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Squalene synthase (SQS) is a key enzyme in the biosynthetic pathway for cholesterol and is a target for improved agents to lower plasma levels of low-density lipoprotein (LDL). A series of novel 3' substituted quinuclidines have been discovered as inhibitors of the rat liver microsomal enzyme. In this study, we demonstrate the inhibitory effects in vitro and in vivo, of two examples of the series. When microsomes were preincubated with compounds, before addition of substrate, both 3-(biphenyl-4-yl)quinuclidine (BPQ) and 3-(biphenyl-4-yl)-3-hydroxyquinuclidine (BPQ-OH) were found to cause biphasic inhibition of the enzyme with apparent inhibition constants (K'i) for the sensitive phases of 12 nM and 15 nM, respectively. The K'i values for the insensitive phases were 1.8 microM and 2.9 microM, respectively. The two examples inhibited equally both steps of the SQS-catalysed reaction, as shown by parallel inhibition of 3H+ release and labelled squalene formation from [1-3H]farnesyl pyrophosphate (FPP). BPQ and BPQ-OH were shown to be inhibitors of hepatic sterol synthesis from mevalonate with ED50 values of 10.6 and 7.1 mg/kg, respectively, after acute oral administration to the rat. BPQ-OH was chosen for further study and, to determine its selectivity of effect on the mevalonate pathway in vivo, the effect of a dose of 70 mg/kg on the pattern of labelled mevalonate incorporation into the various lipid fractions of the rat liver was examined. As expected, the incorporation into squalene and sterol products was inhibited by about 70%. An appearance of label in fractions corresponding to farnesyl and geranylgeranylpyrophosphates, as well as the corresponding alcohols, was observed in treated but not control animals. In addition, the administration of compound resulted in the appearance of peaks of mevalonate-derived radioactivity in an acidic fraction believed to represent metabolites of farnesol. Such results are consistent with inhibition of the mevalonate pathway at, and not before, SQS. In contrast, there was a significant increase in the incorporation of labelled mevalonate into ubiquinone 10, and the synthesis of dolichols was apparently unchanged. The results suggest a specific effect of BPQ-OH on rat liver SQS. The compound is, therefore, an interesting lead for further investigation of this class of compounds.
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
September 2021,
Natural product research,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
October 1996,
Biochimica et biophysica acta,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
February 2008,
Archives of biochemistry and biophysics,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
March 1995,
Phytochemistry,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
January 2007,
Current atherosclerosis reports,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
April 2005,
Bioorganic & medicinal chemistry letters,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
November 2013,
The international journal of biochemistry & cell biology,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
September 1992,
Archives of biochemistry and biophysics,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
August 1999,
Archives of biochemistry and biophysics,
F McTaggart, and
G R Brown, and
R G Davidson, and
S Freeman, and
G A Holdgate, and
K B Mallion, and
D J Mirrlees, and
G J Smith, and
W H Ward
July 2010,
The Journal of organic chemistry,
