Insulin-like growth factor binding protein-3 (IGFBP-3) potentiates paclitaxel-induced apoptosis in human breast cancer cells

Variability in response to chemotherapy is poorly understood. Paclitaxel-induced apoptosis was assessed in human Hs578T breast cancer cells, using the MTT assay, cell counting, morphological features and flow cytometry. Pre-dosing cells with non-glycosylated insulin-like growth factor binding protein-3 (ngIGFBP-3) had no effect on the cells per se but accentuated paclitaxel-induced apoptosis. The apoptotic pathway was further examined by measuring caspase-3 activity in cell lysates at time points over 48 hr after dosing with paclitaxel. Activity increased significantly, and Western immunoblots for caspase-3 in conditioned media showed that the inactive precursor decreased after incubation with paclitaxel. Endogenous production of IGFBP-3 by the cells after incubation with paclitaxel was evaluated using Western ligand blotting, specific IGFBP-3 immunoblotting and radioimmunoassay. Paclitaxel increased endogenous IGFBP-3, which was further increased if the cells had been pre-dosed with ngIGFBP-3. These findings suggest that IGFBP-3 may be an important modulator of paclitaxel-induced apoptosis.     

Insulin-like growth factor binding protein-3 inhibits the growth of non-small cell lung cancer

Insulin-like growth factors (IGFs) have mitogenic and antiapoptotic properties and have been implicated in the development of lung cancer. The effects of IGFs are modulated by insulin-like growth factor binding proteins (IGFBPs). This study explored the effects of IGFBP-3 on non-small cell lung cancer (NSCLC) cells after infection with an adenovirus constitutively expressing IGFBP-3 under the control of the cytomegalovirus promoter (Ad5CMV-BP3). We found that IGFs, especially IGF-I, stimulated the growth of NSCLC cells, and Ad5CMV-BP3 suppressed this IGF-I-induced NSCLC cell growth. We also found that the clonogenicity of H1299 cells in soft agar was markedly reduced by Ad5CMV-BP3. Furthermore, direct injection of Ad5CMV-BP3 into H1299 NSCLC xenografts s.c. established in athymic nude mice induced massive destruction of the tumors. Ad5CMV-BP3 did not induce detectable cytotoxicity on normal human bronchial epithelial cells, suggesting therapeutic efficacy of this virus. Ad5CMV-BP3 infection was accompanied by apoptotic cell death in vitro as detected by flow cytometry, DNA fragmentation analysis, and Western blot analysis on the expression of Bcl-2 and on the cleavage of poly(ADP-ribose) polymerase, a substrate of caspase 3. Immunofluorescence confocal microscopy was also used to show the apoptotic effect of Ad5CMV-BP3 in H1299 tumors established in nude mice. These findings indicated that IGFBP-3 was a potent inducer of apoptosis in NSCLC cells in vitro and in vivo. To delineate the underlying mechanism, we examined the effect of IGFBP-3 on Akt/protein kinase B and glycogen synthase kinase-3beta, downstream mediators of the phosphatidylinositol 3-kinase pathway, and on mitogen-activated protein kinase (MAPK), all three of which are activated by IGF-mediated signaling pathways and have important roles in cell survival. IGFBP-3 overexpression inhibited the phosphorylation of Akt and glycogen synthase kinase-3beta and the activity of MAPK. Furthermore, IGF-I rescued the NSCLC cells from serum depletion-induced apoptosis, and this rescue was blocked in Ad5CMV-BP-3-infected H1299 NSCLC cells. Transient transfection with activated Akt or constitutively active MAPK kinase-1, an upstream activator of MAPK, partially blocked IGFBP-3-induced apoptosis of NSCLC cells. These findings suggested that the growth-regulatory effect of IGFBP-3 on NSCLC cells was attributable in part to the inhibition of the IGF-induced survival pathway. These data demonstrate the importance of IGFBP-3 in the regulation of NSCLC cell proliferation, clonogenicity, and tumor growth, suggesting that IGFBP-3 is a target for the treatment of lung cancer and that Ad5CMV-BP3 is a potential therapeutic agent.     

Insulin-like growth factor binding protein-6 inhibits neuroblastoma cell proliferation and tumour development

In neuroblastoma cells, survival and proliferation are dependent upon the insulin-like growth factor (IGF) system. IGFs actively participate in cell growth, whereas IGFBP-6, is associated with the arrest of growth. With a view to blocking IGF-II action, we produced recombinant human IGFBP-6 capable of binding IGFs with affinities between 1.23 and 6.36 x 10(9) M(-1). Ex vivo mitogenic activities were tested on two human neuroblastoma cell lines, in which 100 ng/ml IGFBP-6 completely abolished the effects of both endogenous and exogenous IGF-II. In vivo, nude mice previously injected with neuroblastoma cells were submitted to either 15 daily injections of 4-20 microg IGFBP-6 or implantation of mini-pumps diffusing 20-100 microg IGFBP-6 over 2 weeks. The result was an average 18% reduction in the incidence and development of tumours. Delivery of the IGFBP-6 via mini-pumps also delayed tumour appearance by 6-15 days. Our results therefore show the involvement of IGFBP-6 in neuroblastoma cell growth, both ex vivo in terms of proliferation and in vivo in terms of tumour development.     

Insulin-like growth factor binding protein-1 over-expression in transgenic mice inhibits hepatic preneoplasia

Insulin-like growth factor binding protein-1 (IGFBP-1) is synthesized in the liver and regulates the mitogenic effects of the insulin-like growth factors (IGFs). The evidence that IGFBP-1 plays a role in hepatocarcinogenesis, however, is equivocal. We have, therefore, investigated the development of preneoplastic hepatic lesions in transgenic mice in which the human IGFBP-1 gene is under the control of the mouse metallothionein promoter. The lesions were induced by treating 15-d-old male mice with a single intraperitoneal injection of 5 mg/kg diethylnitrosamine (DENA). Lesions were scored when the mice were 28 wk of age. Quantitative microscopy of liver sections revealed that significantly fewer transgenic mice treated with zinc to activate the transgene had focal lesions compared to either transgenic mice not treated with zinc or wild-type mice treated with zinc (36.4% versus 85.7% and 83.3%, respectively, P < 0.05 in each case). Zinc-treated transgenic mice also had significantly fewer lesions per liver (11.5 +/- 5.0 versus 74.7 +/- 18.4 and 59.4 +/- 15.6, respectively, P < 0.01 in each case) and a smaller percentage of liver volume occupied by lesions (0.2 +/- 0.1 versus 1.4 +/- 0.3 and 1.1 +/- 0.4 respectively, P < 0.05 in each case). Immunohistochemical staining showed that both IGF-I and IGF-II were overexpressed in most of the lesions. These results show that expression of the IGFBP-1 transgene leads to a marked inhibition of hepatic preneoplasia, possibly by decreasing the mitogenic activity of IGF-I and/or IGF-II. This study adds new evidence to the notion that the IGF axis plays an important role in liver cancer development.     

Insulin-like growth factor binding protein-3 (IGFBP-3) acts as an invasion-metastasis suppressor in ovarian endometrioid carcinoma

Metastasis and invasion occur in the majority of epithelial ovarian carcinoma at diagnosis. To delineate the molecular signature in ovarian cancer invasion, we established and characterized a human ovarian endometrioid carcinoma (EC) cell line OVTW59-P0 and its invasion-related sublines (P1-P4, in the order of increasing invasive activity). P4 showed faster migration and larger xenograft formation with metastasis than P0. By microarray analysis of different gene expression among P0-P4 sublines, one group of gene was found negatively correlated with cancer invasion. Among these genes, IGFBP-3 was identified as one of the most remarkably suppressed gene that showed lower gene expression in P4 than P0. Re-expression of IGFBP-3 in P4 effectively inhibited cell migration, invasion and metastasis, but did not affect cell proliferation. In 35 patients with EC tumors, low IGFBP-3 expression correlated clinically with higher tumor grade, advanced stage and poor survival. Our results provide evidence and indicate that IGFBP-3 plays an important role as an invasion-metastasis suppressor in ovarian EC.     

Clinical significance of serum insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) in patients with breast cancer

Insulin-like growth factor-1 (IGF-1) and its primary binding protein-3 (IGFBP-3) play an important role in cellular proliferation, differentiation and apoptosis in many tumors, including breast cancer (BC). The objective of this study was to determine the clinical significance of the serum levels of IGF-1 and IGFBP-3 in BC patients. A total of 96 patients with a pathologically confirmed diagnosis of BC were enrolled into this study. Serum IGF-1 and IGFBP-3 levels were determined by the solid-phase sandwich enzyme-linked immunosorbent assay (ELISA) methods. Age- and sex-matched 30 healthy controls were included in the analysis. The median age of diagnosis was 48 years (range: 29–80). Thirty-seven (39 %) consisted of metastatic disease. No significant difference in baseline serum was found in both IGF-1 and IGFBP-3 levels between BC patients and healthy controls (p?=?0.92 and p?=?0.26, respectively). None of the prognostic parameters analyzed was correlated significantly with the serum assay concentrations. Likewise, no correlations were also found between these serum concentrations and response to chemotherapy. No significant correlation was found between serum IGF-1 and IGFBP-3 levels in BC patients (r _s?=?0.048, p?=?0.66).The patients with elevated serum IGF-1 levels had favorable in survival than those with lower levels (p?=?0.05). However, serum IGFBP-3 concentrations were found no prognostic role for outcome (p?=?0.35). In conclusion, elevated serum IGF-1 level is afavorable prognostic factor for overall survival in BC patients.     

Insulin-like growth factor binding protein-6 activates programmed cell death in non-small cell lung cancer cells

Insulin-like growth factor binding proteins (IGFBPs) are secreted into the extra-cellular matrix and inhibit cell growth through IGF-dependent and -independent mechanisms. In this study, we investigated the role of IGFBP-6, a relatively unexplored member of the IGFBP family, in the proliferation of non-small cell lung cancer (NSCLC) cells. Infection of NSCLC cell lines in vitro with an adenovirus expressing human IGFBP-6 under the control of a CMV promoter (Ad5CMV-BP6) reduced NSCLC cell number through activation of programmed cell death, as shown by cell staining with Hoechst 33342 or DNA end-labeling with bromodeoxyuridine triphosphate. The growth regulatory effect of IGFBP-6 was investigated in vivo by intratumoral injection of Ad5CMV-BP6 in NSCLC xenografts established in nu/nu mice. A single injection of Ad5CMV-BP6 reduced the size of NSCLC xenografts by 45%. These findings indicate that IGFBP-6 is a potent inducer of programmed cell death in cancer cells and support investigations into IGFBP-6 as a potential target in cancer therapeutics.     

Insulin-like growth factor binding proteins 1 and 3 and breast cancer outcomes

The IGF family of growth factors is believed to play a role in the development and progression of breast cancer. We recently identified an adverse prognostic effect of insulin in breast cancer; we now report prognostic effects of circulating IGFBP's 1 and 3. 512 women with T1-3, N0-1, M0 breast cancer provided fasting blood which was analysed for IGFBP's 1 and 3. Information on body size, diet and traditional prognostic factors and treatment was obtained; women were followed for recurrence and death. IGFBP-1 levels correlated inversely with insulin levels (Spearman r = –0.60, p < 0.0001), reflecting known inhibition of IGFBP-1 gene expression by insulin. Insulin explained 36% of the variance in IGFBP-1 levels. IGFBP-1 levels were also correlated with obesity and diet. Levels of IGFBP-1 significantly predicted distant recurrence and death, hazard ratio (95% CI) for lower versus upper quartile 2.08 (1.20–3.61) and 3.0 (1.45–6.21), respectively. These effects persisted after adjustment for tumor-related variables and treatment but were not independent of insulin levels. High levels of IGFBP-3 predicted distant recurrence (hazard ratio upper v.s. lower quartile 1.8, 95% CI 1.1–3.0) but not death (hazard ratio 1.0, 95% CI 0.5–1.9). The effect on distant recurrence was restricted to postmenopausal women (hazard ratio 3.8, 95% CI 1.6–9.0) and to those with estrogen receptor positive tumors (p = 0.002). Prognostic effects of IGFBP-1 appear related to the known effect of insulin on IGFBP-1 gene expression. The adverse effect of IGFBP-3 on distant recurrence in postmenopausal women with estrogen receptor positive breast cancer should be further investigated.     

Insulin-like growth factor binding protein-3 interacts with autocrine motility factor/phosphoglucose isomerase (AMF/PGI) and inhibits the AMF/PGI function

Autocrine motility factor/phosphoglucose isomerase (AMF/PGI) was identified as a binding partner for insulin-like growth factor binding protein-3 (IGFBP-3) in solubilized T47D and MCF-7 human breast cancer cell membranes. The interaction between AMF/PGI and IGFBP-3 was verified by cross-linking biotinylated IGFBP-3 to intact cells. After solubilization of the membranes, the biotinylated complexes were precipitated with streptavidin-agarose conjugate and analyzed by SDS-PAGE. A M(r) approximately 80,000 complex was identified when the nitrocellulose membranes were probed either with streptavidin-horseradish peroxidase conjugate or AMF/PGI antiserum confirming the cross-linking of IGFBP-3 to AMF/PGI. The interaction between IGFBP-3 and AMF/PGI was also further confirmed by ligand blotting of purified AMF/PGI using biotinylated IGFBP-3. Both glycosylated and nonglycosylated IGFBP-3 inhibited the catalytic activity of AMF/PGI in a dose-dependent fashion. In addition, IGFBP-3 inhibited the binding of AMF/PGI to breast cancer cells and AMF/PGI-induced migration of both T47D and MCF-7 human breast cancer cells. IGFBP-3 also decreased the phosphorylation of AMF/PGI and reduced the translocation of AMF/PGI to the cell membrane and AMF/PGI. AMF/PGI resulted in a dose-dependent inhibition of IGFBP-3 induced apoptosis in T47D and MCF-7 cells. In summary, we have identified AMF/PGI as a membrane-associated binding partner for IGFBP-3 in breast cancer cells. The ability of IGFBP-3 to bind and inhibit the actions of AMF/PGI may have some role in the antiproliferative proapoptotic effects of IGFBP-3.     

Insulin-like growth factor–binding protein-3 and breast cancer survival

Insulin-like growth factors (IGFs) are potent mitogens involved in the regulation of cell proliferation and apoptosis. The action of IGFs is mediated through a specific cell membrane receptor (IGF-IR), and the interactions between IGFs and this receptor are regulated by IGF-binding proteins (IGFBPs). IGFBP-3 is one such protein which either suppresses or enhances the actions of IGFs. Findings from most in vitro studies suggest that IGFBP-3 inhibits breast cancer cell growth and facilitates apoptosis, but clinical studies have found that high levels of IGFBP-3 in breast cancer tissues are associated with unfavourable prognostic indicators of the disease, such as large tumour size, low levels of steroid hormone receptors, elevated S-phase fraction and DNA aneuploidy. To further examine the role of IGFBP-3 in breast cancer recurrence and survival, we conducted the following nested case-control study. From a cohort of 1,000 women treated surgically for primary breast cancer, we consecutively selected 100 patients who developed recurrent disease after surgery and 100 age- and year of diagnosis-matched patients who had no relapse. Concentrations of IGFBP-3 in breast tissue extracts were determined with an ELISA. Inverse correlations of IGFBP-3 were revealed with estrogen receptor expression and patient age but not with tumour size or S-phase fraction. Levels of IGFBP-3 in breast tissues were slightly higher in the recurrent patients than in controls, but the differences were not statistically significant. No significant association was found between IGFBP-3 and breast cancer recurrence. Survival analysis, however, indicated that the risk of death was increased with higher IGFBP-3 levels, and the association was independent of other prognostic markers. In conclusion, our results demonstrate that high levels of IGFBP-3 are associated with unfavourable prognostic features of breast cancer. Int. J. Cancer (Pred. Oncol.) 79:624–628, 1998. © 1998 Wiley-Liss, Inc.     

Insulin-like growth factor receptor (IGF-1R) in breast cancer subtypes

Insulin-like growth factor-1 receptor (IGF-1R) is expressed in normal and malignant breast tissue and has been implicated in cell survival and resistance to cytotoxic therapies. We sought to assess the prognostic impact of IGF-1R expression among patients with early breast cancer and among breast cancer subtypes. Patients with stages I–III breast cancer with archival tumor tissue were included. Paraffin tissue blocks were used to construct a tissue microarray that was stained for ER, PR, Ki-67, HER2, EGFR, and cytokeratins 5/6 to classify the breast subgroups and for expression of IGF-1R, p27, and Bcl2 by immunohistochemistry. Kaplan–Meier plots were created by subtypes. Associations between IGF-1R and prognostic variables were examined in multivariate analysis. Among 2,871 eligible women the prognostic cut point for IGF-1R expression for breast-cancer-specific survival (BCSS) was Allred score <7 versus ≥7. IGF-1R was ≥7 in 52% (LuminalA), 57.5% (LuminalB), 44.8% (LuminalHER2), 9.7% HER2-enriched, and 22.5% (Basal-like), P = 1.3 × 10⁻⁵². IGF-1R+ was associated with age ≥50, lower histopathology grade, ER+, HER2 negativity (−), high p27 and high Bcl2 score. IGF-1R ≥7 was associated with better BCSS among LuminalB patients, hazard ratio = 0.64 (0.49–0.84); P = 1.2 × 10^−3, and worse outcome in the HER2-enriched subtype, hazard ratio = 2.37 (1.21–4.64); P = 0.012. IGF-1R correlates with good prognostic markers among patients with early breast cancer and is differentially expressed with variable prognostic impact among breast cancer subtypes. Results may have relevance to the development of therapeutics targeting IGF-1R.     

Insulin-like growth factor-binding protein-1 (IGFBP-1) regulates human schwannoma proliferation, adhesion and survival

Merlin is a tumour suppressor involved in the development of a variety of tumours including mesotheliomas. Neurofibromatosis type 2 (NF2), a dominantly inherited tumour disease, is also caused by loss of merlin. NF2 patients suffer from multiple genetically well-defined tumours, schwannomas are most frequent among those. Using our in vitro model for human schwannoma, we found that schwannoma cells display enhanced proliferation because of the overexpression/activation of platelet-derived growth factor receptor and ErbB2/3, increased cell-matrix adhesion because of the overexpression of integrins, and decreased apoptosis. Mechanisms underlying schwannomas basal proliferation and cell-matrix adhesion are not understood. Here, we investigated insulin-like growth factor-binding protein-1 (IGFBP-1), which is expressed and released from central nervous system tumours and strongly overexpressed in schwannoma at the mRNA level. IGFBP-1 acts via β1-integrin and focal-adhesion-kinase (FAK), which are strongly overexpressed and basally activated in schwannoma. Using short hairpin RNA knockdown, small inhibitors and recombinant IGFBP-1, we demonstrate that schwannoma cells, in contrast to Schwann cells, release IGFBP-1 that activates the Src/FAK pathway, via integrin β1, potentiating schwannoma's proliferation and cell-matrix adhesion. We show that FAK localizes to the nucleus and Src triggers IGFBP-1 production. Further, we observed downregulation of the tumour-suppressor phosphatase and tensin homolog in schwannoma cells leading to increased activity of anti-apoptotic AKT. Thus, IGFBP-1/integrin β1/Src/FAK pathway has a crucial role in merlin-related tumourigenesis and therefore represents an important therapeutic target in the treatment of merlin-deficient tumours.     

Insulin-like growth factor binding protein-6 inhibits prostate cancer cell proliferation: implication for anticancer effect of diethylstilbestrol in hormone refractory prostate cancer

Diethylstilbestrol (DES) is a synthetic oestrogen, and its anticancer effects are exerted in androgen-dependent prostate cancer. The administration of DES decreases serum testosterone to castration levels. However, in androgen-independent prostate cancer patients, who are already orchiectomised, the administration of DES improves symptoms and decreases prostate-specific antigen (PSA). The mechanisms responsible for these direct inhibitory effects have been explained as biological actions not mediated by oestrogen receptors. We assessed the gene expression profiles of prostate cancer cells treated with DES, and investigated direct inhibitory effects of DES. DES inhibited the proliferation of LNCaP and PC-3 cells. cDNA microarray analysis showed that expression of many genes was downregulated by DES. However, insulin-like growth factor binding protein 6 (IGFBP-6) gene expression levels were upregulated in PC-3 cells. IGFBP-6 gene expression and protein levels significantly increased after DES treatment. Recombinant IGFBP-6 inhibited cell proliferation, and the inhibitory effect of DES was neutralised by anti-IGFBP-6 antibody. From the immunohistochemical analysis of IGFBP-6 using biopsy samples from androgen-independent prostate cancer, we found IGFBP-6 expression in androgen independent prostate cancer, and that DES treatment increased the IGFBP-6 staining intensity of the cancer cells in one sample. These findings suggested that DES induces IGFBP-6, which inhibits cell proliferation in an androgen-independent prostate cancer cell line, PC-3. IGFBP-6 therefore might be involved in the direct effects of DES in androgen-independent prostate cancer.     

Insulin-like growth factor (IGF)-binding protein-4 inhibits colony formation of colorectal cancer cells by IGF-independent mechanisms

Effects of insulin-like growth factor-binding protein-4 (IGFBP-4) on proliferation, colony formation, and cell migration were assessed in IGF-sensitive and -insensitive colorectal cancer cell lines. In IGF-insensitive Isreco-1 cells, overexpression of IGFBP-4 reduced colony formation but not cell proliferation and migration, whereas exogenous IGF-II had no effect. In IGF-dependent LS1034 cells, IGFBP-4 inhibited all parameters of growth tested, whereas IGF-II partially restored reduced proliferation and cell migration only. In Isreco-2 cells, which lack endogenous IGF expression but are IGF sensitive, colony formation was also reduced by IGFBP-4. Therefore, specific parameters of malignant progression of colon carcinoma cells are distinctly affected by IGF-dependent and IGF-independent effects of IGFBP-4.     

Clinical significance of serum insulin-like growth factor-1 (IGF-1) and insulinlike growth factor binding protein-3 (IGFBP-3) in patients with epithelial ovarian cancer

Insulin-like growth factor-1 (IGF-1) and its primary binding protein IGFBP-3 play an important role in cellular proliferation, differentiation, and apoptosis in many tumors, including ovarian cancer. The objective of this study was to determine the clinical significance of the serum levels of IGF-1 and IGFBP-3 in epithelial ovarian cancer (EOC) patients. A total of 50 patients with a pathologically confirmed diagnosis of EOC were enrolled into this study. Serum IGF-1 and IGFBP-3 levels were determined by the solid-phase sandwich ELISA method. Twenty age- and sex-matched healthy controls were included in the analysis. Median age of patients was 56.5 years old (range 22 to 83 years). Majority of the patients had advanced disease (FIGO stage III–IV; 90 %). No significant difference was observed in baseline serum IGF-1 and IGFBP-3 levels between EOC patients and healthy controls (p?=?0.99 and p?=?0.80, respectively). The young patients had higher serum IGF-1 and IGFBP-3 concentrations (p?=?0.04 and p?=?0.02, respectively). Patients with normal CA-125 levels had higher serum IGFBP-3 concentrations compared with those with higher CA-125 levels (p?=?0.008). However, no other clinical variables including histology, tumor grade, stage of disease, and response to chemotherapy were found to be correlated with serum IGF assays (p?>?0.05). A trend to significant relationship was found between the serum levels of IGF-1 and IGFBP-3 (r _s?=?0.212, p?=?0.07). The patients with elevated serum IGF-1 levels had favorable progression-free and overall survivals than those with lower levels (p?=?0.04 and p?=?0.03, respectively). However, serum IGFBP-3 concentrations were found to have no prognostic role for both survivals (p?=?0.12 and p?=?0.26, respectively). In conclusion, elevated serum level of IGF-1 is associated with favorable progression-free and overall survivals in EOC patients.     

Insulin-like growth factor binding protein 2 promotes ovarian cancer cell invasion

Background  

Insulin-like growth factor binding protein 2 (IGFBP2) is overexpressed in ovarian malignant tissues and in the serum and cystic fluid of ovarian cancer patients, suggesting an important role of IGFBP2 in the biology of ovarian cancer. The purpose of this study was to assess the role of increased IGFBP2 in ovarian cancer cells.     

Insulin-like growth factor (IGF)–binding protein-3 (IGFBP-3) proteolysis in patients with colorectal cancer: possible association with the metastatic potential of the tumor

The limited proteolysis of insulin-like growth factor (IGF)–binding protein (IGFBP)-3 is a key event in the regulation of endocrine bioavailability of IGFs. Here, we investigated IGFBP-3 and IGFBP-3 proteolysis in serum from patients with colorectal cancer both before and at different times following surgery. In vivo IGFBP-3 proteolysis, estimated by immunoblot analysis of IGFBP-3 fragments in serum, andin vitro IGFBP-3 protease activity of serum, estimated by a ¹²⁵I-IGFBP-3 degradation assay, allowed us to identify 2 groups of patients (IGF-M vs. IGF-NM) with respect to their status for mobilizing the IGF system. In IGF-M patients, in vivo and in vitro IGFBP-3 proteolysis were significantly elevated (156% and 181% of the age-matched control pool, respectively) and accompanied by a decrease in intact IGFBP-3 (38% of the control pool). The IGFBP-3 proteolytic processing was further increased in response to surgical ablation of the tumor (mean increase 45–55%), then gradually returned to levels comparable with controls. In contrast, IGF-NM patients exhibited a minimal alteration of in vitro IGFBP-3 protease activity and even an inhibition of in vivo IGFBP-3 proteolysis, whereas intact IGFBP-3 was unaltered when compared with controls. Moreover, this pattern was not further significantly altered in response to the surgical stress. None (0/6) of the IGF-M patients vs. 70% (5/7) of the IGF-NM patients developed a metastatic disease (median duration of follow-up 26 months). Neither elevated amounts of pro-IGF-II nor presence of detectable IGFBP-3 protease inhibitors in the circulation could explain the observed suppression of IGFBP-3 proteolytic processing in IGF-NM patients. These results indicate that inhibition of IGFBP-3 proteolysis and invasive properties of cancer cells are related in colorectal cancer patients. Int. J. Cancer (Pred. Oncol.) 79:460–467, 1998.© 1998 Wiley-Liss, Inc.