Structural Characterization and Anticancer Activity of a New Anthraquinone from <em>Senna velutina</em>

Cancer is a complex disease, considered a major public health problem worldwide. Among the types of cancer, melanoma, and leukemias present high mortality rates in Brazil and worldwide. Currently, conventional cytotoxic treatments cause severe side effects by the non-selectivity between normal cells and cancer cells. Therefore, molecules of natural origin with more efficient anticancer properties and that present fewer adverse effects are of extreme importance for cancer therapy and improvement in patients’ quality of life. This study isolated, identified, and characterized the chemical structure of a new anthraquinone present in the extract of the roots of Senna velutina. In addition, we sought to evaluate the anticancer potential of this molecule against melanoma and leukemic cell lines and identify the pathways of cell death involved. To this end, a novel anthraquinone was isolated from the barks of the roots of S. velutina, analyzed by HPLC-DAD, and its molecular structure was determined by NMR. Subsequently, their cytotoxic activity was evaluated by the MTT method against non-cancerous, melanoma, and leukemic cells. The migration of melanoma cells was evaluated by the scratch assay. By flow cytometry technique, the apoptosis process, caspase-3 activation, analysis of mitochondrial membrane potential, and measurement of ROS were evaluated. In addition, the pharmacological cell death inhibitors NEC-1, RIP-1, BAPTA, Z-VAD, and Z-DEVD were used to confirm the related cell death mechanisms. With the results, it was possible to elucidate the novel compound characterized as 2'-OH-Torosaol I. In normal cells, the compound showed no cytotoxicity in PBMC but reduced the cell viability of all melanoma and leukemic cell lines evaluated. 2'-OH-Torosaol I inhibited chemotaxis of B16F10-Nex2, SK-Mel-19, SK-Mel28 and SK-Mel-103. The cytotoxicity of the compound was induced by apoptosis via the intrinsic pathway with reduced mitochondrial membrane potential, increased levels of reactive oxygen species, and activation of caspase-3. In addition, the inhibitors demonstrated the involvement of necroptosis and CA+ in the death process and confirmed caspase-dependent apoptosis death as one of the main programmed-cell death pathways induced by 2'-OH-Torosaol I. Taken together, the data characterize the novel anthraquinone 2'-OH-Torosaol I, demonstrating its anticancer activity and potential application in cancer therapy.