Cannabidiol Suppresses Metastatic Castration-Resistant Prostate Cancer Progression and Recurrence through Modulating Tryptophan Catabolism.

Metastatic castration-resistant prostate cancer (mCRPC) is an aggressive phenotype of prostate cancer (PC). Tryptophan oxidative catabolism by indoleamine 2,3-dioxygenase-1 (IDO1) cleaves the indole ring to kynurenine (Kyn), an endogenous ligand for the aryl hydrocarbon receptor (AhR), which activates multiple tumorigenesis pathways. The IDO1-Kyn-AhR axis is aberrantly dysregulated in mCRPC. (-)-Cannabidiol (CBD) is a nonpsychoactive phytocannabinoid. CBD showed antitumor activities against human malignancies, including PC. CBD showed potent in vitro dose-dependent reduction of viability and clonogenicity of diverse human PC cell lines. CBD reduced the expression of IDO1 and AhR in PC cells. A daily 15 mg/kg oral dose of CBD for 30 days effectively suppressed the progression of the mCRPC CWR-R1ca-Luc cells xenografted in male nude mice. Continued CBD oral dosing for an additional 45 days suppressed the CWR-R1ca-Luc tumor locoregional and distant recurrences after the primary tumors' surgical excision. Collected CBD-treated tumors showed a reduced level of IDO1 expression. CBD-treated mice displayed a significant systemic reduction of Kyn. CBD is a novel, nonpsychoactive phytocannabinoid lead useful for the control of mCRPC via targeting the tryptophan catabolism.