Aldosterone synthase (
CYP11B2) represents a promising
drug target because its genetic dysregulation is causally associated with
cardiovascular disease, its autonomous activity leads to primary
aldosteronism, and its deficiency leads to
salt wasting syndromes. The serendipitous discovery that the dextro-rotatory stereoisomer of the racemic
aromatase (CYP19A1) inhibitor
CGS16949A mediates potent
CYP11B2 inhibition led to the purification and clinical development of dexfadrostat
phosphate. To characterize the pharmacophore of dexfadrostat
phosphate, structure-based
enzyme coordination with
CYP11B2,
CYP11B1 and CYP19A1 was combined with
steroid turnover upon in vitro and clinical treatment. Dexfadrostat, but not its 5S-enantiomer (5S-fadrozole), precisely coordinates with the catalytic
heme moiety in the space of the
CYP11B2 substrate binding pocket forming a tight and stable complex. Conversely, neither rigid nor flexible docking led to a plausible coordination geometry for dexfadrostat in
steroid 11β-hydroxylase (
CYP11B1 - orthologue to
CYP11B2) or in CYP19A1. The inhibitory preference of dexfadrostat was confirmed in vitro using an adrenal cortex-derived cell line. Dexfadrostat
phosphate treatment of healthy subjects in the context of a clinical phase 1 study led to a dose-dependent decrease in urinary
aldosterone secretion, accompanied by an increase in urinary
corticosterone and
deoxycorticosterone metabolites. Increased urinary
corticosterone metabolites are indicative of
CYP11B2 (18-oxidase) inhibition with clinical features reminiscent of patients with inborn
corticosterone methyloxidase type II deficiency. An off-target effect on CYP19A1 was not observed as indicated by no clinical changes in
testosterone and
estradiol levels. Therefore, dexfadrostat exhibits the ideal structural features for binding and catalytic inhibition of
CYP11B2 but not
CYP11B1. Clinically, treatment with dexfadrostat
phosphate leads to suppression of
aldosterone levels by inhibiting predominantly one or both final CYP11B2-mediated reactions.