Abstract 5651: p53-mediated apoptotic signaling overcomes the resistance to oncolytic adenovirus in human osteosarcoma cells

Abstract

Abstract Despite major advances in the treatment of bone and soft tissue sarcomas, about one fourth of the patients show a poor response to conventional therapy, resulting in subsequent recurrence and leading to a poor prognosis. Therefore, the development of a novel therapeutic strategy is required to cure patients with bone and soft tissue sarcomas. We previously developed an oncolytic adenovirus, OBP-301, in which human telomerase reverse transcriptase (hTERT) gene promoter drives viral E1 gene for replication. OBP-301 induces tumor-specific oncolytic cell death in a telomerase-dependent manner. Recently, we revealed that OBP-301 shows cytopathic activity in human bone and soft tissue sarcoma cells. However, some human osteosarcoma cells were less sensitive to cytopathic activity of OBP-301. To enhance the cytopathic activity of OBP-301, we recently developed a novel telomerase-specific oncolytic adenovirus, OBP-702, which expresses tumor suppressor p53 gene. In this study, we investigated the antitumor effect of OBP-702 in OBP-301-sensitive (OST, HOS and U2OS) and OBP-301-resistant (MNNG/HOS and SaOS-2) human osteosarcoma cells. We compared the antitumor effects of OBP-702 and OBP-301 using XTT assay. The 50% inhibiting dose (ID50) value of OBP-702 and OBP-301 for each cell was calculated using cell viability data obtained on day 5 after virus infection. We further evaluated the expression of p53, p21 and cleaved poly (ADP-ribose) polymerase (PARP) proteins using western blot analysis in both OBP-301-sensitive and OBP-301-resistant osteosarcoma cells after infection with OBP-702 or Ad-p53, which is a p53-expressing replication-defective adenovirus. OBP-702 showed more cytopathic activity compared to OBP-301 in both OBP-301-sensitive and OBP-301-resistant osteosarcoma cells. The ID50 value of OBP-702 was lower than that of OBP-301 in all cell lines. OBP-702 induced not only oncolysis, but also apoptotic cell death with the cleavage of PARP. OBP-702 infection induced more profound p53 expression than Ad-p53. However, p53-downstream target p21 proteins were not activated by OBP-702. Taken together, we demonstrated that the p53-expressing oncolytic adenovirus OBP-702 has a much stronger antitumor effect than OBP-301 in human osteosarcoma cells. Oncolytic adenovirus-mediated p53 gene transduction would induce profound apoptosis through p53 upregulation without p21 activation, resulting in the enhancement of antitumor effect by OBP-301. OBP-702 would be a promising antitumor reagent for the treatment of OBP-301-resistant human osteosarcoma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5651. doi:1538-7445.AM2012-5651