Mechanistic insight into ligand binding to G-quadruplex DNA

Specific guanine-rich regions in human genome can form higher-order DNA structures called G-quadruplexes, which regulate many relevant biological processes. For instance, the formation of G-quadruplex at telomeres can alter cellular functions, inducing apoptosis. Thus, developing small molecules that are able to bind and stabilize the telomeric G-quadruplexes represents an attractive strategy for antitumor therapy. An example is 3-(benzo[d]thiazol-2-yl)-7-hydroxy-8-((4-(2-hydroxyethyl)piperazin-1-yl)methyl)-2H-chromen-2-one (compound 1), recently identified as potent ligand of the G-quadruplex [d(TGGGGT)]4 with promising in vitro antitumor activity. The experimental observations are suggestive of a complex binding mechanism that, despite efforts, has defied full characterization. Here, we provide through metadynamics simulations a comprehensive understanding of the binding mechanism of 1 to the G-quadruplex [d(TGGGGT)]4. In our calculations, the ligand explores all the available binding sites on the DNA structure and the free-energy landscape of the whole binding process is computed. We have thus disclosed a peculiar hopping binding mechanism whereas 1 is able to bind both to the groove and to the 3' end of the G-quadruplex. Our results fully explain the available experimental data, rendering our approach of great value for further ligand/DNA studie

Molecular View on the iRGD Peptide Binding Mechanism: Implications for Integrin Activity and Selectivity Profiles

Receptor-selective peptides are widely used as smart carriers for specific tumor-targeted delivery. A remarkable example is the cyclic nonapeptide iRGD (CRGDKPGDC, 1) that couples intrinsic cytotoxic effects with striking tumor-homing properties. These peculiar features are based on a rather complex multistep mechanism of action, where the primary event is the recognition of RGD integrins. Despite the high number of preclinical studies and the recent success of a phase I trial for the treatment of pancreatic ductal adenocarcinoma (PDAC), there is little information available about the iRGD three-dimensional (3D) structure and integrin binding properties. Here, we re-evaluate the peptide's affinity for cancer-related integrins including not only the previously known targets alpha v beta 3 and alpha v beta 5 but also the alpha v beta 6 isoform, which is known to drive cell growth, migration, and invasion in many malignancies including PDAC. Furthermore, we use parallel tempering in the well-tempered ensemble (PT-WTE) metadynamics simulations to characterize the in-solution conformation of iRGD and extensive molecular dynamics calculations to fully investigate its binding mechanism to integrin partners. Finally, we provide clues for fine-tuning the peptide's potency and selectivity profile, which, in turn, may further improve its tumor-homing properties

Broad-spectrum coronavirus 3C-like protease peptidomimetic inhibitors effectively block SARS-CoV-2 replication in cells: Design, synthesis, biological evaluation, and X-ray structure determination

Despite the approval of vaccines, monoclonal antibodies and restrictions during the pandemic, the demand for new efficacious and safe antivirals is compelling to boost the therapeutic arsenal against the COVID-19. The viral 3-chymotrypsin-like protease (3CLpro) is an essential enzyme for replication with high homology in the active site across CoVs and variants showing an almost unique specificity for Leu-Gln as P2–P1 residues, allowing the development of broad-spectrum inhibitors. The design, synthesis, biological activity, and cocrystal structural information of newly conceived peptidomimetic covalent reversible inhibitors are herein described. The inhibitors display an aldehyde warhead, a Gln mimetic at P1 and modified P2–P3 residues. Particularly, functionalized proline residues were inserted at P2 to stabilize the β-turn like bioactive conformation, modulating the affinity. The most potent compounds displayed low/sub-nM potency against the 3CLpro of SARS-CoV-2 and MERS-CoV and inhibited viral replication of three human CoVs, i.e. SARS-CoV-2, MERS-CoV, and HCoV 229 in different cell lines. Particularly, derivative 12 exhibited nM-low μM antiviral activity depending on the virus, and the highest selectivity index. Some compounds were co-crystallized with SARS-CoV-2 3CLpro validating our design. Altogether, these results foster future work toward broad-spectrum 3CLpro inhibitors to challenge CoVs related pandemics

Elective surgery cancellations due to the COVID-19 pandemic: global predictive modelling to inform surgical recovery plans.

BACKGROUND: The COVID-19 pandemic has disrupted routine hospital services globally. This study estimated the total number of adult elective operations that would be cancelled worldwide during the 12 weeks of peak disruption due to COVID-19. METHODS: A global expert response study was conducted to elicit projections for the proportion of elective surgery that would be cancelled or postponed during the 12 weeks of peak disruption. A Bayesian β-regression model was used to estimate 12-week cancellation rates for 190 countries. Elective surgical case-mix data, stratified by specialty and indication (surgery for cancer versus benign disease), were determined. This case mix was applied to country-level surgical volumes. The 12-week cancellation rates were then applied to these figures to calculate the total number of cancelled operations. RESULTS: The best estimate was that 28 404 603 operations would be cancelled or postponed during the peak 12 weeks of disruption due to COVID-19 (2 367 050 operations per week). Most would be operations for benign disease (90·2 per cent, 25 638 922 of 28 404 603). The overall 12-week cancellation rate would be 72·3 per cent. Globally, 81·7 per cent of operations for benign conditions (25 638 922 of 31 378 062), 37·7 per cent of cancer operations (2 324 070 of 6 162 311) and 25·4 per cent of elective caesarean sections (441 611 of 1 735 483) would be cancelled or postponed. If countries increased their normal surgical volume by 20 per cent after the pandemic, it would take a median of 45 weeks to clear the backlog of operations resulting from COVID-19 disruption. CONCLUSION: A very large number of operations will be cancelled or postponed owing to disruption caused by COVID-19. Governments should mitigate against this major burden on patients by developing recovery plans and implementing strategies to restore surgical activity safely

Mechanistic insight into ligand binding to G-quadruplex DNA

Specific guanine-rich regions in human genome can form higher-order DNA structures called G-quadruplexes, which regulate many relevant biological processes. For instance, the formation of G-quadruplex at telomeres can alter cellular functions, inducing apoptosis. Thus, developing small molecules that are able to bind and sta- bilize the telomeric G-quadruplexes represents an attractive strategy for antitumor therapy. An example is 3-(benzo[d]thiazol-2-yl)-7-hydroxy-8-((4- (2-hydroxyethyl)piperazin-1-yl)methyl)-2H-chromen- 2-one (compound 1), recently identified as potent ligand of the G-quadruplex [d(TGGGGT)]4 with promising in vitro antitumor activity. The experi- mental observations are suggestive of a complex binding mechanism that, despite efforts, has defied full characterization. Here, we provide through metadynamics simulations a comprehensive un- derstanding of the binding mechanism of 1 to the G-quadruplex [d(TGGGGT)]4 . In our calculations, the ligand explores all the available binding sites on the DNA structure and the free-energy landscape of the whole binding process is computed. We have thus disclosed a peculiar hopping binding mechanism whereas 1 is able to bind both to the groove and to the 3??? end of the G-quadruplex. Our results fully explain the available experimental data, rendering our approach of great value for further ligand/DNA studies

Ligand Binding to Telomeric DNA G-quadruplex through Metadynamics Calculations

Telomeres are DNA-proteins complexes which protect the ends of human chromosomes. Telomeric DNA consists of repetitive Guanine-rich (G-rich) sequences which can fold into unusual structural motifs termed G-quadruplexes (G4). In recent times, DNA G4 have emerged as promising targets in anticancer therapy since G4 ligands are able to promote apoptosis in tumor cells. Most of G4 binders are end-stackers whose clinical use is hampered by poor drug-like properties and weak selectivity. Such properties are instead improved in G4 groove binders. Among these, 3-benzothiazol-2-yl-7-hydroxy-8-{[4-(2-hydroxyethyl)piperazinyl]methyl}chrom-en-2-one has been identified as a potent groove binder of the G4 [d(TGGGGT)]4. Here we have set up a metadynamics-based protocol to disclose at molecular level the binding mechanism of this compound to the G4 [d(TGGGGT)]4. Our approach has allowed dealing with target flexibility and solvation during ligand binding and computing the binding free energy of the ligand/DNA G4 complex. Finally, once the binding free energy surface was converged, the lowest energy binding modes have been identified. Our computational protocol is of valuable help for future studies on ligand/DNA interaction and the development of new potent and selective DNA binders

Targeting SARS-CoV-2 Proteases and Polymerase for COVID-19 Treatment: State of the Art and Future Opportunities

The newly emerged coronavirus, called SARS-CoV-2, is the causing pathogen of pandemic COVID-19. The identification of drugs to treat COVID-19 and other coronavirus diseases is an urgent global need, thus different strategies targeting either virus or host cell are still under investigation. Direct-acting agents, targeting protease and polymerase functionalities, represent a milestone in antiviral therapy. The 3C-like (or Main) protease (3CLpro) and the nsp12 RNA-dependent RNA-polymerase (RdRp) are the best characterized SARS-CoV-2 targets and show the highest degree of conservation across coronaviruses fostering the identification of broad-spectrum inhibitors. Coronaviruses also possess a papain-like protease, another essential enzyme, still poorly characterized and not equally conserved, limiting the identification of broad-spectrum agents. Herein, we provide an exhaustive comparative analysis of SARS-CoV-2 proteases and RdRp with respect to other coronavirus homologues. Moreover, we highlight the most promising inhibitors of these proteins reported so far, including the possible strategies for their further development

Bioinformatics and Biosimulations as Toolbox for Peptides and Peptidomimetics Design: Where Are We?

Peptides and peptidomimetics are strongly re-emerging as amenable candidates in the development of therapeutic strategies against a plethora of pathologies. In particular, these molecules are extremely suitable to treat diseases in which a major role is played by protein–protein interactions (PPIs). Unlike small organic compounds, peptides display both a high degree of specificity avoiding secondary off-targets effects and a relatively low degree of toxicity. Further advantages are provided by the possibility to easily conjugate peptides to functionalized nanoparticles, so improving their delivery and cellular uptake. In many cases, such molecules need to assume a specific three-dimensional conformation that resembles the bioactive one of the endogenous ligand. To this end, chemical modifications are introduced in the polypeptide chain to constrain it in a well-defined conformation, and to improve the drug-like properties. In this context, a successful strategy for peptide/peptidomimetics design and optimization is to combine different computational approaches ranging from structural bioinformatics to atomistic simulations. Here, we review the computational tools for peptide design, highlighting their main features and differences, and discuss selected protocols, among the large number of methods available, used to assess and improve the stability of the functional folding of the peptides. Finally, we introduce the simulation techniques employed to predict the binding affinity of the designed peptides for their targets

Synthesis of new oxadiazole derivatives as potent and selective FXR antagonists

In this comunication was reported that the manipulation of the oxadiazole scaffold, modifying both substituents at C-3 and C-5, led to the synthesis of a small library of derivatives some of which characterized by a potent FXR antagonistic activity and promising pharmacokinetic properties

Structure-based drug design targeting the cell membrane receptor GPBAR1: exploiting the bile acid scaffold towards selective agonism

Bile acids can regulate nutrient metabolism through the activation of the cell membrane receptor GPBAR1 and the nuclear receptor FXR. Developing an exogenous control over these receptors represents an attractive strategy for the treatment of enterohepatic and metabolic disorders. A number of dual GPBAR1/FXR agonists are known, however their therapeutic use is limited by multiple unwanted effects due to activation of the diverse downstream signals controlled by the two receptors. On the other hand, designing selective GPBAR1 and FXR agonists is challenging since the two proteins share similar structural requisites for ligand binding. Here, taking advantage of our knowledge of the two targets, we have identified through a rational drug design study a series of amine lithocholic acid derivatives as selective GPBAR1 agonists. The presence of the 3α-NH2 group on the steroidal scaffold is responsible for the selectivity over FXR unveiling unprecedented structural insights into bile acid receptors activity modulation