Among the neoplastic disorders, preinvasive, microinvasive, and poorly differentiated neoplasms received the most attention. Specific criteria were recommended and will be discussed. Transitions between neoplastic states were of particular concern. Preinvasive neoplasias of the mouse prostate were recognized as focal, atypical, and progressive lesions. These lesions were designated as mouse prostatic intraepithelial neoplasia (mPIN). Some atypical lesions were identified in mouse models without evidence of progression to malignancy. The panel recommended that mPIN lesions not be given histological grades, but that mPIN be further classified as to the absence or presence of documented associated progression to invasive carcinoma. Criteria for recognizing microinvasion, for classification of invasive gland-forming adenocarcinomas, and for characterizing poorly differentiated tumors, including neuroendocrine carcinomas, were developed and are discussed. The uniform application of defined terminology is essential for correlating results between different laboratories and models. It is recommended that investigators use the Bar Harbor Classification system when characterizing new GEM models or when conducting experimental interventions that may alter the phenotype or natural history of lesion progression in existing models.

This study will serve as the basis for the rational design of pre-clinical studies with genetically engineered mouse models.

ABSTRACTy-Glutamyl transpeptidase (GGT) is an ectoenzyme that catalyzes the first step in the cleavage of glutathione (GSH) and plays an essential role in the metabolism of GSH and GSH conjugates of carcinogens, toxins, and eicosanoids. To learn more about the role of GGT in metabolism in vivo, we used embryonic stem cell technology to generate GGT-deficient (GGTml/GGTml) mice. GGTdeficient mice appear normal at birth but grow slowly and by 6 weeks are about half the weight of wild-type mice. They are sexually immature, develop cataracts, and have coats with a gray cast. Most die between 10 and 18 weeks. Plasma and urine GSH levels in the GGTml/GGTml mice are elevated 6-fold and 2500-fold, respectively, compared with wild-type mice. Tissue GSH levels are markedly reduced in eye, liver, and pancreas.Plasma cyst(e)ine levels in GGTm'/GGTml mice are reduced to '20% of wild-type mice. Oral administration of Nacetylcysteine to GGTml/GGTml mice results in normal growth rates and partially restores the normal agouti coat color. These findings demonstrate the importance of GGT and the y-glutamyl cycle in cysteine and GSH homeostasis.

Glutathione (GSH) is a major source of reducing equivalents in mammalian cells. To examine the role of GSH synthesis in development and cell growth, we generated mice deficient in GSH by a targeted disruption of the heavy subunit of ␥-glutamylcysteine synthetase (␥GCS-HS tm1 ), an essential enzyme in GSH synthesis. Embryos homozygous for ␥GCS-HS tm1 fail to gastrulate, do not form mesoderm, develop distal apoptosis, and die before day 8.5. Lethality results from apoptotic cell death rather than reduced cell proliferation. We also isolated cell lines from homozygous mutant blastocysts in medium containing GSH. These cells also grow indefinitely in GSH-free medium supplemented with N-acetylcysteine and have undetectable levels of GSH; further, they show no changes in mitochondrial morphology as judged by electron microscopy. These data demonstrate that GSH is required for mammalian development but dispensable in cell culture and that the functions of GSH, not GSH itself, are essential for cell growth.

The ability to manipulate gene expression in specific cell types at specific times utilizing transgenic technology has allowed the development of novel mouse model systems that can mimic human disease. We have previously established the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) model for prostate cancer using the rat probasin promoter to direct expression of the SV40 early genes to prostate epithelium. Male TRAMP mice exhibit consistent prostate-specific patterns of expression and develop prostatic intraepithelial neoplasia that will become invasive and metastasize primarily to the lymph nodes and lungs. In this paper we report our continued experience with this model and present a standardized histologic grading system to designate low and high grade prostatic intraepithelial neoplasia and well, moderate, and poorly differentiated prostate adenocarcinoma. In addition, we demonstrate the persistence of androgen receptor expression during pathologic progression and characterize heterogeneous cytokeratin expression in localized and metastatic prostate cancer. Finally, we report on our observations that phenotypic variability in tumor and pathologic progression in TRAMP occurs as a function of genetic background.