Evaluation of the bystander effect in experimental brain tumors bearing herpes simplex virus-thymidine kinase gene by serial magnetic resonance imaging

Sitimagene ceradenovec: a gene-based drug for the treatment of operable high-grade glioma

The field of gene therapy for malignant glioma has made important advances since the first gene transfer studies were performed 20 years ago. Multiple Phase I/II trials and two Phase III trials have been performed and have demonstrated the feasibility and safety of intratumoral vector delivery in the brain. Sitimagene ceradenovec is an adenoviral vector encoding the herpes simplex thymidine kinase gene, developed by Ark Therapeutics Group plc (UK and Finland) for the treatment of patients with operable high-grade glioma. In preclinical and Phase I/II clinical studies, sitimagene ceradenovec exhibited a significant increase in survival. Although the preliminary results of a Phase III clinical study demonstrated a significant positive effect of sitimagene ceradenovec treatment on time to reintervention or death when compared with standard care treatment (hazard ratio: 1.43; 95% CI: 1.06-1.93; p < 0.05), the European Committee for Medicinal Products for Human Use did not consider the data to provide sufficient evidence of clinical benefit. Further clinical evaluation, powered to demonstrate a benefit on a robust end point, is required. This article focuses on sitimagene ceradenovec and provides an overview of the developments in the field of gene therapy for malignant glioma.

Tissue specific cytotoxicity of colon cancer cells mediated by nanoparticle-delivered suicide gene in vitro and in vivo

PURPOSE

This study aimed to develop an efficient and safe strategy to introduce suicide genes into colon cancer cells.

EXPERIMENTAL DESIGN

In this study, we fused an enhanced carcinoembryonic antigen promoter (CEA) to a suicide gene, cytosine deaminase (CD). This construct was delivered into colon cancer cells using calcium phosphate nanoparticles (CPNP). The cells were then treated with the prodrug 5-FC. The therapeutic effect was evaluated in vitro and in vivo.

RESULTS

Our study showed that the CEA promoter-driven, CPNP-delivered suicide gene was only expressed in CEA-positive colon cancer cells, and resulted in significant cytotoxicity after administration of the prodrug 5-FC in vitro. Moreover, our in vivo study showed that CPNP-mediated CEA-CD delivery, together with 5-FC treatment, resulted in significant tumor growth delay in xenograft human colon carcinoma.

CONCLUSIONS

Our study indicates that the combination of CPNP and CEA-CD gene expression represents a novel approach for CEA-positive tumor gene therapy.

Exogenous wt-p53 enhances the antitumor effect of HSV-TK/GCV on C6 glioma cells

OBJECTIVE

To study on the antitumor effect of combining wt-p53 gene with suicide gene therapy (HSV-tk+GCV) for malignant gliomas.

METHODS

AdCMV-p53 was transfected into C6 glioma cells at MOI of (Multiplicity of infection) 0(G100), 10(TPG1), 100(TPG2), then AdCMV-tk was transducted to C6 glioma cells of G100, TPG1 and TPG2, respectively, at MOI of 100. The C6 glioma cells tranfected with both AdCMV-p53 and AdCMV-tk were exposed to various concentration of GCV. The cell survival rate was measured by MTT assay in vitro. Rat glioma model was established by injecting 5 x 10(5) C6 glioma cells into right caudate nucleus of SD rats. AdCMV-p53 and AdCMV-tk were injected into glioma on day 5 and 6, respectively. On day 7, ganciclovir (GCV) was administrated intraperitoneally at 15 mg/kg/day for 14 days. The survival time of all rats was observed. The growth of intracerebral tumors was monitored dynamically by enhanced MRI. Cell apoptosis was evaluated by TUNEL method. Expression of HSV-tk gene was identified by in situ hybridization and expression of exogenous p53 gene was detected with Western blotting.

RESULTS

In vitro, wt-p53 significantly enhanced antitumor effect of HSV-tk/GCV. The concentration of GCV for ID50 of TPG2 cells (0.001 microg/ml GCV) was 10 times lower than that for the cells of tk-GCV group (MOI = 100), while the concentration of GCV for ID100 of TPG2 (0.01 microg/ml GCV) and TPG1(0.1 microg/ml GCV) was 100 and 10 times lower than that for the cells of tk-GCV group (MOI = 100), respectively. Apoptosis of C6 glioma cells also could be induced by transfection with wt-p53 gene slightly. For in vivo study, the survival time of tumor-bearing rats treated with HSV-TK/GCV or wt-p53 combined with HSV-TK/GCV was significantly prolonged and the intracerebral tumors were regressed and disappeared earlier in the combined gene therapy group than those in the HSV-TK/GCV therapy group as shown in enhanced MRI. However, only half dose of GCV for the rats treated with both wt-p53 and HSV-TK/GCV was needed to obtain the same efficacy as those rats treated with HSV-TK/GCV alone. These results indicate that the transfection of wt-p53 potentiates the effect of HSV-TK/GCV therapy.

CONCLUSIONS

The combination of HSV-tk/GCV system with wt-p53 gene transduction is optimal for clinical therapeutic trials of suicide gene therapy for malignant gliomas.

Bystander effect-mediated gene therapy of gliomas using genetically engineered neural stem cells

Since neural stem cells (NSCs) have the ability to migrate toward a tumor mass, genetically engineered NSCs were used for the treatment of gliomas. We first evaluated the "bystander effect" between NSCs transduced with the herpes simplex virus-thymidine kinase (HSVtk) gene (NSCtk) and C6 rat glioma cells under both in vitro and in vivo conditions. A potent bystander effect was observed in co-culture experiments of NSCtk and C6 cells. In the intracranial co-implantation experiments in athymic nude mice and Sprague-Dawley rats, the animals co-implanted with NSCtk and C6 cells and treated with ganciclovir (GCV) showed no intracranial tumors and survived more than 100 days, while those treated with physiological saline (PS) died of tumor progression. We next injected NSCtk cells into the pre-existing C6 tumor in rats and treated them with GCV or PS. The tumor volume was serially measured by magnetic resonance imaging. The tumor disappeared in six out of nine rats in the NSCtk/GCV group, while all the rats treated with PS died of tumor progression by day 21. The results indicate the feasibility of a novel gene therapy strategy for gliomas through a bystander effect generated by intratumoral injection of NSCtk cells and systemic GCV administration.

Recombinant Sendai virus vector induces complete remission of established brain tumors through efficient interleukin-2 gene transfer in vaccinated rats

PURPOSE

Sendai virus (SeV), a murine parainfluenza virus type I, replicates independent of cellular genome and directs high-level gene expressions when used as a viral vector. We constructed a nontransmissible recombinant SeV vector by deleting the matrix (M) and fusion (F) genes from its genome (SeV/DeltaMDeltaF) to enhance its safety. We also estimated the therapeutic efficacy of the novel vector system against a rat glioblastoma model.

EXPERIMENTAL DESIGN

We administered the recombinant SeV vector carrying the lacZ gene or the human interleukin-2 (hIL-2) gene into established 9L brain tumors in vivo simultaneous with peripheral vaccination using irradiated 9L cells. Sequential monitoring with magnetic resonance imaging was used to evaluate the therapeutic efficacy.

RESULTS

We found extensive transduction of the lacZ gene into the brain tumors and confirmed sufficient amounts of interleukin 2 (IL-2) production by hIL2-SeV/DeltaMDeltaF both in vitro and in vivo. The magnetic resonance imaging study showed that the intracerebral injection of hIL2-SeV/DeltaMDeltaF brought about significant reduction of the tumor growth, including complete elimination of the established brain tumors. The (51)Cr release assay showed that significant amounts of 9L-specific cytotoxic T cells were induced by the peripheral vaccination. Immunohistochemical analysis revealed that CD4(+) T cells and CD8(+) T cells were abundantly infiltrated in the target tumors.

CONCLUSION

The present results show that the recombinant nontransmissible SeV vector provides efficient in vivo gene transfer that induces significant regression of the established brain tumors and suggest that it will be a safe and useful viral vector for the clinical practice of glioma gene therapy.

Antitumor effect of genetically engineered mesenchymal stem cells in a rat glioma model

The prognosis of patients with malignant glioma is extremely poor, despite the extensive surgical treatment that they receive and recent improvements in adjuvant radio- and chemotherapy. In the present study, we propose the use of gene-modified mesenchymal stem cells (MSCs) as a new tool for gene therapy of malignant brain neoplasms. Primary MSCs isolated from Fischer 344 rats possessed excellent migratory ability and exerted inhibitory effects on the proliferation of 9L glioma cell in vitro. We also confirmed the migratory capacity of MSCs in vivo and showed that when they were inoculated into the contralateral hemisphere, they migrated towards 9L glioma cells through the corpus callosum. MSCs implanted directly into the tumor localized mainly at the border between the 9L tumor cells and normal brain parenchyma, and also infiltrated into the tumor bed. Intratumoral injection of MSCs caused significant inhibition of 9L tumor growth and increased the survival of 9L glioma-bearing rats. Gene-modification of MSCs by infection with an adenoviral vector encoding human interleukin-2 (IL-2) clearly augmented the antitumor effect and further prolonged the survival of tumor-bearing rats. Thus, gene therapy employing MSCs as a targeting vehicle would be promising as a new therapeutic approach for refractory brain tumor.

Local inflammation and devascularization--in vivo mechanisms of the "bystander effect" in VPC-mediated HSV-Tk/GCV gene therapy for human malignant glioma

Somatic gene therapy with the herpes simplex virus type I thymidine kinase gene/ganciclovir (HSV-Tk/GCV) system and murine retroviral vector producer cells (VPCs) was introduced as a new adjuvant treatment modality to treat tumor bulk and to prevent tumor recurrence in patients harboring malignant glioma. The single-center experience after treatment of 27 patients undergoing tumor resection followed by intracerebral VPC injection for HSV-Tk suicide gene therapy will be presented focused on findings of systematic and close MRI follow-up and a few histological specimens. The data indicate that hemorrhagic necrosis due to endothelial cell transfection mediated vessel necrosis and that local inflammatory immune response occurs frequently after gene therapy. These phenomena seem to be specific because none of the patients of a control group showed any similar features. The prognosis (time to progression, survival) of the patients with "bystander effects" after gene therapy was better, but compared to those patients without bystander effects, they were also privileged by a favorable constellation of prognostic factors. Therefore, the appearance of these neuroradiologic features cannot serve as an indicator for treatment effectiveness and outcome.

Imaging Techniques for Gene Therapy: SPECT, PET, and MRI

Gene therapy by the transfer and expression of suicide genes is performed using genes coding for nonmammalian enzymes that transform nontoxic prodrugs into toxic metabolites. Employing radiolabeled specific substrates and scintigraphic procedures to determine the functional activity of the recombinant enzyme in vivo, a therapeutic window of maximal gene expression and consecutive drug administration may be defined. If the gene therapy approach is based on the transduction of receptor genes, the recombinant gene expression in tumor cells can be monitored with radiolabeled ligands. Transfer of transporter genes as the sodium iodide transporter may also lead to the visualization of transduction via accumulation of iodide or pertechnetate. Furthermore, imaging based on transchelation of oxotechnetate to a polypeptide motif from a biocompatible complex with a higher dissociation constant than that of a diglycilcysteine complex or tyrosinase gene transfer for metal ion scavenging have been described. In addition, therapy effects may be assessed by the evaluation of the morphological changes of the tumor using magnetic resonance imaging or, more effectively, by the measurement of changes in metabolism with positron emission tomography employing tracers of tumor metabolism and proliferation. Finally, enzyme or receptor genes may serve as noninvasive reporter genes, if applied in the context of bicistronic vectors leading to coexpression of the therapeutic gene and the noninvasive reporter gene.

Efficacy of the bystander effect in the herpes simplex virus thymidine kinase-mediated gene therapy is influenced by the expression of connexin43 in the target cells

Tumoricidal "bystander effect" observed in the herpes simplex virus thymidine kinase (HSVtk)/ganciclovir (GCV) gene therapy was studied between different rat glioma cell lines (9L and C6 cells) under both in vitro and in vivo conditions. For that purpose, mixed populations of wild-type cells (9Lwt and C6wt) and respective HSVtk gene-transduced cells (9Ltk and C6tk) were examined for their sensitivity to GCV. A potent in vitro bystander effect was observed in 9Lwt/9Ltk and 9Lwt/C6tk combinations but not in C6wt/9Ltk and C6wt/C6tk combinations. In vivo bystander effect studied in a subcutaneous tumor model in athymic nude mice was also potent in 9Lwt/9Ltk and 9Lwt/C6tk combinations. Because the expression of connexin43, a major protein in the connexin family gene products, in 9L cells is much higher than that in C6 cells, the results suggest that the amount of connexin in target (wild-type) cells but not in effector (HSVtk gene-bearing) cells is important for the generation of the bystander effect. This hypothesis was further confirmed by the observation that in vitro bystander effect in C6wt/C6tk combination was potentiated by transduction of the connexin43 gene to the target cells.

Genetic prodrug activation therapy (GPAT) in two rat prostate models generates an immune bystander effect and can be monitored by magnetic resonance techniques

Treatment of hormone refractory prostate cancer requires new treatment strategies. Genetic prodrug activation therapy (GPAT) may provide a new therapeutic avenue. In this study the antitumour efficacy of the gene encoding herpes simplex virus thymidine kinase (HSVtk) activating the prodrug ganciclovir (GCV) was compared in two models of ectopic (subcutaneous) rat prostate cancer. Both models, which differ in their characteristics, were previously shown to be weakly immunogenic but susceptible to immunotherapy. Tumour cell lines were stably transfected with HSVtk and were rendered highly sensitive to GCV. Little or no bystander killing effect was observed by tk-transfected cells on wild-type cells in vitro. However, a significant in vivo bystander effect was observed suggesting an immune-mediated response. Indeed, such an immune response was capable of slowing the growth of distant wild-type tumours and increased overall animal survival. A T helper 1 immune response was generated as a result of GCV activation and cell kill, demonstrated by the secretion of IFNgamma by cultured splenocytes in response to tumour cells. BrDU staining of tk-transfected cells treated with GCV in vitro suggested apoptotic cell death, but Annexin V staining was less marked for one of the cell lines. Serial in vivo monitoring by non-invasive magnetic resonance spectroscopy (MRS) of the tk-transfected MATLyLu tumours demonstrated a decreased ATP/Pi ratio (a measure of cell energy status) during growth and an increase in the ATP/Pi ratio during regression initiated by treatment with GCV. Further, significant differences were found in the phosphomonester (PME) to total phosphate (SigmaP) ratios in treated compared with untreated tumours, a result rarely seen in animal models, but commonly observed in patients. This study showed that a Th1-biased immune response generated by killing prostate tumour cells with tk/GCV can kill distant as well as local wild-type tumour cells. These findings suggest that GPAT may have a potential application in patients with both confined and metastatic prostate cancer and MRS may provide a method of monitoring response to treatment.

Gene therapy of malignant glioma: recent advances in experimental and clinical studies

Recent advances in molecular tumor biology and gene technology have provided the possibility to treat patients with malignant brain tumors by altering gene expression in tumor cells. Tumor development and progression involves alterations in a wide spectrum of genes, therefore a variety of gene therapy approaches for malignant gliomas have been proposed. In this review article, we discuss some principles of current gene therapeutic strategies that are under investigation in laboratories and in clinics. In addition, some general issues that remain to be resolved for clinical application of gene therapy in patients with malignant gliomas will be addressed.

Beta-galactosidase gene transfer to human malignant glioma in vivo using replication-deficient retroviruses and adenoviruses

Both retro- and adenovirus-mediated gene therapy have been suggested as a novel approach to the treatment of malignant brain tumors. However, little information is available about the gene transfer efficiency in human malignant glioma in vivo. We compared the feasibility and safety of retrovirus- and adenovirus-mediated beta-galactosidase gene transfer in human malignant glioma. Beta-galactosidase gene was transferred to 10 patients with malignant glioma via a catheter inserted into the tumor. The catheter was left in place until the tumor resection. To maximize gene transfer efficiency, gene transfer vectors (BAG retroviruses, titer, 6 x 10(5) CFU; and adenoviruses, titer from 3 x 10(8) to 3 x 10(10) PFU) were injected into the tumor via the catheter once a day for three consecutive days, followed by tumor resection 1-2 days later. Tumor was resected in such a way that the catheter was still in place inside the tumor, which permitted accurate histological analysis of the transduced tumors. X-Gal staining for beta-galactosidase activity was used to study gene transfer efficiency and distribution of the marker gene. Beta-galactosidase gene transfer was well tolerated with both vectors. Except for two patients with clear increases in serum adenovirus antibody titers, no adverse tissue responses or systemic complications were noticed in any of the patients. Gene transfer was successful in all patients. Gene transfer efficiency varied between <0.01 and 4% with retroviruses and between <0.01 and 11% with adenoviruses. However, the transgene activity was not evenly distributed in the tumors. Both glioma cells and endothelium in the tumor blood vessels were transduced with retro- and adenovirus vectors. In conclusion, the safety and feasibility of in vivo gene transfer to human malignant glioma was established with retro- and adenovirus vectors. Adenoviruses were more efficient than retroviruses in achieving in vivo gene transfer. Transduction of endothelial cells may have important consequences for the proposed treatment strategies and selection of treatment genes. The results justify clinical gene therapy trials for malignant glioma.

Design of metal-binding green fluorescent protein variants

Diglycylcysteine motifs bind reduced oxo-compounds of technetium-99m, an important isotope in nuclear imaging. We suggested a system for detecting gene expression employing the effect of oxo[99mTc]technetate (Tc(V)O3+) transchelation and coordination with redox amino acid motifs. DNA fragments encoding diglycylcysteine (GGC) binding motifs were prepared by PCR and positioned downstream from the green fluorescent protein (GFP) cDNA insert. Using a Bluescript (+) vector with the fusion protein positioned under the control of a lac promoter, we obtained several E. coli clones expressing the following GFP fusion peptides: (1) GFP-P1 bearing a 'hydrophilic' C-terminal peptide (LEGGGCEGGC) containing two residues of glutamic acid and C-terminal cysteine (2) GFP-P2 carrying a 'hydrophobic' (LGGGGCGGGCGI) peptide (3) a control GFP fusion peptide with deleted C-terminal portion. Bacterial lysates obtained from the corresponding clones were tested for oxo[99mTc] technetate transchelation from a glucoheptonate complex. We found, using a solid phase assay, that radioactivity associated with protein lysates obtained from clones expressing GFP-P2 fusions were 3-4 fold higher than lysates prepared from a clone expressing a truncated GFP fusion protein lacking the C-terminal GGC motifs. High expression of GFP fusions (5-21% of total protein) was demonstrated by electrophoresis and verified by immunoblotting. Specific association of the isotope with GFP-P2 fusion proteins was detected upon incubation of gels in the presence of [99mTc]glucoheptonate, while no binding of oxo[99mTc]technetate to GFP-P1 was revealed. We demonstrated, by using semi-quantitative autoradiography, that there is a 10-fold higher binding of oxotechnetate to GFP-P2 than to a control GFP fusion protein. The implications of the study for in vivo gene expression imaging are discussed.

Glucose and methionine uptake by rat brain tumor treated with prodrug-activated gene therapy

The effect of acyclovir (ACV) on the metabolism of rat 9L-gliosarcoma cells expressing the herpes simplex virus-thymidine kinase gene was studied using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) and L-[methyl-11C]methionine. Though the average weight of the tumors treated with ACV was significantly lower than that of the saline-injected control group, FDG and methionine uptake per weight of tumor tissue was not different between the two groups. This result exhibits a striking contrast to the metabolic pattern observed after radiation therapy, suggesting the different pathways regarding tumor cell death between the therapies.

Bystander effect-mediated therapy of experimental brain tumor by genetically engineered tumor cells

Transfer of the herpes simplex virus-thymidine kinase (HSV-tk) gene, followed by administration of ganciclovir (GCV), generates the "bystander effect," in which HSV-tk-negative wild-type cells, as well as HSV-tk-expressing cells, are killed by GCV. To eradicate an intracranial tumor by this bystander effect, we injected the tumor cells transduced with the HSV-tk gene (TK cells) in the vicinity of the preimplanted wild-type tumor and then administered GCV. Wild-type 9L-gliosarcoma cells (1 x 10[5]) were implanted into the brain of syngeneic Fisher rats. On the next day, rats were injected with TK cells (1 x 10(5) or 3 x 10[5]) or medium alone at the same brain coordinate and then treated with GCV or saline. Administration of GCV significantly prolonged the survival of the rats injected with TK cells compared with that injected with medium alone (p < 0.01). Reduction in tumor size and retardation of tumor growth were observed by serial magnetic resonance imaging in the rats that received the combination of TK cells and GCV. The results show that the bystander effect is also achieved in vivo even when TK cells and wild-type cells are not simultaneously implanted. This treatment modality circumvents potential risks accompanied with in vivo gene transfer. Because there remained substantially no HSV-tk-positive cells in the recurrent tumors, this modality offers a "safe" therapeutic strategy against human malignant gliomas.

Variable efficiency of the thymidine kinase/ganciclovir system in human glioblastoma cell lines: implications for gene therapy

The gene therapy strategy using the hsvl-thymidine kinase gene (TK) and ganciclovir (GCV) injections that has been used for treating human glioblastomas has not been as effective as expected after the first animal experiments. A better understanding of the different steps involved in this treatment, like gene transfer, gene expression, and sensitivity of the recipient cells, is needed. After proposing sensitivity criteria for the TK/GCV system and for the bystander effect, based on the levels of GCV that can be reached in vivo, we studied seven human glioblastoma cell lines (U87, U118, U251, SNB19, SNB75, SF295, SF539) for their sensitivity to the TK/GCV system. We also studied their in vitro bystander effect and their in vitro transfectability using LipofectAMINE as a transfection enhancer. Among six human glioblastoma cell lines stably transfected with the TK gene, five were sensitive to TK/GCV, and two had a good in vitro bystander effect. The in vitro transfectability of the cell lines tested was low (< or = 1%) compared to that of an established animal cell line, C6 rat glioma, in which 20-30% of the cells can be transfected routinely. According to this in vitro analysis, most of the glioblastoma cell lines should be sensitive to the TK/GCV system, but there is an urgent need for agents to increase transfection efficiency.