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Journal of Clinical Oncology, Vol 25, No 16 (June 1), 2007: pp. 2281-2287 © 2007 American Society of Clinical Oncology. DOI: 10.1200/JCO.2006.09.0795 Whole Genome Oligonucleotide-Based Array Comparative Genomic Hybridization Analysis Identified Fibroblast Growth Factor 1 As a Prognostic Marker for Advanced-Stage Serous Ovarian Adenocarcinomas
From the Cell and Cancer Biology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD; Department of Obstetrics and Gynecology, Gynecologic Oncology; and the Department of Pathology, Brigham and Women's Hospital, Harvard Medical School; Department of Biostatistics, Harvard School of Public Health; Gillette Center for Women's Cancer, Dana-Farber Harvard Cancer Center, Boston, MA; Department of Gynecologic Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX; and the Department of Obstetrics and Gynecology, Saint Vincent Hospital, The Catholic University of Korea, Suwon, Korea Address reprint requests to Samuel C. Mok, PhD, Laboratory of Gynecologic Oncology Brigham and Women's Hospital, BLI-447, 221 Longwood Ave, Boston, MA 02115; e-mail: scmok{at}rics.bwh.harvard.edu
Purpose To identify markers that can predict overall survival in patients with high-grade advanced stage serous adenocarcinomas. Patients and Methods Oligonucleotide array comparative genomic hybridization (aCGH) was performed on 42 microdissected high-grade serous ovarian tumor samples. aCGH segments were obtained and a prediction Cox model was built and validated by the standard leave one out analysis. Both DNA and mRNA copy numbers of selected genes located on the candidate aCGH segments were determined by quantitative polymerase chain reaction (qPCR) and quantitative reverse transcriptase PCR (qRT-PCR) analyses. The gene that showed the highest correlation was further validated on an independent set of specimens and was selected for further functional studies. Results Two chromosomal regions, 4p16.3 and 5q31-5q35.3, exhibited the strongest correlation with overall survival (P < .01). From the 5q31 region, fibroblast growth factor 1 (FGF-1) was selected for further validation study. FGF-1 mRNA copy number was significantly correlated with DNA copy number and protein expression levels (P = .021 and < .001), and both FGF-1 mRNA and protein levels were significantly associated with overall survival (P = .018 and .042). This association was validated for protein expression on an independent set of 81 samples, significant to P = .006. Further studies showed significant correlation between FGF-1 protein expression and CD31+ staining in the tumor stroma (P = .024). Finally, both cancer cells and endothelial cells treated with exogenous FGF-1 showed a significant increase in cell motility and survival. Conclusion Amplification of FGF-1 at 5q31 in ovarian cancer tissues leads to increased angiogenesis, and autocrine stimulation of cancer cells, which may result in poorer overall survival in patents with high-grade advanced stage serous ovarian cancer.
Advanced ovarian cancer (stages III and IV) accounted for the majority (> 75%) of the approximately 20,180 new cases of epithelial ovarian cancer in 2006 in the United States.1 More than 16,000 deaths per year result from ovarian cancer, making this cancer the most lethal gynecologic malignancy. Minimal improvements have been made in overall survival over the past three decades. Ovarian cancer is notable for initial chemotherapy sensitivity using combination platinum and taxane chemotherapy after debulking surgery. However, the vast majority of these women will have their cancer recur within 12 to 24 months after diagnosis and will die of progressively chemotherapy-resistant tumor.2 Prognostic factors for ovarian cancer include stage, grade of the tumor, extent of debulking surgery, and platinum and taxane sensitivity. Debulking surgery has been called an independent predictor for prognosis but many argue that the ability to optimally debulk ovarian cancer to smaller than 1 cm of tumor may reflect an intrinsically biologically more favorable and indolent cancer. Prediction for platinum and taxane sensitivity has not yet been accomplished but is reflected clinically by decrease in serum CA125 during initial chemotherapy, platinum-free interval, and long-term survival. Despite these findings, prognostic biomarkers for ovarian cancer are still lacking. Multiple comparative genome hybridization (CGH) platforms have been developed, and have been used to identify prognostic markers for ovarian cancer.3,4 Although BAC array CGH (aCGH) allows for the identification of DNA copy number variation at an increased mapping resolution on a locus-by-locus basis, the identification of specific genes that are involved remains tedious and challenging. cDNA array analysis is an alternative platform which can be used to assess DNA copy number variation on a gene-by-gene basis. Such an approach has been used successfully to identify DNA copy number changes in specific genes in breast cancer,5,6 ovarian cancer cell lines,7 and microdissected ovarian tumor tissue samples.4 Taken together, CGH analyses have identified multiple prognostic markers in ovarian cancer. However, most of these markers have limited discriminatory power due to the fact that the number of patients used in the studies is small, and clinical outcomes are influenced by multiple factors, which have not been taken into consideration. This is particularly true in ovarian cancer, which is a heterogeneous type of disease. In this study, we report the use of a new 60-mer 22K oligonucleotide-based aCGH platform combined with DNA isolated from microdissected tumor tissue samples to identify DNA copy number abnormalities that may be used as prognostic markers for patients with advanced stage serous adenocarcinomas.
Oligonucleotide Array Preparations The Human Release 1.0 oligonucleotide library, containing 60-mer oligonucleotides representing 22,000 unique genes were obtained from Sigma-Genosys (Sigma, St Louis, MO). The oligonucleotides were dissolved at 10 µmol/L concentration in 50 mmol/L sodium phosphate buffer pH 8.5 and single spotted onto CodeLink slides, using an OmniGrid 100 microarrayer (Genomic Solutions, Ann Arbor, MI) at the Advanced Technology Center (Rockville, MD).
CGH
Identification of Chromosome Segments Associated With Cancer Survival The test for association of the aCGH profile with survival was conducted in two steps. In the first step, the prediction model was trained, where one of 42 samples was reserved for validation and the remaining 41 samples were used in active training. For each aCGH segment, a Cox proportional hazard model (adjusted for debulking status) was fitted, and the two segments with the largest Cox scores were selected as signature associated with survival time. The prediction model was then built. In the second step, the hazard of the one reserved sample based on its aCGH profile and debulking was predicted. The standard leave one out procedure was then conducted by repeating the aforementioned two steps 42 times, where each sample was in turn reserved for validation. To generate the predicted hazard for each patient, and to evaluate the accuracy of our prediction, the samples were equally divided into low- or high-risk group using median predicted hazard as cutoff. The nonparametric log-rank test was used to determine significance.
Segment Validation by Real-Time Quantitative PCR
Validation of Candidate Gene Expression in Selected Regions by Real-Time Quantitative Reverse-Transcriptase PCR Immunohistochemistry. Immunolocalization of fibroblast growth factor 1 (FGF-1) protein and CD31+ endothelial cells was performed on 50 formalin-fixed paraffin-embedded samples (including the 42 samples used for CGH analysis) using a commercially available anti-FGF-1 polyclonal antibody (R&D Systems, Minneapolis, MN), and an anti-CD31 monoclonal antibody (Dako Cytomation, Carpinteria, CA), respectively. FGF-1 protein expression grading was conducted by determining color intensity by the Image-Pro Plus 5.1 software (Media Cybermetics, Silver Spring, MD) in three different areas of both tumor and stroma at 10x magnification. Intensity scores were calculated as the average difference in staining intensity between the tumor and stroma areas. CD31 staining was localized to blood vessels in and around tumor areas. Grading was performed by manual count of stained blood vessels in the three highest expressing areas of each sample, observed at 20x magnification. Scoring was performed by reviewers blinded to any clinical data associated with the investigation.
Validation Studies
Effects of Exogenous FGF-1 on Cell Proliferation, Motility, and Survival
Identification of CNA on Two Chromosome Segments That Are Associated With Survival A total of 176 unique chromosomal segments showing CNA were identified (Fig 1). The nonparametric log-rank test showed the high- and low-risk groups were significantly different (P < .001) in survival (Figs 2 and 3). Amplification in section 5q31-35 was found to be significantly associated with poor survival (P = .003; Figs 2 and 3). Deletion within the 4p16.3 section was conversely shown to offer a strong protective effect on overall patient survival (P = .003; Figs 2 and 3).
qPCR analysis of chromosome segments. A total of five genes located on chromosome 4p16.3 and 12 genes located on 5q31-35 were selected for further validation studies. These genes were chosen at random, equally spaced throughout the regions. The 12 genes chosen from 5q31-35 correlate to P = .006 by Cox regression analysis, when analyzed alongside age and debulking status. When considered individually, statistically significant correlations, as determined by Cox regression, were found for genes FGF-1, RNF14, and ADRB2 (Table A1, online only) from the 5q31-35 region. Of these three genes, FGF-1 showed the most significant association with survival. Patients with high FGF-1 copy numbers had a higher risk of death than those with low copy numbers (hazard ratio [HR], 1.35; 95% CI, 1.07 to 1.70; P = .011). The overall correlation became stronger when considered alongside with either genes RNF14 and ADRB2 or age (Table 1). Further, expression array data generated previously on the same set of specimens11 and an independent validation set (n = 15) of specimens showed that FGF-1 mRNA expression significantly correlated with poor survival (Cox HR = 49.3 and 222.8; P < .001 and .017, respectively). For these reason, we chose to focus on FGF-1, located on 5q31-35, which exhibited the strongest correlation with survival, for further validation studies. The 4p16.3 region showed a strong (P = .069), but not statistically significant correlation with survival by Kaplan-Meier analysis. Genes within this region were not significant (P > .05) either individually or when considered concurrently by Cox regression.
Correlation between FGF-1 DNA copy number, mRNA, and protein expression levels. A significant correlation between FGF-1 mRNA and DNA copy numbers was observed, as determined by Spearman's rho (P = .021), suggesting a functional relationship between DNA copy number changes and subsequent mRNA expression. Furthermore, a correlation study on FGF-1 mRNA and protein expression levels was performed. The association was also statistically significant as determined by Spearman's rho (P < .001).
Correlation Between FGF-1 mRNA and Protein Expression Levels and Overall Survival
Validation Study on Independent Sets of Specimens Using a separate set of 17 DNA samples, the association between FGF-1 copy number and survival, adjusted with age and debulking, was confirmed (P = .046). In addition, the association between FGF-1 protein expression and survival was further supported by an independent validation set of 81 high-grade late-stage serous adenocarcinoma samples (HR = 1.04; 95% CI, 1.01 to 1.07; P = .006), after adjusting for debulking status and age.
FGF-1 Expression Levels Correlated With Microvessel Densities
Differential Expression of FGF Receptors in Ovarian Tumor Tissue The receptors of FGF-1, fibroblast growth factor receptors (FGFR) 1, FRFR2, FGFR3, and FGFR4, have all been shown to play a role in gene activation, though their roles in ovarian cancer are not yet known. All four receptors were investigated in microdissected ovarian tumor tissue by qRT-PCR. FGFR1 and FGFR4 were expressed in 66% and 43%, of the tissue samples, respectively (Fig A1, online only). However, FGFR2 and FGFR3 were detectable in only 4% of all cases. FGFR1 and FGFR4 expression showed statistically significant correlations with FGF-1 expression (P = .007 and P = .024, respectively, by Spearman's rho). Despite this correlation, neither receptor exhibited a significant correlation to overall survival.
Biologic Effects of FGF-1 on HUVEC
Biologic effects of FGF-1 on human ovarian cancer cell lines. Because most advance stage papillary serous tumors express both FGF-1 and FGF receptors, we tested the effects of FGF-1 on multiple ovarian cancer cell lines derived from papillary serous ovarian cancer. Fifty percent of the cell lines (three of six) tested demonstrated a dose-dependent increase in cell motility (Table A2, online only). Eighty-three percent of cell lines (five of six; including the three cell lines which did not demonstrate an increase in cell motility) showed a significant increase in cell survival by FGF-1 when grown under low serum conditions (Table A2, online only). Finally, 17% of cell lines (one of six) demonstrated an increase in cellular proliferation to FGF-1. Of note, there was no correlation between receptor expression pattern and biologic response to FGF-1 in these cell lines (data not shown). These data demonstrate biologic effects of FGF-1 on ovarian cancer cell lines, which are consistent with tumors associated with a poor prognosis.
In this study, we identify FGF-1 as an amplified and overexpressed gene which can serve as a prognostic marker that can be used to predict survival in patients with high-grade, advanced-stage serous ovarian adenocarcinoma using a 22K 60-mer oligonucleotide aCGH platform, and DNA isolated from microdissected tumor tissue samples, combined with multivariate Cox regression analysis. The spotted 60-mer oligonucleotide array platform used in this study, together with other commercially available oligonucleotide microarray platforms, has been successfully used for aCGH.12-16 Using this platform, we identified a total of 176 unique chromosomal segments showing CNA in high-grade advanced-stage serous ovarian adenocarcinomas. Multivariate Cox regression followed by standard leave one out procedure identified an amplicon on chromosome segment 5q31-35 associated with patient survival. We did not apply any arbitrary cutoff so that we could directly treat the DNA copy number as a continuous variable in the Cox regression model. Subsequent validation studies using independent sets of cases showed that FGF-1 DNA and RNA copy numbers as well as protein levels significantly associated with survival time. These data suggest that FGF-1 is a candidate prognostic marker for high-grade late-stage ovarian cancer. FGF-1 or acidic FGF belongs to a family of structurally related fibroblast growth factor polypeptides that have been shown to have mitogenic activities on a broad range of cell types and be to mediators of a wide spectrum of developmental and pathophysiological processes.17 FGF-1 in particular, has been shown to regulate the growth and migration of the endothelial cells.18 Because tumor growth and progression depend on angiogenesis,19-22 we hypothesized that tumor cells secreting high levels of FGF-1 may stimulate endothelial cell growth, and motility of the endothelial cells. Our in vitro data clearly demonstrate increased proliferation, survival, and motility of endothelial cells by physiologic levels of FGF-1. We predict that this biologic activity should produce an increase in microvessel densities and the development of more aggressive ovarian tumors. Our results showed that tumors expressing high levels of FGF-1 indeed had significantly higher CD31-positive microvessel densities, suggesting that FGF-1 secreted by ovarian tumor cells stimulates angiogenesis, which may lead to poor patient survival rates. In fact, miocrovessel density has been shown to be a prognostic marker for different types of tumors.23-26 Like other FGFs, the effect of FGF-1 is mediated primarily through its binding to FGFRs.27 To date, four FGFRs (FGFR1, FGFR2, FGFR3, and FGFR4) have been shown to bind to the FGF-1 ligand.17 To evaluate whether FGF-1 secreted by ovarian cancer cells can stimulate ovarian cancer growth, motility, or invasive activity through an autocrine loop, FGFRs expression patterns were determined. The results showed that ovarian cancer cells expressed predominantly FGFR1 and FGFR4, suggesting that secreted FGF-1 may also activate ovarian cancer cells through binding to its receptors on the cancer cell surface. The biologic significance of this autocrine loop is reflected in our in vitro assays, which showed that FGF-1 increased the motility, survival, and proliferation of ovarian cancer cell lines. The observed biologic effects are diverse among the ovarian cancer cell lines and there was no correlation between receptor status and biologic response to FGF-1. This is consistent with the complexity of the FGF ligand where biologic specificity is dependent in addition to ligand, and receptor also downstream signaling factors.27 These biologic effects would likely lead to the development of more aggressive tumors. The clinical implications of these findings are important. This is one of a very limited number of amplicons identified in ovarian cancer with prognostic value.3 The prognostic stratification of patients with advanced disease has not been possible to date. Further, the identification of a druggable target (within the amplicon), which stratifies patients into prognostic groups, allows for this finding to be incorporated into the design of phase III clinical trials. This is particularly important as antiangiogenesis therapy has recently been shown to be effective in ovarian cancer. In conclusion, oligonucleotide-based aCGH has identified amplification of FGF-1 on 5q31 as a prognostic marker for high-grade advanced-stage serous ovarian adenocarcinomas. Results from validation and subsequent correlation studies suggest that FGF-1 overexpression may lead to increased angiogenesis, resulting in poorer overall patient survival. These findings imply that FGF-1 may be used as a therapeutic target for ovarian cancer.
The authors indicated no potential conflicts of interest.
Conception and design: Michael J. Birrer, Ke Hao, Kwong-Kwok Wong, Dong-Choon Park, Samuel C. Mok Provision of study materials or patients: William R. Welch, Ross S. Berkowitz Collection and assembly of data: Michael J. Birrer, Michael E. Johnson, Ke Hao, Samuel C. Mok, Aaron Bell Data analysis and interpretation: Michael J. Birrer, Michael E. Johnson, Ke Hao, Kwong-Kwok Wong, Dong-Choon Park, Samuel C. Mok Manuscript writing: Michael J. Birrer, Dong-Choon Park, William R. Welch, Ross S. Berkowitz, Samuel C. Mok, Michael E. Johnson Final approval of manuscript: Michael J. Birrer, Michael E. Johnson, Ke Hao, Kwong-Kwok Wong, Dong-Choon Park, William R. Welch, Ross S. Berkowitz, Samuel C. Mok
Supported in part by Dana-Farber/Harvard Cancer Center Ovarian Cancer SPORE Grants No. P50CA105009, R33CA103595, and M.D. Anderson Ovarian SPORE Grant No. P50CA083639 from National Institutes of Health, Department of Health and Human Services, Gillette Center for Women's Cancer, Adler Foundation Inc, Edgar Astrove Fund, the Ovarian Cancer Research Fund Inc, the Morse Family fund, the Natalie Pihl fund, the Ruth N. White research fellowship, Friends of Dana Farber Cancer Institute, the Robert and Deborah First fund, and the intramural research program of the National Cancer Institute. Presented in part at the 97th Annual Meeting of the American Association for Cancer Research, April 1-5, 2006, Washington, DC. M.J.B. and M.E.J. contributed equally to this study. Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.
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Copyright © 2007 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
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