A hypothetical mode of inhibition of protein kinase C (PKC) by the natural product staurosporine has been used as a basis for the design of substituted bisindolylmaleimides with improved potency over the parent compound. Structure-activity relationships were consistent with the interaction of a cationic group in the inhibitor with a carboxylate group in the enzyme, and the most potent compound had a Ki of 3 nM. The inhibitors were competitive with ATP but inhibited cAMP-dependent protein kinase (PKA) only at much higher concentrations despite the extensive sequence homology between the ATP-binding regions of PKA and PKC. Three compounds were evaluated further and found to inhibit a human allogeneic mixed lymphocyte reaction pointing to the potential utility of PKC inhibitors in immunosuppressive therapy. One of these compounds was orally absorbed in the rat and represents an attractive lead in the development of PKC inhibitors as drugs.

The design and synthesis of a series of novel inhibitors of protein kinase C (PKC) is described. These 2,3-bisarylmaleimides were derived from the structural lead provided by the indolocarbazoles, staurosporine and K252a. Optimum activity required the imide NH, both carbonyl groups, and the olefinic bond of the maleimide ring. 2,3-Bisindolylmaleimides were the most active, and the potency of these was improved by a chloro substituent at the 5-position of one indole ring (compound 28, IC50 0.11 microM). In a series of (phenylindolyl)maleimides, nitro compound 74 was most active (IC50 0.67 microM). Naphthalene 19 and benzothiophene 21 showed greater than 100-fold selectivity for inhibition of PKC over the closely related cAMP-dependent protein kinase (PKA).

The in vivo role of endogenous interleukin-18 (IL-18) in modulating gamma interferon (IFN-␥)-mediated resolution of replicativeLegionella pneumophila, the causative agent of Legionnaires' disease, is an intracellular pathogen of host mononuclear phagocytic cells (MPCs), primarily alveolar macrophages (19,24,27). Resistance to primary replicative L. pneumophila lung infection is dependent on the induction of cellular immunity and is mediated in part by cytokines, including gamma interferon (IFN-␥) (8, 9). Growth of L. pneumophila within permissive MPCs requires iron. IFN-␥ limits MPC iron, creating an intracellular environment that is nonpermissive for L. pneumophila replication (8, 9). IFN-␥ in combination with other cytokines, including tumor necrosis factor alpha (TNF-␣), facilitates elimination of L. pneumophila from infected MPCs, likely through the induction of effector molecules, including nitric oxide (7).Interleukin-18 (IL-18) is a cytokine isolated from the livers of mice sequentially injected with heat-killed Propionibacterium acnes and lipopolysaccharide (28,29). Originally termed IFN-␥-inducing factor because of its ability to induce IFN-␥ in mice, IL-18 is now recognized to have pleotropic effects including (i) induction of proliferation of activated T cells; (ii) enhancement of the lytic activity of NK cells; (iii) induction of IFN-␥ and granulocyte-macrophage colony-stimulating factor production by activated T cells, B cells, and/or NK cells; and (iv) promotion of T helper type 1 (Th1) responses (20,22,25,29,39,40,44). Responsiveness to IL-18 is conferred by IL-18 binding to its cognate receptor, which consists of the IL-1 receptor (IL-1R)-related protein 1 chain (IL-1Rrp1) (also known as IL-1R5) and the IL-1R accessory protein-like chain (IL-1RAcPL) (also known as IL-1R7) (4, 38, 42; R. Debets, J. C. Timans, T. Churakowa, S. Zurawski, R. de Waal-Malefyt, K. W. Moore, J. S. Abrams, A. O'Garra, J. F. Bazan, and R. A. Kastelein, unpublished data). Recent studies have demonstrated that IL-18-mediated cell activation can be prevented by inhibiting IL-18 ligand receptor interaction, by administration of anti-IL18 antibody (28) or by administration of monoclonal antibodies which recognize either the IL-1R5 chain (42) of the IL-1R7 chain (Debets et al., unpublished data) or the IL-18R.Synergistic effects of IL-18 with other cytokines, including IL-12, have been described in vitro, including markedly increased IFN-␥ production by T cells in comparison to that induced by either cytokine alone (1,33,37,43). The molecular mechanism underlying the synergy between IL-18 and IL-12 may be explained in part by reciprocal modulation of cytokine receptor expression. Specifically, IL-18 has been demonstrated to upregulate IL-12R expression (42), while IL-12 has been shown to upregulate expression of the IL-18R (1, 43).IL-18 has been shown to play a key role in innate immunity to intracellular pathogens, including Mycobacterium tuberculosis (35) and Cryptococcus neoformans (32). However, the potential role of endogen...

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