Neurotoxicity of intracerebral injection of a replication-defective adenoviral vector in a semipermissive species (cotton rat)

Adenoviral-mediated Cre expression effectively suppresses GlyT1 binding in the thalamic area of GlyT1 conditional knock-out mice

To properly understand the function of genes of neurological interest, in vivo manipulation in the adult is essential, particularly when the target gene is involved in brain development. Moreover, since the physiological effects of target protein may be region-specific, targeting a distinct brain region could be required to dissect these effects in specific brain locations. Infection of somatic tissues of transgenic mice bearing loxP-flanked gene sequences with a viral vector expressing Cre recombinase provides a means of allowing flexible spatio-temporal control of target gene expression. Viral vector-mediated Cre expression could be used to mediate localized gene modulation in a specific brain region. In the present study this technology was applied to the glycine transporter type-1 (GlyT1) protein which is responsible for the uptake of synaptic glycine in the forebrain and has been implicated as a therapeutic target for the treatment of schizophrenia. Since GlyT1 is widely expressed in glial cells, we employed an adenoviral-based vector (Ad5) to deliver Cre protein, due to the preferentially transduction of glial cells by adenoviral vectors in rodent brain. We show significant reduced GlyT1 binding specifically in the thalamic area of conditional GlyT1 (GlyT1c) transgenic mice injected with Ad5-Cre virus, as measured by GlyT1 autoradiography. In conclusion, we demonstrated the validity of viral vector-mediated delivery of Cre to loxP targeted transgenic mice as a novel strategy to investigate target gene function in selected subregions of the adult brain, which provides a valuable technique to investigate gene function both in normal physiology and in disease models.

Immunocompetent syngeneic cotton rat tumor models for the assessment of replication-competent oncolytic adenovirus

Oncolytic adenoviruses as a treatment for cancer have demonstrated limited clinical activity. Contributing to this may be the relevance of preclinical animal models used to study these agents. Syngeneic mouse tumor models are generally non-permissive for adenoviral replication, whereas human tumor xenograft models exhibit attenuated immune responses to the vector. The cotton rat (Sigmodon hispidus) is susceptible to human adenovirus infection, permissive for viral replication and exhibits similar inflammatory pathology to humans with adenovirus replicating in the lungs, respiratory passages and cornea. We evaluated three transplantable tumorigenic cotton rat cell lines, CCRT, LCRT and VCRT as models for the study of oncolytic adenoviruses. All three cells lines were readily infected with adenovirus type-5-based vectors and exhibited high levels of transgene expression. The cell lines supported viral replication demonstrated by the induction of cytopathogenic effect (CPE) in tissue culture, increase in virus particle numbers and assembly of virions seen on transmission electron microscopy. In vivo, LCRT and VCRT tumors demonstrated delayed growth after injection with replicating adenovirus. No in vivo antitumor activity was seen in CCRT tumors despite in vitro oncolysis. Adenovirus was also rapidly cleared from the CCRT tumors compared to LCRT and VCRT tumors. The effect observed with the different cotton rat tumor cell lines mimics the variable results of human clinical trials highlighting the potential relevance of this model for assessing the activity and toxicity of oncolytic adenoviruses.

The combination of adenoviral HSV TK gene therapy and radiation is effective in athymic mouse glioblastoma xenografts without increasing toxic side effects

OBJECT

In mouse models of prostate and breast cancer therapeutic effects are enhanced when adenoviral HSV TK gene therapy is combined with ionizing radiation. In the present study, we adopted this approach for the treatment of human glioblastoma xenografts in an athymic mouse model and assessed treatment results as well as toxic side effects.

METHODS

About 72 nude mice received intracerebral inoculations of 2 x 10(5) U87deltaEGFR cells. On day 7 after tumor implantation the study population was randomized into six treatment arms: (1) intratumoral buffer inoculation on day 7, (2) intratumoral adenoviral vector injection (2 x 10(9) vp) on day 7, (3) single dose radiation (2.1 Gy) on day 9, (4) adenoviral injection + radiation, (5) adenoviral injection + ganciclovir (GCV) (20 microg/g twice daily from day 8 to 17), (6) adenoviral injection + GCV + radiation. On day 21 half of the animals were sacrificed for histological evaluation of the brain tumors, the other half was assessed for survival.

RESULTS

This study showed significantly prolonged median survival time of 5 days for the GCV treated groups. The addition of radiation decreased the frequency of neurological symptoms and delayed the onset of deficits without altering the expression of thymidine kinase in the tumor cells.

CONCLUSIONS

We conclude that adenoviral HSV TK gene therapy in combination with adjuvant radiotherapy does not generate increased toxic side effects in glioblastoma treatment. The prolonged survival time of animals receiving gene therapy and the reduced occurrence of neurological symptoms in irradiated mice constitute promising features of the combined treatment.

Evolution of a gene therapy clinical trial. From bench to bedside and back

Developing and conducting gene therapy clinical trials poses unique challenges which must be addressed to satisfy regulatory requirements and, most importantly, to protect human subjects. Experimental products used for gene transfer studies, such as viral vectors, are often complex and cannot be sterilized or completely characterized to the extent of a typical pharmaceutical. Thus, quality and characterization must be built into the production process. Extensive preclinical studies must be performed to determine the feasibility of the approach, the safety of the product, and the appropriate dose range to evaluate in humans. Once a clinical trial is initiated, subjects must be followed carefully for short- and long-term toxicity especially since preclinical studies may not adequately predict the toxicity profile of these novel, complicated products. Results of early phase studies in gene therapy have often sent the investigators back to the laboratory to improve the delivery vector or identify a more potent or less toxic gene. This circular developmental process is expected for the early stages of a new technology such as gene therapy. Although these hurdles appear extensive, they can be overcome, as evidenced by the initiation of more than 500 clinical gene therapy trials in the United States to date, and are imperative for the maintenance of high-quality studies and public trust. This article describes the step-by-step process for developing a gene therapy trial incorporating specific examples relevant to neuro-oncology.

Treatment of relapsed malignant glioma with an adenoviral vector containing the herpes simplex thymidine kinase gene followed by ganciclovir

Between November 1998 and December 2001, we treated 14 patients with advanced recurrent high-grade gliomas with a total dose of 4.6 x 10(8), 4.6 x 10(9), 4.6 x 10(10), or 4.6 x 10(11) viral particles (VP) of a replication-incompetent adenoviral vector harboring the herpes simplex virus thymidine kinase gene driven by the adenoviral major late promoter (IG.Ad.MLPI.TK), followed by ganciclovir (GCV) treatment. The VP-to-infectious-unit ratio was 40. The vector was administered by 50 intraoperative wound-bed injections of 0.2 ml each (total volume 10 ml). The study's primary objective was to determine the safety of this treatment and establish the maximum tolerated dose (MTD). Injection of all doses of IG.Ad.MLPI.TK followed by GCV was safely tolerated and MTD was not reached. All patients had recurrence or progression of the tumor 1-24 months (median 3.5 months) after gene therapy. The overall median survival was 4 months. Four patients survived longer than 1 year following gene therapy. One patient is still alive, with histologically confirmed progression of the tumor, 29 months after treatment. Ten patients died within 8 months of treatment, all from progression of the tumor. In 5 patients residual and measurable tumor was visible on the direct (<48 h) postoperative MRI. No objective radiological response was documented on subsequent MRI. None of the patients came to autopsy. In conclusion, the administration of 4.6 x 10(11) VP of IG.Ad.MLPI.TK by 50 injections into the wound bed following resection of recurrent malignant glioma, followed by GCV treatment, was well tolerated.

Histologic and immunohistochemical analysis of tissue response to adenovirus-mediated herpes simplex thymidine kinase gene therapy of ovarian cancer

Herpes simplex virus (HSV) thymidine kinase (tk) gene incorporated into adenovirus was delivered intraperitoneally (ip) followed by an antiherpetic prodrug and topotecan in patients with recurrent epithelial ovarian cancer. Tissue response was evaluated. Ten patients underwent secondary debulking with subsequent delivery of ADV-HSV-tk therapy. Two patients each were treated at dose level 1 (2 x 10(10) vector particles = VP), 2 (2 x 10(11) VP), and 3 (2 x 10(12) VP); four patients were treated at dose level 4 (2 x 10(13) VP). Five patients underwent second-look surgery about one month after gene therapy (GT). Treatment response, presence of vector DNA, protein expression of steroid hormone receptors, p53, c-erbB2 and Ki67 protein were analyzed. At second-look, two out of five patients were tumor-free and none of their peritoneal biopsies showed vector DNA. After GT, the vital tumor mass was smaller, desmoplastic reaction had increased, and tumors were less differentiated with an increase of Ki67 expression. There was no change in expression of hormone receptors, p53, or c-erbB2. ADV-HSV-tk GT appears to eliminate cells with higher differentiation first and might induce fibrosis. Dedifferentiation might render residual cells more sensitive to chemotherapy secondary to their subsequent higher mitotic activity.

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 p53 gene therapy for human gliomas

OBJECTIVE

The rationale and current evidence for using p53 gene replacement as a potential treatment for human gliomas are reviewed. The possible benefits of and obstacles to this approach are delineated.

METHODS

One approach to overcoming the poor outcomes associated with conventional glioma therapies involves the replacement of tumor suppressor genes that are fundamental to glioma development. The p53 gene is one of the most frequently mutated genes in human gliomas, and loss of p53 function is critical to the development of glial neoplasms. Consequently, replacement of the p53 gene using viral vectors may be a potential treatment for human gliomas.

RESULTS

In vitro studies demonstrate that adenovirus-mediated p53 gene transfer into gliomas with mutant p53 results in massive apoptosis. Similarly, transfer of p53 inhibits tumor growth in vivo. In contrast to mutant p53 gliomas, wild-type p53 glioma cells are resistant to the apoptotic effects of p53 transfer, but this resistance can be overcome by the addition of deoxyribonucleic acid-damaging agents such as ionizing radiation or chemotherapy. The main obstacle to p53 gene therapy involves the limitations associated with current modes of delivery.

CONCLUSION

Preclinical data strongly support the use of p53 gene transfer as a potential treatment for human gliomas.

A model for long-term transgene expression in spinal cord regeneration studies

In order to determine the suitability of first generation adenoviral vectors for gene delivery into spinal cord white matter, four different titres of beta-galactosidase-expressing adenovirus were injected into spinal cord white matter of adult rats. At titres > or =106 p.f.u., transgene expression was extensive but severe tissue damage was observed in the form of axon degeneration, demyelination and astrocyte loss. When < or = 105 p.f.u. were injected, only low levels of axon degeneration and demyelination were observed. beta-Galactosidase activity was detectable at 72 days and did not diminish significantly with time. The immune response in the spinal cord to 105 p.f.u. over 72 days was minimal, and indistinguishable from that to injection of buffer. A prominent immune response was observed when 107 p.f.u. was injected into the spinal cord of PVG rats, and when 105 or 107 p.f.u. was injected into AO rats. These results indicate that the immune response in PVG rats to betagal-expressing adenovirus is both strain and titre dependent. First generation adenoviral vectors, therefore, induce moderate and long-lived transgene expression with minimal tissue damage and immune response when an appropriate titre is injected into the low responder PVG rat strain, providing a suitable model for assessing the effect of gene delivery in models of spinal cord injury.

Adenovirus-mediated wild-type p53 expression induces apoptosis and suppresses tumorigenesis of experimental intracranial human malignant glioma

Adenoviral-mediated gene transfer for the treatment of experimental intrinsic malignant brain neoplasms holds promise. The role, however, of intracellular, adenoviral-mediated p53 expression to inhibit growth of experimental human intracranial malignant gliomas remains largely unexplored. Using the AdCMV.p53 vector we measured the in vitro expression of p53 and the resultant effect upon U251 human malignant glioma cellular proliferation. We further measured the survival of nude mice after intracranial injection of the infected vs. control U251 cells. The growth of the infected U251 cells was inhibited when compared to both the uninfected cells and cells infected with the control vector (AdCMV.Null). Agarose gel electrophoresis confirmed the AdCMV.p53-dependent cellular apoptosis. Nude mice having intracranial injections of the U251 cells infected with the control (AdCMV.Null) vector showed diminished survival. In contrast, mice having intracranial injections of the cells infected with the AdCMV.p53 vector showed 100% survivorship measured 100 days after treatment. Gene therapy via the AdCMV.p53 viral vector holds promise for the clinical treatment of human malignant gliomas.