Inhibition of 2,3-oxidosqualene cyclase and sterol biosynthesis by 10- and 19-azasqualene derivatives.
The inhibition of 2,3-oxidosqualene-lanosterol cyclase (EC 5.4.99.7) (OSC) by new azasqualene derivatives, mimicking the proC-8 and proC-20 carbocationic high-energy intermediates of the cyclization of 2,3-oxidosqualene to lanosterol, was studied using pig liver microsomes, partially purified preparations of OSC, and yeast microsomes. The azasqualene derivatives tested were: 6E- and 6Z-10aza-10,11-dihydrosqualene-2,3-epoxide 17 and 18, 19-aza-18,19,22,23-tetrahydrosqualene-2,3-epoxide 19 and its corresponding N-oxide 20, and 19-aza-18,19,22,23-tetrahydrosqualene 21. The compounds 17 and 19 (i.e. the derivatives bearing the 2,3-epoxide ring and the same geometrical configuration as the OSC substrate) were effective inhibitors, as shown by the Ki obtained using partially purified OSC: 2.67 microM and 2.14 microM, respectively. Compound 18, having an incorrect configuration and the 19-aza derivative 21, lacking the 2,3-epoxide ring, were poor inhibitors, with IC50 of 44 microM and 70 microM, respectively. Compound 21 was a competitive inhibitor of OSC, whereas 17 and 19 were noncompetitive inhibitors, and showed a biphasic time-dependent inactivation of OSC, their apparent binding constants being 250 microM and 213 microM, respectively. The inhibition of sterol biosynthesis was studied using human hepatoma HepG2 cells. The incorporation of [14C] acetate in the C27 sterols was reduced by 50% by 0.55 microM 17, 0.22 microM 19, and 0.45 microM 21, whereas 2 microM 18 did not affect sterol biosynthesis. In the presence of 17, 19 and 21, only the intermediate metabolites 2,3-oxidosqualene and 2,3,22,23-dioxidosqualene accumulated, demonstrating a very specific inhibition of OSC.
Viola
F
F
Istituto di Chimica Farmaceutica Applicata, Università di Torino, Italy.
Brusa
P
P
Balliano
G
G
Ceruti
M
M
Boutaud
O
O
Schuber
F
F
Cattel
L
L
D000818:Animals; D004852:Epoxy Compounds / Q000494:pharmacology*; D006801:Humans; D019751:Intramolecular Transferases; D007535:Isomerases / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008862:Microsomes, Liver / Q000201:enzymology; D051381:Rats; D013185:Squalene / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D013237:Stereoisomerism; D013261:Sterols / Q000096:biosynthesis*; D013552:Swine; D014407:Tumor Cells, Cultured
C002821:2,3-oxidosqualene; D004852:Epoxy Compounds; D013261:Sterols; C015171:2,3,22,23-dioxidosqualene; C076124:2,3-epoxy-10-aza-10,11-dihydrosqualene; D013185:Squalene; D007535:Isomerases; D019751:Intramolecular Transferases; C021924:lanosterol synthase