Microenvironment mediated drug resistance in melanoma.

描述（由申请人提供）：这项工作的长期目标是开发治疗策略，以提高播散性黑色素瘤患者的生存率。已经有充分的证据表明突变BRAF是50%以上黑色素瘤的真正治疗靶点，并且使用小分子BRAF抑制剂（如PLX4032）可以实现令人印象深刻但短暂的临床反应。在临床上，BRAF抑制剂的耐药遵循一个过程，即肿瘤消退，然后是静止和最终复发。总的假设是，BRAF抑制重塑了黑色素瘤和宿主微环境，为逃避治疗的少数黑色素瘤细胞提供了一个保护性的“避难所”。从概念上讲，人们认为至少有两种形式的环境介导的治疗逃避；第一种被定义为“肿瘤固有”，在缺乏PTEN功能（PTEN-）的黑色素瘤细胞系中观察到，涉及自分泌整合素/细胞外基质（ECM）信号环的建立，该信号环绕过BRAF信号传导并下调细胞凋亡。第二种是宿主介导的，在原代人成纤维细胞中BRAF抑制矛盾地激活AKT和MEK信号，导致PDGF-D、VEGF和Notch配体Jagged的表达，并增加纤维连接蛋白、胶原和层粘连蛋白的沉积。第一个目的是研究BRAF抑制如何导致获得自分泌ecm驱动的信号环，并确定这些改变的粘附信号如何“重新连接”逃逸种群的信号，并导致采用缓慢增殖、抗凋亡和促侵袭的表型。然后，我们将测试治疗靶向黑色素瘤细胞/ECM相互作用是否通过阻止微环境介导的黑色素瘤信号网络重组来改善内在抗性。在目标2中，我们将验证BRAF抑制激活宿主成纤维细胞导致“避难所”血管微环境的创建的假设，该环境允许PTEN+黑色素瘤细胞逃避治疗。我们将讨论正常宿主成纤维细胞中的BRAF抑制如何导致自分泌生长因子信号循环的建立，从而驱动其激活。然后，我们将使用新的3D黑色素瘤/成纤维细胞/内皮细胞共培养和体内异种移植模型来研究抑制成纤维细胞中BRAF驱动血管生成反应的机制，并将阐明血管生态位作为逃逸黑色素瘤细胞的保护性“避难所”的作用。预计从这项工作中获得的知识将为临床克服BRAF抑制剂耐药性提供新的治疗策略。1

DESCRIPTION (provided by applicant): The long-term goals of this work are the development of therapeutic strategies to improve the survival of patients with disseminated melanoma. There is already good evidence that mutated BRAF is a bona fide therapeutic target in over 50% of melanomas, and that impressive but short-lived clinical responses can be achieved with small molecule BRAF inhibitors (such as PLX4032). Clinically, BRAF inhibitor resistance follows a course where tumor regression is followed by quiescence and eventual relapse. The overall hypothesis is that BRAF inhibition remodels both the melanoma and host microenvironments to provide a protective "sanctuary" for the minor populations of melanoma cells that escape therapy. Conceptually, it is believed that there are at least two forms of environment-mediated therapeutic escape; the first, defined as "tumor intrinsic", was observed in melanoma cell lines that lack PTEN function (PTEN-) and involved the establishment of autocrine integrin/extracellular matrix (ECM) signaling loops that bypass BRAF signaling and downregulate apoptosis. The second was host-mediated, where BRAF inhibition in primary human fibroblasts paradoxically activated AKT and MEK signaling leading to the expression of PDGF-D, VEGF and the Notch ligand Jagged as well as increasing the deposition of fibronectin, collagens and laminin. The first aim will investigate how BRAF inhibition leads to the acquisition of autocrine ECM-driven signaling loops and will determine how these altered adhesion signals "re-wire" the signaling of the escaping population and leads to the adoption of a phenotype that is slow-proliferating, apoptosis resistant and pro-invasive. We will then test whether therapeutic targeting of the melanoma cell/ECM interactions ameliorates intrinsic resistance by preventing the microenvironment- mediated reorganization of the melanoma signaling network. In aim 2, we will test the hypothesis that BRAF inhibition activates host fibroblasts leading to the creation of a "refuge" vascular microenvironment that allows PTEN+ melanoma cells to escape from therapy. We will address how BRAF inhibition in normal host fibroblasts leads to the establishment of autocrine growth factor signaling loops that drives their activation. We will then use novel 3D melanoma/fibroblast/endothelial cell co-culture and in vivo xenograft models to investigate the mechanisms by which inhibition of BRAF in fibroblasts drives the angiogenic response and will elucidate the role of the vascular niche as a protective "sanctuary" for the escaping melanoma cells. It is expected that knowledge gained from this work will provide novel therapeutic strategies for overcoming BRAF inhibitor resistance in the clinic. 1