Fast and easy in vitro screening assay for cholesterol biosynthesis inhibitors in the post-squalene pathway

A whole-cell assay for screening cholesterol biosynthesis inhibitors in the post-squalene pathway has been developed. HL 60 cells were incubated for 24 h with test substances. The nonsaponifiable lipids were extracted by means of liquid–liquid extraction using tert-butylmethylether. The raw extracts were purified by dispersive solid phase extraction using a primary–secondary amine material (PSA) and dried using sodium sulphate. The sterols were derivatized using N-trimethylsilylimidazole. GLC/MS analysis was carried out in less than 12.5 min using fast GLC mode. The obtained sterol patterns indicated which enzyme had been inhibited. Specific sterol patterns which reflect the different enzyme inhibitions were obtained using established inhibitors of cholesterol biosynthesis like AY 9944, NB 598, clotrimazole, aminotriazole and DR 258, a Δ24-reductase inhibitor prepared in our working group. For characterizing IC50 values we used sodium 2-13C-acetate and quantified the incorporation of it into cholesterol relative to control levels after the samples had been normalized to their protein content.