Johannes Aebi

Insight Into Steroid Scaffold Formation from the Structure of Human Oxidosqualene Cyclase

In higher organisms the formation of the steroid scaffold is catalysed exclusively by the membrane-bound oxidosqualene cyclase (OSC; lanosterol synthase). In a highly selective cyclization reaction OSC forms lanosterol with seven chiral centres starting from the linear substrate 2,3-oxidosqualene. Valuable data on the mechanism of the complex cyclization cascade have been collected during the past 50 years using suicide inhibitors, mutagenesis studies and homology modelling. Nevertheless it is still not fully understood how the enzyme catalyses the reaction. Because of the decisive role of OSC in cholesterol biosynthesis it represents a target for the discovery of novel anticholesteraemic drugs that could complement the widely used statins. Here we present two crystal structures of the human membrane protein OSC: the target protein with an inhibitor that showed cholesterol lowering in vivo opens the way for the structure-based design of new OSC inhibitors. The complex with the reaction product lanosterol gives a clear picture of the way in which the enzyme achieves product specificity in this highly exothermic cyclization reaction.

α-alkylation of serine with self-reproduction of the center of chirality

The lithium enolate 6 of methyl (2R,4S)-2-t-butyl-3-formyl-oxazolidine-4-carboxylate (4b) derived from (s)-(+)-serine can be generated with LDA in THF solution at −75°C. Alkylations (→ 9) and hydroxyalkylations (→ 10, 11) occur preferentially (>95:5) from the Re-face of the donor center (relative topicity lk). This stereochemical course is derived from the absolute configuration of 2-deuterio- and 2-methyl-serine (12, 13) obtained through the enolate 6.

α-Alkylation of threonine

The (S,S)- and the (S,R)-oxazolines 4, both readily available from l-threonine, are deprotonated with lithium diisopropylamide (lda, → 5) and alkylated diastereoselectively (95 % ds) to yield the 4.4-disubstituted oxazolines 7. The product of methylation (7a, E = CH3) is shown to be formed with relative topicity ul-1.2.

Endothelin-Converting Enzyme Inhibition Ameliorates Angiotensin II–Induced Cardiac Damage

Abstract—We tested the hypothesis that endothelin-converting enzyme (ECE) inhibition ameliorates end-organ damage in rats harboring both human renin and human angiotensinogen genes (dTGR). Hypertension develops in the animals, and they die by age 7 weeks of heart and kidney failure. Three groups were studied: dTGR (n=12) receiving vehicle, dTGR receiving ECE inhibitor (RO0687629; 30 mg/kg by gavage; n=10), and Sprague-Dawley control rats (SD; n=10) receiving vehicle, all after week 4, with euthanasia at week 7. Systolic blood pressure was not reduced by ECE inhibitor compared with dTGR (205±6 versus 206±6 mm Hg at week 7, respectively). In contrast, ECE inhibitor treatment significantly reduced mortality rate to 20% (2 of 10), whereas untreated dTGR had a 52% mortality rate (7 of 12). ECE inhibitor treatment ameliorated cardiac damage and reduced left ventricular ECE activity below SD levels. Echocardiography at week 7 showed reduced cardiac hypertrophy (4.8±0.2 versus 5.7±0.2 mg/g, P <0.01) and increased left ventricular cavity diameter (5.5±0.3 versus 3.1±0.1 mm, P <0.001) and filling volume (0.42±0.04 versus 0.16±0.06 mL, P <0.05) after ECE inhibitor compared with untreated dTGR. ECE inhibitor treatment also reduced cardiac fibrosis, tissue factor expression, left ventricular basic fibroblast growth factor mRNA levels, and immunostaining in the vessel wall, independent of high blood pressure. In contrast, the ECE inhibitor treatment showed no renoprotective effect. These data are the first to show that ECE inhibition reduces angiotensin II–induced cardiac damage.

A Novel Inhibitor of Oxidosqualene:Lanosterol Cyclase Inhibits Very Low–Density Lipoprotein Apolipoprotein B100 (ApoB100) Production and Enhances Low-Density Lipoprotein ApoB100 Catabolism Through Marked Reduction in Hepatic Cholesterol Content

Objective—Inhibition of 2,3-oxidosqualene:lanosterol cyclase (OSC), an enzyme in the cholesterol synthesis pathway, has the unique ability to inhibit cholesterol synthesis while simultaneously enhancing oxysterol synthesis. Our objectives were to determine, in vivo, if a novel OSC inhibitor reduced low-density lipoprotein (LDL) cholesterol and to define the mechanism(s) involved. Methods and Results—Miniature pigs received the OSC inhibitor RO0717625 or placebo and a diet containing fat (34% of energy) and 400 mg per day of cholesterol. Treatment decreased plasma total cholesterol (−20%) and LDL cholesterol (−29%). Apolipoprotein B (apoB) kinetic parameters were determined. Very low–density lipoprotein (VLDL) apoB pool size decreased 22% because of inhibition of VLDL production (−43%). LDL apoB pool size decreased 22% because of a 1.5-fold increase in fractional catabolic rate (FCR). The increased FCR was associated with a 2-fold increase in hepatic LDL receptor mRNA. Hepatic total and microsomal cholesterol were reduced by 16% and 27%, respectively. Plasma lathosterol concentrations decreased 57%, reflecting inhibition of hepatic cholesterol synthesis. Treatment reduced plasma plant sterols and decreased postprandial cholesterol transport in chylomicrons. Conclusions—A novel OSC inhibitor, RO0717625, decreased VLDL and LDL apoB100 through decreased VLDL production and enhanced LDL clearance. Thus, OSC represents a potential therapeutic target for dyslipidemia.

Structure‐Based Design, Synthesis, and in vitro Evaluation of Nonpeptidic Neprilysin Inhibitors

Neprilysin (NEP, neutral endopeptidase, EC 3.4.24.11) is a mammalian zinc(ii)-dependent, membrane-bound endopeptidase. NEP is widely distributed in the organs, particularly in the kidneys and lungs, and is involved in the metabolism of a number of smaller regulatory peptides of the nervous, cardiovascular, inflammatory, and immune systems. Enkephalins are among its natural substrates, and blocking NEP would increase their level, thereby generating an analgetic response. Furthermore, NEP cleaves ANP (atrial natriuretic peptide) and bradykinin, which both reduce blood pressure, and NEP inhibitors could therefore be possible antihypertensive agents. On the other hand, NEP has recently been shown to cleave amyloid b-peptide, the deposition of which in the brain is part of the initiation of Alzheimers disease. These therapeutic and basic pharmacological research interests led us to develop new nonpeptidic inhibitors of Neprilysin by X-ray structurebased de novo design. Many peptidic NEP inhibitors are known, but only a few nonpeptidic ones have been report-

Cytotoxic effects of combination of oxidosqualene cyclase inhibitors with atorvastatin in human cancer cells.

Ten oxidosqualene cyclase inhibitors with high efficacy as cholesterol-lowering agents and of different chemical structure classes were evaluated as potential anticancer agents against human cancer cells from various tissue origins and nontumoral human-brain-derived endothelial cells. Inhibition of cancer cell growth was demonstrated at micromolar concentrations, comparable to the concentrations of statins necessary for antitumor effect. Human glioblastoma cells were among the most sensitive cells. These compounds were also able to decrease the proliferation of angiogenic brain-derived endothelial cells, as a model of tumor-induced neovasculation. Additive effects in human glioblastoma cells were also demonstrated for oxidosqualene cyclase inhibitors in combination with atorvastatin while maintaining selectivity against endothelial cells. Thus, not only statins targeting the 3-hydroxy-3-methylglutaryl coenzyme A reductase but also inhibitors of oxidosqualene cyclase decrease tumor growth, suggesting new therapeutic opportunities of combined anti-cholesterol agents for dual treatment of glioblastoma.

Discovery of Fluoromethylketone-Based Peptidomimetics as Covalent ATG4B (Autophagin-1) Inhibitors

ATG4B or autophagin-1 is a cysteine protease that cleaves ATG8 family proteins. ATG4B plays essential roles in the autophagosome formation and the autophagy pathway. Herein we disclose the design and structural modifications of a series of fluoromethylketone (FMK)-based peptidomimetics as highly potent ATG4B inhibitors. Their structure-activity relationship (SAR) and protease selectivity are also discussed.

Oxidosqualene cyclase from Saccharomyces cerevisiae, Trypanosoma cruzi, Pneumocystis carinii and Arabidopsis thaliana expressed in yeast: a model for the development of novel antiparasitic agents.

A series of 25 compounds, some of which previously were described as inhibitors of human liver microsomal oxidosqualene cyclase (OSC), were tested as inhibitors of Saccharomyces cerevisiae, Trypanosoma cruzi, Pneumocystis carinii and Arabidopsis thaliana OSCs expressed in an OSC-defective strain of S. cerevisiae. The screening identified three derivatives particularly promising for the development of novel anti-Trypanosoma agents and eight derivatives for the development of novel anti-Pneumocystis agents.

Discovery of 4-Aryl-5,6,7,8-tetrahydroisoquinolines as Potent, Selective, and Orally Active Aldosterone Synthase (CYP11B2) Inhibitors: In Vivo Evaluation in Rodents and Cynomolgus Monkeys.

Inappropriately high levels of aldosterone are associated with many serious medical conditions, including renal and cardiac failure. A focused screen hit has been optimized into a potent and selective aldosterone synthase (CYP11B2) inhibitor with in vitro activity against rat, mouse, human, and cynomolgus monkey enzymes, showing a selectivity factor of 160 against cytochrome CYP11B1 in the last species. The novel tetrahydroisoquinoline compound (+)-(R)-6 selectively reduced aldosterone plasma levels in vivo in a dose-dependent manner in db/db mice and cynomolgus monkeys. The selectivity against CYP11B1 as predicted by cellular inhibition data and free plasma fraction translated well to Synacthen challenged cynomolgus monkeys up to a dose of 0.1 mg kg(-1). This compound, displaying good in vivo potency and selectivity in mice and monkeys, is ideally suited to perform mechanistic studies in relevant rodent models and to provide the information necessary for translation to non-human primates and ultimately to man.