Regulation of stress-induced cytokine production by pyridinylimidazoles; inhibition of CSBP kinase.

Members of three classes of pyridinylimidazoles bind with varying affinities to CSBP (p38) kinase which is a member of a stress-induced signal transduction pathway. Based upon SAR and protein homology modeling, the pharmacophore and three potential modes of binding to the enzyme are presented. For a subset of pyridinylimidazoles, binding is shown to correlate with inhibition of CSBP kinase activity, whereas no significant inhibition of PKA, PKC alpha and ERK kinase activity is observed.

1-substituted 4-aryl-5-pyridinylimidazoles: a new class of cytokine suppressive drugs with low 5-lipoxygenase and cyclooxygenase inhibitory potency.

A series of 1-alkyl- or -aryl-4-aryl-5-pyridinylimidazoles (A) were prepared and tested for their ability to bind to a recently discovered protein kinase termed CSBP and to inhibit lipopolysaccharide (LPS)-stimulated TNF production in mice. The kinase, CSBP, appears to be involved in a signaling cascade initiated by a number of inflammatory stimuli and leading to the biosynthesis of the inflammatory cytokines IL-1 and TNF. Two related imidazole classes (B and C) had previously been reported to bind to CSBP and to inhibit LPS-stimulated human monocyte IL-1 and TNF production. The members of the earlier series exhibited varying degrees of potency as inhibitors of the enzymes of arachidonic acid metabolism, PGHS-1 and 5-LO. Several of the more potent CSBP ligands and TNF biosynthesis inhibitors among the present series of N-1-alkylated imidazoles (A) were tested as inhibitors of PGHS-1 and 5-LO and were found to be weak to inactive as inhibitors of these enzymes. One of the compounds, 9 (SB 210313) which lacked measureable activity as an inhibitor of the enzymes of arachidonate metabolism, and had good potency in the binding and in vivo TNF inhibition assays, was tested for antiarthritic activity in the AA rat model of arthritis. Compound 9 significantly reduced edema and increased bone mineral density in this model.

Evaluation of human cytokine production and effects of pharmacological agents in a heterologous system in vivo.

The ability of human monocytes adoptively transferred into the peritoneal cavity of BALB/c mice to produce tumor necrosis factor-alpha (TNF) and interleukin 1 beta (IL-1) was studied. Human monocytes were isolated from fresh, heparinized blood obtained by venipuncture. BALB/c mice were administered 2-10 x 10(6) cells and challenged with lipopolysaccharide intraperitoneally. 2 h later, they were killed and a peritoneal washout was obtained. The washouts were assayed for TNF and, in some cases, IL-1 content using a species specific enzyme-linked immunosorbant assay (ELISA). This model allowed for the simultaneous evaluation of the production of mouse and human inflammatory cytokines. Significant levels of both human and mouse TNF were seen as early as 60 min after challenge. Peak levels for both were seen at 120 min post administration of LPS. Both human and mouse TNF concentrations declined at the 2 h time point. The phosphodiesterase type 4 inhibitor, R-rolipram was found to inhibit both human and mouse TNF production while SB CSAID, novel kinase inhibitor SB 203580 inhibited human IL-1 and TNF as well as mouse TNF. This model was reliable, reproducible and allowed evaluation of pharmacological agents for their effect on human cytokine production in a heterologous setting in vivo.

A protein kinase involved in the regulation of inflammatory cytokine biosynthesis.

Production of interleukin-1 and tumour necrosis factor from stimulated human monocytes is inhibited by a new series of pyridinyl-imidazole compounds. Using radiolabelled and radio-photoaffinity-labelled chemical probes, the target of these compounds was identified as a pair of closely related mitogen-activated protein kinase homologues, termed CSBPs. Binding of the pyridinyl-imidazole compounds inhibited CSBP kinase activity and could be directly correlated with their ability to inhibit cytokine production, suggesting that the CSBPs are critical for cytokine production.

Effects of pyridinyl imidazole compounds on murine TNF-alpha production.

The effects of SK&F 86002 and other pyridinyl imidazole compounds on murine cytokine production were investigated. In vitro, SK&F 86002 inhibited LPS stimulated TNF-alpha production by the RAW 264.7 cell line and by oil elicited peritoneal macrophages with an IC50 of 5 microM. In general, the activity was reflective of previous results obtained with human monocytes as SK&F 86002 and its analogs demonstrated identical rank order potency for TNF-alpha inhibition in both species. These compounds also inhibited TNF-alpha in vivo in a murine model of endotoxin shock. Following oral administration, SK&F 86002 and its analogs reduced serum TNF-alpha levels by > 80% and afforded 100% protection from lethality. In contrast, tenidap, a novel anti-inflammatory drug, had minimal to no effect on murine TNF-alpha production in the same assays. These data further extend the pharmacological profile of the pyridinyl imidazoles by demonstrating that these compounds potently inhibit murine TNF-alpha production both in vitro and in vivo.

Effect of a human immunodeficiency virus protease inhibitor on human monocyte function.

Human immunodeficiency virus (HIV) is the cause of acquired immunodeficiency syndrome (AIDS). Encoded by the HIV genome are several precursor proteins that undergo proteolytic cleavage to yield functional proteins. The env precursor protein is cleaved by a cellular protease. The gag precursor protein of HIV (p55), however, is cleaved by a virally encoded aspartate protease (HIV Protease). Cleavage of p55 is required for viral maturation and infectivity. There are also several host cell aspartate proteases that serve important homeostatic functions. Cathepsins D and E are lysosomal aspartate proteases which are believed to play an important role in macrophage function, and it has been suggested that inhibition of these enzymes by an HIV protease inhibitor may exacerbate immunosuppression in AIDS patients. We have studied the effect of SK&F 107461 (a hydroxyethylene dipeptide isostere inhibitor of HIV protease), on various host defense functions of human monocytes. Pepstatin A (an inhibitor of most aspartate proteases) and leupeptin (an inhibitor of serine and cysteine proteases) were included as controls. Although less potent than the prototypic aspartate protease inhibitor pepstatin, SK&F 107461 inhibited partially purified cathepsin D in vitro. However, in cell-based assays, SK&F 107461 had no effect on the degradation of hemoglobin, antigen processing of the protein antigen streptokinase, or secretion of 17-kD IL-1 beta by monocytes at concentrations which inhibit maturation of intracellular virus in HIV infected monocytes. Furthermore, SK&F 107461 had no effect on constitutive candidacidal activity. In contrast, leupeptin and pepstatin A partially inhibited accessory cell function of monocytes in the proliferative response to the recall antigen streptokinase. In addition, leupeptin partially inhibited degradation of hemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of SK&F 86002 on cytokine production by human monocytes.

Human monocytes respond to a variety of stimuli in vitro by producing a number of physiologically important macromolecules including the cytokines. SK&F 86002, a dual inhibitor of the arachidonate metabolism, has been shown to inhibit LPS induced IL-1 production in human monocytes. We examined its effect on the production of other cytokines which are coordinately expressed as a result of LPS stimulation such as tumor necrosis factor alpha (TNF), alpha interferon (IFN-A), interferon beta-2 (IL-6) and granulocyte colony stimulating factor (g-CSF). The IC50 of SK&F 86002 for the TNF production was 5-8 microM, and greater than 20 microM for the other three cytokines. These IC50s were significantly higher than that previously reported for IL-1 production (1-2 microM). Taken together these data indicate that the inhibitory effect of SK&F 86002 on IL-1 production is selective and the production of cytokines in drug treated monocytes can be differentially affected.

A modified assay for interleukin-1 (IL-1).

A simple and reliable biological assay for interleukin-1 (IL-1) was developed, based on the production of interleukin-2 (IL-2) from the EL-4 murine T-cell lymphoma cell line, in the presence of 2-5 X 10(-7) M calcium ionophore A23187. The assay was generally performed in 2 stages ((a) IL-1-dependent IL-2 production, and (b) IL-2 assay) and took 36-48 h to complete. This assay was found to be 10-25 times more sensitive than the mouse thymus cell assay, was not sensitive to the presence of bacterial endotoxin, and had the advantage of not requiring the use of animal tissue as a source of cells. The assay was used in our laboratory to detect human, mouse, rat, and rabbit IL-1 of all isoelectric-point types.