Hello, this is Eric Thompson, and I'm going to be discussing the oncolytic activity of the oncolytic poliovirus recombinant, PVS-RIPO, in medulloblastoma is mediated by oxidative distress. I have no relevant disclosures. So currently at Duke, we're enrolling patients into a phase 1b study of PVS-RIPO for recurrent malignant brain tumors in children, and this includes the pathologies medulloblastoma, ATRT, anaplastic ependymoma, and malignant glioma. We do know based on work in the lab that poliovirus receptor is avidly expressed in pediatric brain tumors, making these a good target for this entity. However, we don't completely understand the molecular mechanism of how the oncolytic process in medulloblastoma particularly works. So the objective of this study was to elucidate the mechanism of oncolysis of PVS-RIPO in order to improve its efficacy. So first, we demonstrated that PVS-RIPO effectively kills medulloblastoma in a dose-dependent manner, and this is a dose-response curve. On the y-axis is percent cell survival. On the x-axis is MOI, or a multiplicity of infection, and these different cell lines, including 8A, 283, 425, 458, and 556 are all different medulloblastoma cell lines that we looked at. Next we demonstrated that PVS-RIPO induces a profound oxidative stress response. So this is a flow cytometric quantification showing different cell lines on the x-axis here. And what's really interesting here is we found that the 283 cell line does not express a high degree of ROS, or reactive oxygen species, in response to the poliovirus like the other cell lines did, and even at the positive control, which is sodium hydroxide, was very resistant to this. Next, this is a glutathione assay, and the reduced glutathione is GSH, and this fits with our previous data in the reactive oxygen species. So glutathione, in its reduced form, combats oxidative stress. So it makes sense that 283 would have the highest baseline levels of glutathione, and the ratio of reduced glutathione to oxidized glutathione on the right panel. Next we combined known pro-oxidants with PVS-RIPO to see if this has a synergistic effect, and in fact we found this. So BSO is a profound oxidative stress inducer, and what we found was when we combined it, PVS-RIPO with BSO, there was somewhat of a synergistic effect here. This is also found in arastin, which is a potent oxidative stress inducer. In contrast, we found that antioxidants, such as glutathione, actually aggregate PVS-RIPO oncolysis, highlighted here in red. So in conclusion, we found that PVS-RIPO kills cells via an oxidative burst and subsequent apoptosis, that pro-oxidants enhance the efficacy of PVS-RIPO, antioxidants abrogate its efficacy, and we're currently studying the combination of pro- versus antioxidants in combination with PVS-RIPO in vivo. I'd like to acknowledge my funding for this, and my lab's funding for this work, primarily through the DoD grant and the Mussela Foundation, and particularly acknowledge Wafa Hassan, who did a lot of this work in my lab. Thank you very much.

PVS-RIPO

medulloblastoma

efficacy

oxidative stress response

combination therapy