PROJECT SUMMARY Obesity is a growing epidemic in the United States, leading to increases in cases of nonalcoholic fatty liver disease (NAFLD), cardiovascular disease, and type II diabetes. A common characteristic of these diseases is aberrant lipid and glucose metabolism. This proposal centers on the nuclear hormone receptor, Liver Receptor Homolog 1 (LRH-1), which acts as an important regulator of lipid metabolism, reverse cholesterol transport, glucose sensing, and homeostasis. As such, LRH-1 represents a novel therapeutic target for metabolic diseases. LRH-1 binds to phospholipids (PLs) and is activated by the unusual PL dilauroylphosphatidylcholine (DLPC) which shows potent anti-diabetic effects. The discovery that LRH-1 is regulated by PL ligands reveals an exciting potential to tune LRH-1 activity for the treatment of metabolic diseases. However, PLs are labile and not suitable for clinical use, necessitating the development of small molecule agonists. This has proved challenging thus far, since very few small molecules can displace endogenous lipids from the large, lipophilic binding pocket. Recent studies in our lab have characterized a class of small molecules that are capable of this feat. Using robust SAR and innovative chemistry, we have designed potent LRH-1 agonists that display biological activity. We have modified our most potent and efficacious agonists to improve their biophysical properties, making them suitable for in vivo studies. The advancement of LRH-1 agonists as therapeutics has also been hindered by the lack of appropriate rodent models to screen potential candidates due to small sequence differences in the binding pocket of rodent and human LRH-1. To overcome this barrier, we used a CRISPR-Cas9 strategy to humanize the mouse LRH-1 ligand binding pocket. This permits activation by synthetic agonists while minimizing changes to endogenous interaction surfaces. These leaps forward in lead compound development and mouse model generation, in combination with our deep knowledge of LRH-1 structure and function, create an ideal platform to develop candidate preclinical LRH-1 modulators for metabolic disease. Here, we have developed a strategy to define mechanisms of action, target engagement, pharmacology, and disease efficacy of our lead compounds. In aim 1, we generate compounds with improved biophysical properties that mimic PL-like activation. We will perform mechanistic characterization of these compounds to explore how contacting the PL-binding site with different polar moieties improves LRH-1 activation. In aim 2, we will examine the behavior of our lead compounds from an ADME perspective. The primary objective will be to establish tractability of the compounds using our humanized mice, so that pharmacokinetic relationships can be established. In aim 3, we will use our humanized mice and a model of diet-induced obesity to evaluate the in vivo efficacy of our lead LRH-1 compounds to improve glucose tolerance and insulin ...