Tumor metastasis in an orthotopic murine model of head and neck cancer: Possible role of TGF‐beta 1 secreted by the tumor cells

In an orthotopic murine model of head and neck cancer, combined subcutaneous and intratumoral vaccination with recombinant vaccinia virus expressing interleukin-2 (rvv-IL-2) induced significant tumor regression early on therapy. However, its efficacy was restricted by recurrent tumor growth and loco-regional metastases. In this study, we explored the mechanism of tumor metastasis. We compared the levels of expression of a number of molecules involved in tumor metastasis, which included transforming growth factor-beta1 (TGF-beta1), E-cadherin, matrix metalloproteinases (MMPs): MT1-MMP, MMP-2, MMP-9, their tissue inhibitors (TIMPs): TIMP-1/TIMP-2, and pro-angiogenic factors CD31, VEGF-R2, and iNOS between primary and metastatic tumors by real-time RT-PCR and immunohistochemistry. We detected spontaneous lymph node and tongue metastasis. Metastasis was delayed in rvv-IL-2 treated mice. Cultured tumor cells expressed negligible amount of TGF-beta1. Untreated or metastatic tumors, on the other hand, expressed high levels of TGF-beta1 and secreted TGF-beta1 in the sera of tumor-bearing mice. Levels of TGF-beta1 in the sera suddenly jumped at the time when tumor metastasis started. In the metastatic tumors, levels of MT1-MMP, MMP-2, and MMP-9 were significantly elevated (P < 0.001), while levels of TIMP-1/TIMP-2 and E-cadherin were decreased (P < 0.001) compared to control or primary tumors. Levels of CD31, VEGF-R2, and iNOS were also significantly elevated in the metastatic lesions (P < 0.001). The concurrence of high levels of TGF-beta1 in the sera, expression of proteins involved in metastasis and initiation of metastasis suggested possible role of TGF-beta1 in on setting the metastatic cascade in this model.