TY - JOUR T1 - Interactions of indoles with specific binding sites for 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat liver. JF - Molecular Pharmacology JO - Mol Pharmacol SP - 357 LP - 363 VL - 28 IS - 4 AU - M Gillner AU - J Bergman AU - C Cambillau AU - B Fernström AU - J A Gustafsson Y1 - 1985/10/01 UR - http://molpharm.aspetjournals.org/content/28/4/357.abstract N2 - In order to identify some of the structural requirements for binding of indoles to the receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we have investigated the capacity of various indoles to inhibit specific [1,6-3H]TCDD binding in rat liver cytosol, as analyzed by electrofocusing in polyacrylamide gel. Of these indoles, indolo[3,2-b]carbazole was the most active. The IC50 value for receptor binding of indolo[3,2-b]carbazole as well as for 2,3,7,8-tetrachlorodibenzofuran was 3.6 nM, whereas that of 5,6-benzoflavone was 26 nM. Both indolo[3,2-b]carbazole and 2,3,7,8-tetrachlorodibenzofuran competitively inhibited the binding of [3H]TCDD to the receptor. The well-known microsomal enzyme inducer 3,3'-diindolymethane did not interact significantly with the TCDD receptor. Previous concepts of structure-activity relationships for binding of chlorinated dioxins to the TCDD receptor fail to account for the receptor binding of unhalogenated aryl hydrocarbon hydroxylase inducers such as 5,6-benzoflavone. We have instead considered the true three-dimensional space occupied by some receptor ligands by means of a computer using crystallographic data as inputs. When the atomic van der Waals radii were included, all potent receptor ligands studied could be fitted into a rectangle of 6.8 X 13.7 A. ER -