Design, Synthesis, and Pharmacological Evaluation of Sulfur-Containing Pitolisant Analogs as Potent H3R Antagonists for Epilepsy Therapy

Abstract

Although multiple antiseizure drugs (ASDs) are clinically accessible, epilepsy remains a debilitating neurological disorder with a high unmet need for more effective and better-tolerated therapies. Antagonism of the histamine H₃ receptor (H₃R) represents a promising alternative strategy, exemplified by the clinically approved inverse agonist/antagonist pitolisant (PIT) for narcolepsy. Herein, we designed a novel series of non-imidazole H₃R antagonists by introducing a sulfur atom into the PIT scaffold to modulate lipophilicity, flexibility, and target binding. The synthesis and pharmacological evaluation of 12 target compounds (3a–3h, 5a–5d) are reported. Compounds 3e and 3f showed potent H₃R antagonism with IC₅₀ values of 0.18 µM and 0.036 µM, respectively, with the latter more active than PIT (IC₅₀ = 0.1 µM). In the maximal electroshock (MES) model, 3f exhibited superior antiseizure activity (ED₅₀ = 14.0 mg/kg) compared to PIT (ED₅₀ = 16.3 mg/kg). What's more, compounds 3e and 3f showed significant seizure protection in a zebrafish pentylenetetrazol (PTZ) model, and favorable cytotoxicity and neurotoxicity profiles in cell and animal experiments. Compound 3f exhibits low hERG toxicity risk with an IC₅₀ of 1.83 µM compared to PIT (IC₅₀ = 1.51 µM), and excellent blood-brain barrier penetration with a brain-to-plasma ratio of 4.56. Molecular docking studies revealed stable interactions with key H₃R residues, including ASP114, VAL95, and PHE189. Collectively, these results indicate that 3f shows considerable promise as a lead candidate in the search for new antiepileptic drugs.