Selective Reversal of ADAR1 Splicing Prevents Leukemia Stem Cell Maintenance In Vivo

Introduction

Acute myeloid leukemia (AML) is characterized by a clonal proliferation of myeloid progenitors with a reduced capacity to differentiate into more mature cellular elements. Adenosine deaminase acting on RNA 1 (ADAR1) is an enzyme that is involved in the editing of messenger RNA (mRNA) transcripts (A-to-I RNA editing), which can alter the function of the resulting protein. ADAR1 drives cancer stem cell (CSC) generation and therapeutic resistance in many types of malignancies. As a potent small molecule splicing modulator, Rebecsinib inhibits splicing of ADAR1 into the ADAR1p150 isoform while Fedratinib inhibits JAK/STAT3 mediated activation of ADAR1p150 transcription^{1, 2}.

Methods

To assess the relative ADAR1 inhibitory capacity of Rebecsinib and Fedratinib, humanized sAML mouse models were established with immunomagnetic bead-selected CD34+ cells from primary AML patient samples. Engrafted mice treated with Rebecsinib survived significantly longer compared to those treated with vehicle (p = 0.0003, log-rank test), Fedratinib (p = 0.016, log-rank test), and the combination of Rebecsinib and Fedratinib (p= 0.0002, log-rank test). In comparison, humanized aged normal bone marrow stem cell mouse models established by intravenous transplantation of CD34⁺ cells (obtained according to IRB-approved protocols from the bone marrow of patients undergoing hip replacement surgery), into NSG-SGM3 mice demonstrated increased human CD34⁺ cells engraftment in the bone marrow.

Conclusions

The results suggest that inhibition of ADAR1 splice isoform switching may provide a competitive advantage for normal hematopoietic stem cells compared with leukemia stem cells in the bone marrow niche and lay the foundation for developing clinical ADAR1p150 inhibitory strategies.

References1. Crews L, Balaian L, Delos Santos, NP et al. RNA Splicing Modulation Selectively Impairs Leukemia Stem Cell Maintenance in Secondary Human AML. Cell Stem Cell. 2016; 19: 599-612, PMID: 275700672. Crews L, Ma W, Ladel L, et al. Reversal of Malignant ADAR1 Splice Isoform Switching with Rebecsinib. Cell Stem Cell. 2023.

Jamieson:Aspera Biomedicines: Other: co-founder; Forty Seven Inc.: Patents & Royalties; Impact Biomedicines: Other: co-founded.