Detection of Metastasis in a Patient-derived Orthotopic Xenograft (PDOX) Model of Undifferentiated Pleomorphic Sarcoma with Red Fluorescent Protein.

Background/Aim: Undifferentiated pleomorphic sarcoma (UPS) is a common soft tissue sarcoma and highly recalcitrant. We have previously developed patient-derived orthotopic xenograft (PDOX) mouse models of UPS and other major sarcoma types. Unlike PDOX models of other cancer types, it has been difficult to demonstrate metastasis in the sarcoma PDOX models. Materials and Methods: To visualize metastasis at high resolution in the UPS PDOX model, established tumor fragments were implanted in transgenic nude mice expressing red fluorescent protein (RFP) for one passage. The tumors acquired RFP-expressing stroma from transgenic host. UPS tumor with RFP stromal cells were harvested and implanted orthotopically in non-transgenic nude mice. After six weeks of UPS tumor growth in the PDOX model, the primary tumor was imaged non-invasively and lung, liver, and spleen were resected and imaged ex-vivo in order to visualize the presence of RFP, with a FluorVivo (R) imaging system and FV1000 (R) confocal laser microscope, respectively. Results: The primary tumor was imaged non-invasively. Confocal microscopy visualized the presence of RFP in the lung and liver indicating metastases in these organs. This is the first report of metastasis in a sarcoma PDOX model. Conclusion: This study should prove very useful to screen for anti-metastatic drugs for the PDOX donor patients and to understand the metastatic process in sarcoma.