Abstract by Katrine Schultz-Knudsen
The search for novel treatments for inflammatory and fibrotic diseases has gained significant attention in recent years, driven by the global disease burden and high unmet medical need in these areas. These diseases are often characterized by complex interactions among multiple cell types, rendering the development of effective treatment regimens challenging. Several G protein-coupled receptors that are expressed on fibroblasts, macrophages, and neutrophils, including G protein-coupled receptor 84 (GPR84), free fatty acid receptor (FFA) 2, FFA4, and lysophosphatidic acid receptor 1 (LPA1), have been implicated in the pathogenesis of inflammation and fibrosis. This thesis explores the pharmacology of ligands targeting these receptors in vitro.
GPR84, a receptor that is highly expressed on macrophages and neutrophils, has been identified as a proinflammatory mediator and a potential target for treatment of inflammatory diseases, such as fibrosis and ulcerative colitis. Manuscripts I and II describe the discovery and optimization of a novel GPR84 negative allosteric modulator scaffold, with nanomolar potency, favorable pharmacokinetic properties, and the ability to inhibit GPR84-mediated activation of human polymorphonuclear leukocytes.
Manuscript III focuses on the development of a fluorescent tracer with subnanomolar affinity towards GPR84. This tracer was employed to confirm the allosteric binding mode of the novel GPR84 antagonist series and provided insights into the binding kinetics of several reported GPR84 antagonists. The tracer was also used to reveal that a faster dissociation rate on the mouse GPR84 receptor was a key driver of the lower affinity observed on the mouse receptor ortholog, when compared to the human ortholog. Additionally, the tracer was used to demonstrate the upregulation of GPR84 expression on M1-polarized THP-1 macrophages, following lipopolysaccharide treatment.
FFA2, another immunomodulatory receptor, is currently being studied for its role in inflammation. Manuscript IV presents the optimization of a known FFA2 antagonist scaffold through bioisosteric replacement, resulting in compounds with enhanced potency and physicochemical properties. Notably, this series also includes the first reported FFA2 antagonist with activity on the mouse receptor ortholog.
In Manuscript V, the effects of TUG-891 (an FFA4 agonist), and AM966 (an LPA1 antagonist) on activated human fibroblasts are explored. Treatment with each compound resulted in a concentration-dependent reduction in fibroblast activation, and co-treatment with both compounds produced an additive effect, further potentiating the inhibition of fibroblast activation.
In conclusion, the ligands investigated in this thesis provide novel insights into the pharmacological function and roles of GPR84, FFA2, FFA4, and LPA1 in inflammation and fibrosis. Collectively, the studies highlight the potential of targeting these receptors as therapeutic strategies for managing inflammatory and fibrotic diseases.