Vanadate disrupts mammary gland development in whole organ culture.

Protein tyrosine kinases and phosphatases are signaling molecules involved in all aspects of development, including proliferation, differentiation, and apoptosis. How disruption of protein tyrosine phosphatase affects mammary gland development is not entirely clear. We examined the effects of sodium vanadate, which is known to primarily inhibit tyrosine phosphatases, in mouse mammary gland development in whole organ culture. Mammary epithelial differentiation was effectively inhibited by vanadate in a dose-dependent manner as indicated by lack of epithelial alveoli compared to the contralateral non-treated gland controls. Mammary glands in the differentiation medium after four days in the presence of vanadate did not differentiate into alveoli. Instead, they exhibited prominent terminal end buds and lost the distinctive epithelial structures. The inhibitory effect of vanadate on mammary epithelial cell differentiation was irreversible after one day of treatment. Immunohistochemical staining for PCNA (Proliferating Cell Nuclear Antigen) showed that vanadate-treated glands exhibited elevated proliferation signals in the differentiation medium. Expression of beta-casein protein in the vanadate-treated glands decreased dramatically and progressively. Short-term exposure (up to 72 hours) of mammary glands to vanadate resulted in an increase in mammary epithelial cell density and loss of organization of the mammary structures. TUNEL assay of mammary glands with prolonged exposure to vanadate revealed widespread apoptosis. Furthermore, some cells were still proliferating or expressing beta-casein after prolonged exposure to vanadate. Taken together, these data indicate that vanadate treatment blocks mammary epithelial cell differentiation and promotes abnormal proliferation and apoptosis, likely through the inhibition of protein tyrosine phosphatase-mediated signaling.

Evaluation of three lines of immunodeficient mice for the study of spontaneous metastatic tumors.

Various immunodeficient animals have been used as transplantation recipients for studying the growth of human tumors. We have been assessing the value of immunodeficiencies for the study of naturally arising tumors, using a model system of transgenic mice that spontaneously develop cancer of the pancreas as a result of elastase promoter-driven expression of the large tumor antigen gene of simian virus 40. We previously reported the establishment of transgenic mice that carried the SCID and/or beige mutations, eliminating B- and T-cell function and reducing lytic NK cell activity, respectively. In SCID beige animals, metastasis rates and target organs for metastases were similar to those observed in humans with pancreatic cancer. We describe here analysis of subsequent more highly inbred generations of these mice. The data show that inbreeding has almost negated the value of these immunodeficiencies for enhancing disease progression, and we observe high rates of metastasis even in immunocompetent animals. The data suggest that SCID and beige immunodeficiencies may not always have the same value for the modeling of spontaneous tumors as they do for the study of xenografts.

Enhancement of pancreatic tumor metastasis in transgenic immunodeficient mice.

Metastatic pancreatic cancer presents a bleak prognosis. Typically, human tumor development has been modelled in animals by generating transgenic mice carrying an oncogene, and metastasis studied by engrafting human tumor cells into immunodeficient mice. We derived mouse lines that spontaneously develop metastatic pancreatic cancer by crossing a transgenic line that develops primary pancreatic adenocarcinomas with lines that are deficient for different lymphocyte components of the immune system. We obtained transgenics carrying the SCID mutation resulting in loss of B and T cell function, those carrying the beige mutation resulting in impaired NK cell and macrophage activity, and those carrying both mutations. Although human graft studies indicated that the SCID mutation permits metastasis of different types of tumor cells, in our mice its effect on metastasis of the pancreatic tumor was minimal. In contrast, the beige mutation resulted in metastasis in almost 90% of the animals. The SCID and beige mutations synergistically resulted in faster growing tumors. Both primary tumors and metastases contained undifferentiated and differentiated cell types. The tissue distribution of metastases was similar to that recorded from human patients with pancreatic cancer, suggesting that mechanisms underlying metastasis in these mice could be similar to those involved in human disease.