Christopher P. Sambuco

Inhibition of Ultraviolet Radiation-Induced Skin Tumors in Hairless Mice by Topical Application of the Sunscreen 2-Ethyl Hexyl-P-Methoxycinnamate

AbstractThis 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).

Skin-tumour promoting activity of methyl ethyl ketone peroxide—a potent lipid-peroxidizing agent

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.

Assays for Photocarcinogenesis: Relevance of Animal Models

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.

An Evaluation of the Phototoxicity of Tacrolimus (FK506) Ointment in Hairless Mice

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.

Comparative Histopathologic Appearance of UV-Induced Sicin Tumors in Hairless Mice, Crwtothrix Mice, and Fuzzy Rats

AbstractSquamous 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.

Topical Application of Tacrolimus Ointment Did Not Alter the Cutaneous Pigmentation of Yucatan Micropigs

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<.05) induction of hypopigmentation from week 4 through the end of the study application.

Photocarcinogenesis Safety Testing

IGHT-INDUCED TOXICITY has long been recognized as an important clinical entity; the principal target organs L are skin and eye. Phototoxicology is a subspeciality that addresses both the direct effects of optical radiation (i.e., visible and ultraviolet [UV] radiation) and the added influence of chemical and pharmaceutical agents. At scientific scminars, meetings and product development conferences, and during product reviews at regulatory agencies, many concerns about photocarcinogenesis safety testing have been raised and discussed. The most frequently asked questions, along with the best available current responses, are summarized in the general discussion section below. Guidelines for phototoxicology studies (including photocarcinogcnesis safety testing) are under consideration and have not yet been formalized in the United States. In the meantime, the toxicologists at the U.S. Food and Drug Administration continue to suggest that comp3nies submit protocols for their comment before initiating a testing program. The agency considers the need for phototoxicology data on a case-by-case basis, and an acceptable photocarcinogenesis study design is presented as the topic of this short communication.

Drug Products and Photocarcinogenesis

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.