Promotion of DNA Strand Breaks in CoculturedMononuclear Leukocytes by Protein Kinase C-dependentProoxidative Interactions of Benoxaprofen, Human PolymorphonuclearLeukocytes, and Ultraviolet Radiation1

At concentrations of 5 «ig/mland greater the nonsteroidal antiinflammatory drug benoxaprofen caused dose-related activation of lucigeninenhanced chemiluminescence in human polymorphonuclear leukocytes (PMNL). Benoxaprofen-mediated activation of lucigenin-enhanced chemiluminescence by PMNL was increased by UV radiation and was particularly sensitive to inhibition by the selective protein kinase C inhibitor 11-7. To identify the molecular mechanism of the prooxidative activity of benoxaprofen, the effects of the nonsteroidal antunflammatory drug on the activity of purified protein kinase C in a cell-free system were investigated. Benoxaprofen caused a dose-related activation of pro tein kinase C by interaction with the binding site for the physiological activator phosphatidylserine, but could not replace diacylglycerol. When autologous mononuclear leukocytes (MNL) were cocultured with PMNL and benoxaprofen in combination, but not individually, the frequency of DNA strand breaks in MNL was markedly increased. LTV radiation significantly potentiated damage to DNA mediated by benoxaprofen and PMNL. Inclusion of Superoxide dismutase, H-7, and, to a much lesser extent, catatase during exposure of MNL to benoxaprofen-activated PMNL prevented oxidant damage to DNA. These results clearly dem onstrate that potentially carcinogenic prooxidative interactions, which are unlikely to be detected by conventional assays of mutagenicity, may occur between phagocytes, UV radiation, and certain pharmacological agents.