(P 183) OSTEOSARCOMA ORGANOIDS RECAPITULATE TUMOR CHARACTERISTICS AND MAINTAIN HETEROGENEITY

Objective: Osteosarcoma is a rare and aggressive bone cancer that disproportionately affects children and young adults. These tumors are characterized by extensive histological and genomic diversity. The heterogeneity is a driver of resistance to first- and second-line therapies in many patients, particularly those with non-resectable, refractory osteosarcoma. Thus, there is a need for novel methods to identify and select treatments best suited to individual patients to maximize clinical benefit. Our goal was to validate patient-derived osteosarcoma organoids as a tool for studying the underlying biology of these tumors and identifying personalized candidate therapies.

Methods: We have collected n=69 surgical specimens from 30 patients diagnosed with osteosarcoma. Multiple samples were collected from 12 patients. For seven, we procured tissue from multiple metastatic lesions. We collected tissue from a naïve biopsy and the subsequent tumor resection post-neoadjuvant therapy for five patients. In one case, we procured tissue from the primary lesion as well as a subsequent lung metastasis. Using our mini-ring organoid screening platform (Phan et al, 2019; Nguyen et al, 2020), we have characterized the drug sensitivity profiles of 33 specimens, by growing dissociated tumor cells for 3-4 days followed by two drug treatments over 48 hours. Results of the screening are available within 5 to 6 days of procurement.

Results: The patients enrolled were mostly children and young adults, with 63% AYA, 33% pediatric and 3% adult cases. The patients were predominantly male (n=20), and n=10 were identified as Hispanic or Latino in ethnicity (33%). We could successfully generate organoids from osteosarcoma biopsies and surgical samples, including multiple individual samples from the same patient. We found that the osteosarcoma organoids largely recapitulated molecular and histological features of the tumors of origin. In aggregate, we tested 458 single agents, 17 two-drug combo regimens and 7 three-drug combinations in our high-throughput drug screenings. For most of the molecules tested, we observed distinct subsets of patient-derived organoids with heightened sensitivity to treatment. Interestingly, we observed significant heterogeneity in organoid response to NCCN-recommended therapies, suggesting that some patients may benefit from personalized selection of therapeutic regimens even for established treatments. Lastly, we will present a pathway analysis that evaluates the molecular targets of the drugs screened (Al Shihabi et al, 2022), to identify osteosarcoma vulnerabilities that could be targeted for combinatorial approaches.

Conclusion: Osteosarcoma patient-derived organoids recreate the complexity and heterogeneity of the tumor of origin and are a useful tool in gaining insight into the underlying biology and drivers of these tumors. These organoids may also provide clinically actionable information for selecting personalized treatment regimens through functional drug screening.