Progression/Metastasis of Xenografted Oral Cancer Cell-lines in Mouse Tongue

Objectives: Oral squamous cell carcinoma (SCC) in tongue exhibits rapid progression into the surrounding stroma and is prone to metastasize to regional lymph-nodes. The invasion, metastasis and prognosis of SCC are determined in part by the communication between cancer cells and surrounding microenvironment. The present study aimed to elucidate the tumor-stroma interaction using a mouse xenograft model with focus on the EMT-like phenotypic modulation of tumor cells as monitored by a coupling of E-cadherin downregulation and vimentin upregulation. Methods: Five oral SCC cell-lines (KOSC2, HO-1u1, HSC2, OSC19, and OSC20) were used. Each cell line grown in culture was transplanted (2x10⁵ cells) into a BALB/c nude-mouse tongue. A whole tongue and regional neck lymph-nodes were dissected from the animals at periodical intervals after inoculation and then processed for preparation of paraffin-embedded serial sections (4µm thick). Phenotypic alterations of cancer cells at the primary sites and lymph-nodes were examined by immunohistochemistry and gene expression analysis. Results: Although all cell-lines gave rise formed visible tumor masses (2mm or larger) in the tongue within 2 to 3 weeks, the individual cell-lines showed a marked diversity with respect to proliferation activity measured by MIB1-positive number, induction of blood/lymph vessels, and EMT-like phenotypic alterations. The mode of local invasion was divided into two types: cell-lines with high proliferation exhibited expansive invasion by replacing the muscle tissue, whereas cell-lines with modest proliferation had a tendency to expand through gaps between muscle fibers. Four cell-lines except for KOSC2 were validated to induce lymph-node metastasis. Conclusions: The results obtained support the contention that the progression and regional metastasis of SCC were correlated with the proliferation activity of tumor cells and the angio/lymphangiogenesis in the microenvironment, but the EMT-like phenotypic alteration appears not to be prerequisite for the local progression and regional metastasis.