Genome-Wide CRISPR-Cas9 Screening Identifies a Synergy between Hypomethylating Agents and SUMOylation Blockade in Myelodysplastic Syndromes and Acute Myeloid Leukemia (Screen)

Hypomethylating agents (HMAs) are frontline therapies effective at altering the natural course of Myelodysplastic Neoplasms (MDS). However, acquired resistance and treatment failure are hallmarks of HMA therapy. Developing effective and rational HMA-focused combinatorial therapies is challenging as the underlying mechanisms driving HMA efficacy are complex. To address this clinical need, we performed a genome-wide CRISPR-Cas9 screen in a human MDS-derived cell line, MDS-L, and characterized TOPORS as a highly ranked target that synergizes with HMAs to reduce leukemic burden and improve survival in xenograft models. We demonstrated that the depletion of TOPORS mediates sensitivity to HMAs by predisposing leukemic blasts to an impaired DNA damage response (DDR) accompanied by an accumulation of SUMOylated DNMT1 in HMA-treated TOPORS-depleted cells. Importantly, the combination of HMAs with targeting of TOPORS did not functionally impair healthy hematopoiesis. While inhibitors of TOPORS are currently unavailable, we show that inhibition of SUMOylation (upstream of TOPORS functions) with TAK-981 partially phenocopies HMA-sensitivity and DDR impairment. Overall, our data suggest that the combination of HMAs with the inhibition of SUMOylation demonstrates a favourable therapeutic index and represents a rational framework towards the treatment of High-Risk MDS (HR-MDS) or Acute Myeloid Leukemia (AML). Overall design: To identify novel genetic determinants that regulate Azacitidine sensitivity in MDS, we performed a genome-wide CRISPR-Cas9 screen using MDS-L cells under AZA selection. We transduced MDS-L-Cas9 cells with the Brunello sgRNA library and treated transduced cells with 0.3uM AZA or DMSO until the AZA-treatment arm underwent 12 cellular divisions to ensure robust depletion of essential genes. We performed analyses using the MAGeCKFlute pipeline to identify essential, non-essential, and targeted genes that regulate Azacitidine sensitivity in MDS-L cells.