Background: Oncolytic virotherapy is an upcoming treatment option for many tumor entities. But so far, a first oncolytic virus only was approved for advanced stages of malignant melanomas. Neuroendocrine tumors (NETs) constitute a heterogenous group of tumors arising from the neuroendocrine system at diverse anatomic sites. Due to often slow growth rates and (in most cases) endocrine non-functionality, NETs are often detected only in a progressed metastatic situation, where therapy options are

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... till severely limited. So far, immunotherapies and especially immunovirotherapies are not established as novel treatment modalities for NETs.Methods: In this immunovirotherapy study, pancreatic NET (BON-1, QGP-1), lung NET (H727, UMC-11), as well as neuroendocrine carcinoma (NEC) cell lines (HROC-57, NEC-DUE1) were employed. The well characterized genetically engineered vaccinia virus GLV-1h68, which has already been investigated in various clinical trials, was chosen as virotherapeutical treatment modality. Results: Profound oncolytic efficiencies were found for NET/NEC tumor cells. Besides, NET/NEC tumor cell bound expression of GLV-1h68-encoded marker genes was observed also. Furthermore, a highly efficient production of viral progenies was detected by sequential virus quantifications. Moreover, the mTOR inhibitor everolimus, licensed for treatment of metastatic NETs, was not found to interfere with GLV-1h68 replication, making a combinatorial treatment of both feasible. Conclusions: In summary, the oncolytic vaccinia virus GLV-1h68 was found to exhibit promising antitumoral activities, replication capacities and a potential for future combinatorial approaches in cell lines originating from neuroendocrine neoplasms. Based on these preliminary findings, virotherapeutic effects now have to be further evaluated in animal models for treatment of Neuroendocrine neoplasms (NENs).