Medical uses of mylabris in ancient China and recent studies

Mylabris is the dried body of the Chinese blister beetle. The species used in medicine are Mylabris phalerata and M. cichorii. The use of mylabris as a traditional medicine in China can be traced back more than 2000 years, and it is still used as a folk medicine today. In recent studies, it has been found that mylabris possesses antitumor properties, increases the number of leucocytes, and has irritant effects on the urinary organs. The active constituent of mylabris is cantharidin. The synthesis of cantharidin is rather difficult. In order to find a less toxic analogue of cantharidin, its hydrolytic compound, disodium cantharidate, and its demethylated form, norcantharidin, were prepared. By biochemical and biological methods, it was found that these compounds may affect cancer cells in several ways. In clinical studies, antihepatoma effectiveness sequentially increased from cantharidin to disodium cantharidate to norcantharidin. Disodium cantharidate showed less urinary irritation than cantharidin while norcantharidin showed little to no such irritation. It appears that the two methyl groups of cantharidin are not the main functional groups for antitumor activity and for the stimulation of bone marrow but are associated with urinary irritation. Hydrocantharidimide, methylcantharidimide and dehydronorcantharidin have also been studied. All these compounds, except the last one, have been produced as antitumor agents in China. Since demethylated cantharidin may be prepared by total synthesis, it may be more suitable for medical investigation than cantharidin itself.