Analysis of Stroma Labeling During Multiple Passage of a Sarcoma Imageable Patient‐Derived Orthotopic Xenograft (iPDOX) in Red Fluorescent Protein Transgenic Nude Mice

A patient‐derived orthotopic xenograft (PDOX) model of undifferentiated pleomorphic sarcoma (UPS) was previously established that acquired red fluorescent protein (RFP)‐expressing stroma by growth in an RFP transgenic nude mouse. In the present study, an imageable PDOX model (iPDOX) of UPS was established by orthotopic implantation in the biceps femoris of transgenic RFP nude mice. After the tumors grew to a diameter of 10 mm, they were harvested and the brightest portion of the tumors were subsequently orthotopically transplanted to both RFP and non‐colored nude mice. The UPS PDOX tumor was again transplanted to RFP transgenic and non‐colored nude mice, and finally a 3rd passage was made in the same manner. Five UPS tumors from each passage in both RFP and non‐colored mouse models were harvested. The FV1,000 confocal microscope was used to visualize and quantitate the RFP area of the resected tumors. The average percent fluorescent area in the first passage of RFP mice was 34 ± 22%; in the second passage, 34 ± 20%; and 36 ± 11% in the third passage of RFP transgenic nude mice. The average tumor RFP area in the first passage from RFP mice to non‐colored mice was 20 ± 7%; in the second passage, 28 ± 11%; in the third passage was 27 ± 13%. The present results demonstrate the extensive and stable acquisition of stroma by the UPS‐tumor growing orthotopically in transgenic RFP nude mice (iPDOX). This model can be used for screening for effective drugs for individual patients and drug discovery. J. Cell. Biochem. 118: 3367–3371, 2017. © 2017 Wiley Periodicals, Inc.