[Show abstract][Hide abstract] 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 mug per ovary) of 7,12-dimethylbenz(a)anthracene (DMBA) was applied to the one ovary to maximally preserve its structural integrity. DMBA-induced mutagenesis was additionally combined with repetitive gonadotropin hormone stimulation to induce multiple cycles of active proliferation of the ovarian surface epithelium. Animals were treated in three arms of different doses of DMBA alone or followed by hormone administration. Comparison of the DMBA-treated ovaries with the contralateral control organs revealed the presence of epithelial cell origin lesions at morphologically distinct stages of preneoplasia and neoplasia. Their histopathology 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 progression. 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.
[Show abstract][Hide abstract] ABSTRACT: Tumor cells often appear in a deviant differentiated stage, and dedifferentiation is a hallmark of malignancy; however, the causative mechanism of the global changes in dedifferentiation is not understood. The GATA transcription factors function in cell lineage specification during embryonic development and organ formation. The transcriptional targets of the GATA factors in early embryonic development include Disabled-2 and collagen IV, markers for epithelial lineages. GATA-4 and GATA-6 are expressed strongly and are localized in the nucleus in ovarian surface epithelial cells in tissues or primary cell cultures. By immunohistochemistry, we found that 82% of the 50 tumors analyzed had lost GATA-6 function, either by a complete absence of expression or by cytoplasmic mislocalization. The frequent loss of GATA-6 was also confirmed in a panel of ovarian surface epithelial and tumor cell lines. Although GATA-4 is absent only in a small percentage (14%) of ovarian tumors, it is lost in the majority of established cell lines in culture. The loss of GATA-6 correlates with the loss of Disabled-2, collagen IV, and laminin, markers for epithelial cell types. Loss of GATA factors was also found in an in vitro model for spontaneous transformation of rat ovarian epithelial cells. Repression of GATA-6 by small interfering (si)RNA approach in cultured cells leads to dedifferentiation as indicated by the loss of Disabled-2 and laminin expression. Restoration of GATA factors expression by ectopic transfection suppresses cell growth and is incompatible with the maintenance of the cells in culture. However, restoration of GATA-4 and GATA-6 expression is not able to induce expression of endogenous Disabled-2 in tumor cells, suggesting that the loss of GATA factors and dedifferentiation are irreversible processes. In conclusion, we observed the inappropriate expression and cellular localization of the GATA transcription factors in ovarian tumor tissues and cancer cell lines, and we have demonstrated that down-regulation of GATA factor expression leads to dedifferentiation. We propose that alterations of GATA transcription factor expression and aberrant nucleocytoplasmic localization may contribute to the anomalous epithelial dedifferentiation of the ovarian tumor cells.
[Show abstract][Hide abstract] ABSTRACT: The ovarian-specific promoter, OSP-1, which was cloned from the transcript of a rat retrovirus-like element specifically expressed in ovarian tissue, was tested for its ability to drive ovary-specific transcription in transgenic mice.
Transgenic mice were generated with the lacZ reporter gene (OSP-lacZ) or the early region of SV40 virus (OSP-TAg) placed under the control of the OSP-1 promoter. OSP-lacZ and OSP-TAg transgenic animals were examined, respectively, for the expression of lacZ (OSP-lacZ) or the development of tumors (OSP-TAg).
The expression of lacZ in the resulting OSP-lacZ mice was restricted to the ovary as determined by X-gal staining of multiple organs. Immunohistochemical detection of beta-galactosidase showed lacZ expression mainly in the granulosa cells and ovarian surface epithelial cells. OSP-TAg mice developed tumors in a variety of tissues, including unilateral granulosa cell tumors in two of three female founder mice. In the contralateral ovary of one mouse with a granulosa cell tumor, there were alterations in the ovarian surface epithelial cells suggestive of preneoplasia.
Although the OSP-1 promoter was able to restrict reporter gene expression to the ovary in transgenic mice, the expression of TAg in the OSP-TAg mice resulted in ovarian tumors as well as tumors in numerous other organs. This indicated that although transcription from the OSP-1 promoter occurs predominantly in the ovary, this promoter is sufficiently leaky in cells in other tissues to permit their tumorigenic conversion by SV40 TAg.
No preview · Article · Jun 2003 · Journal of the Society for Gynecologic Investigation
[Show abstract][Hide abstract] ABSTRACT: Ovarian cancer is the leading cause of death among women from gynecological malignancies inthe United States. Resistance to the chemotherapeutic agent cisplatin isa major limitation for the successful treatment of ovarian cancer. In an effort to overcome the cisplatin resistance problem in ovarian cancer treatment, we have sought to enhance cisplatin cytotoxicity by perturbing the nucleotide excision repair (NER) pathway. The NER pathway is responsible for repairing cisplatin bound to DNA. Expression of one of the NER components, ERCC1, is correlated with cisplatin drug resistance. Hence, we targeted ERCC1 by antisense RNA methodologies, and we show that we could sensitize a relatively sensitive A2780 cell line and also the highly resistant OVCAR10 cell line to cisplatin by expressing antisense ERCC1 RNA in them as measured with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The A2780 cell lines expressing antisense ERCC1 had 1.9-8.1-fold enhancements in cisplatin sensitivity. The OVCAR10 antisense ERCC1 cell lines had IC(50) values ranging from 2.28 microM to 2.7 microM cisplatin as compared with 9.52 micro M for control OVCAR10 cells. The OVCAR10 antisense ERCC1 cells also show reduced DNA-damage repair capacity as assessed by host cell reactivation. Furthermore, immunocompromised mice transplanted with the antisense cell lines survived longer than the mice bearing control cells after response to cisplatin treatment. These data suggest that it is possible to substantially enhance the cisplatin cytotoxicity by disturbing the NER pathway in cisplatin-resistant cell lines and to enhance the survival capacity of mice in an ovarian cancer xenograft model.
[Show abstract][Hide abstract] ABSTRACT: In women, >80% of malignant ovarian tumors are of epithelial origin. Early detection of these tumors is very challenging,and extensive i.p. dissemination is common by the time of diagnosis. The lack of adequate geneticmouse models of ovarian carcinomas significantly delays advances in early detection and treatment. We report that female transgenic mice expressing the transforming region of SV40 under control of the Mullerian inhibitory substance type II receptor gene promoter develop bilateral ovarian tumors in approximately 50% of cases. Histologically, these tumors are poorly differentiated carcinomas with occasional cysts and papillary structures present at the surface of the ovary. These tumors disseminate i.p., invade omentum, and form ascites as do human ovarian carcinomas. The epithelial origin of these tumors is supported by detection of cytokeratins 8 and 19, and the absence of alpha-inhibin, a protein characteristically expressed in normal granulosa cells and most granulosa cell tumors. Cell lines derived from the ascites exhibit the properties of epithelial ovarian cancer, such as anchorage-independent growth, tumorigenicity in immunocompromised mice, expression of epithelial cell markers, and organotropic implantation. The availability of a transgenic mouse model of disseminated ovarian carcinoma and respective cell lines should advance our understanding of this neoplasm, and serve as a useful tool for the evaluation of emerging detection and treatment strategies.
[Show abstract][Hide abstract] ABSTRACT: Survivin, a member of the IAP (inhibitor of apoptosis) gene family, appears to be overexpressed in common cancers but not in corresponding normal adult tissues. To investigate whether the survivin promoter controls cancer cell-specific gene expression, we determined whether the survivin gene promoter could regulate reporter gene expression in cancer cell lines and xenografts.
Survivin protein levels were determined in human and murine cancer cell lines and in normal tissues of adult C57BL/6 mice by Western blot analysis. A reporter construct in which a portion of the survivin gene promoter was used to drive transcription of a human secreted alkaline phosphatase (SEAP) gene was transiently transfected into cancer cells, and promoter activity was extrapolated from SEAP activity. A2780 human ovarian cancer cells were transfected with this construct, and stable transfectants were injected into the intrabursal ovarian space of immunodeficient mice. Tumor growth was monitored, and plasma SEAP levels were used as a measure of survivin promoter activity in vivo.
Survivin protein was detected in all cancer cell lines examined but not in most normal adult mouse tissues. After transfection, the survivin promoter was more active in all cancer cell lines than in normal ovarian surface epithelial cells or mouse 3T3 cells. After 0.8 x 10(6) stable transfectant cells were injected into the intrabursal cavity of mouse ovaries, plasma SEAP activity was detected within 24 hours, and the activity increased with time and tumor growth.
Transfection experiments indicate that survivin protein expression in cancer tissue appears to be regulated, at least in part, transcriptionally. Thus, the survivin promoter may be useful in controlling gene expression in cancer cells.
Full-text · Article · May 2002 · JNCI Journal of the National Cancer Institute
[Show abstract][Hide abstract] ABSTRACT: The "suicide" gene therapy of cancer using promoters such as cytomegalovirus could cause severe toxicity to normal tissues due to a lack of specificity of prodrug activation. Therefore, we investigated gene therapy of ovarian cancer using ovarian-specific promoter (OSP1) to limit the synthesis of the prodrug activating enzyme HSVtk to ovarian cancer cells.
The HSVtk expressing plasmid pOSP1-HSVtk was created and transfected into an ovarian cancer cell line OVCAR3. The ganciclovir (GCV) sensitivity of the stable transfectants was evaluated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. Tissue specificity of this promoter was evaluated by comparing the sensitivity to GCV between ovarian and nonovarian cancer cell lines after they were transfected with pOSP1-HSVtk. One transfectant sensitive to GCV was implanted intraperitoneally to immunocompromised mice which were treated subsequently with GCV. Furthermore, this ovarian cancer survival model was used to evaluate the in vivo efficacy of cationic lipid mediated pOSP1-HSVtk gene delivery followed by GCV treatment.
Stable transfectants of OVCAR3 cells bearing OSP1-HSVtk became more sensitive to GCV treatment compared to the parental cell line and vector transfected OVCAR3 cell line. OSP1-HSVtk could specifically sensitize the OVCAR3 ovarian cancer cell line to GCV. SCID mice transplanted with the OVCAR3 transfectant and treated with GCV survived longer than the mice without GCV treatment (P = 0.032). In vivo gene delivery mediated by a cationic lipid (GL67) followed by GCV treatment yielded a longer survival in the OVCAR3 survival model (P = 0.016).
The OSP1 promoter can selectively direct suicide gene therapy of ovarian cancer and the in vivo efficacy is improved by using a cationic lipid GL67 as delivery vehicle as opposed to the direct injection of plasmid.
Full-text · Article · Mar 2002 · Gynecologic Oncology
[Show abstract][Hide abstract] ABSTRACT: We have isolated 462 bp of sequence termed ovarian-specific promoter 1 (OSP-1) that is part of a retrovirus-like element specifically expressed in the rat ovary. We have evaluated the ability of OSP-1 to activate gene expression in normal and neoplastic cell lines derived from the ovaries of rats and women. We have found that there was marked specificity in the ability of OSP-1 to drive reporter gene expression in an ovarian epithelial cell lineage manner. The expression of herpes simplex virus thymidine kinase (HSV-TK) under OSP-1 control was sufficiently ovarian cancer cell line specific to render ganciclovir approximately 50-fold more toxic in the A2780 human ovarian cancer cell line compared with clones of the HCT-116 and HT-29 colon cancer cell lines. Furthermore, ganciclovir had marked antitumor efficacy in vivo in severe combined immunodeficient mice bearing A2780OSP-1-HSV-TK as a s.c. xenograft. We suggest that these data support the use of OSP-1 as a tool to provide specificity to the gene therapy of ovarian cancer and to drive ovarian-specific oncogene expression for the creation of transgenic mouse models of ovarian cancer.
[Show abstract][Hide abstract] ABSTRACT: A limitation to preclinical evaluation of possible anticancer therapy is the objective assessment of efficacy, especially in the presence of small tumor burden or inaccessible disease. This study is designed to test whether human secreted alkaline phosphatase (SEAP) could be used as a soluble marker for in vivo tumor burden.
A SEAP expression construct under control of the CMV promoter was created. The SEAP activity in the conditioned medium was evaluated at 24 h and 48 h after the A2780 cell line was transiently transfected with the SEAP vector using Superfect reagent. Stable transfection of A2780 was accomplished by selection of transfectants in G418. SEAP activity of the stable transfectant was determined in conditioned medium and its relationship to tumor cell number was examined. A highly expressing stable transfectant was implanted into immunocompromised mice (2 x 10(6) subcutaneously and 5 x 10(6) intraperitoneally) and peripheral blood was obtained by orbital puncture every 5 days. The relationship between blood SEAP activity and tumor burden was studied. The usefulness of this marker in preclinical assessment of anticancer drug efficacy was evaluated by studying the plasma SEAP activity in xenografted mice treated or not treated with paclitaxel.
After transient transfection of the A2780 cell line (5 x 10(5)) with the plasmid, SEAP activity was found in the medium at 24 h (482.0 +/- 2.0 ng/ml) and 48 h (1296.0 +/- 1.0 ng/ml). The in vitro study using a stable transfectant demonstrated that SEAP activity was linearly related to cell numbers (r = 0.99). The in vivo study demonstrated that SEAP was detectable in plasma one day postinjection, long before measurable tumor or detectable intraperitoneal tumor was present. Once detectable SC tumor was present, the SEAP activity correlated well with tumor volume (r = 0. 94-0.97). The plasma SEAP level was reduced after xenografted mice were treated with paclitaxel (20 mg/kg, weekly x5) compared with untreated mice in both SC and IP tumor models (P = 0.05, P = 0.025, respectively).
These data suggest that the plasma SEAP activity can be used as an alternative to survival or tumor measurement in evaluating anticancer agents for efficacy, especially in the case of minimal or inaccessible disease.
Full-text · Article · Oct 2000 · Gynecologic Oncology
[Show abstract][Hide abstract] ABSTRACT: We previously reported cloning the rLot1 gene, and its human homolog (hLOT1), through analysis of differential gene expression in normal and malignant rat ovarian surface epithelial cells. Both human and rat ovarian carcinoma cell lines exhibited lost or decreased expression of this gene. Interestingly, the LOT1 gene localized at band q25 of human chromosome 6 which is a frequent site for LOH in many solid tumors including ovarian cancer. In this report we have further characterized the potential role of LOT1 in malignant transformation and developed evidence that the gene is a novel target of growth factor signaling pathway. Assays using transient transfections showed that LOT1 is a nuclear protein and may act as a transcription factor. In vitro and in vivo studies involving ovarian cancer cell lines revealed that expression of LOT1 is directly associated with inhibition of cellular proliferation and induction of morphological transformations. Additionally, we show that in normal rat ovarian surface epithelial cells Lot1 gene expression is responsive to growth factor stimulation. Its mRNA is strongly down-regulated by epidermal growth factor receptor (EGFR) ligands, namely EGF and TGF-alpha. Blocking the ligand-activated EGFR signal transduction pathway by the specific EGF receptor inhibitor, tyrphostin AG1478, and the MEK inhibitor, PD098059, restores the normal level of Lot1 gene expression. It appears that the regulation of Lot1 gene is unique to these ligands, as well as the growth promoting agent TPA, since other factors either did not affect Lot1 expression, or the effect was modest and transient. Altogether, the results suggest that Lot1 expression is primarily mediated via EGF receptor or a related pathway and it may regulate the growth promoting signals as a zinc-finger motif containing nuclear transcription factor.