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 DL76. Three series of compounds (1–18) were synthesised and characterised, including simple chalcones (1–9) and piperidinyl chalcones (10–18). All piperidinyl derivatives exhibited nanomolar affinity for human H3R (hH3R), with compounds 10–12 achieving Ki values ≤ 30 nM. Simple chalcones showed potent human MAO-B (hMAO-B) inhibition (IC50: 0.85–337 nM), especially 3,4-dichloro derivatives. Compound 15 was the most active hybrid, with a Ki 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 15 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 (15, DL76, 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.