Betulinic acid induces apoptosis in rhabdomyosarcoma cell lines

446

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma in childhood with a still dismal prognosis for patients with a chemo-refractory tumor. Our previous work in the Patched1 knock-outmouse model has shown that RMS characteristically displays an activation of cell survival promoting and anti-apoptotic proteins such as Igf2, Akt, and Bcl-2. Thus, we suggested that RMS might be associated with the ability of tumor cells to resist apoptosis. Betulinic acid (BA) is a plant-derived pentacyclic triterpenoid inhibiting tumor cell growth by the induction of apoptosis. In this study, we provide evidence that BA is a hopeful candidate for new strategies in treatment of RMS. We show that BA has a strong cytotoxic effect on RMS cells in a dose- and time-dependent manner. We furthermore demonstrate that the dramatic decrease in viability of RMS cells is caused by a massive induction of apoptosis, as shown by morphological changes and DNA fragmentation. BA specifically activates caspase 3, caspase 8 and PARP by their proteolytic cleavage, which could be inhibited by the broad-range caspase inhibitor zVAD.fmk. Moreover, BA induced loss of mitochondrial membrane potential. In conclusion, our results suggest that BA is capable of inducing apoptosis in RMS cells and thereby might be of uttermost interest for the treatment of chemo-refractory RMS.