LAUSR

Differentiation blockade is a hallmark of AML. Strategy to overcome such blockade is a promising approach against the disease. Lack of understanding underlying mechanisms hampers development of such strategy. Dysregulated ribonucleotide reductase (RNR) is considered a druggable target in proliferative cancers susceptible to deoxynucleoside triphosphates (dNTPs) depletion. Herein, we report an unanticipated discovery that hyperactivating RNR enables differentiation and decreases leukemia cell growth. We integrate pharmacogenomics and metabolomics analyses to identify that pharmacologically (e.g., nelarabine) or genetically upregulating RNR subunit M2 (RRM2) level, creates a dNTP pool imbalance and overcomes differentiation arrest. Moreover, R-loop mediated DNA replication stress signaling is responsible for RRM2 activation by nelarabine treatment. Further aggravating dNTP imbalance by depleting the dNTP hydrolase SAM domain and HD domain-containing protein 1 (SAMHD1) enhances ablation of leukemia stem cells by RRM2 hyperactivation. Mechanistically, excessive activation of ERK signaling downstream of the imbalance contributes to cellular outcomes of RNR hyperactivation. A CRISPR screen identifies a synthetic lethal interaction between loss of DUSP6, an ERK negative regulator, and nelarabine treatment. These data demonstrate that dNTP homeostasis governs leukemia maintenance, and combination of DUSP inhibition and nelarabine represents a therapeutic strategy.