Microsomal prostaglandin E synthase 1 (mPGES-1) is an α-helical homotrimeric integral membrane inducible enzyme that catalyzes the formation of prostaglandin E2 (PGE2) from prostaglandin H2 (PGH2). Inhibition of mPGES-1 has been proposed as a therapeutic strategy for the treatment of pain, inflammation, and some cancers. Interest in mPGES-1 inhibition can, in part, be attributed to the potential circumvention of cardiovascular risks associated with anti-inflammatory cyclooxygenase 2 inhibitors (coxibs) by targeting the prostaglandin pathway downstream of PGH2 synthesis and avoiding suppression of antithrombotic prostacyclin production. We determined the crystal structure of mPGES-1 bound to four potent inhibitors in order to understand their structure-activity relationships and provide a framework for the rational design of improved molecules. In addition, we developed a light-scattering-based thermal stability assay to identify molecules for crystallographic studies.

As part of a program aimed at the discovery of antinociceptive therapy for inflammatory conditions, a screening hit was found to inhibit microsomal prostaglandin E synthase-1 (mPGES-1) with an IC50 of 17.4 μM. Structural information was used to improve enzyme potency by over 1000-fold. Addition of an appropriate substituent alleviated time-dependent cytochrome P450 3A4 (CYP3A4) inhibition. Further structure-activity relationship (SAR) studies led to 8, which had desirable potency (IC50 = 12 nM in an ex vivo human whole blood (HWB) assay) and absorption, distribution, metabolism, and excretion (ADME) properties. Studies on the formulation of 8 identified 8·H3PO4 as suitable for clinical development. Omission of a lipophilic portion of the compound led to 26, a readily orally bioavailable inhibitor with potency in HWB comparable to celecoxib. Furthermore, 26 was selective for mPGES-1 inhibition versus other mechanisms in the prostanoid pathway. These factors led to the selection of 26 as a second clinical candidate.

Two 2-aminoimidazole-based inhibitors, LY3031207 (1) and LY3023703 (2), of the microsomal prostaglandin E synthase-1 (mPGES-1) enzyme were found to cause drug-induced liver injury (DILI) in humans. We studied imidazole ring substitutions to successfully mitigate reactive metabolite (RM) formation. These studies support the conclusion that RM formation may play a role in the observations of DILI and the consideration of 2-aminoimidazoles as structure alerts, due to the high likelihood of bioactivation to generate RMs.

Two allosteric modulators of the Group I metabotropic glutamate receptors (mGluR1 & mGluR5) were evaluated as positron emission tomography (PET) radioligands for mGluR1. Methods LY2428703, a full mGluR1 antagonist (IC50 = 8.9 nM) and partial mGluR5 antagonist (IC50 = 118 nM) and LSN2606428, a full mGluR1 and mGluR5 antagonist (IC50 = 35.3 nM and 10.2 nM, respectively) were successfully labeled with carbon-11 and evaluated as radioligands for mGluR1. A comprehensive assessment of the in vitro and in vivo pharmacology, Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS) biodistribution, and rat PET imaging of LY2428703 was conducted. In contrast, LSN2606428 was only evaluated in vitro; further evaluation was stopped due to its unfavorable pharmacological properties and binding affinity. Results 11C-LY2428703 showed promising characteristics, including: 1) high potency for binding to human mGluR1 (IC50 = 8.9 nM) with no significant affinity for other human mGlu receptors (mGluR2 through 8); 2) binding to brain displaceable by administration of an mGluR1 antagonist; 3) only one major radiometabolite in both plasma and brain, having negligible brain concentration (~3.5% of the total radioactivity in cerebellum) and no receptor affinity; 4) a large specific and displaceable signal in the mGluR1-rich cerebellum with no significant in vivo affinity for mGluR5, as shown with PET studies in rats; and 5) lack of substrate behavior for efflux transporters at the blood-brain barrier, as shown with PET studies conducted in wild-type and knock-out mice. Conclusion 11C-LY2428703, a new PET radioligand for mGluR1 quantification, displayed promising characteristics both in vitro and in vivo in rodents.