Updated project metadata. Resistance to asparaginase, an antileukemic enzyme that depletes asparagine, is a common clinical problem. Using a genome-wide CRISPR/Cas9 screen, we found a synthetic lethal interaction between Wnt pathway activation and asparaginase in acute leukemias resistant to this enzyme. Wnt pathway activation induced asparaginase sensitivity in distinct treatment-resistant subtypes of acute leukemia, but not in normal hematopoietic progenitors. Sensitization to asparaginase was mediated by Wnt-dependent stabilization of proteins (Wnt/STOP), which inhibits GSK3-dependent protein ubiquitination and proteasomal degradation, a catabolic source of asparagine. Inhibiting the alpha isoform of GSK3 phenocopied this effect, and pharmacologic GSK3 inhibition profoundly sensitized drug-resistant leukemias to asparaginase. Our findings provide a molecular rationale for activation of Wnt/STOP signaling to improve the therapeutic index of asparaginase. To gain further insights into mechanisms of cytotoxicity of this combination, we applied unbiased mass spectrometry proteomics to CCRF-CEM cells, a human T-cell acute lymphoblastic leukemia cell line, treated with vehicle, asparaginase alone, the GSK3 inhibitor BRD0705 (which phenocopies Wnt/STOP pathway activation), or the combination of asparaginase and BRD0705.