Discovery and characterization of a novel tryptophan hydroxylase 1 inhibitor as a prodrug

Serotonin (5-HT) is an important neurotransmitter and paracrine signaling molecule in the gastrointestinal tract. Two distinct tryptophan hydroxylases (TPH), TPH1 and TPH2, are the rate-limiting enzymes in the 5-HT biosynthesis process. TPH1 expression is mainly limited in the enterochromaffin cells and distributed in peripheries such as the skin and gut, while TPH2 is the predominant isoform in the CNS. In this study, mol002291 was screened as a drug-like compound from the TCM database for the inhibitor of TPH. After the enzymological analysis of mol002291, the analgesic effect of mol002291 was also further investigated in a PI-IBS visceral hyperalgesia rat model. Results from kinetic analysis showed that mol002291 specifically inhibited the TPH1 but did not act on TPH2, and the inhibitory action displayed characteristics of competitive inhibition. In addition, the results from abdominal withdrawal reflex (AWR) tests and electromyography (EMG) recordings showed that mol002291 significantly (p<.05) alleviated the visceral hyperalgesia. This result is entirely consistent with the fact that mol002291 significantly decreased the 5-HT content. These data demonstrated that mol002291 can attenuate visceral hyperalgesia mediated via reducing colonic 5-HT content. More important is that mol002291 could be developed as a novel prodrug and offer therapeutic avenues for the diseases where there is dysregulation of peripheral serotonergic pathways.