The rapid outbreak of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China followed by its spread around the world poses a serious global concern for public health. To this date, no specific drugs or vaccines are available to treat SARS-CoV-2 despite its close relation to the SARS-CoV virus that caused a similar epidemic in 2003. Thus, there remains an urgent need for the identification and development of specific antiviral therapeutics against SARS-CoV-2. To conquer viral infections, the inhibition of proteases essential for proteolytic processing of viral polyproteins is a conventional therapeutic strategy. In order to find novel inhibitors, we computationally screened a compound library of over 606 million compounds for binding at the recently solved crystal structure of the main protease (M^pro) of SARS-CoV-2. A screening of such a vast chemical space for SARS-CoV-2 M^pro inhibitors has not been reported before. After shape screening, two docking protocols were applied followed by the determination of molecular descriptors relevant for pharmacokinetics to narrow down the number of initial hits. Next, molecular dynamics simulations were conducted to validate the stability of docked binding modes and comprehensively quantify ligand binding energies. After evaluation of potential off-target binding, we report a list of 12 purchasable compounds, with binding affinity to the target protease that is predicted to be more favorable than that of the cocrystallized peptidomimetic compound. In order to quickly advise ongoing therapeutic intervention for patients, we evaluated approved antiviral drugs and other protease inhibitors to provide a list of nine compounds for drug repurposing. Furthermore, we identified the natural compounds (−)-taxifolin and rhamnetin as potential inhibitors of M^pro. Rhamnetin is already commercially available in pharmacies.

Oxidative reactions catalyzed by Cytochrome P450 enzymes (CYPs), which constitute the most relevant group of drug-metabolizing enzymes, are enabled by their redox partner Cytochrome P450 reductase (CPR). Both proteins are anchored to the membrane of the endoplasmic reticulum and the CPR undergoes a conformational change in order to interact with the respective CYP and transfer electrons. Here, we conducted over 22 microseconds of molecular dynamics (MD) simulations in combination with protein–protein docking to investigate the conformational changes necessary for the formation of the CPR–CYP complex. While some structural features of the CPR and the CPR–CYP2D6 complex that we highlighted confirmed previous observations, our simulations revealed additional mechanisms for the conformational transition of the CPR. Unbiased simulations exposed a movement of the whole protein relative to the membrane, potentially to facilitate interactions with its diverse set of redox partners. Further, we present a structural mechanism for the susceptibility of the CPR to different redox states based on the flip of a glycine residue disrupting the local interaction network that maintains inter-domain proximity. Simulations of the CPR–CYP2D6 complex pointed toward an additional interaction surface of the FAD domain and the proximal side of CYP2D6. Altogether, this study provides novel structural insight into the mechanism of CPR–CYP interactions and underlying conformational changes, improving our understanding of this complex machinery relevant for drug metabolism.

The rapid outbreak of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China followed by its spread around the world poses a serious global concern for public health with almost 90000 people infected and thousands of fatalities. To conquer viral infections, the inhibition of proteases essential for proteolytic processing of viral polyproteins is a conventional therapeutic strategy. To this date, no specific drugs or vaccines are available to treat SARS-CoV-2 despite its close relation to the SARS-CoV-1 virus that caused a similar epidemic in 2003. Thus, there remains an urgent need for the development of specific antiviral therapeutics to conquer SARS-CoV-2. In order to find novel inhibitors, we computationally screened a compound library of over 687 million compounds for binding at the recently solved crystal structure of the main protease of SARS-CoV-2. A screening of such a vast chemical space for SARS-CoV-2 protease inhibitors has not been reported before. After shape screening, two docking protocols were applied followed by the determination of pharmacokinetically relevant molecular descriptors to narrow down the initial hits. Next, molecular dynamics simulations were conducted to validate the stability of docked binding modes and comprehensively quantify ligand binding energies. After evaluation of off-target binding, we report a list of 11 drug-like compounds with improved binding free energy to the target protease in contrast to the cocrystallized peptidomimetic lead compound that suffers from poor pharmacokinetic properties. Furthermore, we identified one potent binder with comparable properties from the natural compound library.

The rapid outbreak of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in China followed by its spread around the world poses a serious global concern for public health with almost 90000 people infected and thousands of fatalities. To conquer viral infections, the inhibition of proteases essential for proteolytic processing of viral polyproteins is a conventional therapeutic strategy. To this date, no specific drugs or vaccines are available to treat SARS-CoV-2 despite its close relation to the SARS-CoV-1 virus that caused a similar epidemic in 2003. Thus, there remains an urgent need for the development of specific antiviral therapeutics to conquer SARS-CoV-2. In order to find novel inhibitors, we computationally screened a compound library of over 687 million compounds for binding at the recently solved crystal structure of the main protease of SARS-CoV-2. A screening of such a vast chemical space for SARS-CoV-2 protease inhibitors has not been reported before. After shape screening, two docking protocols were applied followed by the determination of pharmacokinetically relevant molecular descriptors to narrow down the initial hits. Next, molecular dynamics simulations were conducted to validate the stability of docked binding modes and comprehensively quantify ligand binding energies. After evaluation of off-target binding, we report a list of 11 drug-like compounds with improved binding free energy to the target protease in contrast to the cocrystallized peptidomimetic lead compound that suffers from poor pharmacokinetic properties. Furthermore, we identified one potent binder with comparable properties from the natural compound library.

Pre-clinical studies suggest that extracts prepared from the fruits of Vitex agnus castus (VAC) interact with dopamine D2 receptors, leading to reduced prolactin secretion. In previous experiments, dopaminergic activity was mostly evaluated using radioligand binding assays or via the inhibition of prolactin release from rat pituitary cells. Diterpenes featuring a clerodadienol scaffold were identified as major active compounds, but no conclusive data regarding their potency and intrinsic activity are available. Utilising advances in chromatography, we re-examined this topic using HPLC-based tracking of bioactivity via microfractionation of the VAC extract Ze 440. Using a cAMP-based assay, we measured dopaminergic activity in CHO-K1 cells that overexpress the human D2 receptor. Six diterpenes were isolated from two active HPLC microfractions. Viteagnusin I emerged as the most potent diterpene (EC₅₀: 6.6 µM), followed by rotundifuran (EC₅₀: 12.8 µM), whereas vitexilactone was inactive (EC₅₀: >50 µM). Interestingly, triterpenes were also identified as active, with 3-epi-maslinic acid being the most active compound (EC₅₀: 5.1 µM). To better understand these interactions at the molecular level, selected diterpenes and triterpenes were analysed through molecular docking against D2 receptor structures. Our data show that the dopaminergic activity of VAC diterpenes seems to depend on the configuration and on ring substitution in the side chain. This study also highlights for the first time the dopaminergic contribution of triterpenes such as 3-epi-maslinic acid.

The pandemic of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) poses a serious global health threat. Since no specific therapeutics are available, researchers around the world screened compounds to inhibit various molecular targets of SARS-CoV-2 including its main protease (M^pro) essential for viral replication. Due to the high urgency of these discovery efforts, off-target binding, which is one of the major reasons for drug-induced toxicity and safety-related drug attrition, was neglected. Here, we used molecular docking, toxicity profiling, and multiple molecular dynamics (MD) protocols to assess the selectivity of 33 reported non-covalent inhibitors of SARS-CoV-2 M^pro against eight proteases and 16 anti-targets. The panel of proteases included SARS-CoV M^pro, cathepsin G, caspase-3, ubiquitin carboxy-terminal hydrolase L1 (UCHL1), thrombin, factor Xa, chymase, and prostasin. Several of the assessed compounds presented considerable off-target binding towards the panel of proteases, as well as the selected anti-targets. Our results further suggest a high risk of off-target binding to chymase and cathepsin G. Thus, in future discovery projects, experimental selectivity assessment should be directed toward these proteases. A systematic selectivity assessment of SARS-CoV-2 M^pro inhibitors, as we report it, was not previously conducted.