Bovine herpesvirus tegument protein VP22 enhances thymidine kinase/ganciclovir suicide gene therapy for neuroblastomas compared to herpes simplex virus VP22

Killing Effect of the Herpes Simplex Virus Thymidine Kinase/Ganciclovir Enzyme/Prodrug System on Human Nasopharyngeal Carcinoma Cells

A promising new approach for the gene therapy of cancer is the introduction of the herpes simplex virus thymidine kinase (HSV tk) gene into tumour cells, where the HSV tk gene product converts the non-toxic prodrug ganciclovir (GCV) into its cytotoxic metabolite. We constructed a recombinant plasmid containing the HSV tk gene using standard molecular biology techniques in order to investigate whether the HSV tk/GCV enzyme/prodrug system could kill the human nasopharyngeal carcinoma cell line HNE-1. The recombinant plasmid pcDNA3.1(–) CMV.TK was transfected into the HNE-1 cells by electroporation. The expression of HSV tk by the transfected HNE-1/TK cells was confirmed by mRNA amplification and Western blotting. The growth of HNE-1/TK cells was inhibited by GCV in a dose-dependent manner. The HSV tk/GCV system also demonstrated a considerable bystander effect on co-cultured wild type HNE-1 cells. We conclude that the HSV tk/GCV system could be used as gene therapy for nasopharyngeal carcinoma.

Gene therapy as a potential tool for treating neuroblastoma-a focused review

Neuroblastoma, a solid tumor caused by rapid division of undifferentiated neuroblasts, is the most common childhood malignancy affecting children aged <5 years. Several approaches and strategies developed and tested to cure neuroblastoma have met with limited success due to different reasons. Many oncogenes are deregulated during the onset and development of neuroblastoma and thus offer an opportunity to circumvent this disease if the expression of these genes is restored to normalcy. Gene therapy is a powerful tool with the potential to inhibit the deleterious effects of oncogenes by inserting corrected/normal genes into the genome. Both viral and non-viral vector-based gene therapies have been developed and adopted to deliver the target genes into neuroblastoma cells. These attempts have given hope to bringing in a new regime of treatment against neuroblastoma. A few gene-therapy-based treatment strategies have been tested in limited clinical trials yielding some positive results. This mini review is an attempt to provide an overview of the available options of gene therapy to treat neuroblastoma.

Suicide gene therapy for hepatocellular carcinoma cells by survivin promoter-driven expression of the herpes simplex virus thymidine kinase gene

The aim of this study was to investigate the selective killing effect of the herpes simplex virus-thymidine kinase/ganciclovir (TK/GCV) suicide gene system controlled by the survivin promoter on hepatocellular carcinoma (HCC) cells in vitro. Recombinant plasmid vectors driven by the survivin promoter were constructed. HepG2 HCC and LO2 normal human liver cells were transfected with the recombinant plasmids, green fluorescent protein (GFP)/pSURV, TK/pSURV and TAT-TK/pSURV. GFP expression was detected by fluoroscopy and flow cytometry (FCM). TK gene expression was detected using RT-PCR and western blot analysis. The selective killing effects after GCV application were evaluated by tetrazolium assay, FCM and western blot analysis. Statistical analysis was performed by ANOVA. After transfection with GFP/pSURV, TK/pSURV and TAT-TK/pSURV for 48 h, GFP expression was observed in the HepG2 cells, but not in the L02 cells and TK gene expression was evidently detected by RT-PCR and western blot analysis in the HepG2 cells. Three stably transfected cell lines (HepG2/pSURV, HepG2/TK/pSURV and HepG2/TAT-TK/pSURV) were successfully established. Compared with the HepG2/TK/pSURV group, a significant ‘bystander effect’ was observed in the HepG2/TAT-TK/pSURV group with the incorporation of unmodifed HepG2 cells at different ratios. Following transfection with TK/pSURV and TAT-TK/pSURV, the growth of HepG2 cells in the presence of GCV was markedly inhibited. This finding was further corroborated by FCM and immunoblot analysis revealed the repressed expression of proliferating cell nuclear antigen (PCNA). Our results showed that the plasmid vectors carrying the TK and TAT-TK fusion protein gene driven by the survivin promoter were successfully constructed and their specific expression in HepG2 cells provided the basis for the targeted gene therapy of HCC.

Bystander or no bystander for gene directed enzyme prodrug therapy

Gene directed enzyme prodrug therapy (GDEPT) of cancer aims to improve the selectivity of chemotherapy by gene transfer, thus enabling target cells to convert nontoxic prodrugs to cytotoxic drugs. A zone of cell kill around gene-modified cells due to transfer of toxic metabolites, known as the bystander effect, leads to tumour regression. Here we discuss the implications of either striving for a strong bystander effect to overcome poor gene transfer, or avoiding the bystander effect to reduce potential systemic effects, with the aid of three successful GDEPT systems. This review concentrates on bystander effects and drug development with regard to these enzyme prodrug combinations, namely herpes simplex virus thymidine kinase (HSV-TK) with ganciclovir (GCV), cytosine deaminase (CD) from bacteria or yeast with 5-fluorocytodine (5-FC), and bacterial nitroreductase (NfsB) with 5-(azaridin-1-yl)-2,4-dinitrobenzamide (CB1954), and their respective derivatives.

Combination effect of oncolytic adenovirus therapy and herpes simplex virus thymidine kinase/ganciclovir in hepatic carcinoma animal models

AIM

Oncolytic adenovirus, also called conditionally replicating adenovirus (CRAD), can selectively propagate in tumor cells and cause cell lysis. The released viral progeny can infect neighboring cancer cells, initiating a cascade that can lead to the ultimate destruction of the tumor. Suicide gene therapy using herpes simplex virus thymidine kinase (HSV-TK) and ganciclovir (GCV) offers a potential treatment strategy for cancer and is undergoing preclinical trials for a variety of tumors. We hypothesized that HSV-TK gene therapy combined with oncolytic adenoviral therapy would have an enhanced effect compared with the individual effects of the therapies and is a potential novel therapeutic strategy to treat liver cancer.

METHODS

To address our hypothesis, a novel CRAD was created, which consisted of a telomerase-dependent oncolytic adenovirus engineered to express E1A and HSV-TK genes (Ad-ETK). The combined effect of Ad-ETK and GCV was assessed both in vitro and in vivo in nude mice bearing HepG2 cell-derived tumors. Expression of the therapeutic genes by the transduced tumor cells was analyzed by RT-PCR and Western blotting.

RESULTS

We confirmed that Ad-ETK had antitumorigenic effects on human hepatocellular carcinoma (HCC) both in vitro and in vivo, and the TK/GCV system enhanced oncolytic adenoviral therapy. We confirmed that both E1A and HSV-TK genes were expressed in vivo.

CONCLUSION

The Ad-ETK construct should provide a relatively safe and selective approach to killing cancer cells and should be investigated as an adjuvant therapy for hepatocellular carcinoma.

Enhanced immune response and protection efficacy of a DNA vaccine constructed by linkage of the Mycobacterium tuberculosis Ag85B-encoding gene with the BVP22-encoding gene

Plasmid DNA vaccines have been widely explored for use in tuberculosis immunization but their immunogenicity needs improvement. In the present study, we incorporated the bovine herpesvirus 1 VP22 (BVP22)-encoding gene, which encodes a protein that demonstrates a capability for disseminating the expressed antigen to neighbouring cells, into a DNA vector in which it was fused to the Ag85B-encoding gene of Mycobacterium tuberculosis (Mtb), and investigated whether this linkage could enhance immune response and protective efficacy in C57BL/6 mice compared to plasmid DNA encoding Ag85B alone. After immunization in mice, Ag85B-specific ELISA antibodies and spleen lymphocyte proliferative responses induced by DNA co-expressing BVP22 and Ag85B were significantly higher than those obtained in mice immunized with Ag85B-encoding DNA alone, except for the number of gamma interferon secreting cells. In addition, based on histopathological examination and bacterial-load determination in lung and spleen, protection against intravenous Mtb H37Rv challenge evoked by the BVP22–Ag85B DNA immunization exceeded the response elicited by Ag85B DNA alone, which was not significantly different from that provided by Bacillus Calmette–Guérin (BCG). These results suggested that DNA vaccine consisting of BVP22 and Ag85B-encoding DNA enhanced immune response and protection against intravenous Mtb H37Rv challenge in mice, indicating that BVP22-encoding DNA might be a promising tool to enhance TB DNA vaccine efficacy.

Enhanced effect of microdystrophin gene transfection by HSV-VP22 mediated intercellular protein transport

Background

Duchenne musclar dystrophy (DMD) is an X-linked recessive disease caused by mutations of dystrophin gene, there is no effective treatment for this disorder at present. Plasmid-mediated gene therapy is a promising therapeutical approach for the treatment of DMD. One of the major issues with plasmid-mediated gene therapy for DMD is poor transfection efficiency and distribution. The herpes simplex virus protein VP22 has the capacity to spread from a primary transduced cell to surrounding cells and improve the outcome of gene transfer. To improve the efficiency of plasmid-mediated gene therapy and investigate the utility of the intercellular trafficking properties of VP22-linked protein for the treatment for DMD, expression vectors for C-terminal versions of VP22-microdystrophin fusion protein was constructed and the VP22-mediated shuttle effect was evaluated both in vitro and in vivo.

Results

Our results clearly demonstrate that the VP22-microdystrophin fusion protein could transport into C2C12 cells from 3T3 cells, moreover, the VP22-microdystrophin fusion protein enhanced greatly the amount of microdystrophin that accumulated following microdystrophin gene transfer in both transfected 3T3 cells and in the muscles of dystrophin-deficient (mdx) mice.

Conclusion

These results highlight the efficiency of the VP22-mediated intercellular protein delivery for potential therapy of DMD and suggested that protein transduction may be a potential and versatile tool to enhance the effects of gene delivery for somatic gene therapy of DMD.

Evidence for intercellular trafficking of VP22 in living cells

The intercellular trafficking property of the herpes simplex virus type 1 tegument protein VP22 makes it a promising tool for overcoming low transduction efficiencies in gene therapy. However, recent reports suggest not only that VP22 cannot facilitate intercellular spreading and that trafficking of VP22 fusion proteins results from artifacts of cell fixation only. To provide direct evidence for the presence or absence of VP22-mediated intercellular trafficking, we generated an adenoviral vector with a dual expression cassette for VP22 fused to green fluorescent protein (VP22 GFP) and DsRed under the control of distinct human cytomegalovirus immediate-early enhancer/promoter regions. Using this vector, we were able to distinguish clearly between primary transduced cells and cells taking up VP22GFP by intercellular trafficking. To our knowledge, for the first time, we could demonstrate by live-cell confocal fluorescence microscopy that VP22GFP can be found intracellularly in unfixed recipient cells. The extent of VP22 spread was similar in paraformaldehyde-fixed cells and unfixed cells as demonstrated by fluorescence-activated cell sorting analysis. We thus confirmed the ability of VP22-mediated intercellular trafficking in live unfixed cells.

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

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

Development of a topical protein therapeutic for human papillomavirus and associated cancers

Human papillomaviruses (HPVs) are the causative agents of several disease states, including genital warts and cervical cancer. There are around 500 million cases of genital warts per annum worldwide and around 450,000 cases of cervical cancer. Although HPV vaccines should eventually reduce the incidence of these diseases, new and effective treatments are still urgently required. The E2 (early) proteins from some HPV types induce growth arrest and apoptosis, and these proteins could be used as therapeutics for HPV-induced disease. A major obstacle to this approach concerns the delivery of the protein to HPV-transformed cells and/or HPV-infected cells in vivo. One possible solution is to use recombinant viruses to deliver E2. Another possible solution is to use purified E2 proteins or E2 fusion proteins. The herpes simplex virus VP22 protein is one of a small number of proteins that have been shown to cross the cell membrane with high efficiency. VP22-E2 fusion proteins produced in bacterial cells are able to enter mammalian cells and induce apoptosis. This suggests that VP22-E2 fusion proteins could be topically applied as a treatment for HPV-induced diseases, most probably post-surgery. In this review, we discuss this and other approaches to the topical delivery of selective therapeutic agents against HPV-associated conditions.

In vitro validation of bioluminescent monitoring of disease progression and therapeutic response in leukaemia model animals

PURPOSE

The application of in vivo bioluminescence imaging to non-invasive, quantitative monitoring of tumour models relies on a positive correlation between the intensity of bioluminescence and the tumour burden. We conducted cell culture studies to investigate the relationship between bioluminescent signal intensity and viable cell numbers in murine leukaemia model cells.

METHODS

Interleukin-3 (IL-3)-dependent murine pro-B cell line Ba/F3 was transduced with firefly luciferase to generate cells expressing luciferase stably under the control of a retroviral long terminal repeat. The luciferase-expressing cells were transduced with p190 BCR-ABL to give factor-independent proliferation. The cells were cultured under various conditions, and bioluminescent signal intensity was compared with viable cell numbers and the cell cycle stage.

RESULTS

The Ba/F3 cells showed autonomous growth as well as stable luciferase expression following transduction with both luciferase and p190 BCR-ABL, and in vivo bioluminescence imaging permitted external detection of these cells implanted into mice. The bioluminescence intensities tended to reflect cell proliferation and responses to imatinib in cell culture studies. However, the luminescence per viable cell was influenced by the IL-3 concentration in factor-dependent cells and by the stage of proliferation and imatinib concentration in factor-independent cells, thereby impairing the proportionality between viable cell number and bioluminescent signal intensity. Luminescence per cell tended to vary in association with the fraction of proliferating cells.

CONCLUSION

Although in vivo bioluminescence imaging would allow non-invasive monitoring of leukaemia model animals, environmental factors and therapeutic interventions may cause some discrepancies between tumour burden and bioluminescence intensity.

Fusion of the HSV-1 tegument protein vp22 to cytosine deaminase confers enhanced bystander effect and increased therapeutic benefit

A major limitation in cancer gene therapy, specifically gene-dependent enzyme prodrug therapy (GDEPT), is inefficient gene delivery and expression. The suicide gene cytosine deaminase (CD) and its substrate, 5-fluorocytosine (5-FC), have been extensively explored due to the inherent 'bystander' effect achieved through diffusion of the toxic metabolite 5-fluorouracil (5-FU). In this study, we aimed to enhance this 'bystander' effect by fusing the Saccharomyces cerevisiae CD to the HSV-1 tegument protein vp22, a novel translocating protein. Two constructs were created: one with vp22 fused to CD (vp22CD) and a second wherein a truncated vp22, lacking the necessary residues for trafficking, fused to CD (delvp22CD). The generated 9L stable lines exhibited similar growth rates, enzyme expression, CD activity, and sensitivity to 5-FC and 5-FU. However, mixed population colony formation assays demonstrated greater bystander effect with the vp22CD fusion as compared to delvp22CD. This enhancement was maintained in vivo where 9L tumors expressing 20 or 50% vp22CD exhibited increased growth delay compared to the respective delvp22CD tumors. Moreover, adenoviral transduction of established wild-type 9L tumors showed increased growth delay with vp22CD (Ad-EF_vp22CD) as compared to equivalent CD (Ad-EF_CD) transduced tumors. Finally, confirming the increased efficacy, (19)F magnetic resonance spectroscopy (MRS) of vp22CD-expressing tumors demonstrated increased 5-FU levels as compared to tumors expressing the nontranslocating CD. These results together demonstrated that fusion of vp22 to CD resulted in CD translocation, which in turn amplified conversion of 5-FC to 5-FU in vivo and enhanced the therapeutic benefit of this GDEPT strategy.

Protein transduction with bacterial cytosine deaminase fused to the TLM intercellular transport motif induces profound chemosensitivity to 5-fluorocytosine in human hepatoma cells

BACKGROUND/AIMS

This study investigates the application of protein based therapeutic suicide enzyme/prodrug approaches providing novel means for both safe and effective local therapeutic regimes in solid tumors.

METHODS

Employing a novel cell permeable peptide, known as the translocation motif (TLM) of hepatitis B virus, E. coli cytosine deaminase (BCDase) suicide fusion proteins were generated.

RESULTS

TLM fusion proteins formed hexamers (as do parental wtBCDase proteins) and retained the specific enzymatic activity of cytosine conversion to uracil also being comparable to parental wtBCDase proteins. However, only BCDase-TLM fusion proteins, but not TLM-BCDase fusion nor parental wtBCDase proteins were found to be taken up to the cytoplasm of target cells as demonstrated both by confocal laser scanning microscopy and cell fractionation. Uptake of BCDase-TLM worked both efficiently and rapidly and was found to be independent from the endosomal pathway. Since BCDase-TLM fusion proteins completely retained their suicide enzymatic activity in the course of translocation across the plasma membrane their usage as profound inducers of chemo-sensitivity to 5-FC strongly is suggested.

CONCLUSIONS

Future therapeutic local application of cell-permeable BCDase-TLM fusion proteins together with a systemic 5-FC prodrug application could result in profound antitumor activities without apparent side effects.

Bovine Herpesvirus VP22 Induces Apoptosis in Neuroblastoma Cells by Upregulating the Expression Ratio of Bax to Bcl-2

Herpesvirus tegument protein VP22 has been shown to have biotherapeutic potential in tumor gene therapy. Some studies indicate that VP22 may enhance the transfer efficiency of therapeutic proteins by delivering them to more cells while trafficking. Our previous study showed that bovine herpesvirus VP22 (BVP22) enhanced equine herpesvirus thymidine kinase-ganciclovir (Etk-GCV) suicide gene therapy by an unknown intracellular effect. In this study, the interaction between BVP22 and host tumor cells was studied in neuroblastoma NXS2 cells. Cell cycle analysis was performed to determine whether BVP22 possesses biotherapeutic potential by altering the cell cycle, making cells more sensitive to therapeutic genes. As a result, the cell cycle was not affected by the transfection of BVP22 into NXS2 cells. However, cytotoxicity induced by BVP22 was observed in NXS2 cells on the second and third days after transient transfection. Further, analyses of caspase-3 activity and apoptosis suggested that BVP22 induces apoptosis in host tumor cells by upregulating the expression ratio of Bax to Bcl-2.

VP22-mediated intercellular transport correlates with enhanced biological activity of MybEngrailed but not (HSV-I) thymidine kinase fusion proteins in primary vascular cells following non-viral transfection

BACKGROUND

The intercellular transport properties of the herpes simplex virus (HSV) protein VP22 have been harnessed to enhance the effectiveness of viral gene transfer. We investigated the intercellular transport and biological effects of VP22 fused with the dominant negative c-Myb chimera, MybEngrailed (MybEn) and HSV-I thymidine kinase (TK), in primary vascular smooth muscle cells (VSMC) following non-viral transfection.

MATERIALS AND METHODS

Porcine VSMC transfected with plasmids encoding MybEn, TK and their respective N- and C-terminal VP22 fusion proteins were assayed for the extent and distribution of transgene expression (by immunohistochemistry), culture growth and apoptosis.

RESULTS

The N-terminal MybEn fusion with VP22 (MybEnVP22) and both TK fusions, but not VP22MybEn, exhibited intercellular spread from primary transfected to up to 200 surrounding cells. pMybEnVP22-transfected cultures exhibited growth inhibition and apoptosis rates that were 10.6 +/- 3.6 and 3.2 +/- 1.0 fold higher than in pMybEn-transfected cultures; pVP22MybEn-transfected cultures showed no difference in these parameters. pTK-transfected cultures underwent 60-70% cell death in the presence of ganciclovir despite <2% primary transfection, which was not increased in cultures transfected with plasmids encoding VP22-TK fusions.

CONCLUSIONS

The close correlation between immunocytochemical and biological assays suggests that intercellular transport is crucial to the enhanced biological activity of the MybEnVP22 fusion. The "intrinsic" bystander activity of TK was 4-fold greater than was "engineered" by VP22 fusion, probably reflecting the abundance of gap junctions between VSMC. VP22 fusion may enhance the efficiency of non-viral gene delivery when combined with the appropriate therapeutic transgene, target tissue and transfection method.