Adenovirus-mediated gene therapy in an experimental model of breast cancer metastatic to the brain

Animal models of tumour-associated epilepsy

Brain tumours cause a sizeable proportion of epilepsies in adulthood, and actually can be etiologically responsible also for childhood epilepsies. Conversely, seizures are often first clinical signs of a brain tumour. Nevertheless, several issues of brain-tumour associated seizures and epilepsies are far from understood, or clarified regarding clinical consensus. These include both the specific mechanisms of epileptogenesis related to different tumour types, the possible relationship between malignancy and seizure emergence, the interaction between tumour mass and surrounding neuronal networks, and - not least - the best treatment options depending on different tumour types. To investigate these issues, experimental models of tumour-induced epilepsies are necessary. This review concentrates on the description of currently used models, focusing on methodological aspects. It highlights advantages and shortcomings of these models, and identifies future experimental challenges.

Flt3L and TK gene therapy eradicate multifocal glioma in a syngeneic glioblastoma model

The disseminated characteristics of human glioblastoma multiforme (GBM) make it a particularly difficult tumor to treat with long-term efficacy. Most preclinical models of GBM involve treatment of a single tumor mass. For therapeutic outcomes to translate from the preclinical to the clinical setting, induction of an antitumor response capable of eliminating multifocal disease is essential. We tested the hypothesis that expression of Flt3L (human soluble FMS-like tyrosine kinase 3 ligand) and TK (herpes simplex virus type 1-thymidine kinase) within brain gliomas would mediate regression of the primary, treated tumor mass and a secondary, untreated tumor growing at a distant site from the primary tumor and the site of therapeutic vector injection. In both the single-GBM and multifocal-GBM models used, all saline-treated control animals succumbed to tumors by day 22. Around 70% of the animals bearing a single GBM mass treated with an adenovirus expressing Flt3L (AdFlt3L) and an adenovirus expressing TK (AdTK + GCV) survived long term. Approximately 50% of animals bearing a large primary GBM that were implanted with a second GBM in the contralateral hemisphere at the same time the primary tumors were being treated with AdFlt3L and AdTK also survived long term. A second multifocal GBM model, in which bilateral GBMs were implanted simultaneously and only the right tumor mass was treated with AdFlt3L and AdTK, also demonstrated long-term survival. While no significant difference in survival was found between unifocal and multifocal GBM-bearing animals treated with AdFlt3L and AdTK, both treatments were statistically different from the saline-treated control group (p < 0.05). Our results demonstrate that combination therapy with AdFlt3L and AdTK can eradicate multifocal brain tumor disease in a syngeneic, intracranial GBM model.

A novel rat model for the study of intraosseous metastatic spine cancer

Object. Although metastatic spinal disease constitutes a significant percentage of all spinal column tumors, an accessible and reproducible animal model has not been reported. In this study the authors describe the technique for creating an intraosseous spinal tumor model in rats and present a functional and histological analysis.

Methods. Eighteen female Fischer 344 rats were randomized into two groups. Group 1 animals underwent a transabdominal exposure and implantation of CRL-1666 breast adenocarcinoma into the L-6 vertebral body (VB). Animals in Group 2 underwent a sham operation. Hindlimb function was tested daily by using the Basso-Beattie-Bresnahan scale. Sixteen days after tumor implantation, animals were killed and their spines were removed for histological assessment. Statistical analysis was performed using the Wilcoxon signed-rank test.

By Day 15 functional analysis showed a significant decrease in motor function in Group 1 animals (median functional score 2 of 21) compared with Group 2 rats (median functional score 21 of 21) (p = 0.0217). The onset of paraparesis in Group 1 occurred within 14 to 16 days of surgery. Histopathological analysis showed tumor proliferation through the VB and into the spinal canal, with marked osteolytic activity and spinal cord compression.

Conclusions. Analysis of these findings demonstrates the consistency of tumor growth in this model and validates the utility of functional testing for onset of paresis. This new rat model allows for the preclinical evaluation of novel therapeutic treatments for patients harboring metastatic spine disease.

Adenoviral vectors: development and application

One of the prerequisites for the successful application of gene vaccination and therapy is the development of efficient gene delivery vectors. The rate-limiting nature of vectors was clearly manifested during the first wave of gene therapy testing, resulting in the demand for more effective and suitable vector systems. Adenoviral (Ad) vectors have recently played a central role in the development of gene-vector technology due to their practical advantages and potential applications. A large number of preclinical and clinical studies both have generated an overwhelming amount of data and literature on this vector system. It is the intention of this article to provide a systematic and broad spectrum review of this system, outlining the principle, potential, and limitations, and evaluating the rational development of this delivery approach. Recombinant adenoviruses (Ad), helper cell lines, and related technologies have been developed and applied to many indications owing to progress in virological research, molecular and cellular biology, eukaryotic protein expression, recombinant vaccines, and gene therapy. The technical depth this article covers should be useful to both the experienced researcher and to beginners in this field.

Adenoviral gene therapy

As of May 2001, 532 gene therapy protocols had been approved for evaluation in clinical trials; however, only five of those had been evaluated in phase III clinical trials. Among the most commonly used vectors for the delivery of genetic material into human cells are the adenoviruses. Remarkable progress has been made with these vectors in the last decade, but some shortcomings continue to challenge investigators. The newly acquired knowledge of the adenoviral life cycle and the positive outcomes from phase II clinical trials have led to the application of vectors engineered to selectively target tumor tissue under controlled promoters.

Phase I study of adenoviral delivery of the HSV-tk gene and ganciclovir administration in patients with current malignant brain tumors

Between December 1996 and September 1998, 13 patients with advanced recurrent malignant brain tumors (9 with glioblastoma multiforme, 1 with gliosarcoma, and 3 with anaplastic astrocytoma) were treated with a single intratumoral injection of 2 x 10(9), 2 x 10(10), 2 x 10(11), or 2 x 10(12) vector particles (VP) of a replication-defective adenoviral vector bearing the herpes simplex virus thymidine kinase gene driven by the Rous sarcoma virus promoter (Adv.RSVtk), followed by ganciclovir (GCV) treatment. The VP to infectious unit ratio was 20:1. Our primary objective was to determine the safety of this treatment. Injection of Adv.RSVtk in doses <==2 x 10(11) VP, followed by GCV, was safely tolerated. Patients treated with the highest dose, 2 x 10(12) VP, exhibited central nervous system toxicity with confusion, hyponatremia, and seizures. One patient is living and stable 29.2 months after treatment. Two patients survived >25 months before succumbing to tumor progression. Ten patients died within 10 months of treatment, 9 from tumor progression and 1 with sepsis and endocarditis. Neuropathologic examination of postmortem tissue demonstrated cavitation at the injection site, intratumoral foci of coagulative necrosis, and variable infiltration of the residual tumor with macrophages and lymphocytes.

Adenovirus-mediated suicide gene therapy in an in vitro model of reactive gliosis

Adenovirus-mediated herpes simplex thymidine kinase/ganciclovir (HSV-tk/GCV) system has been demonstrated to be efficient for the treatment of experimental brain tumors. However, no study has been directed to the elimination of proliferating cellular populations in other pathological conditions. In this study we used this suicide gene approach in a primary culture of astrocytes, as a model of reactive gliosis, in order to evaluate its efficiency as a therapeutic strategy for post-traumatic astrogliosis in vivo. First, we evaluated the peak of astrocytic proliferation to characterize our model. Second, the efficiency of adenovirus-mediated lacZ gene transfer is shown to be dependent on vector multiplicity of infection (MOI). As expected, the cells transfected with the HSV-tk gene showed an increase in sensibility to GCV compared with cells transfected with lacZ gene. Finally, an unexpected interaction between the adenoviral vector and bromodeoxyuridine (BrdU) or [3H]-Thymidine ([3H]-Thy) was evidenced in transfected cultures, whose interpretation is discussed. The present study demonstrates that a recombinant adenoviral vector carrying the tk gene confers to in vitro cultured astrocytes a cytotoxic sensibility to GCV, and that this system constitutes a potentially efficient tool to eliminate the hyperplasia of astrocytes following injury to the central nervous system in vivo.

Treatment of human breast cancer in a brain metastatic model by G207, a replication-competent multimutated herpes simplex virus 1

We investigated the therapeutic efficacy of G207, a replication-competent multimutated herpes simplex virus type 1, for the treatment of human malignant mammary tumors metastatic to the brain. In vitro studies demonstrated that G207 efficiently destroyed three of four human malignant breast cancer cell lines. MDA-MB-435 was most susceptible and MDA-MB-231 was least susceptible to G207. In athymic mice harboring subcutaneous or intracerebral MDA-MB-435 cells, intraneoplastic inoculation of G207 caused growth inhibition and/or prolonged survival. In contrast, G207 had minimal effects on MDA-MB-231 subcutaneous tumor growth or survival in the intracerebral tumor model. The efficacy of G207 therapy in vivo correlated well with the susceptibility of the human cancer cells to G207 in vitro. Histological studies indicate that G207 replication is restricted to tumor cells in vivo and does not occur in the surrounding brain tissue. These results suggest that G207 shows particular promise for use as a novel antineoplastic agent for metastatic brain tumors and that in vitro testing may predict which tumors will be most responsive in vivo.

Conditionally replicative adenoviruses for cancer therapy

The delineation of the genetic etiology of cancer makes gene therapy a rational approach for the molecular treatment of cancer. Many gene delivery systems have been developed, with viral vectors being the most effective. Underlying cancer gene therapy protocols is the recognition that quantitative tumor transduction cannot be achieved with the vector systems available at the present time. One way to overcome this problem could be to amplify the transduction efficiency through the use of vectors capable of replicating specifically in tumor cells. We are currently developing an adenoviral vector in which viral replication will be restricted to the target tumor cells by limiting the expression of viral genes essential for the virus replication only to the tumor cells of interest.

Adenovirus-mediated gene transfer to the central nervous system for Parkinson's disease

Gene therapy is a potentially powerful approach to the treatment of neurological diseases. The discovery of neurotrophic factors inhibiting neurodegenerative processes and the isolation of genes encoding neurotransmitter synthesizing enzymes provide the basis for current gene therapy strategies for Parkinson's disease. Adenovirus vectors have been shown recently to allow efficient gene transfer to the brain. One of the advantages of recombinant adenovirus is that it can transduce both quiescent and actively dividing cells. Thus expression of transgenes in neurons using adenoviruses is possible after either direct in vivo gene transfer or ex vivo gene transfer. In vivo gene transfer, consisting of the direct intracerebral injection of genetic material, is a novel method that is particularly efficient with the adenoviral vector. Ex vivo gene transfer, combining gene transduction with intracerebral transplantation, is a way to improve the classical grafts which are limited by poor cell survival in Parkinson's disease. Probably because the brain is a partially immunologically privileged site, the expression of adenoviral vectors persists for several months with little inflammation. Recombinant adenoviruses are currently being improved, particularly by inactivating viral genes controlling the expression of immunodominant viral proteins.

A novel gene therapy strategy for elimination of prostate carcinoma cells from human bone marrow

We report a novel means to purge bone marrow of a specific subset of prostate carcinoma cells based on transductional and genetic selectivity. Using both adenovirus-polylysine-DNA complexes and E1A/B-deleted replication-deficient adenoviruses, we have demonstrated a transductional preference of these vectors for the prostate carcinoma cell lines DU 145, LNCaP, and PC-3 over primary human bone marrow cells and the leukemia cell line KG-1. We have also shown a genetic selectivity of an anti-erbB-2 intracellular single-chain antibody (sFv) encoding adenovirus, Ad21, for the erbB-2-positive prostate carcinoma cell lines DU 145 and LNCaP. Delivery of Ad21 resulted in cytotoxicity to the DU 145 and LNCaP, but not PC-3, cell lines and reduced the clonogenic capacity of DU 145 cells cultured alone or mixed with various ratios of irradiated human bone marrow. Finally, quantitative, competitive reverse transcription polymerase chain reaction (QC-RT-PCR) analysis demonstrated that Ad21 could effectively reduce DU 145 and erbB-2-positive primary prostate tumor contamination in bone marrow cultures. Delivery of Ad21 had no effect on the ability of progenitor cells to form colonies. These results suggest that an anti-erbB-2 sFv-encoding adenoviral vector is efficacious for removal of erbB-2-positive prostate carcinoma cells from human bone marrow, and demonstrates a novel method for ex vivo genetic purge of malignant cells from bone marrow for autologous bone marrow transplantation (ABMT) therapy.

Adenoviral-mediated thymidine kinase gene transfer into the primate brain followed by systemic ganciclovir: pathologic, radiologic, and molecular studies

Transduction of experimental gliomas with the herpes simplex virus thymidine kinase gene (HSV-tk) using a replication-defective adenoviral vector (ADV/RSV-tk) confers sensitivity to ganciclovir (GCV) leading to tumor destruction and prolonged host survival in rodents. To determine treatment tolerance prior to clinical trials, we conducted toxicity studies in 6 adult baboons (Papio sp.). The animals received intracerebral injections of either a high dose of ADV/RSV-tk [1.5 x 10(9) plaque-forming units (pfu)] with or without GCV, or a low dose of ADV/RSV-tk (7.5 x 10(7) pfu) with GCV. The low dose corresponded to the anticipated therapeutic dose; the high dose was expected to be toxic. Magnetic resonance imaging (MRI) of the brain was obtained before treatment and at 3 and 6 weeks after treatment. Animals receiving the high-dose vector and GCV either died or became moribund and required euthanasia during the first 8 days of treatment. Necropsies revealed cavities of coagulative necrosis at the injection sites. Animals receiving only the high-dose vector were clinically normal; however, lesions were detected with MRI at the injection sites corresponding to cystic cavities at necropsy. Animals receiving the low-dose vector and GCV were clinically normal, exhibited small MRI abnormalities, and, although no gross lesions were present at necropsy, microscopic foci of necrosis were present. The vector sequence was detected by polymerase chain reaction (PCR) at the injection sites and in non-adjacent central nervous system tissue in all animals. Recombinant DNA sequence was detected outside of the nervous system in some animals, and persisted up to 6 weeks. The viral vector injections stimulated the production of neutralizing antibodies in the animals. No shedding of the vector was found in urine, feces, or serum 7 days after intracerebral injection. This study suggests that further investigations including clinical toxicity trials of this form of brain tumor therapy are warranted.

Transduction of the herpes thymidine kinase gene into premalignant murine mammary epithelial cells renders subsequent breast cancers responsive to ganciclovir therapy

Drug sensitivity ("suicide") genes can sensitize cancer cells to chemotherapy, but therapeutic use of these genes is limited by difficulties in delivering them to all areas of established cancers. An alternative strategy entails preemptive introduction of suicide genes into tissues at risk for cancer, thereby imparting drug sensitivity as a clonal property to cancers arising from sensitized cells. To test the preemptive approach, a retroviral vector was used to transduce the herpes thymidine kinase gene into the TM4 line of preneoplastic murine mammary epithelial cells to yield a clonal subline sensitized to the guanosine analog ganciclovir. Ganciclovir therapy of tumors that arose from the transduced cells retarded tumor growth and induced durable regressions in 7/20 mice; ganciclovir was ineffective against control tumors. The results imply the possibility of reducing cancer lethality by actions taken before cancers arise.