Arsenic-induced carcinogenesis is a worldwide problem for which there is currently limited means for control. Recently, we showed that arsenite in drinking water significantly potentiates solar ultraviolet radiation (UVR) induced skin cancer in mice at concentrations as low as 1.25 mg/l. In this study, we examined the protective efficacy of vitamin E and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) against tumors induced by UVR and UVR + arsenite. Hairless mice were exposed to UVR alone (1.0 kJ x 3 times weekly) or UVR + arsenite (5mg/l in drinking water) and fed lab chow supplemented or not with vitamin E (RRR-alpha-tocopheryl acetate, 62.5 IU/kg diet) or p-XSC (10 ppm) for 26 weeks. The tumor yield for mice receiving UVR alone was 3.5 tumors/mouse and the addition of arsenite to the drinking water increased the yield to 7.0 tumors/mouse (p<0.05). Vitamin E and p-XSC reduced the tumor yield in mice given UVR + arsenite by 2.1-fold (p=0.001) and 2-fold (p=0.013), respectively. Vitamin E, but not p-XSC, reduced the tumor yield induced by UVR alone by 30% (p<0.05). No significant difference in tumor types or grade of malignancy was observed in mice treated with or without chemopreventives. Immunostaining of mouse skin for 8-oxo-2’-deoxyguanosine (8-oxo-dG) revealed a significant reduction of 8-oxo-dG formation in mice treated with vitamin E or p-XSC compared with those treated with UVR + arsenite. These results indicate that vitamin E and p-XSC protects strongly against arsenite-induced enhancement of UVR carcinogenesis. The data support the hypothesis that the protection is mediated by an anti-oxidative mechanism.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]