Nobiletin in Cancer Therapy; Mechanisms and Therapy Perspectives

Cancer has remained to be one of the major challenges in medicine and regarded as the second leading cause of death worldwide. Different types of cancer may resist anti-cancer drugs following certain mutations such as those in tumor suppressor genes, exhaustion of the immune system, and overexpression of drug resistance mediators, which increase the required concentration of anticancer drugs so as to overcome drug resistance. Moreover, treatment with a high dose of such drugs is highly associated with severe normal tissue toxicity. Administration of low-toxic agents has long been an intriguing idea to enhance tumor suppression. Naturally occurring agents e.g., herb-derived molecules have shown a dual effect on normal and malignant cells. On the one hand, these agents may induce cell death in malignant cells, while on the other hand reduce normal cell toxicity. Nobiletin, one of the well-known polymethoxyflavones (PMFs), has reportedly shown various beneficial effects on the suppression of cancer and the protection of normal cells against different toxic agents. Our review aims to explain the main mechanisms underlying nobiletin as an inhibitor of cancer. We have reviewed the mechanisms of cancer cell death caused by nobiletin, such as stimulation of reactive oxygen species (ROS), modulation of immune evasion mechanisms, targeting tumor suppressor genes, and modulation of epigenetic modulators, among others; the inhibitory mechanisms of nobiletin affecting tumor resistance properties such as modulation of hypoxia, multidrug resistance, angiogenesis, epithelial-mesenchymal transition (EMT) have been fully investigated. Also, the inhibition of anti-apoptotic and invasive mechanisms induced by nobiletin will later be discussed. In the end, protective mechanisms of nobiletin on normal cells/tissue, clinical trial results, and future perspectives are reviewed.