Gli1-selective inhibitors of the Hedgehog signaling pathway

 描述(申请人提供)：不受控制的Gli转录因子活性导致几种人类癌症，包括基底细胞癌、髓母细胞瘤、脑膜瘤和横纹肌肉瘤。致癌的Gli功能常常源于Hedgehog(HH)通路的失调，而这一发育信号通路的化学抑制剂目前正在临床上使用。尽管我们在了解和治疗依赖谷氨酸的癌症方面取得了这些重大进展，但目前的HH通路靶向治疗有几个局限性。首先，几乎所有针对HH途径的药物都抑制Smoothens(Smo)，Smo是HH信号转导所需的一种G蛋白偶联受体样蛋白。因此，它们基本上是有效的。 抗因Smo的跨膜抑制因子Patched1(Ptch1)缺失或Smo的某些激活突变引起的癌症。由下游或平行信号机制启动的Gli依赖型肿瘤对这些化合物不敏感。其次，Smo拮抗剂引起的肿瘤退化通常是短暂的，因为耐药癌细胞会迅速出现。第三，Smo靶向药物可以扰乱正常的HH途径依赖的生理学，临床前研究进一步表明，Smo阻断可能导致儿童发育缺陷。作用于Smo下游并更直接抑制Gli功能的HH途径抑制剂可以克服这些限制。特别是，选择性抑制Gli1的化合物可能是更通用和有效的抗癌药物，因为这种Gli亚型是一个强大的癌基因，但对于哺乳动物的发育和生理来说是必不可少的。为此，我们实验室最近调查了325,120个化合物，以了解它们在缺乏融合(Sufu)(直接的Gli拮抗剂)抑制因子的细胞中抑制结构性Gli活性的能力。通过这种大规模的化学筛选，我们已经鉴定出一种咪唑类化合物(格列咪唑)，它可以抑制Gli1功能，但对Gli2或Gli3没有明显的作用。我们还在基于细胞的分析中开发了几个具有纳摩尔效力的格列咪唑类似物，利用光亲和标记发现了一种可能连接线粒体信号和Gli1调节的特异性格列咪唑结合蛋白，并证明了这些Gli1选择性抑制剂在体外和体内阻止肿瘤生长的能力。我们现在正在进行所需的下一步工作，以建立格列咪唑类化合物作为一种新的HH途径靶向化疗药物。我们的目标是：(1)表征在我们的光亲和标记实验中发现的格列咪唑靶标，并确定其在Gli1调节中的作用；(2)开发具有优化的效力、靶标选择性和药代动力学特性的格列咪唑类似物；以及(3)在小鼠髓母细胞瘤模型中比较选定的格列咪唑类分子与Smo拮抗剂的疗效。综上所述，我们的研究将为Gli1调节机制提供新的见解，发现抗癌治疗的新靶点，并为未来的药物开发努力提供化学先导。

 DESCRIPTION (provided by applicant): Uncontrolled Gli transcription factor activity causes several human cancers, including basal cell carcinoma, medulloblastoma, meningioma, and rhabdomyosarcoma. Oncogenic Gli function frequently stems from Hedgehog (Hh) pathway dysregulation, and chemical inhibitors of this developmental signaling pathway are now in clinical use. Despite these significant advances in our understanding and treatment of Gli- dependent cancers, current Hh pathway-targeting therapies have several limitations. First, nearly all Hh pathway-targeting drugs inhibit Smoothened (Smo), a G protein-coupled receptor-like protein that is required for Hh signal transduction. As a result, they are primarily effective against cancers caused by loss of Patched1 (Ptch1), a transmembrane repressor of Smo, or by certain activating mutations in Smo. Gli-dependent tumors initiated by downstream or parallel signaling mechanisms are insensitive to these compounds. Second, tumor regressions induced by Smo antagonists are often transient, as drug-resistant cancer cells can rapidly emerge. Third, Smo-targeting drugs can disrupt normal Hh pathway-dependent physiology, and preclinical studies further suggest that Smo blockade could cause developmental defects in children. Hh pathway inhibitors that act downstream of Smo and more directly suppress Gli function could overcome these constraints. In particular, compounds that selectivity inhibit Gli1 could be more general and effective anti-cancer agents, since this Gli isoform is a potent oncogene but dispensable for mammalian development and physiology. Toward this goal, our laboratory recently surveyed 325,120 compounds for their ability to inhibit the constitutive Gli activity in cells lacking Suppressor of Fused (Sufu), a direct Gli antagonist. Through this large-scale chemical screen, we have identified an imidazole derivative ("glimidazole") that can inhibit Gli1 function but has no apparent effect on Gli2 or Gli3. We have also developed several glimidazole analogs with nanomolar potencies in cell-based assays, used photoaffinity labeling to discover a specific glimidazole-binding protein that may link mitochondrial signaling and Gli1 regulation, and demonstrated the ability of these Gli1-selective inhibitors to block tumor growth in vitro and in vivo. We are now pursuing the next steps required to establish glimidazole-based compounds as a new class of Hh pathway-targeting chemotherapies. Our aims are: (1) to characterize the glimidazole target discovered in our photoaffinity labeling experiments and determine its roles in Gli1 regulation; (2) to develop glimidazole analogs with optimized potency, target selectivity, and pharmacokinetic properties; and (3) to compare the efficacy of selected glimidazole-class molecules to Smo antagonists in murine models of medulloblastoma. Taken together, our studies will provide new insights into the mechanisms of Gli1 regulation, uncover novel targets for anti-cancer therapies, and yield chemical leads for future drug development efforts.