Objective-The ability of the potent cholesteryl ester transfer protein (CETP) inhibitor torcetrapib 414) to raise high-density lipoprotein cholesterol (HDL-C) levels in healthy young subjects was tested in this initial phase 1 multidose study. Methods and Results-Five groups of 8 subjects each were randomized to placebo (nϭ2) or torcetrapib (nϭ6) at 10, 30, 60, and 120 mg daily and 120 mg twice daily for 14 days. Torcetrapib was well tolerated, with all treated subjects completing the study. The correlation of plasma drug levels with inhibition (EC50ϭ43 nM) was as expected based on in vitro potency (IC50 Ϸ50 nM), and increases in CETP mass were consistent with the proposed mechanism of inhibition. CETP inhibition increased with escalating dose, leading to elevations of HDL-C of 16% to 91%. Total plasma cholesterol did not change significantly because of a reduction in nonHDL-C, including a 21% to 42% lowering of low-density lipoprotein cholesterol at the higher doses. Apolipoprotein A-I and E were elevated 27% and 66%, respectively, and apoB was reduced 26% with 120 mg twice daily. Cholesteryl ester content decreased and triglyceride increased in the nonHDL plasma fraction, with contrasting changes occurring in HDL. studies, the inverse correlation between high-density lipoprotein (HDL) levels and premature coronary heart disease (CHD) has been strengthened. A 1% decrease in HDL cholesterol (HDL-C) has been associated with a 1% to 2% increase in risk for CHD, 3 and lipid intervention trials have demonstrated that increases in HDL-C 4 and its main apoprotein, A-I, 5 contribute to reduced CHD, even in the absence of any change in low-density lipoprotein cholesterol (LDL-C). 6 However, current therapies for raising HDL are limited. The fibrates and statins produce only modest elevations in HDL, and the use of niacin, although somewhat more effective, has been hampered by side effects. 7 In a recent study, the combination of lovastatin and extended-release niacin (Advicor) was able to increase HDL levels by 20% to 32%, 8 but withdrawal rates for incidents of flushing and other adverse events were relatively high. Conclusions-TheseThe marked increase in HDL associated with human deficiency of cholesteryl ester transfer protein (CETP) 9 has See page 387 and cover suggested CETP inhibition as a means of elevating HDL. Expression of CETP in transgenic mice under different metabolic settings has produced mixed results regarding its atherogenicity, whereas inhibition of endogenous CETP in rabbits has more consistently been antiatherogenic. 10 With regard to human CETP mutations and the associated reduction in CETP levels, recent analysis of prospective data from the Honolulu Heart Study 10 is consistent with the results of a previous study of Japanese subjects 11 in concluding that CETP deficiency is protective when associated with HDL-C levels Ն60 mg/dL.The results for a phase 2 study testing the synthetic CETP inhibitor JTT-705 in subjects with mild hyperlipidemia have been reported. 12 At 900 mg daily, JTT-705 led to ...

Considerable evidence supports the involvement of acyl-CoA:cholesterol acyltransferase (ACAT) in the maintenance of intracellular cholesterol homeostasis. A number of recently developed ACAT inhibitors may have potential use as pharmacological agents to reduce the development of atherosclerosis. Recently, however, reports arose describing cytotoxic effects following administration of a specific ACAT inhibitor to experimental animals. In order to address the specific intracellular mechanisms involved with the cytotoxic effect, we examined the consequences of ACAT inhibition in cholesterol-enriched mouse peritoneal macrophages. Mouse peritoneal macrophages were cholesterol-enriched by incubation with acetylated low density lipoprotein and free cholesterol:phospholipid dispersions prior to the addition of an ACAT inhibitor, either Sandoz 58-035 or Pfizer CP-113,818. The adenine pool of the macrophages was radiolabeled prior to addition of the ACAT inhibitors, in order to monitor the release of radiolabeled adenine, a technique shown to be a sensitive method to monitor drug-induced toxicity. The ACAT inhibitors were added for up to 48 h and at concentrations up to 2 micrograms/ml. These conditions resulted in an approximately 2-fold increase in adenine release. The increase in cell toxicity paralleled an increase in the cellular free cholesterol content. Reducing the cellular free cholesterol content, by the addition of extracellular acceptors, decreased the cytotoxic effects of the ACAT inhibitors. Addition of an intracellular cholesterol transport inhibitor, either progesterone or U18666A, together with CP-113,818 blocked the toxic effect of CP-113,818. These results suggest that ACAT inhibition of cholesterol-enriched macrophages increases cell toxicity due to the buildup of cellular free cholesterol. Removal of free cholesterol by the addition of extracellular cholesterol acceptors or by blocking intracellular sterol transport relieves the ACAT inhibitor-induced toxicity.

Objective-This study examines the effects of pharmacological inhibition of cholesteryl ester transfer protein (CETP) on the ability of high-density lipoprotein particles (HDL) to promote net cholesterol efflux from human THP-1 macrophage foam cells. Methods and Results-Two groups of 8 healthy, moderately hyperlipidemic subjects received the CETP inhibitor torcetrapib at 60 or 120 mg daily for 8 weeks. Torcetrapib increased HDL cholesterol levels in both groups by 50% and 60%, respectively. Compared with baseline, torcetrapib 60 mg daily increased HDL-mediated net cholesterol efflux from foam cells primarily by increasing HDL concentrations, whereas 120 mg daily torcetrapib increased cholesterol efflux both by increasing HDL concentration and by causing increased efflux at matched HDL concentrations. There was an increased content of lecithin:cholesterol acyltransferase (LCAT) and apolipoprotein E (apoE) in HDL-2 only at the 120 mg dose. ABCG1 activity was responsible for 40% to 50% of net cholesterol efflux to both control and T-HDL. Conclusions-These data indicate that inhibition of CETP by torcetrapib causes a modest increase in the ability of HDL to promote net cholesterol efflux at the 60 mg dose, and a more dramatic increase at the 120 mg dose in association with enhanced particle functionality. The HDL-mediated removal of excess free cholesterol (FC) from macrophage foam cells is thought to play a major role in the protection against the development of atherosclerosis. 2 However, current therapies for raising HDL are limited. Despite the favorable effects of statins on coronary heart disease, these agents have only modest effects on HDL-C levels. 3,4 Fibrates and niacin can raise HDL-C, but the increases are rarely Ͼ30% and only some of the fibrate trials have shown prevention of coronary events in patients with low HDL, and niacin is often not well tolerated. 5,6 Novel targets to raise HDL-C have emerged from the recent understanding of HDL synthesis, maturation, and catabolism. In humans, cholesteryl ester (CE) generated by the lecithin:cholesterol acyltransferase (LCAT) enzyme in HDL is transferred to apoB-lipoproteins by the cholesteryl ester transfer protein (CETP). CETP promotes the removal of cholesteryl ester (CE) from antiatherogenic HDL to atherogenic apoB-containing particles in exchange for triglycerides (TGs). 7 The marked increase in HDL cholesterol associated with human deficiency of CETP has suggested CETP inhibition as a potential strategy to treat atherosclerotic disease. 8,9 However, there has been concern that HDL particles accumulating in CETP deficiency might be dysfunctional. 10 We recently reported that large CE-rich HDL particles from 4 subjects with complete CETP deficiency (CETP-D) showed increased ability to promote cholesterol efflux from macrophage foam cells. 11 Central to this observation was the key role of LCAT and apolipoprotein E (apoE) present at high levels in CETP-D HDL driving net cholesterol efflux. Cholesterol efflux from cells to HDL can occur by passive diffusion...