Patient-derived xenograft model of well-differentiated pancreatic neuroendocrine tumor in immunodeficient Balb/c Nude mice

Background: Orthotopic patient-derived xenografts (PDX) in immunodeficient mice are recognized as the most adequate neoplastic model due to their ability to maintain primary tumor properties after implantation. They can be used to study anti-neoplastic effects of pharmacological substances in vivo and to investigate characteristics and mechanisms of carcinogenesis. Results of preclinical studies of pharmacological substances obtained with PDX models are virtually no different from those of subsequent clinical trials. Aim: To develop an orthotopic PDX model of a highly differentiated human pancreatic neuroendocrine tumor (pNET) by implanting a fragment of the patient's tumor into the pancreas of immunodeficient mice. Materials and methods: A tumor fragment was obtained from a patient with a highly differentiated pNET G2 and liver metastasis. Fifteen (15) male immunodeficient Balb/c Nude mice with a mass of 22-24 grams were used to establish the orthotopic PDX model of human well-differentiated pNET. A fragment of primary pNET was orthotopically transplanted into the pancreas of 10 animals. A fragment of the metastatic lesion was transplanted into the liver of 5 animals. The animals were followed for up to 45 days. In vivo monitoring of the tumor growth was performed with a magnetic resonance imaging (MRI) system (ClinScan, Bruker BioSpin, Rheinstetten, Germany). At the end of the experiment, animals were euthanized and autopsies were performed, with routine histopathological examination and immunohistochemical study with antibodies to human chromogranin A, synaptophysin, and the marker of proliferative activity (Ki-67) of both original donor tumor and orthotopic pancreatic and liver xenografts. Results: Obvious changes in the mice condition were noticed at 30 days after surgery. They manifested as an increase in abdominal distension, swelling, and cyanosis in the projection of the pancreas. MRI showed a homogeneous neoplasm in the pancreas. At autopsy, the engraftment rate was 73% of all study animals, with yellow masses with even contours and a volume of about 100 cm³ present within the yellow-pink pancreatic tissues. The morphological assessment showed histological similarity between the original patient's tumor and patient-derived xenografts, which were identified as highly differentiated G2 pNETs. At immunohistochemical assessment, the patient's primary and metastatic tumor tissue specimens expressed anti-chromogranin A (full-blown cytoplasmic reaction) and anti-synaptophysin (mild cytoplasmic reaction) antibodies. Ki-67 was positive in 5.2% of the cells. An immunohistochemical study of the orthotopic tumor fragments and heterotopic tumor fragments showed moderate cytoplasmic staining with antibodies to chromogranin A and synaptophysin. The rate of Ki-67 in the orthotopic pNET model and metastatic model does not exceed 5% and 8%, respectively. Conclusion: Engraftment of tumor material after transplantation of human pancreatic cancer was observed in 73% of the cases, which should be considered a good first passage implantation result. The morphological studies confirmed that the orthotopic PDX was a well-differentiated pNET, histologically corresponding to the donor tumor. The model created in the experiment mirrors the histological characteristics of the donor tumor and can be used in preclinical studies of new treatments for well-differentiated pNETs, including those of antitumor activity of new pharmacological substances.