Introduction

Hyperlipidemia has long been an established risk factor for atherosclerosis, and low-density lipoprotein cholesterol (LDL-C) is recognized as being causally associated with atherosclerotic cardiovascular disease (ASCVD) [1]. The fundamental framework that governed most contemporary cholesterol-lowering agents, which include statins and other small molecule drugs such as ezetimibe and bempedoic acid, is the lowering of LDL-C [2,3,4].

The advent of genome-wide association and Mendelian randomization instruments have allowed for our expanded understanding into the complex genetic drivers in dyslipidemia and ASCVD, as well as the identification of important genetic mediators including PCSK9, ANGPTL3, APOC3, and LPA [5,6,7]. Some of these genes and their gene products, such as proprotein convertase subtilisin/kexin type 9 (PCSK9), directly affect serum LDL-C level. However, as a result of these genetic linkage studies, other lipids including triglyceride-rich lipoproteins (TRLs) and lipoprotein(a) (Lp[a]) are now also thought to be causally associated with ASCVD [8].

The identification of new therapeutic targets has in turn heralded a new era of drug discovery in lipid-lowering therapy [9]. As the paradigm of the mechanism underlying ASCVD has evolved, so too has the therapeutic design of lipid-lowering medications, and many of the new agents that have been developed or in the pipeline are biologics-based—consisting of monoclonal antibodies (mAb), RNA interference (RNAi), and more recently gene editing technologies (Fig. 1). In the sections below, we highlight these biotechnological drug classes and discuss current clinical evidence on the efficacy and safety of biologic lipid-lowering therapies (Table 1).

Fig. 1
figure 1

Lipid-lowering biologics that are in clinical use or are currently under investigation in various phases of clinical trials

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Table 1 Summary of lipid-lowering biologics that are currently available or undergoing clinical trials.
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Overview of Types of Biotechnological Therapies

Multiple modalities of lipid-lowering biologics have been developed and are under investigation. The two major classes of biotechnological therapies that are either available commercially or under investigation in human trials can be organized into mAbs and RNAi technologies (Fig. 2). A third class, gene editing using CRISPR-Cas9 techniques is being developed to treat hyperlipidemia disorders though studies are still in animal phase [10]. The mAb class of agents acts by binding and inactivating the target protein. Lipid-lowering mAb agents include the PCSK9 inhibitors, alirocumab and evolocumab, both of which are commercially available and have shown efficacy in the secondary prevention of ASCVD as well as management of familial hypercholesterolemia (FH) [11, 12]. Additionally, evinacumab is a mAb against angiopoietin-like protein 3 (ANGPTL3) currently undergoing clinical trials [13]. It is important to note that the above agents are human mAbs. Bococizumab, which is a humanized mAb against PCSK9 with approximately 3% of murine sequence, was shown to elicit high rates of antidrug antibodies in clinical trials, and development of this agent has been subsequently discontinued [14].

Fig. 2
figure 2

Molecular targets of novel lipid-lowering biologics include targeting of proteins by monoclonal antibodies (mAb), messenger RNA (mRNA) by antisense oligonucleotide (ASO), and small interfering RNA (siRNA) therapeutics. CRISPR gene-editing technology that works at the DNA level is also being developed

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A second strategy to inhibit proteins of interest is via gene silencing through RNAi. Gene expression at the transcription level can be disrupted by RNAi biologics either by small interfering RNAs (siRNA) or by antisense oligonucleotides (ASO). SiRNA agents consist of short, double-stranded RNA molecules that bind to RNA-induced silencing complex (RISC), which then targets the complementary mRNA molecules inducing cleavage and degradation. A single siRNA-bound RISC is able to bind and cleave many mRNA transcripts [15]. Meanwhile, ASOs act by directly binding to their complementary messenger RNA (mRNA) molecules, resulting in RNase-mediated degradation [16].

As the liver is central to lipid metabolism, current siRNA and ASO agents are conjugated to N-acetylgalactosamine carbohydrates (GalNAc), which binds asialoglycoprotein receptors (ASGPR) on hepatocytes [17]. This strategy facilitates drug delivery to the liver and allows for lowering dosing of medication. The redesign resolved issues with adverse side effects including significant thrombocytopenia which was observed during earlier RNAi agents prior to the incorporation of GalNAc when much higher dosages were tested [18, 19]. The current RNAi biologics undergoing clinical trials include inclisiran, a siRNA agent targeting PCSK9 and ASO therapeutics against the mRNAs of apolipoprotein C3 (APOC3), ANGPTL3, and Lp(a). Other siRNA-based therapies include those against ANGPTL3, APOC3, and Lp(a) though limited clinical data have been published regarding these agents [20]. The ASO inhibitor, mipomersen, which targets apolipoprotein B-100 (apoB-100) was an orphan drug previously available for the treatment of homozygous FH (HoFH). However, mipomersen has been associated with significant hepatotoxicity, injection reactions, and flu-like symptoms and at the time of this review has been discontinued from the market [21, 22].

Current Clinical Evidence by Drug Targets

PCSKS9

In humans, the PCSK9 proteins bind to low-density lipoprotein receptor (LDLR), which leads to receptor degradation and lowered LDL cholesterol removal from the circulation. Individuals with loss-of-function PCSK9 genetic variants were found to have lower LDL-C and incidence of coronary heart disease (CHD). Meanwhile, gain-of-function PCSK9 variants lead to increased LDL-C and familial hypercholesterolemia [23]. PCSK9i is a class of monoclonal antibodies that acts to lower LDL-C by inhibiting the PCSK9 proteins and thus preventing LDLR degradation. While PCSK9 inhibitors dramatically reduce LDL-C, these agents do not significantly alter high sensitivity C-reactive protein (hs-CRP), a marker of inflammation [24, 25].

Approved by the FDA in 2015, evolocumab is a fully human monoclonal antibody that inhibits PCSK9 to lower LDL-C cholesterol. The FOURIER study was a randomized, parallel, double-blind, placebo-controlled trial of 27,564 patients with clinical ASCVD (prior MI, non-hemorrhagic stroke, symptomatic PAD) and LDL-C ≥ 70 mg/dL or a non-HDL-C level ≥ 100 mg/dL who were receiving optimized lipid-lowering preferably using high-intensity statin or at least atorvastatin 20 mg with or without ezetimibe. Patients were randomized to evolocumab 140 mg subcutaneous every 2 weeks or 420 mg monthly versus placebo every 2 weeks [12]. Among the trial participants, 69% were on a high-intensity statin, and 30% were on a moderate-intensity statin, and 5.2% were on ezetimibe, with median LDL-C of 92 mg/dl. The primary outcome, a composite of cardiovascular death, MI, stroke, hospitalization for unstable angina, or coronary revascularization, occurred in 9.8% in the evolocumab group compared to 11.3% of the placebo group (hazard ratio [HR] 0.85, 95% confidence interval [CI] 0.79–0.92, p < 0.001) at a median follow-up of 2.2 years. Among individual endpoints, individuals in the evolocumab group had lower rates of MI, strokes, and coronary revascularization but did not have significant difference in cardiovascular deaths compared with placebo. At 48 weeks, LDL-C was reduced by a least-squares mean percentage of 59% in the evolocumab group compared with placebo. Absolute reduction in LDL-C was 56 mg/dl in the evolocumab group compared to placebo. Evolocumab was found to be safe with no significant difference in adverse outcomes compared to placebo (serious adverse event [SAE] was 24.8% with evolocumab versus 24.7% with placebo). There have been concerns regarding the very low levels of LDL-C achieved in patients on PCSK9i and potential association with neurocognitive side effects. However, analysis from the EBBINGHAUS study demonstrate no significant difference in cognitive function between those on evolocumab compared with placebo over 19 months follow-up [26]. In post hoc analysis, individuals with high-risk features including more recent MIs, ≥ 2 prior MIs, and presence of residual multivessel coronary artery are at the highest risk for major vascular events and had the greatest risk reduction with evolocumab [27]. In sub-analysis of FOURIER patients with PAD, though the relative risk reduction for clinical outcomes were similar between participants with and without PAD, the absolute risk reduction of evolocumab in patients with PAD were higher given the greater underlying risk [28].

The efficacy and safety of alirocumab was established in the landmark ODYSSEY OUTCOMES trial [11]. The trial randomized 18,924 patients who had an acute coronary syndrome in the preceding 1 to 12 months. Alirocumab was titrated between 75 and 150 mg to keep LDL-C between 25 and 50 mg/dl and to avoid LDL-C levels below 15 mg/dl on a consistent basis. Over a follow-up duration of 2.8 years, the primary outcome (composite of death from coronary heart disease, nonfatal myocardial infarction, fatal or nonfatal ischemic stroke, or unstable angina requiring hospitalization) for alirocumab vs placebo was 9.5% vs 11.1% (HR 0.85, 95% CI 0.78–0.93, p < 0.001). Among secondary outcomes, alirocumab group to placebo group was found to have lower major coronary heart disease events (8.4% vs. 9.5%, p = 0.006), any cardiovascular event (13.7% vs 15.6%, p < 0.001) as well as composite of death from any cause/nonfatal MI/nonfatal ischemic stroke (10.3% vs. 11.9%, p < 0.001) but not death from CHD, death from CVD cause, or death from any cause. Mean at LDL-C at 48 months was 66 mg/dL in the alirocumab group compared with 103 mg/dL in the placebo group. In on-treatment analysis, there was a 54.7% lower LDL-C in the alirocumab group compared to placebo at 48 months. The rate of adverse events was similar among participants in the alirocumab compared with those in the placebo group (SAE 23.3% vs 24.9% in the alirocumab vs placebo groups, respectively). Of note, a third humanized PCSK9i, bococizumab, was studied in the SPIRE-1 and SPIRE-2 trials. In the SPIRE-1 outcome study, no significant difference in the primary endpoint (non-fatal MI, non-fatal stroke, hospitalization for unstable angina requiring urgent revascularization, or CV death) was observed among enrolled patients with LDL-C greater than 70 mg/dl at 7 months. In the SPIRE-2 trial, at 12 months, there was a 21% reduction in the primary end point among patients enrolled with LDL-C greater than 100 mg/dl, suggesting that longer treatment duration might be beneficial. However, in 2016, the drug’s development was discontinued prematurely by sponsors based on the trials’ lipid-lowering results [14].

In addition to monoclonal antibodies, small interfering double-stranded RNA has also been developed to inhibit PCSK9 production. Inclisiran, currently under investigation, is a siRNA that works by directly inhibiting the translation of the PCSK9 protein in hepatic cells, thus lowering LDL-C levels in the circulation. The safety and efficacy of inclisiran in patients with heterozygous familial hypercholesterolemia (HeFH), ASCVD, or ASCVD risk-equivalents have been studied in the ORION-9, ORION-10, and ORION-11 trials, respectively. ORION-9, a phase 3, randomized clinical trial, showed that inclisiran sodium 300 mg administered subcutaneously at days 1, 90, 270, and 450 was effective in lowering LDL-C by 47.9% compared with placebo at 18 months (time averaged mean reduction of 44.3% compared to placebo) among subjects with heterozygous familial hypercholesterolemia with LDL-C level > 100 mg/dl at time of enrollment [29]. No significant difference in adverse side effects was noted between inclisiran sodium and placebo groups. In ORION-10, subjects with ASCVD on maximum-tolerated statin therapy and elevated LDL-C cholesterol (LDL-C > 70 mg/dl) were randomized to inclisiran 284 mg (equivalent to 300 mg of inclisiran sodium; administered at day 1, day 90, and every 6 months thereafter) versus placebo with 18 months follow-up. At 510 days, there was a between-group difference of − 52.3% (p < 0.001) in LDL-C when comparing inclisiran and placebo groups. The time-averaged change in LDL-C was − 53.8% when comparing inclisiran to placebo. Again, no significant difference in serious adverse events was noted between inclisiran and placebo groups. In the ORION-11 trial, patients with ASCVD or ASCVD risk-equivalents were randomized to inclisiran 284 mg injection versus placebo. Mean percent change in LDL-C at 510 days, was − 49.9% (p < 0.001) in the inclisiran group compared with the placebo group. The time-averaged reduction in LDL-C for the inclisiran vs placebo groups was − 49.2 (p < 0.001). There was no significant difference in adverse events between the groups [30]. Overall, the three ORION trials have established the LDL-C–lowering efficacy and safety of inclisiran in managing patients with HeFH, ASCVD, or ASCVD risk equivalents with elevated LDL-C.

Based on the 2018 American College of Cardiology (ACC)/American Heart Association (AHA) Multisociety Cholesterol guidelines, PCSK9i have a class IIb indication to be considered in patients 30–75 years of age with heterozygous FH and elevated LDL-C level (≥ 100 mg/dL) while on maximally tolerated statin and ezetimibe therapy. In addition, in patients with hypercholesterolemia (baseline LDL-C level of 220 mg/dl or higher) between the age of 40 and 75 years, whose LDL-C remains above 130 mg/dl despite maximally tolerated statin and ezetimibe therapy, PCSK9i may also be considered (IIb indication). In patients with clinical ASCVD who are at very high risk and whose LDL-C remains ≥ 70mg/dl or whose non-HDL-C level remains ≥ 100 mg/dl despite maximally tolerated lipid-lowering agents (statins and ezetimibe), a PCSK9i may be considered after discussion of benefits, safety, and costs between clinician and patient (class IIa indication) [31, 32]. Very high risk is defined as a history of multiple major ASCVD events (recent ACS within the past 12 months, history of MI, history of ischemic stroke or symptomatic PAD) or 1 major ASCVD event plus multiple high-risk conditions (age ≥ 65 years, heterozygous familial hypercholesterolemia, history of coronary revascularization outside of the major ASCVD events, diabetes mellitus, hypertension, chronic kidney disease, current smoking, persistently elevated LDL-C ≥ 100 mg/dL despite maximally tolerated statin and ezetimibe, or history of congestive heart failure).

However, cost remains a concern for PCSK9i [33]. The initial price of these agents made them cost ineffective in many cost-effectiveness analysis models. Newer analysis based on reduced pricing of these agents has found PCSK9i to be more cost effective [34]. It remains to be seen whether the price reduction of evolocumab and alirocumab will impact their scope of use.

ANGPTL3

ANGPTL3 is a protein predominantly found in the liver that acts by inhibiting lipoprotein lipase and endothelial lipase, which are important in TRL metabolism and the regulation of TGs and HDL-C. ANGPTL3 mutations have also been linked to reduced LDL-C, potentially via increased clearance of lipoprotein particles though the precise mechanisms have yet to be elucidated [35, 36]. Loss of function (LOF) mutation in ANGPLT3 results in familial combined hypolipoproteinemia, characterized phenotypically by low plasma triglycerides, LDL-C, and HDL-C [37]. In the DiscovEHR human genetics study, heterozygous carriers of LOF variants of ANGPTL3 were associated with 27% lower TG, 9% lower LDL-C, and 4% lower HDL-C compared with noncarriers after adjustment for co-variates [13]. Moreover, the presence of an ANGPTL3 LOF variant was associated with 41% lower odds of coronary artery disease (OR 0.59, 95% CI 0.41–0.85, p = 0.004) compared with noncarriers. In mice, treatment of monoclonal antibody against ANGPTL3 was found to reduce total cholesterol (TC) by − 52% (p < 0001) and TGs by − 84% (p < 0.001) as well as the decrease in atherosclerotic lesion size and necrotic content in atherosclerotic plaques when compared with control.

The mAb, evinacumab, and ASO therapy, IONIS-ANGPTL3-LRx, against ANGPLT3 are currently undergoing clinical trial investigation. In a phase I, single-ascending-dose trial of evinacumab of 83 healthy human participants with mild to moderately elevated TG (150–450 mg/dL) or LDL-C (≥100 mg/dL) randomized 3:1 to either single dose administration of evinacumab or placebo, the magnitude of reduction in TG, non-HDL-C, LDL-C, and HDL-C were observed in a dose-dependent manner [38]. The greatest reduction in TGs after a single subcutaneous dose was observed in the 250 mg group at 55.5% when compared to placebo. The greatest reduction in TGs for IV dosing was noted in the 10 mg/kg group at 88.0% when compared with placebo. No serious treatment emergent adverse event (TEAE) was observed, with 51.6% vs 42.9% of participants in the treatment vs placebo group experiencing at least 1 TEAE. There were 11.3% vs 0% of subjects in the treatment vs placebo group who experienced elevated alanine aminotransferase levels, and 6.5% vs 0% had increase in aspartate aminotransferase levels.

Similarly, in a phase I multiple ascending dose study of 56 healthy individuals with TG 150–500 mg/dL) or LDL-C ≥ 100 mg/dL randomized 3:1 to evinacumab (subcutaneously at 150/300/450 mg once weekly, 300/450 mg every 2 weeks, or intravenously at 20 mg/kg once every 4 weeks up to day 56), there was a median reduction in TG and VLDL-C of ~ 70% at day 57 observed in the 300 mg SC every week, 450 mg SC every week, and 20 mg/kg IV every 4 week dosing groups [38]. LDL-C reduction was also observed in all evinacumab groups with the greatest reduction at 57 days in the 300 mg SC every week and the 20 mg/kg IV groups (22.0%, p = 0.0194 and 25.1%, p = 0.0074, respectively). With respect to safety, 67.7% in the treatment group and 75% in the placebo group experienced at least 1 TEAE with headache being the most common. There were no serious TEAEs, death, or discontinuation due to TEAEs during the study.

Meanwhile, in the phase I trial of IONIS-ANGPTL3-LRx, per weekly SC administration of ASO therapy for 6 weeks resulted in up to 63.1% reduction in TGs, 36.6% reduction in non-HDL-C, and 25.7% reduction in apoB levels [39]. No serious adverse events were documented during the trial. No significant thrombocytopenia, coagulation abnormalities, bleeding episodes, or evidence of liver or renal dysfunction were observed. Three individuals in the treatment arm and three from the control arm developed dizziness or headache.

SiRNA therapeutics against ANGPTL3 are also being developed. In an early phase 1/2a single-ascending dose study of 40 healthy volunteers, ARO-ANG3 administered was found to reduce TG by 47–53% and VLDL-C by 49–51% at 200 mg and 300 mg SC doses after 16 weeks. Meanwhile, LDL-C was found to be reduced by 33–46% from baseline. No serious adverse effects were noted [8].

One potential utilization of ANGPTL3 inhibition is in the treatment of homozygous familial hypercholesterolemia (HoFH). HoFH is a rare condition but carries significant morbidity and mortality [7, 40]. Current lipid-lowering therapies including statins, ezetimibe, and PCSK9i have had limited success in the treatment of HoFH as they work in an LDL-R–dependent fashion. Evinacumab, which likely acts independently of LDL-R pathway, has shown potential as an effective therapy for this difficult to treat disease. In a single group open-label study of 9 patients with HoFH who were already on aggressive lipid-lowering therapy, treatment with evinacumab 250 mg SC on day 1 and then 15 m/kg IV on day 15 resulted in a mean reduction in LDL-C by 49 ± 23% at week 4 [41]. Preliminary data from a phase 3 randomized controlled trial of evinacumab in the treatment of HoFH, which have not yet been published as of the writing of this review, was presented at the American College of Cardiology 2020 Scientific Session [42]. The study enrolled patients with a diagnosis of HoFH (by at least 1 of the following criteria: homozygous mutations in both LDLR alleles; homozygous or compound heterozygous mutations in APOB or PCSK9; double heterozygous mutations or patients with homozygous LDLRAP1 mutations; untreated TC > 500 mg/dL and TG < 300 mg/dL; and both parents with history of TC > 250 mg/dL or cutaneous or tendinous xanthomas before age 10 years), and with LDL-C ≥ 70mg/dL on stable, maximally tolerated lipid-lowering therapy.

A total of 65 participants were randomized 2:1 to either evinacumab 15 mg/kg IV every 4 weeks or placebo IV every 4 weeks for 24 weeks. The mean baseline LDL-C was 259.5 mg/dL for the evinacumab group and 246.5 mg/dL for the placebo group. At 24 weeks, the least square (LS) mean difference for LDL-C percent change in the evinacumab group versus placebo was − 49.0 ± 8.0%, p < 0.0001. The LS mean difference of absolute change in LDL-C was − 132.1 ± 21.5 mg/dL, p < 0.0001. Importantly, the significant effect was observed even among individuals with null/null mutations. A significant LS mean reduction was also observed in TC (− 48.4%, p < 0.0001), apoB (− 36.9%, p < 0.0001), non-HDL-C (− 51.7%, p < 0.0001), and triglycerides (− 50.4%, p < 0.0001). With regard to safety, there were numerically less TEAEs in the evinacumab compared with the placebo group (65.9% vs 81.0%). However, there were numerically more, though rare, serious adverse events (SAEs) in the evinacumab group compared with placebo (4.5% vs 0%).

ApoC3

A causal relationship between TRL, including very low-density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and remnant particles, with ASCVD is suggested in Mendelian randomization studies [5, 43]. Though elevated serum TG represent a marker for ASCVD risk, it is not clear if the TGs within these lipoprotein particles directly lead to atherogenesis or if other properties of the TRL including size and cholesterol content are more contributory [44]. For instance, larger TG-rich particles such as chylomicrons are too large to cross arterial walls; smaller TRLs such as remnant particles are thought to be atherogenic [45, 46]. Severely elevated TGs can also lead to acute pancreatitis, which confers significant morbidity and mortality.

ApoC3 is glycoprotein present on VLDL, LDL, Lp(a), and HDL particles. It is a key regulator of TRL metabolism via inhibition of lipoprotein lipase (LPL) activity and interference of hepatic uptake of TRL likely by disruption of binding to LDLR [47, 48]. In genetic studies, heterozygous carriers of LOF mutations of APOC3 were found to have 46% lower levels of APOC3, 39% lower TG level, and 40% lower risk for CHD compared with non-carriers [49]. In models adjusted for age and sex, each reduction of apoC3 by 1 mg/dL was estimated to be associated with 4% risk reduction in CHD.

Volanesorsen is a subcutaneously injected ASO against apoC3 mRNA. In a phase 2, dose-ranging trial, 57 patients with untreated hypertriglyceridemia (350 to 2000 mg/dL) or treated hypertriglyceridemia (225 to 2000 mg/dL) on stable fibrate therapy were randomized to doses from 100 to 300 mg of volanesorsen or placebo every week for 13 weeks [50]. The mean baseline TG in the untreated cohort was 581 ± 291mg/dL and 376 ± 188mg/dL in the fibrate-treated cohort. Treatment with volanesorsen resulted in a dose-dependent reduction in apoC3 level of up to approximately 80% with a concurrent reduction of TG of approximately 71%. Furthermore, the inhibition of APOC3 by volanesorsen was found to lower apoC3 on apoB-100, Lp(a) and apolipoprotein A-I (apoA-I) lipoproteins, plasma levels of apoC2, triacylglycerols and diacylglycerols as well as increase levels of apoA-I, apoA-2, and apoM, and improved insulin sensitivity [51, 52].

Volanesorsen has further been studied in 2 phase 3 trials in patients with severely elevated TGs. In the APPROACH trial, 66 patients with familial chylomicronemia syndrome (FCS) with median fasting TG 1985 mg/dL were randomized to weekly volanesorsen 300 mg administered subcutaneously vs placebo over 52 weeks. At 3 months, there was a significant mean reduction of apoC3 by 84% observed in the volanesorsen group vs 6.1% increase in the placebo group [19]. Patients on treatment showed a 77% decrease in mean TGs compared with 18% increase in the placebo group. However, there was a significant number of patients in the treatment group with thrombocytopenia (15 of 33 with plt < 100,000 and 2 patients with platelets < 25,000 per microliter). In the COMPASS trial, 113 patients with baseline TG ≥ 500mg/dL were randomized 2:1 to receive subcutaneous volanesorsen vs placebo for 26 weeks. At 3 months, patients on volanesorsen achieved an approximately 73% reduction in TG compared with 2% mean reduction in those treated with placebo [53]. There was further a significant reduction in pancreatitis in the volanesorsen group compared with placebo in the APPROACH and COMPASS trials [54]. A retrospective survey of 22 patients with FCS treated with volanesorsen suggests an improvement in symptoms including steatorrhea, pancreatic pain, and emotional stress [55]. Due to concern over thrombocytopenia, volanesorsen was not approved for commercial use by the Food and Drug Administration but was approved by the European Medicines Agency (EMA).

Another ASO therapy against apoC3 is currently under investigation. This new-generation design incorporates the GalNac conjugate allowing localization of drug to the liver. In multi-dose dose-escalation trial (15 or 30 mg weekly or 60 mg every 4 weeks administered subcutaneously) over 3 months, AKCEA-APOCIII-LRx was found to reduce TG by up to 73% (in the 30 mg weekly group) after 43 days [18]. Moreover, non-HDL-C was reduced up to 30.7%, LDL-C was reduced up to 21.6%, and HDL-C increased up to 75.8% (all in the 60 mg every 4 weeks group). Overall, the study drug was well tolerated with similar rates of TEAE between groups and without evidence of significant thrombocytopenia.

Finally, ARO-APOC3 is a siRNA biologic that is in early stage clinical trial. In a phase 1/2 a single dose-ranging study, 40 healthy volunteers with fasting TG > 80 mg/dL were randomized to either treatment or placebo. The reduction in TG and VLDL-C was 41–55% and 42–53% respectively after 16 weeks. There were not serious adverse events noted during the study [8].

Lp(a)

Lp(a) has been shown to be a risk factor for atherosclerosis in epidemiology, and Mendelian randomization studies suggest a likely causal association between elevated Lp(a) levels and premature ASCVD [56,57,58,59,60,61,62]. In a large epidemiological study, association between Lp(a) and CHD appeared to be curvilinear, with increased relative risk (RR) of CHD estimated to be 1.13, 95% CI 1.09–1.18 per 3.5-fold (1 SD) increase in Lp(a) after adjustment for traditional risk factors including total cholesterol [63]. It is a cholesterol-rich lipoprotein bound by apoB in addition to apoliprotein (a) (apo [a]), which is encoded by the LPA gene and contains from 3 to > 50 kringle motifs similar to those found on plasminogen but does not have any fibrinolytic activity. These molecular properties are thought to contribute to increased atherothrombotic properties. Moreover, Lp(a) has been shown to bind oxidized phospholipids and localize within the arterial wall, contributing to increased inflammation and atherogenesis. Lp(a) level is strongly determined by genetics with genotype accounting for 90% of the plasma concentration [64].

With growing recognition of Lp(a) as a risk factor for ASCVD, testing for Lp(a) has made its way into mainstream cardiology practice. In a European Society of Cardiology (ESC) consensus document, screening for Lp(a) is recommended in those with elevated CVD/CHD risk [64]. The 2018 Multi-society Guideline on the Management of Blood Cholesterol has included Lp(a) ≥ 50 mg/dL or ≥ 125 nmol/L (if measured) as a risk-enhancing factor [65]. Currently, therapies that lower Lp(a) levels are limited. Niacin decreases Lp(a) level but is not always well tolerated and has limited use in patients with diabetes mellitus. PCSK9 inhibitors have also demonstrated some efficacy in reducing Lp(a), but the degree of reduction may not be sufficient in significantly impacting progression of atherosclerosis and reducing ASCVD risk independent of effect on LDL-C [66,67,68].

The development of an ASO against apo(a), AKCEA-APO(a)-LRx, provides a potential means of directly targeting Lp(a). In a phase 2 dose-ranging, randomized, placebo-controlled trial involving 286 participants with established CVD and Lp(a) of 150 nmol/L were randomized 5:1 to receive subcutaneous AKCEA-APO(a)-LRx (20, 40, or 60 mg every 4 weeks; 20 mg every 2 weeks; or 20 mg every week) or placebo for 6 to 12 months [69]. The median baseline Lp(a) levels in the different groups ranged from 205 to 247 nmol/L. A dose-dependent response in decrease in Lp(a) was observed. The maximum mean decrease in Lp(a) was 80% at 6 months, observed with the 20 mg every week dosing. Mean percent decreases of Lp(a) among other dosing regimen ranged from 35 to 72% compared with 6% observed with placebo at 6 months. Adverse events occurred in 90% of patients in the treatment groups and 83% of those in the placebo group. Serious adverse events occurred in 10% of patients receiving active therapy and 2% of those receiving placebo. The most common adverse side effect was injection site reactions. There were no significant changes in platelet, renal, or liver functions observed. Genetic and epidemiological data predicts decrease in risk for coronary artery disease with pharmacologic reduction of Lp(a) among patients with high levels [70]. However, a Mendelian randomization analysis showed that Lp(a) concentration may need to be lowered significantly, approximately by 100 mg/dL in order to achieve the same level in CHD risk reduction as can be achieved by lowering LDL-C by ~ 39 mg/dL [58]. The phase 3 outcome study of AKCEA-APO(a)-LRx, Lp(a)HORIZON, is currently underway to assess the efficacy and safety of this agent in the reduction of ASCVD risk. The trial has an estimated enrollment of over 7000 participants with established ASCVD, Lp(a) ≥ 70mg/dL at screening, and on optimal LDL-C– lowering therapy [71]. Lastly, the phase 1 study of the siRNA agent targeting Lp(a), AMG890, is being conducted [72].

Future Directions

While LDL-C remains an important contributor to ASCVD risk, genetic studies coupled with large epidemiological data have identified other causal risk factors including TRLs and Lp(a), which have in turn become therapeutic targets for novel drug development. There is a wide array of biotechnological therapies under clinical investigation. The therapies discussed above have demonstrated powerful effect in the reduction of targeted lipid parameters in short-term studies. Outside of PCSK9i mAbs, these agents still require validation in reducing ASCVD risk in cardiovascular outcome trials and must demonstrate safety in long-term studies. Moreover, there remains a need for therapies that address high-risk primary prevention, and future studies are warranted to assess the utility of the above novel agents in this patient population. Aside from the significant reduction in lipids, the advantage of these agents compared with small molecule medications is the duration of effect, which allows for longer duration between doses and has the potential of improving medication adherence. In fact, in the case of gene-editing therapies, patients may only need a single treatment which will last for life.

One important consideration for these new technologies will be cost-effectiveness, which can impact their scope of use. These agents will likely be first used in patients with the highest risk for ASCVD, i.e., high-risk secondary prevention patients or patients with FH. As the field of cardiac prevention continues to evolve, a more personalized approach may include more detailed characterization of a patient’s dyslipidemia and ASCVD risk profile through deep phenotyping or genotyping, which can then dictate the regimen of the most effective lipid-lowering therapies.