Review Article
Antihyperlipidemic Therapies Targeting PCSK9 Michael Weinreich, MD,* and William H. Frishman, MD†
Abstract: Hyperlipidemia is a major cause of cardiovascular disease despite the availability of first-line cholesterol-lowering agents such as statins. A new therapeutic approach to lowering low-density lipoprotein-cholesterol (LDL-C) acts by blocking LDL-receptor degradation by serum proprotein convertase subtilisin kexin 9 (PCSK9). Human monoclonal antibodies that target PCSK9 and its interaction with the LDL receptor are now in clinical trials (REGN727/SAR23653, AMG145, and RN316). These agents are administered by either subcutaneous or intravenous routes, and have been shown to have major LDL-C and apolipoprotein B effects when combined with statins. A phase III clinical trial program evaluating clinical endpoints is now in progress. Other PCSK9-targeted approaches are in early stages of investigation, including natural inhibitors of PCSK9, RNA interference, and antisense inhibitors. Key Words: proprotein convertase subtilisin kexin 9 inhibition, monoclonal antibodies, low-density lipoprotein reduction (Cardiology in Review 2014;22: 140–146)
H
ypercholesterolemia is a leading contributor to cardiovascularrelated morbidity and mortality around the world.1 In the United States, approximately 14% of all adults have total cholesterol levels of 240 mg/dL or more.2 It is well established that hypercholesterolemia is associated with atherosclerotic vascular disease and adverse events including myocardial infarction, cerebrovascular accidents, and transient ischemic attacks.3–8 The National Cholesterol Education Program has established guidelines for the detection, evaluation, and treatment of hypercholesterolemia based on epidemiological studies, showing a clear association between total cholesterol serum concentration and risk of coronary artery disease.9 These guidelines, the Adult Treatment Panel III, take into account both a patient’s low-density lipoprotein (LDL) concentration and their cardiac risk factors.9 The first-line pharmacologic treatment for hypercholesterolemia is hydroxyl-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor (statin) therapy, based on the class’s efficacy. This class of drugs has been shown to reduce LDL-C levels by up to 63% from baseline.10 The American College of Cardiology Foundation and The American Heart Association recommend the use of statins in secondary prevention of hyperlipidemia to achieve LDL-C goal levels less than 100 mg/dL or less than 70 mg/dL in patients who are at very high risk.11 Second-line lipid-lowering agents include bile acid sequestrants, fibrates, niacin, and ezetimibe. However, these therapies do not adequately lower cholesterol to goal levels or yield clinical benefit in many patients.12–14
Although statin therapy has been hailed for its efficacy in approximately 20 million users, nearly 20% of individuals experience side effects that hinder the drug’s ability to achieve target LDL levels.15,16 These statin-induced side effects include myopathy, myalgia, hepatic dysfunction, renal dysfunction, diabetes mellitus, and psychiatric changes including irritability and aggression.17–23 Compounding the issue are reports of intronic single-nucleotide polymorphisms (SNPs) that are linked to resistance to statin therapy.24,25 As a result of these goal-limiting factors, there has been an ongoing search for nonstatin cholesterol-lowering agents. Especially for those individuals with familial hypercholesterolemia, alternative therapy could be life-saving and extending. Three major pharmaceutical teams, Sanofi US (Bridgewater, NJ)/Regeneron Inc. (Tarrytown, NY), Amgen Inc. (Thousand Oaks, CA), and Pfizer Inc. (New York, NY) have invested extensive research efforts into exploring the potential of blocking LDL-receptor (LDLR) degradation by serum proprotein convertase subtilisin kexin 9 (PCSK9)26 via the human monoclonal antibodies designated REGN727/SAR236553 (subcutaneous administration), AMG 145 (subcutaneous administration), and RN316 (intravenous administration), respectively. PCSK9 has a known function in the control of LDLR surface expression by hepatocytes. This newly discovered member of the subtilisin serine protease family binds to extracellular LDL receptors and subsequently marks them for internalization and intracellular degradation via a lysosomal-mediated pathway (Fig. 1).27 Thus, hepatocyte capacity for extraction of LDL-C from the circulation is decreased.28,29 REGN727/SAR236553, AMG 145, and RN316 act by targeting PCSK9 and blocking its interaction with the LDL receptor.30 This article will examine the current research surrounding anti-PCSK9 therapies, with a special focus on monoclonal antibody development, and their efficacy to lower LDL-C levels in patients with hypercholesterolemia.
BASIC SCIENCE/TRANSLATIONAL RESEARCH
From the *Department of Medicine, North Shore Long Island Jewish Health System/Hofstra University School of Medicine, Manhasset, NY; and †New York Medical College/Westchester Medical Center, Valhalla, NY. Disclosure: The authors declare no conflict of interest. Correspondence: William H. Frishman, MD, Department of Medicine, Munger 263, New York Medical College, Valhalla, NY 10595.E-mail: [email protected]. Copyright © 2014 Lippincott Williams & Wilkins ISSN: 1061-5377/14/2203-0140 DOI: 10.1097/CRD.0000000000000014
The discovery of PCSK9 as a potential antihyperlipidemia pharmacologic target is owed mostly to robust basic science and translational research efforts.31 Before the early 2000s, autosomal dominant hypercholesterolemia (ADH) was known to be associated with genetic mutations in 2 specific genes, LDLR and APOB, which coded for the LDL receptor and apolipoprotein B, respectively.32,33 In 2003, Abifadel et al34 published a report demonstrating a further association between ADH and a mutation mapped to the chromosomal locus 1p32, the site of the PCSK9 gene. A mutation in PCSK9 (which encodes proprotein convertase subtilisin/kexin type 9) was reported in 23 French families with ADH. Mutations in both LDLR and APOB had been previously excluded in these families.34 Although the cholesterol-related mechanism of PCSK9 was unknown, the putative role in cholesterol regulation was established. In a subsequent study, real-time polymerase chain reaction analysis showed that increased cholesterol consumption by mice was associated with down-regulation of PCSK9 mRNA.35 Conversely, expression of PCSK9 mRNA is up-regulated by -CoA reductase inhibitors. As would be expected, the presence of mevalonate, a product of HMG-CoA reductase on HMG-CoA, was found to down-regulate PCSK9 mRNA transcription.36,37 The involvement with the LDL receptor was implicated when Maxwell et al38 showed that overexpression of PCSK9 in
140 | www.cardiologyinreview.com
Cardiology in Review • Volume 22, Number 3, May/June 2014
Cardiology in Review • Volume 22, Number 3, May/June 2014
Antihyperlipidemic Therapies Targeting PCSK9
FIGURE 1. LDLR recycling pathway. Left, PCSK9 binding to extracellular LDLR leads to endocytosis and subsequent degradation via a lysosomal-mediated mechanism. Right, monoclonal antibody binding to PCSK9 inhibits interaction with LDLR, sparing its destruction. LDLR indicates low-density lipoprotein receptor; PCSK9, serum proprotein convertase subtilisin kexin 9. Reprinted with permission from Lambert et al.27 human hepatoma (HepG2) cells did not affect LDLR expression or synthesis/maturation of the receptor, but did greatly accelerate degradation of the LDL receptor. Finally, in 2006 Cohen et al39 reported that African American individuals with nonsense lossof-function mutations at the PCSK9 locus had an associated 28% reduction in mean LDL-C levels and an 88% reduction in the risk of coronary heart disease. Significant, but less impressive, reductions in both parameters were noted in the white subset.39 Further studies confirmed that loss-of-function mutations at the PCSK9 locus were associated with lower circulating LDL-C levels.40–42 Conversely, DNA sequencing in 51 Norwegian patients showed that gain-of-function missense mutations in the PCSK9 gene were associated with ADH.43
ANIMAL STUDIES With PCSK9’s role in regulating LDL receptor expression established, various inhibition methods were explored. In 2009, Chan et al44 engaged in a proof-of-concept study involving PCSK9 inhibition. An anti-PCSK9 antibody, mAb1, was designed to bind to an epitope adjacent to the LDL receptor site on PCSK9, sterically hindering interactions. In vitro studies demonstrated that mAb1 reduced LDL receptor destruction. When mAb1 treatment was combined with statin therapy, LDL receptor expression on HepG2 cells was greater than when either was used as a monotherapy. It was noted that wild-type mice subjected to mAb1 demonstrated a 2-fold increase in LDL receptor expression and a decrease in total serum cholesterol by 36%. This fall in cholesterol was not noted in LDLR knockout mice subjected to mAb1 therapy. A further study in cynomolgus monkeys found that a single injection of mAb1 was associated with an 80% drop of serum LDL-C only 10 days after administration.44 A subsequent study demonstrated that lower PCSK9 levels are associated not just with a reduction in circulating LDL-C, but also with decreased levels of aortic cholesteryl esters plaques.45 In a comparison of wild-type, PCSK9 knockout, and high–PCSK9-expression mice fed on a Westernized diet for 12 months, it was found that knockout mice had a 74% reduction in aortic plaques as compared with the wild-type mice. The high–PCSK9-expression mice had visible, more severe, and an increased number (230% increase) of aortic plaques as compared with wild-type mice.45 © 2014 Lippincott Williams & Wilkins
CLINICAL TRIALS REGN727/SAR236553 (Alircumab) REGN727/SAR236553, a human monoclonal antibody against PCSK9 has been studied in several recent clinical trials. Two phase I, randomized, single, ascending-dose studies of REGN727 administered intravenously (n = 40) or subcutaneously (n = 32) compared cholesterol-lowering efficacy versus placebo in patients with LDL-C levels of 100 mg/dL or more. Intravenously administered participants received doses of study drug up to 12 mg/kg and the subcutaneous arm received doses up to 250 mg. The results demonstrated a 65% reduction in LDL-C as compared with placebo, with the intravenous route showing greater efficacy. The duration of reduction was found to be dose-dependent.46 A third, early phase I, randomized, placebo-controlled, multiple-dose trial included adults with or without heterozygous familial hypercholesterolemia (FH) with LDL-C levels of 100 mg/dL or more while on atorvastatin (n = 51) or non-FH patients with LDL-C levels of 130 mg/dL or more treated with behavioral modification alone (n = 10).46 Participants were administered subcutaneous study drug at 50, 100, and 150 mg doses or placebo. At the conclusion of the treatment period, LDL-C was reduced from baseline by 39.2%, 53.7%, and 61.0%, respectively, as compared with placebo. One participant had a transient increase in creatine kinase to 10 times the upper limit of normal, but with no associated physical or clinical findings. The maximum LDL-C reduction was reached within just 2 weeks, which is notably quicker than with statin therapy.46 The percentage of reduction of LDL-C from baseline in the study drug–plus-statin group (61%) was comparable with that of the earlier-mentioned study drug–only group (65%). However, this phase I trial result does not constitute evidence for monotherapy of REGN727 due to the low sample size of the study population. In phase II trials, REGN727 was evaluated in a double-blind, parallel-group, placebo-controlled, randomized, multicenter, 12-week trial examining the efficacy of REGN727 to lower LDL-C levels as compared with placebo, in patients (N = 183) with LDL-C levels of 100 mg/dL or more and concurrently on variable-dose atorvastatin (10, 20, or 40 mg).47 The goal was to evaluate both dose-dependent and dose-frequency effects of the study drug. Patients were assigned to receive either 50, 100, or 150 mg every 2 weeks (Q2W) or 200 or www.cardiologyinreview.com | 141
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Cardiology in Review • Volume 22, Number 3, May/June 2014
300 mg every 4 weeks (Q4W) alternating with placebo Q2W. Twelve weeks poststudy initiation, the placebo group had a 5% reduction in LDL-C whereas the experimental group had a 40% to 72% reduction, showing dependency both on dosing schedule and level. There was also a decrease in apolipoprotein B and lipoprotein(a) levels. One participant experienced a serious adverse effect of leukocytoclastic vasculitis. Muscle-related incidents were not frequently reported and there was no increase shown in the results of liver function tests or muscle enzymes during the course of the study. The reduction in LDL-C by REGN727 was not affected by the dose of atorvastatin, suggesting an additive relationship between the two therapeutic agents and the study drug’s ability to independently reduce LDL-C levels.47 Leukocytoclastic vasculitis is an adverse effect that has also been noted with several other monoclonal antibody therapies.48,49 The syndrome is generally benign and treated by only discontinuing the inciting agent. Less frequently, patients may require nonsteroidal antiinflammatory, corticosteroid, or immunosuppressive therapy.50,51 Although the occurrence of this vasculitis associated with anti-PCSK9 therapy has remained an isolated event in the published literature, continued monitoring throughout phase III and postmarket studies will be revealing. The safety and efficacy of REGN727 in concurrent use with statin and ezetimibe therapy was evaluated in participants with heterozygous FH in a randomized, multicenter, placebo-controlled, phase II trial (N = 77).52 All participants had LDL-C level higher than 2.6 mM (100 mg/dL) and were on a stable diet with a statin ± ezetimibe. Patients received either subcutaneous 150, 200, or 300 mg of the study drug Q4W or 150-mg study drug Q2W, or placebo Q2W. After 12 weeks, a 67.9% reduction of LDL-C from baseline was reported in the 150-mg Q2W group. Apolipoprotein B levels were reduced by 50.19% from baseline, high-density lipoprotein (HDL)C increased by 12.34% from baseline, and total cholesterol fell by 43.44% from baseline. No study drug-related adverse events were report and there was no increase in liver function tests or creatine kinase >3 the upper limit of normal.52 Approximately 40% of the patients in this trial had known coronary artery disease, indicating a greater level of hypercholesterolemia severity as compared with the previously discussed heterozygous FH phase I trial. This phase II trial provides broader evidence among a larger and more diverse cohort of participants of the benefits provided to patients with FH in achieving goal LDL-C levels. A phase II, multicenter, double-blind, placebo-controlled trial (N = 92) evaluated the efficacy of REGN727 when used with high- or low-dose atorvastatin as compared with high dose alone.53 All participants had LDL-C level of at least 100 mg/dL, even after receiving a baseline treatment of 10-mg atorvastatin for 7 weeks. Participants were randomly assigned to 80-mg atorvastatin plus REGN727 Q2W, 10-mg atorvastatin plus REGN727 Q2W, or 80-mg atorvastatin plus placebo Q2W. The REGN727 dose was administered subcutaneously at 150 mg. After 8 weeks it was noted that the 80-mg statin-plus– study drug group was found to have a 73.2% reduction from baseline LDL-C, the 10-mg statin-plus–study drug group was found to have a 66.2% reduction, whereas the 80-mg statin-plus-placebo group had a 17.3% reduction. All the patients in the study-drug group achieved LDL-C levels less than 100 mg/dL, and 90% achieved levels less than 70 mg/dL. There was no significant difference in LDL-C reduction between the 80-mg and 10-mg statin-plus–study drug groups, suggesting an upper limit to the ability of statins to up-regulate the LDLR.53 Notably, 1 patient in the 80-mg statin-plus–study drug group had mildly increased AST before the study and subsequently had an increase to more than 3 times the upper limit of normal.53 A comprehensive phase III clinical program using REGN727 is now under way.54 The Odyssey Outcomes study is enrolling 18,000 patients aged 40 years or older with a recent acute coronary syndrome
and LDL levels of 70 mg/dL or more.55 Patients are randomized to receive a 1-mL injection of 75 mg of study drug or placebo Q2W, in addition to their regular lipid-lowering therapy. If patients do not reach goal LDL-C levels with initial dosing, the dose will be increased to 150 mg Q2W. Follow-up will continue for 64 months, examining the composite endpoint of coronary artery disease, death, nonfatal myocardial infarction, fatal or nonfatal ischemic stroke, or unstable angina requiring hospitalization. Other studies within the Odyssey trial program include evaluation of patients unable to tolerate statin therapy, the safety or efficacy of REGN727 as a monotherapy, and patients with failure to achieve adequate control with their current lipid modifiers.55
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AMG 145 AMG 145 (Evolocumab) is a similar human monoclonal IgG2 antibody targeting PCSK9. In a phase I, ascending-dose study, the effects of AMG 145 on the LDL-C response were evaluated in both patients with hypercholesterolemia (heterozygous FH and non-FH patients previously requiring statin therapy) and healthy patients (n = 113).56 Healthy participants were randomized to receive either placebo or AMG 145 at 7, 21, 70, 210, or 420 mg subcutaneously or 21 or 420 mg intravenously. Participants with hypercholesterolemia and on low- or moderate-dose statin therapy received AMG 145 subcutaneously at 14 or 35 mg QW or 140 or 280 mg Q2W, or 420 mg Q4W, or placebo. Participants on high-dose statins received either subcutaneous AMG 145 at 140 mg or placebo Q2W. At the conclusion of the study period, AMG 145 had reduced LDL-C levels by 64% after 1 dose of 21 mg or more and by 81% with repeated doses of 35 mg or more, as compared with placebo. There were no serious adverse events reported during the course of the study and the adverse event level was not different between placebo and the study drug.56 To evaluate the efficacy of AMG 145 in patients unable to tolerate statin side effects, the Goal Achievement after Utilizing an anti-PCSK9 antibody in Statin Intolerant Subjects randomized trial (N = 160) examined AMG 145 in a 12-week dose-ranging study. AMG 145 was administered at 280, 350, 420, or 420 mg plus 10 mg ezetimibe, or 10 mg of ezetimibe plus placebo all on a Q4W schedule.57,58 All the patients had a history of muscle-related statin intolerance. The greatest percentage reduction in LDL-C level was 63% from baseline. The most common study-related adverse effect remained myalgia, affecting up to 20% of participants taking both AMG 145 and ezetimibe.57,58 This provides evidence that anti-PCSK9 pharmacologic therapy may provide a reasonable therapeutic alternative for high-risk coronary artery disease patients who are unable to tolerate conventional treatment options. In a phase II dose-ranging study on patients with LDL-C levels more than 2.2 mM (85 mg/dL) concurrently on a statin ± ezetimibe and AMG 145, investigators evaluated the efficacy, safety, and tolerability of the study drug.59 Participants received 70, 100, 140 mg or a placebo Q2W or they received 280, 350, 420 mg or placebo Q4W. A total of 631 participants were examined from the LDL-C Assessment with PCSK9 Monoclonal Antibody Inhibition Combined with Statin Therapy—Thrombolysis in Myocardial Infarction 57 study60–62 and found a reduction in LDL-C of 41.8% to 66.1% for the Q2W group and a 41.8% to 50.3% reduction in LDL-C for the Q4W group after 12 weeks.59 Most patients at highest risk for adverse cardiovascular events achieved the most stringent recommended lipid goals.62 Of particular note, this study is substantially larger (3×) in terms of sample size than other published phase II PCSK9 studies. It also included patients with a lower threshold for hypercholesterolemia (< 2.6 mM vs 2.2 mM;
Antihyperlipidemic Therapies Targeting PCSK9 Michael Weinreich, MD,* and William H. Frishman, MD†
Abstract: Hyperlipidemia is a major cause of cardiovascular disease despite the availability of first-line cholesterol-lowering agents such as statins. A new therapeutic approach to lowering low-density lipoprotein-cholesterol (LDL-C) acts by blocking LDL-receptor degradation by serum proprotein convertase subtilisin kexin 9 (PCSK9). Human monoclonal antibodies that target PCSK9 and its interaction with the LDL receptor are now in clinical trials (REGN727/SAR23653, AMG145, and RN316). These agents are administered by either subcutaneous or intravenous routes, and have been shown to have major LDL-C and apolipoprotein B effects when combined with statins. A phase III clinical trial program evaluating clinical endpoints is now in progress. Other PCSK9-targeted approaches are in early stages of investigation, including natural inhibitors of PCSK9, RNA interference, and antisense inhibitors. Key Words: proprotein convertase subtilisin kexin 9 inhibition, monoclonal antibodies, low-density lipoprotein reduction (Cardiology in Review 2014;22: 140–146)
H
ypercholesterolemia is a leading contributor to cardiovascularrelated morbidity and mortality around the world.1 In the United States, approximately 14% of all adults have total cholesterol levels of 240 mg/dL or more.2 It is well established that hypercholesterolemia is associated with atherosclerotic vascular disease and adverse events including myocardial infarction, cerebrovascular accidents, and transient ischemic attacks.3–8 The National Cholesterol Education Program has established guidelines for the detection, evaluation, and treatment of hypercholesterolemia based on epidemiological studies, showing a clear association between total cholesterol serum concentration and risk of coronary artery disease.9 These guidelines, the Adult Treatment Panel III, take into account both a patient’s low-density lipoprotein (LDL) concentration and their cardiac risk factors.9 The first-line pharmacologic treatment for hypercholesterolemia is hydroxyl-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor (statin) therapy, based on the class’s efficacy. This class of drugs has been shown to reduce LDL-C levels by up to 63% from baseline.10 The American College of Cardiology Foundation and The American Heart Association recommend the use of statins in secondary prevention of hyperlipidemia to achieve LDL-C goal levels less than 100 mg/dL or less than 70 mg/dL in patients who are at very high risk.11 Second-line lipid-lowering agents include bile acid sequestrants, fibrates, niacin, and ezetimibe. However, these therapies do not adequately lower cholesterol to goal levels or yield clinical benefit in many patients.12–14
Although statin therapy has been hailed for its efficacy in approximately 20 million users, nearly 20% of individuals experience side effects that hinder the drug’s ability to achieve target LDL levels.15,16 These statin-induced side effects include myopathy, myalgia, hepatic dysfunction, renal dysfunction, diabetes mellitus, and psychiatric changes including irritability and aggression.17–23 Compounding the issue are reports of intronic single-nucleotide polymorphisms (SNPs) that are linked to resistance to statin therapy.24,25 As a result of these goal-limiting factors, there has been an ongoing search for nonstatin cholesterol-lowering agents. Especially for those individuals with familial hypercholesterolemia, alternative therapy could be life-saving and extending. Three major pharmaceutical teams, Sanofi US (Bridgewater, NJ)/Regeneron Inc. (Tarrytown, NY), Amgen Inc. (Thousand Oaks, CA), and Pfizer Inc. (New York, NY) have invested extensive research efforts into exploring the potential of blocking LDL-receptor (LDLR) degradation by serum proprotein convertase subtilisin kexin 9 (PCSK9)26 via the human monoclonal antibodies designated REGN727/SAR236553 (subcutaneous administration), AMG 145 (subcutaneous administration), and RN316 (intravenous administration), respectively. PCSK9 has a known function in the control of LDLR surface expression by hepatocytes. This newly discovered member of the subtilisin serine protease family binds to extracellular LDL receptors and subsequently marks them for internalization and intracellular degradation via a lysosomal-mediated pathway (Fig. 1).27 Thus, hepatocyte capacity for extraction of LDL-C from the circulation is decreased.28,29 REGN727/SAR236553, AMG 145, and RN316 act by targeting PCSK9 and blocking its interaction with the LDL receptor.30 This article will examine the current research surrounding anti-PCSK9 therapies, with a special focus on monoclonal antibody development, and their efficacy to lower LDL-C levels in patients with hypercholesterolemia.
BASIC SCIENCE/TRANSLATIONAL RESEARCH
From the *Department of Medicine, North Shore Long Island Jewish Health System/Hofstra University School of Medicine, Manhasset, NY; and †New York Medical College/Westchester Medical Center, Valhalla, NY. Disclosure: The authors declare no conflict of interest. Correspondence: William H. Frishman, MD, Department of Medicine, Munger 263, New York Medical College, Valhalla, NY 10595.E-mail: [email protected]. Copyright © 2014 Lippincott Williams & Wilkins ISSN: 1061-5377/14/2203-0140 DOI: 10.1097/CRD.0000000000000014
The discovery of PCSK9 as a potential antihyperlipidemia pharmacologic target is owed mostly to robust basic science and translational research efforts.31 Before the early 2000s, autosomal dominant hypercholesterolemia (ADH) was known to be associated with genetic mutations in 2 specific genes, LDLR and APOB, which coded for the LDL receptor and apolipoprotein B, respectively.32,33 In 2003, Abifadel et al34 published a report demonstrating a further association between ADH and a mutation mapped to the chromosomal locus 1p32, the site of the PCSK9 gene. A mutation in PCSK9 (which encodes proprotein convertase subtilisin/kexin type 9) was reported in 23 French families with ADH. Mutations in both LDLR and APOB had been previously excluded in these families.34 Although the cholesterol-related mechanism of PCSK9 was unknown, the putative role in cholesterol regulation was established. In a subsequent study, real-time polymerase chain reaction analysis showed that increased cholesterol consumption by mice was associated with down-regulation of PCSK9 mRNA.35 Conversely, expression of PCSK9 mRNA is up-regulated by -CoA reductase inhibitors. As would be expected, the presence of mevalonate, a product of HMG-CoA reductase on HMG-CoA, was found to down-regulate PCSK9 mRNA transcription.36,37 The involvement with the LDL receptor was implicated when Maxwell et al38 showed that overexpression of PCSK9 in
140 | www.cardiologyinreview.com
Cardiology in Review • Volume 22, Number 3, May/June 2014
Cardiology in Review • Volume 22, Number 3, May/June 2014
Antihyperlipidemic Therapies Targeting PCSK9
FIGURE 1. LDLR recycling pathway. Left, PCSK9 binding to extracellular LDLR leads to endocytosis and subsequent degradation via a lysosomal-mediated mechanism. Right, monoclonal antibody binding to PCSK9 inhibits interaction with LDLR, sparing its destruction. LDLR indicates low-density lipoprotein receptor; PCSK9, serum proprotein convertase subtilisin kexin 9. Reprinted with permission from Lambert et al.27 human hepatoma (HepG2) cells did not affect LDLR expression or synthesis/maturation of the receptor, but did greatly accelerate degradation of the LDL receptor. Finally, in 2006 Cohen et al39 reported that African American individuals with nonsense lossof-function mutations at the PCSK9 locus had an associated 28% reduction in mean LDL-C levels and an 88% reduction in the risk of coronary heart disease. Significant, but less impressive, reductions in both parameters were noted in the white subset.39 Further studies confirmed that loss-of-function mutations at the PCSK9 locus were associated with lower circulating LDL-C levels.40–42 Conversely, DNA sequencing in 51 Norwegian patients showed that gain-of-function missense mutations in the PCSK9 gene were associated with ADH.43
ANIMAL STUDIES With PCSK9’s role in regulating LDL receptor expression established, various inhibition methods were explored. In 2009, Chan et al44 engaged in a proof-of-concept study involving PCSK9 inhibition. An anti-PCSK9 antibody, mAb1, was designed to bind to an epitope adjacent to the LDL receptor site on PCSK9, sterically hindering interactions. In vitro studies demonstrated that mAb1 reduced LDL receptor destruction. When mAb1 treatment was combined with statin therapy, LDL receptor expression on HepG2 cells was greater than when either was used as a monotherapy. It was noted that wild-type mice subjected to mAb1 demonstrated a 2-fold increase in LDL receptor expression and a decrease in total serum cholesterol by 36%. This fall in cholesterol was not noted in LDLR knockout mice subjected to mAb1 therapy. A further study in cynomolgus monkeys found that a single injection of mAb1 was associated with an 80% drop of serum LDL-C only 10 days after administration.44 A subsequent study demonstrated that lower PCSK9 levels are associated not just with a reduction in circulating LDL-C, but also with decreased levels of aortic cholesteryl esters plaques.45 In a comparison of wild-type, PCSK9 knockout, and high–PCSK9-expression mice fed on a Westernized diet for 12 months, it was found that knockout mice had a 74% reduction in aortic plaques as compared with the wild-type mice. The high–PCSK9-expression mice had visible, more severe, and an increased number (230% increase) of aortic plaques as compared with wild-type mice.45 © 2014 Lippincott Williams & Wilkins
CLINICAL TRIALS REGN727/SAR236553 (Alircumab) REGN727/SAR236553, a human monoclonal antibody against PCSK9 has been studied in several recent clinical trials. Two phase I, randomized, single, ascending-dose studies of REGN727 administered intravenously (n = 40) or subcutaneously (n = 32) compared cholesterol-lowering efficacy versus placebo in patients with LDL-C levels of 100 mg/dL or more. Intravenously administered participants received doses of study drug up to 12 mg/kg and the subcutaneous arm received doses up to 250 mg. The results demonstrated a 65% reduction in LDL-C as compared with placebo, with the intravenous route showing greater efficacy. The duration of reduction was found to be dose-dependent.46 A third, early phase I, randomized, placebo-controlled, multiple-dose trial included adults with or without heterozygous familial hypercholesterolemia (FH) with LDL-C levels of 100 mg/dL or more while on atorvastatin (n = 51) or non-FH patients with LDL-C levels of 130 mg/dL or more treated with behavioral modification alone (n = 10).46 Participants were administered subcutaneous study drug at 50, 100, and 150 mg doses or placebo. At the conclusion of the treatment period, LDL-C was reduced from baseline by 39.2%, 53.7%, and 61.0%, respectively, as compared with placebo. One participant had a transient increase in creatine kinase to 10 times the upper limit of normal, but with no associated physical or clinical findings. The maximum LDL-C reduction was reached within just 2 weeks, which is notably quicker than with statin therapy.46 The percentage of reduction of LDL-C from baseline in the study drug–plus-statin group (61%) was comparable with that of the earlier-mentioned study drug–only group (65%). However, this phase I trial result does not constitute evidence for monotherapy of REGN727 due to the low sample size of the study population. In phase II trials, REGN727 was evaluated in a double-blind, parallel-group, placebo-controlled, randomized, multicenter, 12-week trial examining the efficacy of REGN727 to lower LDL-C levels as compared with placebo, in patients (N = 183) with LDL-C levels of 100 mg/dL or more and concurrently on variable-dose atorvastatin (10, 20, or 40 mg).47 The goal was to evaluate both dose-dependent and dose-frequency effects of the study drug. Patients were assigned to receive either 50, 100, or 150 mg every 2 weeks (Q2W) or 200 or www.cardiologyinreview.com | 141
Weinreich and Frishman
Cardiology in Review • Volume 22, Number 3, May/June 2014
300 mg every 4 weeks (Q4W) alternating with placebo Q2W. Twelve weeks poststudy initiation, the placebo group had a 5% reduction in LDL-C whereas the experimental group had a 40% to 72% reduction, showing dependency both on dosing schedule and level. There was also a decrease in apolipoprotein B and lipoprotein(a) levels. One participant experienced a serious adverse effect of leukocytoclastic vasculitis. Muscle-related incidents were not frequently reported and there was no increase shown in the results of liver function tests or muscle enzymes during the course of the study. The reduction in LDL-C by REGN727 was not affected by the dose of atorvastatin, suggesting an additive relationship between the two therapeutic agents and the study drug’s ability to independently reduce LDL-C levels.47 Leukocytoclastic vasculitis is an adverse effect that has also been noted with several other monoclonal antibody therapies.48,49 The syndrome is generally benign and treated by only discontinuing the inciting agent. Less frequently, patients may require nonsteroidal antiinflammatory, corticosteroid, or immunosuppressive therapy.50,51 Although the occurrence of this vasculitis associated with anti-PCSK9 therapy has remained an isolated event in the published literature, continued monitoring throughout phase III and postmarket studies will be revealing. The safety and efficacy of REGN727 in concurrent use with statin and ezetimibe therapy was evaluated in participants with heterozygous FH in a randomized, multicenter, placebo-controlled, phase II trial (N = 77).52 All participants had LDL-C level higher than 2.6 mM (100 mg/dL) and were on a stable diet with a statin ± ezetimibe. Patients received either subcutaneous 150, 200, or 300 mg of the study drug Q4W or 150-mg study drug Q2W, or placebo Q2W. After 12 weeks, a 67.9% reduction of LDL-C from baseline was reported in the 150-mg Q2W group. Apolipoprotein B levels were reduced by 50.19% from baseline, high-density lipoprotein (HDL)C increased by 12.34% from baseline, and total cholesterol fell by 43.44% from baseline. No study drug-related adverse events were report and there was no increase in liver function tests or creatine kinase >3 the upper limit of normal.52 Approximately 40% of the patients in this trial had known coronary artery disease, indicating a greater level of hypercholesterolemia severity as compared with the previously discussed heterozygous FH phase I trial. This phase II trial provides broader evidence among a larger and more diverse cohort of participants of the benefits provided to patients with FH in achieving goal LDL-C levels. A phase II, multicenter, double-blind, placebo-controlled trial (N = 92) evaluated the efficacy of REGN727 when used with high- or low-dose atorvastatin as compared with high dose alone.53 All participants had LDL-C level of at least 100 mg/dL, even after receiving a baseline treatment of 10-mg atorvastatin for 7 weeks. Participants were randomly assigned to 80-mg atorvastatin plus REGN727 Q2W, 10-mg atorvastatin plus REGN727 Q2W, or 80-mg atorvastatin plus placebo Q2W. The REGN727 dose was administered subcutaneously at 150 mg. After 8 weeks it was noted that the 80-mg statin-plus– study drug group was found to have a 73.2% reduction from baseline LDL-C, the 10-mg statin-plus–study drug group was found to have a 66.2% reduction, whereas the 80-mg statin-plus-placebo group had a 17.3% reduction. All the patients in the study-drug group achieved LDL-C levels less than 100 mg/dL, and 90% achieved levels less than 70 mg/dL. There was no significant difference in LDL-C reduction between the 80-mg and 10-mg statin-plus–study drug groups, suggesting an upper limit to the ability of statins to up-regulate the LDLR.53 Notably, 1 patient in the 80-mg statin-plus–study drug group had mildly increased AST before the study and subsequently had an increase to more than 3 times the upper limit of normal.53 A comprehensive phase III clinical program using REGN727 is now under way.54 The Odyssey Outcomes study is enrolling 18,000 patients aged 40 years or older with a recent acute coronary syndrome
and LDL levels of 70 mg/dL or more.55 Patients are randomized to receive a 1-mL injection of 75 mg of study drug or placebo Q2W, in addition to their regular lipid-lowering therapy. If patients do not reach goal LDL-C levels with initial dosing, the dose will be increased to 150 mg Q2W. Follow-up will continue for 64 months, examining the composite endpoint of coronary artery disease, death, nonfatal myocardial infarction, fatal or nonfatal ischemic stroke, or unstable angina requiring hospitalization. Other studies within the Odyssey trial program include evaluation of patients unable to tolerate statin therapy, the safety or efficacy of REGN727 as a monotherapy, and patients with failure to achieve adequate control with their current lipid modifiers.55
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AMG 145 AMG 145 (Evolocumab) is a similar human monoclonal IgG2 antibody targeting PCSK9. In a phase I, ascending-dose study, the effects of AMG 145 on the LDL-C response were evaluated in both patients with hypercholesterolemia (heterozygous FH and non-FH patients previously requiring statin therapy) and healthy patients (n = 113).56 Healthy participants were randomized to receive either placebo or AMG 145 at 7, 21, 70, 210, or 420 mg subcutaneously or 21 or 420 mg intravenously. Participants with hypercholesterolemia and on low- or moderate-dose statin therapy received AMG 145 subcutaneously at 14 or 35 mg QW or 140 or 280 mg Q2W, or 420 mg Q4W, or placebo. Participants on high-dose statins received either subcutaneous AMG 145 at 140 mg or placebo Q2W. At the conclusion of the study period, AMG 145 had reduced LDL-C levels by 64% after 1 dose of 21 mg or more and by 81% with repeated doses of 35 mg or more, as compared with placebo. There were no serious adverse events reported during the course of the study and the adverse event level was not different between placebo and the study drug.56 To evaluate the efficacy of AMG 145 in patients unable to tolerate statin side effects, the Goal Achievement after Utilizing an anti-PCSK9 antibody in Statin Intolerant Subjects randomized trial (N = 160) examined AMG 145 in a 12-week dose-ranging study. AMG 145 was administered at 280, 350, 420, or 420 mg plus 10 mg ezetimibe, or 10 mg of ezetimibe plus placebo all on a Q4W schedule.57,58 All the patients had a history of muscle-related statin intolerance. The greatest percentage reduction in LDL-C level was 63% from baseline. The most common study-related adverse effect remained myalgia, affecting up to 20% of participants taking both AMG 145 and ezetimibe.57,58 This provides evidence that anti-PCSK9 pharmacologic therapy may provide a reasonable therapeutic alternative for high-risk coronary artery disease patients who are unable to tolerate conventional treatment options. In a phase II dose-ranging study on patients with LDL-C levels more than 2.2 mM (85 mg/dL) concurrently on a statin ± ezetimibe and AMG 145, investigators evaluated the efficacy, safety, and tolerability of the study drug.59 Participants received 70, 100, 140 mg or a placebo Q2W or they received 280, 350, 420 mg or placebo Q4W. A total of 631 participants were examined from the LDL-C Assessment with PCSK9 Monoclonal Antibody Inhibition Combined with Statin Therapy—Thrombolysis in Myocardial Infarction 57 study60–62 and found a reduction in LDL-C of 41.8% to 66.1% for the Q2W group and a 41.8% to 50.3% reduction in LDL-C for the Q4W group after 12 weeks.59 Most patients at highest risk for adverse cardiovascular events achieved the most stringent recommended lipid goals.62 Of particular note, this study is substantially larger (3×) in terms of sample size than other published phase II PCSK9 studies. It also included patients with a lower threshold for hypercholesterolemia (< 2.6 mM vs 2.2 mM;
