Strain C3H-A-vy-fB mice: ninety percent incidence of mammary tumors transmitted by either parent.

Mammary tumorigenesis in C3H-A(vy)fB female mice is not due to milk-borne mammary tumor virus but to factors transmitted at conception. Prominent among these is the A(vy) gene which may increase the virulence or transmissibility of a variant of mammary tumor virus vertically transmitted by either parent, or may increase the tumorigenic response of the mammary tissue. These factors together with the influence of hormones of pregnancy resulted in the high incidence observed.

Cholera toxin treatment stimulates tumorigenicity of Rous sarcoma virus-transformed cells.

Chinese hamster ovary cells transformed by Rous sarcoma virus form tumors poorly in nude mice. Tumorigenicity was markedly stimulated by pretreatment of the cells with cholera toxin, which raises cyclic AMP levels and activates cyclic AMP-dependent protein kinase. Increased tumorigenicity was manifested by a severalfold increase in the rate of tumor formation, as well as earlier appearance and more rapid growth of tumors. In contrast, spontaneously transformed Chinese hamster ovary cells showed decreased tumorigenicity after cholera toxin treatment. The activation of tumorigenic potential in Rous sarcoma virus-transformed Chinese hamster ovary cells by cholera toxin correlated with increased phosphorylation of the viral oncogene product pp60src and stimulation of its tyrosine kinase activity.

Response of C3H-AvyfB female mice to a low oncogenic, milk-borne mammary tumor virus.

When low oncogenic milk-borne mammary tumor virus (MTV) of strain DD was tested in C3H-AvyfB mice, as compared with the similar strain C3HfB, mammary tumors occurred with a higher incidence and at lower age in C3H-AvyfBfDD (with DD-MTV) than in C3HfBfDD (with DD-MTV), as observed in virgin females. Since the effect of breeding tended to mask any difference between the breeders, mammary tumor incidences were similar with a slightly higher age at tumor occurrence in the C3H-AvyfBfDD females. Thus the C3H-AvyfB virgins (with the Avy gene) were almost as susceptible to mammary tumors with the less potent DD-MTV as were C3HfB virgins with the more virulent C3H-MTV of strain C3H.

Possible carcinogenic effects of cedar shavings in bedding of C3H-Avy fB mice.

C3H-AvyfB female mice were tested on bedding consisting only of low-resin pine and on bedding of pine plus cedar shavings. Tumor occurrences were similar in both groups of animals, with a slightly lower incidence and slightly higher average age for mammary gland tumors in the females on bedding of pine plus cedar. From these results, the high incidence of cancer in the C3H-AvyfB strain could not be attributed to the routine use of cedar shavings in the bedding material.

Evaluation of hepatocellular neoplasms in mice.

Thirty C3H-AvyfB male mice from 3 to 15 months of age were killed, and the genesis of their hepatocellular neoplasms was studied. As the mice aged, the number of tumors per liver and mean diameter of the tumors increased. Histologically, the smallest tumors were composed of solid sheets of cells and were better differentiated than the largest tumors. Small foci of hepatocytes in prominent trabeculae formation was a common characteristic of large tumors. In addition, 18 metastatic hepatocellular carcinomas observed in aged C3H-AvyfB, C3HfC, C3H, C3HfB, (C3HfB x YBR)F1, or C57BL/6 mice were also included for a morphologic study of their primary and metastatic lesions. Invariably, the pulmonary metastases were composed of a well-differentiated sheet of hepatocytes that resembled those in the solid liver tumors. The smallest hepatocellular neoplasms appear to represent early stages in the development of metastatic hepatocellular carcinoma.

Effects of the antifertility drug enovid in five strains of mice, with particular regard to carcinogenesis.

PIP: The antifertility drug, Enovid, was tested for possible carcinogenicity in female mice of 5 specially selected strains: BALB/c, C3H, C3HfB, A, and C57BI. Enovid was chosen for testing since it is one of the most widely used oral contraceptives. The 5 strains of mice provided maximum genetic variation in the test animals. The drug was fed at 3 dose levels: 5 mcg/gm, 10 mcg/gm and 20 mcg/gm of food. The lowest dose did not prevent reproduction. The 10 mcg dose prevented some females from reproducing. The 20 mcg dose prevented all females from reproducing. The strains of mice differed in their response to Enovid. Weight gain was reduced in all strains. Effect on life-span varied, partly because of the tumors. Cervical and vaginal lesions showed invasion of the epithelium into the stroma but was limited, with few exceptions to the BALB/c females. In the BALB/c strain these lesions occurred in controls as well, but showed more progression and a higher incidence with the highest dose of Enovid. None of these lesions appeared grossly as tumors and none had extended beyond the vaginal wall or metastasized. They were observed only on histologic sections. Neither ovarian nor mammary gland tumors were increased in any strain. In the C3H strain such tumors seemed to be inhibited. In the C3HfB strain there was some inhibition of hepatomas and in the BALB/c strain some inhibition of adrenocortical adenoma. Chromophobe adenomas of the hypophysis were significantly increased in old C57BI females treated with the highest dose of Enovid. Offspring of Enovid-treated females showed no abnormalities. Enovid increased the occurrence and may have advanced the progression of epithelial lesions of the cervix and vagina of old BALB/c females. A study of the lesions in untreated females of this strain might help the understanding of carcinoma in situ in women and possibly the appearance of adeno-carcinoma of the vagina of young women whose mothers had been treated with stilbestrol during the first trimester to maintain pregnancy. Other neoplasms in this strain were not increased by the Enovid therapy. In the C3H strain mammary tumors were reduced by the Enovid and those that did occur were found later than in controls. Results from experimental animals should be applied to humans with care. Such results are of greatest value in directing attention to certain areas for investigation.^ieng

Transmission of mammary tumor virus in mouse strain DD: further support for the uniqueness of strain GR.

Outcrosses between high tumor mouse strain DD and low-incidence strains BALB/c and C57BL to produce reciprocal F1 susceptible offspring of both types resulted in high incidences of mammary tumors in (DD female X BALB/c male)F1 and (DD female X C57BL male)F1 females but not in the reciprocal hybrids with DD as the male parent. The finding that transmission of murine mammary tumor virus (MuMTV) in DD was through the milk, as most often observed in mouse strains, further supported the uniqueness of strain GR in which MuMTV is transmitted by either parent.

Inability to predict mammary tumorigenesis in strain A mice from presence of mammary tumor virus or antigen in the milk.

Strain A females were milked and their milk was tested for mammary tumor virus (MTV) by the hyperplastic alveolar nodule test and for MTV antigen by microimmunodiffusion. An attempt was made to correlate these results with later occurrence of mammary tumors in the females. There was not full agreement between the results of the test for the presence of the MTV and those of the test for MTV antigen, and from these results it was impossible to predict accurately whether a specific female would later develop a tumor. It is concluded that, in this strain, factors other than the MTV can be the determinant in whether the individual female will develop a tumor.

A biochemical approach to the study of the transmission of mouse mammary tumor viruses in mouse strains RIII and C3H.

Mouse mammary tumor virus (MMTV) proviral sequences were detected in the cellular DNA of mammary tumors and livers of RIII and C3H mice by molecular hybridization with radioactively labelled MMTV 60-70S RNA or tritiated MMTV complementary DNA (cDNA). By means of DNA:DNA reassociation kinetics, the DNA of the mammary tumor cells of these two mouse strains were found to contain more MMTV proviral sequences than the DNA of liver cells of these same tumor-bearing mice. Evidence is also presented that the DNA of the liver cells lacks a part (approximately 25%) of the MMTV proviral sequences found in the mammary tumor cells of these mouse strains. The relationship of the extra MMTV proviral sequences found in mammary tumor cells to the early mammary tumor-igenesis seen in these mouse strains is discussed.

Induction of mammary tumors in C57BL/HAAG female mice by a low oncogenic mammary tumor virus.

Mammary tumor virus (MuMTV)-negative mouse substrain C57BL/Haag foster-nursed by strain DD becomes a line with a moderately high incidence of mammary tumors occurring in the females at a late age. Electron microscopy revealed B particles in the tumors, providing additional evidence for the propagation and transmission of DD-MuMTV in C57BL/HaagfDD. Since both albino strains DD and RIII originated in Europe, develop pregnancy-dependent mammary tumors, carry black and agouti genes (cc, BB, AA), and therefore may be related, evidence is presented which suggests that the two naturally occurring MuMTVs from DD and RIII may also be related, and that they may share a common origin.

Serum, pituitary and urine concentrations of prolactin and growth hormone in eight strains of mice with varying incidence of mammary tumors.

Eight inbred strains of mice with varying incidences of spontaneous mammary tumor were compared in regard to prolactin and growth hormone concentrations in sera, pituitary glands and urine. Serum prolactin was compared under basal conditions as well as after stimulation with perphenazine. Both hormones were measured with specific, homologous radioimmunoassays. Although some strains having a high incidence of mammary tumors had high levels of prolactin in sera, urine and pituitary glands, neither basal nor perphenazine-induced serum concentrations showed a consistent pattern across mouse strains that correlated with the incidence of mammary tumors. Growth hormone levels in sera, pituitary glands and urine also had no characteristic pattern that applied to all strains studied. The ratio of prolactin depleted from the pituitary gland to prolactin detected in serum after perphenazine injection, which reflected the metabolic clearance rate of prolactin, was highest in two strains with a high incidence of mammary tumors and relatively lower in low-tumor strains. These results suggest that if prolactin plays a part in mammary tumor development in mice, its mechanism varies with strains: while hyperprolactinemia may be the means in some strains, a peculiarity in the metabolism of the hormone may be more important in others.

Spontaneous hyperplastic and neoplastic lesions of the uterus in mice.

A histologic study was done on the spontaneously occurring hyperplastic and neoplastic lesions of the uterus, cervix, and vagina taken from a variety of inbred, hybrid, and backcross female mice. The most commonly observed neoplasm of the endometrium was stromal cell sarcoma, followed by adenocarcinoma, which occurred approximately half as frequently. Hyperplasia was the most commonly observed endometrial lesion occurring either as glandular, stromal, or both and was often cystic with the formation of polyps. Among the benign and malignant lesions other than endometrial, leiomyomas, hemangioendotheliomas and leiomyosarcomas were the most commonly encountered. Lesions in the mucosal cervix and vagina were comparatively rare and were observed in only a few animals. Females with hyperplastic and neoplastic lesions of the uterus, cervix, and vagina in this survey represented a small fraction of the large number of animals necropsied, emphasizing the relative infrequency of these spontaneous lesions in mice.