Cannabidiol exerts anti-proliferative activity via a cannabinoid receptor 2-dependent mechanism in human colorectal cancer cells

Colorectal cancer is the third leading cause of cancer incidence and mortality in the United States. Cannabidiol (CBD), the second most abundant phytocannabinoid in Cannabis sativa, has potential use in cancer treatment on the basis of many studies showing its anti-cancer activity in diverse types of cancer, including colon cancer. However, its mechanism of action is not yet fully understood. In the current study, we observed CBD to repress viability of different human colorectal cancer cells in a dose-dependent manner. CBD treatment led to G1-phase cell cycle arrest and an increased sub-G1 population (apoptotic cells); it also downregulated protein expression of cyclin D1, cyclin D3, cyclin-dependent kinase 2 (CDK2), CDK4, and CDK6. CBD further increased caspase 3/7 activity and cleaved poly(ADP-ribose) polymerase, and elevated expression of endoplasmic reticulum (ER) stress proteins including binding immunoglobulin protein (BiP), inositol-requiring enzyme 1α (IRE1α), phosphorylated eukaryotic initiation factor 2α (eIF2α), activating transcription factor 3 (ATF3), and ATF4. We found that CBD repressed cell viability and induced apoptotic cell death through a mechanism dependent on cannabinoid receptor type 2 (CB2), but not on CB1, transient receptor potential vanilloid, or peroxisome proliferator-activated receptor gamma. Anti-proliferative activity was also observed for other non-psychoactive cannabinoid derivatives including cannabidivarin (CBDV), cannabigerol (CBG), cannabicyclol (CBL), and cannabigerovarin (CBGV). Our data indicate that CBD and its derivatives could be promising agents for the prevention of human colorectal cancer.