Abstract 16404: CETP Inhibitor K-312 Lowers PCSK9 Expression and LDL Cholesterol Levels in vivo

Abstract

Background: Despite potent LDL-cholesterol (LDL-C) therapies, substantial residual cardiovascular risk remains. Proprotein convertase subtilisin/kexin 9 (PCSK9) is a promising target for lowering LDL-C. We recently demonstrated that K-312, originally found as a cholesteryl ester transfer protein (CETP) inhibitor, decreased PCSK9 expression in vitro through the reduction of its promoter activity. The present study has further examined the underlying molecular mechanisms and in vivo effects of K-312 on PCSK9 levels using mass spectrometry. Methods and Results: CETP silencing by siRNA in the human hepatocyte cell line HepG2 did not compromise suppression of PCSK9 expression by K-312, indicating a mechanism independent of CETP inhibition. Transcription factors sterol-regulatory element binding protein (SREBP)-1 and SREBP-2 bind to the sterol regulatory element (SRE) of PCSK9 promoter when their precursor forms are cleaved into active forms. K-312 treatment decreased binding of SREBP-1 and SREBP-2 to SRE of the PCSK9 promoter (chromatin immunoprecipitation) and active forms of SREBP-1 and SREBP-2 (western blotting), suggesting the suppression of PCSK9 expression by K-312 involves SREBP-1 and SREBP-2. We then examined the effects of K-312 in cholesterol-fed New Zealand White rabbits administered either vehicle (N=7) or K-312 30 mg/kg (N=7) for 2 weeks. K-312 treatment decreased LDL-C (vehicle: 272.5 ± 42.2 mg/dl; K-312: 193.0 ± 36.5 mg/dl), increased HDL cholesterol (vehicle: 29.9 ± 3.7 mg/dl; K-312: 93.3 ± 14.7 mg/dl) and decreased PCSK9 mRNA levels in the liver by 63%. We further used two mass spectrometry-based approaches to measure PCSK9 levels in rabbit plasma: spectral counting and a novel high resolution (HR)-MS/MS quantification method. Immunoprecipitation of PCSK9 successfully enriched PCSK9 signal. Spectral counting and HR-MS/MS of PCSK9 peptides both demonstrated that K-312 treatment significantly decreased plasma PCSK9 levels by 76% (p<0.01) and 60% (p<0.05), respectively. Conclusion: K-312 may lower LDL cholesterol levels by suppressing CETP activity and PCSK9 expression, serving as a novel therapy for dyslipidemia and cardiovascular disease.