Gene and Virotherapy Against Osteosarcoma

Osteosarcoma is a highly aggressive malignant tumor arising from the bone and most commonly affecting children and young adults. The aim of this experimental study was to investigate the utility of herpes simplex virus type 1 thymidine kinase/ganciclovir (HSV-TK/GCV) suicide gene therapy and oncolytic virotherapy against osteosarcoma. A high gene transfer rate is an important prerequisite for successful gene therapy. Therefore, the capacity of lenti-, adenoand Sindbis virus vectors to efficiently transfer a therapeutic gene into osteosarcoma cells was studied. Adenoand lentivirus vectors demonstrated successful transfer of HSV-TK – green fluorescent protein (TKGFP) suicide-marker fusion gene into three different osteosarcoma cell lines. The subsequent GCV treatment produced efficient cell killing in all of the studied osteosarcoma cell lines. However, since 100 % gene transfer rates cannot be achieved with current vector systems, lateral spread of the toxic effects to the neighbouring tumor cells, termed as a bystander effect, plays an important role in the eventual therapeutic outcome of the HSV-TK/GCV treatment. The extent of the bystander effect varied between different osteosarcoma cell lines, suggesting that there might be variation in the therapeutic efficacy between different osteosarcoma tumors or subpopulations of tumor cells in a single tumor. Evaluation of Sindbis virus vector led to the observation that this vector type could propagate in BHK-21 cells used for vector production. Since wild-type reversion of the vector with the two vector production systems used in this study has not been reported before, the underlying mechanisms of vector propagation were analyzed further to determine i) could the vector spreading be utilized to enhance gene transfer efficiency or ii) would it pose a safety risk. In addition to nonreplicative vectors, oncolytic viruses capable for selective replication in malignant cells and tumor cell killing have been studied against cancer. In this study, two oncolytic viruses, a conditionally replicating adenovirus ∆24 and an oncolytic Semliki Forest virus vector VA7-EGFP, were studied against osteosarcoma in vitro and in vivo. Both vectors could destroy human osteosarcoma cell cultures and showed therapeutic effects in subcutaneous human osteosarcoma xenograft tumors. Compared to ∆24, VA7-EGFP was more efficient and was evaluated further in a highly aggressive orthotopic mouse osteosarcoma model. In this model, intratumoral VA7-EGFP treatment significantly improved survival of the treated mice compared to control animals. As a conclusion, both HSV-TK/GCV approach and oncolytic virotherapy deserve further investigations to evaluate their effects in combination with the chemotherapeutic agents currently used against osteosarcoma. Moreover, it would be of great interest to combine these treatment strategies to immunopotentiation gene therapy to enhance their efficacy against distant osteosarcoma metastases. National Library of Medicine Classification: QW 165.5, QZ 52, QZ 65, WE 258 Medical Subject Headings: Adenoviridae; Cell Line, Tumor; Cell Survival; Gene Deletion; Gene Therapy; Gene Transfer Techniques; Genes, Transgenic, Suicide; Genetic Vectors; Helper Viruses; Herpesvirus 1, Human; Lentivirus; Oncolytic Virotherapy; Osteosarcoma; Semliki forest virus; Sindbis Virus; Thymidine Kinase; Virus Replication