The effects of topical L-selenomethionine on protection against UVB-induced skin cancer when given before, during, and after UVB exposure

Previous studies in mice have shown that topical L-selenomethionine (SeMet) can prevent UVB-induced skin cancer when applied continuously before, during, and after the radiation exposure. With topical application of SeMet, selenium levels were shown to increase in the skin and liver, as well as in tumor tissue. Thus, possibly, the timing of SeMet application could affect the degree of inhibition of UVB-tumorigenesis (or maybe even enhance tumorigenesis at some stage). The goal of this research was to determine whether topical SeMet best inhibits UV-induced skin cancer if (a) begun before and continued during and after UVB exposure, (b) if begun before UVB-exposure and discontinued when tumors are first clinically detected, or (c) if begun only after tumors are first detected and continued thereafter. Groups of ten Skh: 1 hairless, non-pigmented mice were treated topically with vehicle lotion, or with SeMet (0.05%) in that vehicle lotion applied either (a) before, during, and after UV exposure, (b) before UV radiation and continued only until the first tumor was detected, or (c) only after the first tumor was detected. In all cases, UV irradiation was discontinued at the time of detection of the first tumor. Optimal inhibition of skin cancer was achieved by application of topical SeMet before, during, and after exposure; significant protection was also attained with application only after the onset of tumors. Notably, statistically significant protection was not seen with SeMet application only prior to tumor detection. These results suggest that even beginning SeMet supplementation late in the process of tumorigenesis can help protect from UV-induced photodamage and skin cancer.