HDL metabolism and CETP inhibition

High density lipoprotein-cholesterol (HDL-C) concentration in the blood is independently and inversely associated with an increased risk of coronary heart disease. Some of the cholesterol-lowering drugs (niacin, fibrates, and statins) incidentally raise HDL-C. These drugs are not effective in causing major changes in HDL-C. Since the discovery of human genetic cholesteryl ester transfer protein (CETP) deficiency in a Japanese population with high levels of HDL-C and apolipoprotein A-I, CETP inhibition has become a novel strategy for raising HDL-C in humans. Mice, a species naturally lacking CETP, were transduced with the human CETP gene, which resulted in dose-related reductions in HDL-C. Rabbits, a species with naturally high levels of CETP, were fed a synthetic CETP inhibitor, JTT-705, leading to both a 90% increase in HDL-C and a 70% reduction in aortic atherosclerotic lesion area. Human intervention trials with a new potent and selective CETP inhibitor, torcetrapib, have taken place. In a phase I multidose trial, HDL-C increased by 91% with torcetrapib 120 mg twice daily. A phase II trial conducted with multiple combinations of torcetrapib and atorvastatin showed that the combination was well tolerated and doses 30 mg and higher of torcetrapib caused 8.3-40.2% changes from baseline HDL-C across the dose range of atorvastatin at 12 weeks. Recently the phase III clinical trial ILLUMINATE (Investigation of Lipid Level Management to Understand its Impact in Atherosclerotic Events) was prematurely terminated because of an increase in mortality in the torcetrapib/atorvastatin treatment arm compared with atorvastatin used alone. In companion studies no improvement in carotid or coronary atherosclerosis could be detected in patients treated with the torcetrapib/atorvastatin combination despite favorable changes in both low density lipoprotein (LDL)- and HDL-cholesterol levels. The future for CETP inhibition with drug therapy is now unclear, and must include a closer look at CETP inhibitor's effects on blood pressure and HDL itself. Accordingly, it was recently shown in 2 double-blind, placebo-controlled, randomized, phase I studies with the CETP inhibitor anacetrapib in healthy individuals and in patients with dyslipidemias that the drug increased HDL and reduced LDL, while having no effect on blood pressure.