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

"Non-Essential" Proteins of HSV-1 with Essential Roles In Vivo: A Comprehensive Review

Viruses encode for structural proteins that participate in virion formation and include capsid and envelope proteins. In addition, viruses encode for an array of non-structural accessory proteins important for replication, spread, and immune evasion in the host and are often linked to virus pathogenesis. Most virus accessory proteins are non-essential for growth in cell culture because of the simplicity of the infection barriers or because they have roles only during a state of the infection that does not exist in cell cultures (i.e., tissue-specific functions), or finally because host factors in cell culture can complement their absence. For these reasons, the study of most nonessential viral factors is more complex and requires development of suitable cell culture systems and in vivo models. Approximately half of the proteins encoded by the herpes simplex virus 1 (HSV-1) genome have been classified as non-essential. These proteins have essential roles in vivo in counteracting antiviral responses, facilitating the spread of the virus from the sites of initial infection to the peripheral nervous system, where it establishes lifelong reservoirs, virus pathogenesis, and other regulatory roles during infection. Understanding the functions of the non-essential proteins of herpesviruses is important to understand mechanisms of viral pathogenesis but also to harness properties of these viruses for therapeutic purposes. Here, we have provided a comprehensive summary of the functions of HSV-1 non-essential proteins.

The enhanced efficacy of herpes simplex virus by lentivirus mediated VP22 and cytosine deaminase gene therapy against glioma

Despite the comprehensive treatment of surgery following by concurrent radiochemotherapy, the prognosis of malignant glioma remains unsatisfactory with an awful median survival time of only 12-18 months. This might be improved by the development of oncolytic herpes simplex virus. However, the biggest challenge of recombinant herpes simplex virus (rHSV) lies in their limited therapeutic efficiency in clinical trials. This study aims to enhance the efficacy of rHSV against glioma by a HSV-1 tegument protein VP22 modified cytosine deaminase/5-flurocytosine (CD/5-FC) suicide gene system. Stable glioma cell lines carrying CD or VP22-CD fusion gene were successfully obtained by lentiviral infection following Fluorescence-activated cell sorting. The lethal effect of the prodrug 5-FC was significantly increased in the transduced VP22-CD glioma cells compared to the transduced CD glioma cells. Interestingly, VP22 was found to elicit the enhanced efficacy of rHSV-1 against glioma. Furthermore, we detected a synergistic efficacy of rHSV-1 combined with lentivirus mediated VP22 and CD suicide gene therapy in the orthotopic glioma xenograft models. In conclusion, we successfully established the stable cell lines carrying VP22-CD fusion genes. The incorporation of VP22 further induced an enhanced efficacy of rHSV-1 as well as CD suicide gene therapy respectively and synthetically in vitro. Also, we demonstrated an increased therapeutic benefit of rHAV-1 by VP22 modified CD gene therapy against glioma in vivo.

To Infection and Beyond: The Multi-Pronged Anti-Cancer Mechanisms of Oncolytic Viruses

Over the past 1–2 decades we have witnessed a resurgence of efforts to therapeutically exploit the attributes of lytic viruses to infect and kill tumor cells while sparing normal cells. We now appreciate that the utility of viruses for treating cancer extends far beyond lytic cell death. Viruses are also capable of eliciting humoral and cellular innate and adaptive immune responses that may be directed not only at virus-infected cells but also at uninfected cancer cells. Here we review our current understanding of this bystander effect, and divide the mechanisms into lytic, cytokine, innate cellular, and adaptive phases. Knowing the key pathways and molecular players during virus infection in the context of the cancer microenvironment will be critical to devise strategies to maximize the therapeutic effects of oncolytic viroimmunotherapy.

VP22 and cytosine deaminase fusion gene modified tissue-engineered neural stem cells for glioma therapy

PURPOSE

The herpes simplex virus type 1 tegument protein VP22 has the remarkable property of intercellular trafficking, thus making it a promising tool for improving gene transfer efficiency.

METHODS

To investigate whether the fusion of VP22 to the cytosine deaminase (CD) suicide gene could enhance the therapeutic efficiency of neural stem cells (NSCs) in the treatment for C6 glioma, the lentiviral vectors pHIV-VP(22)-EGFP, pHIV-CD, and pHIV-VP(22)-CD were constructed based on the pHIV-EGFP vector. After packaging, vectors were transduced into rat NSCs.

RESULTS

Fluorescence-activated cell sorting analysis revealed that the fusion of VP22-EGFP increased the expression rate of EGFP in NSCs compared with lenti-EGFP transduced cells. Under incubation with the prodrug 5-fluorocytosine (5-FC), the survival rates of C6 cells co-cultured with NSCs/VP(22)-CD (NSCs transduced with lenti-VP(22)-CD) decreased tremendously compared with those of C6 and NSCs/CD. Similar results were also observed in vivo; a significant reduction in tumor volumes in C6 glioma-bearing rats was observed in the NSCs/VP(22)-CD therapy group when compared with other control groups.

CONCLUSIONS

Our results reveal that VP22 increases the transduction efficiency of lentivirus into NSCs and enhances the therapeutic efficacy of CD-engineered rat NSCs in the treatment for C6 glioma, demonstrating that VP22 might be a useful tool for the gene therapy of engineered NSCs and providing a potential novel strategy for enhancing the effectiveness of gene therapy in other diseases.

Cell permeable NFAT inhibitory peptide Sim-2-VIVIT inhibits T-cell activation and alleviates allergic airway inflammation and hyper-responsiveness

Nuclear factor of activated T cells (NFAT) is an important transcription factor for the production of interleukin (IL)-2 upon T-cell receptor (TcR) signaling. Therefore, inhibition of the NFAT-carcineurin pathway is an important target for inflammatory disease inhibition and graft rejection. A novel cell permeable peptide (CPP), Sim-2, has been identified from a human transcription factor, and Sim-2-CPP conjugated to β-galactosidase or EGFP protein was efficiently delivered into cells in vitro and in vivo. A cell permeable form of the NFAT inhibitory peptide VIVIT (Sim-2-VIVIT) was synthesized and showed inhibitory effects on human CD4 or CD8 T-cell activation through NFAT transcriptional activity suppression and IL-2 inhibition. Intranasal administration of the Sim-2-VIVIT peptide in an ovalbumin (OVA)-induced murine asthma model alleviated peribronchial and perivascular infiltration of inflammatory cells in the lung and caused airway remodeling and airway hyper-responsiveness. These results suggest that cell permeable Sim-2-VIVIT peptide has clinical potential as an immunosuppressive agent for inflammatory diseases.

Suicidal gene therapy in the effective control of primary human hepatocellular carcinoma as monitored by noninvasive bioimaging

Hepatocellular carcinoma (HCC) is usually refractory to the available treatments. For cancer gene therapy purposes, real-time imaging of therapeutic gene expression is of great importance because there are multiple factors that modulate the therapeutic gene expression in a complex tumor microenvironment. As a consequence, multiple doses of therapeutic viral vectors may be required for improved efficacy. In the present study, the luciferase reporter gene and the yeast cytosine deaminase (yCD) genes were bicistronically expressed using the foot-and-mouth disease virus 2A peptide under the regulation of the cytomegalovirus (CMV) promoter. The effectiveness of the yCD/5-FC (5-fluorocytosine) killing efficacy mediated by the herpes simplex virus type 1 (HSV-1) amplicon viral vector was shown using HCC and non-HCC cell lines in vitro. In addition, in vivo experiment also showed tumor regression of a primary HCC 26-1004 tumor xenograft in tumor expressing high levels of the yCD gene (as determined by noninvasive imaging) after intratumoral injection of 1.5 × 10(6) TU HGCX-L2C HSV-1 amplicon viral vector and 5-FC administration. The HSV-1 amplicon viral vector coupled with the yCD/5-FC prodrug activated suicide gene could potentially be of use in clinical gene therapy for HCC.

Applications of molecular imaging

Today molecular imaging technologies play a central role in clinical oncology. The use of imaging techniques in early cancer detection, treatment response, and new therapy development is steadily growing and has already significantly impacted on clinical management of cancer. In this chapter, we overview three different molecular imaging technologies used for the understanding of disease biomarkers, drug development, or monitoring therapeutic outcome. They are (1) optical imaging (bioluminescence and fluorescence imaging), (2) magnetic resonance imaging (MRI), and (3) nuclear imaging (e.g., single-photon emission computed tomography (SPECT) and positron emission tomography (PET)). We review the use of molecular reporters of biological processes (e.g., apoptosis and protein kinase activity) for high-throughput drug screening and new cancer therapies, diffusion MRI as a biomarker for early treatment response and PET and SPECT radioligands in oncology.

Evaluation of treatment-associated inflammatory response on diffusion-weighted magnetic resonance imaging and 2-[18F]-fluoro-2-deoxy-D-glucose-positron emission tomography imaging biomarkers

PURPOSE

Functional imaging biomarkers of cancer treatment response offer the potential for early determination of outcome through the assessment of biochemical, physiologic, and microenvironmental readouts. Cell death may result in an immunologic response, thus complicating the interpretation of biomarker readouts. This study evaluated the temporal effect of treatment-associated inflammatory activity on diffusion magnetic resonance imaging and 2-[(18)F]-fluoro-2-deoxy-D-glucose-positron emission tomography imaging (FDG-PET) biomarkers to delineate the effects of the inflammatory response on imaging readouts.

EXPERIMENTAL DESIGN

Rats with intracerebral 9L gliosarcomas were separated into four groups consisting of control, an immunosuppressive agent dexamethasone (Dex), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), and BCNU+Dex. Animals were imaged using diffusion-weighted magnetic resonance imaging and FDG-PET at 0, 3, and 7 days posttreatment.

RESULTS

In the BCNU- and BCNU+Dex-treated animal groups, diffusion values increased progressively over the 7-day study period to approximately 23% over baseline. The FDG percentage change of standard uptake value decreased at day 3 (-30.9%) but increased over baseline levels at day 7 (+20.1%). FDG-PET of BCNU+Dex-treated animals were found to have percentage of standard uptake value reductions of -31.4% and -24.7% at days 3 and 7, respectively, following treatment. Activated macrophages were observed on day 7 in the BCNU treatment group with much fewer found in the BCNU+Dex group.

CONCLUSIONS

Results revealed that treatment-associated inflammatory response following tumor therapy resulted in the accentuation of tumor diffusion response along with a corresponding increase in tumor FDG uptake due to the presence of glucose-consuming activated macrophages. The dynamics and magnitude of potential inflammatory response should be considered when interpreting imaging biomarker results.

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.

Synergy between anti-CCL2 and docetaxel as determined by DW-MRI in a metastatic bone cancer model

Metastatic prostate cancer continues to be the second leading cause of cancer death in American men with an estimated 28,660 deaths in 2008. Recently, monocyte chemoattractant protein-1 (MCP-1, CCL2) has been identified as an important factor in the regulation of prostate metastasis. CCL2, shown to attract macrophages to the tumor site, has a direct promotional effect on tumor cell proliferation, migration, and survival. Previous studies have shown that anti-CCL2 antibodies given in combination with docetaxel were able to induce tumor regression in a pre-clinical prostate cancer model. A limitation for evaluating new treatments for metastatic prostate cancer to bone is the inability of imaging to objectively assess response to treatment. Diffusion-weighted MRI (DW-MRI) assesses response to anticancer therapies by quantifying the random (i.e., Brownian) motion of water molecules within the tumor mass, thus identifying cells undergoing apoptosis. We sought to measure the treatment response of prostate cancer in an osseous site to docetaxel, an anti-CCL2 agent, and combination treatments using DW-MRI. Measurements of tumor apparent diffusion coefficient (ADC) values were accomplished over time during a 14-day treatment period and compared to response as measured by bioluminescence imaging and survival studies. The diffusion data provided early predictive evidence of the most effective therapy, with survival data results correlating with the DW-MRI findings. DW-MRI is under active investigation in the pre-clinical and clinical settings to provide a sensitive and quantifiable means for early assessment of cancer treatment outcome.

Construction of a survivin promoter-mediated adeno-associated virus expression vector carrying a fusion gene constituted with cytosine deaminase and survivin mutant

AIM: To construct a recombinant survivin promoter (SurP)-mediated adeno-associated virus expression vector carrying a fusion gene constituted with cytosine deaminase (CD) gene and glycin-linked survivin mutant (glySurMut), and to examine the expression of CDglySurMut fusion protein in cancer cells transfected with this vector.

METHODS: The CD gene and glySurMut fragments were amplified by polymerase chain reaction (PCR), and cloned into the adeno-associated virus expression vector PAM with survivin promoter (PAM/SurP). The recombinant vector was transformed into E.coli DH5α. and the positive clones were selected. The plasmid DNA was identified using restriction enzyme analysis and sequencing. The recombinant vector pAM/SurP-CDglySurMut was transfected into gastric cancer cells MKN45. The expression of fusion protein in cancer cells was detected using Western blot.

RESULTS: The CD gene and glySurMut were cloned from E.coli and gastric cancer cells, respectively. The restrictive enzyme analysis and sequencing showed that the fusion gene of CD and glySurMut was successfully inserted into the PAM/SurP vector. Western blot showed that the recombinant vector expressed the CDglySurMut fusion protein in gastric cancer cells.

CONCLUSION: Our results show the pAM/SurP-CDglySurMut vector can efficiently express the recombinant CDglySurMut fusion protein in gastric cancer cells, thus provides experiment evidence for targeting cancer gene therapy using this pAM/SurP-CDglySurMut vector.

Transduction of the cytoplasmic domain of CTLA-4 inhibits TcR-specific activation signals and prevents collagen-induced arthritis

CTLA-4 (CD152) negatively regulates T cell activation signaling, and the cytoplasmic domain of CTLA-4 (ctCTLA-4) itself has the capacity to inhibit T cell activation in vitro and in vivo. In this study, the inhibitory mechanisms of the cell-permeable recombinant protein Hph-1-ctCTLA-4 on T cell activation and its ability to prevent collagen-induced arthritis were analyzed. Hph-1-ctCTLA-4 prevented human and mouse T cell activation and proliferation by inhibition of T cell receptor-proximal signaling and the arrest of the cell cycle. Furthermore, Hph-1-ctCTLA-4 protected human umbilical vein endothelial cells (HUVEC) from the human CTL allo-response. The incidence and severity of collagen-induced arthritis were significantly reduced and the erosion of cartilage and bone was effectively prevented by i.v. injection and transdermal administration of Hph-1-ctCTLA-4. Inflammatory cytokine production (IL-1beta, IL-6, TNF-alpha, IL-17A) and collagen-specific antibody levels were significantly reduced, and the numbers of activated T cells and infiltrating granulocytes were substantially decreased. These results demonstrate that systemic or transdermal application of a cell-permeable form of the cytoplasmic domain of CTLA-4 offers an effective therapeutic approach for autoimmune diseases such as rheumatoid arthritis.

Functional diffusion map as an early imaging biomarker for high-grade glioma: correlation with conventional radiologic response and overall survival

PURPOSE

Assessment of radiologic response (RR) for brain tumors utilizes the Macdonald criteria 8 to 10 weeks from the start of treatment. Diffusion magnetic resonance imaging (MRI) using a functional diffusion map (fDM) may provide an earlier measure to predict patient survival.

PATIENTS AND METHODS

Sixty patients with high-grade glioma were enrolled onto a study of intratreatment MRI at 1, 3, and 10 weeks. Receiver operating characteristic curve analysis was used to evaluate imaging parameters as a function of patient survival at 1 year. Both log-rank and Cox proportional hazards models were utilized to assess overall survival.

RESULTS

Greater increases in diffusion in response to therapy over time were observed in those patients alive at 1 year compared with those who died as a result of disease. The volume of tumor with increased diffusion by fDM at 3 weeks was the strongest predictor of patient survival at 1 year, with larger fDM predicting longer median survival (52.6 v 10.9 months; log-rank, P < .003; hazard ratio [HR] = 2.7; 95% CI, 1.5 to 5.9). Radiologic response at 10 weeks had similar prognostic value (median survival, 31.6 v 10.9 months; log-rank P < .0007; HR = 2.9; 95% CI, 1.7 to 7.2). Radiologic response and fDM differed in 25% of cases. A composite index of response including fDM and RR provided a robust predictor of patient survival and may identify patients in whom RR does not correlate with clinical outcome.

CONCLUSION

Compared with conventional neuroimaging, fDM provided an earlier assessment of equal predictive value, and the combination of fDM and RR provided a more accurate prediction of patient survival than either metric alone.

Stem and progenitor cell-mediated tumor selective gene therapy

The poor prognosis for patients with aggressive or metastatic tumors and the toxic side effects of currently available treatments necessitate the development of more effective tumor-selective therapies. Stem/progenitor cells display inherent tumor-tropic properties that can be exploited for targeted delivery of anticancer genes to invasive and metastatic tumors. Therapeutic genes that have been inserted into stem cells and delivered to tumors with high selectivity include prodrug-activating enzymes (cytosine deaminase, carboxylesterase, thymidine kinase), interleukins (IL-2, IL-4, IL-12, IL-23), interferon-beta, apoptosis-promoting genes (tumor necrosis factor-related apoptosis-inducing ligand) and metalloproteinases (PEX). We and others have demonstrated that neural and mesenchymal stem cells can deliver therapeutic genes to elicit a significant antitumor response in animal models of intracranial glioma, medulloblastoma, melanoma brain metastasis, disseminated neuroblastoma and breast cancer lung metastasis. Most studies reported reduction in tumor volume (up to 90%) and increased survival of tumor-bearing animals. Complete cures have also been achieved (90% disease-free survival for >1 year of mice bearing disseminated neuroblastoma tumors). As we learn more about the biology of stem cells and the molecular mechanisms that mediate their tumor-tropism and we identify efficacious gene products for specific tumor types, the clinical utility of cell-based delivery strategies becomes increasingly evident.

A feasibility study evaluating the functional diffusion map as a predictive imaging biomarker for detection of treatment response in a patient with metastatic prostate cancer to the bone

Prostate cancer (PCa) is the most commonly diagnosed cancer in American men with a subset inevitably presenting with metastatic disease to the bone. A well-recognized limitation in evaluating new treatments for metastatic PCa is the inability to use imaging to objectively assess response therapy. In this study, we evaluated the feasibility of clinically translating the functional diffusion map (fDM) imaging biomarker for quantifying the spatiotemporal effects of bone tumor response in a patient treated for metastatic PCa with bone metastases. A patient beginning therapy was scanned using MRI before treatment and again at 2 and 8 weeks post-treatment initiation to quantify changes in tumor diffusion values. Three metastatic lesions were identified for fDM analysis, all of which all demonstrated an early increase in diffusion values at 2 weeks, which increased further at 8 weeks post-treatment initiation. This finding correlated with a decrease in the patient's prostate-specific antigen (PSA) levels suggestive of patient response. CT, bone scans, and anatomic MRI images obtained posttreatment were found to be uninformative for the assessment of treatment effectiveness. This study presents the feasibility of fDM-measurements in osseous lesions over time and shows that changes in fDM values were consistent with therapeutic response. Thus, the fDM imaging biomarker may provide a quantifiable therapeutic endpoint to assess response in patients with metastatic bone cancer.

Magnetic resonance imaging determination of tumor grade and early response to temozolomide in a genetically engineered mouse model of glioma

PURPOSE

The median survival for patients diagnosed with glioblastoma multiforme, the most common type of brain tumor, is less than 1 year. Animal glioma models that are more predictive of therapeutic response in human patients than traditional models and that are genetically and histologically accurate are an unmet need. The nestin tv-a (Ntv-a) genetically engineered mouse spontaneously develops glioma when infected with ALV-A expressing platelet-derived growth factor, resulting in autocrine platelet-derived growth factor signaling.

EXPERIMENTAL DESIGN

In the Ntv-a genetically engineered mouse model, T2-weighted and T1-weighted, contrast-enhanced magnetic resonance images were correlated with histology, glioma grade (high or low), and survival. Magnetic resonance imaging (MRI) was therefore used to enroll mice with high-grade gliomas into a second study that tested efficacy of the current standard of care for glioma, temozolomide (100 mg/kg qdx5 i.p., n=13).

RESULTS

The Ntv-a model generated a heterogeneous group of gliomas, some with high-grade growth rate and histologic characteristics and others with characteristics of lower-grade gliomas. We showed that MRI could be used to predict tumor grade and survival. Temozolomide treatment of high-grade tv-a gliomas provided a 14-day growth delay compared with vehicle controls. Diffusion MRI measurement of the apparent diffusion coefficient showed an early decrease in cellularity with temozolomide, similar to that observed in humans.

CONCLUSIONS

The use of MRI in the Ntv-a model allows determination of glioma grade and survival prediction, distribution of mice with specific tumor types into preclinical trials, and efficacy determination both by tumor growth and early apparent diffusion coefficient response.

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.

Herpes Simplex Virus VP22 Enhances Adenovirus-Mediated Microdystrophin Gene Transfer to Skeletal Muscles in Dystrophin-Deficient (mdx) Mice

One of the obstacles to efficient vector-mediated gene therapy for Duchenne's muscular dystrophy (DMD) is its limited transduction efficiency. The VP22 tegument protein of herpes simplex virus type 1 (HSV-1) is able to cross biological membranes and translocate the VP22 fusion protein from transfected primary cells to surrounding cells and improve the outcome of gene transfer. To improve the efficiency of vector-mediated gene therapy and to investigate the utility of the intercellular trafficking properties of VP22-linked protein for the treatment for DMD, the recombinant adenoviruses Ad-VP22, Ad-MICDYS, and Ad-VP22-MICDYS were constructed and the VP22-mediated shuttle effect was evaluated both in vitro and in vivo. About 92 +/- 3.6% of cells were microdystrophin positive 48 hr postinfection with Ad-VP22-MICDYS. The number of centralized nuclei in Ad-VP22-MICDYS-transduced tibialis anterior (TA) muscle was significantly reduced, from 78 +/- 5.2 to 20 +/- 2.5%, by 2 weeks postinjection. By 2 months postinjection, the average number of microdystrophin-positive fibers in TA muscle injected with Ad-VP22-MICDYS was 2.2 times more than that of TA muscle injected with Ad-MICDYS. Ad-VP22-MICDYS led to significant recovery of force-producing capabilities in TA muscle. These results demonstrate that VP22 greatly augmented adenovirus-mediated microdystrophin delivery to C2C12 cells and to the skeletal muscles of dystrophin-deficient (mdx) mice. These results highlight the efficiency of VP22-mediated intercellular protein delivery for the potential therapy of DMD and suggest that VP22 may be a promising tool with which to enhance the efficacy of adenoviral gene transfer for somatic gene therapy of DMD.

Effect of cell-based intercellular delivery of transcription factor GATA4 on ischemic cardiomyopathy

Recent loss-of-function studies highlight the importance of the transcription factor GATA4 in the myocardial response to injury in the adult heart. However, the potential effects of gain-in-function of GATA4 overexpression, and transcription factors in general, is hindered by the fact that transcription factors are neither secreted nor taken up by cells. Chimeric proteins incorporating motifs of cell-penetrating proteins are secreted from cells and internalized by surrounding cells. We engineered a chimeric protein consisting of GATA4 and the cell-penetrating protein VP22. Cardiac fibroblasts stably transfected with the GATA4:VP22, GFP:VP22, or green fluorescent protein (GFP) constructs were transplanted into Lewis rats 1 month after left anterior descending ligation. GATA4:VP22 expression in the border zone was associated with increased cardiac myosin expression and cardiac myocyte size (30 mum versus 19 mum, P<0.01). Compared with the GFP:VP22 control group, 6 weeks after cardiac fibroblast transplantation (10 weeks after myocardial infarction), animals that received GATA4:VP22-expressing cardiac fibroblasts demonstrated increased cardiac function and less negative remodeling. These data demonstrate a novel strategy for transcription factor delivery to injured myocardium and indicate that the delivery of GATA4 locally to the infarct border zone induces multiple local effects in the border zone cardiac myocytes resulting in beneficial ventricular remodeling and improved global left ventricular function.

Suicide genes for cancer therapy

The principle of using suicide genes for gene directed enzyme prodrug therapy (GDEPT) of cancer has gained increasing significance during the 20 years since its inception. The astute application of suitable GDEPT systems should permit tumour ablation in the absence of off-target toxicity commonly associated with classical chemotherapy, a hypothesis which is supported by encouraging results in a multitude of pre-clinical animal models. This review provides a clear explanation of the rationale behind the GDEPT principle, outlining the advantages and limitations of different GDEPT strategies with respect to the roles of the bystander effect, the immune system and the selectivity of the activated prodrug in contributing to their therapeutic efficacy. An in-depth analysis of the most widely used suicide gene/prodrug combinations is presented, including details of the latest advances in enzyme and prodrug optimisation and results from the most recent clinical trials.

Hypoxia-Induced Cytosine Deaminase Gene Expression for Cancer Therapy

Hypoxia, a hallmark of many solid tumors, is associated with angiogenesis and tumor progression. It activates a signal cascade that culminates in the stabilization of hypoxia-inducible factor-1 (HIF-1) transcription factor and activation of genes that possess hypoxia response elements. The loss of tumor suppressors such as p53 has been shown to stabilize HIF-1alpha, which is overexpressed in the majority of human cancers, and its over-expression correlates with poor prognosis and treatment failure. Here we constructed hypoxia-inducible promoters and examined their activities in murine and human cancer cells with variable p53 status. Loss of p53 function in cancer cells resulted in increased HIF-1-dependent transcriptional activity. To investigate the feasibility of exploiting the hypoxic tumor microenvironment for targeted gene therapy of cancer, we constructed retroviral vectors harboring luciferase or Escherichia coli cytosine deaminase (CD) genes under the control of the hypoxia-inducible promoter. Murine Lewis lung carcinoma (LL2) cells carrying defective p53, when retrovirally transduced with the hypoxia-inducible promoter-driven luciferase gene under hypoxic conditions, increased luciferase reporter gene expression in vitro and in vivo. Significant antitumor effects were achieved in mice bearing LL2 tumors that expressed CD driven by a hypoxia-inducible promoter after treatment with 5-fluorocytosine. These results suggest the potential applications of suicide genes, such as the CD gene, under the control of hypoxia-inducible promoters for cancer gene therapy, which may target efficiently to hypoxic regions of tumors with p53 mutations.

Osteoclasts direct bystander killing of bone cancer

Primary and metastatic bone cancers are difficult to eradicate and novel approaches are needed to improve treatment and extend life. As bone cancer grows, osteoclasts, the principal bone-resorbing cells of the body, are recruited to and activated at sites of cancer. In this investigation, we determined if osteoclast lineage cells could function as a cell-based gene delivery system to bone cancers. We used the cytosine deaminase (CD) 5-fluorocytosine (5-FC) enzyme/prodrug system and studied bone marrow and bones from transgenic mice expressing a novel CD gene regulated by the osteoclast tartrate-resistant acid phosphatase (TRAP) gene promoter (Tg/NCD). DsRed2-labeled 2472 sarcoma cells were placed in Tg/NCD osteoclastogenic cultures and treated with 5-FC. 5-FC treatment resulted in profound bystander killing (90%; P < 0.05). The effect of 5-FC treatment on osteoclast lineage cells was most dramatic when administered at the beginning of the 7-day cultures, suggesting that mature osteoclasts are less sensitive to 5-FC. Evaluation of osteoclast-directed bystander killing in vivo revealed dramatic killing of bone cancer with only a modest effect on osteoclast number. Specifically, 5-FC treatment of tumor-bearing Tg/NCD mice or Tg/NCD bone marrow transplanted C3H mice (Tg/NCD-C3H) resulted in 92% and 44% reductions in tumor area, respectively (P < 0.05). Eight of ten 5-FC-treated Tg/NCD mice had complete bone tumor killing and five of six 5-FC-treated Tg/NCD-C3H mice had reduced tumor compared with controls. In addition, Tg/NCD osteoclasts were resistant to 5-FC treatment in vivo, a very important feature, as it identifies osteoclasts as an ideal CD gene delivery system.

The functional diffusion map: an imaging biomarker for the early prediction of cancer treatment outcome

Functional diffusion map (fDM) has been recently reported as an early and quantitative biomarker of clinical brain tumor treatment outcome. This approach spatially maps and quantifies treatment-induced changes in tumor water diffusion values resulting from alterations in cell density/cell membrane function and microenvironment. This current study was designed to evaluate the capability of fDM for preclinical evaluation of dose escalation studies and to determine if these changes were correlated with outcome measures (cell kill and overall survival). Serial T2-weighted were carried out on rodents with orthotopically implanted 9L brain tumors receiving three doses of 1,3-bis(2-chloroethyl)-1-nitrosourea (6.65, 13.3, and 26.6 mg/kg, i.p.). All images were coregistered to baseline T2-weighted images for fDM analysis. Analysis of tumor fDM data on day 4 posttreatment detected dose-dependent changes in tumor diffusion values, which were also found to be spatially dependent. Histologic analysis of treated tumors confirmed spatial changes in cellularity as observed by fDM. Early changes in tumor diffusion values were found to be highly correlative with drug dose and independent biologic outcome measures (cell kill and survival). Therefore, The fDM imaging biomarker for early prediction of treatment efficacy can be used in the drug development process.