Abstract LB-159: An orthotopic model of head and neck squamous carcinoma reveals that mTOR inhibition with rapamycin halts lymph node metastasis

Abstract

Abstract Despite our improved understanding of cancer as a disease, the 5-year survival rate for head and neck squamous cell carcinomas (HNSCC) still remains relatively unchanged at 50% for the past 3 decades. Since HNSCC frequently metastasize to the lymphatic basins in the neck, treatment is directed to the primary tumor and adjacent lymph nodes. Unfortunately, thus far animal models are unable to reflect disease progression severely limiting our understanding of the molecular basis of this process and thus treatment evaluation. Herein we describe the development of a clinically relevant orthotopic animal model through which stages of HNSCC progression can be monitored, with a potential therapeutic application using rapamycin, an inhibitor of the Akt/mTOR network previously shown to halt tumor growth in HNSCC flank xenograft models. HNSCC orthotopic tumors were induced in SCID-NOD mice by injecting 50 uL of 100,000 GFP labeled OSCC to the back of the tongue. Primary tumors were allowed to progress and growth characteristics were documented weekly. For treatment evaluation, injected mice were randomized at disease onset (tumors <5 mm) into incidence (treated: n=10; control: n=10) and survival (treated: n=10; control: n=15) groups and began daily rapamycin administration (5 mg/kg/day) or vehicle injections for treated and control groups, respectively. A cohort of animals (sentinel) were left untreated to monitor progression, and euthanized at different time points and the cervical lymph nodes studied for metastases. The incidence arm was concluded when sentinel mice presented with lymph node involvement, whereas the survival arm concluded when control mice succumbed to disease. Tissues from the primary tumors and corresponding lymph nodes were histopathologically evaluated. At 1-2 weeks post transplantation into the tongue, tumor cells were infiltrating the surrounding tissues and lymphatic vessels. By 4-6 weeks, metastasis to at least one of the four cervical lymph nodes was observed. Cells in both the primary tumors and lymph nodes expressed high levels of pS6 indicating aberrant Akt/mTOR pathway activity. Conversely, animals on a daily regimen of rapamycin, showed a dramatic reduction in primary tumor burden as well as the extent of local invasion when compared to control. Furthermore, rapamycin treatment was sufficient to ablate incidence of lymph node involvement as well as prolong survival in 100% of the animals assessed. We have successfully developed a HNSCC animal model that effectively emulates the human disease progression from primary tumor characteristics to those of local invasion and metastatic propensities. Furthermore, using this model, we have been able to show that targeting the Akt/mTOR pathway with rapamycin, not only significantly reduces primary tumor size, but may be an effective approach to preventing local invasion and metastasis in HNSCC patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-159.