Abstract 5402: Enhancing autophagy as a novel approach to target osteosarcoma: combination of Oncolytic adenovirus and chemotherapy

Abstract

Abstract Osteosarcoma is the most common malignant bone tumor of childhood and adolescence. Despite multiagent chemotherapy and aggressive surgical resection, 30% of patients with localized disease and 70% of patients with metastatic disease at diagnosis will relapse. Therefore, new therapies are desperately needed. Autophagic cell death is a type of programmed cell death that is an alternative to apoptosis. The morphologic and biochemical features of autophagic cell death and apoptosis are generally distinct and it is therefore very likely that cells that are resistant to apoptosis would display permeable autophagy pathways. If this is the case, the development of autophagy-inducing treatments could be critical to improving the therapy for pediatric osteosarcoma. Recent reports have shown that conditionally replicating adenoviruses cause autophagic cell death. Autophagy (rather than apoptosis) has also been described in sarcoma cells treated with chemotherapeutic agents such as doxorubicin. This study was designed to ascertain whether the combination of the oncolytic adenovirus Delta-24-RGD with doxorubicin (DOX), cisplatin (CDDP) and methotrexate (MTX) would result in an enhanced antisarcoma effect in vitro and in vivo, and whether this combination treatment induces autophagy. In order to characterize the therapeutic potential of Delta-24-RGD in pediatric osteosarcoma, we first performed in vitro studies using 4 different pediatric osteosarcoma cell lines that have been established from patients with metastatic disease: 531MII, 678R, 588M, and 598M. Infectivity studies showed that all the cell lines were susceptible to the Delta-24-RGD infection ranging from 60 to 100% of infected cells at 25 MOI. Delta-24-RGD showed cytopathic effect and replication capacity in all cell lines. Interestingly, the 531MII cell line which has LOH of the RB gene was the most responsive to the oncolytic effect of the virus. Viability assays showed that DOX, CDDP and MTX antitumoral activity was synergistically enhanced by combination with Delta-24-RGD, lowering the IC50 for each of the drugs in at least two logs of concentration. Treatment with either DOX or CDDP resulted in G2-M cell cycle arrest that was overcome by the combination with Delta-24-RGD, indicating that addition of the virus sensitizes these cells to the drugs antitumor effect. Of importance, combination treatment of Delta-24-RGD with either drug induced autophagic cell death as shown by increase in the % of acidic vesicles and LC3 conversion. At the moment, in vivo experiments are on going. In this work we demonstrate that combination of the oncolytic adenovirus Delta-24-RGD with DOX, CDDP or MTX resulted in synergistic cytotoxicity through autophagic cell death. Our data suggests that exploiting autophagic cell death could provide new approaches to antisarcoma therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5402. doi:10.1158/1538-7445.AM2011-5402