Abstract PO-082: Radiation therapy enhances the potential of the oncolytic virus in the treatment of osteosarcoma

Abstract

Abstract Background: Combination of neoadjuvant chemotherapy and surgery is the standard treatment approach for osteosarcoma. Despite aggressive treatment protocol, ~40% of patients do not respond and relapse, the survival rate is poor for these patients. Conditionally replicative adenovirus (CRAds) destroying cancer cell while sparing normal cells is a new treatment approach for cancers. We developed a new oncolytic adenovirus which grows using mRNA stabilization system found in many cancer cells. Our recent report showed that this virus replicated in cancer cells where AU-rich element (ARE) containing mRNA is stabilized. ARE-mRNA is stabilized in the majority types of cancers mediate by binding with HuR (Human antigen R), which exports target ARE-mRNA to the cytoplasm. Radiotherapy (RT) is not a first-line treatment option for osteosarcoma as osteosarcoma cells are not killed by radiation easily. But in certain conditions radiotherapy can be used where surgical resection is not technically possible without undue morbidity or when surgery is refused. In response to ionizing radiation and UV radiation DNA damage response (DDR) can influence HuR action either by the increasing cytoplasmic HuR abundance or affecting the binding affinity to target ARE-mRNA. The purpose of the present study was to analyze the efficacy of the combination treatment of RT and oncolytic adenovirus for osteosarcoma. Materials and Methods: E4rof6-deleted adenovirus (dl355) and human osteosarcoma cell lines U2OS and Saos2 were used in this study. Cell viability assays were carried out to evaluate the cytotoxicity and synergism of dl355 and RT combination. Chou and Talalay’s median-effect method was used to calculate the combination index. CPE assay was used to assess the cytopathic effect of the combination. Viral replication with or without radiation combination was investigated by hexon staining. Western blot analysis was performed to examine viral protein expression. Results: We found that RT treatment enhanced the cytoplasmic relocalization of HuR; thus irradiation up-regulated the propagations of dl355. Also, radiation-induced upregulation of viral protein expression was observed by western blotting. The RT and dl355 combination treatment increased the cytolysis of U2OS, and Saos2 cells in a synergistic manner compared to RT or virus only. Conclusion: Radiotherapy up-regulated of oncolytic adenovirus, which grows using the ARE-mRNA stabilization system, and this cytolytic effect provides a rationale for this combination. This combination approach has the possibility of a promising strategy for osteosarcoma. Citation Format: Elora Hossain, Fumihiro Higashino. Radiation therapy enhances the potential of the oncolytic virus in the treatment of osteosarcoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-082.