Abstract B24: Patient-derived tumor xenograft to study cancer stem cells is pediatric sarcomas
Authors: Rainusso Nino , Hernandez Jose , Marco Rex , Vasudevan Sanjeev , Quintanilla Norma , Hicks John , Allen-Rhoades Wendy , Trucco Matteo , Yustein Jason 
Published: March 2017

Abstract
Tumor heterogeneity is recognized as an important hallmark in cancer. This characteristic allows cancer cells to evolve in time, to survive radiation and cyotoxic therapies, and to thrive in different organ microenvironments. Therefore, the presence of distinct tumor subpopulations, as mainstay feature of tumor heterogeneity, may play a role in tumor progression and treatment resistance. Patient-derived xenografts (PDXs) have been used to discover the molecular signaling pathways involved in tumorigenesis, metastasis formation and radiation/chemotherapy resistance in different epithelial-adult cancers. Our research interest in pediatric sarcomas is to understand the processes that drive tumor heterogeneity, to isolate and characterize cancer stem cells (CSCs), and to elucidate the mechanisms of chemoresistance using a PDX model.
Pediatric patients with suspected or established diagnosis of sarcoma evaluated at Texas Children's Hospital signed an informed consent to provide tumor samples for subcutaneous implantation of tumor explants in the flank of nonobese diabetic severe combined immunodeficient gamma (NSG) mice. Tumor explants were implanted on the same day of collection when was possible. First and subsequent PDX generations were harvested for tumor propagation, tumor histology, tumor cell karyotyping , RNA/DNA extraction for genetic studies and fluorescent activated cell sorting (FACS) analysis for ALDH, CD133, EphA2 and CD47.
Forty-six tumor samples have been collected since June 2013. Half of tumor samples (n=21) corresponded to osteosarcoma patients and 59% of all tumor specimens were obtained at the time of the initial biopsy. Approximately 66% of biopsies have been performed by Interventional Radiology in our institution. All PDXs maintained the same histological characteristics that original tumors, and also presented specific genetic translocations associated with the different sarcoma types. Chemotherapy resistant and very aggressive tumors (metastatic) had short tumor latency and generate tumors in all transplanted mice. We did not observe the formation of metastases (lungs or liver) in any of the transplanted PDX mice.
PDXs significantly increased the amount of tumor material necessary to perform cell culture under stem-like cell conditions and to analyze the expression of CSC markers by FACS. These studies would be very difficult to perform directly from patient tumor biopsies. All tumors harvested (n=15) contained 2-9% of ALDH Hi or stem-like cells. None of the PDXs analyzed expressed CD133 but synovial sarcoma. We found that &gt;90% of sarcoma cells expressed CD47 and EphA2 at different intensity levels. Whole genome sequencing of different tumor cell subpopulations and limiting dilution experiments to validate the presence of CSCs are ongoing.
Core needle biopsies would represent the most common source to obtain tumor specimens before treatment in pediatric sarcomas. The development of PDXs allows the propagation of tumor cell subpopulations, including CSCs, without the biological changes impose by cell culture. PDXs resemble the original tumor and constitute a powerful tool to study tumor heterogeneity. We plan to perform orthotopic transplantation and tail vein injection of PDX cells in an attempt to develop a PDX model of metastatic disease in pediatric sarcomas.
Citation Format: Nino Rainusso, Jose Hernandez, Rex Marco, Sanjeev Vasudevan, Norma Quintanilla, John Hicks, Wendy Allen-Rhoades, Matteo Trucco, Jason Yustein. Patient-derived tumor xenograft to study cancer stem cells is pediatric sarcomas. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr B24.