Preventative topical diclofenac treatment differentially decreases tumor burden in male and female Skh-1 mice in a model of UVB-induced cutaneous squamous cell carcinoma.

Ultraviolet B (UVB) light is the major environmental carcinogen contributing to non-melanoma skin cancer (NMSC) development. There are over 3.5 million NMSC diagnoses in two million patients annually, with men having a 3-fold greater incidence of squamous cell carcinoma (SCC) compared with women. Chronic inflammation has been linked to tumorigenesis, with a key role for the cyclooxygenase-2 (COX-2) enzyme. Diclofenac, a COX-2 inhibitor and non-steroidal anti-inflammatory drug, currently is prescribed to patients as a short-term therapeutic agent to induce SCC precursor lesion regression. However, its efficacy as a preventative agent in patients without evidence of precursor lesions but with significant UVB-induced cutaneous damage has not been explored. We previously demonstrated in a murine model of UVB-induced skin carcinogenesis that when exposed to equivalent UVB doses, male mice had lower levels of inflammation but developed increased tumor multiplicity, burden and grade compared with female mice. Because of the discrepancy in the degree of inflammation between male and female skin, we sought to determine if topical treatment of previously damaged skin with an anti-inflammatory COX-2 inhibitor would decrease tumor burden and if it would be equally effective in the sexes. Our results demonstrated that despite observed sex differences in the inflammatory response, prolonged topical diclofenac treatment of chronically UVB-damaged skin effectively reduced tumor multiplicity in both sexes. Unexpectedly, tumor burden was significantly decreased only in male mice. Our data suggest a new therapeutic use for currently available topical diclofenac as a preventative intervention for patients predisposed to cutaneous SCC development before lesions appear.

Dopamine Prevents Ultraviolet B-induced Development and Progression of Premalignant Cutaneous Lesions through its D2 Receptors.

Although the role of dopamine (DA) in malignant tumors has been reported, its function in premalignant lesions is unknown. Herein we report that the stimulation of DA D2 receptors in endothelial cells in ultraviolet B (UVB)-induced cutaneous lesions in mice significantly reduced the tumor number, tumor burden, and malignant squamous cell carcinoma in these animals. DA D2 receptor agonist inhibited VEGFA-dependent proangiogenic genes in vitro and in vivo. However, the mice pretreated with selective DA D2 receptor antagonist inhibited the actions of the agonist, thereby suggesting that the action of DA was through its D2 receptors in the endothelial cells. To our knowledge, this study is the first to report DA-mediated regulation of pathogenesis and progression of UVB-induced premalignant skin lesions. PREVENTION RELEVANCE: This investigation demonstrates the role of dopamine and its D2 receptors in UVB induced premalignant squamous cell skin lesions and how DA through its D2 receptors inhibits the development and progression of these lesions and subsequently prevents squamous cell carcinoma of the skin.

Celecoxib reduces the effects of acute and chronic UVB exposure in mice treated with therapeutically relevant immunosuppressive drugs.

Solid organ transplant recipients have a greatly increased risk for the development of non-melanoma skin cancers. We have previously shown in our mouse model that sirolimus given in combination with cyclosporine A resulted in fewer and smaller tumors than cyclosporine A alone. In the current study, we tested the hypothesis that an anti-inflammatory agent celecoxib applied topically after UVB exposure would further reduce UVB induced skin cancer in mice treated with cyclosporine A and sirolimus. The effect of celecoxib treatment on acute inflammation, initiation/promotion and tumor development was examined through a set of four experiments. Delayed tumor onset was observed in both tumor development experiments. Reduced tumor size and number compared to vehicle was observed when CX was administered concurrently with UVB and when CX was administered after cessation of UVB treatments, respectively. Prostaglandin E2 was confirmed to be significantly reduced in the dorsal skin of mice concurrently treated with immunosuppressants, CX and UVB for 13 weeks, suggesting a reduction in the inflammatory response could be the mechanism by which CX reduced tumorigenesis. Furthermore, topical celecoxib treatment following acute UVB exposure reduced dermal neutrophil number and activity compared to vehicle. In all of these experiments, unirradiated and vehicle treated mice were utilized as controls. In conclusion, these data suggest that even in the presence of cyclosporine A and sirolimus, topical celecoxib treatment can result in reduced inflammation, tumor number and size; properties which may be beneficial in the therapeutic reduction of skin cancer development in solid organ transplant recipients.

Short-term stress enhances cellular immunity and increases early resistance to squamous cell carcinoma.

In contrast to chronic/long-term stress that suppresses/dysregulates immune function, an acute/short-term fight-or-flight stress response experienced during immune activation can enhance innate and adaptive immunity. Moderate ultraviolet-B (UV) exposure provides a non-invasive system for studying the naturalistic emergence, progression and regression of squamous cell carcinoma (SCC). Because SCC is an immunoresponsive cancer, we hypothesized that short-term stress experienced before UV exposure would enhance protective immunity and increase resistance to SCC. Control and short-term stress groups were treated identically except that the short-term stress group was restrained (2.5h) before each of nine UV-exposure sessions (minimum erythemal dose, 3-times/week) during weeks 4-6 of the 10-week UV exposure protocol. Tumors were measured weekly, and tissue collected at weeks 7, 20, and 32. Chemokine and cytokine gene expression was quantified by real-time PCR, and CD4+ and CD8+ T cells by flow cytometry and immunohistochemistry. Compared to controls, the short-term stress group showed greater cutaneous T-cell attracting chemokine (CTACK)/CCL27, RANTES, IL-12, and IFN-gamma gene expression at weeks 7, 20, and 32, higher skin infiltrating T cell numbers (weeks 7 and 20), lower tumor incidence (weeks 11-20) and fewer tumors (weeks 11-26). These results suggest that activation of short-term stress physiology increased chemokine expression and T cell trafficking and/or function during/following UV exposure, and enhanced Type 1 cytokine-driven cell-mediated immunity that is crucial for resistance to SCC. Therefore, the physiological fight-or-flight stress response and its adjuvant-like immuno-enhancing effects, may provide a novel and important mechanism for enhancing immune system mediated tumor-detection/elimination that merits further investigation.

Chromosomal aberrations in UVB-induced tumors of immunosuppressed mice.

In immunocompromised individuals, such as organ transplant recipients, the risk of cutaneous squamous cell carcinoma (SCC) is increased 60-250 fold, and there is an increased likelihood to develop aggressive, metastatic SCC. An understanding of the genes involved in SCC tumorigenesis is critical to prevent SCC-associated morbidity and mortality. Mouse models show that different immunosuppressive drugs lead to SCCs varying in size, number, and malignant potential. In this study, we used mouse models that mimic adult transplant recipients to study the effect of immunosuppressive drugs and UV light on SCC development. UV-induced tumors from six treatment groups, control, tacrolimus (Tac), rapamycin (Rap), cyclosporin (CsA), mycophenolate mofetil (MMF), and Rap plus CsA, were evaluated by array comparative genomic hybridization. Mouse SCCs appear to show similar genomic aberrations as those reported in human SCCs and offer the ability to identify genomic changes associated with specific and combinatorial effects of drugs. Fewer aberrations were seen in tumors of mice treated with MMF or Rap. Tumors from Tac-treated animals showed the highest number of changes. Calcineurin inhibitors (Tac and CsA) did not cluster together by their genomic aberrations, indicating their contribution to UV mediated carcinogenesis may be through different pathways. The combination treatment (Rap plus CsA) did not cluster with either treatment individually, suggesting it may influence SCC tumorigenesis via a different mechanism. Future studies will identify specific genes mapping to regions of aberration that are different between treatment groups to identify target pathways that may be affected by these drugs.

The hairless mouse in skin research.

The hairless (Hr) gene encodes a transcriptional co-repressor highly expressed in the mammalian skin. In the mouse, several null and hypomorphic Hr alleles have been identified resulting in hairlessness in homozygous animals, characterized by alopecia developing after a single cycle of relatively normal hair growth. Mutations in the human ortholog have also been associated with congenital alopecia. Although a variety of hairless strains have been developed, outbred SKH1 mice are the most widely used in dermatologic research. These unpigmented and immunocompetent mice allow for ready manipulation of the skin, application of topical agents, and exposure to UVR, as well as easy visualization of the cutaneous response. Wound healing, acute photobiologic responses, and skin carcinogenesis have been extensively studied in SKH1 mice and are well characterized. In addition, tumors induced in these mice resemble, both at the morphologic and molecular levels, UVR-induced skin malignancies in man. Two limitations of the SKH1 mouse in dermatologic research are the relatively uncharacterized genetic background and its outbred status, which precludes inter-individual transplantation studies.

Gender differences in UVB-induced skin carcinogenesis, inflammation, and DNA damage.

The American Cancer Society reports the incidence of squamous cell carcinoma in males to be thrice the incidence in females. This increased squamous cell carcinoma incidence has been attributed to men accumulating more sun exposure and using less sun protection than women. To date, there have been no controlled studies examining the effect of gender on skin tumor development following equal doses of UVB. Gender differences in UVB-induced skin carcinogenesis were examined using the Skh-1 mouse model. After chronic exposure to equal doses of UVB, male mice developed tumors earlier and had more tumors than female mice; tumors in male mice tended to be larger, and the total tumor burden was greater than in females. In addition, tumors in males were of more advanced histologic grade compared with those of female mice. To evaluate the contribution of differences in inflammation and DNA damage to differences in skin carcinogenesis, male and female Skh-1 mice were exposed once to 2,240 J/m(2) UVB and examined 48 h after exposure. Surprisingly, male mice developed less of an inflammatory response, as determined by skin fold thickness and myeloperoxidase activity, compared with females. Interestingly, male mice showed more cutaneous oxidative DNA damage than the females and lower antioxidant levels. These results show a gender bias in skin carcinogenesis and suggest that the gender difference in tumor development is more influenced by the extent of oxidative DNA damage and antioxidant capacities than by inflammatory response.

Regulation of scar formation by vascular endothelial growth factor.

Vascular endothelial growth factor (VEGF-A) is known for its effects on endothelial cells and as a positive mediator of angiogenesis. VEGF is thought to promote repair of cutaneous wounds due to its proangiogenic properties, but its ability to regulate other aspects of wound repair, such as the generation of scar tissue, has not been studied well. We examined the role of VEGF in scar tissue production using models of scarless and fibrotic repair. Scarless fetal wounds had lower levels of VEGF and were less vascular than fibrotic fetal wounds, and the scarless phenotype could be converted to a scar-forming phenotype by adding exogenous VEGF. Similarly, neutralization of VEGF reduced vascularity and decreased scar formation in adult wounds. These results show that VEGF levels have a strong influence on scar tissue formation. Our data suggest that VEGF may not simply function as a mediator of wound angiogenesis, but instead may play a more diverse role in the wound repair process.

Hmga1 null mice are less susceptible to chemically induced skin carcinogenesis.

The HMGA1 proteins have a critical role in the process of carcinogenesis. They are overexpressed in most human malignant neoplasias, and the inhibition of their expression has been shown to prevent cell transformation and results in malignant cell death. To determine whether HMGA1 proteins are also required for in vivo carcinogenesis, we compared the tumour susceptibility of mice wild-type or knockout for the Hmga1-null allele using a two-stage chemical skin carcinogenesis protocol. Hmga1-/- mice exhibited a decreased number and a delayed onset of skin papillomas in comparison with wild-type mice. Moreover, the progression of skin papillomas to carcinomas was observed in only 5% of Hmga1-/- compared to 18% of wild-type mice. These results suggest a lower susceptibility of Hmga1-/- mice to skin carcinogenesis induced by chemical agents.

Non-melanoma skin cancer: importance of gender, immunosuppressive status and vitamin D.

Ultraviolet light B (UVB) is responsible for the majority of cutaneous damage and is believed to be the single most important etiologic agent in the development of non-melanoma skin cancers (NMSC). These skin tumors are by far the most common form of cancer in humans, with over 1 million new cases identified in the United States each year. Several risk factors exist, which increase the chance of a patient developing NMSC including gender, immunosuppressive status and more controversially vitamin D levels. The present review provides an overview of each of these areas.

Beta 2-microglobulin deficient mice catabolize IgG more rapidly than FcRn- alpha-chain deficient mice.

FcRn, a nonclassical MHC-I protein bound to beta 2-microglobulin (beta 2m), diverts IgG and albumin from an intracellular degradative fate, prolonging the half-lives of both. While knockout mouse strains lacking either FcRn-alpha-chain (AK) or beta 2m (BK) show much shorter half-lives of IgG and albumin than normal mice, the plasma IgG half-life in the BK and AK strains is different, being shorter in the BK strain. Since beta 2m does not affect the IgG production rate, we tested whether an additional beta 2m-associated mechanism protects IgG from catabolism. First, we compared the fractional disappearance rate in plasma of an intravenous dose of radioiodinated IgG in a mouse strain deficient in both FcRn-alpha-chain and beta 2m (ABK), in the two parental knockout strains (AK and BK), and in the background wild-type (WT) strain. We found that IgG survived longer in the beta 2m-expressing AK strain than in the beta 2m-lacking ABK and BK strains, whereas the IgG half-lives between the ABK and BK strains were identical. Then we compared endogenous concentrations of four typical plasma proteins among the four strains and found that steady-state plasma concentrations of both IgG and albumin were higher in the AK strain than in either the BK or the ABK strain. These results suggest that a beta 2m-associated effect other than FcRn prolongs the survival of both IgG and albumin, although leaky gene transcription in the AK strain cannot be ruled out.

Topical treatment with OGG1 enzyme affects UVB-induced skin carcinogenesis.

Nonmelanoma skin cancer resulting from UVB exposure is a large and growing problem in the United States. Production of reactive oxygen species (ROS) during the UVB-induced inflammatory response results in the formation of oxidative DNA adducts such as 8-hydroxy-2-deoxyguanine (8-oxo-dG), which have been shown to contribute to the development of this cancer. The 8-oxoguanine DNA glycosylase (OGG1) enzyme repairs 8-oxo-dG adducts, suggesting that enhancing its activity in the skin might increase 8-oxo-dG repair thus preventing skin cancer development. We therefore used the SKH-1 murine model to examine the effect of topically applied OGG1 on UVB-induced skin cancer development. Mice were exposed three times weekly to UVB followed immediately by topical treatment with a formulation of liposome-encapsulated OGG1 enzyme for 25 weeks. While this treatment did not affect UVB-induced tumor multiplicity, it did reduce tumor size and dramatically reduced tumor progression, as indicated by tumor grade. These results suggest that oxidative DNA damage contributes to the progression of UVB-induced skin tumors and that a topical formulation containing OGG1, perhaps in conjunction with other DNA repair enzymes such as T4 endonuclease V, could be used in populations at high risk for skin cancer development.

Inflammation and wound healing.

Cutaneous wound healing is a complex process involving several overlapping phases. While we have made great strides in understanding these various phases, there is still much to learn about the cells and soluble mediators that are involved in a successful wound healing event. The current review describes the immuno/inflammatory cells and some less commonly studied soluble mediators involved in the adult healing response.

25-Hydroxyvitamin D3 and its C-3 epimer are elevated in the skin and serum of Skh-1 mice supplemented with dietary vitamin D3.

SCOPE: UV exposure is a risk factor for keratinocyte carcinoma (KC) while critical for endogenous vitamin D production. We investigated dietary modulation of skin and serum 25-hydroxyvitamin D3 (25OHD3 ) and its C-3 epimer (C3epi) in a mouse model of KC. C3epi is an under-investigated metabolite of vitamin D with respect to its biological implications. METHODS AND RESULTS: Male and female Skh-1 mice were supplemented with 25, 150 or 1000 IU/kg diet vitamin D3 for 25 weeks, with some exposed to UV light. Skin and serum vitamin D metabolites were quantitated using HPLC-MS/MS (n = 3 per dose/sex/UV treatment). Serum and skin 25OHD3 and C3epi significantly increased with dose (P<0.0001), but with different response patterns. UV exposure significantly attenuated serum, but not skin, levels of both metabolites (P<0.001, P = 0.0287), while up-regulating expression of renal Cyp24a1 (P < 0.01). A dose by sex interaction trended toward significance with serum and skin levels of C3epi, wherein male mice attained higher levels of C3epi with higher dietary vitamin D3 . This reflected a similar, but non-significant pattern in average tumor size. CONCLUSION: The complex relationship between vitamin D and KC requires further investigation. This study provides insight into modulation of local and systemic vitamin D status with dietary supplementation.

Ultraviolet radiation accelerates NRas-mutant melanomagenesis: A cooperative effect blocked by sunscreen.

To mitigate melanoma risk, sunscreen use is widely advocated; yet, the ability of sunscreens to prevent melanoma remains controversial. Here, we test the tenet that sunscreens limit melanoma risk by blocking ultraviolet radiation (UV)-induced DNA damage using murine models that recapitulate the genetics and spontaneous evolution of human melanoma. We find that a single, non-erythematous dose of UV dramatically accelerates melanoma onset and increases tumor multiplicity in mice carrying an endogenous, melanocyte-specific NRas61R allele. By contrast, transient UV exposure does not alter tumor onset in mice lacking p16INK4a or harboring an NRas12D allele. To block the rapid onset of melanoma cooperatively caused by UV and NRas61R , we employed a variety of aerosol sunscreens. While all sunscreens delayed melanoma formation and blocked UV-induced DNA damage, differences in aerosol output (i.e., amount applied/cm2 ) caused variability in the cancer preventative efficacy of products with identical sunburn protection factor (SPF) ratings.

Tomatoes protect against development of UV-induced keratinocyte carcinoma via metabolomic alterations.

Prolonged tomato consumption can mitigate ultraviolet (UV) light induced sunburn via unknown mechanisms. Dietary carotenoids distributed to skin are hypothesized to protect skin against UV-induced damage, although other phytochemicals may play a role. We hypothesize that tomato consumption would protect against skin cancer. SKH-1 hairless and immunocompetent mice (n = 180) were fed AIN-93G or AIN-93G + 10% tangerine or red tomato powder for 35 weeks. From weeks 11-20, mice (n = 120) were exposed to 2240 J/m2 UV-B light, 3x/week, and tumors were tracked weekly. Control mice were fed the same diets but not exposed to UV. Tumor number was significantly lower in male mice consuming red tomato diets (1.73 ± 0.50, P = 0.015) or pooled tomato diets (2.03 ± 0.45, P = 0.017) compared to controls (4.04 ± 0.65). Carotenoid levels in plasma and skin were quantitated, with total lycopene higher in skin of tangerine fed animals despite a lower dose. Metabolomic analyses elucidated compounds derived from tomato glycoalkaloids (including tomatidine and hydroxylated-tomatidine) as significantly different metabolites in skin after tomato exposure. Here, we describe that tomato consumption can modulate risk for keratinocyte carcinomas; however, the role of the newly identified specific phytochemicals possibly responsible for this action require further investigation.

Importance of the EP(1) receptor in cutaneous UVB-induced inflammation and tumor development.

Chronic exposure to UV light, the primary cause of skin cancer, results in the induction of high levels of cyclooxygenase-2 (COX-2) expression in the skin. The involvement of COX-2 in the carcinogenesis process is mediated by its enzymatic product, prostaglandin E(2) (PGE(2)). PGE(2) has been shown to have a variety of activities that can contribute to tumor development and growth. The effects of PGE(2) on different cell types are mediated by four E prostanoid (EP) receptors, EP(1)-EP(4). While recent studies have demonstrated the importance of EP(1) in the development of colon and breast cancer, the extent of EP(1) involvement in the cutaneous photocarcinogenesis process is unknown. This study found that topical treatment with celecoxib or the specific EP(1) antagonist ONO-8713 decreased acute UVB-induced inflammation in the skin and significantly reduced the number of tumors per mouse following 25 weeks of UVB exposure and topical treatment. This study suggests that drugs designed to block EP(1) may have the potential to be used as anti-inflammatory and/or chemopreventive agents that reduce the risk of skin cancer development.

Cyclosporine A immunosuppression drives catastrophic squamous cell carcinoma through IL-22.

Immune-suppressed organ transplant recipients (OTRs) can develop catastrophic squamous cell carcinoma (SCC), characterized by multiple primary tumors, extensive body surface area involvement, or metastases. There are currently no curative systemic therapies available. We previously showed that IL-22 enhances SCC proliferation. Herein, we examined links between cyclosporine (CSA), IL-22, and SCC in patients, cell lines, and mice with UV light-induced SCC. Eighteen of 114 OTRs developed catastrophic SCC, which was strongly associated with CSA treatment. We found that CSA drives T cell polarization toward IL-22-producing T22 cells, and CSA treatment increased IL-22 receptor in SCC cells. SCC tissue from OTRs showed increased expression of IL-22RA1. CSA potentiated rescue by IL-22 of serum-starved SCC cells; treatment of SCC cells with IL-22 and CSA increased both their migratory and invasive capacity. In a UV-induced model of SCC in SKH-1 immunocompetent mice, treatment with anti-IL-22 antibody reduced tumor number and tumor burden. We found that catastrophic SCC in OTRs is associated with CSA use, which may be acting by favoring T22 polarization. Since anti-IL-22 antibody administration decreased tumor number and tumor burden in vivo, blockade of the IL-22 axis may be developed as a viable therapeutic option for catastrophic SCC.

Depletion of CD8+ or CD4+ lymphocytes enhances susceptibility to transplantable ultraviolet radiation-induced skin tumours.

BACKGROUND: Immunosuppressed patients are extremely susceptible to cutaneous squamous cell carcinoma, suggesting that immunosurveillance by T lymphocytes protects against this ultraviolet radiation-induced tumour. MATERIALS AND METHODS: To determine the relative contribution of CD8+ and CD4+ lymphocytes to immunosurveillance, we tested the effects of CD8+ or CD4+ T lymphocyte depletion on the susceptibility of C3H/HeN mice to a syngeneic UVR-induced skin tumour cell line. RESULTS: Both anti-CD8 and anti-CD4 treatment significantly enhanced the growth of transplanted tumours. In CD8-depleted animals, tumours grew rapidly in all animals. Tumour growth in CD4-depleted animals was slower, and 50% of these mice eventually rejected their tumours. In CD4-depleted mice that did not reject their tumours, an early period of tumour growth was followed by partial regression of the tumour; a second phase of rapid tumour growth then supervened. CONCLUSION: Our findings suggest that both CD8+ and CD4+ lymphocytes contribute to immunosurveillance against skin cancer.

Endogenous Retinoic Acid Required to Maintain the Epidermis Following Ultraviolet Light Exposure in SKH-1 Hairless Mice.

Ultraviolet light B (UVB) exposure induces cutaneous squamous cell carcinoma (cSCC), one of the most prevalent human cancers. Reoccurrence of cSCC in high-risk patients is prevented by oral retinoids. But oral retinoid treatment causes significant side effects; and patients develop retinoid resistance. Exactly how retinoids prevent UVB-induced cSCC is currently not well understood. Retinoid resistance blocks mechanistic studies in the leading mouse model of cSCC, the UVB-exposed SKH-1 hairless mouse. To begin to understand the role of retinoids in UVB-induced cSCC we first examined the localization pattern of key retinoid metabolism proteins by immunohistochemistry 48 h after UVB treatment of female SKH-1 mice. We next inhibited retinoic acid (RA) synthesis immediately after UVB exposure. Acute UVB increased RA synthesis, signaling and degradation proteins in the stratum granulosum. Some of these proteins changed their localization; while other proteins just increased in intensity. In contrast, acute UVB reduced the retinoid storage protein lectin:retinol acyltransferase (LRAT) in the epidermis. Inhibiting RA synthesis disrupted the epidermis and impaired differentiation. These data suggest that repair of the epidermis after acute UVB exposure requires endogenous RA synthesis.