YM-53601, a novel squalene synthase inhibitor, reduces plasma cholesterol and triglyceride levels in several animal species

1 The aim of this study was to evaluate the potency of YM-53601 ((E)-2-[2-fluoro-2-(quinuclidin-3-ylidene) ethoxy]-9H-carbazole monohydrochloride), a new inhibitor of squalene synthase, in reducing both plasma cholesterol and triglyceride levels, compared with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor and fibrates, respectively. 2 YM-53601 equally inhibited squalene synthase activities in hepatic microsomes prepared from several animal species and also suppressed cholesterol biosynthesis in rats (ED50, 32 mg kg(-1)). 3 In guinea-pigs, YM-53601 and pravastatin reduced plasma nonHDL-C (= total cholesterol - high density lipoprotein cholesterol) by 47% (P<0.001) and 33% (P<0.001), respectively (100 mg kg(-1), daily for 14 days). In rhesus monkeys, YM-53601 decreased plasma nonHDL-C by 37% (50 mg kg(-1) twice daily for 21 days, P<0.01), whereas the HMG-CoA reductase inhibitor, pravastatin, failed to do (25 mg kg(-1), twice daily for 28 days). 4 YM-53601 caused plasma triglyceride reduction in hamsters fed a normal diet (81% decrease at 50 mg kg-l, daily for 5 days, P<0.001). In hamsters fed a high-fat diet, the ability of YM-53601 to lower triglyceride (by 73%, P<0.001) was superior to that of fenofibrate (by 53%, P<0.001), the most potent fibrate (dosage of each drug: 100 mg kg(-1), daily for 7 days). 5 This is the first report that a squalene synthase inhibitor is superior to an HMG-CoA reductase inhibitor in lowering plasma nonHDL-C level in rhesus monkeys and is superior to a fibrate in significantly lowering plasma triglyceride level. YM-53601 may therefore prove useful in treating hypercholesterolemia and hypertriglyceridemia in humans.