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Proprotein convertases (PCs), including furin and PC1/3 among nine mammalian homologues, mediate the maturation of numerous secreted substrates by proteolytic cleavage. Disbalance of PC activity is associated with diseases like cancer, fibrosis, neurodegeneration and infections. Therefore, PCs are promising drug targets for the treatment of many diseases. However, the highly conserved active site of PCs complicates the development of specific inhibitors. Here we investigate the activation mechanism of PCs using X-ray crystallography and biochemical methods. The structure-based optimization of the multibasic secondary cleavage site loop not only prevents the prodomain’s proteolytic cleavage but also increases its inhibition of furin. Combination of cleavage-resistant PC1/3-prodomain variants and a furin-specific nanobody in fusion proteins reveal very potent inhibitors (K i  = 1.2 pM) with a more than 25,000-fold higher specificity for furin compared to the closely related PC-member PCSK5. Such fusion proteins effectively suppress the replication of a furin-dependent H7N7-influenza virus in cell-based assays. In this work, the authors investigate the activation mechanism of proprotein convertases (PC) based on the PC1/3-prodomain and the PC furin. They engineer a prodomain-nanobody fusion protein that effectively blocks propagation of a H7N7 bird flu virus.

In a phase 1 trial, healthy volunteers were assigned to an RNAi therapeutic inhibitor of PCSK9 or placebo. Single doses of 300 mg or more reduced LDL cholesterol by up to 50%; multiple-dose regimens reduced LDL cholesterol by up to 59%. No serious adverse events were reported. An elevated level of low-density lipoprotein (LDL) cholesterol is a major risk factor for cardiovascular disease. 1 Despite the use of statin therapy, alone or in combination with other lipid-lowering medications, many at-risk patients continue to have elevated levels of LDL cholesterol. 2 – 4 Hence, there is a need for additional treatment options for lowering of the LDL cholesterol level to reduce cardiovascular risk. Proprotein convertase subtilisin–kexin type 9 (PCSK9) is a recently identified but well-validated target for LDL cholesterol–lowering therapy. 5 This serine protease, which is expressed and secreted into the bloodstream predominantly by the liver, binds LDL receptors both intracellularly and . . .

A monoclonal antibody to PCSK9 was studied in two single-dose trials in healthy volunteers and one multiple-dose trial in patients with familial or nonfamilial hypercholesterolemia. In all three groups, the antibody reduced levels of LDL cholesterol. In 2003, Abifadel and colleagues 1 described two families with autosomal dominant hypercholesterolemia that was associated with gain-of-function mutations in proprotein convertase subtilisin/kexin 9 (PCSK9), one of the serine proteases. These patients had high plasma levels of low-density lipoprotein (LDL) cholesterol, which was associated with an increased incidence of coronary heart disease. Shortly thereafter, studies of animal models identified a role for PCSK9 in the post-translational regulation of LDL-receptor activity. 2 , 3 PCSK9, which is synthesized primarily in the liver, enters the circulation, where it binds to hepatic LDL receptors and targets them for degradation. This process reduces the capacity of the . . .

In six trials comparing the anti–PCSK9 antibody bococizumab with placebo, the reduction in LDL cholesterol at 12 weeks was 55.2 percentage points lower with bococizumab. However, antidrug antibodies that developed in many patients reduced the magnitude of the reduction. Reducing levels of low-density lipoprotein (LDL) cholesterol with statin therapy is a highly effective method for reducing cardiovascular risk. 1 Trial data, observational studies, and genetic analyses indicate that further reductions in LDL cholesterol levels are likely to confer greater cardiovascular benefits. 2 – 4 Yet, recent studies have shown wide variability in the individual response of patients to statin therapy in terms of the percent reduction in LDL cholesterol levels. 5 , 6 Inhibitors of proprotein convertase subtilisin–kexin type 9 (PCSK9) reduce plasma LDL cholesterol levels by slowing PCSK9-mediated degradation of the LDL receptor. 7 Fully human monoclonal antibodies such as alirocumab and evolocumab that . . .

Abstract The kexin-like proprotein convertases perform the initial proteolytic cleavages that ultimately generate a variety of different mature peptide and proteins, ranging from brain neuropeptides to endocrine peptide hormones, to structural proteins, among others. In this review, we present a general introduction to proprotein convertase structure and biochemistry, followed by a comprehensive discussion of each member of the kexin-like subfamily of proprotein convertases. We summarize current knowledge of human proprotein convertase insufficiency syndromes, including genome-wide analyses of convertase polymorphisms, and compare these to convertase null and mutant mouse models. These mouse models have illuminated our understanding of the roles specific convertases play in human disease and have led to the identification of convertase-specific substrates; for example, the identification of procorin as a specific PACE4 substrate in the heart. We also discuss the limitations of mouse null models in interpreting human disease, such as differential precursor cleavage due to species-specific sequence differences, and the challenges presented by functional redundancy among convertases in attempting to assign specific cleavages and/or physiological roles. However, in most cases, knockout mouse models have added substantively both to our knowledge of diseases caused by human proprotein convertase insufficiency and to our appreciation of their normal physiological roles, as clearly seen in the case of the furin, proprotein convertase 1/3, and proprotein convertase 5/6 mouse models. The creation of more sophisticated mouse models with tissue- or temporally-restricted expression of specific convertases will improve our understanding of human proprotein convertase insufficiency and potentially provide support for the emerging concept of therapeutic inhibition of convertases. Graphical Abstract

Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to LDL receptors, leading to their degradation. Genetics studies have shown that loss-of-function mutations in PCSK9 result in reduced plasma LDL cholesterol and decreased risk of coronary heart disease. We aimed to investigate the safety and efficacy of ALN-PCS, a small interfering RNA that inhibits PCSK9 synthesis, in healthy volunteers with raised cholesterol who were not on lipid-lowering treatment. We did a randomised, single-blind, placebo-controlled, phase 1 dose-escalation study in healthy adult volunteers with serum LDL cholesterol of 3·00 mmol/L or higher. Participants were randomly assigned in a 3:1 ratio by computer algorithm to receive one dose of intravenous ALN-PCS (with doses ranging from 0·015 to 0·400 mg/kg) or placebo. The primary endpoint was safety and tolerability of ALN-PCS. Secondary endpoints were the pharmacokinetic characteristics of ALN-PCS and its pharmacodynamic effects on PCSK9 and LDL cholesterol. Study participants were masked to treatment assignment. Analysis was per protocol and we used ANCOVA to analyse pharmacodynamic endpoint data. This trial is registered with ClinicalTrials.gov, number NCT01437059. Of 32 participants, 24 were randomly allocated to receive a single dose of ALN-PCS (0·015 mg/kg [n=3], 0·045 mg/kg [n=3], 0·090 mg/kg [n=3], 0·150 mg/kg [n=3], 0·250 mg/kg [n=6], or 0·400 mg/kg [n=6]) and eight to placebo. The proportions of patients affected by treatment-emergent adverse events were similar in the ALN-PCS and placebo groups (19 [79%] vs seven [88%]). ALN-PCS was rapidly distributed, with peak concentration and area under the curve (0 to last measurement) increasing in a roughly dose-proportional way across the dose range tested. In the group given 0·400 mg/kg of ALN-PCS, treatment resulted in a mean 70% reduction in circulating PCSK9 plasma protein (p<0·0001) and a mean 40% reduction in LDL cholesterol from baseline relative to placebo (p<0·0001). Our results suggest that inhibition of PCSK9 synthesis by RNA interference (RNAi) provides a potentially safe mechanism to reduce LDL cholesterol concentration in healthy individuals with raised cholesterol. These results support the further assessment of ALN-PCS in patients with hypercholesterolaemia, including those being treated with statins. This study is the first to show an RNAi drug being used to affect a clinically validated endpoint (ie, LDL cholesterol) in human beings. Alnylam Pharmaceuticals.

Patients with hyperlipidemia were assigned to receive the PCSK9 antibody evolocumab or placebo on a background of lipid-lowering therapy. At 52 weeks, the least-squares mean reduction in LDL cholesterol from baseline for evolocumab versus placebo was 57%. Proprotein convertase subtilisin/kexin type 9 (PCSK9), a serine protease that is produced predominantly in the liver, is secreted into the plasma and plays a major role in regulating levels of low-density lipoprotein (LDL) cholesterol by binding to hepatic LDL receptors and promoting their degradation. 1 , 2 In short-term (8-to-12-week), placebo-controlled, phase 2 trials, PCSK9 inhibitors have been shown to significantly reduce LDL cholesterol levels. 3 – 9 Four of these trials involved the use of evolocumab (AMG 145), a fully human monoclonal PCSK9 antibody, and assessed different doses and regimens in diverse patient populations with varying lipid phenotypes, cardiovascular disease risks, and baseline . . .

Inclisiran, a small interfering RNA that targets PCSK9 mRNA, was given as a single injection at baseline or in two doses at baseline and 90 days. At 180 days, LDL cholesterol was significantly lowered among persons at high cardiovascular risk who had elevated levels at baseline. Low-density lipoprotein (LDL) cholesterol is a causal factor in atherosclerotic cardiovascular disease. Statins have been shown to reduce LDL cholesterol levels and cardiovascular events in large outcome trials, findings that have made them the therapeutic cornerstone of clinical practice. 1 Despite the proven efficacy of statins, there is considerable variability in individual responses to these drugs. 2 Furthermore, some observational data suggest that as many as half of persons who begin statin therapy discontinue it within a year. 3 Moreover, among patients receiving statin therapy who are at high risk for cardiovascular disease and who have persistent elevation of LDL cholesterol levels, the . . .

The European Atherosclerosis Society Familial Hypercholesterolaemia Studies Collaboration (FHSC) global registry provides a platform for the global surveillance of familial hypercholesterolaemia through harmonisation and pooling of multinational data. In this study, we aimed to characterise the adult population with heterozygous familial hypercholesterolaemia and described how it is detected and managed globally. Using FHSC global registry data, we did a cross-sectional assessment of adults (aged 18 years or older) with a clinical or genetic diagnosis of probable or definite heterozygous familial hypercholesterolaemia at the time they were entered into the registries. Data were assessed overall and by WHO regions, sex, and index versus non-index cases. Of the 61 612 individuals in the registry, 42 167 adults (21 999 [53·6%] women) from 56 countries were included in the study. Of these, 31 798 (75·4%) were diagnosed with the Dutch Lipid Clinic Network criteria, and 35 490 (84·2%) were from the WHO region of Europe. Median age of participants at entry in the registry was 46·2 years (IQR 34·3–58·0); median age at diagnosis of familial hypercholesterolaemia was 44·4 years (32·5–56·5), with 40·2% of participants younger than 40 years when diagnosed. Prevalence of cardiovascular risk factors increased progressively with age and varied by WHO region. Prevalence of coronary disease was 17·4% (2·1% for stroke and 5·2% for peripheral artery disease), increasing with concentrations of untreated LDL cholesterol, and was about two times lower in women than in men. Among patients receiving lipid-lowering medications, 16 803 (81·1%) were receiving statins and 3691 (21·2%) were on combination therapy, with greater use of more potent lipid-lowering medication in men than in women. Median LDL cholesterol was 5·43 mmol/L (IQR 4·32–6·72) among patients not taking lipid-lowering medications and 4·23 mmol/L (3·20–5·66) among those taking them. Among patients taking lipid-lowering medications, 2·7% had LDL cholesterol lower than 1·8 mmol/L; the use of combination therapy, particularly with three drugs and with proprotein convertase subtilisin–kexin type 9 inhibitors, was associated with a higher proportion and greater odds of having LDL cholesterol lower than 1·8 mmol/L. Compared with index cases, patients who were non-index cases were younger, with lower LDL cholesterol and lower prevalence of cardiovascular risk factors and cardiovascular diseases (all p<0·001). Familial hypercholesterolaemia is diagnosed late. Guideline-recommended LDL cholesterol concentrations are infrequently achieved with single-drug therapy. Cardiovascular risk factors and presence of coronary disease were lower among non-index cases, who were diagnosed earlier. Earlier detection and greater use of combination therapies are required to reduce the global burden of familial hypercholesterolaemia. Pfizer, Amgen, Merck Sharp & Dohme, Sanofi–Aventis, Daiichi Sankyo, and Regeneron.

A novel severe acute respiratory syndrome (SARS)-like coronavirus (SARS-CoV-2) is causing the global coronavirus disease 2019 (COVID-19) pandemic. Understanding how SARS-CoV-2 enters human cells is a high priority for deciphering its mystery and curbing its spread. A virus surface spike protein mediates SARS-CoV-2 entry into cells. To fulfill its function, SARS-CoV-2 spike binds to its receptor human ACE2 (hACE2) through its receptor-binding domain (RBD) and is proteolytically activated by human proteases. Here we investigated receptor binding and protease activation of SARS-CoV-2 spike using biochemical and pseudovirus entry assays. Our findings have identified key cell entry mechanisms of SARS-CoV-2. First, SARS-CoV-2 RBD has higher hACE2 binding affinity than SARS-CoV RBD, supporting efficient cell entry. Second, paradoxically, the hACE2 binding affinity of the entire SARS-CoV-2 spike is comparable to or lower than that of SARS-CoV spike, suggesting that SARS-CoV-2 RBD, albeit more potent, is less exposed than SARS-CoV RBD. Third, unlike SARS-CoV, cell entry of SARS-CoV-2 is preactivated by proprotein convertase furin, reducing its dependence on target cell proteases for entry. The high hACE2 binding affinity of the RBD, furin preactivation of the spike, and hidden RBD in the spike potentially allow SARS-CoV-2 to maintain efficient cell entry while evading immune surveillance. These features may contribute to the wide spread of the virus. Successful intervention strategies must target both the potency of SARS-CoV-2 and its evasiveness.