The Significance of IL-3 Receptor beta chain for FLT3-ITD Dependent Oncogeneic Signaling in AML

在AML中，激活FLT 3突变与预后不良相关。FLT 3酪氨酸激酶抑制剂（TKI）的临床活性有限。这种耐药性的机制在大多数情况下是无法解释的。在第一个资助期，我们确定了FLT 3激酶非依赖性耐药的机制。在体外模型中，我们将白血病细胞自分泌趋化因子CCL 5确定为耐药机制，并在患者样本中进行了验证（沃尔德克et al. 2020）。此外，我们证明激活JAK 1/2/3突变可以替代体外FLT 3依赖性CSF 2 RB激活，并且JAK 1/2/3突变发生在FLT 3抑制剂耐药AML患者中（Rummelt et al. Leukemia 2020）。我们证明，他的耐药性可以通过FLT 3和JAK抑制剂的组合来克服。我们发现CSF 2 RB直接与FLT 3-ITD相互作用，并以FLT 3依赖性方式磷酸化。CSF 2 RB敲低抑制细胞生长和STAT 5活化，并与FLT 3抑制剂协同作用。CSF 2 RB缺陷型骨髓表现出较低的转化潜力。在FLT 3-ITD阳性异种移植物中，CSF 2 RB敲低导致STAT 5磷酸化减少和存活延长。CSF 2 RB缺陷骨髓减少FLT 3-ITD诱导的AML的生长，并延长受体动物的存活期。在该后续提案中，我们旨在阐明FLT-ITD依赖性CSF 2 RB激活的机制，特别是酪氨酸在FLT 3-ITD的CSF 3 RB结合基序中的作用以及真正的CSF 2 RB相互作用配偶体（林恩、SRC、SYK）和ER应激信号传导作为FLT 3-ITD依赖性CSF 2 RB激活的可能机制的意义。我们将检验高度临床相关的假设，即已知FLT 3-ITD变体的差异转化能力和预后意义是否归因于FLT 3-ITD中CSF 2 RB结合基序的差异，从而归因于CSF 2 RB结合能力。基于精心设计的相互作用结构域，我们将验证优化的REPLACE肽在体外和体内通过FLT 3-ITD治疗性阻断CSF 2 RB依赖性转化和白血病发生。我们将使用排除尼古丁依赖性作用的实验模型，研究CSF 2 RB在体内的细胞内在的FLT 3-ITD依赖性转化作用，并验证FLT 3抑制剂和CSF 2 RB界面阻断肽模拟物的新型联合治疗用于临床。

In AML, activating FLT3 mutations are associated with poor prognosis. FLT3 tyrosine kinase inhibitors (TKIs) have limited clinical activity. The mechanism of this resistance is in most cases unexplained. In the first funding period, we identified mechanisms of FLT3 kinase-independent resistance. In an in vitro model, we identified autocrine secretion of the chemokine CCL5 by leukemia cells as a resistance mechanism and verified it in patient samples (Waldeck et al. 2020). Moreover, we demonstrated that activating JAK1/2/3 mutations can substitute FLT3-dependent CSF2RB activation in vitro and that JAK1/2/3 mutations occur in patients with FLT3 inhibitor resistant AML (Rummelt et al. Leukemia 2020). We demonstrated that his resistance can be overcome by a combination of FLT3 and JAK inhibitors. We found that CSF2RB interacts directly with FLT3-ITD and is phosphorylated in a FLT3-dependent manner. CSF2RB knockdown inhibited cell growth and STAT5 activation, and acted synergistically with FLT3 inhibitors. CSF2RB-deficient bone marrow showed lower transformation potential. In FLT3-ITD positive xenografts, CSF2RB knockdown resulted in reduced STAT5 phosphorylation and prolonged survival. CSF2RB-deficient bone marrow reduced growth of FLT3-ITD-induced AML and prolonged survival in recipient animals. In this follow-up proposal, we aim to elucidate the mechanism of FLT-ITD dependent CSF2RB activation, specifically the role of tyrosines within the CSF3RB binding motif of FLT3-ITD and the significance of bona fide CSF2RB interaction partners (LYN, SRC, SYK) and ER stress signaling as possible mechanisms of FLT3-ITD dependent CSF2RB activation. We will test the highly clinically relevant hypothesis whether the differential transformation capacity and prognostic significance of known FLT3-ITD variants are due to differences in the binding motif for CSF2RB in FLT3-ITD and thus due to CSF2RB binding ability. Based on the elaborated interaction domains, we will validate optimized REPLACE peptides for therapeutic blockade of CSF2RB-dependent transformation and leukemogenesis by FLT3-ITD in vitro and in vivo. Using experimental models that exclude cytokine-dependent effects, we will investigate the cell-intrinsic, FLT3-ITD-dependent transforming effect of CSF2RB in vivo and validate novel combination therapies of FLT3 inhibitors and CSF2RB interface blocking peptidomimetics for clinical use.