From Discovery to Clinical Trial: YCT-529, an Oral NonHormonal Male Contraceptive Targeting the Retinoic Acid Receptor Alpha

The
retinoic acid receptor alpha (RARα) has emerged
as a
compelling genetically and pharmacologically validated target for
nonhormonal male contraception due to its essential role in spermatogenesis.
In the present study, a search for specific inhibitors of RARα
utilized systematic linker bioisosterism, hydrophobic core modification,
and iterative structure–activity relationship refinement, identified the acid 9, a pyrrole-linked analog that potently
inhibits RARα (IC50 = 1.2 nM) with >300-fold selectivity
over RARβ and RARγ. Sprague–Dawley rat studies
with the sodium salt of 9, YCT-529, showed
good oral bioavailability and dose-proportional pharmacokinetics without
drug accumulation after 28 days of dosing. Once-daily oral administration
(0.75 mg/kg for 28 days) reversibly suppressed epididymal sperm counts
and fertility in rats, with a no-observed-adverse-effect level at
30 mg/kg (highest dose tested), affording a ≥40-fold therapeutic
window. These findings validated aromatic linker substitution as a
powerful design strategy for identifying RARα antagonists and
led to the clinical advancement of YCT-529 as a nonhormonal
male contraceptive.