Clinical candidates of small molecule p38 MAPK inhibitors for inflammatory diseases

The trigger and etiology of chronic inflammatory diseases are not well understood, hindering the development of efficient therapeutic approaches. The observation that abnormal activity of the p38 MAPK is common to all inflammatory diseases raised the expectation that p38 inhibitors would serve as general anti-inflammatory therapeutics. A large number of inhibitors were consequently discovered. Several compounds of different scaffolds, blocking the p38 MAPK signaling pathway, have entered phase II clinical trials for rheumatoid arthritis, chronic obstructive pulmonary disease, pain, cardiovascular diseases, and cancer. As I review here, in almost all cases the clinical trials have failed, leading to re-design of compounds and re-evaluation of p38 as a suitable target. I describe how structural features, unique to p38<span>α</span>, have been employed in the inhibitor design and achieved high degree of kinome selectivity. I then focus on some of the drugs that reached human trials and summarize their <em>in vitro/in vivo</em> pharmacological profiles and the related outcomes from clinical investigations. These compounds include VX-745, VX-702, RO-4402257, SCIO- 469, BIRB-796, SD-0006, PH-797804, AMG-548, LY2228820, SB-681323 and GW-856553. Finally, I discuss novel suggested approaches for the use of p38 inhibitors such as combining p38 inhibition with inhibiting other targets that function in parallel inflammatory pathways for achieving efficacy in treating inflammatory diseases.

JNK inhibitors: is there a future?

JNK is a subfamily of MAP kinases that hat regulates a range of biological processes implicated in response to stress, such as cytokines, ultraviolet irradiation, heat shock, and osmotic shock as well as growth factors like PDGF, EGF, FGF, <em>etc</em>. They were originally identified as kinases that bind and phosphorylate JUN on S63 and Se73 within its transcriptional activation domain. The deregulation of these kinases is shown to be involved in human diseases, such as cancer, immune diseases and neurodegenerative disorders. The realization of the therapeutic potential of the inhibition of JNKs led to a thorough search for small-molecule inhibitors first for research purposes, but later also for therapeutic applications. Here, we discuss some of the most well-known JNK inhibitors and their use in basic research or clinical science.

Expression of ERK1 and ERK2 in prostate cancer

Prostate cancer may emerge as result of dysregulated balance between cell proliferation and death rates, increased angiogenesis and chronic. These processes are regulated by numerous signaling proteins, including the mitogen-activated protein kinases (MAPKs). JNK, p38 and extracellular signal-regulated kinase (ERK) are the three major sub-families of MAPKs. The pro-oncogenic effects of ERK isoforms (ERK1 and ERK2) lie in their aberrant activation through phosphorylation by any mutation along the pathway of receptor tyrosine kinase (RTK)-Ras-Raf-MEK-ERK1/2. Once activated, ERKs phosphorylate cytoskeletal proteins, kinases, and transcription factors. Active ERK proteins induce strong proliferative and anti-apoptotic effects. Our group has tested variations in expression, activation and localization of ERKs in human prostate. Differential ERK1/2 expression and phosphorylation status may be linked to the progression of prostate cancer. The major striking observation is that ERKs are expressed in tumors with higher proportion than normal prostate. We believe that this is an important notion because the status (expression, localization, phosphorylation and the ERK1/ERK2 ratio) of ERK in the prostate may be developed into an important prognostic marker that predicts patient responce to the anti-cancer treatment.

Modulation of host-cell MAPkinase signaling during fungal infection

Fungal infections contribute substantially to human suffering and mortality. The interaction between fungal pathogens and their host involves the invasion and penetration of the surface epithelium, activation of cells of the innate immune system and the generation of an effective response to block infection. Numerous host-cell signaling pathways are activated during fungal infection. This review will focus on the main fungal pathogens <em>Aspergillus fumigatus</em>, <em>Candida albicans</em> and <em>Cryptococcus neoformans</em> and their ability to activate the host MAP-kinase signaling pathways leading to cytokine secretion, increased cell motility and killing of the pathogen. Both epithelial and innate immune cells specifically recognize fungal antigens and in particular cell surface polysaccharides such as <span>β</span>-glucans and react to them by activating multiple signaling pathways, including those containing MAP-kinase modules. Recent findings suggest that the host response to fungal infection utilizes the MAP-kinase pathway to differentiate between commensal and pathogenic fungi to selectively react only to the pathogenic forms. However, the paucity of relevant publications strongly emphasize that our understanding of host MAP-kinase signaling in response to fungal infection is still at a very early stage. It is clear, based on studies of host MAP-kinase signaling during viral and bacterial infections, that in fungi as well, a wealth of exciting findings await us.

The association of the JNK scaffold protein, WDR62, with the mixed lineage kinase 3, MLK3

Mitogen-activated protein kinases (MAPKs) form a kinase tier module in which MAPK, MAP2K and MAP3K are held by scaffold proteins. The scaffold proteins serve as a protein platform for selective and spatial kinase activation. The precise mechanism by which the scaffold proteins function has not yet been fully explained. WD40-repeat protein 62, WDR62 is a novel scaffold protein of the c-Jun N-terminal kinase (JNK) pathway. WDR62 is a 1523 a.a. long protein with no significant sequence homology to a known gene. Previously WDR62 was shown to associate with JNK and MKK4/7 in a modular fashion. Here, we show that WDR62 is able to associate with multiple members of the MAP3K of the mixed lineage kinase family and we map WDR62-MLK3 interacting domains. We identify two separable interacting domains within WDR62 and MLK3 proteins that can cross associate. MLK3 association with WDR62 is independent of JNK and MKK4/7 domains and activities. CDC42 activation disrupts WDR62-MLK3 association independent of MLK3 kinase activity.

Subversion of MAPK signaling by pathogenic bacteria

Bacterial components are recognized by host pattern recognition receptors that trigger signaling cascades, leading to inflammation and eradication of the bacteria. The main proinflammatory signaling pathway is the MAP kinase (MAPK)/NF-κB interwoven cascades, which result in transcription of pro-inflammatory genes. Many bacteria have evolved to interfere with the immune response through a mechanism that involves delivery of virulent proteins to the host cells. These proteins posttranslationally modify key components in the host signaling cascades. This review will describe bacterial strategies to directly manipulate host MAPK signaling, summarizing recent discoveries in the field.