Structure-based Discovery of Conformationally Selective Inhibitors of the Serotonin Transporter

SUMMARYThe serotonin transporter (SERT) removes synaptic serotonin and is the target of anti-depressant drugs. SERT adopts three conformations: outward-open, occluded, and inward-open. All known inhibitors target the outward-open state except ibogaine, which has unusual anti-depressant and substance-withdrawal effects, and stabilizes the inward-open conformation. Unfortunately, ibogaine s promiscuity and cardiotoxicity limits understanding of inward-open state ligands. We docked over 200 million small molecules against the inward-open state of SERT. Thirty-six top-ranking compounds were synthesized and thirteen inhibited with further structure-based optimization leading to the selection of two potent (low nanomolar) inhibitors. These stabilized an outward-closed state of SERT with little activity against common off-targets. A cryo-EM structure of one of these bound to SERT confirmed the predicted geometry. In mouse behavioral assays, both compounds had anxiolytic- and anti-depressant-like activity, with potencies up to 200-fold better than fluoxetine (Prozac), and one substantially reversed morphine withdrawal effects.Graphical AbstractIn Brief:Development of low nM inhibitors conferring anti-depressant-like and anti-opioid withdrawal actions in mice from a large virtual library screened against the inward-open conformation of SERT.