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Molecular Oncology, Markers, Clinical Correlates |
Department of Oncological Diagnostics and Therapy, German Cancer Research Center, D-69120 Heidelberg, Germany
| ABSTRACT |
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| INTRODUCTION |
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OReilly et al. (8) reported that angiostatin, produced by a primary Lewis lung carcinoma, suppressed the growth of lung metastases. Lannutti et al. (9) administered angiostatin to mice with hemangioendothelioma and found that angiostatin significantly reduced tumor volume and increased survival time when compared with the untreated controls. OReilly et al. (10) inhibited the growth of three human and three murine primary carcinomas in mice by systemically administering human angiostatin. They found that the apoptotic index was significantly increased in those tumors treated with angiostatin.
In the present study, we investigated the expression of angiostatin in lung cancer cell lines and the biopsies of lung cancer patients. We compared the expression of angiostatin in NSCLCs with the respective patients actual clinical outcome and examined whether the combined determination of VEGF and angiostatin expression in tumor biopsies can yield improved prognostic information for lung cancer patients.
Furthermore, we evaluated the effect of angiostatin expression on the transplantability into nude mice and also analyzed the histological sections of the primary human tumors for apoptosis.
| MATERIALS AND METHODS |
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Patients and Tumors.
One hundred forty-three consecutive patients with previously untreated
NSCLCs were admitted into this study. All patients (129 men and 14
women) underwent surgery in the Chest Hospital Heidelberg-Rohrbach. The
morphological classification of the carcinomas was conducted according
to the WHO specifications. Of the carcinomas, 81 were squamous
carcinomas, 38 were adenocarcinomas, and 24 were large cell carcinomas.
All patients were staged at the time of their surgery (lobectomy,
n = 95; pneumonectomy, n = 28; partial
resection, n = 20) according to the guidelines of the
American Joint Committee on Cancer. Forty five patients had stage I or
stage II tumors, and 98 patients had stage IIIA tumors. Ninety-eight
patients were treated only by surgical procedures, 13 patients were
additionally treated with cytotoxic drugs, and 31 patients were treated
with radiation (one case could not be defined precisely). The different
treatment procedures had no significant effects on the survival time of
the patients in our study. The average age of the patients was 58
years. Follow-up data were obtained from hospital charts and by
corresponding with the referring physicians. The survival times were
determined from the day of surgery. Only patients who were alive >4
weeks after surgery (n = 134) were included in the
survival analysis.
Immunohistochemistry.
The previously described biotin-streptavidin method was used to detect
the proteins (11
, 12)
. Briefly, formalin-fixed and
paraffin-embedded tissues were deparaffinized and pretreated with
proteinase K (Boehringer, Mannheim, Germany). After incubation with
hydrogen peroxide and protein blocking solution, the primary antibodies
were applied for 16 h at 4°C. After incubation with secondary
antibodies, the streptavidin biotinylated peroxidase complex Strept AB
Complex/HRP (Dako, Denmark) was added, and the peroxidase activity
visualized with 3-amino-9-ethylcarbazole. Counterstaining was performed
with hematoxylin. Negative and positive controls were conducted. As a
further control for specificity, the antibodies were incubated with
blocking peptides (Santa Cruz Biotechnology, Inc., Santa Cruz, CA).
Without having any prior knowledge of each patients clinical data,
three observers independently evaluated the results from the
immunohistochemical staining.
To detect angiostatin, a rabbit polyclonal antibody that was generated by immunizing rabbits with purified angiostatin protein (Ab-1; Oncogene Research Products, Cambridge, MA) was used (dilution, 1:150). Detection of VEGF was carried out using a rabbit polyclonal anti-VEGF antibody (Ab-2, dilution 1:10; Dianova, Hamburg, Germany). To detect caspase-3, we used the mouse monoclonal IgG1 antibody CPP32 p20 (E-8, dilution 1:500; Santa Cruz Biotechnology).
Three observers independently evaluated the results from the immunohistochemical staining without any prior knowledge of each patients clinical data. The few cases with discrepancies among the investigators were reevaluated and then classified according to the classification given most frequently by the observers. To evaluate the protein expression, the percentages of positive cells and the staining intensity were established. The tumors were classified into three groups: tumors without staining, tumors with weak staining, and tumors with moderate to strong staining. Tumors without staining or weak staining were classified as negative.
Western Blot Analysis.
Protein was isolated with the TRI reagent (MRC, Cincinnati, OH). After
electrophoresis on a 12% polyacrylamide gel in the presence of SDS and
transfer to a polyvinylidene difluoride membrane (DuPont NEN, Boston,
MA) by electroblotting, the transferred protein and molecular weight
markers were detected with 0.3% Ponceau S. Blocking in 1% blocking
solution (Western Blocking Reagent; Boehringer Mannheim, Mannheim,
Germany) preceded the 1-h long incubation with the mouse antihuman
angiostatin antibody (clone C91; PharMingen, Becton Dickinson,
Hamburg, Germany) and the rabbit polyclonal antibody (Ab-1; Oncogene
Research Products) diluted in 0.5% blocking solution. Thereafter,
peroxidase-conjugated streptavidin secondary antibodies
Western-Blotting Kit (Boehringer Mannheim) were used to detect the
proteins. All incubations were conducted at room temperature, and
several washing steps followed each incubation. Signals were detected
with chemiluminescence.
Assessment of Apoptosis.
Apoptotic cell death was detected with a nonradioactive 3' end
DNA-labeling technique using the in situ cell death
detection kit (Boehringer Mannheim). The procedure was described
previously (13)
. Briefly, the paraffin-embedded specimens
were dewaxed and then treated with proteinase K. Endogenous peroxidase
was blocked with 0.03% hydrogen peroxide, and the specimens were
incubated with the labeling reaction mixture containing
fluorescein-labeled nucleotides and terminal deoxynucleotidyl
transferase. The peroxidase activity was made visible with
3-amino-9-ethylcarbazole. Negative controls were executed by omitting
terminal deoxynucleotidyl transferase. DNase-treated specimens were
used as positive controls. The apoptotic index was calculated as the
ratio of apoptotic cells to the total number of tumor cells.
Xenotransplantation into Nude Mice.
Of the 143 lung carcinomas, 106 tumors could be heterotransplanted into
nude mice (BALB/c nu/nu mice, females, 610 weeks of age).
Animals were maintained by conventional methods in Macrolon cages at
27°C and at 50% humidity. Autoclaved feed and acidified water were
provided ad libitum. For transplantation, the tumor
specimens were finely minced with scissors and suspended in tissue
culture medium (TCM 199). Medium was added to reach a tissue:medium
ratio of 1:3 by volume. Three hundred µl of each suspension
(>107 cells/mouse) were injected s.c. into the
flanks of three nude mice each with a 1.4-mm trocar needle. Tumor take
was assumed when the presence of growing nodule(s) was noted within 3
months and the tumor histology was confirmed.
Statistical Analysis.
Patient survival time was determined from the date of surgery until the
last follow-up visit or reported death and was evaluated by using life
table analyses according to the method of Kaplan and Meier. Groups were
compared by using the log-rank test and rank sum test. The correlations
between clinical and molecular parameters were statistically evaluated
by using Fishers exact test. This test was used as a statistical
hypothesis test for the presence or absence of a relationship between
two factors. The results were regarded as statistically significant if
P
0.05.
| RESULTS |
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| DISCUSSION |
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In the current study, we evaluated the expression of angiostatin in human lung cancer cell lines and biopsies of human NSCLCs. We determined that angiostatin is expressed in human lung carcinomas.
In addition to pertinent clinical data, new risk factors at the molecular and cellular level are the subject of many ongoing studies. Predictive and prognostic factors can serve many purposes. They are used to understand the natural history of cancer, to identify homogeneous patient populations, to characterize subsets of patients with a potentially favorable or unfavorable outcome, to predict the success of therapy, or to generate follow-up strategies. Therefore, we assessed whether the expression of angiostatin could be used as a prognostic factor for patients with NSCLCs. We found that patients with angiostatin-positive lung cancer survived longer than patients with angiostatin-negative tumors. To determine whether a combination of stimulating and inhibiting factors may result in improved prognostic information, we examined all of the possible combinations of angiostatin and VEGF with regard to patient survival. Our results indicate that evaluating both factors together may very well be more important for the prognostic information than the isolated assessment of either. Therefore, our results demonstrate that the balance of angiogenesis-promoting and angiogenesis-inhibiting factors plays a crucial role in the control of tumor growth.
Tumors are complex cell populations in which cellular gain and loss occurs concurrently (16) . Apart from proliferation, apoptosis or programmed cell death is one of the most important regulatory mechanisms of cellular homeostasis in organisms. The suppression of angiogenesis by angiostatin results in a characteristic pattern in which apoptosis and tumor cell proliferation create a dynamic equilibrium (5 , 14) . It has been suggested that angiogenic inhibitors control growth by indirectly increasing apoptosis in tumor cells (14) . In our lung cancer study, we detected increased caspase-3 in angiostatin-positive lung carcinomas. The apoptotic indices were also higher in angiostatin-positive tumors, as compared with angiostatin-negative tumors, but these results were not statistically significant.
To study the effect of angiostatin expression on the transplantability into nude mice, we compared the angiostatin expression in the primary tumors with the take rate into nude mice. We found that the expression of angiostatin is associated with the growth of human lung cancer after heterotransplantation into nude mice. It was discovered that the take rate of human angiostatin-positive lung carcinomas was reduced compared with the take rate of angiostatin-negative carcinomas; however, this result does not reach statistical significance.
In conclusion, angiostatin is expressed in a subgroup of human NSCLCs. These tumors are characterized by an elevated incidence of apoptosis and a reduced transplantability into nude mice, and the presence of angiostatin in primary lung tumors is associated with longer patient survival.
The discovery of specific endothelial inhibitors such as angiostatin not only increases our understanding of the function of these molecules but also provides an important strategy for cancer treatment. Recent studies have demonstrated that application of angiostatin significantly suppresses the growth of a variety of mouse tumors (9 , 10 , 17) . However, the dosages of angiostatin used in these animal studies is apparently too high for use in clinical trials (18) . Additionally, long-term treatment with angiostatin is required to achieve an antitumor effect. Nevertheless, antiangiogenic substances are another promising tool in anticancer therapy.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 To whom requests for reprints should be
addressed, at Department of Oncological Diagnostics and Therapy, German
Cancer Research Center, Im Neuenheimer Feld 280, D-69120 Heidelberg,
Germany. Fax: 0049-6221-423225. ![]()
2 The abbreviations used are: VEGF, vascular
endothelial growth factor; NSCLC, non-small cell lung carcinoma. ![]()
Received 2/11/00; revised 5/26/00; accepted 5/30/00.
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in human lung cancer. Cancer (Phila.), 71: 3181-3187, 1993.
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