Nonsteroidal antiinflammatory drug-photosensitized formation of pyrimidine dimer in DNA.

Phototoxic nonsteroidal antiinflammatory drugs (NSAIDs) may induce DNA damage in vitro upon irradiation. In this study, we investigated the ability of ketoprofen (KP), tiaprofenic acid (Tia), naproxen (NP) and indomethacin (IND) to photosensitize the formation of pyrimidine dimers and single strand breaks. Both kinds of damage were sought by analyzing DNA-drug mixtures irradiated at 313 nm by agarose gel electrophoresis. The formation of pyrimidine dimers was evidenced by using endonuclease V from bacteriophage T4 and compared to that induced by acetophenone, a well-known photosensitizer of thymine dimerization. Upon irradiation of DNA alone, pyrimidine dimers were observed while single strand breaks were not detected under our conditions. DNA, in the presence of NSAIDs, undergoes single strand breaks, the quantum yield of the DNA cleavage so induced (phiC) varying from 5 x 10(-4) for KP to 10(-5) for IND. The formation of dimers was only increased in the presence of KP or Tia. The quantum yields of pyrimidine dimers formed by photosensitization (phiD) were 2 x 10(-4) for KP and 10(-5) for Tia, respectively. The oxygen and concentration dependence of both processes was analyzed in the case of KP. In aerated solution, KP-photoinduced cleavage of DNA was predominant on the photodimerization process of pyrimidines, whereas in deaerated solution the cleavage was decreased and the dimerization increased. These results reflect competition between a radical process leading to DNA cleavage and a poorly efficient energy transfer between the drug and the pyrimidines at the origin of the dimerization process.