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Aims: 5-Lipoxygenase (5-LO) is the key enzyme of leukotriene (LT) biosynthesis and is critically involved in a number of inflammatory diseases such as arthritis, gout, bronchial asthma, atherosclerosis, and cancer. Because 5-LO contains critical nucleophilic amino acids, which are sensitive to electrophilic modifications, we determined the consequences of a drug-mediated intracellular release of nitric oxide (NO) on 5-LO product formation by human granulocytes and on 5-LO-dependent pulmonary inflammation in vivo. Results: Clinically relevant concentrations of NO-releasing nonsteroidal anti-inflammatory drugs and other agents releasing NO intracellularly suppress 5-LO product synthesis in isolated human granulocytes via direct S-nitrosylation of 5-LO at the catalytically important cysteines 416 and 418. Furthermore, suppression of 5-LO product formation was observed in ionophore-stimulated human whole blood and in an animal model of pulmonary inflammation. Innovation: Here, we report for the first time that drugs releasing NO intracellularly are efficient 5-LO inhibitors in vitro and in vivo at least equivalent to approved 5-LO inhibitors. Conclusion: Our findings provide a novel mechanistic strategy for the development of a new class of drugs suppressing LT biosynthesis by site-directed nitrosylation. The results may also help to better understand the well-recognized anti-inflammatory clinically relevant actions of NO-releasing drugs. Furthermore, our study describes in detail a novel molecular mode of action of NO.

Canonical Wnt signaling is a highly conserved pathway with a prominent role in embryogenic development, adult tissue homeostasis, cell polarization, stem cell biology, cell differentiation, and proliferation. Furthermore, canonical Wnt signaling is of pivotal importance in the pathogenesis of a number of cancer types and crucially affects tumor initiation, cancer cell proliferation, cancer cell apoptosis, and metastasis. Reports over the last decade have provided strong evidence fora pathophysiological role of Wnt signaling in nonmalignant classical inflammatory and neurodegenerative diseases. Although, several agents suppressing the Wnt pathway at different levels have been identified, the development of clinically relevant Wnt-inhibiting agents remains challenging due to selectivity and toxicity issues. Several studies have shown that long-term administration of non-steroidal anti-inflammatory drugs protects against colon cancer and potentially other tumor types by interfering both with the COX and the Wnt pathway. Our own studies have shown that non-steroidal anti-inflammatory drugs suppress Wnt signaling by targeting the pro-inflammatory enzyme 5-lipoxygenase which is the key enzyme pathophysiologically involved in the synthesis of leukotrienes. Furthermore, we found a direct link between the 5-lipoxygenase and Wnt signaling pathways, which is essential for the maintenance of leukemic stem cells. Accordingly, genetic and pharmacological inhibition of 5-lipoxygenase led to an impairment of Wnt-dependent acute and chronic myeloid leukemic stem cells. We believe that 5-lipoxygenase inhibitors might represent a novel type of Wnt inhibitor activating a potentially naturally occurring novel mechanism of suppression of Wnt signaling that is non-toxic, at least in mice, and is potentially well tolerated in patients.