Prediction of Outcome in Canine Appendicular Osteosarcoma
Appendicular osteosarcoma is the most common 1° bone cancer of dogs. Pulmonary metastasis leads to mortality in most cases and chemoresistance is a common sequel. Reliable prognostic tools are lacking, and the standard of care for curative intent has not significantly changed in decades. To improve the management of dogs with appendicular osteosarcoma, new prognostic tests and new treatment strategies are needed. To address this, I began by testing the predictive value of 2 established histologic grading systems; 85 tumours from dogs who received the standard of care were graded by 3 pathologists, and no significant correlations between grade and outcome were identified. These results question the validity of an established prognostic tool, histologic grading, and highlight the need for standardization and validation during the development tests for outcome prediction. To facilitate development of such tests, I constructed a large clinically annotated tissue microarray and performed high-throughput immunohistochemical interrogation of autophagy related protein expression. The cytoprotective properties of autophagy are implicated in the development of chemoresistance in a variety of cancers. p-AKT was identified as a potential predictive biomarker; dogs with low p-AKT expression in their tumours had a median survival time 2.4 times longer than those with high expression. To explore whether autophagy inhibition could enhance chemotherapy treatment, canine osteosarcoma cells were treated with an autophagy inhibitor, spautin-1, prior to treatment with doxorubicin. Using clonogenic assays and cell viability assays, I showed that spautin-1 effectively kills canine osteosarcoma cells and inhibits their ability to form colonies. To investigate the mechanism(s) behind these effects, I evaluated the expression of autophagy related proteins via western blot, in cells that received this combination treatment. Divergent responses were identified when comparing cancer versus non-cancer cells and cells derived from 1° versus 2° osteosarcoma. Based on my findings, histologic grading was not predictive, and further effort is being put towards using molecular markers to predict outcome. My hope is that these findings will eventually lead to improved outcome for dogs with appendicular osteosarcoma, and that further investigation will be made into the role of autophagy in osteosarcoma.