Blaszkiewicz_2026_Cell.Mol.Gastroenterol.Hepatol__101796

BACKGROUND AND AIMS: Homozygous familial hypercholesterolemia (HoFH) is an autosomal genetic disorder that generates increased levels of low-density lipoproteins (LDL) in the serum. Elevated LDL results in hypercholesterolemia leading to potentially fatal cardiovascular disease. HoFH patients are often refractory to standard cholesterol-lowering treatments. Some available pharmaceuticals developed specifically for HoFH can elevate hepatic lipid levels and in other cases have limited accessibility. Previously, we identified a family of triazine thiol compounds that effectively reduce apolipoprotein B-100 (APOB) secretion by hepatocytes. In mice with humanized livers, triazine thiols effectively lowered serum cholesterol, triglycerides, low-density lipoproteins and lipoprotein(a) (Lp(a)). Despite their effectiveness, the mode of action of triazine thiols was unknown. METHODS AND RESULTS: Using affinity-based mass spectrometry we identify Carboxylesterase 1 (CES1) as a triazine thiol binding protein. Through biochemical assays, we show that triazine thiols are slow-binding, allosteric, covalent CES1-specific inhibitors. We use molecular modeling to identify a predicted binding site within CES1 near cysteine 390 and demonstrate that loss of this cysteine leads to resistance to triazine thiol-mediated inhibition. Moreover, we show that hepatocyte-like cells derived from CES1(-/-) induced human pluripotent stem cells have a significant reduction in APOB secretion, mimicking the effect of treating hepatocytes with triazine thiols. CONCLUSIONS: This study establishes triazine thiols as novel, highly specific CES1 inhibitors, providing insight into their mechanism and highlighting CES1 inhibition as an approach for treating hypercholesterolemia.