Progress in the development of oxytocin antagonists for use in preterm labor

Area of Science:

• Pharmacology
• Obstetrics
• Medicinal Chemistry

Background:

• Current treatments for preterm labor, such as beta-mimetics, have limitations in safety and efficacy.
• Oxytocin receptor blockade is a potential alternative for tocolysis, with clinical support from agents like atosiban.
• There is a need for non-peptide oxytocin antagonists suitable for both oral and intravenous administration.

Purpose of the Study:

• To identify and characterize novel non-peptide oxytocin antagonists for preterm labor treatment.
• To evaluate the preclinical profile of L-372,662, a new oxytocin antagonist from a benzoxazinone class.

Main Methods:

• Synthesis and characterization of non-peptide oxytocin antagonists.
• Assay of human oxytocin receptor affinity and selectivity against vasopressin receptors.
• In vivo efficacy studies in late gestation pregnant rhesus monkeys to assess antagonism of oxytocin-induced contractions.
• Evaluation of oral bioavailability in dogs and aqueous solubility.

Main Results:

• L-372,662 exhibits high affinity for the human oxytocin receptor (Ki = 4.9 nM).
• Demonstrated high selectivity for oxytocin receptors over vasopressin receptors (> 500-fold).
• Potent antagonism of oxytocin-induced uterine contractions in rhesus monkeys (AD50 = 36 µg/kg) with excellent oral bioavailability (F = 90% in dogs) and good aqueous solubility (10 mg/mL).

Conclusions:

• L-372,662 represents a promising non-peptide oxytocin antagonist with a favorable preclinical profile.
• Its properties suggest potential for development as an orally administered tocolytic agent for preterm labor.
• This compound offers a potential therapeutic advancement beyond existing beta-mimetic agents.