In Vitro and In Vivo Characterization of a Preclinical Radiation-Adapted Model for Ewing Sarcoma

Publication date: Available online 5 February 2018
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Mary Carroll Shapiro, Tien Tang, Atreyi Dasgupta, Lyazat Kurenbekova, Ryan Shuck, M. Waleed Gaber, Jason T. Yustein
PurposeRadiation therapy (RT) is a viable therapeutic option for Ewing sarcoma (ES) patients. However, little progress has been made to elucidate mechanisms of radioresistance. This study establishes a novel ES radiation-adapted model designed to assess molecular and fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) alterations secondary RT.Methods and MaterialsRadiation-adapted cell lines (RACL) were created in vitro by exposing ES human cell lines to fractionated doses of radiation. Assays to assess migration/invasion potential and RNA expression were performed on the RACL. Orthotopic intra-tibial in vivo investigations were performed with radiation-sensitive and radiation-adapted ES cells to generate tumors. Transplanted mice were imaged using ¹⁸F-FDG-PET followed by fractionated RT directed at the primary tumor. Mice were monitored for tumor regression and change in metabolic activity using ¹⁸F-FDG PET imaging. Protein expression analyses were performed on the RACL and orthotopic tumors.ResultsExposure to fractionated doses of radiation caused a significant increase in migratory and invasive properties in the RACL when compared to non-irradiated wild type ES cells. RACL transcriptomic and proteomic analysis suggests enhanced activation of the mTOR-AKT pathway when compared to wild type ES cells. Radiation-adapted tumors demonstrated significantly less tumor regression (p = 0.03) compared to wild type tumors. Wild type tumors also had decreased expression of lactate dehydrogenase A (LDHA) protein and significantly lower metabolic activity after RT compared to radiation-adapted tumors (p = 0.03).ConclusionsWe developed novel in vitro and in vivo radiation-adapted ES models. In vitro investigations revealed increased migratory and invasive phenotypes in the RACL. In vivo investigations demonstrated increased metabolic activity and significantly decreased sensitivity to RT in the radiation-adapted tumors as demonstrated by growth response curves and ¹⁸F-FDG PET activity. Investigations of the RACL identified possible radiosensitizing-dependent targets in LDHA and mTOR-AKT pathway.

Teaser

Ewing sarcoma (ES) is the second most common pediatric bone cancer, and patients with relapsed/resistant disease have a five-year overall survival rate of only 15-20%. Front-line standard of care treatment for patients with ES includes chemotherapy and local control with surgery and/or radiation. We have developed novel in vitro and in vivo radiation-adapted ES models that demonstrate a relationship between metabolism and radioresistance as well as identify several candidate biomarkers for radioresistant disease in ES.


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