In Vitro cellular response of head and neck squamous cell lines exposed to combined docetaxel-radiotherapy
(2008) 7th International Conference on Head & Neck Cancer — Location: San Francisco USA (19.July.2008)
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- Abstract
- Purpose: Head and neck squamous cell carcinoma (HNSCC) account for 8% of newly diagnosed cancers in adults worldwide. Despite advances in therapeutic approach, locoregional recurrences and 5-years survival of patients with locally advanced HNSCC is still about 60%. To substantially improve the response and survival rates, combined radiotherapy and adjuvant chemotherapy, among which the association docetaxel, cisplatin and fluorouracil, is increasingly used. While improved survival is observed in cases of unresectable HNSCC, contradictory data regarding the combination taxane-radiotherapy has been reported. Accordingly, the cellular and molecular mechanisms induced by the combination taxane-radiotherapy versus taxane alone or radiotherapy alone were assessed in vitro and compared according to the functional p53 status. Methods: Human papillomavirus-free HNSCC cell lines expressing nonfunctional mutated (SC179, SCC61) and functional wild-type p53 (HN30) were grown either in presence of increasing concentration of docetaxel, exposed to graded doses of radiation up to 10 Gy, or to both treatment modalities. Cell death was monitored by using an apoptotic assay (caspase-3 activation) and clonogenic assay (cell-surviving fraction assessed after 15 days incubation). Modulation of gene expression was evaluated by microarray analysis on low density arrays (DualChip Human General; Eppendorf Array Technologies). These low-density chips are indeed designed to specifically investigate some of the most common gene pathways involved in the regulation of cell cycle, apoptosis, and cell proliferation. Results: Regarding the radiosensitivity, the surviving fraction at 2 Gy (SF2) was calculated as the ratio of the plating efficiencies in treated to untreated cells. As expected, radiosensitivity was higher in HN30 (SF2: 3%) compared to the other p53-mutated cell lines (SF2: 16 and 36% for SCC61 and SC179, respectively). Conversely, the p53 status did not influence the sensitivity to docetaxel (IC50: 4.2nM, 4.7nM and 7.8nM for HN30, SCC61 and SC179 respectively). During the combined treatment, a single dose of radiation was administered with docetaxel added once or at different time points (before, concomitantly or after exposure to radiation). An antagonistic effect between docetaxel and radiation was found with each cell line. Although the antagonistic effect is timing independent, its magnitude was correlated to the p53 functional status, leading to a very strong protective effect in HN30 compared to SC179 and SCC61. In the experimental conditions of our study, the apoptotic rate of HN30 was reduced by 60% when drug was applied 24h before radiation exposure and by 40% when given concomitantly or shortly afterwards, compared to ~10% decrease for SSC61 and SC179. Modulation of gene expression experiments have now been completed after confirmation of RNA quality. Recorded data are currently assessed with bioinformatics tools and will be available. Conclusion: To translate in vitro observations of docetaxel-radiotherapy antagonistic effect in the clinical field depends probably on the dose of docetaxel and timing of administration of each therapy in the clinical setting. Further investigations are now pursued with a mouse animal model using the same cell lines and therapeutic modalities, as well as by comparing low density and high density microarray data.
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Bearzatto, B., Van Der Vorst, S., Ambroise, J., Grégoire, V., Gala, J.-L., & Dekairelle, A.-F. (2008). In Vitro cellular response of head and neck squamous cell lines exposed to combined docetaxel-radiotherapy. 7th International Conference on Head & Neck Cancer, San Francisco USA. https://hdl.handle.net/2078.5/227622