Reversal of malignant ADAR1 splice isoform switching with Rebecsinib

Adenosine deaminase acting on RNA1 (ADAR1) preserves genomic integrity by preventing retroviral integration and retrotransposition during stress responses. However, inflammatory-microenvironment-induced ADAR1p110 to p150 splice isoform switching drives cancer stem cell (CSC) generation and therapeutic resistance in 20 malignancies. Previously, predicting and preventing ADAR1p150-mediated malignant RNA editing represented a significant challenge. Thus, we developed lentiviral ADAR1 and splicing reporters for non-invasive detection of splicing-mediated ADAR1 adenosine-to-inosine (A-to-I) RNA editing activation; a quantitative ADAR1p150 intracellular flow cytometric assay; a selective small-molecule inhibitor of splicing-mediated ADAR1 activation, Rebecsinib, which inhibits leukemia stem cell (LSC) self-renewal and prolongs humanized LSC mouse model survival at doses that spare normal hematopoietic stem and progenitor cells (HSPCs); and pre-IND studies showing favorable Rebecsinib toxicokinetic and pharmacodynamic (TK/PD) properties. Together, these results lay the foundation for developing Rebecsinib as a clinical ADAR1p150 antagonist aimed at obviating malignant microenvironment-driven LSC generation. [Display omitted] •ADAR1p150 isoform-mediated A-to-I RNA editing fuels human LSC generation•Lentiviral ADAR1 and splicing reporters enable detection of ADAR1p150 activation•Rebecsinib inhibits ADAR1p150-driven LSC self-renewal while sparing normal HSCs•Rebecsinib pre-IND studies show scalable chemistry and favorable pharmacokinetics Jamieson and colleagues demonstrate that splicing-mediated activation of the inflammation-responsive RNA editase ADAR1 can be inhibited by Rebecsinib, a selective splicing modulator with favorable safety, pharmacokinetic, and pharmacodynamic properties in pre-IND studies. These findings support Rebecsinib development as a potent ADAR1p150 antagonist aimed at preventing leukemia stem cell generation.