Ulrich Tibes

Activation of nuclear factor-κB by lipopolysaccharide in mononuclear leukocytes is prevented by inhibitors of cytosolic phospholipase A2

Abstract In monocytes, lipopolysaccharide induces synthesis and activity of the 85-kDa cytosolic phospholipase A 2 . This enzyme releases arachidonic acid and lyso-phospholipids from membranes which are metabolized to eicosanoids and platelet-activating-factor. These lipid mediators increase activity of transcription factors and expression of cytokine genes indicating a function for cytosolic phospholipase A 2 in signal transduction and inflammation. We have shown previously that trifluoromethylketone inhibitors of cytosolic phospholipase A 2 suppressed interleukin-1β protein and steady-state mRNA levels in human lipopolysaccharide-stimulated peripheral blood mononuclear leukocytes. In this study, the subcellular mechanisms were analyzed by which trifluoromethylketones interfere with gene expression. We found that they reduced the initial interleukin-1β mRNA transcription rate through prevention of degradation of inhibitor-κBα. Consequently, cytosolic activation, nuclear translocation and DNA-binding of nuclear factor-κB were decreased. Trifluoromethylketones ameliorate chronic inflammation in vivo. Thus, this therapeutic potency may reside in retention of inactive nuclear factor-κB in the cytosol thereby abrogating interleukin-1β gene transcription.

Inhibition of cytosolic phospholipase A2 attenuates activation of mitogen-activated protein kinases in human monocytic cells

Eicosanoids and platelet-activating factor generated upon activation of cytosolic phospholipase A(2) enhance activity of transcription factors and synthesis of proinflammatory cytokines. Here, we show that selective inhibitors and antisense oligonucleotides against this enzyme suppressed expression of the interleukin-1beta gene at the level of transcription and promoter activation in human monocytic cell lines. This inhibitory effect was due to failure of activation of mitogen-activated protein kinases (MAPK) through phosphorylation by upstream mitogen-activated protein kinase kinases (MKK). Consequently, phosphorylation and degradation of inhibitor-kappaBalpha (I-kappaBalpha) and subsequent cytoplasmic mobilization, DNA-binding and the transactivating potential of nuclear factor-kappaB (NF-kB), nuclear factor-interleukin-6 (NF-IL6), activation protein-1 (AP-1) and signal-transducer-and-activator-of-transcription-1 (STAT-1) were impaired. It is concluded, that lipid mediators promote activation of MAPKs, which in turn lead to phosphorylation and liberation of active transcription factors. Since inhibition of cytosolic phospholipase A(2) ameliorates inflammation in vivo, this potency may reside in interference with the MAPK pathway.

Histone Deacetylase Inhibitors: A Novel Class of Anti-Cancer Agents on its Way to the Market

Publisher Summary Histone deacetylase (HDAC) is one of the most prominent non-kinase anticancer targets. This chapter summarizes the biological background of HDACs; the consequences of HDAC inhibition at a molecular level; and provides an overview of the achievements in design, synthesis, and optimization of different chemical classes of HDAC inhibitors. Mammalian HDACs belong to an enzyme family comprising 18 isoforms that are grouped into class I, II, and III. HDACs serve a diversity of functions within the body, encompassing gene silencing, cell regulation, growth and differentiation, intracellular protein movements, and degradation. Crystal and co-crystal structures of HDACs with relevant substrates represent an important prerequisite for structure-based drug design. The chapter discusses recent developments and successes in the design, synthesis, and optimization of different chemical classes of class I and II HDAC inhibitors. In addition, the chapter accounts for isoform selectivity of HDAC inhibitors. None of the HDAC inhibitors that are currently in clinical studies selectively inhibits one single HDAC isoform. Certain drugs are currently in phase I–III clinical trials as single agent or as a combination partner for the treatment of various tumour types, and many compounds are in late preclinical development and might enter clinical development soon. A thorough understanding of the mechanism of action and the tumour selectivity of the different HDAC inhibitors is desirable and would be a breakthrough for further development strategies. Predictive markers are important to increase the quality of clinical trials, to maximize the clinical benefit of HDAC inhibitors, and to select responders versus non-responders.