Oncolytic Virotherapy of Neuroendocrine Neoplasms with oncolytic measles vaccine virus

Abstract

Neuroendocrine neoplasms (NENs) comprise a heterogenous group of various malignancies and metastatic disease remains a challenge to treat, leading to a poor prognosis in advanced disease. Therefore, new therapeutic options are desperately needed. Oncolytic viruses are emerging as a new class of anticancer agents, which are successfully used in the treatment of various malignancies, amongst others for NENs. Measles vaccine virus (MeV) has a natural tropism towards tumor cells and has demonstrated strong tumoricidal effects on various tumors. Its efficiency can be further enhanced by the insertion of transgenes. In this thesis, a state-of-the-art suicide-gene (SCD) armed oncolytic measles vaccine virus (MeV-SCD) was tested in five well characterized NEN cell lines of different anatomic origin. First, it was shown that all tested NEN cell lines express the CD46-receptor which is necessary for cell entry of measles vaccine virus. Next, it was proved that measles vaccine virus can successfully infect NEN cell lines by exam ining primary infection rates by flow cytometry and fluorescence microscopy. Western blot analysis of measles vaccine virus N protein as well as SCD protein expression revealed effective replication of the virus and expression of its transgene in vitro. The kinetics of measles vaccine virus replication within NEN tumor cells was further analyzed by viral growth curves. Finally, by measuring cell viability via SRB assay, MeV was shown to be able to successfully oncolyse the NEN cell lines in a MOI-dependent manner. This oncolytic virus based tumoricidal effect could be further enhanced by the addition of the prodrug 5-FC, which is enzymatically converted into the common chemotherapeutic drug 5- FU within infected tumor cells only, thereby sparing healthy tissue and reducing potential side effects, thus exploiting MeV-SCD’s suicide-gene. Since 5-FU is used in clinical practice for NENs and showed high dose-dependent efficiency as a monotherapy in this thesis as well, applying it locally via virotherapy might be a huge benefit for patients suffering from NENs. Additionally, combinatorial regimens using the mTOR-inhibitor everolimus and the senes cence-inducing compound CX-5461 were employed. In summary, this thesis showed that MeV-SCD can successfully (i) infect, (ii) replicate in and (iii) finally oncolyse tumor cells of neuroendocrine origin in a MOI dependent manner, making it a promising treatment option for NEN patients in the future. However, further preclinical and clinical experiments are needed in order to evaluate its effi ciency in vivo and to optimize potential combinatorial therapeutic regimens.