H-101 The development of oncolytic herpes simplex viruses for the treatment of glioblastoma multiforme
Authors: Whitley Richard 
Published: April 2019

In the pursuit of genes that influence the pathogenesis of herpes simplex virus (HSV), the γ134.5 gene was identified between the Roizman and Whitley laboratories. It is a diploid gene that maps in the inverted repeat of the UL segment of the genome. This gene controls neurovirulence, replicating in dividing cells but not post mitotic cells. Studies with an HSV deleted in both copies of γ134.5, demonstrated that direct intracerebral inoculation failed to result inmortality, even at doses of 106 viral particles. A virus in which the gene was re-engineered back into the genome resulted in neurovirulence equivalent to that of wild type virus. Further, it was recognized that this virus was capable of replicating in tumor cells, prompting studies in a variety of different tumor models. Among the most susceptible were cells obtained from patients with glioblastoma multiforme. This first-generation virus, G207, in addition to the deletion of both copies of the γ134.5 gene, also had a second site mutation in ribonucleotide reductase. This latter mutation was introduced to prevent the potential for reversion of G207 to wild type virus, ergo restoring its neurovirulence. In order to improve replication competence of G207, a second-generation virus, M032, was engineered that similarly had deletions in the γ134.5 gene but now expressed human-IL-12 which was capable of inducing an immune response in the brain as well also having anti-angiogenic properties.

In order to test the hypothesis that G207 had a biological effect, studies of intratumoral administration in, first, SCID mice and, then, immune competent mice demonstrated prolonged survival and, in some cases, survival with no evidence of residual tumor. Further, the kinetics of viral replication in these tumors was established which proved enhanced replication with M032 as compared to G207. To determine if it was possible to further enhance viral replication, low grade radiation was introduced into the experimental murine studies. In so doing, viral replication was enhanced by approximately one log additionally.

Biodistribution studies work performed in aotus monkeys proved safety with no evidence of toxicity. Importantly, attempts at reactivation of virus from sensory ganglia and the brain were unsuccessful. With these data, clinical grade production of virus was undertaken, according to GMP regulations.

Three phase 1B studies have been completed in adults with recurrent glioblastoma multiforme utilizing the first generation virus, G207. The studies were dose-escalating and undertaken to prove safety and potential efficacy. With the third study, low-dose radiation was added to the clinical protocol. The following findings were noted. First, there was no evidence of toxicity upon direct occupation of G207 into the tumor bed. Second, no patients excreted G207 from a peripheral site. Third, of the patients entered in the clinical trial, 5 of 27 were long term survivors with no evidence of residual tumor >3 years after inoculation. For our adult studies, M032 was introduced into a similar population to again determine safety and the potential for efficacy in a dose-escalating fashion. These studies are ongoing.

In parallel, studies in children with recurrent glioblastoma multiforme have been initiated with G207. Parenthetically, G207 replicates by a log greater in pediatric tumors as compared to those of adults. The results obtained to date again indicated no evidence of toxicity upon direct intratumoral inoculation in the brain and, more importantly, long-term survival several of these children both without evidence of relapse and an improved Karnosky performance score (5 of 7 patients). Serial imaging of these children demonstrates continued improvement 18 months after a single treatment.

These data taken together for both viruses indicate safety of intracerebral inoculation of an engineered HSV. Specifically, in no patient was there evidence of herpes encephalitis or any other form of encephalitis. In addition, while the data are limited, preliminary findings suggest a beneficial survival effect for the children who participated in this trial. The results of the adult studies with M032 are ongoing. Serial outcome data, including radiological responses will be presented.