pUL21 is a viral phosphatase adaptor that promotes herpes simplex virus replication and spread

The herpes simplex virus (HSV)-1 protein pUL21 is essential for efficient virus replication and dissemination. While pUL21 has been shown to promote multiple steps of virus assembly and spread, the molecular basis of its function remained unclear. Here we identify that pUL21 is a virus-encoded adaptor of protein phosphatase 1 (PP1). pUL21 directs the dephosphorylation of cellular and virus proteins, including components of the viral nuclear egress complex, and we define a conserved non-canonical linear motif in pUL21 that is essential for PP1 recruitment. In vitro evolution experiments reveal that pUL21 antagonises the activity of the virus-encoded kinase pUS3, with growth and spread of pUL21 PP1-binding mutant viruses being restored in adapted strains where pUS3 activity is disrupted. This study shows that virus-directed phosphatase activity is essential for efficient herpesvirus assembly and spread, highlighting the fine balance between kinase and phosphatase activity required for optimal virus replication.

Herpes simplex virus (HSV)-1 is a highly prevalent human virus that causes life-long infections. While the most common symptom of HSV-1 infection is orofacial lesions (‘cold sores’), HSV-1 infection can also cause fatal encephalitis and it is a leading cause of infectious blindness. The HSV-1 genome encodes many proteins that dramatically remodel the environment of infected cells to promote virus replication and spread, including enzymes that add phosphate groups (kinases) to cellular and viral proteins in order to fine-tune their function. Here we identify that pUL21 is an HSV-1 protein that binds directly to protein phosphatase 1 (PP1), a highly abundant cellular enzyme that removes phosphate groups from proteins. We demonstrate that pUL21 stimulates the specific dephosphorylation of both cellular and viral proteins, including a component of the viral nuclear egress complex that is essential for efficient assembly of new HSV-1 particles. Furthermore, our in vitro evolution experiments demonstrate that pUL21 antagonises the activity of the HSV-1 kinase pUS3. Our work highlights the precise control that herpesviruses exert upon the protein environment within infected cells, and specifically the careful balance of kinase and phosphatase activity that HSV-1 requires for optimal replication and spread.

Peptide Inhibitor of Complement C1, RLS-0071, Reduces Zosteriform Spread of Herpes Simplex Virus Type 1 Skin Infection and Promotes Survival in Infected Mice

Herpes simplex virus type 1 (HSV-1) is a prevalent human pathogen primarily transmitted through skin-to-skin contact, especially on and around mucosal surfaces where there is contact with contaminated saliva during periods of viral shedding. It is estimated that 90% of adults worldwide have HSV-1 antibodies. Cutaneous HSV-1 infections are characterized by a sensation of tingling or numbness at the initial infection site followed by an eruption of vesicles and then painful ulcers with crusting. These symptoms can take ten days to several weeks to heal, leading to significant morbidity. Histologically, infections cause ballooning degeneration of keratinocytes and formation of multinucleated giant cells, ultimately resulting in a localized immune response. Commonly prescribed treatments against HSV-1 infections are nucleoside analogs, such as acyclovir (ACV). However, the emergence of ACV-resistant HSV (ACV^R-HSV) clinical isolates has created an urgent need for the development of compounds to control symptoms of cutaneous infections. RLS-0071, also known as peptide inhibitor of complement C1 (PIC1), is a 15-amino-acid anti-inflammatory peptide that inhibits classical complement pathway activation and modulates neutrophil activation. It has been previously shown to aid in the healing of chronic diabetic wounds by inhibiting the excessive activation of complement component C1 and infiltration of leukocytes. Here, we report that treatment of cutaneous infections of HSV-1 and ACV^R-HSV-1 in BALB/cJ mice with RLS-0071 significantly reduced the rate of mortality, decreased zosteriform spread, and enhanced the healing of the infection-associated lesions compared to control-treated animals. Therefore, RLS-0071 may work synergistically with other antiviral drugs to aid in wound healing of HSV-1 cutaneous infection and may potentially aid in rapid wound healing of other pathology not limited to HSV-1.

Species-Specific Deamidation of RIG-I Reveals Collaborative Action between Viral and Cellular Deamidases in HSV-1 Lytic Replication

Retinoic acid-inducible gene I (RIG-I) is a sensor that recognizes cytosolic double-stranded RNA derived from microbes to induce host immune response. Viruses, such as herpesviruses, deploy diverse mechanisms to derail RIG-I-dependent innate immune defense. In this study, we discovered that mouse RIG-I is intrinsically resistant to deamidation and evasion by herpes simplex virus 1 (HSV-1). Comparative studies involving human and mouse RIG-I indicate that N495 of human RIG-I dictates species-specific deamidation by HSV-1 UL37. Remarkably, deamidation of the other site, N549, hinges on that of N495, and it is catalyzed by cellular phosphoribosylpyrophosphate amidotransferase (PPAT). Specifically, deamidation of N495 enables RIG-I to interact with PPAT, leading to subsequent deamidation of N549. Collaboration between UL37 and PPAT is required for HSV-1 to evade RIG-I-mediated antiviral immune response. This work identifies an immune regulatory role of PPAT in innate host defense and establishes a sequential deamidation event catalyzed by distinct deamidases in immune evasion.IMPORTANCE Herpesviruses are ubiquitous pathogens in human and establish lifelong persistence despite host immunity. The ability to evade host immune response is pivotal for viral persistence and pathogenesis. In this study, we investigated the evasion, mediated by deamidation, of species-specific RIG-I by herpes simplex virus 1 (HSV-1). Our findings uncovered a collaborative and sequential action between viral deamidase UL37 and a cellular glutamine amidotransferase, phosphoribosylpyrophosphate amidotransferase (PPAT), to inactivate RIG-I and mute antiviral gene expression. PPAT catalyzes the rate-limiting step of the de novo purine synthesis pathway. This work describes a new function of cellular metabolic enzymes in host defense and viral immune evasion.

Us3 Protein Kinase Encoded by HSV: The Precise Function and Mechanism on Viral Life Cycle

All members of the Alphaherpesvirinae subfamily encode a serine/threonine kinase, designated Us3, which is not conserved in the other subfamilies. Us3 is a significant virulence factor for herpes simplex virus type 1 (HSV-1), which is one of the best-characterized members of the Alphaherpesvirinae family. Accumulating evidence indicates that HSV-1 Us3 is a multifunctional protein that plays various roles in the viral life cycle by phosphorylating a number of viral and cellular substrates. Therefore, the identification of Us3 substrates is directly connected to understanding Us3 functions and mechanisms. To date, more than 23 phosphorylation events upregulated by HSV-1 Us3 have been reported. However, few of these have been shown to be both physiological substrates of Us3 in infected cells and directly linked with Us3 functions in infected cells. In this chapter, we summarize the 12 physiological substrates of Us3 and the Us3-mediated functions. Furthermore, based on the identified phosphorylation sites of Us3 or Us3 homolog physiological substrates, we reverified consensus phosphorylation target sequences on the physiological substrates of Us3 and Us3 homologs in vitro and in infected cells. This information might aid the further identification of novel Us3 substrates and as yet unidentified Us3 functions.

A genome-wide screen of Epstein-Barr virus proteins that modulate host SUMOylation identifies a SUMO E3 ligase conserved in herpesviruses

Many cellular processes pertinent for viral infection are regulated by the addition of small ubiquitin-like modifiers (SUMO) to key regulatory proteins, making SUMOylation an important mechanism by which viruses can commandeer cellular pathways. Epstein-Barr virus (EBV) is a master at manipulating of cellular processes, which enables life-long infection but can also lead to the induction of a variety of EBV-associated cancers. To identify new mechanisms by which EBV proteins alter cells, we screened a library of 51 EBV proteins for global effects on cellular SUMO1 and SUMO2 modifications (SUMOylation), identifying several proteins not previously known to manipulate this pathway. One EBV protein (BRLF1) globally induced the loss of SUMOylated proteins, in a proteasome-dependent manner, as well as the loss of promeylocytic leukemia nuclear bodies. However, unlike its homologue (Rta) in Kaposi's sarcoma associated herpesvirus, it did not appear to have ubiquitin ligase activity. In addition we identified the EBV SM protein as globally upregulating SUMOylation and showed that this activity was conserved in its homologues in herpes simplex virus 1 (HSV1 UL54/ICP27) and cytomegalovirus (CMV UL69). All three viral homologues were shown to bind SUMO and Ubc9 and to have E3 SUMO ligase activity in a purified system. These are the first SUMO E3 ligases discovered for EBV, HSV1 and CMV. Interestingly the homologues had different specificities for SUMO1 and SUMO2, with SM and UL69 preferentially binding SUMO1 and inducing SUMO1 modifications, and UL54 preferentially binding SUMO2 and inducing SUMO2 modifications. The results provide new insights into the function of this family of conserved herpesvirus proteins, and the conservation of this SUMO E3 ligase activity across diverse herpesviruses suggests the importance of this activity for herpesvirus infections.

Prevalence of Intrathecal Acyclovir Resistant Virus in Herpes Simplex Encephalitis Patients

Herpes simplex encephalitis (HSE) is a life-threatening complication of herpes simplex virus (HSV) infection. Acyclovir (ACV) is the antiviral treatment of choice, but may lead to emergence of ACV-resistant (ACV^R) HSV due to mutations in the viral UL23 gene encoding for the ACV-targeted thymidine kinase (TK) protein. Here, we determined the prevalence of intrathecal ACV^R–associated HSV TK mutations in HSE patients and compared TK genotypes of sequential HSV isolates in paired cerebrospinal fluid (CSF) and blister fluid of mucosal HSV lesions. Clinical samples were obtained from 12 HSE patients, encompassing 4 HSV type 1 (HSV-1) and 8 HSV-2 encephalitis patients. HSV DNA load was determined by real-time PCR and complete HSV TK gene sequences were obtained by nested PCR followed by Sanger sequencing. All HSV-1 HSE patients contained viral TK mutations encompassing 30 unique nucleotide and 13 distinct amino acid mutations. By contrast, a total of 5 unique nucleotide and 4 distinct amino acid changes were detected in 7 of 8 HSV-2 patients. Detected mutations were identified as natural polymorphisms located in non-conserved HSV TK gene regions. ACV therapy did not induce the emergence of ACV^R-associated HSV TK mutations in consecutive CSF and mucocutaneous samples of 5 individual patients. Phenotypic susceptibility analysis of these mucocutaneous HSV isolates demonstrated ACV-sensitive virus in 2 HSV-1 HSE patients, whereas in two HSV-2 HSE patients ACV^R virus was detected in the absence of known ACV^R-associated TK mutations. In conclusion, we did not detect intrathecal ACV^R-associated TK mutations in HSV isolates obtained from 12 HSE patients.

Polymeric nanoparticles for nonviral gene therapy extend brain tumor survival in vivo

Biodegradable polymeric nanoparticles have the potential to be safer alternatives to viruses for gene delivery; however, their use has been limited by poor efficacy in vivo. In this work, we synthesize and characterize polymeric gene delivery nanoparticles and evaluate their efficacy for DNA delivery of herpes simplex virus type I thymidine kinase (HSVtk) combined with the prodrug ganciclovir (GCV) in a malignant glioma model. We investigated polymer structure for gene delivery in two rat glioma cell lines, 9L and F98, to discover nanoparticle formulations more effective than the leading commercial reagent Lipofectamine 2000. The lead polymer structure, poly(1,4-butanediol diacrylate-co-4-amino-1-butanol) end-modified with 1-(3-aminopropyl)-4-methylpiperazine, is a poly(β-amino ester) (PBAE) and formed nanoparticles with HSVtk DNA that were 138 ± 4 nm in size and 13 ± 1 mV in zeta potential. These nanoparticles containing HSVtk DNA showed 100% cancer cell killing in vitro in the two glioma cell lines when combined with GCV exposure, while control nanoparticles encoding GFP maintained robust cell viability. For in vivo evaluation, tumor-bearing rats were treated with PBAE/HSVtk infusion via convection-enhanced delivery (CED) in combination with systemic administration of GCV. These treated animals showed a significant benefit in survival (p = 0.0012 vs control). Moreover, following a single CED infusion, labeled PBAE nanoparticles spread completely throughout the tumor. This study highlights a nanomedicine approach that is highly promising for the treatment of malignant glioma.

Herpes simplex virus 1 Us3 deletion mutant is infective despite impaired capsid translocation to the cytoplasm

Herpes simplex virus 1 (HSV-1) capsids are assembled in the nucleus bud at the inner nuclear membrane into the perinuclear space, acquiring envelope and tegument. In theory, these virions are de-enveloped by fusion of the envelope with the outer nuclear membrane and re-enveloped by Golgi membranes to become infective. Us3 enables the nucleus to cytoplasm capsid translocation. Nevertheless, Us3 is not essential for the production of infective progeny viruses. Determination of phenotype distribution by quantitative electron microscopy, and calculation per mean nuclear or cell volume revealed the following: (i) The number of R7041(∆US3) capsids budding at the inner nuclear membrane was significantly higher than that of wild type HSV-1; (ii) The mean number of R7041(∆US3) virions per mean cell volume was 2726, that of HSV-1 virions 1460 by 24 h post inoculation; (iii) 98% of R7041(∆US3) virions were in the perinuclear space; (iv) The number of R7041(∆US3) capsids in the cytoplasm, including those budding at Golgi membranes, was significantly reduced. Cell associated R7041(∆US3) yields were 2.37×10(8) and HSV-1 yields 1.57×10(8) PFU/mL by 24 h post inoculation. We thus conclude that R7041(∆US3) virions, which acquire envelope and tegument by budding at the inner nuclear membrane into the perinuclear space, are infective.

An optimized triple modality reporter for quantitative in vivo tumor imaging and therapy evaluation

We present an optimized triple modality reporter construct combining a far-red fluorescent protein (E2-Crimson), enhanced firefly luciferase enzyme (Luc2), and truncated wild type herpes simplex virus I thymidine kinase (wttk) that allows for sensitive, long-term tracking of tumor growth in vivo by fluorescence, bioluminescence, and positron emission tomography. Two human cancer cell lines (MDA-MB-231 breast cancer and HT-1080 fibrosarcoma cancer) were successfully transduced to express this triple modality reporter. Fluorescence and bioluminescence imaging of the triple modality reporter were used to accurately quantify the therapeutic responses of MDA-MB-231 tumors to the chemotherapeutic agent monomethyl auristatin E in vivo in athymic nude mice. Positive correlation was observed between the fluorescence and bioluminescence signals, and these signals were also positively correlated with the ex vivo tumor weights. This is the first reported use of both fluorescence and bioluminescence signals from a multi-modality reporter construct to measure drug efficacy in vivo.

Two overlapping regions within the N-terminal half of the herpes simplex virus 1 E3 ubiquitin ligase ICP0 facilitate the degradation and dissociation of PML and dissociation of Sp100 from ND10

Herpes simplex virus 1 (HSV-1) establishes a lifelong latent infection in sensory neurons and can reactivate from latency under stress conditions. To promote lytic infection, the virus must interact with specific cellular factors to evade the host's antiviral defenses. The HSV-1 E3 ubiquitin ligase, infected cell protein 0 (ICP0), activates transcription of viral genes, in part, by mediating the degradation of certain cellular proteins that play a role in host antiviral mechanisms. One component of the cellular defenses that ICP0 disrupts is the suborganelle, nuclear domain 10 (ND10), by inducing the degradation and dissociation of the major organizer of ND10, a promyelocytic leukemia (PML) and ND10 constituent, Sp100. Because previously identified domains in ICP0 explain only partially how it directs the degradation and dissociation of PML and Sp100, we hypothesized that additional regions within ICP0 may contribute to these activities, which in turn facilitate efficient viral replication. To test this hypothesis, we used a series of ICP0 truncation mutants and examined PML protein levels and PML and Sp100 immunofluorescence staining in human embryonic lung cells. Our results demonstrate that two overlapping regions within the central N-terminal portion of ICP0 (residues 212 to 311) promoted the dissociation and degradation of PML and dissociation of Sp100 (residues 212 to 427). In conclusion, we have identified two additional regions in ICP0 involved in altering ND10 antiviral defenses in a cell culture model of HSV-1 infection.

Targeting of herpes simplex virus 1 thymidine kinase gene sequences into the OCT4 locus of human induced pluripotent stem cells

The in vitro differentiation of human induced pluripotent stem cells (hiPSC) to generate specific types of cells is inefficient, and the remaining undifferentiated cells may form teratomas. This raises safety concerns for clinical applications of hiPSC-derived cellular products. To improve the safety of hiPSC, we attempted to site-specifically insert a herpes simplex virus 1 thymidine kinase (HSV1-TK) suicide gene at the endogenous OCT4 (POU5F1) locus of hiPSC. Since the endogenous OCT4 promoter is active in undifferentiated cells only, we speculated that the HSV1-TK suicide gene will be transcribed in undifferentiated cells only and that the remaining undifferentiated cells can be depleted by treating them with the prodrug ganciclovir (GCV) prior to transplantation. To insert the HSV1-TK gene at the OCT4 locus, we cotransfected hiPSC with a pair of plasmids encoding an OCT4-specific zinc finger nuclease (ZFN) and a donor plasmid harboring a promoter-less transgene cassette consisting of HSV1-TK and puromycin resistance gene sequences, flanked by OCT4 gene sequences. Puromycin resistant clones were established and characterized regarding their sensitivity to GCV and the site of integration of the HSV1-TK/puromycin resistance gene cassette. Of the nine puromycin-resistant iPSC clones analyzed, three contained the HSV1-TK transgene at the OCT4 locus, but they were not sensitive to GCV. The other six clones were GCV-sensitive, but the TK gene was located at off-target sites. These TK-expressing hiPSC clones remained GCV sensitive for up to 90 days, indicating that TK transgene expression was stable. Possible reasons for our failed attempt to selectively target the OCT4 locus are discussed.

A multi-targeted drug candidate with dual anti-HIV and anti-HSV activity

Human immunodeficiency virus (HIV) infection is often accompanied by infection with other pathogens, in particular herpes simplex virus type 2 (HSV-2). The resulting coinfection is involved in a vicious circle of mutual facilitations. Therefore, an important task is to develop a compound that is highly potent against both viruses to suppress their transmission and replication. Here, we report on the discovery of such a compound, designated PMEO-DAPym. We compared its properties with those of the structurally related and clinically used acyclic nucleoside phosphonates (ANPs) tenofovir and adefovir. We demonstrated the potent anti-HIV and -HSV activity of this drug in a diverse set of clinically relevant in vitro, ex vivo, and in vivo systems including (i) CD4⁺ T-lymphocyte (CEM) cell cultures, (ii) embryonic lung (HEL) cell cultures, (iii) organotypic epithelial raft cultures of primary human keratinocytes (PHKs), (iv) primary human monocyte/macrophage (M/M) cell cultures, (v) human ex vivo lymphoid tissue, and (vi) athymic nude mice. Upon conversion to its diphosphate metabolite, PMEO-DAPym markedly inhibits both HIV-1 reverse transcriptase (RT) and HSV DNA polymerase. However, in striking contrast to tenofovir and adefovir, it also acts as an efficient immunomodulator, inducing β-chemokines in PBMC cultures, in particular the CCR5 agonists MIP-1β, MIP-1α and RANTES but not the CXCR4 agonist SDF-1, without the need to be intracellularly metabolized. Such specific β-chemokine upregulation required new mRNA synthesis. The upregulation of β-chemokines was shown to be associated with a pronounced downmodulation of the HIV-1 coreceptor CCR5 which may result in prevention of HIV entry. PMEO-DAPym belongs conceptually to a new class of efficient multitargeted antivirals for concomitant dual-viral (HSV/HIV) infection therapy through inhibition of virus-specific pathways (i.e. the viral polymerases) and HIV transmission prevention through interference with host pathways (i.e. CCR5 receptor down regulation).

To contain the HIV-1 epidemic, it is necessary to develop antivirals that prevent HIV-1 transmission. It is well known that HIV infection might be accompanied by other pathogens, which often are engaged with HIV-1 in a vicious circle of mutual facilitation. One of the most common of these pathogens is herpes simplex virus (HSV) type 2. Since there is an urgent need for a next generation antivirals that are multi-targeted, we can now report on the development of the first antiviral of this new generation that efficiently suppresses both HIV-1 and HSV-2. We found that the dual-targeted antiviral drug affects several targets for viral replication. It uniquely combines in one molecule three important abilities: (i) to efficiently suppress HSV-encoded DNA polymerase, (ii) to efficiently suppress HIV-1-encoded reverse transcriptase, and (iii) to stimulate secretion of CC-chemokines that downregulate the HIV-1 coreceptor CCR5. The compound suppresses both viruses in a wide-range of in vitro, ex vivo, and in vivo experimental models. The ability of one molecule to suppress HIV-1 and HSV-2 by combining direct activity against their two key enzymes and indirect immunomodulatory effects is unique in the antiviral field.

Synthesis and biological evaluation of a new acyclic pyrimidine derivative as a probe for imaging herpes simplex virus type 1 thymidine kinase gene expression

With the idea of finding a more selective radiotracer for imaging herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene expression by means of positron emission tomography (PET), a novel [¹⁸F]fluorine radiolabeled pyrimidine with 4-hydroxy-3-(hydroxymethyl)butyl side chain at N-1 (HHB-5-[¹⁸F]FEP) was prepared and evaluated as a potential PET probe. Unlabeled reference compound, HHB-5-FEP, was synthesized via a five-step reaction sequence starting from 5-(2-acetoxyethyl)-4-methoxypyrimidin-2-one. The radiosynthesis of HHB-[¹⁸F]-FEP was accomplished by nucleophilic radiofluorination of a tosylate precursor using [¹⁸F]fluoride-cryptate complex in 45% ± 4 (n = 4) radiochemical yields and high purity (>99%). The biological evaluation indicated the feasibility of using HHB-5-[¹⁸F]FEP as a PET radiotracer for monitoring HSV1-tk expression in vivo.

C-5 hydroxyethyl and hydroxypropyl acyclonucleosides as substrates for thymidine kinase of herpes simplex virus type 1 (HSV-1 TK): syntheses and biological evaluation

The efficient syntheses of 5-(2-hydroxyethyl)- and 5-(3-hydroxypropyl)-substituted pyrimidine derivatives bearing 2,3-dihydroxypropyl, acyclovir-, ganciclovir- and penciclovir-like side chains are reported. A synthetic approach that included the alkylation of an N-anionic-5-substituted pyrimidine intermediate (method A) provided the target acyclonucleosides in significantly higher overall yields in comparison to those obtained by method B using sylilation reaction. The phosphorylation assays of novel compounds as potential substrates for thymidine kinase of herpes simplex virus type 1 (HSV-1 TK) showed that solely pyrimidine 5-substituted acyclonucleosides with a penciclovir-like side chain acted as a fraudulent substrates of HSV-1 TK. Moreover, the uracil derivative with penciclovir-like side chain with less bulky 2-hydroxyethyl substituent at C-5 proved to be a better substrate than the corresponding one with a 3-hydroxypropyl substituent. Therefore, this acyclonucleoside was selected as a lead compound for the development of a positron emission tomography HSV-1 TK activity imaging agent.

Real-time dynamic optical imaging of ACC-M tumor cells killed by HSV-tk/ACV system

HSV-tk/ACV induced and killed human adenoid cystic carcinoma cell (ACC-M) in vivo and in vitro, which were observed through optical imaging and green fluorescence protein (GFP) tagging technique. ACC-M was transfected with TK-GFP, and the single clone cell ACC-M-TK-GFP was selected by G418. With fluorescent stereomicroscope, whole-body fluorescent imaging system and fluorescent microscope, we could observe ACV treated ACC-M-TK-GFP cells in cell level and nude mice. The therapies of tumor were visualized clearly with optical imaging. This study proves that optical imaging is a very good approach for studying the effect of HSV-tk/ACV on the ACC-M tumor cells and decreasing the amount of vessel about tumors cell. Optical imaging will become a visual groundwork for monitoring tumor growth and evaluating in vivo curative effect of antitumor drugs.

[Inhibition of herpes simplex virus helicase UL9 by netropsin derivatives and antiviral activities of bis-netropsins]

Data obtained show that antiviral activities of bis-linked netropsin derivatives are targeted by specific complexes formed by helicase UL9 of herpes simplex virus type 1 with viral DNA replication origins, represented by two OriS sites and one OriL site. According to the results of footprinting studies bis-netropsins get bound selectively to an A+T-cluster which separates interaction sites I and II for helicase UL9 in OriS. Upon binding to DNA bis-netropsins stabilize a structure of the A+T-cluster and inhibit thermal fluctuation-induced opening of AT- base pairs which is needed for local unwinding of DNA by helicase UL9. Kinetics of ATP-dependent DNA unwinding in the presence and absence of Pt-bis-netropsin are studied by measuring the efficiency of Forster resonance energy transfer (FRET) between the fluorescent probes attached covalently to 3?- and 5?-ends of the oligonucleotides in the minimal OriS duplex. Pt-bis-netropsin and related molecules inhibit unwinding of OriS duplex by helicase UL9. Pt-bis-netropsin is also able to reduce the rate of unwinding of the AT- rich hairpin formed by the upper strand in the minimal OriS duplex. The antiviral activities and toxicity of bis-linked netropsin derivatives are studied in cell cultured experiments and experiments with animals infected by herpes virus.

[Enzymatic activity of thymidine kinase of herpes simlex virus strain resistant to H-phosphonates of Acv]

Cloned laboratory mutants of herpes simplex virus type I resistant to acycloguanosine H-phosphonate have been investigated. For all clones were shown that mutations resulted to increasing of sensitivity to acting of sidofovir. Thymidine kinase of mutant viruses partially preserves the ability to phosphorilate thymidine, but loses the ability to phosphorilate BVDU.

A Cre-dependent, anterograde transsynaptic viral tracer for mapping output pathways of genetically marked neurons

Neurotropic viruses that conditionally infect or replicate in molecularly defined neuronal subpopulations, and then spread transsynaptically, are powerful tools for mapping neural pathways. Genetically targetable retrograde transsynaptic tracer viruses are available to map the inputs to specific neuronal subpopulations, but an analogous tool for mapping synaptic outputs is not yet available. Here we describe a Cre recombinase-dependent, anterograde transneuronal tracer, based on the H129 strain of herpes simplex virus (HSV). Application of this virus to transgenic or knockin mice expressing Cre in peripheral neurons of the olfactory epithelium or the retina reveals widespread, polysynaptic labeling of higher-order neurons in the olfactory and visual systems, respectively. Polysynaptic pathways were also labeled from cerebellar Purkinje cells. In each system, the pattern of labeling was consistent with classical circuit-tracing studies, restricted to neurons, and anterograde specific. These data provide proof-of-principle for a conditional, nondiluting anterograde transsynaptic tracer for mapping synaptic outputs from genetically marked neuronal subpopulations.

Reduced expression of brain-enriched microRNAs in glioblastomas permits targeted regulation of a cell death gene

Glioblastoma is a highly aggressive malignant tumor involving glial cells in the human brain. We used high-throughput sequencing to comprehensively profile the small RNAs expressed in glioblastoma and non-tumor brain tissues. MicroRNAs (miRNAs) made up the large majority of small RNAs, and we identified over 400 different cellular pre-miRNAs. No known viral miRNAs were detected in any of the samples analyzed. Cluster analysis revealed several miRNAs that were significantly down-regulated in glioblastomas, including miR-128, miR-124, miR-7, miR-139, miR-95, and miR-873. Post-transcriptional editing was observed for several miRNAs, including the miR-376 family, miR-411, miR-381, and miR-379. Using the deep sequencing information, we designed a lentiviral vector expressing a cell suicide gene, the herpes simplex virus thymidine kinase (HSV-TK) gene, under the regulation of a miRNA, miR-128, that was found to be enriched in non-tumor brain tissue yet down-regulated in glioblastomas, Glioblastoma cells transduced with this vector were selectively killed when cultured in the presence of ganciclovir. Using an in vitro model to recapitulate expression of brain-enriched miRNAs, we demonstrated that neuronally differentiated SH-SY5Y cells transduced with the miRNA-regulated HSV-TK vector are protected from killing by expression of endogenous miR-128. Together, these results provide an in-depth analysis of miRNA dysregulation in glioblastoma and demonstrate the potential utility of these data in the design of miRNA-regulated therapies for the treatment of brain cancers.

Effect of ASP2151, a herpesvirus helicase-primase inhibitor, in a guinea pig model of genital herpes

ASP2151 is a herpesvirus helicase-primase inhibitor with antiviral activity against varicella zoster virus and herpes simplex virus types 1 (HSV-1) and 2 (HSV-2). Here, we examined the potency and efficacy of ASP2151 against HSV in vitro and in vivo. We found that ASP2151 was more potent in inhibiting the replication of HSV-1 and HSV-2 in Vero cells in the plaque reduction assay and had greater anti-HSV activity in a guinea pig model of genital herpes than did acyclovir and valacyclovir (VACV), respectively. Oral ASP2151 given from the day of infection reduced peak and overall disease scores in a dose-dependent manner, resulting in complete prevention of symptoms at the dose of 30 mg/kg. The 50% effective dose (ED(50)) values for ASP2151 and VACV were 0.37 and 68 mg/kg, respectively, indicating that ASP2151 was 184-fold more potent than VACV. When ASP2151 was administered after the onset of symptoms, the disease course of genital herpes was suppressed more effectively than by VACV, with a significant reduction in disease score observed one day after starting ASP2151 at 30 mg/kg, whereas the therapeutic effect of VACV was only evident three days after treatment at the highest dose tested (300 mg/kg). This indicated that ASP2151 possesses a faster onset of action and wider therapeutic time window than VACV. Further, virus shedding from the genital mucosa was significantly reduced with ASP2151 at 10 and 30 mg/kg but not with VACV, even at 300 mg/kg. Taken together, our present findings demonstrated the superior potency and efficacy of ASP2151 against HSV.

Long-term observation of herpes simplex virus type 1 (HSV-1) infection in a child with Wiskott-Aldrich syndrome and a possible reactivation mechanism for thymidine kinase-negative HSV-1 in humans

Herpes simplex virus type 1 (HSV-1) infections in a child with congenital immunodeficiency syndrome were observed over a 10-year period. The child suffered from recurrent and severe HSV-1 mucocutaneous infections. He frequently suffered from acyclovir (ACV)-resistant (ACV(r)) HSV-1 infection in the later phase of his life, especially after the episode of ACV(r) HSV-1 infection. Virological analyses on the HSV-1 isolates recovered from this patient revealed that all the ACV(r) HSV-1 isolates were thymidine kinase (TK)-negative (TK(-)) due to a single cytosine (C) deletion within the 4-C residues (positions 1061 to 1064) in the TK gene, indicating that the recurrent TK(-)/ACV(r) HSV-1 infections throughout the patient's life were due to the identical ACV(r) HSV-1 strain. Furthermore, it was found that the ACV-sensitive (ACV(s)) isolate recovered from the skin lesions that appeared between the episodes of ACV(r) infection at the ages of 8 and 9 contained ACV(r) HSV-1 with the same mutation in the TK gene. These results indicate that, although TK activity is required for reactivation of TK(+)/ACV(s) HSV-1 from latency and TK(-)/ACV(r) HSV-1 is unable to reactivate from latency, the TK(-)/ACV(r) HSV-1 strain isolated herein reactivated in this patient, possibly by using the TK activity induced by the latently co-infected TK(+)/ACV(s) HSV-1.

Antiviral drug resistance and helicase-primase inhibitors of herpes simplex virus

A new class of chemical inhibitors has been discovered that interferes with the process of herpesvirus DNA replication. To date, the majority of useful herpesvirus antivirals are nucleoside analogues that block herpesvirus DNA replication by targeting the DNA polymerase. The new helicase-primase inhibitors (HPI) target a different enzyme complex that is also essential for herpesvirus DNA replication. This review will place the HPI in the context of previous work on the nucleoside analogues. Several promising highly potent HPI will be described with a particular focus on the identification of drug-resistance mutations. Several HPI have good pharmacological profiles and are now at the outset of phase II clinical trials. Provided there are no safety issues to stop their progress, this new class of compound will be a major advance in the herpesvirus antiviral field. Furthermore, HPI are likely to have a major impact on the therapy and prevention of herpes simplex virus and varicella zoster in both immunocompetent and immunocompromised patients alone or in combination with current nucleoside analogues. The possibility of acquired drug-resistance to HPI will then become an issue of great practical importance.

[Analysis of mutations in DNA polymerase and thymidine kinase genes of herpes simplex virus clinical isolates resistant to antiherpetic drugs]

The primary structures of DNA-polymerase (ul30) and thymidine kinase (ul23) genes from several herpes simplex virus type 1 (HSV-1) clinical isolates which differed in sensitivity for a number of antiherpetic drugs were determined and compared with those for two laboratory HSV-1 strains one of which was ACV-sensitive (L2), while the another was resistant (L2) to ACV. The phylogenetic analysis of the sequences showed that conserved regions of ul30 gene of HSV-1 clinical isolates and L2 strain were homologous with the exception of point mutations and degenerated substitutions. Several new mutations in the HSV-1 DNA-polymerase and thymidine kinase functional domains were established and identified as the substitutions associated with the strain-resistance to ACV and other drugs.

A novel bicistronic high-capacity gutless adenovirus vector that drives constitutive expression of herpes simplex virus type 1 thymidine kinase and tet-inducible expression of Flt3L for glioma therapeutics

Glioblastoma multiforme (GBM) is a deadly primary brain tumor. Conditional cytotoxic/immune-stimulatory gene therapy (Ad-TK and Ad-Flt3L) elicits tumor regression and immunological memory in rodent GBM models. Since the majority of patients enrolled in clinical trials would exhibit adenovirus immunity, which could curtail transgene expression and therapeutic efficacy, we used high-capacity adenovirus vectors (HC-Ads) as a gene delivery platform. Herein, we describe for the first time a novel bicistronic HC-Ad driving constitutive expression of herpes simplex virus type 1 thymidine kinase (HSV1-TK) and inducible Tet-mediated expression of Flt3L within a single-vector platform. We achieved anti-GBM therapeutic efficacy with no overt toxicities using this bicistronic HC-Ad even in the presence of systemic Ad immunity. The bicistronic HC-Ad-TK/TetOn-Flt3L was delivered into intracranial gliomas in rats. Survival, vector biodistribution, neuropathology, systemic toxicity, and neurobehavioral deficits were assessed for up to 1 year posttreatment. Therapeutic efficacy was also assessed in animals preimmunized against Ads. We demonstrate therapeutic efficacy, with vector genomes being restricted to the brain injection site and an absence of overt toxicities. Importantly, antiadenoviral immunity did not inhibit therapeutic efficacy. These data represent the first report of a bicistronic vector platform driving the expression of two therapeutic transgenes, i.e., constitutive HSV1-TK and inducible Flt3L genes. Further, our data demonstrate no promoter interference and optimum gene delivery and expression from within this single-vector platform. Analysis of the efficacy, safety, and toxicity of this bicistronic HC-Ad vector in an animal model of GBM strongly supports further preclinical testing and downstream process development of HC-Ad-TK/TetOn-Flt3L for a future phase I clinical trial for GBM.

Genetically engineered T-cells expressing a ganciclovir-sensitive HSV-tk suicide gene for the prevention of GvHD

In vitro and in vivo preclinical studies and phase I/II clinical trials have demonstrated that the retroviral-mediated transfer of the suicide gene HSV-thymidine kinase into donor T-cells prior to infusion (ie, a 2-week ex vivo process including activation, retroviral transduction and selection of transduced cells), at the time of T-cell-depleted hematopoietic stem cell transplantation (HSCT) or as donor lymphocyte infusion after relapse, allows for the efficient control of donor T-cell alloreactivity. These donor suicide gene-modified T-cells (SGMTCs) can provide beneficial anti-leukemic, antiviral and immune reconstitution-facilitating effects to the recipient of an allogeneic HSCT. However, if the infused SGMTCs lead to GvHD, a severe complication of HSCT, these cells can be specifically depleted in vivo by the administration of the prodrug ganciclovir (GCV), without any associated immunosuppression. Limitations to this approach include a gene transfer-induced decrease in alloreactivity and antiviral reactivity, the immunogenicity of SGMTCs, and the development of GCV-resistant SGMTCs. However, major improvements that can prevent these limitations, such as introducing CD3/CD28 costimulation and immunomagnetic selection, have been applied to this approach, but further improvements are still required. The efficacy of suicide gene therapy as a safety control system allows the development of this strategy for gene therapy or immunotherapy approaches.

Kupfer-type immunological synapse characteristics do not predict anti-brain tumor cytolytic T-cell function in vivo

To analyze the in vivo structure of antigen-specific immunological synapses during an effective immune response, we established brain tumors expressing the surrogate tumor antigen ovalbumin and labeled antigen-specific anti-glioma T cells using specific tetramers. Using these techniques, we determined that a significant number of antigen-specific T cells were localized to the brain tumor and surrounding brain tissue and a large percentage could be induced to express IFNgamma when exposed to the specific ovalbumin-derived peptide epitope SIINFEKL. Detailed morphological analysis of T cells immunoreactive for tetramers in direct physical contact with tumor cells expressing ovalbumin indicated that the interface between T cells and target tumor cells displayed various morphologies, including Kupfer-type immunological synapses. Quantitative analysis of adjacent confocal optical sections was performed to determine if the higher frequency of antigen-specific antiglioma T cells present in animals that developed an effective antitumor immune response could be correlated with a specific immunological synaptic morphology. Detailed in vivo quantitative analysis failed to detect an increased proportion of immunological synapses displaying the characteristic Kupfer-type morphology in animals mounting a strong and effective antitumor immune response as compared with those experiencing a clinically ineffective response. We conclude that an effective cytolytic immune response is not dependent on an increased frequency of Kupfer-type immunological synapses between T cells and tumor cells.

[Complex of the herpes simplex virus initiator protein UL9 with DNA as a platform for the design of a new type of antiviral drugs]

The protein binding to the origin of replication of the herpes simplex virus type 1 (HSV-1) is DNA helicase encoded by the UL9 gene of the herpes virus. The protein specifically binds to two binding sites in the viral DNA replication origins OriS or OriL. In order to determine the role of the UL9 protein in the initiation of replication and find efficient inhibitors of the UL9 activity, we have synthesized a recombinant UL9 protein expressed in E. coli cells. It was found that the recombinant UL9 protein binds to Boxes I and II in the OriS and possesses the DNA helicase and ATPase activities. In a complex with a fluorescent analog of ATP, two molecules of the ATP analog bind to one protein dimer molecule. It was also found that the UL9 protein in the dimer form can bind simultaneously to two DNA fragments, each containing specific binding sites for the protein. The interaction of the recombinant UL9 protein with the 63-mer double and single-stranded oligonucleotides OriS and OriS* has been investigated, which correspond to the origin of replication of herpes simplex virus. From the titrations of OriS and OriS* by ethidium bromide in the presence and absence of the UL9 protein, the equilibrium affinity constants of the protein binding to OriS and OriS* have been determined. A DNase I footprinting study showed that bis-linked netropsin derivatives exhibit preferences for binding to the AT-cluster in the origin of replication OriS and inhibit the fluctuation opening of AT-base pairs in the AT-cluster. The drugs also prevent the formation of an intermediate conformation of OriS* that involves a disordered tail at the 3'-end and stable Box I-Box III hairpin to which the UL9 helicase selectively binds. The stabilization by bis-netropsins of the AT-rich hairpin at its 3' end can inhibit the helicase activity. It was concluded that the antiviral activity of bis-netropsins may be associated with the inhibitory effects of bis-netropsins on these two stages of the reaction catalyzed by helicase UL9.

Different strategies for reducing intestinal background radioactivity associated with imaging HSV1-tk expression using established radionucleoside probes

One limitation of HSV1-tk reporter positron emission tomography (PET) with nucleoside analogues is the high background radioactivity in the intestine. We hypothesized that endogenous expression of thymidine kinase in bacterial flora could phosphorylate and trap such radiotracers, contributing to the high radioactivity levels in the bowel, and therefore explored different strategies to increase fecal elimination of radiotracer. Intestinal radioactivity was assessed by in vivo microPET imaging and ex vivo tissue sampling following intravenous injection of 18F-FEAU, 124I-FIAU, or 18F-FHBG in a germ-free mouse strain. We also explored the use of an osmotic laxative agent and/or a 100% enzymatically hydrolyzed liquid diet. No significant differences in intestinal radioactivity were observed between germ-free and normal mice. 18F-FHBG-derived intestinal radioactivity levels were higher than those of 18F-FEAU and 124I-FIAU; the intestine to blood ratio was more than 20-fold higher for 18F-FHBG than for 18F-FEAU and 124I-FIAU. The combination of Peptamen and Nulytely lowered intestinal radioactivity levels and increased (2.2-fold) the HSV1-tk transduced xenograft to intestine ratio for 18F-FEAU. Intestinal bacteria in germ-free mice do not contribute to the high intestinal levels of radioactivity following injection of radionucleoside analogues. The combination of Peptamen and Nulytely increased radiotracer elimination by increasing bowel motility without inducing dehydration.

In vivo characterization of a reporter gene system for imaging hypoxia-induced gene expression

PURPOSE

To characterize a tumor model containing a hypoxia-inducible reporter gene and to demonstrate utility by comparison of reporter gene expression to the uptake and distribution of the hypoxia tracer (18)F-fluoromisonidazole ((18)F-FMISO).

METHODS

Three tumors derived from the rat prostate cancer cell line R3327-AT were grown in each of two rats as follows: (1) parental R3327-AT, (2) positive control R3327-AT/PC in which the HSV1-tkeGFP fusion reporter gene was expressed constitutively, (3) R3327-AT/HRE in which the reporter gene was placed under the control of a hypoxia-inducible factor-responsive promoter sequence (HRE). Animals were coadministered a hypoxia-specific marker (pimonidazole) and the reporter gene probe (124)I-2'-fluoro-2'-deoxy-1-beta-d-arabinofuranosyl-5-iodouracil ((124)I-FIAU) 3 h prior to sacrifice. Statistical analysis of the spatial association between (124)I-FIAU uptake and pimonidazole fluorescent staining intensity was then performed on a pixel-by-pixel basis. Utility of this system was demonstrated by assessment of reporter gene expression versus the exogenous hypoxia probe (18)F-FMISO. Two rats, each bearing a single R3327-AT/HRE tumor, were injected with (124)I-FIAU (3 h before sacrifice) and (18)F-FMISO (2 h before sacrifice). Statistical analysis of the spatial association between (18)F-FMISO and (124)I-FIAU on a pixel-by-pixel basis was performed.

RESULTS

Correlation coefficients between (124)I-FIAU uptake and pimonidazole staining intensity were: 0.11 in R3327-AT tumors, -0.66 in R3327-AT/PC and 0.76 in R3327-AT/HRE, confirming that only in the R3327-AT/HRE tumor was HSV1-tkeGFP gene expression associated with hypoxia. Correlation coefficients between (18)F-FMISO and (124)I-FIAU uptakes in R3327-AT/HRE tumors were r=0.56, demonstrating good spatial correspondence between the two tracers.

CONCLUSIONS

We have confirmed hypoxia-specific expression of the HSV1-tkeGFP fusion gene in the R3327-AT/HRE tumor model and demonstrated the utility of this model for the evaluation of radiolabeled hypoxia tracers.

PET imaging of HSV1-tk mutants with acquired specificity toward pyrimidine- and acycloguanosine-based radiotracers

PURPOSE

The aim of this study was to create an alternative mutant of the herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene with reduced phosphorylation capacity for acycloguanosine derivatives, but not pyrimidine-based compounds that will allow for successful PET imaging.

METHODS

A new mutant of HSV1-tk reporter gene, suitable for PET imaging using pyrimidine-based radiotracers, was developed. The HSV1-tk mutant contains an arginine-to-glutamine substitution at position 176 (HSV1-R176Qtk) of the nucleoside binding region of the enzyme.

RESULTS

The mutant-gene product showed favorable enzymatic characteristics toward pyrimidine-based nucleosides, while exhibiting reduced activity with acycloguanosine derivatives. In order to enhance HSV1-R176Qtk reporter activity with pyrimidine-based radiotracers, we introduced the R176Q substitution into the more active HSV1-sr39tk mutant. U87 human glioma cells transduced with the HSV1-R176Qsr39tk double mutant reporter gene showed high (3)H-FEAU pyrimidine nucleoside and low (3)H-penciclovir acycloguanosine analog uptake in vitro. PET imaging also demonstrated high (18)F-FEAU and low (18)F-FHBG accumulation in HSV1-R176Qsr39tk+ xenografts. The feasibility of imaging two independent nucleoside-specific HSV1-tk mutants in the same animal with PET was demonstrated. Two opposite xenografts expressing the HSV1-R176Qsr39tk reporter gene and the previously described acycloguanosine-specific mutant of HSV1-tk, HSV1-A167Ysr39tk reporter gene, were imaged using a short-lived pyrimidine-based (18)F-FEAU and an acycloguanosine-based (18)F-FHBG radiotracer, respectively, administered on 2 consecutive days.

CONCLUSION

We conclude that in combination with acycloguanosine-specific HSV1-A167Ysr39tk reporter gene, a HSV1-tk mutant containing the R176Q substitution could be used for PET imaging of two different cell populations or concurrent molecular biological processes in the same living subject.

D-(+)-iso-methanocarbathymidine: a high-affinity substrate for herpes simplex virus 1 thymidine kinase

The stereoselective syntheses of the (+)-D and (-)-L enantiomers of iso-methanocarbathymidine (iso-MCT) was achieved through two independent linear approaches that converged on two antipodal enantiomers, common to a key precursor used in the synthesis of racemic iso-MCT. In the study reported herein we identified (+)-3 [D-(+)-iso-MCT] as the active enantiomer that was exclusively recognized by the herpes simplex virus 1 thymidine kinase (HSV1-tk), as was predicted by molecular modeling. For this purpose, a human osteosarcoma (HOS) cell line modified to contain and express HSV1-tk from herpes simplex virus 1 (HSV1) was used to determine the cytotoxicity of the compounds by an assay that measures the level of ATP in the cells. The work demonstrates that changes in the substitution pattern of rigid bicyclo[3.1.0]hexane nucleosides, which, relative to normal nucleosides, appear unconventional, can lead to the spatial optimization of pharmacophores and vastly improved substrate recognition.

Virological pattern in plasma, peripheral blood mononuclear cells and liver tissue and clinical outcome in chronic hepatitis B and C virus coinfection

BACKGROUND

We aim to evaluate in chronic hepatitis B virus-hepatitis C virus (HBV-HCV) coinfection the interplay of these viruses in liver tissue, peripheral blood mononuclear cells (PBMC), and plasma and to analyze the effect on disease course and response to treatment.

METHODS

We enrolled 19 patients with chronic HBV-HCV coinfection, 20 with chronic HCV and 20 with chronic HBV infection at their first liver biopsy, all were naive for antiviral therapy. The patients' plasma, PBMC and liver biopsy samples were tested for HBV DNA and/or HCV RNA by real-time PCR, according to the presence/absence of hepatitis B surface antigen and antibodies against HCV in the serum.

RESULTS

Contemporary presence of HBV DNA and HCV RNA was rare in plasma (5.3% of cases) and PBMC (10.6%), but frequent in liver tissue (52.6%). Of 10 cases circulating only HCV RNA and treated with pegylated interferon (PEG-IFN) plus ribavirin for 12 months, two showed a sustained response, and eight cleared HCV RNA but became HBV-DNA-positive in plasma; these eight had detectable HBV DNA in liver at baseline. One patient, who was plasma HBV-DNA-positive/HCV-RNA-negative at baseline, showed a sustained response after 18 months of PEG-IFN treatment; another, who was plasma HBV-DNA/HCV-RNA-positive at baseline, cleared only HCV RNA during 12 months of PEG-IFN plus ribavirin treatment. Seven cases remained untreated.

CONCLUSION

Despite a reciprocal inhibition in plasma, HBV and HCV frequently coexist in liver tissue, a condition to be taken into consideration when deciding therapy.

Flt3L in combination with HSV1-TK-mediated gene therapy reverses brain tumor-induced behavioral deficits

Glioblastoma multiforme (GBM) is an invasive and aggressive primary brain tumor which is associated with a dismal prognosis. We have earlier developed a macroscopic, intracranial, syngeneic GBM model, in which treatment with adenoviral vectors (Ads) expressing herpes simplex virus type 1 thymidine kinase (HSV1-TK) plus ganciclovir (GCV) resulted in survival of approximately 20% of the animals. In this model, treatment with Ads expressing Fms-like tyrosine kinase 3 ligand (Flt3L), in combination with Ad-HSV1-TK improves the survival rate to approximately 70% and induces systemic antitumor immunity. We hypothesized that the growth of a large intracranial tumor mass would cause behavioral abnormalities that can be reversed by the combined gene therapy. We assessed the behavior and neuropathology of tumor-bearing animals treated with the combined gene therapy, 3 days after treatment, in long-term survivors, and in a recurrent model of glioma. We demonstrate that the intracranial GBM induces behavioral deficits that are resolved after treatment with Ad-Flt3L/Ad-TK (+GCV). Neuropathological analysis of long-term survivors revealed an overall recovery of normal brain architecture. The lack of long-term behavioral deficits and limited neuropathological abnormalities demonstrate the efficacy and safety of the combined Ad-Flt3L/Ad-TK gene therapy for GBM. These findings can serve to underpin further developments of this therapeutic modality, leading toward implementation of a Phase I clinical trial.

Escherichia coli Nissle 1917 facilitates tumor detection by positron emission tomography and optical imaging

PURPOSE

Bacteria-based tumor-targeted therapy is a modality of growing interest in anticancer strategies. Imaging bacteria specifically targeting and replicating within tumors using radiotracer techniques and optical imaging can provide confirmation of successful colonization of malignant tissue.

EXPERIMENTAL DESIGN

The uptake of radiolabeled pyrimidine nucleoside analogues and [18F]FDG by Escherichia coli Nissle 1917 (EcN) was assessed both in vitro and in vivo. The targeting of EcN to 4T1 breast tumors was monitored by positron emission tomography (PET) and optical imaging. The accumulation of radiotracer in the tumors was correlated with the number of bacteria. Optical imaging based on bioluminescence was done using EcN bacteria that encode luciferase genes under the control of an l-arabinose-inducible P(BAD) promoter system.

RESULTS

We showed that EcN can be detected using radiolabeled pyrimidine nucleoside analogues, [18F]FDG and PET. Importantly, this imaging paradigm does not require transformation of the bacterium with a reporter gene. Imaging with [18F]FDG provided lower contrast than [18F]FEAU due to high FDG accumulation in control (nontreated) tumors and surrounding tissues. A linear correlation was shown between the number of viable bacteria in tumors and the accumulation of [18F]FEAU, but not [18F]FDG. The presence of EcN was also confirmed by bioluminescence imaging.

CONCLUSION

EcN can be imaged by PET, based on the expression of endogenous E. coli thymidine kinase, and this imaging paradigm could be translated to patient studies for the detection of solid tumors. Bioluminescence imaging provides a low-cost alternative to PET imaging in small animals.

[Construction and expression of recombinant adeno-associated virus vector containing HSV1-TK gene]

OBJECTIVE

To construct the recombinant adeno-associated virus(rAAV) vector plasmid pSNAV2.0-TK containing HSV1-TK gene, to produce recombinant adeno-associated virus rAAV2/HSV1-TK, and to detect the integration and expression of HSV1-TK gene in lens epithelial cells transfected by rAAV2/HSV1-TK, and to provide foundation for gene therapy of posterior capsular opacification.

METHODS

The recombinant vector plasmid constructed by gene recombinant technology was analyzed by PCR and restriction enzyme digestion. The cell strain BHK-21/TK was screened by G418 after the plasmid was transfected into BHK-21 cells,with the helper virus HSV1-rc/UL2 to produce the recombinant virus rAAV2/HSV1-TK. The purity of rAAV2/HSV1-TK was detected by SDS-PAGE and HPLC, and the titre of rAAV2/HSV1-TK was observed by dot blot hybridization. The HSV1-TK gene in lens epithelial cells transfected by rAAV2/HSV-TK was investigated by PCR and RT-PCR.

RESULTS

The recombinant plasmid proved successful by PCR and restriction enzyme digestion. The recombinant virus rAAV2/HSV1-TK was produced successfully and its titre was 1 x 10(12) v.g./mL by dot blot hybridization. The HSV1-TK gene was integrated and expressed in lens epithelial cells.

CONCLUSION

The recombinant adeno-associated virus vector plasmid containing HSV1-TK gene is successfully constructed, and high titre recombinant adeno-associated virus (rAAV2/HSV1-TK) is obtained. The HSV1-TK gene in lens epithelial cells is expressed after being transfected by rAAV2/HSV1-TK.

Synthesis of 99mTc(CO)3-deoxyuridine derivatives as potential HSV1-tk gene expression imaging agents

In this study, we synthesized (99m)Tc(CO)(3)-2'-aminomethylpyridyl-2'-deoxyuridine ((99m)Tc(CO)(3)-AMPDU) and (99m)Tc(CO)(3)-aminoethylpyridyl-2'-deoxyuridine ((99m)Tc(CO)(3)-AEPDU) as potential agents for imaging the expression of the non-invasive herpes simplex virus type-1 thymidine kinase. AMPDU and AEPDU were synthesized from uridine in five chemical steps and then labeled with [(99m)Tc(CO)(3)(H(2)O)(3)](+) (370MBq/0.5 mL) at 100 degrees C for 10 min. Under optimal conditions (0.5 and 1.0mg for AMPDU and AEPDU and heating for 10 min), the labeling efficiency was 95.3+/-2.8% for AMPDU and 94.2+/-5.1% for AEPDU. To validate the chemical structure of (99m)Tc(CO)(3)-labeled compounds, we also synthesized ReBr(CO)(3)-AMPDU and ReBr(CO)(3)-AEPDU by reacting [Et(4)N][ReBr(3)(CO)(3)] and AMPDU or AEPDU in methanol at 25 degrees C for 6h. (99m)Tc(CO)(3)-AMPDU and (99m)Tc(CO)(3)-AEPDU had the same retention time on HPLC analysis as ReBr(CO)(3)-AMPDU and ReBr(CO)(3)-AEPDU. (99m)Tc(CO)(3)-AMPDU and (99m)Tc(CO)(3)-AEPDU had high radiochemical stabilities of 98.1+/-1.5% and 98.0+/-1.7% for 6h, respectively.

Replication-competent, oncolytic herpes simplex virus type 1 mutants induce a bystander effect following ganciclovir treatment

Cells expressing herpes simplex virus (HSV) thymidine kinase (tk) are killed by ganciclovir (GCV). Adjacent cells without HSV-tk also die, a phenomenon known as the 'bystander effect'. However, there is no evidence that replication-competent HSV induces a bystander effect in the presence of GCV. Therefore, we investigated the bystander effect in HEp-2 cells infected with replication-competent, oncolytic HSV-1 mutants, hrR3 and HF10. In cells infected at a multiplicity of infection (MOI) of 3, GCV did not induce apoptosis. At low MOIs of 0.3 and 0.03, however, a number of adjacent, uninfected cells apoptosed following GCV treatment. Irrespective of GCV treatment, HEp-2 cells expressed minimal levels of connexin 43 (Cx43). However, Cx43 expression was enhanced by GCV in response to infection with HF10 at an MOI of 0.3, but not at an MOI of 3. Expression of other proteins involved in gap junctions, including Cx26 and Cx40, was not augmented under these conditions. The PKA and PI3K signal transduction pathways are likely involved in enhanced Cx43 expression as inhibitors of these pathways prevented Cx43 upregulation. These results suggest that infection with replication-competent HSV-1 induces the bystander effect in cells treated with GCV because of efficient intercellular transport of active GCV through abundant gap junctions.

Lentiviral vector conferring resistance to mycophenolate mofetil and sensitivity to ganciclovir for in vivo T-cell selection

Several clinical studies of gene-modified T cells have shown limited in vivo function of the cells, immunogenicity of the transgene, and lack of a selective advantage for gene-modified T cells. To address these problems, we developed a lentiviral vector (LV) that provides a selectable, proliferative advantage and potentially decreases immunogenicity for transduced T cells. The bicistronic vector expressed two genes linked with an internal ribosomal entry site. One gene is a variant of the inosine monophosphate dehydrogenase 2, inosine monophosphate dehydrogenase (IMPDH(IY)), conferring resistance to the immunosuppressive drug mycophenolate mofetil (MMF). The other is a suicide gene, herpes simplex virus thymidine kinase (HSV-TK), rendering proliferating cells sensitive to ablation with ganciclovir, fused to the selectable transmembrane marker DeltaCD34 (DeltaCD34/TK). Cells transduced with LV-DeltaCD34/TK.IMPDH(IY) were efficiently enriched by immunomagnetic selection for CD34, proliferated in 0.5-5 microM MMF, and were killed by 0.5-25 microg ml(-1) ganciclovir. We demonstrate efficient selection and killing of gene-modified cells and suggest LV-DeltaCD34/TK.IMPDH(IY)-transduced T cells could be used to facilitate allogeneic hematopoietic cell engraftment. The expression of IMPDH(IY) would allow in vivo selection with MMF, and DeltaCD34/TK expression would allow rapid and safe elimination of transduced T cells if graft-versus-host disease developed.

Preparation and biological evaluation of 2-amino-6-[18F]fluoro-9-(4-hydroxy-3-hydroxy-methylbutyl) purine (6-[18F]FPCV) as a novel PET probe for imaging HSV1-tk reporter gene expression

INTRODUCTION

2-Amino-6-[(18)F]fluoro-9-(4-hydroxy-3-hydroxy-methylbutyl) purine (6-[(18)F]FPCV) was prepared via a one-step nucleophilic substitution and evaluated as a novel probe for imaging the expression of herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene.

METHODS

Log P of 6-[(18)F]FPCV was calculated in octanol/phosphate-buffered saline (PBS). Stability studies were performed in PBS and bovine serum albumin (BSA). Cell uptake was performed at various time points in wild-type cells and transduced cells. For in vivo studies, tumors were grown in nude mice by inoculation with C6 cells, wild type and tk positive. The radiotracer was intravenously injected to animals, and micro-PET imaging was performed. Biodistribution of 6-[(18)F]FPCV was performed on another group of animals at different time points.

RESULTS

Log P of 6-[(18)F]FPCV was -0.517. 6-[(18)F]FPCV was fairly stable in PBS and BSA at 6 h. The tracer uptake in C6-tk cells was 5.5-18.8 times higher than that in wild-type cells. The plasma half-life of 6-[(18)F]FPCV was as follows: alpha t(1/2)=1.2 min and beta t(1/2)=73.7 min. The average ratio of tumor uptake between the transduced tumor and the wild-type tumor was 1.69 at 15 min.

CONCLUSION

Biological evaluation showed that 6-[(18)F]FPCV is a potential probe for imaging HSV1-tk gene expression. However, its in vivo defluorination may limit its application in PET imaging of gene expression.

An importin alpha/beta-recognized bipartite nuclear localization signal mediates targeting of the human herpes simplex virus type 1 DNA polymerase catalytic subunit pUL30 to the nucleus

Although the 1235 amino acids human herpes simplex virus type 1 (HSV-1) DNA polymerase catalytic subunit, pUL30, is essential for HSV-1 replication in the nucleus of host cells, little information is available regarding its nuclear import mechanism. The present study addresses this issue directly, characterizing pUL30's nuclear import pathway for the first time using quantitative confocal laser scanning microscopy (CLSM) on living cells, and fluorescent binding assays. In addition to a previously described nuclear localization signal (NLS) located within the pUL30 binding site for the polymerase accessory protein (PAP) pUL42, that appears to be dispensable for nuclear targeting, pUL30 possesses three putative basic NLSs. Intriguingly, the core of pUL30-NLS2 (residues 1114-1120) is highly homologous to that of the recently described NLS, similarly located upstream of the PAP binding site, of the human cytomegalovirus (HCMV) DNA polymerase catalytic subunit, pUL54. Here we show for the first time that pUL30-NLS2 itself is only partially functional in terms of nuclear import due to residue P1118 present in position 3 of the NLS core. Intriguingly, pUL30-NLS2 together with pUL30-NLS3 (residues 1133-1136) represents a fully functional bipartite NLS (pUL30-NLSbip), required for nuclear targeting of pUL30, and able to confer nuclear localization on heterologous proteins by conferring high-affinity interaction with the importin (IMP) alpha/beta heterodimer. Since nuclear targeting of HSV-1 proteins forming the replication fork is crucial for viral replication, the pUL30-NLSbip emerges for the first time as a viable therapeutic target.

A method for quantification of nucleotides and nucleotide analogues in thymidine kinase assays using lanthanum phosphate coprecipitation

Current methodologies for quantifying radiolabeled nucleoside monophosphates and nucleoside analogues result in high retention of unphosphorylated guanosine nucleosides in the case of lanthanum chloride precipitation or inconsistent retention of nucleotides in the case of DEAE cellulose filter papers. This study describes an innovative method for quantifying thymidine kinase (TK) activity that is compatible with both purine and pyrimidine nucleoside analogues by using lanthanum phosphate coprecipitation at pH 4.0. This methodology maintains quantitative precipitation of nucleoside monophosphates and yields minimal background binding from a variety of nucleoside analogues. In addition, use of PCR thermocyclers enhances the temporal precision of TK assays. This method was shown to be useful for assaying TK activity in a broad range of biochemically relevant systems, including purified enzymes, stable cell lines, and virally infected cells. Use of this methodology should aid researchers in the evaluation of novel nucleoside analogues and TK enzymes while decreasing radioactive waste, minimizing assay time, increasing accuracy, and enhancing dynamic range.

Enzymatic therapeutic index of acyclovir. Viral versus human polymerase gamma specificity

We have examined the kinetics of incorporation of acyclovir triphosphate by the herpes simplex virus-1 DNA polymerase holoenzyme (Pol-UL42) and the human mitochondrial DNA polymerase using transient kinetic methods. For each enzyme, we compared the kinetic parameters for acyclovir to those governing incorporation of dGTP. The favorable ground state dissociation constant (6 microM) and rate of polymerization (10 s(-1)) afford efficient incorporation of acyclovir triphosphate by the Pol-UL42 enzyme. A discrimination factor of approximately 50 favors dGTP over acyclovir triphosphate, mostly due to a faster maximum rate of dGTP incorporation. Once incorporated, acyclovir is removed with a half-life of approximately 1 h in the presence of a normal concentration of deoxynucleoside triphosphates, leading to a high toxicity index (16,000) toward viral replication. To assess the potential for toxicity toward the host we examined the incorporation and removal of acyclovir triphosphate by the human mitochondrial DNA polymerase. These results suggest moderate inhibition of mitochondrial DNA replication defining a toxicity index of 380. This value is much higher than the value of 1.5 determined for tenofovir, another acyclic nucleoside analog. The enzymatic therapeutic index is only 42 in favoring inhibition of the viral polymerase over polymerase gamma, whereas that for tenofovir is greater than 1,200. Mitochondrial toxicity is relatively low because acyclovir is activated only in infected cells by the promiscuous viral thymidine kinase and otherwise, mitochondrial toxicity would accumulate during long term treatment.

Evaluation of herpes simplex virus 1 thymidine kinase-mediated trapping of (131)I FIAU and prodrug activation of ganciclovir as a synergistic cancer radio/chemotherapy

PURPOSE

Evaluation of selective killing of Herpes Simplex Virus 1 thymidine kinase (HSV1-tk) expressing tumors by radiolabeled (131)I-fialuridine (FIAU), and of synergy between (131)I-FIAU and Ganciclovir (GCV).

PROCEDURES

HSV1-tk-expressing cell lines and parental cell lines were exposed to (131)I-FIAU alone, GCV alone, or combinations. Activity and concentration were varied widely, concurrent and sequential administrations tested, and dose rate effects were studied.

RESULTS

HSV1-tk-expressing cells accumulated up to 15.7-fold more (131)I-FIAU, were growth inhibited by 2 muCi/ml, or 5 muCi/ml (131)I-FIAU, and were inhibited by two log orders lower concentrations of GCV than parental cells. However, no synergy or additive effect was observed. Dose rate variations, or sequential treatment, did not alter outcome.

CONCLUSION

Radioisotope therapy of HSV1-tk-expressing tumor cells with (131)I-FIAU is reported for the first time. Lack of synergy between (131)I-FIAU and GCV does not warrant further investigation of combination treatment with the two agents.

Antitumor effects of non-replicative herpes simplex vectors expressing antiangiogenic proteins and thymidine kinase on Lewis lung carcinoma establishment and growth

There is growing evidence that combinations of antiangiogenic proteins with other antineoplastic treatments such as chemo- or radiotherapy and suicide genes-mediated tumor cytotoxicity lead to synergistic effects. In the present work, we tested the activity of two non-replicative herpes simplex virus (HSV)-1-based vectors, encoding human endostatin::angiostatin or endostatin::kringle5 fusion proteins in combination with HSV-1 thymidine kinase (TK) molecule, on endothelial cells (ECs) and Lewis lung carcinoma (LLC) cells. We observed a significant reduction of the in vitro growth, migration and tube formation by primary ECs upon direct infection with the two recombinant vectors or cultivation with conditioned media obtained from the vector-infected LLC cells. Moreover, direct cytotoxic effect of HSV-1 TK on both LLC and ECs was demonstrated. We then tested the vectors in vivo in two experimental settings, that is, LLC tumor growth or establishment, in C57BL/6 mice. The treatment of pre-established subcutaneous tumors with the recombinant vectors with ganciclovir (GCV) induced a significant reduction of tumor growth rate, while the in vitro infection of LLC cells with the antiangiogenic vectors before their implantation in mice flanks, either in presence or absence of GCV, completely abolished the tumor establishment.

A mutation in the human herpes simplex virus type 1 UL52 zinc finger motif results in defective primase activity but can recruit viral polymerase and support viral replication efficiently

Herpes simplex virus type 1 (HSV-1) encodes a heterotrimeric helicase/primase complex consisting of UL5, UL8, and UL52. UL5 contains conserved helicase motifs, while UL52 contains conserved primase motifs, including a zinc finger motif. Although HSV-1 and HSV-2 UL52s contain a leucine residue at position 986, most other herpesvirus primase homologues contain a phenylalanine at this position. We constructed an HSV-1 UL52 L986F mutation and found that it can complement a UL52 null virus more efficiently than the wild type (WT). We thus predicted that the UL5/8/52 complex containing the L986F mutation might possess increased primase activity; however, it exhibited only 25% of the WT level of primase activity. Interestingly, the mutant complex displayed elevated levels of DNA binding and single-stranded DNA-dependent ATPase and helicase activities. This result confirms a complex interdependence between the helicase and primase subunits. We previously showed that primase-defective mutants failed to recruit the polymerase catalytic subunit UL30 to prereplicative sites, suggesting that an active primase, or primer synthesis, is required for polymerase recruitment. Although L986F exhibits decreased primase activity, it can support efficient replication and recruit UL30 efficiently to replication compartments, indicating that a partially active primase is capable of recruiting polymerase. Extraction with detergents prior to fixation can extract nucleosolic proteins but not proteins bound to chromatin or the nuclear matrix. We showed that UL30 was extracted from replication compartments while UL42 remained bound, suggesting that UL30 may be tethered to the replication fork by protein-protein interactions.

Intercellular trafficking and cytotoxicity of recombinant HSV-1 thymidine kinase fused with HSV-2 US11 RXP repeat peptide

To improve the therapeutic efficacy of herpes simplex virus type 1 (HSV-1) thymidine kinase (tk)/ganciclovir (GCV) therapy, we have made recombinant tk chimeras fused with the arginine-rich (RXP) repeat of herpes simplex virus type 2 (HSV-2) US11 and examined their activity of intercellular trafficking and cytotoxicity. When examined the immunofluorescence staining patterns of RXP/tk fusion proteins in transfected COS7 cells, the RXP chimeras revealed a conservation of the trafficking activity of RXP. We also found that transfection of tkC Delta 6-RXP (lacking the C-terminal six amino residues of tk), tk-RXP, and tkN Delta 66-RXP (lacking the N-terminal 66 amino residues of tk) induced apoptosis even in the absence of GCV. The results suggest that these tk/RXP chimeras themselves have apoptosis-inducing activity, and that the HSV tk nucleoside-binding domain may be involved in the induction of apoptosis. Furthermore, treatment with 5 muM GCV induced efficient cell death in cells tranfected with tk-RXP in comparison to the cells transfected with tk (P < 0.0001).

Fusion of herpes simplex virus thymidine kinase to VP22 does not result in intercellular trafficking of the protein

Suicide gene therapy is a promising approach for the treatment of cancer. Current protocols, however, suffer from low efficiency. We tried to alleviate this problem by developing a transgene that will spread from the initially transduced cell to the surrounding cells (transmission). We used herpes simplex virus (HSV) VP22 as a signal for cellular uptake of HSV-1 thymidine kinase (TK). By co-culturing naive cells with cells producing a TK-VP22 fusion protein, we detected intercellular trafficking of this protein. We used a variety of techniques, including two-color flow cytometry and cytotoxicity assays to detect the presence of TK in the non-producing cells. We confirmed intercellular migration of VP22. We did not detect any intercellular trafficking of the TK-VP22 fusion protein, by various fixation methods or flow cytometry. In ganciclovir sensitivity assays, we found no difference between the efficiency of TK (IC50=3.15+/-0.76 microg/ml) and TK-VP22 (IC50=2.27+/-0.59 microg/ml). Using a cell-free enzyme activity assay we showed that fusion of TK to VP22 did not change the enzyme activity. In conclusion, we described novel and robust methods to detect intercellular trafficking. From our data we concluded that protein transmission of TK by VP22 for gene therapy is not likely to be successful. In addition, we described a useful and quantifiable assay to measure the enzymatic activity of TK and TK fusion proteins, and described some common properties of VP22 fusion proteins that may explain the different results that have been obtained by others.

Diverse herpes simplex virus type 1 thymidine kinase mutants in individual human neurons and Ganglia

Mutations in the thymidine kinase gene (tk) of herpes simplex virus type 1 (HSV-1) explain most cases of virus resistance to acyclovir (ACV) treatment. Mucocutaneous lesions of patients with ACV resistance contain mixed populations of tk mutant and wild-type virus. However, it is unknown whether human ganglia also contain mixed populations since the replication of HSV tk mutants in animal neurons is impaired. Here we report the detection of mutated HSV tk sequences in human ganglia. Trigeminal and dorsal root ganglia were obtained at autopsy from an immunocompromised woman with chronic mucocutaneous infection with ACV-resistant HSV-1. The HSV-1 tk open reading frames from ganglia were amplified by PCR, cloned, and sequenced. tk mutations were detected in a seven-G homopolymer region in 11 of 12 ganglia tested, with clonal frequencies ranging from 4.2 to 76% HSV-1 tk mutants per ganglion. In 8 of 11 ganglia, the mutations were heterogeneous, varying from a deletion of one G to an insertion of one to three G residues, with the two-G insertion being the most common. Each ganglion had its own pattern of mutant populations. When individual neurons from one ganglion were analyzed by laser capture microdissection and PCR, 6 of 14 HSV-1-positive neurons were coinfected with HSV tk mutants and wild-type virus, 4 of 14 were infected with wild-type virus alone, and 4 of 14 were infected with tk mutant virus alone. These data suggest that diverse tk mutants arise independently under drug selection and establish latency in human sensory ganglia alone or together with wild-type virus.

Sculpting the bicyclo[3.1.0]hexane template of carbocyclic nucleosides to improve recognition by herpes thymidine kinase

The replacement of the furanose ring by a cyclopentane in nucleosides generates a group of analogues known generically as carbocyclic nucleosides. These compounds have increased chemical and enzymatic stability due to the absence of a true glycosyl bond that characterizes conventional nucleosides. The additional fusion of a cyclopropane ring to the cyclopentane produces a bicyclo[3.1.0]hexane system that depending on its location relative to the nucleobase is able to lock the embedded cyclopentane ring into conformations that mimic the typical north and south conformations of the furanose ring in conventional nucleosides. These bicyclo[3.1.0]hexane templates have already provided important clues to differentiate the contrasting conformational preferences between kinases and polymerases. Herein, we describe the design, synthesis, and phosphorylation pattern of a new bicyclo[3.1.0]hexane thymidine analogue that seems to possess an ideal spatial distribution of pharmacophores for an optimal interaction with herpes simplex 1 thymidine kinase. The bicyclo[3.1.0]hexane template represents a privileged rigid template for sculpting other carbocyclic nucleosides to meet the demands of specific receptors.