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Molecular Oncology, Markers, Clinical Correlates |
1 Pathology Division, National Cancer Center Research Institute East and 2 Department of Surgery, National Cancer Center Hospital East, Kashiwa, Chiba, Japan; and 3 Department of Gastroenterology and Hematology, Hokkaido University Graduate School of Medicine, Sapporo, Japan
| ABSTRACT |
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Experimental Design: Immunohistochemical staining for IGF-1R was done on formalin-fixed, paraffin-embedded specimens from 161 patients with curatively resected Dukes C CRC and at least 5-year follow-up periods. We investigated the association between the levels of IGF-1R expression and the clinicopathologic parameters. To evaluate the accurate prognostic value of IGF-1R expression, we investigated two patterns of recurrence-free survival (RFS) according to the mode of recurrence, the hepatic-RFS (H-RFS), and the nonhepatic-RFS (nH-RFS). The influence of the pattern of IGF-1R immunostaining (membranous or cytoplasmic) on RFS was also estimated.
Results: High (diffuse staining) and low (focal staining) levels of IGF-1R expression were found in 45 (28%) and 116 (72%) specimens, respectively. The recurrence rate was significantly higher in the latter group (49 of 116) than the former group (9 of 45; P = 0.01). H-RFS was significantly longer for the former group than the latter group (P = 0.021), whereas no difference was found in nH-RFS between the two groups (P = 0.121). In multivariate analysis, the level of IGF-1R expression was an independent factor for H-RFS (P = 0.015) as were the depth of invasion and lymph vessel invasion (P = 0.006 and 0.022, respectively). Using a combination of the level of IGF-1R expression and these two factors, the prognostic value was further increased. When IGF-1R staining patterns (membranous or cytoplasmic) were compared, membrane staining of IGF-1R possessed prognostic significance.
Conclusions: In Dukes C CRC, focal membrane expression of IGF-1R in the primary tumor can predict a high risk of recurrence, especially liver metastasis. Understanding the mechanisms involved could lead to new therapeutic approaches for advanced CRC.
| INTRODUCTION |
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The insulin-like growth factor (IGF) system is associated with the regulation of cell growth, transformation, and apoptosis in CRCs (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17) . Overexpression of IGF-1R has also been described in several colon cancer cell lines and in human colorectal cancer tissues (18, 19, 20, 21, 22, 23) . Although some studies have attempted to show the prognostic value of IGF-1R expression in CRC by immunohistochemical analysis, the importance of IGF-1R in the recurrence of CRC has not been elucidated (20, 21, 22) . Hakam et al. (20) reported a correlation between the intensity of the IGF-1R staining and CRC tumors of high grade and high stage. Weber et al. (21) showed significantly stronger IGF-1R immunostaining in CRC cells compared with adjacent normal colonic epithelial cells. However, these two reports did not refer to any correlation between IGF-1R expression and patient survival rate. On the other hand, Peters et al. (22) reported that univariate survival analyses for IGF-1R had revealed no relevant findings because almost all cases (99.6%) were positive for IGF-1R expression in the primary CRC. It is noteworthy that all these reports investigated all recurrences of CRCs and did not focus on liver-specific recurrence. Recently, IGFs have also been noted to play a critical role in CRC liver metastasis as well as in primary tumor growth (7 , 17 , 24, 25, 26, 27, 28) . We developed a hypothesis that the levels of IGF-1R in CRC primary tumor might predict liver metastasis.
We investigated the expression of IGF-1R immunohistochemically in 161 curatively resected Dukes C CRC tissue samples, using an anti-IGF-1R mouse monoclonal antibody that recognizes the
subunit of IGF-1R. To estimate the prognostic value of IGF-1R, we separated the population into a recurrence-free group (n = 103), a recurrence to the liver group (n = 31), and a recurrence to other sites group (n = 27), and we investigated the relations between each group and IGF-1R levels. We also examined the influence of different staining patterns of IGF-1R (membrane or cytoplasmic) on the recurrence-free survival (RFS) rate.
| PATIENTS AND METHODS |
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Antibodies.
To evaluate functional IGF-1R expression, we tested five commercially available mouse monoclonal antibodies against human IGF-1R
subunit, MAB1120, MAB1122 (clone 2431 and 2457, respectively; CHEMICON International, Inc., Temecula, CA), 2C8 (sc-463; Santa Cruz Biotechnology, Inc., Santa Cruz, CA), Ab-1 (clone
IR-3; Oncogene Research Products, San Diego, CA), and Ab-4 (clone 2460; Lab Vision Corporation, Fremont, CA). The results of preliminary experiments clearly showed that MAB1120 is the most suitable for immunohistochemical analysis in formalin-fixed paraffin-embedded sections. To confirm the reproducibility of previous reports using an antibody against human IGF-1R ß subunit (20
, 22)
, an anti-IGF-1Rß rabbit polyclonal antibody C-20 (sc-713; Santa Cruz Biotechnology, Inc.) was selected.
Expression of IGF-1R.
All tumor tissues used in this study were derived from the routine formalin-fixed pathologic samples taken from the resected colorectal specimens. One block with the most deeply invasive edge was selected from each specimen, after a review of H&E-stained slides of the surgical specimens. Sections (5 µm) were cut from the paraffin blocks and mounted on silanized slides. The sections were deparaffinized in xylene, dehydrated with graded EtOH, and then immersed in methanol with 0.3% hydrogen peroxide for 20 minutes to inhibit endogenous peroxidase activity. After being washed with distilled water, the sections were placed in a 10 mmol/L citrate buffer solution.
For antigen retrieval, the slides were heated twice at 95°C for 10 minutes in a microwave oven (H2800 Microwave Processor, Energy Beam Sciences Inc.) and then cooled for 1 hour at room temperature. The slides were washed three times in PBS, then nonspecific binding was blocked by preincubation with 2% normal swine serum in PBS (blocking buffer) for 60 minutes at room temperature. Individual slides were then incubated overnight at 4°C with anti-IGF-1R antibody, MAB1120 or C-20, at a final concentration of 2 µg/mL (dilution 1:100) in the blocking buffer. The slides were washed five times with PBS, then incubated with a peroxidase-labeled polymer conjugated to goat antimouse IgG (DAKO EnVision Peroxidase Mouse, code K4000; Dako Corp., Carpinteria, CA) and goat antirabbit IgG (DAKO EnVision Peroxidase Rabbit, code K4002; Dako Corp.) for 1 hour at room temperature. After extensive washing with PBS, the color reaction was developed in 2% 3,3'-diaminobenzidine in 50 mmol/L Tris-buffer (pH 7.6) containing 0.3% hydrogen peroxide for 5 to 10 minutes. The sections were then counterstained with Meyers hematoxylin, dehydrated, and mounted.
In the negative controls, the primary antibody solution was substituted with the blocking buffer.
Immunoabsorption.
An anti-IGF-1R antibody MAB1120 was incubated overnight at 4°C with 50-fold quantity of a recombinant human IGF-1R
(catalogue number 391-GR; R&D Systems, Inc., Minneapolis, MN) derived from a DNA sequence encoding the extracellular domain of IGF-1R prepropeptide (MAB1120/recombinant human IGF-1R
, 400 ng/20µg). The mixture was centrifuged at 15,000 x g for 30 minutes at 4°C. Supernatant (immunoabsorbed fraction) was used as a substitute for the primary antibody.
Western Blotting.
Total cell lysate from human colon cancer cells (HT29) was collected as described previously (26)
. Samples of 40 µg of total cell lysate were electrophoresed on a 7.5% SDS-polyacrylamide mini-gel, and the separated proteins blotted electrophoretically onto a polyvinylidene difluoride membrane (Millipore Corp., Bedford, MA). Nonspecific binding was blocked for 1 hour with 5% nonfat dry milk and 1% BSA in PBS (pH 7.4) containing 0.1% Tween 20 at room temperature. The membrane was incubated overnight in the anti-IGF-1R antibody MAB1120 (1:250) or the supernatant of immunoabsorption test (1:250) at 4°C and then for 1 hour with peroxidase-labeled rabbit antimouse antibody (1:3,000; Zymed Laboratories, Inc., San Francisco, CA). The IGF-1R bands were visualized with Lumi-Light PLUS (Roche Diagnostics Corp., Indianapolis, IN).
In the negative controls, the primary antibody solution was replaced by the blocking buffer.
Evaluation of Immunostaining.
Immunohistochemical staining was evaluated independently by three investigators (M. N, S. M, and A. O) who were blinded to the clinical outcomes. To evaluate functional IGF-1R expression, we used an anti-IGF-1R antibody MAB1120 and evaluated focusing on only the cell membrane expression and ignoring cytoplasmic staining (defined as CRITERIA-1). The immunohistochemical results for IGF-1R were classified under the "diffuse-positive pattern" if the tumor cells showed an unequivocally strong membranous reaction in >50% of the carcinoma cells (Fig. 2C)
. Cases with faint staining or with a positive reaction in <50% of tumor cells were classified under the "focal-positive pattern" (Fig. 2D)
. Two different criteria were applied for evaluation: CRITERIA-1, in which positive staining was evaluated in membranous staining alone, and CRITERIA-2, in which evaluation of either membranous or cytoplasmic staining was done. CRITERIA-1 was used because of the importance of evaluating membrane staining alone. CRITERIA-2, which had been used in previous studies (20, 21, 22)
, was used to enable comparison with the earlier immunohistochemical staining studies. When evaluating the staining pattern of anti-IGF-1Rß antibody C-20, we targeted cytoplasmic staining alone.
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Statistical Analysis.
In the analysis of H-RFS or nH-RFS, patients who died of a disease other than colon cancer recurrence were censored at the date of death. Statistical analysis of the association between the levels of IGF-1R expression and clinicopathologic parameters was based on Fishers exact test. The association between the clinicopathologic parameters and the risk of recurrence was evaluated with the Cox proportional hazard model. We plotted H-RFS and nH-RFS curves as graphs using calculations based on the Kaplan-Meier method. Survival differences between the two groups were assessed with the log-rank test. The observations determined to be statistically significant in the univariate analysis were subsequently subjected to a multivariate analysis. In all analyses, a P value <0.05 was considered statistically significant.
| RESULTS |
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For at least 5 years after curative surgery, all patients were carefully followed to determine postoperative survival. During this period, tumors recurred in 58 patients (36%). Sites of recurrence included the liver in 31 patients, lung in 8 patients, lymph nodes in 5 patients, the peritoneum in 4 patients, bone in 1 patient, and the recurrence was local in 9 patients.
Specificity of an Anti-IGF-1R Antibody MAB1120.
We did an immunoabsorption test to confirm the specificity of the anti-IGF-1R antibody, MAB1120. The immunoreactivity of IGF-1R by MAB1120 (Fig. 1A)
was diminished after immunoabsorption by recombinant human IGF-1R
(Fig. 1B)
to the level of the negative control (Fig. 1C)
. Furthermore, the specificity was also tested by Western blot analysis against the lysates of HT-29 cells expressing IGF-1R. A band corresponding to the
subunit of the IGF-1R (Mr 130,000) was detected by MAB1120, and this band disappeared after the immunoabsorption procedure (Fig. 1D)
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antibody, MAB1120, for the further evaluation of IGF-1R expression in this study.
Relations between the Levels of IGF-1R Expression and Clinicopathologic Factors.
Using MAB1120, we observed two typical immunostaining patterns for IGF-1R according to CRITERIA-1 (Fig. 2C
, diffuse-positive case; 2D, focal-positive case). Of the 161 colorectal cancers analyzed, 45 (28%) were classified as diffuse-positive cases, and 116 (72%) were focal-positive cases. Expression levels of IGF-1R in CRCs were first compared with the clinicopathologic factors. In the various clinicopathologic factors, the recurrence rate was significantly higher in focal-positive cases than in diffuse-positive cases [42% (49 of 116) versus 20% (9 of 45), respectively; P = 0.01]. The association between the IGF-1R expression level and recurrence was more evident in the cases with metastases to the liver than to other sites (Table 1)
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Influence of Clinicopathologic Factors, Including IGF-1R Expression, on Recurrence-Free Survival.
To elucidate the prognostic factors for Dukes C CRC patients, we investigated IGF-1R expression and several clinicopathologic factors for liver metastasis using CRITERIA-1 evaluated by membranous staining alone. A univariate analysis showed that the depth of invasion, lymph vessel invasion, venous invasion, and IGF-1R expression pattern was associated with H-RFS (P = 0.003, 0.023, 0.02, and 0.021, respectively; Table 2
). The specimens with focal-positive IGF-1R expression had a significantly shorter H-RFS than those with diffuse-positive expression (P = 0.021, Fig. 3A
), whereas IGF-1R expression was not associated with nH-RFS (Fig. 3B)
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| DISCUSSION |
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Previous reports that evaluated the prognostic value of IGF-1R expression using immunohistochemical techniques did not take account of the mode of recurrence (20, 21, 22) . IGFs are noted to play a critical role in not only the primary growth but also in liver metastasis from CRCs (7 , 17 , 24, 25, 26, 27, 28, 29) . One reason why we could show the prognostic significance of IGF-1R may be attributable to the focus of the study on the mode of recurrence, especially liver metastases.
Another reason is the difference in our definition of IGF-1R expression. In all previous studies evaluating the prognostic value of IGF-1R expression in CRCs, the levels of IGF-1R expression were defined both by cell membrane staining and by cytoplasmic staining (CRITERIA-2). Because IGF-1R is a transmembrane tyrosine kinase receptor, like the members of the human epidermal growth receptor family, it is reasonable that only membranous staining of IGF-1R, which implies a functional receptor, had prognostic significance in H-RFS. Conversely, cytoplasmic staining of IGF-1R may imply a nonfunctional receptor, including precursor molecules of the receptor and degraded and recycled receptors (30)
. Our results correspond to several immunohistochemical studies in breast cancer that regarded membranous staining as the only evidence for the assessment of human epidermal growth receptor-2 expression (31)
. Moreover, it might be more difficult to evaluate the membrane staining precisely with an anti-IGF-1R antibody toward the ß subunit (intracellular) portion of the receptor, which could not discriminate between cell membrane staining and cytoplasmic staining of the receptor. However, we used an antibody that recognized the extracellular
subunit of the receptor, showed no cross-reaction with the insulin receptor, and could simplify the evaluation of IGF-1R expression.
Our results, which indicated an association between low levels of IGF-1R and a high risk of metastasis, may be paradoxical. However, similar results have been reported in several studies that used clinical samples of breast and prostate cancers (32, 33, 34, 35) . In animal models, Pennisi et al. (36) described that a decrease in the expression of IGF-1R in MCF-7 cells led to increased motility and decreased ability to form aggregates in culture, resulting in characteristics consistent with a more metastatic phenotype. Mauro et al. (37) showed that overexpression of IGF-1R significantly decreased the invasiveness of MCF-7/6 cells and suggested that overexpression of IGF-1R might reduce metastatic potential in E-cadherinpositive cells. Lee et al. (38) suggested two possible explanations in their review of the IGF system in breast cancer. First, a high expression of IGF-1R may reflect an absence of ligands and low receptor signaling, whereas a low IGF-1R content may indicate that the receptor is fully active, thus stimulating tumor growth and leading to a worse prognosis. Second, IGF-1R expression could also identify a relatively well-differentiated tumor that still requires IGF for proliferation. In addition, on the basis of a report indicating that tumor microenvironmental stress, like hypoxia, low pH, and low glucose, could increase the IGF-1R expression (39) , we speculated that IGF-1R expression might indicate the requirement of the IGF system for adapting to tumor microenvironmental stress. Conversely, the cancer cells with low levels of IGF-1R may represent a subpopulation that was able to adapt to the stress and thus develop a more metastatic phenotype.
In conclusion, IGF-1R expression is useful for predicting liver metastasis from Dukes C CRCs. However, additional studies are needed to clarify the role of the IGF system in liver metastasis of CRCs.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: Atsushi Ochiai, Pathology Division, National Cancer Center Research Institute East, 6-5-1, Kashiwanoha, Kashiwa, Chiba 277-8577, Japan. Phone: 81-471-34-6855; Fax: 81-471-34-6865; E-mail: aochiai{at}east.ncc.go.jp
Received 3/11/04; revised 6/15/04; accepted 7/ 1/04.
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