Abstract 280: Aberrant β-catenin signaling from the bone marrow niche leads to transformation of IDH1/2-mutant hematopoietic stem cells and compromises response to IDH1/2 inhibitors
Authors: Vgenopoulou Paraskevi , Flores Luis , Mosialou Ioanna , Zhao Junfei , Liu X. Shawn , Sung Pamela , Penard-Lacronique Virginie , Carroll Martin , Kousteni Stavroula 
Published: March 2024

Abstract
Our purpose is to identify stromal-derived signals required for IDH1/2-mut hematopoietic stem cells (HSCs) to become leukemogenic. Mutations in IDH genes are found in 20% of acute myeloid leukemia (AML) patients and are not transformative. They produce the oncometabolite 2HG which inhibits key epigenetic regulators. We explored whether epigenetic changes in the bone marrow (BM) niche could provide cooperative signals to IDH-mut HSCs leading to their transformation and disease development. We found that 2HG is elevated in the BM plasma of MDS/AML patients with IDH1/2 mutations as compared to IDH-wt patients. Interestingly, 2HG is taken up by BM stromal cells (BMSCs) suggesting it may induce aberrant methylation patterns in them. Indeed, methylome analysis showed hypermethylation in BMSCs of AML patients with IDH1/2 mutations compared to wt. Among the most hypermethylated genes in the IDH-mut stroma are AXIN1, AXIN2 and NDK2, all negative regulators of β-catenin; this pathway activation was previously shown to cause MDS/AML in mice and present in 38% of patients. In agreement with these findings βcat activation in the stroma of IDH-mut vs IDH-wt AML patients showed a strong positive correlation as 50% of IDH-mut patients had activated βcat in their BMSCs. Inquiring whether stroma methylation precedes HSC transformation, we analyzed samples from healthy individuals with IDH-mut clonal hematopoiesis. They exhibited increased global and AXIN1 promoter methylation compared to samples without such clones, but not active βcat in osteoblasts, indicating this might be a later step along with disease development. In fact, transplantation of HSCs from Idh2-mut mice to recipients expressing active βcat in osteoblasts led to increase in blasts and shortened survival compared to wt mice transplanted with Idh2-mut HSCs. As many patients relapse following treatment with IDH inhibitors, we investigated a potential role for βcat signaling in treatment outcome. IDH-mut AML patients who do not respond to treatment with the IDHi present more frequently with activated βcat in osteoblasts compared to responders. Analyzing samples from the same patient pre- and post-treatment with IDHi, we found before treatment most patients were positive for βcat stromal activation, whereas after treatment, all patients with complete response were negative, while patients with progressive disease remained positive. Our model suggests IDH-mut HSCs secrete 2HG inducing epigenetic alterations in the niche, some of which cause activation of the βcat pathway. In turn, this additional signal leads to the transformation of HSCs to dysplastic cells and MDS/AML development. This work uncovers a new mechanism for transformation to MDS/AML and resistance to IDHi treatment. Thus, targeting βcat activation in the stroma, in combination with IDHi, could improve treatment outcome.
Citation Format: Paraskevi Vgenopoulou, Luis Flores, Ioanna Mosialou, Junfei Zhao, X. Shawn Liu, Pamela Sung, Virginie Penard-Lacronique, Martin Carroll, Stavroula Kousteni. Aberrant β-catenin signaling from the bone marrow niche leads to transformation of IDH1/2-mutant hematopoietic stem cells and compromises response to IDH1/2 inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 280.