The endocannabinoid system, particularly cannabinoid receptor 2 (CB2 in mice and CNR2 in humans), has controversial pathophysiological implications in colon cancer. Here, we investigate the role of CB2 in potentiating the immune response in colon cancer in mice and determine the influence of CNR2 variants in humans. Comparing wild-type (WT) mice to CB2 knockout (CB2−/−) mice, we performed a spontaneous cancer study in aging mice and subsequently used the AOM/DSS model of colitis-associated colorectal cancer and a model for hereditary colon cancer (ApcMin/+). Additionally, we analyzed genomic data in a large human population to determine the relationship between CNR2 variants and colon cancer incidence. Aging CB2−/− mice exhibited a higher incidence of spontaneous precancerous lesions in the colon compared to WT controls.
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.