Enhanced Water Solubility and Anti-Tumor Activity of Oleanolic Acid through Chemical Structure Modification

Cancer has been a major health problem in the world in the past decades. It is urgent to develop new, effective and safe drugs for the treatment of cancer. There are many pentacyclic triterpenoids with positive anti-tumor activity and safety in nature. Oleanolic acid (OA), as one of the pentacyclic triterpenoids, also has broad biological activities including liver protection, anti-inflammatory, hypoglycemic, antiviral and anti-tumor. Therefore, to investigate its anti-tumor activity and mechanism, many OA derivatives have been developed. Some derivatives are less toxic to normal hepatocytes, which may be due to the strong liver protection ability of OA. However, the poor water solubility of OA is one of the main reasons for the weak anti-tumor activity. It is reported that some OA derivatives could enhance solubility by chemically linking some hydrophilic groups to improve anti-tumor activity. This review not only summarizes the highly water-soluble OA derivatives that can improve anti-tumor activity reported in recent years, but also introduces their possible anti-tumor mechanisms.