Anticancer Activity of Cannabidiol (CBD) in Human Colorectal Cancer Cells: A Mechanistic Study

OBJECTIVES: Cannabidiol (CBD) is a major non-psychoactive bioactive component of the phytocannabinoids abundant in cannabis. Its potential use for treatment of colorectal cancer has been proposed by several studies. This study investigated the anti-cancer activity of CBD and the mechanism of that activity in human colorectal cancer cells. METHODS: Human colorectal cancer cell lines (SW620, SW480, HCT116, and Caco-2) and a human normal colon cell line (CCD18CO) were maintained in DMEM supplemented with 10% FBS and antibiotics. Cell viability was measured by MTT assay. Cell cycle phase was measured by flow cytometry. Apoptosis was analyzed by measuring caspase 3/7 enzyme activity. Western blotting was performed to compare expression of proteins regulating cell cycle arrest, apoptosis, and endoplasmic reticulum (ER) stress. Selective inhibitors for cannabinoid receptors were used to test the relevance of each receptor for CBD-mediated cell viability repression and apoptosis induction. Different types of CBD derivatives were tested for effects on cell viability. Data were analyzed using one-way analysis of variance (ANOVA), or two-way ANOVA followed by Bonferroni post-hoc tests (Dunnett T3 tests for unequal variance) for intergroup comparisons. RESULTS: CBD repressed viability of SW620, SW480, HCT116, and Caco-2 human colorectal cancer cells, with respective IC50 values of 5.4, 10.4, 10.8, and 20 μM for 24-hour treatment and 4.7, 5.8, 5.7, and 13.8 μM for 48-hour treatment. Moreover, CBD treatment led to G1-phase cell cycle arrest and an increased sub-G1 population with downregulation of cyclin D1, cyclin D3, CDK2, CDK4, and CDK6. It also increased activity of caspase 3/7, production of cleaved PARP, and expression of ER stress proteins (BiP, IRE1α, p-eIF2, ATF3 and ATF4). Repression of cell viability and induction of apoptotic cell death occurred through a mechanism dependent on cannabinoid receptor type 2 (CB2). Suppression of cell viability was also observed in cells treated with other of non-psychoactive cannabinoid derivatives (cannabidivarin, cannabigerol, cannabicyclol, cannabigerovarin). CONCLUSIONS: Our data indicate that CBD and its derivatives could be promising agents for the prevention of human colorectal cancer. FUNDING SOURCES: No funding source.