The role of the bone marrow niche in the maintenance of cancer stem cells in chronic myeloid leukaemia (CML)

开发根除癌症干细胞(CSC)并治愈这种疾病的癌症疗法具有巨大的挑战性。这一点在慢性髓系白血病(CML)中得到了证明，这是CSC研究的一种高级范式，BCR-ABL1将正常的造血干细胞(HSC)转化为白血病干细胞(LSC)。大多数CML患者处于慢性期(CP)，在此期间，BCR-ABL1驱动LSC的分子变化，根据达尔文原理，这些变化可能增加他们的“适合度”，并驱动他们的克隆性扩张。在更糟糕的情况下，这些变化导致对标准护理酪氨酸激酶抑制剂(TKI)的完全抵抗，并促进疾病进展到加速期，然后发展到最终的原始细胞阶段。治疗慢性粒细胞白血病的关键瓶颈是骨髓(BM)中持续存在的LSC亚群(S)，正是在这些亚群中发生耐药和疾病进展。TKI耐药的LSC在患者中维持残留的CML，通过克隆进化驱动TKI耐药和疾病进展，并允许在TKI中断时复发。到目前为止，我们对LSC生物学的知识一直基于对诊断或复发时从患者样本中提取的大量细胞群的分析。然而，对于接受TKI治疗的患者中对TKI耐药的LSC，我们对它们如何演变的分子机制，它们需要什么途径，以及它们在患者中的差异知之甚少。这是因为(1)耐TKI的LSC在骨髓中非常罕见(尤其是在MMR中)，以及(2)到目前为止，LSC还不能选择性地从正常的HSC中分离出来，这些HSC在TKI治疗期间重建了BM中的正常造血。基于这些原因，毫不奇怪，尽管在过去的15年里，LSC已经确定了40多种药物靶点，但进入临床试验的药物相对较少，而且没有一种药物取代或补充TKI作为治疗标准。Holyoake是第一个证明CML-CSCs不会对癌基因上瘾的人。自2007年以来，Holyoake等人编制了描述CML-CSC的30个内部/公共多组学数据集(LEUKology，STEMFORMATICS内特定于CML的领域。LSCs的存活不需要BCR-ABL-激酶活性，在CP患者中也不存在BCR-ABL激活域突变，推测它们是通过BCR-ABL-激酶非依赖的途径存活的。数据挖掘揭示了控制CML-CSC内在网络的三个关键枢纽(P53、c-Myc、PRC2)。利用小鼠干细胞白血病(SCL)基因3‘增强子、反式激活蛋白(TTA)、BCR-ABL(SCL-TTA-BCR-ABL)模型，我们将能够通过四环素停药(SCL-TTA-BCR-ABL)诱导BCR-ABL表达，这类似于慢性期CML。扩展当前的合作，以提供CML-CSC和支持CSC的关键BM利基组件的全面转录图景。我的研究将：1.确定哪些利基细胞亚群(间充质干细胞和巨噬细胞)支持CML-CSCs改变CML的疾病动力学和在已有描述的CML转基因(SCL-TTA-BCR-ABL)小鼠模型中的TKI反应2。确定CML-CSC是否依赖于骨髓/脾脏壁龛内的MSC或巨噬细胞(就疾病的起始、维持、治疗反应和复发而言)。然后，将使用全球最大的CML生物库，在人类CML样本和异种移植NSG模型中调查阳性发现。

Developing cancer therapies that eradicate cancer stem cells (CSC) and cure the disease is hugely challenging. This is exemplified in chronic myeloid leukaemia (CML), an advanced paradigm of CSC research, where BCR-ABL1 transforms a normal haemopoietic stem cell (HSC) into a leukaemic stem cell (LSC). Most CML patients present in chronic phase (CP), during which BCR-ABL1 drives molecular changes in the LSC that may increase their "fitness" and drive their clonal expansion according to Darwinian principles. In worse case scenarios, these changes result in total resistance to standard-of-care tyrosine kinase inhibitors (TKI) and promotes disease progression to accelerated phase and then to terminal blast phase. The key bottleneck to curing CML is the sub-population(s) of LSC in the bone marrow (BM) that persists throughout TKI treatment, it is these populations in which drug resistance and disease progression occur. TKI-resistant LSCs sustain residual CML in patients, drive TKI-resistance and disease progression through clonal evolution and allows for relapse upon TKI discontinuation.To date, our knowledge of LSC biology has been based on analysis of bulk cell populations taken from patient samples at diagnosis or relapse. However, for TKI-resistant LSC in patients on TKI, we know very little about the molecular mechanisms of how they evolve, what pathways they require, and how they vary among patients. This is because (1) the TKI-resistant LSC are extremely rare in the BM (particularly in MMR), and (2) to date, LSC cannot be selectively isolated from normal HSC that reconstitute normal haemopoiesis in the BM during TKI therapy. For these reasons, it is not surprising that, despite the identification of more than 40 drug targets in LSC over the last 15 years, relatively few drugs reach clinical trials, and none have replaced, or even supplemented TKI as the standard-of-care.Holyoake was the first to demonstrate that CML-CSCs are not oncogene-addicted. Since 2007, Holyoake, et al have compiled (LEUKomics, CML-specific domain within STEMFORMATICS, >30 in-house/public multi-omics datasets describing CML-CSCs. LSCs do not require BCR-ABL-kinase activity for survival, nor do they have BCR-ABL kinase domain mutations in patients during CP, inferring that they survive through BCR-ABL-kinase-independent pathways. Data-mining has revealed three key hubs (p53, c-Myc, PRC2) controlling a targetable CML-CSC intrinsic network. Demonstrating interactions between CML-CSC and their BM microenvironment, revealing cytokines/chemokines, JAK/STAT, N-cadherin/WNT/b-catenin and hedgehog signalling as potential key players.Using the murine stem cell leukaemia (SCL) gene 3' enhancer, transactivator protein (Tta), BCR-ABL (SCL-tTA-BCR-ABL) model we will be able to induce BCR-ABL expression via tetracycline withdrawal (driven off SCL promotion), which resembles chronic phase CML. Extending current collaborations to provide a comprehensive transcriptomic landscape of CML-CSC and key BM niche components that support CSC. My research will:1. Determine which niche cell subsets (mesenchymal stem cells (MSC) and macrophages) support CML-CSCs altering the disease kinetics of CML and TKI-response in a well-described CML transgenic (SCL-tTA-BCR-ABL) mouse model2. Determine whether CML-CSC are dependent (in terms of disease initiation, maintenance, response to therapy and relapse) on either MSC or macrophages within the BM/spleen niche. Positive findings would then be investigated in human CML samples and in the xenograft NSG model, using the CML biobank, the largest of its kind worldwide.