PROJECT SUMMARY In the US, nearly half of all pregnant women are treated with a synthetic version of the neuropeptide oxytocin to induce or augment labor or prevent postpartum hemorrhage. However, women require a wide range of oxytocin doses to elicit an appropriate degree of uterine contractility. Furthermore, the oxytocin receptor (OXTR) can cease to respond to oxytocin (become desensitized) after long-term oxytocin administration, often leading to the need for cesarean delivery. Failure of OXTR activation can lead to substantial maternal morbidity and, in extreme cases, mortality due to postpartum hemorrhage. Our long-term goal is to develop strategies to improve OXTR responsiveness and thereby improve safety for pregnant women. In our parent grant, we hypothesized that OXTR genetic variants are contributing to the observed differences in individual response to oxytocin and propose to quantitate these effects in order to build a computational model able to predict response. In this supplement, we propose to develop a new approach for regulation of OXTR activity by identifying and characterizing OXTR positive allosteric modulators (PAMs). OXTR PAMs would be ideal therapeutics because they do not activate their target receptor in the absence of an agonist. Instead, they enhance endogenous ligand activity by binding to the receptor outside of the native ligand binding site. Thus, OXTR PAMs would predominantly enhance OXTR activation in the uterus, where oxytocin concentration is highest, and follow the same temporal OXTR activation pattern brought about by pulsatile oxytocin release during labor. We will pursue two Specific Aims: 1) Identify and validate positive allosteric modulators of OXTR, and 2) Determine how the top hit compounds enhance OXTR signaling. In order to identify the PAMs, we will perform a large-scale screen of diverse small-molecule compounds. In characterizing PAM effects on OXTR signaling, we will also obtain quantitative data to enhance our computational approaches. Together, data from the funded R01 and this supplement will lead to individualized oxytocin administration and an alternative pharmacologic approach to activate OXTR to induce or augment labor.