1)-phase arrest of cell cycle and induction of apoptosis in human epidermoid carcinoma A431 cells, Clin. Cancer Res. 7 (2001) 1466– 1473. Q.B. She, A.M. Bode, W.Y. Ma, N.Y. Chen, Z. Dong, Resveratrol-induced activation of p53 and apoptosis is mediated by extracellular-signal-regulated protein kinases and p38 kinase, Cancer Res. 61 (2001) 1604–1610. I.R. Record, I.E. Dreosti, Protection by tea against UV-A + Binduced skin cancers in hairless mice, Nutr. Cancer 32 (1998) 71–75. J. Kim, J.S. Hwang, Y.K. Cho, Y. Han, Y.J. Jeon, K.H. Yang, Protective effects of (−)-epigallocatechin-3-gallate on UVAand UVB-induced skin damage, Skin Pharmacol. Appl. Skin Physiol. 14 (2001) 11–19. D.F. Birt, D. Mitchell, B. Gold, P. Pour, H.C. Pinch, Inhibition of ultraviolet light induced skin carcinogenesis in SKH-1 mice by apigenin, a plant flavonoid, Anticancer Res. 17 (1997) 85–91. R.J. Haslam, H.B. Koide, B.A. Hemmings, Pleckstrin domain homology, Nature 363 (1993) 309–310. M. Andjelkovic, D.R. Alessi, R. Meier, A. Fernandez, N.J. Lamb, M. Frech, P. Cron, P. Cohen, J.M. Lucocq, B.A. Hemmings, Role of translocation in the activation and function of protein kinase B, J. Biol. Chem. 272 (1997) 31515–31524. H. Welch, A. Eguinoa, L.R. Stephens, P.T. Hawkins, Protein kinase B and rac are activated in parallel within a phosphatidylinositide 3OH-kinase-controlled signaling pathway, J. Biol. Chem. 273 (1998) 11248–11256. K.M. Nicholson, N.G. Anderson, The protein kinase B/Akt signalling pathway in human malignancy, Cell Signal. 14 (2002) 381–395. S.R. Datta, A. Brunet, M.E. Greenberg, Cellular survival: a play in three Akts, Genes Dev. 13 (1999) 2905–2927. C. Huang, J. Li, M. Ding, S.S. Leonard, L. Wang, V. Castranova, V. Vallyathan, X. Shi, UV Induces phosphorylation of protein kinase B (Akt) at Ser-473 and Thr-308 in mouse epi-

[106]

[107]

[108]

[109]

[110]

[111]

[112] [113]

[114]

[115]

[116]

[117]

[118]

[119]

dermal Cl 41 cells through hydrogen peroxide, J. Biol. Chem. 276 (2001) 40234–40240. H.Q. Wang, T. Quan, T. He, T.F. Franke, J.J. Voorhees, G.J. Fisher, Epidermal growth factor receptor-dependent, NFkappaB-independent activation of the phosphatidylinositol 3kinase/Akt pathway inhibits ultraviolet irradiation-induced caspases-3, -8, and -9 in human keratinocytes, J. Biol. Chem. 278 (2003) 45737–45745. B.D. Butts, K.A. Kwei, G.T. Bowden, M.M. Briehl, Elevated basal reactive oxygen species and phospho-Akt in murine keratinocytes resistant to ultraviolet B-induced apoptosis, Mol. Carcinog. 37 (2003) 149–157. B. Zhang, D.F. Spandau, A. Roman, E5 protein of human papillomavirus type 16 protects human foreskin keratinocytes from UV B-irradiation-induced apoptosis, J. Virol. 76 (2002) 220–231. J. Umeda, S. Sano, K. Kogawa, N. Motoyama, K. Yoshikawa, S. Itami, G. Kondoh, T. Watanabe, J. Takeda, In vivo cooperation between Bcl-xL and the phosphoinositide 3-kinaseAkt signaling pathway for the protection of epidermal keratinocytes from apoptosis, FASEB J. 17 (2003) 610–620. D. Decraene, P. Agostinis, R. Bouillon, H. Degreef, M. Garmyn, Insulin-like growth factor-1-mediated AKT activation postpones the onset of ultraviolet B-induced apoptosis, providing more time for cyclobutane thymine dimer removal in primary human keratinocytes, J. Biol. Chem. 277 (2002) 32587–32595. M. Nomura, A. Kaji, Z. He, W.Y. Ma, K. Miyamoto, C.S. Yang, Z. Dong, Inhibitory mechanisms of tea polyphenols on the ultraviolet B-activated phosphatidylinositol 3kinase-dependent pathway, J. Biol. Chem. 276 (2001) 46624– 46631. P.A. Baeuerle, D. Baltimore, NF-kappa B: ten years after, Cell 87 (1996) 13–20. S. Ghosh, M.J. May, E.B. Kopp, NF-kappa B Rel proteins: evolutionarily conserved mediators of immune responses, Annu. Rev. Immunol. 16 (1998) 225–260. A.S. Baldwin Jr., The NF-kappa B and I kappa B proteins: new discoveries and insights, Annu. Rev. Immunol. 14 (1996) 649–683. K. Deacon, P. Mistry, J. Chernoff, J.L. Blank, R. Patel, p38 mitogen-activated protein kinase mediates cell death and p21activated kinase mediates cell survival during chemotherapeutic drug-induced mitotic arrest, Mol. Biol. Cell 14 (2003) 2071–2087. K.C. Das, C.W. White, Activation of NF-kappaB by antineoplastic agents: role of protein kinase C, J. Biol. Chem. 272 (1997) 14914–14920. J.D. Woronicz, X. Gao, Z. Cao, M. Rothe, D.V. Goeddel, IkappaB kinase-beta: NF-kappaB activation and complex formation with IkappaB kinase-alpha and NIK, Science 278 (1997) 866–869. D.M. Rothwarf, E. Zandi, G. Natoli, M. Karin, IKK-gamma is an essential regulatory subunit of the IkappaB kinase complex, Nature 395 (1998) 297–300. M.A. Jordan, K. Wendell, S. Gardiner, W.B. Derry, H. Copp, L. Wilson, Mitotic block induced in HeLa cells by low con-

F. Afaq et al. / Mutation Research 571 (2005) 153–173

[120]

[121]

[122]

[123]

[124]

[125]

[126]

[127]

[128]

[129]

[130]

[131] [132]

[133]

centrations of paclitaxel (Taxol) results in abnormal mitotic exit and apoptotic cell death, Cancer Res. 56 (1996) 816–825. N. Ahmad, S. Gupta, H. Mukhtar, Green tea polyphenol epigallocatechin-3-gallate differentially modulates nuclear factor-kappaB in cancer cells versus normal cells, Arch. Biochem. Biophys. 376 (2000) 338–346. V.M. Adhami, F. Afaq, N. Ahmad, Suppression of ultraviolet B exposure-mediated activation of NF-kappaB in normal human keratinocytes by resveratrol, Neoplasia 5 (2003) 74–82. C. Saliou, M. Kitazawa, L. McLaughlin, J.P. Yang, J.K. Lodge, T. Tetsuka, K. Iwasaki, J. Cillard, T. Okamoto, L. Packer, Antioxidants modulate acute solar ultraviolet radiation-induced NF-kappa-B activation in a human keratinocyte cell line, Free Radic. Biol. Med. 26 (1999) 174–183. K. Abeyama, W. Eng, J.V. Jester, A.A. Vink, D. Edelbaum, C.J. Cockerell, P.R. Bergstresser, A. Takashima, A role for NFkappaB-dependent gene transactivation in sunburn, J. Clin. Invest. 105 (2000) 1751–1759. A.A. Beg, W.C. Sha, R.T. Bronson, D. Baltimore, Constitutive NF-␬B activation, enhanced granulopoiesis, and neonatal lethality in I␬B␣-deficient mice, Genes Dev. 9 (1995) 2736–2746. J.F. Klement, N.R. Rice, B.D. Car, S.J. Abbondanzo, G.D. Powers, P.H. Bhatt, C.H. Chen, C.A. Rosen, C.L. Stewart, I␬B␣ deficiency results in sustained NF-␬B response and severe widespread dermatitis in mice, Mol. Cell. Biol. 16 (1996) 2341–2349. C. Saliou, G. Rimbach, H. Moini, L. McLaughlin, S. Hosseini, J. Lee, R.R. Watson, L. Packer, Solar ultraviolet-induced erythema in human skin and nuclear factor-kappa-B-dependent gene expression in keratinocytes are modulated by a French maritime pine bark extract, Free Radic. Biol. Med. 30 (2001) 154–160. J. Kim, J.S. Hwang, Y.K. Cho, Y. Han, Y.J. Jeon, K.H. Yang, Protective effects of (−)-epigallocatechin-3-gallate on UVAand UVB-induced skin damage, Skin Pharmacol. Appl. Skin Physiol. 14 (2001) 11–19. G.J. Fisher, S.C. Datta, H.S. Talwar, Z.Q. Wang, J. Varani, S. Kang, J.J. Voorhees, Molecular basis of sun-induced premature skin ageing and retinoid antagonism, Nature 379 (1996) 335–339. J.T. Hong, E.J. Kim, K.S. Ahn, K.M. Jung, Y.P. Yun, Y.K. Park, S.H. Lee, Inhibitory effect of glycolic acid on ultravioletinduced skin tumorigenesis in SKH-1 hairless mice and its mechanism of action, Mol. Carcinog. 31 (2001) 152–160. S. Maalouf, M. El-Sabban, N. Darwiche, H. Gali-Muhtasib, Protective effect of Vitamin E on ultraviolet B light-induced damage in keratinocytes, Mol. Carcinog. 34 (2002) 121–130. E. Shaulian, M. Karin, AP-1 in cell proliferation and survival, Oncogene 20 (2001) 2390–2400. Z. Assefa, M. Garmyn, R. Bouillon, W. Merlevede, J.R. Vandenheede, P. Agostinis, Differential stimulation of ERK and JNK activities by ultraviolet B irradiation and epidermal growth factor in human keratinocytes, J. Invest. Dermatol. 108 (1997) 886–891. W. Chen, Z. Dong, S. Valcic, B.N. Timmermann, G.T. Bowden, Inhibition of ultraviolet B-induced c-fos gene expression

[134]

[135]

[136]

[137]

[138]

[139]

[140]

[141]

[142]

[143]

[144]

[145]

171

and p38 mitogen-activated protein kinase activation by (−)epigallocatechin gallate in a human keratinocyte cell line, Mol. Carcinog. 24 (1999) 79–84. M. Barthelman, W.B. Bair 3rd, K.K. Stickland, W. Chen, B.N. Timmermann, S. Valcic, Z. Dong, G.T. Bowden, (−)Epigallocatechin-3-gallate inhibition of ultraviolet B-induced AP-1 activity, Carcinogenesis 19 (1998) 2201–2204. M. Nomura, W.Y. Ma, C. Huang, C.S. Yang, G.T. Bowden, K. Miyamoto, Z. Dong, Inhibition of ultraviolet B-induced AP-1 activation by theaflavins from black tea, Mol. Carcinogen. 28 (2000) 148–155. P. Brenneisen, J. Wenk, L.O. Klotz, M. Wlaschek, K. Briviba, T. Krieg, H. Sies, K. Scharffetter-Kochanek, Central role of ferrous/ferric iron in the ultraviolet B irradiationmediated signaling pathway leading to increased interstitial collagenase (matrix-degrading metalloprotease (MMP)-1) and stromelysin-1 (MMP-3) mRNA levels in cultured human dermal fibroblasts, J. Biol. Chem. 273 (1998) 5279–5287. C. Huang, W.Y. Ma, C.A. Ryan, Z. Dong, Proteinase inhibitors I and II from potatoes specifically block UV-induced activator protein-1 activation through a pathway that is independent of extracellular signal-regulated kinases, c-Jun N-terminal kinases, and P38 kinase, Proc. Natl. Acad. Sci. U.S.A. 94 (1997) 11957–11962. G. Liu, N. Chen, A. Kaji, A.M. Bode, C.A. Ryan, Z. Dong, Proteinase inhibitors I and II from potatoes block UVB-induced AP-1 activity by regulating the AP-1 protein compositional patterns in JB6 cells, Proc. Natl. Acad. Sci. U.S.A. 98 (2001) 5786–5791. M. Ding, Y. Lu, L. Bowman, V. Huang, S. Leonard, L. Wang, V. Vallyathan, V. Castranova, X. Shi, Inhibition of AP-1 and neoplastic transformation by fresh apple peel extract, J. Biol. Chem. 279 (2004) 10670–10676. W.B. Bair 3rd, N. Hart, J. Einspahr, G. Liu, Z. Dong, D. Alberts, G.T. Bowden, Inhibitory effects of sodium salicylate and acetylsalicylic acid on UVB-induced mouse skin carcinogenesis, Cancer Epidemiol. Biomarkers Prev. 11 (2002) 1645–1652. K. Kramer-Stickland, A. Edmonds, W.B. Bair 3rd, G.T. Bowden, Inhibitory effects of deferoxamine on UVB-induced AP1 transactivation, Carcinogenesis 20 (November (11)) (1999) 2137–2142. M. Barthelman, W. Chen, H.L. Gensler, C. Huang, Z. Dong, G.T. Bowden, Inhibitory effects of perillyl alcohol on UVBinduced murine skin cancer and AP-1 transactivation, Cancer Res. 58 (1998) 711–716. D. Peus, R.A. Vasa, A. Beyerle, A. Meves, C. Krautmacher, M.R. Pittelkow, UVB activates ERK1/2 and p38 signaling pathways via reactive oxygen species in cultured keratinocytes, J. Invest. Dermatol. 112 (1999) 751–756. D. Peus, R.A. Vasa, A. Meves, M. Pott, A. Beyerle, K. Squillace, M.R. Pittelkow, H2 O2 is an important mediator of UVB-induced EGF-receptor phosphorylation in cultured keratinocytes, J. Invest. Dermatol. 110 (1998) 966–971. R. Pfundt, M. Wingens, M. Bergers, M. Zweers, M. Frenken, J. Schalkwijk, TNF-alpha and serum induce SKALP/elafin gene expression in human keratinocytes by a p38 MAP

172

[146]

[147]

[148]

[149]

[150]

[151]

[152]

[153]

[154]

[155]

[156]

[157]

[158]

F. Afaq et al. / Mutation Research 571 (2005) 153–173 kinase-dependent pathway, Arch. Dermatol. Res. 292 (2000) 180–187. W. Chen, G.T. Bowden, Activation of p38 MAP kinase and ERK are required for ultraviolet-B induced c-fos gene expression in human keratinocytes, Oncogene 18 (1999) 7469–7476. M. Nomura, A. Kaji, Z. He, W.Y. Ma, K. Miyamoto, C.S. Yang, Z. Dong, Inhibitory mechanisms of tea polyphenols on the ultraviolet B-activated phosphatidylinositol 3-kinasedependent pathway, J. Biol. Chem. 276 (2001) 46624–46631. S.P. Singh, A.K. Tyagi, J. Zhao, R. Agarwal, Silymarin inhibits growth and causes regression of established skin tumors in SENCAR mice via modulation of mitogen-activated protein kinases and induction of apoptosis, Carcinogenesis 23 (2002) 499–510. N. Bhatia, C. Agarwal, R. Agarwal, Differential responses of skin cancer-chemopreventive agents silibinin, quercetin, and epigallocatechin 3-gallate on mitogenic signaling and cell cycle regulators in human epidermoid carcinoma A431 cells, Nutr. Cancer 39 (2001) 292–299. D. Peus, A. Meves, M. Pott, A. Beyerle, M.R. Pittelkow, Vitamin E analog modulates UVB-induced signaling pathway activation and enhances cell survival, Free Radic. Biol. Med. 30 (2001) 425–432. M.V. Catani, A. Rossi, A. Costanzo, S. Sabatini, M. Levrero, G. Melino, L. Avigliano, Induction of gene expression via activator protein-1 in the ascorbate protection against UV-induced damage, Biochem. J. 356 (2001) 77–85. P. De Haes, M. Garmyn, H. Degreef, K. Vantieghem, R. Bouillon, S. Segaert, 1,25-Dihydroxyvitamin D3 inhibits ultraviolet B-induced apoptosis, Jun kinase activation, and interleukin-6 production in primary human keratinocytes, J. Cell Biochem. 89 (2003) 663–673. S.Y. Buckman, A. Gresham, P. Hale, G. Hruza, J. Anast, J. Masferrer, A.P. Pentland, COX-2 expression is induced by UVB exposure in human skin: implications for the development of skin cancer, Carcinogenesis 19 (1998) 723– 729. Q. Tang, M. Gonzales, H. Inoue, G.T. Bowden, Roles of Akt and glycogen synthase kinase 3beta in the ultraviolet B induction of cyclooxygenase-2 transcription in human keratinocytes, Cancer Res. 61 (2001) 4329–4332. C.S. Williams, M. Mann, R.N. DuBois, The role of cyclooxygenases in inflammation, cancer, and development, Oncogene 18 (1999) 7908–7916. G. Liu, W.Y. Ma, A.M. Bode, Y. Zhang, Z. Dong, NS-398 and piroxicam suppress UVB-induced activator protein 1 activity by mechanisms independent of cyclooxygenase-2, J. Biol. Chem. 278 (2003) 2124–2130. T.A. Wilgus, A.T. Koki, B.S. Zweifel, D.F. Kusewitt, P.A. Rubal, T.M. Oberyszyn, Inhibition of cutaneous ultraviolet light B-mediated inflammation and tumor formation with topical celecoxib treatment, Mol. Carcinog. 38 (2003) 49–58. K.P. An, M. Athar, X. Tang, S.K. Katiyar, J. Russo, J. Beech, M. Aszterbaum, L. Kopelovich, E.H. Epstein Jr., H. Mukhtar, D.R. Bickers, Cyclooxygenase-2 expression in murine and human nonmelanoma skin cancers: implications for therapeutic approaches, Photochem. Photobiol. 76 (2002) 73–80.

[159] M. Soriani, P. Luscher, R.M. Tyrrell, Direct and indirect modulation of ornithine decarboxylase and cyclooxygenase by UVB radiation in human skin cells, Carcinogenesis 20 (1999) 727–732. [160] S.K. Katiyar, N.J. Korman, H. Mukhtar, R. Agarwal, Protective effects of silymarin against photocarcinogenesis in a mouse skin model, J. Natl. Cancer Inst. 89 (1997) 556–566. [161] F. Afaq, V.M. Adhami, N. Ahmad, Prevention of short-term ultraviolet B radiation-mediated damages by resveratrol in SKH-1 hairless mice, Toxicol. Appl. Pharmacol. 186 (2003) 28–37. [162] E.E. Vanderveen, R.C. Grekin, N.A. Swanson, K. Kragballe, Arachidonic acid metabolites in cutaneous carcinomas, Arch. Dermatol. 122 (1986) 407–412. [163] K. Muller-Decker, G. Reinerth, P. Krieg, R. Zimmermann, H. Heise, C. Bayerl, F. Marks, G. Furstenberger, ProstaglandinH-synthase isozyme expression in normal and neoplastic human skin, Int. J. Cancer. 82 (1999) 648–656. [164] A.R. Brecher, The role of cyclooxygenase-2 in the pathogenesis of skin cancer, J. Drugs Dermatol. 1 (2002) 44–47. [165] S.M. Fischer, C.J. Conti, J. Viner, C.M. Aldaz, R.A. Lubet, Celecoxib and difluoromethylornithine in combination have strong therapeutic activity against UV-induced skin tumors in mice, Carcinogenesis 24 (2003) 945–952. [166] E. Fosslien, Molecular pathology of cyclooxygenase-2 in cancer-induced angiogenesis, Ann. Clin. Lab. Sci. 31 (2001) 325–348. [167] S.M. Fischer, H.H. Lo, G.B. Gordon, K. Seibert, G. Kelloff, R.A. Lubet, C.J. Conti, Chemopreventive activity of celecoxib, a specific cyclooxygenase-2 inhibitor, and indomethacin against ultraviolet light-induced skin carcinogenesis, Mol. Carcinog. 25 (1999) 231–240. [168] T.A. Wilgus, M.S. Ross, M.L. Parrett, T.M. Oberyszyn, Topical application of a selective cyclooxygenase inhibitor suppresses UVB mediated cutaneous inflammation, Prostaglandins Other Lipid Mediat. 62 (2000) 367–384. [169] A.L. Hsu, T.T. Ching, D.S. Wang, X. Song, V.M. Rangnekar, C.S. Chen, The cyclooxygenase-2 inhibitor celecoxib induces apoptosis by blocking Akt activation in human prostate cancer cells independently of Bcl-2, J. Biol. Chem. 275 (2000) 11397–11403. [170] J. Zhu, X. Song, H.P. Lin, D.C. Young, S. Yan, V.E. Marquez, C.S. Chen, Using cyclooxygenase-2 inhibitors as molecular platforms to develop a new class of apoptosis-inducing agents, J. Natl. Cancer Inst. 94 (2002) 1745–1757. [171] T.A. Wilgus, T.S. Breza Jr., K.L. Tober, T.M. Oberyszyn, Treatment with 5-fluorouracil and celecoxib displays synergistic regression of ultraviolet light B-induced skin tumors, J. Invest. Dermatol. 122 (2004) 1488–1494. [172] S. Zhaorigetu, N. Yanaka, M. Sasaki, H. Watanabe, N. Kato, Inhibitory effects of silk protein, sericin on UVB-induced acute damage and tumor promotion by reducing oxidative stress in the skin of hairless mouse, J. Photochem. Photobiol. B 71 (2003) 11–17. [173] L.J. Marton, A.E. Pegg, Polyamines as targets for therapeutic intervention, Annu. Rev. Pharmacol. Toxicol. 35 (1995) 55–91.

F. Afaq et al. / Mutation Research 571 (2005) 153–173 [174] M. Auvinen, A. Paasinen, L.C. Andersson, E. Holtta, Ornithine decarboxylase activity is critical for cell transformation, Nature 360 (1992) 355–358. [175] M. Auvinen, Cell transformation, invasion, and angiogenesis: a regulatory role for ornithine decarboxylase and polyamines? J. Natl. Cancer Inst. 89 (1997) 533–537. [176] H. Hibshoosh, M. Johnson, I.B. Weinstein, Effects of overexpression of ornithine decarboxylase (ODC) on growth control and oncogene-induced cell transformation, Oncogene 6 (1991) 739–743. [177] J. Moshier, J. Dosescu, M. Skunca, G.D. Luck, Transformation of NIH 3T3 cells by ornithine decarboxylase overexpression, Cancer Res. 53 (1993) 2618–2622. [178] E. Holtta, M. Auvinen, L.C. Andersson, Polyamines are essential for cell transformation by pp60 v-src delineation of molecular events relevant for the transformed phenotype, J. Cell Biol. 122 (1993) 903–914. [179] L. Sistonen, E. Holtta, H. Lehvasliaiho, L. Lehtola, K. Alitalo, Activation of chimeric EGF-R/neu tyrosine kinase induces fos/jun transcription factor complex, glucose transporter, and ornithine decarboxylase, J. Cell Biol. 109 (1989) 1911–1919. [180] E. Holtta, L. Sistonen, K. Alitalo, The mechanism of ornithine decarboxylase deregulation in c-Ha-ras oncogenetransformed NIH 3T3 cells, J. Biol. Chem. 263 (1988) 4500–4507. [181] A. Clifford, D. Morgan, S.H. Yuspa, A.P. Solar, S. Gilmour, Role of ODC in epidermal tumorigenesis, Cancer Res. 55 (1995) 1680–1686.

173

[182] L. Megosh, S. Gilmour, D. Rosson, A.P. Soler, M. Blessing, J.A. Sawicki, T.G. O’Brien, Increased frequency of spontaneous skin tumors in transgenic mice which overexpress ornithine decarboxylase, Cancer Res. 55 (1995) 4205– 4209. [183] N. Ahmad, A.C. Gilliam, S.K. Katiyar, T.G. O’Brien, H. Mukhtar, A definitive role of ornithine decarboxylase in photocarcinogenesis, Am. J. Pathol. 159 (2001) 885– 892. [184] S.M. Fischer, M. Lee, R.A. Lubet, Difluoromethylornithine is effective as both a preventive and therapeutic agent against the development of UV carcinogenesis in SKH hairless mice, Carcinogenesis 22 (2001) 83–88. [185] D.S. Alberts, R.T. Dorr, J.G. Einspahr, M. Aickin, K. Saboda, M.J. Xu, Y.M. Peng, R. Goldman, J.A. Foote, J.A. Warneke, S. Salasche, D.J. Roe, G.T. Bowden, Chemoprevention of human actinic keratoses by topical 2-(difluoromethyl)-dl-ornithine, Cancer Epidemiol. Biomarkers Prev. 9 (2000) 1281– 1286. [186] R. Agarwal, S.K. Katiyar, S.G. Khan, H. Mukhtar, Protection against ultraviolet B radiation-induced effects in the skin of SKH-1 hairless mice by a polyphenolic fraction isolated from green tea, Photochem. Photobiol. 58 (1993) 695–700. [187] X. Tang, A.L. Kim, D.J. Feith, A.E. Pegg, J. Russo, H. Zhang, M. Aszterbaum, L. Kopelovich, E.H. Epstein Jr., D.R. Bickers, M. Athar, Ornithine decarboxylase is a target for chemoprevention of basal and squamous cell carcinomas in Ptch1+/− mice, J. Clin. Invest. 113 (2004) 867–875.