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Abstract

Abstract

Pancreatic adenocarcinoma has a very poor prognosis with currently existing therapies prolonging patient life for only a few weeks. Therefore novel therapy options are urgently needed. Present theories maintain that only a small fraction of tumour cells (the cancer stem cells (CSC)) are responsible for the highly aggressive behaviour of pancreatic cancer. These cells show a stem cell like phenotype and a high resistance to chemotherapy. Oncolytic viruses are promising candidates for therapeutic agents. Besides being replicated inside of host cells they can be attenuated to malignant cells and armed with therapeutic genes that will be translated by infected cells. They were demonstrated to efficiently eliminate pancreatic CSC in vitro. A major issue limiting the efficiency of virus therapies so far is their delivery. Systemic injected viruses are cleared from the blood by the liver and inactivated by the immune system. To enhance delivery and shield the viruses from the host’s immune system mesenchymal stem cells (MSC) isolated from the bone marrow are used in the present project. MSC exhibit a strong homing ability towards tumour tissue. Migration assays in vitro ascertained that homing is still present after infection with the oncolytic adenoviruses. The invasion of tumour transplants in vivo was successfully demonstrated after injection of infected MSC into blood vessels. For the in vivo experiments xenografts transplanted to fertilized chicken eggs, where they formed stroma-enriched tumours resembling patient samples, were used. Infection with an oncolytic adenovirus markedly reduced tumour growth in this model. The infected tumours exhibited a strong cytopathic effect with altered morphology. Injection of adenovirus-infected MSC in arteries leading towards the tumour after transplantation reduced tumour growth depending of the adenovirus type used. Viruses with enhanced lytic or anti-tumourigenic activity showed a superior performance, while unmodified viruses did not reduce tumour growth. A TRAIL expressing virus demonstrated the strongest anti-tumourigenic effect. This was confirmed by a reduction of proliferation and CSC marker expression and elevation of apoptosis. Therefore, the application of oncolytic adenoviruses using MSC as cell carriers is a promising strategy in combating pancreatic cancer, especially when viruses with enhanced anti-tumour effects are used.