Abstract:
The present invention relates to a novel composition and method to potentiate the antitumor effect of an oncolytic virus by providing for resistance against a host&#39;s innate interferon response. Particularly, a B18R gene is incorporated into an oncolytic virus. During treatment of a host with the modified oncolytic virus, the oncolytic virus retains its phenotype, and the host&#39;s innate immune response has a minimal affect on viral replication.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional application No. 61/453,887, filed on Mar. 17, 2011, which is herein incorporated by reference in its entirety. 
     
    
     GOVERNMENTAL SPONSORSHIP 
       [0002]    The U.S. Government has a paid-up license in this invention and the rights in limited circumstances to require the patent owners to license others on reasonable terms as provided for by the terms of grant No. 7R01CA132792-03 awarded by the National Cancer Institute. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to a novel composition and method to potentiate the antitumor effect of an oncolytic virus by providing for resistance against a host&#39;s innate interferon response. 
       BACKGROUND OF THE INVENTION 
       [0004]    Tumor virotherapy involves the application of a natural or genetically modified virus that can specifically replicate in cancer cells for the treatment of malignant diseases. Extensive preclinical studies and early stage clinical trials have shown that these so-called oncolytic viruses are safe for in vivo administration, and in many instances, have shown great potential for clinical applications. However, despite the demonstrated potency in lysing tumor cells in vitro, the success of virotherapy in vivo can be limited by the complex interplay of virus replication and host resistance factors. One of the major resistance factors is the host&#39;s immune defense system, which can restrict the ability of the virus to replicate and spread within tumors. More specifically, the host&#39;s innate immune system is rapidly activated during replication of the oncolytic virus in vivo. Thus, since the antitumor effect of an oncolytic virus is mainly generated during the acute phase of virus replication, the innate immune system may play a more pivotal role in dictating or inhibiting the initial extent of virus replication and spread in the tumor tissues than the classical adaptive immune responses of T and B lymphocytes. 
         [0005]    Among a host&#39;s first lines of innate immune defense against the oncolytic activity of virotherapy are the interferons (IFNs). IFNs compose three major classes: type 1 (IFN-α and -β), type II (IFN-γ) and type III (IFN-λ). Upon viral infection, IFN release can be induced almost instantly, and the IFNs then bind to their receptors to activate signal transducer and activator of transcription (STAT) complexes. This activation triggers expression of a series of interferon-responsive genes such as protein kinase R (PKR) and 2′-5′-OAS/RNaseL, which convert cells into an antiviral state. The antiviral effect of IFNs is potent and rapid. Consequently, many viruses have developed diverse strategies to counteract the interferon activity. These include direct prevention of interferon synthesis, blockage of the effect of downstream signaling events triggered by receptor binding, and inhibition of the functions of antiviral effectors induced by IFNs. For example, herpes simplex virus (HSV) has employed diverse mechanisms to counteract the antiviral effect of IFNs. Several viral gene products, including ICP0 and ICP27 act by inhibiting the function of interferon regulatory factors (IRF) 3 and 7. Other HSV gene products, such as ICP34.5 and Us11, have been found to interact directly with the effector protein PKR and prevent its downstream effect—phosphorylation of eIF-2α. Vaccinia, another large DNA virus, also contains several genes whose products, through distinct mechanisms, function to limit the antiviral effect of IFNs. One of these viral products is the B18R gene, which is a secreted molecule that acts as a decoy receptor to intercept type I IFNs from various species, thus preventing these IFNs from binding to their receptors. 
         [0006]    Despite HSV&#39;s reported ability to evade the antiviral effect of IFNs, the outcome of in vivo HSV infection is still largely dictated by the interferon status of the host. This has been demonstrated in several animal experiments (Conrady, C. D., Halford, W. P., and Carr, D. J. (2011). Loss of the type I interferon pathway increases vulnerability of mice to genital herpes simplex virus 2 infection. J Virol 85: 1625-1633; Carr, D. J., Al-khatib, K., James, C. M., and Silverman, R. (2003). Interferon-beta suppresses herpes simplex virus type 1 replication in trigeminal ganglion cells through an RNase L-dependent pathway. Journal of neuroimmunology 141: 40-46; Sainz, B., Jr., and Halford, W. P. (2002). Alpha/Beta interferon and gamma interferon synergize to inhibit the replication of herpes simplex virus type 1. J Virol 76: 11541-11550). Furthermore, clinical observations of patients with a genetic defect in the intracellular protein UNC-93B, which results in impaired cellular interferon-α/β and -λ antiviral responses, has shown that these patients are prone to more severe infections, such as HSV encephalitis (Casrouge, A., Zhang, S. Y., Eidenschenk, C., Jouanguy, E., Puel, A., Yang, K., et al. (2006). Herpes simplex virus encephalitis in human UNC-93B deficiency. Science 314: 308-312). Together, these indicate that strategies enabling an oncolytic HSV to ward off the host&#39;s interferon antiviral effect will enhance the therapeutic effect of oncolytic virotherapy. Thus, there is need in the art for a modified oncolytic virus that provides for resistance against the antiviral effects of a host&#39;s interferon response. 
       SUMMARY OF THE INVENTION 
       [0007]    In one embodiment of the invention, a medicament containing a modified oncolytic virus is administered to a host. The oncolytic virus is modified by having incorporated the B18R gene into the genome of the oncolytic virus. The B18R gene (DCT.VV.Orf107) was obtained from the National Institute of Allergy and Infectious Diseases, and was stored at Addgene. 
         [0008]    Another embodiment of the invention discloses a method of generating a modified oncolytic virus. The modified oncolytic virus is generated by incorporating a B18R gene into the oncolytic virus. 
         [0009]    In a further embodiment of the invention, a modified oncolytic virus includes an incorporated B18R gene. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. For the purpose of illustration, there is shown in the drawings certain embodiments of the present disclosure. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
           [0011]      FIG. 1 . Shows that B18R is correctly expressed once the gene is inserted into the genome of an oncolytic HSV and that incorporation of the B18R gene into an oncolytic HSV (Synco-2D) does not change its phenotype (fusogenic phenotype). 
           [0012]      FIG. 2 . Shows that B18R released from Synco-B18R can effectively antagonize IFN-α to improve viral replication in human colon and liver cancer cells. 
           [0013]      FIG. 3 . Shows that B18R released from Synco-B18R can effectively antagonize both IFN-α and IFN-β to improve viral replication. 
           [0014]      FIG. 4 . Shows that B18R released from Synco-B18R can potentiate the oncolytic HSV replication in resistant tumor cells. 
           [0015]      FIG. 5 . Shows that incorporation of B18R can increase the killing ability of oncolytic HSV against permissive human cancer cells in the presence of high concentration IFN-α. 
           [0016]      FIG. 6 . Shows that incorporation of B18R can increase the killing ability of oncolytic HSV against resistant cancer cells (LL/2). 
           [0017]      FIG. 7 . Shows that incorporation of B18R can increase the killing ability of oncolytic HSV against semi-permissive Hepa1-6 (7A) and ID8 (7B) tumor cells. 
           [0018]      FIG. 8 . Shows that incorporation of B18R can significantly potentiate the antitumor efficacy of oncolytic HSV against established tumors. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. It should be understood that any one of the features of the invention may be used separately or in combination with other features. Other systems, methods, features, and advantages of the invention will be or become apparent to one with skill in the art upon examination of the drawings and the detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims. 
         [0020]    The present invention is directed to compositions and methods to potentiate the antitumor effect of an oncolytic virus. According to the present invention, incorporation of an interferon-antagonizing molecule into an oncolytic virus can improve the antitumor effect of the oncolytic virus (the B18R gene starting materials (DCT.VV.Orf107) disclosed herein were obtained from the National Institute of Allergy and Infectious Diseases, and were stored at Addgene). In one embodiment, B18R gene from vaccinia virus is incorporated into an oncolytic HSV to significantly potentiate its antitumor effects. This is because the interferon-antagonizing genes of HSV (e.g., ICP0, ICP34.5) mainly act intracellularly, while B18R is secreted to the outside of cells and its decoy effect on interferon works mainly extracellularly. Thus incorporating B18R gene into an oncolytic HSV provides the virus with additional ability to antagonize the interferon antiviral effect from outside of the cells, allowing the virus to replicate and spread more effectively within the tumor tissues for a maximal antitumor effect. 
         [0021]    In another embodiment, Synco-B18R (exemplary genome sequence provided in SEQ ID NO: 2) is constructed by inserting the B18R gene into the internal repeat region of the genome of Synco-2D (exemplary genome sequence provided in SEQ ID NO: 1), an HSV-1-based oncolytic virus. In vitro data shown herein demonstrate that the tumor-killing ability of Synco-B18R is largely maintained in the presence of high levels of type I interferons, while the oncolytic effect of the parental virus (Synco-2D) is severely compromised. In vivo data shown herein demonstrate that Synco-B18R has a significantly superior antitumor activity than Synco-2D against established tumors. Our results thus confirm that the incorporation of the B18R gene of vaccinia virus can potentiate the antitumor effect of an oncolytic HSV, and such a strategy may be applicable to other types of oncolytic viruses. 
         [0022]    In another embodiment of the present invention, the B18R gene is inserted into the genome of an oncolytic herpes simplex virus. The B18R gene was cut out from DCT.VV.Orf107 (obtained from the National Institute of Allergy and Infectious Diseases, and stored at Addgene). Add and cloned into pSZ-EGFP, which contains the green fluorescent protein marker gene (GFP) in addition to the repeat sequence of HSV in the internal junction region. The DNA sequence from the repeated region of HSV would allow the plasmid to recombine to the viral genome, and the GFP marker would facilitate the screening for positive recombinant virus. The new plasmid was transfected into Vero cells, which were then infected with Synco-2D. Virus was harvested 24 h later and GFP-positive plaques (green plaques) were picked up during the subsequent passage of the virus in Vero cells in 10 cm 6-well plates. The virus pick-up was subjected to another 5 more rounds of plaque purification until the GFP-positive virus reached 100% homogeneity. 
         [0023]    In another preferred embodiment of the present invention, insertion of the vaccinia B18R gene into the Synco-2D genome does not change the fusogenic phenotype of the virus. The parental Synco-2D is a fusogenic oncolytic HSV—infection of tumor cells by the virus induces a widespread membrane fusion and thus syncytia formation (Fu, X., Tao, L., Jin, A., Vile, R., Brenner, M., and Zhang, X. (2003). Expression of a fusogenic membrane glycoprotein by an oncolytic herpes simplex virus provides potent synergistic anti-tumor effect. Mol. Ther. 7: 748-754; Nakamori, M., Fu, X., Pettaway, C. A., and Zhang, X. (2004). Potent antitumor activity after systemic delivery of a doubly fusogenic oncolytic herpes simplex virus against metastatic prostate cancer. Prostate 60: 53-60). To determine if the fusogenic phenotype of the virus has been changed by the insertion of the B18R gene, Vero cells are infected with Synco-B18R at 0.1 plaque-forming unit (pfu) per cell.  FIG. 1A  shows a strong band of the right size for B18R in lysates of Synco-B18R infected cells, but not in the sample infected with Synco-2D. Like the parental Synco-2D, Synco-B18R infection also showed a typical syncytial phenotype. For example,  FIG. 1B  shows a typical micrograph taken 24 hours after infection. In  FIG. 1B , the uninfected cells (labeled as UI) are seen as a monolayer without any cytopathic effect. However, the cells infected by Synco-2D and Synco-B18R both show clear membrane fusion (syncytium formation) under the phase contrast field (top panel). Under the dark field (bottom panel), only the cells infected with Synco-B18R are visible since the green fluorescent protein (GFP) gene was inserted into the viral genome together with the B18R gene. In contrast, only a dark field is visible in the cells infected with Synco-2D as it does not contain the GFP gene. Thus, insertion of the vaccinia B18R gene into the Synco-2D genome does not change the fusogenic phenotype of the virus. 
         [0024]    In a further embodiment of the present invention, incorporation of the B18R gene into an oncolytic HSV provides the virus with the ability to ward off the inhibitory effect of type I interferons. To show that Synco-B18R resists the inhibitory effect of interferons, Synco-B18R is directly compared with the parental Synco-2D for their ability to replicate in human tumor cells in the presence of externally added type I interferons. Human tumor cell lines SW480 (a human colon cancer cell line) and Huh7 (a human hepatocellular carcinoma line) were infected with either Synco-2D or Synco-B18R at 0.1 pfu/cell with or without an increasing amount of IFN-α in the medium. The viruses were harvested 24 h later and quantitated by plaque assay. As show in  FIGS. 2A and 2B , the replication of Synco-2D was severely affected by the added IFN-α in both cell lines. However, the inhibitory effect of IFN-α on the replication of Synco-B18R was much less severe. In Huh7 cells, the titer of Synco-B18R was reduced by less than 1 fold even where IFN-α was added to a very high concentration (500 units). 
         [0025]    In one embodiment, incorporation of the B18R gene into an oncolytic HSV provides the virus with the ability to ward off both IFN-α and IFN-β, either individually or in combination. To show the effects of both IFN-α and IFN-β, either individually or in combination, on the replication of Synco-2D and Synco-B18R, an experiment is conducted on a time course, in which the virus is harvested either at 24 h or 48 h after infection. In the presence of IFN-α and IFN-β, either individually or in combination at a relatively high dose (500 units), Synco-B18R titer was significantly higher than that of Synco-2D. The difference was particularly dramatic at 48 h after infection, when the titer of Synco-B18R was 5 to 9 fold higher than that of Synco-2D ( FIGS. 3B , C and D). Together, these results clearly demonstrate that incorporation of the B18R gene into an oncolytic HSV renders the virus with the ability to ward off the inhibitory effect of type I interferons. 
         [0026]    In another embodiment of the present invention, incorporation of B18R into an oncolytic HSV allows the oncolytic virus to replicate more efficiently in resistant tumor cells, such as LL/2 (a murine lung cancer cell line) and H7 (a murine pancreatic cancer line). Some tumor cells are more resistant than other tumor cells (e.g., those used in  FIGS. 2 and 3 ) to HSV replication. Usually this resistance is due to the host&#39;s innate defense mechanisms, including the effects of IFNs. Referring to  FIG. 4 , the replication of Synco-2D and Synco-B18R is compared in two tumor cell lines that are more resistant to virus replication than SW480 or Huh7. Among them, LL/2 is a murine lung cancer cell line (Lewis lung cancer cell line) and H7 is a murine pancreatic cancer line. Due to their relative resistance, these cells were infected with the viruses at relatively higher virus doses (at 1 pfu and 5 pfu per cell, respectively), and the viruses were harvested at 24 h and 48 h after infection. Viral replication was calculated by dividing the virus yield at 24 h or 48 h after infection with the input virus (1 h after infection). The results show that, despite the resistant nature of these tumor cells, Synco-B18R had replicated by almost 10-fold, while Synco-2D had only less than a 2-fold replication. 
         [0027]    Another preferred embodiment of the present invention teaches that the incorporation of the B18R gene into an oncolytic HSV dramatically increases the virus replication and killing effect in tumor cells, in some cases even in the presence of high amount of IFNs in the culture medium. To demonstrate that the incorporation of B18R increases the killing ability of oncolytic HSV, it is determined if the increased replication ability seen in Synco-B18R transforms into an increased killing ability against tumor cells. The killing activity of Synco-2D and Synco-B18R is directly compared in a series of tumor cells. These include: SW480 human colon cancer cells ( FIG. 5A ) and human hepatocellular carcinoma cells ( FIG. 5B ), murine Lewis lung carcinoma ( FIG. 6 ), murine hepatocellular carcinoma cell line Hepa1-6 ( FIG. 7A ) or murine ovarian cancer cell line ID8 ( FIG. 7B ). In all these tumor cells, Synco-B18R killed cells much more effectively than Synco-2D, with or without the presence of added interferons in the medium. These results, together with the results shown in  FIGS. 2 ,  3 , and  4  demonstrate that incorporation of B18R gene into an oncolytic HSV dramatically increases the virus replication and killing effect in tumor cells even in the presence of high amounts of IFNs in the culture medium. 
         [0028]    Another preferred embodiment of the present invention teaches that the incorporation of B18R gene into an oncolytic virus significantly enhances its antitumor effect (and hence its therapeutic effect), due to its ability to antagonize the host&#39;s interferon antiviral effect. Hepa1-6 murine hepatocellular carcinoma cells were implanted into immune competent B6 mice. Once the tumor reached the approximate size of 5 mm in diameter, mice were randomly divided into 3 groups and were treated with 1) PBS (as a negative control), 2) 1×10 7  pfu of Synco-2D or 3) 1×10 7  pfu of Synco-B18R. The tumor size was measured on a regular basis and the tumor size was determined by the formula: tumor volume [mm 3 ]=(length [mm])×(width [mm]) 2 ×0.52. The results show that, despite the effective antitumor effect of Synco-2D, Synco-B18R was even better than Synco-2D at all of the time points after the mice received the virotherapy treatment (see  FIG. 8 ). Moreover, 4/5 mice in the group treated with Synco-B18R became tumor-free at day 14 after virotherapy, while no tumor-free animal was recorded in other groups (See Table 1 Below). These results demonstrate that the incorporation of the B18R gene into an oncolytic virus (in this case a type I herpes simplex virus based oncolytic virus) significantly enhances its antitumor effect, due to its ability to antagonize the host&#39;s interferon antiviral effect. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Incorporation of B18R can significantly potentiate the antitumor 
               
               
                 efficacy of oncolytic HSV against established tumors. 
               
             
          
           
               
                   
                 Treatment 
                 Tumor-free animals 1   
               
               
                   
                   
               
               
                   
                 PBS 
                 0/5 
               
               
                   
                 Synco-2D 
                 0/5 
               
               
                   
                 Synco-B18R 
                 4/5 
               
               
                   
                   
               
               
                   
                   1 Recorded on day 14 after the start of virotherapy. 
               
             
          
         
       
     
         [0029]    While the invention described here specifically focuses on a novel method to significantly increase the antitumor effect of HSV-based oncolytic virus by incorporating the B18R gene, one of ordinary skills in the art, with the benefit of this disclosure, would recognize the extension of the approach to other types of oncolytic viruses. Furthermore, for the sake of convenience, the B18R gene was inserted into the internal repeat region of the viral genome during the construction of Synco-B18R. A person of ordinary skill in the art would understand that the B18R gene can be inserted into any region of the viral genome, as long as it is sufficiently expressed, and that the expression of B18R from genes inserted in any locus of the viral genome will satisfy the ultimate goal of antagonizing the interferon antiviral mechanism. 
         [0030]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that the invention disclosed herein is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims. 
       EXAMPLES 
     Example 1 
     B18R Expression and Phenotypic Characterization of Synco-B18R 
       [0031]    Synco-B18R is constructed by inserting the B18R gene into the genome of an oncolytic HSV (Synco-2D), which has a fusogenic phenotype. Exemplary genome sequences of Synco-2D and Synco-B18R are provided in SEQ ID NO: 1 and SEQ ID NO: 2 respectively. The B18R gene is located in the region between nucleotides 1 and 7409. To measure the expression of B18R from Synco-B18R, vero cells were infected with either Synco-B18R or Synco-2D for 24 h. Cells were then collected and lysed for detection of B18R by far western blotting analysis. This was done by first incubating the separated proteins on the membrane with 10 μg/ml of IFNβ for 1 h, and then by incubating with DSS crosslinking agent. The membrane was washed three times with PBS and incubated overnight with goat anti-human IFNβ antibody. After two washes with PBS, 1:1000 dilution of HRP-conjugated donkey anti-goat IgG was added and incubated for 1 h. After wash, band detection was performed by using ECL Plus Western Blotting Detection system. To phenotypically characterize Synco-B18R, Vero cells were infected with Synco-B18R at a multiplicity of infection (MOI) of 0.1 pfu/cell. Micrographs were taken 24 h after infection (original magnification: 200×). The results ( FIG. 1 ) show that incorporation of the B18R gene into an oncolytic HSV (Synco-2D) does not change its phenotype (fusogenic phenotype). 
       Example 2 
     B18R Released from Synco-B18R can Effectively Antagonize IFN-α to Improve Viral Replication in Human Colon and Liver Cancer Cells 
       [0032]    Sw480 (Colon Cancer) and Huh7 (liver Cancer) cells were seeded into 24-well plates and were infected with either Synco-2D or Synco-B18R at 0.1 pfu/cell. The infected cells were then cultured with medium with or without the indicated amount of IFN-α (100 or 500 units). The virus was harvested 24 h later and titrated by plaque assay. While the added IFN-α severely reduced the replication of the parental Synco-2D, it had much less inhibitory effect on the replication of Synco-B18R. These results ( FIG. 2 ) show that B18R can help the virus ward off the antiviral effects of IFN-α. 
       Example 3 
     B18R Released from Synco-B18R can Effectively Antagonize Both IFN-α and IFN-β to Improve Viral Replication 
       [0033]    SW480 cells were seeded into 24-well plates and were infected with either Synco-2D or Synco-B18R at 0.1 pfu/cell. The infected cells were then cultured with medium with or without 500 units of either IFN-α or IFN-β alone or in combination (labeled as IFNαβ). The virus was harvested 24 h and 48 h later and titrated by plaque assay. While the added IFN-α and IFN-β severely reduced the replication of the parental Synco-2D, they had much less inhibitory effect on the replication of Synco-B18R. These results ( FIG. 3 ) show that B18R can help the virus ward off the antiviral effects of both IFN-α and IFN-β. 
       Example 4 
     B18R Released from Synco-B18R can Potentiate the Oncolytic HSV Replication in Resistant Tumor Cells 
       [0034]    As compared with other tumor cells, LL/2 and H7 cells are more resistant to oncolytic HSV replication. This resistance is mainly due to the innate interferon antiviral effect. Thus, Synco-B18R is tested to determine if it could replicate better than Synco-2D in these cells. LL/2 or H7 cells seeded in 96-well plates were infected with Synco-2D or Synco-B18R at 1 pfu/cell ( FIGS. 4A and 4B ) or 5 pfu/cell ( FIG. 4C ). The virus was harvested at 24 h or 48 h after infection and quantitated by plaque assay. The fold of virus replication was calculated by dividing the virus yield at 24 h or 48 h after infection with the input virus (1 h after infection). While the parental Synco-2D hardly grows in these resistant cells, the yield of Synco-B18R was significantly increased in these cells. These data thus indicate that expression of B18R from the virus can reverse the resistance of these tumor cells to the replication of oncolytic HSV. 
       Example 5 
     Incorporation of B18R can Increase the Killing Ability of Oncolytic HSV Against Permissive Human Cancer Cells in the Presence of High Concentration IFN-α 
       [0035]    SW480 ( FIG. 5A ) and Huh7 ( FIG. 5B ) cells seeded in 24-well plates were infected with either Synco-2D or Synco-B18R at 0.1 pfu/cell and cultured in medium with or without the indicated amount of IFN-α. Cells were harvested 24 h later and cell viability was determined by trypan blue staining. The percentage of cell survival was calculated by dividing the number of viable cells from the infected well with that from a non-infected well. The results show that B18R can increase the killing effect of the oncolytic virus against these tumor cells in the presence of high concentration of type I interferon. 
       Example 6 
     Incorporation of B18R can Increase the Killing Ability of Oncolytic HSV Against Resistant Cancer Cells (LL/2) 
       [0036]    LL/2 cells seeded in 24-well plates were infected with Synco-2D or Synco-B18R at either 1 pfu/cell ( FIG. 6A ) or 5 pfu/cell ( FIG. 6B ). Cells were harvested 24 h later and cell viability was determined by trypan blue staining. The percentage of cell killing was calculated by the following formula: Cell killing (%)=(1−(viable cell number in infected well)/(viable cell number in control well))×100. The results show that B18R can facilitate the oncolytic HSV to efficiently kill tumor cells that are otherwise resistant to the oncolytic effect of the virus. 
       Example 7 
     Incorporation of B18R can Increase the Killing Ability of Oncolytic HSV Against Semi-Permissive Hepa1-6 and ID8 Tumor Cells 
       [0037]    Cells seeded in 24-well plates were infected with Synco-2D or Synco-B18R at 0.05 or 1 pfu/cell ( FIG. 7A ) or at 5 pfu/cell ( FIG. 7B ). Cells were harvested either at either 24 h or 48 h ( FIG. 7A ) or at 48 h after infection ( FIG. 7B ) and cell viability was determined by trypan blue staining. The percentage of cell killing was calculated by the following formula: Cell killing (%)=(1−(viable cell number in infected well)/(viable cell number in control well))×100. The results show that B18R can enhance the killing effect of oncolytic HSV against tumor cells that are only semi-permissive to the oncolytic effect of the virus. 
       Example 8 
     Incorporation of B18R can Significantly Potentiate the Antitumor Efficacy of Oncolytic HSV Against Established Tumors 
       [0038]    Murine hepatocellular carcinoma was established at the right flank of immune-competent B6 mice by subcutaneous implantation of Hepa1-6 cells. Once the tumor reached the approximate size of 5 mm in diameter, mice received intratumoral injection of either PBS (as a negative control), the Synco-2D or Synco-B18R viruses. Tumor size was measured at the indicated time and tumor volume determined by the formula: tumor volume [mm 3 ]=(length [mm])×(width [mm]) 2 ×0.52. The results ( FIG. 8 ) show that B18R can further increase the therapeutic efficacy of a potent oncolytic HSV such as Synco-2D.