A functional and quantitative mutational analysis of p53 mutations in yeast indicates strand biases and different roles of mutations in DMBA- and BBN-induced tumors in rats

The N-butyl-N-4-hydroxybutyl Nitrosamine Mouse Urinary Bladder Cancer Model

Urinary bladder cancer (UBC) is a common and complex malignancy, with a multifactorial etiology, like environmental factors, such as cigarette smoking, occupational exposure, and genetic factors.UBC exhibits considerable genotypic and phenotypic heterogeneity. Among all UBC lesions, urothelial carcinoma is the most frequently observed histological type. Despite all the developments made in urologic oncology field, therapeutic options remain inadequate. There is urgency for the identification and development of new antineoplastic drugs to replace or improve current protocols and in vivo models have been proven to be essential for this step. There are different animal models of UBC: Spontaneous and experimentally induced models (genetically engineered, transplantable-xenograft and syngeneic animals- and chemically induced models). N-butyl-N(4-hydroxybutil)nitrosamine (BBN) is the most suitable reagent to generate chemically induced in vivo models of UBC and to study bladder carcinogenesis. BBN has proven, over the years, to be very realistic and reliable. It is bladder specific, and induces high tumor incidence.

Enhanced susceptibility to chemical induction of ovarian tumors in mice with a germ line p53 mutation

Mice with a germ line p53 mutation (p53(Ala135Val/wt)) display increased susceptibility to lung, skin, and colon carcinogenesis. Here, we show that p53(Ala135Val/wt) mice developed ovarian tumors significantly more rapidly than their wild-type littermates after 7,12-dimethylbenz(a)anthracene (DMBA) treatment. Approximately 50% of the ovarian tumors in p53(wt/wt) mice and 23% in p53(Ala135Val/wt) mice are adenocarcinomas and the remaining tumors were adenocarcinoma mixed with sarcoma or ovarian sarcomas. All of the p53(Ala135Val/wt) mice had died of ovarian tumors 25 weeks after the initial DMBA treatment, whereas >50% of p53(wt/wt) mice were still alive. These mice not only have a shortened tumor latency but also closely resemble a subset of human ovarian tumors containing the p53 mutation. Microarray and GenMAPP analyses revealed that the mutant p53 (Ala135Val) affected several cellular processes, including the cell cycle, apoptosis, and Wnt pathways. These findings indicate that a germ line p53 mutation significantly enhanced DMBA-induced ovarian tumor development and progression.

p53 mutation profiling of multiple esophageal carcinoma using laser capture microdissection to demonstrate field carcinogenesis

Inactivation of the p53 tumor suppressor gene is one of the most frequent genetic alterations observed in human esophageal carcinomas. In patients with esophageal carcinoma, one of the significant pathological features of the tumor is the presence of multiple lesions within the esophagus. However, the molecular mechanisms involved in the occurrence of multiple lesions have remained elusive. To characterize p53 alterations in multiple esophageal carcinomas and to study their roles in carcinogenesis, we performed p53 immunohistochemical and p53 mutation analyses using laser capture microdissection on surgically resected human esophageal carcinomas from 11 patients: 9 patients with multiple esophageal carcinomas, 1 with an intramural metastasis lesion within the esophagus and 1 with an intraepithelial carcinoma lesion contiguous to the main lesion. In each of the patients with multiple esophageal carcinomas, we examined samples from 1 main lesion and 1 representative concomitant lesion. Molecular analyses of samples from fresh-frozen normal tissues and tumor tissues of the main lesion (whole tumor) were also performed by the same method. p53 protein accumulation was observed in 16 (72.7%) of 22 lesions from the 11 cases. No p53 mutation was found in normal esophageal tissues. In the 9 cases of multiple esophageal carcinomas, point mutations were detected in the whole tumor in 1 (11.1%) case, in the microdissected tumor samples of main lesions in 3 (33.3%) cases and in the microdissected tumor samples of concomitant lesions in 3 (33.3%) cases. For the microdissected tumor samples, there was a 54.5% (12/22) concordance rate between the results of immunostaining and molecular analysis. In the 8 cases of whole tumors in which a p53 mutation was not observed, 2 cases revealed p53 mutation in the microdissected tumor samples of the main lesion. All 6 cases of multiple esophageal carcinomas that showed a p53 mutation in the microdissected tumor sample had a discordant p53 mutational status between the main and concomitant lesions. In contrast, both the intramural metastasis lesion and the intraepithelial carcinoma contiguous to the main lesion showed p53 mutational patterns identical to those of the main lesions. In conclusion, the analysis of microdissected DNA by laser capture microdissection is useful for characterizing the heterogeneity of the p53 gene mutation in multiple carcinoma lesions that cannot be accurately analyzed in whole esophageal tumor DNA. The finding of different p53 gene mutations among multiple esophageal carcinoma lesions suggest further evidence of multicentric or field carcinogenesis of the human esophagus.

Production of knockout rats using ENU mutagenesis and a yeast-based screening assay

The rat is a widely used model in biomedical research and is often the preferred rodent model in many areas of physiological and pathobiological research. Although many genetic tools are available for the rat, methods to produce gene-disrupted knockout rats are greatly needed. In this study, we developed protocols for creating N-ethyl-N-nitrosourea (ENU)-induced germline mutations in several rat strains. F1 preweanling pups from mutagenized Sprague Dawley (SD) male rats were then screened for functional mutations in Brca1 and Brca2 using a yeast gap-repair, ADE2-reporter truncation assay. We produced knockout rats for each of these two breast cancer suppressor genes.

Isolation of differentiated squamous and undifferentiated spindle carcinoma cell lines with differing metastatic potential from a 4-nitroquinoline N-Oxide-induced tongue carcinoma in a F344 rat

One differentiated squamous cell carcinoma (SCC) cell line (RSC3-E2) and two undifferentiated tumor cell lines (RSC3-LM and RSC3-E2R) with different metastatic potential were established from a 4-nitroquinoline N-oxide (4NQO)-induced differentiated SCC in F344 rat tongue. The RSC3-E2 subline was isolated from a parental cell line (RSC3-P) by single cell cloning in vitro, whereas the RSC3-LM subline was isolated from a lung metastatic focus after subcutaneous (s.c.) injection of RSC3-P cells. The RSC3-E2R cell line was isolated from a lung metastatic focus following s.c. injection of RSC3-E2 cells after X-irradiation in vitro. The RSC3-E2 cell line is keratin-positive and grows as a keratinizing tumor in nude mice, whereas RSC3-LM and RSC3-E2R cells are keratin-negative, vimentin-positive and form undifferentiated tumors. When s.c. injected into nude mice, the RSC3-E2 cell line proved to be non-metastatic, while the RSC3-LM cell line was metastatic by both hematogenous and lymphogenous routes, and the RSC3-E2R cell line was metastatic only hematogenously. In vitro relative growth rates and in vitro invasion activity of these cell lines were in the order RSC3-LM > RSC3-E2R > RSC3-E2. Chromosome analysis revealed two peaks with modal chromosome numbers of 83 and 78 for RSC3-P cells and single peaks at 83, 78 and 56 for RSC3-LM, RSC3-E2 and RSC3-E2R cell lines, respectively. Common structural abnormalities on chromosome 11 were shared by all cell lines. Mutation analysis of the p53 gene using a yeast functional assay demonstrated RSC3-LM cell line to have a point mutation at codon 269, whereas RSC3-E2 and RSC3-E2R had double mutations at codons 106 and 170 on each allele. These results suggest that the two undifferentiated RSC3-LM and RSC3-E2R tumor cell lines with different metastatic potential were generated from differentiated SCC cells via different genetic pathways as a consequence of tumor progression in vivo and in vitro, respectively. These cell lines should provide a useful model for understanding mechanisms of hematogenous and lymphogenous metastasis, as well as tumor progression of oral SCCs.