Axel Metzger

The Discovery of Novel Chemotypes of p38 Kinase Inhibitors

In the late 1970s and the early 1980s the initial p38 chemotype, the triaryl imidazoles, was discovered as an off-target effect during the development of cyclooxygenase and 5-lipoxygenase inhibitors long before the identity of the p38 kinase was known. During the last 10 years a number of novel p38 chemotypes were discovered via high throughput screening. More recently, the first series of p38 inhibitors discovered by xray crystallographic and virtual screening was announced. Finally, throughout the life span of p38 drug discovery programs significant medicinal chemistry effort has continually been placed on the design of new inhibitors from known chemotypes using molecular modeling, protein crystallography, hybrid design and simply sound intuition. Indeed, the search for p38 kinase inhibitors offers an excellent historical perspective as to how technological changes that have taken place in the pharmaceutical industry over the last decade, have affected the ways in which new leads are discovered and advanced. It is the intent of this review to highlight the discoveries of novel p38 chemotypes, emphasizing where possible the key technologies used in the discoveries and the knowledge gained from each discovery.

Synthesis of 2-amino-5-benzoyl-4-(2-furyl)thiazoles as adenosine A(2A) receptor antagonists.

The discovery and synthesis of a series of 2-amino-5-benzoyl-4-(2-furyl)thiazoles as adenosine A(2A) receptor antagonists from a small-molecule combinatorial library using a high-throughput radioligand-binding assay is described. Antagonists were further characterized in the A(2A) binding assay and an A(1) selectivity assay. Selected examples exhibited excellent affinity for A(2A) and good selectivity versus the A(1) receptor.

Discovery and characterization of triaminotriazine aniline amides as highly selective p38 kinase inhibitors.

The p38 mitogen-activated protein (MAP) kinases are a family of serine/threonine protein kinases that play important roles in cellular responses to inflammation and external stress. Inhibitors of the p38 MAP kinase have shown promise for potential treatment of inflammatory disorders such as rheumatoid arthritis, acute coronary syndrome, psoriasis, and Crohns disease. We identified a novel class of p38 inhibitors via high-throughput screening. PS200981 [3-(4-(1,4-diazepan-1-yl)-6-(((1S,2R,5S)-6,6-dimethylbicyclo[3.1.1]heptan-2-yl)methylamino)-1,3,5-triazin-2-ylamino)-4-methylbenzamide], a representative compound identified from screening a collection of combinatorial libraries, amounting to 2.1 million compounds, inhibits p38α kinase and the lipopolysaccharide (LPS)-induced increase in tumor necrosis factor (TNF) α levels in cell media of human monocytes with IC50 values of 1 μM. The screening data revealed a preferred synthon, 3-amino-4-methyl benzamide, which is critical for the activity against p38. This synthon appeared almost exclusively in screening hits including PS200981, and slight variations of this synthon including 3-amino benzamide and 2-amino-4-methyl benzamide also contained in the library were inactive. PS200981 is equally potent against the α and β forms of p38 but did not inhibit p38γ and is >25-fold selective versus a panel of other kinases. PS200981 inhibited the LPS-induced increase in TNFα levels when administered at 30 mg/kg to mice. Selectivity and in vivo activity of this class of p38 inhibitors was further demonstrated by PS166276 [(R)-3-(4-(isobutyl(methyl)-amino)-6-(pyrrolidin-3-ylamino)-1,3,5-triazin-2-ylamino)-4-methylbenzamide], a highly structurally related but more potent and less cytotoxic inhibitor, in several intracellular signaling assays, and in LPS-challenged mice. Overall, this novel class of p38 inhibitors is potent, active in vitro and in vivo, and is highly selective.

Sulfonamido-aryl ethers as bradykinin B1 receptor antagonists.

The synthesis and identification of sulfonamido-aryl ethers as potent bradykinin B1 receptor antagonists from a approximately 60,000 member encoded combinatorial library are reported. Two distinct series of compounds exhibiting different structure-activity relationships were identified in a bradykinin B1 whole-cell receptor-binding assay. Specific examples exhibit K(i) values of approximately 10nM.

Successful Screening of Large Encoded Combinatorial Libraries Leading to the Discovery of Novel p38 MAP Kinase Inhibitors

Screening of more than 2 million compounds comprising 41 distinct encoded combinatorial libraries revealed a novel structural class of p38 mitogen-activated protein (MAP) kinase inhibitors. The methodology used for screening large encoded combinatorial libraries combined with the statistical interpretation of screening results is described. A strong preference for a particular triaminotriazine aniline amide was discovered based on biological activity observed in the screening campaign. Additional screening of a focused follow-up combinatorial library yielded data expanding the unique combinatorial SAR and emphasizing an extraordinary preference for this particular building block and structural class. The preference is further highlighted when the p38 inhibitor data set is compared to data obtained for a panel of other kinases.