Origins of BRAF-mutant hematologic malignancies and their therapeutic resistance

总结 虽然丝氨酸-苏氨酸激酶BRAF的激活突变发生在约8%的实体瘤中，但它们是罕见的。 在造血系统恶性肿瘤中，毛细胞白血病（HCL）和系统性组织细胞病（SH）除外 朗格汉斯细胞组织细胞增生症和Erdheim-Chester病特异性BRAFV 600 E的存在 近100%的HCL患者和40-60%的SH患者的突变为我们理解 这些鲜为人知的疾病的病理生理学。BRAF靶向抑制剂的研究进展 或其下游介质来治疗实体瘤已经导致了重大的治疗进展，并且最近 该范例已应用于HCL和SH。我们的跨学科团队利用了这些优势 BRAFV 600 E突变生物学和治疗学的进展，最近发表了其研究结果， HCL起源于造血干细胞，并开发了遗传准确的HCL小鼠模型。更 最近，我们已经证实了BRAFV 600 E突变在造血干细胞和祖细胞中的存在， SH患者的细胞，产生SH的小鼠模型，确定了与SH细胞共存的复发性突变。 HCL和SH中的BRAFV 600 E突变，并完成了维罗非尼治疗HCL和SH的临床试验 患者虽然我们的初步数据提供了大量证据表明HSPCs有助于疾病 在HCL和SH两者中通过其获得BRAFV 600 E突变的发病机制，尚不清楚如何 这种常见的突变驱动了这种表型和临床上不同的疾病的发展。 此外，尽管我们已经注意到HCL和SH患者对以下药物表现出显著的临床反应： 我们已经开始确定HCL中vemurafenib耐药的遗传机制， 我们有独特的机会来开发治疗这些疾病的下一系列治疗策略， 紊乱因此，本提案的总体目标是描述细胞和功能要求， HCL和SH发病机制，并利用这些信息来确定耐药突变的起源， 在BRAF靶向治疗的背景下出现。我们假设BRAFV 600 E突变体 蛋白质是活性的和/或协作突变的存在在确定疾病中起主要作用 表型和对BRAF抑制的反应。我们将在以下目标中解决这个假设：1）描绘 BRAFV 600 E突变对造血的功能性影响，基于其在其中具有活性的细胞，2） 鉴定HCL和SH中与BRAFV 600 E突变共存的突变群，以及3） 确定BRAF抑制剂耐药的机制。该项目将提供全面的 细胞起源的表征和产生HCL和SH的协同突变。而且这 这项工作将描述造血系统恶性肿瘤中BRAF抑制剂耐药的机制， 对目前治疗无效的BRAF突变型癌症患者的更大人群具有更广泛的益处 BRAF抑制剂。

Summary While activating mutations of the serine-threonine kinase BRAF occur in ~8% of solid tumors, they are rare among hematopoietic malignancies except in hairy cell leukemia (HCL) and the systemic histiocytoses (SH) Langerhans Cell Histiocytosis and Erdheim-Chester Disease. The presence of the specific BRAFV600E mutation in nearly 100% of HCL and 40-60% of SH patients has provided major insights into our understanding of the pathophysiology of these poorly understood diseases. The development of targeted inhibitors of BRAF or its downstream mediators to treat solid tumors has led to major therapeutic advances, and more recently this paradigm has been applied in HCL and SH. Our interdisciplinary team has taken advantage of these advances in BRAFV600E mutation biology and therapeutics and recently published its findings tracing the origin of HCL to the hematopoietic stem cell and developed genetically accurate murine models of HCL. More recently, we have confirmed the presence of the BRAFV600E mutation in hematopoietic stem and progenitor cells in SH patients, generated mouse models of SH, identified recurrent mutations co-existing with the BRAFV600E mutation in both HCL and SH, and completed clinical trials of vemurafenib for HCL and SH patients. Although our preliminary data provide substantial evidence that HSPCs contribute to disease pathogenesis in both HCL and SH through their acquisition of BRAFV600E mutations, it is not yet clear how this common mutation drives the development of such phenotypically and clinically distinct disorders. Moreover, although we have noted that HCL and SH patients exhibit remarkable clinical responses to vemurafenib, we have begun to identify genetic mechanisms of vemurafenib resistance in HCL, which provides us with the unique opportunity to develop the next line of therapeutic strategies in the treatment of these disorders. Thus, the overall goal of this proposal is to delineate the cellular and functional requirements for HCL and SH pathogenesis and to utilize this information to identify the origins of resistance mutations that arise in the context of BRAF targeted therapy. We hypothesize that the cell in which the BRAFV600E mutant protein is active and/or the presence of collaborating mutations play a major role in determining disease phenotype and response to BRAF inhibition. We will address this hypothesis in the following Aims: 1) Delineate the functional effects of the BRAFV600E mutation on hematopoiesis based on the cell in which it is active, 2) Identify the constellation of mutations co-existing with the BRAFV600E mutation in HCL and SH, and 3) Identify the mechanisms of BRAF inhibitor resistance. This project will provide a comprehensive characterization of the cellular origins and cooperating mutations that give rise to HCL and SH. Moreover, this work will delineate mechanisms of BRAF inhibitor resistance in hematopoietic malignancies - an effort that may have broader benefits to the larger population of BRAF-mutant cancer patients ineffectively treated with current BRAF inhibitors.