Discovery, Synthesis, and Preclinical Characterization of N-(3-Chloro-4-fluorophenyl)-1H-pyrazolo[4,3-b]pyridin-3-amine (VU0418506), a Novel Positive Allosteric Modulator of the Metabotropic Glutamate Receptor 4 (mGlu4).

The efficacy of positive allosteric modulators (PAMs) of the metabotropic glutamate receptor 4 (mGlu4) in preclinical rodent models of Parkinson's disease has been established by a number of groups. Here, we report an advanced preclinically characterized mGlu4 PAM, N-(3-chloro-4-fluorophenyl)-1H-pyrazolo[4,3-b]pyridin-3-amine (VU0418506). We detail the discovery of VU0418506 starting from a common picolinamide core scaffold and evaluation of a number of amide bioisosteres leading to the novel pyrazolo[4,3-b]pyridine head group. VU0418506 has been characterized as a potent and selective mGlu4 PAM with suitable in vivo pharmacokinetic properties in three preclinical safety species.

Evaluation of six proton pump inhibitors as inhibitors of various human cytochromes P450: focus on cytochrome P450 2C19.

Six proton pump inhibitors (PPIs), omeprazole, lansoprazole, esomeprazole, dexlansoprazole, pantoprazole, and rabeprazole, were shown to be weak inhibitors of cytochromes P450 (CYP3A4, -2B6, -2D6, -2C9, -2C8, and -1A2) in human liver microsomes. In most cases, IC50 values were greater than 40 µM, except for dexlansoprazole and lansoprazole with CYP1A2 (IC50 = ∼8 µM) and esomeprazole with CYP2C8 (IC50 = 31 µM). With the exception of CYP2C19 inhibition by omeprazole and esomeprazole (IC50 ratio, 2.5 to 5.9), there was no evidence for a marked time-dependent shift in IC50 (IC50 ratio, ≤ 2) after a 30-min preincubation with NADPH. In the absence of preincubation, lansoprazole (IC50 = 0.73 µM) and esomeprazole (IC50 = 3.7 µM) were the most potent CYP2C19 inhibitors, followed by dexlansoprazole and omeprazole (IC50 = ∼7.0 µM). Rabeprazole and pantoprazole (IC50 = ≥ 25 µM) were the weakest. A similar ranking was obtained with recombinant CYP2C19. Despite the IC50 ranking, after consideration of plasma levels (static and dynamic), protein binding, and metabolism-dependent inhibition, it is concluded that omeprazole and esomeprazole are the most potent CYP2C19 inhibitors. This was confirmed after the incubation of the individual PPIs with human primary hepatocytes (in the presence of human serum) and by monitoring their impact on diazepam N-demethylase activity at a low concentration of diazepam (2 µM). Data described herein are consistent with reports that PPIs are mostly weak inhibitors of cytochromes P450 in vivo. However, two members of the PPI class (esomeprazole and omeprazole) are more likely to serve as clinically relevant inhibitors of CYP2C19.