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1.  Targeting of Interferon-Beta to Produce a Specific, Multi-Mechanistic Oncolytic Vaccinia Virus 
PLoS Medicine  2007;4(12):e353.
Oncolytic viruses hold much promise for clinical treatment of many cancers, but a lack of systemic delivery and insufficient tumor cell killing have limited their usefulness. We have previously demonstrated that vaccinia virus strains are capable of systemic delivery to tumors in mouse models, but infection of normal tissues remains an issue. We hypothesized that interferon-beta (IFN-β) expression from an oncolytic vaccinia strain incapable of responding to this cytokine would have dual benefits as a cancer therapeutic: increased anticancer effects and enhanced virus inactivation in normal tissues. We report the construction and preclinical testing of this virus.
Methods and Findings
In vitro screening of viral strains by cytotoxicity and replication assay was coupled to cellular characterization by phospho-flow cytometry in order to select a novel oncolytic vaccinia virus. This virus was then examined in vivo in mouse models by non-invasive imaging techniques. A vaccinia B18R deletion mutant was selected as the backbone for IFN-β expression, because the B18R gene product neutralizes secreted type-I IFNs. The oncolytic B18R deletion mutant demonstrated IFN-dependent cancer selectivity and efficacy in vitro, and tumor targeting and efficacy in mouse models in vivo. Both tumor cells and tumor-associated vascular endothelial cells were targeted. Complete tumor responses in preclinical models were accompanied by immune-mediated protection against tumor rechallenge. Cancer selectivity was also demonstrated in primary human tumor explant tissues and adjacent normal tissues. The IFN-β gene was then cloned into the thymidine kinase (TK) region of this virus to create JX-795 (TK−/B18R−/IFN-β+). JX-795 had superior tumor selectivity and systemic intravenous efficacy when compared with the TK−/B18R− control or wild-type vaccinia in preclinical models.
By combining IFN-dependent cancer selectivity with IFN-β expression to optimize both anticancer effects and normal tissue antiviral effects, we were able to achieve, to our knowledge for the first time, tumor-specific replication, IFN-β gene expression, and efficacy following systemic delivery in preclinical models.
Stephen Thorne and colleagues describe, in a mouse model, an oncolytic vaccinia virus with interferon-dependent cancer selectivity that allows tumor-specific replication; it also expresses the IFN-β gene and hence has efficacy against tumors.
Editors' Summary
Normally, throughout life, cell division (which produces new cells) and cell death are carefully balanced to keep the body in good working order. But sometimes cells acquire changes (mutations) in their genetic material that allow them to divide uncontrollably to form cancers—disorganized masses of cells. Cancers can develop anywhere in the body and, as they develop, their cells acquire other genetic changes that enable them to move and start new tumors (metastases) elsewhere. Chemotherapy drugs kill rapidly dividing cancer cells but, because some normal cells are also sensitive to these drugs, it is hard to destroy the cancer without causing serious side effects. Consequently, researchers are trying to develop “targeted” therapies that attack the changes in cancer cells that allow them to divide uncontrollably but leave normal cells unscathed. One promising class of targeted therapies is oncolytic viruses. These viruses make numerous copies of themselves inside cancer cells (but not inside normal cells). Eventually the cancer cell bursts open (lyses), releases more of the therapeutic agent, and dies.
Why Was This Study Done?
Existing oncolytic viruses have two major disadvantages: they have to be injected directly into tumors, and therefore they can't destroy distant metastases; and they don't kill cancer cells particularly efficiently. In this study, the researchers have tried to adapt vaccinia virus (a virus that infects humans and which has recently been shown to kill tumor cells when injected into the bloodstream) in two ways: to both infect cancer cells selectively and then to kill them effectively.
They hypothesized that putting a gene that causes expression of a protein called interferon-beta (IFN-β) in a particular virus strain that is itself incapable of responding to IFN-β might achieve these aims. Human cells infected with viruses usually release IFNs, which induce an antiviral state in nearby cells. But vaccinia virus makes anti-IFN proteins that prevent IFN release. If the viral genes that encode these proteins are removed from the virus, the virus cannot spread through normal cells. However, many cancer cells have defective IFN signaling pathways so the virus can spread through them. IFN-β expression by the virus, however, should improve its innate anticancer effects because IFN-β stops cancer cells dividing, induces an antitumor immune response, and stops tumors developing good blood supplies.
What Did the Researchers Do and Find?
The researchers selected a vaccinia virus strain called WR-delB18R in which the B18R gene, which encodes an anti-IFN protein, had been removed from the virus. (WR is a wild-type virus.) In laboratory experiments, IFN treatment blocked the spread of WR-delB18R in normal human cells but not in human tumor cells. After being injected into the veins of tumor-bearing mice, WR-delB18R was rapidly cleared from normal tissues but persisted in the tumors. A single injection of WR-delB18R directly into the tumor killed most of the tumor cells. A similar dose injected into a vein was less effective but nevertheless increased the survival time of some of the mice by directly killing the tumor cells, by targeting the blood supply of the tumors, and by inducing antitumor immunity. Finally, when the researchers inserted the IFN-β gene into this WR-delB18R, the new virus—JX-795—was much better at killing tumors after intravenous injection than either WR or WR-delB18R.
What Do These Findings Mean?
These findings indicate that the vaccinia virus can be adapted so that it replicates only in tumor cells and kills these cells effectively after intravenous injection. In particular, they show that the strategy adopted by the researchers both optimizes the anticancer effects of the virus and minimizes viral replication in normal tissues. JX-795 is a promising oncolytic virus, therefore, particularly since vaccinia virus has been safely used for many years to vaccinate people against smallpox. Nevertheless, it will be some years before JX-795 can be used clinically. Vaccinia virus constructs like this need to be tested extensively in the laboratory and in animals before any attempt is made to test them in people and, even if they passes all these preclinical tests with flying colors, only clinical trials will reveal whether they can treat human cancer. Several related strains of vaccinia virus are currently undergoing clinical testing.
Additional Information.
Please access these Web sites via the online version of this summary at
The US National Cancer Institute provides information on all aspects of cancer (in English and Spanish)
CancerQuest, from Emory University, provides information on all aspects of cancer (in several languages)
The UK charity Cancerbackup also provides information on all aspects of cancer
Wikipedia has a page on oncolytic viruses (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
A short interview about oncolytic viruses with researcher Dr. John Bell is available on the Insidermedicine Web site
The Oncolytic virus Web page provides lists of oncolytic viruses classified by type
PMCID: PMC2222946  PMID: 18162040
2.  Redirecting Coronavirus to a Nonnative Receptor through a Virus-Encoded Targeting Adapter 
Journal of Virology  2006;80(3):1250-1260.
Murine hepatitis coronavirus (MHV)-A59 infection depends on the interaction of its spike (S) protein with the cellular receptor mCEACAM1a present on murine cells. Human cells lack this receptor and are therefore not susceptible to MHV. Specific alleviation of the tropism barrier by redirecting MHV to a tumor-specific receptor could lead to a virus with appealing properties for tumor therapy. To demonstrate that MHV can be retargeted to a nonnative receptor on human cells, we produced bispecific adapter proteins composed of the N-terminal D1 domain of mCEACAM1a linked to a short targeting peptide, the six-amino-acid His tag. Preincubation of MHV with the adapter proteins and subsequent inoculation of human cells expressing an artificial His receptor resulted in infection of these otherwise nonsusceptible cells and led to subsequent production of progeny virus. To generate a self-targeted virus able to establish multiround infection of the target cells, we subsequently incorporated the gene encoding the bispecific adapter protein as an additional expression cassette into the MHV genome through targeted RNA recombination. When inoculated onto murine LR7 cells, the resulting recombinant virus indeed expressed the adapter protein. Furthermore, inoculation of human target cells with the virus resulted in a His receptor-specific infection that was multiround. Extensive cell-cell fusion and rapid cell killing of infected target cells was observed. Our results show that MHV can be genetically redirected via adapters composed of the S protein binding part of mCEACAM1a and a targeting peptide recognizing a nonnative receptor expressed on human cells, consequently leading to rapid cell death. The results provide interesting leads for further investigations of the use of coronaviruses as antitumor agents.
PMCID: PMC1346946  PMID: 16415002
3.  Coronavirus Genetically Redirected to the Epidermal Growth Factor Receptor Exhibits Effective Antitumor Activity against a Malignant Glioblastoma▿  
Journal of Virology  2009;83(15):7507-7516.
Coronaviruses are positive-strand RNA viruses with features attractive for oncolytic therapy. To investigate this potential, we redirected the coronavirus murine hepatitis virus (MHV), which is normally unable to infect human cells, to human tumor cells by using a soluble receptor (soR)-based expression construct fused to an epidermal growth factor (EGF) receptor targeting moiety. Addition of this adapter protein to MHV allowed infection of otherwise nonsusceptible, EGF receptor (EGFR)-expressing cell cultures. We introduced the sequence encoding the adaptor protein soR-EGF into the MHV genome to generate a self-targeted virus capable of multiround infection. The resulting recombinant MHV was viable and had indeed acquired the ability to infect all glioblastoma cell lines tested in vitro. Infection of malignant human glioblastoma U87ΔEGFR cells gave rise to release of progeny virus and efficient cell killing in vitro. To investigate the oncolytic capacity of the virus in vivo, we used an orthotopic U87ΔEGFR xenograft mouse model. Treatment of mice bearing a lethal intracranial U87ΔEGFR tumor by injection with MHVsoR-EGF significantly prolonged survival compared to phosphate-buffered saline-treated (P = 0.001) and control virus-treated (P = 0.004) animals, and no recurrent tumor load was observed. However, some adverse effects were seen in normal mouse brain tissues that were likely caused by the natural murine tropism of MHV. This is the first demonstration of oncolytic activity of a coronavirus in vivo. It suggests that nonhuman coronaviruses may be attractive new therapeutic agents against human tumors.
PMCID: PMC2708613  PMID: 19439466
4.  Preclinical Therapy of Disseminated HER-2+ Ovarian and Breast Carcinomas with a HER-2-Retargeted Oncolytic Herpesvirus 
PLoS Pathogens  2013;9(1):e1003155.
Oncolytic viruses aim to specifically kill tumor cells. A major challenge is the effective targeting of disseminated tumors in vivo. We retargeted herpes simplex virus (HSV) tropism to HER-2 oncoprotein p185, overexpressed in ovary and breast cancers. The HER-2-retargeted R-LM249 exclusively infects and kills tumor cells expressing high levels of human HER-2. Here, we assessed the efficacy of systemically i.p. delivered R-LM249 against disseminated tumors in mouse models that recapitulate tumor spread to the peritoneum in women. The human ovarian carcinoma SK-OV-3 cells implanted intraperitoneally (i.p.) in immunodeficient Rag2−/−;Il2rg−/− mice gave rise to a progressive peritoneal carcinomatosis which mimics the fatal condition in advanced human patients. I.p. administration of R-LM249 strongly inhibited carcinomatosis, resulting in 60% of mice free from peritoneal diffusion, and 95% reduction in the total weight of neoplastic nodules. Intraperitoneal metastases are a common outcome in breast cancer: i.p. administration of R-LM249 strongly inhibited the growth of ovarian metastases of HER-2+ MDA-MB-453 breast cells. Brain metastases were also reduced. Cumulatively, upon i.p. administration the HER-2-redirected oncolytic HSV effectively reduced the growth of ovarian and breast carcinoma disseminated to the peritoneal cavity.
Author Summary
In the genome of human herpes simplex virus (HSV) we have replaced part of the sequences encoding the receptor-binding glycoprotein with antibody fragments directed against the oncoprotein HER-2, overexpressed in human breast and ovarian cancers. The retargeted HSV only infects and kills human cancer cells expressing high levels of HER-2. Earlier experiments showed that the retargeted HSV injected inside localized tumors inhibits human tumor growth in immunodeficient mice. As tumor dissemination is the major cause of cancer mortality, we have now used the HER-2-retargeted HSV to treat disseminated HER-2+ ovarian and breast cancer in immunodeficient mice. Intraperitoneal treatments significantly inhibited the peritoneal spread (carcinomatosis and ascites formation) of ovarian cancer cells and the metastatic growth of breast cancer cells in the ovaries. Brain metastases were also inhibited. Our results showed that a HER-2-redirected oncolytic HSV is an effective therapeutic agent against metastatic HER-2+ cancers and, more generally, provide the first demonstration of the efficacy of a systemically-administered, retargeted oncolytic HSV.
PMCID: PMC3561254  PMID: 23382683
5.  Permissiveness of Human Cancer Cells to Oncolytic Bovine Herpesvirus 1 Is Mediated in Part by KRAS Activity 
Journal of Virology  2014;88(12):6885-6895.
Oncolytic viruses (OVs) are attractive avenues of cancer therapy due to the absence of toxic side effects often seen with current treatment modalities. Bovine herpesvirus 1 (BHV-1) is a species-specific virus that does not induce cytotoxicity in normal primary human cells but can infect and kill various human immortalized and transformed cell lines. To gain a better understanding of the oncolytic breadth of BHV-1, the NCI panel of established human tumor cell lines was screened for sensitivity to the virus. Overall, 72% of the panel is permissive to BHV-1 infection, with corresponding decreases in cellular viability. This sensitivity is in comparison to a sensitivity of only 32% for a herpes simplex virus 1 (HSV-1)-based oncolytic vector. Strikingly, while 35% of the panel supports minimal or no BHV-1 replication, significant decreases in cellular viability still occur. These data suggest that BHV-1 is an OV with tropism for multiple tumor types and is able to induce cytotoxicity independent of significant virus replication. In contrast to other species-specific OVs, cellular sensitivity to BHV-1 does not correlate with type I interferon (IFN) signaling; however, mutations in KRAS were found to correlate with high levels of virus replication. The knockdown or overexpression of KRAS in human tumor cell lines yields modest changes in viral titers; however, overexpression of KRAS in normal primary cells elicits permissivity to BHV-1 infection. Together, these data suggest that BHV-1 is a broad-spectrum OV with a distinct mechanism of tumor targeting.
IMPORTANCE Cancer remains a significant health issue, and novel treatments are required, particularly for tumors that are refractory to conventional therapies. Oncolytic viruses are a novel platform given their ability to specifically target tumor cells while leaving healthy cells intact. For this strategy to be successful, a fundamental understanding of virus-host interactions is required. We previously identified bovine herpesvirus 1 as a novel oncolytic virus with many unique and clinically relevant features. Here, we show that BHV-1 can target a wide range of human cancer types, most potently lung cancer. In addition, we show that enhanced KRAS activity, a hallmark of many cancers, is one of the factors that increases BHV-1 oncolytic capacity. These findings hold potential for future treatments, particularly in the context of lung cancer, where KRAS mutations are a negative predictor of treatment efficacy.
PMCID: PMC4054371  PMID: 24696490
6.  Retargeting Vesicular Stomatitis Virus Using Measles Virus Envelope Glycoproteins 
Human Gene Therapy  2011;23(5):484-491.
Oncolytic vesicular stomatitis virus (VSV) has potent antitumor activity, but infects a broad range of cell types. Here, we used the measles virus (MV) hemagglutinin (H) and fusion (F) envelope glycoproteins to redirect VSV entry and infection specifically to tumor-associated receptors. Replication-defective VSV, deleted of its glycoprotein gene (VSVΔG), was pseudotyped with MV-F and MV-H displaying single-chain antibodies (scFv) specific for epidermal growth factor receptor (EGFR), folate receptor (FR), or prostate membrane-specific antigen (PSMA). Viral titers were ∼105 PFU/ml, but could be concentrated to 107 PFU/ml. Immunoblotting confirmed incorporation of the MV-H-scFv and MV-F into functional VSV virions. Although VSV-G was able to infect all tumor cell lines tested, the retargeted VSV infected only cells that expressed the targeted receptor. In vivo specificities of the EGFR-, FR-, and PSMA-retargeted VSV were assessed by intratumoral injection into human tumor xenografts. Analysis of green fluorescent protein reporter gene expression indicated that VSV infection was restricted to receptor-positive tumors. In summary, we have demonstrated for the first time that VSV can be efficiently retargeted to different cellular receptors using the measles display technology, yielding retargeted VSV vectors that are highly specific for tumors that express the relevant receptor.
Ayala-Breton and colleagues use the measles virus (MV) hemagglutinin (H) and fusion (F) envelope glycoproteins to redirect vesicular stomatitis virus (VSV) entry and infection specifically to tumor-associated receptors such as epidermal growth factor receptor, folate receptor, and prostate membrane-specific antigen. In vivo expression of the all retargeted VSV was restricted to receptor-positive human tumor xenografts.
PMCID: PMC3360499  PMID: 22171635
7.  Characteristics of Oncolytic Vesicular Stomatitis Virus Displaying Tumor-Targeting Ligands 
Journal of Virology  2013;87(24):13543-13555.
We sought proof of principle that tumor-targeting ligands can be displayed on the surface of vesicular stomatitis virus (VSV) by engineering its glycoprotein. Here, we successfully rescued VSVs displaying tumor vasculature-targeting ligands. By using a rational approach, we investigated various feasible insertion sites on the G protein of VSV (VSV-G) for display of tumor vasculature-targeting ligands, cyclic RGD (cRGD) and echistatin. We found seven sites on VSV-G that tolerated insertion of the 9-residue cRGD peptide, two of which could tolerate insertion of the 49-amino acid echistatin domain. All of the ligand-displaying viruses replicated as well as the parental virus. In vitro studies demonstrated that the VSV-echistatin viruses specifically bound to targeted integrins. Since the low-density lipoprotein receptor (LDLR) was recently identified as a major receptor for VSV, we investigated the entry of ligand-displaying viruses after masking LDLR. The experiment showed that the modified viruses can enter the cell independently of LDLR, whereas entry of unmodified virus is significantly blocked by a specific monoclonal antibody against LDLR. Both parental and ligand-displaying viruses displayed equal oncolytic efficacies in a syngeneic mouse myeloma model. We further demonstrated that single-chain antibody fragments against tumor-specific antigens can be inserted at the N terminus of the G protein and that corresponding replication-competent VSVs can be rescued efficiently. Overall, we demonstrated that functional tumor-targeting ligands can be displayed on replication-competent VSVs without perturbing viral growth and oncolytic efficacy. This study provides a rational foundation for the future development of fully retargeted oncolytic VSVs.
PMCID: PMC3838279  PMID: 24089573
8.  Retargeting Adenoviral Vectors to Improve Gene Transfer into Tumors 
Cancer gene therapy  2010;18(4):275-287.
Gene targeting to tumors using adenoviral vectors holds great potential for cancer imaging and therapy, but the limited efficacy of current methods used to improve delivery to target tissues and reduce unwanted interactions remain substantial barriers to further development. Progress in characterizing the set of molecular interactions used by adenoviral vectors to infect particular tissues has aided the development of novel strategies for retargeting vectors to tumor cells. One method is chemical retargeting of adenovirus using bispecific antibodies against both viral capsid proteins and tumor-specific cell surface molecules. This approach can be combined either with competitive inhibitors designed to reduce viral tropism in undesired tissues, or with traditional therapeutics to increase the expression of surface molecules for improved tumor targeting. Ablating liver cell-specific interactions through mutation of capsid proteins or chemical means are promising strategies for reducing adenovirus-induced liver toxicity. The nature of tumor neovasculature also influences adenoviral delivery, and the use of vascular disrupting agents such as combretastatin can help elucidate these contributions. In this investigation, we evaluate a variety of these methods for retargeting adenoviral vectors to tumor cells in vitro and in vivo, and assess the contributions of specific molecular and tissue interactions that affect adenoviral transgene delivery.
PMCID: PMC3060954  PMID: 21183946
adenovirus; Bavituximab; bispecific antibody; fiber; targeting
9.  Immune Suppression during Oncolytic Virotherapy for High-Grade Glioma; Yes or No? 
Journal of Cancer  2015;6(3):203-217.
Oncolytic viruses have been seriously considered for glioma therapy over the last 20 years. The oncolytic activity of several oncolytic strains has been demonstrated against human glioma cell lines and in in vivo xenotransplant models. So far, four of these stains have additionally completed the first phase I/II trials in relapsed glioma patients. Though safety and feasibility have been demonstrated, therapeutic efficacy in these initial trials, when described, was only minor. The role of the immune system in oncolytic virotherapy for glioma remained much less studied until recent years. When investigated, the immune system, adept at controlling viral infections, is often hypothesized to be a strong hurdle to successful oncolytic virotherapy. Several preclinical studies have therefore aimed to improve oncolytic virotherapy efficacy by combining it with immune suppression or evasion strategies. More recently however, a new paradigm has developed in the oncolytic virotherapy field stating that oncolytic virus-mediated tumor cell death can be accompanied by elicitation of potent activation of innate and adaptive anti-tumor immunity that greatly improves the efficacy of certain oncolytic strains. Therefore, it seems the three-way interaction between oncolytic virus, tumor and immune system is critical to the outcome of antitumor therapy. In this review we discuss the studies which have investigated how the immune system and oncolytic viruses interact in models of glioma. The novel insights generated here hold important implications for future research and should be incorporated into the design of novel clinical trials.
PMCID: PMC4317755  PMID: 25663937
glioblastoma; oncolytic virotherapy; antitumor immunity
10.  The GM2 Glycan Serves as a Functional Coreceptor for Serotype 1 Reovirus 
PLoS Pathogens  2012;8(12):e1003078.
Viral attachment to target cells is the first step in infection and also serves as a determinant of tropism. Like many viruses, mammalian reoviruses bind with low affinity to cell-surface carbohydrate receptors to initiate the infectious process. Reoviruses disseminate with serotype-specific tropism in the host, which may be explained by differential glycan utilization. Although α2,3-linked sialylated oligosaccharides serve as carbohydrate receptors for type 3 reoviruses, neither a specific glycan bound by any reovirus serotype nor the function of glycan binding in type 1 reovirus infection was known. We have identified the oligosaccharide portion of ganglioside GM2 (the GM2 glycan) as a receptor for the attachment protein σ1 of reovirus strain type 1 Lang (T1L) using glycan array screening. The interaction of T1L σ1 with GM2 in solution was confirmed using NMR spectroscopy. We established that GM2 glycan engagement is required for optimal infection of mouse embryonic fibroblasts (MEFs) by T1L. Preincubation with GM2 specifically inhibited type 1 but not type 3 reovirus infection of MEFs. To provide a structural basis for these observations, we defined the mode of receptor recognition by determining the crystal structure of T1L σ1 in complex with the GM2 glycan. GM2 binds in a shallow groove in the globular head domain of T1L σ1. Both terminal sugar moieties of the GM2 glycan, N-acetylneuraminic acid and N-acetylgalactosamine, form contacts with the protein, providing an explanation for the observed specificity for GM2. Viruses with mutations in the glycan-binding domain display diminished hemagglutination capacity, a property dependent on glycan binding, and reduced capacity to infect MEFs. Our results define a novel mode of virus-glycan engagement and provide a mechanistic explanation for the serotype-dependent differences in glycan utilization by reovirus.
Author Summary
Receptor utilization plays an important role in viral disease. Viruses must recognize a receptor or sometimes multiple receptors to infect a cell. Mammalian orthoreoviruses (reoviruses) serve as useful models for studies of viral receptor binding and pathogenesis. The reovirus experimental system allows manipulation of both the virus and the host to define mechanisms of viral attachment and disease. Like many viruses, reoviruses engage carbohydrate molecules on the cell-surface, but the oligosaccharide sequences bound and the function of glycan binding in infection were not known prior to this study. We used glycan array screening to determine that serotype 1 reoviruses bind ganglioside GM2 and found that this interaction is required for efficient infection of some types of cells. To better understand how reovirus engages GM2, we determined the structure of the reovirus attachment protein σ1 in complex with the GM2 glycan and defined residues that are required for functional receptor binding. Reoviruses are being tested in clinical trials for efficacy in the treatment of cancer. Cancer cells commonly have altered glycan profiles. Therefore, understanding how reoviruses engage cell-surface glycans might lead to improvements in oncolytic therapy.
PMCID: PMC3516570  PMID: 23236285
11.  Serotype Chimeric Human Adenoviruses for Cancer Gene Therapy 
Viruses  2010;2(10):2196-2212.
Cancer gene therapy consists of numerous approaches where the common denominator is utilization of vectors for achieving therapeutic effect. A particularly potent embodiment of the approach is virotherapy, in which the replication potential of an oncolytic virus is directed towards tumor cells to cause lysis, while normal cells are spared. Importantly, the therapeutic effect of the initial viral load is amplified through viral replication cycles and production of progeny virions. All cancer gene therapy approaches rely on a sufficient level of delivery of the anticancer agent into target cells. Thus, enhancement of delivery to target cells, and reduction of delivery to non-target cells, in an approach called transductional targeting, is attractive. Both genetic and non-genetic retargeting strategies have been utilized. However, in the context of oncolytic viruses, it is beneficial to have the specific modification included in progeny virions and hence genetic modification may be preferable. Serotype chimerism utilizes serotype specific differences in receptor usage, liver tropism and seroprevalence in order to gain enhanced infection of target tissue. This review will focus on serotype chimeric adenoviruses for cancer gene therapy applications.
PMCID: PMC3185575  PMID: 21994616
adenoviruses; serotype chimerism; neutralizing antibodies; tumor targeting; liver detargeting
12.  Targeting HSV-1 virions for specific binding to epidermal growth factor receptor-vIII bearing tumor cells 
Cancer gene therapy  2010;17(9):655-663.
Oncolytic herpes simplex virus (HSV) vectors have been used in early phase human clinical trials as a therapy for recurrent malignant glioblastoma. This treatment proved safe but limited improvements in patient survival were observed. The potency of these vectors might be enhanced by targeting vector infectivity to tumor cells. Glioma tumors often express a mutant form (vIII) of the epidermal growth factor receptor (EGFR) resulting in the presence of a novel epitope on the cell surface. This epitope is specifically recognized by a single chain antibody designated MR1-1. HSV-1 infection involves initial binding to heparan sulfate (HS) on the cell surface mediated primarily by the viral envelope, glycoprotein C (gC). Here we joined the MR1-1 single chain antibody (scFv) to the gC sequence deleted for the HS binding domain (HSBD) as a means of targeting viral attachment to EGFRvIII on glial tumor cells. Virions bearing MR1-1-modified-gC had 5-fold increased infectivity for EGFRvIII-bearing human glioma U87 cells compared to mutant receptor-deficient cells. Further, MR1-1/EGFRvIII mediated infection was more efficient for EGFRvIII-positive cells than was wild-type virus for either positive or negative cells. Sustained infection of EGFRvIII+ glioma cells by MR1-1-modified-gC bearing oncolytic virus, as compared to wild-type gC oncolytic virus, was also shown in subcutaneous tumors in vivo using firefly luciferase as a reporter of infection. These data demonstrate that HSV tropism can be manipulated so that virions recognize a cell specific binding site with increased infectivity for the target cell. The retargeting of HSV infection to tumor cells should enhance vector specificity, tumor cell killing and vector safety.
PMCID: PMC2923688  PMID: 20508670
EGFR; oncolytic; HSV; glioma; tropism; glycoprotein C; mouse tumor model; HSV vector retargeting
13.  Targeting Pediatric Cancer Stem Cells with Oncolytic Virotherapy 
Pediatric research  2012;71(4 Pt 2):500-510.
Cancer stem cells (CSC), also termed “cancer initiating cells” or “cancer progenitor cells”, which have the ability to self-renew, proliferate, and maintain the neoplastic clone, have recently been discovered in a wide variety of pediatric tumors. These CSC are thought to be responsible for tumorigenesis, tumor maintenance, aggressiveness and recurrence due to inherent resistance to current treatment modalities such as chemotherapy and radiation. Oncolytic virotherapy offers a novel, targeted approach for eradicating pediatric CSC by utilizing mechanisms of cell killing that differ from conventional therapies. Moreover, oncolytic viruses have the ability to target specific features of CSC such as cell surface proteins, transcription factors, and the CSC microenvironment. Through genetic engineering, a wide variety of foreign genes may be expressed by oncolytic viruses to augment the oncolytic effect. We review the current data regarding the ability of several types of oncolytic viruses (herpes simplex virus-1 (HSV-1), adenovirus, reovirus, Seneca Valley virus, vaccinia virus, Newcastle disease virus, myxoma virus, vesicular stomatitis virus) to target and kill both CSC and tumor cells in pediatric tumors. We highlight advantages and limitations of each virus and potential ways next-generation engineered viruses may target resilient CSC.
PMCID: PMC3607376  PMID: 22430386
14.  Complex Spatial Dynamics of Oncolytic Viruses In Vitro: Mathematical and Experimental Approaches 
PLoS Computational Biology  2012;8(6):e1002547.
Oncolytic viruses replicate selectively in tumor cells and can serve as targeted treatment agents. While promising results have been observed in clinical trials, consistent success of therapy remains elusive. The dynamics of virus spread through tumor cell populations has been studied both experimentally and computationally. However, a basic understanding of the principles underlying virus spread in spatially structured target cell populations has yet to be obtained. This paper studies such dynamics, using a newly constructed recombinant adenovirus type-5 (Ad5) that expresses enhanced jellyfish green fluorescent protein (EGFP), AdEGFPuci, and grows on human 293 embryonic kidney epithelial cells, allowing us to track cell numbers and spatial patterns over time. The cells are arranged in a two-dimensional setting and allow virus spread to occur only to target cells within the local neighborhood. Despite the simplicity of the setup, complex dynamics are observed. Experiments gave rise to three spatial patterns that we call “hollow ring structure”, “filled ring structure”, and “disperse pattern”. An agent-based, stochastic computational model is used to simulate and interpret the experiments. The model can reproduce the experimentally observed patterns, and identifies key parameters that determine which pattern of virus growth arises. The model is further used to study the long-term outcome of the dynamics for the different growth patterns, and to investigate conditions under which the virus population eliminates the target cells. We find that both the filled ring structure and disperse pattern of initial expansion are indicative of treatment failure, where target cells persist in the long run. The hollow ring structure is associated with either target cell extinction or low-level persistence, both of which can be viewed as treatment success. Interestingly, it is found that equilibrium properties of ordinary differential equations describing the dynamics in local neighborhoods in the agent-based model can predict the outcome of the spatial virus-cell dynamics, which has important practical implications. This analysis provides a first step towards understanding spatial oncolytic virus dynamics, upon which more detailed investigations and further complexity can be built.
Author Summary
Traditional chemotherapy of cancers is characterized by strong side effects, while showing a low success rate in the long term control of tumors. Besides small molecule inhibitors, which have shown great promise, oncolytic viruses present an emerging specific treatment approach. They are engineered viruses that spread from tumor cell to tumor cell, killing them in the process. Non-tumor cells are generally not infected. While clinical trials have given rise to promising results, reliable success remains elusive. Besides experiments, computational approaches provide a valuable tool to better understand the dynamics of virus spread through a growing population or tumor cells. Combining in vitro experimental approaches with computational models, we study the principles of virus spread through a spatially structured population of cells, which is of fundamental importance to understanding virus treatment of solid tumors. We describe different growth patterns that can occur, interpret them, and explore how they relate to the ability of the virus to induce tumor regression. We further define how these spatial dynamics relate to settings where cells and viruses mix more readily, such as in many cell culture experiments that are used to evaluate candidate viruses.
PMCID: PMC3375216  PMID: 22719239
15.  A Structure-Guided Mutation in the Major Capsid Protein Retargets BK Polyomavirus 
PLoS Pathogens  2013;9(10):e1003688.
Viruses within a family often vary in their cellular tropism and pathogenicity. In many cases, these variations are due to viruses switching their specificity from one cell surface receptor to another. The structural requirements that underlie such receptor switching are not well understood especially for carbohydrate-binding viruses, as methods capable of structure-specificity studies are only relatively recently being developed for carbohydrates. We have characterized the receptor specificity, structure and infectivity of the human polyomavirus BKPyV, the causative agent of polyomavirus-associated nephropathy, and uncover a molecular switch for binding different carbohydrate receptors. We show that the b-series gangliosides GD3, GD2, GD1b and GT1b all can serve as receptors for BKPyV. The crystal structure of the BKPyV capsid protein VP1 in complex with GD3 reveals contacts with two sialic acid moieties in the receptor, providing a basis for the observed specificity. Comparison with the structure of simian virus 40 (SV40) VP1 bound to ganglioside GM1 identifies the amino acid at position 68 as a determinant of specificity. Mutation of this residue from lysine in BKPyV to serine in SV40 switches the receptor specificity of BKPyV from GD3 to GM1 both in vitro and in cell culture. Our findings highlight the plasticity of viral receptor binding sites and form a template to retarget viruses to different receptors and cell types.
Author Summary
Viruses need to bind to receptors on host cells for viral entry and infection, and the type of receptor bound determines the range of hosts and tissues the virus can infect. Viruses within a family often vary in their tissue distribution and pathogenicity because changes in receptor specificity can produce a virus with different spread and infectivity. In fact, many transmissions between species are based on a virus acquiring binding capability for a new receptor. The structural changes that underlie such receptor switching are not well understood. We have analyzed the structural requirements for receptor binding and switching of the human BK polyomavirus (BKPyV), the causative agent of polyomavirus-associated nephropathy. We show that BKPyV uses specific gangliosides that all contain a common α2,8-disialic acid motif to infect cells, and have characterized the interaction in atomic detail. Our data explains the requirement for this disialic acid motif and in particular highlights a single amino acid that is central to determining specificity. Mutation of this residue switches the receptor specificity, enabling BKPyV to infect cells bearing a different class of gangliosides. Our findings highlight the plasticity of viral receptor binding sites and form a template to retarget viruses to different receptors and cell types.
PMCID: PMC3795024  PMID: 24130487
16.  The Utility of a Tissue Slice Model System to Determine Breast Cancer Infectivity by Oncolytic Adenoviruses 
The Journal of surgical research  2010;163(2):270-275.
Due to advances in viral design, oncolytic adenoviruses have emerged as a promising approach for treatment of breast cancer. Tumor tissue slices offer a stringent model system for preclinical evaluation of adenovirus therapies, since the slices retain a morphology and phenotype that more closely resembles the in vivo setting than cell line cultures, and it has been shown to have utility in the evaluation of viral infectivity and replication. In this study, we evaluated the efficacy of viral infection and replication using a tropism-modified oncolytic adenovirus.
Breast tumor tissue slices were infected with a tropism-modified oncolytic adenovirus, and a wild-type adenovirus for comparison. Efficiency of infection was evaluated using fluorescent microscopy, as the viruses used have been modified to express red fluorescent protein. Replication of the viruses was evaluated with quantitative real-time PCR to assay viral E4 genome copy number, a surrogate indicator for the number of virions. The breast tumor tissue slices were evaluated for the expression of CD46 expression by immunohistochemistry.
Infection and replication of our tropism modified oncolytic virus has been observed in breast cancer tissue slice model system and is comparative to wild-type virus. A qualitative increase in the number of cells showing RFP expression was observed correlating with increasing multiplicity of infection. Higher relative infectivity of the virus was observed in tumor tissue compared with normal breast tissue. Replication of the virus was demonstrated through increases in E4 copy number at 48 and 72 hours after infection in human breast tumor slices.
We have shown that a tropism modified oncolytic oncolytic adenovirus can infect and replicate in breast cancer tissue slices, which may be an important preclinical indicator for its therapeutic utility.
PMCID: PMC3015137  PMID: 20691986
adenovirus; breast cancer; CD46; CAR; oncolytic; tissue slice model
Cancer research  2009;69(4):1459-1468.
Oncolytic measles virus (MV) induces cell fusion and cytotoxicity in a CD46 dependent manner. Development of fully retargeted oncolytic MVs would improve tumor selectivity. The urokinase receptor (uPAR) is a tumor and stromal target overexpressed in multiple malignancies. MV-H glycoproteins fully retargeted to either human or murine uPAR were engineered and their fusogenic activity was determined. Recombinant human (MV-h-uPA) and murine (MV-m-uPA) uPAR retargeted MVs expressing eGFP were rescued and characterized. Viral expression of chimeric MV-H was demonstrated by RT-PCR and Western Blot. In vitro viral replication was comparable to MV-GFP control. Receptor and species specificity of MV-uPAs were demonstrated in human and murine cells with different levels of uPAR expression. Removal of the ATF ligand from MV-uPA -by Factor Xa treatment- ablated MV-uPA’s functional activity. Cytotoxicity was demonstrated in uPAR expressing human and murine cells. MV-h-uPA efficiently infected human endothelial cells and capillary tubes in vitro. Intravenous administration of MV-h-uPA delayed tumor growth and prolonged survival in the MDA-MB-231 breast cancer xenograft model. Viral tumor targeting was confirmed by immunohistochemistry. MV-m-uPA transduced murine mammary tumors (4T1) in vivo, after intratumor administration. MV-m-uPA targeted murine tumor vasculature after systemic administration, as demonstrated by dual (CD31 and MV-N) staining of tumor capillaries in the MDA-MB-231 model. In conclusion, MV-uPA is a novel oncolytic MV associated with potent and specific antitumor effects and tumor vascular targeting. This is the first retargeted oncolytic MV able to replicate in murine cells and target tumor vasculature in an uPAR dependent manner.
PMCID: PMC2739455  PMID: 19208845
18.  Structure of Reovirus σ1 in Complex with Its Receptor Junctional Adhesion Molecule-A 
PLoS Pathogens  2008;4(12):e1000235.
Viral attachment to specific host receptors is the first step in viral infection and serves an essential function in the selection of target cells. Mammalian reoviruses are highly useful experimental models for studies of viral pathogenesis and show promise as vectors for oncolytics and vaccines. Reoviruses engage cells by binding to carbohydrates and the immunoglobulin superfamily member, junctional adhesion molecule-A (JAM-A). JAM-A exists at the cell surface as a homodimer formed by extensive contacts between its N-terminal immunoglobulin-like domains. We report the crystal structure of reovirus attachment protein σ1 in complex with a soluble form of JAM-A. The σ1 protein disrupts the JAM-A dimer, engaging a single JAM-A molecule via virtually the same interface that is used for JAM-A homodimerization. Thus, reovirus takes advantage of the adhesive nature of an immunoglobulin-superfamily receptor by usurping the ligand-binding site of this molecule to attach to the cell surface. The dissociation constant (KD) of the interaction between σ1 and JAM-A is 1,000-fold lower than that of the homophilic interaction between JAM-A molecules, indicating that JAM-A strongly prefers σ1 as a ligand. Analysis of reovirus mutants engineered by plasmid-based reverse genetics revealed residues in σ1 required for binding to JAM-A and infectivity of cultured cells. These studies define biophysical mechanisms of reovirus cell attachment and provide a platform for manipulating reovirus tropism to enhance vector targeting.
Author Summary
Mammalian orthoreoviruses (reoviruses) are useful models for studies of virus–receptor interactions and viral pathogenesis. They are closely related in structure to adenoviruses and share similar mechanisms of cell attachment and entry. The receptor for reovirus, junctional adhesion molecule-A (JAM-A), is a component of cellular junctions and also used as a receptor by feline calicivirus. To better understand how viruses engage cellular receptors, we determined the structure of reovirus attachment protein σ1 bound to JAM-A. The structure provides an understanding of the biological function of the interaction and yields information that may enable targeting of reovirus to alternate receptors. Since the repertoire of receptors bound by a virus contributes importantly to determining which types of cells are infected, such targeting plays an essential role in gene delivery for vaccine or therapeutic applications. New cancer therapy approaches include the use of viruses, including reovirus, to lyse tumor cells. New knowledge about reovirus attachment to cellular receptors at an atomic level will help to harness the therapeutic potential of this virus.
PMCID: PMC2588538  PMID: 19079583
19.  Oncolytic Newcastle Disease Virus as Cutting Edge between Tumor and Host 
Biology  2013;2(3):936-975.
Oncolytic viruses (OVs) replicate selectively in tumor cells and exert anti-tumor cytotoxic activity. Among them, Newcastle Disease Virus (NDV), a bird RNA virus of the paramyxovirus family, appears outstanding. Its anti-tumor effect is based on: (i) oncolytic activity and (ii) immunostimulation. Together these activities facilitate the induction of post-oncolytic adaptive immunity. We will present milestones during the last 60 years of clinical evaluation of this virus. Two main strategies of clinical application were followed using the virus (i) as a virotherapeutic agent, which is applied systemically or (ii) as an immunostimulatory agent combined with tumor cells for vaccination of cancer patients. More recently, a third strategy evolved. It combines the strategies (i) and (ii) and includes also dendritic cells (DCs). The first step involves systemic application of NDV to condition the patient. The second step involves intradermal application of a special DC vaccine pulsed with viral oncolysate. This strategy, called NDV/DC, combines anti-cancer activity (oncolytic virotherapy) and immune-stimulatory properties (oncolytic immunotherapy) with the high potential of DCs (DC therapy) to prime naive T cells. The aim of such treatment is to first prepare the cancer-bearing host for immunocompetence and then to instruct the patient’s immune system with information about tumor-associated antigens (TAAs) of its own tumor together with danger signals derived from virus infection. This multimodal concept should optimize the generation of strong polyclonal T cell reactivity targeted against the patient’s TAAs and lead to the establishment of a long-lasting memory T cell repertoire.
PMCID: PMC3960873  PMID: 24833054
RNA virus; tumor immunology; immunotherapy of solid tumors; tumor vaccination; virus; dendritic cells; danger signals; CD8 T-lymphocytes
20.  Combined transductional untargeting/retargeting and transcriptional restriction enhance adenovirus gene targeting and therapy for hepatic colorectal cancer tumors 
Cancer research  2009;69(2):554.
Unresectable hepatic colorectal cancer (CRC) metastases are a leading cause of cancer mortality. These tumors, and other epithelial tumors, often express both cyclooxygenase 2 (COX-2) and carcinoembryonic antigen (CEA). Because adenovirus vectors infect liver and lack tumor tropism, they cannot be utilized for systemic therapy of hepatic metastases. We used COX-2 transcriptional restriction, in combination with transductional adenovirus hepatic untargeting and tumor retargeting by a bispecific adapter, sCARhMFE, composed of sCAR (the Coxsackie and Adenovirus Receptor ectodomain) and MFE-23 (a single-chain anti-CEA antibody), to untarget liver following intravenous administration of adenovirus vectors expressing firefly luciferase and to retarget virus to hepatic colorectal tumor xenografts and non-small cell lung tumor xenografts. To improve both liver untargeting and tumor retargeting, we developed sCARfMFE, a trimerized sCARhMFE adapter. Trimerization greatly improves both untargeting of CAR-dependent adenovirus infection and CEA-dependent virus retargeting, in culture and in vivo.
Combining sCARfMFE bispecific adapter transductional liver untargeting and transductional tumor retargeting with COX-2 transcriptional tumor-restricted transgene expression increases systemically-administered adenovirus therapeutic efficacy for hepatic CRC tumors, using Herpes Virus Type 1 thymidine kinase as a therapeutic gene in conjunction with the prodrug ganciclovir. Both transductional untargeting and COX-2 transcriptional restriction also reduce HSV1-tk/GCV hepatic toxicity. In addition, transductional sCARfMFE untargeting reduces the innate immune response to systemic adenovirus administration. Combined transductional liver Ad untargeting, transductional tumor retargeting and transcriptional transgene restriction suggests a means to engineer practical, effective therapeutic agents for hepatic CRC metastases in particular, as well as hepatic metastases of other epithelial cancers.
PMCID: PMC2823090  PMID: 19147569
adenovirus; colorectal cancer; COX-2 transcriptional restriction; transductional retargeting
21.  Granulocyte-Macrophage Colony-Stimulating Factor-Armed Oncolytic Measles Virus Is an Effective Therapeutic Cancer Vaccine 
Human Gene Therapy  2013;24(7):644-654.
Oncolytic measles viruses (MV) derived from the live attenuated vaccine strain have been engineered for increased antitumor activity, and are currently under investigation in clinical phase 1 trials. Approaches with other viral vectors have shown that insertion of immunomodulatory transgenes enhances the therapeutic potency. In this study, we engineered MV for expression of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF). For the first time, therapeutic efficacy and adaptive immune response in the context of MV oncolysis could be evaluated in the previously established immunocompetent murine colon adenocarcinoma model MC38cea. MC38cea cells express the human carcinoembryonic antigen (CEA), allowing for infection with retargeted MV. Intratumoral application of MV-GMCSF significantly delayed tumor progression and prolonged median overall survival compared with control virus-treated mice. Importantly, more than one-third of mice treated with MV-GMCSF showed complete tumor remission and rejected successive tumor reengraftment, demonstrating robust long-term protection. An enhanced cell-mediated tumor-specific immune response could be detected by lactate dehydrogenase assay and interferon-γ enzyme-linked immunospot assay. Furthermore, MV-GMCSF treatment correlated with increased abundance of tumor-infiltrating CD3+ lymphocytes analyzed by quantitative microscopy of tumor sections. These findings underline the potential of oncolytic, GM-CSF-expressing MV as an effective therapeutic cancer vaccine actively recruiting adaptive immune responses for enhanced therapeutic impact and tumor elimination. Thus, the treatment benefit of this combined immunovirotherapy approach has direct implications for future clinical trials.
Grossardt and colleagues engineer measles viruses (MV) for expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) and evaluate its therapeutic efficacy and immune response in an established immunocompetent murine colon adenocarcinoma model. Intratumoral application of MV-GMCSF delayed tumor progression and significantly prolonged median overall survival, with more than one third of mice showing complete tumor remission as well as resistance to tumor re-engraftment.
PMCID: PMC3719441  PMID: 23642239
22.  Construction of a Fully Retargeted Herpes Simplex Virus 1 Recombinant Capable of Entering Cells Solely via Human Epidermal Growth Factor Receptor 2 ▿ †  
Journal of Virology  2008;82(20):10153-10161.
A novel frontier in the treatment of tumors that are difficult to treat is oncolytic virotherapy, in which a replication-competent virus selectively infects and destroys tumor cells. Herpes simplex virus (HSV) represents a particularly attractive system. Effective retargeting to tumor-specific receptors has been achieved by insertion in gD of heterologous ligands. Previously, our laboratory generated an HSV retargeted to human epidermal growth factor receptor 2 (HER2), a receptor overexpressed in about one-third of mammary tumors and in some ovarian tumors. HER2 overexpression correlates with increased metastaticity and poor prognosis. Because HER2 has no natural ligand, the inserted ligand was a single-chain antibody to HER2. The objective of this work was to genetically engineer an HSV that selectively targets the HER2-expressing tumor cells and that has lost the ability to enter cells through the natural gD receptors, HVEM and nectin1. Detargeting from nectin1 was attempted by two different strategies, point mutations and insertion of the single-chain antibody at a site in gD different from previously described sites of insertion. We report that point mutations at gD amino acids 34, 215, 222, and 223 failed to generate a nectin1-detargeted HSV. An HSV simultaneously detargeted from nectin1 and HVEM and retargeted to HER2 was successfully engineered by moving the site of single-chain antibody insertion at residue 39, i.e., in front of the nectin1-interacting surface and not lateral to it, and by deleting amino acid residues 6 to 38. The resulting recombinant, R-LM113, entered cells and spread from cell to cell solely via HER2.
PMCID: PMC2566291  PMID: 18684832
23.  Targeting of Adenovirus Serotype 5 Pseudotyped with Short Fiber from Serotype 41 to c-erbB2-Positive Cells Using Bispecific Single-Chain Diabody 
Journal of molecular biology  2009;388(3):443-461.
The purpose of the current study was to alter the broad native tropism of human adenovirus for virus targeting to c-erbB2-positive cancer cells. First, we engineered a single-chain antibody (scFv) against the c-erbB2 oncoprotein into minor capsid protein IX (pIX) of adenovirus serotype 5 (Ad5) in a manner commensurate with virion integrity and binding to the soluble extracellular c-erbB2 domain. To ablate native viral tropism and facilitate binding of the pIX-incorporated scFv to cellular c-erbB2 we replaced the Ad5 fiber with the Ad41 short (41s) fiber devoid of all known cell-binding determinants. The resultant Ad5F41sIX6.5 vector demonstrated increased cell binding and gene transfer as compared to the Ad5F41s control, however, this augmentation of virus infectivity was not c-erbB2-specific. Incorporation of a six histidine (His6) peptide into the C-terminus of the 41s fiber protein resulted in markedly increased Ad5F41s6H infectivity in 293AR cells, which express a membrane-anchored scFv against the C-terminal oligo-histidine tag, as compared to the Ad5F41s vector and the parental 293 cells. These data suggested that a 41s fiber-incorporated His6 tag could serve for attachment of an adapter protein designed to guide Ad5F41s6H infection in a c-erbB2-specific manner. We therefore engineered a bispecific scFv diabody (scDb) combining affinities for both c-erbB2 and the His6 tag and showed its ability to provide up to 25-fold increase of Ad5F41s6H infectivity in c-erbB2-positive cells. Thus, Ad5 fiber replacement by a His6–tagged 41s fiber coupled with virus targeting mediated by an scDb adapter represents a promising strategy to confer Ad5 vector tropism for c-erbB2-positive cancer cells.
PMCID: PMC2696239  PMID: 19285990
Adenovirus; c-erbB2; serotype 41 short fiber; capsid protein IX; single-chain diabody
24.  Structures of B-Lymphotropic Polyomavirus VP1 in Complex with Oligosaccharide Ligands 
PLoS Pathogens  2013;9(10):e1003714.
B-Lymphotropic Polyomavirus (LPyV) serves as a paradigm of virus receptor binding and tropism, and is the closest relative of the recently discovered Human Polyomavirus 9 (HPyV9). LPyV infection depends on sialic acid on host cells, but the molecular interactions underlying LPyV-receptor binding were unknown. We find by glycan array screening that LPyV specifically recognizes a linear carbohydrate motif that contains α2,3-linked sialic acid. High-resolution crystal structures of the LPyV capsid protein VP1 alone and in complex with the trisaccharide ligands 3′-sialyllactose and 3′-sialyl-N-acetyl-lactosamine (3SL and 3SLN, respectively) show essentially identical interactions. Most contacts are contributed by the sialic acid moiety, which is almost entirely buried in a narrow, preformed cleft at the outer surface of the capsid. The recessed nature of the binding site on VP1 and the nature of the observed glycan interactions differ from those of related polyomaviruses and most other sialic acid-binding viruses, which bind sialic acid in shallow, more exposed grooves. Despite their different modes for recognition, the sialic acid binding sites of LPyV and SV40 are half-conserved, hinting at an evolutionary strategy for diversification of binding sites. Our analysis provides a structural basis for the observed specificity of LPyV for linear glycan motifs terminating in α2,3-linked sialic acid, and links the different tropisms of known LPyV strains to the receptor binding site. It also serves as a useful template for understanding the ligand-binding properties and serological crossreactivity of HPyV9.
Author Summary
Viruses must engage specific receptors on host cells in order to initiate infection. The type of receptor and its concentration on cells determine viral spread and tropism, but for many viruses, the receptor and the mode of recognition by the virus are not known. We have characterized the structural requirements for receptor binding of B-lymphotropic polyomavirus (LPyV). This virus was originally isolated from African Green Monkey lymph node cultures and attracted interest because of its narrow tropism for a human tumor cell line. LPyV is also the closest relative of the recently discovered Human Polyomavirus 9 (HPyV9). We screened the LPyV coat protein VP1 on an carbohydrate microarray and found that it specifically recognizes a linear sugar motif that terminates in α2,3-linked sialic acid. We then determined the structures LPyV VP1 bound to these carbohydrates. The protein has a preformed, deeply recessed binding site for sialic acid. The binding site differs in both architecture and mode of recognition from the binding sites of other viruses. LPyV only binds linear carbohydrates that are able to penetrate into the binding slot.
PMCID: PMC3814675  PMID: 24204265
25.  Complementary Induction of Immunogenic Cell Death by Oncolytic Parvovirus H-1PV and Gemcitabine in Pancreatic Cancer 
Journal of Virology  2014;88(10):5263-5276.
Novel therapies employing oncolytic viruses have emerged as promising anticancer modalities. The cure of particularly aggressive malignancies requires induction of immunogenic cell death (ICD), coupling oncolysis with immune responses via calreticulin, ATP, and high-mobility group box protein B1 (HMGB1) release from dying tumor cells. The present study shows that in human pancreatic cancer cells (pancreatic ductal adenocarcinoma [PDAC] cells; n = 4), oncolytic parvovirus H-1 (H-1PV) activated multiple interconnected death pathways but failed to induce calreticulin exposure or ATP release. In contrast, H-1PV elevated extracellular HMGB1 levels by 4.0 ± 0.5 times (58% ± 9% of total content; up to 100 ng/ml) in all infected cultures, whether nondying, necrotic, or apoptotic. An alternative secretory route allowed H-1PV to overcome the failure of gemcitabine to trigger HMGB1 release, without impeding cytotoxicity or other ICD activities of the standard PDAC medication. Such broad resistance of H-1PV-induced HMGB1 release to apoptotic blockage coincided with but was uncoupled from an autocrine interleukin-1β (IL-1β) loop. That and the pattern of viral determinants maintained in gemcitabine-treated cells suggested the activation of an inflammasome/caspase 1 (CASP1) platform alongside DNA detachment and/or nuclear exclusion of HMGB1 during early stages of the viral life cycle. We concluded that H-1PV infection of PDAC cells is signaled through secretion of the alarmin HMGB1 and, besides its own oncolytic effect, might convert drug-induced apoptosis into an ICD process. A transient arrest of cells in the cyclin A1-rich S phase would suffice to support compatibility of proliferation-dependent H-1PV with cytotoxic regimens. These properties warrant incorporation of the oncolytic virus H-1PV, which is not pathogenic in humans, into multimodal anticancer treatments.
IMPORTANCE The current therapeutic concepts targeting aggressive malignancies require an induction of immunogenic cell death characterized by exposure of calreticulin (CRT) as well as release of ATP and HMGB1 from dying cells. In pancreatic tumor cells (PDAC cells) infected with the oncolytic parvovirus H-1PV, only HMGB1 was released by all infected cells, whether nondying, necrotic, or succumbing to one of the programmed death pathways, including contraproductive apoptosis. Our data suggest that active secretion of HMGB1 from PDAC cells is a sentinel reaction emerging during early stages of the viral life cycle, irrespective of cell death, that is compatible with and complements cytotoxic regimens. Consistent induction of HMGB1 secretion raised the possibility that this reaction might be a general “alarming” phenomenon characteristic of H-1PV's interaction with the host cell; release of IL-1β points to the possible involvement of a danger-sensing inflammasome platform. Both provide a basis for further virus-oriented studies.
PMCID: PMC4019131  PMID: 24574398

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