title: Sunscreens protect from UV-promoted squamous cell carcinoma in mice chronically irradiated with doses of UV radiation insufficient to cause edema.
abstract: Previously we reported that the broad-spectrum sunscreen microfine titanium dioxide (MTD) could completely protect C3H/HeJ mice from UV radiation-induced immunosuppression to a contact sensitizer. In contrast, 2-ethylhexyl p-methoxycinnamate (2-EHMC), a UVB-absorbing sunscreen, only partially protected the skin immune system. In this study we investigated further this differential protection of the skin immune system by comparing the ability of 2-EHMC and MTD to protect these mice from the promotion phase of tumorigenesis. The mice were initiated using a single subcarcinogenic dose of 7,12-dimethylbenz(alpha)anthracene (DMBA) followed by promotion with chronic low-dose solar-simulated UV radiation for 32 weeks. We used doses of UV insufficient to cause edema in order to simulate daily human exposure to solar UV radiation. Mice were observed for the appearance of squamous cell carcinomas for 48 weeks. The DMBA-initiation alone and DMBA-initiated, sunscreen-treated groups did not develop tumors. Ultra-violet alone induced the appearance of tumors in 46% of mice at week 48 and therefore some tumors were initiated by UV. Initiation with DMBA prior to UV irradiation enhanced tumorigenesis such that 87% of mice at week 48 had tumors. Both 2-EHMC and MTD completely protected these mice from UV-induced promotion as well as from complete carcinogenesis despite the different UV-absorption spectra of the sunscreens and their differential abilities to protect from UV-induced immuno-suppression. Furthermore, we have shown that, if UV exposure is not increased to compensate for tolerance to edema, protection from tumorigenesis is afforded by sunscreens.
authors.affiliation: Department of Medicine (Dermatology), University of Sydney, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Bestak
authors.forename: G M
authors.initials: GM
authors.lastname: Halliday
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000517:prevention & control*; D002934:Cinnamates / Q000494:pharmacology; D005260:Female; D006801:Humans; D051379:Mice; D008809:Mice, Inbred C3H; D009381:Neoplasms, Radiation-Induced / Q000517:prevention & control*; D012878:Skin Neoplasms / Q000517:prevention & control*; D013473:Sunscreening Agents / Q000494:pharmacology*; D014025:Titanium / Q000494:pharmacology; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D002934:Cinnamates; D013473:Sunscreening Agents; C009495:titanium dioxide; C118580:octylmethoxycinnamate; D014025:Titanium