Targeting vismodegib-resistant tumors using BH3 mimetics

 描述（由申请人提供）：分泌的Hedgehog（Hh）信号分子对于多细胞生物体中细胞命运决策的协调至关重要。在婴儿和儿童中分别发现的大约50%和40%的髓母细胞瘤是由七跨膜Hh通路效应物Smoothened（Smo）的异常激活引起的，Smo是临床批准的抗癌剂Vismodegib的靶点。另外40%的婴儿髓母细胞瘤携带融合抑制因子（Sufu）突变，融合抑制因子是一种直接抑制Gli DNA结合蛋白活性的蛋白质，而Gli DNA结合蛋白对Hh依赖性转录活性至关重要。因此，患有髓母细胞瘤的婴儿还受到频繁存在的不能被Smo拮抗剂对抗的Sufu突变的挑战。尽管在用Vismodegib治疗的儿童和成人患者中观察到肿瘤消退的快速发生，但在大多数治疗的髓母细胞瘤患者中，通过Smo非依赖性机制重新参与Gli转录活性表明耐药性几乎是普遍的。为了描绘用于管理Smo拮抗剂难治的Hh相关癌症的新化学空间，我们已经完成了基因组规模的cDNA文库筛选，并且已经鉴定了五个抗凋亡Bcl-2家族成员中的三个（Mcl-1、Bcl-2和Bcl-xL），以通过直接接合腐乳中先前未鉴定的BH 3序列来驱动Gli蛋白活化。这种相互作用可能通过稳定腐乳中的低Gli亲和力构象而导致腐乳结合并抑制Gli介导的转录活性的能力降低。相同Bcl-2基因的转录受Gli活性调节，从而揭示了协同作用。 促生存Bcl-2蛋白通过前馈抑制Sufu活性进行自我调节。 靶向促存活Bcl-2蛋白（BH 3模拟物）的小分子通过破坏Mcl-1/Bcl-2/Bcl-xL与Sufu的相互作用来破坏这种促进癌症的信号传导机制，从而能够抑制Gli活性，而不管癌细胞对Vismodegib的敏感性如何。本提案中概述的研究将利用新型BH 3模拟物以及晚期临床试验中的那些，以使用横纹肌肉瘤和髓母细胞瘤（两种Hh相关恶性肿瘤）中的表型和分子读数来评估我们的发现的治疗前景。

 DESCRIPTION (provided by applicant): The secreted Hedgehog (Hh) signaling molecules are essential to the coordination of cell-fate decision-making in multicellular organisms. Approximately 50% and 40% of medulloblastomas found in infants and children, respectively, are caused by deviant activation of the seven transmembrane Hh pathway effector Smoothened (Smo), the target of the clinically approved anti-cancer agent Vismodegib. An additional 40% of infant medulloblastomas harbor mutations in Suppressor of fused (Sufu), a protein that directly suppresses the activity of the Gli DNA binding proteins which are essential to Hh-dependent transcriptional activities. Infants with medulloblastomas are thus additionally challenged by the frequent presence of Sufu mutations which cannot be countered by Smo antagonists. Despite the rapid onset of tumor regression observed in children and adult patients treated with Vismodegib, the re-engagement of Gli transcriptional activity by Smo-independent mechanisms in the majority of treated medulloblastoma patients suggests drug resistance will be nearly universal. To delineate novel chemical space for managing Hh-related cancers that are refractory to Smo antagonists, we have completed a genome-scale cDNA library screen and have identified three out of the five anti-apoptotic Bcl-2 family members (Mcl-1, Bcl-2, and Bcl- xL) to drive Gli protein activation by directly engaging a previously unidentified BH3 sequence in Sufu. This interaction results in decreased Sufu ability to bind to and suppress Gli-mediated transcriptional activity likely by stabilizing a low Gli affinity conformation in Sufu. The transcription of the same Bcl-2 genes is regulated by Gli activity, thus revealing a concerted role of prosurvival Bcl-2 proteins in self-regulation through feed-forward suppression of Sufu activity. Small molecules targeting prosurvival Bcl-2 proteins (BH3 mimetics) disrupt this cancer-promoting signaling mechanism by breaking Mcl-1/Bcl-2/Bcl-xL interactions with Sufu and thereby enabling the means to inhibit Gli activity regardless of cancer cell sensitivity to Vismodegib. The studies outlined in this proposal will leverage novel BH3 mimetics as well as those in late stage clinical testing for evaluating the therapeutic promise of our findings using phenotypic and molecular read-outs in rhabdomyosarcoma and medulloblastomas, two Hh- associated malignancies.