靶向MDM2小分子抑制药:肿瘤治疗的新方法

癌蛋白MDM2可与p53蛋白结合形成复合物,抑制p53基因的反式激活,而p53的缺失可诱导肿瘤发生。设计针对MDM2与p53蛋白间相互作用的小分子抑制药(如Nutlins),可再激活p53基因,利于肿瘤治疗。本文综述了MDM2小分子抑制药的特点、作用机制与治疗潜力等最新进展。     

抑癌基因p53、癌基因MDM2与乳腺癌关系的研究进展

目的:为乳腺癌的基因治疗提供参考。方法:以"p53""MDM2"和"乳腺癌"为关键词,查阅2001-2013年国内外相关文献,结合临床前和临床研究数据,分析抑癌基因p53、癌基因MDM2与乳腺癌的关系。结果:抑癌基因p53、癌基因MDM2在乳腺癌的形成、发展及预后中具有重要作用;p53-MDM2之间失衡可导致MDM2上调和p53失活,最终诱发肿瘤;抑制p53、MDM2复合体形成,下调MDM2表达,激活p53通路是研究抗肿瘤药物的关键。结论:以抑癌基因p53、癌基因MDM2为靶点,有望设计出对乳腺癌治疗效果较好的小分子抑制剂,其在乳腺癌的诊断与治疗中前景广阔。     

MDMX 与 CK1α对 p53 抑癌蛋白调节机制的研究进展

作为抑癌蛋白, p53 参与了细胞内多种信号转导过程, 并在细胞周期调控、 细胞凋亡及衰老等过程中发挥了重要的作用。鼠双微基因 （murine double minute, MDM） 2 和 MDMX （又称 MDM4, murine double minute 4） 是 p53 两个重要的调控因子。其中, MDMX 能够通过与 p53 蛋白的相互作用以及转录后修饰来调节 p53 蛋白功能。虽然MDMX 与 MDM2 蛋白结构同源, 但是由于 MDMX 缺少 E3 连接酶, 因此无法介导 p53 蛋白的降解。然而, MDMX 本身能够通过分子内部结构的折叠与展开, 与 p53 蛋白相互作用后调节其活性。在该过程中, MDMX 的主要分子伴侣——CK1α（casein kinase 1 alpha）通过磷酸化 MDMX 并干扰其分子内部结合, 从而协同调节 p53 蛋白。因而,MDMX 及 CK1α对 p53 蛋白的调节是一个多步骤、 多因素参与的复杂过程。本文拟就 MDMX 以及CK1α对 p53蛋白的具体调节机制进行综述。     

MDM2-p53通路在脑胶质瘤中的表达及其意义探讨

目的探讨MDM2蛋白、p53在脑胶质瘤的表达及其在肿瘤发生发展中的作用。方法应用免疫组化技术检测35例胶质瘤组织中MDM2、p53的表达。结果MDM2、p53在胶质瘤中的表达率分别为17·1%(6/35),45·7%(16/35)。MDM2表达与突变型p53表达呈负相关,Pearson相关系数(r=-0·531)。两者均与胶质瘤病理分型相关,标准回归系数(Beta)值分别为:MDM20·443,p530·74。结论Mdm2的表达与p53的表达存在负相关,是肿瘤高度恶性的生物学标志。     

骨肉瘤多基因表达的同步检测

目的 探讨骨肉瘤多基因表达的方法。方法 通过免疫组化S—P法检测30例人骨肉瘤和15例正常骨组织中p16、MDM2、Rb和p53表达的情况,并进行统计学分析。结果30例骨肉瘤p16、MDM2、Rb、和p53表达阳性率分别为36．7％、76．7％、40％、63、3％;与正常骨组织相比,骨肉瘤组织中p16、Rb蛋白表达水平降低。MDM2和p53蛋白表达水平增高,其差异均有统计学意义（P〈0．05）;骨肉瘤中p16和Rb蛋白表达无相关关系;p53和MDM：蛋白表达结果呈负相关关系。结论 骨肉瘤的发生和多基因的改变及其联合作用有关,     

细胞周期调节因子在肺结核合并肺癌组织中的表达

目的探讨细胞周期调节因子在肺结核合并肺癌中的作用.方法LsAB法同时检测69例肺结核合并肺癌患者组织中p53、MDM2、p21ras和p21WAF1蛋白的表达.结果复发癌与原发癌相比：阳性表达率方面,p53蛋白（78%和80%）或MDM2蛋白（84%和83%）很相近,p21ras蛋白（73%和93%）或p21WAF1蛋白（52%和84%）明显下降;高表达率方面,p53蛋白（42%和51%）很相近,MDM2蛋白（57%和32%）明显升高,p21ras蛋白（16%和65%）或p21WAF1蛋白（17%和46%）明显下降.其中,MDM2蛋白表达水平在复发癌明显升高主要见于复发间期＜34个月患者组（P＜0.05）,p21ras蛋白和p21WAF1蛋白表达水平在复发癌明显下降见于复发间期＜34个月和≥34个月患者组（均＜0.02以下）.结论肺结核合并肺癌,p53蛋白和MDM2蛋白过度表达以及p21WAF1蛋白低表达或不表达可能仍然对肺结核合并肺癌的复发起重要作用;MDM2蛋白表达水平显著升高和p21WAF1蛋白表达水平显著下降可能进一步加促肺结核合并肺癌的过程.     

鼠双微染色体2作为肿瘤治疗新靶点的研究进展

鼠双微染色体2(mdm2)是一种进化保守的癌基因,其编码蛋白参与细胞调控的多条通路,在肿瘤的发生和发展过程中发挥重要作用。很多人类肿瘤中都存在着mdm2基因扩增和(或)MDM2蛋白的过度表达。MDM2主要通过与P53蛋白中Phe19,Trp23和Leu26位点的结合参与MDM2-P53作用的负反馈环。P53蛋白可以促进MDM2的表达,而MDM2则可以通过与P53蛋白的结合介导其出核,减弱其转录活性,并促进其降解,发挥P53依赖性的MDM2活性作用。同时,MDM2还可以通过与P21蛋白、早幼粒细胞白血病蛋白、成视网膜细胞瘤蛋白Rb等的结合而不依赖于P53促进肿瘤的生长。低氧环境及肿瘤抑制因子PTEN、抑癌蛋白ARF等刺激因子均可以通过对MDM2的活性调控影响MDM2的功能发挥。在此基础上,针对MDM2-P53之间相互作用的化合物研究受到了较大关注。其中MDM2特异性拮抗剂nutlins高度模拟了P53肽段进而与P53竞争结合MDM2表面的P53口袋域,干扰MDM2-P53的相互作用,从而导致了P53的稳定以及P53通路的激活。关于nutlins在肿瘤细胞周期、凋亡、新生血管形成及药物合用等方面的研究结果表明,其作为分子工具可有效地抑制或阻断MDM2作用,为肿瘤的治疗提供了全新的思路和策略。     

P53、MDM2蛋白在宫颈癌中的表达及相关性研究

目的 探讨MDM2及p53蛋白在宫颈癌中表达及两者的相关性.方法 用免疫组织化学EnVision法,检测37例宫颈鳞癌(SCC)、16例宫颈腺癌(AUC)、45例宫颈上皮内瘤样变(CIN)及20例正常宫颈(NC)组织中MDM2及p53蛋白的表达.结果 p53蛋白在NC、CIN、AUC、SCC中的阳性率分别为0、26.67%(12/45)、68.75%(11/16)及59.46%(22/37),在AUC、SCC中的阳性率均明显高于NC及CIN组(P＜0.01、P＜0.01;P＜0.01、P＜0.01),在CIN组的阳性率明显高于NC组(P＜0.05);MDM2蛋白在NC、CIN、AUC、SCC中的阳性率分别为0、13.33%(6/45)、43.75%(7/16)及43.24%(16/37),在AUC、SCC组中的阳性率均明显高于NC及CIN组,差异有显著性(P＜0.01、P＜0.01;P＜0.05、P＜0.01);在CIN和SCC的p53 组中,MDM2 阳性率(41.67%、54.54%)明显高于p53组(3.03%、6.67%)(P＜0.01、P＜0.01),列联系数分别为0.503、0.610.结论 p53、MDM2蛋白的异常表达可能是宫颈癌中的基因事件,与宫颈癌的发生、发展密切相关;宫颈癌中p53和MDM2蛋白表达呈明显的正相关性.     

p53、p21、MDM2蛋白在卵巢子宫内膜异位症病人血清、异位及在位内膜组织中的表达及相关性

目的 探讨p53、p21、MDM2蛋白在卵巢子宫内膜异位症病人血清、异位及在位内膜组织中的表达及相关性。方法 采用随机数字表法选取2012年1月至2017年3月在郑州人民医院收治的卵巢子宫内膜异位症病人手术切除的异位内膜组织50例作为异位组、子宫内膜异位症病人自愿刮宫术取得的在位子宫内膜组织40例作为在位组,刮宫术取得非子宫内膜异位症病人的正常子宫内膜组织35例作为对照组,异位组及在位组病人(共90例,为观察组)。使用免疫组化染色法(S-P法)对p53、p21、MDM2蛋白的表达情况进行检测。结果 异位组p53、p21表达阳性率(12.00%、10.00%)明显低于对照组(37.14%、31.43%)及在位组(35.00%、30.00%),P＜0.05;异位组MDM2表达阳性率(52.00%)明显高于对照组(5.71%)及在位组(7.50%),P＜0.05;在位组与对照组比较(35.00%、30.00%、7.50% 比37.14%、31.43%、5.71%),p53、p21、MDM2表达阳性率差异无统计学意义(P＞0.05);对照组、在位组分泌期p53、p21表达(66.67%、60.00%;61.11%、61.11%)均明显高于组内增生期(15.00%、10.00%;13.64%、13.64%),P＜0.05,对照组、在位组、异位组分泌期MDM2表达阳性率(6.67%、11.11%、47.83%)与组内增生期(5.00%、4.55%、55.56%)比较,均差异无统计学意义(P＞0.05);子宫内膜异位症病人的异位子宫内膜组织中p53表达与p21表达呈正相关(r＝0.721,P＜0.01);p53表达与MDM2表达呈负相关(r＝-0.421,P＜0.01);p21表达与MDM2表达无相关性(r＝0.308,P＞0.05)。观察组血清p53、p21水平［(0.86±0.23) kU/L、(1.04±0.12) kU/L］明显低于对照组［(1.38±0.19) kU/L、(1.68±0.24) kU/L］,MDM2水平［(2.19±0.33) kU/L］明显高于对照组［(1.03±0.15) kU/L］,P＜0.05。结论 p53、p21、MDM2蛋白表达在子宫内膜异位症的发生发展中起着重要作用,且它们之间有一定的相关性。     

能阻断Hdm2：p53复合物形成的抗肿瘤药物

肿瘤抑制转录因子p53在DNA损伤的细胞响应、细胞周期阻滞和凋亡中具有关键作用。在近一半的癌症中，出现p53基因的功能缺失性突变，导致肿瘤细胞的迅速生长和耐药性产生。Hdm2蛋白是主要的p53负性调节子，通过两种不同机制起作用：（1）直接与p53结合，抑制其正常结合功能，使之不能形成转录复合物。（2）通过蛋白体途径靶向p53，使其泛素化并降解。野生型p53的肿瘤抑制作用会因为Hdm2的过度表达而减弱，因而抑制Hdm2与p53相互作用，已成为近年肿瘤药物研究的一个主要领域。     

MDM2 splice variants and their therapeutic implications

MDM2 splice variants have now been identified in many different tumor types, and their expression has been associated with advanced disease. However, published data concerning their function is contradictory, and therefore their role in tumorigenesis and their potential as a therapeutic target are unclear. Expression of a specific splice variant, MDM2-B, in a transgenic mouse model results in tumor development; and expression of several splice variants has been shown to enhance tumor formation in Emu-myc transgenic mice. However, expression of similar variants in vitro results in growth inhibition, an observation inconsistent with a transformed phenotype. The observed growth inhibition is p53-dependent, resulting from the binding of splice variants with an intact C-terminal RING finger domain to full-length MDM2 protein. In doing so, p53 can no longer bind MDM2, and p53 activity is elevated. Subsequent inactivation of p53 or p53-mediated apoptosis could contribute to the MDM2 splice variant-mediated tumorigenesis observed in vivo. However, MDM2 splice variants, like full-length MDM2, probably display p53-independent activities. Therefore, the potential for MDM2 splice variants as therapeutic targets will be dependent upon their phenotype within specific tumor types.     

Peptide activators of the p53 tumor suppressor

The oncoproteins MDM2 and MDMX negatively regulate the activity and stability of the p53 tumor suppressor, directly contributing to the development and progression of many tumors harboring wild type p53. Antagonizing MDM2 and MDMX to activate the p53 pathway has thus become an attractive new strategy for anticancer drug design. Several different classes of MDM2 and MDMX antagonists have been reported, including low molecular weight compounds, small peptides, miniature proteins, and peptidomimetics. This review aims to summarize the latest progress in the design of peptide activators of the p53 tumor suppressor.     

Small molecule inhibitors of p53/MDM2 interaction

The discovery of the key negative regulator MDM2 (mouse double minute 2, also termed HDM2 for its human equivalent) provided a great opportunity to manipulate the levels of the tumor suppressor p53 in cancer cells. Activation of p53 in tumor cells by inhibiting the interaction of MDM2 with p53 has therefore been the focus of a large effort in drug discovery. The modulation of protein-protein interactions, however, has historically been very difficult to achieve owing to the large surface area of interaction. In this article, we review the recent accomplishments in this area and our quest for a clinically viable MDM2 inhibitor.     

Small molecule antagonists of the MDM2 oncoprotein as anticancer agents

In this early phase of the new era of molecularly targeted patient friendly cancer chemotherapy, there is a need for novel viable anticancer molecular targets. The MDM2 oncoprotein has been validated as a potential target for cancer drug development. MDM2 amplification and/or overexpression occur in a wide variety of human cancers, several of which can be treated experimentally with MDM2 antagonists. MDM2 interacts primarily with the p53 tumor suppressor protein in an autoregulatory negative feedback loop to attenuate p53's cell cycle arrest and apoptosis functions. Inhibition of the p53-MDM2 interaction has been shown to cause selective cancer cell death, as well as sensitize cancer cells to chemotherapy or radiation effects. Consequently, this interaction has been the main focus of anticancer drug discovery targeted to MDM2. The promotion of the proteasomal degradation of the p53 protein by MDM2 is central to its repression of the tumor suppressor functions of p53, and many proteins impinge upon this activity, either enhancing or inhibiting it. MDM2 also has oncogenic activity independent of its interaction with p53, but this has so far not been explored for drug discovery. Among the approaches for targeting MDM2 for cancer therapy, small molecule antagonists have recently featured as effective anticancer agents in experimental models, although the repertoire is currently limited and none has yet entered human clinical trials. Small molecules that have been reported to disrupt the p53-MDM2 binding, thereby enhancing p53 activity to elicit anticancer effects include the following: synthetic chalcones, norbornane derivatives, cis-imidazoline derivatives (Nutlins), a pyrazolidinedione sulfonamide and 1,4-benzodiazepine-2,5-diones, as well as tryptophan derivatives. In addition to compounds disrupting p53pMDM2 binding, three compounds have been discovered that are effective in inhibiting the E3 ligase activity of MDM2 towards p53, and should serve as leads for drug discovery targeting this aspect of the p53-MDM2 interaction as well. These compounds were discovered from library screening and/or structure-based rational drug design strategies.     

Identification of FDA-approved Drugs that Computationally Bind to MDM2

The integrity of the p53 tumor suppressor pathway is compromised in the majority of cancers. In 7% of cancers p53 is inactivated by abnormally high levels of MDM2 - an E3 ubiquitin ligase that polyubiquitinates p53, marking it for degradation. MDM2 engages p53 through its hydrophobic cleft, and blockage of that cleft by small molecules can re-establish p53 activity. Small molecule MDM2 inhibitors have been developed, but there is likely to be a high cost and long time period before effective drugs reach the market. An alternative is to repurpose FDA-approved drugs. This report describes a new approach, called Computational Conformer Selection, to screen for compounds that potentially inhibit MDM2. This screen was used to computationally generate up to 600 conformers of 3244 FDA-approved drugs. Drug conformer similarities to 41 computationally-generated conformers of MDM2 inhibitor nutlin 3a were ranked by shape and charge distribution. Quantification of similarities by Tanimoto combo scoring resulted in scores that ranged from 0.142 to 0.802. In silico docking of drugs to MDM2 was used to calculate binding energies and to visualize contacts between the top-ranking drugs and the MDM2 hydrophobic cleft. We present 15 FDA-approved drugs predicted to inhibit p53/MDM2 interaction.     

Small-molecule correctors and stabilizers to target p53

The tumor suppressor p53 is the most frequently mutated protein in human cancer and tops the list of high-value precision oncology targets. p53 prevents initiation and progression of cancer by inducing cell-cycle arrest and various forms of cell death. Tumors have thus evolved ways to inactivate p53, mainly by TP53 mutations or by hyperactive p53 degradation. This review focuses on two types of p53 targeting compounds, MDM2 antagonists and mutant p53 correctors. MDM2 inhibitors prevent p53 protein degradation, while correctors restore tumor suppressor activity of p53 mutants by enhancing thermodynamic stability. Herein we explore both novel and repurposed p53 targeting compounds, discuss their mode of action, and examine the challenges in advancing them to the clinic.