**10. Discussion**

156 Otolaryngology

It has been well documented that many cancer cells lose most of their epithelial characteristics during progression and metastasis, through the process of EMT (Thiery 2002). Generally, EMT causes increased motility and invasiveness of cancer cells due to decreased cell-cell adhesion. Snail, a zinc finger transcription factor, triggers EMT through direct repression of E-cadherin transcription (Batlle et al. 2000; Cano et al. 2000). The reverse correlation of snail and E-cadherin expression has been reported for various human cancers, including SCC (Yokoyama et al. 2001). Accordingly, we investigated the snail and Ecadherin expression levels to assess whether cisplatin and/or docetaxel at IC10 differently influences EMT. Snail was decreasing over a time course (Fig.7.). Conversely E-cadherin was increasing over a time course (Fig.7.). But the levels of these proteins were not significantly different between cisplatin, docetaxel and no treatment. These results indicate that docetaxel

**8. Docetaxel treatment did not promote epithelial-mesenchymal transition** 

Fig. 7. Time course of snail and E-cadherin expression of HEp-2 cells and Ca9-22 cells

β-actin was probed for loding control. 3 replicate were used in each experiments and

treated with IC10 concentration of cisplatin or docetaxel.

experiments were repeated 3 times.

treatment does not promote EMT at least in these cell lines.

**(EMT)** 

The metastatic process has traditionally been viewed as follows: (1) detachment of individual cells from the primary lesion (2) invasion of local stroma (3) entry of single cells or aggregates of tumor cells into blood vessels directly or via lymphatic channels (intravasation) (4) sticking to the vasculature distant from their origin followed by extravasation, and (5) invasion into the parenchyma of the target organ site. The newly formed lesions can themselves become the source of disseminating cells which repeat this cycle, giving rise to tertiary metastasis. Thus, Inhibition of invasion in the primary lesion

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should result in preventing the distant metastasis. From this point of view, our results suggest that docetaxel, which decreased local invasiveness, may prevent distant metastasis. Although the effect of docetaxel on cell migration or invasiveness of ovary cancer cells (Bijman et al. 2008) and umbilical vein endothelial cells (Bijman et al. 2006) have been described, its effect on head and neck cancer cells has not been evaluated.

Actin cytoskeleton provides the driving force for cell migration, while microtubules are required to establish cell polarity during motility in fibroblasts (Bershadsky et al. 1991). Actin is regulated by Rho family small GTPases, and it is indicated that microtubules may influence actin cytoskeleton through modulation of the activity of Rho GTPases (Wittmann et al. 2001). Among Rho GTPases, cdc42 was reported to control the polarity of actin and microtubule through distinct signal transduction pathways (Cau et al. 2005). It is possible that the abnormal tubulin bundle induced by docetaxel lead to suppression of cdc42 activity. This decreased cdc42 activity could affect actin filament and decrease the migration of the head and neck cancer cells.

In contrast, we could not find definitive evidence for docetaxel to directly affect actin cytoskeleton regulation. It did not affect EMT processes or MMP production of these head and neck cancer cell lines.
