G207 is a conditionally replicating derivative of herpes simplex virus (HSV) type-1 strain F engineered with deletions of both ␥ 1 34.5 loci and a lacZ insertion disabling the U L 39 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 у70, recurrence despite surgery and radiation therapy, and an enhancing lesion greater than 1 cm in diameter.

We have created a double mutant of the herpes simplex virus (HSV) type 1 (termed G207) with favourable properties for treating human malignant brain tumours: replication-competence in glioblastoma cells (and other dividing cells), attenuated neurovirulence, temperature sensitivity, ganciclovir hypersensitivity, and the presence of an easily detectable histochemical marker. G207 has deletions at both gamma 34.5 (RL1) loci and a lacZ gene insertion inactivating the ICP6 gene (UL39). G207 kills human glioma cells in monolayer cultures. In nude mice harbouring subcutaneous or intracerebral U-87MG gliomas, intraneoplastic inoculation with G207 causes decreased tumour growth and/or prolonged survival. G207 is avirulent upon intracerebral inoculation of mice and HSV-sensitive non-human primates. These results suggest that G207 should be considered for clinical evaluation in the treatment of glioblastomas.

Herpes simplex virus type 1 (HSV-1) mutants that are attenuated for neurovirulence are being used for the treatment of cancer. We have examined the safety of G207, a multimutated replication-competent HSV-1 vector, in mice. BALB/c mice inoculated intracerebrally or intracerebroventricularly with 10 7 PFU of G207 survived for over 20 weeks with no apparent symptoms of disease. In contrast, over 80% of animals inoculated intracerebrally with 1.5 ؋ 10 3 PFU of HSV-1 wild-type strain KOS and 50% of animals inoculated intracerebroventricularly with 10 4 PFU of wild-type strain F died within 10 days. Similarly, after intrahepatic inoculation of G207 (3 ؋ 10 7 PFU) all animals survived for over 10 weeks, whereas no animals survived for even 1 week after inoculation with 10 6 PFU of KOS. After intracerebroventricular inoculation, LacZ expression was initially observed in the cells lining the ventricles and subarachnoid space; expression decreased until almost absent within 5 days postinfection, with no apparent loss of ependymal cells. G207 DNA could be detected by PCR in the brains of mice 8 weeks after intracerebral inoculation; however, no infectious virus could be detected after 2 days. As a model for latent HSV in the brain, we used survivors of an intracerebral inoculation of HSV-1 KOS at the 50% lethal dose. Inoculation of a high dose of G207 at the same stereotactic coordinates did not result in reactivation of detectable infectious virus or symptoms of disease. We conclude that G207 is safe at or above doses that were efficacious in mouse tumor studies.Herpes simplex virus type 1 (HSV-1) is a neurotropic DNA virus which infects a wide range of cell types in different animals. Natural infections either follow a lytic, replicative cycle or establish latency. Latency is characterized by the long-term persistence of viral DNA in latently infected neurons, the lack of infectious or replicating virus, the lack of viral gene expression except for the latency-associated transcripts (LATs), and in some situations episodic reactivation of infectious virus (74). In humans, the natural host, HSV-1 causes a number of diseases, including gingivostomatitis and pharyngitis after primary oral-facial infection, recurrent herpes labialis, genital herpes, keratitis after eye infection, disseminated visceral infections in immunocompromised patients, hepatitis, and encephalitis after spread to the central nervous system (CNS) (13).HSV encephalitis is the most common CNS viral infection, occurring in two to three persons per million (13). Brain pathology is usually localized to the temporal lobe and limbic system, with asymmetric necrotizing encephalitis, inflammation, and hemorrhage (19, 33). The majority of cases of encephalitis occur in patients with recurrent HSV who are seropositive at onset of disease. Even with acyclovir therapy, mortality is about 20%, and about 20% of survivors have longterm morbidity, including cognitive abnormalities (23, 51).A number of animal models of HSV encephalitis involving spread from peripheral in...

This study examined the safety of intracerebral inoculation of G207, an attenuated, replication-competent herpes simplex virus type 1 (HSV-1) recombinant, in nonhuman primates. Sixteen New World owl monkeys (Aotus nancymae [karyotype 1, formerly believed to be A. trivirgatus]), known for their exquisite susceptibility to HSV-1 infection, were evaluated. Thirteen underwent intracerebral inoculation with G207 at doses of 107 or 109 PFU, two were vehicle inoculated, and one served as an infected wild-type control and received 103 PFU of HSV-1 strain F. HSV-1 strain F caused rapid mortality and symptoms consistent with HSV encephalitis, including fever, hemiparesis, meningitis, and hemorrhage in the basal ganglia. One year after G207 inoculation, seven of the animals were alive and exhibited no evidence of clinical complications. Three deaths resulted from nonneurologic causes unrelated to HSV infection, and three animals were sacrificed for histopathologic examination. Two animals were reinoculated with G207 (107 PFU) at the same stereotactic coordinates 1 year after the initial G207 inoculation. These animals were alive and healthy 2 years after the second inoculation. Cerebral magnetic resonance imaging studies performed both before and after G207 inoculation failed to reveal radiographic evidence of HSV-related sequelae. Despite the lack of outwardly observable HSV pathology, measurable increases in serum anti-HSV titers were detected. Histopathological examination of multiple organ tissues found no evidence of HSV-induced histopathology or dissemination. We conclude that intracerebral inoculation of up to 109 PFU of G207, well above the efficacious dose in mouse tumor studies, is safe and therefore appropriate for human clinical trials.

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