Polymethoxyflavones: Chemistry and Molecular Mechanisms for Cancer Prevention and Treatment

Polymethoxyflavones (PMFs) are one group of the flavonoid compounds, with tangeretin (Tan) and nobiletin (Nob) being the most abundant PMFs in citrus peel. Numerous biological activities of PMFs have been intensively studied, including anti-inflammatory and anticancer activities. Because of their methoxy groups, PMFs are more lipophilic than hydroxyl flavones, which may affect their biological activities. In addition, researchers found that hydroxylated PMFs (HPMFs) are one of the major metabolites of PMFs in animal urine and feces. Although PMF and HPMFs do show anticancer activity against different types of cancers, but their low hydrophilicity is still a crucial factor that may affect their biological effectiveness. Therefore, from the pharmaceutical aspect, chemical modifications of PMFs have been carried out to obtain acetylated PMFs (Ac-PMFs) for enhancing their biological effects. From the past centuries to the present, cancer is still a critical disease that needs to be solved. Carcinogenesis can be simply divided into three stages: initiation, promotion, and progression. These three stages involve different biological events, such as DNA mutation, cell proliferation, cell growth, and metastasis. In this paper, we aim to illustrate the biological effects of different PMFs, HPMFs, PMF derivatives, and metabolites against different types of cancer and related molecular mechanisms.