Discovery of a First-in-Class Gut-Restricted RET Kinase Inhibitor as a Clinical Candidate for the Treatment of IBS

Abstract

Abdominal pain and abnormal bowel habits represent major symptoms for irritable bowel syndrome (IBS) patients that are not adequately managed. Although the etiology of IBS is not completely understood, many of the functions of the gastrointestinal (GI) tract are regulated by the enteric nervous system (ENS). Inflammation or stress-induced expression of growth factors or cytokines may lead to hyperinnervation of visceral afferent neurons in GI tract and contribute to the pathophysiology of IBS. Rearranged during transfection (RET) is a neuronal growth factor receptor tyrosine kinase critical for the development of the ENS as exemplified by Hirschsprung patients who carry RET loss-of-function mutations and lack normal colonic innervation leading to colonic obstruction. Similarly, RET signaling in the adult ENS maintains neuronal function by contributing to synaptic formation, signal transmission, and neuronal plasticity. Inhibition of RET in the ENS represents a novel therapeutic strategy for the normalization of neuronal function and the symptoms of IBS patients. Herein, we describe our screening effort and subsequent structure-activity relationships (SARs) in optimizing potency, selectivity, and mutagenicity of the series, which led to the discovery of a first-in-class, gut-restricted RET kinase inhibitor, 2-(4-(4-ethoxy-6-oxo-1,6-dihydropyridin-3-yl)-2-fluorophenyl)--(5-(1,1,1-trifluoro-2-methylpropan-2-yl)isoxazol-3-yl)acetamide (, GSK3179106), as a clinical candidate for the treatment of IBS. GSK3179106 is a potent, selective, and gut-restricted pyridone hinge binder small molecule RET kinase inhibitor with a RET IC of 0.3 nM and is efficacious .

Enteric RET inhibition attenuates gastrointestinal secretion and motility via cholinergic signaling in rat colonic mucosal preparations

“…To understand the function of enteric RET, a potent, selective, and GI-restricted small molecule inhibitor of RET, GSK3179106, was employed. 12 We demonstrate that RET inhibition had profound effects on intestinal epithelial permeability, carbachol-induced secretion, and neostigmine-induced motility. Our data suggest that RET kinase activity in the adult gut functions as part of intrinsic neural pathways regulating gut mucosal and smooth muscle function.…”

“…To understand the functional implications of RET inhibition within the bowel, we used GSK3179106, a potent, selective, reversible, and GI‐restricted RET inhibitor that is equally potent against the human and rat RET enzymes . It is active in multiple cell‐based assays of functional RET activity and is highly selective for RET as demonstrated by in vitro kinase assays and proteomic profiling in colon lysates.…”

“…However, while we are confident that RET is the likely target for the observed findings utilizing GSK3179106 based on our findings and published literature, we cannot rule out the potential effects GSK3179106 may have on DDR1 and DDR2 as well as other kinases at high concentrations. Moreover, GSK3179106 is minimally absorbed through the GI tract when dosed orally resulting in low systemic bioavailability and negligible brain penetration . These characteristics make GSK3179106 a useful tool for studying the effects of RET inhibition within the ENS without affecting systemic or central targets.…”

“…Our data revealed that RET transcripts were co‐expressed with ChAT in enteric ganglia. To understand the function of enteric RET, a potent, selective, and GI‐restricted small molecule inhibitor of RET, GSK3179106, was employed . We demonstrate that RET inhibition had profound effects on intestinal epithelial permeability, carbachol‐induced secretion, and neostigmine‐induced motility.…”

Measurement of novel intestinal secretory and barrier pathways and effects of proteases

“…In response to EFS, Russell et al noted a significant reduction in ion transport when RET was inhibited with GSK3179106 and normalization of fecal output in a rat model of neostigmine induced accelerated transit. GSK3179106 is a gut‐restricted pyridine hinge binder small‐molecule RET kinase inhibitor shown to reduce colonic hypersensitivity in a mouse model of acute irritation stress . The observation that GSK3179106 also reduces ionic transports demonstrates RET has a functional role beyond ENS development.…”