OPRM1 and lung cancer: In human lung cancer H358 cells, MOR ligands as morphine, [D-Ala2, MePhe4, Gly(ol)5]enkephalin (DAMGO), or fentanyl were proved to upregulate vimentin, SNAIL, and SLUG expression that entailed concomitant downregulation of claudin-1 and ZO-1 levels in a concentration-dependent manner (Table 2).