Phytocannabinoids for Cancer Therapeutics: Recent Updates and Future Prospects.

Phytocannabinoids (pCBs) are lipid-soluble phytochemicals present in the plant, Cannabis sativa L. and non-cannabis plants which have a long history in recreation and traditional medicine. The plant and the constituents isolated were central in the discovery of the endocannabinoid system (ECS), the most new target for drug discovery. The ECS includes two G-protein-coupled receptors; the cannabinoid receptors-1 and -2 (CB1 and CB2) for marijuana's psychoactive principle Δ(9)-tetrahydrocannabinol (Δ(9)-THC), their endogenous small lipid ligands; namely anandamide (AEA) and 2-arachidonoylglycerol (2-AG), also known as endocannabinoids and the enzymes for endocannabinoid biosynthesis and degradation such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). The ECS has been suggested as a pro-homeostatic and pleiotropic signaling system activated in a time- and tissue-specific way during pathological conditions including cancer. Targeting the CB1 receptors becomes a concern because of adverse psychotropic reactions. Hence, targeting the CB2 receptors or the endocannabinoid metabolizing enzymes by pCBs obtained from plants lacking psychotropic adverse reactions has garnered interest in drug discovery. These pCBs derived from plants appear safe and effective with a wider access and availability. In the recent years, several pCBs derived other than non-cannabinoid plants have been reported to bind to and functionally interact with cannabinoid receptors and appear promising candidate for drug development including cancer therapeutics. Several of them also targets the endocannabinoid metabolizing enzymes that control endocannabinoid levels. In this article, we summarize and critically discuss the updates and future prospects of the pCBs as novel and promising candidates for cancer therapeutics.