[CANCER RESEARCH 64, 8177– 8183, November 15, 2004] Characterization of a Carcinogenesis Rat Model of Ovarian Preneoplasia and Neoplasia Sherri L. Stewart, 1 Troy D. Querec, 1 Alexander R. Ochman, 1 Briana N. Gruver, 1 Rudi Bao, 1 James S. Babb, 2 Thang S. Wong, 1 Theodoros Koutroukides, 1 Aaron D. Pinnola, 1 Andres Klein-Szanto, 1 Thomas C. Hamilton, 1 and Christos Patriotis 1 1 Medical Science Division and 2 Department of Biostatistics, Fox Chase Cancer Center, Philadelphia, Pennsylvania ABSTRACT Animal models of ovarian cancer are crucial for understanding the pathogenesis of the disease and for testing new treatment strategies. A model of ovarian carcinogenesis in the rat was modified and improved to yield ovarian preneoplastic and neoplastic lesions that pathogenetically resemble human ovarian cancer. A significantly lower dose (2 to 5 g per ovary) of 7,12-dimethylbenz(a)anthracene (DMBA) was applied to the one ovary to maximally preserve its structural integrity. DMBA-induced mu- tagenesis was additionally combined with repetitive gonadotropin hor- mone stimulation to induce multiple cycles of active proliferation of the ovarian surface epithelium. Animals were treated in three arms of differ- ent doses of DMBA alone or followed by hormone administration. Com- parison of the DMBA-treated ovaries with the contralateral control or- gans revealed the presence of epithelial cell origin lesions at morphologically distinct stages of preneoplasia and neoplasia. Their his- topathology and path of dissemination to other organs are very similar to human ovarian cancer. Hormone cotreatment led to an increased lesion severity, indicating that gonadotropins may promote ovarian cancer pro- gression. Point mutations in the Tp53 and Ki-Ras genes were detected that are also characteristic of human ovarian carcinomas. Additionally, an overexpression of estrogen and progesterone receptors was observed in preneoplastic and early neoplastic lesions, suggesting a role of these receptors in ovarian cancer development. These data indicate that this DMBA animal model gives rise to ovarian lesions that closely resemble human ovarian cancer and it is adequate for additional studies on the mechanisms of the disease and its clinical management. INTRODUCTION Ovarian cancer is one of the leading causes of cancer-related deaths among women (1, 2). The understanding of the molecular pathogen- esis of ovarian cancer has been hindered by the lack of sufficient numbers of specimens at early-stage disease because of its frequent diagnosis at advanced stages (3, 4). Consequently, the existence of identifiable precursor lesions that ultimately develop into ovarian cancer is still debatable (5, 6). More than 80% of ovarian cancers originate in the ovarian surface epithelium (7–12). Incessant ovulation, postmenopausal increase of gonadotropin hormone levels, chronic inflammation, and environmen- tal carcinogens are assumed to play key roles in ovarian oncogenesis (13–16). Animal models that closely recapitulate human ovarian cancer are crucial for understanding its pathogenesis and for testing new treat- ment strategies. A number of models have been developed to date on the basis of carcinogen treatment, gonadotropin/steroid hormone stim- ulation, and genetic modeling (for review, see refs. 17, 18). The latter is based on the introduction of genetic alterations through the germ line or conditional inactivation of certain tumor suppressor genes, such as Tp53 and pRb (19), or the ectopic expression of certain oncogenes, or a combination of both (20). Transgenic models, how- ever, depend strongly on the specificity and timing of expression of the used promoter in the ovary and, more specifically, in the ovarian surface epithelium, which until recently was unavailable. Further- more, most incorporated gene changes thus far are associated with advanced human ovarian cancer, and their role in early-stage disease is unknown. Recently, the MISRII promoter, which exhibits a rela- tively restricted pattern of expression, was used to drive the expres- sion of the SV40 large T-antigen in the ovarian surface epithelium (21). Approximately 50% of the female mice bearing the MISRII–T- antigen transgene developed bilateral, poorly differentiated ovarian tumors by 6 to 13 weeks of age. Similarly, most genetic models developed to date are unable to reproduce the histopathological di- versity of human ovarian cancer and give rise to rapidly developing, advanced-stage disease at very young age. Hence, although very important for understanding the role of discrete genes in ovarian cancer, these models are inadequate for studying the preneoplastic and early neoplastic stages of the disease or for prevention studies. In contrast, the ovarian lesions induced by carcinogens and hormones in general display all three stages of cancer development (initiation, promotion, and progression). The direct implantation of chemical carcinogens, such as 7,12-dimethylbenz(a)anthracene (DMBA) in the rat ovary (22–24), leads to the induction of ovarian tumors at an incidence of 37%. These include adenocarcinomas, as well as stroma and mesothelial tumors (22, 23, 25). There is, however, lack of information regarding the nature and sequence of events elicited by DMBA and leading to ovarian cancer development. To improve its usage and physiologic relevance to the human disease, the DMBA model of ovarian cancer was modified (a) by significantly decreasing the DMBA dose, thereby preserving maxi- mally the integrity of the organ and (b) by incorporating multiple gonadotropin hormone treatments, thus introducing an additional risk factor associated with human ovarian cancer, known also to induce hyperovulation and enhanced mitogenesis of the ovarian surface ep- ithelium (26). Characterization of this modified animal model re- vealed the appearance of early and advanced lesions with a progres- sive nature that range from nonneoplastic to preneoplastic to malignant. Their histopathology and path of dissemination strongly resemble human ovarian cancer. MATERIALS AND METHODS Animals and In vivo Treatments Six-week-old virgin Sprague Dawley rats (Taconic Farms, Germantown, NY) were used following NIH and Fox Chase Cancer Center animal care guidelines. DMBA mixed with beeswax was directly applied to the right ovary Received 5/17/04; revised 9/2/04; accepted 9/17/04. Grant support: NIH Grant P50-CA83638 (R. Ozols), Liz Tilberis Scholar Award of the Ovarian Cancer Research Fund, Inc., (C. Patriotis), and NIH Training Grant CA- 09035-27 (S. Stewart). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: S. Stewart is currently at the Division of Cancer Control and Prevention, NCCPHP, Centers for Disease Control and Prevention, Atlanta, GA; T. Querec is cur- rently at Immunology and Molecular Pathogenesis Program, Emory University, Atlanta, GA; and R. Bao is currently at the Novartis Oncology/Pharmacology, Summit, NJ; Supplementary data for this article can be found at Cancer Research Online (http:// cancerres.aacrjournals.org). Requests for reprints: Christos Patriotis, Division of Medical Science, 333 Cottman Avenue, W348, Philadelphia, PA 19111. Phone: (215) 728-3636; Fax: (215) 728-2741; E-mail: Christos.Patriotis@FCCC.edu. 8177 Research. on January 9, 2016. © 2004 American Association for Cancer cancerres.aacrjournals.org Downloaded from