Constance Farley

Comparison of the activity and disposition of the novel cholesterol absorption inhibitor, SCH58235, and its glucuronide, SCH60663.

Previous studies described the metabolism‐based discovery of a potent, selective inhibitor of intestinal absorption of cholesterol, SCH58235 (Ezetimibe). Here we demonstrate that the phenolic glucuronide (SCH60663) of SCH58235, was more potent at inhibiting cholesterol absorption in rats than SCH58235, when administered by the intraduodenal route. To understand the increased potency of the glucuronide, the metabolism and distribution of SCH58235 and SCH60663 were studied in bile duct‐cannulated rats. One minute after intraduodenal delivery of SCH58235, significant levels of compound were detected in portal plasma; >95% was glucuronidated, indicating that the intestine was metabolizing SCH58235 to its glucuronide. When intraduodenally delivered as SCH58235, the compound was glucuronidated, moved through the intestinal wall, into portal plasma, through the liver, and into bile. However, when delivered as SCH60663, >95% of the compound remained in the intestinal lumen and wall, which may explain its increased potency. Significant inhibition of cholesterol absorption and glucuronidation of SCH58235 occurred when SCH58235 was intravenously injected into bile duct‐cannulated rats. Autoradiographic analysis demonstrated that drug related material was located throughout the intestinal villi, but concentrated in the villus tip. These data indicate that (a) SCH58235 is rapidly metabolized in the intestine to its glucuronide; (b) once glucuronidated, the dose is excreted in the bile, thereby delivering drug related material back to the site of action and (c) the glucuronide is more potent than the parent possibly because it localizes to the intestine. Taken together, these data may explain the potency of SCH58235 in the rat (ID50=0.0015 mg kg−1) and rhesus monkey (ID50=0.0005 mg kg−1).

Ezetimibe selectively inhibits intestinal cholesterol absorption in rodents in the presence and absence of exocrine pancreatic function

Ezetimibe potently inhibits the transport of cholesterol across the intestinal wall, thereby reducing plasma cholesterol in preclinical animal models of hypercholesterolemia. The effect of ezetimibe on known absorptive processes was determined in the present studies. Experiments were conducted in the hamster and/or rat to determine whether ezetimibe would affect the absorption of molecules other than free cholesterol, namely cholesteryl ester, triglyceride, ethinylestradiol, progesterone, vitamins A and D, and taurocholic acid. In addition, to determine whether exocrine pancreatic function is involved in the mechanism of action of ezetimibe, a biliary anastomosis model, which eliminates exocrine pancreatic function from the intestine while maintaining bile flow, was established in the rat. Ezetimibe reduced plasma cholesterol and hepatic cholesterol accumulation in cholesterol‐fed hamsters with an ED50 of 0.04 mg kg−1. Utilizing cholesteryl esters labelled on either the cholesterol or the fatty acid moiety, we demonstrated that ezetimibe did not affect cholesteryl ester hydrolysis and the absorption of fatty acid thus generated in both hamsters and rats. The free cholesterol from this hydrolysis, however, was not absorbed (92 – 96% inhibition) in the presence of ezetimibe. Eliminating pancreatic function in rats abolished hydrolysis of cholesteryl esters, but did not affect the ability of ezetimibe to block absorption of free cholesterol (−94%). Ezetimibe did not affect the absorption of triglyceride, ethinylestradiol, progesterone, vitamins A and D, and taurocholic acid in rats. Ezetimibe is a potent inhibitor of intestinal free cholesterol absorption that does not require exocrine pancreatic function for activity. Ezetimibe does not affect the absorption of triglyceride as a pancreatic lipase inhibitor (Orlistat) would, nor does it affect the absorption of vitamin A, D or taurocholate, as a bile acid sequestrant (cholestyramine) would.

Ezetimibe potently inhibits cholesterol absorption but does not affect acute hepatic or intestinal cholesterol synthesis in rats

Ezetimibe (1‐(4‐fluorophenyl)‐(3R)‐[3‐(4‐fluorophenyl)‐(3S)‐hydroxypropyl]‐(4S)‐(4‐hydroxyphenyl)‐2‐azetidinone) and its analog SCH48461 are potent and selective cholesterol absorption inhibitors that inhibit the transport of cholesterol across the intestinal wall, thereby lowering plasma cholesterol. After a dose response for ezetimibe in rats was established, experiments were conducted to determine whether acute administration could alter hepatic or intestinal cholesterol synthesis. To determine whether this class of intestinal cholesterol absorption inhibitors could discriminate between newly synthesized cholesterol in the intestine versus exogenously administered cholesterol, rats were intraduodenally dosed with 14C‐cholesterol and 3H‐mevalonate, and mesenteric lymph was analyzed for radiolabeled cholesterol and cholesteryl ester content. Ezetimibe attenuated diet‐induced hypercholesterolemia 60–94% at doses of 0.1–3 mg kg−1 in rats. A single administration of ezetimibe did not have a direct effect on intestinal or hepatic cholesterol synthesis, while ketoconazole significantly inhibited cholesterol synthesis after a single dose. The ezetimibe analog, SCH48461, inhibited the movement of exogenously administered cholesterol into lymph, but did not affect the appearance of newly synthesized cholesterol into lymph. These data suggest that this class of cholesterol absorption inhibitors does discriminate by blocking the movement of exogenous cholesterol in the enterocyte before it reaches the intracellular cholesterol pool to be incorporated into intestinal lipoproteins, without affecting the incorporation of newly synthesized cholesterol into intestinal lipoproteins.

Discovery of SCH 900271, a Potent Nicotinic Acid Receptor Agonist for the Treatment of Dyslipidemia.

Structure-guided optimization of a series of C-5 alkyl substituents led to the discovery of a potent nicotinic acid receptor agonist SCH 900271 (33) with an EC50 of 2 nM in the hu-GPR109a assay. Compound 33 demonstrated good oral bioavailability in all species. Compound 33 exhibited dose-dependent inhibition of plasma free fatty acid (FFA) with 50% FFA reduction at 1.0 mg/kg in fasted male beagle dogs. Compound 33 had no overt signs of flushing at doses up to 10 mg/kg with an improved therapeutic window to flushing as compared to nicotinic acid. Compound 33 was evaluated in human clinical trials.