Steroids interfere with human carbonic anhydrase activity by using alternative binding mechanisms

Area of Science:

• Biochemistry and enzymology
• Medicinal chemistry
• Structural biology

Background:

• Bile acids are known inhibitors of human carbonic anhydrases (hCA) in the gastrointestinal tract.
• Previous X-ray crystallography elucidated the inhibition mechanism of cholate to hCA II.

Purpose of the Study:

• To extend bile acid inhibition studies to a broader range of steroids against four hCA isoforms.
• To investigate the inhibition mechanisms of various steroid chemotypes against cytosolic and tumor-associated carbonic anhydrases.

Main Methods:

• Enzyme inhibition assays were performed on four human carbonic anhydrase isoforms.
• Molecular docking studies were utilized to predict binding modes and inhibition mechanisms.
• Molecular dynamics simulations were employed to assess the stability of steroid-hCA complexes.

Main Results:

• Steroids with carboxylate, phenolic, or sulfonate groups appended to the tetracyclic ring inhibited hCA II and hCA IX.
• Inhibition occurred in the medium micromolar range (38.9–89.9 µM).
• Docking and MD studies provided insights into the distinct inhibition mechanisms and binding stability.

Conclusions:

• Various functionalized steroids exhibit inhibitory activity against key human carbonic anhydrase isoforms.
• These findings contribute to understanding steroid-CA interactions and developing novel CA-targeting agents.