As a precursor of the auxin, tryptophol not only possesses hypnotic effect [103] and reduces the production of Prostaglandin E2 (PGE2), TNFα, and IFNγ [104,105], but also inhibits the activity of butyrylcholinesterase [106] and the proliferation of leukemia U937 cells [107]. Here, BCHE is linked to leukemia.