Abstract 17608: Identification of a Tissue-specific Very Long-chain Acyl-CoA Synthetase Involved in the Inhibition of ATP-Citrate Lyase (ACL) by ETC-1002: A Novel Mechanism for Cholesterol Biosynthesis Inhibition in the Liver

Abstract

ETC-1002 is a first-in-class oral small molecule that significantly lowers levels of low- density lipoprotein-cholesterol (LDL-C) by 30-40% in hypercholesterolemic patients with reduced potential for muscle-related adverse events. Our previous investigations into the mechanism of action demonstrated a requirement for acyl-CoA synthetase- (ACS) dependent coenzyme A (CoA) activation of ETC-1002 (ETC-1002-CoA) to inhibit its molecular target, ATP-citrate lyase (ACL), an enzyme upstream of HMG-CoA reductase in the cholesterol biosynthesis pathway. In the present study, we have elucidated a mechanistic basis for tissue-specific inhibition of ACL by providing evidence that ACSVL1 is the ACS isoform that catalyzes the CoA activation of ETC-1002. Genetic silencing of ACSVL1 in McArdle cells prevented the CoA activation of ETC-1002 and consequently its inhibition of de novo cholesterol synthesis. We demonstrate that ACSVL1 is highly expressed in primary human hepatocytes and human liver microsomes. Furthermore, we establish a statin-like regulatory link between ACL activity and cholesterol metabolism by showing that ACL siRNA silencing or pharmacological inhibition by ETC-1002-CoA, leads to increased LDLR expression and activity. Using primary human hepatocytes, we demonstrate the concentration-dependent inhibition of cholesterol synthesis by ETC-1002, an associated increase in mRNA expression of the sterol responsive genes srebp2, hmgr, pcsk9, and ldlr mRNA, and increased LDLR activity. In addition, we demonstrate that ACSVL1 is not expressed in L6 myotubes, primary human skeletal muscle cells, or human skeletal muscle microsomes. Unlike statins, ETC-1002 did not inhibit the de novo synthesis of sterols in skeletal muscle cell cultures, nor promote caspase 3/7 activation. Therefore, by establishing a regulatory link between ACL inhibition and LDLR up-regulation, and by identifying ACSVL1 as the ACS isoform that catalyzes the CoA activation of ETC-1002, we provide evidence for the tissue-specific inhibition of ACL by ETC-1002-CoA that results in LDL-C-lowering without activity in skeletal muscle or associated side effects.