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: James L Thomas, Kevin M Bucholtz, Balint Kacsoh
• Journal: The Journal of steroid biochemistry and molecular biology (J Steroid Biochem Mol Biol) Vol. 125 Issue 1-2 Pg. 57-65 (May 2011) ISSN: 1879-1220 [Electronic] England
• PMID: 20736065 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Review)
• Copyright: Copyright © 2010 Elsevier Ltd. All rights reserved.

Chemical References

• Isoenzymes
• Steroids
• 3-Hydroxysteroid Dehydrogenases

Topics

• 3-Hydroxysteroid Dehydrogenases (antagonists & inhibitors, genetics, metabolism)
• Breast Neoplasms (drug therapy, enzymology)
• Cell Line
• Female
• Humans
• Isoenzymes (antagonists & inhibitors, genetics, metabolism)
• Models, Molecular
• Molecular Structure
• Mutation
• Protein Conformation
• Steroids (chemistry, metabolism)