Discovery of the Oral Leukotriene C4 Synthase Inhibitor (1S,2S)-2-({5-[(5-Chloro-2,4-difluorophenyl)(2-fluoro-2-methylpropyl)amino]-3-methoxypyrazin-2-yl}carbonyl)cyclopropanecarboxylic Acid (AZD9898) as a New Treatment for Asthma.

While bronchodilators and inhaled corticosteroids are the mainstay of asthma treatment, up to 50% of asthmatics remain uncontrolled. Many studies show that the cysteinyl leukotriene cascade remains highly activated in some asthmatics, even those on high-dose inhaled or oral corticosteroids. Hence, inhibition of the leukotriene C4 synthase (LTC4S) enzyme could provide a new and differentiated core treatment for patients with a highly activated cysteinyl leukotriene cascade. Starting from a screening hit (3), a program to discover oral inhibitors of LTC4S led to (1S,2S)-2-({5-[(5-chloro-2,4-difluorophenyl)(2-fluoro-2-methylpropyl)amino]-3-methoxypyrazin-2-yl}carbonyl)cyclopropanecarboxylic acid (AZD9898) (36), a picomolar LTC4S inhibitor (IC50 = 0.28 nM) with high lipophilic ligand efficiency (LLE = 8.5), which displays nanomolar potency in cells (peripheral blood mononuclear cell, IC50,free = 6.2 nM) and good in vivo pharmacodynamics in a calcium ionophore-stimulated rat model after oral dosing (in vivo, IC50,free = 34 nM). Compound 36 mitigates the GABA binding, hepatic toxicity signal, and in vivo toxicology findings of an early lead compound 7 with a human dose predicted to be 30 mg once daily.

An Angle on MK2 Inhibition-Optimization and Evaluation of Prevention of Activation Inhibitors.

The mitogen-activated protein kinase p38α pathway has been an attractive target for the treatment of inflammatory conditions such as rheumatoid arthritis. While a number of p38α inhibitors have been taken to the clinic, they have been limited by their efficacy and toxicological profile. A lead identification program was initiated to selectively target prevention of activation (PoA) of mitogen-activated protein kinase-activated protein kinase 2 (MK2) rather than mitogen- and stress-activated protein kinase 1 (MSK1), both immediate downstream substrates of p38α, to improve the efficacy/safety profile over direct p38α inhibition. Starting with a series of pyrazole amide PoA MK2 inhibitor leads, and guided by structural chemistry and rational design, a highly selective imidazole 9 (2-(3'-(2-amino-2-oxoethyl)-[1,1'-biphenyl]-3-yl)-N-(5-(N,N-dimethylsulfamoyl)-2-methylphenyl)-1-propyl-1H-imidazole-5-carboxamide) and the orally bioavailable imidazole 18 (3-methyl-N-(2-methyl-5-sulfamoylphenyl)-2-(o-tolyl)imidazole-4-carboxamide) were discovered. The PoA concept was further evaluated by protein immunoblotting, which showed that the optimized PoA MK2 compounds, despite their biochemical selectivity against MSK1 phosphorylation, behaved similarly to p38 inhibitors in cellular signaling. This study highlights the importance of selective tool compounds in untangling complex signaling pathways, and although 9 and 18 were not differentiated from p38α inhibitors in a cellular context, they are still useful tools for further research directed to understand the role of MK2 in the p38α signaling pathway.