A Small Molecule Inhibitor of Scavenger Receptor BI-mediated Lipid Uptake—Probe 1

Scavenger receptor class B, type I (SR-BI) mediates selective uptake of Cholesterol from high-density lipoprotein (HDL) particles, a poorly understood process that is distinct from endocytic uptake of lipoproteins, such as low-density lipoprotein (LDL). We set out to find small molecules that inhibit SR-BI function and could be used to characterize the mechanisms involved in HDL uptake. Using a cell-based DiI-HDL uptake assay, we performed a high-throughput screen (HTS) of the National Institutes of Health Molecular Libraries Probe Production Centers Network (NIH MLPCN) compound library. Of 319,533 compounds, 3,046 compounds (0.96%) were classified as inhibitors of DiI-HDL uptake. MLS001217863 (SID 49678600, CID 24761960) was identified in the primary HTS as an inhibitor. It had potent activity in the primary assay, a low hit rate in Other MLPCN screens, and possessed structural properties suitable for analog synthesis. Structure activity relationship (SAR) studies were performed to improve potency and to minimize deleterious properties. These efforts generated a probe (CID 53377439/ML278), a low nanomolar inhibitor with improved potency and decreased toxicity liabilities. ML278 was tested for lipid efflux inhibition, modulation of HDL binding to SR-, and inhibition of endocytosis. ML278 functions by inhibiting both SR-BI-mediated lipid uptake and efflux of free Cholesterol to HDL particles. As a tool compound, ML278 is superior to existing small-molecule inhibitors of SR-BI (e.g., BLT-1 and ITX-5061) and will be useful in elucidating how SR-BI mediates lipid transport. In addition, it could clarify the role of SR-BI in a number of biological processes where it plays a crucial role.