Inhibition of 2,3-oxidosqualene cyclases

ABSTRACT:Recently, a number of inhibitors of the enzyme oxidosqualene cyclase (OSC; EC 5.4.99.7), a key enzyme in sterol biosynthesis, were shown to inhibit in mammalian cells the multiplication of Trypanosoma cruzi, the parasite agent of Chagas' disease. The gene coding for the OSC of T. cruzi has been cloned and expressed in Saccharomyces cerevisiae. The expression in yeast cells could be a safe and easy model for studying the activity and the selectivity of the potential inhibitors of T. cruzi OSC. Sterols are eukaryotic membrane components that are necessary to support cell growth and differentiation. Sterol biosynthesis is a well-established chemotherapeutic target in pathogenic eukaryotes, such as fungi (1,2). The final product of the sterol biosynthetic pathway in fungi is the 24-alkyl sterol ergosterol. Ergosterol or similar 24-alkyl sterols are also the final products of the sterol synthetic pathway of some pathogenic protozoa including Trypanosoma species. These organisms cannot completely substitute these sterols with the cholesterol biosynthesized in host mammalian cells and need to synthesize at least some of their own distinctive sterols (3-5). This dependence on sterols suggests that sterol biosynthesis inhibitors may be useful antiprotozoal drugs. The sterol biosynthetic pathway ( Fig. 1) offers many potential targets for therapeutic purposes. Many effective antifungal drugs already in use act by inhibiting different enzymes of sterol biosynthesis; the allylamine antifungal drug terbinafine inhibits squalene epoxidase (6), and azole drugs such as ketoconazole and itraconazole are inhibitors of lanosterol C 14 -demethylase (7). The activity of these inhibitors can be explained as a consequence either of depletion of the ergosterol or of accumulation of toxic intermediates or side products. In addition to the antifungal activity, some of these compounds Acetyl-CoAwere shown to inhibit the growth of Trypanosoma and other kinetoplastid parasites (8). Kinetoplastid parasites have also been shown recently to be susceptible to inhibitors of squalene synthase (9,10) and oxidosqualene cyclase (11,12). The enzyme oxidosqualene cyclase (OSC; EC 5.4.99.7), which catalyzes the formation of the first cyclic precursor of sterols, is considered a good target for the inhibition of sterol biosynthesis in both humans and fungi. Many inhibitors, designed on the basis of the complex cyclization mechanism of OSC (13), are active on the enzyme and have been investigated as potential cholesterol-lowering or antifungal drugs (1,2,13). The recent crystallization of human OSC as a complex with the potent inhibitor RO48-8071 opens the way to new structurebased studies of the cyclization mechanism (14).We have designed and tested against mammalian and fungal OSC many acyclic substrate analogs modified either to mimic the high-energy carbocationic intermediates (compounds 1-3 of Fig. 2) or to bear reactive functions able to interact with the active site residues, as the methylidene (compounds 4-8), vinyl sulfide (compounds 9...

Section: Inhibition Of T Cruzi Osc In Cell-free Homogenate Ofsupporting

confidence: 76%

Analogs of squalene and oxidosqualene inhibit oxidosqualene cyclase of Trypanosoma cruzi expressed in Saccharomyces cerevisiae

Oliaro‐Bosso

Ceruti

Balliano

et al. 2005

“…Compound 7 was obtained starting from aldehyde 2 by using the same method as described for 6, as a mixture (about 1:1) of 1E and 1Z isomers, in 33% yield. 1 5,9,13,17,Scheme 2). Compound 8 was obtained starting from aldehyde 4 using the same method as described for 6, except for the amount of phenyllithium (1.40 equiv).…”

Section: Methodsmentioning

confidence: 99%

Vinyl sulfide derivatives of truncated oxidosqualene as selective inhibitors of oxidosqualene and squalene‐hopene cyclases

Ceruti

Balliano

Rocco

et al. 2001

Various vinyl sulfide and ketene dithioacetal derivatives of truncated 2,3-oxidosqualene were developed. These compounds, having the reactive functions at positions C-2, C-15 and C-19 of the squalene skeleton, were studied as inhibitors of pig liver and Saccharomyces cerevisiae oxidosqualene cyclases (OSC) (EC 5.4.99.7) and of Alicyclobacillus acidocaldarius squalene hopene cyclase (SHC) (EC 5.4.99.-). They contain one or two sulfur atoms in alpha-skeletal position to carbons considered to be cationic during enzymatic cyclization of the substrate and should strongly interact with enzyme nucleophiles of the active site. Most of the new compounds are inhibitors of the OSC and of SHC, with various degrees of selectivity. The methylthiovinyl derivative, having the reactive group at position 19, was the most potent and selective inhibitor of the series toward S. cerevisiae OSC, with a concentration inhibiting 500% of the activity of 50 nM, while toward the animal enzyme it was 20 times less potent. These results could offer new insight for the design of antifungal drugs.

“…Acyclic squalene-derived inhibitors, in which the positively charged carbocation was replaced by a nitrogen, were initially developed (22,23). Various mono-, bi-, and tricyclic aza derivatives, analogs of partially cyclized sterol intermediates, some of which display high activity, have been obtained (24). Among the substrate mimics, 2,3;18,19-dioxidosqualene shows strong inhibitory potency (25).…”

mentioning

confidence: 99%

Conjugated methyl sulfide and phenyl sulfide derivatives of oxidosqualene as inhibitors of oxidosqualene and squalene‐hopene cyclases

Rocco

Bosso

Viola

et al. 2003

Various (1E,3E)- and (1Z,3E)-conjugated methylthio derivatives of oxidosqualene (OS) and conjugated and non-conjugated phenylthio derivatives of OS were obtained. These compounds, designed as inhibitors of pig liver and Saccharomyces cerevisiae 2,3-oxidosqualene-lanosterol cyclases (OSC) (EC 5.4.99.7) and of Alicyclobacillus acidocaldarius squalene-hopene cyclase (SHC) (EC 5.4.99.-), contain the reactive function adjacent to carbons involved in the formation of the third and the fourth cycle during OS cyclization. All the new compounds are inhibitors of OSC and SHC, with various degrees of selectivity. The conjugated methylthio derivatives behaved as potent inhibitors of S. cerevisiae OSC, whereas most of the phenylthio derivatives were especially active toward SHC.