Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB213

Poster Communications

Cholesterol metabolism and cancers: Toward new perspectives in breast cancer treatment

R. Bartölke1, S. Silvente-Poirot1, M. Poirot1

1. Cancer Research Center of Toulouse, UMR1037-INSERM- University of Toulouse, Toulouse, France.

Breast cancer (BC) is the most common cancer in women worldwide and still many of them either fail to respond or develop resistance to existing therapies, stressing the need for alternatives. We have recently shown that cholesterol-5,6-epoxide (5,6-EC) metabolism is deregulated in BC in favor of cholestane-3β,5α,6β-triol (CT) production, which is then further transformed into 6-oxo-cholestan-3β,5α-diol (OCDO), a novel oncometabolite stimulating tumor growth by binding to the glucocorticoid receptor. Inhibition of this pathway may thus lead to new perspectives in BC treatment. The enzyme producing OCDO was identified as 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), known to regulate glucocorticoid metabolism by converting active cortisol into inactive cortisone. The aim of the present study was to determine the enzymatic parameters of the enzyme for its oxysterol substrate and to determine the pharmacological profiles of 11β-HSD2 toward OCDO and cortisone production. The enzymatic reaction of the conversion of [14C]-CT into [14C]-OCDO was studied in HEK293T cells transfected with either a control plasmid or a plasmid encoding 11β-HSD2, as well as in different BC cell lines in comparison to its enzymatic activity for the conversion of [3H]-cortisol into [3H]-cortisone. Enzymatic measurements of 11β-HSD2 in cell lysates revealed an apparent Km value of 5±1 µM for CT, which is in the range of the intratumor CT concentrations measured in BC. Cortisol inhibited OCDO production with a Ki of 259±73 nM, while 10 µM CT did not inhibit cortisol conversion. The Michaelis constant (Km) and inhibitory constants (Ki) ± S.E. were determined in at least three individual experiments by nonlinear regression analysis using GraphPad Prism version 6. The inhibition of 11β-HSD2 for both OCDO and cortisone production was further tested with a series of molecules including cholesterol metabolites, oxysterols, pentacyclic triterpenoids, steroid hormones and their synthetic analogues, bile acids as well as various pharmacologically active agents. Triterpenoids were found to strongly inhibit both reactions, as did 18β-glycyrrhetinic acid and its derivative carbenoxolone. Dexamethasone, a synthetic steroid used in the treatment of many pathologies including cancer, inhibits OCDO production with a Ki of 1.6±0.5 µM, thus likely affecting this pathway in treated patients. Interestingly, OCDO production, but not cortisone production, was specifically inhibited by two compounds, indicating differences in the binding site of 11β-HSD2 for CT and cortisol. This shows that 11β-HSD2 can be specifically targeted to inhibit the production of the tumor-promoting oncometabolite OCDO, representing new therapeutic opportunities for BC treatment.

Where applicable, experiments conform with Society ethical requirements