Microenvironmental Regulation of Leukemia Stem Cells

项目总结摘要 慢性粒细胞白血病(CML)是由BCR-1诱导的造血干细胞(HSC)转化而来的 ABL致癌酪氨酸激酶。酪氨酸激酶抑制剂(TKI)在诱导缓解和 延长CML患者的生存期，但不能消除原始的、静止的白血病干细胞(LSC) 负责白血病的繁殖和再生。因此，大多数患者都经历了快速白血病 TKI停药后复发。然而，获得长期深度缓解的患者的一部分可能 成功停止TKI治疗，未见白血病复发。我们的研究重点是了解 LSC对TKI的抗性机制及其针对LSC及其微环境的研究进展 预防白血病复发，提高治疗无缓解(TFR)。我们现在明白，病人 达到TFR继续有少量的BCR-ABL+LSC，这表明微环境或 免疫因素可能调节LSC再生白血病的潜能。骨髓微环境， 它包括多种造血细胞和非造血细胞，在HSC的调节中起着关键作用。在……里面 相比之下，对LSC增长的微环境调控还没有得到很好的理解。在这里，我们建议将 维持LSC的关键生态位调节机制，这可能有助于白血病复发 停止TKI治疗后。我们已经证明，CML的发展导致几个关键因素水平的提高 BM中的炎性细胞因子，可为CML LSC提供选择性生长优势。我们的预赛 研究表明，炎症信号可以改变CML BM MSC，从而增强对CML的支持 LSC，减少对正常HSC的支持。在目标1中，我们将探讨TNFa在调节脑组织中的变化中的作用。 骨髓间充质干细胞，导致炎性趋化因子CXCL1表达增加，信号增强 通过CXCR2受体，在TKI治疗后LSC维持和白血病再生中发挥作用。多面性 间充质基质细胞(MSC)，根据Lepr、Nestin或PRX1的表达而鉴定，代表 维持正常HSC的专门BM壁龛。我们的初步研究表明，CXCL12从 PRX1+MSC导致LSC静息消失，对TKI治疗的敏感性增强。在目标2中，我们将 表达CXCL12的骨髓间充质干细胞调控LSC周期及耐药机制的研究 利基，重点是调节LSC中的EZH2活性。我们还将研究CXCL12和CXCL12之间的相互作用 炎症信号在改变MSC巢功能中的作用。这些研究将使用小鼠模型进行 和原代人类慢性粒细胞白血病细胞。更好地理解微环境调控的机制 对恶性干细胞的研究将有助于指导新策略的开发，以增强CML患者的TFR。我们 进一步预计，拟议的研究结果将对其他白血病产生更广泛的影响 和实体瘤。

PROJECT SUMMARY ABSTRACT Chronic myelogenous leukemia (CML) results from hematopoietic stem cell (HSC) transformation by the BCR- ABL oncogenic tyrosine kinase. Tyrosine kinase inhibitors (TKI) are highly effective in inducing remission and prolonging survival in CML patients, but do not eliminate primitive, quiescent leukemia stem cells (LSC) responsible for leukemia propagation and regeneration. As a result most patients experience rapid leukemia relapse after TKI discontinuation. However, a subset of patients achieving prolonged, deep remission can successfully discontinue TKI treatment without leukemia recurrence. Our research focuses on understanding mechanisms of LSC resistance to TKI, and development of strategies to target LSC and their microenvironment to prevent leukemia recurrence and enhance treatment free remission (TFR). We now understand that patients achieving TFR continue to harbor small numbers of BCR-ABL+ LSC, suggesting that microenvironmental or immune factor may regulate LSC potential to regenerate leukemia. The bone marrow (BM) microenvironment, which includes diverse hematopoietic and non-hematopoietic cells, plays a critical role in HSC regulation. In contrast, microenvironmental regulation of LSC growth is not well understood. Here we propose to characterize critical niche regulatory mechanisms for maintenance of LSC, and that may contribute to leukemia recurrence after stopping TKI treatment. We have shown that CML development leads to increased levels of several key inflammatory cytokines in the BM, which can provide a selective growth advantage to CML LSC. Our preliminary studies suggest that inflammatory signaling can modify CML BM MSC, resulting in enhanced support for CML LSC, and reduced support of normal HSC. In Aim 1, we will explore the role of TNFa in mediating alterations in BM MSC, resulting in increased expression of the inflammatory chemokine CXCL1 and enhanced signaling through CXCR2 receptor, in LSC maintenance and leukemia regeneration after TKI treatment. Multipotent mesenchymal stromal cells (MSC), identified on the basis of expression of LepR, nestin or Prx1, represent specialized BM niches that maintain normal HSC. Our preliminary studies show that CXCL12 deletion from Prx1+MSC leads to loss of LSC quiescence and enhanced sensitivity to TKI treatment. In Aim 2, we will investigate mechanisms of regulation of LSC cycling and treatment resistance by CXCL12-expressing BM MSC niches, focusing on regulation of EZH2 activity in LSC. We will also study the interaction between CXCL12 and inflammatory signaling in modifying MSC niche function. These studies will be conducted using murine models and primary human CML cells. Better understanding of mechanisms underlying microenvironmental regulation of malignant stem cells will help guide development of novel strategies to enhance TFR in CML patients. We further expect that the results of the proposed research will have broader implication towards other leukemias and solid tumors.