The antiproliferative activity of Varronia dardani (Taroda) JS Mill. roots against human melanoma cells and the isolation of a new hydroanthraquinone

The Caatinga is a unique Brazilian semi-arid biome in the north-east of the country, containing endemic plant species. Among these, Cordiaceae are traditionally used by local communities for the treatment of various diseases such as gastric pain, menstrual colic and arthritis. In this work, the antiproliferative activity of the species Varronia dardani was evaluated in chemoresistant human melanoma cells. The ethanolic extract of V.dardani root exerted high antiproliferative activity in A2058 cells and was selected for further phytochemical characterization and bioguided purification of antimelanoma compounds. The isopropanol fraction was the most active and contained a novel hydroanthraquinone which was isolated, characterized and named vardanone. This molecule is the first hydroanthraquinone reported in V. dardani and UPLC-MS/MS analysis revealed that it was composed of a mixture of isomers. When tested in melanoma cells, vardanone didn't induce the inhibition of A2058 cell growth, indicating that the fraction's antimelanoma activity is attributable to other molecules which will be further characterized. This study is the first to demonstrate the presence of a hydroanthraquinone in V. dardani and paves the way for the identification of new antimelanoma phytochemicals in this species.