P450-mediated O-demethylated metabolite is responsible for rat hepatobiliary toxicity of pyridyltriazine-containing PI3K inhibitors.

The dysregulation of phosphatidylinositol 3-kinase (PI3K)-dependent pathways is implicated in several human cancers making it an attractive target for small molecule PI3K inhibitors. A series of potent pyridyltriazine-containing inhibitors of class Ia PI3Ks were synthesized and a subset of compounds was evaluated in exploratory repeat-dose rat toxicology studies. Daily oral dosing of compound 1: in Sprague Dawley rats for four consecutive days was associated with hepatobiliary toxicity that included biliary epithelial hyperplasia and hypertrophy, periductular edema, biliary stasis, and acute peribiliary inflammatory infiltrates. These histological changes were associated with clinical pathology changes that included increased serum liver enzymes, total bile acids, and bilirubin. The predominant clearance pathway of 1: was shown in vitro and in a bile-duct cannulated rat (14)C-ADME study to be P450-mediated oxidative metabolism. An O-demethylated pyridine metabolite, M3: , was identified as a candidate proximal metabolite that caused the hepatotoxicity. Co-administration of the pan-P450 inhibitor 1-aminobenzotriazole with 1: to rats significantly reduced the formation of M3: and prevented liver toxicity, whereas direct administration of M3: reproduced the toxicity. Structural changes were introduced to 1: to make the methoxypyridine ring less susceptible to P450 oxidation (compound 2: ), and addition of a methyl group to the benzylic carbon (compound 3: ) improved the pharmacokinetic profile. These changes culminated in the successful design of a clinical candidate 3: (AMG 511) that was devoid of liver toxicity in a 14-day rat toxicity study. Herein, we describe how a metabolism-based structure-activity relationship analysis allowed for the successful identification of a PI3K inhibitor devoid of off-target toxicity.

Selective class I phosphoinositide 3-kinase inhibitors: optimization of a series of pyridyltriazines leading to the identification of a clinical candidate, AMG 511.

The phosphoinositide 3-kinase family catalyzes the phosphorylation of phosphatidylinositol-4,5-diphosphate to phosphatidylinositol-3,4,5-triphosphate, a secondary messenger which plays a critical role in important cellular functions such as metabolism, cell growth, and cell survival. Our efforts to identify potent, efficacious, and orally available phosphatidylinositol 3-kinase (PI3K) inhibitors as potential cancer therapeutics have resulted in the discovery of 4-(2-((6-methoxypyridin-3-yl)amino)-5-((4-(methylsulfonyl)piperazin-1-yl)methyl)pyridin-3-yl)-6-methyl-1,3,5-triazin-2-amine (1). In this paper, we describe the optimization of compound 1, which led to the design and synthesis of pyridyltriazine 31, a potent pan inhibitor of class I PI3Ks with a superior pharmacokinetic profile. Compound 31 was shown to potently block the targeted PI3K pathway in a mouse liver pharmacodynamic model and inhibit tumor growth in a U87 malignant glioma glioblastoma xenograft model. On the basis of its excellent in vivo efficacy and pharmacokinetic profile, compound 31 was selected for further evaluation as a clinical candidate and was designated AMG 511.

Structure-activity relationships of phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitors: investigations of various 6,5-heterocycles to improve metabolic stability.

N-(6-(6-Chloro-5-(4-fluorophenylsulfonamido)pyridin-3-yl)benzo[d]thiazol-2-yl)acetamide (1) is a potent and efficacious inhibitor of PI3Kα and mTOR in vitro and in vivo. However, in hepatocyte and in vivo metabolism studies, 1 was found to undergo deacetylation on the 2-amino substituent of the benzothiazole. As an approach to reduce or eliminate this metabolic deacetylation, a variety of 6,5-heterocyclic analogues were examined as an alternative to the benzothiazole ring. Imidazopyridazine 10 was found to have similar in vitro potency and in vivo efficacy relative to 1, while only minimal amounts of the corresponding deacetylated metabolite of 10 were observed in hepatocytes.