HGG-15. THE IMIPRIDONE ONC201 IN COMBINATION WITH THE ONCOLYTIC ADENOVIRUS DELTA-24-RGD HAS A SYNERGISTIC EFFECT IN PRECLINICAL MODELS OF PHGGS AND DMGS

Pediatric High Grade Gliomas (pHGGs), including Diffuse Midline Gliomas (DMGs), are aggressive pediatric tumors with a poor overall survival. In the last years, ONC201 has emerged as a promising agent in the field of pediatric brain tumors. Another interesting approach is virotherapy; Delta-24-RGD, which is an oncolytic virus, has demonstrated safety and effectiveness in different preclinical models and in clinical trials. Therefore, in this work we set to evaluate whether the combination of ONC201 with Delta-24-RGD could result in an increased therapeutic benefit in pHGGs and DMGs. Given that ONC201 targets mitochondrial metabolism in a preclinical setting, we assessed potential negative interactions of the combination therapy. While ONC201 treatment resulted in decreased viral protein load (E1A and fiber), there was no significant negative impact on the viral replication (measured by hexon staining). ONC201 did not disrupt the activation of mTORC1 pathway by the adenovirus. Furthermore, Delta-24-RGD did not affect the decrease in basal oxygen consumption rate induced by ONC201. Our results suggested that ONC201 and Delta-24-RGD are not antagonistic. Evaluation of the in vitro cytotoxicity in different human pHGG (CHLA-03-AA and SF188) and DMG (TP-54 and SU-DIPG-IV) cell lines showed that the combination treatment was significantly better that either agent alone. In vivo, a single local injection of Delta-24-RGD followed by a weekly ONC201 of mice bearing CHLA-03-AA cell line orthotopically significantly increased the median overall survival (PBS: 48 days; ONC201: 54.5 days; Delta-24-RGD: 62 days; ONC201+Delta-24-RGD: 95 days (P=0.0008)) of these mice leading to 20% long-term survivors, free of disease. Currently, we are evaluating the effect of the combination in immunosuppressed and immunocompetent models of DMGs. In summary, our data indicate ONC201 in combination with Delta-24-RGD could be a potential therapeutic choice for patients affected by pHGGs and DMGs.