Discovery of a new class of p38 kinase inhibitors

Pyrazolyl-Ureas as Interesting Scaffold in Medicinal Chemistry

The pyrazole nucleus has long been known as a privileged scaffold in the synthesis of biologically active compounds. Within the numerous pyrazole derivatives developed as potential drugs, this review is focused on molecules characterized by a urea function directly linked to the pyrazole nucleus in a different position. In the last 20 years, the interest of numerous researchers has been especially attracted by pyrazolyl-ureas showing a wide spectrum of biological activities, ranging from the antipathogenic activities (bacteria, plasmodium, toxoplasma, and others) to the anticarcinogenic activities. In particular, in the anticancer field, pyrazolyl-ureas have been shown to interact at the intracellular level on many pathways, in particular on different kinases such as Src, p38-MAPK, TrKa, and others. In addition, some of them evidenced an antiangiogenic potential that deserves to be explored. This review therefore summarizes all these biological data (from 2000 to date), including patented compounds.

Modulation of sensitivity and resistance to multikinase inhibitors by microenvironmental platelet factors in HCC

INTRODUCTION

Response of a tumor to chemotherapy or multikinase inhibitor therapy has been traditionally thought to be a reflection of the sum of the characteristics of both the drug and of the tumor cell resistance mechanisms. More recently, there has been a growing awareness of the role of non-tumor factors-both cellular and humoral-in the tumor microenvironment that can increase or decrease the tumor cellular responses to the therapy. This article focuses on platelet factors in clinical HCC and experimental evidence that they provide growth stimulants that can antagonize the growth inhibitory effects of therapy.

AREAS COVERED

Review of the mechanisms of multikinase cancer growth inhibitors and of the role of platelets in providing growth factors that can antagonize their effects.

EXPERT OPINION

These new ideas and data show that the response of a tumor to multikinase inhibitors or chemotherapy may be strongly influenced by microenvironmental factors. Conversely, antagonists to these environmental factors, such as EGFR inhibitors and IGF1-R inhibitors, might be expected to augment the anti-tumor effect of both chemotherapy and multikinase inhibitors.

Fluoro-Sorafenib (Regorafenib) effects on hepatoma cells: growth inhibition, quiescence, and recovery

To evaluate the growth-inhibitory properties of the potent multi-kinase antagonist Regorafenib (Fluoro-Sorafenib), which was synthesized as a more potent Sorafenib, a Raf inhibitor and to determine whether similar mechanisms were involved, human hepatoma cell lines were grown in the presence or absence of Regorafanib and examined for growth inhibition. Western blots were performed for Raf targets, apoptosis, and autophagy. Regorafenib inhibited growth of human Hep3B, PLC/PRF/5, and HepG2 cells in a concentration- and time-dependent manner. Multiple signaling pathways were altered, including MAP kinases phospho-ERK and phospho-JNK and its target phospho-c-Jun. There was evidence for apoptosis by FACS, cleavage of caspases and increased Bax levels; as well as induction of autophagy, as judged by increased Beclin-1 and LC3 (II) levels. Prolonged drug exposure resulted in cell quiescence. Full growth recovery occurred after drug removal, unlike with doxorubicin chemotherapy. Regorafenib is a potent inhibitor of cell growth. Cells surviving Regorafenib treatment remain viable, but quiescent and capable of regrowth following drug removal. The reversibility of tumor cell growth suppression after drug removal may have clinical implications.

Docking, synthesis and pharmacological activity of novel urea-derivatives designed as p38 MAPK inhibitors

p38 mitogen-activated protein kinase (p38 MAPK) is an important signal transducing enzyme involved in many cellular regulations, including signaling pathways, pain and inflammation. Several p38 MAPK inhibitors have been developed as drug candidates to treatment of autoimmune disorders, such as rheumatoid arthritis. In this paper we reported the docking, synthesis and pharmacological activity of novel urea-derivatives (4a-e) designed as p38 MAPK inhibitors. These derivatives presented good theoretical affinity to the target p38 MAPK, standing out compound 4e (LASSBio-998), which showed a better score value compared to the prototype GK-00687. This compound was able to reduce in vitro TNF-α production and was orally active in a hypernociceptive murine model sensible to p38 MAPK inhibitors. Otherwise, compound 4e presented a dose-dependent analgesic effect in a model of antigen (mBSA)-induced arthritis and anti-inflammatory profile in carrageenan induced paw edema, indicating its potential as a new antiarthritis prototype.

Allosteric IGF-1R Inhibitors

Targeting allosteric protein sites is a promising approach to interfere selectively with cellular signaling cascades. We have discovered a novel class of allosteric insulin-like growth factor-I receptor (IGF-1R) inhibitors. 3-Cyano-1H-indole-7-carboxylic acid {1-[4-(5-cyano-1H-indol-3-yl)butyl]piperidin-4-yl}amide (10) was found with nanomolar biochemical, micromolar, cellular IGF-1R activity and no relevant interference with cellular insulin receptor signaling up to 30 μM. The allosteric binding site was characterized by X-ray crystallographic studies, and the structural information was used to explain the unique mode of action of this new class of inhibitors.

Are MAP kinases drug targets? Yes, but difficult ones

Pharmaceutical companies are facing an increasing interest in new target identification and validation. In particular, extensive efforts are being made in the field of protein kinase inhibitors research and development, and the past ten years of effort in this field have altered our perception of the potential of kinases as drug targets. Therefore, in the drug discovery process, the selection of relevant, susceptible protein kinase targets combined with searches for leads and candidates have become a crucial approach. The success of recent launches of protein kinase inhibitors (Gleevec, Imatinib, Sutent, Iressa, Nexavar, Sprycel) gave another push to this field. Numerous other kinase inhibitors are currently undergoing clinical trials or clinical development. Some questions are nevertheless unanswered, mostly related to the great number of known kinases in the human genome, to their similarity with each other, to the existence of functionally redundant kinases for specific pathways, and also because the connection between particular pathways and diseases is not always clear. The review is leading the reader through a panoramic view of protein kinase inhibition with a major focus on MAPK, successful examples and clinical candidates.

Biological targets for therapeutic interventions in COPD: clinical potential

COPD is a widespread inflammatory respiratory disorder characterized by a progressive, poorly reversible airflow limitation. Currently available therapies are mostly based on those used to treat asthma. However, such compounds are not able to effectively reduce the gradual functional deterioration, as well as the ongoing airway and lung inflammation occurring in COPD patients. Therefore, there is an urgent need to improve the efficacy of the existing drug classes and to develop new treatments, targeting the main cellular and molecular mechanisms underlying disease pathogenesis. These therapeutic strategies will be highlighted in the present review.

Pyrazolo[1,5-a]pyridines as p38 Kinase Inhibitors

[reaction: see text] A convergent synthesis of substituted pyrazolo[1,5-a]pyridines has been achieved either via a regioselective [3 + 2] cycloaddition of N-aminopyridines with alkynes or by thermal cyclization of disubstituted azirines. Subsequent palladium-catalyzed introduction of pyridines or de novo synthesis of pyrimidines affords inhibitors of p38 kinase.

Practical Synthesis of Unsymmetrical Ureas from Isopropenyl Carbamates

A very convenient method for the synthesis of unsymmetrical ureas is described, based on isopropenyl carbamates. The synthetic efficiency of traditional methods for urea formation, such as use of phosgene or alkyl and aryl carbamates, is limited by the formation of symmetrical urea side products or reaction reversibility. Isopropenyl carbamates react with amines cleanly and irreversibly and give unsymmetrical ureas in high yield and purity. This method is ideal for the rapid synthesis of compound libraries.

Mitogen-activated protein kinases and asthma

Mitogen-activated protein kinases (MAPKs) are evolutionary conserved enzymes which play a key role in signal transduction mediated by cytokines, growth factors, neurotransmitters and various types of environmental stresses. In the airways, these extracellular stimuli elicit complex inflammatory and structural changes leading to the typical features of asthma including T cell activation, eosinophil and mast cell infiltration, as well as bronchial hyperresponsiveness and airway remodelling. Because MAPKs represent an important point of convergence for several different signalling pathways, they affect multiple aspects of normal airway function and also significantly contribute to asthma pathophysiology. Therefore, this review focuses on the crucial involvement of MAPKs in asthma pathogenesis, thus also discussing their emerging role as molecular targets for anti-asthma drugs.

Small molecular anti-cytokine agents

The recent successful introduction of the anti-cytokine biologicals Etanercept, Infliximab, Adalimumab, and Anakinra has stimulated the search for anti-cytokine small-molecules. A number of molecular targets have been identified for the development of such small molecular anti-cytokine agents. The focus of this review will be on those inhibitors of cytokine production, which target either p38 mitogen activated protein (MAP) kinase, TNF-alpha converting enzyme (TACE), or IL-1beta converting enzyme (ICE). P38 MAP kinase occupies a central role in the signaling network responsible for the upregulation of proinflammatory cytokines like interleukin 1beta (IL-1beta) and TNF-alpha, and regulates their biosynthesis at both the transcriptional and translational level. TACE and ICE are two proteases required for the processing of proTNF-alpha and proIL-1beta, respectively into their mature, proinflammatory form. Since the mid-1990s, a plethora of inhibitors of p38 MAP kinase, TACE, and ICE has been characterized in vitro, and individual representatives from all three inhibitor classes have in the meantime been advanced into clinical trials. This review will highlight the correlation between effective inhibition at the molecular target and cellular activity in functional assays of cytokine, particularly TNF-alpha and IL-1beta, production. Structure-activity relationships (SAR) will be discussed regarding activity at the respective enzyme target, but also with regard to properties required for efficient in vitro and in vivo cellular activity (e.g., oral availability, solubility, cell penetration, etc.).

A novel 3D-QSAR comparative molecular field analysis (CoMFA) model of imidazole and quinazolinone functionalized p38 MAP kinase inhibitors

In this study we describe a new comparative molecular field analysis (CoMFA) model of dihydroquinazolinone and tetrasubstituted imidazole compounds with p38 MAPK inhibitory activity. A series of 51 (a training set of 40 and a test set of 11) dihydroquinazolinone [Bioorg. Med. Chem. Lett. 2003, 13, 277.] and tetrasubstituted imidazole [J. Med. Chem. 1999, 42, 2180.] derivatives known as p38 mitogen-activated protein kinase (p38 MAPK) selective inhibitors was studied by quantitative structure-activity relationship (3D-QSAR) analysis using comparative molecular field analysis. The 3D-QSAR models were generated and evaluated by a scheme that combines a genetic algorithm (GA) optimization with partial least squares (PLS) regression and by crossvalidation using the leave-one-out technique. The model was able to efficiently predict the activities of the compounds of the test set, suggesting that it can be used for the planning of new p38 MAPK inhibitor candidates useful to treat chronic inflammatory states.

Kinomics-structural biology and chemogenomics of kinase inhibitors and targets

Classifying kinases based entirely on small molecule selectivity data is a new approach to drug discovery that allows scientists to understand relationships between targets. This approach combines the understanding of small molecules and targets, and thereby assists the researcher in finding new targets for existing molecules or understanding selectivity and polypharmacology of molecules in related targets. Currently, structural information is available for relatively few of the protein kinases encoded in the human genome (7% of the estimated 518); however, even the current knowledge base, when paired with structure-based design techniques, can assist in the identification and optimization of novel kinase inhibitors across the entire protein class. Chemogenomics attempts to combine genomic data, structural biological data, classical dendrograms, and selectivity data to explore, define, and classify the medicinally relevant kinase space. Exploitation of this information in the discovery of kinase inhibitors defines practical kinase chemogenomics (kinomics). In this paper, we review the available information on kinase targets and their inhibitors, and present the relationships between the various classification schema for kinase space. In particular, we present the first dendrogram of kinases based entirely on small molecule selectivity data. We find that the selectivity dendrogram differs from sequence-based clustering mostly in the higher-level groupings of the smaller clusters, and remains very comparable for closely homologous targets. Highly homologous kinases are, on average, inhibited comparably by small molecules. This observation, although intuitive, is very important to the process of target selection, as one would expect difficulty in achieving inhibitor selectivity for kinases that share high sequence identity.

Benzimidazolone p38 inhibitors

The synthesis and in vitro p38 alpha activity of a novel series of benzimidazolone inhibitors is described. The p38 alpha SAR is consistent with a mode of binding wherein the benzimidazolone carbonyl serves as the H-bond acceptor to Met109 of p38 alpha in a manner analogous to the pyridine nitrogen of prototypical pyridylimidazole p38 inhibitors. Potent p38 alpha activity comparable to that of several previously reported p38 inhibitors is observed for this novel chemotype.

Lead compounds discovered from libraries: part 2

Many lead compounds with the potential to progress to viable drug candidates have been identified from libraries during the past two years. There are two key strategies most often employed to find leads from libraries: first, high-throughput biological screening of corporate compound collections; and second, synthesis and screening of project-directed libraries (i.e. target-based libraries). Numerous success stories, including the discovery of several clinical candidates, testify to the utility of chemical library collections as proven sources of new leads for drug development.

Activation of the glucose transporter GLUT4 by insulin

The transport of glucose into cells and tissues is a highly regulated process, mediated by a family of facilitative glucose transporters (GLUTs). Insulin-stimulated glucose uptake is primarily mediated by the transporter isoform GLUT4, which is predominantly expressed in mature skeletal muscle and fat tissues. Our recent work suggests that two separate pathways are initiated in response to insulin: (i) to recruit transporters to the cell surface from intracellular pools and (ii) to increase the intrinsic activity of the transporters. These pathways are differentially inhibited by wortmannin, demonstrating that the two pathways do not operate in series. Conversely, inhibitors of p38 mitogen-activated protein kinase (MAPK) imply that p38 MAPK is involved only in the regulation of the pathway leading to the insulin-stimulated activation of GLUT4. This review discusses the evidence for the divergence of GLUT4 translocation and activity and proposed mechanisms for the regulation of GLUT4.

p38MAP kinase inhibitors. Part 1: design and development of a new class of potent and highly selective inhibitors based on 3,4-dihydropyrido[3,2-d]pyrimidone scaffold

A new class of p38 antagonists based on 3,4-dihydropyrido[3,2,-d]pyrimidine scaffold has been developed. These inhibitors exhibit unprecedented selectivity towards p38 over other very closely related kinases. Compounds 25, 33, and 34 were identified as benchmark analogues for follow-up studies. They show good potency for enzyme inhibition and excellent functional activity.

Targeting signal transduction with large combinatorial collections

The large-scale application of combinatorial chemistry to drug discovery is an endeavor that is now more than ten years old. The growth of chemical libraries together with the influx of novel genomic targets has led to a reconstruction of the drug-screening paradigm. The drug discovery industry faces a post-genomic world where the interplay between tens-of-thousands of proteins must be addressed. To compound this complexity, there now exists the ability to screen millions of compounds against a single target. This review focuses on the practice and use of selecting individual compounds from large chemical libraries that act on targets relevant to signal transduction.

Synthesis and pharmacological characterization of a potent, orally active p38 kinase inhibitor

Inhibitors of the MAP kinase p38 provide a novel approach for the treatment of osteoporosis, inflammatory disorders, and cancer. We have identified N-(3-tert-butyl-1-methyl-5-pyrazolyl)-N'-(4-(4-pyridinylmethyl)phenyl)urea as a potent and selective p38 kinase inhibitor in biochemical and cellular assays. This compound is orally active in two acute models of cytokine release (TNF-induced IL-6 and LPS-induced TNF) and a chronic model of arthritis (20-day murine collagen-induced arthritis).

Newer immunosuppressive drugs: their potential role in rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is a chronic immune-mediated disease characterised by chronic synovitis, which leads to cartilage damage and joint destruction. It is generally a progressive disease with radiographic evidence of joint damage, functional status decline and premature mortality. Proinflammatory cytokines, such as interleukin 1 and tumour necrosis factor alpha, play an important role in maintaining the chronicity of RA and mediating tissue damage. New approaches in the therapy of RA with anticytokine biological agents, which neutralise or block cytokines or their receptors, are now the first generation antirheumatic drugs in clinical practice. A better understanding of the signal transduction systems and gene regulation by transcription factors involved in cytokine production has opened the way for the discovery of novel therapeutic compounds useful in treating patients with RA. Overactivation of selective kinases or aberrant function of downstream transcription factors could help convert a normal immune response to a chronic disease state. This provides a unique opportunity for novel therapeutic interventions, since specific signal transduction or transcription factor targets might interrupt the perpetuation mechanisms in RA. The availability of potent and selective p38 mitogen activated protein kinase inhibitors provide a means in further dissecting the pathways implicated in cytokine production, which in turn maintain the chronicity of RA. Many studies conclude that these compounds are very useful in the treatment of chronic synovitis and therefore are very promising for RA treatment.

Discovery of heterocyclic ureas as a new class of raf kinase inhibitors: identification of a second generation lead by a combinatorial chemistry approach

Heterocyclic ureas, such as N-3-thienyl N'-aryl ureas, have been identified as novel inhibitors of raf kinase, a key mediator in the ras signal transduction pathway. Structure-activity relationships were established, and the potency of the screening hit was improved 10-fold to IC(50)=1.7 microM. A combinatorial synthesis approach enabled the identification of a breakthrough lead (IC(50)=0.54 microM) for a second generation series of heterocyclic urea raf kinase inhibitors.

Lead compounds discovered from libraries

Lead compounds with the potential to progress to viable drug candidates have been identified from libraries using several strategies. These include rapid screening of large diverse collections, thematic libraries, project-directed libraries, and three-dimensional molecular models of corporate databases. There have been numerous success stories, including the identification of several clinical candidates.

p38 kinase inhibitors for the treatment of arthritis and osteoporosis: thienyl, furyl, and pyrrolyl ureas

Inhibitors of the MAP kinase p38 are potentially useful for the treatment for osteoporosis, arthritis, and other inflammatory diseases. A series of thienyl, furyl, and pyrrolyl ureas has been identified as potent p38 inhibitors, displaying in vitro activity in the nanomolar range.