Human in vitro skin organ culture as a model system for evaluating DNA repair

Background: UV-exposures result in accumulation of genetic lesions that facilitate the development of skin cancer. Numerous pharmacologic agents are currently under development to both inhibit formation of DNA lesions and enhance repair. Drugs must be evaluated in vitro, currently performed in cell culture systems, before being tested on humans. Current systems do not account for the architecture and diverse cellularity of intact human skin. Objective: To establish a novel, functionally viable, and reproducible in vitro skin organ culture system for studying the effects of various pharmacologic agents on DNA repair. Methods: Human skin was obtained from neonatal foreskins. Intact skin punches derived from foreskins were cultured in vitro prior to exposure to UV-irradiation, and evaluated for DNA-damage using a DNA dot blot. Serial skin biopsies were obtained from patients with actinic keratoses treated with topical imiquimod. Expression of immune-stimulating and DNA repair genes was evaluated in ex vivo and in vitro samples. Results: DNA dot blots revealed active repair of UV induced lesions in our in vitro skin organ culture. The photo-protective effect of sunscreen was detected, while imiquimod treatment did not enhance DNA repair in vitro. The DNA repair molecules XPA and XPF were up-regulated in the skin of imiquimod treated patients with actinic keratoses and imiquimod treated bone marrow-derived cell lines, but not keratinocytes. Conclusion: Our in vitro human skin organ culture model detected repair of UV-induced DNA lesions, and may be easily adapted to investigate various photo-protective drugs intended to prevent or treat skin cancer.