Abstract 6725: Targeting urea cycle dysfunction to prevent and treat osteosarcoma

Abstract

Abstract Introduction: Osteosarcoma (OS) is the most common primary malignant bone tumor in adolescents and young adults. Intensive multimodal treatment cures almost 75% of patients who present with localized disease; however, only 25% of patients who present with metastases become long term survivors, and those who suffer a metastatic relapse are almost never cured. Polyamine metabolism and signaling play important roles in multiple cancers but have not previously been studied in osteosarcoma. D, L-alpha-difluoromethylornithine (DFMO) is an irreversible inhibitor of ornithine decarboxylase (ODC), the initial, rate-limiting enzyme within the polyamine biosynthetic pathway, and has been studied in a number of different cancers as either a therapeutic or a chemopreventive agent. We investigated the role of polyamines in OS proliferation and metastasis and whether blocking the polyamine synthetic pathway with DFMO had therapeutic potential in the treatment of OS. Methods: We evaluated proliferation, apoptosis, clonogenic growth and the ability to grow under nonadherent conditions in vitro using established OS lines. To investigate the effect of DFMO on tumor growth in vivo, we implanted fragments of patient derived xenograft into the tibias of NOD/SCID/IL-2Rγ null mice. Upon confirmation of tumor growth, mice were randomized to either receive drinking water or drinking water supplemented with 2% DFMO. A third cohort of mice received water supplemented with 2% DFMO only after hindlimb amputation. Results: DFMO has a profound effect on the proliferation of OS cell lines in vitro. Utilizing caspase assays, we determined that DFMO does not induce apoptosis, but is cytostatic and inhibits proliferation. We found that DFMO prevents the clonogenic growth of 3 different OS cell lines in soft agar and prevents spheroid formation under non-adherent conditions. Interestingly, once established, spheroidss were not disrupted by the addition of DFMO. In vivo, administration of 2% DFMO after hindlimb amputation decreased local recurrence and limited metastasis (p=0.02). Conclusion: DFMO inhibits proliferation and clonogenic growth in vitro, and decreases distant metastasis in vivo. Since pediatric dosing and safety data are already established, our findings are readily translatable to clinical trials. Citation Format: Rachel Offenbacher, Paul Ciero, David Loeb. Targeting urea cycle dysfunction to prevent and treat osteosarcoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6725.