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。在婴儿和儿童中发现的髓母细胞瘤中，分别有大约50%和40%是由临床批准的抗癌药物vismodegib的靶点七个跨膜HH途径效应器平滑(Smo)的异常激活引起的。另外40%的婴儿髓母细胞瘤存在融合抑制蛋白(Sufu)的突变，Sufu是一种直接抑制Gli DNA结合蛋白活性的蛋白质，Gli DNA结合蛋白是HH依赖的转录活动所必需的。因此，患有髓母细胞瘤的婴儿还面临着频繁存在的Sufu突变的挑战，这是Smo拮抗剂无法对抗的。尽管在接受vismodegib治疗的儿童和成人患者中观察到肿瘤迅速消退，但在大多数接受治疗的髓母细胞瘤患者中，通过Smo非依赖机制重新参与Gli转录活性表明，耐药性将几乎是普遍存在的。为了描绘新的化学空间来管理对Smo拮抗剂无效的HH相关癌症，我们完成了基因组规模的cDNA文库筛选，并从五个抗凋亡的Bcl-2家族成员中鉴定了三个成员(Mcl-1，Bcl-2和Bcl-xl)，通过直接与Sufu中先前未知的BH3序列结合来驱动Gli蛋白的激活。这种相互作用导致Sufu结合和抑制Gli介导的转录活性的能力降低，可能是通过稳定Sufu中的低Gli亲和力构象来实现的。同样的Bcl-2基因的转录受Gli活性的调节，因此显示出协同作用 通过前馈抑制Sufu活性进行自我调节的存活的Bcl2蛋白。 靶向生存期蛋白的小分子(BH3模拟物)通过破坏Mcl-1/Bcl2/Bclxl与Sufu的相互作用来破坏这一促癌信号机制，从而使该方法能够抑制Gli活性，而不管癌细胞对vismodegib的敏感性如何。这项提案中概述的研究将利用新的BH3模拟药物以及那些处于后期临床测试的药物，通过对横纹肌肉瘤和髓母细胞瘤这两种与HH相关的恶性肿瘤的表型和分子读出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.