Small-molecule Activators Specific to Adenine Base Editors through Blocking Canonical TGF-beta Pathway

ABEs were developed to catalyze an A-to-G conversion, thus holding therapeutic potentials for treating the major class of human pathogenic SNPs. However, robust and precise editing at diverse genome loci in a controllable manner remains challenging. Here, through a high-throughput chemical screen of ~ 8,000 small molecules, we identified and validated a spectrum of small molecules that target the canonical TGF-beta pathway as ABE activators. Among those, SB505124, a selective ALK5 inhibitor, promotes ABE editing most. Treating cells with SB505124 dramatically enhanced on-target editing at multiple genome loci, including the refractory regions, while exhibiting little effect on off-target conversion on the genome, eliminating the major concern for clinical applications. Furthermore, SB505124 facilitates the editing of disease-associated genes in vitro and in vivo. Intriguingly, SB505124 serves as a specific activator by selectively promoting the activity of ABEs, rather than CBEs or Cas9. Our finding equips the ABE with precise chemical control, and more importantly, reveals a so-far-unreported role of the canonical TGF-beta pathway on gene editing. Cells were seeded on 24-well plates, transfected with a plasmid expressing ABE7.10 and gRNA targeting site 18. Twelve hours after transfection, cells were re-plated into 24-well plates as 1.4×10^5 cells per well. The chemicals were added individually. Seventy-two hours after treatment, the total RNA was isolated by TRNzol Universal reagent according to the standard protocol then used to construct high-throuput sequencing libraries for RNA-seq. ITD 1 is a selective inhibitor of TGF-β signaling. SB-505124 is a selective inhibitor of TGF-β Receptor type I receptors.