The triple threat of HIV-1 protease inhibitors

Genome-Wide Characterization of SARS-CoV-2 Cytopathogenic Proteins in the Search of Antiviral Targets

Therapeutic inhibition of critical viral functions is important for curtailing coronavirus disease 2019 (COVID-19). We sought to identify antiviral targets through the genome-wide characterization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins that are crucial for viral pathogenesis and that cause harmful cytopathogenic effects. All 29 viral proteins were tested in a fission yeast cell-based system using inducible gene expression. Twelve proteins, including eight nonstructural proteins (NSP1, NSP3, NSP4, NSP5, NSP6, NSP13, NSP14, and NSP15) and four accessory proteins (ORF3a, ORF6, ORF7a, and ORF7b), were identified that altered cellular proliferation and integrity and induced cell death. Cell death correlated with the activation of cellular oxidative stress. Of the 12 proteins, ORF3a was chosen for further study in mammalian cells because it plays an important role in viral pathogenesis and its activities are linked to lung tissue damage and a cytokine storm. In human pulmonary and kidney epithelial cells, ORF3a induced cellular oxidative stress associated with apoptosis and necrosis and caused activation of proinflammatory response with production of the cytokines tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and IFN-β1, possibly through the activation of nuclear factor kappa B (NF-κB). To further characterize the mechanism, we tested a natural ORF3a Beta variant, Q57H, and a mutant with deletion of the highly conserved residue, ΔG188. Compared with wild-type ORF3a, the ΔG188 variant yielded more robust activation of cellular oxidative stress, cell death, and innate immune response. Since cellular oxidative stress and inflammation contribute to cell death and tissue damage linked to the severity of COVID-19, our findings suggest that ORF3a is a promising, novel therapeutic target against COVID-19. IMPORTANCE The ongoing COVID-19 pandemic caused by SARS-CoV-2 has claimed over 5.5 million lives with more than 300 million people infected worldwide. While vaccines are effective, the emergence of new viral variants could jeopardize vaccine protection. Treatment of COVID-19 by antiviral drugs provides an alternative to battle against the disease. The goal of this study was to identify viral therapeutic targets that can be used in antiviral drug discovery. Utilizing a genome-wide functional analysis in a fission yeast cell-based system, we identified 12 viral candidates, including ORF3a, which cause cellular oxidative stress, inflammation, apoptosis, and necrosis that contribute to cytopathogenicity and COVID-19. Our findings indicate that antiviral agents targeting ORF3a could have a great impact on COVID-19.

Nanoscale flow cytometry reveals interpatient variability in HIV protease activity that correlates with viral infectivity and identifies drug-resistant viruses

HIV encodes an aspartyl protease that is activated during, or shortly after, budding of viral particles from the surface of infected cells. Protease-mediated cleavage of viral polyproteins is essential to generating infectious viruses, a process known as ‘maturation’ that is the target of FDA-approved antiretroviral drugs. Most assays to monitor protease activity rely on bulk analysis of millions of viruses and obscure potential heterogeneity of protease activation within individual particles. In this study we used nanoscale flow cytometry in conjunction with an engineered FRET reporter called VIral ProteasE Reporter (VIPER) to investigate heterogeneity of protease activation in individual, patient-derived viruses. We demonstrate previously unappreciated interpatient variation in HIV protease processing efficiency that impacts viral infectivity. Additionally, monitoring of protease activity in individual virions distinguishes between drug sensitivity or resistance to protease inhibitors in patient-derived samples. These findings demonstrate the feasibility of monitoring enzymatic processes using nanoscale flow cytometry and highlight the potential of this technology for translational clinical discovery, not only for viruses but also other submicron particles including exosomes, microvesicles, and bacteria.

Enzymatic Transition States and Drug Design

Transition state theory teaches that chemically stable mimics of enzymatic transition states will bind tightly to their cognate enzymes. Kinetic isotope effects combined with computational quantum chemistry provides enzymatic transition state information with sufficient fidelity to design transition state analogues. Examples are selected from various stages of drug development to demonstrate the application of transition state theory, inhibitor design, physicochemical characterization of transition state analogues, and their progress in drug development.

Evolution of gag and gp41 in Patients Receiving Ritonavir-Boosted Protease Inhibitors

Several groups have proposed that genotypic determinants in gag and the gp41 cytoplasmic domain (gp41-CD) reduce protease inhibitor (PI) susceptibility without PI-resistance mutations in protease. However, no gag and gp41-CD mutations definitively responsible for reduced PI susceptibility have been identified in individuals with virological failure (VF) while receiving a boosted PI (PI/r)-containing regimen. To identify gag and gp41 mutations under selective PI pressure, we sequenced gag and/or gp41 in 61 individuals with VF on a PI/r (n = 40) or NNRTI (n = 20) containing regimen. We quantified nonsynonymous and synonymous changes in both genes and identified sites exhibiting signal for directional or diversifying selection. We also used published gag and gp41 polymorphism data to highlight mutations displaying a high selection index, defined as changing from a conserved to an uncommon amino acid. Many amino acid mutations developed in gag and in gp41-CD in both the PI- and NNRTI-treated groups. However, in neither gene, were there discernable differences between the two groups in overall numbers of mutations, mutations displaying evidence of diversifying or directional selection, or mutations with a high selection index. If gag and/or gp41 encode PI-resistance mutations, they may not be confined to consistent mutations at a few sites.

Synthetic, structural mimetics of the β-hairpin flap of HIV-1 protease inhibit enzyme function

Small-molecule mimetics of the β-hairpin flap of HIV-1 protease (HIV-1 PR) were designed based on a 1,4-benzodiazepine scaffold as a strategy to interfere with the flap-flap protein-protein interaction, which functions as a gated mechanism to control access to the active site. Michaelis-Menten kinetics suggested our small-molecules are competitive inhibitors, which indicates the mode of inhibition is through binding the active site or sterically blocking access to the active site and preventing flap closure, as designed. More generally, a new bioactive scaffold for HIV-1PR inhibition has been discovered, with the most potent compound inhibiting the protease with a modest K(i) of 11 μM.