Characterization of pancreatic lesions from MT-tgf alpha, Ela-myc and MT-tgf alpha/Ela-myc single and double transgenic mice

Abstract

In order to identify good animal models for investigating therapeutic and preventive strategies for pancreatic cancer, we analyzed pancreatic lesions from several transgenic models and made a series of novel findings. Female MT-tgf alpha mice of the MT100 line developed pancreatic proliferation, acinar-ductal metaplasia, multilocular cystic neoplasms, ductal adenocarcinomas and prominent fibrosis, while the lesions in males were less severe. MT-tgf alpha-ES transgenic lines of both sexes developed slowly progressing lesions that were similar to what was seen in MT100 males. In both MT100 and MT-tgf alpha-ES lines, TGF alpha transgene was expressed mainly in proliferating ductal cells. Ela-myc transgenic mice with a mixed C57BL/6, SJL and FVB genetic background developed pancreatic tumors at 2-7 months of age, and half of the tumors were ductal adenocarcinomas, similar to what was reported originally by Sandgren et al 1. However, in 20% of the mice, the tumors metastasized to the liver. MT100/Ela-myc and MT-tgf alpha-ES/Ela-myc double transgenic mice developed not only acinar carcinomas and mixed carcinomas as previously reported but also various ductal-originated lesions, including multilocular cystic neoplasms and ductal adenocarcinomas. The double transgenic tumors were more malignant and metastasized to the liver at a higher frequency (33%) compared with the Ela-myc tumors. Sequencing of the coding region of p16ink4, k-ras and Rb cDNA in small numbers of pancreatic tumors did not identify mutations. The short latency for tumor development, the variety of tumor morphology and the liver metastases seen in Ela-myc and MT-tgf alpha/Ela-myc mice make these animals good models for investigating new therapeutic and preventive strategies for pancreatic cancer.

Figure 1

Histological alterations of the pancreas from MT-tgfα transgenic mice. A: a representative area of the pancreas from a 3-month-old female MT100 mouse, showing formation of fibrosis, proliferating ductal lesions (arrow) that manifest intraductal mucinous changes. B: a pancreas from an 8-month-old female MT100 mouse showing prominent fibrosis and severe loss of acini, with features of chronic pancreatitis. C: hyperplastic ducts (arrows) in an islet resembling ductuloinsular body in humans, from a 6-month-old female MT100 mouse. D: Large necrotic areas seen in an islet, from a 6-month-old female MT100 mouse. E: Low magnification of multiocular cystic neoplasms from an 8-month-old female MT100 mouse. F: Well differentiated ductal adenocarcinomas with chronic pancreatitis, from a 6-month-old female MT100 mouse. G: A representative area of the pancreas from a 9-month-old female MT-tgfα-ES mouse, showing early formation of small cysts and fibrosis. H: A representative area of the pancreas from a 9-month-old male MT-tgfα-ES mouse, which was a littermate of the female shown in G. I: Immunohistochemical staining of TGFα in a 3-month-old female MT100 mouse, noting that within the same acinar-ductal loop, only the ductal cells, but not the acinar cells, are positive.

Figure 2

Alterations of the pancreas from Ela-myc transgenic mice. A: a photo showing a huge nodular pancreatic tumor (arrows). Note that one tumor nodule is in red color while other tumor nodules are in white color. B: liver metastases (arrows) of a pancreatic tumor. C: histological examination confirming that the liver tumors are pancreatic origin (acinar cell carcinoma). D: a typical histology of acinar cell carcinoma that shows red color macroscopically. E: a typical histology of the acinar cell carcinoma that shows white color macroscopically. Note that there are many apoptotic cells that are organized in clusters, coined as "death cell islands" (arrows). F: a typical area of mixed acinar and ductal adenocarcinomas. G: a pancreatic ductal adenocarcinoma. Note that the tumor contains abundant stroma. H: another typical ductal adenocarcinoma. I: an acinar cell carcinoma within an islet (arrow).

Figure 3

Histological alterations of the pancreas from MT-tgfα/Ela-myc double transgenic mice. A: multilocular cystic neoplasms mixed with acinar tumor cells (arrows). B: a large benign multilocular cystic neoplasm. C: a typical acinar cell carcinoma. D: one type of ductal adenocarcinoma. E: another type of ductal adenocarinoma. F: a much less differentiated ductal adenocarcinoma with feature of desmoplasia. G: a mixed acinar and ductal adenocarcinoma. H: an area showing feature of mouse PanIN3 or ductal adenocarcinomas (dark arrows) with acinar tumor cells (yellow arrows) in the surrounding. I: a tumor area showing squamous differentiation.

Figure 4

Immunohistochemical staining for c-Myc and TGFα in human pancreatic ductal adenocarcinomas. 4A, 4B and 4C: c-Myc staining showing that most tumor cells manifest positive nuclear staining. 4D and 4E: TGFα staining showing most tumor cells are positive for TGFα. Note that the staining is mainly localized in the cytoplasm of most tumor cells, but it is also localized in the nucleus (arrows) of some tumor cells. 4F: a "normal" area of pancreatic tissue adjacent to cancer, showing that ductal cells (arrows), but not acinar cells, are positive for TGFα.

Figure 5

Sequencing data of k-ras and Rb cDNA. Panel A, chromatogram showing nucleotide change of k-ras; panel B and C, chromatograms showing nucleotide changes of Rb; panel D, Comparison of part of the amino acid sequences of the Rb proteins among mouse, rat and human. The single-letter amino acid sequence of the mouse, rat and human Rb protein is represented. A vertical bar represents amino acid identity between any two of the three species.