LP-533401 is an inhibitor of Tryptophan hydroxylase 1. It is used for regulates serotonin production in the gut.

At a dose of 1 μM, LP-533401 fully suppresses serotonin production in Tph1–expressing cells [1].

Mice treated repeatedly with LP-533401 (30–250 mg/kg per day) exhibit marked 5-HT content reductions in the gut, lungs, and blood, but not in the brain. Adult, healthy mice treated with the Tph-1 inhibitor LP-533401 display a 30% decrease in circulating serotonin levels, with a consequent 30% increase in osteoblast numbers. Pharmacokinetic studies in rodents show that the LP-533401 level in the brain is negligible following oral administration, indicating that it is virtually unable to cross the blood-brain barrier[1]. Lung and gut 5-HT contents decrease by 50%, after a single LP533401 dose (250 mg/kg), whereas blood 5-HT levels remain unchanged, suggesting gut and lung 5-HT synthesis[2]. Administration of LP533401 to mice injected with EL4 cells inhibits the decrement in osteoblast numbers and trabecular bone volume prolongs survial, and decreases leukemic infiltration[3].