Protective Effect of Dermal Brimonidine Applications Against UV Radiation-induced Skin Tumors, Epidermal Hyperplasia and Cell Proliferation in the Skin of Hairless Mice.

Brimonidine at 0.18%, 1% and 2% concentrations applied topically in hairless mice significantly decreased tumor burden and incidences of erythema, flaking, wrinkling and skin thickening induced by UVR. The unbiased median week to tumor 1 mm was increased by the 1% and 2% concentrations. The tumor yield was reduced by all concentrations at week 40 for all tumor sizes but the 4 mm tumors with the 0.18% concentration. At week 52, the tumor yield was reduced for all tumor sizes and all brimonidine concentrations. The tumor incidence was reduced by all concentrations at week 40 for all tumor sizes, but the 4 mm tumor with the 0.18% concentration and at week 52 for all tumor sizes with the 1% and 2% concentrations and with the 0.18% concentration only for the 4 mm tumors. Reductions in 4 mm tumor incidences compared to the vehicle control group were 54%, 91% and 86% by week 52 for the 0.18%, 1% and 2% concentrations, respectively. Brimonidine at 2% applied 1 h before or just after UVB irradiation on hairless mice decreased epidermal hyperplasia by 23% and 32% and epithelial cell proliferation by 59% and 64%, respectively, similar to an epidermal growth factor receptor (EGFR) inhibitor.