A Primary Mouse Model Of Aml As A New Way To Screen Novel Therapeutics And Treatment Combinations

Introduction Acute myeloid leukemia (AML) is a disease characterized by the proliferation of undifferentiated myeloid blasts, promoting bone marrow failure, infectious complications, and death. Progress in developing treatments for AML has been slow and clinical outcomes outside of bone marrow transplant are poor. A limitation to progress is the availability of reproducible murine models of AML. As such, there is a critical need to develop new models to quickly screen new therapeutics and treatment combinations. Here we have optimized the engraftment of a spontaneous Idh2R140Q/Flt3ITD murine AML (developed by Shih et al 2017) for rapid in vivo screening of compounds and combination strategies. Methods Spleen derived AML cells from a spontaneous Idh2R140Q/Flt3ITD murine AML were engrafted i.v. into NCG mice. Disease progression was monitored by flow cytometry and LC-MS/MS measurement of plasma D-2-hydroxyglutarate (D2HG), the product of mutant IDH2. At 1 week post-engraftment animals were enrolled onto treatment arms, which included enasidenib (IDH2), gilteritinib (Flt3), a dihydroorotate dehydrogenase (DHODH) inhibitor, and combination arms. In follow-up studies, non-tumor bearing C57Bl/6 mice were treated with various doses of treatment combinations and blood counts, serum liver chemistry, and weight loss were used to evaluate toxicity. Results The time from engraftment to terminal disease can be precisely adjusted to experimental needs, enabling an aggressive 21-day disease course for rapid screening or a more protracted 1.5 month course that limits the initial number of cells required and allows for the testing of slower-acting differentiating agents. We show that enasidenib, gilteritinib, and a DHODH inhibitor all slow disease progression and prolong survival, and that DHODH inhibition may have a greater effect on survival than IDH2 inhibition. We also show that DHODH inhibition lowers plasma D2HG. Importantly, we identify that combining DHODH and IDH2 inhibition is untenable and results in lethal GI toxicity. This was validated in non-tumor bearing mice, where even low doses of DHODH/IDH2 inhibitors in combination resulted in cytopenias and rapid weight loss. Discussion Developing combination treatment regimens is likely to be key to achieving long-term remission for many AML patients; however, efforts to develop these combinations are often stymied by in vitro results that fail to translate to the in vivo setting, particularly unexpected toxicities that are not recognized in vitro. We show that our AML engraftment model can be used to identify and develop pre-clinical compounds and allow us to quickly identify and abandon treatment combinations that are toxic in vivo. Our hope is that this work enables the rapid identification and development of the best novel therapeutics and treatment combinations, such that valuable time and resources can be utilized to their greatest translational effect. Citation Format: Mariah L. Johnson, Ola A. Elgamal, Bonnie Harrington, Allison Mustonen, Amy Lehman, Chad Bennett, Kyle R. Dzwigalski, Kasey L. Hill, Mitch A. Phelps, Jean Truxall, Thomas Goodwin, Alan H. Shih, Ross L. Levine, Erin Hertlein, John C. Byrd. A primary mouse model of AML as a new way to screen novel therapeutics and treatment combinations [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6118.