Targeting ribonucleotide reductase to overcome FLT3 Inhibitor Resistance in acute myeloid leukemia

Abstract Acute myeloid leukemia (AML), the most common acute leukemia in adults, is frequently characterized by chemotherapy resistance and relapse. Mutations in FLT3 occur in approximately 30% of AML cases and are associated with poor prognosis. While FLT3 inhibitors (FLT3is) represent a significant therapeutic advance, resistance remains a major clinical challenge. We previously demonstrated that loss of SPRY3—an upstream suppressor of the RAS/MAPK pathway—drives FLT3i resistance through RAS pathway activation. Similarly, NRAS mutations (e.g., G12C, Q61K), present in ~15% of AML cases, also promote FLT3i resistance. Our recent work identified ribonucleotide reductase (RNR), a key enzyme in dNTP synthesis essential for DNA replication and repair, as a critical mediator of NRAS-driven FLT3i resistance. NRAS-mutant AML cells dramatically upregulate RNR expression, leading to dNTP imbalance. Strikingly, pharmacologic or genetic inhibition of RNR reversed resistance by depleting dNTPs and synergized with FLT3is to kill NRAS-mutated AML in vitro and in both cell line-derived (CDX) and patient-derived xenograft (PDX) models in vivo. Notably, several FDA-approved drugs, such as clofarabine and fludarabine, are known RNR inhibitors. We propose repurposing these agents to overcome FLT3i resistance in AML. Together, these findings establish RNR as a promising therapeutic target to circumvent NRAS-mediated FLT3i resistance in AML.