Internal tandem duplications (ITD) in fms-like tyrosine kinase 3 (FLT3) represent the most common genetic alteration in de novo acute myeloid leukemia (AML). Here, we identify ribosomal protein s6 kinase a1 (RSK1) as a core dependency in FLT3-ITD AML and unveil the existence of crucial bi-directional regulation. RSK1 perturbation resulted in marked apoptosis and abrogated phosphorylation of FLT3 and associated downstream signaling cascades in FLT3-ITD AML cell lines. Using cycloheximide, MG-132, and ubiquitination assays, we further demonstrate mechanistically that RSK1 regulates FLT3-ITD activity, and protein stability through deubiqutinase USP1, which we identify as a second dependency. Importantly, multivariate analysis revealed heightened expression of RPS6KA1 and USP1 to be associated with poor patient prognosis, and these effectors may serve as biomarkers predictive of patient survival and therapeutic response to FLT3-ITD inhibitors. Lastly, RSK1 inhibition utilizing a first-in-class RSK inhibitor, PMD-026, that is currently undergoing Phase 2 development for breast cancer, diminished leukemic disease burden in MV4-11 xenograft and syngeneic Flt3^ITDTet2^KO leukemia models. These findings illustrate an unconventional and promising therapeutic strategy targeting FLT3-ITD leukemia.

fms 样酪氨酸激酶 3 （FLT3） 中的内部串联重复 （ITD） 代表了新发急性髓性白血病 （AML） 中最常见的遗传改变。在这里，我们确定核糖体蛋白 s6 激酶 a1 （RSK1） 是 FLT3-ITD AML 的核心依赖性，并揭示了关键双向调节的存在。RSK1 扰动导致 FLT3-ITD AML 细胞系中 FLT3 和相关下游信号级联的显着细胞凋亡和磷酸化被消除。使用放线菌酮、MG-132 和泛素化测定，我们进一步从机制上证明 RSK1 通过去泛素酶 USP1 调节 FLT3-ITD 活性和蛋白质稳定性，我们将其确定为第二个依赖性。重要的是，多变量分析显示 RPS6KA1 和 USP1 的表达升高与患者预后不良有关，这些效应子可作为预测患者生存率和对 FLT3-ITD 抑制剂治疗反应的生物标志物。最后，利用目前正在进行乳腺癌 2 期开发的一流 RSK 抑制剂 PMD-026 抑制 RSK1，减少了 MV4-11 异种移植物和同基因 Flt3^ITDTet2^KO 白血病模型中的白血病负担。这些发现说明了一种针对 FLT3-ITD 白血病的非常规且有前途的治疗策略。