Abstract 10829: Biological and Pharmacological Properties of the Protease Proprotein Convertase Subtilisin-Like Kexin Type 9 Antagonists (Best of Basic Science Abstract)

Protease proprotein convertase subtilisin-like kexin type 9 (PCSK9) is a new important target for the treatment of hypercholesterolemia. Currently, several pharmaceutical companies are racing to develop new drugs against PCSK9, which could be the newest weapon against heart disease since the introduction of statins in the 80’s. However, those companies have focused primarily on the development of mAbs, not small molecules, as drugs. PCSK9 is a serine protease that is synthesized as a zymogen that undergoes autocatalytic processing and secretion. Secreted PCSK9 binds to the LDL-receptor (LDLR) and chaperones it to the degradation pathway. This study focused on the identification of antagonists of the PCSK9/LDLR interaction and explored their mechanism of action using a range of functional assays, as well as determined pharmacokinetic (PK) and pharmacodynamic (PD) properties of the lead compounds. Potential inhibitors of the PCSK9/LDLR interaction were identified through a virtual screen at the PCSK9 surface where the LDLR-EGF-A binds. The top hits exhibited inhibition of PCSK9/LDLR binding in the low micromolar (μM) range, a 5-fold upregulation of the LDLR at an inhibitor concentration of 1.6 μM in recombinant cell-based assays, and an increase in the fluorescently labeled DiI-LDL uptake in the nanomolar (nM) range in situ . Pharmacological studies revealed that subcutaneous injection of 4 mg/kg of one of these compounds resulted in a 32% reduction of the total cholesterol and 20% reduction in LDL-C levels in mice fed a high fat/high cholesterol diet. Moreover, administration of 40mg/kg of atorvastatin resulted in a 27% total cholesterol reduction and 20% reduction in LDL-C level. Additional studies were performed to evaluate the effect of the combination of our PCSK9 inhibitor with atorvastatin. Administration of the PCSK9 inhibitor (4 mg/ kg) in combination with atorvastatin (40 mg/kg) resulted in more than a 40% reduction in LDL-C in mice fed a high fat/high cholesterol diet. In vivo PK and PD evaluation of our lead PCSK9 inhibitor demonstrated that it was efficacious and exhibited 13% oral bioavailability. To our knowledge, no small molecule orally bioavailable antagonist against PCSK9 has been reported, only mAbs.