Receptor-Selective Modulation of Cannabinoid Signaling by Cardamonin: Integrating Molecular Dynamics, Free Energy Calculations, and Behavioral Validation.

Cardamonin, a naturally occurring chalcone derivative, has demonstrated potential as a modulator of the endocannabinoid system (ECS). However, its interactions with cannabinoid receptors CB1 and CB2 are not fully understood. This work integrates in silico and in vivo methodology to examine the structural dynamics and pharmacological effects of cardamonin. Molecular dynamics simulations spanning 1000 ns demonstrated that cardamonin shows modest, receptor-dependent effects on CB1 dynamics, as shown by diminished root-mean-square deviation (RMSD) and fluctuation (RMSF), reduced solvent-accessible surface area (SASA), and increased hydrogen bonding. Principal component analysis (PCA) further demonstrated increased conformational sampling in CB1 following ligand binding, implying alteration of receptor flexibility. Conversely, CB2 had little structural alterations, indicating weaker or less selective binding. MM/PBSA binding energy calculations corroborated these findings, revealing that cardamonin exhibited comparable binding affinity at CB1 (-19.58 ± 6.49 kcal/mol) and CB2 (-18.76 ± 3.97 kcal/mol), with only a slight numerical tendency toward CB1. Both interactions were mild relative to the native ligands. Functional validation using Von Frey and Hargreaves behavioral experiments indicated that cardamonin markedly reduced mechanical and thermal hypersensitivity in mouse models. Significantly, some analgesic effects were maintained even with specific CB1 or CB2 blockade, suggesting receptor-biased or multitarget action. The robust alignment between computational predictions and behavioral evidence identifies cardamonin as a receptor-selective, physically stabilizing, and functionally significant modulator of CB1, with potential implications in nonopioid pain treatment approaches.