HSV G207 With a Single Radiation Dose in Children With Recurrent High-Grade Glioma

Outcomes for children with recurrent or progressive high-grade glioma (brain tumor) are very poor, and there are a lack of effective salvage therapies once a patient fails standard treatments. Novel innovative treatments are greatly needed. G207 is an oncolytic herpes simplex virus-1 (HSV) that has been successfully engineered to introduce mutations in the virus that enable it to selectively replicate in and kill cancer cells, but not normal cells. Replication of G207 in the tumor not only kills the infected tumor cells, but causes the tumor cell to act as a factory to produce new virus. These virus particles are released as the tumor cell dies, and can then proceed to infect other tumor cells in the vicinity, and continue the process of tumor kill. In addition to this direct oncolytic activity, the virus engenders an anti-tumor immune response; the virus is immunogenic and produces a debris field which exposes cancer cell antigens to immune cells, which can target other cancer cells. Thus, the oncolytic effect of the virus and the immune response that the virus stimulates provide a dual attack against cancer cells. In preclinical studies, a single 5 Gy dose of radiation within 24 hours of virus inoculation to the tumor increased virus replication and tumor cell killing. Radiation may also enhance the immune response against the tumor. The University of Alabama at Birmingham has conducted three phase I trials of G207 injected into the recurrent tumor alone or combined with a single dose of radiation in adults with recurrent high-grade gliomas. In these trials, high doses (up to 3 x 10\^9 plaque-forming units) of virus were safely injected directly into the tumor or surrounding brain tissue without serious toxicities. Radiographic and neuropathologic evidence of an antitumor response was seen in some patients. Preclinical laboratory studies have demonstrated that a variety of aggressive pediatric brain tumor types are sensitive to G207. A Phase I study of intratumoral G207 alone or combined with a 5 Gy dose of radiation in children ages 3-18 with biopsy-confirmed recurrent/progressive supratentorial brain tumors recently completed the highest planned dose level (UAB1472; NCT02457845). The study used a 3 + 3 design with 4 dose cohorts.12 Patients underwent stereotactic placement of up to 4 intratumoral catheters. The following day they received a single controlled-rate infusion of G207 (1 x 10\^7 or 1 x 10\^8 pfu) over 6 hours. Cohorts 3 and 4 received a 5 Gy radiation fraction to the gross tumor volume within 24 hours of G207. Twelve subjects with progressive high-grade glioma received G207. Twenty adverse events, all grade 1, were attributed to G207. G207 was determined to be safe and tolerable in children and a recommended Phase 2 was established (1 x10\^8 followed by 5 Gy radiation to the tumor). This study is a phase II, open-label, single arm clinical trial of G207 alone or combined with a single low dose of radiation in children with recurrent or progressive high grade glioma. The primary objective is to assess the efficacy. The secondary objectives are to confirm the safety and tolerability of G207, to survey for virologic shedding following G207, to evaluate immunologic responses to G207, and to assess for radiographic changes from baseline. Subjects will receive G207 at 1 x 10\^8 plaque-forming units (pfu), intratumorally via controlled rate infusion through up to 4 silastic catheters over a 6 hour period. The subject will then receive a single 5 Gy dose of radiation to the tumor within 24 hours of virus inoculation.