Design, synthesis, and biological evaluation of aminopyrazine derivatives as inhibitors of mitogen-activated protein kinase-activated protein kinase 2 (MK-2).

Several series of novel non-thiourea-containing aminopyrazine derivatives were designed based on the MK-2 inhibitors 1-(2-aminopyrazin-3-yl)methyl-2-thioureas. These compounds were synthesized and evaluated for their inhibitory activity against MK-2 enzyme in vitro. Compounds with low micromolar to sub-micromolar IC50 values were identified, and several compounds were also found to be active in suppressing the lipopolysaccharide (LPS)-stimulated TNFα production in THP-1 cells with minimum shift compared to their enzyme activity.

Novel 1-(2-aminopyrazin-3-yl)methyl-2-thioureas as potent inhibitors of mitogen-activated protein kinase-activated protein kinase 2 (MK-2).

Novel 1-(2-aminopyrazin-3-yl)methyl-2-thioureas are described as inhibitors of mitogen-activated protein kinase-activated protein kinase 2 (MK-2). These compounds demonstrate potent in vitro activity against the enzyme with IC(50) values as low as 15 nM, and suppress expression of TNFalpha in THP-1 cells and in vivo in an acute inflammation model in mice. The synthesis, structure-activity relationship (SAR), and biological evaluation of these compounds are discussed.

Hybrid-designed inhibitors of p38 MAP kinase utilizing N-arylpyridazinones.

Imidazo[1,2-a]pyridyl N-arylpyridazinones were hybridized from the classic pyridinylimidazoles and the more recent dual hydrogen bond acceptors, resulting in a new structural class of selective p38 MAP kinase inhibitors.

p38 MAP kinase inhibitors: metabolically stabilized piperidine-substituted quinolinones and naphthyridinones.

Quinolinones and naphthyridinones with C7 N-t-butyl piperidine substituents were found to be potent p38 MAP kinase inhibitors. These compounds significantly suppress TNF-alpha release in both cellular and LPS-stimulated whole blood assays. They also displayed excellent PK profiles across three animal species. Quinolinone at 10 mpk showed comparable oral efficacy to that of dexamethasone at 1 mpk in a murine collagen-induced arthritis model.

Time-resolved Forster resonance energy transfer assays for the binding of nucleotide and protein substrates to p38alpha protein kinase.

We have developed assays for the binding of nucleotide and protein substrates to p38alpha protein kinase based on time-resolved Forster resonance energy transfer. p38alpha was biotinylated by addition of a sequence that targets biotin to a single lysine when coexpressed with biotin ligase in Escherichia coli, allowing formation of a complex between a streptavidin "LANCE" europium chelate conjugate and p38alpha. When this reagent was combined with M39AF, a p38 inhibitor containing a fluorescent moiety whose excitation wavelengths match the emission wavelengths of the europium chelate, a change in ratio of light emitted at 665 nm/615 nm is detected. Less than 100pM complex was detected with a signal/background ratio of >30-fold. The complex exhibits slow, tight binding kinetics where the apparent K(d) decreases with a relaxation time of 21 min at 125 pM biotin-p38alpha. Preincubating inhibitors or ATP with biotin-p38alpha and adding M39AF as a competitor yielded IC(50)s consistent with those measured by enzyme assay for the activated form of biotin-p38alpha. The same technique was also used to measure affinity of inhibitors for the unphosphorylated and catalytically inactive form of biotin-p38alpha. To measure affinity of p38alpha for its protein substrate MK2, we incubated biotin-p38alpha with a glutathione S-transferase MK2 fusion protein. Detection of the complex after incubation with streptavidin-allophycocyanin and a LANCE-conjugated anti-GST allowed measurement of affinity of MK2 for biotin-p38alpha and detection of 0.5 nM p38alpha.MK2 complex with signal/background ratio >5-fold. Competition with unbiotinylated p38alpha yielded an IC(50) value of 5 nM. Activation of either p38alpha or MK2 had no effect on the measured K(d). M39AF was found to bind in a ternary complex with p38alpha.MK2 with lower affinity than that observed in the binary complex with p38alpha alone.

Mechanism of Janus kinase 3-catalyzed phosphorylation of a Janus kinase 1 activation loop peptide.

A high-affinity IL-2 receptor requires two Janus protein tyrosine kinases (JAKs) for IL-2 signal transduction: JAK1 and JAK3. Since transphosphorylation of the two kinases is presumed to occur after receptor engagement we examined the phosphorylation by recombinant JAK3 of a peptide substrate corresponding to the JAK1 activation loop (KAIETDKEYYTVKD), which has two adjacent tyrosines. Mass spectral analysis of the enzymatically phosphorylated peptide showed that the second tyrosine was phosphorylated at a 30-fold greater rate than the first tyrosine. Moreover, no doubly phosphorylated peptide was detected by this analysis. Kinetic analysis of the reactions of singly phosphorylated JAK1 activation loop peptides showed that phosphorylating the first or second tyrosine decreased the k(cat)/K(m) for the phosphorylation of the other 115- and 26-fold, respectively. Singly changing each side chain of the KEYYTV portion of the peptide to a methyl group (alanine) yielded substrates comparable to the wild-type sequences in all cases except that of the first or second tyrosine, which showed a 153- or 70-fold drop in k(cat)/K(m), respectively. Using libraries of immobilized peptides with all 20 naturally occurring amino acids substituted for Y9 or T11 showed that the JAK3 tolerated substitution at T11 but prefers large hydrophobic amino acids at Y9. These results show that JAK3 does not act processively on the JAK1 activation loop in vitro and illustrate the role of Y9 in the recognition of the preferred site of phosphorylation which is Y10.