Antiproliferative effects of SR31747A in animal cell lines are mediated by inhibition of cholesterol biosynthesis at the sterol isomerase step

Authors


  • Correspondence to C. Labit-Le Bouteiller, Sarofi Recherche, Centre de Labège, B.P. 137, F-31676 Labège Cedex, France

  • Abbreviations. FCS, foetal calf serum; GC-MS, gas chromatography coupled to mass spectroscopy; HMG-CoA reductase, 3-hydroxy-3-methylglutaryl-CoA reductase; IC50, concentration causing 50 % inhibition; IL2, interleukin 2; IL6, interleukin 6; LDL, low density lipoprotein; MTT, 3-(4,5-dimethylthiazol 2-yl)3,5diphenylformazan; 3.PPP, HOPh-Pip-Pr.

Abstract

SR31747A is a new sigma ligand exhibiting immunosuppressive properties and antiproliferative activity on lymphocyte cells. Only two subtypes of sigma receptor, namely the sigma1 receptor and emopamil-binding protein, have been characterised molecularly. Only the σ1 receptor has been shown to bind (Z)N-cyclohexyl-N-ethyl-3-(3-chloro4-cyclohexylphenyl)propen-2-ylamine hydrochloride (SR31747A) with high affinity. It was demonstrated that the SR31747A effect on the inhibition of T-cell proliferation was consistent with a sigma1 receptor-mediated event. In this report, binding experiments and sterol isomerase assays, using recombinant yeast strains, indicate that the recently cloned emopamil-binding protein is a new SR31747A-binding protein whose activity is inhibited by SR31747A. Sterol analyses reveal the accumulation of a Δ8-cholesterol isomer at the expense of cholesterol in SR31747A-treated cells, suggesting that cholesterol biosynthesis is inhibited by SR31747A at the Δ8-Δ7 sterol isomerase step in animal cells. This observation is consistent with a sterol isomerase role of the emopamil-binding protein in the cholesterol biosynthetic pathway in animal cells. In contrast, there is no evidence for such a role of the sigma1 receptor, in spite of the structural similarity shared by this protein and yeast sterol isomerase. We have found that SR31747A also exerts anti-proliferative effects at nanomolar concentrations on various established cell lines. The antiproliferative activity of SR31747A is reversed by cholesterol. Sterol-isomerase overproduction enhances resistance of CHO cells. This last observation strongly suggests that sterol isomerase is implicated in the antiproliferative effect of the drug in established cell lines.

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