Identification of inhibitors of tryptophan hydroxylase 1

Background: In this study we use molecular docking to find compounds that interact with the enzyme tryptophan hydroxylase (TPH), followed by experimental validation. TPH is a tetrahydrobiopterin (BH4) dependent enzyme that catalyze the conversion of L-tryptophan to 5-hydroxytryptophan (5-OH-Trp). The reaction is the first and also rate limiting step in the synthesis of serotonin (5-hydroxytryptamine, 5-HT) which is precursor for the biosynthesis of melatonin. It was long believed that TPH was encoded by a single gene, but in 2003 Walther et al. reported that TPH was encoded by two genes in mammals, encoding two different enzymes (TPH1 and TPH2). TPH2 is mostly expressed in the brain being responsible for physiological processes like sexual behaviour, appetite, mood and learning. TPH1 is most abundantly expressed in the gastrointestinal tract where it is involved in several biological functions and is the enzyme we have focused on in this study. Serotonin is an important regulator of GI function. Dysregulation of the serotonin production in this area is associated with symptoms of irritable bowel syndrome (IBS), such as abdominal pain and diarrhea, chemotherapy-induced nausea and vomiting and pulmonary hypertension. Direct inhibition of TPH1 is an approach that has been very little explored as a therapeutic approach, due to the importance of 5-HT in the brain and the challenges in selective reduction of 5-HT in the periphery. The discovery of the two distinct genes that encodes two distinct enzymes, TPH1 and TPH2, provides the possibility of selective inhibition of TPH1. Method: In this thesis both virtual and experimental methods were used. In order to find potential inhibitors of TPH1, molecular docking of a large virtual database was performed, followed by activity measurements in the laboratory. Results: From the molecular docking together with experimental validation we found 11 compounds that inhibited TPH1 activity significantly. 4 of these compounds also decreased the thermal stability of TPH1. Conclusion: We have found one compound that is a potent inhibitor of TPH1 and could be a valuable starting point for hit-to-lead optimization