Skin Cancer Formation Research Articles

Curcumin Inhibits UV Radiation–Induced Skin Cancer in SKH‐1 Mice

As skin cancer incidence increases, research has focused on novel chemopreventive agents that inhibit tumor formation. In prior experimentation, curcumin, a naturally occurring food substance and anticarcinogenic agent, inhibited cutaneous squamous cell carcinoma xenograft growth. We hypothesize curcumin will inhibit UVB radiation-induced skin cancer growth in mice, approximating a human chemopreventive model. Randomized experimental animal and laboratory study. Louisiana State University Health Sciences Center-Shreveport, Louisiana. SKH-1 mice were pretreated with oral or topical curcumin or oral or topical control (n = 11/group) for 14 days. Mice received UVB radiation 3 times weekly for 24 weeks or were not radiated. Number of tumors formed and time to tumor onset for each mouse were recorded through tumor harvest after week 24. Tumor multiplicity and time to tumor onset were compared. Time to tumor onset was significantly shorter in control mice compared to mice receiving either oral (P = .025) or topical (P = .015) curcumin. A significant difference in the average number of tumors formed per mouse was seen, as fewer tumors were formed in the oral curcumin (P = .01) and topical curcumin (P = .01) groups, compared with respective controls. No significant difference in average number of tumors per mouse was seen between oral and topical curcumin (P = .56), suggesting that both routes were equally effective. Curcumin appears to inhibit skin cancer formation and prolong time to tumor onset when administered by either an oral or topical route. These data suggest that curcumin may have chemopreventive potential against skin cancer, necessitating future experimentation with human subjects.

GSK3β signaling is involved in ultraviolet B-induced activation of autophagy in epidermal cells

Ultraviolet B (UVB) exposure causes damage to skin and represents the primary etiological agent for skin cancer formation. UVB induces DNA damage and apoptosis in epidermal cells. In this study, we demonstrated that UVB activated autophagy in JB6 epidermal cells, which was evident by the formation of LC3 puncta, the induction of LC3 lipidation, the increase in beclin 1 expression, and the decrease in the levels of p62. Autophagy appeared to be a protective response to UVB-induced damage because inhibition of autophagy exacerbated UVB-induced cell death, and stimulation of autophagy offered protection. Furthermore, we demonstrated that glycogen synthase kinase 3β (GSK3β) was involved in UVB-induced autophagy. UVB inhibited GSK3β activation by simultaneously enhancing phosphorylation at Ser9 and suppressing Tyr216 phosphorylation. GSK3β negatively regulated autophagy; overexpression of wild-type or S9A (constitutive-active) GSK3β mutant inhibited UVB-mediated autophagy, while overexpression of a dominant-negative K85R mutant enhanced UVB-mediated autophagy. Inhibition of GSK3β also offered protection against UVB-mediated damage. UVB activated AMP-activated protein kinase (AMPK), an important regulator of autophagy through the inhibition of GSK3β. Taken together, our results suggest that UVB-stimulated autophagy is a protective response for epidermal cells and is mediated by the GSK3β/AMPK pathway.

Curcumin Inhibits UV Radiation–Induced Skin Cancer In Vivo

Objective: As skin cancer incidence increases, research has focused on novel chemopreventive agents that inhibit tumor formation. In prior experimentation, curcumin, a naturally occurring food substance and anti-carcinogenic agent, inhibited cutaneous squamous cell carcinoma xenograft growth. We hypothesize curcumin will inhibit UVB-radiation–induced skin cancer growth in mice, approximating a human chemopreventive model. Method: A randomized experimental animal and laboratory study is presented. SKH-1 mice were pre-treated with oral or topical curcumin, or oral or topical control (n = 22/group), for 14 days. Mice received UVB radiation 3 times weekly for 24 weeks or were not radiated. Tumor number, volume, and onset were compared. Results: Time to tumor onset was significantly shorter in control mice compared to mice receiving either oral ( P = .025) or topical ( P = .015) curcumin. A significant difference in the average number of tumors formed per mouse was seen, as fewer tumors were formed in the oral curcumin ( P = .01) and topical curcumin ( P = .01) groups, compared with their respective controls. Once tumors formed, no significant difference in tumor volume was noted at 24 weeks. Conclusion: Curcumin appears to inhibit skin cancer formation and prolong time to tumor onset when administered by either an oral or topical route. These data suggest that curcumin may have chemopreventive potential against skin cancer necessitating future experimentation with human subjects.

Mice lacking epidermal PPARγ exhibit a marked augmentation in photocarcinogenesis associated with increased UVB‐induced apoptosis, inflammation and barrier dysfunction

Recent studies suggest that peroxisome proliferator-activated receptor gamma (PPARγ) agonists may have cancer chemopreventive activity. Other studies have shown that loss of epidermal PPARγ results in enhanced chemical carcinogenesis in mice via unknown mechanisms. However, ultraviolet B (UVB) exposure represents the primary etiological agent for skin cancer formation and the role of PPARγ in photobiology and photocarcinogenesis is unknown. In previous studies, we demonstrated that UVB irradiation of cells results in the formation of oxidized glycerophosphocholines that exhibit PPARγ ligand activity. We therefore hypothesized that PPARγ would prove to be a chemopreventive target in photocarcinogenesis. We first showed that UVB irradiation of mouse skin causes generation of PPARγ agonist species in vivo. We then generated SKH-1 hairless, albino mice deficient in epidermal Pparg (Pparg-/-(epi)) using a cytokeratin 14 driven Cre-LoxP strategy. Using a chronic model of UVB photocarcinogenesis, we next showed that Pparg-/-(epi) mice exhibit an earlier onset of tumor formation, increased tumor burden and tumor progression. Increased tumor burden in Pparg-/-(epi) mice was accompanied by a significant increase in epidermal hyperplasia and p53 positive epidermal cells in surrounding skin lacking tumors. After acute UVB irradiation, Pparg-/-(epi) mice exhibited an augmentation of both UVB-induced Caspase 3/7 activity and inflammation. Increased apoptosis and inflammation was also observed after treatment with the PPARγ antagonist GW9662. With chronic UVB irradiation, Pparg-/-(epi) mice exhibited a sustained increase in erythema and transepidermal water loss relative to wildtype littermates. This suggests that PPARγ agonists could have possible chemopreventive activity in non-melanoma skin cancer.

Abstract 3429: AKAP12/SSeCKS inhibits peritoneal metastasis by regulating chemokine production

Abstract AKAP12/SSeCKS/Gravin (AKAP12) is thought to act as a metastasis suppressor through its direct scaffolding of major signaling proteins such as PKC, PKA and Src, in a spatiotemporal manner (1). For example, AKAP12 inhibition of Src-mediated oncogenic signaling, including induction of VEGF secretion by tumor cells, correlates with inhibition of neovascularization at metastatic sites (2). We have established AKAP12-null (KO) mice and demonstrated that they are cancer-prone in regards to the formation of spontaneous prostatic dysplasia and to carcinogen-induced skin cancer formation (3, 4). However, the role of AKAP12 in host microenvironment in regards to tumor or metastasis control has yet to be elucidated. In this study, we utilized an orthotropic, subcutaneous injection model of B16F10 melanoma to address whether the loss of AKAP12 in the host facilitates metastasis. Although the size of the primary tumors was similar in WT vs. KO mice, KO mice exhibited increased rates of peritoneal metastasis. The peritoneal fluid (PF) of KO mice was more potent than WT-PF in inducing in vitro chemotaxis. Comparison of the cytokines/chemokines using antibody arrays showed a severe upregulation of multiple potential chemoattractants in the KO-PF, including CXCL9/10/11, known ligands for CXCR3, a chemokine receptor upregulated 12-fold in B16F10 versus the low-metastatic B16F0 variant. Pre-injection of KO-PF, but not WT-PF, into WT mice was sufficient to induce high levels of peritoneal metastasis from subcutaneous sites. Taken together, our study suggests that AKAP12 controls metastasis by regulating the production of chemoattractants in the peritoneum, produced either by local microenvironmental cells or by recruited inflammatory cells.

TCF/Lef1-Mediated Control of Lipid Metabolism Regulates Skin Barrier Function

Defects in the function of the skin barrier are associated with a wide variety of skin diseases, many of which are not well characterized at the molecular level. Using Lef1 (lymphoid enhancer-binding factor 1) dominant-negative mutant mice, we demonstrate here that altered epidermal TCF (T cell factor)/Lef1 signaling results in severe impairment of the stratum corneum skin barrier and early postnatal death. Barrier defects were accompanied by major changes in lipid composition and ultrastructural abnormalities in assembly and extrusion of lipid lamellae of the interfollicular epidermis, as well as abnormal processing of profilaggrin. In contrast, tight-junction formation and stratified organization of the interfollicular epidermis was not obviously disturbed in Lef1 mutant mice. Molecular analysis revealed that TCF/Lef1 signaling regulates expression of lipid-modifying enzymes, such as Elovl3 and stearoyl coenzyme A desaturase 1 (SCD1), which are key regulators of barrier function. Promoter analysis and chromatin immunoprecipitation experiments indeed showed that SCD1 is a direct target of Lef1. Together, our data demonstrate that functional TCF/Lef1 signaling governs important aspects of epidermal differentiation and lipid metabolism, thereby regulating skin barrier function.

Proteomic analysis of UVB-induced protein expression- and redox-dependent changes in skin fibroblasts using lysine- and cysteine-labeling two-dimensional difference gel electrophoresis

UVB is the most energetic and DNA-damaging to humans in ultraviolet radiation. Previous research has suggested that exposure to UVB causes skin pathologies because of direct DNA damage and the generation of reactive oxygen species (ROS). However, the detailed molecular mechanisms by which UVB leads to skin cancer have yet to be clarified. In the current study, normal skin fibroblast cells (CCD-966SK) were exposed to various doses of UVB, and the changes in protein expression and thiol reactivity were monitored with lysine- and cysteine-labeling 2D-DIGE and MALDI-TOF mass spectrometry. Our proteomic analysis revealed that 89 identified proteins showed significant changes in protein expression, and 37 in thiol reactivity. Many proteins that are known to be involved in protein folding, redox regulation and nucleotide biosynthesis were up-regulated under UVB irradiation. In contrast, proteins responsible for biosynthesis and protein degradation were down-regulated. In addition, the thiol-reactivity of proteins involving cytoskeleton, metabolism, and signal transduction were altered by UVB. In summary, these UVB-modulated cellular proteins and redox-regulated proteins might play important roles in the early stages of skin cancer formation and photoaging induced by UVB-irradiation. Such proteins might provide a potential target for the rational design of drugs to prevent UVB-induced diseases.

PTEN Positively Regulates UVB-Induced DNA Damage Repair

Nonmelanoma skin cancer is the most common cancer in the United States, where DNA-damaging ultraviolet B (UVB) radiation from the sun remains the major environmental risk factor. However, the critical genetic targets of UVB radiation are undefined. Here we show that attenuating PTEN in epidermal keratinocytes is a predisposing factor for UVB-induced skin carcinogenesis in mice. In skin papilloma and squamous cell carcinoma (SCC), levels of PTEN were reduced compared with skin lacking these lesions. Likewise, there was a reduction in PTEN levels in human premalignant actinic keratosis and malignant SCCs, supporting a key role for PTEN in human skin cancer formation and progression. PTEN downregulation impaired the capacity of global genomic nucleotide excision repair (GG-NER), a critical mechanism for removing UVB-induced mutagenic DNA lesions. In contrast to the response to ionizing radiation, PTEN downregulation prolonged UVB-induced growth arrest and increased the activation of the Chk1 DNA damage pathway in an AKT-independent manner, likely due to reduced DNA repair. PTEN loss also suppressed expression of the key GG-NER protein xeroderma pigmentosum C (XPC) through the AKT/p38 signaling axis. Reconstitution of XPC levels in PTEN-inhibited cells restored GG-NER capacity. Taken together, our findings define PTEN as an essential genomic gatekeeper in the skin through its ability to positively regulate XPC-dependent GG-NER following DNA damage.

Photoirradiation of dehydropyrrolizidine alkaloids—Formation of reactive oxygen species and induction of lipid peroxidation

Pyrrolizidine alkaloid (PA)-containing plants are widespread in the world and are probably the most common poisonous plants affecting livestock, wildlife, and human. PAs require metabolic activation to generate pyrrolic metabolites (dehydro-PAs) that bind cellular protein and DNA, leading to hepatotoxicity and genotoxicity, including tumorigenicity. In this study we report that UVA photoirradiation of a series of dehydro-PAs, e.g., dehydromonocrotaline, dehydroriddelliine, dehydroretrorsine, dehydrosenecionine, dehydroseneciphylline, dehydrolasiocarpine, dehydroheliotrine, and dehydroretronecine (DHR) at 0–70 J/cm 2 in the presence of a lipid, methyl linoleate, resulted in lipid peroxidation in a light dose–responsive manner. When irradiated in the presence of sodium azide, the level of lipid peroxidation decreased; lipid peroxidation was enhanced when methanol was replaced by deuterated methanol. These results suggest that singlet oxygen is a photo-induced product. When irradiated in the presence of superoxide dismutase, the level of lipid peroxidation decreased, indicating that lipid peroxidation is also mediated by superoxide. Electron spin resonance (ESR) spin trapping studies confirmed that both singlet oxygen and superoxide anion radical were formed during photoirradiation. These results indicate that UVA photoirradiation of dehydro-PAs generates reactive oxygen species (ROS) that mediated the initiation of lipid peroxidation. UVA irradiation of the parent PAs and other PA metabolites, including PA N-oxides, under similar experimental conditions did not produce lipid peroxidation. It is known that PAs induce skin cancer and are secondary (hepatogenous) photosensitization agents. Our results suggest that dehydro-PAs are the active metabolites responsible for skin cancer formation and PA-induced secondary photosensitization.

An Experimental Population Study of Nucleotide Excision Repair as a Risk Factor for UVB-induced Melanoma

Nucleotide excision repair (NER) is the primary defense against the DNA damage implicit in skin cancer formation and is negatively affected by chronic exposure to UVB radiation. However, in situ and in vitro studies consistently yield equivocal results when addressing individual DNA repair capacity and melanoma susceptibility. The primary objective of this study was to determine if individual global NER capacity is a risk factor for melanoma formation in a prominent UVB-inducible melanoma model, hybrid Xiphophorus fishes. After neonatal UVB irradiation, adult tumor-bearing and tumor-free fish were given a challenge UVB dose and (6-4) photoproduct repair was quantified in individual fish at 24 h using radioimmunoassay. Despite considerable inter-individual variation in repair capacity, ranging from 13% to 91%, we found no difference in mean NER capacity between fish with and without melanomas, thus detaching global NER from melanomagenesis. Furthermore, despite epidemiological data indicating that sex and age are important risk factors underlying melanoma susceptibility, we found no difference in mean NER rates among the sexes or as a function of age. We conclude with a discussion of the apparent paradox of how inter-individual variation in NER is not a risk factor given the clear evidence that DNA damage underlies melanoma susceptibility.

Chemical Peels May Prevent Skin Cancers

Chemical peels are popular procedures for the rejuvenation of photoaged skin. They improve skin texture and improve dyspigmentation by controlled injury to the epidermis and dermis. Because this procedure is used on skin with a heightened risk for neoplastic transformation, its effect on nonmelanoma skin cancer formation comes into question. On the one …

UVB Radiation Induces Apoptosis in Keratinocytes by Activating a Pathway Linked to “BLT2-Reactive Oxygen Species”

The role of reactive oxygen species (ROS) in UVB-induced apoptosis has been established, but the molecular mechanisms of their production in response to UVB irradiation in keratinocytes are not well understood. In this study, we demonstrate that levels of BLT2, a low-affinity leukotriene B(4) receptor, and its ligands (LTB(4) and 12(S)-HETE) are greatly increased by UVB irradiation and are responsible for the UVB-induced ROS generation in human keratinocytes. Blockade of BLT2 with a BLT2-specific antagonist, LY255283, or with siBLT2 attenuated ROS production and apoptotic cell death detected by a number of criteria. Moreover, we found that the NADPH oxidase family protein Nox1 lies downstream of BLT2 and mediates UVB-induced ROS production and apoptosis. Topical treatment of mouse epidermal skin with LY255283 gave significant protection against UVB-induced sunburn-associated apoptotic damage. Finally, when BLT2-overexpressing transgenic mice were irradiated with UVB, we observed more extensive skin apoptosis. Taken together, our results demonstrate that a "BLT2-Nox1"-linked pathway has a crucial role in UVB-induced ROS generation and mediates apoptosis in human keratinocytes.

Melanoma Associated With Long-term Voriconazole Therapy

Voriconazole is a triazole antifungal agent approved by the US Food and Drug Administration for serious fungal infections, including with Aspergillus, Fusarium, Pseudallescheria, and Scedosporium species. In initial clinical trials, approximately 2% of patients developed cutaneous reactions, including photosensitivity, cheilitis, and xerosis. Subsequent reports have implicated voriconazole as a cause of severe photosensitivity and accelerated photoaging, pseudoporphyria cutanea tarda, and aggressive squamous cell carcinoma. We report 5 melanoma in situ lesions in the setting of extreme photosensitivity associated with long-term voriconazole therapy. We recommend surveillance for skin cancer formation in all patients who require long-term voriconazole treatment, particularly those who manifest signs or symptoms of photosensitivity or chronic photodamage. Further study of the mechanism underlying voriconazole photosensitivity and oncogenesis is warranted.

Inhibition of immune responses by Dasatinib may account for its different effects on neuroblastoma between in vitro and in vivo

Nonreceptor tyrosine kinase Src is found to be overexpressed in many cancers and plays an important role in cancer formation, progression and metastasis via the activation of several downstream signal pathways and cytoskeleton.1-3 Overexpression of Src negative regulator csk suppresses tumor metastasis in a mouse colon cancer model.4 Thus, inhibition of Src could be used for the treatment of those cancers with overexpressed Src. Many small molecules have been developed for the purpose, and several agents are currently under clinical trials.1 Dasatinib is a second-generation Src inhibitor with stronger effect on cancer cells.5 Except Src, Dasatinib also inhibits other kinases or nonkinase proteins. However, its actual effect in cancer treatment still needs further investigation. The article “activity of tyrosine kinase inhibitor Dasatinib in neuroblastoma cells in vitro and in orthotopic mouse model” by Vitali et al. published in your journal is highly interesting. The study provides an important observation that Dasatinib strongly inhibits the growth of neuroblastoma cells and induces senescence and apoptosis in vitro. However, Dasatinib does not produce the expected effect in vivo. This important issue has to be further understood to improve clinical implication of Dasatinib. I think that this phenomenon may be explained by the inhibition of the immune system in vivo by Dasatinib via Src. Although overexpression of Src plays an important role in the pathogenesis of cancer, the normal expression of Src is necessary for the immune responses.6, 7 Immune responses are critical for surveillance and eradication of cancer cells. In the cancer treatment, weaken cancer cells need to be cleaned by immune cells. Thus, immunotherapy has been used to increase the effect of chemotherapy and reduce the dose of cytotoxicity drugs and therefore reduce their side effects.8 Many studies have demonstrated that inhibition of Src affects both innate and adaptive immune responses. Src has been demonstrated to be important in the activation of macrophage, dendritic cells and natural killer cells.7, 9 It has also been shown to control cytokine production such as production of TNF-alpha stimulated by LPS, which is inhibited by Dasatinib.10 Through DC and cytokine production, it can affect adaptive immunity. Evidence has shown the important role of Src in T-cell development.11 Indeed, Dasatinib has been shown to inhibit effector CD4+, CD8+ T-cells,12, 13 NK cells9 and CD4+ CD25+ regulatory T cells.14 A recent study has investigated Dasatinib for its immunosuppression effect in 16 CML patients at a dose of 140 mg/day.15 In these patients, Dasatinib has caused decreases in cell numbers of T-cells, B-cells and natural killer cells. The decreased immune responses caused by Dasatinib may be associated with observed increased infections and formation of skin cancer in Dasatinib-treated patients.15 It will be interesting to further examine the immune system in the model used by Vitali et al. The insight into immune responses altered by Dasatinib may have implications in the design of therapy regime either by adding immune therapy agents or reducing the dosage but used with other chemotherapy drugs so that the immune system is well maintained when aiming to weaken cancer cells by the inhibition of the Src signal pathway. Indeed, the combination therapy with cytotoxic agent has been used to achieve good outcome. The combination with immunotherapy may also produce better outcome. Yours sincerely, Jiezhong Chen.

The UV response of the skin: a review of the MAPK, NFκB and TNFα signal transduction pathways

The sun emits different types of ultraviolet (UV) light. Our skin is a natural target of UV radiation which is involved in vitamin D3 production in our body. UV radiation at high doses is an environmental carcinogen which can elicit skin damage as well as inducing skin cancer. It can mediate inflammatory and immunological reactions through activation of receptors, DNA/RNA damage and production of reactive oxygen species. It is also involved in the release of pro-inflammatory cytokines, of which TNFalpha has been implicated in tumorigenic activities. In order to mediate its effects, UV radiation is known to activate multiple signalling cascades such as the p38 MAPK, Jun N-terminal kinase, extracellular signal-regulated kinase 1/2 and NFkappaB pathways in skin cells. The role each of these pathways plays in mediating the release of cytokines such as TNFalpha remains to be fully characterized. Once the function of these pathways is known, this information may provide for the formulation of therapy which will prevent the release of immunosuppressive cytokines resulting in a reduction in skin cancer formation.

Flash Photolysis of Cutinase: Identification and Decay Kinetics of Transient Intermediates Formed upon UV Excitation of Aromatic Residues

Aromatic amino acids play an important role in ultraviolet (UV)-induced photochemical reactions in proteins. In this work, we aim at gaining insight into the photochemical reactions induced by near-UV light excitation of aromatic residues that lead to breakage of disulfide bridges in our model enzyme, Fusarium solani pisi cutinase, a lipolytic enzyme. With this purpose, we acquired transient absorption data of cutinase, with supplemental experimental data on tryptophan (Trp) and lysozyme as reference molecules. We here report formation kinetics and lifetimes of transient chemical species created upon UV excitation of aromatic residues in proteins. Two proteins, lysozyme and cutinase, as well as the free amino acid Trp, were studied under acidic, neutral, and alkaline conditions. The shortest-lived species is assigned to solvated electrons (lifetimes of a few microseconds to nanoseconds), whereas the longer-lived species are assigned to aromatic neutral and ionic radicals, Trp triplet states, and radical ionic disulphide bridges. The pH-dependent lifetimes of each species are reported. Solvated electrons ejected from the side chain of free Trp residues and aromatic residues in proteins were observed 12 ns after excitation, reaching a maximum yield after ∼40 ns. It is interesting to note that the formation kinetics of solvated electrons is not pH-dependent and is similar in the different samples. On the other hand, a clear increase of the solvated electron lifetime is observed with increasing pH. This observation is correlated with H3O+ being an electron scavenger. Prolonged UV illumination of cutinase leads to a larger concentration of solvated electrons and to greater absorption at 410 nm (assigned to disulphide electron adduct RSSR •−), with concomitant faster decay kinetics and near disappearance of the Trp• radical peak at 330 nm, indicating possible additional formation of TyrO• formed upon reaction of Trp• with Tyr residues. Prolonged UV illumination of cutinase also leads to a larger concentration of free thiol groups, known to originate from the dissociation of RSSR •−. Additional mechanisms that may lead to the near disappearance of Trp• are discussed. Our study provides insight into one key UV-light-induced reaction in cutinase, i.e., light-induced disruption of disulphide bridges mediated by the excitation of aromatic residues. Knowledge about the nature of the formed species and their lifetimes is important for the understanding of UV-induced reactions in humans that lead to light-induced diseases, e.g., skin cancer and cataract formation.

Activation of P2X7-mediated apoptosis Inhibits DMBA/TPA-induced formation of skin papillomas and cancer in mice

BackgroundThe study tested the hypothesis that apoptosis can prevent and control growth of neoplastic cells. Previous studies in-vitro have shown that the pro-apoptotic P2X7 receptor regulates growth of epithelial cells. The specific objective of the present study was to understand to what degree the P2X7 system controls development and growth of skin cancer in vivo, and what cellular and molecular mechanisms are involved in the P2X7 action.MethodsSkin neoplasias in mice (papillomas, followed by squamous spindle-cell carcinomas) were induced by local application of DMBA/TPA. Experiments in-vitro utilized cultured epidermal keratinocytes generated from wild-type or from P2X7-null mice. Assays involved protein immunostaining and Western blots; mRNA real-time qPCR; and apoptosis (evaluated in situ by TUNEL and quantified in cultured keratinocytes as solubilized DNA or by ELISA). Changes in cytosolic calcium or in ethidium bromide influx (P2X7 pore formation) were determined by confocal laser microscopy.Results(a) Co-application on the skin of the P2X7 specific agonist BzATP inhibited formation of DMBA/TPA-induced skin papillomas and carcinomas. At the completion of study (week 28) the proportion of living animals with cancers in the DMBA/TPA group was 100% compared to 43% in the DMBA/TPA+BzATP group. (b) In the normal skin BzATP affected mainly P2X7-receptor – expressing proliferating keratinocytes, where it augmented apoptosis without evoking inflammatory changes. (c) In BzATP-treated mice the degree of apoptosis was lesser in cancer than in normal or papilloma keratinocytes. (d) Levels of P2X7 receptor, protein and mRNA were 4–5 fold lower in cancer tissues than in normal mouse tissues. (e) In cultured mouse keratinocytes BzATP induced apoptosis, formation of pores in the plasma membrane, and facilitated prolonged calcium influx. (f) The BzATP-induced apoptosis, pore-formation and augmented calcium influx had similar dose-dependence for BzATP. (g) Pore formation and the augmented calcium influx were depended on the expression of the P2X7 receptor, while the BzATP-induced apoptosis depended on calcium influx. (h) The BzATP-induced apoptosis could be blocked by co-treatment with inhibitors of caspase-9 and caspase-3, but not of caspase-8.Conclusion(a) P2X7-dependent apoptosis is an important mechanism that controls the development and progression of epidermal neoplasia in the mouse. (b) The P2X7-dependent apoptosis is mediated by calcium influx via P2X7 pores, and involves the caspase-9 (mitochondrial) pathway. (c) The diminished pro-apoptotic effect of BzATP in mouse cancer keratinocytes is possibly the result of low expression of the P2X7 receptor. (d) Activation of P2X7-dependent apoptosis, e.g. with BzATP could be a novel chemotherapeutic growth-preventive modality for papillomas and epithelial cancers in vivo.

Vol. 42, No. 1, pp.1‐6, 2008 Overview of cosmetic dermatological approach for photoaging

Photoaging could be induced by accumulated DNA damage on skin cells. Photoaged skin has such characteristics as a nodular leathery surface with fine and coarse wrinkles, blotches and yellowing, dryness, and teleangiectasia, and finally skin cancer formation. For this condition, chemical peeling, iontophoresis, laser and phototherapy are used with some improvement, especially in wrinkles and pigmentary uniformity. Now the mechanisms of these treatments on photoaging have been studied. Glycolic acid may act on skin cells via keratinocytes and activate the cytokine network, which results in the remodeling of tissue construct and elimination of pigment. Heat generated by non‐ablative laser or phototherapy might induce heat shock proteins which induce new collagen formation, and eliminate oxidized abnormal materials. This type of research is expected to disclose the cellular and molecular mechanisms of photoaging, and to lead to the establishment of further effective photoaging treatment.Keywords: photoaging, cosmetic dermatology, chemical peeling, glycolic acid, skin rejuvenation, non‐ablative laser, Intense pulsed light (IPL), heat shock protein (hsp), matrix metalloproteinase (MMP), thermal stimulation, advanced glycation end products (AGE), oxidative stress

Imiquimod treatment associated with a reduction in new skin cancer formation

Conflict of interest: none declared. Patients who have had skin cancer have a high risk of developing new skin cancers. A prospective study from Australia found that two‐thirds of patients develop new skin cancers within 5 years but that the risk varies depending on the number of cancers removed. All of those who had developed ≥ 3 tumours developed new tumours.1 Further study revealed that patients who had had ≥ 3 skin cancers developed new lesions at a constant rate over 10 years.2 We report a case where the use of imiquimod to treat basal cell carcinomas (BCCs) resulted in a significant decrease in the number of new tumours over 7 years. The patient, a man currently aged 67 years, was first seen in April 1996 when he presented with multiple skin cancers. He had had several skin cancers removed in the preceding years by other doctors. He was in good health and did not have any other illnesses. In 1996, 17 BCCs were surgically removed and a further 34 were removed up to the end of 2000. From early 2001, imiquimod was used to treat new BCCs. The patient or his wife applied the cream once a day for 6 weeks to each lesion. Between 2001 and 2005, 16 histologically confirmed new BCCs were treated with imiquimod and three cancers were surgically excised. In 2005, the patient developed lung cancer despite never having smoked. The lung cancer was treated by surgical excision and chemotherapy with carbopatin and gencitabine.

Keratinocyte-specific Smad2 ablation results in increased epithelial-mesenchymal transition during skin cancer formation and progression

TGF-beta and its signaling mediators, Smad2, -3, and -4, are involved with tumor suppression and promotion functions. Smad4-/- mouse epidermis develops spontaneous skin squamous cell carcinomas (SCCs), and Smad3-/- mice are resistant to carcinogen-induced skin cancer; however, the role of Smad2 in skin carcinogenesis has not been explored. In the present study, we found that Smad2 and Smad4, but not Smad3, were frequently lost in human SCCs. Mice with keratinocyte-specific Smad2 deletion exhibited accelerated formation and malignant progression of chemically induced skin tumors compared with WT mice. Consistent with the loss of Smad2 in poorly differentiated human SCCs, Smad2-/- tumors were poorly differentiated and underwent epithelial-mesenchymal transition (EMT) prior to spontaneous Smad4 loss. Reduced E-cadherin and activation of its transcriptional repressor Snail were also found in Smad2-/- mouse epidermis and occurred more frequently in Smad2-negative human SCCs than in Smad2-positive SCCs. Knocking down Snail abrogated Smad2 loss-associated EMT, suggesting that Snail upregulation is a major mediator of Smad2 loss-associated EMT. Furthermore, Smad2 loss led to a significant increase in Smad4 binding to the Snail promoter, and knocking down either Smad3 or Smad4 in keratinocytes abrogated Smad2 loss-associated Snail overexpression. Our data suggest that enhanced Smad3/Smad4-mediated Snail transcription contributed to Smad2 loss-associated EMT during skin carcinogenesis.