Analysis of pharmacologic inhibitors of Jun N-terminal kinases

Design and characterization of a potent and selective dual ATP- and substrate-competitive subnanomolar bidentate c-Jun N-terminal kinase (JNK) inhibitor

c-Jun N-terminal kinases (JNKs) represent valuable targets in the development of new therapies. Present on the surface of JNK is a binding pocket for substrates and the scaffolding protein JIP1 in close proximity to the ATP binding pocket. We propose that bidentate compounds linking the binding energies of weakly interacting ATP and substrate mimetics could result in potent and selective JNK inhibitors. We describe here a bidentate molecule, 19, designed against JNK. 19 inhibits JNK kinase activity (IC(50) = 18 nM; K(i) = 1.5 nM) and JNK/substrate association in a displacement assay (IC(50) = 46 nM; K(i) = 2 nM). Our data demonstrate that 19 targets for the ATP and substrate-binding sites on JNK concurrently. Finally, compound 19 successfully inhibits JNK in a variety of cell-based experiments, as well as in vivo where it is shown to protect against Jo-2 induced liver damage and improve glucose tolerance in diabetic mice.

Inhibitors of mitogen-activated protein kinases differentially regulate costimulated T cell cytokine production and mouse airway eosinophilia

Background

T cells play a dominant role in the pathogenesis of asthma. Costimulation of T cells is necessary to fully activate them. An inducible costimulator (ICOS) of T cells is predominantly expressed on Th2 cells. Therefore, interference of signaling pathways precipitated by ICOS may present new therapeutic options for Th2 dominated diseases such as asthma. However, these signaling pathways are poorly characterized in vitro and in vivo.

Methods

Human primary CD4⁺ T cells from blood were activated by beads with defined combinations of surface receptor stimulating antibodies and costimulatory receptor ligands. Real-time RT-PCR was used for measuring the production of cytokines from activated T cells. Activation of mitogen activated protein kinase (MAPK) signaling pathways leading to cytokine synthesis were investigated by western blot analysis and by specific inhibitors. The effect of inhibitors in vivo was tested in a murine asthma model of late phase eosinophilia. Lung inflammation was assessed by differential cell count of the bronchoalveolar lavage, determination of serum IgE and lung histology.

Results

We showed in vitro that ICOS and CD28 are stimulatory members of an expanding family of co-receptors, whereas PD1 ligands failed to co-stimulate T cells. ICOS and CD28 activated different MAPK signaling cascades necessary for cytokine activation. By means of specific inhibitors we showed that p38 and ERK act downstream of CD28 and that ERK and JNK act downstream of ICOS leading to the induction of various T cell derived cytokines. Using a murine asthma model of late phase eosinophilia, we demonstrated that the ERK inhibitor U0126 and the JNK inhibitor SP600125 inhibited lung inflammation in vivo. This inhibition correlated with the inhibition of Th2 cytokines in the BAL fluid. Despite acting on different signaling cascades, we could not detect synergistic action of any combination of MAPK inhibitors. In contrast, we found that the p38 inhibitor SB203580 antagonizes the action of the ERK inhibitor U0126 in vitro and in vivo.

Conclusion

These results demonstrate that the MAPKs ERK and JNK may be suitable targets for anti-inflammatory therapy of asthma, whereas inhibition of p38 seems to be an unlikely target.

Expression and purification of recombinant tristetraprolin that can bind to tumor necrosis factor-alpha mRNA and serve as a substrate for mitogen-activated protein kinases

Tristetraprolin (TTP) is an mRNA-binding protein, but studies of this interaction have been difficult due to problems with the purification of recombinant TTP. In the present study, we expressed human and mouse TTP as glutathione S-transferase and maltose-binding protein (MBP) fusion proteins in Escherichia coli, and purified them by affinity resins and Mono Q chromatography. TTP cleaved from the fusion protein was identified by immunoblotting, MALDI-MS, and protein sequencing, and was further purified to homogeneity by continuous-elution SDS-gel electrophoresis. Purified recombinant TTP bound to the AU-rich element of tumor necrosis factor-alpha (TNFalpha) mRNA and this binding was dependent on Zn(2+). Results from sizing columns suggested that the active species might be in the form of an oligomer of MBP-TTP. Recombinant TTP was phosphorylated by three members of the mitogen-activated protein (MAP) kinase family, p42, p38, and JNK, with half-maximal phosphorylation occurring at approximately 0.5, 0.25, and 0.25 microM protein, respectively. Phosphorylation by these kinases did not appear to affect the ability of TTP to bind to TNFalpha mRNA under the assay conditions. This study describes a procedure for purifying nonfusion protein TTP to homogeneity, demonstrates that TTP's RNA-binding activity is zinc dependent, and that TTP can be phosphorylated by JNK as well as by the other members of the greater MAP kinase family.

Ras-MAP kinase signaling pathways and control of cell proliferation: relevance to cancer therapy

The mitogen-activated protein (MAP) kinase pathways represent several families of signal transduction cascades that mediate information provided by extracellular stimuli. MAP kinase pathways regulate a wide range of physiological responses, including cell proliferation, apoptosis, cell differentiation, and tissue development. Constitutive activation of MAP kinase proteins in experimental models has been shown to cause cell transformation and is implicated in tumorigenesis. Of clinical importance, MAP kinase pathways are regulated by Ras G-proteins, which are found to be mutated and constitutively active in approximately 30% of all human cancers. Thus, a major goal in the treatment of cancer is the development of specific compounds that target Ras and critical downstream signaling proteins responsible for uncontrolled cell growth. A variety of biochemical, molecular, and structural approaches have been used to develop drug compounds that target signaling proteins important for MAP kinase pathway activation. These compounds have been useful tools for identifying the mechanisms of MAP kinase pathway signaling and hold promise for clinical use. This review will present an overview of the major proteins involved in Ras and MAP kinase signaling pathways and their function in regulating cell cycle events and proliferation. In addition, some of the relevant compounds that have been developed to inhibit the activities of these proteins and MAP kinase signaling are discussed.

SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase

Jun N-terminal kinase (JNK) is a stress-activated protein kinase that can be induced by inflammatory cytokines, bacterial endotoxin, osmotic shock, UV radiation, and hypoxia. We report the identification of an anthrapyrazolone series with significant inhibition of JNK1, -2, and -3 (K(i) = 0.19 microM). SP600125 is a reversible ATP-competitive inhibitor with >20-fold selectivity vs. a range of kinases and enzymes tested. In cells, SP600125 dose dependently inhibited the phosphorylation of c-Jun, the expression of inflammatory genes COX-2, IL-2, IFN-gamma, TNF-alpha, and prevented the activation and differentiation of primary human CD4 cell cultures. In animal studies, SP600125 blocked (bacterial) lipopolysaccharide-induced expression of tumor necrosis factor-alpha and inhibited anti-CD3-induced apoptosis of CD4(+) CD8(+) thymocytes. Our study supports targeting JNK as an important strategy in inflammatory disease, apoptotic cell death, and cancer.