Nirmatrelvir for Vaccinated or Unvaccinated Adult Outpatients with Covid-19

BACKGROUND

Nirmatrelvir in combination with ritonavir is an antiviral treatment for mild-to-moderate coronavirus disease 2019 (Covid-19). The efficacy of this treatment in patients who are at standard risk for severe Covid-19 or who are fully vaccinated and have at least one risk factor for severe Covid-19 has not been established.

METHODS

In this phase 2-3 trial, we randomly assigned adults who had confirmed Covid-19 with symptom onset within the past 5 days in a 1:1 ratio to receive nirmatrelvir-ritonavir or placebo every 12 hours for 5 days. Patients who were fully vaccinated against Covid-19 and who had at least one risk factor for severe disease, as well as patients without such risk factors who had never been vaccinated against Covid-19 or had not been vaccinated within the previous year, were eligible for participation. Participants logged the presence and severity of prespecified Covid-19 signs and symptoms daily from day 1 through day 28. The primary end point was the time to sustained alleviation of all targeted Covid-19 signs and symptoms. Covid-19-related hospitalization and death from any cause were also assessed through day 28.

RESULTS

Among the 1296 participants who underwent randomization and were included in the full analysis population, 1288 received at least one dose of nirmatrelvir-ritonavir (654 participants) or placebo (634 participants) and had at least one postbaseline visit. The median time to sustained alleviation of all targeted signs and symptoms of Covid-19 was 12 days in the nirmatrelvir-ritonavir group and 13 days in the placebo group (P = 0.60). Five participants (0.8%) in the nirmatrelvir-ritonavir group and 10 (1.6%) in the placebo group were hospitalized for Covid-19 or died from any cause (difference, -0.8 percentage points; 95% confidence interval, -2.0 to 0.4). The percentages of participants with adverse events were similar in the two groups (25.8% with nirmatrelvir-ritonavir and 24.1% with placebo). In the nirmatrelvir-ritonavir group, the most commonly reported treatment-related adverse events were dysgeusia (in 5.8% of the participants) and diarrhea (in 2.1%).

CONCLUSIONS

The time to sustained alleviation of all signs and symptoms of Covid-19 did not differ significantly between participants who received nirmatrelvir-ritonavir and those who received placebo. (Supported by Pfizer; EPIC-SR ClinicalTrials.gov number, NCT05011513.).

Safety, Tolerability, and Pharmacokinetics of Single and Multiple Ascending Intravenous Infusions of PF-07304814 (Lufotrelvir) in Participants Hospitalized With COVID-19

BACKGROUND

An urgent need remains for antiviral therapies to treat patients hospitalized with COVID-19. PF-07304814-the prodrug (lufotrelvir) and its active moiety (PF-00835231)-is a potent inhibitor of the SARS-CoV-2 3CL protease.

METHOD

Eligible participants were 18 to 79 years old and hospitalized with confirmed COVID-19. This first-in-human phase 1b study was designed with 2 groups: single ascending dose (SAD) and multiple ascending dose (MAD). Participants could receive local standard-of-care therapy. In SAD, participants were randomized to receive a 24-hour infusion of lufotrelvir/placebo. In MAD, participants were randomized to receive a 120-hour infusion of lufotrelvir/placebo. The primary endpoint was to assess the safety and tolerability of lufotrelvir. The secondary endpoint was to evaluate the pharmacokinetics of lufotrelvir and PF-00835231.

RESULTS

In SAD, participants were randomized to receive 250 mg lufotrelvir (n = 2), 500 mg lufotrelvir (n = 2), or placebo (n = 4) by continuous 24-hour infusion. In MAD, participants were randomized to receive 250 mg lufotrelvir (n = 7), 500 mg lufotrelvir (n = 6), or placebo (n = 4) by continuous 120-hour infusion. No adverse events or serious adverse events were considered related to lufotrelvir. At doses of 250 and 500 mg, concentrations for the prodrug lufotrelvir and active moiety PF-00835231 increased in a dose-related manner. Unbound concentrations of the lufotrelvir active metabolite reached steady state approximately 2- and 4-fold that of in vitro EC90 following 250- and 500-mg doses, respectively.

CONCLUSIONS

These safety and pharmacokinetic findings support the continued evaluation of lufotrelvir in clinical studies. Clinical Trials Registration. ClinicalTrials.gov NCT04535167.

Antitumor Necrosis Factor-like Ligand 1A Therapy Targets Tissue Inflammation and Fibrosis Pathways and Reduces Gut Pathobionts in Ulcerative Colitis

BACKGROUND

The first-in-class treatment PF-06480605 targets the tumor necrosis factor-like ligand 1A (TL1A) molecule in humans. Results from the phase 2a TUSCANY trial highlighted the safety and efficacy of PF-06480605 in ulcerative colitis. Preclinical and in vitro models have identified a role for TL1A in both innate and adaptive immune responses, but the mechanisms underlying the efficacy of anti-TL1A treatment in inflammatory bowel disease (IBD) are not known.

METHODS

Here, we provide analysis of tissue transcriptomic, peripheral blood proteomic, and fecal metagenomic data from the recently completed phase 2a TUSCANY trial and demonstrate endoscopic improvement post-treatment with PF-06480605 in participants with ulcerative colitis.

RESULTS

Our results revealed robust TL1A target engagement in colonic tissue and a distinct colonic transcriptional response reflecting a reduction in inflammatory T helper 17 cell, macrophage, and fibrosis pathways in patients with endoscopic improvement. Proteomic analysis of peripheral blood revealed a corresponding decrease in inflammatory T-cell cytokines. Finally, microbiome analysis showed significant changes in IBD-associated pathobionts, Streptococcus salivarius, S. parasanguinis, and Haemophilus parainfluenzae post-therapy.

CONCLUSIONS

The ability of PF-06480605 to engage and inhibit colonic TL1A, targeting inflammatory T cell and fibrosis pathways, provides the first-in-human mechanistic data to guide anti-TL1A therapy for the treatment of IBD.

Use of a Plasmodium vivax genetic barcode for genomic surveillance and parasite tracking in Sri Lanka

Background

Sri Lanka was certified as a malaria-free nation in 2016; however, imported malaria cases continue to be reported. Evidence-based information on the genetic structure/diversity of the parasite populations is useful to understand the population history, assess the trends in transmission patterns, as well as to predict threatening phenotypes that may be introduced and spread in parasite populations disrupting elimination programmes. This study used a previously developed Plasmodium vivax single nucleotide polymorphism (SNP) barcode to evaluate the population dynamics of P. vivax parasite isolates from Sri Lanka and to assess the ability of the SNP barcode for tracking the parasites to its origin.

Methods

A total of 51 P. vivax samples collected during 2005–2011, mainly from three provinces of the country, were genotyped for 40 previously identified P. vivax SNPs using a high-resolution melting (HRM), single-nucleotide barcode method. Minor allele frequencies, linkage disequilibrium, pair-wise F_ST values, and complexity of infection (COI) were evaluated to determine the genetic diversity. Structure analysis was carried out using STRUCTURE software (Version 2.3.4) and SNP barcode was used to identify the genetic diversity of the local parasite populations collected from different years. Principal component analysis (PCA) was used to determine the clustering according to global geographic regions.

Results

The proportion of multi-clone infections was significantly higher in isolates collected during an infection outbreak in year 2007. The minor allele frequencies of the SNPs changed dramatically from year to year. Significant linkage was observed in sample sub-sets from years 2005 and 2007. The majority of the isolates from 2007 consisted of at least two genetically distinct parasite strains. The overall percentage of multi-clone infections for the entire parasite sample was 39.21%. Analysis using STRUCTURE software (Version 2.3.4) revealed the high genetic diversity of the sample sub-set from year 2007. In-silico analysis of these data with those available from other global geographical regions using PCA showed distinct clustering of parasite isolates according to geography, demonstrating the usefulness of the barcode in determining an isolate to be indigenous.

Conclusions

Plasmodium vivax parasite isolates collected during a disease outbreak in year 2007 were more genetically diverse compared to those collected from other years. In-silico analysis using the 40 SNP barcode is a useful tool to track the origin of an isolate of uncertain origin, especially to differentiate indigenous from imported cases. However, an extended barcode with more SNPs may be needed to distinguish highly clonal populations within the country.

Zika virus evolution and spread in the Americas

Although the recent Zika virus (ZIKV) epidemic in the Americas and its link to birth defects have attracted a great deal of attention, much remains unknown about ZIKV disease epidemiology and ZIKV evolution, in part owing to a lack of genomic data. Here we address this gap in knowledge by using multiple sequencing approaches to generate 110 ZIKV genomes from clinical and mosquito samples from 10 countries and territories, greatly expanding the observed viral genetic diversity from this outbreak. We analysed the timing and patterns of introductions into distinct geographic regions; our phylogenetic evidence suggests rapid expansion of the outbreak in Brazil and multiple introductions of outbreak strains into Puerto Rico, Honduras, Colombia, other Caribbean islands, and the continental United States. We find that ZIKV circulated undetected in multiple regions for many months before the first locally transmitted cases were confirmed, highlighting the importance of surveillance of viral infections. We identify mutations with possible functional implications for ZIKV biology and pathogenesis, as well as those that might be relevant to the effectiveness of diagnostic tests.

Genomic epidemiology reveals multiple introductions of Zika virus into the United States

Zika virus (ZIKV) is causing an unprecedented epidemic linked to severe congenital abnormalities. In July 2016, mosquito-borne ZIKV transmission was reported in the continental United States; since then, hundreds of locally acquired infections have been reported in Florida. To gain insights into the timing, source, and likely route(s) of ZIKV introduction, we tracked the virus from its first detection in Florida by sequencing ZIKV genomes from infected patients and Aedes aegypti mosquitoes. We show that at least 4 introductions, but potentially as many as 40, contributed to the outbreak in Florida and that local transmission is likely to have started in the spring of 2016-several months before its initial detection. By analysing surveillance and genetic data, we show that ZIKV moved among transmission zones in Miami. Our analyses show that most introductions were linked to the Caribbean, a finding corroborated by the high incidence rates and traffic volumes from the region into the Miami area. Our study provides an understanding of how ZIKV initiates transmission in new regions.

Development of a single nucleotide polymorphism barcode to genotype Plasmodium vivax infections

Plasmodium vivax, one of the five species of Plasmodium parasites that cause human malaria, is responsible for 25–40% of malaria cases worldwide. Malaria global elimination efforts will benefit from accurate and effective genotyping tools that will provide insight into the population genetics and diversity of this parasite. The recent sequencing of P. vivax isolates from South America, Africa, and Asia presents a new opportunity by uncovering thousands of novel single nucleotide polymorphisms (SNPs). Genotyping a selection of these SNPs provides a robust, low-cost method of identifying parasite infections through their unique genetic signature or barcode. Based on our experience in generating a SNP barcode for P. falciparum using High Resolution Melting (HRM), we have developed a similar tool for P. vivax. We selected globally polymorphic SNPs from available P. vivax genome sequence data that were located in putatively selectively neutral sites (i.e., intergenic, intronic, or 4-fold degenerate coding). From these candidate SNPs we defined a barcode consisting of 42 SNPs. We analyzed the performance of the 42-SNP barcode on 87 P. vivax clinical samples from parasite populations in South America (Brazil, French Guiana), Africa (Ethiopia) and Asia (Sri Lanka). We found that the P. vivax barcode is robust, as it requires only a small quantity of DNA (limit of detection 0.3 ng/μl) to yield reproducible genotype calls, and detects polymorphic genotypes with high sensitivity. The markers are informative across all clinical samples evaluated (average minor allele frequency > 0.1). Population genetic and statistical analyses show the barcode captures high degrees of population diversity and differentiates geographically distinct populations. Our 42-SNP barcode provides a robust, informative, and standardized genetic marker set that accurately identifies a genomic signature for P. vivax infections.

Plasmodium vivax malaria is a major global public health problem, with nearly 2.5 billion people at risk for infection and approximately 132–391 million clinical infections annually. It has a wide geographical range, with a high disease burden in Asia, Central and South America, the Middle East, Oceania, and East Africa. Advances in sequencing technology and sample processing have made it possible to characterize the genetic diversity of P. vivax populations. This genetic variation provides a means to identify parasites by unique genetic signatures, or “barcodes.” We developed such a genetic barcode for P. vivax, composed of 42 robust and informative variants. Here we report its development and validation based on 87 clinical samples identified by microscopy to contain P. vivax from geographically diverse parasite populations from South America (Brazil, French Guiana), Africa (Ethiopia) and Asia (Sri Lanka). We show that the SNP barcode provides a genotyping tool that can be performed at low cost, providing a means to uniquely identify parasite infections and distinguish geographic origins, and that barcode data may offer new insights into P. vivax population structure and diversity.

Acceptability of a nipple shield delivery system administering antiviral agents to prevent mother-to-child transmission of HIV through breastfeeding

BACKGROUND

Breastfeeding is a route of mother-to-child transmission (MTCT) of the human immunodeficiency virus (HIV). The World Health Organization recommends antiretroviral (ARV) prophylaxis as the best method to prevent mother-to-child transmission of HIV (PMTCT) during breastfeeding. The nipple shield delivery system (NSDS) is being developed as an accessible method to deliver ARVs to infants and PMTCT during breastfeeding. The NSDS can potentially circumvent hygiene and storage issues in delivering drugs to infants in low-resource settings.

OBJECTIVES

The primary objective was to determine acceptability of the NSDS for PMTCT in Kenya. Secondary objectives included assessing mothers' understanding of MTCT and identifying cultural and implementation issues that might affect NSDS acceptability.

METHODS

Eleven focus group discussions were conducted, each group consisting of 7 to 12 participants. Seven focus group discussions consisted of HIV-positive mothers, 2 included grandmothers/mothers-in-law, and 2 included fathers/husbands. Ten in-depth interviews were also conducted with individual maternal/child health care providers. Topics included infant feeding and HIV stigma, as well as safety, effectiveness, and feasibility of the NSDS. Device prototypes were used in discussions.

RESULTS

Participants felt that the NSDS could be trusted if validated scientifically and promoted by health care professionals. HIV-related stigma, access, efficacy, and hygiene were identified as important considerations for acceptance.

CONCLUSION

The NSDS is a potentially acceptable method of PMTCT during breastfeeding. Further studies are needed to confirm acceptability, safety, and efficacy. For NSDS adoption to PMTCT, strategies will need to be developed to minimize HIV-related stigma and to ensure that continuous hygiene of the device is maintained.

Regulation of a viral proteinase by a peptide and DNA in one-dimensional space: III. atomic resolution structure of the nascent form of the adenovirus proteinase

The adenovirus proteinase (AVP), the first member of a new class of cysteine proteinases, is essential for the production of infectious virus, and here we report its structure at 0.98 Å resolution. AVP, initially synthesized as an inactive enzyme, requires two cofactors for maximal activity: pVIc, an 11-amino acid peptide, and the viral DNA. Comparison of the structure of AVP with that of an active form, the AVP-pVIc complex, reveals why AVP is inactive. Both forms have an α + β fold; the major structural differences between them lie in the β-sheet domain. In AVP-pVIc, the general base His-54 Nδ1 is 3.9 Å away from the Cys-122 Sγ, thereby rendering it nucleophilic. In AVP, however, His-54 Nδ1 is 7.0 Å away from Cys-122 Sγ, too far away to be able to abstract the proton from Cys-122. In AVP-pVIc, Tyr-84 forms a cation-π interaction with His-54 that should raise the pK(a) of His-54 and freeze the imidazole ring in the place optimal for forming an ion pair with Cys-122. In AVP, however, Tyr-84 is more than 11 Å away from its position in AVP-pVIc. Based on the structural differences between AVP and AVP-pVIc, we present a model that postulates that activation of AVP by pVIc occurs via a 62-amino acid-long activation pathway in which the binding of pVIc initiates contiguous conformational changes, analogous to falling dominos. There is a common pathway that branches into a pathway that leads to the repositioning of His-54 and another pathway that leads to the repositioning of Tyr-84.

High-throughput Plasmodium falciparum growth assay for malaria drug discovery

New therapeutic agents for the treatment of malaria, the world's most deadly parasitic disease, are urgently needed. Malaria afflicts 300 to 500 million people and results in 1 to 2 million deaths annually, and more than 85% of all malaria-related mortality involves young children and pregnant women in sub-Saharan Africa. The emergence of multidrug-resistant parasites, especially in Plasmodium falciparum, has eroded the efficacy of almost all currently available therapeutic agents. The discovery of new drugs, including drugs with novel cellular targets, could be accelerated with a whole-organism high-throughput screen (HTS) of structurally diverse small-molecule libraries. The standard whole-organism screen is based on incorporation of [3H]hypoxanthine and has liabilities, such as limited throughput, high cost, multiple labor-intensive steps, and disposal of radioactive waste. Recently, screens have been reported that do not use radioactive incorporation, but their reporter signal is not robust enough for HTS. We report a P. falciparum growth assay that is technically simple, robust, and compatible with the automation necessary for HTS. The assay monitors DNA content by addition of the fluorescent dye 4',6-diamidino-2-phenylindole (DAPI) as a reporter of blood-stage parasite growth. This DAPI P. falciparum growth assay was used to measure the 50% inhibitory concentrations (IC50s) of a diverse set of known antimalarials. The resultant IC50s compared favorably with those obtained in the [3H]hypoxanthine incorporation assay. Over 79,000 small molecules have been tested for antiplasmodial activity using the DAPI P. falciparum growth assay, and 181 small molecules were identified as highly active against multidrug-resistant parasites.

Specific interactions of the adenovirus proteinase with the viral DNA, an 11-amino-acid viral peptide, and the cellular protein actin

The adenovirus proteinase (AVP) is synthesized in an inactive form that requires cofactors for activation. The interaction of AVP with two viral cofactors and with a cellular cofactor, actin, is characterized by quantitative analyses. The results are consistent with a specific model for the regulation of AVP. Late in adenovirus infection, inside nascent virions, AVP becomes partially activated by binding to the viral DNA, allowing it to cleave out an 11-amino-acid viral peptide, pVIc, that binds to AVP and fully activates it. Then, about 70 AVP-pVIc complexes move along the viral DNA, via one-dimensional diffusion, cleaving virion precursor proteins 3200 times to render a virus particle infectious. Late in adenovirus infection, in the cytoplasm, the cytoskeleton is destroyed. The amino acid sequence of the C terminus of actin is homologous to that of pVIc, and actin, like pVIc, can act as a cofactor for AVP in the cleavage of cytokeratin 18 and of actin itself. Thus, AVP may also play a role in cell lysis.

Nitric oxide inhibits the adenovirus proteinase in vitro and viral infectivity in vivo

Nitric oxide (NO) is an antiviral effector of the innate immune system, but few of the viral targets of NO have been identified. We now show that NO inhibits adenovirus replication by targeting the adenovirus proteinase (AVP). NO generated from diethylamine NONOate (DEA-NONOate) or spermine NONOate (Sp-NONOate) inhibited the AVP. Inhibition was reversible with dithiothreitol. The equilibrium dissociation constant for reversible binding to the AVP by Sp-NONOate, or Ki, was 0.47 mM, and the first-order rate constant for irreversible inhibition of the AVP by Sp-NONOate, or ki, was 0.0036 s(-1). Two hallmarks of a successful adenovirus infection were abolished by the NO donors: the appearance of E1A protein and the cleavage of cytokeratin 18 by AVP. Treatment of infectious virus by DEA-NONOate dramatically decreased viral infectivity. These data suggest that NO may be a useful antiviral agent against viruses encoding a cysteine proteinase and in particular may be an antiadenovirus agent.

Actin can act as a cofactor for a viral proteinase in the cleavage of the cytoskeleton

Cytoskeletal proteins are exploited by many viruses during infection. We report a novel finding that actin can act as a cofactor for the adenovirus proteinase (AVP) in the degradation of cytoskeletal proteins. Transfection studies in HeLa cells revealed AVP localized with cytokeratin 18, and this was followed by destruction of the cytokeratin network. For AVP to cleave cytokeratin 18, a cellular cofactor was shown to be required, consistent with AVP being synthesized as an inactive proteinase. Actin was considered a cellular cofactor for AVP, because the C terminus of actin is homologous to a viral cofactor for AVP. AVP was shown to bind to the C terminus of actin, and in doing so AVP exhibited full enzymatic activity. In vitro, actin was a cofactor in the cleavage of cytokeratin 18 by AVP. The proteinase alone could not cleave cytokeratin 18, but in the presence of actin, AVP cleaved cytokeratin 18. Indeed, actin itself was shown to be a cofactor and a substrate for its own destruction in that it was cleaved by AVP in vitro. Cleavage of cytoskeletal proteins weakens the structure of the cell, and therefore, actin as a cofactor may play a role in cell lysis and release of nascent virions.

Adenovirus proteinase: crystallization and preliminary X-ray diffraction studies to atomic resolution

Adenovirus proteinase (AVP) is required for the synthesis of infectious virus and is a target for antiviral therapy. The enzyme requires two viral cofactors for activation: pVIc, an 11-amino acid peptide, and the viral DNA. The structure of the enzyme in the absence of cofactors has not been observed. Single crystals of AVP were obtained via microseeding using the hanging-drop vapour-diffusion method with sodium acetate and sodium citrate as precipitants. At the National Synchrotron Light Source at Brookhaven National Laboratory, the native crystal diffracted to a resolution of 0.98 A and an isomorphous heavy-atom derivative diffracted to 1.9 A. Comparison of the structure of AVP with that of the AVP-pVIc complex should reveal the structural basis of activation of the enzyme by pVIc.

Roles of two conserved cysteine residues in the activation of human adenovirus proteinase

The roles of two conserved cysteine residues involved in the activation of the adenovirus proteinase (AVP) were investigated. AVP requires two cofactors for maximal activity, the 11-amino acid peptide pVIc (GVQSLKRRRCF) and the viral DNA. In the AVP-pVIc crystal structure, conserved Cys104 of AVP has formed a disulfide bond with conserved Cys10 of pVIc. In this work, pVIc formed a homodimer via disulfide bond formation with a second-order rate constant of 0.12 M(-1) s(-1), and half of the homodimer could covalently bind to AVP via thiol-disulfide exchange. Alternatively, monomeric pVIc could form a disulfide bond with AVP via oxidation. Regardless of the mechanism by which AVP becomes covalently bound to pVIc, the kinetic constants for substrate hydrolysis were the same. The equilibrium dissociation constant, K(d), for the reversible binding of pVIc to AVP was 4.4 microM. The K(d) for the binding of the mutant C10A-pVIc was at least 100-fold higher. Surprisingly, the K(d) for the binding of the C10A-pVIc mutant to AVP decreased at least 60-fold, to 6.93 microM, in the presence of 12mer ssDNA. Furthermore, once the mutant C10A-pVIc was bound to an AVP-DNA complex, the macroscopic kinetic constants for substrate hydrolysis were the same as those exhibited by wild-type pVIc. Although the cysteine in pVIc is important in the binding of pVIc to AVP, formation of a disulfide bond between pVIc and AVP was not required for maximal stimulation of enzyme activity by pVIc.

Human adenovirus proteinase: DNA binding and stimulation of proteinase activity by DNA

The interaction of the human adenovirus proteinase (AVP) with various DNAs was characterized. AVP requires two cofactors for maximal activity, the 11-amino acid residue peptide from the C-terminus of adenovirus precursor protein pVI (pVIc) and the viral DNA. DNA binding was monitored by changes in enzyme activity or by fluorescence anisotropy. The equilibrium dissociation constants for the binding of AVP and AVP-pVIc complexes to 12-mer double-stranded (ds) DNA were 63 and 2.9 nM, respectively. DNA binding was not sequence specific; the stoichiometry of binding was proportional to the length of the DNA. Three molecules of the AVP-pVIc complex bound to 18-mer dsDNA and six molecules to 36-mer dsDNA. When AVP-pVIc complexes bound to 12-mer dsDNA, two sodium ions were displaced from the DNA. A Delta of -4.6 kcal for the nonelectrostatic free energy of binding indicated that a substantial component of the binding free energy results from nonspecific interactions between the AVP-pVIc complex and DNA. The cofactors altered the interaction of the enzyme with the fluorogenic substrate (Leu-Arg-Gly-Gly-NH)2-rhodamine. In the absence of any cofactor, the Km was 94.8 microM and the kcat was 0.002 s(-1). In the presence of adenovirus DNA, the Km decreased 10-fold and the kcat increased 11-fold. In the presence of pVIc, the Km decreased 10-fold and the kcat increased 118-fold. With both cofactors present, the kcat/Km ratio increased 34000-fold, compared to that with AVP alone. Binding to DNA was coincident with stimulation of proteinase activity by DNA. Although other proteinases have been shown to bind to DNA, stimulation of proteinase activity by DNA is unprecedented. A model is presented suggesting that AVP moves along the viral DNA looking for precursor protein cleavage sites much like RNA polymerase moves along DNA looking for a promoter.

Interaction of the human adenovirus proteinase with its 11-amino acid cofactor pVIc

The interaction of the human adenovirus proteinase (AVP) and AVP-DNA complexes with the 11-amino acid cofactor pVIc was characterized. The equilibrium dissociation constant for the binding of pVIc to AVP was 4.4 microM. The binding of AVP to 12-mer single-stranded DNA decreased the K(d) for the binding of pVIc to AVP to 0.09 microM. The pVIc-AVP complex hydrolyzed the substrate with a Michaelis constant (K(m)) of 3.7 microM and a catalytic rate constant (k(cat)) of 1.1 s(-1). In the presence of DNA, the K(m) increased less than 2-fold, and the k(cat) increased 3-fold. Alanine-scanning mutagenesis was performed to determine the contribution of individual pVIc side chains in the binding and stimulation of AVP. Two amino acid residues, Gly1' and Phe11', were the major determinants in the binding of pVIc to AVP, while Val2' and Phe11' were the major determinants in stimulating enzyme activity. Binding of AVP to DNA greatly suppressed the effects of the alanine substitutions on the binding of mutant pVIcs to AVP. Binding of either or both of the cofactors, pVIc or the viral DNA, to AVP did not dramatically alter its secondary structure as determined by vacuum ultraviolet circular dichroism. pVIc, when added to Hep-2 cells infected with adenovirus serotype 5, inhibited the synthesis of infectious virus, presumably by prematurely activating the proteinase so that it cleaved virion precursor proteins before virion assembly, thereby aborting the infection.

A New Form of Antiviral Combination Therapy Predicted to Prevent Resistance from Arising, and A Model System to Test It

Combination therapy in the treatment of viral infections in which, for example, three different drugs against three different targets on three independent proteins are administered, has been highly successful clinically. However, it is only a matter of time before a virus will arise resistant to all three drugs, because the mutations leading to drug resistance are independent of each other. But, what if the mutations leading to drug resistance are not independent of each other, but confer some cost to the virus? If the cost is too great, than resistance may not arise. To impose such a cost in the clinical treatment of viral infections, we propose a new form of combination therapy. Here, three different drugs against three different targets on the same virus-coded protein are administered. If the physiological functions of the three different target sites are not independent of each other, then, a mutation at one site may alter the physiological functions at the other sites. We present a model system in which to test the efficacy of this new form of triple combination therapy. Human adenovirus has a virus-coded proteinase that is essential for the synthesis of infectious virus. It contains an active site and two cofactor binding sites; the functions of the active site are dependent upon the cofactors interacting with their binding sites. We describe how to obtain drugs against the three different sites.

Prevention of viral drug resistance by novel combination therapy

A new form of antiviral clinical therapy is proposed in which three different drugs are administered against three different targets on the same virus-coded protein. If the physiological functions of the three different target sites are not independent of each other, then a mutation conferring drug resistance at one site may alter the physiological functions at the other sites and further drug resistance may not arise. The adenovirus proteinase, with its two cofactors that act synergistically on enzyme activity, may be a good model system within which to test the efficacy of this form of combination therapy.