title: Selective inhibition of human 3β-hydroxysteroid dehydrogenase type 1 as a potential treatment for breast cancer.
abstract: Human 3β-hydroxysteroid dehydrogenase/isomerase type 1 (3β-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3β-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3β-HSD1 or 3β-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3β-HSD1 cells with 12-16-fold lower IC(50) values compared to the MCF-7 3β-HSD2 cells. Trilostane and epostane also competitively inhibit purified human 3β-HSD1 with 12-16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3β-HSD2. Using our structural model of 3β-HSD1, trilostane was docked in the active site of 3β-HSD1, and Arg195 in 3β-HSD1 or Pro195 in 3β-HSD2 was identified as a potentially critical residue. The R195P-1 mutant of 3β-HSD1 and the P195R-2 mutant of 3β-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high-affinity, competitive inhibition of 3β-HSD1 by trilostane may be related to the presence of Arg195 in 3β-HSD1 versus Pro195 in 3β-HSD2. In addition, His156 in 3β-HSD1 may play a role in the higher affinity of 3β-HSD1 for substrates and inhibitors compared to 3β-HSD2 containing Try156. Structural modeling of the 3β-HSD1 dimer identified a possible interaction between His156 on one subunit and Gln105 on the other. Kinetic analyses of the H156Y-1, Q105M-1 and Q105M-2 support subunit interactions that contribute to the higher affinity of 3β-HSD1 for the inhibitor, epostane, compared to 3β-HSD2. Article from the Special issue on Targeted Inhibitors.
authors.affiliation: Division of Basic Medical Sciences, Mercer University School of Medicine, 1550 College St, Macon, GA 31207, USA. Thomas J@mercer.edu
authors.forename: James L
authors.initials: JL
authors.lastname: Thomas
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Bucholtz
authors.forename: Balint
authors.initials: B
authors.lastname: Kacsoh
mesh_terms: D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology*; D002460:Cell Line; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D009154:Mutation; D011487:Protein Conformation; D013256:Steroids / Q000737:chemistry / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D013256:Steroids; D015096:3-Hydroxysteroid Dehydrogenases