Betulinic acid, a small molecule from pentacyclic triterpenes class, has been widely studied for its antitumor activity, revealing that it induces the apoptosis of tumor cells in a selective manner. In recent years, digoxin, a cardiac glycoside found particularly in the plant species Digitalis lanata, has drawn interest for its potential antitumor properties. The present study was designed to evaluate the antimelanoma potential of betulinic acid (BA), digoxin (DG), and their association (DG + BA). In vitro assessments were performed 24 h post-treatment on two human melanoma cell lines (SK-Mel-28 and RPMI-7951). In addition, the potential irritant effects of the test samples were evaluated using the chorioallantoic membrane of hen's eggs. BA and DG exhibit a concentration-dependent cytotoxic activity, with the combination of the two having a more marked effect on the decrease in cell viability (~17% for SK-Mel-28 cells and ~23% for RPMI-7951 cells). Further, morphological changes (rounding of the cells and their separation from the plaque) and alterations in the nucleus and actin fibers (condensation of chromatin and actin fibers, formation of apoptotic bodies) were observed, indicating an apoptotic-like process. Moreover, no irritating effects were observed in ovo. As a result, DG + BA acid may have synergistic potential in the antitumor treatment of melanoma, but future studies are needed in order to clarify the biological mechanisms involved.
Keywords: F-actin fibers; HET-CAM assay; betulinic acid; digoxin; melanoma cells; synergic effect.