With current treatment options, the five-year survival rate of patients with glioblastoma (GBM) is only 5%. Oncolytic viruses are promising treatments against solid tumors, including malignant gliomas. In a phase I clinical trial evaluating Delta-24-RGD, an oncolytic adenovirus characterized in our laboratory, 20% of recurrent GBM patients receiving the virus achieved a durable response, surviving more than 3 years from the time of treatment, suggesting the existence of a subgroup of patients who would respond to adenoviral treatments. The clinical trial also showed that the efficacy of Delta-24-RGD was due to not only direct tumor cell oncolysis, but also indirect activation of anti-tumor immune responses, a paradigm-shifting finding that radically repositions virotherapy as a type of immunotherapy. Therefore, understanding the interplay between the oncolytic effects of adenoviruses and the viral-mediated anti-glioma immune activation is critical in determining how to increase the efficacy of these promising agents. Our group generated and preclinically characterized an immune agonist-armed version of Delta-24-RGD, named Delta-24-RGDOX, which expresses the T-cell activator OX40L, which will be soon translated to the clinical setting. In this project, we aim to amplify the effect of Delta-24-RGDOX with the administration of inhibitors of the factors that maintain the immunosuppression characteristic of gliomas. Because indoleamine-2,3-dioxgenase (IDO) expression increases significantly after virus infection, we are particularly interested in developing strategies to downmodulate IDO during virotherapy. The catabolism of tryptophan by IDO has important metabolic effects in glioma cells. In addition, the metabolites of tryptophan, including kynurenine (Kyn), activate the aryl hydrocarbon receptor (AhR) that induces Treg differentiation and CD8+ T-cell dysfunction. The central hypothesis of this study is that therapy consisting of Delta-24-RGDOX in combination with IDO and AhR inhibitors will stimulate a cytotoxic immune effect and inhibit the suppressive immune response against the tumor cells, thereby providing a potential effective novel treatment for malignant gliomas. To test this hypothesis, we propose three aims:
Specific Aim 1 : Examine the activation of the IDO-Kyn-AhR pathway during the infection of gliomas with Delta-24-RGDOX oncolytic adenovirus;
Specific Aim 2 : Identify the metabolic and immune modifications in the tumor microenvironment produced by the inhibition of the IDO-Kyn-AhR pathway in gliomas treated with Delta-24- RGDOX;
and Specific Aim 3 : Test the combination of Delta-24-RGDOX and IDO/AhR inhibitors in pre- clinically relevant models of gliomas. This project is the next step in achieving our long-term goal of legitimizing viro-immunotherapy as standard treatment for malignant gliomas.
Malignant gliomas are among the most deadly human cancers. Enhancing Delta-24-RGDOX anti-glioma effects represents a major step forward in improving immunotherapy for cancer and in broadening the spectrum of treatments for patients with this deadly disease for whom there are currently only minimally effective therapies.
