Expression of platelet-derived growth factor and activated receptor in clinical specimens of epithelial ovarian cancer and ovarian carcinoma cell lines
Introduction
Ovarian cancer is the second most common malignancy of the female genital tract in the United States but the leading cause of death from gynecologic cancer [1] because, unfortunately, the majority of patients present with metastatic disease. Modern surgical techniques and platinum-based chemotherapy have not lowered ovarian cancer mortality from the 1979 rate [2]. Despite initial response rates of 80% [3], most patients with advanced ovarian cancer ultimately relapse and develop drug-resistant disease [4], [5]. Currently available second-line agents, all of which have response rates of approximately 15–25%, include doxil, topotecan, gemcitabine, oral etoposide, tamoxifen, and vinorelbine [6]. Because of the relatively low rates of response to all known active agents, there is a critical need for novel therapeutic strategies to delay recurrence or treat recurrent and progressive epithelial ovarian cancer.
Platelet-derived growth factor (PDGF) and its receptor (PDGF-R) are potentially important novel targets for ovarian cancer therapy. PDGF and the corresponding receptors are critical for many normal physiologic functions, such as embryogenesis, wound healing, and the development of the vascular system [7]. PDGF has been implicated in carcinogenesis, is the cellular homologue of v-sis, and causes transformation in vitro [8]. PDGF and PDGF-R have been shown to participate in the progressive growth of ovarian cancer. PDGF-Rα and β are present on human ovarian surface epithelial (HOSE) cells. Hence, PDGF can enhance the in vitro proliferation of these cells [9]. The epithelium of the normal ovary and benign ovarian neoplasms does not express PDGF or PDGF-Rα, but 73% of ovarian carcinomas express PDGF and 36% express PDGF-Rα. In addition, the expression of PDGF-Rα is an independent indicator of a poor prognosis [10]. Another study showed that six epithelial ovarian tumor cell lines expressed the PDGF A- and B-chain genes [11]. Collectively, these data suggest a possible role of PDGF and PDGF-R in the progressive growth of ovarian cancer. However, their expression in progressively growing neoplasms has not been reported.
We conducted a series of immunohistochemical assays to measure the in vitro and in vivo expression of PDGF and PDGF-R in ovarian cancer, and specifically in epithelial ovarian cancer cells and their vasculature. Furthermore, because the activation status of a receptor determines its importance for targeted therapy and the phosphorylation status of PDGF-R in ovarian cancer is currently unknown, we also assayed phosphorylated PDGF-R (p-PDGF-R) expression in clinical specimens of human ovarian cancer. We characterized their expression in human ovarian cancer cells growing in culture and in the peritoneal cavity of nude mice. Our results indicate that the Hey A8 and SKOV3ipl cell lines are suitable models for examining the molecular basis of human ovarian cancer progression and treatment.
Section snippets
Human epithelial ovarian cancer specimens
Twenty frozen surgical specimens of high-grade serous ovarian carcinoma obtained from The University of Texas M.D. Anderson Cancer Center's Gynecologic Oncology Tumor Bank were analyzed. Institutional Review Board approval was obtained before conducting the study.
Human ovarian cancer cell lines and culture conditions
The Hey human ovarian cancer cell line, originally obtained from Dr. G. Mills (M. D. Anderson Cancer Center, Houston, TX), was derived from a peritoneal deposit of a patient with moderately differentiated papillary adenocarcinoma of
Expression of PDGF and PDGF-R in human ovarian cancer specimens
Twenty frozen specimens of high-grade serous ovarian carcinoma were obtained from the University of Texas M.D. Anderson Cancer Center's Gynecologic Oncology Tumor Bank. Double-labeled fluorescence IHC was performed on all samples. Of the 20 samples, 10 were not evaluable because of severe fragmentation or high background fluorescence in negative controls. Representative images of positive PDGF AA and PDGF BB staining are shown in Fig. 1. All 10 evaluable tumors expressed PDGF AA and BB.
Discussion
This report shows that PDGF and its activated receptor are expressed on cells within human surgical specimens and in two human ovarian cancer cell lines growing in vitro and orthotopically in nude mice. The presence of activated PDGF-R on tumor cells as well as tumor-associated endothelial cells has potentially important implications. The literature suggests that PDGF and PDGF-R could play an important role in the progressive growth of ovarian cancer. This study confirms PDGF-R expression in
Acknowledgements
This work was supported in part by Cancer Center Support Core Grant CA16672 and SPORE in Ovarian Cancer Grant CA93639 from the National Cancer Institute, National Institutes of Health. We thank Walter Pagel for critical editorial comments and Lola Lopez for expert assistance in the preparation of the manuscript.
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