YA-101

Inhibition of H(+),K(+)-ATPase is accepted as the most effective way of controlling gastric acid secretion. However, current acid suppressant therapy for gastroesophageal reflux disease, using histamine H(2) receptor antagonists and proton pump inhibitors, does not fully meet the needs of all patients because of their mechanism of action. This study sought to characterize the in vitro and in vivo pharmacology of a novel acid pump antagonist, N-(2-Hydroxyethyl)-N,2-dimethyl-8-{[(4R)-5-methyl-3,4-dihydro-2H-chromen-4-yl]amino}imidazo[1,2-a]pyridine-6-carboxamide (PF-03716556), and to compare it with other acid suppressants. Porcine, canine, and human recombinant gastric H(+),K(+)-ATPase activities were measured by ion-leaky and ion-tight assay. The affinities for a range of receptors, ion channels, and enzymes were determined to analyze selectivity profile. Acid secretion in Ghosh-Schild rats and Heidenhain pouch dogs were measured by titrating perfusate and gastric juice samples. PF-03716556 demonstrated 3-fold greater inhibitory activity than 5,6-dimethyl-2-(4-fluorophenylamino)-4-(1-methyl-1,2,3,4-tetrahydroisoquinoline-2-yl)pyrimidine (revaprazan), the only acid pump antagonist that has been available on the market, in ion-tight assay. The compound did not display any species differences, exhibiting highly selective profile including the canine kidney Na(+),K(+)-ATPase. Kinetics experiments revealed that PF-03716556 has a competitive and reversible mode of action. More rapid onset of action than 5-methoxy-2-{[(4-methoxy-3,5-dimethyl-2-pyridyl)methyl]-sulfinyl}-benzimidazole (omeprazole) and 3-fold greater potency than revaprazan were observed in Ghosh-Schild rats and Heidenhain pouch dogs. PF-03716556, a novel acid pump antagonist, could improve upon or even replace current pharmacological treatment for gastroesophageal reflux disease.

5-Methoxy-2-{(4-methoxy-3,5-dimethyl-pyridin-2-yl)methylsulfinyl}-3H-benzoimidazole (omeprazole), a benzoimidazole-derived gastric H(+)/K(+)-ATPase proton pump inhibitor (PPI) extensively prescribed for the treatment of gastroesophageal acid reflux disease, can stimulate the expression of CYP1A1 via activation of the human aryl hydrocarbon receptor (hAhR) in an apparent nonligand-binding manner. Here, we have examined the effect of nonclassical, i.e., nonligand binding, AhR activation by omeprazole upon human insulin-like growth factor binding protein (hIGFBP)-1, a secreted phosphoprotein involved in regulation of insulin-like growth factor-I/II bioavailability and mitogenic activity. Analysis of the proximal promoter of the hIGFBP-1 gene reveals the presence of an aryl hydrocarbon binding/dioxin response element (DRE). Quantitative mRNA analysis revealed hIGFBP-1 expression to be responsive to both ligand (TCDD) and nonligand (omeprazole) modes of hAhR activation in the human hepatocarcinoma HepG2 cell line. Furthermore, mutagenesis of the DRE renders the hIGFBP-1 promoter unresponsive to both compounds in HepG2 cells. Likewise, small interfering RNA-mediated hAhR ablation inhibits TCDD and omeprazole-dependent hIGFBP-1 induction, as determined by quantitative mRNA analysis. Cotreatment with cycloheximide further suggests a direct transcriptional role for hAhR at the hIGFBP-1 promoter. Omeprazole exposure prompted a significant increase in both hIGFBP-1 mRNA and secreted protein from HepG2 cells. In addition, we present in vitro evidence indicating that omeprazole at a concentration comparable with that found circulating in subjects undergoing PPI therapy can stimulate the expression of hIGFBP-1. These data demonstrate that activation of hAhR by pharmaceuticals such as omeprazole can alter IGFBP-1 expression and thus may influence IGFBP-1-dependent physiological processes.