Abstract 5188: Molecular radiosensitization in soft tissue sarcomas by telomerase-specific oncolytic adenovirus
Authors: Komatsubara Tadashi , Omori Toshinori , Tazawa Hiroshi , Sugiu Kazuhisa , Mochizuki Yusuke , Yamakawa Yasuaki , Osaki Shuhei , Hasei Joe , Fujiwara Tomohiro , Kunisada Toshiyuki , Urata Yasuo , Ozaki Tsoshifumi , Fujiwara Toshiyoshi 
Published: July 2017

INTRODUCTION:Treatment options for soft tissue sarcoma (STS) include surgical resection and adjuvant chemotherapy and radiotherapy. Despite the development of combined modality treatments in recent years, a significant proportion of patients with sarcomas respond poorly to adjuvant therapy, leading to local recurrence or distant metastasis. Therefore, there is an urgent need to develop novel therapeutic strategies for improvement of patient prognoses. We previously reported the therapeutic potential of OBP-301, a telomerase-specific oncolytic adenoviruses, and OBP-702, an armed OBP-301 expressing the wild-type p53 tumor suppressor gene against bone and soft tissue sarcoma cells. Furthermore, the synergistic anti-tumor effect of OBP-301 in combination with radiation has been observed. While OBP-702 suppressed the viability of OBP-301-sensitive and -resistant osteosarcoma cells more efficiently, the combination effect of OBP-702 and radiotherapy has been unknown. In this study, we investigated the radiosensitizing effect of OBP-702 against human STS cells.

METHODS:We used four human STS cell lines, HT1080 (fibrosarcoma), NMS-2 (malignant peripheral nerve sheath tumor), and SYO-1 (synovial sarcoma). Cells were irradiated 24 h after infection with OBP-301 and OBP-702, and cell viability was assessed by XTT assay 4 days after irradiation. Combined effect of radiation with OBP-301 and OBP-702 was analyzed with the CalcuSyn software (BioSoft). These cells were also analyzed for apoptosis and DNA damage using Western blot analysis.

RESULTS:While OBP-301 and OBP-702 showed anti-tumor effect for STS cell lines respectively, HT1080 and NMS-2 were highly resistant to radiation. When combined with radiation, not only OBP-301 but also OBP-702 enhanced the inhibitory anti-tumor effect in all STS cell lines. The calculation of combination index demonstrated additive or synergistic anti-tumor effect in combination therapy. Further analysis revealed that OBP-301 and OBP-702 increased radiation-induced apoptosis in STS cells. Notably, the radio-sensitizing effect of OBP-702 was associated with increase of p53 expression and interruption of anti-apoptotic myeloid cell leukemia 1 (MCL1) expression.

DISCUSSION:Our study demonstrated that OBP-702 had much stronger anti-tumor effect compared to OBP-301, and sensitized radiotherapy to various types of osteosarcoma cell lines. Currently, the clinical trial of OBP-301 is performed, and preclinically OBP-702 accumulates good therapeutic results in various tumors. Thus, OBP-702 may provide a novel treatment strategy for STSs and wide application of radiotherapy for localized as well as advanced STSs.

Citation Format: Tadashi Komatsubara, Toshinori Omori, Hiroshi Tazawa, Kazuhisa Sugiu, Yusuke Mochizuki, Yasuaki Yamakawa, Shuhei Osaki, Joe Hasei, Tomohiro Fujiwara, Toshiyuki Kunisada, Yasuo Urata, Tsoshifumi Ozaki, Toshiyoshi Fujiwara. Molecular radiosensitization in soft tissue sarcomas by telomerase-specific oncolytic adenovirus [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5188. doi:10.1158/1538-7445.AM2017-5188