Abstract 4446: Collateral drug screening throughout the evolution of osteosarcoma drug resistance

Abstract Introduction: Osteosarcoma is the most common primary malignant bone tumor in childhood. Advancements in therapy have been stagnant for over 40 years and the prognosis for osteosarcoma remains challenging. The 5-year relative survival rate of localized osteosarcoma is 75%. If disease is metastatic upon diagnosis or first line therapy fails, survival rate falls to approximately 25%. First line therapy consists of alternating cycles of methotrexate with doxorubicin and cisplatin (MAP). In contrast, second line therapy is not standardized, and outcomes after salvage therapy remain poor. Identifying better second line agents may be an avenue to successful salvage therapy. Cancer is a dynamic state and can be viewed through an evolutionary framework. When cancer cells are exposed to chemotherapy, resistant cells may be selected for and proliferate. These resistant cells may exhibit a different resistance/sensitivity profile to other therapy options, termed collateral changes. By correlating these collateral changes with genomic and transcriptomic data, we can theoretically develop a library of gene/gene expression markers that correlate with resistance or sensitivity to a panel of drugs. Methods: We have exposed an osteosarcoma cell line, MG63.3, in cell culture to a clinically relevant sequential therapy that models MAP. 5 evolutionary replicates were exposed to combination cisplatin and doxorubicin, followed by methotrexate. 3 control replicates were exposed to solvent without drug. Once cells returned to confluency after each exposure to chemotherapy, we performed drug assays to a panel of 16 second-line drugs and drug combinations, in addition to radiation therapy, and extracted DNA/RNA from each replicate. Results: As a result of this work, we created a heatmap displaying the development of sensitivity and resistance to this treatment panel, based on the change in half maximal effective concentration (EC50) over time and have found variable collateral changes indicating timepoints in which cells are significantly more sensitive or resistant to second line agents as our evolutionary replicates evolved resistance to frontline therapy. Conclusions: This heat map can serve as a springboard for transcriptomic and genomic analyses to correlate the changes with resistance and sensitivity. This may allow future researchers to correlate our findings with patient derived genomics and transcriptomics to ultimately choose better second line therapeutics for patients who do not respond to MAP therapy. Citation Format: Gabriel Mandel, Elizabeth Nowak, Jarrel Imamur, Kristi Lin-Rahrdja, Mina Dinh, Masahiro Hitomi, Jacob Scott, Zachary Burke. Collateral drug screening throughout the evolution of osteosarcoma drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4446.