Identification and Characterization of Orally Bioavailable Small Molecule Protease Proprotein Convertase Subtilisin-like Kexin Type 9 Inhibitors (Best of Basic Science Abstract)

Intervention with drugs to reduce low density lipoprotein-cholesterol (LDL-C) has proven to decrease mortality and morbidity. Here, we report the development of small molecules that lower LDL-C by targeting the LDL-receptor (LDLR) degradation pathway, which is modulated by the protease proprotein convertase subtilisin-like kexin type 9 (PCSK9). PCSK9 is synthesized as a 72-kDa zymogen that undergoes autocatalytic processing between the prodomain and catalytic domain, an important step that is absolutely required for secretion of PCSK9 and its function. Secreted PCSK9 binds to the LDLR and enhances its degradation. We have identified inhibitors of the autocatalytic processing by virtual docking of millions of commercial compounds into the atomic structure of the PCSK9 active site. Top scoring compounds that showed the best fit in the active site were selected for screening. These compounds were tested for their ability to inhibit the autocatalytic processing/secretion of PCSK9. The most potent compounds exhibited a concentration-dependent inhibition of the PCSK9 processing/secretion with IC50’s in the nanomolar range. These compounds were tested for selectivity against other PCSK’s. The data demonstrated that these compounds were selective in that they inhibit PCSK9 processing/secretion without affecting the secretion of other related PCSK’s. Furthermore, these compounds exhibited a 5- to 10-fold LDLR upregulation at 1.6 μM in two recombinant cell-based assays as well as exhibited an increase in the fluorescently labeled DiI-LDL uptake in situ in the nanomolar range. In animal studies, intraperitoneal (IP) injection of these compounds administered alone resulted in more than 20% reduction in LDL-C in mice fed a high fat/high cholesterol diet and over 40% reduction in LDL-C if administered in combination with atorvastatin. In vivo pharmacokinetic (PK) and pharmacodynamic (PD) evaluation of these compounds demonstrated that they are orally efficacious, with one compound exhibiting 43% oral bioavailability. Thus, identifying small molecule, orally active PCSK9 modulators represents a significant advance and opportunityfor drug development.