K. Majumder1, S. Modi1, N. Arora1, R. Chugh1, A. Nomura1, S. Banerjee1, R. Dawra1, A. Saluja1, V. Dudeja1 1University Of Minnesota,Surgery,Minneapolis, MN, USA
Introduction: The development of novel therapeutics for pancreatic cancer has been hindered by a lack of relevant preclinical models. The introduction of the KPC (KrasLSL.G12D/+; p53R172H/+; PdxCretg/+) mouse model has shed some light on tumorigeneis and progression in pancreatic cancer and has been a step in the right direction. An accurate tumor model, besides recapitulating the tumorigenic properties, has to recapitulate the immune and stromal microenvironment, the components lacking in commonly used subcutaneous or orthotopic models in immunodeficient mice (SCID, Athymic nude). While these components are present in the KPC model, this genetic model is fraught with inconsistency making this unsuitable for study of various component of tumorigenesis as well as the study of novel therapies. For example, the time to invasive disease in this model varies from 47-355 days of life. The amount of pre-invasive disease and invasive adenocarcinoma varies between litter mates and up to 20% of animals never develop tumor. Furthermore, the entire pancreas in this model has Kras-p53 mutation as opposed to the sporadic mutations generally seen in human pancreatic cancer. We therefore propose a novel orthotopic tumor model with tumors from KPC mice implanted in C57Black6 mice, which recapitulates the tumor microenvironment and circumvents the drawbacks of the above mentioned models.
Methods: 6 month KPC mice with palpable pancreatic tumors were sacrificed and the tumors were cut into ~3mm3 pieces using core biopsy punch. Laparotomy was performed using a midline incision on female C57BL/6 mice and the tumor piece was sewn into a pocket of pancreas using a figure of 8 stitch of 7-0 prolene incorporating the superior and inferior border of the pancreas. Mice were sacrificed at two time points, 4-weeks and 8 weeks after implantation. Tumor volume and weight was measured. Stromal component and immune infiltration were studied by immunohistochemistry.
Results: Tumor take rate was ~90%. Tumor volume was very similar in all mice suggesting similar growth rate (tumor volume. 4 weeks: 331 ± 122 mm3, 8 weeks: 433 ± 77 mm3). Mortality at 8 weeks was ~20%. Immunohistochemistry confirmed presence of pancreatic adenocarcinoma at both time points. Staining for stromal components (collagen and αSMA) showed intense desmoplastic stromal reaction at both 4 and 8 weeks after implantation. CD45 staining demonstrated intense infiltration of tumor and surrounding pancreas with leukocytes.
Conclusion: The proposed model of pancreatic cancer offers all the advantage of state of the art genetic model along with the predictability of a conventional orthotopic model. This model mimics the stromal reaction and immune infiltration observed in human pancreatic ductal adenocarcinoma as well as circumvents the issue of variability seen in previous mouse models. This clinically relevant model can be a valuable tool to evaluate novel therapeutics in pancreatic cancer.