Inhibition of DNA and protein synthesis in UV-irradiated mouse skin by 2-difluoromethylornithine, methylglyoxal bis(guanylhydrazone), and their combination.

Exposure of mouse skin to UVB irradiation greatly enhanced the biosynthesis and accumulation of putrescine and spermidine before or concomitantly with stimulation of epidermal macromolecular (DNA and protein) synthesis. Topical treatment of UV-exposed skin with 2 inhibitors of polyamine biosynthesis, 2-difluoromethylornithine (DFMO) and methylglyoxal bis(guanylhydrazone) (MGBG) prevented the enhanced epidermal accumulation of polyamines, especially spermidine, and also inhibited the incorporation of radioactive precursors into DNA and protein. When applied in combination, these 2 antimetabolites of polyamines produced an inhibition of macromolecular synthesis that was at least additive: [3H]thymidine incorporation decreased by 80% and [14C]leucine incorporation by 44% as compared with the UVB-irradiated control mice. A slight decrease in the ratio of [3H]histidine/[14C]leucine incorporation indicated that protein synthesis of the differentiating cell layers was also affected by the inhibitors. The effects of the combined DFMO and MGBG treatment were partially reversed by concomitant topical application of spermidine.