A Phase I Trial of IRS-1 HSV C134 Administered Intratumorally in Patients With Recurrent Malignant Glioma

The efficacy of herpes simplex virus (HSV) as a treatment for brain tumors has been demonstrated experimentally. The earliest studies used an HSV that was genetically engineered so that the gene for an important enzyme, thymidine kinase (tk) was deleted. This engineered virus still killed tumor cells but was not toxic. Martuza and colleagues demonstrated that tumors implanted in mice shrank following treatment with varying doses of this virus.

Additional modified viruses based on the HSV backbone have been developed and tested with encouraging results.Viruses containing deletions in other important viral genes (e.g., DNA polymerase and the gene which can make the virus neurotoxic, γ134.5), also retained the capability of killing cultured human tumors but did not injure mice; in particular, they were safe for use in the brain. These viruses retained the viral tk gene, and so are susceptible to the antiviral drug acyclovir which is routinely used to treat HSV Infection, making them even more safe .

Martuza and colleagues generated G207, a modified HSV that contains (1) deletions of both copies of γ134.5 and (2) another gene called ribonucleotide reductase, was disabled secondary to disruption of the U139 gene by insertion of the E. coli LacZ coding region . G207 significantly prolonged survival of nude mice bearing human tumors. In addition, virus injected into the brains of the HSV sensitive primates (Aotus) did not produce any deleterious side effects.

G207 and 1716 have both been used in human trials. A dose-escalating phase 1 study of G207 was completed in patients with recurrent, progressive malignant glioma . The trial was conducted at University of Alabama at Birmingham and Georgetown University Medical Center. Twenty-one patients were enrolled in a total of seven dose-escalating cohorts, with three patients per cohort. Patients were stereotactically inoculated with G207 in the enhancing portions of their tumors. Five separate loci were inoculated in the final cohort; all previous cohorts were inoculated in a single locus within the enhancing tissue only. No toxicity definitively related to G207 was observed at doses up to 3 x 109 plaque forming units (pfu-these are active viral particles). In fact, a toxic dose level was not attained during this trial. This was due to viral processing techniques, limiting the total dose that could be administered.

In a Phase IB study, six patients with recurrent, resectable malignant glioma were enrolled at the University of Alabama at Birmingham, in a trial examining a split dose administration strategy of G207. Patients underwent inoculation of G207 into their tumors, followed two to five days later by resection of the tumor and reinoculation of G207 into the tumor cavity. No dose limiting toxicities were seen in the trial, although one patient suffered a twelve hour period of mental status changes, weakness, and an elevated temperature when a protocol deviation resulted in an inadvertent partial dose of virus being administered intraventricularly, into the cerebrospinal fluid chamber of the brain. The patient fully recovered quickly and fully. One of the six patients went nearly two years before remote recurrence of her glioblastoma multiforme resulted in her death. A third study in 9 patients with recurrent malignant glioma was completed in which G207 was being administered followed by a single small dose of 5Gy of radiation. Nine patients were followed without any dose limiting toxicity, and some patients had remarkable responses to treatment. Currently, two clinical studies of oncolytic HSV are underway that examine G207 in pediatric patients as well as a novel oncolytic HSV expressing IL- 12, in adult patients. No findings of these two studies have yet been reported.