⇦Chinese Physics Letters, 2017, Vol. 34, No. 11, Article code 118701 Mechanism of Competition between Nutlin3 and p53 for Binding with Mdm2 * Shu-Xia Liu(刘书霞)1, Shi-Wei Yan(晏世伟)2** Affiliations 1College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 2Department of Physics, Beijing Normal University, Beijing 100875 Received 11 July 2017 *Supported by the National Natural Science Foundation of China under Grant No 11675018, the Beijing Natural Science Foundation under Grant No 1172008, and the Fundamental Research Funds for the Central Universities under Grant No 2015KJJCB01.
**Corresponding author. Email: yansw@bnu.edu.cn Citation Text: Shu-Xia Liu and Yan S W 2017 Chin. Phys. Lett. 34 118701 Abstract The tumour suppressor p53 is a transcription factor that regulates multiple biological functions including metabolism, DNA repair, cell cycle arrest, apoptosis and senescence. About half of human cancers show a normal TP53 gene and aberrant overexpression of Mdm2. This fact promotes a promising cancer therapeutic strategy by inhibiting the interactions between p53 and Mdm2. Various inhibitors have been designed to achieve this novel approach for cancer therapy. However, the detailed competition mechanism between these inhibitors and the p53 molecule in their binding process to Mdm2 is still unclear. We investigate this competition mechanism between Nutlin3 and p53 using molecular dynamics simulations. It is found that Nutlin3 binds faster than the p53 molecule to Mdm2 to prevent p53 binding to Mdm2 when Nutlin3 and p53 have equal distance from Mdm2. Nutlin3 can also bind to the p53-Mdm2 complex to disturb and weaken the interactions between p53 and Mdm2. Consequently, p53 cannot bind to Mdm2 and its tumour suppression function is reactivated. These results provide the detailed competition mechanism between Nutlin3 and p53 in their binding to Mdm2. Because the binding site of most other inhibitors to Mdm2 is the same as Nutlin3, therefore this competition mechanism can extend to most inhibitors which target the p53-Mdm2 interaction. DOI:10.1088/0256-307X/34/11/118701 PACS:87.19.xj, 87.10.Tf, 87.15.km © 2017 Chinese Physics Society Article Text The tumor suppressor protein p53 plays a pivotal role in protecting against tumorigenesis and faulty development that may arise from various cellular stresses, such as DNA damage, hypoxia, oncogenic activation, and telomere erosion.[1-4] The expression level of p53 is tightly controlled and kept at low concentration by its master regulator Mdm2 (the murine double minute-2, Hdm2 in humans) protein through a negative feedback loop.[3-6] About half of human cancers show a mutational TP53 gene which encodes p53 protein; nevertheless, the other half have a normal TP53 gene and aberrant overexpression of Mdm2. In the latter case, the concentration level of p53 is suppressed by Mdm2 protein. This fact promotes a cancer therapeutic strategy to reactivate the tumor-suppression function of p53 by inhibiting the interactions of p53 and Mdm2.[7-12] The inhibiting is achieved through designing p53-like inhibitors which occupy the p53-binding site of Mdm2 to prevent the binding of p53 to Mdm2. As a result, the concentration of p53 cumulates to a high level and the tumor-suppression function of p53 is reactivated. Various inhibitors have been designed to achieve this approach.[13-18] The Nutlin family is a group of well studied inhibitors which show high efficiency for tumor suppression.[13-18] The crystal structure of the p53-Mdm2 complex reveals that three hydrophobic residues, Phe19, Trp23 and Leu26, of p53 protein tightly insert into the hydrophobic cleft of Mdm2 protein. This character is highly conserved in interactions between Mdm2 and molecules of the Nutlin family. Rauf et al.[17] investigated interactions between p53/Nutlin3-Mdm2 theoretically and pointed out that there are three (four) hydrogen bonds between p53 (Nutlin3) and Mdm2 with hydrogen bonding energy $-$12.90 kcal/mol ($-$18.12 kcal/mol). From the above comparison, they summarized that Nutlin3 blocks the p53 binding pocket of Mdm2 due to higher interaction energy. However, our previous work using full-atomic molecular dynamics (MD) simulations with explicit water environment shows that two of the three hydrogen bonds between p53 and Mdm2 are very unstable and Nutlin3 cannot form a stable hydrogen bond with Mdm2.[19] Therefore, the detailed mechanism of competition between Nutlin3 and p53 in their binding process to Mdm2 is still controversial. To dynamically show how Nutlin3 inhibits p53-Mdm2 interaction, we investigate the competition mechanism of Nutlin3-p53 using MD simulations. By placing Nutlin3 and p53 molecules outside the p53-binding site of Mdm2 with equal distance, we find that Nutlin3 binds to Mdm2 faster than p53 due to its small molecular weight and occupies the hydrophobic domain occupied by p53 in p53-Mdm2 complexes. In addition, Nutlin3 can also weaken the interaction between p53 and Mdm2 when p53 already binds to Mdm2. In these ways, Nutlin3 effectively inhibits the p53-Mdm2 interaction. We conduct four simulations. Simulations are first conducted for the p53-Mdm2 complex (PDB ID: 1YCR[20]) and Nutlin3-Mdm2 complex (PDB ID: 4HG7[21]) to investigate their binding structures and interaction. We then conduct a simulation of the Nutlin3-(p53-Mdm2) system, in which the p53 and Mdm2 bind with each other (crystal structure of 1YCR was used), whereas Nutlin3 is put beside the p53 protein. Lastly, we conduct a simulation of the Nutlin3-p53-Mdm2 system, in which both Nutlin3 and p53 do not interact with Mdm2, and the distances between Nutlin3 and p53 to the binding cavity of Mdm2 are equivalent. The systems were solvated by the TIP3P[22] water model. The 150 mM NaCl was added to mimic the physiological ion strength. In our MD simulations, the $\alpha$-carbons of Glu25, Tyr60 and Val109 residues of Mdm2 are fixed to prevent significant conformation change of Mdm2 in the MD simulations. We use VMD (version 1.9)[23] to prepare the systems, and use NAMD (version 2.9)[24] to perform the MD simulations. The CHARMM force field[25] is used to carry out the simulations at 310 K and 1 bar. The non-bonded Coulomb and van der Waals interactions are switched off between 13 Å and 15 Å. The integration time step is 2 fs.
cpl-34-11-118701-fig1.png
Fig. 1. The characters of p53 and Nutlin3 binding to Mdm2. (a) The RMSD of the simulation with p53 and Nutlin3 bind to Mdm2. The RMSD curves show that the simulation is of equilibrium after 5 ns simulation. The simulation of the last 45 ns is used to analyze the characters of p53 and Nutlin3 binding to Mdm2. (b) The interaction between p53 and Mdm2. Three amino acids (Phe19, Trp23 and Leu26) of p53 insert into the hydrophobic cavity of Mdm2 and form the hydrophobic interaction. There are three hydrogen bonds between p53 and Mdm2. The hydrogen bonds formed by Phe19, Trp23 and Leu26 of p53 and Gln72, Leu54 and Val93 of Mdm2. (c) Three functional groups (like the amino acids Phe19, Trp23 and Leu26 of p53) insert into the hydrophobic cavity of Mdm2.
Interactions between p53/Mdm2-Nutlin3 have already been intensively investigated.[8,17,20,26-28] The capture of crystal structures of p53/Nutlin3-Mdm2 complex provides us with the key information of their interaction.[20,21] However, the static crystal structures were obtained in low temperature, which are different under the physiological condition. To investigate the binding characteristics of p53/Nutlin3 to Mdm2 in a physiological environment, we solvate the crystal structures of p53/Nutlin3-Mdm2 complexes in explicit water molecules and run 50 ns MD simulation for two models, respectively. After 5 ns of the total simulation time, the two systems reach equilibrium and the subsequent 45 ns simulation trajectories are extracted to perform analysis to obtain the characteristics of the p53/Nutlin3-Mdm2 interaction (Fig. 1(a)). We analyze the interaction between p53 and Mdm2 in the stable p53-Mdm2 complex and confirm that hydrophobic interaction and hydrogen-bond interaction are important for the binding of p53 to Mdm2. This result is consistent with the previous works.[8,17,20,26,29-34] The Phe19, Trp23, and Leu26 residues of p53 protein inserted into the hydrophobic pocket of Mdm2 protein to form the hydrophobic interaction (Fig. 1(b)). Moreover, there are three hydrogen bonds formed among Phe19, Trp23 and Leu26 of p53 and Gln72, Leu54 and Val93 of Mdm2 (Fig. 1(b)). Consistent with our previous work, hydrogen bonds of Phe19-Gln72 and Leu26-Val93 are unstable.[19] The total non-bonded interaction energy between p53 and Mdm2 is $-$162 kcal/mol. This energy includes van der Waals energy ($-$62 kcal/mol) and electrostatic interaction energy ($-$100 kcal/mol). The binding site of Nutlin3 on Mdm2 is the same as p53. From Fig. 1(c), three functional groups of Nutlin3 are inserted into the hydrophobic pocket of Mdm2, like the three key residues of p53 (Phe19, Trp23 and Leu26). Consistent with our previous work, there is no hydrogen bond between Nutlin3 and Mdm2.[19] The non-bonded interaction energy between Nutlin3 and Mdm2 is $-$43 kcal/mol, which is higher than that of p53-Mdm2. The van der Waals energy and electrostatic interaction energy are $-$45 kcal/mol and 2 kcal/mol, respectively. Therefore, the binding energy between Nutlin3 and Mdm2 is mainly contributed by the van der Waals interaction. The repulsive electrostatic energy between Nutlin3 and Mdm2 also proves that there is no hydrogen bond between Nutlin3 and Mdm2. We calculate the energies of RG7112-Mdm2 and RG7388-Mdm2. The energies of RG7112-Mdm2 and RG7388-Mdm2 are $-$46 kcal/mol and $-$50 kcal/mol, respectively. This tendency of energy is similar with the experiment. The energy calculated by NAMD is as follows: $$\begin{alignat}{1} &U_{\rm non-bonded}=U_{\rm vdW}+U_{\rm coulomb},~~ \tag {1} \end{alignat} $$ $$\begin{alignat}{1} &U_{\rm vdW}=\sum_{i}\sum_{j>i}4\varepsilon_{ij} \Big[\Big(\frac{\sigma_{ij}}{r_{ij}}\Big)^{12}-\Big(\frac{\sigma_{ij}}{r_{ij}}\Big)^6\Big],~~ \tag {2} \end{alignat} $$ $$\begin{alignat}{1} &U_{\rm coulomb}=\sum_{i}\sum_{j>i}\frac{q_{i}q_{j}}{4\pi\varepsilon_{0}r_{ij}}.~~ \tag {3} \end{alignat} $$ From the above results of calculations, the binding energy between p53 and Mdm2 is larger than that between Nutlin3 and Mdm2. This result is different from the conclusion of Rauf et al.[17] that Nutlin3 can inhibit p53-Mdm2 interaction due to its larger binding energy with Mdm2 with the contribution of four higher energy hydrogen bonds than p53. It is experimentally proved that Nutlin3 can inhibit p53's binding to Mdm2 and can enhance the concentration of p53 to suppress cancer.[35] The reason why this study is more reasonable than the work of Rauf is that we use the full-atomic and explicit water model, and the model adds 150 mM sodium chloride ion. Our model is closer to the real biological system and the simulation time is longer than that of Rauf's simulation, thus our results are more real, responding to the situation in the body. From the above facts, we propose that there may be two inhibiting mechanisms between Nutlin3, p53 and Mdm2. Firstly, Nutlin3 can disrupt the interactions between p53 and Mdm2 and can cause detachment of p53 from Mdm2. Secondly, Nutlin3 binds to Mdm2 faster than p53 and occupies the p53-binding site of Mdm2. Both of these mechanisms can inhibit the p53-Mdm2 interaction and lead to cumulation of p53 protein. We design two simulation models to evaluate these two mechanisms. The detailed results are shown in the following.
cpl-34-11-118701-fig2.png
Fig. 2. The initial structure and the final structure of Nutlin3 bind to the p53-Mdm2 complex. The $\alpha$ helix with pink flat ribbon is the initial structure of p53. The $\alpha$ helix with blue flat ribbon is the final structure of p53. The small molecule shown by the ball and stick is Nutlin3.
cpl-34-11-118701-fig3.png
Fig. 3. The hydrogen bonds's distance and the energy between p53 and Mdm2. (a) The distance-time curves of the three hydrogen bonds between p53 and Mdm2. (b) The energy-time curve of the electric interaction and van der Waals interaction between p53 and Mdm2.
We evaluate the possible competition mechanism that Nutlin3 can bind to the p53-Mdm2 complex and disrupt their interaction. In the modeling, we put Nutlin3 molecule 30 Å away from the p53-Mdm2 complex. The whole system is solvated in an explicit water environment. After 180 ns MD simulation, Nutlin3 binds to the p53-Mdm2 complex and locates at the p53-Mdm2 interface (see Fig. 2). In the whole simulation process, p53 interacts with Mdm2, i.e., Nutlin3 cannot totally destroy the interaction between p53 and Mdm2 to cause detachment of p53 from Mdm2. However, we should note that the three hydrogen bonds between p53 and Mdm2 are destroyed and the binding energy between p53 and Mdm2 are decreased in our MD simulations (Fig. 3). From the simulation trajectory, we can find that p53 binds stably to Mdm2 at the initial conformation and Nutlin3 is away from the p53-Mdm2 complex (Fig. 2). In this initial conformation, Nutlin3 is attracted by the p53-Mdm2 complex through long range electrostatic interaction and moves towards the complex within 2 ns. The binding sites of Nutlin3 molecules on the complex locate on the interface between p53 and Mdm2 (Fig. 2). In this conformation, the Nutlin3 molecule interacts with Mdm2 mainly through van der Walls interaction (Fig. 4(a)). Because the binding site is occupied by p53, Nutlin3 cannot totally bind to Mdm2 and the VDW energy in this conformation is much smaller than that calculated by the complex of Mdm2 and Nutlin3. The sequential simulation shows that the complex of p53-Mdm2-Nutlin3 approaches equilibrium state and further large conformational change is not observed (Fig. 4(b)). Comparison between interactions of p53-Mdm2 in this conformation and that in the p53-Mdm2 stably binding conformation shows that, affected by the binding of Nutlin3, the three hydrogen bonds between p53 and Mdm2 are totally destroyed in the p53-Mdm2-Nutlin3 complex (Fig. 3(a)) and the interaction between p53-Mdm2 is partly damaged already (Fig. 3(b)).
cpl-34-11-118701-fig4.png
Fig. 4. The energy and RMSD curves between Nutlin3 and Mdm2 during the process of Nutlin3 combining to Mdm2. (a) The energy-distance curves between Nutlin3 and Mdm2. (b) The RMSD-time curves between Nutlin3 and Mdm2.
The above results of the simulation show that Nutlin3 can bind to the interface between p53 and Mdm2 and can weaken the p53-Mdm2 interaction effectively. Within 180 ns MD simulation, we cannot capture the detachment of p53 from Mdm2. Moreover, we change the position of Nutlin3 in a small range and the results are the same as above. The energy of Nutlin3 and Mdm2 is around $-$23 kcal/mol (Fig. 5). Figure 5 can explain that the energy between p53-Mdm2 and Nutlin3-Mdm2 is mostly the electrostatic energy and VdW energy. However, since Nutlin3 can effectively decrease the interaction between p53 and Mdm2, this result cannot exclude the possibility that p53 may detach from Mdm2 under other perturbation or given longer time.
cpl-34-11-118701-fig5.png
Fig. 5. The energy between p53-Mdm2 and Nutlin3-Mdm2 during the process of Nutlin3 combining to Mdm2. (a) The energy-time curve between p53 and Mdm2. (b) The energy-time curve between Nutlin3 and Mdm2.
cpl-34-11-118701-fig6.png
Fig. 6. The snapshots of the process of Nutlin3 binding to Mdm2 at 0 (a), 20 (b), 40 (c), 60 (d), 80 (e) and 100 ns (f) in the simulation. Nutlin3 binds to Mdm2 faster than p53 and occupies the p53-binding site of Mdm2 when they are outside of the p53-binding site of Mdm2 with equal distance from Mdm2. The proteins with flat ribbon are p53 and Mdm2. The small molecular shown by the ball and stick is Nutlin3.
cpl-34-11-118701-fig7.png
Fig. 7. The RMSD of the process of Nutlin3 binding to Mdm2 of the MD simulation.
We then examine the second possible inhibiting mechanism in which Nutlin3 binds to Mdm2 faster than p53 and occupies the p53-binding site of Mdm2. To evaluate this proposed mechanism, we put both Nutlin3 and p53 molecules outside of the p53-binding site of Mdm2 with equal distance from Mdm2 (the center-of-mass distances between Mdm2 and p53/Nutlin3 are both 30 Å). After 30 ns MD simulation, Nutlin3 binds to Mdm2 stably. The conformation of the Nutlin3-Mdm2 complex structure is similar with the crystal structure and the stable structures are obtained from our MD simulations (Figs. 6 and 7). Though p53 contacts with Mdm2, it cannot bind to Mdm2 stably since its binding site on Mdm2 is occupied by Nutlin3 already (Fig. 7).
cpl-34-11-118701-fig8.png
Fig. 8. Energies of Nutlin3-Mdm2 and p53-Mdm2 in the MD simulation. (a) The energy of Nutlin3-Mdm2 changes from 0 kcal/mol in 0 ns to $-$40 kcal/mol in 2 ns indicating that Nutlin3 binds tightly to Mdm2. (b) The energy of p53-Mdm2 is 0 kcal/mol indicating that p53 cannot bind to Mdm2.
cpl-34-11-118701-fig9.png
Fig. 9. The energy between Nutlin3-Mdm2 and p53-Mdm2 during the process of Nutlin3 and p53 combining to Mdm2. (a) The energy-time curve between Nutlin3 and Mdm2. (b) The energy-time curve between p53 and Mdm2.
It seems that this simulation result contradicts the calculations of the Mdm2-p53/Nutlin3 complex in which the binding energy of p53-Mdm2 is larger than that of Nutlin3-Mdm2. However, the binding energy calculation is based on the crystal structures and process of p53/Nutlin3 binding to Mdm2. In this competitive simulation, Nutlin3 binds to Mdm2 faster than p53 and occupies the p53-binding site of Mdm2 to form a stable structure. We calculate the energy of Nutlin3/p53 binding to Mdm2 in the dynamical process (Fig. 8) respectively. The energy of the initial structure is 0 kcal/mol, which illustrates that there is no interaction between the p53/Nutlin3 and Mdm2 at the beginning of the simulation. From Fig. 8(a), we can find that, from 0.6 ns to 2.4 ns, the energy of the interactions between Nutlin3 and Mdm2 is increased and then becomes stable. During the simulation times, the energy between Nutlin3 and Mdm2 is 40 kcal/mol mostly the van der Walls interaction in the simulation time (Fig. 8(a)). This result is consistent with that of the characteristics of p53/Nutlin3 which binds to Mdm2. The energy between p53 and Mdm2 is mostly the electrostatic energy which is small (Fig. 8(b)). The small molecular of Nutlin3 can bind to Mdm2 in 2 ns. Due to the strong interaction between Nutlin3 and Mdm2, Nutlin3 can bind to Mdm2 faster than p53 and occupies the p53-binding site of Mdm2. In addition, we exchange the position of p53 and Mdm2, and the result is similar to the above simulation. The energy of Nutlin3 and Mdm2 is $-$40 kcal/mol (Fig. 9). From the above results and analysis, though the total binding energy between p53 and Mdm2 is larger than that of Nutlin3 and Mdm2 ($-$162 kcal/mol versus $-$43 kcal/mol), the van der Waals energy between Nutlin3 and Mdm2 is close to that between p53 and Mdm2 ($-$45 kcal/mol versus $-$62 kcal/mol). This result proves that Nutlin3 resembles p53 in the aspect of the shape effect during the MD simulation. The main difference between p53-Mdm2 interaction energy and Nutlin3-Mdm2 interaction energy arises from the electrostatic interaction ($-$100 kcal/mol versus 2 kcal/mol). However, this advantage of p53 is eliminated considering the size difference between Nutlin3 and p53. Therefore, Nutlin3 can win the competition with p53 in their binding to Mdm2 and effectively reactivate the tumor-suppression function of p53-protein. In summary, we have investigated the competition mechanism between Nutlin3 and p53 in their binding processes to Mdm2. We propose two possible competition mechanisms. Firstly, Nutlin3 can disrupt the interactions between p53 and Mdm2 and can cause detachment of p53 from Mdm2. Secondly, Nutlin3 binds to Mdm2 faster than p53 and occupies the p53-binding site of Mdm2. We evaluate these two proposed mechanisms through full-atomic analysis and find that the main inhibition mechanism is the second one. Due to the small size of Nutlin3, though the binding energy between p53-Mdm2 is larger than that of Nutlin3-Mdm2, Nutlin3 binds faster to Mdm2 than p53 and occupies the p53-binding site of Mdm2. Under the condition that p53 already binds to Mdm2, Nutlin3 also can effectively decrease the p53-Mdm2 interaction and contribute to detachment of p53 from Mdm2. Because the binding site of most other inhibitors to Mdm2 is the same as Nutlin3, the competition mechanism investigated here can extend to most other inhibitors which target the p53-Mdm2 interaction. References p53, the Cellular Gatekeeper for Growth and DivisionSurfing the p53 networkDrugging the p53 pathway: understanding the route to clinical efficacyThe p53-mdm-2 autoregulatory feedback loop.Mdm2 in EvolutionThe Structure-Based Design of Mdm2/Mdmx-p53 Inhibitors Gets SeriousInhibiting the p53–MDM2 interaction: an important target for cancer therapySmall-Molecule Inhibitors of the MDM2-p53 Protein-Protein Interaction to Reactivate p53 Function: A Novel Approach for Cancer TherapyRestoration of p53 to limit tumor growthMDM2 oncogene as a target for cancer therapy: An antisense approach.Robust Generation of Lead Compounds for Protein-Protein Interactions by Computational and MCR Chemistry: p53/Hdm2 AntagonistsMDM2 Small-Molecule Antagonist RG7112 Activates p53 Signaling and Regresses Human Tumors in Preclinical Cancer ModelsDiscovery of RG7388, a Potent and Selective p53–MDM2 Inhibitor in Clinical DevelopmentPreclinical Optimization of MDM2 Antagonist Scheduling for Cancer Treatment by Using a Model-Based ApproachMDM2 inhibitors for cancer therapyHow Nutlin-3 disrupts the MDM2–p53 interaction: a theoretical investigationActivation of p53 by the MDM2 inhibitor RG7112 impairs thrombopoiesisStructural effects and competition mechanisms targeting the interactions between p53 and MDM2 for cancer therapyStructure of the MDM2 Oncoprotein Bound to the p53 Tumor Suppressor Transactivation DomainThe structure of an MDM2–Nutlin-3a complex solved by the use of a validated MDM2 surface-entropy reduction mutantComparison of simple potential functions for simulating liquid waterVMD: Visual molecular dynamicsScalable molecular dynamics with NAMDAll-Atom Empirical Potential for Molecular Modeling and Dynamics Studies of Proteins †Structural Biology of the Tumor Suppressor p53Transient stability of the helical pattern of region F19–L22 of the N-terminal domain of p53: A molecular dynamics simulation studyDifferential binding of p53 and nutlin to MDM2 and MDMX: Computational studiesThe Structure-Based Design of Mdm2/Mdmx-p53 Inhibitors Gets SeriousTransient Protein States in Designing Inhibitors of the MDM2-p53 InteractionFlexible lid to the p53-binding domain of human Mdm2: Implications for p53 regulationQuantitative Lid Dynamics of MDM2 Reveals Differential Ligand Binding Modes of the p53-Binding CleftInterrogation of MDM2 Phosphorylation in p53 Activation Using Native Chemical Ligation: The Functional Role of Ser17 Phosphorylation in MDM2 ReexaminedChalcone Derivatives Antagonize Interactions between the Human Oncoprotein MDM2 and p53 †In Vivo Activation of the p53 Pathway by Small-Molecule Antagonists of MDM2
[1] Levine A J 1997 Cell 88 323
[2] Vogelstein B et al 2000 Nature 408 307
[3] Khoo K H et al 2014 Nat. Rev. Drug Disc. 13 217
[4]Liu Z Z et al 2014 Chem. Bio. Durg. 85 411
[5] Wu X et al 1993 Genes Dev. 7 1126
[6] Lane D P et al 2012 Genes Cancer 3 320
[7] Popowicz G M et al 2011 Chem. Int. Ed. 50 2680
[8] Chene P et al 2003 Nat. Rev. Cancer 3 102
[9] Shangary S et al 2009 Annu. Rev. Pharmacol. Toxicol. 49 223
[10] Wang W et al 2008 Curr. Opinion Oncology 20 90
[11] Wang H et al 1999 Int. J. Oncology 15 653
[12] Czzrna A et al 2010 Chem. Int. Ed. 49 5352
[13] Tovar S et al 2013 Cancer Res. 73 2587
[14] Ding Q J et al 2013 Med. Chem. 56 5979
[15] Higgins B 2014 Clinical Cancer Res. 20 3742
[16] Vassilev L 2007 Trends Mol. Med. 13 23
[17] Rauf S 2014 Med. Chem. Res. 23 1998
[18] Rubin C et al 2014 Exp. Hematology 42 137
[19] Liu S 2017 Front. Phys. 12 128908
[20] Kussie P H et al 1996 Science 274 948
[21] Noble M E et al 2013 Acta Crystallogr. Sect. D 69 1358
[22] Jorgensen W J et al 1983 J. Chem. Phys. 79 926
[23] Humphrey W et al 1996 J. Mol. Graphics 14 33
[24] Phillips J C et al 2005 J. Comput. Chem. 26 1781
[25] MacKerell A D et al 1998 J. Phys. Chem. 102 3586
[26] Joerger A C et al 2008 Annu. Rev. Biochem 77 557
[27] Espinoza-Fonseca L et al 2006 Biophys. Res. Commun. 343 110
[28] Joseph T et al 2010 Cell Cycle 9 1167
[29] Popowicz G M et al 2011 Angew. Chem. Int. Ed. 50 2680
[30] Bista M et al 2013 Structure 21 2143
[31] McCoy M A et al 2003 Proc. Natl. Acad. Sci. USA 100 1645
[32] Showalter S A et al 2008 J. Am. Chem. Soc. 130 6472
[33] Zhan C Y et al 2012 J. Am. Chem. Soc. 134 6855
[34] Stoll R et al 2001 Biochemistry 40 336
[35] Vassilev L T et al 2004 Science 303 844