Research Article |
Corresponding author: Mansour Al-Sayed Ahmad ( 6450@ammanu.edu.jo ) Academic editor: Emilio Mateev
© 2024 Mansour Al-Sayed Ahmad, Belal O. Al-Najjar, Ashok Shakya.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Al-Sayed Ahmad M, Al-Najjar BO, Shakya A (2024) Novel glucokinase activators: A structure-based pharmacophore modeling, QSAR analysis, and molecular dynamics approach. Pharmacia 71: 1-9. https://doi.org/10.3897/pharmacia.71.e131072
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Glucokinase (GK) activators are promising candidates for type 2 diabetes treatment. This study utilized structure-based pharmacophore modeling and QSAR analysis to identify novel activators. Virtual screening of a 250,000-compound library yielded eight new candidates with significant in vitro activity (over 50% activation at 25 µg/mL) and diverse structures. Molecular dynamics simulations revealed a potential mechanism involving a transient loop flip in the GK allosteric site, aligning with known activator behavior. The leading candidate, NSC12516, displayed superior hydrogen bonding with key residues (compared to known activator MRK501) and potentially stronger binding affinity due to favorable energetics. These findings clear the way for developing potent and selective GK activators for type 2 diabetes.
glucokinase, virtual screening, pharmacophore, QSAR, molecular dynamics
Glucokinase (GK), also known as hexokinase 4, belongs to the hexokinase family and is an inducible enzyme that is made up of 465 amino acids with a molecular mass of 52 kDa. GK’s three-dimensional structure (Fig.
GK exhibits three different forms, namely closed, open, and super-open conformations, depending on the binding of endogenous ligands or substrates to the connected domain (Fig.
Since the 1960s, numerous studies have been conducted that have highlighted the dual functions of GK. The enzyme was identified as a glucose sensor in pancreatic β-cells and as a pacemaker in hepatic glucose conversion to glycogen. Further research discovered that GK expression in pancreatic β-cells and hepatocytes was differentially regulated by glucose and insulin, respectively. (
3D pharmacophores provide a highly abstract representation of the binding modes between ligands and their macromolecular targets. This abstraction allows for rationalization of binding modes even for chemically diverse ligands. Furthermore, it enables efficient virtual screening of molecular databases, facilitating rapid identification of potential ligands with desired binding characteristics. The use of 3D pharmacophores streamlines the process of identifying and evaluating new molecules with therapeutic potential. (
Within this context, 3D-QSAR has emerged as a logical progression from traditional methods. It leverages the three-dimensional attributes of ligands to anticipate their biological effects by employing robust chemometric techniques. (
Since the initial introduction of the first glucokinase activator in 2003, numerous activators belonging to this class have been developed and subjected to evaluation. These activators are characterized by their small molecular size, enabling them to bind to a specific allosteric site on the enzyme. When these polymers occupy this unique site, they promote the stabilization of a conformation of GK that exhibits a notably high affinity, ultimately facilitating the activation of the enzyme. Remarkably, it has been observed that this allosteric cleft is in the hinge region (Fig.
Many chemical groups were reported by previous studies as potential GK activators, like azole derivatives, pyridine derivatives, azole-pyridine derivatives, or miscellaneous. (
But the use of older-generation GKAs raised concerns about both efficacy and safety. Key issues included the risk of hypoglycemia, induction of fatty liver disease, dyslipidemia, and a decrease in long-term efficacy. The appearance of hypoglycemia and dyslipidemia, which were attributed to excessive stimulation of pancreatic and liver glucokinase, respectively, were identified as potential risks early in the development of GKA (
In this study, we adopted the structure-based pharmacophore modeling procedure reported by Al-Najjar and coworkers (2023). The study initially started by generating valid pharmacophore models using Biovia Discovery Studio 3.1 (Biovia Dassault Systems, Discovery Studio 2016). Those models were subjected to QSAR analysis to generate a representative equation that explains the activity. Next, the selected pharmacophore models that appeared in the QSAR equation were used to screen 264,000 compounds from the NCI database. Finally, the successful candidates were tested for their biological activity. (
More than 50 X-ray crystal structures in the Protein Data Bank (https://www.rcsb.org) for glucokinase were reviewed to choose one structure according to the following criteria: (1) high resolution; (2) without glucokinase regulatory protein in its structure; and (3) co-crystallized with an activator.
The crystal structure of 3F9M co-crystallized with its activator, MRK501, was selected according to the mentioned criteria.
The generated pharmacophore models were validated by assessing their abilities to selectively capture diverse active compounds from a large testing list of actives and decoys. The list of studied compounds as glucokinase activators was downloaded from the ChEMBL database (https://www.ebi.ac.uk/chembl/).
The list was composed of synthetic or organic compounds listed as glucokinase activators and then divided into active and inactive compounds according to their EC50 values to make a training set that serves as a template for evaluating the predictive accuracy of pharmacophore models in identifying known active compounds.
The data set prepared previously was uploaded to the ‘Pharmacophore Generation Protocol’ impeded in Biovia Discovery Studio® software. The inputs in the protocol were the (3F9M) protein and the training set, and then we changed a number of parameters to create the different pharmacophoric hypotheses. The parameters were (omitted features between 0 and 1; minimum interference distance 2, 2.5, and 3 Å; and maximum exclusion volume 4 and 5 Å3); and the output is a set of pharmacophores suggested to be suitable for interaction with the activators at the allosteric site. An internal validation was performed by supplying a collection of both active and inactive ligands, and the outcomes were visualized in the form of a receiver operating characteristic (ROC) curve.
More than 100 pharmacophores were generated in step (3), and then the pharmacophores were tested against a test data set to choose the best pharmacophore that could recognize the active compounds and differentiate them from the inactive compounds.
The selected pharmacophores were employed in a ligand pharmacophore fitting approach for the ligands, using the optimal fit option in DS. The calculated descriptors contained (log P, molecular weight, number of aromatic numberings, number of H-bond acceptors, number of H-bond doners, number of rotatable bonds, polar surface area, extended-connectivity fingerprints (ECFPs), as well as the fitting values of the generated pharmacophores). The results were uploaded to the ‘Create Genetic Function Approximation Model’ protocol.
The QSAR equation and the chosen pharmacophore models were used as parameters to virtually screen a large chemical database composed of more than 250,000 compounds obtained from the National Cancer Institute (https://www.cancer.gov/).
A total of 250 conformers were generated using the BEST conformation method, ensuring comprehensive and enhanced coverage of the conformational space. To be considered a hit, a selected molecule from the screening process should successfully match all the pharmacophoric features. The fit values and associated molecular descriptors of each hit were incorporated into the previously prepared QSAR equation. The top-ranked compounds, determined through QSAR predictions, were subsequently subjected to in vitro evaluation against the glucokinase enzyme.
The bioassay is based on the enzymatic phosphorylation of D-glucose by GK, which results in the formation of D-glucose-6-phosphate. This product is further oxidized by the glucose-6-phosphate dehydrogenase (G6PD) enzyme in the presence of NADP, leading to the production of 6-phospho-D-gluconate and NADPH. The NADPH molecule exhibits maximum absorbance (λmax) at 340 nm. The rate at which NADPH is generated is directly proportional to the catalytic activity of GK. (
In the experimental procedure, stock solutions of the test samples are initially prepared using dimethyl sulfoxide (DMSO). These stock solutions are then diluted in deionized water in a serial manner to achieve the desired working concentrations for the bioassay.
All chemicals needed for the bioassay were acquired from Sigma-Aldrich Company and used without further purification.
To perform the bioassay, the following procedure was followed:
A total of 10 µL of the tested sample solution was added to a reaction mixture containing the following components: Tris-HCl buffer (75 mM, pH 9.0 at 30 °C) -24 mL, MgCl2 (600 mM in deionized water) -1 mL (equivalent to 20.10 mM in the reaction mixture), ATP (120 mM in deionized water) -1 mL (equivalent to 4.02 mM in the reaction mixture), D(+)glucose (360 mM in deionized water) -1 mL (equivalent to 12.10 mM in the reaction mixture, which is close to the S0.5 reported for GK, i.e., 8 mM), NADP (27 mM in deionized water) -1 mL (equivalent to 0.90 mM in the reaction mixture). Subsequently, G6PD (1000 U/mL in cold deionized water) -3 µL (equivalent to 0.031 U/L in the reaction mixture) was added. This was followed by the addition of human GK solution (Sigma-Aldrich, CAS Number 9001-51-8) (0.05 units/mL) -3 µL (equivalent to 1.56 × 10^-6 U/L in the reaction mixture), which was prepared in cold tris buffer (pH 8.5, 4 °C). The addition of the human GK solution initiated the reaction in the bioassay (in all experiments and controls, samples were prepared in triplicate).
Molecular dynamics simulations were initiated and conducted for 25 ns.
The receptor-ligand pharmacophore generation protocol in Discovery Studio was used to create more than 100 pharmacophore models. The models were generated by varying parameters such as maximum features, minimum inter-feature distance, and maximum exclusion volume distance.
To assess the efficacy of the pharmacophoric model in distinguishing active and inactive compounds, the area under the ROC curve was calculated. (Suppl. material
In this study, classical QSAR analysis was performed to identify the optimal combination of pharmacophores and other 2D and 3D descriptors that can explain the biological activities of the ligands. The goal was to develop a robust QSAR equation that accurately predicts the activities of novel compounds.
Multiple linear regression and GFA (genetic function approximation) were employed to obtain the best QSAR equation. The fit values obtained from the pharmacophoric mapping of the dataset were combined with various physicochemical descriptors of the ligands.
By integrating the information from the pharmacophoric models and the additional descriptors, the QSAR analysis aimed to establish a quantitative relationship between the structural and physicochemical properties of the ligands and their biological activities. This approach allows for the identification of key molecular features and properties that contribute to the observed activity, facilitating the design and discovery of novel pharmacologically active compounds. The selected QSAR equation is:
Log (1/EC50) =-1.0397 + 0.56233 * ALogP + 3.5554 * Count<ECFP_6:914325265>+ 1.3589 * Count<ECFP_6:-797085356> - 1.1095 * Count<ECFP_6:-177264675>+ 0.75328 * Count<ECFP_6:-1059365320> + 3.7999 * Count<ECFP_6:864909220> - 1.997* Count<ECFP_6:432225086> + 0.53069 * R1T1D2.5P6 - 0.23105 * R2T1D3P10 + 0.43508 * R2T1D3P7
r 2 = 0.9864 r2(adj) = 0.9767 r2(pred) = 0.9180
Equation 1; where EC50: Half maximal effective concentration; ALogP: Log of the octanol-water partition coefficient using Ghose and Crippen’s method; ECFP: Extended-Connectivity Fingerprints; r2 is the correlation coefficient against the testing compounds; r2(adj) is r2 adjusted for the number of terms in the model; r2(pred) is the prediction r2, equivalent to q2 from a leave-1-out cross-validation.
In the QSAR equation (Equation (1)), R1T1D2.5P6 refers to the fit values of the ligands against the sixth pharmacophoric hypothesis. This calculation involves the interfacial distance of 2.5 Å from the first trial and so on for the other two pharmacophoric hypotheses present in the equation (R2T1D3P7 and R2T1D3P10). The inclusion of the pharmacophoric model in the equation indicates that two of the pharmacophores (which are the pharmacophoric hypotheses with the positive factors R1T1D2.5P6 and R2T1D3P7) are able to effectively explain the observed bioactivities. But on the contrary, if the ligands fit the third pharmacophoric hypothesis (R2T1D3P10), it will be bad for activity.
The QSAR equation and its associated parameters are utilized to establish a quantitative relationship between the structural features of molecules and their biological activities, so it becomes possible to predict and analyze the bioactivity of similar ligands based on their adherence to the defined pharmacophoric model.
Fig.
As mentioned earlier, a data set consisting of 250,000 compounds obtained from NCI was screened against the QSAR equation, and the pharmacophore models with the highest ranking of 30 compounds based on their predicted EC50 (Suppl. material
During the in-vitro assay of selected compounds, absorbance readings were recorded. Out of the tested compounds, eight exhibited significantly higher positive activity compared to the control (the reaction mixture without any tested compound). The chemical structures of the specific compounds demonstrating such activity are detailed in Suppl. material
Each one of the eight compounds was tested at (25 μg/mL) concentration, and the test was repeated three times. Then the average reading of each compound was divided by the average reading of the vehicle. The results are summarized in Fig.
We noticed that at 25 µg/mL concentration, all the compounds showed good activity except (10666), which demonstrated moderate activity as a GK activator.
As we can see, the chemical structures for the eight compounds are miscellaneous with no similarity to any reported group, but in silico they preserve the interactions with the pharmacophore.
Suppl. material
In QSAR analysis, parameters appeared in the equation, i.e., ALogP: Log of the octanol-water partition coefficient; ECFP: extended-connectivity fingerprints; and the pharmacophoric model R1T1D2.5P6. This indicates a positive correlation between those parameters and the activity predicted. The positive correlation of AlogP may indicate that compounds with higher LogP values tend to have a greater ability to interact with hydrophobic binding pockets, resulting in increased binding affinity and activity. The positive correlation between a specific ECFP and the predicted activity means that the presence or occurrence of that particular ECFP feature tends to be associated with higher activity levels. In other words, compounds that possess this ECFP feature are more likely to exhibit the desired activity.
Finally, experimental validation of the previous in silico procedure has shown that selected compounds were active, which provides strong evidence that the predicted pharmacophore models and the pharmacophoric features are functionally relevant. The activity of the selected compounds indicates that these interactions play a crucial role in the binding and potential efficacy of the compound.
To validate our in vitro bioassay findings and gain deeper insights into the compound-glucokinase (GK) interactions, we performed 25 ns molecular dynamics (MD) simulations. (
The first system simulated the crystal structure of GK complexed with the known activator MRK501 (PDB ID: 3F9M). The second system investigated NSC12516, the compound exhibiting the highest in vitro activity. The root mean square deviation (RMSD) of the protein backbone over the simulation trajectory was monitored (Fig.
Detailed analysis of the RMSF profile (Fig.
These results suggest that the identified activators might induce a similar loop movement, potentially contributing to their mechanism of action.
The observed fluctuations around residues 50–65 suggest potential movement within the broader allosteric region beyond the immediate binding pocket. These fluctuations might be independent of ligand binding or could represent a “domino effect” propagating through the protein structure. Next, we investigated hydrogen bond interactions between the amino acid residues lining the allosteric site of GK and the bound ligands (Table
Hydrogen bond interaction analyses of NSC12516 and MRK501 in complex with GK.
Acceptor | Doner | Occupancies (%) | Average Distance (Å) | Average Angle | |
---|---|---|---|---|---|
NSC12516-GK Complex | NSC12516@H43/N5 | 74.57 | 2.85 | 157.91 | |
NSC12516@H48/O2 | 18.61 | 2.71 | 155.38 | ||
GLU67@OE1 | NSC12516@H48/O2 | 17.6 | 2.71 | 155.58 | |
NSC12516@O2 | GLU67@H/N | 1.54 | 2.94 | 155.21 | |
MRK501-Gk Complex | MRK501@N4 | ARG63@H/N | 4.22 | 2.94 | 154.39 |
MRK501@N17 | SER64@HG/OG | 3.28 | 2.91 | 151.58 |
NSC12516 was able to maintain 3 hydrogen bonds as an accepter from Arg63 (74.57%), Glu67 (81.61% and 17.6%), and 1 hydrogen bond as a doner for Glu67 (1.54%), while MRK501 maintained only 2 hydrogen bonds as an accepter from Arg63 (4.22%), and Ser64 (3.28%). Overall, the higher number and occupancy rates of hydrogen bonds formed by NSC12516 suggest that it might have a stronger affinity and potentially better stability when bound to glucokinase compared to MRK501.
To further understand the binding interactions, we calculated the energetic components between NSC12516 and MRK501 in complex with GK using the MM-PBSA method (Table
Predicted energy components and binding affinities of NSC12516 and MRK501 towards the allosteric site of GK using the MM-PBSA approach for the last 5 ns of the molecular dynamics’s simulations.
Energy component (kcal/mol) | Energy value (kcal/mol) per complex | |
---|---|---|
NSC12516-GK | MRK501-GK | |
van der Waals Energy (∆EvdW) | -61.9288 | -25.5885 |
Electrostatic Energy (∆EEL) | -34.4406 | -44.1295 |
Polar Solvation Energy (∆EPB) | 48.1815 | 49.8056 |
Non-Polar Solvation Energy (∆ENPOLAR) | -4.036 | -2.5816 |
Total Gas Phase Free Energy (∆Ggas) | -96.3694 | -69.7181 |
Total Solvation Free Energy (∆Gsolv) | 44.1455 | 47.224 |
Total Energy (∆Gbind) | -52.2239 | -22.4941 |
This study successfully identified eight novel glucokinase activators with promising in vitro activity through a structure-based approach. Molecular dynamics simulations suggest a potential mechanism involving a loop flip in the allosteric site, and the leading candidate, NSC12516, exhibits superior binding characteristics compared to a known activator. These findings lay the groundwork for further development of potent and selective GK activators as a therapeutic strategy for type 2 diabetes. Further investigation is warranted to fully elucidate the mechanism of action and translate these promising candidates into clinical applications.
The authors would like to acknowledge Al Ahliyya Amman University for funding this project.
Pharmacophore models generated by Receptor-ligand pharmacophore generation protocol embedded in Discovery Studio
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List of 30 compounds chosen for in-vitro assay
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Chemical structures of 8 highest in-vitro activity
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Chemical structures of 8 highest activity and MRK501 mapped against R1T1D2.5P6 pharmacophore
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Intermolecular interactions between the chemical compounds and the amino acids in the active site of (3F9M Protein)
Data type: docx