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Molecular Oncology, Markers, Clinical Correlates |
Departments of Surgery [J. T., B. P., M. C. L., F. E., M. N.] and Pathology [S. H. B., S. N.], University of California, Los Angeles, California 90095-1782, and Department of Surgery, Harvard Medical School, Boston, Massachusetts 02115 [S. S.],3
| ABSTRACT |
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| INTRODUCTION |
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Another application of angiogenesis research, as determined by the amount of vascularity in the tumor specimen, was first shown to have prognostic significance in breast cancer by Weidner et al. (5) in 1991. The number of vessels in a tumor specimen correlates with the disease stage and can add prognostic prediction independent of other routinely used markers. Since 1991, an overwhelming majority of published reports have shown a significant correlation between the density of intratumoral microvessels of invasive breast carcinoma and the incidence of metastases and/or patient survival. Similar associations have now been reported for patients with gastrointestinal carcinoma, melanoma, prostate carcinoma, testicular carcinoma, ovarian carcinoma, bladder carcinoma, central nervous system tumors, multiple myeloma, non-small cell lung carcinoma, and squamous carcinoma of the head and neck (6) .
Although vascular density has been prognostic in carcinomas, two recent reports showed that microvessel counts in sarcomas do not correlate with patient outcome (7 , 8) . We therefore set out to investigate whether microvessel count correlates with clinical outcome in our patient population with soft tissue sarcomas.
| MATERIALS AND METHODS |
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Immunohistochemistry.
The specimens were obtained from archival paraffin-embedded tissues of the above 25 patients as well as from selected cases of breast carcinoma. Sections (5 µm) were cut, and H&E preparations of each specimen were performed to confirm the presence of nonnecrotic tumor. Immunostaining was performed with an avidin-biotin-peroxidase complex technique (9)
. The slides were sequentially incubated at room temperature as follows: (a) in 0.3% H2O2 to block the endogenous peroxidase activity; (b) in 5% serum to block nonspecific antibody binding; (c) with the specific primary antibody overnight; (d) with the secondary antibody; (e) with avidin and biotinylated horseradish peroxidase (Vector, Burlingame, CA); and (f) with 3,3'-diaminobenzidine and H2O2 (Vector). The tissues were then stained with Gills hematoxylin and NH4OH, dehydrated, and mounted. The rabbit antihuman vWf4
antibody was purchased from Dako (Carpinteria, CA) and used at 1 µg/ml. Negative controls included staining with mouse IgG1 (Becton Dickinson, San Jose, CA). Secondary antibodies were used at 1:200 dilution and included biotinylated antimouse IgG made in horse and biotinylated antirabbit IgG made in goat (Vector).
Positively stained vessels were counted in five separate fields for each specimen using an Olympus model BH2 microscope. In keeping with the protocol developed by Weidner et al. (5)
, fields containing the highest density of vWf-positive vessels, i.e., "bursts," were identified at scanning power and then counted at x400. The numbers for the five fields were averaged. However, the vessel counts used to calculate the SD values depicted in Fig. 3
were obtained from 10 representative fields of the tumor specimen, which would include both "bursts" as well as areas with sparse vessels. Fig. 3
represents the SD in individual cases averaged together.
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2 and Wilcoxon tests were used for univariate analysis. Statistical significance was defined by P < 0.05.
Western Analysis of Tumor Matrix.
Five sarcoma and five breast carcinoma specimens were used for matrix extraction according to a protocol described previously (10)
. These specimens were obtained either fresh or fresh frozen. Briefly, the tissue fragments were pelleted and homogenized in
3 volumes of high salt extraction buffer (3.5 M NaCl and 50 mM Tris-HCl, pH 7.4) containing proteinase inhibitors. The homogenate was centrifuged at 12,000 x g for 15 min, and the high salt extraction was repeated. The insoluble material was again pelleted and extracted overnight in an equivalent volume of 2 M urea, 50 mM Tris-HCl buffer (pH 7.4) with constant stirring. The urea extract was centrifuged at 12,000 x g for 15 min, and the supernatant was dialyzed against several changes of Tris-buffered saline (TBS; 150 mM NaCl, 50 mM Tris-HCl, pH 7.4) containing proteinase inhibitors. High salt extracts were also dialyzed against TBS. Proteins in the media were precipitated overnight at 4°C with ammonium sulfate at 50% saturation. The precipitate was collected by centrifugation at 10,000 x g for 1 h and dissolved in 1 ml of TBS with proteinase inhibitors. The high salt and urea extracts and the media fractions were stored at -80°C.
Subsequently, the protein contents were measured and normalized for Western analysis. Tissue extracts were resolved on nonreducing SDS-PAGE mini-gels and transferred to nitrocellulose membranes by electrophoretic blotting. Membranes were blocked for 2 h at room temperature in PBS-Tween (PBS and 0.1% Tween 20) containing 1% BSA and 1% gelatin and then incubated for 1 h with primary antibody in PBS-Tween. The primary antibodies used were against VEGF, bFGF, aFGF, TGF-
, TGF-
, PD-ECGF, angiogenin, and IFN-
obtained from R&D (Minneapolis, MN). Other sources were used for the antibodies to TIMP-1 (Chemicon, Temecula, CA), thrombospondin (Dr. Luisa Iruela Arispe, UCLA), and plasminogen fragment (American Diagnostica, Inc., Greenwich, CT). The concentration of these primary antibodies was 1 µg/ml. Membranes were then washed three times over a 30-min period in PBS-Tween, incubated for 1 h with the appropriate horseradish peroxidase-conjugated secondary antibody (mouse monoclonal antirabbit IgG or sheep antimouse IgG; Amersham, Piscataway, NJ) diluted 1:5000 in PBS-Tween, and washed in PBS-Tween as before. The membranes were then developed using the ECL Western blotting detection system according to the manufacturers instructions (Amersham).
In Situ Hybridization.
In situ hybridization studies were conducted with riboprobes made from the full-length TIMP-1 cDNA (provided by Dr. Judith Gasson, UCLA). The pBluescript SK plasmid (Stratagene, La Jolla, CA) containing a 0.5-kb EcoRI fragment of the human TIMP-1 gene was linearized with XbaI for antisense strand preparation from the T7 promoter and with HindIII for sense strand preparation from the T3 promoter (11)
. [35S]UTP-labeled RNA transcripts were synthesized at concentrations of 4 to 6 x 105 cpm/µl. Paraffin-embedded sections were deparaffinized, fixed in 4% paraformaldehyde in PBS, rehydrated, washed in 0.5x SSC, and digested with proteinase K at room temperature for 10 min. The sections were acetylated using 0.25% acetic anhydride and 0.1 M triethanolamine HCl rinsed with 0.5x SSC and dehydrated with ethanol and finally dried. A TIMP-1 riboprobe was applied in a hybridization mixture containing deionized formamide (50%), dextran sulfate (10%), tRNA (0.5 mg/l), salmon sperm DNA (1 mg/ml), 10 mM DTT, 0.3 M NaCl, 5 mM EDTA, 20 mM Tris-HCl, and 10 mM NaPO4 (pH 6.8). The mixture was heated at 65°C for 15 min and chilled on ice. Fresh DTT was added to achieve a concentration of 20 mM. Then 120 µl of the mixture were applied to each section, and Parafilm coverslips were applied. Hybridizations were carried out in humidified chambers overnight at 55°C. Coverslips were removed in 5x SSC, 10 mM DTT at 55°C. Sections were washed with 2x SSC containing 2-mercaptoethanol and EDTA, treated with RNase A, and washed in 0.1x SSC at 62°C for 3 h (high stringency). Slides were then washed for 5 min at room temperature in 0.5x SSC without 2-mercaptoethanol or EDTA. The sections were dehydrated with ethanol and air dried. The slides were exposed to Ilford K5D emulsion and stored in the dark at 4°C until developed, which took at least 1014 days. Digital image analysis was then used to compare the signal intensities with the antisense probe with the signal intensities of the sense probe (background) over the corresponding areas of tumor cells and stroma in the carcinomas. Digital image analysis was composed of a Leitz Dialux microscope linked to a Vidicon camera, an IBM PC with PCVision digitizer, and Microscience software.
| RESULTS |
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60 vessel count/field. There was no correlation found between metastatic disease (present and future) or survival and the number of "burst" vessels stained by vWf (Fig. 2)
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, PD-ECGF, angiogenin, and TIMP-1. The carcinoma matrix contained VEGF, TGF-
, PD-ECGF, angiogenin, and TIMP-1. Overall, there were no significant differences in the angiogenic profile of the soluble matrix components of sarcomas and carcinomas.
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| DISCUSSION |
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Ohsawa et al. (7) concluded that "angiogenesis is apparently not a key factor in the formation of metastasis by sarcomas." We do not equate lack of prognostic significance to lack of functional importance. In fact, much evidence suggests that sarcomas are angiogenesis dependent. Sarcomas are known to express potent angiogenic factors (13 , 14) . In animal models of rhabdomyosarcoma, an antiangiogenic drug, TNP-470, inhibited tumor growth (15) . Preliminary results from human clinical trials with various antiangiogenic drugs suggested that suppression of neovascularization can also stop tumor growth in patients with sarcomas. There was objective response when TNP-470 was given to patients with Kaposis sarcoma (16 , 17) . Similar promising results were observed with other antiangiogenic drugs including thalidomide, pentosan polysulfate, tecogalan, suramin, and platelet factor-4 (18, 19, 20, 21, 22) .
In the process of determining vascular density for this study, we have observed that the pattern of blood vessel distribution is different in the sarcoma specimens than in the carcinoma specimens. Whereas the carcinoma vessels often cluster in "bursts," the sarcoma vessels are more homogeneously and diffusely distributed. This is manifested in the larger SD of vessel counts in the typical carcinoma specimen. In carcinomas, the vessels are in general found in the stroma adjacent to the infiltrative tumor. On the other hand, the sarcoma vessels are often seen inside the tumor mass.
Carcinomas are composed of two compartments: an epithelial compartment of malignant epithelial cells and a stromal compartment of fibroblasts and myofibroblasts. This desmoplastic benign stroma can account for 3090% of the specimens. Both compartments contribute to the tumoral matrix in terms of their respective gene products. Sarcomas, on the other hand, are composed of predominantly only one compartment, the malignant mesenchymal cell that largely synthesizes the sarcoma matrix and contributes mostly to its gene products. Although sarcomas also contain a benign stromal part, this component is often observed to be <1% of the specimens. Therefore, the single predominant compartment in sarcomas is comprised of the malignant mesenchymal cells.
Angiogenesis is thought to be regulated by the balance of positive and negative factors in a particular microenvironment. The Western analysis performed showed that the stroma of the two tumor types contained both angiogenic stimulators and inhibitors. However, in situ hybridization with one angiogenic inhibitor, TIMP-1 (23) , showed that it localized predominantly to the stromal fibroblasts and myofibroblasts and not within the carcinoma cells. In carcinomas, two compartments contribute to this balance. Angiogenesis may occur when the influence of one compartment exceeds the other. In areas near the malignant epithelial cells, angiogenic stimulation predominates and results in "bursts" of vessels. On the other hand, the region near the stromal fibroblasts and myofibroblasts would contain more angiogenic inhibitors and would be less vascular. Angiogenesis thus becomes an all-or-none phenomenon, dependent upon the contributions of both compartments. Classic clustered bursts of angiogenesis in carcinoma are thus the example of this phenomenon. Sarcomas, on the other hand, are governed predominantly by the contributions of a single compartment, the sarcomal cells themselves. Hence, their contribution would be more constitutive, stable, and predictable and not confused by the presence of another compartment. The diffuse vessel density of sarcomas that we have observed in the present study would be the consequence of the influence of a single compartment.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 Supported by NIH Grant CA69433 and grants from the American Cancer Society and the UCLA Jonsson Comprehensive Cancer Center. J. T. is a recipient of a National Research Service Award. ![]()
2 To whom requests for reprints should be addressed, at UCLA Surgery/Oncology, Box 951782, Los Angeles, CA 90095-1782. Phone: (310) 206-2215; Fax: (310) 825-7575. ![]()
3 Research was performed at the University of California Los Angeles Medical Center, Los Angeles, CA 90095. ![]()
4 The abbreviations used are: vWf, von Willebrand factor; VEGF, vascular endothelial growth factor; bFGF, basic fibroblast growth factor; aFGF, acidic FGF; TGF, transforming growth factor; PD-ECGF, platelet-derived endothelial cell growth factor; TIMP, tissue inhibitor of metalloproteinase. ![]()
Received 5/12/99; revised 8/17/99; accepted 8/20/99.
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