Cytotoxic and cytostatic activity of orcinol-type depsides of lichens

Lichens synthesize unique secondary metabolites, most of which are not found in other living organisms. More than 800 such metabolites are known, which can be found in various parts of the lichen thallus. Typically, their content varies from 1 to 6 % of the dry weight of the thallus, but sometimes can reach 20 %. In recent years, interest in these metabolites has increased due to their biological and pharmacological activities, including antioxidant, cytotoxic, antimicrobial, anti-inflammatory and analgesic properties. This makes them promising sources of new pharmaceutical substances, although the molecular cellular mechanisms of their action require further study. The most numerous classes of lichen metabolites are depsides, formed via the acetate-polymalonate pathway. They are conjugated from two or three phenolic rings of the orcinol or β-orcinol type. To date, about 141 orcinol-type depside compounds are known, but biological activity has been described for less than 10 % of them. This review summarizes the data on the cytotoxic and antitumor effects, as well as the molecular cellular mechanisms of action of the orcinol-type depsides and tridepsides, emphasizing the need for further study of this group of compounds, for most of which the biological activity has not yet been studied.