Testicular (Sertoli's cell)-like tumors of the ovary induced by N-ethyl-N-nitrosourea (ENU) in rats

Induction of a menopausal state alters the growth and histology of ovarian tumors in a mouse model of ovarian cancer

OBJECTIVE

Ovarian cancer is often diagnosed in women after menopause when the levels of the serum gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are increased because of the depletion of growing follicles within the ovary. The ability of FSH and LH to modulate the disease has not been well studied owing to a lack of physiologically relevant models of ovarian cancer. In this study, 4-vinylcyclohexene diepoxide (VCD) was used to deplete ovarian follicles and increase the levels of circulating FSH and LH in the tgCAG-LS-TAg mouse model of ovarian cancer.

METHODS

VCD-induced follicle depletion was performed either before or after induction of the oncogene SV40 large and small T-antigens in the ovarian surface epithelial cells of tgCAG-LS-TAg mice, which was mediated by the intrabursal delivery of an adenovirus expressing Cre recombinase (AdCre).

RESULTS

tgCAG-LS-TAg mice injected with AdCre developed undifferentiated ovarian tumors with mixed epithelial and stromal components and some features of sex cord stromal tumors. Treatment with VCD before or after AdCre injection yielded tumors of similar histology, but with the unique appearance of Sertoli cell nests. In mice treated with VCD before the induction of tumorigenesis, the ovarian tumors tended to grow more slowly. The human ovarian cancer cell lines SKOV3 and OVCAR3 responded similarly to increased levels of gonadotropins in a second model of menopause, growing more slowly in ovariectomized mice compared with cycling controls.

CONCLUSIONS

These results suggest that follicle depletion and increased gonadotropin levels can alter the histology and the rate of growth of ovarian tumors.

Loss of ovarian function and the risk of ovarian cancer

Animal models with premature ovarian failure resulting from the loss or depletion of germ cells consistently develop ovarian surface epithelial cell hyperplasia with invasion into the stroma and the development of ovarian tubular adenomas. In human ovaries, deep epithelial invaginations and inclusion cysts occur at increasing frequency with age and are thought to be the structures from which the majority of ovarian cancers arise. A feature that is common to these animal models and to post-menopausal women is a deficiency in the number of oocytes. The potential consequences of the loss or depletion of female germ cells, naturally or otherwise, include failure of follicle development, significant reductions in oestrogen and progesterone levels and elevation of circulating levels of gonadotropins. This review will consider the way in which these structural and hormonal changes affect ovarian cancer risk. Some lessons may be learned from gonad formation, since notable similarities exist between ovarian tumorigenesis and embryonic gonadogenesis including fragmentation of the basement membrane underlying the coelomic (surface) epithelium, the potential for the migration of epithelial cells into the gonad and the importance of the germ cells for the regulation of ovarian structure and function.

Animal models of ovarian cancer

Ovarian cancer is the most lethal of all of the gynecological cancers and can arise from any cell type of the ovary, including germ cells, granulosa or stromal cells. However, the majority of ovarian cancers arise from the surface epithelium, a single layer of cells that covers the surface of the ovary. The lack of a reliable and specific method for the early detection of epithelial ovarian cancer results in diagnosis occurring most commonly at late clinical stages, when treatment is less effective. In part, the deficiency in diagnostic tools is due to the lack of markers for the detection of preneoplastic or early neoplastic changes in the epithelial cells, which reflects our rather poor understanding of this process. Animal models which accurately represent the cellular and molecular changes associated with the initiation and progression of human ovarian cancer have significant potential to facilitate the development of better methods for the early detection and treatment of ovarian cancer. This review describes some of the experimental animal models of ovarian tumorigenesis that have been reported, including those involving specific reproductive factors and environmental toxins. Consideration has also been given to the recent progress in modeling ovarian cancer using genetically engineered mice.

High yields of granulosa cell tumors/luteomas in F344 rat ovaries after transplacental administration of N-nitrosobis(2-oxopropyl)amine

Ovarian tumors were induced at very high incidence in the offspring of F344 rats receiving 3 subcutaneous injections of 10 mg/kg of N-nitrosobis(2-oxopropyl)amine on the 14th, 18th and 20 days of gestation. Histologically, all ovarian tumors were of the granulosa cell tumor and/or luteoma type. Many of them consisted of large, polygonal cells with abundant eosinophilic or vacuolated cytoplasm, arranged in sheets or in a pseudo-palisaded pattern separated by thin fibrovascular stroma, and they exhibited typical luteoma morphological character. The high yields, and the similarities in morphology as well as putative hormonal influence suggest that this experimental system may serve as a good animal model for granulosa cell tumor and/or luteoma development in women.

Morphology of canine ovarian Sertoli-Leydig cell neoplasms. A report of 12 cases

Of 71 dogs with primary ovarian neoplasms, 12 (17%) had Sertoli-Leydig cell tumors. Five dogs had Sertoli-Leydig cell tumors, four had pure Sertoli cell tumors, and three had Sertoli-Leydig cell tumors with a retiform pattern. Variously differentiated Sertoli cells were seen in the Sertoli-Leydig cell tumors, and one of these metastasized to the peritoneum. The pure Sertoli cell tumors were similar to these tumors in male dogs. The retiform pattern in the third group of tumors was characterized by tubuloalveolar structures resembling rete testes. Heterologous elements were seen in seven tumors (58%)--enteric glands in three Sertoli-Leydig cell tumors and one Sertoli-Leydig cell tumor with retiform pattern, and neuroendocrine carcinoma in one pure Sertoli cell tumor and two Sertoli-Leydig cell tumors with retiform pattern. The uterus was examined in seven dogs, and six (87%) had endometrial hyperplasia.

In vitro malignant transformation of in vivo ENU-induced rat ovarian Sertoli cell tumor (adenoma)

An N-ethyl-N-nitrosourea-induced rat ovarian Sertoli cell tumor was grown in tissue culture in Dulbecco's modified Eagle's medium (DMEM) supplemented with 25% horse serum (HS) and a hormone combination of 20 ng/ml each of hydrocortisone, insulin, and prolactin. This tissue culture derived from a nonsteroid hormone-producing tumor. Cytofluorometry and karyotyping of the nonhormone-producing tumor cell line (SCTL-1) revealed a diploid pattern for the early passage (P1), which became hyperdiploid (P10), and then aneuploid (P20). These cells had an epitheloid pattern, grew in a monolayer at early passages. After P10 the cells were transplanted into newborn rats and nude mice and resulted in high incidences of tumors (up to 100%). The cell line (SCTL-1) continued to grow in DMEM, 10% HS, and no hormone supplementation after P10. This study revealed that a benign rat ovarian Sertoli cell tumor after multiple passages in vitro underwent sequential genotypic and phenotypic changes and became highly malignant.