Prädiktive und prognostische Marker in pankreatischen neuroendokrinen Neoplasien in vitro und in vivo

Pancreatic neuroendocrine neoplasms (PNEN) form a rare and heterogenous group of tumors that originate from the endocrine cells of the pancreas. Biomarkers that allow an effective selection of patients for individualized systemic chemotherapy, as well as markers of prognostic relevance for the course of the disease however are still lacking. Therefore, the aim of this work was to identify and evaluate potential biomarkers in vitro, in a xenograft mouse model and in human tissues. The transcription factor CUX1, which is known to regulate genes implicated in proliferation, resistance to apoptosis and cell migration mechanisms was in focus of this study. Previous investigations performed by our group showed that the CUX1 expression is significantly increased in invasive human insulinomas. Stably overexpressing CUX1 Bon1 cells demonstrated in vitro the pro-proliferative, anti-apoptotic and pro-angiogenic properties of CUX1 in vitro. In the current work, these tumorigenic features of CUX1 were confirmed using a xenograft mouse model. CUX1 overexpressing tumors significantly modulated proliferation and apoptosis detected via immunohistochemistry. Based on these in vitro and in vivo data, another objective was to evaluate the relevance of the transcription factor CUX1 in patients with PNEN who had received a 5-fluorouracil (5-FU)- or dacarbazine (DTIC)-based chemotherapy. In patients with a 5-FU-based therapy a strong immunohistochemical CUX1 expression was associated with a significantly shorter progression free survival (PFS). However, neither the proliferation index Ki-67 nor overall survival correlated with CUX1 expression. Searching for proliferation-independent mechanisms mediating CUX1-induced resistance to chemotherapy, potential CUX1-associated miRNAs and drug metabolismassociated enzymes were evaluated. However, no miRNAs were identified that were conclusively are regulated by CUX1. Likewise, the enzymes thymidylate synthase (TS), dihydropyrimidine dehydrogenase (DPD) and O-6-methylguanine-DNA methyltransferase (MGMT) exhibited no CUX1-dependent regulation. Since literature reports suggest that these enzymes could have prognostic and predictive significance in other tumor entities, the expression levels were evaluated in tissue samples of a PNEN cohort. The increased DPD expression was significantly correlated with the increased objective response rate (ORR). TS was associated with prolonged progression free survival (PFS) and showed a non-significant trend towards prolonged disease control rate (DCR). In contrast, MGMT showed no prognostic or predictive value in patients who received a DTIC-based therapy. Potential biomarkers, as described in this study, should be further evaluated in prospective trials.