Effects of anacetrapib on plasma lipids, apolipoproteins and PCSK9 in healthy, lean rhesus macaques

Generation and Characterization of a Novel Small Biologic Alternative to Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Antibodies, DS-9001a, Albumin Binding Domain-Fused Anticalin Protein

Since it was recently reported that an antibody for proprotein convertase subtilisin/kexin type 9 (PCSK9) reduces the risk of cardiovascular events in a clinical context, PCSK9 inhibition is thought to be an attractive therapy for dyslipidemia. In the present study, we created a novel small biologic alternative to PCSK9 antibodies called DS-9001a, comprising an albumin binding domain fused to an artificial lipocalin mutein (ABD-fused Anticalin protein), which can be produced by a microbial production system. DS-9001a strongly interfered with PCSK9 binding to low-density-lipoprotein receptor (LDL-R) and PCSK9-mediated degradation of LDL-R. In cynomolgus monkeys, single DS-9001a administration significantly reduced the serum LDL-C level up to 21 days (62.4% reduction at the maximum). Moreover, DS-9001a reduced plasma non-high-density-lipoprotein cholesterol and oxidized LDL levels, and their further reductions were observed when atorvastatin and DS-9001a were administered in combination in human cholesteryl ester transfer protein/ApoB double transgenic mice. Additionally, their reductions on the combination of atorvastatin and DS-9001a were more pronounced than those on the combination of atorvastatin and anacetrapib. Besides its favorable pharmacologic profile, DS-9001a has a lower molecular weight (about 22 kDa), yielding a high stoichiometric drug concentration that might result in a smaller administration volume than that in existing antibody therapy. Since bacterial production systems are viewed as more suited to mass production at low cost, DS-9001a may provide a new therapeutic option to treat patients with dyslipidemia. In addition, considering the growing demand for antibody-like drugs, ABD-fused Anticalin proteins could represent a promising new class of small biologic molecules.

Effect of atorvastatin, cholesterol ester transfer protein inhibition, and diabetes mellitus on circulating proprotein subtilisin kexin type 9 and lipoprotein(a) levels in patients at high cardiovascular risk

BACKGROUND

Proprotein subtilisin kexin type 9 (PCSK9) and lipoprotein (a) [Lp(a)] levels are causative risk factors for coronary heart disease.

OBJECTIVES

The objective of the study was to determine the impact of lipid-lowering treatments on circulating PCSK9 and Lp(a).

METHODS

We measured PCSK9 and Lp(a) levels in plasma samples from Investigation of Lipid Level Management to Understand its Impact in Atherosclerotic Events trial patients with coronary heart disease and/or type II diabetes (T2D) mellitus. Patients received atorvastatin, which was titrated (10, 20, 40, or 80 mg/d) to achieve low-density lipoprotein cholesterol levels <100 mg/dL (baseline) and were subsequently randomized either to atorvastatin + torcetrapib, a cholesterol ester transfer protein inhibitor, or to atorvastatin + placebo.

RESULTS

At baseline, both plasma PCSK9 and Lp(a) were dose-dependently increased with increasing atorvastatin doses. Compared with patients without T2D, those with T2D had higher PCSK9 (357 ± 123 vs 338 ± 115 ng/mL, P = .0012) and lower Lp(a) levels (28 ± 32 vs 32 ± 33 mg/dL, P = .0005). Plasma PCSK9 levels significantly increased in patients treated with torcetrapib (+13.1 ± 125.3 ng/mL [+3.7%], P = .005), but not in patients treated with placebo (+2.6 ± 127.9 ng/mL [+0.7%], P = .39). Plasma Lp(a) levels significantly decreased in patients treated with torcetrapib (-3.4 ± 10.7 mg/dL [-11.1%], P < .0001), but not in patients treated with placebo (+0.3 ± 9.4 mg/dL [+0.1%], P = .92).

CONCLUSION

In patients at high cardiovascular disease risk, PCSK9 and Lp(a) are positively and dose-dependently correlated with atorvastatin dosage, whereas the presence of T2D is associated with higher PCSK9 but lower Lp(a) levels. Cholesterol ester transfer protein inhibition with torcetrapib slightly increases PCSK9 levels and decreases Lp(a) levels.

Dose-dependent effects of siRNA-mediated inhibition of SCAP on PCSK9, LDLR, and plasma lipids in mouse and rhesus monkey

SREBP cleavage-activating protein (SCAP) is a key protein in the regulation of lipid metabolism and a potential target for treatment of dyslipidemia. SCAP is required for activation of the transcription factors SREBP-1 and -2. SREBPs regulate the expression of genes involved in fatty acid and cholesterol biosynthesis, and LDL-C clearance through the regulation of LDL receptor (LDLR) and PCSK9 expression. To further test the potential of SCAP as a novel target for treatment of dyslipidemia, we used siRNAs to inhibit hepatic SCAP expression and assess the effect on PCSK9, LDLR, and lipids in mice and rhesus monkeys. In mice, robust liver Scap mRNA knockdown (KD) was achieved, accompanied by dose-dependent reduction in SREBP-regulated gene expression, de novo lipogenesis, and plasma PCSK9 and lipids. In rhesus monkeys, over 90% SCAP mRNA KD was achieved resulting in approximately 75, 50, and 50% reduction of plasma PCSK9, TG, and LDL-C, respectively. Inhibition of SCAP function was demonstrated by reduced expression of SREBP-regulated genes and de novo lipogenesis. In conclusion, siRNA-mediated inhibition of SCAP resulted in a significant reduction in circulating PCSK9 and LDL-C in rodent and primate models supporting SCAP as a novel target for the treatment of dyslipidemia.

Circulating PCSK9 levels and CETP plasma activity are independently associated in patients with metabolic diseases

BACKGROUND

PCSK9 inhibition is a new powerful cholesterol-lowering strategy. Recently, it was reported that CETP inhibitors influence PCSK9 levels as an off-target effect. We explored the relationship between circulating PCSK9 levels and CETP activity in patients with metabolic disease who were not on lipid-lowering therapy.

METHODS

Plasma CETP activity and PCSK9 levels were measured in 450 participants (median age, 58 years; 49 % women) who attended the metabolism unit because of metabolic syndrome (MetS) (78 %), atherogenic dyslipidemia (32 %), obesity (50 %), type 2 diabetes mellitus (72 %), and other risk factors (13 %). A 6 week lipid-lowering drug wash-out period was established in treated patients.

RESULTS

Both PCSK9 levels and CETP activity were higher in patients with an increasing number of MetS components. PCSK9 levels were positively correlated with CETP activity in the entire cohort (r = 0.256, P < 0.0001) independent of age, gender, body mass index (BMI), systolic blood pressure (SBP), LDL cholesterol (LDL-C), triglycerides and glucose. Individuals with the loss-of-function PCSK9 genetic variant rs11591147 (R46L) had lower levels of PCSK9 (36.5 %, P < 0.0001) and LDL-C (17.8 %, P = 0.010) as well as lower CETP activity (10.31 %, P = 0.009). This association remained significant in the multiple regression analysis even after adjusting for gender, age, BMI, LDL-C, triglycerides, glucose, lecithin-cholesterol acyltransferase, SBP and MetS (P = 0.003).

CONCLUSIONS

Our data suggest a metabolic association between PCSK9 and CETP independent of lipid-lowering treatment. The clinical implications of this metabolic relationship could be relevant for explaining the effect of PCSK9 and CETP inhibition on overall lipid profiles.

Proprotein convertase subtilisin kexin type 9 and high-density lipoprotein metabolism: experimental animal models and clinical evidence

Proprotein convertase subtilisin kexin type 9 (PCSK9) belongs to the proprotein convertase family. Several studies have demonstrated its involvement in the regulation of low-density lipoprotein (LDL) cholesterol levels by inducing the degradation of the LDL receptor (LDLR). However, experimental, epidemiologic, and pharmacologic data provide important evidence on the role of PCSK9 also on high-density lipoproteins (HDLs). In mice, PCSK9 regulates the HDL cholesterol (HDL-C) levels by the degradation of hepatic LDLR, thus inhibiting the uptake of apolipoprotein (Apo)E-containing HDLs. Several epidemiologic and genetic studies reported positive relationship between PCSK9 and HDL-C levels, likely by reducing the uptake of the ApoE-containing HDL particles. PCSK9 enhances also the degradation of LDLR's closest family members, ApoE receptor 2, very low-density lipoprotein receptor, and LDLR-related protein 1. This feature provides a molecular mechanism by which PCSK9 may affect HDL metabolism. Experimental studies demonstrated that PCSK9 directly interacts with HDL by modulating PCSK9 self-assembly and its binding to the LDLR. Finally, the inhibition of PCSK9 by means of monoclonal antibodies directed to PCSK9 (ie, evolocumab and alirocumab) determines an increase of HDL-C fraction by 7% and 4.2%, respectively. Thus, the understanding of the role of PCSK9 on HDL metabolism needs to be elucidated with a particular focus on the effect of PCSK9 on HDL-mediated reverse cholesterol transport.

Disposition into Adipose Tissue Determines Accumulation and Elimination Kinetics of the Cholesteryl Ester Transfer Protein Inhibitor Anacetrapib in Mice

The cholesteryl ester transfer protein (CETP) inhibitor anacetrapib exhibits a long terminal half-life (t½) in humans; however, the dispositional mechanisms that lead to this long t½ are still being elucidated. As it is hypothesized that disposition into adipose tissue and binding to CETP might play a role, we sought to delineate the relative importance of these factors using a preclinical animal model. A multiple-dose pharmacokinetic study was conducted in C57BL6 wild-type (WT) lean, WT diet-induced obese (DIO), natural flanking region (NFR) CETP-transgenic lean, and NFR-DIO mice. Mice were dosed orally with 10 mg/kg anacetrapib daily for 42 days. Drug concentrations in blood, brown and white adipose tissue, liver, and brain were measured up to 35 weeks postdose. During dosing, a 3- to 9-fold accumulation in 72-hour postdose blood concentrations of anacetrapib was observed. Drug concentrations in white adipose tissue accumulated ∼20- to 40-fold, whereas 10- to 17-fold accumulation occurred in brown adipose and approximately 4-fold in liver. Brain levels were very low (<0.1 μM), and a trend of accumulation was not seen. The presence of CETP as well as adiposity seems to play a role in determining the blood concentrations of anacetrapib. The highest blood concentrations were observed in NFR DIO mice, whereas the lowest concentrations were seen in WT lean mice. In adipose and liver tissue, higher concentrations were seen in DIO mice, irrespective of the presence of CETP. This finding suggests that white adipose tissue serves as a potential depot and that disposition into adipose tissue governs the long-term kinetics of anacetrapib in vivo.

Anacetrapib reduces (V)LDL cholesterol by inhibition of CETP activity and reduction of plasma PCSK9

Recently, we showed in APOE*3-Leiden cholesteryl ester transfer protein (E3L.CETP) mice that anacetrapib attenuated atherosclerosis development by reducing (V)LDL cholesterol [(V)LDL-C] rather than by raising HDL cholesterol. Here, we investigated the mechanism by which anacetrapib reduces (V)LDL-C and whether this effect was dependent on the inhibition of CETP. E3L.CETP mice were fed a Western-type diet alone or supplemented with anacetrapib (30 mg/kg body weight per day). Microarray analyses of livers revealed downregulation of the cholesterol biosynthesis pathway (P < 0.001) and predicted downregulation of pathways controlled by sterol regulatory element-binding proteins 1 and 2 (z-scores -2.56 and -2.90, respectively; both P < 0.001). These data suggest increased supply of cholesterol to the liver. We found that hepatic proprotein convertase subtilisin/kexin type 9 (Pcsk9) expression was decreased (-28%, P < 0.01), accompanied by decreased plasma PCSK9 levels (-47%, P < 0.001) and increased hepatic LDL receptor (LDLr) content (+64%, P < 0.01). Consistent with this, anacetrapib increased the clearance and hepatic uptake (+25%, P < 0.001) of [(14)C]cholesteryl oleate-labeled VLDL-mimicking particles. In E3L mice that do not express CETP, anacetrapib still decreased (V)LDL-C and plasma PCSK9 levels, indicating that these effects were independent of CETP inhibition. We conclude that anacetrapib reduces (V)LDL-C by two mechanisms: 1) inhibition of CETP activity, resulting in remodeled VLDL particles that are more susceptible to hepatic uptake; and 2) a CETP-independent reduction of plasma PCSK9 levels that has the potential to increase LDLr-mediated hepatic remnant clearance.

Anacetrapib lowers LDL by increasing ApoB clearance in mildly hypercholesterolemic subjects

BACKGROUND

Individuals treated with the cholesteryl ester transfer protein (CETP) inhibitor anacetrapib exhibit a reduction in both LDL cholesterol and apolipoprotein B (ApoB) in response to monotherapy or combination therapy with a statin. It is not clear how anacetrapib exerts these effects; therefore, the goal of this study was to determine the kinetic mechanism responsible for the reduction in LDL and ApoB in response to anacetrapib.

METHODS

We performed a trial of the effects of anacetrapib on ApoB kinetics. Mildly hypercholesterolemic subjects were randomized to background treatment of either placebo (n = 10) or 20 mg atorvastatin (ATV) (n = 29) for 4 weeks. All subjects then added 100 mg anacetrapib to background treatment for 8 weeks. Following each study period, subjects underwent a metabolic study to determine the LDL-ApoB-100 and proprotein convertase subtilisin/kexin type 9 (PCSK9) production rate (PR) and fractional catabolic rate (FCR).

RESULTS

Anacetrapib markedly reduced the LDL-ApoB-100 pool size (PS) in both the placebo and ATV groups. These changes in PS resulted from substantial increases in LDL-ApoB-100 FCRs in both groups. Anacetrapib had no effect on LDL-ApoB-100 PRs in either treatment group. Moreover, there were no changes in the PCSK9 PS, FCR, or PR in either group. Anacetrapib treatment was associated with considerable increases in the LDL triglyceride/cholesterol ratio and LDL size by NMR.

CONCLUSION

These data indicate that anacetrapib, given alone or in combination with a statin, reduces LDL-ApoB-100 levels by increasing the rate of ApoB-100 fractional clearance.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00990808.

FUNDING

Merck & Co. Inc., Kenilworth, New Jersey, USA. Additional support for instrumentation was obtained from the National Center for Advancing Translational Sciences (UL1TR000003 and UL1TR000040).