The pharmacology and off-target effects of some cholesterol ester transfer protein inhibitors

Role of CETP, PCSK-9, and CYP7-alpha in cholesterol metabolism: Potential targets for natural products in managing hypercholesterolemia

Cardiovascular diseases (CVDs) are a leading cause of mortality worldwide, primarily affecting the heart and blood vessels, with atherosclerosis being a major contributing factor to their onset. Epidemiological and clinical studies have linked high levels of low-density lipoprotein (LDL) emanating from distorted cholesterol homeostasis as its major predisposing factor. Cholesterol homeostasis, which involves maintaining the balance in body cholesterol level, is mediated by several proteins or receptors, transcription factors, and even genes, regulating cholesterol influx (through dietary intake or de novo synthesis) and efflux (by their conversion to bile acids). Previous knowledge about CVDs management has evolved around modulating these receptors' activities through synthetic small molecules/antibodies, with limited interest in natural products. The central roles of the cholesteryl ester transfer protein (CETP), proprotein convertase subtilisin/kexin type 9 (PCSK9), and cytochrome P450 family 7 subfamily A member 1 (CYP7A1), among other proteins or receptors, have fostered growing scientific interests in understanding more on their regulatory activities and potential as drug targets. We present up-to-date knowledge on the contributions of CETP, PCSK9, and CYP7A1 toward CVDs, highlighting the clinical successes and failures of small molecules/antibodies to modulate their activities. In recommendation for a new direction to improve cardiovascular health, we have presented recent findings on natural products (including functional food, plant extracts, phytochemicals, bioactive peptides, and therapeutic carbohydrates) that also modulate the activities of CETP, PCSK-9, and CYP7A1, and emphasized the need for more research efforts redirected toward unraveling more on natural products potentials even at clinical trial level for CVD management.

CETP Inhibitors: Should We Continue to Pursue This Pathway?

PURPOSE OF REVIEW

For more than 20 years there has been considerable interest in the development of pharmacological inhibitors of cholesteryl ester transfer protein (CETP) by virtue of their ability to raise levels of high-density lipoprotein cholesterol. This review endeavors to integrate existing data from prior clinical trials with emerging data to understand whether there is a pathway forward to develop CETP inhibitors to prevent cardiovascular disease.

RECENT FINDINGS

Large clinical trials have proved disappointing with successive reports of a failure to reduce cardiovascular events. The one clinical development program that did demonstrate a reduction in cardiovascular risk found adipose tissue accumulation and did not proceed for regulatory approval. More recent observations suggest that less CETP activity may prevent cardiovascular events, but due to lipid lowering rather than raising high-density lipoprotein cholesterol. In addition, treatment with CETP inhibitors appears to have a beneficial impact on glycemic control in the setting of diabetes. Advances in the field of CETP inhibition suggest a potentially protective effect on the risk of both cardiovascular disease and diabetes. This has implications for how to best design future clinical development programs and leaves the door open to potentially bring CETP inhibitors to the preventive cardiology clinic.

Can we revive CETP-inhibitors for the prevention of cardiovascular disease?

PURPOSE OF REVIEW

To review recent developments in the field of cholesteryl ester transfer protein (CETP) inhibition from clinical trials and genomic analyses which have the potential to impact future clinical programs.

RECENT FINDINGS

CETP plays an important role in remodelling of lipoproteins. A large body of evidence suggests that the presence of low CETP activity should have favourable effects on lipid profiles and cardiovascular risk. However, a number of clinical development programs of pharmacological CETP inhibitors have been disappointing with reports of toxicity and clinical futility. These findings have led many to consider abandoning CETP inhibition as a potential strategy for cardiovascular prevention. However, recent observations from genomic analyses and post hoc observations of prior clinical trials have given greater insights into the potential relationship between CETP inhibition and cardiovascular risk. This has highlighted the importance of lowering levels of atherogenic lipoproteins.

SUMMARY

These findings provide a pathway for ongoing clinical development of CETP inhibitors, where the potential to play an important role in the prevention of cardiovascular disease may still be possible. The lessons learned and pathway forward for new CETP inhibitors will be reviewed.

An update on emerging drugs for the treatment of hypercholesterolemia

INTRODUCTION

Elevated levels of low-density lipoprotein (LDL) cholesterol have been unequivocally demonstrated to play a causal role in atherosclerotic cardiovascular disease. The last thirty years have witnessed a generation of clinical trials that have demonstrated a reduction in cardiovascular risk with the use of increasing intensive lipid lowering regimens involving statin therapy in combination with other agents. However, many patients fail to achieve treatment mandated LDL cholesterol goals. This highlights the need to develop additional approaches to lower LDL cholesterol levels.

AREAS COVERED

(i) Contemporary data highlighting the atherogenicity of LDL cholesterol and cardiovascular benefits of current lipid lowering therapies. (ii) Importance of statin intolerance and inability to achieve LDL cholesterol goals in driving ongoing cardiovascular risk. (iii) Emergence of new therapeutic agents designed to achieve more effective lowering of LDL cholesterol.

EXPERT OPINION

Effective lowering of LDL cholesterol plays a critical role in approaches to the prevention of cardiovascular disease. A greater number of patients will require combinations of agents to achieve optimal lipid control. Accordingly, new agents will be required to provide sufficient choice for patients at high cardiovascular risk.

The role of intracoronary imaging in translational research

Atherosclerotic cardiovascular disease is a key public health concern worldwide and leading cause of morbidity, mortality and health economic costs. Understanding atherosclerotic plaque microstructure in relation to molecular mechanisms that underpin its initiation and progression is needed to provide the best chance of combating this disease. Evolving vessel wall-based, endovascular coronary imaging modalities, including intravascular ultrasound (IVUS), optical coherence tomography (OCT) and near-infrared spectroscopy (NIRS), used in isolation or as hybrid modalities, have been advanced to allow comprehensive visualization of the pathological substrate of coronary atherosclerosis and accurately measure temporal changes in both the vessel wall and plaque characteristics. This has helped further our appreciation of the natural history of coronary artery disease (CAD) and the risk for major adverse cardiovascular events (MACE), evaluate the responsiveness to conventional and experimental therapeutic interventions, and assist in guiding percutaneous coronary intervention (PCI). Here we review the use of different imaging modalities for these purposes and the lessons they have provided thus far.

An update on trials of novel lipid-lowering drugs

PURPOSE OF REVIEW

A number of novel trials have assessed the efficacy of new lipid-lowering therapies in cardiovascular disease (CVD).

RECENT FINDINGS

Proprotein convertase subtilisin kexin-9 inhibitors reduce low-density lipoprotein cholesterol (LDL-C) by 50-55%. A CVD outcome trial in patients with acute coronary syndromes with evolocumab achieved a LDL-C of 0.8 mmol/l (31 mg/dl) and a 20% relative risk reduction in CVD events in 2.2 years. Cholesterol ester transfer protein inhibitors raise high-density lipoprotein cholesterol and can lower LDL-C. Anacetrapib reduced coronary artery disease events by 7%, but not wider composite CVD outcomes, in a population with chronic CVD with pretreatment LDL-C of 1.6 mmol/l (62 mg/dl). The conflicting outcomes of cholesterol ester transfer protein inhibitor trials means these compounds are not being developed further. Trials using lipid drugs targeting inflammation have previously been generally unsuccessful, but recent data on the interleukin-1B receptor antagonist canakinumab has proven the concept of intervention on inflammation in atherosclerosis by showing a reduction in acute coronary interventions, but at the predictable cost of increased infections.

SUMMARY

Despite the success of proprotein convertase subtilisin kexin-9 inhibition, the ability to achieve low LDL-C with off-patent medications and the costs of novel therapies will limit their use even in high-risk patients and confine them to the highest-risk sub-groups of patients.

Effect of Food on the Pharmacokinetics of 2 Formulations of DRL-17822, a Novel Selective Cholesteryl Ester Transfer Protein (CETP) Inhibitor, in Healthy Males

DRL-17822 is a novel selective cholesteryl ester transfer protein inhibitor that showed an increased exposure, including an increase of >20-fold of maximum concentration and area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration, following a high-fat breakfast using a nanocrystal formulation. To reduce this effect of food, we generated an amorphous solid dispersion formulation. In this study, we compared the food effect of both formulations of DRL-17822 in a 2-part randomized, open-label, 4-way crossover study involving healthy adult males 18-45 years of age. In both parts of the study, 12 subjects received both formulations of DRL-17822 in both the fasted and fed states; a low-fat breakfast was provided in the first part and a high-fat breakfast in the second part. Compared to the nanocrystal formulation, the amorphous solid dispersion formulation substantially increased DRL-17822 exposure in the fasted state, including increased maximum concentration, area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration, and area under plasma concentration-time curve from time zero to infinity. Following a high-fat breakfast, DRL-17822 exposure was increased to a lesser extent in the amorphous solid dispersion formulation compared to the nanocrystal formulation (P < .001). Moreover, compared to the nanocrystal formulation the amorphous solid dispersion formulation caused a more pronounced increase in high-density lipoprotein in the fasted state. Consuming breakfast increased the effect of DRL-17822 on high-density lipoprotein. Taken together, our results indicate that by improving its formulation, DRL-17822 has a favorable exposure profile and therefore a more predictable food effect profile.

CETP-Inhibition and HDL-Cholesterol: A Story of CV Risk or CV Benefit, or Both

Inhibitors of cholesteryl ester transfer protein (CETP) were developed due to their ability to raise HDL-C levels. Preclinical studies demonstrated favorable effects on atherosclerotic plaque with CETP inhibitory approaches in animal models. While these agents raise HDL-C and lower LDL-C, most have not proven to reduce cardiovascular event rates in large outcome trials. The state of opinion after all of these clinical trials is reviewed.

Anacetrapib as a potential cardioprotective strategy

Cholesteryl ester transfer protein (CETP) facilitates movement of esterified cholesterol between high-density lipoproteins (HDLs) and apolipoprotein B-containing lipoproteins. By virtue of their ability to raise HDL cholesterol and lower low-density lipoprotein cholesterol, pharmacological inhibitors of CETP have received considerable attention as potential new agents in cardiovascular prevention. While early studies of CETP inhibitors have demonstrated a lack of clinical efficacy and potential toxicity, development of the potent CETP inhibitor, anacetrapib, has moved forward, with emerging evidence suggesting a role in reducing cardiovascular events. The experience with anacetrapib and its potential for use in clinical practice are reviewed here.

Clinical trials with cholesteryl ester transfer protein inhibitors

PURPOSE OF REVIEW

Inhibition of cholesteryl ester transfer protein (CETP) has received considerable interest by virtue of its favorable effects on atherogenic and protective lipid parameters. The impact of CETP inhibitors in large clinical outcome trials will be reviewed.

RECENT FINDINGS

Population and genetic studies demonstrate that low CETP activity associates with lower rates of cardiovascular events. Inhibiting CETP activity in animal models has a favorable impact on experimental atherosclerosis. Although the first CETP inhibitor to advance to an outcome trial proved to have adverse clinical effects and the next agent, a more modest inhibitor, was clinically futile, there continues to be immense interest in the potential to develop nontoxic, potent CETP inhibitors to reduce cardiovascular risk.

SUMMARY

The current status of CETP inhibitors in the context of large outcomes trials will be reviewed.

Therapeutic modulation of the natural history of coronary atherosclerosis: lessons learned from serial imaging studies

Despite advances in risk prediction, preventive and therapeutic strategies, atherosclerotic cardiovascular disease remains a major public health challenge worldwide, carrying considerable morbidity, mortality and health economic burden. There continues to be a need to better understand the natural history of this disease to guide the development of more effective treatment, integral to which is the rapidly evolving field of coronary artery imaging. Various imaging modalities have been refined to enable detailed visualization of the pathological substrate of atherosclerosis, providing accurate and reproducible measures of coronary plaque burden and composition, including the presence of high-risk characteristics. The serial application of such techniques, including coronary computed tomography angiography (CTA), intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have uncovered important insights into the progression of coronary plaque over time in patients with stable and unstable coronary artery disease (CAD), and its responsiveness to therapeutic interventions. Here we review the use of different imaging modalities for the surveillance of coronary atherosclerosis and the lessons they have provided about the modulation of CAD by both traditional and experimental therapies.

Assessment of the clinical effects of cholesteryl ester transfer protein inhibition with evacetrapib in patients at high-risk for vascular outcomes: Rationale and design of the ACCELERATE trial

BACKGROUND

Potent pharmacologic inhibition of cholesteryl ester transferase protein by the investigational agent evacetrapib increases high-density lipoprotein cholesterol by 54% to 129%, reduces low-density lipoprotein cholesterol by 14% to 36%, and enhances cellular cholesterol efflux capacity. The ACCELERATE trial examines whether the addition of evacetrapib to standard medical therapy reduces the risk of cardiovascular (CV) morbidity and mortality in patients with high-risk vascular disease.

STUDY DESIGN

ACCELERATE is a phase 3, multicenter, randomized, double-blind, placebo-controlled trial. Patients qualified for enrollment if they have experienced an acute coronary syndrome within the prior 30 to 365 days, cerebrovascular accident, or transient ischemic attack; if they have peripheral vascular disease; or they have diabetes with coronary artery disease. A total of 12,092 patients were randomized to evacetrapib 130 mg or placebo daily in addition to standard medical therapy. The primary efficacy end point is time to first event of CV death, myocardial infarction, stroke, hospitalization for unstable angina, or coronary revascularization. Treatment will continue until 1,670 patients reached the primary end point; at least 700 patients reach the key secondary efficacy end point of CV death, myocardial infarction, and stroke, and the last patient randomized has been followed up for at least 1.5 years.

CONCLUSIONS

ACCELERATE will establish whether the cholesteryl ester transfer protein inhibition by evacetrapib improves CV outcomes in patients with high-risk vascular disease.

Novel insights on the treatment of hypercholesterolemia

The diagnosis of dyslipidemia is increasing both in adulthood and in childhood because of not only the steadily increasing prevalence of obesity but also a rise of medical attention in detecting unfavorable genetic conditions in patients of all ages. Attempts in lifestyle changes are frequently failing and thus the pharmacological treatment of dyslipidemia is spreading in medical practice to reduce cardiovascular risk. In childhood, statins are authorized by 8 years of age. Nevertheless, data on their long-term safety and efficacy are still lacking, especially in ones with high cardiovascular risk and/or primary dyslipidemia such as homozygous familial hypercholesterolemia, considerable as a mainly exclusively pediatric disease. Thus, new pharmacological approaches are needed and have to be evaluated in all categories of patients. In this context, the update and the critical revision of new medications have become a new duty for scientists and clinicians.

Dyslipidaemia: what's around the corner?

Hyperlipidaemia is a major risk factor for the development of atherosclerosis and cardiovascular disease. Statins are the mainstay of therapy and new guidelines focus on the use of these agents without specific targets for low-density lipoprotein (LDL)-cholesterol or non high-density lipoprotein (HDL)-cholesterol. However, patients remain at risk of cardiovascular disease despite statin therapy so new drugs are required. This article reviews therapies in development to further lower LDL-cholesterol (Proprotein convertase subtilisin/kexin-9 (PCSK-9) inhibitors), raise HDL-holesterol (cholesterol ester transfer protein inhibitors (CETPIs)) and reduce triglycerides (novel peroxisome proliferator-activated receptor (PPAR)-agonists and omega-3 fatty acid preparations). Specialised therapies are in development for treatment of orphan disoders such as homozygous familial hypercholesterolaemia (lomitapide) or familial chylomicroaemia (alipogene tiparvovec). These novel lipid-lowering agents are likely to find uses in treating patients at the highest cardiovascular risk.

Interrogating causal pathways linking genetic variants, small molecule metabolites, and circulating lipids

BACKGROUND

Emerging technologies based on mass spectrometry or nuclear magnetic resonance enable the monitoring of hundreds of small metabolites from tissues or body fluids. Profiling of metabolites can help elucidate causal pathways linking established genetic variants to known disease risk factors such as blood lipid traits.

METHODS

We applied statistical methodology to dissect causal relationships between single nucleotide polymorphisms, metabolite concentrations, and serum lipid traits, focusing on 95 genetic loci reproducibly associated with the four main serum lipids (total-, low-density lipoprotein-, and high-density lipoprotein- cholesterol and triglycerides). The dataset used included 2,973 individuals from two independent population-based cohorts with data for 151 small molecule metabolites and four main serum lipids. Three statistical approaches, namely conditional analysis, Mendelian randomization, and structural equation modeling, were compared to investigate causal relationship at sets of a single nucleotide polymorphism, a metabolite, and a lipid trait associated with one another.

RESULTS

A subset of three lipid-associated loci (FADS1, GCKR, and LPA) have a statistically significant association with at least one main lipid and one metabolite concentration in our data, defining a total of 38 cross-associated sets of a single nucleotide polymorphism, a metabolite and a lipid trait. Structural equation modeling provided sufficient discrimination to indicate that the association of a single nucleotide polymorphism with a lipid trait was mediated through a metabolite at 15 of the 38 sets, and involving variants at the FADS1 and GCKR loci.

CONCLUSIONS

These data provide a framework for evaluating the causal role of components of the metabolome (or other intermediate factors) in mediating the association between established genetic variants and diseases or traits.

Future of cholesteryl ester transfer protein (CETP) inhibitors: a pharmacological perspective

In almost 30 years since the introduction of HMG-CoA reductase inhibitors (statins), no other class of lipid modulators has entered the market. Elevation of high-density lipoprotein-cholesterol (HDL-C) via inhibiting cholesteryl ester transfer protein (CETP) is an attractive strategy for reducing the risk of cardiovascular events in high-risk patients. Transfer of triglyceride and cholesteryl ester (CE) between lipoproteins is mediated by CETP; thus inhibition of this pathway can increase the concentration of HDL-C. Torcetrapib was the first CETP inhibitor evaluated in phase III clinical trials. Because of off-target effects, torcetrapib raised blood pressure and increased the concentration of serum aldosterone, leading to higher cardiovascular events and mortality. Torcetrapib showed positive effects on cardiovascular risk especially in patients with a greater increase in HDL-C and apolipoprotein A-1 (apoA-1) levels. The phase III clinical trial of dalcetrapib, the second CETP inhibitor that has entered clinical development, was terminated because of ineffectiveness. Dalcetrapib is a CETP modulator that elevated HDL-C levels but did not reduce the concentration of low-density lipoprotein cholesterol (LDL-C). Both heterotypic and homotypic CE transfer between lipoproteins are mediated by some CETP inhibitors, including torcetrapib, anacetrapib, and evacetrapib, while dalcetrapib only affects the heterotypic CE transfer. Dalcetrapib has a chemical structure that is distinct from other CETP inhibitors, with a smaller molecular weight and a lack of trifluoride moieties. Moreover, dalcetrapib is a pro-drug that must be hydrolyzed to a pharmacologically active thiol form. Two other CETP inhibitors, anacetrapib and evacetrapib, are currently undergoing evaluation in phase III clinical trials. Both molecules have shown beneficial effects by increasing HDL-C and decreasing LDL-C concentration. The success of anacetrapib and evacetrapib remains to be confirmed upon the completion of phase III clinical trials in 2017 and 2015, respectively. Generally, the concentration of HDL-C has been considered a biomarker for the activity of CETP inhibitors. However, it is not clear whether a fundamental relationship exists between HDL-C levels and the risk of coronary artery diseases. The most crucial role for HDL is cholesterol efflux capacity in which HDL can reverse transport cholesterol from foam cells in atherosclerotic plaques. In view of the heterogeneity in HDL particle size, charge, and composition, the mere concentration of HDL-C may not be a good surrogate marker for HDL functionality. Recent clinical studies have reported that increased HDL functionality inversely correlates with the development of atherosclerotic plaque. Future development of CETP inhibitors may therefore benefit from the use of biomarkers of HDL functionality.

Cholesteryl ester transfer protein inhibitors in the treatment of dyslipidemia: a systematic review and meta-analysis

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.

ABCA1 mutation carriers with low high-density lipoprotein cholesterol are characterized by a larger atherosclerotic burden

AIMS

Low HDL-C is a potent risk factor for cardiovascular disease (CVD). Yet, mutations in ABCA1, a major determinant of circulating HDL-C levels, were previously not associated with CVD risk in cohort studies. To study the consequences of low plasma levels of high-density lipoprotein cholesterol (HDL-C) due to ATP-binding cassette transporter A1 (ABCA1) dysfunction for atherosclerotic vascular disease in the carotid arteries.

METHODS AND RESULTS

We performed 3.0 Tesla magnetic resonance imaging (MRI) measurements of the carotid arteries in 36 carriers of high impact functional ABCA1 mutations and 36 normolipidemic controls. Carriers presented with 42% lower HDL-C levels (P < 0.001), a larger mean wall area (18.6 ± 6.0 vs. 15.8 ± 4.3 mm(2); P = 0.02), a larger mean wall thickness (0.82 ± 0.21 vs. 0.70 ± 0.14 mm; P = 0.005), and a higher normalized wall index (0.37 ± 0.06 vs. 0.33 ± 0.04; P = 0.005) compared with controls, retaining significance after adjustment for smoking, alcohol consumption, systolic blood pressure, diabetes, body mass index, history of CVD, LDL-C, and statin use (P = 0.002).

CONCLUSION

Carriers of loss of function ABCA1 mutations display a larger atherosclerotic burden compared with age and sex-matched controls, implying a higher risk for CVD. Further studies are needed to elucidate the full function of ABCA1 in the protection against atherosclerosis. These data support the development of strategies to up-regulate ABCA1 in patients with established CVD.

ApoA-I induction as a potential cardioprotective strategy: rationale for the SUSTAIN and ASSURE studies

BACKGROUND

Considerable interest has focused on the development of therapies that target the functionality of high-density lipoproteins (HDL). Upregulation of endogenous synthesis of the major protein on HDL particles, apolipoprotein A-I (apoA-I), represents a novel approach to generation of new HDL particles. The Study of Quantitative Serial Trends in Lipids with Apolipoprotein A-I Stimulation (SUSTAIN, NCT01423188) study aims to evaluate the lipid efficacy, safety and tolerability of an apoA-I inducer (RVX-208). The ApoA-I Synthesis Stimulation and Intravascular Ultrasound for Coronary Atheroma Regression Evaluation (ASSURE, NCT01067820) study aims to evaluate the effect of RVX-208 on plaque burden.

METHODS

In SUSTAIN, 172 patients with low levels of HDL-C will be randomized to receive RVX-208 100 mg bid or placebo for 24 weeks. The primary efficacy parameter will be the percentage change in HDL-C levels. In ASSURE, 310 patients with angiographic coronary artery disease and low HDL-C levels will be randomized to receive RVX-208 100 mg bid or placebo for 26 weeks. The primary efficacy parameter will be the nominal change in percent atheroma volume (PAV), determined by analysis of intravascular ultrasound (IVUS) images of matched coronary artery segments acquired at baseline and at 26-week follow-up. The effect of RVX-208 on other lipid and inflammatory markers, safety and tolerability will also be assessed in both studies.

CONCLUSION

ApoA-I induction represents a potential novel strategy to reduce cardiovascular risk, by generating nascent HDL particles. These studies will provide early evaluation of the effects of RVX-208 on lipids and atherosclerotic plaque.

HDL-C: does it matter? An update on novel HDL-directed pharmaco-therapeutic strategies

It has long been recognized that elevated levels of low-density lipoprotein cholesterol (LDL-C) increase the risk of cardiovascular disease (CHD) and that pharmacologic therapy to decrease LDL-C significantly reduces cardiovascular events. Despite the effectiveness of statins for CHD risk reduction, even optimal LDL-lowering therapy alone fails to avert 60% to 70% of CHD cases. A low plasma concentration of high-density lipoprotein cholesterol (HDL-C) is also associated with increased risk of CHD. However, the convincing epidemiologic data linking HDL cholesterol (HDL-C) to CHD risk in an inverse correlation has not yet translated into clinical trial evidence supporting linearity between HDL-C increases and CHD risk reduction. It is becoming clear that a functional HDL is a more desirable target than simply increasing HDL-C levels. Discoveries in the past decade have shed light on the complex metabolic and antiatherosclerotic pathways of HDL. These insights, in turn, have fueled the development of new HDL-targeted drugs, which can be classified according to four different therapeutic approaches: directly augmenting the concentration of apolipoprotein A-I (apo A-I), the major protein constituent of HDL; indirectly augmenting the concentration of apo A-I and HDL cholesterol; mimicking the functionality of apo A-I and enhancing reverse cholesterol transport. This review discusses the latest in novel HDL directed therapeutic strategies.

Effect of dalcetrapib plus pravastatin on lipoprotein metabolism and high-density lipoprotein composition and function in dyslipidemic patients: results of a phase IIb dose-ranging study

BACKGROUND

Cholesteryl ester transfer protein (CETP) is involved in high-density lipoprotein (HDL) remodeling and transfer of lipids between HDL particles and other lipoproteins. Epidemiologic studies show that both elevated HDL-cholesterol (HDL-C) and reduced CETP activity attenuate cardiovascular risk, making inhibition or modulation of CETP a potential therapeutic target. This study analyzed the effect of dalcetrapib on lipoprotein profile, CETP activity, and cellular cholesterol efflux when co-administered with pravastatin in patients with low or average HDL-C.

METHODS

Patients were randomized in a double-blind fashion to receive placebo or dalcetrapib 300, 600, or 900 mg once daily for 12 weeks. All patients were concomitantly treated to their low-density lipoprotein cholesterol target with pravastatin. Lipoprotein profile was analyzed by nuclear magnetic resonance spectroscopy and polyacrylamide gradient gel electrophoresis. Composition of the HDL fraction was assessed after polyethylene glycol precipitation. Contribution of this fraction to cholesterol efflux was assessed using radiolabeled donor cells.

RESULTS

Co-administration of dalcetrapib with pravastatin increased HDL-C, apolipoproteins (apo) A-I and A-II, and CETP mass, and decreased CETP activity. A relative increase in large HDL and low-density lipoprotein subparticle fractions was observed. High-density lipoprotein composition showed increased association of esterified cholesterol, free cholesterol, phospholipids, apo A-I, and apo E. Adenosine 5'-triphosphate-binding cassette A1- and scavenger receptor type BI-mediated cholesterol efflux increased.

CONCLUSIONS

Dalcetrapib up to 600 mg, combined with pravastatin, increased HDL-C and altered lipoprotein profile, HDL composition, and HDL function, with little further change at a 900-mg dose. The impact on cardiovascular events in dyslipidemic patients is being evaluated.

Familial hypercholesterolemia: present and future management

Patients suffering from familial hypercholesterolemia (FH) are characterized by increased plasma levels of low-density lipoprotein cholesterol (LDL-C) levels and are at increased risk for premature cardiovascular disease (CVD). Current guidelines emphasize the need to aggressively lower LDL-C in FH patients, and statins are the cornerstone in the current regimen. However, additional therapies are eagerly awaited, especially for those patients not tolerating statin therapy or not reaching the goals for therapy. Our understanding of LDL metabolism has improved over the last years and an increasing number of potential novel targets for therapy have been recently identified. Apart from novel targets, we have also been confronted with novel modalities of treatment, such as mRNA antisense therapy. Some of these emerging therapies have proven to be effective in lowering plasma LDL-C levels and are as such expected to have beneficial effects on CVD. Hopefully, they will enrich our armamentarium against the severe dyslipidemia observed in FH patients in the not too distant future.

Apo a-I modulating therapies

The substantial residual risk of cardiovascular events despite the implementation of effective lowering of low-density lipoprotein cholesterol highlights the need to develop additional cardioprotective therapies. Evidence from population and animal studies suggests that high-density lipoproteins (HDLs), the protective lipid particles, may represent a target for therapeutic modification. As a result intensive efforts are in progress to develop new agents that promote HDL activity. Among these different approaches, a range of strategies that target apolipoprotein A-I, the major protein carried on HDL, are being evaluated.

Novel HDL-directed pharmacotherapeutic strategies

The burden of atherothrombotic cardiovascular disease remains high despite currently available optimum medical therapy. To address this substantial residual risk, the development of novel therapies that attempt to harness the atheroprotective functions of HDL is a major goal. These functions include the critical role of HDL in reverse cholesterol transport, and its anti-inflammatory, antithrombotic, and antioxidant activities. Discoveries in the past decade have shed light on the complex metabolic and antiatherosclerotic pathways of HDL. These insights have fueled the development of HDL-targeted drugs, which can be classified among four different therapeutic approaches: directly augmenting apolipoprotein A-I (apo A-I) levels, such as with apo A-I infusions and upregulators of endogenous apo A-I production; indirectly augmenting apo A-I and HDL-cholesterol levels, such as through inhibition of cholesteryl ester transfer protein or endothelial lipase, or through activation of the high-affinity niacin receptor GPR109A; mimicking the functionality of apo A-I with apo A-I mimetic peptides; and enhancing steps in the reverse cholesterol transport pathway, such as via activation of the liver X receptor or of lecithin-cholesterol acyltransferase.

Diversity through phosphine catalysis identifies octahydro-1,6-naphthyridin-4-ones as activators of endothelium-driven immunity

The endothelium plays a critical role in promoting inflammation in cardiovascular disease and other chronic inflammatory conditions, and many small-molecule screens have sought to identify agents that prevent endothelial cell activation. Conversely, an augmented immune response can be protective against microbial pathogens and in cancer immunotherapy. Yet, small-molecule screens to identify agents that induce endothelial cell activation have not been reported. In this regard, a bioassay was developed that identifies activated endothelium by its capacity to trigger macrophage inflammatory protein 1 beta from primary monocytes. Subsequently, a 642-compound library of 39 distinctive scaffolds generated by a diversity-oriented synthesis based on the nucleophilic phosphine catalysis was screened for small molecules that activated the endothelium. Among the active compounds identified, the major classes were synthesized through the sequence of phosphine-catalyzed annulation, Tebbe reaction, Diels-Alder reaction, and in some cases, hydrolysis. Ninety-six analogs of one particular class of compounds, octahydro-1,6-naphthyridin-4-ones, were efficiently prepared by a solid-phase split-and-pool technique and by solution phase analog synthesis. Structure-function analysis combined with transcriptional profiling of active and inactive octahydro-1,6-naphthyridin-4-one analogs identified inflammatory gene networks induced exclusively by the active compound. The identification of a family of chemical probes that augment innate immunity through endothelial cell activation provides a framework for understanding gene networks involved in endothelial inflammation as well as the development of novel endothelium-driven immunotherapeutic agents.

ETC-216 for coronary artery disease

INTRODUCTION

Increasing attention has focused on the role of high-density lipoprotein function as a target for cardiprotection. Apolipoprotein A-I(Milano) (AIM) involves a single amino-acid mutation of the major wild-type protein carried on high-density lipoprotein (HDL) particles. Early evidence of beneficial activities of AIM has stimulated support in its development as a potential therapy to reduce cardiovascular risk.

AREAS COVERED

The importance of HDL as a target and early data supporting the beneficial effects of AIM are reviewed. All clinical studies of AIM found in PubMed are reviewed.

EXPERT OPINION

ETC-216 represents a lipid-deplete form of HDL containing recombinant AIM. While early evidence suggests that administration of ETC-216 promotes rapid regression of coronary atherosclerosis, bringing this compound to clinical practice will require further trials that evaluate its impact on cardiovascular events.

Anacetrapib and dalcetrapib: two novel cholesteryl ester transfer protein inhibitors

OBJECTIVE

To evaluate the role of cholesteryl ester transfer protein (CETP) in the cholesterol transport system and review the pharmacology, pharmacokinetic properties, efficacy, and adverse effects of the CETP inhibitors, anacetrapib and dalcetrapib, for the treatment of dyslipidemia.

DATA SOURCES

A literature search was conducted in Ovid/MEDLINE (1950 to week 4 December 2010), PubMed/MEDLINE (up to December 2010), EMBASE (2000 to December 2010), and International Pharmaceutical Abstracts (1970 to December 2010) using the MeSH terms and key words anacetrapib, MK 0859, dalcetrapib, and JTT 705. The search was limited to publications in English.

STUDY SELECTION AND DATA EXTRACTION

Studies evaluating the pharmacology, pharmacokinetics, safety, and efficacy of anacetrapib and dalcetrapib for the treatment of dyslipidemia were included. Clinical reviews evaluating the characterization of CETP and its inhibition as a mechanism for reducing cardiovascular risk were also included.

DATA SYNTHESIS

Anacetrapib and dalcetrapib represent a novel treatment option for patients who have dyslipidemia and low levels of high-density lipoprotein cholesterol (HDL-C). Anacetrapib and dalcetrapib increase HDL-C by inhibiting CETP-mediated transfer of cholesteryl ester and triglyceride. Studies evaluating the safety and efficacy of anacetrapib and dalcetrapib concluded that both agents safely and effectively augment HDL-C. Their mechanism of action, potential for significant raising of HDL-C, once-daily dosing regimen, and favorable lipid-altering effects when added to hydroxymethylglutaryl-CoA reductase inhibitors are key elements. Anacetrapib and dalcetrapib are well tolerated, with mild gastrointestinal complaints reported more than with placebo. Although another CETP inhibitor, torcetrapib, was withdrawn from clinical development secondary to increased morbidity and mortality, neither anacetrapib nor dalcetrapib has demonstrated the adverse off-target effects portrayed with torcetrapib.

CONCLUSIONS

Inhibition of CETP by anacetrapib and dalcetrapib represents an encouraging development in the management of dyslipidemia, particularly in patients with low HDL-C levels. Results of future trials are much anticipated, as these will clarify the role of anacetrapib and dalcetrapib in reduction of cardiovascular disease.

The HDL hypothesis: does high-density lipoprotein protect from atherosclerosis?

There is unequivocal evidence of an inverse association between plasma high-density lipoprotein (HDL) cholesterol concentrations and the risk of cardiovascular disease, a finding that has led to the hypothesis that HDL protects from atherosclerosis. This review details the experimental evidence for this "HDL hypothesis". In vitro studies suggest that HDL has a wide range of anti-atherogenic properties but validation of these functions in humans is absent to date. A significant number of animal studies and clinical trials support an atheroprotective role for HDL; however, most of these findings were obtained in the context of marked changes in other plasma lipids. Finally, genetic studies in humans have not provided convincing evidence that HDL genes modulate cardiovascular risk. Thus, despite a wealth of information on this intriguing lipoprotein, future research remains essential to prove the HDL hypothesis correct.