VXX-401, a novel anti-PCSK9 vaccine, reduces LDL-C in cynomolgus monkeys

Abstract

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of disease burden in the world and is highly correlated with chronic elevations of LDL-C. LDL-C-lowering drugs, such as statins or monoclonal antibodies against proprotein convertase subtilisin/kexin type 9 (PCSK9), are known to reduce the risk of cardiovascular diseases; however, statins are associated with limited efficacy and poor adherence to treatment, whereas PCSK9 inhibitors are only prescribed to a "high-risk" patient population or those who have failed other therapies. Based on the proven efficacy and safety profile of existing monoclonal antibodies, we have developed a peptide-based vaccine against PCSK9, VXX-401, as an alternative option to treat hypercholesterolemia and prevent ASCVD. VXX-401 is designed to trigger a safe humoral immune response against PCSK9, resulting in the production of endogenous antibodies and a subsequent 30-40% reduction in blood LDL-C. In this article, VXX-401 demonstrates robust immunogenicity and sustained serum LDL-C-lowering effects in nonhuman primates. In addition, antibodies induced by VXX-401 bind to human PCSK9 with high affinity and block the inhibitory effect of PCSK9 on LDL-C uptake in a hepatic cell model. A repeat-dose toxicity study conducted in nonhuman primates under good laboratory practices toxicity indicated a suitable safety and tolerability profile, with injection site reactions being the main findings. As a promising safe and effective LDL-C-lowering therapy, VXX-401 may represent a broadly accessible and convenient option to treat hypercholesterolemia and prevent ASCVD.

Keywords: PCSK9 inhibitor; PCSK9 vaccine; atherosclerosis; atherosclerotic cardiovascular disease; hypercholesterolemia; hyperlipidemia.

Fig. 1

The cholesterol-lowering action of VXX-401. A: Unprocessed human PCSK9 harbors three distinct regions plus an N-terminal signal peptide. The black arrow indicates the location of p5494a, the B-cell epitope of VXX-401, in the catalytic domain. B: LDL-C is removed from circulation by hepatic uptake via LDLR. After binding, the LDL-LDLR complex is internalized and delivered to the endosome. In the absence of PCSK9, the acidic pH induces dissociation. The receptor is recycled back to the cell surface for reuse, whereas the LDL-C is broken down in the late endosome and lysosome. When PCSKS9 is present, it binds to the receptor and is internalized alongside the complex, preventing the endosomal dissociation of LDLR from LDL-C. Thus, the receptor is degraded along with LDL-C. Reductions in cell surface-associated LDLR blunt the liver’s ability to absorb LDL-C, leading to an increase that may trigger atherosclerosis. By binding to PCSK9, VXX-401 antibodies prevent the hepatic degradation of LDLR and promote endocytic recycling, thus preserving LDL-C absorption. Diagram created with BioRender.com.

Fig. 2

Vaccination against PCSK9 elicits a robust antibody response in cynomolgus monkeys and significantly reduces serum levels of LDL-C. A, B: Anti-PCSK9 titers and 2 week LDL-C metrics from the pilot study. The green triangle marks the time at which a comparator group received evolocumab. C, D: Anti-PCSK9 titers and 3 week LDL-C metrics from the dose-ranging study. E, F: Anti-PCSK9 titers and 3 week LDL-C averages in the GLP toxicity study. Arrows indicate the prime and boost schedule. All titers are expressed as the log₁₀ value of the EC₅₀. LDL-C is presented as percent change from baseline. Error bars represent the standard error of the mean. Asterisks denote a significant difference between treatment and control based on P ≤ 0.05 (∗) or P ≤ 0.01 (∗∗).

Fig. 3

VXX-401 induces the production of highly potent and functionally active anti-PCSK9 antibodies. A: PCSK9 binding potency dose curve comparing affinity-purified antibodies from the 100 μg VXX-401 dosage group of the NHP GLP toxicity study to evolocumab. B: Bar graph showing uptake of pHrodo-conjugated LDL-C in HepG2 cells ± PCSK9 and the protective effect of affinity-purified VXX-401 antibodies. Uptake is expressed as the percent of baseline. C–E: SX5 images showing pHrodo-LDL-C uptake (blue mask) in HepG2 cells at baseline, with PCSK9 treatment, and rescue of uptake by VXX-401-derived antibodies. Error bars represent the standard error of the mean. Asterisks denote a significant difference between treatment and control based on P ≤ 0.05 (∗) or P ≤ 0.01 (∗∗).

Fig. 4

VXX-401 induces a humoral IgG₁ immune response. IgG subtype-specific titers at week 9 for the saline placebo, adjuvant control, and 100 μg/dose treatment groups of the dose-ranging study. The dashed line indicates the lower limits of quantification for the subtype-specific ELISA titers. Asterisks denote a significant difference based on P ≤ 0.05 (∗) or P ≤ 0.01 (∗∗).

Fig.5

VXX-401 does not induce autoimmunity against endogenous PCSK9. A, B: Spot-forming units (SFUs) per million PBMC collected preimmunization. C, D: SFU per million PBMC collected postimmunization. E, F: Representative ELISpot scans for PBMC secretion of IFN-γ and IL-4 preimmunization and postimmunization. Error bars represent the standard error of the mean.