Flow cytometric DNA measurement and cytomorphometric analysis of formalin fixed rat mammary tumours

Histopathologic characterization of mammary neoplastic lesions induced with 7,12 dimethylbenz(alpha)anthracene in the rat: a comparative analysis with human breast tumors

CONTEXT

The dimethylbenz(alpha)anthracene (DMBA) breast cancer model induced in the rat is used for the study of mammary carcinogenesis because it closely mimics human breast disease.

OBJECTIVE

To analyze the histopathologic features of mammary carcinomas induced in the DMBA experimental model, in a manner similar to that used in human pathology, to allow a comparative analysis between both systems.

DESIGN

Three experimental series of 20 animals were used. At 53 days of age, a single dose of 5 mg of DMBA per rat was given. Mammary tumors were collected when the rats were killed. Several histopathologic parameters were studied. For grading, the parameters described in the modified Scarff-Bloom-Richardson scheme were used, adapted to rat mammary tumors.

RESULTS

More than 50% of the carcinomas presented a pattern grade I, a nuclear grade I or II, and fewer than 10 mitoses/10 high-power fields (P <.05). Although the tumors were generally well differentiated, they showed a range of differentiation. More than 85% of carcinomas did not display tumoral necrosis (P <.05). This feature was observed mostly in high-grade carcinomas. There was no or scanty lymphoplasmacytic infiltration in more than 70% of carcinomas (P <.05). The degree of infiltration increased with the histologic grade. Microcalcifications were found rarely (P <.05). The carcinomas exhibited a mixed structural pattern, most with a predominant cribriform pattern (P <.05). No or light (+) stromal response was seen in most cases (P <.05). Some carcinomas, especially when poorly differentiated, presented a desmoplastic reaction. Most carcinomas presented scanty mast cell infiltration (P <.05), no features of secretion (P <.05), and absence of microcribriform pattern (P <.05). These features were seen more often in low-grade carcinomas.

CONCLUSIONS

Despite the presence of some structural differences, rat mammary adenocarcinomas and the most common human breast carcinomas share several morphologic similarities. Moreover, some features could be related to the aggressive behavior of the tumor. The analysis carried out in this study, similar to that done in human pathology, allows a more extensive understanding of mammary tumors in rats, as well as a more accurate use of this animal model, and has made it possible to develop an innovative classification of rat mammary lesions.

Characterization of brain and bone-metastasizing clones selected from an ethylnitrosourea-induced rat mammary carcinoma

An animal model for breast cancer, brain and bone metastasis was developed using ENU1564, a cell line established from a metastatic mammary adenocarcinoma induced by N-ethyl-N-nitrosourea in a female Berlin-Druckrey IV rat. The original tumor isolate (designated FP1) spontaneously metastasizes to regional lymph nodes and lung following orthotopic inoculation into mammary fat pad (mfp) and metastasizes widely following left cardiac ventricle (LV) inoculation. From FP1, two sublines were selected from brain metastases (designated Br7-C5) or from slowly growing colonies in vitro (FP2-A11), then cloned and compared in assays of spontaneous and experimental metastasis. After inoculation of 10(5) cells into mfp, Br7-C5 formed large tumors at the inoculation site (9.4 +/- 3.3 g) and spontaneously metastasized to lung and lymph node by 55 days post-inoculation (dpi). In contrast, FP2-A11 produced much smaller tumors within mfp (0.6 +/- 0.3 g) and failed to metastasize by 55 dpi. Rats inoculated via the LV with 10(4) Br7-C5 cells developed signs of weight loss, head tilt, and dyspnea by 24 +/- 1.4 dpi with consistent colonization of brain, bone, lung, heart, kidney, and stomach. Rats inoculated similarly with FP2-A11 showed no signs until 53 +/- 12.3 dpi, when all developed rear limb paresis. There was significant colonization of only brain and bone, with only minor lung involvement. These ENU1564 sublines thus differ in their apparent rates of tumor growth and lesion development in vivo, their capacity to metastasize from orthotopic implantation sites, and in the spectrum of tissues colonized in experimental metastasis assays. Both clones provide reproducible models of breast cancer metastasis in syngeneic hosts, particularly to brain and bone.

Nonhomologous recombination in human cells

Nonhomologous recombination (NHR) is a major pathway for the repair of chromosomal double-strand breaks in the DNA of somatic cells. In this study, a comparison was made between the nonhomologous end joining of transfected adenovirus DNA fragments in vivo and the ability of purified human proteins to catalyze nonhomologous end joining in vitro. Adenovirus DNA fragments were shown to be efficiently joined in human cells regardless of the structure of the ends. Sequence analysis of these junctions revealed that the two participating ends frequently lost nucleotides from the 3' strands at the site of the joint. To examine the biochemical basis of the end joining, nuclear extracts were prepared from a wide variety of mammalian cell lines and tested for their ability to join test plasmid substrates. Efficient ligation of the linear substrate DNA was observed, the in vitro products being similar to the in vivo products with respect to the loss of 3' nucleotides at the junction. Substantial purification of the end-joining activity was carried out with the human immature T-cell-line HPB-ALL. The protein preparation was found to join all types of linear DNA substrates containing heterologous ends with closely equivalent efficiencies. The in vitro system for end joining does not appear to contain any of the three known DNA ligases, on the basis of a number of criteria, and has been termed the NHR ligase. The enriched activity resides in a high-molecular-weight recombination complex that appears to include and require the human homologous pairing protein HPP-1 as well as the NHR ligase. Characterization of the product molecules of the NHR ligase reaction suggests that they are linear oligomers of the monomer substrate joined nonrandomly head-to-head and/or tail-to-tail. The joined ends of the products were found to be modified by a 3' exonuclease prior to ligation, and no circular DNA molecules were detected. These types of products are similar to those required for the breakage-fusion-bridge cycle, a major NHR pathway for chromosome double-strand break repair.

Nonhomologous recombination in human cells

Nonhomologous recombination (NHR) is a major pathway for the repair of chromosomal double-strand breaks in the DNA of somatic cells. In this study, a comparison was made between the nonhomologous end joining of transfected adenovirus DNA fragments in vivo and the ability of purified human proteins to catalyze nonhomologous end joining in vitro. Adenovirus DNA fragments were shown to be efficiently joined in human cells regardless of the structure of the ends. Sequence analysis of these junctions revealed that the two participating ends frequently lost nucleotides from the 3' strands at the site of the joint. To examine the biochemical basis of the end joining, nuclear extracts were prepared from a wide variety of mammalian cell lines and tested for their ability to join test plasmid substrates. Efficient ligation of the linear substrate DNA was observed, the in vitro products being similar to the in vivo products with respect to the loss of 3' nucleotides at the junction. Substantial purification of the end-joining activity was carried out with the human immature T-cell-line HPB-ALL. The protein preparation was found to join all types of linear DNA substrates containing heterologous ends with closely equivalent efficiencies. The in vitro system for end joining does not appear to contain any of the three known DNA ligases, on the basis of a number of criteria, and has been termed the NHR ligase. The enriched activity resides in a high-molecular-weight recombination complex that appears to include and require the human homologous pairing protein HPP-1 as well as the NHR ligase. Characterization of the product molecules of the NHR ligase reaction suggests that they are linear oligomers of the monomer substrate joined nonrandomly head-to-head and/or tail-to-tail. The joined ends of the products were found to be modified by a 3' exonuclease prior to ligation, and no circular DNA molecules were detected. These types of products are similar to those required for the breakage-fusion-bridge cycle, a major NHR pathway for chromosome double-strand break repair.