A Caged Ligand for a Telomeric G-Quadruplex
A Caged Ligand for a Telomeric G-Quadruplex
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DOI：
10.1002/cbic.201200013
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发表时间：
2012-04-16
期刊：
影响因子：
3.2
通讯作者：
Nagasawa, Kazuo
中科院分区：
文献类型：
--
作者：
Nakamura, Takahiro;Iida, Keisuke;Nagasawa, Kazuo
人类端粒DNA位于染色体末端，含有重复的单链（TTAGGG）n序列。[1]这些富含G的链形成了一种独特的堆叠三维结构，称为G-四链体（G4）。[2]端粒G4的稳定化已被证明可以抑制端粒酶的活性，[3]端粒酶是一种在大多数肿瘤细胞中选择性表达的酶，在端粒维持和细胞永生化中起关键作用。[4]此外，端粒G4稳定化还刺激POT 1和TRF 2（端粒相关蛋白）的解离，其保护染色体末端免于降解和不适当的DNA修复并诱导肿瘤细胞凋亡。[5]因此，端粒G4结构的稳定化被认为是一种有前途的抗癌策略。各种天然和合成的小分子，稳定端粒G4已被调查。[6]然而，额外的功能，即端粒G4和双链体DNA之间的选择性，以及正常细胞和癌细胞之间的选择性，是需要实际有用的分子。虽然最近在小分子对G4的选择性结构识别方面取得了进展，但在特定靶细胞（例如癌细胞）中稳定G4结构仍然很困难。我们认为，笼策略可能有助于克服这些特异性问题，并有助于候选药物的开发。笼状化合物是光敏配体，其中生物活性所需的一个或多个重要官能团被一个或多个光不稳定基团掩蔽。因此，笼状化合物在生物学上无活性。然而，当它们通过照射“解开”时，生物活性被揭开，因此笼状化合物的潜在生物活性原则上可以通过光照射以高空间和时间特异性或在特定分子靶点被激活。[7]在这里，我们描述的设计，合成和特性的第一个例子的笼化合物靶向端粒G4。证实了通过辐射解除束缚导致端粒酶活性在体外的抑制和几种癌细胞系的生长抑制。我们最近报道了一系列大环聚恶唑-6 OTD（方案1），[8a，B] 6 M（4）OTD，[8 c]和7 OTD [8d]-作为G4配体，其灵感来自于分离自环状链霉菌3533-SV 4的高效天然G4配体端粒抑素（1）。[9]6 OTD和6 M（4）OTD各自在大环核心结构上具有两个侧链，并且它们的G4稳定能力可以通过改变侧链上的官能团来调节。[8a]在侧链中安装氨基官能团增加了配体的G4稳定能力，推测是通过与DNA中的磷酸基团相互作用。然而，G4稳定活性可以简单地通过用乙酰基保护胺来掩蔽。[8a]考虑到这些因素，我们设计了笼状G4配体Y2 Nv 2 - 6 M（4）OTD（2b），其在6 M（4）OTD的侧链上具有酚部分。已知酚羟基通过氢键与DNA相互作用，[10]并且可以很容易地被硝基藜芦基（Nv）基团作为光不稳定的保护（笼状）基团掩蔽。Y2 H2 - 6 M（4）OTD（2a，方案1）的合成是通过先前开发的方法从L-酪氨酸进行的（见支持性信息）。[8c]然后在碳酸钾的DMF溶液中，用Nv溴化物处理，用Nv基团掩蔽2a的酚羟基，生成Y2 Nv 2 - 6 M（4）OTD（2b）作为笼状G4配体（参见支持信息）。第一，稳定…
Human telomeric DNA, located at the ends of chromosomes, contains repeating single-strand (TTAGGG) n sequences.[1] These G-rich strands form a characteristic stacked three-dimensional structure, called the G-quadruplex (G4).[2] Stabilization of telomeric G4 has been shown to inhibit the activity of telomerase,[3] an enzyme that is selectively expressed in most tumor cells and plays key roles in telomere maintenance and cellular immortalization.[4] Furthermore, telomeric G4 stabilization also stimulates dissociation of POT1 and TRF2 (telomere-related proteins), which protect chromosome ends from degradation and inappropriate DNA repair and induce apoptosis of tumor cells.[5] Stabilization of the telomeric G4 structure is thus considered to be a promising anticancer strategy. Various natural and synthetic small molecules that stabilize telomeric G4 have been investigated.[6] However, additional features—that is, selectivity between telomeric G4 and duplex DNA, as well as selectivity between normal cells and cancer cells—are required for practically useful molecules. Although there has been recent progress in selective structural recognition of G4 by small molecules, stabilization of the G4 structure in specific target cells—cancer cells, for example—is still difficult. We considered that a caging strategy might be useful for overcoming these specificity issues and to aid the development of candidate drugs. Caged compounds are light-sensitive ligands in which one or more significant functional group (s) required for biological activity is/are masked with one or more photolabile group (s). Caged compounds are therefore biologically inactive. When they are “uncaged” by irradiation, however, the biological activity is unmasked, and so the latent biological activities of caged compounds can in principle be activated with high spatial and temporal specificity, or at specific molecular targets, by means of light irradiation.[7] Here we describe the design, synthesis, and characteristics of the first example of a caged compound targeting telomeric G4. Uncaging by irradiation was confirmed to result in inhibition of telomerase activity in vitro and in growth inhibition of several cancer cell lines. We have recently reported a series of macrocyclic polyoxazoles—6OTDs (Scheme 1),[8a, b] 6M (4) OTDs,[8c] and 7OTD [8d]—as G4 ligands inspired by the highly potent natural G4 ligand telomestatin (1), isolated from Streptomyces annulatus 3533-SV4.[9] The 6OTDs and 6M (4) OTDs each have two side chains on a macrocyclic core structure, and their G4-stabilizing abilities can be tuned by varying the functional groups on the side chains.[8a] Installation of amino functional groups in the side chains increases the G4-stabilizing abilities of the ligands, presumably through interaction with phosphate groups in DNA. However, the G4-stabilizing activity can be masked simply by protection of the amine with an acetyl group.[8a] With these considerations in mind, we designed the caged G4 ligand Y2Nv2-6M (4) OTD (2b), which has phenolic moieties on the side chains of 6M (4) OTD. Phenolic hydroxy groups are known to interact with DNA through hydrogen bonding,[10] and can easily be masked with the nitroveratryl (Nv) group as a photolabile protecting (caging) group. The synthesis of Y2H2-6M (4) OTD (2a, Scheme 1) was carried out from L-tyrosine by the previously developed procedure (see the Supporting Information).[8c] The phenolic hydroxy groups of 2a were then masked with Nv groups by treatment with Nv bromide in the presence of potassium carbonate in DMF to generate Y2Nv2-6M (4) OTD (2b) as a caged G4 ligand (see the Supporting Information). Firstly, stabilization …