Downregulation of uPAR confirms link in growth and metastasis of osteosarcoma

The uPA/uPAR system is involved in tumour progression and metastasis of a variety of cancers. Previously, we have shown that increased expression of urokinase plasminogen activator (uPA) correlated with malignancy grade in certain sarcomas. A study looking at in vivo inhibition of this system has not been done to date for osteosarcoma. More recently, this laboratory developed a clinically relevant mouse model where intratibial injection of UMR106- 01 cells resulted in the development of osteosarcoma and lung metastases. Expression of uPA and its receptor (uPAR) were localised to the invading front of the tumours. Pulmonary metastasis is a predominant feature of the disease and is the major cause of death in patients. In the present study, the effects of down-regulating uPAR were observed in vitro and in vivo. UMR106-01 cells were transfected with either antisense-uPAR or vector control plasmids. Two antisense clones, exhibiting uPAR downregulation, demonstrated decreased adhesion, migration and invasion in cell-based assays in vitro (P<0.05). Cellular proliferation was not affected by uPAR downregulation. In vivo, a marked reduction of 80% in tibial tumour volumes (P