VB-84922 is a small molecule that inhibits ER-to-Golgi transport of SREBPs-SCAP complexes

Abstract

The sterol response element binding proteins (SREBPs), SREBP-1a/c and SREBP-2, are sterol-regulated transcription factors that control the expression of cholesterol and fatty acid-raising genes. Elevated expression of SREBPs has been linked to increased morbidity and mortality rates associated with conditions including obesity, cancer, and cardiovascular disease. Therefore, the development of new therapeutics to inhibit SREBP activity may be beneficial for treating various diseases associated with altered lipid levels. In their inactive state, SREBPs remain sequestered in the ER membrane in a complex with SREBP cleavage activating proteins (SCAP) and one of two ER-anchoring proteins, Insig-1 or Insig-2. Activation proceeds through dissociation of SREBP/SCAP from Insigs, SCAP-assisted translocation to the Golgi, proteolytic membrane release and nuclear import. We employed a high-throughput enzyme complementation assay to identify inhibitors of SREBP-2 translocation to the nucleus, resulting in the identification of VB-84922 having an IC50 value of 0.45 + 0.052 μM. VB-84922-mediated inhibition of nuclear translocation was confirmed by fluorescence microscopy with an mNeonGreen-SREBP-2 fusion protein. Crucially, VB-84922 inhibited the lovastatin-induced activity of an SREBP-responsive reporter construct and suppressed the expression of endogenous SREBP target genes. Co-transfection assays using an SREBP reporter and fluorescence microscopy were used to delineate the target of VB-84922 in the SREBP activation pathway. The drug blocked ER export of wild-type SCAP but had no effect on SREBP activity in cells expressing the nuclear form of SREBP-1a, or mutated versions of SCAP that are unable to bind Insigs and that chaperone SREBP to the Golgi constitutively. These results suggest that VB-84922 targets a step upstream of ER export in the SREBP activation cascade. VB-87496, a therapeutic lead compound, developed from VB-84922, demonstrated in vivo efficacy within a murine acute fasting-refeeding model by inhibiting full-length SREBP protein maturation and SREBP-dependent transcription. VB-87496 represents a specific SREBPs-SCAP inhibitor that has potential for further lead optimization medicinal chemistry efforts to generate a potent and selective pre-clinical candidate for treating lipid-related diseases.