External Beam Radiation Therapy and Enadenotucirev: Inhibition of the DDR and Mechanisms of Radiation-Mediated Virus Increase

Abstract

Ionising radiation causes cell death through the induction of DNA damage, particularly double-stranded DNA (dsDNA) breaks. Evidence suggests that adenoviruses inhibit proteins involved in the DNA damage response (DDR) to prevent recognition of double-stranded viral DNA genomes as cellular dsDNA breaks. We hypothesise that combining adenovirus treatment with radiotherapy has the potential for enhancing tumour-specific cytotoxicity through inhibition of the DDR and augmentation of virus production. We show that EnAd, an Ad3/Ad11p chimeric oncolytic adenovirus currently being trialled in colorectal and other cancers, targets the DDR pathway at a number of junctures. Infection is associated with a decrease in irradiation-induced 53BP1 and Rad51 foci formation, and in total DNA ligase IV levels. We also demonstrate a radiation-associated increase in EnAd production in vitro and in a pilot in vivo experiment. Given the current limitations of in vitro techniques in assessing for synergy between these treatments, we adapted the plaque assay to allow monitoring of viral plaque size and growth and utilised the xCELLigence cell adhesion assay to measure cytotoxicity. Our study provides further evidence on the interaction between adenovirus and radiation in vitro and in vivo and suggests these have at least an additive, and possibly a synergistic, impact on cytotoxicity.

The Role of Adenovirus in Cancer Therapy

“…In vivo experiments using xenograft models in SCID mice showed an additive, and possibly a synergistic, effect when combining EnAd (hybrid of two group B adenoviruses-Ad3 and Ad11p) with low-dosage radiation. This study complements previous findings of OAd having the potential to serve as radiosensitizers [8].…”

“…Moreover, they showed that Paclitaxel treatment synergistically enhanced the oncolytic activity of AdAREF (also known as Ad-fosARE) both in vitro and in vivo [6], and also demonstrated that the combination of adenovirus and Cisplatin increased cell killing and increased virus replication both in vitro and in vivo [7]. In terms of combination therapy, another interesting report in this issue by Pokrovska et al highlights the potential benefits of combining radiation therapy with oncolytic viruses [8]. In vivo experiments using xenograft models in SCID mice showed an additive, and possibly a synergistic, effect when combining EnAd (hybrid of two group B adenoviruses-Ad3 and Ad11p) with low-dosage radiation.…”

En Guard! The Interactions between Adenoviruses and the DNA Damage Response

“…Because numerous Ad proteins, and especially E4 proteins, contribute to inhibition of the DDR and, therefore, sensitize cells to the toxic effects of DNA damage, it was suggested that addition of DNA-damaging drugs or irradiation may synergistically augment cancer virotherapy by oncolytic Ads. This hypothesis was confirmed by several studies [ 158 , 159 , 160 ]. In such studies, utilization of many different Ad vectors in various cell types as well as in tumor xenografts, demonstrated that a combination of Ad infection and DNA damage induced by drugs or irradiation was significantly more toxic than either treatment alone [ 160 , 161 , 162 , 163 ].…”

“…This hypothesis was confirmed by several studies [ 158 , 159 , 160 ]. In such studies, utilization of many different Ad vectors in various cell types as well as in tumor xenografts, demonstrated that a combination of Ad infection and DNA damage induced by drugs or irradiation was significantly more toxic than either treatment alone [ 160 , 161 , 162 , 163 ]. Moreover, DDR inhibition by drugs also enhanced the impact of oncolytic viruses in tumor cells [ 158 , 159 ].…”

Clinical landscape of oncolytic virus research in 2020

“…Prodrugs and radiation therapy were also being investigated in combination with OV; and there is clinical data supporting these concepts. [27][28][29] The use of chemotherapy may be a reflection of the tumors being studied and indeed the most common regimens were not specified with the selection of the chemotherapy left to investigator choice or carboplatin/paclitaxel regimens, commonly used in studies of patients with non-small cell lung cancer. Chemotherapy administration did appear to be associated with expected adverse events but it did not appear to be significantly worse with associated OV treatment.…”