An antibody‐free strategy for screening putative HDM2 inhibitors using crude bacterial lysates expressing GST‐HDM2 recombinant protein

Targeting the interaction of p53 with its natural inhibitor MDM2 by the use of small synthetic molecules has emerged as a promising pharmacological approach to restore p53 oncosuppressor function in cancers retaining wild‐type p53. The first critical step in the experimental validation of newly synthesized small molecules developed to inhibit MDM2‐p53 interaction is represented by the evaluation of their efficacy in preventing the formation of the MDM2‐p53 complex. This can be achieved using the in vitro reconstructed recombinant MDM2‐p53 complex in cell‐free assays. A number of possible approaches have been proposed, which are however not suitable for screening large chemical libraries, due to the high costs of reagents and instrumentations, or the need of large amounts of highly pure recombinant proteins. Here we describe a rapid and cheap method for high‐throughput screening of putative inhibitors of MDM2‐p53 complex formation – based on the use of GST‐recombinant proteins – that does not require antibodies and recombinant protein purification steps from bacterial cell lysates. Copyright © 2013 John Wiley & Sons, Ltd.     

A Re‐examination of the MDM2/p53 Interaction Leads to Revised Design Criteria for Novel Inhibitors

The general model of epitope‐type MDM2 inhibitor was developed based on the structural information on the complexes between MDM2 and various low molecular weight ligands found in the PDB database. Application of this model to our in‐house library has led us to a new scaffold capable of interrupting protein–protein interactions. A synthetic library based on this and related scaffolds resulted in new classes of compounds that possess biochemical and cellular activity and good pharmacokinetic properties. We assume that such general approach to PPI inhibitors design may be useful for the development of inhibitors of various PPI types, including Bcl/XL.     

Proposing novel MDM2 inhibitors: Combined physics‐driven high‐throughput virtual screening and in vitro studies

The mouse double minute 2 (MDM2) protein acts as a negative regulator of the p53 tumor suppressor. It directly binds to the N terminus of p53 and promotes p53 ubiquitination and degradation. Since the most common p53‐suppressing mechanisms involve the MDM2, proposing novel inhibitors has been the focus of many in silico and also experimental studies. Thus, here we screened around 500,000 small organic molecules from Enamine database at the binding pocket of this oncogenic target. The screening was achieved systematically with starting from the high‐throughput virtual screening method followed by more sophisticated docking approaches. The initial high number of screened molecules was reduced to 100 hits which then were studied extensively for their therapeutic activity and pharmacokinetic properties using binary QSAR models. The structural and dynamical profiles of the selected molecules at the binding pocket of the target were studied thoroughly by all‐atom molecular dynamics simulations. The free energy of the binding of the hit molecules was estimated by the MM/GBSA method. Based on docking simulations, binary QSAR model results, and free energy calculations, 11 compounds ( E1 – E11 ) were selected for in vitro studies. HUVEC vascular endothelium, colon cancer, and breast cancer cell lines were used for testing the binding affinities of the identified hits and for further cellular effects on human cancer cell. Based on in vitro studies, six compounds ( E1 , E2 , E5 , E6 , E9 , and E11 ) in breast cancer cell lines and six compounds ( E1 , E2 , E5 , E6 , E8 , and E10 ) in colon cancer cell lines were found as active. Our results showed that these compounds inhibit proliferation and lead to apoptosis.     

Inhibiting mechanism of small molecule toward the p53‐MDM2 interaction: A molecular dynamic exploration

Disruption of the p53‐MDM2 interaction has been an efficient strategy to renew the function of wild‐type p53. In this work, molecular dynamic simulations, molecular mechanics–generalized Born surface area method, and principal component analysis were combined to probe interaction mechanism of inhibitors 2TZ, 2U0, 2U1, 2U5, 2U6, and 2U7 with MDM2. The rank of our current predicted binding free energies is in agreement with that of the experimental values. The results demonstrate that the introductions of thiazole and pyridine rings into 2TZ as well as the change in the orientation of inhibitors lead to the increase in the polar interactions of 2U0, 2U1, 2U5, 2U6, and 2U7 with MDM2 relative to 2TZ. The information derived from principal component analysis suggests that inhibitor bindings produce significant effect on the binding cleft of MDM2 and make the binding cleft wider and bigger so as to accommodate different type inhibitors. This study is looked forward to contributing theoretical hints for designs of potent inhibitors targeting the p53‐MDM2 interaction.     

Small molecule inhibitors of the p53-MDM2

Recent researches have discovered that MDM2 (murine double minute 2, or HDM2 for the human congener) protein is the main negative regulator of p53, which is an attractive therapeutic target in oncology because its tumor-suppressor activity which can be stimulated to eradicate tumor cells. Inhibiting the p53-MDM2 interaction is a promising approach for activating p53, because this association is well characterized at the structural and biological levels. A number of drug screening approaches and technologies have been used to identity novel inhibitors of the p53-MDM2 interaction. This review will detail the development history of MDM2 protein and the p53-MDM2 interaction, the major classes of novel small-molecular p53-MDM2 binding inhibitors, key medicinal action with the protein-protein interaction and in vitro or in vivo biological activities.     

小分子p53-MDM2抑制剂先导化合物苄普地尔的研究

目的 采用老药新用药物设计方法,探寻p53-MDM2蛋白结合小分子抑制剂的先导化合物.方法 通过荧光偏振(FP)法和蛋白印迹试验法,分别测定化合物的p53-MDM2蛋白结合抑制活性和相关蛋白的表达变化,采用四甲基偶氮唑盐微量酶反应比色法(MTT法)测试其体外抗肿瘤活性,并且测定人肝微粒体中代谢产物.结果 发现苄普地尔具...     

Pharmacologic activation of p53 by small-molecule MDM2 antagonists

Restoring p53 activity by inhibiting the interaction between p53 and MDM2 represents an attractive approach for cancer therapy. To this end, a number of small-molecule p53-MDM2 binding inhibitors have been developed during the past several years. Nutlin-3 is a potent and selective small-molecule MDM2 antagonist that has shown considerable promise in pre-clinical studies. This review will highlight recent advances in the development of small-molecule MDM2 antagonists as potential cancer therapeutics, with special emphasis on Nutlin-3.     

Characterizing the Free‐Energy Landscape of MDM2 Protein–Ligand Interactions by Steered Molecular Dynamics Simulations

Inhibition of p53–MDM2 interaction by small molecules is considered to be a promising approach to re‐activate wild‐type p53 for tumor suppression. Several inhibitors of the MDM2–p53 interaction were designed and studied by the experimental methods and the molecular dynamics simulation. However, the unbinding mechanism was still unclear. The steered molecular dynamics simulations combined with Brownian dynamics fluctuation–dissipation theorem were employed to obtain the free‐energy landscape of unbinding between MDM2 and their four ligands. It was shown that compounds 4 and 8 dissociate faster than compounds 5 and 7 . The absolute binding free energies for these four ligands are in close agreement with experimental results. The open movement of helix II and helix IV in the MDM2 protein‐binding pocket upon unbinding is also consistent with experimental MDM2‐unbound conformation. We further found that different binding mechanisms among different ligands are associated with H‐bond with Lys51 and Glu25. These mechanistic results may be useful for improving ligand design.     

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.     

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.     

Probing the Origin of Structural Stability of Single and Double Stapled p53 Peptide Analogs Bound to MDM2

The stabilization of secondary structure is believed to play an important role in the peptide–protein binding interaction. In this study, the α‐helical conformation and structural stability of single and double stapled all‐hydrocarbon cross‐linked p53 peptides when bound and unbound to MDM2 are investigated. We determined the effects of the peptide sequence, the stereochemistry of the cross‐linker, the conformation of the double bond in the alkene bridge, and the length of the bridge, to the relative stability of the α‐helix structure. The binding affinity calculations by WaterMap provided over one hundred hydration sites in the MDM2 binding pocket where water density is greater than twice that of the bulk, and the relative value of free energy released by displacing these hydration sites. In agreement with the experimental data, potentials of mean force obtained by weighted histogram analysis methods indicated the order of peptides from lowest to highest binding affinity. Our study provides a comprehensive rationalization of the relationship between peptide stapling strategy, the secondary structural stability, and the binding affinity of p53/MDM2 complex. We hope our efforts can help to further the development of a new generation p53/MDM2 inhibitors that can reactivate the function of p53 as tumor suppressor gene.     

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.     

抗肿瘤药物研制的新靶点MDM2-p53

癌基因MDM2编码的蛋白可与抑癌蛋白p53结合并抑制p53的功能，促进p53的降解。MDM2的过度表达是肿瘤发生和发展的重要因素之一。本文简述了MDM2的结构与功能，MDM2与p53相互作用的机制与模式，以及根据MDM2－p53复合物结构研制开发抗肿瘤药物的进展与前景。     

Hsp90 inhibitor BIIB021 enhances triptolide-induced apoptosis of human T-cell acute lymphoblastic leukemia cells in vitro mainly by disrupting p53-MDM2 balance

Aim:

To investigate the effects of BIIB021, an inhibitor of heat shock protein 90 (Hsp90) alone or in combination with triptolide (TPL) on T-cell acute lymphoblastic leukemia (T-ALL) and the mechanisms of action.

Methods:

Human T-ALL cells line Molt-4 was examined. The cell viability was measured using MTT assay. Apoptotic cells were studied with Hoechst 33258 staining. Cell apoptosis and cell cycle were analyzed using flow cytometry with Annexin V/PI staining and PI staining, respectively. The levels of multiple proteins, including Akt, p65, CDK4/6, p18, Bcl-2 family proteins, MDM2, and p53, were examined with Western blotting. The level of MDM2 mRNA was determined using RT-PCR.

Results:

Treatment of Molt-4 cells with BIIB021 (50–800 nmol/L) inhibited the cell growth in a dose-dependent manner (the IC₅₀ value was 384.6 and 301.8 nmol/L, respectively, at 48 and 72 h). BIIB021 dose-dependently induced G₀/G₁ phase arrest, followed by apoptosis of Molt-4 cells. Furthermore, BIIB021 increased the expression of p18, decreased the expression of CDK4/6, and activated the caspase pathway in Molt-4 cells. Moreover, BIIB021 (50–400 nmol/L) dose-dependently decreased the phospho-MDM2 and total MDM2 protein levels, but slightly increased the phospho-p53 and total p53 protein levels, whereas TPL (5–40 nmol/L) dose-dependently enhanced p53 activation without affecting MDM2 levels. Co-treatment with BIIB021 and TPL showed synergic inhibition on Molt-4 cell growth. The co-treatment disrupted p53-MDM2 balance, thus markedly enhanced p53 activation. In addition, the co-treatment increased the expression of Bak and Bim, followed by increased activation of caspase-9.

Conclusion:

The combination of BIIB021 and TPL may provide a novel strategy for treating T-ALL by overcoming multiple mechanisms of apoptosis resistance.     

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。     

Association of p38MAPK‐p53‐Fas aggregation in S‐allyl cysteine mediated regulation of hepatocarcinoma

Bioactive components of dietary phytochemicals have been reported to possess antitumor activities. Evidences suggested key role of stress responsive p38MAPK in the induction of nutraceuticals mediated apoptosis in hepatocellular carcinoma (HCC). Current study demonstrated detailed molecular bagatelle associated with p38 MAPK mediated effective suppression of cell growth both in HepG2 and chemically induced liver carcinoma after S‐allyl cysteine (SAC) treatment. SAC promoted p38MAPK activity responsible for p53 phosphorylation, its stabilization followed by nuclear translocation leading to induction in expression and oligomerization of Fas protein. Distinctive p38MAPK‐p53 axis dependent Fas‐FasL‐FADD mediated caspase activities along with perturbed cell cycling became normalized with continuation of SAC treatment for another month to diethylnitrosamine induced liver carcinoma. Co‐treatment with SB203580, the p38MAPK inhibitor, prevented pro‐apoptotic effect of SAC by altering p53 phosphorylation and death inducing signaling complex conformation in HepG2 and induced HCC. Collectively study suggested significant contribution of p38MAPK‐p53‐DISC‐Caspase pathway in the regulation of anti‐neoplastic activity of SAC against HCC.