[Melatonin and metformin inhibit skin carcinogenesis induced by benz(a)pyrene in mice]

One hundred and twenty SHR male mice were randomly divided into 4 groups. Their clean-shaven backs were painted with 0.2 ml of 0.05% acetone solution of benz(a)pyrene (BP) twice a week. Group 1 was in control and received no additional treatment. From beginning to end (6 months), the remaining mice received melatonin 2 mg/l with drinking water at nighttime (group 2), metformin 200 mg/l with drinking water during 24 hrs (group 3), melatonin and metformin as in groups 2 and 3 (group 4). There was a separate group of intact animals. Skin tumor frequency decreased: among melatonin/metformin-treated mice (groups 1-4) - 83.3%, 66.7%, 60%83 and 50%; squamous cell carcinoma - 56.73%, 36.7%, 20% and 20%. Treatment with melatonin and metformin and their combinations was followed by significantly lower tumor multiplicity and smaller size, longer latency period and survival of tumor-bearers. After BP, levels of malonic dialdehyde (MDA) and catalase rose in blood serum while concentrations of the latter in skin tumors were higher than in cutaneous homogenates in intact animals. Melatonin and metformin significantly lowered MDA content of blood serum as compared with group 1. Blood serum catalase fell after their joint administration whereas it was 2.6 times as high in cutaneous homogenates after metformin. However, it decreased after melatonin.