Myxoma virus oncolytic efficiency can be enhanced through chemical or genetic disruption of the actin cytoskeleton

Myxoma virus (MYXV) is one of many animal viruses that exhibit oncolytic properties in transformed human cells. Compared to orthopoxviruses like vaccinia (VACV), MYXV spreads inefficiently, which could compromise its use in treating tumors and their associated metastases. The VACV F11 protein promotes virus exit and rapid spread by inhibiting Rho signalling, which results in a disruption of cortical actin. We have previously shown that although MYXV lacks an F11 homolog, the F11L gene can be introduced into MYXV promoting the spread of this Leporipoxvirus in natural host cells. Here we show that the F11-encoding (F11L⁺) MYXV strain replicates to higher levels in a number of human cancer cells. We also show that F11L⁺ MYXV induces better tumor control and prolonged survival of mice bearing MDA-MB-231 cancer cells. Furthermore, we show that this virus also spreads more efficiently from the site of growth in one injected tumor, to a second untreated tumor.

While we focused mostly on the use of a modified MYXV we were able to show that the effects of F11 on MYXV growth in cancer cells could be mimicked through the use of pharmacological inhibition or siRNA-mediated silencing of key regulators of cortical actin (RhoA, RhoC, mDia1, or LIMK2). These data suggest that it may be possible to increase the oncolytic efficacy of wild-type MYXV using chemical inhibitors of RhoA/C or their downstream targets. Furthermore, since all viruses must overcome barriers to exit posed by structures like cortical actin, these findings suggest that the oncolytic activity of other viruses may be enhanced through similar strategies.

Detailed computational study of the active site of the hepatitis C viral RNA polymerase to aid novel drug design

The hepatitis C virus (HCV) RNA polymerase, NS5B, is a leading target for novel and selective HCV drug design. The enzyme has been the subject of intensive drug discovery aimed at developing direct acting antiviral (DAA) agents that inhibit its activity and hence prevent the virus from replicating its genome. In this study, we focus on one class of NS5B inhibitors, namely nucleos(t)ide mimetics. Forty-one distinct nucleotide structures have been modeled within the active site of NS5B for the six major HCV genotypes. Our comprehensive modeling protocol employed 287 different molecular dynamics simulations combined with the molecular mechanics/Poisson-Boltzmann surface area (MM-PBSA) methodology to rank and analyze these structures for all genotypes. The binding interactions of the individual compounds have been investigated and reduced to the atomic level. The present study significantly refines our understanding of the mode of action of NS5B-nucleotide-inhibitors, identifies the key structural elements necessary for their activity, and implements the tools for ranking the potential of additional much needed novel inhibitors of NS5B.

A longitudinal assessment of acute cough

RATIONALE

Cough can be assessed with visual analog scales (VAS), health status measures, and 24-hour cough frequency monitors (CF(24)). Evidence for their measurement properties in acute cough caused by upper respiratory tract infection (URTI) and longitudinal data is limited.

OBJECTIVES

To assess cough longitudinally in URTI with subjective and objective outcome measures and determine sample size for future studies.

METHODS

Thirty-three previously healthy subjects with URTI completed cough VAS, Leicester Cough Questionnaire (LCQ-acute), and CF(24) monitoring (Leicester Cough Monitor) on three occasions, 4 days apart. Changes in subjects' condition were assessed with a global rating of change questionnaire. The potential for baseline first-hour cough frequency (CF(1)), VAS, and LCQ to identify low CF(24) was assessed.

MEASUREMENTS AND MAIN RESULTS

Mean ± SD duration of cough at visit 1 was 4.1 ± 2.5 days. Geometric mean ± log SD baseline CF(24) and median (interquartile range) cough bouts were high (14.9 ± 0.4 coughs/h and 85 [39-195] bouts/24 h). Health status was severely impaired. There was a significant reduction in CF(24) and VAS, and improvement in LCQ, from visits 1-3. At visit 3, CF(24) remained above normal limits in 52% of subjects. The smallest changes in CF(24), LCQ, and VAS that subjects perceived important were 54%, 2- and 17-mm change from baseline, respectively. The sample sizes required for parallel group studies to detect these changes are 27, 51, and 25 subjects per group, respectively. CF(1) (<20.5 coughs/h) was predictive of low CF(24).

CONCLUSIONS

CF(24), VAS, and LCQ are responsive outcome tools for the assessment of acute cough. The smallest change in cough frequency perceived important by subjects is 54%. The sample sizes required for future studies are modest and achievable.

Genomic analysis of vaccinia virus strain TianTan provides new insights into the evolution and evolutionary relationships between Orthopoxviruses

Vaccinia virus (VACV) strain TianTan was used for much of China's modern history to vaccinate against smallpox, however the only genome sequence contains errors. We have sequenced additional examples of TianTan to obtain a better picture of this important virus. We detected two different subclones. One (TP03) encodes large deletions in the terminal repeats that extend into both VEGF genes and create a small plaque variant. The second clone (TP05) encodes a nearly intact complement of genes in the terminal repeats, except for an insertion of sequences resembling the telomeric 69 bp repeats. The TP05 genome spans 196,260 bp and encodes 219 genes. The revised sequence documents the integrity of all the genes in the conserved virus core. Phylogenetic methods show that TianTan belongs to a unique clade of VACV, but probably also share a common origin with strains belonging to the Copenhagen/Lister lineage and distinct from the Wyeth/Dryvax lineage.

Assessment of reverse flow as a means of cerebral protection during carotid artery stent placement with diffusion-weighted and transcranial Doppler imaging

PURPOSE

To assess the effectiveness of flow reversal as an alternative means of cerebral protection by using transcranial Doppler recordings and diffusion-weighted imaging (DWI) as surrogate markers of brain injury.

MATERIALS AND METHODS

Eighteen patients with symptomatic carotid artery disease were recruited. Magnetic resonance imaging was performed before the intervention and at 3 and 24 hours and 30 days after the intervention to detect new ischemic lesions with DWI. Transcranial Doppler recordings were made during the procedure to assess for microembolic signals (MESs). Data were compared against data from a historical control cohort of patients who underwent CAS placement with or without filter protection (n = 15 each) under the same protocol in a different study.

RESULTS

There were fewer periprocedural new lesions on DWI in the reverse-flow cohort compared with the historical control cohort with filter protection (P = .084). Reverse flow revealed significantly fewer MESs during the whole procedure compared with the filter-protected group (P = .01) but not the unprotected group (P = .55). There was a marked decrease in MES counts for reverse flow protection during the embologenic stages of the procedure (P = .004).

CONCLUSIONS

Use of the reverse flow device was associated with fewer overall lesions on DWI and proportionately fewer positive scans compared with the use of filter-type devices (P = .08, not significant). Transcranial Doppler recordings demonstrated a significant reduction in embolization to the brain during carotid artery stent placement with the use of reverse-flow cerebral protection.

'Calling executives and clinicians to account': user involvement in commissioning cancer services

BACKGROUND

English NHS guidance emphasizes the importance of involving users in commissioning cancer services. There has been considerable previous research on involving users in service improvement, but not on involvement in commissioning cancer services.

OBJECTIVE

To identify how users were involved as local cancer service commissioning projects sought to implement good practice and what has been learned.

DESIGN

Participatory evaluation with four qualitative case studies based on semi-structured interviews with project stakeholders, observation and documentary analysis. Users were involved in every stage from design to analysis and reporting.

SETTING AND PARTICIPANTS

Four English cancer network user involvement in commissioning projects, with 22 stakeholders interviewed.

RESULTS

Thematic analysis identified nine themes: initial involvement, preparation for the role, ability to exercise voice, consistency and continuity, where decisions are made, closing the feedback loop, assessing impact, value of experience and diversity.

DISCUSSION

Our findings on the impact of user involvement in commissioning cancer services are consistent with other findings on user involvement in service improvement, but highlight the specific issues for involvement in commissioning. Key points include the different perspectives users and professionals may have on the impact of user involvement in commissioning, the time necessary for meaningful involvement, the importance of involving users from the beginning and the value of senior management and PPI facilitator support and training.

CONCLUSIONS

Users can play an important role in commissioning cancer services, but their ability to do so is contingent on resources being available to support them.

Four-hour cough frequency monitoring in chronic cough

BACKGROUND

The recent development of automated cough monitors has enabled objective assessment of cough frequency. A study was undertaken to determine whether short-duration recordings( < 6 h) accurately reflect 24-h cough frequency and to investigate their responsiveness.

METHODS

One hundred adults with chronic cough underwent 24-h cough frequency monitoring with the Leicester Cough Monitor and completed cough visual analog scales (VASs) and the Leicester Cough Questionnaire (LCQ). Cough recordings were analyzed using customized software to derive cough frequencies from 1 to 6 h and 24-h recordings. Responsiveness was assessed with repeat assessments following therapeutic trials.

RESULTS

The median (interquartile range) 24-h cough frequency was 11.5 (5.8-26.6) coughs/h. Four hours was considered the shortest recording duration that represented 24-h cough frequency( ρ= 0.9, P ≤ .001). Median 4-h cough frequency was 16.6 (7.3-36.8) coughs/h. Both 4-h and 24-h cough frequency correlated moderately with cough VAS ( ρ= 0.49, P ≤ .01 and ρ= 0.44, P ≤ .01)and LCQ ( ρ = - 0.48, P ≤ .01; ρ = - 0.50, P ≤ .01). Four-hour cough frequency was responsive to improvements in cough severity following trials of therapy.

CONCLUSIONS

Four-hour cough frequency correlates highly with 24-h cough frequency recordings and relates equally well with subjective measures in chronic cough. Short-duration cough monitoring could be a practical tool to validate the presence of cough and assess response to trials of therapy in the clinic setting.

Isotopic tracing of the impact of mobility on infectious disease: The origin of people with treponematosis buried in hull, England, in the late medieval period

Treponematosis has been one of the most studied and debated infectious diseases in paleopathology, particularly from the standpoint of its origin, evolution, and transmission. This study links evidence for treponematosis in skeletons from the 14th-16th century AD cemetery of the Augustinian friary of Hull Magistrates Court, England, with data from stable isotope analysis to test the hypothesis that the people with treponemal disease buried at this site were not locally born and raised. The objective is to explore the potential of using stable isotope data to track the place of origin and extent of mobility of individuals with an infectious disease. Dental enamel samples of 12 skeletons were selected for strontium ((87) Sr/(86) Sr ratio) and oxygen (δ(18) O) stable isotope analysis based on the presence (six - diseased) or absence (six - controls) of bone changes associated with treponemal disease. The oxygen isotope ratios of all but three individuals (1047, 1121, 823) overlapped at two standard deviations with the inferred local precipitation range, and only one individual (1216) had a strontium isotope ratio outside the regional range. Two of the four had probable/possible treponemal bone changes. Those with treponemal bone changes were not demonstrably more likely to be migrants than those without such lesions. However, because of extensive documentary evidence for trade with the Baltic Sea area, and for merchants from towns such as Stralsund, Danzig and Elbing being in Hull, it is very plausible that the four migrants came from the Baltic area or even southern Sweden.

Guideline for Technical Quality Assurance (TQA) of ultrasound devices (B-Mode)--version 1.0 (July 2012): EFSUMB Technical Quality Assurance Group--US-TQA/B

The Technical Quality Assurance group was initiated by the EFSUMB Board in 2007 and met firstly in 2008 to discuss and evaluate methods and procedures published for performing technical quality assurance for diagnostic ultrasound devices. It is the aim of this group of experts to advise the EFSUMB Board of effective and efficacious methods for routine use and to make recommendations regarding the technical aspects of EFSUMB by-law 9, parts 11.6. & 11.7. The group's work focused on new developments and related European projects to establish a common guideline. There is a great need of a well established protocol and dedicated processing software for the performance testing of medical ultrasound equipment. The measurements should be user independent as much as physically possible. Only if these goals are achieved in an international (firstly European) context, the optimal quality of ultrasound imaging can be offered and maintained to the medical community. This guideline aims to offer and summarize suitable procedures and evaluation processes to lend support for an optimal Technical Quality Assurance (TQA) scheme. The content of this guideline was presented to the EFSUMB Board of Directors (delegates) and approved by the EFSUMB Executive Board (ExB) at the regular meeting during EUROSON 2012 in Madrid April 2012.

The antiviral activity and mechanism of action of (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides

One class of compounds that has shown promise as antiviral agents are the (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides, members of the broader class of acyclic nucleoside phosphonates. These HPMP nucleosides are nucleotide analogs and have been shown to be effective inhibitors of a wide range of DNA viruses. Prodrugs of these compounds, which achieve higher levels of the active metabolites within the cell, have an expanded activity spectrum that also includes RNA viruses and retroviruses. Because they are analogs of natural nucleotide substrates, HPMP nucleosides are predicted to target polymerases (DNA polymerases, RNA polymerases and reverse transcriptases), resulting in the inhibition of viral genome replication. Previous work using the replicative enzymes of different viruses including human cytomegalovirus (HCMV) and vaccinia virus DNA polymerases and human immunodeficiency virus type 1 (HIV-1) reverse transcriptase has shown that the activated forms of these compounds are substrates for viral polymerases and that incorporation of these compounds into either the primer strand or the template strand inhibits, but does not necessarily terminate, further nucleic acid synthesis. The activity of these compounds against other viruses that do not encode their own polymerases, like polyoma viruses and papilloma viruses, suggests that host cell DNA polymerases are also targeted. This complex mechanism of action and broad activity spectrum has implications for the development of resistance and host cell genome replication, and suggests these compounds may be effective against other viruses such as influenza virus, respiratory syncytial virus and Dengue virus. This class of nucleotide analogs also points to a potential avenue for the development of newer antivirals.

Sizing gaseous emboli using Doppler embolic signal intensity

Extension of transcranial Doppler embolus detection to estimation of bubble size has historically been hindered by difficulties in applying scattering theory to the interpretation of clinical data. This article presents a simplified approach to the sizing of air emboli based on analysis of Doppler embolic signal intensity, by using an approximation to the full scattering theory that can be solved to estimate embolus size. Tests using simulated emboli show that our algorithm is theoretically capable of sizing 90% of "emboli" to within 10% of their true radius. In vitro tests show that 69% of emboli can be sized to within 20% of their true value under ideal conditions, which reduces to 30% of emboli if the beam and vessel are severely misaligned. Our results demonstrate that estimation of bubble size during clinical monitoring could be used to distinguish benign microbubbles from potentially harmful macrobubbles during intraoperative clinical monitoring.

Grading carotid stenosis using ultrasonic methods

The controversy as to whether Doppler ultrasonic methods should play a role in clinical decision-making in the prevention of stroke is attributable to reported disagreement between angiographic and ultrasonic results and the lack of internationally accepted ultrasound criteria for describing the degree of stenosis. Foremost among the explanations for both is the broad scatter of peak systolic velocities in the stenosis, the criterion that has so far received most attention. Grading based on a set of main and additional criteria can overcome diagnostic errors. Morphological measurements (B-mode images and color flow imaging) are the main criteria for low and moderate degrees of stenosis. Increased velocities in the stenosis indicate narrowing, but the appearance of collateral flow and decreased poststenotic flow velocity prove a high degree stenosis (≥70%), additionally allowing the estimation of the hemodynamic effect in the category of high-degree stenosis. Additional criteria refer to the effect of a stenosis on prestenotic flow (common carotid artery), the extent of poststenotic flow disturbances, and derived velocity criteria (diastolic peak velocity and the carotid ratio). This multiparametric approach is intended to increase the reliability and the standard of reporting of ultrasonic results for arteriosclerotic disease of the carotid artery.

In-fusion® cloning with vaccinia virus DNA polymerase

Vaccinia virus DNA polymerase (VVpol) encodes a 3'-to-5' proofreading exonuclease that can degrade the ends of duplex DNA and expose single-stranded DNA tails. The reaction plays a critical role in promoting virus recombination in vivo because single-strand annealing reactions can then fuse molecules sharing complementary tails into recombinant precursors called joint molecules. We have shown that this reaction can also occur in vitro, providing a simple method for the directional cloning of PCR products into any vector of interest. A commercial form of this recombineering technology called In-Fusion(®) that facilitates high-throughput directional cloning of PCR products has been commercialized by Clontech. To effect the in vitro cloning reaction, PCR products are prepared using primers that add 16-18 bp of sequence to each end of the PCR amplicon that are homologous to the two ends of a linearized vector. The linearized vector and PCR products are coincubated with VVpol, which exposes the complementary ends and promotes joint molecule formation. Vaccinia virus single-stranded DNA binding protein can be added to enhance this reaction, although it is not an essential component. The resulting joint molecules are used to transform E. coli, which convert these noncovalently joined molecules into stable recombinants. We illustrate how this technology works by using, as an example, the cloning of the vaccinia N2L gene into the vector pETBlue-2.

Peptide vaccination is superior to genetic vaccination using a recombineered bacteriophage λ subunit vaccine

Genetic immunization holds promise as a vaccination method, but has so far proven ineffective in large primate and human trials. Herein, we examined the relative merits of genetic immunization and peptide immunization using bacteriophage λ. Bacteriophage λ has proven effective in immune challenge models using both immunization methods, but there has never been a direct comparison of efficacy and of the quality of immune response. In the current study, this vector was produced using a combination of cis and trans phage display. When antibody titers were measured from immunized animals together with IL-2, IL-4 and IFNγ production from splenocytes in vitro, we found that proteins displayed on λ were superior at eliciting an immune response in comparison to genetic immunization with λ. We also found that the antibodies produced in response to immunization with λ displayed proteins bound more epitopes than those produced in response to genetic immunization. Finally, the general immune response to λ inoculation, whether peptide or genetic, was dominated by a Th1 response, as determined by IFNγ and IL-4 concentration, or by a higher concentration of IgG2a antibodies.

Urotensin II and its receptor in the killifish gill: regulators of NaCl extrusion

The peptide urotensin II (UII) and its receptor (UT) mediate cardiovascular and renal effects in both mammals and fishes. In both groups, vasopressor and diuretic responses predominate, although, in mammals, some secondary vasodilatation is found, mediated by secondary release of nitric oxide or prostacyclin. In fishes, gill extrusion of NaCl is inhibited by UII, but a single study has determined that UT is expressed in gill vasculature, not on the epithelium that mediates the transport. To begin to clarify the pathways involved in UII inhibition of gill transport, we have cloned the cDNA encoding UII and UT from the euryhaline killifish (Fundulus heteroclitus L.) gill and spinal cord, quantified UT mRNA expression in various tissues and measured relative expression in gill tissue from fish acclimated to seawater (SW) vs fresh water (FW). We have also localized UT in the gill epithelium, and measured the effect of UII on ion transport across the opercular epithelium. We found that both UII and UT are synthesized in the gill of F. heteroclitus and that gill UT mRNA levels are ∼80% higher in SW- vs FW-acclimated individuals. In addition, UII inhibits NaCl transport across the opercular epithelium in a concentration-dependent manner, and this inhibition is at least partially mediated by both nitric oxide and a prostanoid.

Renal responses to salinity change in snakes with and without salt glands

To understand renal responses to salinity change in aquatic reptiles, we examined the structure and function of the kidney in three species of snake: a marine species with a salt gland (Laticauda semifasciata), a marine species without a salt gland (Nerodia clarkii clarkii) and a freshwater species without a salt gland (Nerodia fasciata). Both marine species maintained relatively constant plasma ions, even after acclimation to saltwater. By contrast, both plasma Cl(-) and mortality increased with salinity in the freshwater species. To investigate putative renal ion regulatory mechanisms, we examined the distribution and abundance of Na(+)/K(+)-ATPase (NKA) and the Na(+)/K(+)/2Cl(-) cotransporter (NKCC2). In all species, NKA localized to the basolateral membranes of the distal tubule and the connecting segments and collecting ducts only; there was no effect of salinity on the distribution of NKA or on the abundance of NKA mRNA in any species. NKCC2 protein was undetectable in the kidney of any of the species and there was no effect of salinity on NKCC2 mRNA abundance. We also examined the distribution and abundance of aquaporin 3 (AQP3) in the kidney of these species; although putative AQP3 localized to the basolateral membranes of the connecting segments and collecting ducts of all three species, there was no effect of salinity on the localization of the protein or the abundance of the transcript. Interestingly, we found very few differences across species, suggesting that the snake kidney may play a trivial role in limiting habitat use.

A selectable and excisable marker system for the rapid creation of recombinant poxviruses

BACKGROUND

Genetic manipulation of poxvirus genomes through attenuation, or insertion of therapeutic genes has led to a number of vector candidates for the treatment of a variety of human diseases. The development of recombinant poxviruses often involves the genomic insertion of a selectable marker for purification and selection purposes. The use of marker genes however inevitably results in a vector that contains unwanted genetic information of no therapeutic value.

METHODOLOGY/PRINCIPAL FINDINGS

Here we describe an improved strategy that allows for the creation of marker-free recombinant poxviruses of any species. The Selectable and Excisable Marker (SEM) system incorporates a unique fusion marker gene for the efficient selection of poxvirus recombinants and the Cre/loxP system to facilitate the subsequent removal of the marker. We have defined and characterized this new methodological tool by insertion of a foreign gene into vaccinia virus, with the subsequent removal of the selectable marker. We then analyzed the importance of loxP orientation during Cre recombination, and show that the SEM system can be used to introduce site-specific deletions or inversions into the viral genome. Finally, we demonstrate that the SEM strategy is amenable to other poxviruses, as demonstrated here with the creation of an ectromelia virus recombinant lacking the EVM002 gene.

CONCLUSION/SIGNIFICANCE

The system described here thus provides a faster, simpler and more efficient means to create clinic-ready recombinant poxviruses for therapeutic gene therapy applications.

Ultrasonic colour Doppler imaging

Ultrasonic colour Doppler is an imaging technique that combines anatomical information derived using ultrasonic pulse-echo techniques with velocity information derived using ultrasonic Doppler techniques to generate colour-coded maps of tissue velocity superimposed on grey-scale images of tissue anatomy. The most common use of the technique is to image the movement of blood through the heart, arteries and veins, but it may also be used to image the motion of solid tissues such as the heart walls. Colour Doppler imaging is now provided on almost all commercial ultrasound machines, and has been found to be of great value in assessing blood flow in many clinical conditions. Although the method for obtaining the velocity information is in many ways similar to the method for obtaining the anatomical information, it is technically more demanding for a number of reasons. It also has a number of weaknesses, perhaps the greatest being that in conventional systems, the velocities measured and thus displayed are the components of the flow velocity directly towards or away from the transducer, while ideally the method would give information about the magnitude and direction of the three-dimensional flow vectors. This review briefly introduces the principles behind colour Doppler imaging and describes some clinical applications. It then describes the basic components of conventional colour Doppler systems and the methods used to derive velocity information from the ultrasound signal. Next, a number of new techniques that seek to overcome the vector problem mentioned above are described. Finally, some examples of vector velocity images are presented.

Freshwater fish gill ion transport: August Krogh to morpholinos and microprobes

August Krogh proposed that freshwater fishes (and other freshwater animals) maintain body NaCl homoeostasis by extracting these ions from the environment via separate Na(+) /NH(4)(+) and Cl(-) /HCO(3)(-) exchangers in the gill epithelium. Subsequent data from other laboratories suggested that Na(+) uptake was more probably coupled to H(+) secretion via a vesicular proton pump (V-ATPase) electrically coupled to a Na(+) channel. However, despite uncertainty about electrochemical gradients, evidence has accrued that epithelial Na(+) /H(+) exchange indeed may be an alternative pathway for Na(+) uptake. The specific pathways for Na(+) uptake may be species and environment specific. An apical Cl(-) /HCO(3)(-) exchanger is generally accepted for most species (some species do not extract Cl(-) from freshwater), but the relative roles of anion exchanger-like (SLC4A1) vs. pendrin-like (SLC26Z4) exchangers are unknown, and also may be species specific. Most recently, data have supported the presence of an apical Na(+) + Cl(-) cotransporter (NCC-type), despite thermodynamic uncertainty. Ammonia extrusion may be via NH(3) diffusing through the paracellular junctions or NH(4) (+) substitution on both basolateral and apical ionic exchangers (Na(+) + K(+) -ATPase; Na(+) + K(+) + Cl(-) - cotransporter; and Na(+) /H(+) exchanger), but recent evidence suggests that Rhesus-glycoproteins mediate both basolateral and apical movement of ammonia.

Solution structure of a DNA duplex containing the potent anti-poxvirus agent cidofovir

Cidofovir (1(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]cytosine, CDV) is a potent inhibitor of orthopoxvirus DNA replication. Prior studies have shown that, when CDV is incorporated into a growing primer strand, it can inhibit both the 3'-to-5' exonuclease and the 5'-to-3' chain extension activities of vaccinia virus DNA polymerase. This drug can also be incorporated into DNA, creating a significant impediment to trans-lesion DNA synthesis in a manner resembling DNA damage. CDV and deoxycytidine share a common nucleobase, but CDV lacks the deoxyribose sugar. The acyclic phosphonate bears a hydroxyl moiety that is equivalent to the 3'-hydroxyl of dCMP and permits CDV incorporation into duplex DNA. To study the structural consequences of inserting CDV into DNA, we have used (1)H NMR to solve the solution structures of a dodecamer DNA duplex containing a CDV molecule at position 7 and of a control DNA duplex. The overall structures of both DNA duplexes were found to be very similar. We observed a decrease of intensity (>50%) for the imino protons neighboring the CDV (G6, T8) and the cognate base G18 and a large chemical shift change for G18. This indicates higher proton exchange rates for this region, which were confirmed using NMR-monitored melting experiments. DNA duplex melting experiments monitored by circular dichroism revealed a lower T(m) for the CDV DNA duplex (46 °C) compared to the control (58 °C) in 0.2 M salt. Our results suggest that the CDV drug is well accommodated and stable within the dodecamer DNA duplex, but the stability of the complex is less than that of the control, suggesting increased dynamics around the CDV.

Vaccinia virus-encoded ribonucleotide reductase subunits are differentially required for replication and pathogenesis

Ribonucleotide reductases (RRs) are evolutionarily-conserved enzymes that catalyze the rate-limiting step during dNTP synthesis in mammals. RR consists of both large (R1) and small (R2) subunits, which are both required for catalysis by the R1₂R2₂ heterotetrameric complex. Poxviruses also encode RR proteins, but while the Orthopoxviruses infecting humans [e.g. vaccinia (VACV), variola, cowpox, and monkeypox viruses] encode both R1 and R2 subunits, the vast majority of Chordopoxviruses encode only R2 subunits. Using plaque morphology, growth curve, and mouse model studies, we investigated the requirement of VACV R1 (I4) and R2 (F4) subunits for replication and pathogenesis using a panel of mutant viruses in which one or more viral RR genes had been inactivated. Surprisingly, VACV F4, but not I4, was required for efficient replication in culture and virulence in mice. The growth defects of VACV strains lacking F4 could be complemented by genes encoding other Chordopoxvirus R2 subunits, suggesting conservation of function between poxvirus R2 proteins. Expression of F4 proteins encoding a point mutation predicted to inactivate RR activity but still allow for interaction with R1 subunits, caused a dominant negative phenotype in growth experiments in the presence or absence of I4. Co-immunoprecipitation studies showed that F4 (as well as other Chordopoxvirus R2 subunits) form hybrid complexes with cellular R1 subunits. Mutant F4 proteins that are unable to interact with host R1 subunits failed to rescue the replication defect of strains lacking F4, suggesting that F4-host R1 complex formation is critical for VACV replication. Our results suggest that poxvirus R2 subunits form functional complexes with host R1 subunits to provide sufficient dNTPs for viral replication. Our results also suggest that R2-deficient poxviruses may be selective oncolytic agents and our bioinformatic analyses provide insights into how poxvirus nucleotide metabolism proteins may have influenced the base composition of these pathogens.

Efficient genome replication is central to the virulence of all DNA viruses, including poxviruses. To ensure replication efficiency, many of the more virulent poxviruses encode their own nucleotide metabolism machinery, including ribonucleotide reductase (RR) enzymes, which act to provide ample DNA precursors for replication. RR enzymes require both large (R1) and small (R2) subunit proteins for activity. Curiously, some poxviruses only encode R2 subunits. Other poxviruses, such as the smallpox vaccine strain, vaccinia virus (VACV), encode both R1 and R2 subunits. We report here that the R2, but not the R1, subunit of VACV RR is required for efficient replication and virulence. We also provide evidence that several poxvirus R2 proteins form novel complexes with host R1 subunits and this interaction is required for efficient VACV replication in primate cells. Our study explains why some poxviruses only encode R2 subunits and identifies a role for these proteins in poxvirus pathogenesis. Furthermore, we provide evidence that mutant poxviruses unable to generate R2 proteins may become entirely dependent upon host RR activity. This may restrict their replication to cells that over-express RR proteins such as cancer cells, making them potential therapeutics for human malignancies.