Mechanistic investigations of test article-induced pancreatic toxicity at the endocrine-exocrine interface in the rat.

Pancreatic toxicity commonly affects the endocrine or exocrine pancreas. However, it can also occur at the endocrine-exocrine interface (EEI), where the capillary network of the islet merges with the capillaries of the surrounding acinar tissue, that is, the insulo-acinar portal system. The goal of this article is to describe a novel, test article-induced pancreatic toxicity that originated at the EEI and to summarize investigations into the mechanistic basis of the injury. This injury was initially characterized by light microscopy in 7/14 day-toxicity studies in Sprague-Dawley (Crl: CD®[SD]) rats with undisclosed test articles. Microvascular injury at the interface resulted in peri-islet serum exudation, fibrin deposition, hemorrhage, inflammation, and secondary degeneration/necrosis of surrounding exocrine tissue. More chronic injury presented as islet fibrosis and lobular atrophy. Direct cytotoxicity affecting the capillary endothelium at the EEI was confirmed ultrastructurally on day 4. Endothelial microparticle and blood flow studies further confirmed endothelial involvement. Similar lesions occurred less frequently in 2 other rat strains and not in the mouse, dog, or cynomolgus macaque. In summary, in vivo and investigative study data confirmed primary endothelial cytotoxicity in the pathogenesis of this lesion and suggested that the lesion may be rat/rat strain-specific and of uncertain relevance for human safety risk assessment.

Substituted N-aryl-6-pyrimidinones: a new class of potent, selective, and orally active p38 MAP kinase inhibitors.

A novel series of highly potent and selective p38 MAP kinase inhibitors was developed originating from a substituted N-aryl-6-pyrimidinone scaffold. SAR studies coupled with in vivo evaluations in rat arthritis model culminated in the identification of 10 with excellent oral efficacy. Compound 10 exhibited a significantly enhanced dissolution rate compared to 1, translating to a high oral bioavailability (>90%) in rat. In animal studies 10 inhibited LPS-stimulated production of tumor necrosis factor-α in a dose-dependent manner and demonstrated robust efficacy comparable to dexamethasone in a rat streptococcal cell wall-induced arthritis model.

Identification of SD-0006, a potent diaryl pyrazole inhibitor of p38 MAP kinase.

Starting from an initial HTS screening lead, a novel series of C(5)-substituted diaryl pyrazoles were developed that showed potent inhibition of p38alpha kinase. Key to this outcome was the switch from a pyridyl to pyrimidine at the C(4)-position leading to analogs that were potent in human whole blood based cell assay as well as in a number of animal efficacy models for rheumatoid arthritis. Ultimately, we identified a clinical candidate from this substrate; SD-0006.

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.

Anti-inflammatory properties of a novel N-phenyl pyridinone inhibitor of p38 mitogen-activated protein kinase: preclinical-to-clinical translation.

Signal transduction through the p38 mitogen-activated protein (MAP) kinase pathway is central to the transcriptional and translational control of cytokine and inflammatory mediator production. p38 MAP kinase inhibition hence constitutes a promising therapeutic strategy for treatment of chronic inflammatory diseases, based upon its potential to inhibit key pathways driving the inflammatory and destructive processes in these debilitating diseases. The present study describes the pharmacological properties of the N-phenyl pyridinone p38 MAP kinase inhibitor benzamide [3- [3-bromo-4-[(2,4-difluorophenyl)methoxy]-6-methyl-2- oxo-1(2H)-pyridinyl]-N,4-dimethyl-, (-)-(9CI); PH-797804]. PH-797804 is an ATP-competitive, readily reversible inhibitor of the alpha isoform of human p38 MAP kinase, exhibiting a K(i) = 5.8 nM. In human monocyte and synovial fibroblast cell systems, PH-797804 blocks inflammation-induced production of cytokines and proinflammatory mediators, such as prostaglandin E(2), at concentrations that parallel inhibition of cell-associated p38 MAP kinase. After oral dosing, PH-797804 effectively inhibits acute inflammatory responses induced by systemically administered endotoxin in both rat and cynomolgus monkeys. Furthermore, PH-797804 demonstrates robust anti-inflammatory activity in chronic disease models, significantly reducing both joint inflammation and associated bone loss in streptococcal cell wall-induced arthritis in rats and mouse collagen-induced arthritis. Finally, PH-797804 reduced tumor necrosis factor-alpha and interleukin-6 production in clinical studies after endotoxin administration in a dose-dependent manner, paralleling inhibition of the target enzyme. Low-nanomolar biochemical enzyme inhibition potency correlated with p38 MAP kinase inhibition in human cells and in vivo studies. In addition, a direct correspondence between p38 MAP kinase inhibition and anti-inflammatory activity was observed with PH-797804, thus providing confidence in dose projections for further human studies in chronic inflammatory disease.

Discovery of N-(4-Fluoro-3-methoxybenzyl)-6-(2-(((2S,5R)-5-(hydroxymethyl)-1,4-dioxan-2-yl)methyl)-2H-tetrazol-5-yl)-2-methylpyrimidine-4-carboxamide. A Highly Selective and Orally Bioavailable Matrix Metalloproteinase-13 Inhibitor for the Potential Treatment of Osteoarthritis.

Matrix metalloproteinase-13 (MMP-13) is a zinc-dependent protease responsible for the cleavage of type II collagen, the major structural protein of articular cartilage. Degradation of this cartilage matrix leads to the development of osteoarthritis. We previously have described highly potent and selective carboxylic acid containing MMP-13 inhibitors; however, nephrotoxicity in preclinical toxicology species precluded development. The accumulation of compound in the kidneys mediated by human organic anion transporter 3 (hOAT3) was hypothesized as a contributing factor for the finding. Herein we report our efforts to optimize the MMP-13 potency and pharmacokinetic properties of non-carboxylic acid leads resulting in the identification of compound 43a lacking the previously observed preclinical toxicology at comparable exposures.

Predicting drug-drug interactions in drug discovery: where are we now and where are we going?

Pressure on drug discovery research teams to identify successful drug candidates earlier on in the drug discovery process has led to the development of a variety of ADME in vitro assays, intended to guide chemists and biologists in their decision-making process. The role of these early assays is to indicate liabilities in scaffolds relating to the absorption, distribution, metabolism and cytochrome P450 (CYP) inhibition potential of new chemical entities. Current efforts in drug-drug interaction (DDI) screening can be divided into four basic categories: bioanalytical method development, strategies relating to enzyme kinetics, recognition of CYP allelic variants and generation of computational models to predict CYP interactions. Collectively, DDI screening represents an important means not only for assessing and ranking potential drug candidates, but also for aiding in the development of mechanisms for predicting and retrospectively explaining in vivo drug performance.