A bi-functional antibody-receptor domain fusion protein simultaneously targeting IGF-IR and VEGF for degradation.

Bi-specific antibodies (BsAbs), which can simultaneously block 2 tumor targets, have emerged as promising therapeutic alternatives to combinations of individual monoclonal antibodies. Here, we describe the engineering and development of a novel, human bi-functional antibody-receptor domain fusion molecule with ligand capture (bi-AbCap) through the fusion of the domain 2 of human vascular endothelial growth factor receptor 1 (VEGFR1) to an antibody directed against insulin-like growth factor - type I receptor (IGF-IR). The bi-AbCap possesses excellent stability and developability, and is the result of minimal engineering. Beyond potent neutralizing activities against IGF-IR and VEGF, the bi-AbCap is capable of cross-linking VEGF to IGF-IR, leading to co-internalization and degradation of both targets by tumor cells. In multiple mouse xenograft tumor models, the bi-AbCap improves anti-tumor activity over individual monotherapies. More importantly, it exhibits superior inhibition of tumor growth, compared with the combination of anti-IGF-IR and anti-VEGF therapies, via powerful blockade of both direct tumor cell growth and tumor angiogenesis. The unique "capture-for-degradation" mechanism of the bi-AbCap is informative for the design of next-generation bi-functional anti-cancer therapies directed against independent signaling pathways. The bi-AbCap design represents an alternative approach to the creation of dual-targeting antibody fusion molecules by taking advantage of natural receptor-ligand interactions.

Id1-induced IGF-II and its autocrine/endocrine promotion of esophageal cancer progression and chemoresistance--implications for IGF-II and IGF-IR-targeted therapy.

PURPOSE: To investigate the autocrine/endocrine role of Id1-induced insulin-like growth factor-II (IGF-II) in esophageal cancer, and evaluate the potential of IGF-II- and IGF-type I receptor (IGF-IR)-targeted therapies. EXPERIMENTAL DESIGN: Antibody array-based screening was used to identify differentially secreted growth factors from Id1-overexpressing esophageal cancer cells. In vitro and in vivo assays were performed to confirm the induction of IGF-II by Id1, and to study the autocrine and endocrine effects of IGF-II in promoting esophageal cancer progression. Human esophageal cancer tissue microarray was analyzed for overexpression of IGF-II and its correlation with that of Id1 and phosphorylated AKT (p-AKT). The efficacy of intratumorally injected IGF-II antibody and intraperitoneally injected cixutumumab (fully human monoclonal IGF-IR antibody) was evaluated using in vivo tumor xenograft and experimental metastasis models. RESULTS: Id1 overexpression induced IGF-II secretion, which promoted cancer cell proliferation, survival, and invasion by activating AKT in an autocrine manner. Overexpression of IGF-II was found in 21 of 35 (60%) esophageal cancer tissues and was associated with upregulation of Id1 and p-AKT. IGF-II secreted by Id1-overexpressing esophageal cancer xenograft could instigate the growth of distant esophageal tumors, as well as promote metastasis of circulating cancer cells. Targeting IGF-II and IGF-IR had significant suppressive effects on tumor growth and metastasis in mice. Cixutumumab treatment enhanced the chemosensitivity of tumor xenografts to fluorouracil and cisplatin. CONCLUSIONS: The Id1-IGF-II-IGF-IR-AKT signaling cascade plays an important role in esophageal cancer progression. Blockade of IGF-II/IGF-IR signaling has therapeutic potential in the management of esophageal cancer.

Insulin and IGFs in obesity-related breast cancer.

Obesity and the Metabolic Syndrome are associated with multiple factors that may cause an increased risk for cancer and cancer-related mortality. Factors involved include hyperinsulinemia, hyperglycemia, hyperlipidemia and IGFs. Insulin resistance is also associated with alterations in the levels of proinflammatory cytokines, chemokines, adipokines (leptin, adiponectin) that may also be contributing factors. The insulin family of proteins is ubiquitously expressed and has pleiotropic effects on metabolism and growth. However insulin, IGF-1 and particularly IGF-2 have been identified as tumor promoters in multiple studies. Mouse models have focused on insulin and IGF-1 and their receptors as being involved in tumor progression and metastases. The role of the insulin receptor as either mediating the effects on tumors or as compensating for the insulin-like growth factor receptor has arisen. Its role has been supported by preclinical studies and the importance of insulin resistance and hyperinsulinemia in obesity and early diabetes. Since the focus of this review is the insulin-family we will focus on insulin, IGF-1 and IGF-2.

Hyperinsulinemia promotes metastasis to the lung in a mouse model of Her2-mediated breast cancer.

The Her2 oncogene is expressed in ∼25% of human breast cancers and is associated with metastatic progression and poor outcome. Epidemiological studies report that breast cancer incidence and mortality rates are higher in women with type 2 diabetes. Here, we use a mouse model of Her2-mediated breast cancer on a background of hyperinsulinemia to determine how elevated circulating insulin levels affect Her2-mediated primary tumor growth and lung metastasis. Hyperinsulinemic (MKR(+/+)) mice were crossed with doxycycline-inducible Neu-NT (MTB/TAN) mice to produce the MTB/TAN/MKR(+/+) mouse model. Both MTB/TAN and MTB/TAN/MKR(+/+) mice were administered doxycycline in drinking water to induce Neu-NT mammary tumor formation. In tumor tissues removed at 2, 4, and 6 weeks of Neu-NT overexpression, we observed increased tumor mass and higher phosphorylation of the insulin receptor/IGF1 receptor, suggesting that activation of these receptors in conditions of hyperinsulinemia could contribute to the increased growth of mammary tumors. After 12 weeks on doxycycline, although no further increase in tumor weight was observed in MTB/TAN/MKR(+/+) compared with MTB/TAN mice, the number of lung metastases was significantly higher in MTB/TAN/MKR(+/+) mice compared with controls (MTB/TAN/MKR(+/+) 16.41±4.18 vs MTB/TAN 5.36±2.72). In tumors at the 6-week time point, we observed an increase in vimentin, a cytoskeletal protein and marker of mesenchymal cells, associated with epithelial-to-mesenchymal transition and cancer-associated fibroblasts. We conclude that hyperinsulinemia in MTB/TAN/MKR(+/+) mice resulted in larger primary tumors, with more mesenchymal cells and therefore more aggressive tumors with more numerous pulmonary metastases.

Insulin-like growth factors and insulin: at the crossroad between tumor development and longevity.

Numerous lines of evidence indicate that insulin-like growth factor signaling plays an important role in the regulation of life span and tumor development. In the present paper, the role of individual components of insulin-like growth factor signaling in aging and tumor development has been extensively analyzed. The molecular mechanisms underlying aging and tumor development are frequently overlapping. Although the link between reduced insulin-like growth factor signaling and suppressed tumor growth and development is well established, it remains unclear whether extended life span results from direct suppression of insulin-like growth factor signaling or this effect is caused by indirect mechanisms such as improved insulin sensitivity.

Hyperinsulinemia enhances c-Myc-mediated mammary tumor development and advances metastatic progression to the lung in a mouse model of type 2 diabetes.

INTRODUCTION: Hyperinsulinemia, which is common in early type 2 diabetes (T2D) as a result of the chronically insulin-resistant state, has now been identified as a specific factor which can worsen breast cancer prognosis. In breast cancer, a high rate of mortality persists due to the emergence of pulmonary metastases. METHODS: Using a hyperinsulinemic mouse model (MKR+/+) and the metastatic, c-Myc-transformed mammary carcinoma cell line Mvt1, we investigated how high systemic insulin levels would affect the progression of orthotopically inoculated primary mammary tumors to lung metastases. RESULTS: We found that orthotopically injected Mvt1 cells gave rise to larger mammary tumors and to a significantly higher mean number of pulmonary macrometastases in hyperinsulinemic mice over a period of six weeks (hyperinsulinemic, 19.4 ± 2.7 vs. control, 4.0 ± 1.3). When Mvt1-mediated mammary tumors were allowed to develop and metastasize for approximately two weeks and were then surgically removed, hyperinsulinemic mice demonstrated a significantly higher number of lung metastases after a four-week period (hyperinsulinemic, 25.1 ± 4.6 vs. control, 7.4 ± 0.42). Similarly, when Mvt1 cells were injected intravenously, hyperinsulinemic mice demonstrated a significantly higher metastatic burden in the lung than controls after a three-week period (hyperinsulinemic, 6.0 ± 1.63 vs. control, 1.5 ± 0.68). Analysis of Mvt1 cells both in vitro and in vivo revealed a significant up-regulation of the transcription factor c-Myc under hyperinsulinemic conditions, suggesting that hyperinsulinemia may promote c-Myc signaling in breast cancer. Furthermore, insulin-lowering therapy using the beta-adrenergic receptor agonist CL-316243 reduced metastatic burden in hyperinsulinemic mice to control levels. CONCLUSIONS: Hyperinsulinemia in a mouse model promotes breast cancer metastasis to the lung. Therapies to reduce insulin levels in hyperinsulinemic patients suffering from breast cancer could lessen the likelihood of metastatic progression.

Blockade of insulin-like growth factor type-1 receptor with cixutumumab (IMC-A12): a novel approach to treatment for multiple cancers.

Insulin-like growth factor type-1 receptor (IGF-1R) plays a central role in cell proliferation and survival and is overexpressed in many tumor types. Notably, IGF-1R-mediated signaling confers resistance to diverse cytotoxic, hormonal, and biologic agents, suggesting that therapies targeting IGF-1R may be effective against a broad range of human malignancies. Cixutumumab (IMC-A12; ImClone Systems) is a fully human immunoglobulin G1 (IgG1) monoclonal antibody that specifically inhibits IGF-1R signaling. Binding of cixutumumab to IGF-1R results in receptor internalization and degradation. Because cixutumumab is an IgG1 monoclonal antibody, it may induce additional cytotoxicity via immune effector mechanisms such as antibody-dependent cellular cytotoxicity. In preclinical studies, cixutumumab monotherapy resulted in growth inhibition of multiple experimental cancers. Moreover, cixutumumab safely enhanced the tumor growth inhibitory and cytotoxic effects of a broad range of chemotherapeutics, and modulated the action of agents that target hormone receptors and signal transduction, which may have implications for cancer therapy. Herein, we review published preclinical and clinical data for cixutumumab and provide a comprehensive overview of selected clinical studies.

Mammalian target of rapamycin inhibition abrogates insulin-mediated mammary tumor progression in type 2 diabetes.

Type 2 diabetes increases breast cancer risk and mortality, and hyperinsulinemia is a major mediator of this effect. The mammalian target of rapamycin (mTOR) is activated by insulin and is a key regulator of mammary tumor progression. Pharmacological mTOR inhibition suppresses tumor growth in numerous mammary tumor models in the non-diabetic setting. However, the role of the mTOR pathway in type 2 diabetes-induced tumor growth remains elusive. Herein, we investigated whether the mTOR pathway is implicated in insulin-induced mammary tumor progression in a transgenic mouse model of type 2 diabetes (MKR mice) and evaluated the impact of mTOR inhibition on the diabetic state. Mammary tumor progression was studied in the double transgenic MMTV-Polyoma Virus middle T antigen (PyVmT)/MKR mice and by orthotopic inoculation of PyVmT- and Neu/ErbB2-driven mammary tumor cells (Met-1 and MCNeuA cells respectively). mTOR inhibition by rapamycin markedly suppressed tumor growth in both wild-type and MKR mice. In diabetic animals, however, the promoting action of insulin on tumor growth was completely blunted by rapamycin, despite a worsening of the carbohydrate and lipid metabolism. Taken together, pharmacological mTOR blockade is sufficient to abrogate mammary tumor progression in the setting of hyperinsulinemia, and thus mTOR inhibitors may be an attractive therapeutic modality for breast cancer patients with type 2 diabetes. Careful monitoring of the metabolic state, however, is important as dose adaptations of glucose- and/or lipid-lowering therapy might be necessary.

Insulin-like growth factor-I regulates the liver microenvironment in obese mice and promotes liver metastasis.

Among the mechanisms implicated in the tumor-promoting effects of obesity, signaling by insulin-like growth factor-I (IGF-I) and insulin has received considerable attention. However, the emerging realization that obesity is associated with chronic inflammation has prompted other consideration of how the IGF-I axis may participate in cancer progression. In the present study, we used two mouse models of chronic (LID) and inducible (iLID) igf-1 gene deficiency in the liver to investigate the role of IGF-I in regulating the host microenvironment and colorectal carcinoma growth and metastasis in obese mice. Obese mice had a heightened inflammatory response in the liver, which was abolished in mice with chronic IGF-I deficiency (LID). In control animals changes to the hepatic microenvironment associated with obesity sustained the presence of tumor cells in the liver and increased the incidence of hepatic metastases after intrasplenic/portal inoculation of colon carcinoma cells. These changes did not occur in LID mice with chronic IGF-1 deficiency. In contrast, these changes occurred in iLID mice with acute IGF-1 deficiency, in the same manner as the control animals, revealing a fundamental difference in the nature of the requirement for IGF-1 on tumor growth and metastasis. In the setting of obesity, our findings imply that IGF-1 is critical to activate and sustain an inflammatory response in the liver that is needed for hepatic metastasis, not only through direct, paracrine effect on tumor cell growth, but also through indirect effects involving the tumor microenvironment.

Insulin-mediated acceleration of breast cancer development and progression in a nonobese model of type 2 diabetes.

Epidemiologic studies suggest that type 2 diabetes (T2D) increases breast cancer risk and mortality, but there is limited experimental evidence supporting this association. Moreover, there has not been any definition of a pathophysiological pathway that diabetes may use to promote tumorigenesis. In the present study, we used the MKR mouse model of T2D to investigate molecular mechanisms that link T2D to breast cancer development and progression. MKR mice harbor a transgene encoding a dominant-negative, kinase-dead human insulin-like growth factor-I receptor (IGF-IR) that is expressed exclusively in skeletal muscle, where it acts to inactivate endogenous insulin receptor (IR) and IGF-IR. Although lean female MKR mice are insulin resistant and glucose intolerant, displaying accelerated mammary gland development and enhanced phosphorylation of IR/IGF-IR and Akt in mammary tissue, in the context of three different mouse models of breast cancer, these metabolic abnormalities were found to accelerate the development of hyperplastic precancerous lesions. Normal or malignant mammary tissue isolated from these mice exhibited increased phosphorylation of IR/IGF-IR and Akt, whereas extracellular signal-regulated kinase 1/2 phosphorylation was largely unaffected. Tumor-promoting effects of T2D in the models were reversed by pharmacological blockade of IR/IGF-IR signaling by the small-molecule tyrosine kinase inhibitor BMS-536924. Our findings offer compelling experimental evidence that T2D accelerates mammary gland development and carcinogenesis,and that the IR and/or the IGF-IR are major mediators of these effects.

Insulin-sensitizing therapy attenuates type 2 diabetes-mediated mammary tumor progression.

OBJECTIVE: Type 2 diabetes increases breast cancer risk and mortality, and hyperinsulinemia has been identified as a major factor linking these two diseases. Thus, we hypothesized that pharmacological reduction of elevated insulin levels would attenuate type 2 diabetes-mediated mammary tumor progression. RESEARCH DESIGN AND METHODS: We studied mammary tumor development in MKR(+/+) mice, a nonobese, hyperinsulinemic mouse model of type 2 diabetes. MKR(+/+) mice were either crossed with mice expressing the polyoma virus middle T oncogene specifically in the mammary gland or inoculated orthotopically with the mouse mammary tumor cell lines Met-1 and MCNeuA. MKR(+/+) or control mice harboring tumors were treated with CL-316243, a specific beta3-adrenergic receptor agonist, which sensitizes insulin action but has no direct effect on the mouse mammary epithelium or Met-1 and MCNeuA cells. RESULTS: CL-316243 treatment significantly reduced the elevated insulin levels in MKR(+/+) mice and, as a consequence, attenuated mammary tumor progression in the three tumor models tested. This effect was accompanied by reductions in phosphorylation of insulin and IGF-I receptors in transformed mammary tissue. CONCLUSIONS: Insulin-sensitizing treatment is sufficient to abrogate type 2 diabetes-mediated mammary tumor progression. Therefore, early administration of insulin-sensitizing therapy may reduce breast cancer risk and mortality in patients with type 2 diabetes.

Biological effects of growth hormone on carbohydrate and lipid metabolism.

This review will summarize the metabolic effects of growth hormone (GH) on the adipose tissue, liver, and skeletal muscle with focus on lipid and carbohydrate metabolism. The metabolic effects of GH predominantly involve the stimulation of lipolysis in the adipose tissue resulting in an increased flux of free fatty acids (FFAs) into the circulation. In the muscle and liver, GH stimulates triglyceride (TG) uptake, by enhancing lipoprotein lipase (LPL) expression, and its subsequent storage. The effects of GH on carbohydrate metabolism are more complicated and may be mediated indirectly via the antagonism of insulin action. Furthermore, GH has a net anabolic effect on protein metabolism although the molecular mechanisms of its actions are not completely understood. The major questions that still remain to be answered are (i) What are the molecular mechanisms by which GH regulates substrate metabolism? (ii) Does GH affect substrate metabolism directly or indirectly via IGF-1 or antagonism of insulin action?

Increased tumor growth in mice with diet-induced obesity: impact of ovarian hormones.

Obesity increases the risk of many cancers in both males and females. This study describes a link between obesity, obesity-associated metabolic alterations, and the risk of developing cancer in male and female mice. The goal of this study was to evaluate the relationship between gender and obesity and to determine the role of estrogen status in obese females and its effect on tumor growth. We examined the susceptibility of C57BL/6 mice to diet-induced obesity, insulin resistance/glucose intolerance, and tumors. Mice were injected sc with one of two tumorigenic cell lines, Lewis lung carcinoma, or mouse colon 38-adenocarcinoma. Results show that tumor growth rate was increased in obese mice vs. control mice irrespective of the tumor cell type. To investigate the effect of estrogen status on tumor development in obese females, we compared metabolic parameters and tumor growth in ovariectomized (ovx) and intact obese female mice. Obese ovx female mice developed insulin resistance and glucose intolerance similar to that observed in obese males. Our results demonstrate that body adiposity increased in ovx females irrespective of the diet administered and that tumor growth correlated positively with body adiposity. Overall, these data point to more rapid tumor growth in obese mice and suggest that endogenous sex steroids, together with diet, affect adiposity, insulin sensitivity, and tumor growth in female mice.

Crosstalk between PDGF and IGF-I receptors in rat liver myofibroblasts: implication for liver fibrogenesis.

Insulin-like growth factor I (IGF-I) and platelet-derived growth factor (PDGF) have been identified as significant mitogens for liver myofibroblasts (LMFs), one of the cell populations playing a role in liver fibrogenesis. In the present work, we aimed to elucidate a possible interaction between PDGF receptor (PDGFR) and IGF-I receptor (IGF-IR) signaling in LMFs. Among different rat liver cells, PDGFR alpha- and beta-subunits were mainly expressed in hepatic stellate cells and LMFs, and were upregulated during their in vitro cultivation. In LMFs, PDGF-BB (10 ng/ml) stimulated DNA synthesis approximately two-fold and this effect was similar to that of IGF-I. IGF-I and PDGF-BB differentially affected IGF-IR and PDGFR signaling. High concentrations of IGF-I decreased levels of IGF-IR and IRS-1 and inhibited the expression and activation of PDGFRalpha. PDGF-BB prevented IGF-I-induced downregulation of the IGF-IR, but did not affect expression of its cognate receptor subunits. Transphosphorylation of PDGFR and IGF-IR was not observed. PDGF effectively activated terminal MAP kinases, PI3 kinase and Akt kinase, whereas IGF-I demonstrated weaker effects. PLCgamma(1) was phosphorylated only in response to PDGF, but not to IGF-I. In rat LMFs, blockade of the IGF-IR via inhibition of the IGF-IR kinase completely abrogated IGF- and PDGF-induced mitogenesis and the ability of PDGF to phosphorylate PLCgamma(1). In conclusion, the presented data demonstrate that the PDGFR signaling requires a functional IGF-IR and that PDGF-BB stabilizes the IGF-IR function through preventing the IGF-I-induced downregulation of the IGF-IR. These interactions might be relevant in vivo for the fibroproliferative response during liver injury.

Upregulation of heme oxygenase-1 gene by turpentine oil-induced localized inflammation: involvement of interleukin-6.

Heme oxygenase-1 (HO-1) is the inducible isoform of an enzyme family responsible for heme degradation and was suggested to be involved in the acute phase response in the liver. However, the mechanisms of the HO-1 regulation under inflammatory conditions are poorly understood. Therefore, the purpose of the current work was to study the expression of HO-1 in the liver and other organs of rats with a localized inflammation after intramuscular injection of turpentine oil (TO). Since interleukin-6 (IL-6) is known to be a principal mediator of inflammation, the levels of this cytokine were also estimated in the animal model used. HO-1 and IL-6 expression was evaluated by Northern blot, in situ hybridization, Western blot, immunohistochemistry and enzyme-linked immunosorbent assay. In the liver and injured muscle, the HO-1 mRNA levels were dramatically increased 4-6 h after TO administration. HO-1 protein levels in the liver were elevated starting from 6-12 h after the treatment. In other internal organs such as the heart, kidney and large intestine, only a slight induction of HO-1 mRNA was observed. IL-6-specific transcripts appeared only in the injured muscle and were in accordance with serum levels of IL-6. In turn, temporal expression of IL-6 in the muscle and circulatory IL-6 levels correlated well with HO-1 expression in the liver and injured muscle. In the liver of control rats HO-1 protein was detected in Kupffer cells, while in TO-injected rats also hepatocytes became strongly HO-1 positive. Conversely, in the injured muscle, HO-1 immunoreactivity was attributed only to macrophages. Our data demonstrate that during localized inflammation HO-1 expression was rapidly and strongly induced in macrophages of injured muscle and in hepatocytes, and IL-6 derived from injured muscle seems to be responsible for the HO-1 induction in the liver.

Expression and regulation of the insulin-like growth factor axis components in rat liver myofibroblasts.

UNLABELLED: Apart from hepatic stellate cells (HSC), liver myofibroblasts (MF) represent a second mesenchymal cell population involved in hepatic fibrogenesis. The IGF system including the insulin-like growth factors I and II (IGF-I, -II), their receptors (IGF-I receptor, IGF-IR; IGF-II/mannose 6-phosphate receptor, IGF-II/M6-PR), and six high affinity IGF binding proteins (IGFBPs) participate in the regulation of growth and differentiation of cells of the fibroblast lineage, possibly contributing to the fibrogenic process. The aim of this work was to study the expression and regulation of the IGF axis components in rat liver MF. METHODS: Cultures of MF from passages 1 to 4 (P1-4) were studied. IGFBP secretion was analyzed by [(125)I]-IGF-I ligand and immunoblotting. IGF-I, IGF-IR, IGF-II/M6-PR, and IGFBP messenger RNA (mRNA) expression was assessed by Northern blot hybridization. DNA synthesis was evaluated by 5-bromo-2'-deoxyuridine (BrdU) incorporation assay. RESULTS: MF from P1 to 4 constitutively expressed mRNA transcripts specific for IGF-I, IGF-IR, and IGF-II/M6-PR. In MF, biosynthesis of IGFBP-3 and -2 was observed that was stimulated by IGF-I, insulin, and transforming growth factor beta (TGF-beta), whereas platelet-derived growth factor (PDGF-BB) revealed inhibitory effects. IGF-I and to a lesser extent insulin increased DNA synthesis of MF. Simultaneous addition of recombinant human IGFBP-2 or -3 with IGF-I diminished the mitogenic effect of IGF-I on MF whereas preincubation of MF with IGFBP-2 or -3 further potentiated the IGF-I stimulated DNA synthesis. In conclusion, the present study demonstrates that the IGF axis may play a role in the regulation of MF proliferation in vitro which might be relevant in vivo for the process of fibrogenesis during acute and chronic liver injury.

Insulin-like growth factor (IGF)-binding protein-1 is highly induced during acute carbon tetrachloride liver injury and potentiates the IGF-I-stimulated activation of rat hepatic stellate cells.

Hepatic stellate cells (HSC) play a pivotal role in hepatic tissue repair and fibrogenesis. IGF-I has been considered a mitogenic signal for activation and proliferation of HSC in vitro. In the present study IGF-I and IGF-binding protein (IGFBP) gene expression was studied in a model of acute liver injury induced by a single intragastric dose of carbon tetrachloride (CCl(4)) in adult rats. Northern blot analysis revealed a marked increase in IGFBP-1 mRNA levels, with a maximum between 3 and 9 h after CCl(4) application, whereas steady state mRNA levels of IGF-I were only moderately altered. In situ hybridization experiments demonstrated that this increase in IGFBP-1 mRNA was due to a strong expression of IGFBP-1 in the perivenous region 6-12 h after CCl(4) application, extending to the midzonal region of the acinus within 24-48 h. Consequently, a prominent immunostaining for IGFBP-1 was observed in perivenous areas, with a maximum 24-48 h after intoxication. Preincubation of early cultured HSC with a nonphosphorylated IGFBP-1 from human amniotic fluid resulted in a 3.4-fold increase in IGF-I-induced DNA synthesis. The mitogenic effect of IGF-I was also potentiated when HSC were cocultivated with IGFBP-1-overexpressing BHK-21 cells compared with nontransfected cells. These data suggest that IGFBP-1 released during the early steps of liver tissue damage and repair may interact with HSC and potentiate the sensitivity of IGF-I to mitogenic signals.