Cannabinoid receptors orchestrate distinct anti-tumour pathways in gastric cancer via and beyond specialized pro-resolving mediators

Endocannabinoids (ECS) and specialized pro-resolving mediators (SPMs) are both lipid-based compounds, but differ significantly in origin, mechanisms, and functions. Their mechanistic interaction in cancer remains undefined, particularly in gastric cancer (GC). Several interconnections have been described between these two "bioactive lipids" involved in inflammation resolution, homeostatic and anti-tumour functions. Cannabinoid signalling can modulate SPM biosynthesis in immune cells, thus we investigated whether this crosstalk operates in GC cells, and whether SPMs mediate part of the anti-tumour activity of cannabinoid receptors. Using synthetic and selective agonists for the cannabinoid G-protein-coupled receptors CB1 and CB2 (ACEA and JWH133, respectively), we found that receptor activation in GC cells (AGS and MKN45) sustains the synthesis of two SPMs, Resolvin D1 and Lipoxin B4, which in turn suppresses the angiogenic potential of GC cells. These CB1/CB2-driven activities required a SRC/MAPK signalling. At physiological concentrations, these SPMs further enhanced the binding affinity of ACEA and JWH133 for CB1 and CB2, indicating a functional crosstalk between the two systems. Beyond angiogenesis, CB1/2 stimulation reduced cell proliferation and viability, induced apoptosis, impaired the migration and the epithelial-to-mesenchymal program in GC cells. Only CB2 activation reduced the stemness properties of GC cells. Interestingly, while the anti-angiogenic properties of CB1 and CB2 required SPM production, their other anti-tumour actions were independent of the pro-resolving pathway. Our results extend the current knowledge of the endocannabinoid system by defining a new dual mechanism, SPM-dependent and SPM-independent, that restrains GC progression and identify the ECS-SPM axis as a potential target for therapeutic intervention.