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Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal malignancies and new therapeutic options are urgently needed. Personalized tumor models derived from xenotransplantation of fresh patient tissue to mice are emerging as a promising tool for therapy studies, but ethical concerns, long experimental duration and high costs limit the efficacy. In the present study, we asked if the xenotransplantation of freshly resected PDA tissues to the chick chorioallantoic membrane (CAM) might be superior. Neoplastic tissue of pancreatic origin from 42 patients, including 23 PDA tumors, was transplanted to the CAM, which resulted in the growth of solid, neovascularized tumors. The median grafting efficiency of PDA tumors was 70 %, which was higher than in a murine model. The time until tumor growth became evident on the CAM (latency) was on average 3 days and thus shorter than that of tumors cultivated in mice. Importantly, the morphology with a pronounced tumor stroma resembled the primary tumors. The immunohistochemical analysis of the established markers for cancer stem cells (CSCs), k-Ras and fibronectin revealed that the histological features of the original tumors remain stable in their corresponding egg xenografts. Also, this model is suited for personalized therapeutic evaluation as shown by our data measuring tumor take, tumor volume and proliferation of untreated, gemcitabine and dexamethasone pre-treated tumors, as well as tumor volume and proliferation under in ovo treatment by intratumoral and intravenous injection of gemcitabine. Furthermore the cultivation of giant cell tumor of bone tumors (GCTBs), derived from stromal cells of 8 different patients and osteosarcoma tumors, derived from three cell lines, was established on the CAM. The replacement of rodent models with the CAM model may also contribute to a more ethical experimental technique. Fertilized chicken eggs are widely used in the biomedical research and have been suggested as an alternative to mammalian models.
Unfortunately, it is mostly not taken into account, that the chick embryo is susceptible to pain from day 7 of breeding. In my view, this model is only in accordance with the “3 R” principles of ethical experimentation, if an appropriate anaesthesia of the chick embryo in potentially painful procedures is provided. Although many experimental approaches are performed on the non-innervated CAM, the euthanasia of the embryo strongly requires a more humane technique than freezing at -20° C, decapitation or in ovo fixation with paraformaldehyde without prior anaesthesia. These methods are commonly applied and are not acceptable. However, protocols regarding feasible and ethical methods for anaesthesia and euthanasia of avian embryos are currently not available. Therefore, we established an easy and readily achievable method for the euthanasia and short-term anaesthesia of the chick embryo.
In summary, the CAM is a promising model to accelerate data acquisition in personalized medicine and to promote progress towards a more ethical biomedical research.