The novel cholesterol-lowering drug SR-12813 inhibits cholesterol synthesis via an increased degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase.
SR-12813 (tetra-ethyl 2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethenyl-1, 1-bisphosphonate) lowers plasma cholesterol in five species. In this paper we investigate the underlying mechanism using Hep G2 cells. SR-12813 inhibited incorporation of tritiated water into cholesterol with an IC50 of 1.2 microM but had no effect on fatty acid synthesis. Furthermore, SR-12813 reduced cellular 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity with an IC50 of 0.85 microM. The inhibition of HMG-CoA reductase activity was rapid with a T1/2 of 10 min. After a 16-h incubation with SR-12813, mRNA levels of HMG-CoA reductase and low density lipoprotein (LDL) receptor were increased. The increased expression of LDL receptor translated into a higher LDL uptake, which can explain the primary hypocholesterolemic effect of SR-12813 in vivo. Western blot analysis indicated that the amount of HMG-CoA reductase protein rapidly decreased in the presence of SR-12813. Pulse-chase experiments with [35S]methionine showed that the T1/2 of HMG-CoA reductase degradation decreased in the presence of SR-12813 from 90 to 20 min. Pre-incubation with 50 microM of lovastatin did not prevent the effects of SR-12813 on HMG-CoA reductase degradation, indicating that the compound does not need mevalonate-derived regulators for its action. It is concluded that SR-12813 inhibits cholesterol synthesis mainly by an enhanced degradation of HMG-CoA reductase.
Berkhout
T A
TA
Department of Vascular Biology, Smithkline Beecham Pharmaceuticals, The Frythe, Welwyn, Herts. AL6 9AR, United Kingdom.
Simon
H M
HM
Patel
D D
DD
Bentzen
C
C
Niesor
E
E
Jackson
B
B
Suckling
K E
KE
D000085:Acetates / Q000378:metabolism; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002784:Cholesterol / Q000096:biosynthesis*; D004164:Diphosphonates / Q000494:pharmacology*; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology; D006903:Hydroxymethylglutaryl CoA Reductases / Q000096:biosynthesis / Q000378:metabolism*; D007700:Kinetics; D007810:Lanosterol / Q000031:analogs & derivatives / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000378:metabolism; D008113:Liver Neoplasms; D008148:Lovastatin / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D011973:Receptors, LDL / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000187:drug effects; D014316:Tritium; D014407:Tumor Cells, Cultured
D000085:Acetates; D000924:Anticholesteremic Agents; D004164:Diphosphonates; D006888:Hydroxycholesterols; D008077:Lipoproteins, LDL; D012333:RNA, Messenger; D011973:Receptors, LDL; C100355:SR 12813; D014316:Tritium; C071375:SK&F 104976; D007810:Lanosterol; C007997:25-hydroxycholesterol; D002784:Cholesterol; D008148:Lovastatin; D006903:Hydroxymethylglutaryl CoA Reductases