Structural Basis of Nanomolar Inhibition of Tumor-Associated Carbonic Anhydrase IX: X‑Ray Crystallographic and Inhibition Study of Lipophilic Inhibitors with Acetazolamide Backbone

This study provides a structure–activity
relationship study
of a series of lipophilic carbonic anhydrase (CA) inhibitors with
an acetazolamide backbone. The inhibitors were tested against the
tumor-expressed CA isozyme IX (CA IX), and the cytosolic CA I, CA
II, and membrane-bound CA IV. The study identified several low nanomolar
potent inhibitors against CA IX, with lipophilicities spanning two
log units. Very potent pan-inhibitors with nanomolar potency against
CA IX and sub-nanomolar potency against CA II and CA IV, and with
potency against CA I one order of magnitude better than the parent
acetazolamide 1 were also identified in this study, together
with compounds that displayed selectivity against membrane-bound CA
IV. A comprehensive X-ray crystallographic study (12 crystal structures),
involving both CA II and a soluble CA IX mimetic (CA IX-mimic), revealed
the structural basis of this particular inhibition profile and laid
the foundation for further developments toward more potent and selective
inhibitors for the tumor-expressed CA IX.