The role of low-density lipoproteins (LDLs) in the development of atherosclerotic disease is proven.1 Several approaches to lowering LDL-cholesterol (LDL-C) exist, including blocking dietary cholesterol absorption (ezetimibe) or restricting cholesterol synthesis (statins and bempedoic acid). All three of these medication types result in a decreased intracellular cholesterol concentration, which, in turn, activates LDL-receptor expression. As we have seen in the previous article (pages S7–S12), increasing the quantity or durability of LDL-receptors on the hepatocyte surface enhances LDL-C clearance from the bloodstream. Guidelines recommend statins as first-line pharmacotherapy for LDL-C reduction.2-4 However, statins, similar to ezetimibe and bempedoic acid, are small molecules requiring daily dosing. This necessitates optimal adherence from patients to achieve sustained LDL-C reductions and, thus, maximise cardiovascular (CV) benefit.5 However, several factors could impact adherence,6 and long-term reductions in LDL-C may be suboptimal.
Therapeutic inhibition of free proprotein convertase subtilisin/kexin type 9 (PCSK9) is now an established approach through which to achieve additional cholesterol-lowering, currently achieved through use of monoclonal antibodies (mAbs) that bind extracellular circulating PCSK9.7-9 Through bi-weekly or monthly self-injections, PCSK9 mAbs can achieve a reduction of approximately 60% in LDL-C from baseline.3,8,9 However, the use of mAbs is limited to a narrow group of patients with very high cardiovascular risk and higher LDL-C levels in National Institute for Health and Care Excellence (NICE)2 and American Heart Association (AHA)/American College of Cardiology (ACC) 20184 guidelines. An alternate mechanism that targets PCSK9 has recently been developed, known as small-interfering RNA (siRNA). Inclisiran, the first in this class, inhibits PCSK9 synthesis at the mRNA level, preventing the translation of the message into the protein, thus, directly decreasing PCSK9 levels intra- and extracellularly, and indirectly LDL-C levels.10,11 Here, we review inclisiran’s positioning among lipid-lowering therapies, including mode of action, phase III clinical trial evidence, indication and potential impact on patient management.
Inclisiran’s mode of action and pharmacokinetics
In the liver, the double-stranded inclisiran siRNA molecules engage the intrinsic pathway of RNA interference.10,11 This process of RNA interference causes sequence-specific gene silencing and is an emerging approach to modulate protein expression.12 One strand – the guide strand – carries the information to recognise the target gene and reprogramme (silence) it; the second strand – the passenger strand – serves as a prodrug that helps loading into the RNA-induced silencing complex (RISC). Once the guide strand has entered the RISC, it cleaves the PCSK9 mRNA, making it unavailable for protein translation, resulting in decreased levels of the PCSK9 protein. A single siRNA-bound RISC is catalytic and cleaves many transcripts. This characteristic may be important during use of statins, which are known to up-regulate the production of PCSK9, potentially limiting the effectiveness of the drugs.10,11
Reducing PCSK9 levels in the circulation through reduced hepatic production decreases the likelihood of LDL-receptor (LDL-R) degradation, which results in an overall longer survival of LDL-R. Through a combination of statins and PCSK9-targeting medication, two factors enhancing LDL-C clearance can be targeted: the number of LDL-Rs (density) on the surface of hepatocytes and their longevity (figure 1). Hepatic PCSK9 production accounts for about 80% of circulating PCSK9.13 Whereas mAbs block plasma PCSK9, inclisiran interferes with its intracellular production in hepatocytes, targeting its principal source.13
Inclisiran is conjugated to a carbohydrate terminus, known as triantennary N-acetylgalactosamine (GalNAc). This facilitates uptake by hepatocytes through an asialoglycoprotein receptor highly expressed in the liver, which naturally recognises the GalNAc carbohydrate terminus often expressed in senescent cells. Adding GalNAc to the double-stranded synthetic RNA, thus, provides a highly efficient ligand, facilitating rapid uptake.10,11,14
After subcutaneous injection, plasma inclisiran concentrations reach peak approximately four hours post-dose, and reach undetectable levels within 48 hours post-dosing.14 Based on non-clinical data, inclisiran has been shown to have high uptake into and selectivity for the liver, the target organ for cholesterol-lowering.14
Inclisiran’s lipid-lowering effects
Dose finding and dosing frequency
The ORION-1 trial established the dose and dosing interval to be taken forward into phase III pivotal trials. The efficacy of different inclisiran dosing regimens was studied among 501 patients at high risk of atherosclerotic cardiovascular events (ASCVE) with elevated LDL-C levels despite receiving maximally tolerated statins.15 The primary end point of the study was the percentage change from baseline in LDL-C at month six (day 180). The greatest reduction in LDL-C (52.6%; 95% confidence interval [CI] −57.1 to −48.1; p<0.001) was seen with the two-dose 300 mg* regimen of inclisiran.15 In the one-year follow-up study to look at the time course to inform subsequent dosing,16 this regimen provided the greatest mean reduction in LDL-C over one year. The addition of a second dose at day 90 allowed for a 50% reduction in LDL-C to be maintained for at least six months (figure 2). Therefore, inclisiran administered at day one, day 90, and twice a year thereafter should enable patients to achieve stable and meaningful reductions in LDL-C. This dosing regimen was taken forward into phase III trials.16
*Note: In clinical studies the 284 mg inclisiran dose is equivalent and referred to as 300 mg inclisiran sodium salt
ORION-10 and -11: inclisiran in a secondary prevention population and patients at high risk of ASCVE
In the phase III trials of the ORION programme, inclisiran’s efficacy and safety were assessed among patients at high cardiovascular risk with a dosing regimen of 300 mg on day one, day 90 and every 180 days over 540 days.17,18
ORION-10 took place in the US and included 1,561 patients (mean age 66 years, 31% female) with ASCVD (secondary prevention). ORION-11 was conducted in Europe and South Africa and included 1,617 patients (mean age 65 years, 28% female) with established atherosclerotic cardiovascular disease (ASCVD) or very high-risk primary prevention because of familial hypercholesterolaemia (FH),** type 2 diabetes, or a combination of risk factors such that the 10-year risk of a cardiovascular event was ≥20% assessed by the Framingham Risk Score for Cardiovascular Disease or equivalent; 87% had manifest ASCVD and 13% ASCVD risk equivalent (primary prevention). The inclusion criteria were similar for both trials requiring an LDL-C ≥1.8 mmol/L for established ASCVD or ≥2.6 mmol/L in primary prevention despite maximally tolerated statin. Stable use of other lipid-lowering therapies was allowed but patients receiving treatment with PCSK9 inhibitors within 90 days before screening were excluded.
**Note: Inclisiran is not licensed in homozygous FH
In ORION-10, 89% received statin therapy at baseline (68% high-intensity statins) and 10% ezetimibe. In ORION-11, the majority of patients (95%) were on statin therapy at baseline, and 79% received high-intensity statins and 7% ezetimibe. Mean LDL-C levels at baseline were comparable in both trials at 2.7 ± 1.0 mmol/L. The co-primary end points in each trial were the placebo-corrected percentage change in LDL-C level from baseline to day 510 and the time-adjusted percentage change in LDL-C level from baseline after day 90 and up to day 540.
Percentage LDL-C reductions from baseline to day 510 compared with placebo, were 52.3% (95%CI 55.7 to 48.8; p<0.001) and 49.9% (95%CI 53.1 to 46.6; p<0.001) in ORION-10 and ORION-11, respectively. The mean between-group differences in absolute change from baseline to day 510 in the two trials were −1.40 mmol/L (95%CI −1.48 to −1.32; p<0.001) and −1.34 mmol/L (95%CI −1.42 to −1.26; p<0.001), respectively.
Looking at the time-adjusted percentage LDL-C reduction from baseline after day 90 and up to day 540, this was 53.8% (95%CI 56.2 to 51.3; p<0.001) in ORION-10 and 49.2% (95%CI 51.6 to 46.8; p<0.001) in ORION-11. The mean between-group differences in the time-adjusted absolute change in LDL-C level from baseline after day 90 and up to day 540 were −1.38 mmol/L (95%CI −1.44 to −1.31; p<0.001) and −1.26 mmol/L (95%CI −1.33 to −1.20; p<0.001), respectively.
ORION-9: inclisiran in patients with heterozygous FH
Heterozygous familial hypercholesterolaemia (HeFH) is a genetic condition with a prevalence in the region of one in 250.18 The three mainly affected genes code for LDL-R, apolipoprotein B (ApoB) and PCSK9.19 These genetic variants lead to high LDL-C levels and cause high risk of ASCVD and premature occurrence of coronary artery disease.19 Their high risk for ASCVD and insufficient LDL-C goal attainment through statin therapy alone often warrants the use of adjunct lipid-lowering treatments like PCSK9-targeting medications.
Inclisiran’s efficacy was assessed in HeFH in the ORION-9 trial, which included 482 patients with LDL-C ≥2.6 mmol/L despite background lipid-lowering therapy.18 Mean age was 56 years, 53% were women and mean baseline LDL-C levels were 4.0 ± 1.4 mmol/L. High-intensity statin therapy was prescribed to approximately three-quarters of patients, with more than half also receiving ezetimibe (56% in the inclisiran group and 50% in the placebo group). Percentage LDL-C reduction from baseline to day 510 compared with placebo, was 47.9% (95%CI 53.5 to 42.3; p<0.001). The mean between-group difference in absolute change in LDL-C from baseline to day 510 was 1.8 mmol/L (95%CI −2.0 to −1.6; p<0.001).
The between-group difference in time-averaged percentage change in the LDL-C level from baseline after day 90 and up to day 540 was −44.3% (95%CI −48.5 to −40.1; p<0.001). The between-group difference in time-averaged observed difference in LDL-C levels between day 90 and day 540 was −1.6 mmol/L (p<0.001). Importantly, LDL-C reduction by inclisiran was achieved irrespective of genetic background.
Pooled analysis of the ORION-9, -10, and -11 trials suggest no difference in treatment effect between patients with and without background lipid-lowering therapy or between statin intensity at baseline.20
As with all LDL-C treatments, inclisiran significantly reduced other potentially atherogenic lipids and lipoprotein levels like non-high-density lipoprotein cholesterol (non-HDL-C), ApoB, and lipoprotein(a), with the latter being assessed as an exploratory end point (table 1).20
Table 1. Inclisiran’s effect on lipids, lipoproteins and proprotein convertase subtilisin/kexin type 9 (PCSK9) (percentage change from baseline to day 510+)20
|Mean percentage change (95%CI) in the inclisiran group||Mean percentage change (95%CI) in the placebo group||p value|
|Total cholesterol||–29.5 (–30.4, –28.5)||3.0 (2.0, 3.9)||<0.001|
|Non-HDL-C||–42.6 (–43.9, –41.3)||3.7 (2.3, 5.0)||<0.001|
|HDL-C*||7.7 (–5, 19)||1.5 (–8, 13)||<0.0001|
|ApoB||–40.0 (–41.1, –38.9)||1.7 (0.6, 2.8)||<0.001|
|Lp(a)*+||–19.5 (–34, –2)||0.7 (–13, 20)||<0.0001|
|Triglycerides*||–13.3 (–33, 9)||–3.4 (–24, 22)||<0.0001|
|PCSK9||–65.0 (–67.1, –63.0)||15.9 (13.8, 18.0)||<0.001|
|*Reported values are median (Q1, Q3).
+For Lp(a) the percentage change is from baseline to day 540.
Key: ApoB = apolipoprotein B; CI = confidence interval; HDL-C = high-density lipoprotein cholesterol; Lp = lipoprotein; PCSK9 = proprotein convertase subtilisin/kexin type 9; Q = quartile
Safety and tolerability
The three phase III ORION trials provided safety data on a total of 5,274 patient-years of follow-up.20 A similar frequency of adverse events of any kind appeared in the inclisiran group (78.0%) and the placebo group (77.3%), which were mostly mild or moderate. Patients treated with inclisiran experienced more frequent reactions at the injection site (injection-site reaction, injection-site erythema, injection-site rash, injection-site pruritis, injection-site hypersensitivity) with 5.0% compared with 0.7% treated with placebo. All injection site reactions were non-persistent and of mild-to-moderate severity. If injection site reactions reoccurred, severity was mostly stable; an increase in severity was reported in 0.3% and a decrease in 0.2%. Liver and renal safety were similar between the inclisiran and placebo groups with similar platelet and creatinine kinase levels.
Inclisiran’s efficacy and tolerability among patients with renal impairment were assessed in ORION-7, a single-dose, open-label trial (n=31).21 Here, it was demonstrated that renal impairment did not influence the pharmacodynamic effects of inclisiran, and no dose adjustments are required in these patients, although use with caution is advised in patients with severe renal failure due to limited experience and haemodyalysis should not be performed for at least 72 hours after inclisiran dosing. Similar to patients with normal renal function, no circulating inclisiran could be detected in patient’s serum 48 hours post-injection.
Indications and contraindications
In December 2020, inclisiran was authorised for use in the European Union under the name Leqvio® for adults as an adjunct to diet and maximally tolerated statin therapy to treat primary hypercholesterolaemia (HeFH and non-familial) and mixed dyslipidaemia if LDL-C goals were not attained.14 In statin-intolerant patients, inclisiran may be used alone or in combination with other lipid-lowering treatments, e.g. ezetimibe. No dose adjustments or special precautions are recommended for elderly patients or those with mild-to-moderate liver or renal impairment, but haemodialysis should not be performed for at least 72 hours after inclisiran administration. Inclisiran should be used with caution in patients with severe hepatic impairment due to lack of data.
Inclisiran is contraindicated in patients with known hypersensitivity to the active substance or one of the other ingredients. Use of inclisiran during pregnancy is not recommended as no data exist. Similarly, there are no data on inclisiran use while breastfeeding. No harmful effects were observed during animal studies although animal studies suggest that inclisiran is secreted with the milk.
Inclisiran is a generally well-tolerated cholesterol-lowering agent, and with its long duration of efficacy, it may have significant implications for ASCVD prevention through sustained LDL-C lowering (figure 3). There remains an unmet need for effective combination therapy regimens as guideline-recommended LDL-C goal attainment is low,22 especially for those at highest risk of ASCVD for whom the lowest goals are advocated.23 For instance, in ORION-9, only 9% of patients assigned to placebo achieved LDL-C levels <2.6 mmol/L, despite maximally tolerated statin therapy, compared with 65.3% of patients treated with inclisiran. Furthermore, inclisiran’s long duration of effect and mode of administration may have additional benefits.
First, inclisiran’s long efficacy duration results in low LDL-C variability.16 Higher LDL-C variability, as seen in statin-treated patients, has been demonstrated to increase risk of ASCVD events independent of the achieved LDL-C reduction.24 Whether any benefit of low LDL-C variability in reducing the risk of ASCVD events exists remains to be determined.
Second, the low administration frequency brings a benefit known to facilitate patient’s adherence, namely reduced additional medication burden. The healthcare professional-led administration regimen can also ensure that the level of adherence to the regimen is known. Due to the rate of return of LDL-C to baseline being 2% per month,16 if a planned dose is missed by less than three months, inclisiran should be administered and dosing continued according to the patient’s original schedule.14
By improving patient adherence, long-acting agents have the potential to lower long-term exposure to LDL-C.25 Whether inclisiran treatment improves cardiovascular outcomes is being assessed in the ongoing ORION-4 trial, and first results are expected in 2024.
Inclisiran reduces LDL-C levels in addition to other lipid-lowering treatments by approximately 50%, with a modest risk of injection-site reactions. Through administration by healthcare professionals and with an infrequent dosing regimen, inclisiran may help to overcome the issues of poor medication adherence associated with other lipid-lowering medications and favourably impact population health.
- Inclisiran is a first-in-class lipid-lowering agent
- This small-interfering RNA lowers hepatic proprotein convertase subtilisin/kexin type 9 (PCSK9) synthesis by using the intrinsic cellular pathway of RNA interference
- Inclisiran has been shown to achieve an average low-density lipoprotein cholesterol (LDL-C) reduction of approximately 50% with an infrequent maintenance dosing regimen of two injections per year following initial doses at day one and day 90
- Inclisiran is effective and generally well tolerated among patients at high risk of cardiovascular events because of established atherosclerotic cardiovascular disease, heterozygous familial hypercholesterolaemia, or other high-risk conditions, like diabetes or high (i.e. ≥20%) 10-year risk estimated through a risk calculator
Conflicts of interest
JB receives research grant support from Astra Zeneca. KKR reports personal fees for consultancy from Abbvie, Amgen, Astra Zeneca, Sanofi, Regeneron MSD, Pfizer, Resverlogix, Akcea, Boehringer Ingelheim, Novo Nordisk, Takeda, Kowa, Algorithm, Cipla, Cerenis, Dr Reddys, Lilly, Zuellig Pharma, Bayer, Daiichi Sankyo, The Medicines Company; Esperion and research grant support from Pfizer, Amgen, Sanofi, Astra Zeneca, Regeneron and MSD.
KKR acknowledges support from the Imperial NIHR Biomedical Research Centre. The views expressed in this publication are those of the author(s) and not necessarily those of the National Institute for Health Research or the Department of Health and Social Care.
Research Associate (Imperial Centre for Cardiovascular Disease Prevention), and Clinical Researcher and Resident (University Hospital Aachen, Germany)
Kausik K Ray
Professor of Public Health, and Honorary Consultant Cardiologist
Imperial College London, Reynolds Building, St. Dunstan’s Road, London, W6 8RP
Articles in this supplement
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14. Novartis. Inclisiran summary of product characteristics. Available from: https://www.ema.europa.eu/en/documents/product-information/leqvio-epar-product-information_en.pdf
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16. Ray KK, Stoekenbroek RM, Kallend D et al. Effect of 1 or 2 doses of inclisiran on low-density lipoprotein cholesterol levels: one-year follow-up of the ORION-1 randomized clinical trial. JAMA Cardiol 2019;4:1067–75. https://doi.org/10.1001/jamacardio.2019.3502
17. Ray KK, Wright RS, Kallend D et al.; ORION-10 and ORION-11 Investigators. Two phase 3 trials of inclisiran in patients with elevated LDL cholesterol. N Engl J Med 2020;382:1507–19. https://doi.org/10.1056/NEJMoa1912387
18. Raal FJ, Kallend D, Ray KK et al. Inclisiran for the treatment of heterozygous familial hypercholesterolemia. N Engl J Med 2020;382:1520–30. https://doi.org/10.1056/NEJMoa1913805
19. Nordestgaard BG, Chapman MJ, Humphries SE et al. Familial hypercholesterolaemia is underdiagnosed and undertreated in the general population: guidance for clinicians to prevent coronary heart disease: consensus statement of the European Atherosclerosis Society. Eur Heart J 2013;34:3478–90. https://doi.org/10.1093/eurheartj/eht273
20. Wright RS, Ray KK, Raal FJ et al. Pooled patient-level analysis of inclisiran trials in patients with familial hypercholesterolemia or atherosclerosis. J Am Coll Cardiol 2021;77:1182–93. https://doi.org/10.1016/j.jacc.2020.12.058
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