Novel 5-HT receptor antagonists modulate intestinal immune responses and reduce severity of colitis.

Inflammatory bowel disease (IBD) encompasses several debilitating chronic gastrointestinal (GI) inflammatory disorders, including Crohn's disease and ulcerative colitis. In both conditions, mucosal inflammation is a key clinical presentation associated with altered serotonin (5-hydroxytryptamine or 5-HT) signaling. This altered 5-HT signaling is also found across various animal models of colitis. Of the 14 known receptor subtypes, 5-HT receptor type 7 (5-HT) is one of the most recently discovered. We previously reported that blocking 5-HT signaling with either a selective 5-HT receptor antagonist (SB-269970) or genetic ablation alleviated intestinal inflammation in murine experimental models of colitis. Here, we developed novel antagonists, namely, MC-170073 and MC-230078, which target 5-HT receptors with high selectivity. We also investigated the in vivo efficacy of these antagonists in experimental colitis by using dextran sulfate sodium (DSS) and the transfer of CD4CD45RB T cells to induce intestinal inflammation. Inhibition of 5-HT receptor signaling with the antagonists, MC-170073 and MC-230078, ameliorated intestinal inflammation in both acute and chronic colitis models, which was accompanied by lower histopathological damage and diminished levels of proinflammatory cytokines compared with vehicle-treated controls. Together, the data reveal that the pharmacological inhibition of 5-HT receptors by these selective antagonists ameliorates the severity of colitis across various experimental models and may, in the future, serve as a potential treatment option for patients with IBD. In addition, these findings support that 5-HT is a viable therapeutic target for IBD. This study demonstrates that the novel highly selective 5-HT receptor antagonists, MC-170073 and MC-230078, significantly alleviated the severity of colitis across models of experimental colitis. These findings suggest that inhibition of 5-HT receptor signaling by these new antagonists may serve as an alternative mode of treatment to diminish symptomology in those with inflammatory bowel disease.