Table 1.

Inhibitory effect of topical applications of caffeine on the formation of phospho-Chk1 (Ser317) in skin tumors of high-risk mice previously treated with chronic UVB

TreatmentNo. of tumors examinedNo. of cells examinedPercent tumor cells with caspase 3–positive stainingPercent phospho- Chk1 (Ser317)- positive tumorsPercent tumor cells with phospho-Chk1 (Ser317)-positive stainingphospho-Chk1 (Ser317) staining (intensity score)
Keratoacanthoma
 Acetone59258,0000.194 ± 0.020415.84 ± 1.430.68 ± 0.16
 Caffeine50176,0000.469 ± 0.045a18a2.09 ± 0.94b0.18 ± 0.06a
 Percent change142–56−64−74
Squamous cell carcinoma
 Acetone33555,0000.196 ± 0.0226411.97 ± 3.361.49 ± 0.30
 Caffeine10110,0000.376 ± 0.056a4010.45 ± 4.850.40 ± 0.16b
 Percent change92–38−13−73

NOTE: Female SKH-1 mice (7–8 weeks old) were irradiated with UVB (30 mJ/cm2) twice a week for 20 weeks and UVB treatment was stopped. Three weeks later, these tumor-free high-risk mice were randomized and divided into 2 groups (30 mice per group) and treated topically with 100 μL acetone or with caffeine (6.2 μmoles) in 100 μL acetone once daily 5 days a week for 18 weeks. Phospho-Chk1 (Ser317) and caspase 3–positive cells were determined immunohistochemically. Substantially stronger staining for phospho-Chk1 (Ser317) was observed in islands of positive cells in squamous cell carcinomas than in islands of positive cells in keratoacanthomas, and treatment with caffeine decreased the intensity of staining in both types of tumors. The intensity of staining was quantified from all tumor cells by using the following intensity scoring system: 0, no to very weak; 1, very weak; 2, weak; 3, moderate; 4, strong; 5, very strong. Each value represents the mean ± SE.