Development of a Second-Generation RARα Selective Antagonist as an Orally Bioavailable, Effective, Safe, and...

Area of Science:

• Medicinal Chemistry
• Reproductive Biology
• Pharmacology

Background:

• Retinoic acid receptor alpha (RARα) plays a crucial role in spermatogenesis.
• Targeting RARα presents a potential strategy for non-hormonal male contraception.
• Previous inhibitors lacked optimal potency, selectivity, or pharmacokinetic profiles.

Purpose of the Study:

• To design and synthesize novel benzopyran, benzofuran, and benzothiophene derivatives as RARα inhibitors.
• To identify potent and selective RARα inhibitors with favorable ADMET properties for male contraception.
• To evaluate the in vivo efficacy and pharmacokinetic profile of lead compounds in a mouse model.

Main Methods:

• Structure-activity relationship (SAR) studies were conducted on novel heterocyclic scaffolds.
• In vitro assays were used to determine RARα inhibitory potency and selectivity against RARβ and RARγ.
• In vivo studies in mice assessed oral bioavailability, sperm count reduction, and reversibility.
• Imaging mass spectrometry was employed to analyze compound distribution in testicular tissues.

Main Results:

• Compound 23, a benzopyran derivative, emerged as a highly potent RARα inhibitor (IC50 = 0.051 nM) with excellent selectivity.
• Compound 23 demonstrated good oral bioavailability and effectively reduced sperm counts in mice at low doses (0.3-1 mg/kg/day).
• Spermatogenesis was restored upon drug withdrawal, indicating reversibility, and compound 23 did not cross the blood-testis barrier.

Conclusions:

• Compound 23 is a promising non-hormonal male contraceptive candidate targeting RARα.
• Its high potency, selectivity, oral bioavailability, and reversible efficacy support further development.
• Understanding its mechanism of action within the seminiferous tubules provides insights for future drug design.