Histone Deacetylase Inhibitors Enhance CRISPR‐Cas9 Cutting Efficiency

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The CRISPR/Cas9 technology is a prominent genome‐editing tool as an adaptable nuclease capable of producing a double strand break at almost any genomic loci. However, the modification of hematopoietic stem and progenitor cells (HSPC) via the homology directed repair (HDR) pathway is still inefficient. We hypothesize that histone deacetylase inhibitors (HDACi), such as Valproic Acid (VPA) and Sodium Butyrate (NaB), could enhance HDR efficiency by increasing the accessibility of the genome‐editing machinery. To address the potential utilization of HDACi therapeutically, we began by assessing the effect of VPA and NaB on cell growth and viability. No statistically significant effect on cell growth or viability was observed at concentrations as high as 50mM in a myeloid‐erythroid leukemic cell line (K562 cells). However, K562 cells only represent one lineage of the HSPC progeny. Therefore, we also treated an immortalized T lymphocyte cell line (Jurkat cells), representative of the lymphoid lineage, with either VPA or NaB. No effect on the growth pattern or viability of Jurkat cells was evident at concentrations as high as 5mM VPA and NaB. However, Jurkat cells did appear to be more susceptible to HDACi. Therefore, we ascertained that concentrations of HDACi lower than 5mM would be tolerated in HSPCs. At concentrations as low as 0.0005mM HDACi an enhancement in CRISPR cutting efficiency was evidenced as assessed in both K562 cells and Jurkat cells. This enhancement did not appear to be locus specific, in that two sets of CRISPR guide RNAs were analyzed revealing similar trends of enhancement. If the same trend follows, treatment with HDACi can be expanded to virtually any genome editing experiment utilizing the CRISPR‐Cas9 system to enhance cutting and thus therapeutic gene editing.Support or Funding InformationCSUPERBEffect of Valproic Acid and Butyrate on the Growth Curve of Hematopoietic Cell Lines A) Schematic representation of the experimental design utilized to test the effect of HDACi on the division of two hematopoietic cell lines. B) K562 cells treated with 300mM and 100mM VPA were not observed to divide. C) K562 cells treated with 500mM NaB were not observed to divide. D) Jurkat cells appear to be more susceptible to VPA. E) Jurkat cells treated with 50mM NaB proliferated at a much slower rate.Figure 1