(P 171) CANINE-DERIVED OSTEOSARCOMA ORGANOIDS MODEL TUMOR HETEROGENEITY AND CHEMOTHERAPY RESISTANCE

Objective: Through utilization of a comparative oncology canine-derived osteosarcoma organoid platform, our objectives are to (1) model inter- and intra-tumoral heterogeneity in drug response, (2) pinpoint actionable collateral sensitivities in chemotherapy-resistant tumors, and (3) capitalize on tumor heterogeneity in chemotherapy resistance as a predictive biomarker for patient outcomes.

Methods: Naturally occurring canine-derived osteosarcoma tumor samples are obtained through collaboration with veterinary partners and are divided into spatially distinct sections. Tumor sections are cultured in three-dimensional scaffold matrices within 24 hours of tissue biopsy to generate osteosarcoma organoids. Following adequate expansion over 2-4 weeks, organoids are allocated for drug screening with doxorubicin or carboplatin, RNA-sequencing, or banking (Figure 1). Organoid response to treatment is assessed by cell viability normalized to control, and response of carboplatin treated organoids is compared to canine clinical outcomes, when available. Organoids undergo RNA sequencing to identify targets upregulated in chemotherapy resistant organoids.

Results: The canine-derived osteosarcoma organoid platform has highlighted inter- and intratumoral heterogeneity in response to single-agent treatment with doxorubicin. Responses ranged from >50% reduction in viability in some tumor sections to complete resistance to doxorubicin (Figure 2). RNA-sequencing from doxorubicin-treated canine osteosarcoma organoids demonstrating therapy resistance identified upregulation in actionable signaling pathways, including MET. Organoids generated from three canine osteosarcoma patients who received first-line carboplatin following amputation have been treated with carboplatin and early clinical outcome data obtained. Correlation of results of in vitro treatment of organoids with clinical response will be presented.

Conclusion: The canine-derived osteosarcoma organoid platform uniquely combines a comparative oncology approach to overcome limitations associated with the rarity of human osteosarcoma with 3D model systems to capture tumor heterogeneity and model therapy resistance. Following determination of chemotherapy responsiveness within < 6 weeks of tissue biopsy, drug resistant organoids can be further profiled to identify biomarkers of response and actionable targets. Early investigation in the correlation of organoid response to canine clinical outcomes demonstrates feasibility of this pipeline to more extensively study the predictive capacity of patient-derived osteosarcoma organoids.