Ezetimibe is a potent inhibitor of cholesterol absorption that has been approved for the treatment of hypercholesterolemia, but its molecular target has been elusive. Using a genetic approach, we recently identified Niemann-Pick C1-Like 1 (NPC1L1) as a critical mediator of cholesterol absorption and an essential component of the ezetimibe-sensitive pathway. To determine whether NPC1L1 is the direct molecular target of ezetimibe, we have developed a binding assay and shown that labeled ezetimibe glucuronide binds specifically to a single site in brush border membranes and to human embryonic kidney 293 cells expressing NPC1L1. Moreover, the binding affinities of ezetimibe and several key analogs to recombinant NPC1L1 are virtually identical to those observed for native enterocyte membranes. KD values of ezetimibe glucuronide for mouse, rat, rhesus monkey, and human NPC1L1 are 12,000, 540, 40, and 220 nM, respectively. Last, ezetimibe no longer binds to membranes from NPC1L1 knockout mice. These results unequivocally establish NPC1L1 as the direct target of ezetimibe and should facilitate efforts to identify the molecular mechanism of cholesterol transport.cholesterol ͉ intestinal brush border membranes

(3R)-(3-Phenylpropyl)-1,(4S)-bis(4-methoxyphenyl)-2-azetidinone (2, SCH 48461), a novel inhibitor of intestinal cholesterol absorption, has recently been described by Burnett et al. and has been demonstrated to lower total plasma cholesterol in man. The potential sites of metabolism of 2 were considered, and the most probable metabolites were prepared. The oral cholesterol-lowering efficacy of the putative metabolites was evaluated in a 7-day cholesterol-fed hamster model for the reduction of serum total cholesterol and liver cholesteryl esters versus control. On the basis of our analysis of the putative metabolite structure-activity relationship (SAR), SCH 58235 (1, 1-(4-fluorophenyl)-(3R)-[3-(4-fluorophenyl)-(3S)-hydroxypropyl]-(4S)- (4-hydroxyphenyl)-2-azetidinone) was designed to exploit activity enhancing oxidation and to block sites of potential detrimental metabolic oxidation. Additionally, a series of congeners of 2 were prepared incorporating strategically placed hydroxyl groups and fluorine atoms to further probe the SAR of 2-azetidinone cholesterol absorption inhibitors. Through the SAR analysis of a series of putative metabolites of 2, compound 1 was targeted and found to exhibit remarkable efficacy with an ED50 of 0.04 mg/kg/day for the reduction of liver cholesteryl esters in a 7-day cholesterol-fed hamster model.

No abstract

No abstract

A series of azetidinone cholesterol absorption inhibitors related to SCH 48461 ((-)-6) has been prepared, and compounds were evaluated for their ability to inhibit hepatic cholesteryl ester formation in a cholesterol-fed hamster model. Although originally designed as acyl CoA: cholesterol acyltransferase (ACAT) inhibitors, comparison of in vivo potency with in vitro activity in a microsomal ACAT assay indicates no correlation between activity in these two models. The molecular mechanism by which these compounds inhibit cholesterol absorption is unknown. Despite this limitation, examination of the in vivo activity of a range of compounds has revealed clear structure-activity relationships consistent with a well-defined molecular target. The details of these structure-activity relationships and their implications on the nature of the putative pharmacophore are discussed.