Structure activity relationships of new inhibitors of mammalian 2,3-oxidosqualene cyclase designed from isoquinoline derivatives

Design strategies of oxidosqualene cyclase inhibitors: Targeting the sterol biosynthetic pathway

Targeting the sterol biosynthesis pathway has been explored for the development of new bioactive compounds. Among the enzymes of this pathway, oxidosqualene cyclase (OSC) which catalyzes lanosterol cyclization from 2,3-oxidosqualene has emerged as an attractive target. In this work, we reviewed the most promising OSC inhibitors from different organisms and their potential for the development of new antiparasitic, antifungal, hypocholesterolemic and anticancer drugs. Different strategies have been adopted for the discovery of new OSC inhibitors, such as structural modifications of the natural substrate or the reaction intermediates, the use of the enzyme's structural information to discover compounds with novel chemotypes, modifications of known inhibitors and the use of molecular modeling techniques such as docking and virtual screening to search for new inhibitors. This review brings new perspectives on structural insights of OSC from different organisms and reveals the broad structural diversity of OSC inhibitors which may help evidence lead compounds for further investigations with various therapeutic applications.

Potential role of nonstatin cholesterol lowering agents

Although statins, 3β-hydroxy-3β-methylglutaryl coenzyme A reductase (HMGR) inhibitors, have revolutionized the management of cardiovascular diseases by lowering serum low density lipoproteins, many patients suffer from their side effects. Whether the statin side effects are related to their intrinsic toxicity or to the decrease of HMGR main isoprenoid end products, which are essential compounds for cell viability, is still debated. In addition to HMGR, the key and rate limiting step of cholesterol synthesis, many enzymes are involved in this multi-step pathway whose inhibition could be taken into account for a "nonstatin approach" in the management of hypercholesterolemia. In particular, due to their unique position downstream from HMGR, the inhibition of squalene synthase, farnesyl diphosphate farnesyltransferase (FDFT1), squalene epoxidase (SQLE), and oxidosqualene cyclase:lanosterol synthase (OSC) should decrease plasma levels of cholesterol without affecting ubiquinone, dolichol, and isoprenoid metabolism. Thus, although FDFT1, SQLE and OSC are little studied, they should be considered as perspective targets for the development of novel drugs against hypercholesterolemia. Here, structure-function relationships of FDFT1, SQLE, and OSC are reviewed highlighting the advantages that the downstream inhibition of HMGR could provide when compared to the statin-based therapy.

Dibasic non-imidazole histamine H3 receptor antagonists with a rigid biphenyl scaffold

A class of rigid, dibasic, non-imidazole H3 antagonists was developed, starting from a series of previously described flexible compounds. The original polymethylene chain between two tertiary amine groups was replaced by a rigid scaffold, composed by a phenyl ring or a biphenyl fragment. Modulation of the distance between the two amine groups, and of their alkyl substituents, was driven by superposition of molecular models and docking into a receptor model, resulting in the identification of 1,1'-[biphenyl-4,4'-diylbis(methylene)]bis-piperidine (5) as a subtype-selective H3 antagonist with high binding affinity (pKi=9.47) at human H3 histamine receptor.

Synthesis and biological evaluation of novel PDMP analogues

A new series of hybrid PDMP analogues, based both on PDMP and styryl analogues of natural ceramide, has been synthesized from D-serine. The synthetic route was developed such that future introduction of different aryl groups is straightforward. Biological evaluation, both in vitro on rat liver Golgi fractions as well as in HEK-293 and COS-7 cells, revealed two lead compounds with comparable inhibitory potency as PDMP, which could be elaborated to more potent inhibitors.

Umbelliferone aminoalkyl derivatives as inhibitors of oxidosqualene cyclases from Saccharomyces cerevisiae, Tripanosoma cruzi, and Pneumocystis carinii

A series of umbelliferone aminoalkyl derivatives, previously studied as inhibitors of squalene-hopene cyclase, were tested as inhibitors of yeast (Saccharomyces cerevisiae) oxidosqualene cyclase (OSC) and OSC from Trypanosoma cruzi and Pneumocystis carinii expressed in yeast. Enzymes from these pathogens were included in this study to provide a preliminary screening for antiparasitic activity. Tests were carried out both on cell homogenates incubated with radiolabeled oxidosqualene and on spheroplasts incubated with radiolabeled acetate. Derivatives bearing a methylallylamino group were the most effective on all of the three enzymes. The P. carinii enzyme was the most susceptible to the action of the inhibitors, with IC50 values for almost all of them ranging from 0.1 to 1 microM. The T. cruzi enzyme was appreciably inhibited (IC50 4-5 microM) only by derivatives bearing a methylallylaminoalkyl flexible chain. Results identify a particularly promising new family of OSC inhibitors, for the development of novel antiparasitic agents.

Synthesis and structure-activity studies of novel orally active non-terpenoic 2,3-oxidosqualene cyclase inhibitors

New orally active non-terpenoic inhibitors of human 2,3-oxidosqualene cyclase (hOSC) are reported. The starting point for the optimization process was a set of compounds derived from a fungicide project, which in addition to showing high affinity for OSC from Candida albicans showed also high affinity for human OSC. Common structural elements of these inhibitors are an amine residue and an electrophilic carbonyl C atom embedded in a benzophenone system, which are at a distance of about 10.7 A. Considering that the keto moiety is in a potentially labile position, modifications of the substitution pattern at the benzophenone as well as annelated heteroaryl systems were explored. Our approach combined testing of the compounds first for increased binding affinity and for increased stability in vitro. Most promising compounds were then evaluated for their efficacy in lowering plasma total cholesterol (TC) and plasma low-density lipoprotein cholesterol (LDL-C) in hyperlipidemic hamsters. In this respect, the most promising compounds are the benzophenone derivative 1.fumarate and the benzo[d]isothiazol 24.fumarate, which lowered TC by 40% and 33%, respectively.

Binding structures and potencies of oxidosqualene cyclase inhibitors with the homologous squalene-hopene cyclase

The binding structures of 11 human oxidosqualene cyclase inhibitors designed as cholesterol-lowering agents were determined for the squalene-hopene cyclase from Alicyclobacillus acidocaldarius, which is the only structurally known homologue of the human enzyme. The complexes were produced by cocrystallization, and the structures were elucidated by X-ray diffraction analyses. All inhibitors were bound in the large active center cavity. The detailed binding structures are presented and discussed in the light of the IC50 values of these 11 as well as 17 other inhibitors. They provide a consistent picture for the inhibition of the bacterial enzyme and can be used to adjust and improve homology models of the human enzyme. The detailed active center structures of the two enzymes are too different to show an IC50 correlation.