Chronic inflammation plays a multifaceted role in carcinogenesis. Mounting evidence from preclinical and clinical studies suggests that persistent inflammation functions as a driving force in the journey to cancer. The possible mechanisms by which inflammation can contribute to carcinogenesis include induction of genomic instability, alterations in epigenetic events and subsequent inappropriate gene expression, enhanced proliferation of initiated cells, resistance to apoptosis, aggressive tumor neovascularization, invasion through tumor-associated basement membrane and metastasis, etc. Inflammation-induced reactive oxygen and nitrogen species cause damage to important cellular components (e.g., DNA, proteins and lipids), which can directly or indirectly contribute to malignant cell transformation. Overexpression, elevated secretion, or abnormal activation of proinflammatory mediators, such as cytokines, chemokines, cyclooxygenase-2, prostaglandins, inducible nitric oxide synthase, and nitric oxide, and a distinct network of intracellular signaling molecules including upstream kinases and transcription factors facilitate tumor promotion and progression. While inflammation promotes development of cancer, components of the tumor microenvironment, such as tumor cells, stromal cells in surrounding tissue and infiltrated inflammatory/immune cells generate an intratumoral inflammatory state by aberrant expression or activation of some proinflammatory molecules. Many of proinflammatory mediators, especially cytokines, chemokines and prostaglandins, turn on the angiogenic switches mainly controlled by vascular endothelial growth factor, thereby inducing inflammatory angiogenesis and tumor cell-stroma communication. This will end up with tumor angiogenesis, metastasis and invasion. Moreover, cellular microRNAs are emerging as a potential link between inflammation and cancer. The present article highlights the role of various proinflammatory mediators in carcinogenesis and their promise as potential targets for chemoprevention of inflammation-associated carcinogenesis.

Inflammation: gearing the journey to cancer.

Aging is a complex, multifactorial process resulting in several functional and esthetic changes in the skin. These changes result from intrinsic as well as extrinsic processes, such as ultraviolet radiation. Recent advances in skin biology have increased our understanding of skin homeostasis and the aging process, as well as the mechanisms by which ultraviolet radiation contributes to photoaging and cutaneous disease. These advances in skin biology have led to the development of a diversity of treatments aimed at preventing aging and rejuvenating the skin. The focus of this review is the mechanism of photoaging and the pathophysiology underlying the treatments specifically designed for its prevention and treatment. Learning objectives At the conclusion of this learning activity, participants should be familiar with the mechanism of photoaging, the treatments for photoaging, and the data that supports the use of these treatments.

Photoaging: Mechanisms and repair

Signal transduction pathways regulating cyclooxygenase-2 expression: potential molecular targets for chemoprevention.

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 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.

Photochemoprevention of ultraviolet B signaling and photocarcinogenesis

https://piel-l.org/blog/wp-content/uploads/2014/04/2008.Photoproteccion.Clinics-Dermatology_2008_266_614-626.pdf

The latest on skin photoprotection.

Inflammation, which includes the release of growth factors, proinflammatory cytokines and prostaglandins, the infiltration and activation of inflammatory cells, and the induction of oxidative DNA damage, is known to play a role in cancer development. The combination of damage to the skin resulting from chronic ultraviolet light B (UVB) exposure itself and the inflammatory response it induces is a major source of skin cancer development. Cyclooxygenase-2 (COX-2), an inflammatory enzyme responsible for the production of prostaglandins, is now implicated in the development of epithelial cancers, including squamous cell carcinoma in the skin. Previous work conducted in our laboratory has shown that topical treatment with celecoxib following UVB irradiation inhibits several parameters of acute inflammation, including vascular permeability, the infiltration and activation of neutrophils, and the production of prostaglandin E(2) (PGE(2)). The present studies expanded these observations, demonstrating the ability of topical celecoxib to inhibit acute oxidative damage. In addition, long-term studies illustrate the effectiveness of topical treatment with this drug in reducing chronic inflammation and UVB-induced papilloma/carcinoma formation. This data provides compelling evidence to explore the clinical efficacy of topically applied COX-2 inhibitors for the prevention of human skin cancers.

Inhibition of cutaneous ultraviolet light B–mediated inflammation and tumor formation with topical celecoxib treatment

Over a million nonmelanoma skin cancer cases will be reported in the United States this year alone. Currently the primary form of treatment for these types of skin tumors is excision. However, excision of the initial lesion may not be curative because almost 50% of patients with one nonmelanoma skin cancer lesion develop another tumor within the next 5 yr at the site or adjacent to the site of excision. As with other types of epithelial based cancers, there is mounting evidence for the role of cyclooxygenase-2 (COX-2) and its products, particularly prostaglandin E2 (PGE2), in the development of nonmelanoma skin cancer. To avoid the excision process, the present study was designed to evaluate the possible chemotherapeutic effect of directly treating established tumors with a topical formulation of the specific COX-2 inhibitor celecoxib. Skh/hr hairless mice were irradiated three times per wk for 16 wk to induce tumor formation. The mice were then divided into two groups and treated topically with either 500 μg celecoxib or the vehicle for 6 wk. Our results demonstrated that although topical treatment with celecoxib was not able to induce regression of established tumors, it did prevent new tumor formation after the onset of photocarcinogenesis. Although further studies are warranted, these data suggest that topical celecoxib treatment may prove to be effective in preventing the recurrence of tumors at the site of nonmelanoma skin cancer excision. © 2003 Wiley-Liss, Inc.

Patricia A. Rubal

Papers

Inhibition of cutaneous ultraviolet light B–mediated inflammation and tumor formation with topical celecoxib treatment

Chemotherapeutic efficacy of topical celecoxib in a murine model of ultraviolet light B-induced skin cancer.