Rational Design, Synthesis and Pharmacological Evaluation of Chalcones as Dual-Acting Compounds—Histamine H3 Receptor Ligands and MAO-B Inhibitors

Chalcone-based derivatives were designed as dual-acting ligands targeting the histamine H₃ receptor (H₃R) and monoamine oxidase B (MAO-B), based on the lead compound <b>DL76</b>. Three series of compounds (<b>1</b>-<b>18</b>) were synthesised and characterised, including simple chalcones (<b>1</b>-<b>9</b>) and piperidinyl chalcones (<b>10</b>-<b>18</b>). All piperidinyl derivatives exhibited nanomolar affinity for human H₃R (hH₃R), with compounds <b>10</b>-<b>12</b> achieving K_i values ≤ 30 nM. Simple chalcones showed potent human MAO-B (hMAO-B) inhibition (IC₅₀: 0.85-337 nM), especially 3,4-dichloro derivatives. Compound <b>15</b> was the most active hybrid, with a K_i of 46.8 nM for hH₃R and an IC₅₀ of 212.5 nM for hMAO-B. Molecular docking and 250 ns simulations revealed stabilising interactions at both binding sites and clarified structural features behind dual activity. Preliminary ADMET profiling showed low Caco-2 permeability and rapid microsomal metabolism, mainly via hydroxylation. Compound <b>15</b> exhibited micromolar cytotoxicity in SH-SY5Y and HepG2 cells, induced G2/M arrest, disrupted mitochondrial homeostasis, and was genotoxic in Peripheral Blood Mononuclear Cells (PBMCs). Additionally, for H₃R ligands (<b>15</b>, <b>DL76</b>, pitolisant), the study reports the first use of Surface Plasmon Resonance Microscopy (SPRM) to assess their interactions with this receptor. Therefore, piperidinyl chalcones show promise as ligands with dual action on H₃R and MAO-B, useful in the treatment of neurodegeneration and/or CNS cancers.