Effect of cannabinoids on the efficacy and side effects of anticancer therapeutic strategies – Current status of preclinical and clinical research

Cannabinoids have attracted increasing attention in cancer research in recent decades. A major focus of current preclinical and clinical studies is on the interactions and potential risks when combined with chemotherapeutic agents, targeted therapies and other anticancer strategies. Given the extensive preclinical data on additive, synergistic and, in some cases, antagonistic tumor cell killing effects of chemotherapeutic agents and cannabinoids when co-administered, a critical analysis of these data seems essential. The available data mainly relate to combination treatments for glioblastoma, hematological malignancies and breast cancer, but also for other cancer types. Such an analysis also appears necessary because cannabinoids are used as an option to treat nausea and vomiting caused by chemotherapy, as well as tumor-related pain, and cancer patients sometimes take cannabinoids without a medical prescription. In addition, numerous recent preclinical studies also suggest cannabinoid-mediated relief of other chemotherapy-related side effects such as peripheral neuropathy, nephrotoxicity, cardiotoxicity, cystitis, bladder complications and mucositis. To summarize, the data available to date raise the prospect that cannabinoids may increase the efficacy of chemotherapeutic agents while reducing their side effects. However, preclinical studies on anticancer interactions are mostly limited to cytotoxicity analyses. An equally thorough investigation of the effects of such combinations on the immune system and on the tumorigenic levels of angiogenesis, invasion and metastasis is still pending. On this basis, a comprehensive understanding for the evaluation of a targeted additional treatment of various cancers with cannabinoids could be established.