Antisense oligonucleotides have recently been identified as new anticancer agents. Since human head and neck cancer cells highly express the antiapoptotic protein myeloid cell leukemia-1 (Mcl-1), the aim of this study was to explore the efficacy of the Mcl-1 suppression in combination with various cytotoxic agents in the head and neck cancer cell line SCC9. After oligonucleotide transfection and/or treatment with cisplatin, 5-fluorouracil (5-FU), gemcitabine, paclitaxel or cetuximab, proliferation assays were performed to determine cell viability. The expression patterns of Mcl-1, Bax and Bak were assessed by Western blot analysis and the apoptotic cells were determined by immunohistochemistry using the M30 antibody. A combined Mcl-1 antisense oligonucleotide treatment with paclitaxel, cetuximab and gemcitabine led to a significant reduction in the viable cells. However, the combination with cisplatin and 5-FU showed only moderate synergistic cytotoxic effects. According to the cytotoxic data, distinct apoptosis rates were observed after the combined treatment with the different substances. Western blot analysis also showed a significant suppression of the Mcl-1 synthesis. Our data show that the Mcl-1 antisense oligonucleotide in combination with certain cytotoxic agents has the potential to significantly decrease cell viability in vitro.

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