P419: harnessing mirna-193b-3p mimic as a potent therapeutic option in acute myeloid leukemia

Background: One of the greatest obstacles in treating acute myeloid leukemia (AML) is managing toxicity, particularly in terms of bone marrow regeneration and the restoration of normal hematopoiesis. Thus, a key objective of AML research is to develop novel molecularly targeted treatment approaches to effectively eradicate leukemia and reduce the harm to healthy hematopoietic stem/progenitor cells. We found previously that the tumor suppressor microRNA-193b-3p (miR-193b) is a strong independent prognostic marker in AML and its lower expression is associated with poor clinical outcomes. In contrast, miR-193b is upregulated in normal hematopoietic stem cells and hence represses the down-stream MAPK/ERK cascade. Aims: The aim of this study was to preclinicaly investigate the feasibility of restoring miR-193b functions as a viable safe treatment for pediatric AML. Methods: We encapsulated a miR-193b mimic in DLin-MC3-DMA lipid nanoparticles (LNPs) using a microfluidic system and tested their antileukemic activity in vitro using patient-derived xenografts (PDXs) in proliferation, apoptosis, and colony formation assays. We tested the safety of the LNPs on immunocompetent C57BL/6B mice in vivo, where we assessed naïve hematopoiesis and the stem cell compartments using multicolor flow cytometry. We evaluated the efficacy of the LNPs in vivo on four PDXs engrafted in immunodeficient humanized mice. Results: Treatment of AML PDXs representing KMT2Ar, AMKL, and ML-DS leukemias with LNPs encapsulating miR-193b mimic demonstrated potent antileukemic activity. The restoration of miR-193b function inhibited proliferation, rapidly induced apoptosis, and halted colony formation capacity. In vivo LNP treatment of immunodeficient humanized mice injected with AML PDXs halted leukemia progression, decreased chimerism in the peripheral blood of recipient mice, and significantly prolonged the overall survival of all treated xenografts (Figure A). Importantly, restoration of miR-193b function was well-tolerated in humanized mice, and a safety experiment in C57BL/6B mice showed no effect on the long-term hematopoietic stem cells (Figure B), as the numbers and frequency of isolated lineage-negative cells remained unchanged.Figure A. survival experiment of immunodeficient humanized mice harbouring AML PDXs and treated with LNPs encapsulating either miR-193b or negative control mimics. Top, percentage of human CD45+ cells in the periphery of transplanted mice. Blood sampling was performed one day before the start of the treatment and after two weeks. Lines represent the mean and statistical significance was calculated based on one-way ANOVA. Bottom, Kaplan-Meier survival curves of LNP-treated PDXs. Statistical significance was calculated using the log-rank test. Figure B. In vivo safety experiment in C57BL/6B mice. Top, representative flow cytometry plots of murine LK and LSK, and long-term stem cells following two weeks of LNPs treatment. Bottom, absolute cell number of LSK cells and the respective percentages of LSK and stem cells compartments. Summary/Conclusion: Taken together, our comprehensive assays in vitro and in vivo on AML xenografts demonstrate that restoration of miR-193b function is safe and effective in restricting leukemia progression. These results provide promising evidence for miR-193b-based interventions in AML. Keywords: Hematopoietic stem cell, Acute myeloid leukemia, Targeted therapy