MIST · Application of Mesenchymal stem cells in tumour therapeutic approaches

Final Activity Report Summary - MIST (Application of Mesenchymal Stem Cells in Tumour Therapeutic Approaches)

Our main goal was to develop a cell-gene therapy system based on mesenchymal stem cells (MSCs) to deliver the cancer cell-killing protein TRAIL to tumours. First, we demonstrated the feasibility of our approach in a lung cancer model. We demonstrated the ability of an adenoviral vector expressing TRAIL (Ad.TR) to transduce MSCs and show the apoptosis-inducing activity of these TRAIL-carrying MSCs on A549 lung carcinoma cells. Intriguingly, using MSCs transduced with Ad.EGFP we could show transfer of viral DNA to co-cultured A549 cells resulting in transgenic protein production in these cells, which was not inhibited by exposure of MSCs to human serum containing high levels of adenovirus neutralising antibodies. Furthermore, Ad.TR transduced MSCs were shown not to induce T-cell proliferation, which may have resulted in cytotoxic T-cell mediated apoptosis induction in the Ad.TR transduced MSCs. Apoptosis was also induced in A549 cells by Ad.TR transduced MSCs in the presence of physiological concentrations of white blood cells, erythrocytes and sera from human donors that inhibit or neutralise adenovirus alone. Moreover, we could show tumour growth reduction with TRAIL-loaded MSCs in an A549 xenograft mouse model. This was the first study that demonstrated the potential therapeutic utility of Ad.TR transduced MSCs in cancer cells and the stability of this vector in the context of the blood environment. However, further improvements were needed and were introduced to our system, in order to better tackle the primary tumour but also to reach disseminated tumour cells and metastases. Disseminating tumours are one of the gravest medical problems. We combined the tumour-specific apoptosis-inducing activity of TNF-related apoptosis-inducing ligand (TRAIL) with the ability of MSCs to infiltrate both tumour and lymphatic tissues to target primary tumours as well as disseminated cancer cells in a human pancreatic cancer mouse model. Furthermore, we targeted XIAP by RNAi inside the cancer cells to make use of the apoptosis sensitisation as well the anti-metastatic effect that is afforded by XIAP silencing. We generated MSCs, termed MSC.sTRAIL that express and secrete a trimeric form of soluble TRAIL (sTRAIL). MSC.sTRAIL triggered limited apoptosis in human pancreatic carcinoma cells that were resistant to soluble recombinant TRAIL, which is most likely due to the enhanced effect of the direct, cell mediated delivery of trimeric TRAIL. MSC.sTRAIL-mediated cell death was markedly increased by concomitant knockdown of XIAP by RNAi in the cancer cells. These findings were confirmed in xenograft models, in which tumours from the parental pancreatic carcinoma cells showed only growth retardation upon treatment with MSC.sTRAIL, whereas tumours with silenced XIAP that were treated with MSC.sTRAIL went into remission. Moreover, animals with XIAP-negative xenografts treated with MSC.sTRAIL were almost free of lung metastasis, whereas animals treated with control MSCs showed substantial metastatic growth in the lungs. In addition, we could not detect any side-effects of the treatment in the animals. In summary, we demonstrated that a combined approach using systemic MSC-mediated delivery of sTRAIL together with XIAP inhibition suppresses metastatic growth of pancreatic carcinoma. In conclusion, we have generated a safe and efficacious cell-gene therapy system based on MSCs that is capable to deliver TRAIL not only to primary tumours, but also to metastatic lesions, and provides a novel therapeutic avenue for the treatment of cancer that warrants further exploration in the future.

Data: CORDIS, © European Union