The cholesterol-5,6-epoxide hydrolase (ChEH) is the last epoxyde hydrolase which coding gene remains to be identified. The ChEH catalyzes the hydration of 5,6α-epoxy-cholestanol (α-CE) and 5,6β-epoxy-cholestanol (β-CE), two autoxydation products of cholesterol, into cholestane-3β,5α,6β-triol (CT). We earlier reported that the antiestrogen binding site (AEBS) was a hetero-oligomeric complex made of two subunits: the 3β-hydroxysterol-Δ7-reductase (DHCR7) and 3β-hydroxysterol- Δ8- Δ7-isomerase (D8D7I), two enzymes involved in post-lanosterol cholesterol biosynthesis (Kedjouar et al, J Biol Chem, 2004). We have recently reported that AEBS ligands induced differentiation and apoptosis of human breast cancer cell lines through the intracellular accumulation of autoxydation products of sterols such as α-CE and β-CE (Payre et al, Mol Cancer Ther, 2008; de Medina et al, Cell Death & Differ, 2009). Because the ChEH and AEBS displayed some biochemical similitudes, we have investigated, in the present study, the potential relationship that may exist between the ChEH and AEBS. We established that α-CE and β-CE (the substrates of the ChEH) and CT (the product of the catalytic activity of the ChEH), were high-affinity and competitive ligands of AEBS. AEBS ligands include selective estrogen receptors modulators (SERMs) such as tamoxifen and raloxifene, poly unsaturated fatty acids such as docosahexaenoic acid (DHA), oxysterols such as 7-hydroxycholesterol and 7-ketocholesterol, and diphenylmethane compounds such as N-Pyrrolidino-4-(phenylmethyphenoxyl)-ethanamine (PBPE) and tesmilifene. We established that all AEBS ligands were inhibitors of the ChEH at pharmacological concentrations. We demonstrated a positive correlation between the binding to AEBS and the inhibition of the ChEH catalytic activity by AEBS ligands (r2 = 0.95, n = 39, p < 0.0001) and showed that AEBS and the ChEH had the same pharmacological profile. Finally, the structural similarity between the ChEH and AEBS was established by co-expression or genetic invalidation in mammalian cells of the D8D7I and the DHCR7, which respectively allowed the reconstitution or the impairment of both AEBS and the ChEH activity. Collectively, these data demonstrate that AEBS and the ChEH are molecularly and pharmacologically similar. These results provide the first evidence of the molecular identification of the ChEH, which coding gene had never been reported. In conclusion, we have identified a mechanism by which AEBS ligands induce the accumulation of sterol autoxidation products that were previously shown to induce breast cancer cell differentiation and apoptosis. The ChEH constitutes a new target for the chemoprevention and the treatment of breast cancers.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2918.