The More the Lipid-Lowering Agents, the Merrier: Welcome to Combination Therapy With Cholesteryl Ester Transfer Protein Inhibitors!

Elevated blood pressure was an unexpected outcome in some cholesteryl ester transfer protein (CETP) inhibitor trials, possibly due to vascular effects of these drugs. We investigated whether CETP inhibitors (torcetrapib, dalcetrapib, anacetrapib) influence vascular function and explored the putative underlying molecular mechanisms. Resistance arteries and vascular smooth muscle cells (VSMC) from rats, which lack the CETP gene, were studied. CETP inhibitors increased phenylephrine-stimulated vascular contraction (logEC50 (:) 6.6 ± 0.1; 6.4 ± 0.06, and 6.2 ± 0.09 for torcetrapib, dalcetrapib, and anacetrapib, respectively, versus control 5.9 ± 0.05). Only torcetrapib reduced endothelium-dependent vasorelaxation. The CETP inhibitor effects were ameliorated by N-acetylcysteine (NAC), a reactive oxygen species (ROS) scavenger, and by S3I-201 [2-hydroxy-4-[[2-(4-methylphenyl)sulfonyloxyacetyl]amino]benzoic acid], a signal transducer and activator of transcription 3 (STAT3) inhibitor. CETP inhibitors increased the phosphorylation (2- to 3-fold) of vascular myosin light chain (MLC) and myosin phosphatase target subunit 1 (MYPT1) (procontractile proteins) and stimulated ROS production. CETP inhibitors increased the phosphorylation of STAT3 (by 3- to 4-fold), a transcription factor important in cell activation. Activation of MLC was reduced by NAC, GKT137831 [2-(2-chlorophenyl)-4-[3-(dimethylamino)phenyl]-5-methyl-1H-pyrazolo[4,3-c]pyridine-3,6-dione] (Nox1/4 inhibitor), and S3I-201. The phosphorylation of STAT3 was unaffected by NAC and GKT137831. CETP inhibitors did not influence activation of mitogen-activated proteins kinases (MAPK) or c-Src. Our data demonstrate that CETP inhibitors influence vascular function and contraction through redox-sensitive, STAT3-dependent, and MAPK-independent processes. These phenomena do not involve CETP because the CETP gene is absent in rodents. Findings from our study indicate that CETP inhibitors have vasoactive properties, which may contribute to the adverse cardiovascular effects of these drugs such as hypertension.

Despite large improvements in cardiovascular disease mortality, coronary heart disease (CHD) and stroke remain the leading causes of death in most nations around the world [1,101]. Statins are the foundation for cardiovascular prevention, with up to 50% reductions in cardiovascular risk with the more potent statins [2]. In both statin-treated and -untreated patients, low levels of high-density lipoprotein cholesterol (HDL-C) are an important predictor of subsequent cardiovascular risk [3,4]. In epidemiologic studies, each 1 mg/dl (0.03 mmol, or ~2–3%, depending on baseline HDL-C level) increase in HDL-C is associated with a 2–4% reduction in the risk of CHD events, independent of low-density lipoprotein cholesterol (LDL-C) levels [5]. Of the drugs currently on the market, niacin is the most effective at raising HDL-C (~25% at the 2-g dose), while statins and fibrates have more modest HDL-C-raising effects (3–10%) [6]. However, it is not clear that pharmacologically raising HDL-C per se with these agents reduces cardiovascular risk. A meta-ana lysis of HDL-C-raising drugs found that after adjusting for LDL-C-lowering, raising HDL-C (or lowering triglycerides) was not associated with further cardiovascular risk reduction [6]. Several classes of HDL-C-raising agents with novel mechanisms of action are under development [7]. Farthest along are the cholesteryl ester transfer protein (CETP) inhibitors. CETP mediates the transfer of cholesteryl esters from HDL to proatherogenic apolipoprotein B-lipoproteins for transportation of cholesterol back to the cells; blocking CETP increases levels of mature HDL-C particles. The first CETP inhibitor to move into clinical trials was torcetrapib (Pfizer, Inc). Despite large increases in HDL-C, development of torcetrapib was terminated due to excess mortality in the torcetrapib group of the large outcomes trial, Investigation of Lipid Level management to Understand its Impact in Atherosclerotic Events (ILLUMINATE). Increased mortality in the torcetrapib-treated group occurred despite a 72% increase in HDL-C and a 25% decrease in LDL-C [8]. Torcetrapib also had no benefit on atherosclerotic progression in two noninvasive imaging studies, despite similar lipid changes [9,10]. The adverse mortality effect of torcetrapib has been largely attributed to accelerated hypertension due to activation of the renin–angiotensin–aldosterone system through a non-CETP-dependent effect [11]. Other mechanisms, such as lack of HDL functionality and proinflammatory effects, have also been proposed to explain torcetrapib’s adverse effects. Two CETP inhibitors are still in development, anacetrapib and dalcetrapib. Neither agent has been found to increase blood pressure or influence the renin– angiotensin–aldosterone axis in studies to date [7]. The more potent CETP inhibitor, anacetrapib, comes from the same chemical class as torcetrapib and strongly binds to the CETP molecule. Added to optimal statin therapy, anacetrapib 100 mg has been shown to increase HDL-C by 138% and reduce LDL-C an additional 40%, with modest triglyceride-lowering effects [12]. The less potent dalcetrapib is from a different chemical class, binds reversibly to and induces a different conformational “Given the excess mortality caused by torcetrapib, it is unlikely that any CETP inhibitor will receive regulatory approval prior to the completion of the long-term cardiovascular end point trials...”

Objective To investigate the effects on cardiovascular outcomes of drug interventions that increase high density lipoprotein levels.Design Meta-analysis.Studies reviewed Therapeutic benefit of niacin, fibrates, and cholesteryl ester transfer protein (CETP)...

Cholesteryl ester transfer protein (CETP) inhibitors raise high-density lipoprotein (HDL) cholesterol, but torcetrapib, the first-in-class inhibitor tested in a large outcome trial, caused an unexpected blood pressure elevation and increased cardiovascular events. Whether the hypertensive effect resulted from CETP inhibition or an off-target action of torcetrapib has been debated. We hypothesized that common single-nucleotide polymorphisms in the CETP gene could help distinguish mechanism-based from off-target actions of CETP inhibitors to inform on the validity of CETP as a therapeutic target. We compared the effect of CETP single-nucleotide polymorphisms and torcetrapib treatment on lipid fractions, blood pressure, and electrolytes in up to 67 687 individuals from genetic studies and 17 911 from randomized trials. CETP single-nucleotide polymorphisms and torcetrapib treatment reduced CETP activity and had a directionally concordant effect on 8 lipid and lipoprotein traits (total, low-density lipoprotein, and HDL cholesterol; HDL2; HDL3; apolipoproteins A-I and B; and triglycerides), with the genetic effect on HDL cholesterol (0.13 mmol/L, 95% confidence interval [CI] 0.11 to 0.14 mmol/L) being consistent with that expected of a 10-mg dose of torcetrapib (0.13 mmol/L, 95% CI 0.10 to 0.15). In trials, 60 mg of torcetrapib elevated systolic and diastolic blood pressure by 4.47 mm Hg (95% CI 4.10 to 4.84 mm Hg) and 2.08 mm Hg (95% CI 1.84 to 2.31 mm Hg), respectively. However, the effect of CETP single-nucleotide polymorphisms on systolic blood pressure (0.16 mm Hg, 95% CI -0.28 to 0.60 mm Hg) and diastolic blood pressure (-0.04 mm Hg, 95% CI -0.36 to 0.28 mm Hg) was null and significantly different from that expected of 10 mg of torcetrapib. Discordance in the effects of CETP single-nucleotide polymorphisms and torcetrapib treatment on blood pressure despite the concordant effects on lipids indicates the hypertensive action of torcetrapib is unlikely to be due to CETP inhibition or shared by chemically dissimilar CETP inhibitors. Genetic studies could find a place in drug-development programs as a new source of randomized evidence for drug-target validation in humans.

ABSTRACTIntroduction: Cholesteryl ester transfer protein (CETP) inhibitors substantially increase the concentration of high-density lipoprotein cholesterol (HDL-C), which may have a possible beneficial effect for cardiovascular disease risk reduction.Areas covered: Current data regarding the effects of CETP inhibitors on cardiovascular disease risk and possible mechanisms for their effects and safety are presented in this review.Expert commentary: The first CETP inhibitor, torcetrapib, was discontinued because of increased off-target adverse effects (increased serum aldosterone and blood pressure levels). The development program of dalcetrapib and evacetrapib, which were not associated with increased blood pressure, was terminated due to futility (insufficient efficacy) concerning cardiovascular outcomes. Although the failure of torcetrapib has been attributed to specific off-target effects, there are some common characteristics between CETP inhibitors pointing to the possibility that certain adverse effects may be class-specific. The newer CETP inhibitors anacetrapib and TA-8995 have promising effects on lipid profile and metabolism (increase of HDL-C and reduction of both low-density lipoprotein cholesterol and lipoprotein (a) levels), but their cardiovascular effects and safety profile have not yet been confirmed in large outcome trials.

Hyperaldosteronism and hypertension were unexpected side effects observed in trials of torcetrapib, a cholesteryl ester-transfer protein (CETP) inhibitor that increases high-density lipoprotein. Given that CETP inhibitors are lipid soluble, accumulate in adipose tissue, and have binding sites for proteins involved in adipogenesis, and that adipocytes are a source of aldosterone, we questioned whether CETP inhibitors (torcetrapib, dalcetrapib, and anacetrapib) influence aldosterone production by adipocytes. Studies were performed using human adipocytes (SW872), which express CETP, and mouse adipocytes (3T3-L1), which lack the CETP gene. Torcetrapib, dalcetrapib, and anacetrapib increased expression of CYP11B2, CYP11B1, and steroidogenic acute regulatory protein, enzymes involved in mineralocorticoid and glucocorticoid generation. These effects were associated with increased reactive oxygen species formation. Torcetrapib, dalcetrapib, and anacetrapib upregulated signal transducer and activator of transcription 3 (STAT3) and peroxisome proliferation-activated receptor-γ, important in adipogenesis, but only torcetrapib stimulated production of chemerin, a proinflammatory adipokine. To determine mechanisms whereby CETP inhibitors mediate effects, cells were pretreated with inhibitors of Nox1/Nox4 [GKT137831; 2-(2-chlorophenyl)-4-[3-(dimethylamino)phenyl]-5-methyl-1H-pyrazolo[4,3-c]pyridine-3,6(2H,5H)-dione], Nox1 (ML171 [2-acetylphenothiazine]), mitochondria (rotenone), and STAT3 (S3I-201 [2-hydroxy-4-(((4-methylphenyl)sulfonyloxy)acetyl)amino)-benzoic acid]). In torcetrapib-stimulated cells, Nox inhibitors, rotenone, and S3I-201 downregulated CYP11B2 and steroidogenic acute regulatory protein and reduced aldosterone. Dalcetrapib and anacetrapib effects on aldosterone were variably blocked by GKT137831, ML171, rotenone, and S3I-201. In adipocytes, torcetrapib, dalcetrapib, and anacetrapib inhibit enzymatic pathways responsible for aldosterone production through Nox1/Nox4- and mitochondrial-generated reactive oxygen species and STAT3. CETP inhibitors also influence adipokine production. These processes may be CETP independent. Our findings identify novel adipocyte-related mechanisms whereby CETP inhibitors increase aldosterone production. Such phenomena may contribute to hyperaldosteronism observed in CETP inhibitor clinical trials.

To examine the recent advances in our knowledge of cholesteryl ester transfer protein (CETP) inhibitors, heart disease risk reduction, and human lipoprotein metabolism. CETP inhibitors block the transfer of cholesteryl ester from HDLs to triglyceride-rich lipoproteins (TRLs), thereby raising HDL cholesterol and lowering TRL cholesterol, and in some cases LDL cholesterol. Two CETP inhibitors, dalcetrapib and torcetrapib, have been tested in large clinical trials in statin-treated coronary heart disease patients and have shown no clinical benefit compared to placebo. Anacetrapib and evacetrapib, two potent CETP inhibitors, are now being tested in large clinical trials. Torcetrapib has been shown to decrease the fractional catabolic rate (FCR) of HDL apolipoproteins (apo) A-I and A-II, enhance the FCR of TRL apoB-100 and apoE, and decrease TRL apoB-48 production, but has no significant effects on fecal cholesterol excretion in humans. Anacetrapib also delays the FCR of HDL apoA-I. CETP inhibitors form a complex between themselves, CETP, and HDL particles, which may interfere with the many physiologic functions of HDL, including reverse cholesterol transport. Available data would suggest that CETP inhibitors will fail as lipid-altering medications to reduce coronary heart disease risk because of interference with normal human HDL metabolism.

The effects of cholesteryl ester transfer protein (CETP) inhibition on the serum lipoprotein profile in both normocholesterolemic and hypercholesterolemic hamsters has been determined following subcutaneous injection of 12.5 mg/kg of the CETP neutralizing monoclonal antibody, TP2. Inhibition of CETP activity was greater than 60% and resulted in a 30-40% increase in high density lipoprotein (HDL) in both normal and hypercholesterolemic animals. These HDL effects were observed 1 day post-injection, were maximal by 4 days, and returned to control values by 14 days. Inhibition of CETP activity resulted in a decrease in both low density lipoprotein (LDL) and very low density lipoprotein (VLDL) cholesterol concomitant with HDL increase, and in hypercholesterolemic animals resulted in increased total serum cholesterol. In addition to the quantitative differences in LDL and HDL, there were significant increases in the size of the HDL, a shift to smaller LDL particles, and changes in apolipoprotein (apo) composition as evaluated by FPLC and Western blot analysis. Large apoA-I-poor and apoE-containing HDL became prevalent in hypercholesterolemic hamsters after CETP inhibition. In addition, the size of the CETP-containing HDL particles increased with inhibition of transfer activity. While these effects were apparent in normocholesterolemic animals, the changes in apolipoprotein distribution and HDL subspecies as detected on native gels were more significant in the hypercholesterolemic animals. The changes in the HDL profile and apolipoprotein distribution after CETP inhibition in hamsters were similar to those reported in CETP-deficient Japanese subjects, suggesting the utility of the hypercholesterolemic hamster as an in vivo model for the understanding of the lipoprotein changes associated with CETP inhibition.

Properly designed and conducted randomized controlled clinical trials (RCTs) are the premier tool for both testing mechanistic hypotheses and critically ascertaining the risks and benefits of a therapy or strategy for clinical care. The sample size of a trial is mainly a function of the rates of its primary objectives and the presumed influence of the intervention. Trials focusing on a primary outcome variable that can be readily quantified in each subject, such as blood pressure or plasma cholesterol levels, require substantially fewer participants and shorter durations to determine whether their predefined measurement is altered compared with a morbidity and mortality trial. Trials designed to determine whether clinical prognosis is altered by an intervention depend on the proportion of patients experiencing the predefined adverse clinical event(s) and often require 100s-fold–greater patient-time exposures to test their primary hypothesis and provide even modest information about safety. These resource-intense morbidity and mortality trials are generally only performed when information from observational studies as well as smaller mechanistic and surrogate- outcomes RCTs are so highly supportive of a favorable outcome that they justify the effort. Despite this understandable stacking of the cards with the best available information, many of the morbidity and mortality trials conducted to test for a potential favorable impact of an intervention conclude by not supporting the prestudy hypothesis-generating data.1 The lessons in humility offered by these neutral or negative outcomes trials underscore the importance of obtaining crucial risk–benefit data before widespread adoption of even an apparently favorable therapy.2 Articles pp 2506 and 2515 For rational therapeutic decision making, we would ideally like to have both a framework of reliable mechanistic information and robust clinical outcomes and safety data. Sometimes major clinical outcomes trials are designed with a complement of embedded ancillary trials to generate a more complete picture …

Cholesteryl ester transfer protein (CETP) inhibitors are gaining substantial research interest for raising high density lipoprotein cholesterol levels. The aim of the research was to estimate the efficacy and safety of cholesteryl ester transfer protein inhibitors as novel lipid modifying drugs. Systematic searches of English literature for randomized controlled trials (RCT) were collected from MEDLINE, EBASE, CENTRAL and references listed in eligible studies. Two independent authors assessed the search results and only included the double-blind RCTs by using cholesteryl ester transfer protein inhibitors as exclusively or co-administrated with statin therapy irrespective of gender in enrolled adult subjects. Two independent authors extracted the data by using predefined data fields. Of 503 studies identified, 14 studies met the inclusion criteria, and 12 studies were included into the final meta-analysis. Our meta-analysis revealed that CETP inhibitors increased the HDL-c levels (n = 2826, p<0.00001, mean difference (MD) = 20.47, 95% CI [19.80 to 21.15]) and total cholesterol (n = 3423, p = 0.0002, MD = 3.57, 95%CI [1.69 to 5.44] to some extent combined with a reduction in triglyceride (n = 3739, p<0.00001, MD = −10.47, 95% CI [−11.91 to −9.03]) and LDL-c (n = 3159, p<0.00001, MD = −17.12, 95% CI [−18.87 to −15.36]) irrespective of mono-therapy or co-administration with statins. Subgroup analysis suggested that the lipid modifying effects varied according to the four currently available CETP inhibitors. CETP inhibitor therapy did not increase the adverse events when compared with control. However, we observed a slight increase in blood pressure (SBP, n = 2384, p<0.00001, MD = 2.73, 95% CI [2.14 to 3.31], DBP, n = 2384, p<0.00001, MD = 1.16, 95% CI [0.73 to 1.60]) after CETP inhibitor treatment, which were mainly ascribed to the torcetrapib treatment subgroup. CETP inhibitors therapy is associated with significant increase in HDL-c and decrease in triglyceride and LDL-c with satisfactory safety and tolerability in patients with dyslipidemia. However, the side-effect on blood pressure deserves more consideration in future studies.

Background: Cholesteryl ester transfer protein (CETP) inhibitors increase serum high-density lipoprotein cholesterol (HDL-c) concentration; however, their impact on cardiovascular outcomes is not clear. This systematic review examines the effect of CETP inhibitors on serum lipid profiles, cardiovascular events, and all-cause mortality. Methods: We searched MEDLINE, Embase, and the Cochrane Library of Clinical Trials for placebo-controlled randomized controlled trials (RCTs) that examined the effect of a CETP inhibitor (dalcetrapib, anacetrapib, evacetrapib, or TA-8995) on all-cause mortality, major adverse cardiovascular events (MACE), or the components of MACE at ≥6 months. Data were pooled using random-effects models. Results: A total of 11 RCTs (n = 62,431) were included in our systematic review; 4 examined dalcetrapib (n = 16,612), 6 anacetrapib (n = 33,682), and 1 evacetrapib (n = 12,092). Compared to dalcetrapib, ana­cetrapib and evacetrapib were more efficacious at raising HDL-c levels (∼100–130 vs. ∼30%). Anacetrapib and evacetrapib also decreased low-density lipoprotein cholesterol (LDL-c) by approximately 30% while dalcetrapib did not affect the LDL-c level. Overall, CETP inhibitors were not associated with the incidence of MACE (pooled relative risk [RR]: 0.97; 95% confidence interval [CI]: 0.91–1.04). CETP inhibitors may decrease the risks of nonfatal myocardial infarction (MI) (RR: 0.93; 95% CI: 0.87–1.00) and cardiovascular death (RR: 0.92; 95% CI: 0.83–1.01), though these trends did not reach statistical significance. Conclusions: CETP inhibitors are not associated with an increased risk of MACE or all-cause mortality. There is a trend towards small reductions in nonfatal MI and cardiovascular death, though the clinical im­portance of such reductions is likely modest.

2D and 3D QSAR models for identifying diphenylpyridylethanamine based inhibitors against cholesteryl ester transfer protein.

Systematic identification of protein-drug interaction networks is crucial to correlate complex modes of drug action to clinical indications. We introduce a novel computational strategy to identify protein-ligand binding profiles on a genome-wide scale and apply it to elucidating the molecular mechanisms associated with the adverse drug effects of Cholesteryl Ester Transfer Protein (CETP) inhibitors. CETP inhibitors are a new class of preventive therapies for the treatment of cardiovascular disease. However, clinical studies indicated that one CETP inhibitor, Torcetrapib, has deadly off-target effects as a result of hypertension, and hence it has been withdrawn from phase III clinical trials. We have identified a panel of off-targets for Torcetrapib and other CETP inhibitors from the human structural genome and map those targets to biological pathways via the literature. The predicted protein-ligand network is consistent with experimental results from multiple sources and reveals that the side-effect of CETP inhibitors is modulated through the combinatorial control of multiple interconnected pathways. Given that combinatorial control is a common phenomenon observed in many biological processes, our findings suggest that adverse drug effects might be minimized by fine-tuning multiple off-target interactions using single or multiple therapies. This work extends the scope of chemogenomics approaches and exemplifies the role that systems biology has in the future of drug discovery.

Statins effectively lower plasma low-density lipoprotein cholesterol (LDL-C) levels and reduce the risk of vascular events. However, this benefit might be improved by dealing with other vascular risk factors such as high-density lipoprotein cholesterol (HDL-C). It follows that there has been an interest in drugs that raise plasma HDL-C levels. Among these drugs are the cholesteryl ester transfer protein (CETP) inhibitors. The first CETP inhibitor to be evaluated in an event-based trial was torcetrapib. This drug can considerably elevate serum HDL-C levels (e.g., by 72%). However, a recently published trial (ILLUMINATE) showed that torcetrapib used in combination with atorvastatin was associated with significantly more vascular events and deaths than atorvastatin alone. This finding resulted in the discontinuation of the torcetrapib development programme. The cause(s) of the adverse outcome remain speculative. It has been suggested that a significant rise in systolic blood pressure and possibly the quality of the HDL produced may be relevant. Despite this disappointing outcome it seems to be too early to close the book on CETP inhibitors because two other members of this class are being evaluated. These drugs (JTT-705 and anacetrapib) may be devoid of the adverse effect on systolic blood pressure. Eventually only appropriately designed, event-based trials, will settle the issue of whether CETP inhibitors are clinically useful.

Cholesteryl ester transfer protein (CETP) inhibitors based on cyclic urea, bicyclic urea and bicyclic sulfamide cores