Betulinic acid (BetA), a new experimental cytotoxic compound that is active against human melanoma cells and neuroectodermal tumor cells, has recently been shown to be also effective against head and neck squamous carcinoma cells (HNSCC). In this study we investigated BetA in combination with cisplatin in squamous cell carcinoma cell lines of the tongue. SCC25 and SCC9 were treated with BetA and/or cisplatin. Cells were counted with an automated analyzing system. Caspase activation was determined using the M30 Cyto-Death ELISA, expression of the anti-apoptotic protein Mcl-1 by Western blot analysis. Visualization of apoptotic cells was achieved by immunohistochemistry. Synergistic cytotoxic effect and the induction of apoptosis under combined treatment was observed in SCC25 cells only after 24 or 48 h, whereas treatment of SCC25 cells for 72 h with BetA and cisplatin showed antagonism or subadditive effects. In SCC9 cells, antagonism occurred over an increase of dose and time during treatment. Furthermore, we could not demonstrate a significant alteration in the expression of the anti-apoptotic protein, Mcl-1. Our in vitro data demonstrate that BetA seems to be an unlikely candidate for combination with cisplatin in the treatment of head and neck cancer.

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