Changes in the chikungunya virus E1 glycoprotein domain II and hinge influence E2 conformation, infectivity, and virus-receptor interactions.

In a previous study to understand how the chikungunya virus (CHIKV) E1 glycoprotein ß-strand c functions, we identified several attenuating variants at E1 residue V80 and the emergence of second-site mutations in the fusion loop (E1-M88L) and hinge region (E1-N20Y) with the V80 variants in vivo. The emergence of these mutations led us to question how changes in E1 may contribute to CHIKV infection at the molecular level. Here, we use molecular dynamics to understand how changes in the E1 glycoprotein may influence the CHIKV glycoprotein E1-E2 complex. We found that E1 domain II variants lead to E2 conformational changes, allowing us to hypothesize that emerging variants E1-M88L and E1-N20Y could also change E2 conformation and function. We characterized CHIKV E1-M88L and E1-N20Y in vitro and in vivo to understand how these regions of the E1 glycoprotein contribute to host-specific infection. We found that CHIKV E1-N20Y enhanced infectivity in mosquito cells, while the CHIKV E1-M88L variant enhanced infectivity in both BHK-21 and C6/36 cells and led to changes in viral cholesterol-dependence. Moreover, we found that E1-M88L and E1-N20Y changed E2 conformation, heparin binding, and interactions with the receptor Mxra8. Interestingly, the CHIKV E1-M88L variant increased replication in Mxra8-deficient mice compared to WT CHIKV, yet was attenuated in mouse fibroblasts, suggesting that residue E1-M88 may function in a cell-type-dependent entry. Taken together, these studies show that key residues in the CHIKV E1 domain II and hinge region function through changes in E1-E2 dynamics to facilitate cell- and host-dependent entry.IMPORTANCEArboviruses are significant global public health threats, and their continued emergence around the world highlights the need to understand how these viruses replicate at the molecular level. The alphavirus glycoproteins are critical for virus entry in mosquitoes and mammals, yet how these proteins function is not completely understood. Therefore, it is critical to dissect how distinct glycoprotein domains function in vitro and in vivo to address these gaps in our knowledge. Here, we show that changes in the CHIKV E1 domain II and hinge alter E2 conformations leading to changes in virus-receptor and -glycosaminoglycan interactions and cell-specific infection. These results highlight that adaptive changes in E1 can have a major effect on virus attachment and entry, furthering our knowledge of how alphaviruses infect mammals and insects.

Challenges and approaches in the discovery of human immunodeficiency virus type-1 non-nucleoside reverse transcriptase inhibitors.

The type I human immunodeficiency virus (HIV-1) pandemic affecting over 37 million people worldwide continues, with 1.8 million people newly infected each year. Highly active antiretroviral therapy is efficient at reducing viral load and nearly one-half of the infected population is on treatment. One of the most successful approaches for the treatment of HIV infections is the use of inhibitors for human immunodeficiency virus type-1 reverse transcriptase (HIV-1 RT). At present, there are six nonnucleoside reverse transcriptase inhibitors (NNRTIs) approved for clinical use: nevirapine (NVP), delavirdine (DLV), efavirenz (EFV), etravirine (ETV), rilpivirine (RPV), and elsulfavirine. In this review, we will cover the development of different classes of NNRTIs over the last two decades. We will give an overview of traditional medicinal chemistry strategies for structural modification as bioisosterism principles, scaffold hopping, substitute decoration, and molecular hybridization. Furthermore, computer-aid design as virtual screening, de novo design and free-energy perturbation will be described in details.

Identification of potent bovine viral diarrhea virus inhibitors by a structure-based virtual screening approach.

Bovine viral diarrhea virus (BVDV) is a pestivirus whose infection in cattle is globally distributed. The use of antivirals could complement vaccination as a tool of control and reduce economic losses. The RNA-dependent RNA polymerase (RdRp) of the virus is essential for its genome replication and constitutes an attractive target for the identification of antivirals. With the aim of obtaining selective BVDV inhibitors, the crystal structure of BVDV RdRp was used to perform a virtual screening. Approximately 15,000 small molecules from commercial and in-house databases were evaluated and several structurally different compounds were tested in vitro for antiviral activity. Interestingly, of twelve evaluated compounds, five were active and displayed EC50 values in the sub and low-micromolar range. Time of drug addition experiment and measured intracellular BVDV RNA showed that compound 7 act during RNA synthesis. Molecular Dynamics and MM/PBSA calculation were done to characterize the interaction of the most active compounds with RdRp, which will allow future ligand optimization. These studies highlight the use of in silico screening to identify a new class of BVDV inhibitors.

The chikungunya virus E1 glycoprotein fusion loop and hinge alter glycoprotein dynamics leading to cell and host specific changes in infectivity.

Alphaviruses infect both mammals and insects, yet the distinct mechanisms that alphaviruses use to infect different hosts are not well defined. In this study, we characterize CHIKV E1 variants in the fusion loop (E1-M88L) and hinge region (E1-N20Y) in vitro and in vivo to understand how these regions of the E1 glycoprotein contribute to host-specific infection. Through cell culture assays, we found that CHIKV E1-N20Y enhanced infectivity in mosquito cells while the CHIKV E1-M88L variant enhanced virus binding and infectivity in both BHK-21 and C6/36 cells, and led to changes in the virus cholesterol-dependence in BHK-21 cells. Given these in vitro results and that residue E1-M88L is in a defined Mxra8 interacting domain, we hypothesized that this residue may be important for receptor usage. However, while the CHIKV E1-M88L variant increased replication in Mxra8-deficient mice compared to WT CHIKV, it was attenuated in vitro in mouse fibroblasts, suggesting that residue E1-M88 may function in a cell-type dependent manner to alter entry. Finally, using molecular dynamics to understand how potential changes in the E1 glycoprotein may impact the CHIKV glycoprotein E1-E2 complex, we found that E1-M88L and other E1 domain II variants lead to changes in both E1 and E2 dynamics. Taken together, these studies show that key residues in the CHIKV E1 fusion loop and hinge region function through changes in E1-E2 dynamics to facilitate cell- and host-dependent entry. Importance: Arthropod-borne viruses (arboviruses) are significant global public health threats, and their continued emergence around the world highlights the need to understand how these viruses replicate at the molecular level. The alphavirus class II glycoproteins are critical for virus entry in mosquitoes and mammals, yet how these proteins function is not completely understood. Therefore, to address these gaps in our knowledge, it is critical to dissect how distinct glycoprotein domains function in vitro and in vivo . Here, we show that changes in the CHIKV E1 fusion loop and hinge contribute to host-specific entry and E1-E2 dynamics, furthering our knowledge of how alphaviruses infect mammals and insects.

Discovery of a Potent and Selective Chikungunya Virus Envelope Protein Inhibitor through Computer-Aided Drug Design.

The worldwide expansion of chikungunya virus (CHIKV) into tropical and subtropical areas in the last 15 years has posed a currently unmet need for vaccines and therapeutics. The E2-E1 envelope glycoprotein complex binds receptors on the host cell and promotes membrane fusion during CHIKV entry, thus constituting an attractive target for the development of antiviral drugs. In order to identify CHIKV antivirals acting through inhibition of the envelope glycoprotein complex function, our first approach was to search for amenable druggable sites within the E2-E1 heterodimer. We identified a pocket located in the interface between E2 and E1 around the fusion loop. Then, via a structure-based virtual screening approach and in vitro assay of antiviral activity, we identified compound 7 as a specific inhibitor of CHIKV. Through a lead optimization process, we obtained compound 11 that demonstrated increased antiviral activity and low cytotoxicity (EC50 1.6 µM, CC50 56.0 µM). Molecular dynamics simulations were carried out and described a possible interaction pattern of compound 11 and the E1-E2 dimer that could be useful for further optimization. As expected from target site selection, compound 11 inhibited virus internalization during CHIKV entry. In addition, virus populations resistant to compound 11 included mutation E2-P173S, which mapped to the proposed binding pocket, and second site mutation E1-Y24H. Construction of recombinant viruses showed that these mutations conferred antiviral resistance in the parental background. Finally, compound 11 presents acceptable solubility values and is chemically and enzymatically stable in different media. Altogether, these findings uncover a suitable pocket for the design of CHIKV entry inhibitors with promising antiviral activity and pharmacological profiles.

Design and Optimization of Quinazoline Derivatives: New Non-nucleoside Inhibitors of Bovine Viral Diarrhea Virus.

Bovine viral diarrhea virus (BVDV) belongs to the Pestivirus genus (Flaviviridae). In spite of the availability of vaccines, the virus is still causing substantial financial losses to the livestock industry. In this context, the use of antiviral agents could be an alternative strategy to control and reduce viral infections. The viral RNA-dependent RNA polymerase (RdRp) is essential for the replication of the viral genome and constitutes an attractive target for the identification of antiviral compounds. In a previous work, we have identified potential molecules that dock into an allosteric binding pocket of BVDV RdRp via a structure-based virtual screening approach. One of them, N-(2-morpholinoethyl)-2-phenylquinazolin-4-amine [1, 50% effective concentration (EC50) = 9.7 ± 0.5 µM], was selected to perform different chemical modifications. Among 24 derivatives synthesized, eight of them showed considerable antiviral activity. Molecular modeling of the most active compounds showed that they bind to a pocket located in the fingers and thumb domains in BVDV RdRp, which is different from that identified for other non-nucleoside inhibitors (NNIs) such as thiosemicarbazone (TSC). We selected compound 2-[4-(2-phenylquinazolin-4-yl)piperazin-1-yl]ethanol (1.9; EC50 = 1.7 ± 0.4 µM) for further analysis. Compound 1.9 was found to inhibit the in vitro replication of TSC-resistant BVDV variants, which carry the N264D mutation in the RdRp. In addition, 1.9 presented adequate solubility in different media and a high-stability profile in murine and bovine plasma.

Synthesis, 2D-QSAR Studies and Biological Evaluation of Quinazoline Derivatives as Potent Anti-Trypanosoma cruzi Agents.

BACKGROUND: Chagas disease affects about 7 million people worldwide. Only two drugs are currently available for the treatment for this parasite disease, namely, benznidazol (Bzn) and nifurtimox (Nfx). Both drugs have limited curative power in the chronic phase of the disease. Therefore, continuous research is an urgent need so as to discover novel therapeutic alternatives. OBJECTIVE: The development of safer and more efficient therapeutic anti-T. cruzi drugs continues to be a major goal in trypanocidal chemotherapy. METHOD: Synthesis, 2D-QSAR and drug-like physicochemical properties of a set of quinazolinone and quinazoline derivatives were studied as trypanocidal agents. All compounds were screened in vitro against Trypanosoma cruzi (Tulahuen strain, Tul 2 stock) epimastigotes and bloodstream trypomastigotes. RESULTS: Out of 34 compounds synthesized and tested, six compounds (5a, 5b, 9b, 9h, 13f and 13p) displayed significant activity against both epimastigotes and tripomastigotes, without exerting toxicity on Vero cells. CONCLUSION: The antiprotozoal activity of these quinazolinone and quinazoline derivatives represents an interesting starting point for a medicinal chemistry program aiming at the development of novel chemotherapies for Chagas disease.

De novo design approaches targeting an envelope protein pocket to identify small molecules against dengue virus.

Dengue fever is a mosquito-borne viral disease that has become a major public health concern worldwide. This disease presents with a wide range of clinical manifestations, from a mild cold-like illness to the more serious hemorrhagic dengue fever and dengue shock syndrome. Currently, neither an approved drug nor an effective vaccine for the treatment are available to fight the disease. The envelope protein (E) is a major component of the virion surface. This protein plays a key role during the viral entry process, constituting an attractive target for the development of antiviral drugs. The crystal structure of the E protein reveals the existence of a hydrophobic pocket occupied by the detergent n-octyl-ß-d-glucoside (ß-OG). This pocket lies at the hinge region between domains I and II and is important for the low pH-triggered conformational rearrangement required for the fusion of the virion with the host's cell. Aiming at the design of novel molecules which bind to E and act as virus entry inhibitors, we undertook a de novo design approach by "growing" molecules inside the hydrophobic site (ß-OG). From more than 240000 small-molecules generated, the 2,4 pyrimidine scaffold was selected as the best candidate, from which one synthesized compound displayed micromolar activity. Molecular dynamics-based optimization was performed on this hit, and thirty derivatives were designed in silico, synthesized and evaluated on their capacity to inhibit dengue virus entry into the host cell. Four compounds were found to be potent antiviral compounds in the low-micromolar range. The assessment of drug-like physicochemical and in vitro pharmacokinetic properties revealed that compounds 3e and 3h presented acceptable solubility values and were stable in mouse plasma, simulated gastric fluid, simulated intestinal fluid, and phosphate buffered saline solution.