Investigating CXCR4 Expression in Canine Appendicular Osteosarcoma

Background: Chemokine receptors (CXCRs) are transmembrane proteins classically studied for their participation in leukocyte homing. By their binding of cognate ligands, CXCRs orchestrate key cellular processes, including directional migration. Several different CXCRs are expressed on cancer cells and dictate tissue‐specific metastases. In pediatric osteosarcoma (OSA), CXCR4 expression by tumor cells may participate in metastasis to tissues containing CXCL12, the partnering ligand for CXCR4. Canine and pediatric OSA share many biological similarities, including preferential metastasis to lung, bone, and lymph node. Hypothesis: In canine immortalized cell lines and naturally occurring tumor samples, OSA cells will express CXCR4. In canine OSA cell lines, CXCR4 will participate in directional cell migration. Methods: In vitro, CXCR4 expression in canine OSA cell lines was assessed by reverse‐transcriptase polymerase chain reaction, Western blot analysis, flow cytometry, and immunocytochemistry. In vitro, involvement of CXCR4‐mediated signaling for directional migration was investigated with a commercial assay. In vivo, CXCR4 expressions were evaluated in primary tumors and pulmonary metastases with immunocytochemistry and immunohistochemistry, respectively. Results: In vitro, canine OSA cells express CXCR4 mRNA and protein. Ligation of CXCR4 with exogenous CXCL12 results in directional migration of canine OSA cell lines. In vivo, majority (8/11) of the canine OSA primary tumors, but minority (2/8) of the pulmonary metastases express CXCR4 protein. Conclusions and Clinical Importance: Canine OSA cells express CXCR4, and its signaling participates in directional migration. Most dogs with spontaneously arising OSA express CXCR4 within their primary tumors.