Computational studies of darunavir into HIV-1 protease and DMPC bilayer: necessary conditions for effective binding and the role of the flaps

Structural and Synthetic Aspects of Small Ring Oxa- and Aza-Heterocyclic Ring Systems as Antiviral Activities

Antiviral properties of different oxa- and aza-heterocycles are identified and properly correlated with their structural features and discussed in this review article. The primary objective is to explore the activity of such ring systems as antiviral agents, as well as their synthetic routes and biological significance. Eventually, the structure-activity relationship (SAR) of the heterocyclic compounds, along with their salient characteristics are exhibited to build a suitable platform for medicinal chemists and biotechnologists. The synergistic conclusions are extremely important for the introduction of a newer tool for the future drug discovery program.

Molecular simulations of fluoxetine in hydrated lipid bilayers, as well as in aqueous solutions containing β-cyclodextrin

Fluoxetine, which is a well-known antidepressant drug, is studied in hydrated cholesterol-free and cholesterol-containing lipid bilayers through unbiased and biased atomistic molecular dynamics simulations. The latter are conducted for the calculation of the potential of mean force (PMF) of fluoxetine along an axis perpendicular to the two leaflets of the bilayer. The PMF indicates that the drug prefers to reside inside the lipid phase and allows us to calculate important thermodynamic properties, such as the Gibbs energy difference of partitioning from the water to the lipid phase and the Gibbs energy barrier for hopping events between the two leaflets of the bilayer. The results from the biased simulations are in accord with the mass density profiles calculated from the unbiased simulations. Moreover, we estimate the effect of fluoxetine mole fraction on the order parameters of the lipid alkyl chains and on the area per lipid. It is also found that fluoxetine forms a hydrogen bond network with lipids and water molecules penetrating into the lipid phase. In addition, fluoxoetine is studied in detail in aqueous solutions containing β-cyclodextrin. It is observed from unbiased molecular dynamics simulations that the two aforementioned molecules form a noncovalent complex spontaneously and the calculated binding free energy is in agreement with the literature.

Identification of 1H-purine-2,6-dione derivative as a potential SARS-CoV-2 main protease inhibitor: molecular docking, dynamic simulations, and energy calculations

The rapid spread of the coronavirus since its first appearance in 2019 has taken the world by surprise, challenging the global economy, and putting pressure on healthcare systems across the world. The introduction of preventive vaccines only managed to slow the rising death rates worldwide, illuminating the pressing need for developing effective antiviral therapeutics. The traditional route of drug discovery has been known to require years which the world does not currently have. In silico approaches in drug design have shown promising results over the last decade, helping to decrease the required time for drug development. One of the vital non-structural proteins that are essential to viral replication and transcription is the SARS-CoV-2 main protease (Mpro). Herein, using a test set of recently identified COVID-19 inhibitors, a pharmacophore was developed to screen 20 million drug-like compounds obtained from a freely accessible Zinc database. The generated hits were ranked using a structure based virtual screening technique (SBVS), and the top hits were subjected to in-depth molecular docking studies and MM-GBSA calculations over SARS-COV-2 Mpro. Finally, the most promising hit, compound (1), and the potent standard (III) were subjected to 100 ns molecular dynamics (MD) simulations and in silico ADME study. The result of the MD analysis as well as the in silico pharmacokinetic study reveal compound 1 to be a promising SARS-Cov-2 MPro inhibitor suitable for further development.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

In silico study of levodopa in hydrated lipid bilayers at the atomistic level

This article presents atomistic molecular dynamics and umbrella sampling simulations of levodopa at various concentrations in hydrated cholesterol-free 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol-containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers. Levodopa is the standard medication for Parkinson's disease and is marketed under various trade names; in the context of this article, the levodopa molecule is mostly studied in its zwitterionic form but some results concerning the neutral levodopa are presented as well for comparison purposes. The motivation is to study in detail how levodopa behaves in different hydrated lipid membranes, primarily from the thermodynamic point of view, and reveal aspects of mechanism of its permeation through them. Dependencies of properties on the levodopa concentration are also investigated. Special attention is paid to the calculation of mass density profiles, order parameters and self-diffusion coefficients. Levodopa zwitterions, which form a hydrogen bond network with water and phospholipid molecules, are found to be preferentially located at the water/lipid interface, as well as in the aqueous phase surrounding the cholesterol-free and cholesterol-containing bilayers. This is concluded from the potentials of mean force calculated by umbrella sampling simulations as levodopa is transferred from the lipid to the aqueous phase along an axis perpendicular to the two leaflets of the membranes.

A Novel Ultra Performance Liquid Chromatography-PDA Method Development and Validation for Darunavir in Bulk and Its Application to Marketed Dosage Form

Aims and Objective:

The aim of this study was to develop and validate a novel ultra-performance liquid chromatographic method for estimation of darunavir in a bulk and tablet dosage form.

Materials and Methods:

The chromatographic separation was achieved using DIKMA Endoversil (2.1mm x 50mm, 1.7 µm) column. A mixture of 40% buffer (0.1% octa sulfonic acid) and 60% acetonitrile was used as a mobile phase with the isocratic elution mode and eluent was monitored at 281nm using UV detector. The method was continued and validated in accordance with International Conference on Harmonization Guidelines. Validation study revealed the specificity and reliability of the method.

Results:

In this method, darunavir was eluted with retention time of 0.516 min. Calibration curve plots were found linear over the concentration ranges 10–50 μg/mL for darunavir. Limit of detection was 0.02 μg/mL and limit of quantification was found 0.07 μg/mL. The present method was also found stable in force degradation study.

Conclusion:

The empirical evidences of all the study results revealed the suitability of the estimation of darunavir in bulk and tablet dosage form without any interference from the excipients.

Covid-19 Pandemic and Current Medical Interventions

First humanoid coronavirus was discovered in the middle of 1960s, the class of viruses are considered to be a huge threat. The first onset of human coronavirus, SARS (SARS-CoV) appeared in 2003 which spanned five continents having lethal effects on human population accompanied by The Middle East Respiratory Syndrome Coronavirus in 2012 with a death rate of 35%. The viruses remain a threat till date and are of serious concern since no vaccine or specified drug therapy has been approbated for treating human coronaviruses. The viruses became a pandemic worldwide with the emergence of Wuhan coronavirus (2019-nCoV). SARS-CoV2 viral manifestation poses a serious human life risk by causing acute lung injury and various respiratory outcomes and has become a global concern. High pathogenicity and transmission rate of the viral strain has become the spotlight of research community throughout the world. With the ongoing studies on viral structure and host interactions, the intricacy of the viral proteome structure and replication cycle proposes a need to explore our understanding of host factors playing role in viral multiplication cycle. This review provides insight into our prevalent perception of coronavirus-host interactions, structure of SARS-CoV2, receptor mediated entry of virus inside the human cells, ongoing clinical trials, drug therapies and treatments that are being used to combat COVID-19 targeting viral fusion, replication and its multiplication.

Possible therapeutic agents for COVID-19: a comprehensive review

INTRODUCTION

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has emerged in China. There are no available vaccines or antiviral drugs for COVID-19 patients. Herein, we represented possible therapeutic agents that may stand as a potential therapy against COVID-19.

AREAS COVERED

We searched PubMed, Google Scholar, and clinicaltrials.gov for relevant papers. We showed some agents with potentially favorable efficacy, acceptable safety as well as good pharmacokinetic profiles. Several therapies are under assessment to evaluate their efficacy and safety for COVID-19. However, some drugs were withdrawn due to their side effects after demonstrating some clinical efficacy. Indeed, the most effective therapies could be organ function support, convalescent plasma, anticoagulants, and immune as well as antiviral therapies, especially anti-influenza drugs due to the similarities between respiratory viruses regarding viral entry, uncoating, and replication. We encourage giving more attention to favipiravir, remdesivir, and measles vaccine.

EXPERT OPINION

A combination, at least dual or even triple therapy, of the aforementioned efficacious and safe therapies is greatly recommended for COVID-19. Further, patients should have a routine assessment for their coagulation and bleeding profiles as well as their inflammatory and cytokine concentrations.

The Human Coronavirus Disease COVID-19: Its Origin, Characteristics, and Insights into Potential Drugs and Its Mechanisms

The emerging coronavirus disease (COVID-19) swept across the world, affecting more than 200 countries and territories. Genomic analysis suggests that the COVID-19 virus originated in bats and transmitted to humans through unknown intermediate hosts in the Wuhan seafood market, China, in December of 2019. This virus belongs to the Betacoronavirus group, the same group of the 2003 severe acute respiratory syndrome coronavirus (SARS-CoV), and for the similarity, it was named SARS-CoV-2. Given the lack of registered clinical therapies or vaccines, many physicians and scientists are investigating previously used clinical drugs for COVID-19 treatment. In this review, we aim to provide an overview of the CoVs origin, pathogenicity, and genomic structure, with a focus on SARS-CoV-2. Besides, we summarize the recently investigated drugs that constitute an option for COVID-19 treatment.

Interactive molecular dynamics in virtual reality for accurate flexible protein-ligand docking

Simulating drug binding and unbinding is a challenge, as the rugged energy landscapes that separate bound and unbound states require extensive sampling that consumes significant computational resources. Here, we describe the use of interactive molecular dynamics in virtual reality (iMD-VR) as an accurate low-cost strategy for flexible protein-ligand docking. We outline an experimental protocol which enables expert iMD-VR users to guide ligands into and out of the binding pockets of trypsin, neuraminidase, and HIV-1 protease, and recreate their respective crystallographic protein-ligand binding poses within 5-10 minutes. Following a brief training phase, our studies shown that iMD-VR novices were able to generate unbinding and rebinding pathways on similar timescales as iMD-VR experts, with the majority able to recover binding poses within 2.15 Å RMSD of the crystallographic binding pose. These results indicate that iMD-VR affords sufficient control for users to carry out the detailed atomic manipulations required to dock flexible ligands into dynamic enzyme active sites and recover crystallographic poses, offering an interesting new approach for simulating drug docking and generating binding hypotheses.

Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance

Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.

Structural Adaptation of Darunavir Analogues against Primary Mutations in HIV-1 Protease

HIV-1 protease is one of the prime targets of agents used in antiretroviral therapy against HIV. However, under selective pressure of protease inhibitors, primary mutations at the active site weaken inhibitor binding to confer resistance. Darunavir (DRV) is the most potent HIV-1 protease inhibitor in clinic; resistance is limited, as DRV fits well within the substrate envelope. Nevertheless, resistance is observed due to hydrophobic changes at residues including I50, V82, and I84 that line the S1/S1' pocket within the active site. Through enzyme inhibition assays and a series of 12 crystal structures, we interrogated susceptibility of DRV and two potent analogues to primary S1' mutations. The analogues had modifications at the hydrophobic P1' moiety compared to DRV to better occupy the unexploited space in the S1' pocket where the primary mutations were located. Considerable losses of potency were observed against protease variants with I84V and I50V mutations for all three inhibitors. The crystal structures revealed an unexpected conformational change in the flap region of I50V protease bound to the analogue with the largest P1' moiety, indicating interdependency between the S1' subsite and the flap region. Collective analysis of protease-inhibitor interactions in the crystal structures using principle component analysis was able to distinguish inhibitor identity and relative potency solely based on van der Waals contacts. Our results reveal the complexity of the interplay between inhibitor P1' moiety and S1' mutations and validate principle component analyses as a useful tool for distinguishing resistance and inhibitor potency.

Discovery of HIV Type 1 Aspartic Protease Hit Compounds through Combined Computational Approaches

A combination of computational techniques and inhibition assay experiments was employed to identify hit compounds from commercial libraries with enhanced inhibitory potency against HIV type 1 aspartic protease (HIV PR). Extensive virtual screening with the aid of reliable pharmacophore models yielded five candidate protease inhibitors. Subsequent molecular dynamics and molecular mechanics Poisson-Boltzmann surface area free-energy calculations for the five ligand-HIV PR complexes suggested a high stability of the systems through hydrogen-bond interactions between the ligands and the protease's flaps (Ile50/50'), as well as interactions with residues of the active site (Asp25/25'/29/29'/30/30'). Binding-energy calculations for the three most promising compounds yielded values between -5 and -10 kcal mol(-1) and suggested that van der Waals interactions contribute most favorably to the total energy. The predicted binding-energy values were verified by in vitro inhibition assays, which showed promising results in the high nanomolar range. These results provide structural considerations that may guide further hit-to-lead optimization toward improved anti-HIV drugs.

Development and validation of a selective, sensitive and stability indicating UPLC-MS/MS method for rapid, simultaneous determination of six process related impurities in darunavir drug substance

In this study a sensitive and selective gradient reverse phase UPLC-MS/MS method was developed for the simultaneous determination of six process related impurities viz., Imp-I, Imp-II, Imp-III, Imp-IV, Imp-V and Imp-VI in darunavir. The chromatographic separation was performed on Acquity UPLC BEH C18 (50 mm×2.1mm, 1.7μm) column using gradient elution of acetonitrile-methanol (80:20, v/v) and 5.0mM ammonium acetate containing 0.01% formic acid at a flow rate of 0.4mL/min. Both negative and positive electrospray ionization (ESI) modes were operated simultaneously using multiple reaction monitoring (MRM) for the quantification of all six impurities in darunavir. The developed method was fully validated following ICH guidelines with respect to specificity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, precision, robustness and sample solution stability. The method was able to quantitate Imp-I, Imp-IV, Imp-V at 0.3ppm and Imp-II, Imp-III, and Imp-VI at 0.2ppm with respect to 5.0mg/mL of darunavir. The calibration curves showed good linearity over the concentration range of LOQ to 250% for all six impurities. The correlation coefficient obtained was >0.9989 in all the cases. The accuracy of the method lies between 89.90% and 104.60% for all six impurities. Finally, the method has been successfully applied for three formulation batches of darunavir to determine the above mentioned impurities, however no impurity was found beyond the LOQ. This method is a good quality control tool for the trace level quantification of six process related impurities in darunavir during its synthesis.

A Comprehensive Computational Study of the Interaction between Human Serum Albumin and Fullerenes

Human serum albumin (HSA) is the most abundant blood plasma protein, which transports fatty acids, hormones, and drugs. We consider nanoparticle-HSA interactions by investigating the binding of HSA with three fullerene analogs. Long MD simulations, quantum mechanical (fragment molecular orbital, energy decomposition analysis, atoms-in-molecules), and free energy methods elucidated the binding mechanism in these complexes. Such a systematic study is valuable due to the lack of comprehensive theoretical approaches to date. The main elements of the mechanism include the following: binding to IIA site results in allosteric modulation of the IIIA and heme binding sites with an increase in α-helical structure of IIIA. Fullerenes displayed high binding affinities for HSA; therefore, HSA can be used as a fullerene carrier, facilitating any toxic function the fullerene may exert. Complex formation is driven by hydrogen bonding, van der Waals, nonpolar, charge transfer, and dispersion energy contributions. Proper functionalization of C60 has enhanced its binding to HSA by more than an order of magnitude. This feature may be important for biological applications (e.g., photodynamic therapy of cancer). Satisfactory agreement with relevant experimental and theoretical data has been obtained.

The impact of molecular dynamics on drug design: applications for the characterization of ligand-macromolecule complexes

Among all tools available to design new drugs, molecular dynamics (MD) simulations have become an essential technique. Initially developed to investigate molecular models with a limited number of atoms, computers now enable investigations of large macromolecular systems with a simulation time reaching the microsecond range. The reviewed articles cover four years of research to give an overview on the actual impact of MD on the current medicinal chemistry landscape with a particular emphasis on studies of ligand-protein interactions. With a special focus on studies combining computational approaches with data gained from other techniques, this review shows how deeply embedded MD simulations are in drug design strategies and articulates what the future of this technique could be.

Exploring the drug resistance of V32I and M46L mutant HIV-1 protease to inhibitor TMC114: flap dynamics and binding mechanism

Inhibitors of HIV-1 protease (HIV-1-pr) generally only bind to the active site of the protease. However, for some mutants such as V32I and M46L the TMC114 can bind not only to the active cavity but also to the groove of the flexible flaps. Although the second binding site suggests the higher efficiency of the drug against HIV-1-pr, the drug resistance in HIV-1-pr due to mutations cannot be ignored, which prompts us to investigate the molecular mechanisms of drug resistance and behavior of double bound TMC114 (2T) to HIV-1-pr. The conformational dynamics of HIV-1-pr and the binding of TMC114 to the WT, V32I and M46L mutants were investigated with all-atom molecular dynamic (MD) simulation. The 20 ns MD simulation shows many fascinating effects of the inhibitor binding to the WT and mutant proteases. MM-PBSA calculations explain the binding free energies unfavorable for the M46L and V32I mutants as compared to the WT. For the single binding (1T) the less binding affinity can be attributed to the entropic loss for both V32I-1T and M46L-1T. Although the second binding of TMC114 with flap does increase binding energy for the mutants (V32I-2T and M46L-2T), the considerable entropy loss results in the lower binding Gibbs free energies. Thus, binding of TMC114 in the flap region does not help much in the total gain in binding affinity of the system, which was verified from this study and thereby validating experiments.

Systematic molecular dynamics, MM-PBSA, and ab initio approaches to the saquinavir resistance mechanism in HIV-1 PR due to 11 double and multiple mutations

Mutations in the human immunodeficiency virus (HIV) enable virus replication even when appropriate antiretroviral therapy is followed, thus leading to the emergence of drug resistance. In a previous work, we systematically examined seven single mutations that are associated with saquinavir (SQV) resistance in HIV-1 protease (Tzoupis, H.; Leonis, G.; Mavromoustakos, T.; Papadopoulos, M. G. J. Chem. Theory Comput. 2013, 9, 1754-1764). Herein, we extend our analysis, which includes seven double (G48V-V82A, L10I-G48V, G48V-L90M, I84V-L90M, L10I-V82A, L10I-L63P, A71V-G73S) and four multiple (L10I-L63P-A71V, L10I-G48V-V82A, G73S-I84V-L90M, L10I-L63P-A71V-G73S-I84V-L90M) SQV-HIV-1 PR mutant complexes, in an attempt to generalize our findings and formulate the main elements of the SQV resistance mechanism in the protease. On the basis of molecular dynamics (MD), molecular mechanics Poisson-Boltzmann surface area (MM-PBSA), and ab initio computational approaches, we identified specific features that constitute the HIV-1 PR mechanism of resistance at the molecular level: the low flexibility of SQV in the binding cavity and the preservation of hydrogen bonding (HB) and van der Waals interactions between SQV and several active-site (Gly27/27', Asp29/29'/30/30', especially Asp25/25') and flap (Ile50/50', Gly48/48') residues of the protease contribute significantly to efficient binding. The total enthalpy loss in all mutants is mostly due to the loss in enthalpy of the active-site region. Furthermore, it was observed that mutation accumulation may induce stabilization to SQV and to the flaps through enhanced HB interactions that lead to improved inhibition (e.g., accumulation of mutations in complexes containing L10I, G48V, L63P, I84V, or L90M single mutations). It was also concluded that permanent flap closure is obtained independently of mutations and SQV binding is mostly driven by van der Waals, nonpolar, and exchange-energy contributions. Importantly, it was indicated that the optimal positioning of SQV and the structure of the binding cavity are tightly coupled, since small changes in geometry may affect the binding energy greatly. The results of our theoretical approaches are in agreement with experimental evidence and provide a reliable description of SQV resistance in HIV-1 PR.