Abstract A52: In vivo model of Ewings sarcoma metastases
Authors: Hong Sung-Hyeok , Galli Susana , Tilan Jason , Christian David , Horton Meredith , Rodriguez Olga , Albanese Christopher , Kitlinska Joanna 
Published: May 2015

Abstract
Ewings sarcoma (ES) is an aggressive malignancy affecting children and adolescents. The presence of metastases is the single most powerful adverse prognostic factor in ES, with a 5-year event-free survival (EFS) at 72% and 3-year EFS at 27% for patients with localized and metastatic disease, respectively. While pulmonary metastases are the most common, the prognosis is worse for patients with bone involvement, particularly when both bone and lung metastases are present (8-14% EFS), and dismal for rare cases with brain metastases (2.7 months median survival). Thus, the treatment of metastatic ES and prevention of its further dissemination is a crucial problem in clinical management of this disease. Despite this, however, our understanding of mechanisms governing ES metastases formation remains poor and appropriate animal models allowing for identifying factors involved in ES metastases are missing. Thus, the goal of our study was to establish and characterize a model recapitulating metastatic processes occurring in ES patients. To this end, ES cells were injected into gastrocnemius muscles of SCIG/bg mice. Once primary tumors reached a volume of 1cm3, tumor-bearing hindlimbs were amputated and mice monitored by periodical MRI for 1-2 months. Moreover, tumor cell dissemination was assessed by histopathological analysis and real-time RT-PCR for EWS-FLI1 transcript. Using this approach, we were able to achieve high frequency of metastases formation. The pattern of metastases was dependent on the ES cell line used. Injection of SK-ES1 cells resulted in formation of multiple distant metastases in 100% of mice. These included soft tissue tumors in the thoracic region (60% of mice), brain metastases (40%), limb metastases (20%) and jaw metastases (20%). Moreover, marked bone invasion was detected in primary tumors and limb metastases. The presence of tumor cell dissemination to bone marrow and other organs (liver, lungs) was also confirmed and quantified by EWS-FLI1 real-time RT-PCR. In contrast, orthotopic injection of TC71 cells resulted primarily in formation of macroscopic lung metastases, but no brain and soft tissue thoracic tumors. Thus, the orthotopic ES xenografts followed by limb amputation provide a robust model of ES metastases suitable for identifying factors involved in ES dissemination and testing new therapeutic strategies. Moreover, the cell line-dependent specificity of the metastatic pattern may allow evaluating and therapeutically targeting particular metastatic processes, such as bone invasion or lung colonization.
Citation Format: Sung-Hyeok Hong, Susana Galli, Jason Tilan, David Christian, Meredith Horton, Olga Rodriguez, Christopher Albanese, Joanna Kitlinska. In vivo model of Ewings sarcoma metastases. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr A52.