The role of the IGF system in cancer growth and metastasis: overview and recent insights

Lack of functional pregnancy-associated plasma protein-A (PAPPA) compromises mouse ovarian steroidogenesis and female fertility

The insulin-like growth factor (IGF) system plays an important role in regulating ovarian follicular development and steroidogenesis. IGF binding proteins (IGFBP) mostly inhibit IGF actions, and IGFBP proteolysis is a major mechanism for regulating IGF bioavailability. Pregnancy-associated plasma protein-A (PAPPA) is a secreted metalloprotease responsible for cleavage of IGFBP4 in the ovary. The aim of this study was to investigate whether PAPPA plays a role in regulating ovarian functions and female fertility by comparing the reproductive phenotype of wild-type (WT) mice with mice heterozygous or homozygous for a targeted Pappa gene deletion (heterozygous and PAPP-A knockout [KO] mice, respectively). When mated with WT males, PAPP-A KO females demonstrated an overall reduction in average litter size. PAPP-A KO mice had a reduced number of ovulated oocytes, lower serum estradiol levels following equine chorionic gonadotropin administration, lower serum progesterone levels after human chorionic gonadotropin injection, and reduced expression of ovarian steroidogenic enzyme genes, compared to WT controls. In PAPP-A KO mice, inhibitory IGFBP2, IGFBP3, and IGFBP4 ovarian gene expression was reduced postgonadotropin stimulation, suggesting some compensation within the ovarian IGF system. Expression levels of follicle-stimulating hormone receptor, luteinizing hormone receptor, and genes required for cumulus expansion were not affected. Analysis of preovulatory follicular fluid showed complete loss of IGFBP4 proteolytic activity in PAPP-A KO mice, demonstrating no compensation for loss of PAPPA proteolytic activity by other IGFBP proteases in vivo in the mouse ovary. Taken together, these data demonstrate an important role of PAPPA in modulating ovarian function and female fertility by control of the bioavailability of ovarian IGF.

Safety, pharmacokinetics, and preliminary activity of the anti-IGF-1R antibody figitumumab (CP-751,871) in patients with sarcoma and Ewing's sarcoma: a phase 1 expansion cohort study

BACKGROUND

Figitumumab is a fully human IgG2 monoclonal antibody targeting the insulin-like growth-factor-1 receptor (IGF-1R). Preclinical data suggest a dependence on insulin-like growth-factor signalling for sarcoma subtypes, including Ewing's sarcoma, and early reports show antitumour activity of IGF-1R-targeting drugs in these diseases.

METHODS

Between January, 2006, and August, 2008, patients with refractory, advanced sarcomas received figitumumab (20 mg/kg) in two single-stage expansion cohorts within a solid-tumour phase 1 trial. The first cohort (n=15) included patients with multiple sarcoma subtypes, age 18 years or older, and the second cohort (n=14) consisted of patients with refractory Ewing's sarcoma, age 9 years or older. The primary endpoint was to assess the safety and tolerability of figitumumab. Secondary endpoints included pharmacokinetic profiling and preliminary antitumour activity (best response by Response Evaluation Criteria in Solid Tumours [RECIST]) in evaluable patients who received at least one dose of medication. This study is registered with ClinicalTrials.gov, number NCT00474760.

FINDINGS

29 patients, 16 of whom had Ewing's sarcoma, were enrolled and received a total of 177 cycles of treatment (median 2, mean 6.1, range 1-24). Grade 3 deep venous thrombosis, grade 3 back pain, and grade 3 vomiting were each noted once in individual patients; one patient had grade 3 increases in aspartate aminotransferase and gammaglutamyltransferase concentrations. This patient also had grade 4 increases in alanine aminotransferase concentrations. The only other grade 4 adverse event was raised concentrations of uric acid, noted in one patient. Pharmacokinetics were comparable between patients with sarcoma and those with other solid tumours. 28 patients were assessed for response; two patients, both with Ewing's sarcoma, had objective responses (one complete response and one partial response) and eight patients had disease stabilisation (six with Ewing's sarcoma, one with synovial sarcoma, and one with fibrosarcoma) lasting 4 months or longer.

INTERPRETATION

Figitumumab is well tolerated and has antitumour activity in Ewing's sarcoma, warranting further investigation in this disease.

FUNDING

Pfizer Global Research and Development.

The current status of IGF-I assays--a 2009 update

For almost three decades, the measurement of circulating IGF-I has constituted a highly important biochemical tool in the management of GH disorders. In fact, in acromegaly the importance of circulating IGF-I has increased following the introduction of the GH receptor antagonist pegvisomant, as the use of this drug makes it impossible to use circulating GH as a monitor of disease activity. In addition, determination of circulating IGF-I constitutes a valuable scientific tool in various research areas, from epidemiological investigations through clinical trials and experimental studies. The multiple facets of IGF-I physiology and patho-physiology may explain why numerous endocrine laboratories have invested in IGF-I assays, by means of either in-house assays or commercial kits. However, despite its widespread use, the measurement of IGF-I is by no means trivial. On the contrary, the pronounced binding of IGF-I to the high-affinity IGF-binding proteins (IGFBPs) constitutes a notorious source of error, which has necessitated the development of methods that more or less successfully circumvent interference from the IGFBPs. Furthermore, there are some unsolved issues with the international standardization of the different IGF-I assays and there is no consensus regarding the procedures used when collecting and storing samples for measurement of circulating IGF-I. The aim of this review is to discuss the current state of the art of IGF-I immunoassays and to present the current analytical problems with IGF-I measurements. Finally, we would like to suggest an agenda that may be used when trying to produce internationally accepted uniform requirements for future IGF-I assays.

Prolactin enhances insulin-like growth factor I receptor phosphorylation by decreasing its association with the tyrosine phosphatase SHP-2 in MCF-7 breast cancer cells

Normal mammary development requires coordinated interactions of numerous factors, including prolactin (PRL) and insulin-like growth factor I (IGF-I), both of which have also been implicated in breast cancer pathogenesis and progression. We previously reported that PRL and IGF-I synergize in breast cancer cells to activate ERK1/2 and AKT, leading to increased proliferation, survival, and invasion. Intriguingly, PRL co-treatment with IGF-I augments IGF-I receptor (IGF-IR) phosphorylation 2-fold higher than IGF-I alone. Here, we showed the importance of the tyrosine phosphatase SHP-2 in this cross-talk using pharmacological inhibition and small interfering RNA. SHP-2 recruitment to IGF-IR was significantly attenuated by PRL co-treatment. Src family kinase activity was required for IGF-IR association with SHP-2, ligand-induced IGF-IR internalization, and PRL-enhanced IGF-IR phosphorylation. Inhibition of internalization, via knockdown of the GTPase, dynamin-2, prevented not only IGF-IR dephosphorylation, but also PRL-enhanced IGF-IR phosphorylation. Consistently, PRL diminished IGF-I-induced IGF-IR internalization, which may result from reduced SHP-2 association with IGF-IR, because we demonstrated an essential role for SHP-2 in IGF-IR internalization. Together, these findings describe a novel mechanism of cross-talk between PRL and IGF-I in breast cancer cells, with implications for our understanding of tumor progression and potential therapeutic strategies.

Loss of imprinting of the insulin-like growth factor II (IGF2) gene in esophageal normal and adenocarcinoma tissues

To evaluate loss of imprinting (LOI) and expression of the IGF2 gene in matched esophageal normal and adenocarcinoma tissues, we studied a prospective cohort of 77 patients who underwent esophageal resection between 1998 and 2003. IGF2 imprinting status was determined by reverse transcription-polymerase chain reaction (PCR) following ApaI digestion, and quantitative PCR was used to evaluate IGF2 expression, which was correlated with clinicopathologic findings, disease-free and overall survival. In total, 32% (14/44) of informative tissues showed loss of IGF2 imprinting, with a strong correlation between the tumor and normal esophageal epithelia (Kappa = 0.89, P < 0.01). Normal epithelia with LOI had increased expression of IGF2 [median: 2.91, 95% confidence interval (CI): 0.93-5.06] compared with imprinted normal epithelia (median: 1.13, 95% CI: 0.85-1.39) (P = 0.03). In contrast, tumors with LOI had significantly reduced IGF2 expression (median: 1.87, 95% CI: 0.53-5.21) compared with normally imprinted tumors (median: 6.79, 95% CI: 3.39-15.89) (P = 0.016). Patients below the age of 65 years with normally imprinted tumors had significantly reduced 5 year disease-free survival (DFS) (24%) compared with patients whose tumors had LOI for IGF2 (55%) (P = 0.03). Cox regression analysis showed that IGF2 overexpression was associated with significantly reduced disease-free survival (P = 0.04). We conclude that in a subgroup of younger patients, loss of IGF2 imprinting was associated with improved outcome following esophageal resection. Expression of IGF2 in esophageal adenocarcinoma and normal esophageal epithelia depended on imprinting status and tissue type, suggesting novel molecular regulatory mechanisms in esophageal tumorigenesis.

Basic and clinical significance of IGF-I-induced signatures in cancer

The insulin-like growth factor (IGF) system mediates growth, differentiation and developmental processes; it is also involved in various metabolic activities. Deregulation of IGF system expression and action is linked to diverse pathologies, ranging from growth deficits to cancer development. Targeting of the IGF axis emerged in recent years as a promising therapeutic approach in cancer and other medical conditions. Rational use of IGF-I-induced gene signatures may help to identify patients who might benefit from IGF axis-directed therapeutic modalities. In the accompanying research article in BMC Medicine, Rajski et al. show that IGF-I-induced gene expression in primary breast and lung fibroblasts accurately predict outcomes in breast and lung cancer patients.See the associated research paper by Rajski et al: http://www.biomedcentral.com/1741-7015/8/1.

The rationale and development of therapeutic insulin-like growth factor axis inhibition for lung and other cancers

The insulin-like growth factor (IGF) axis involves elements of endocrine, paracrine, and autocrine control. It is centrally involved in normal development and growth. Core signaling is driven through the IGF-1 receptor (IGF-1R) in either homo-multimeric complexes or hetero-multimeric complexes with the insulin receptor (IR). Signaling is affected by a large number of upstream and downstream factors, including the differential expression of various intracellular IR substrates, a range of stimulatory ligands (insulin, IGF-1, and IGF-2), the expression of specific clearance receptors (eg, IGF-2R), and different IGF-binding proteins. Considerable evidence exists to implicate aspects of the IGF axis in the development and maintenance of many different nonneoplastic and neoplastic diseases, including both small-cell lung cancer and non-small-cell lung cancer (NSCLC). A large number of different anticancer strategies directed against the IGF axis are being developed. Monoclonal antibodies directed against the IGF-1R are the furthest advanced clinically. Hyperglycemia appears to be a class effect. To date, the major difference among the antibodies used in clinical trials seems to be their plasma half-lives, leading to a number of different administration regimens being taken forward. Early signals of monotherapy activity have been notably reported in patients with Ewing sarcoma and in several other cancers. Encouraging increases in the NSCLC response rate have already been reported after the addition of an anti-IGF-1R antibody to first-line carboplatin and paclitaxel. Explorations of aspects of ligands, binding proteins, receptors, and receptor substrates are all ongoing to identify potential biomarkers predictive of benefit from IGF axis intervention.

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.

Downregulation of IGF-IR expression by RNAi inhibits proliferation and enhances chemosensitization of human colon cancer cells

PURPOSE

Colon cancer is the second leading cause of cancer death worldwide. Elevated expression of insulin-like growth factor-I receptor (IGF-IR) is a frequent genetic abnormality seen in this malignancy. For a better understanding of its role in maintaining the malignant phenotype, we used RNA interference (RNAi) directed against IGF-IR in our study. The aim of this study was to examine the anti-proliferation and chemosensitization effects elicited by a decrease in the transcription and protein levels of IGF-IR by RNAi in SW480 colon cancer cells.

METHODS

A plasmid-based polymerase III promoter system was used to deliver and express short interfering RNA (siRNA) targeting IGF-IR to reduce its expression in SW480 cells. Western blot analysis was used to measure the protein level of IGF-IR. We assessed the effects of IGF-IR silencing on cancer cell growth by a cell growth curve. The effect of the 5-fluorouracil (5-FU)-induced cell death by knockdown of IGF-IR was also investigated by methyl thiazolyl tetrazolium assay.

RESULTS

Transfection of siRNA targeting IGF-IR was shown to reduce IGF-IR messenger RNA levels by 95%. Western blotting detected a similar inhibition of IGF-IR protein levels in those cells. The cells transfected with PKD-short hairpin RNA-IGF-IR-V2 significantly decreased cell growth and rendered cells more sensitive to chemotherapy. The highest proliferation inhibitory and chemosensitization ratios were 53 +/- 2% and 1.78, respectively.

CONCLUSION

This study indicates that downregulation of IGF-IR results in significant inhibition of tumor growth in vitro. It also provides a promising strategy to chemotherapy efficacy in human tumors and forming a basis for future in vivo trials.

IGF-IR and its inhibitors in gastrointestinal carcinomas (Review)

The type I insulin-like growth factor receptor (IGF-IR) and its associated signaling system play a significant role in tumorigenesis, tumor survival and progression, and cancer therapeutic resistance, and thus has provoked great interest as a promising target for cancer treatment. In this report we present the role of IGF-IR in gastrointestinal carcinomas whose pathology has been identified as tightly correlated with an abnormal expression and activation of IGF-IR. Reported data from experimental studies suggest the feasibility of targeted IGF-IR therapy in gastrointestinal carcinomas. Many types of inhibitors against IGF-IR have been developed. Inhibitors with anti-IGF-IR monoclonal antibodies and tyrosine kinase inhibitors currently undergoing preclinical and clinical evolution are also reviewed.

Selective disruption of insulin-like growth factor-1 (IGF-1) signaling via phosphoinositide-dependent kinase-1 prevents the protective effect of IGF-1 on human cancer cell death

Insulin-like growth factor-1 (IGF-1) signaling system exerts a broad antiapoptotic function and plays a crucial role in resistance to anticancer therapies. Exposure of MCF-7 breast cancer cells to IGF-1 rapidly and transiently induced tyrosine phosphorylation and activation of phosphoinositide-dependent kinase-1 (PDK1). This was paralleled by Akt/protein kinase B and protein kinase C-zeta phosphorylation, at Thr(308) and Thr(410), respectively. IGF-1 treatment also enhanced PDK1 interaction with IGF-1 receptor (IGF-1R) in intact MCF-7 cells. Pulldown assays revealed that PDK1 bound IGF-1R in vitro and that the region encompassing amino acids 51-359 of PDK1 was necessary for the interaction. Synthetic peptides corresponding to IGF-1R C terminus amino acids 1295-1337 (C43) and to PDK1 amino acids 114-141 reduced in vitro IGF-1R/PDK1 interaction in a concentration-dependent manner. Loading of fluoresceinated-C43 (fluorescein isothiocyanate (FITC)-C43) into MCF-7 cells significantly reduced IGF-1R/PDK1 interaction and phosphorylation of PDK1 substrates. Moreover, FITC-C43 intracellular loading reverted the protective effect of IGF-1 on growth factor deprivation-induced cell death. Finally, the inhibition of IGF-1R/PDK1 interaction and signaling by FITC-C43 was accompanied by 2-fold enhanced killing capacity of cetuximab in human GEO colon adenocarcinoma cells and was sufficient to restore cell death in cetuximab-resistant cell clones. Thus, disruption of PDK1 interaction with IGF-1R reduces IGF-1 survival effects in cancer cells and may enhance cell death by anticancer agents.

SiRNA-mediated IGF-1R inhibition sensitizes human colon cancer SW480 cells to radiation

PURPOSE

Insulin like growth factor receptor 1 (IGF-1R) is well-documented to play a key role in radiation response and tumor radiosensitivity, thus offering an attractive clinic drug target to enhance tumor sensitivity to anti-cancer radiotherapy.

MATERIAL AND METHODS

Human colon carcinoma SW480 cells were transfected with the specific small interference RNA (siRNA) expression vector (pkD-shRNA-IGF-1R-V2) designed to target IGF-1R mRNA. The expression of IGF-1R mRNA and its protein among the transfected and untransfected cells were detected by semi-quantitative RT-PCR and ELISA assay. The changes in cell radiosensitivity were examined by MTT assay.

RESULTS

Transfection of mammalian expression vector pkD containing IGF-1R siRNA was shown to reduce IGF-1R mRNA levels by up to 95%. ELISA assay detected a similar inhibition of IGF-1R protein levels in cells transfected with IGF-1R siRNA. SW480 cells transfected with the expression vector for siRNA significantly rendered cells more sensitive to radiation and the highest radiation enhancement ratio was 2.02 +/- 0.08.

CONCLUSION

These data provide the first evidence that specific siRNA fragment (pkD-shRNA-IGF-1R-V2) targeting human IGF-1R mRNA is able to enhance colon cancer radiosensitivity. Also results indicated that, combining IGF-1R siRNA and radiation significantly enhances antitumor efficacy compared with either modality alone.

Effects of endogenous insulin-like growth factor binding protein-3 on cell cycle regulation in breast cancer cells

High tissue insulin-like growth factor binding protein-3 (IGFBP-3) expression in breast cancers is associated in some studies with rapid growth and poor outcome. This study examined the effects of endogenous IGFBP-3 in Hs578T breast cancer cells, which are IGF-unresponsive and grow aggressively despite relatively high IGFBP-3 expression. IGFBP-3 downregulation using siRNA was associated with increases in DNA synthesis, the percentage of cells in S phase and viable cell numbers, accompanied by increases in cyclins A and D1, a decrease in p27 expression, and increased phosphorylation of retinoblastoma (Rb) on Ser795. Downregulation of IGFBP-3 inhibited extracellular signal-regulated kinase (ERK) activation and cell migration in a monolayer wound healing assay. These results indicate that endogenous IGFBP-3 is anti-proliferative and pro-migratory in Hs578T cells and that these effects are IGF-independent. Poor outcome in breast tumours expressing high levels of IGFBP-3 may be due to the effects of IGFBP-3 on cell migration rather than cell growth.

The role of insulin-like growth factors (IGF) in cell division processes and in malignancy

Az inzulinszerű növekedési faktor (IGF) szerepe a sejtosztódásban és a daganatképződésben kiterjedt kutatás tárgyát képezi. Korábban nyilvánvalóvá vált, hogy az IGF- és a hozzá kötődő jelátviteli rendszer proliferatív, differenciálódást elősegítő és antiapoptotikus hatást vált ki. Az IGF májban történő fiziológiás termelődésén túl jelentős mennyiségben kerül előállításra a daganatos sejtekben, s a keringésben fiziológiásan elérhető mennyiséget az IGF-kötő fehérjék (IGFBP) szabályozzák. A receptor-ligand kapcsolódást követően kialakuló tirozinkináz-aktivitás a foszfatidil-inozitol-3-kináz (PI3-K), valamint p38 mitogén aktiválta proteinkináz (MAPK) útvonalakon keresztül fejti ki hatását a sejtciklusra. Áttekintésre kerül a ligand, valamint a receptor bioszintézise, a jelátviteli rendszer működése és a daganatos sejtekben betöltött szerepe. A terápiás lehetőségek áttekintése során elemzésre kerülnek a preklinikai stádiumban levő szerek fontosabb ismérvei.

Targeting the IGF1 axis in cancer proliferation

The IGF network of ligands, cell-surface receptors and IGF-binding proteins has important roles at multiple levels, including the cellular, organ and organism levels. The IGF system mediates growth, differentiation and developmental processes, and is also involved in various metabolic activities. Dysregulation of IGF system expression and action is linked to diverse pathologies, ranging from growth deficits to cancer development. Targeting of the IGF axis emerged in recent years as a promising therapeutic approach in conditions in which the IGF system is involved. Specific IGF1 receptor (IGF1R) targeting, in particular, produced the best experimental and clinical results so far, and generated significant optimism in the field. This review provides a basic analysis of the role of the IGF1R in cancer biology and explores the functional interactions between the IGF signaling pathways and various cancer genes (e.g., oncogenes, tumor suppressors). In addition, we review a number of specific malignancies in which the IGF system is involved and summarize recent data on preclinical and clinical studies employing IGF1R-targeted modalities.

Insulin-like growth factor type I receptor gene expression and obesity in esophageal adenocarcinoma

The objective of this exploratory study was to evaluate the role of the insulin-like growth factor I receptor (IGF-IR) in esophageal adenocarcinoma (EADC). Using quantitative PCR, we studied IGF-IR mRNA expression in 52 well-characterized surgically resected EADC and matched histologically normal esophageal tissues, and examined IGF-IR expression levels in relation to clinicopathologic characteristics, body mass index (BMI), and the common IGF-IR polymorphism (G1013A), recently proposed to modify risk of obesity for EADC. Expression levels of IGF-IR mRNA were not significantly different between EADC and matched histologically normal esophageal epithelia. Although no significant associations were found between IGF-IR expression and BMI, tumor differentiation, stage or survival, when stratified by genotype, patients with the polymorphic A variant had significantly higher IGF-IR expression in EADC tissues compared with matched normal epithelia. These findings suggest that G1013A most likely modulates IGF-IR function, possibly by influencing gene transcription or mRNA stability, and represents a plausible mechanistic link underlying the association between obesity and esophageal malignancy.

Differential roles of insulin-like growth factor receptor- and insulin receptor-mediated signaling in the phenotypes of hepatocellular carcinoma cells

Intrahepatic and extrahepatic metastases are common findings in hepatocellular carcinoma (HCC). Insulin-like growth factor 2 (IGF2) expression is frequently induced in HCC, and serum IGF2 levels correlate with the presence of extrahepatic metastases. Yet, the role of IGF-induced signaling in the dissemination of HCC remains unclear. We have previously observed elevated IGF2 levels in tumors with metastatic potential in an HCC mouse model. Here, we demonstrate that inhibition of IGF2, or its receptor IGF1R, impairs the migration and invasion activities of murine HCC cells. Furthermore, inhibition of IGF1R also impairs the ability of HCC cells to colonize the lungs after introduction into the circulation through the tail vein but does not impair subcutaneous tumor growth. Collectively, these findings suggest that IGF1R-mediated signaling plays a causative role in tumor dissemination but is not required for tumor growth per se. Although previous studies indicate that IGF ligands can signal through IGF1R/insulin receptor (IR) heterodimers, and IR-A homodimers, we demonstrate that the IR is not required for invasion and metastasis by HCC cells. Finally, we identify matrix metalloproteinase 2 as a mediator of the invasive phenotype downstream of IGF1R-induced signaling. Thus, our studies demonstrate the importance of IGF2-induced signaling in the dissemination of HCC cells.

Heme-binding protein HRG-1 is induced by insulin-like growth factor I and associates with the vacuolar H+-ATPase to control endosomal pH and receptor trafficking

Endocytosis and trafficking of receptors and nutrient transporters are dependent on an acidic intra-endosomal pH that is maintained by the vacuolar H(+)-ATPase (V-ATPase) proton pump. V-ATPase activity has also been associated with cancer invasiveness. Here, we report on a new V-ATPase-associated protein, which we identified in insulin-like growth factor I (IGF-I) receptor-transformed cells, and which was separately identified in Caenorhabditis elegans as HRG-1, a member of a family of heme-regulated genes. We found that HRG-1 is present in endosomes but not in lysosomes, and it is trafficked to the plasma membrane upon nutrient withdrawal in mammalian cells. Suppression of HRG-1 with small interfering RNA causes impaired endocytosis of transferrin receptor, decreased cell motility, and decreased viability of HeLa cells. HRG-1 interacts with the c subunit of the V-ATPase and enhances V-ATPase activity in isolated yeast vacuoles. Endosomal acidity and V-ATPase assembly are decreased in cells with suppressed HRG-1, whereas transferrin receptor endocytosis is enhanced in cells that overexpress HRG-1. Cellular uptake of a fluorescent heme analogue is enhanced by HRG-1 in a V-ATPase-dependent manner. Our findings indicate that HRG-1 regulates V-ATPase activity, which is essential for endosomal acidification, heme binding, and receptor trafficking in mammalian cells. Thus, HRG-1 may facilitate tumor growth and cancer progression.

The IGF-I receptor can alter the matrix metalloproteinase repertoire of tumor cells through transcriptional regulation of PKC-{alpha}

The IGF-I receptor (IGF-IR) was identified as a tumor progression factor, but its role in invasion and metastasis has been the subject of some controversy. Previously we reported that in murine lung carcinoma M-27 cells, overexpression of IGF-IR increased the synthesis and activation of matrix metalloproteinase (MMP)-2 via Akt/phosphatidylinositol 3-kinase signaling. In contrast, we show here that in these and other cells, IGF-IR overexpression reduced the constitutive and phorbol 12-myristate 13-acetate (PMA)-inducible expression of three protein kinase C (PKC)-regulated metalloproteinases, MMP-3, MMP-9, and MMP-13, in cultured cells as well as in vivo in sc tumors. To elucidate the underlying mechanism, we analyzed the effect of IGF-IR on PKC expression and activity using wild-type and IGF-IR-overexpressing (M-27(IGFIR)) tumor cells. Our results show that overexpression and activation of IGF-IR reduced PKC-alpha expression, PKC activity, and downstream ERK1/2 signaling, and these effects were reversed in cells expressing kinase (Y(1131,1135,1136)F) or C-terminal (Y(1250/51)F) domain mutants of IGF-IR. This reduction was due to transcriptional down-regulation of PKC-alpha as evidenced by reduced PKC-alpha mRNA expression in a phosphatidylinositol 3-kinase-dependent manner and a blockade of PKC-alpha promoter activation as revealed by a reporter gene assay. Finally, reconstitution of PKC-alpha levels could restore MMP-9 expression levels in these cells. Collectively, these results show that IGF-IR can inhibit PKC-alpha gene transcription and thereby block the synthesis of PMA-regulated MMPs, suggesting that within the same cells, IGF-IR can act as both a positive and negative regulator of MMP expression and function.

Treatment of dwarfism with recombinant human insulin-like growth factor-1

BACKGROUND

The growth hormone-IGF (insulin-like growth factor) system plays a central role in hormonal growth regulation. Recombinant human (rh) growth hormone (GH) has been available since the late 1980s for replacement therapy in GH-deficient patients and for the stimulation of growth in patients with short stature of various causes. Growth promotion by GH occurs in part indirectly through the induction of IGF-1 synthesis. In primary disturbances of IGF-1 production, short stature can only be treated with recombinant human IGF-1 (rhIGF-1). rhIGF-1 was recently approved for this indication but can also be used to treat other conditions.

METHODS

Selective review of the literature on IGF-1 therapy, based on a PubMed search.

RESULTS AND CONCLUSION

In children with severe primary IGF-1 deficiency (a rare condition whose prevalence is less than 1:10,000), the prognosis for final height is very poor (ca. 130 cm), and IGF-1 therapy is the appropriate form of pathophysiologically based treatment. There is no alternative treatment at present. The subcutaneous administration of IGF-1 twice daily in doses of 80 to 120 microg/kg accelerates growth and increases final height by 12 to 15 cm, according to current data. There is, however, a risk of hypoglycemia, as IGF-1 has an insulin-like effect. As treatment with IGF-1 is complex, this new medication should only be prescribed, for the time being, by experienced pediatric endocrinologists and diabetologists.

Growth hormone-activated STAT5 may indirectly stimulate IGF-I gene transcription through HNF-3{gamma}

IGF-I is abundantly expressed in the liver under the stimulation of GH. We showed previously that expression of hepatocyte nuclear factor (HNF)-3gamma, a liver-enriched transcription factor, was strongly stimulated by GH in bovine liver. In this study, we determined whether GH-increased HNF-3gamma might contribute to GH stimulation of IGF-I gene expression in bovine liver and the underlying mechanism. A sequence analysis of the bovine IGF-I promoter revealed three putative HNF-3 binding sites, which all appear to be conserved in mammals. Chromatin immunoprecipitation assays showed that GH injection increased binding of HNF-3gamma to the IGF-I promoter in bovine liver. Gel-shift assays indicated that one of the three putative HNF-3 binding sites, HNF-3 binding site 1, bound to the HNF-3gamma protein from bovine liver with high affinity. Cotransfection analyses demonstrated that this HNF-3 binding site was essential for the transcriptional response of the IGF-I promoter to HNF-3gamma in CHO cells and to GH in primary mouse hepatocytes. Using similar approaches, we found that GH increased binding of the signal transducer and activator of transcription 5 (STAT5) to the HNF-3gamma promoter in bovine liver, that this binding occurred at a conserved STAT5 binding site, and that this STAT5 binding site was necessary for the HNF-3gamma promoter to respond to GH. Taken together, these results suggest that in addition to direct action, GH-activated STAT5 may also indirectly stimulate IGF-I gene transcription in the liver by directly enhancing the expression of the HNF-3gamma gene.

Beyond antiepidermal growth factor receptors and antiangiogenesis strategies for nonsmall cell lung cancer: exploring a new frontier

PURPOSE OF REVIEW

Integrating targeted therapies against the epidermal growth factor receptor (EGFR) and angiogenesis pathways into standard treatment paradigms for advanced nonsmall cell lung cancer (NSCLC) have been successful, but not yet curative. Two treatment strategies, in development, seem particularly appealing for further study: insulin-like growth factor receptor (IGF-1R) and histone deacetylase (HDAC) inhibition. Several lines of evidence suggest that these novel approaches may play a relevant role in the future treatment of NSCLC.

RECENT FINDINGS

Preliminary results of a phase II trial combining an anti-IGF-1R monoclonal antibody with platinum-based chemotherapy in untreated NSCLC patients have shown an encouraging response rate, particularly in those with squamous cell carcinoma, where IGFR expression is typically high. Recent data also support the clinical development of HDAC inhibitors as a strategy to counter epigenetic gene silencing and transcriptional repression of key anticancer genes. Moreover, research efforts are focusing on identifying predictive markers to appropriately select patients for maximal therapeutic benefit.

SUMMARY

Here, we briefly review data regarding anti-EGFR and antiangiogenesis agents before discussing the potential roles for IGF-1R and HDAC inhibitors in NSCLC management, and the need for optimizing treatment by seeking a more personalized approach to care.

Reduced susceptibility to azoxymethane-induced aberrant crypt foci formation and colon cancer in growth hormone deficient rats

OBJECTIVES

To evaluate the role of GH in colon carcinogenesis, we examined the formation of aberrant crypt foci (ACFs) and tumor development in wild type (WT) and GH-deficient, spontaneous dwarf rats (SDRs) exposed to the carcinogen azoxymethane (AOM).

DESIGN

ACF were quantified by stereomicroscopy and tumor number and weights were recorded for each animal. Cell proliferation was measured by vincristine metaphase arrest, flow cytometry, and bromodeoxyuridine (BrdU) incorporation. Apoptosis was measured by TUNEL staining and cleaved caspase-3 immunohistochemistry. IGF-I was measured by radioimmunoassay (RIA). Hexokinase activity was measured by spectrophotometric assay. PARP cleavage, and IGF-IR, and p27(kip/cip) expression were measured by Western blotting.

RESULTS

ACFs detected by stereomicroscopy were markedly reduced ( approximately 85%) in SDRs vs. WT rats at 10, 25, and 28 weeks after AOM. Tumor incidence, number, and weight also were reduced in SDR vs. WT animals. AOM treatment increased cell proliferation in the distal colon (where tumors occur) of WT rats but not SDRs, and these changes corresponded to increased ACF and tumor formation. Apoptosis rates were similar in AOM-treated WT and SDRs. Alterations in serum IGF-I levels may contribute to differences in the proliferative response to AOM and decreased ACF formation in SDR vs. WT rats.

CONCLUSIONS

We conclude that early neoplastic lesions (ACFs) were reduced in GH-deficient animals. This effect corresponds with differences in AOM-induced proliferation, but not apoptosis. These data indicate that GH is required for the full effect of AOM on colon ACF and tumor development, and that the SDR rat is a promising model for studies regarding the role of GH/IGF system in the initiation and promotion of colon cancer.

Insulin receptor isoforms and insulin receptor/insulin-like growth factor receptor hybrids in physiology and disease

In mammals, the insulin receptor (IR) gene has acquired an additional exon, exon 11. This exon may be skipped in a developmental and tissue-specific manner. The IR, therefore, occurs in two isoforms (exon 11 minus IR-A and exon 11 plus IR-B). The most relevant functional difference between these two isoforms is the high affinity of IR-A for IGF-II. IR-A is predominantly expressed during prenatal life. It enhances the effects of IGF-II during embryogenesis and fetal development. It is also significantly expressed in adult tissues, especially in the brain. Conversely, IR-B is predominantly expressed in adult, well-differentiated tissues, including the liver, where it enhances the metabolic effects of insulin. Dysregulation of IR splicing in insulin target tissues may occur in patients with insulin resistance; however, its role in type 2 diabetes is unclear. IR-A is often aberrantly expressed in cancer cells, thus increasing their responsiveness to IGF-II and to insulin and explaining the cancer-promoting effect of hyperinsulinemia observed in obese and type 2 diabetic patients. Aberrant IR-A expression may favor cancer resistance to both conventional and targeted therapies by a variety of mechanisms. Finally, IR isoforms form heterodimers, IR-A/IR-B, and hybrid IR/IGF-IR receptors (HR-A and HR-B). The functional characteristics of such hybrid receptors and their role in physiology, in diabetes, and in malignant cells are not yet fully understood. These receptors seem to enhance cell responsiveness to IGFs.

Knockdown of IGF-IR by RNAi inhibits SW480 colon cancer cells growth in vitro

BACKGROUND AND AIMS

Colon cancer is the second leading cause of death due to cancer worldwide. Elevated expression of IGF-IR is a frequent genetic abnormality seen in this malignancy. The aim of the study was to examine the anti-growth effects elicited by a decrease in the protein level of IGF-IR by RNA interference (RNAi) in SW480 cells.

METHODS

A plasmid-based polymerase III promoter system was used to deliver and express short interfering RNA (siRNA) targeting IGF-IR to reduce its expression in SW480 cells. The expression of IGF-1R protein was detected by Western blot. We assessed the effects of IGF-IR silencing on cancer cell growth by a growth curve.

RESULTS

We prepared a type of IGF-IR short hairpin RNA (shRNA) expression vector that could efficiently inhibit the expression of IGF-IR in SW480 cells. At 48 h after transfection, the expression inhibition rate was 92 +/- 2% at mRNA level detected by RT-PCR analysis. Western blotting detected a similar inhibition of IGF-IR protein levels in cells transfected with pkD-shRNA-IGF-IR-V2. Downregulation of IGF-IR resulted in significant inhibition of cancer cell growth in vitro. The cell growth inhibition rates at 24, 48, and 72 h after pkD-shRNA-IGF-IR-V2 transfection were 32.06, 47.61, and 35.36%, respectively.

CONCLUSIONS

Our data show that decreasing the IGF-IR protein level in SW480 cells by RNAi could significantly inhibit tumor growth in vitro, implying the therapeutic potential of RNAi on the treatment of colon cancer by targeting overexpression oncogenes such as IGF-IR. IGF-IR may be a potential therapeutic target for human colon cancer.

Development of IGF-IR Inhibitors in Pediatric Sarcomas

For approximately two decades, the insulin-like growth factor (IGF) has been implicated in the pathogenesis of numerous pediatric malignancies, including osteosarcoma, Ewing sarcoma, and rhabdomyosarcoma. In the past, major toxicities have limited the clinical development of IGF-targeted therapies. However, recent interest has been heightened by the availability of increasingly specific small molecules and antibodies directed at IGF-I receptor. Preclinical data using these inhibitors against xenograft models of pediatric sarcomas, coupled with responses in adults with Ewing sarcoma, have generated significant excitement about the clinical potential of this class of drugs and have driven the rapid development of numerous clinical trials now under way. This article reviews the preclinical data and the ongoing clinical trials, as well as issues regarding the further development of these drugs specifically for pediatric malignancies.

Design of an insulin analog with enhanced receptor binding selectivity: rationale, structure, and therapeutic implications

Insulin binds with high affinity to the insulin receptor (IR) and with low affinity to the type 1 insulin-like growth factor (IGF) receptor (IGFR). Such cross-binding, which reflects homologies within the insulin-IGF signaling system, is of clinical interest in relation to the association between hyperinsulinemia and colorectal cancer. Here, we employ nonstandard mutagenesis to design an insulin analog with enhanced affinity for the IR but reduced affinity for the IGFR. Unnatural amino acids were introduced by chemical synthesis at the N- and C-capping positions of a recognition alpha-helix (residues A1 and A8). These sites adjoin the hormone-receptor interface as indicated by photocross-linking studies. Specificity is enhanced more than 3-fold on the following: (i) substitution of Gly(A1) by D-Ala or D-Leu, and (ii) substitution of Thr(A8) by diaminobutyric acid (Dab). The crystal structure of [D-Ala(A1),Dab(A8)]insulin, as determined within a T(6) zinc hexamer to a resolution of 1.35 A, is essentially identical to that of human insulin. The nonstandard side chains project into solvent at the edge of a conserved receptor-binding surface shared by insulin and IGF-I. Our results demonstrate that modifications at this edge discriminate between IR and IGFR. Because hyperinsulinemia is typically characterized by a 3-fold increase in integrated postprandial insulin concentrations, we envisage that such insulin analogs may facilitate studies of the initiation and progression of cancer in animal models. Future development of clinical analogs lacking significant IGFR cross-binding may enhance the safety of insulin replacement therapy in patients with type 2 diabetes mellitus at increased risk of colorectal cancer.

Oxidative stress inhibits insulin-like growth factor-I induction of chondrocyte proteoglycan synthesis through differential regulation of phosphatidylinositol 3-Kinase-Akt and MEK-ERK MAPK signaling pathways

The ability of insulin-like growth factor I (IGF-I) to stimulate cartilage matrix synthesis is reduced in aged and osteoarthritic cartilage. Aging and osteoarthritis are associated with an increase in reactive oxygen species, which we hypothesized would interfere with normal IGF-I signaling. We compared IGF-I signaling in normal and osteoarthritic human articular chondrocytes and investigated the effects of oxidative stress induced by tert-butylhydroperoxide (tBHP). In normal human chondrocytes, IGF-I initiated a strong and sustained phosphorylation of IRS-1 (Tyr-612) and Akt (Ser-473) and transient ERK phosphorylation. In contrast, in osteoarthritic chondrocytes, which possessed elevated basal IRS-1 (Ser-312) and ERK phosphorylation, IGF-I failed to stimulate IRS-1 (Tyr-612) or Akt phosphorylation. In normal human chondrocytes, tBHP triggered strong IRS-1 (Ser-312 and Ser-616) and ERK phosphorylation and inhibited IGF-I-induced IRS-1 (Tyr-612) and Akt phosphorylation. Lentivirus-mediated overexpression of constitutively active (CA) Akt significantly enhanced proteoglycan synthesis, whereas both dominant negative Akt and CA MEK inhibited proteoglycan synthesis. CA Akt also promoted type II collagen and Sox9 expression, whereas tBHP treatment and CA MEK inhibited aggrecan, collagen II, and Sox9 mRNA expression. In osteoarthritic chondrocytes, the antioxidants Mn(III) tetrakis(4-benzoic acid)porphyrin and N-acetylcysteine increased the ratio of Akt to ERK phosphorylation and promoted IGF-I-mediated proteoglycan synthesis. Chemical inhibition of ERK significantly enhanced IGF-I phosphorylation of Akt and alleviated tBHP inhibition of Akt phosphorylation. These results demonstrate opposing roles for phosphatidylinositol 3-kinase-Akt and MEK-ERK in cartilage matrix synthesis and suggest that elevated levels of reactive oxygen species cause chondrocyte IGF-I resistance by altering the balance of Akt to ERK activity.

Physical activity, obesity and risk for esophageal adenocarcinoma

Over the past three decades, an increasing incidence of esophageal adenocarcinoma (EADC) has been reported throughout North America and Europe at a rate exceeding that of any other human solid tumor. Recent studies have clearly implicated chronic gastroesophageal reflux disease and several lifestyle risk factors, including tobacco consumption, diet and obesity, to be associated with increased risk of EADC. Although physical inactivity is now recognized as a risk factor for several chronic diseases including cancer, only a very limited number of studies have specifically evaluated the association between physical activity and esophageal malignancy. Furthermore, the precise biological mechanisms underlying the association between physical activity, obesity and cancer risk remain unclear. Since successful promotion of healthy body weight and exercise may substantially reduce the future incidence of cancer in the population, the purpose of this review is to explore current evidence linking physical activity, obesity and risk of malignancy – specifically EADC.

Elevated levels of insulin-like growth factor (IGF)-I in serum rescue the severe growth retardation of IGF-I null mice

IGF-I plays a vital role in growth and development and acts in an endocrine and an autocrine/paracrine fashion. The purpose of the current study was to clarify whether elevated levels of IGF-I in serum can rescue the severe growth retardation and organ development and function of igf-I null mice. To address that, we overexpressed a rat igf-I transgene specifically in the liver of igf-I null mice. We found that in the total absence of tissue IGF-I, elevated levels of IGF-I in serum can support normal body size at puberty and after puberty but are insufficient to fully support the female reproductive system (evident by irregular estrous cycle, impaired development of ovarian corpus luteum, reduced number of uterine glands and endometrial hypoplasia, all leading to decreased number of pregnancies and litter size). We conclude that most autocrine/paracrine actions of IGF-I that determine organ growth and function can be compensated by elevated levels of endocrine IGF-I. However, in mice, full compensatory responses are evident later in development, suggesting that autocrine/paracrine IGF-I is critical for neonatal development. Furthermore, we show that tissue IGF-I is necessary for the development of the female reproductive system and cannot be compensated by elevated levels of serum IGF-I.

The influence of glucose-lowering therapies on cancer risk in type 2 diabetes

AIMS/HYPOTHESIS

The risk of developing a range of solid tumours is increased in type 2 diabetes, and may be influenced by glucose-lowering therapies. We examined the risk of development of solid tumours in relation to treatment with oral agents, human insulin and insulin analogues.

METHODS

This was a retrospective cohort study of people treated in UK general practices. Those included in the analysis developed diabetes >40 years of age, and started treatment with oral agents or insulin after 2000. A total of 62,809 patients were divided into four groups according to whether they received monotherapy with metformin or sulfonylurea, combined therapy (metformin plus sulfonylurea), or insulin. Insulin users were grouped according to treatment with insulin glargine, long-acting human insulin, biphasic analogue and human biphasic insulin. The outcome measures were progression to any solid tumour, or cancer of the breast, colon, pancreas or prostate. Confounding factors were accounted for using Cox proportional hazards models.

RESULTS

Metformin monotherapy carried the lowest risk of cancer. In comparison, the adjusted HR was 1.08 (95% CI 0.96-1.21) for metformin plus sulfonylurea, 1.36 (95% CI 1.19-1.54) for sulfonylurea monotherapy, and 1.42 (95% CI 1.27-1.60) for insulin-based regimens. Adding metformin to insulin reduced progression to cancer (HR 0.54, 95% CI 0.43-0.66). The risk for those on basal human insulin alone vs insulin glargine alone was 1.24 (95% CI 0.90-1.70). Compared with metformin, insulin therapy increased the risk of colorectal (HR 1.69, 95% CI 1.23-2.33) or pancreatic cancer (HR 4.63, 95% CI 2.64-8.10), but did not influence the risk of breast or prostate cancer. Sulfonylureas were associated with a similar pattern of risk as insulin.

CONCLUSIONS/INTERPRETATION

Those on insulin or insulin secretagogues were more likely to develop solid cancers than those on metformin, and combination with metformin abolished most of this excess risk. Metformin use was associated with lower risk of cancer of the colon or pancreas, but did not affect the risk of breast or prostate cancer. Use of insulin analogues was not associated with increased cancer risk as compared with human insulin.

IGF-1 released by corneal epithelial cells induces up-regulation of N-cadherin in corneal fibroblasts

Interactions between epithelial cells and fibroblasts play important roles in tissue homeostasis. With the use of a coculture system in which human corneal fibroblasts and epithelial cells are cultured on opposite sides of a collagen (vitrigel) membrane, we have examined the effects of epithelial cells on expression of the adherens-junction protein N-cadherin in fibroblasts. Reverse transcription-polymerase chain reaction and immunoblot analyses showed that the presence of epithelial cells increased the expression of N-cadherin in fibroblasts at the mRNA and protein levels. This effect of epithelial cells was mimicked by insulin-like growth factor-1 (IGF-1) but not by epidermal growth factor or fibroblast growth factor. Depletion of IGF-1 in epithelial cells by RNA interference abolished the effect of these cells on N-cadherin expression in fibroblasts. The presence of epithelial cells activated the IGF-1 receptor as well as up-regulated expression of the transcriptional regulator ZEB1 in fibroblasts. RNA interference-mediated depletion of IGF-1 in epithelial cells prevented the effect of these cells on ZEB1 expression in fibroblasts. These results suggest that IGF-1 released from corneal epithelial cells up-regulates the expression of N-cadherin in corneal fibroblasts.

Profile of mecasermin for the long-term treatment of growth failure in children and adolescents with severe primary IGF-1 deficiency

Growth hormone insensitivity syndrome (GHI) or insulin-like growth factor-1 (IGF-1) deficiency (IGFD) is characterized by deficit of IGF-1 production due to alteration of response of growth hormone (GH) receptor to GH. This syndrome is due to mutation of GH receptor or IGF-1 gene and patients affected showed no response to GH therapy. The only treatment is recombinant IGF-1 (mecasermin), which has been available since 1986, but approved in the United States by the US Food and Drug Administration only in 2005 and in Europe by the European Medicines Agency in 2007. To date, few studies are available on long-term treatment with mecasermin in IGFD patients and some of them have a very small number of subjects. In this review we discuss briefly clinical features of severe primary IGFD, laboratory findings, and indications for treatment. Results of long-term therapy with rhIGF1 (mecasermin) in patients affected by severe primary IGFD and possible side effects are explained.

Safety, tolerability, and pharmacokinetics of the anti-IGF-1R monoclonal antibody figitumumab in patients with refractory adrenocortical carcinoma

PURPOSE

Insulin-like growth factor 1 receptor signaling through upregulation of the stimulatory ligand IGF-II has been implicated in the pathogenesis of adrenocortical carcinoma. As there is a paucity of effective therapies, this dose expansion cohort of a phase 1 study was undertaken to determine the safety, tolerability, pharmacokinetics, and effects on endocrine markers of figitumumab in patients with adrenocortical carcinoma.

METHODS

Figitumumab was administered on day 1 of each 21-day cycle at the maximal feasible dose (20 mg/kg) to a cohort of patients with metastatic, refractory adrenocortical carcinoma. Serum glucose, insulin, and growth hormone were measured pre-study, at cycle 4 and study end. Pharmacokinetic evaluation was performed during cycles 1 and 4.

RESULTS

Fourteen patients with adrenocortical carcinoma received 50 cycles of figitumumab at the 20 mg/kg. Treatment-related toxicities were generally mild and included hyperglycemia, nausea, fatigue, and anorexia. Single episodes of grade 4 hyperuricemia, proteinuria, and elevated gamma-glutamyltransferase were observed. Pharmacokinetics of figitumumab was comparable to patients with solid tumors other than adrenocortical carcinoma. Treatment with figitumumab increased serum insulin and growth hormone levels. Eight of 14 patients (57%) had stable disease.

CONCLUSIONS

The side effect profile and pharmacokinetics of figitumumab were similar in patients with adrenocortical carcinoma in comparison to patients with other solid tumors. While hyperglycemia was the most common adverse event, no clear patterns predicting severity were observed. The majority of patients receiving protocol therapy with single agent figitumumab experienced stability of disease, warranting further evaluation.

The role of liver-derived insulin-like growth factor-I

IGF-I is expressed in virtually every tissue of the body, but with much higher expression in the liver than in any other tissue. Studies using mice with liver-specific IGF-I knockout have demonstrated that liver-derived IGF-I, constituting a major part of circulating IGF-I, is an important endocrine factor involved in a variety of physiological and pathological processes. Detailed studies comparing the impact of liver-derived IGF-I and local bone-derived IGF-I demonstrate that both sources of IGF-I can stimulate longitudinal bone growth. We propose here that liver-derived circulating IGF-I and local bone-derived IGF-I to some extent have overlapping growth-promoting effects and might have the capacity to replace each other (= redundancy) in the maintenance of normal longitudinal bone growth. Importantly, and in contrast to the regulation of longitudinal bone growth, locally derived IGF-I cannot replace (= lack of redundancy) liver-derived IGF-I for the regulation of a large number of other parameters including GH secretion, cortical bone mass, kidney size, prostate size, peripheral vascular resistance, spatial memory, sodium retention, insulin sensitivity, liver size, sexually dimorphic liver functions, and progression of some tumors. It is clear that a major role of liver-derived IGF-I is to regulate GH secretion and that some, but not all, of the phenotypes in the liver-specific IGF-I knockout mice are indirect, mediated via the elevated GH levels. All of the described multiple endocrine effects of liver-derived IGF-I should be considered in the development of possible novel treatment strategies aimed at increasing or reducing endocrine IGF-I activity.

Short-term effects of the long-acting insulin analog detemir and human insulin on plasma levels of insulin-like growth factor-I and its binding proteins in humans

OBJECTIVE

The objective of the study was to compare responses of plasma levels of IGF-I and IGF binding proteins (IGFBP-1 and IGFBP-3) induced by human regular insulin (HI) and the long-acting insulin analog detemir (IDet) at doses equivalent with respect to the glucose-lowering effect.

EXPERIMENTAL DESIGN

Ten nondiabetic subjects (six males, four females; age, 36 +/- 7 yr; body mass index, 22.9 +/- 2.6 kg/m(2)) were studied on four randomized occasions with iv infusion of IDet (2 mU/kg . min for 4 h, followed by 4 mU/kg . min for 1 h) or HI (1 mU/kg . min for 4 h, followed by 2 mU/kg . min for 1 h) in euglycemia [plasma glucose (PG), 90 mg/dl] or during stepped hypoglycemia (PG, 90, 78, 66, 54, and 42 mg/dl).

RESULTS

PG was maintained at preselected plateaus, without any significant difference between IDet and HI (P > 0.2). Plasma insulin concentrations were on average approximately nine times greater with IDet than HI (749 +/- 52 vs. 83 +/- 19 muU/ml, respectively). Plasma IGF-I concentrations did not change from baseline during insulin infusion in euglycemia (IDet, 147 +/- 16 ng/ml; HI, 155 +/- 15 ng/ml) and hypoglycemia (IDet, 163 +/- 14 ng/ml; HI, 165 +/- 14 ng/ml) with no differences between the two insulins (P > 0.2). A similar pattern was observed for plasma IGFBP-3 levels. Insulin infusion resulted in a suppression of plasma IGFBP-1 concentrations with no differences between IDet (baseline, 16.6 +/- 3.8 ng/ml; endpoint, 2.0 +/- 0.6 ng/ml) and HI (baseline, 16.6 +/- 4.1 ng/ml; endpoint, 2.6 +/- 1.4 ng/ml) (P > 0.2) and study conditions (P > 0.2).

CONCLUSIONS

The greater plasma insulin concentrations obtained with IDet exert effects on plasma levels of IGF-I, IGFBP-1, and IGFBP-3 similar to those of HI. Additional studies are needed to confirm these short-term results in patients with diabetes mellitus on long-term treatment with IDet.

Molecular classification and prognostication of adrenocortical tumors by transcriptome profiling

PURPOSE

Our understanding of adrenocortical carcinoma (ACC) has improved considerably, yet many unanswered questions remain. For instance, can molecular subtypes of ACC be identified? If so, what is their underlying pathogenetic basis and do they possess clinical significance?

EXPERIMENTAL DESIGN

We did a whole genome gene expression study of a large cohort of adrenocortical tissues annotated with clinicopathologic data. Using Affymetrix Human Genome U133 Plus 2.0 oligonucleotide arrays, transcriptional profiles were generated for 10 normal adrenal cortices (NC), 22 adrenocortical adenomas (ACA), and 33 ACCs.

RESULTS

The overall classification of adrenocortical tumors was recapitulated using principal component analysis of the entire data set. The NC and ACA cohorts showed little intragroup variation, whereas the ACC cohort revealed much greater variation in gene expression. A robust list of 2,875 differentially expressed genes in ACC compared with both NC and ACA was generated and used in functional enrichment analysis to find pathways and attributes of biological significance. Cluster analysis of the ACCs revealed two subtypes that reflected tumor proliferation, as measured by mitotic counts and cell cycle genes. Kaplan-Meier analysis of these ACC clusters showed a significant difference in survival (P < 0.020). Multivariate Cox modeling using stage, mitotic rate, and gene expression data as measured by the first principal component for ACC samples showed that gene expression data contains significant independent prognostic information (P < 0.017).

CONCLUSIONS

This study lays the foundation for the molecular classification and prognostication of adrenocortical tumors and also provides a rich source of potential diagnostic and prognostic markers.

Emerging role of insulin-like growth factor receptor inhibitors in oncology: early clinical trial results and future directions

Preclinical evidence that targeting the insulin-like growth factor receptor (IGF-IR) is effective in cancer treatment has been accumulating for almost two decades. Efforts to develop drugs began in the late 1990s, and initial data from clinical trials were reported in 2006. The biological rationale for IGF-IR targeting has potential relevance to many tumor types, and early results have justified expanded programs to evaluate IGF-IR-targeting agents in many areas of clinical need. More than two dozen drug candidates have been developed and clinical trials are underway for at least 12 of these. Early clinical trials reveal an acceptable safety profile together with pharmacodynamic evidence that the receptor can be successfully targeted. It is premature to draw conclusions regarding efficacy, but well-documented instances of single-agent activity were noted during phase I evaluations, and recent evidence from a phase II study suggests that co-administration of an anti-IGF-IR antibody with chemotherapy for non-small-cell lung cancer improves objective response rate and progression-free survival. With more than 70 trials involving a variety of drug candidates underway, the IGF-IR is becoming one of the most intensively investigated molecular targets in oncology. Early results justify the continuation of ongoing research across a broad range of cancer indications.

Association between serum insulin-like growth factor (IGF) I and IGF binding protein-3 and lung function

BACKGROUND

There is strong evidence that IGF-I and IGF binding protein 3 (IGFBP-3), as central mediators of endocrine and finally metabolic or anabolic effects of GH, were associated with increased lung size in acromegaly or a decrease of respiratory muscle pressures in patients with GH deficiency. The aim of the present study was to further clarify the impact of IGF-I and IGFBP-3 levels on lung volumes and respiratory pressures in a general adult population.

MATERIAL AND METHODS

From the Study of Health in Pomerania, 1326 subjects aged 25 to 85 yr participated in standardized pulmonary function testing. IGF-I and IGFBP-3 levels were measured with the Immulite 2500 system. Multivariable linear regression analyses adjusted for age, sex, body mass index, physical activity, and smoking were performed.

RESULTS

In men, positive linear associations between IGF-I and IGF-I/IGFBP-3 ratio with forced expiratory volume in 1 sec (FEV1) as well as with forced vital capacity (FVC) were detected across all ages, whereas in women this positive association was only detectable above 50 yr. Furthermore, the analyses indicated positive linear relations of IGF-I/IGFBP-3 ratio with FEV1 and FVC, respectively. No significant relations between IGF-I or IGFBP-3 and maximal inspiratory pressure was detectable in both sexes.

CONCLUSION

In conclusion, higher IGF-I levels were associated with higher lung volumes in men, whereas in women this association was only detectable in subjects older than 50 yr. Higher IGF-I values were not associated with increased respiratory muscle strength measured as maximal inspiratory pressure.

New target genes for the peroxisome proliferator-activated receptor-γ (PPARγ) antitumour activity: Perspectives from the insulin receptor

The insulin receptor (IR) plays a crucial role in mediating the metabolic and proliferative functions triggered by the peptide hormone insulin. There is considerable evidence that abnormalities in both IR expression and function may account for malignant transformation and tumour progression in some human neoplasias, including breast cancer. PPARγ is a ligand-activated, nuclear hormone receptor implicated in many pleiotropic biological functions related to cell survival and proliferation. In the last decade, PPARγ agonists—besides their known action and clinical use as insulin sensitizers—have proved to display a wide range of antineoplastic effects in cells and tissues expressing PPARγ, leading to intensive preclinical research in oncology. PPARγ and activators affect tumours by different mechanisms, involving cell proliferation and differentiation, apoptosis, antiinflammatory, and antiangiogenic effects. We recently provided evidence that PPARγ and agonists inhibit IR by non canonical, DNA-independent mechanisms affecting IR gene transcription. We conclude that IR may be considered a new PPARγ “target” gene, supporting a potential use of PPARγ agonists as antiproliferative agents in selected neoplastic tissues that overexpress the IR.

Resistance to age-dependent thymic atrophy in long-lived mice that are deficient in pregnancy-associated plasma protein A

Pregnancy-associated plasma protein A (PAPPA) is a metalloproteinase that controls the tissue availability of insulin-like growth factor (IGF). Homozygous deletion of PAPPA in mice leads to lifespan extension. Since immune function is an important determinant of individual fitness, we examined the natural immune ecology of PAPPA(-/-) mice and their wild-type littermates reared under specific pathogen-free condition with aging. Whereas wild-type mice exhibit classic age-dependent thymic atrophy, 18-month-old PAPPA(-/-) mice maintain discrete thymic cortex and medulla densely populated by CD4(+)CD8(+) thymocytes that are capable of differentiating into single-positive CD4 and CD8 T cells. Old PAPPA(-/-) mice have high levels of T cell receptor excision circles, and have bone marrows enriched for subsets of thymus-seeding progenitors. PAPPA(-/-) mice have an overall larger pool of naive T cells, and also exhibit an age-dependent accumulation of CD44(+)CD43(+) memory T cells similar to wild-type mice. However, CD43(+) T cell subsets of old PAPPA(-/-) mice have significantly lower prevalence of 1B11 and S7, glycosylation isoforms known to inhibit T cell activation with normal aging. In bioassays of cell activation, splenic T cells of old PAPPA(-/-) mice have high levels of activation antigens and cytokine production, and also elicit Ig production by autologous B cells at levels equivalent to young wild-type mice. These data suggest an IGF-immune axis of healthy longevity. Controlling the availability of IGF in the thymus by targeted manipulation of PAPPA could be a way to maintain immune homeostasis during postnatal development and aging.

Dual silencing of insulin-like growth factor-I receptor and epidermal growth factor receptor in colorectal cancer cells is associated with decreased proliferation and enhanced apoptosis

Overexpression and activation of tyrosine kinase receptors are common features of colorectal cancer. Using the human colorectal cancer cell lines DLD-1 and Caco-2, we evaluated the role of the insulin-like growth factor-I (IGF-I) receptor (IGF-IR) and epidermal growth factor receptor (EGFR) in cellular functions of these cells. We used the small interfering RNA (siRNA) technology to specifically down-regulate IGF-IR and EGFR expression. Knockdown of IGF-IR and EGFR resulted in inhibition of cell proliferation of DLD-1 and Caco-2 cells. An increased rate of apoptosis was associated with siRNA-mediated silencing of IGF-IR and EGFR as assessed by activation of caspase-3/caspase-7. The combined knockdown of both EGFR and IGF-IR decreased cell proliferation and induced cell apoptosis more effectively than did silencing of either receptor alone. Comparable effects on cell proliferation and apoptosis were observed after single and combinational treatment of cells by the IGF-IR tyrosine kinase inhibitor NVP-AEW541 and/or the EGFR tyrosine kinase inhibitor erlotinib. Combined IGF-IR and EGFR silencing by either siRNAs or tyrosine kinase inhibitors diminished the phosphorylation of downstream signaling pathways AKT and extracellular signal-regulated kinase (ERK)-1/2 more effectively than did the single receptor knockdown. Single IGF-IR knockdown inhibited IGF-I-dependent phosphorylation of AKT but had no effect on IGF-I- or EGF-dependent phosphorylation of ERK1/2, indicating a role of EGFR in ligand-dependent ERK1/2 phosphorylation. The present data show that inhibition of the IGF-IR transduction cascade augments the antipoliferative and proapoptotic effects of EGFR inhibition in colorectal cancer cells. A clinical application of combination therapy targeting both EGFR and IGF-IR could be a promising therapeutic strategy.

Inhibition of IGF-IR tyrosine kinase induces apoptosis and cell cycle arrest in imatinib-resistant chronic myeloid leukaemia cells

Although signalling through the type I insulin-like growth factor receptor (IGF-IR) maintains the survival of haematopoietic cells, a specific role of IGF-IR in haematological neoplasms remains largely unknown. Chronic myeloid leukaemia (CML) is the most common subtype of chronic myeloproliferative diseases. Typically, CML evolves as a chronic phase (CP) disease that progresses into accelerated (AP) and blast phase (BP) stages. In this study, we show that IGF-IR is universally expressed in four CML cell lines. IGF-IR was expressed in only 30% and 25% of CP and AP patients, respectively, but its frequency of expression increased to 73% of BP patients. Increased expression levels of IGF-IR with CML progression was supported by quantitative real-time PCR that demonstrated significantly higher levels of IGF-IR mRNA in BP patients. Inhibition of IGF-IR decreased the viability and proliferation of CML cell lines and abrogated their growth in soft agar. Importantly, inhibition of IGF-IR decreased the viability of cells resistant to imatinib mesylate including BaF3 cells transfected with p210 BCR-ABL mutants, CML cell lines and primary neoplastic cells from patients. The negative effects of inhibition of IGF-IR were attributable to apoptosis and cell cycle arrest due to alterations of downstream target proteins. Our findings suggest that IGF-IR could represent a potential molecular target particularly for advanced stage or imatinib-resistant cases.

A polymorphic variant of the insulin-like growth factor type I receptor gene modifies risk of obesity for esophageal adenocarcinoma

BACKGROUND

To investigate potential biologic mechanisms underlying the association between obesity and risk for esophageal adenocarcinoma (EADC), we studied the frequency of a common polymorphism of the insulin-like growth factor I receptor (IGF-IR) gene in patients with either gastroesophageal reflux disease (GERD), premalignant Barrett esophagus (BE) and or invasive EADC.

METHODS

Using a well characterized series of 431 individuals enrolled in a case-control study, we studied the frequency of the IGF-IR gene polymorphism, G1013A.

RESULTS

On multivariate analysis controlling for age and gender, in comparison to asymptomatic controls, obese individuals with the polymorphic A-variant (G/A, A/A) were found to have significantly increased risk for EADC (OR 4.81; 95%CI 1.09-21.15), whereas obese individuals with the G/G variant were not at statistically significant increased risk (OR 2.69; 95%CI 0.41-17.62). Similarly, compared to asymptomatic controls, only obese individuals with the A-variant (G/A, A/A) were at increased risk for BE (OR 3.11; 95%CI 1.12-8.63), while obese individuals with the G/G variant were not at increased risk for BE (OR 2.91; 95%CI 0.69-12.15).

CONCLUSION

We conclude that the common IGF-IR gene polymorphism G1013A modulates the risk of obesity for EADC, an effect most likely mediated by altered the receptor function by influencing gene transcription or mRNA stability. These findings further implicate the insulin-like growth factor axis in the molecular pathogenesis of EADC, and represent a plausible mechanistic link underlying the association between obesity and malignancy.

IGF-IR tyrosine kinase interacts with NPM-ALK oncogene to induce survival of T-cell ALK+ anaplastic large-cell lymphoma cells

Type I insulin-like growth factor receptor (IGF-IR) tyrosine kinase plays important roles in the pathogenesis of several malignancies. Although it promotes the growth of stimulated hematopoietic cells, a direct role of IGF-IR in malignant lymphoma has not been identified. Anaplastic lymphoma kinase-positive anaplastic large-cell lymphoma (ALK(+) ALCL) is a unique type of T-cell lymphoma. Approximately 85% of ALK(+) ALCL cases harbor the translocation t(2;5)(p23;q35), which generates the chimeric oncogene NPM-ALK. In the present study, we explored a possible role of IGF-IR in ALK(+) ALCL. Our results demonstrate that IGF-IR and IGF-I are widely expressed in ALK(+) ALCL cell lines and primary tumors. Importantly, we identified novel reciprocal functional interactions between IGF-IR and NPM-ALK. Antagonism of IGF-IR decreased the viability, induced apoptosis and cell-cycle arrest, and decreased proliferation and colony formation of ALK(+) ALCL cell lines. These effects could be explained by alterations of cell survival regulatory proteins downstream of IGF-IR signaling. Our findings improve current understanding of the biology of IGF-IR and NPM-ALK and have significant therapeutic implications as they identify IGF-IR signaling as a potential therapeutic target in ALK(+) ALCL and possibly other types of malignant lymphoma.

The insulin-like growth factor-I receptor as an oncogene

The insulin-like growth factor-I receptor (IGF-IR) mediates the biological actions of both IGF-I and IGF-II. The IGF-IR is expressed in most transformed cells, where it displays potent antiapoptotic, cell-survival, and transforming activities. IGF-IR expression is a fundamental prerequisite for the acquisition of a malignant phenotype, as suggested by the finding that IGF-IR-null cells (derived from IGF-IR knock-out embryos) are unable to undergo transformation when exposed to cellular or viral oncogenes. This review article will focus on the underlying molecular mechanisms that are responsible for the normal, physiological control of IGF-IR gene expression, as well as the cellular pathways that underlie its aberrant expression in cancer. Examples from the clinics will be presented, including a description of how the IGF system is involved in breast, prostate, pediatric, and gynecological cancers. Finally, current attempts to target the IGF-IR as a therapeutic approach will be described.