Endocrine Abstracts

Pancreatic endocrine tumours (PETs) have a low proliferation index and this partially accounts for their lack of response to chemotherapy. The assessment of proliferation rates relies largely on the use of markers such as Ki67 in patients, and uptake of DNA nucleotide precursors such as tritiated thymidine or 5-bromo-2-deoxyuridine (BrdU) in animals. Amongst these, BrdU is recognised to be the most reliable marker of cell proliferation as it allows the substitution of an endogenous DNA base, thymidine, with the BrdU analogue, ensuring specific labelling during S-phase of only the dividing cells. We have therefore used continuous long-term BrdU labelling, to assess proliferation rates of PETs in a multiple endocrine neoplasia type 1 (MEN1) knockout mouse (+/−) model, which develops PETs that are predominantly insulinomas. Mice were kept in accordance with UK Home Office welfare guidelines and project licence restrictions. Drinking water containing BrdU at 1 mg/ml was given to wild-type (+/+) and Men1 (+/−) littermates for 1–12 weeks. Pancreatic sections were immunofluorescently labelled with DAPI, insulin and BrdU, and 6 islets or insulinomas from each of 4 animals per genotype were analyzed to determine the percent of BrdU-positive cells. The mean (±S.E.M.) proliferation rate of normal beta-cells in wild-type (+/+) mice was 0.075% (±0.010%) per day. In contrast, the mean proliferation rate of insulinoma cells in the Men1 (+/−) mice was significantly (P<0.001) higher at 0.323% (±0.031%) per day. These respective proliferation rates in the wild-type (+/+) and Men1 (+/−) mice, that had received BrdU for 1, 4, 8 and 12 weeks, were similar. Thus, our studies have established a method to measure the in vivo proliferation rates of insulinomas in Men1+/− mice, and this opens the way to assess the effectiveness of new therapies in reducing the growth of pancreatic endocrine tumours.