Modeling Distinct Osteosarcoma Subtypes Using Cre:LoxP and Lineage Restricted Transgenic shRNA in vivo

Tony J Mutsaers1,2, Alvin JM Ng2, Megan R Russell2, Meaghan Wall3, Emma K Baker2, Alistair M Chalk2, Patricia Ho2, Brian Liddicoat2, John Slavin4, T John Martin2, Ankita Goradia2, Louise E Purton2, Ross Dickins5, Carl R Walkley2

1. Department of Clinical Studies, Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada; 2. St. Vincent’s Institute of Medical Research, Fitzroy, Victoria, Australia; 3. Victorian Cancer Cytogenetics Service, St. Vincent’s Hospital, Fitzroy, Victoria, Australia; 4. Department of Pathology, St. Vincent’s Hospital, Fitzroy, Victoria, Australia; 5. Molecular Medicine Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia

Osteosarcoma is the most common primary cancer of bone and one that predominantly affects children and adolescents. Osteoblastic osteosarcoma represents the major subtype of this tumor, with approximately equal representation of fibroblastic and chondroblastic subtypes. We and others have previously described murine models of osteosarcoma based on osteoblast-restricted Cre:lox deletion of tumour suppressor genes Trp53 (p53) and Rb1 (Rb), resulting in a phenotype most similar to fibroblastic osteosarcoma in humans. We now report a model of the most prevalent form of human osteosarcoma, the osteoblastic subtype. In contrast to other osteosarcoma models that have used Cre:lox mediated gene deletion, this model was generated through shRNA-based knockdown of p53. As is the case with the human disease the shRNA tumors most frequently present in the long bones and preferentially disseminate to the lungs; features less consistently modeled using Cre:lox approaches. Our approach allowed direct comparison of the in vivo consequences of targeting the same genetic drivers using two different technologies: Cre:lox and shRNA. This comparison demonstrated that the effects of Cre:lox and shRNA mediated knock-down are qualitatively different, at least in the context of osteosarcoma, and yielded distinct subtypes of the disease. Through the use of complementary genetic modification strategies we have established a model of the most common clinical subtype of osteosarcoma that was not previously represented and more fully recapitulated the clinical spectrum of this cancer.