Computational analysis for selectivity of histone deacetylase inhibitor by replica-exchange umbrella sampling molecular dynamics simulations

In silico profiling of histone deacetylase inhibitory activity of compounds isolated from Cajanus cajan

Background

Cancer is responsible for high morbidity and mortality globally. Because the overexpression of histone deacetylases (HDACs) is one of the molecular mechanisms associated with the development and progression of some diseases such as cancer, studies are now considering inhibition of HDAC as a strategy for the treatment of cancer. In this study, a receptor-based in silico screening was exploited to identify potential HDAC inhibitors among the compounds isolated from Cajanus cajan, since reports have earlier confirmed the antiproliferative properties of compounds isolated from this plant.

Results

Cajanus cajan-derived phytochemicals were docked with selected HDACs, with givinostat as the reference HDAC inhibitor, using AutodockVina and Discovery Studio Visualizer, BIOVIA, 2020. Furthermore, absorption, distribution, metabolism and excretion (ADME) drug-likeness analysis was done using the Swiss online ADME web tool. From the results obtained, 4 compounds; betulinic acid, genistin, orientin and vitexin, were identified as potential inhibitors of the selected HDACs, while only 3 compounds (betulinic acid, genistin and vitexin) passed the filter of drug-likeness. The molecular dynamic result revealed the best level of flexibility on HDAC1 and HDAC3 compared to the wild-type HDACs and moderate flexibility of HDAC7 and HDAC8.

Conclusions

The results of molecular docking, pharmacokinetics and molecular dynamics revealed that betulinic acid might be a suitable HDAC inhibitor worthy of further investigation in order to be used for regulating conditions associated with overexpression of HDACs. This knowledge can be used to guide experimental investigation on Cajanus cajan-derived compounds as potential HDAC inhibitors.

Comparative QM/MM Molecular Dynamics and Umbrella Sampling Simulations: Interaction of the Zinc-Bound Intermediate Gem-Diolate Trapoxin A Inhibitor and Acetyl-l-lysine Substrate with Histone Deacetylase 8

Targeting the genetic material without destruction is a priority to develop safe anticancer drugs. Histone deacetylase 8 (HDAC8), which is proved to be involved in carcinogenesis, is an enzyme associated with the chromatin for post-translational deacetylation of acetylated lysine. In this study, HDAC8 co-crystallized with the intermediate state tetrapeptide Trapoxin A (TA) inhibitor and the holoenzyme are utilized to find their conformational ensembles. Furthermore, the co-crystallized intermediate gem-diolate TA was used to find optimum interactions with the active site residues by conventional molecular dynamics (MD) simulation and QM/MM umbrella sampling. Finally, the intermediate state of the acetyl-l-lysine substrate was explored by QM/MM steered MD and compared to the binding of the intermediate state of the inhibitor. This research showed that HDAC8 is flexible and exists in conformational ensembles in its holoenzyme state. Binding of the intermediate state TA stabilizes its conformation. The optimum binding to the active site of HDAC8 for structures of gem-diolate TA (intermediate state) and acetyl-l-lysine (intermediate state) was determined according to the corresponding energy profiles. The use of these models will aid in the design of potentially reversible, potent, and selective inhibitors of HDAC8 for cancer treatment.

Exploring the concerted mechanistic pathway for HIV-1 PR-substrate revealed by umbrella sampling simulation

HIV-1 protease (HIV-1 PR) is an essential enzyme for the replication process of its virus, and therefore considered an important target for the development of drugs against the acquired immunodeficiency syndrome (AIDS). Our previous study shows that the catalytic mechanism of subtype B/C-SA HIV-1 PR follows a one-step concerted acyclic hydrolysis reaction process using a two-layered ONIOM B3LYP/6-31++G(d,p) method. This present work is aimed at exploring the proposed mechanism of the proteolysis catalyzed by HIV-1 PR and to ensure our proposed mechanism is not an artefact of a single theoretical technique. Hence, we present umbrella sampling method that is suitable for calculating potential mean force (PMF) for non-covalent ligand/substrate-enzyme association/dissociation interactions which provide thermodynamic details for molecular recognition. The free activation energy results were computed in terms of PMF analysis within the hybrid QM(DFTB)/MM approach. The theoretical findings suggest that the proposed mechanism corresponds in principle with experimental data. Given our observations, we suggest that the QM/MM MD method can be used as a reliable computational technique to rationalize lead compounds against specific targets such as the HIV-1 protease.