Search

Background and Objectives The effects of chronic sun damage including telangiectasias, solar lentigos, rhytides, enlarged pores, sagging skin, and pre-cancerous and cancerous growths are among the most common presenting complaints in a dermatologist's office. These changes are often worse on the driver's side of the face, emphasizing the role of UVA exposure received while driving in producing these changes. This study was undertaken to measure the ability of car window glass alone and in combination with ultraviolet (UV)-absorbing film to reduce UV-damage as measured using an established in vitro model of photoprotection. Study Design Materials and Methods Using the 3T3 neutral red uptake photoprotection assay with solar simulating radiation (SSR) administered by a xenon arc solar simulator, we measured the photoprotection ability of auto glass, window film that filters UV radiation, and the combination of window film and auto glass. Results As measured by the 3T3 neutral red uptake photoprotection assay, auto glass reduced cell death from SSR by 29%, while window film reduced it 90%, and the combination of auto glass and film reduced cell death by 93%, when compared to unfiltered SSR. Conclusions Window film that filters UV radiation results in dramatic reductions in cytotoxicity when measured by the neutral red uptake photoprotection assay. Widespread use of window film provides an ever-present barrier to ultraviolet A (UVA) exposure and could potentially reduce the detrimental effects of UVA, including photoaging, skin cancer, and ocular damage, such as cataracts. In addition, such film is essential for patients suffering from conditions sensitive to UV radiation, such as lupus erythematosis. Lasers Surg. Med. 38:337–342, 2006. © 2006 Wiley-Liss, Inc.

A multiple induction test procedure that extends a single induction test procedure proposed by Kodell and Chen (Biometrical J. 43(4) (2001) 447) based on the work of Kokoska et al. (Anticancer Res. 13 (1993) 1357) is introduced. The new procedure can detect overall differences between two groups as well as isolate differences in the distribution of the number of induced tumors and the distribution of their times to observation. This “frequency-latency” procedure is illustrated with an analysis of data from a multiple dosing experiment, using a likelihood ratio method of testing. The results of the frequency-latency test are compared to those of the logrank test, the negative binomial test, and the test proposed by Dunson et al. (Toxicol. Sci. 55 (2000) 293). A Monte Carlo simulation study is performed to evaluate the accuracy of the parameter estimates of the frequency-latency procedure as well as to study the Type I error rates of the frequency-latency test, the logrank test, and the negative binomial test.

New drugs undergo safety evaluations of many types. For some drugs, a photocarcinogenesis study forms one of the elements in the overall toxicology package. Photocarcinogenesis studies are designed to evaluate a drug's ability to modify the growth and development of ultraviolet radiation (UVR)-induced skin tumors in albino hairless mice. "Exposure control" groups in such studies receive the UVR, either alone, or in combination with the "vehicle" or carrier associated with each study. This report presents skin tumor data from control groups compiled from nine consecutive studies conducted at this testing facility. The endpoints evaluated included median tumor onset, mortality-free prevalence and tumor yield. "Historical control data" are considered essential for designing, monitoring, interpreting and evaluating studies of a given type. In addition, a compilation of such control data can illustrate trends or provide measures of reproducibility more reliably than can individual studies. This data set shows how clearly the UVR-induced skin tumor onset time is dependent on UVR dose, how skin tumors develop sooner in female mice than in male mice at a low UVR exposure dose, and that topical administration of certain vehicle formulations can enhance photocarcinogenesis.

Tacrolimus is a potent immunosuppressant marketed for the prevention of rejection in liver and kidney transplantation. Topical tacrolimus has been shown to be effective in the treatment of atopic dermatitis, a disease with an immunologic basis, and is currently being developed for this indication. The objective of the current study was to determine whether repeated topical application of tacrolimus ointment could result in hypopigmentation at the application site(s). Each of 10 Yucatan miniature pigs received topical application of 0.03%, 0.1%, and 0.3% tacrolimus ointment, positive control (a combination of 2% 4-hydroxyanisole and 0.01% all-trans-retinoic acid, 4-HAArRA), and a negative control (vehicle placebo) to five test sites (approximately 12.5 cm2) along either side of the dorsal midline (10 sites per animal). Tacrolimus and controls were randomly assigned to the test site on each animal and were applied unoccluded twice daily for 8 weeks at a dose volume of 0.1 ml per site for tacrolimus and vehicle control and 0.025 ml per site for the positive control. Topical application of tacrolimus ointment in concentrations of up to 0.3% for 8 weeks had no effect on the cutaneous pigmentation of Yucatan miniature swine. In contrast, the application of 4-HAArRA produced a statistically significant (P

The acute phototoxic potential of tacrolimus (FK506) ointment was investigated in Crl:SKH1-hr hairless mice. Response toa series of ultravioletradiation (UVR) site exposures in males (five group) following a single topical administration of tacrolimus ointment (0%[vehicle], 0.03%, 0.1%, 0.3%, 1%, or 3%) indicated that tacrolimus ointment was neither photoprotective or phototoxic. However, a slight but dose-related decrease in body weight relative to the vehicle control was found at the end of the 4-day observation period in the tacrolimus ointment-treated groups. The same concentrations of tacrolimus ointment were applied to the back and sides of mice (five sex group; ∼40% of total body surface area) 5 days week in a 13-week range-finding study to assess the tolerance to the ointment and UVR exposure. Untreated animals served as a control group. Mice were exposed to 72 minutes of UVR from a 6.5-kW xenon lamp. Mortality occurred in the 0.3%, 1%, and 3% ointment groups. Application of 3% tacrolimus ointment was associated with reduced body weight. Mild to moderate erythema and/or edema were noted in all tacrolimus ointment-treated groups. Histopathologi-cal examination indicated a mild increase in the prominence of the stratum granulosum and mild acanthosis of the epidermis in both vehicle-treated and tacrolimus ointment-treated mice. Stomach, esophageal, and/ or abdominal cavity lesions, indicative of systemic toxicity and possibly associated with the in gestion of ointment vehicle during preening, were observed during necropsy. There was minimal photo-mediated dermal toxicity of tacrolimus ointment in the 13 weeks of exposure in the present study.

In the three and a half decades since the first published reports of squamous cell carcinomas in the skin of hairless mice exposed to ultraviolet radiation, this animal model has been developed and utilized extensively in basic and applied photobiology. Quantitative aspects of photocarcinogenesis had been investigated initially in haired mice; subsequently, the discipline of photoimmunology has developed largely on the basis of information derived from haired animals. Classical selective breeding methods, a few fortuitous mutations along the way, and the advent of genetic engineering have all enhanced the utility of the laboratory animal models. The benefits have included advances in our understanding of many influences on photocarcinogenesis such as genetic diversity, animal age, epidermal DNA damage and repair, wavelength dependency (action spectrum), ultraviolet radiation dose and its delivery, interactions with chemicals, and nutrition. As in other fields of basic and biomedical research, photobiological data have not been considered journalistically newsworthy or particularly contentious until they acquired potential economic impact. Thus, photocarcinogenesis became a more familiar word (at least along the Washington Beltway) when stratospheric ozone first appeared to be threatened by chlorofluorocarbons, and trends in photocarcinogenesis seemed less arcane when it appeared that the trends might be modified by consumer products and pharmaceuticals. The greatest challenge has not been in finding imaginative ways to exploit the models and to push the frontiers of science, but rather has been the uncertainty about quantitatively extrapolating the findings to humans. Research models would hardly be useful if they were not different from people (i.e., smaller, quicker to respond, shorter lived), and that fact encompasses differences in anatomy, physiology, metabolism, surface-to-weight ratios, etc. Selected examples from photomedicine (e.g., chronic solar damage, occupational exposure to tar, psoriasis phototherapy) tend to confirm that several basic principles about photocarcinogenesis are shared by man and mouse; other risk assessments await development and refinement, or remain to be corrected by experience.

Photosafety testing is an important component in preclinical drug development, but one that is not well understood as to the accepted methodologies, when to initiate evaluation, the expectations of the regulatory agencies, and how to interpret results. The lack of clarity in current regulatory guidances, controversy over the interpretation of in vitro assays and the absence of formally-validated/accepted in vivo assays have affected the ability to clearly understand how to evaluate photosafety in a drug discovery program. Experience with current test models, borne of experience, does allow for evaluation of the phototoxic potential of drugs and chemicals, but ambiguity remains. Over the past five years, serious efforts to address this uncertainty have been initiated but further work is needed to critically evaluate and, as necessary, refine the current methods, propose new methods and clearly state regulatory expectations. However, work remains.

Summary: Photocarcinogenesis is the production of tumors by sunlight. Since consumer products have been found to modify the course of cutaneous photocarcinogenesis in animal models, and since this modification is thought to be clinically relevant, we have developed and implemented procedures to evaluate a test article/substance as a potential modifier of photocarcinogenesis. Prior to beginning a photocarcinogenesis study, range-finding studies are conducted to determine certain characteristics of the test article/substance and its vehicle (e.g., primary irritancy, photosensitivity, and photoprotection). Additionally, the doses of test article/substance, the doses of sunlight exposure, and the most appropriate sequence for administering these two variables are determined from the range-finding studies and the intended use of the test article/substance. The test system is the Crl:SKH1 (hr/hr)BR, albino, hairless mouse. The source of “sunlight” is a 6.5 kW xenon arc lamp modified to emit radiation th...

Skin tumors, including malignant melanomas, squamous cell carcinomas and basal cell carcinomas, are the most frequently occurring tumors in man. Squamous cell carcinomas are readily induced in mice by topical administration of chemical carcinogens (e.g., 9,10-dimethyl-1,2-benzanthracene, DMBA) or exposure to ultraviolet radiation (UVR). Mammalian models for the induction of malignant melanomas and basal cell carcinomas are not readily available [1–12]. We investigated the occurrences of melanotic lesions and non-melanotic skin tumors in pigmented hairless mice using a variety of treatment regimens with topical DMBA administration and UVR exposure.

Most safety tests are designed to determine whether an agent, such as a drug or chemical, will adversely affect some normal physiological component or process. In contrast, most photobiological safety tests seek to determine whether a chemical can amplify the known noxious effects of an external agent, ultraviolet radiation (UVR). Tests for phototoxicity, for example, determine whether suberythemal doses of radiation will produce acute damage in the presence of the test agent: such tests are always preceded by a determination that the agent alone does not produce such damage. It is understood that higher doses of UVR (or, in some cases, different radiation spectra) are capable of producing erythema in the absence of the test agent, but for testing purposes the effects of low doses of UVR are regarded as the “normal” state against which toxic effects are to be evaluated. Tests for photoallergic properties may go even further in altering the reference “normal” state, by imposing various forms of trauma at either initiation or elicitation stages. The justification for introducing external trauma in a photobiological safety test is the assumption that some exposure to environmental UVR is virtually inevitable; thus an agent which can intensify trauma induced by UVR is capable of intensifying a “normal” and expected biological response.

Sunscreen preparations can reduce the erythemogenic (sunburning) effects of solar ultraviolet radiation (UVR). Less is known about the ability of sunscreens to protect against other forms of UYR-induced damage. This study was designed to yield data on epidermal cell damage at UVR doses sufficient to provoke vascular changes (edema and erythema) in hairless mice, and to determine the comparative effectiveness of a commercial sunscreen in protecting against these two criteria of injury. The sunscreen (Piz Buin 12 Sun Protection Cream) was used at full concentration and at three serial dilutions. The dorsa of 144 hairless mice were treated with one of six sunscreen or vehicle preparations and subsequently irradiated with one of six exposures to an appropriately filtered xenon arc solar simulator. Vascular responses were determined by observing the animals for alterations in the gross appearance of the treated and irradiated sites (edema and erythema). Epidermal cell damage was assessed by determining the sunburn cell (SBC) indices in the epidermis removed 24 hours after irradiation. Both the vascular responses and SBC indices indicated that the sunscreen provided concentration-dependent protection against radiation damage. Furthermore, SBC indices provided a relatively continuous variable for quantification of sunscreen effectiveness.

This study used simulated solar ultraviolet radiation (UVR) exposure of hairless mice to produce skin tumors and 12-o-tetradecanoyl-phorbol-13-acetate (TPA) to increase the likelihood of tumor expression. We evaluated the protection afforded by several concentrations of a sunscreen ingredient (by measuring reduction of “promotable” effects initiated by UVR); the data show that 2-ethyl hexyl-p-methoxycinnamate (2-EHMC) provided protection against photocarcinogenesis (the level of protection increasing with concentration of sunscreen). A second sample of 2-EHMC (drawn from a different production batch) also suppressed photocarcinogenesis but less effectively than the first sample. The study was also useful for evaluating whether the test agents could act as initiators in the two-stage process of tumorigenesis. The data show that repeated applications of TPA did not promote tumor growth in skin pretreated with any sunscreen ingredients alone (i.e., either sample of 2-EHMC in the absence of UVR).

Squamous cell papillomas and carcinomas occur spontaneously with very low frequency in the skin of laboratory mice and rats. The incidence of tumors is markedly increased with ultraviolet (UV) irradiation. Skin tumors can be produced in animals from varied genetic backgrounds when subjected to simulated sunlight. The incidence within a given stock/strain may be altered by UV dose or by chemical enhancers; less information is available on tumor types as a function of the genetic origin (stock/strain) of animals. The hypotrichotic condition of hairless (hr) mice, cryptothrix (crh) mice, and fuzzy (fz) rats is attained by different mechanisms and the adult skin differs histologically. Others have reported that UV-irradiated skin of shaved haired mice produces a spindle cell tumor of epithelial origin; hr mice develop squamous cell papillomas and carcinomas. Crh mice and fz rats have tumors with histologic features that are influenced by their genetic origin.

The tumour-promoting activity of methyl ethyl ketone peroxide (MEKP) was tested on the skin of hairless mice using a two-stage initiation-promotion protocol. When ultraviolet radiation in the UVB region (280-320 nm) was used as tumour initiator, MEKP showed weak promoting activity. The promotional activity of MEKP was potentiated by diethyl maleate, which is known to deplete intracellular glutathione, suggesting that lipid peroxidation may be important in the tumour promotion.