Systemic antitumor immunity in experimental brain tumor therapy using a multimutated, replication-competent herpes simplex virus

Viral shedding and biodistribution of G207, a multimutated, conditionally replicating herpes simplex virus type 1, after intracerebral inoculation in aotus

G207 is a multimutated, conditionally replicating herpes simplex virus type 1 (HSV-1) that is currently in clinical trial for patients with malignant glioma. G207 exhibits an efficient oncolytic activity in tumor cells, yet minimal toxicity in normal tissue when injected into the brains of HSV-susceptible mice or nonhuman primates. In this study, we evaluated the shedding and biodistribution of clinical-grade G207 after intracerebral inoculation (3 x 10(7) pfu) in four New World owl monkeys (Aotus nancymae). Using PCR analyses and viral cultures, neither infectious virus nor viral DNA was detected from tear, saliva, or vaginal secretion samples at any time point up to 1 month postinoculation. Analyses of tissues obtained at necropsy at 1 month from two of the four monkeys, plus one monkey inoculated with laboratory-grade G207 (10(9) pfu) 2 years earlier, showed the distribution of G207 DNA restricted to the brain, although infectious virus was not isolated. Histopathology revealed normal brain tissues including the sites of inoculation. A measurable increase of serum anti-HSV antibody titer was observed in all monkeys, as early as 21 days postinoculation. The results ascertain the safety of G207 in the brain and indicate that strict biohazard management may not be required for G207-treated patients.

Recombinant measles viruses efficiently entering cells through targeted receptors

We sought proof of principle that one of the safest human vaccines, measles virus Edmonston B (MV-Edm), can be genetically modified to allow entry via cell surface molecules other than its receptor CD46. Hybrid proteins consisting of the epidermal growth factor (EGF) or the insulin-like growth factor 1 (IGF1) linked to the extracellular (carboxyl) terminus of the MV-Edm attachment protein hemagglutinin (H) were produced. The standard H protein gene was replaced by one coding for H/EGF or H/IGF1 in cDNA copies of the MV genome. Recombinant viruses were rescued and replicated to titers approaching those of the parental strain. MV displaying EGF or IGF1 efficiently entered CD46-negative rodent cells expressing the human EGF or the IGF1 receptor, respectively, and the EGF virus caused extensive syncytium formation and cell death. Taking advantage of a factor Xa protease recognition site engineered in the hybrid H proteins, the displayed domain was cleaved off from virus particles, and specific entry in rodent cells was abrogated. These studies prove that MV can be engineered to selectively eliminate cells expressing a targeted receptor and provide insights into the mechanism of MV entry.

Effect of preexisting anti-herpes immunity on the efficacy of herpes simplex viral therapy in a murine intraperitoneal tumor model

HSV-1716, a replicating nonneurovirulent herpes simplex virus type 1, has shown efficacy in treating multiple types of human tumors in immunodeficient mice. Since the majority of the human population has been previously exposed to herpes simplex virus, the efficacy of HSV-based oncolytic therapy was investigated in an immunocompetent animal tumor model. EJ-6-2-Bam-6a, a tumor cell line derived from h-ras-transformed murine fibroblast, exhibit a diffuse growth pattern in the peritoneal cavity of BALB/c mice and replicate HSV-1716 to titers observed in human tumors. An established intraperitoneal (ip) tumor model of EJ-6-2-Bam-6a in naive and HSV-immunized mice was used to evaluate the efficacy of single or multiple ip administrations of HSV-1716 (4 x 10(6) pfu/treatment) or of carrier cells, which are irradiated, ex vivo virally infected EJ-6-2-Bam-6a cells that can amplify the viral load in situ. All treated groups significantly prolonged survival versus media control with an approximately 40% long-term survival rate (cure) in the multiply treated, HSV-naive animals. Prior immunization of the mice with HSV did not significantly decrease the median survival of the single or multiply treated HSV-1716 or the carrier cell-treated groups. These studies support the development of replication-selective herpes virus mutants for use in localized intraperitoneal malignancies.

Conditionally replicating herpes simplex virus mutant, G207 for the treatment of malignant glioma: results of a phase I trial

G207 is a conditionally replicating derivative of herpes simplex virus (HSV) type-1 strain F engineered with deletions of both gamma(1)34.5 loci and a lacZ insertion disabling the UL39 gene. We have demonstrated the efficacy of G207 in treating malignant glial tumors in athymic mice, as well as the safety of intracerebral G207 inoculation in mice and in Aotus nancymai. We sought to determine the safety of G207 inoculation into cerebral malignant glial tumors in humans. Criteria for inclusion into this dose-escalation study were the diagnosis of histologically proven malignant glioma, Karnofsky score > or = 70, recurrence despite surgery and radiation therapy, and an enhancing lesion greater than 1 cm in diameter. Serial magnetic resonance images were obtained for volumetric analysis. The trial commenced at a dose of 10(6) plaque forming units (p.f.u.) inoculated at a single enhancing site and was completed when the 21st patient was inoculated with 3x10(9) p.f.u. at five sites. While adverse events were noted in some patients, no toxicity or serious adverse events could unequivocally be ascribed to G207. No patient developed HSV encephalitis. We found radiographic and neuropathologic evidence suggestive of anti-tumor activity and long-term presence of viral DNA in some cases.

Replicating herpes simplex virus vectors for cancer gene therapy

Attenuated viral vectors based on herpes simplex virus (HSV) are capable of killing cancer cells directly while sparing normal tissue in animal models of disease. This selective ability is likely due to the evolutionary constraints on the virus to establish lifelong infection in its host without causing destruction of normal tissues. However, extensive experimental animal data show that cancer cells are able to sustain a productive viral infection, which ultimately leads to cell death and tumour regression. Moreover, preliminary results generated in two Phase I clinical studies of modified replicating HSV for the treatment of brain tumours (e.g., glioblastoma multiforme) have been encouraging and suggest that the safety data generated in animals are predictive of human safety. Although much progress has been made in developing oncolytic HSV vectors for clinical use, there is still a long way to go to determine which combinations of virus, surgery, radiation and chemotherapy will provide improved therapy for the control and eradication of a variety of human cancers.

Targeted cytotoxic gene delivery to malignant gliomas via the fibroblast growth factor receptor

Object

The use of gene therapy for the treatment of malignant gliomas has been disappointing. In an effort to increase the viral transduction efficiency in delivering cytotoxic genes to malignant gliomas, the authors have used a novel retargeting schema that redirects the adenovirus to fibroblast growth factor receptors present on the cell surface of both proliferating glioma cells and glioma endothelial cells.

Methods

Using this targeted adenovirus, the authors demonstrated an increase in expression of the luciferase marker gene in human glioma cells and glioma endothelial cells. Transduction with the herpes simplex thymidine kinase gene resulted in greater cytotoxicity when treated with ganciclovir for both cell types. This increased cytotoxity was sustained for up to 6 days after administration of ganciclovir.

Conclusions

The mechanism of cytotoxicity was determined to be apoptosis by using the terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling assay. Increasing the specificity of adenovirus targeting may be crucial to decrease the number of adenoviral vectors necessary to create adequate levels of gene transfer in malignant gliomas, thus reducing the risk of vector-related immunogenicity and toxicity, as well as increasing the overall effectiveness of cytotoxic gene therapy.

Corticosteroid administration does not affect viral oncolytic activity, but inhibits antitumor immunity in replication-competent herpes simplex virus tumor therapy

A multimutated, conditionally replicating herpes simplex virus type 1, G207, has been developed as an effective means of treating human malignant brain tumors. We have shown that intraneoplastic inoculation of G207 induces a specific and systemic antitumor immune response that plays an important role in the antitumor activity, in addition to the direct oncolytic action of G207. Since a large number of malignant brain tumor patients are treated with corticosteroids, it is important to evaluate whether the therapeutic efficacy of G207 is affected by corticosteroid-induced immunosuppression. For a tumor model, we used G207-permissive N18 murine neuroblastoma cells implanted subcutaneously in syngeneic A/J mice. Intraneoplastic inoculation of G207 (10(7) PFU) induced significant suppression of tumor growth whether or not dexamethasone (5 mg/kg) was given. When dexamethasone was given for an extensive time (16 days starting on day -2), all G207-treated mice showed tumor growth despite initial shrinkage, whereas in the saline group, four of eight of the G207-treated mice were cured. Dexamethasone administration significantly reduced serum neutralizing antibodies against G207 at 14 and 21 days after intraneoplastic G207 inoculation. However, there was no difference between the dexamethasone and saline groups in terms of the amount of infectious G207 isolated from tumors. Dexamethasone administration completely abolished G207-induced cytotoxic T lymphocyte activity against N18 cells. These results indicate that the oncolytic activity of G207 is retained under corticosteroid administration. However, intensive immunosuppression may diminish the long-term efficacy of G207 owing to suppression of tumor-specific cytotoxic T lymphocyte induction.