Acute lymphoid and gastrointestinal toxicity induced by selective p38alpha map kinase and map kinase-activated protein kinase-2 (MK2) inhibitors in the dog.

Exposure to moderately selective p38alpha mitogen-activated protein kinase (MAPK) inhibitors in the Beagle dog results in an acute toxicity consisting of mild clinical signs (decreased activity, diarrhea, and fever), lymphoid necrosis and depletion in the gut-associated lymphoid tissue (GALT), mesenteric lymph nodes and spleen, and linear colonic and cecal mucosal hemorrhages. Lymphocyte apoptosis and necrosis in the GALT is the earliest and most prominent histopathologic change observed, followed temporally by neutrophilic infiltration and acute inflammation of the lymph nodes and spleen and multifocal mucosal epithelial necrosis and linear hemorrhages in the colon and cecum. These effects are not observed in the mouse, rat, or cynomolgus monkey. To further characterize the acute toxicity in the dog, a series of in vivo, in vitro, and immunohistochemical studies were conducted to determine the relationship between the lymphoid and gastrointestinal (GI) toxicity and p38 MAPK inhibition. Results of these studies demonstrate a direct correlation between p38alpha MAPK inhibition and the acute lymphoid and gastrointestinal toxicity in the dog. Similar effects were observed following exposure to inhibitors of MAPK-activated protein kinase-2 (MK2), further implicating the role of p38alpha MAPK signaling pathway inhibition in these effects. Based on these findings, the authors conclude that p38alpha MAPK inhibition results in acute lymphoid and GI toxicity in the dog and is unique among the species evaluated in these studies.

Evaluation of Misoprostol and Analogs as Inhibitors of T-Cell Activation.

Prostaglandin E(2) (PGE(2)) is known to inhibit in vitro T-cell responses to mitogenic and antigenic stimuli. Interaction of PGE(2) with a G protein-coupled receptor activates adenylyl cyclase, leading to cAMP formation and inhibition of interleukin-2 (IL-2) production and T-cell proliferation. Despite these effects, the application of PGE(2) as an anti-inflammatory agent has been compromised by its unfavorable pharmacodynamic and side-effect profile. Because of the potential utility of synthetic analogs as prostaglandin-based therapeutics, we evaluated the effect of misoprostol and over 100 structural analogs on cAMP formation and T-cell activation. Our results indicate that micromolar concentrations of misoprostol and particular analogs elicited a rapid and substantial rise in cAMP levels in human peripheral blood mononuclear cells. Analogs which increased cAMP also suppressed IL-2 production and T-cell growth in vitro, whereas those devoid of suppressive activity weakly induced nucleotide synthesis. Despite extensive chemical alteration of the prostanoid structure, no single analog was superior to misoprostol in inducing cAMP or modulating T-cell activity. Misoprostol and suppressive analogs were also evaluated in vivo in a murine model of antigen-induced T-cell proliferation. Prostaglandins, administered at maximum tolerable doses, were ineffective in blocking a T-cell response to alloantigenic stimulation, whereas cyclosporine and prednisolone were potent inhibitors of this response. Overall, our results indicate that misoprostol and related analogs suppress T-cell activation in vitro but require concentrations 1000-fold greater than the low nanomolar plasma levels achieved with clinical doses of misoprostol. Whether misoprostol analogs of sufficient potency can be developed for pharmacologic attentuation of T-cell activation in vivo remains to be determined.