IGFBP7 reduces breast tumor growth by induction of senescence and apoptosis pathways.

Insulin-like growth factor binding protein 7 (IGFBP7) has been shown to be a tumor suppressor in a variety of cancers. We previously have shown that IGFBP7 expression is inversely correlated with disease progression and poor outcome in breast cancer. Overexpression of IGFBP7 in MDA-MB-468, a triple-negative breast cancer (TNBC) cell line, resulted in inhibition of growth and migration. Xenografted tumors bearing ectopic IGFBP7 expression were significantly growth-impaired compared to IGFBP7-negative controls, which suggested that IGFBP7 treatment could inhibit breast cancer cell growth. To confirm this notion, 14 human patient primary breast tumors were analyzed by qRTPCR for IGFBP7 expression. The TNBC tumors expressed the lowest levels of IGFBP7 expression, which also correlated with higher tumorigenicity in mice. Furthermore, when breast cancer cell lines were treated with IGFBP7, only the TNBC cell lines were growth inhibited. Treatment of NOD/SCID mice harboring xenografts of TNBC cells with IGFBP7 systemically every 3-4 days inhibited tumorigenesis, with associated anti-angiogenic effects, together with increased apoptosis. Upon examining the mechanism of IGFBP7-mediated growth inhibition in TNBC cells, we found that cells not only were arrested in G1 phase of the cell cycle but also underwent senescence as a result of treatment with IGFBP7. Interestingly, IGFBP7 treatment was also associated with strong activation of the stress-associated p38 MAPK pathway, together with upregulation of p53 and the cyclin-dependent protein kinase (CDK) inhibitor, p21(cip1). Prolonged treatment of cells with IGFBP7 resulted in increased cell death, marked by an increase in apoptotic cells and associated cleaved PARP. This is the first study showing that exogenous IGFBP7 inhibits TNBC cell growth both in vitro and in vivo. Taken together, these results suggest IGFBP7 treatment might have therapeutic potential for TNBC.

IGF binding protein-3 treatment alters intestinal cell proliferation but not body weight of adult cystic fibrosis transmembrane conductance regulator deficient mice.

The intestinal phenotype of cystic fibrosis (CF) transmembrane conductance regulator deficient mice includes altered cell homeostasis and a distended crypt-villus axis, which, in previous work, was inversely proportional to body weight. To investigate this correlation, herein, we treated CF mice with IGF binding protein-3 (IGFBP-3), a protein which, as it has potent effects on cell proliferation and apoptosis, we hypothesized would alter the intestinal cell homeostasis, and assessed body weight. Six-week-old C57BL/6JxBALB F2 CF and WT mice received recombinant human IGFBP-3 (rhIGFBP-3, 20 mg/kg) or vehicle treatment, and weight gain, serum protein levels, and intestinal histology were assessed. Administration of rhIGFBP-3 to CF mice significantly increased the number of Igfbp-3 positive cells in the intestine and partially reversed the hyperproliferative phenotype of intestinal crypts and muscularis externa, while not affecting apoptosis. Serum Igfbp-3 levels were increased, and Igf-I, albumin, and triglycerides measures were decreased in CF compared with WT mice. rhIGFBP-3 treatment significantly increased serum albumin and triglycerides but did not affect weight gain in CF mice. We have identified rhIGFBP-3 treatment to reduce intestinal cell proliferation, resulting in decreases in crypt depth and muscularis externa thickness in CF mice.

A pharmacokinetic and dosing study of intravenous insulin-like growth factor-I and IGF-binding protein-3 complex to preterm infants.

In preterm infants, low levels of insulin like growth factor 1 (IGF-I) have been associated with impaired growth and retinopathy of prematurity. Our objective was to study safety and pharmacokinetics of i.v. administered rhIGF-I with its binding protein 3 (rhIGFBP-3) to preterm infants. At 3 d chronological age, an i.v. 3 h infusion of rhIGF-I/rhIGFBP-3 was administered followed by serial measurements of IGF-I and IGFBP-3. Infants were evaluated for physiologic safety measurements. The individual dose of rhIGF-I ranged from 1 to 12 microg/kg. The study was conducted at Queen Silvia Children's Hospital, Gothenburg, Sweden, between January and November 2007. Five patients (3 F) with mean (range) post menstrual age 27 wk (26-29) and birth weight 1022 g (810-1310) participated. IGF-I and IGFBP-3 levels before infusion were median (range) 18 (12-28) and 771 (651-1047) ng/mL, respectively. Immediately after study drug infusion, serum IGF-I and IGFBP-3 levels were 38 (25-59) and 838 (754-1182) ng/mL, respectively. Median (range) half-life for IGF-I and IGFBP-3 was 0.79 (0.59-1.42) and 0.87 (0.85-0.94) hours, respectively. Blood glucose, insulin, sodium, potassium, and physiologic safety measures were within normal ranges. The rhIGF-I/rhIGFBP-3 equimolar proportion was effective in increasing serum IGF-I levels and administration under these study conditions was safe and well tolerated.

Contrasting bone effects of temporary versus permanent IGFBP administration in rodents.

Transgenic animal technology has tremendously improved our current comprehension of IGFBP biology. The high potential of IGFBP transgenic mouse models is due to the fact that they mimic elevated serum IGFBP levels, which are diagnosed under the conditions of impaired growth or critical illness. In general, long term elevated levels of IGFBPs in transgenic mouse models almost exclusively resulted in inhibitory phenotypes e.g. of body or organ growth, indicating specific effects in different cell types. This holds especially for the distinct cellular populations present in the bone environment. After establishing transgenic mouse lines modelling permanent increases of IGFBPs, a second question now poses challenge to current functional genome analysis: what is the function of temporary exposure of a certain cell type to isolated IGFBPs? This question is particularly important due to the fact that elevated IGFBP expression is often found in a conditional fashion and in line with the contradictory findings after long or short term IGFBP exposure in rodent models. In order to understand the potential roles of the conditional increases of IGFBP expression, e.g. during illness, and to further study the adaptive or even therapeutic potential of IGFBPs for certain applications like osteoporosis, it is imperative to take a closer look also to the acute effects of the IGFBPs.

Recombinant human insulin-like growth factor-binding protein 3 inhibits tumor growth and targets the Akt pathway in lung and colon cancer models.

OBJECTIVE: Insulin-like growth factor-binding protein 3 (IGFBP-3) can induce antiproliferative and proapoptotic effects in human cancer cells, by IGF-I independent mechanisms. The antitumor efficacy of recombinant human IGFBP-3 (rhIGFBP-3) and its interaction with chemotherapy in lung and colon cancers, in vitro and in vivo was evaluated. The effects of the different treatments on IGF-IR signaling pathways were also examined. DESIGN: Antiproliferative in vitro assay using rhIGFBP-3, as single agent or in combination with carboplatin or irinotecan against the murine Lewis Lung (M-3LL) and LoVo cell lines, respectively was performed. In the M-3LL model in vivo model, mice were treated with rhIGFBP-3 (3 or 10 mg/kg), carboplatin (25 or 50 mg/kg) alone or in combined treatments. In the LoVo xenograft model, mice were treated with rhIGFBP-3 (3, 10 or 30 mg/kg), irinotecan (10 or 20 mg/kg), as monotherapies or in combinations. RESULTS: rhIGFBP-3 elicited a dose-dependent tumor growth inhibition on the M-3LL model and produced a significant tumor growth inhibition at the highest dose tested. However, it failed to improve the antitumor response to carboplatin. In the LoVo colorectal xenograft model, rhIGFBP-3 caused significant single-agent inhibitory effect and enhanced the antitumor activity of irinotecan at their lowest doses tested. Western blot analysis suggests that the observed tumor growth inhibition by rhIGFBP-3 correlates with decreased Akt phosphorylation in both M-3LL and LoVo cell lines in vitro. CONCLUSIONS: Our novel findings provide evidence for in vivo activity of rhIGFBP-3 against lung and colon tumor models and reveal new insight into its interaction with chemotherapeutic drugs. The antitumor effects of rhIGFBP-3 are associated with a downregulation of AKT signaling.