Simian virus 40 large tumor antigen is unable to transform mouse embryonic fibroblasts lacking type 1 insulin-like growth factor receptor

Insulin-like growth factor system on adrenocortical tumorigenesis

The insulin-like growth factor (IGF) signaling pathway has many important roles in normal cell growth and development. Remarkably, all of the components of this system (IGFs, receptors, and binding proteins) are expressed in human fetal adrenals. Beckwith-Wiedemann syndrome, a congenital overgrowth disorder characterized by a high risk of development of childhood tumors, is also distinguished by a high incidence of adrenocortical carcinomas. This disease has been associated with structural abnormalities at the 11p15 locus, which harbors the IGF2 gene as well as the genes coding for insulin, H19, and p57kip2. Notably, rearrangements at the 11p15 locus and overexpression of IGF2 were also described in sporadic adrenocortical tumors. In addition, the IGF2 overexpression was exclusively demonstrated in adults with adrenocortical tumors as a frequent feature of the malignant state. More recent studies demonstrated that the interaction of IGF-2 with IGF receptor type 1 (IGF-1R) plays also a pivotal role in adrenocortical tumorigenesis. IGF1R expression levels were significantly higher in pediatric adrenocortical carcinomas, suggesting that IGF1R expression represents a potential prognostic marker in this group of patients. These findings indicate that the IGF system is an important pathway for autonomous growth of adrenocortical cells and potential inhibitors of this system could be a rational therapeutic target for adrenocortical tumors.

Targeting insulin-like growth factor in breast cancer therapeutics

The insulin-like growth factor (IGF) pathway holds crucial role in cell growth, differentiation and proliferation. Aberrant regulation of the IGF system has been attributed to the pathogenesis of breast cancer and has been shown to contribute to various stages of breast carcinogenesis. Therefore, targeting the IGF-related axis represents a promising strategy, mainly aiming to bypass the resistance of currently employed treatment options in breast cancer patients. Nevertheless, major limitations have aroused despite the early stage of clinical development of various IGF-system modulators. The present review highlights the current status and considers the future perspectives of IGF-system targeting in breast cancer therapeutics.

Targeting the insulin-like growth factor receptor pathway in lung cancer: problems and pitfalls

The insulin-like growth factor (IGF) pathway is a complex pathway involving interactions between membrane-bound receptors, ligands, binding proteins, downstream effectors, and other receptor tyrosine kinase signaling cascades. The IGF pathway has been identified as a potential therapeutic target in non-small cell lung cancer (NSCLC) based on the following provocative factors. Preclinical observations in NSCLC have shown that this pathway is involved in tumor cell proliferation, survival, and invasiveness. In addition, IGF-1R protein expression is found in a significant number of non-small cell tumor specimens. Initial therapeutic efforts involved the development of monoclonal antibodies and tyrosine kinase inhibitors that target IGF-1R, a transmembrane receptor tyrosine kinase. Enthusiasm for targeting this pathway increased when a randomized phase II study showed that combining an anti-IGF-1R monoclonal antibody (figitumumab) with a platinum doublet resulted in a higher response rate and trends for superior progression-free survival and overall survival. Subsequently, a phase III study failed to confirm the promising results observed in the phase II trial. Currently, investigators are studying different monoclonal antibodies and tyrosine kinases targeting IGF-1R. In unselected patients, results presented thus far do not suggest efficacy of this agent. However, retrospective subgroup analyses suggest that circulating IGF-1 levels might identify patients who could benefit from treatment with an IGF-1R monoclonal antibody and may warrant further exploratory studies for predictive molecular markers. The purpose of this paper is to briefly discuss the IGF pathway and its relationship with other signaling pathways in lung cancer and to review the ongoing IGF clinical trials and efforts to identify predictive molecular markers.

The insulin and insulin-like growth factor receptor family in neoplasia: an update

Although several early phase clinical trials raised enthusiasm for the use of insulin-like growth factor I receptor (IGF1R)-specific antibodies for cancer treatment, initial Phase III results in unselected patients have been disappointing. Further clinical studies may benefit from the use of predictive biomarkers to identify probable responders, the use of rational combination therapies and the consideration of alternative targeting strategies, such as ligand-specific antibodies and receptor-specific tyrosine kinase inhibitors. Targeting insulin and IGF signalling also needs to be considered in the broader context of the pathophysiology that relates obesity and diabetes to neoplasia, and the effects of anti-diabetic drugs, including metformin, on cancer risk and prognosis. The insulin and IGFI receptor family is also relevant to the development of PI3K-AKT pathway inhibitors.

Role of the insulin-like growth factor 1 axis and visceral adiposity in oesophageal adenocarcinoma

BACKGROUND

Epidemiological studies have linked obesity with many cancers. The insulin-like growth factor (IGF) 1 axis may be an important mediator in obesity-associated cancer. This study examined the relationship between IGF-1 and its receptor (IGF-1R) in oesophageal adenocarcinoma, a cancer strongly linked to obesity.

METHODS

Patients with oesophageal adenocarcinoma considered suitable for attempted curative treatment were studied. Visceral adiposity was defined by waist circumference or visceral fat area. Free and total IGF-1 in serum were measured by enzyme-linked immunosorbent assay. Quantitative polymerase chain resection was used to determine mRNA expression of IGF-1 and IGF-1R in resected tumour samples. IGF-1R expression in tissue microarrays (TMAs) was quantified by immunohistochemistry.

RESULTS

A total of 220 patients were studied. Total and free IGF-1 levels were significantly increased in the serum of viscerally obese patients. Gene expression analysis revealed a significant association between obesity status and both IGF-1R (P = 0·021) and IGF-1 (P = 0·031) in tumours. TMA analysis demonstrated that IGF-1R expression in resected tumours was significantly higher in viscerally obese patients than in those of normal weight (P = 0·023). Disease-specific survival was longer in patients with negative IGF-1R expression than in those with IGF-1R-positive tumours (median 60·0 versus 23·4 months; P = 0·027).

CONCLUSION

This study highlighted the association of the IGF axis with visceral obesity, and a potential impact on the biology of oesophageal adenocarcinoma through its receptor. Targeting the IGF axis may have a rationale in future studies.

Epithelial-mesenchymal transition predicts sensitivity to the dual IGF-1R/IR inhibitor OSI-906 in hepatocellular carcinoma cell lines

A growing body of data indicates that inhibiting the type 1 insulin-like growth factor receptor (IGF-1R) might be an effective treatment strategy for hepatocellular carcinoma (HCC). OSI-906 is a dual IGF-1R/IR kinase inhibitor currently in phase II clinical development for HCC. However, biomarkers are lacking to help identify patients with HCC who are more likely to benefit from OSI-906 treatment. We sought to determine the effect of OSI-906 on proliferation against a panel of 21 HCC cell lines and to investigate molecular determinants of responsiveness to OSI-906. We identified a subset of HCC cell lines that was sensitive to OSI-906, and sensitivity is associated with elevated phosphorylation levels of IGF-1R and IR and greater inhibition of AKT signaling. Dual targeting of both receptors seems to be important for maximal inhibition as treatment with a selective IGF-1R-neutralizing antibody was associated with increased IR signaling, whereas OSI-906 fully inhibited both phosphorylated IR and IGF-1R and resulted in greater inhibition of the IRS/AKT pathway. Epithelial-mesenchymal transition (EMT) seems to predict HCC cell sensitivity to OSI-906, as the epithelial phenotype is strongly associated with expression of IGF-2 and IR, activation of IGF-1R and IR, and sensitivity to OSI-906, alone or in combination with erlotinib. Induction of EMT upon treatment with TGFβ reduced sensitivity to OSI-906. Collectively, these data support the concept for dual IGF-1R/IR targeting in HCC, where EMT status and expressions of IGF-2 and IR may be used to identify those patients who are most likely to benefit from treatment with an IGF-1R/IR dual inhibitor.

Insulin-like growth factor-I receptor (IGF-IR) translocates to nucleus and autoregulates IGF-IR gene expression in breast cancer cells

The insulin-like growth factor (IGF) system plays an important role in mammary gland biology as well as in the etiology of breast cancer. The IGF-I receptor (IGF-IR), which mediates the biological actions of IGF-I and IGF-II, has emerged in recent years as a promising therapeutic target. The IGF and estrogen signaling pathways act in a synergistic manner in breast epithelial cells. The present study was aimed at investigating 1) the putative translocation of IGF-IR and the related insulin receptor (IR) to the nucleus in breast cancer cells, 2) the impact of IGF-IR and IR levels on IGF-IR biosynthesis in estrogen receptor (ER)-positive and ER-depleted breast cancer cells, and 3) the potential transcription factor role of IGF-IR in the specific context of IGF-IR gene regulation. We describe here a novel mechanism of autoregulation of IGF-IR gene expression by cellular IGF-IR, which is seemingly dependent on ER status. Regulation of the IGF-IR gene by IGF-IR protein is mediated at the level of transcription, as demonstrated by 1) binding assays (DNA affinity chromatography and ChIP) showing specific IGF-IR binding to IGF-IR promoter DNA and 2) transient transfection assays showing transactivation of the IGF-IR promoter by exogenous IGF-IR. The IR is also capable of translocating to the nucleus and binding the IGF-IR promoter in ER-depleted, but not in ER-positive, cells. However, transcription factors IGF-IR and IR display diametrically opposite activities in the context of IGF-IR gene regulation. Thus, whereas IGF-IR stimulated IGF-IR gene expression, IR inhibited IGF-IR promoter activity. In summary, we have identified a novel mechanism of IGF-IR gene autoregulation in breast cancer cells. The clinical implications of these findings and, in particular, the impact of IGF-IR/IR nuclear localization on targeted therapy require further investigation.

POTENTIAL MECHANISMS OF CANCER PREVENTION BY WEIGHT CONTROL

Weight control via dietary caloric restriction and/or physical activity has been demonstrated in animal models for cancer prevention. However, the underlying mechanisms are not fully understood. Body weight loss due to negative energy balance significantly reduces some metabolic growth factors and endocrinal hormones such as IGF-1, leptin, and adiponectin, but enhances glucocorticoids, that may be associated with anti-cancer mechanisms. In this review, we summarized the recent studies related to weight control and growth factors. The potential molecular targets focused on those growth factors- and hormones-dependent cellular signaling pathways are further discussed. It appears that multiple factors and multiple signaling cascades, especially for Ras-MAPK-proliferation and PI3K-Akt-anti-apoptosis, could be involved in response to weight change by dietary calorie restriction and/or exercise training. Considering prevalence of obesity or overweight that becomes apparent over the world, understanding the underlying mechanisms among weight control, endocrine change and cancer risk is critically important. Future studies using "-omics" technologies will be warrant for a broader and deeper mechanistic information regarding cancer prevention by weight control.

Generation of a conditionally transformed murine embryonic fibroblast cell line using doxycycline-dependent IGF-1R overexpression

The insulin-like growth factor I receptor (IGF1-R) system has long been implicated in cancer and is a promising target for tumor therapy. Besides in vitro screening assays, the discovery of specific inhibitors against IGF-1R requires relevant cellular models, ideally applicable to both in vitro and in vivo studies. With this aim in mind, the authors generated an inducible cell line using the tetracycline-responsive gene expression system to mimic the effects of therapeutic inhibition of the IGF-1R both in vitro and on established tumors in vivo. Inducible overexpression of IGF-1R in murine embryonic fibroblasts was achieved and resulted in the transformation of the cells as verified by their ability to grow in soft agar and in nude mice. Continuous repression of exogenous IGF-1R expression completely prevented outgrowth of the tumors. Furthermore, induced repression of IGF-1R expression in established tumors resulted in regression of the tumors. Interestingly, however, IGF-1R-independent relapse of tumor growth was observed upon prolonged IGF-1R repression. The IGF-1R cell line generated using this approach was successfully employed to test reference small-molecule inhibitors in vitro and an IGF-1R-specific inhibitory antibody, EM164, in vivo. Besides efficacy as a read-out, phospho-AKT could be identified as a pharmacodynamic biomarker, establishing this cell line as a valuable tool for the preclinical development of IGF-1R inhibitors.

Expression of the IGF axis is decreased in local prostate cancer but enhanced after benign prostate epithelial differentiation and TGF-β treatment

The insulin-like growth factor (IGF) axis is a molecular pathway intensively investigated in cancer research. Clinical trials targeting the IGF1 receptor (IGF1R) in different tumors, including prostate cancer, are under way. Although studies on the IGF axis in prostate cancer have already entered into clinical trials, the expression and functional role of the IGF axis in benign prostate and in prostate cancer needs to be better defined. We determined mRNA expression levels of the IGF axis in microdissected tissue specimens of local prostate cancer using quantitative PCR. All members of the IGF axis, including IGF1, IGF2, IGF binding proteins 1 through 6, and insulin receptor, were measured in both the stromal and epithelial compartments of the prostate. IGF1, IGF2, IGF1R, and insulin receptor were down-regulated in local prostate cancer tissue compared with matched benign tissue, suggesting that the IGF axis is not induced during prostate cancer development. Using a new prostate epithelial differentiation model, we demonstrate that the expression of the IGF axis is enhanced during normal prostate epithelial differentiation and regulated by tumor growth factor (TGF)-β. Our data reveal a functional role of the IGF axis in prostate differentiation, underscoring the importance of the IGF axis in normal development and emphasizing the importance of accurate target validation before moving to advanced clinical trials.

Critical appraisal of the recent data published on the link between insulin and cancer

Recent publications indicate a possible association between newer analogue insulin Glargine and cancer. However all these data were observational in nature and subject to lot of methodological errors. It is practically impossible to derive at a cause and effect relationship based on these observational studies. There are several confounding factors like hyperinsulinemia, obesity and smoking, which independently can be associated with cancer risk. This review looks into the recently published observational studies from the methodological point of view and whether such a negative association can indeed be drawn as a conclusion. Several methodological defects were identified in the process of scrutiny and we concluded it is not possible to conclude that there is an association between Glargine use and cancer. However long-term prospective data is required to come to definite conclusion.

Plasma and tissue insulin-like growth factor-I receptor (IGF-IR) as a prognostic marker for prostate cancer and anti-IGF-IR agents as novel therapeutic strategy for refractory cases: a review

Cancer database analysis indicates that prostate cancer is one of the most seen cancers in men meanwhile composing the leading cause of morbidity and mortality among developed countries. Current available therapies are surgery, radiotherapy and androgene ablation for prostate carcinoma. The response rate is as high nearly 90% however, most of these recur or become refractory and androgene independent (AI). Therefore recent studies intensified on molecular factors playing role on development of prostate carcinoma and novel treatment strategies targetting these factors and their receptors. Insulin-like growth factor-I (IGF-I) and its primary receptor insulin-like growth factor receptor-I (IGF-IR) are among these factors. Biologic functions and role in malign progression are primarily achieved via IGF-IR which is a type 2 tyrosine kinase receptor. IGF-IR plays an important role in mitogenesis, angiogenesis, transformation, apoptosis and cell motility. It also generates intensive proliferative signals leading to carcinogenesis in prostate tissue. So IGF-IR and its associated signalling system have provoked considerable interest over recent years as a novel therapeutic target in cancer. In this paper it is aimed to sum up the lately published literature searching the relation of IGF-IR and prostate cancer in terms of incidence, pathologic features, and prognosis. This is followed by a discussion of the different possible targets within the IGF-1R system, and drugs developed to interact at each target. A systems-based approach is then used to review the in vitro and in vivo data in the published literature of the following compounds targeting IGF-1R components using specific examples: growth hormone releasing hormone antagonists (e.g. JV-1-38), growth hormone receptor antagonists (e.g. pegvisomant), IGF-1R antibodies (e.g. CP-751,871, AVE1642/EM164, IMC-A12, SCH-717454, BIIB022, AMG 479, MK-0646/h7C10), and IGF-1R tyrosine kinase inhibitors (e.g. BMS-536942, BMS-554417, NVP-AEW541, NVP-ADW742, AG1024, potent quinolinyl-derived imidazo (1,5-a)pyrazine PQIP, picropodophyllin PPP, nordihydroguaiaretic acid Insm-18/NDGA). And the other end point is to yield an overview on the recent progress about usage of this receptor as a novel anticancer agent of targeted therapies in treatment of prostate carcinoma.

Insulin therapy in diabetes and cancer risk: current understanding and implications for future study: proceedings from a meeting of a European Insulin Safety Consensus Panel, convened and sponsored by Novo Nordisk, held Tuesday October 5, 2010 at The Radisson Edwardian Heathrow Hotel, Hayes, Middlesex, UK

INTRODUCTION

Interest in the possibility of certain insulin treatments having the potential to modify cancer development and prognosis was reawakened in 2009, following publication of several epidemiological studies addressing this issue. This interest extends to how diabetes itself and cancer might be linked, and makes desirable an exchange of expert views and knowledge to enhance understanding in this subject among those treating diabetes and cancer, or those developing diabetes therapies.

METHODS

A European meeting was convened with participants invited based on known relevant interests in endocrinology, oncology, epidemiology, and insulin analog design and investigation. Experts in these fields were invited to present on relevant topics, with open discussions held after each presentation.

RESULTS

Concern over the potential mitogenic properties of certain insulin analogs has arisen from some (but not all) epidemiological studies, although confounding factors render interpretation controversial. Future epidemiological studies are likely to strengthen confidence in drawing conclusions. Meanwhile, pharmacological studies, and a consideration of cancer pathophysiology, implicate increased insulin-like growth factor-1 receptor affinity, and/or deranged insulin receptor interaction/signaling properties as possible a priori causes for concern with some insulin analogs. Again, interpretation of the body of pharmacological evidence is confounded by the array of test systems and methodologies used, and by studies frequently succumbing to methodological pitfalls. Reassuringly, most available insulin analogs do not differ in their receptor interaction response profile to human insulin, and for those that do there are reasons to question any potential clinical relevance. Nevertheless, it is desirable that new experimental models are devised that can better determine the likely clinical consequences of any variance in receptor response profile versus human insulin.

CONCLUSION

More data are required to increase our understanding of this issue. To facilitate and disseminate such understanding, close cooperation and communication between diabetologists, epidemiologists, oncologists, and insulin engineers will be essential.

The efficacy of IGF-I receptor monoclonal antibody against human gastrointestinal carcinomas is independent of k-ras mutation status

PURPOSE

Insulin-like growth factor (IGF)-I receptor (IGF-IR) signaling is required for carcinogenicity and proliferation of gastrointestinal cancers. We have previously shown successful targeting therapy for colorectal, pancreatic, gastric, and esophageal carcinomas using recombinant adenoviruses expressing dominant negative IGF-IR. Mutation in k-ras is one of key factors in gastrointestinal cancers. In this study, we sought to evaluate the effect of a new monoclonal antibody for IGF-IR, figitumumab (CP-751,871), on the progression of human gastrointestinal carcinomas with/without k-ras mutation.

EXPERIMENTAL DESIGN

We assessed the effect of figitumumab on signal transduction, proliferation, and survival in six gastrointestinal cancer cell lines with/without k-ras mutation, including colorectal and pancreatic adenocarcinoma, esophageal squamous cell carcinoma, and hepatoma. Combination effects of figitumumab and chemotherapy were also studied. Then figitumumab was evaluated in the treatment of xenografts in nude mice.

RESULTS

Figitumumab blocked autophosphorylation of IGF-IR and its downstream signals. The antibody suppressed proliferation and tumorigenicity in all cell lines. Figitumumab inhibited survival by itself and up-regulated chemotherapy (5-FU and gemcitabine) induced apoptosis. Moreover, the combination of this agent and chemotherapy was effective against tumors in mice. The effect of figitumumab was not influenced by the mutation status of k-ras. Figitumumab reduced expression of IGF-IR but not insulin receptor in these xenografted tumors. The drug did not affect murine body weight or blood concentrations of glucose, insulin, IGF binding protein 3, and growth hormone.

CONCLUSIONS

IGF-IR might be a good molecular therapeutic target and figitumumab may thus have therapeutic value in human gastrointestinal malignancies even in the presence of k-ras mutations.

Insulin-like growth factor-I receptor blockade reduces tumor angiogenesis and enhances the effects of bevacizumab for a human gastric cancer cell line, MKN45

BACKGROUND

Insulin-like growth factor (IGF)-I receptor (IGF-IR) signaling is required for tumorigenicity and tumor progression of gastrointestinal cancers. The authors previously reported the success of therapy for gastrointestinal cancers using adenoviruses that expressed dominant-negative IGF-IR (IGF-IR/dn). In addition, it has been demonstrated that IGF-IR signaling affects vascular endothelial growth factor (VEGF) expression in some other types of tumors. The objective of the current study was to evaluate this interaction by studying the roles of IGF-IR in tumor angiogenesis and lymphangiogenesis and their implications for targeted therapy in gastric cancer.

METHODS

The impact of IGF signals on the expression of VEGF-A and VEGF-C in a human gastric cancer cell, MKN45, and vascular formation were assessed. The effects of IGF-IR/dn with or without bevacizumab on angiogenesis, lymphangiogenesis, and tumor suppression in mouse xenografts were assessed.

RESULTS

IGFs induced the expression of VEGF ligands and up-regulated in vitro vascular vessel formation. IGF-IR/dn reduced VEGF expression, reduced the activation of both protein kinase B (Akt) and mitogen-activated protein kinase (MAPK), and reduced vascular formation, indicating that IGF-IR/dn inhibited tumor growth in mice by inhibiting both angiogenesis and lymphangiogenesis. However, IGF-IR/dn did not affect either blood sugar or body weight in these mice. The combination of IGF-IR/dn and bevacizumab was highly effective against these xenograft tumors, and only this combination resulted in the complete regression of 43% of tumors, reduced the expression of VEGF, and induced apoptosis.

CONCLUSIONS

The current results indicated that IGF-IR is involved in angiogenesis and lymphangiogenesis through the modulation of VEGF ligand expression in the gastric cancer cell line MKN45. Targeting IGF-IR in combination with agents that block the VEGF pathway may have therapeutic utility for gastric cancer therapy.

Molecular targeted therapy in advanced renal cell carcinoma: A review of its recent past and a glimpse into the near future

Renal cell carcinoma (RCC) is the most lethal of all urologic malignancies. Recent translational research in RCC has led to the discovery of a new class of therapeutics that specifically target important signaling molecules critical in the pathogenesis of the disease. It is now clear that these new molecular targeted agents have revolutionized the management of patients with metastatic RCC. However, the exact molecular mechanism accounting for their clinical effect is largely unknown and a significant proportion of patients with metastatic RCC do not respond to these therapeutics. This review presents the relevant background leading to the development of molecular targeted therapy for patients with advanced RCC and summarizes current management issues in particular relating to the emerging problem of treatment resistance and the need for clinical and laboratory biomarkers to predict treatment outcomes in these patients. In addition, this paper will also address surgical issues in the era of molecular targeted therapy including the role of cytoreductive surgery and surgical safety issues post-molecular therapy. Lastly, this review will also address the need to explore new molecular treatment targets in RCC and briefly present our work on one of the promising molecular targets - the type 1 insulin-like growth factor receptor (IGF1R), which may in the near future lead to the development of anti-IGF1R therapy for patients with advanced RCC.

Targeting insulin-like growth factor axis in hepatocellular carcinoma

The insulin-like growth factor (IGF) axis contains ligands, receptors, substrates, and ligand binding proteins. The essential role of IGF axis in hepatocellular carcinoma (HCC) has been illustrated in HCC cell lines and in animal xenograft models. Preclinical evidence provides ample indication that all four components of IGF axis are crucial in the carcinogenic and metastatic potential of HCC. Several strategies targeting this system including monoclonal antibodies against the IGF 1 receptor (IGF-1R) and small molecule inhibitors of the tyrosine kinase function of IGF-1R are under active investigation. This review describes the most up-to-date understanding of this complex axis in HCC, and provides relevant information on clinical trials targeting the IGF axis in HCC with a focus on anti-IGF-1R approach. IGF axis is increasingly recognized as one of the most relevant pathways in HCC and agents targeting this axis can potentially play an important role in the treatment of HCC.

Targeting insulin-like growth factor axis in hepatocellular carcinoma

The insulin-like growth factor (IGF) axis contains ligands, receptors, substrates, and ligand binding proteins. The essential role of IGF axis in hepatocellular carcinoma (HCC) has been illustrated in HCC cell lines and in animal xenograft models. Preclinical evidence provides ample indication that all four components of IGF axis are crucial in the carcinogenic and metastatic potential of HCC. Several strategies targeting this system including monoclonal antibodies against the IGF 1 receptor (IGF-1R) and small molecule inhibitors of the tyrosine kinase function of IGF-1R are under active investigation. This review describes the most up-to-date understanding of this complex axis in HCC, and provides relevant information on clinical trials targeting the IGF axis in HCC with a focus on anti-IGF-1R approach. IGF axis is increasingly recognized as one of the most relevant pathways in HCC and agents targeting this axis can potentially play an important role in the treatment of HCC.

Visceral adiposity, insulin resistance and cancer risk

BACKGROUND

There is a well established link between obesity and cancer. Emerging research is characterising this relationship further and delineating the specific role of excess visceral adiposity, as opposed to simple obesity, in promoting tumorigenesis. This review summarises the evidence from an epidemiological and pathophysiological perspective.

METHODS

Relevant medical literature was identified from searches of PubMed and references cited in appropriate articles identified. Selection of articles was based on peer review, journal and relevance.

RESULTS

Numerous epidemiological studies consistently identify increased risk of developing carcinoma in the obese. Adipose tissue, particularly viscerally located fat, is metabolically active and exerts systemic endocrine effects. Putative pathophysiological mechanisms linking obesity and carcinogenesis include the paracrine effects of adipose tissue and systemic alterations associated with obesity. Systemic changes in the obese state include chronic inflammation and alterations in adipokines and sex steroids. Insulin and the insulin-like growth factor axis influence tumorigenesis and also have a complex relationship with adiposity. There is evidence to suggest that insulin and the IGF axis play an important role in mediating obesity associated malignancy.

CONCLUSIONS

There is much evidence to support a role for obesity in cancer progression, however further research is warranted to determine the specific effect of excess visceral adipose tissue on tumorigenesis. Investigation of the potential mechanisms underpinning the association, including the role of insulin and the IGF axis, will improve understanding of the obesity and cancer link and may uncover targets for intervention.

Small molecule inhibitors of the IGF-1R/IR axis for the treatment of cancer

INTRODUCTION

The IGF-1 receptor (IGF-1R) is a receptor tyrosine kinase and is well established as a key regulator of tumor cell growth and survival. There is also a growing body of data to support a role for the structurally and functionally related insulin receptor (IR) in human cancer. Bidirectional crosstalk between IGF-1R and IR is observed, where specific inhibition of either receptor confers a compensatory increase in the activity for the reciprocal receptor, therefore dual inhibition of both IGF-1R and IR may be important for optimal efficacy. The importance of IGF-1R and IR as targets in cancer is further underscored by their contribution to resistance against both cytotoxic and molecularly targeted anti-cancer therapeutics. Currently, both IGF-1R-neutralizing antibodies and small-molecule tyrosine kinase inhibitors of IGF-1R/IR are in clinical development.

AREAS COVERED

The importance of IGF-1R and IR as cancer targets and how IGF-1R/IR inhibitors may sensitize tumor cells to the anti-proliferative and pro-apoptotic effects of other anti-tumor agents. The potential advantages of small molecule IGF-1R/IR inhibitors compared with IGF-1R-specific neutralizing antibodies, and the characteristics of small-molecule IGF-1R inhibitors that have entered clinical development.

EXPERT OPINION

Because of compensatory crosstalk between IGF-1R and IR, dual IGF-1R and IR tyrosine kinase inhibitors may have superior anti-tumor activity compared to anti-IGF-1R specific antibodies. The clinical success for IGF-1R/IR inhibitors may ultimately be dependent upon our ability to correctly administer these agents to the right niche patient subpopulation using single agent therapy, when appropriate, or using the right combination therapy.

Expression and effects of inhibition of type I insulin-like growth factor receptor tyrosine kinase in mantle cell lymphoma

BACKGROUND

Type I insulin-like growth factor receptor (IGF-IR) tyrosine kinase induces significant oncogenic effects. Strategies to block IGF-IR signaling are being tested in clinical trials that include patients with aggressive solid malignancies. Mantle cell lymphoma is a B-cell neoplasm with poor prognosis and a tendency to develop resistance. The expression and potential significance of IGF-IR in mantle cell lymphoma are not known.

DESIGN AND METHODS

We used reverse transcriptase polymerase chain reaction, quantitative real-time polymerase chain reaction, immunoprecipitation, western blotting, flow cytometry, and immunohistochemistry to analyze the expression of IGF-IR mRNA, and IGF-IR and pIGF-IR proteins in mantle cell lymphoma cell lines and patients' specimens. Selective and specific blockade of IGF-IR was achieved using picropodophyllin and short-interfering RNA, respectively. Cell viability, apoptosis, cell cycle, cellular morphology, cell proliferation, and target proteins were then analyzed.

RESULTS

We detected the expression of IGF-IR and pIGF-IR in mantle cell lymphoma cell lines. Notably, IGF-IR molecules/cell were markedly increased in mantle cell lymphoma cell lines compared with human B-lymphocytes. IGF-IR and pIGF-IR were also detected in 78% and 74%, respectively, of 23 primary mantle cell lymphoma specimens. Treatment of serum-deprived mantle cell lymphoma cell lines with IGF-I salvaged these cells from apoptosis. Selective inhibition of IGF-IR by picropodophyllin decreased the viability and proliferation of mantle cell lymphoma cell lines, and induced apoptosis and cell cycle arrest. Selective inhibition of IGF-IR was associated with caspase-3, caspase-8, caspase-9, and PARP cleavage, cytochrome c release, up-regulation of cyclin B1, and down-regulation of cyclin D1, pCdc2, pIRS-1, pAkt, and pJnk. Similar results were obtained by using IGF-IR short-interfering RNA. In addition, picropodophyllin decreased the viability and proliferation of primary mantle cell lymphoma cells that expressed IGF-IR.

CONCLUSIONS

IGF-IR is up-regulated and frequently activated in mantle cell lymphoma. Our data suggest that IGF-IR could be a molecular target for the treatment of mantle cell lymphoma.

Growth hormone receptor deficiency is associated with a major reduction in pro-aging signaling, cancer, and diabetes in humans

Mutations in growth signaling pathways extend life span, as well as protect against age-dependent DNA damage in yeast and decrease insulin resistance and cancer in mice. To test their effect in humans, we monitored for 22 years Ecuadorian individuals who carry mutations in the growth hormone receptor (GHR) gene that lead to severe GHR and IGF-1 (insulin-like growth factor-1) deficiencies. We combined this information with surveys to identify the cause and age of death for individuals in this community who died before this period. The individuals with GHR deficiency exhibited only one nonlethal malignancy and no cases of diabetes, in contrast to a prevalence of 17% for cancer and 5% for diabetes in control subjects. A possible explanation for the very low incidence of cancer was suggested by in vitro studies: Serum from subjects with GHR deficiency reduced DNA breaks but increased apoptosis in human mammary epithelial cells treated with hydrogen peroxide. Serum from GHR-deficient subjects also caused reduced expression of RAS, PKA (protein kinase A), and TOR (target of rapamycin) and up-regulation of SOD2 (superoxide dismutase 2) in treated cells, changes that promote cellular protection and life-span extension in model organisms. We also observed reduced insulin concentrations (1.4 μU/ml versus 4.4 μU/ml in unaffected relatives) and a very low HOMA-IR (homeostatic model assessment-insulin resistance) index (0.34 versus 0.96 in unaffected relatives) in individuals with GHR deficiency, indicating higher insulin sensitivity, which could explain the absence of diabetes in these subjects. These results provide evidence for a role of evolutionarily conserved pathways in the control of aging and disease burden in humans.

Dual IGF-I/II-neutralizing antibody MEDI-573 potently inhibits IGF signaling and tumor growth

Insulin-like growth factors (IGF), IGF-I and IGF-II, are small polypeptides involved in regulating cell proliferation, survival, differentiation, and transformation. IGF activities are mediated through binding and activation of IGF-1R or insulin receptor isoform A (IR-A). The role of the IGF-1R pathway in promoting tumor growth and survival is well documented. Overexpression of IGF-II and IR-A is reported in multiple types of cancer and is proposed as a potential mechanism for cancer cells to develop resistance to IGF-1R-targeting therapy. MEDI-573 is a fully human antibody that neutralizes both IGF-I and IGF-II and inhibits IGF signaling through both the IGF-1R and IR-A pathways. Here, we show that MEDI-573 blocks the binding of IGF-I and IGF-II to IGF-1R or IR-A, leading to the inhibition of IGF-induced signaling pathways and cell proliferation. MEDI-573 significantly inhibited the in vivo growth of IGF-I- or IGF-II-driven tumors. Pharmacodynamic analysis demonstrated inhibition of IGF-1R phosphorylation in tumors in mice dosed with MEDI-573, indicating that the antitumor activity is mediated via inhibition of IGF-1R signaling pathways. Finally, MEDI-573 significantly decreased (18)F-fluorodeoxyglucose ((18)F-FDG) uptake in IGF-driven tumor models, highlighting the potential utility of (18)F-FDG-PET as a noninvasive pharmacodynamic readout for evaluating the use of MEDI-573 in the clinic. Taken together, these results demonstrate that the inhibition of IGF-I and IGF-II ligands by MEDI-573 results in potent antitumor activity and offers an effective approach to selectively target both the IGF-1R and IR-A signaling pathways.

Growth hormone, the insulin-like growth factor axis, insulin and cancer risk

Growth hormone (GH), insulin-like growth factor (IGF)-I and insulin have potent growth-promoting and anabolic actions. Their potential involvement in tumor promotion and progression has been of concern for several decades. The evidence that GH, IGF-I and insulin can promote and contribute to cancer progression comes from various sources, including transgenic and knockout mouse models and animal and human cell lines derived from cancers. Assessments of the GH-IGF axis in healthy individuals followed up to assess cancer incidence provide direct evidence of this risk; raised IGF-I levels in blood are associated with a slightly increased risk of some cancers. Studies of human diseases characterized by excess growth factor secretion or treated with growth factors have produced reassuring data, with no notable increases in de novo cancers in children treated with GH. Although follow-up for the vast majority of these children does not yet extend beyond young adulthood, a slight increase in cancers in those with long-standing excess GH secretion (as seen in patients with acromegaly) and no overall increase in cancer with insulin treatment, have been observed. Nevertheless, long-term surveillance for cancer incidence in all populations exposed to increased levels of GH is vitally important.

Combination mTOR and IGF-1R inhibition: phase I trial of everolimus and figitumumab in patients with advanced sarcomas and other solid tumors

PURPOSE

Preclinical models demonstrate synergistic antitumor activity with combination blockade of mTOR and IGF-1R signaling. We aimed to determine the safety, tolerability, and recommended phase II dose (RP2D) of the combination of figitumumab, a fully human IgG(2) anti-insulin-like growth factor-1 receptor (IGF-1R) monoclonal antibody (Pfizer) and the mTOR inhibitor, everolimus (Novartis). Pharmacokinetics and preliminary antitumor effects of the combination were evaluated.

EXPERIMENTAL DESIGN

Phase I trial in patients with advanced sarcomas and other solid tumors. Initial cohort combined full phase 2 dose figitumumab (20 mg/kg IV every 21 days) with full dose everolimus (10 mg orally once daily). Intercohort dose de-escalation was planned for unacceptable toxicities. Dose modifications were allowed beyond cycle 1.

RESULTS

No DLTs were observed in the initial cohort during cycle one, therefore full dose figitumumab and everolimus was declared the RP2D. In total, 21 patients were enrolled on study. Most toxicities were grade 1 or 2, and were similar to reported toxicities of the single agents. Mucositis was the most frequently observed grade 3 toxicity. Median time on study was 104 days (range 17-300). Of 18 patients evaluable for response, best response was partial response in 1 patient with malignant solitary fibrous tumor and, stable disease in 15 patients. There were no apparent pharmacokinetic interactions between everolimus and figitumumab.

CONCLUSIONS

Combination figitumumab plus everolimus at full doses appears safe and well tolerated with no unexpected toxicities. Dose reductions in everolimus may be required after prolonged drug administration. This regimen exhibits interesting antitumor activity warranting further investigation.

A candidate targeting molecule of insulin-like growth factor-I receptor for gastrointestinal cancers

Advances in molecular research in cancer have brought new therapeutic strategies into clinical usage. One new group of targets is tyrosine kinase receptors, which can be treated by several strategies, including small molecule tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs). Aberrant activation of growth factors/receptors and their signal pathways are required for malignant transformation and progression in gastrointestinal (GI) carcinomas. The concept of targeting specific carcinogenic receptors has been validated by successful clinical application of many new drugs. Type I insulin-like growth factor (IGF) receptor (IGF-IR) signaling potently stimulates tumor progression and cellular differentiation, and is a promising new molecular target in human malignancies. In this review, we focus on this promising therapeutic target, IGF-IR. The IGF/IGF-IR axis is an important modifier of tumor cell proliferation, survival, growth, and treatment sensitivity in many malignant diseases, including human GI cancers. Preclinical studies demonstrated that downregulation of IGF-IR signals reversed the neoplastic phenotype and sensitized cells to anticancer treatments. These results were mainly obtained through our strategy of adenoviruses expressing dominant negative IGF-IR (IGF-IR/dn) against gastrointestinal cancers, including esophagus, stomach, colon, and pancreas. We also summarize a variety of strategies to interrupt the IGFs/IGF-IR axis and their preclinical experiences. Several mAbs and TKIs targeting IGF-IR have entered clinical trials, and early results have suggested that these agents have generally acceptable safety profiles as single agents. We summarize the advantages and disadvantages of each strategy and discuss the merits/demerits of dual targeting of IGF-IR and other growth factor receptors, including Her2 and the insulin receptor, as well as other alternatives and possible drug combinations. Thus, IGF-IR might be a candidate for a molecular therapeutic target in human GI carcinomas.

Discovery of an Orally Efficacious Imidazo[5,1-f][1,2,4]triazine Dual Inhibitor of IGF-1R and IR

This report describes the investigation of a series of 5,7-disubstituted imidazo[5,1-f][1,2,4]triazine inhibitors of insulin-like growth factor-1 receptor (IGF-1R) and insulin receptor (IR). Structure-activity relationship exploration and optimization leading to the identification, characterization, and pharmacological activity of compound 9b, a potent, selective, well-tolerated, and orally bioavailable dual inhibitor of IGF-1R and IR with in vivo efficacy in tumor xenograft models, is discussed.

Strong expression of IGF1R in pediatric gastrointestinal stromal tumors without IGF1R genomic amplification

Wildtype (WT) gastrointestinal stromal tumors (GISTs), lacking mutations in KIT or PDGFRA, represent 85% of GISTs in pediatric patients. Treatment options for pediatric WT GIST are limited. Recently, expression profiling of a limited number of pediatric and adult WT GISTs and more in depth study of a single pediatric WT GIST implicated the insulin-like growth factor 1 receptor (IGF1R) as a potential therapeutic target in pediatric WT GIST. We performed immunoblotting, SNP and FISH studies to determine the extent of expression, biochemical activation and genomic amplification of IGF1R in a larger number of pediatric WT GISTs. Pediatric WT GISTs expressed IGF1R strongly, whereas typical adult KIT mutant GISTs did not. IGF1R gene amplification was not detected in pediatric WT GISTs, and some KIT-mutant GISTs had IGF1R gene deletion due to monosomy 15. Despite the absence of apparent genomic activation mechanisms accounting for overexpression, clinical study of IGF1R-directed therapies in pediatric WT GIST is warranted.

Insulin-like growth factor receptor type I as a target for cancer therapy

In recent years, improvements in the understanding of oncogenesis has permitted the identification of new molecular targets for cancer therapy. Among all the different approaches, inhibition of tyrosine kinase receptor activity using small molecules or biomolecules for controlling cancer growth has been successful and has brought new therapeutic opportunities to the medical community. After more than 20 years of extensive work, insulin-like growth factor receptor I (IGF-IR) is becoming an attractive target for drug development. Owing to its close homology to insulin receptor, IGF-IR is of interest for antibody design while its specificity allows us to discriminate between the two receptors. Major efforts from a large number of pharmaceutical companies are invested in evaluating the efficacy of such molecules in humans. Discovery of biomarkers associated with efficacy and patient selection are the main challenges that we will have to deal with in order to target the appropriate patient population that will most benefit from anti-IGF-IR monoclonal antibodies and combined treatments. This review will provide an overview of the current knowledge on IGF-IR and ongoing clinical trials.

Proprotein convertase inhibition results in decreased skin cell proliferation, tumorigenesis, and metastasis

PACE4 is a proprotein convertase (PC) responsible for cleaving and activating proteins that contribute to enhance tumor progression. PACE4 overexpression significantly increased the susceptibility to carcinogenesis, leading to enhanced tumor cell proliferation and premature degradation of the basement membrane. In the present study, we sought to evaluate a novel approach to retard skin tumor progression based on the inhibition of PACE4. We used decanoyl-RVKR-chloromethylketone (CMK), a small-molecule PC inhibitor, for in vitro and in vivo experiments. We found that CMK-dependent blockage of PACE4 activity in skin squamous cell carcinoma cell lines resulted in impaired insulin-like growth factor 1 receptor maturation, diminished its intrinsic tyrosine kinase activity, and decreased tumor cell proliferation. Two-stage skin chemical carcinogenesis experiments, together with topical applications of CMK, demonstrated that this PC inhibitor markedly reduced tumor incidence, tumor multiplicity, and metastasis, pointing to a significant delay in tumor progression in wild-type and PACE4 transgenic mice. These results identify PACE4, together with other PCs, as suitable targets to slow down or block tumor progression, suggesting that PC inhibition is a potential approach for therapy for solid tumors.

Insulin-like growth factors and insulin control a multifunctional signalling network of significant importance in cancer

Insulin-like growth factor (IGF) and insulin (INS) proteins regulate key cellular functions through a complex interacting multi-component molecular network, known as the IGF/INS axis. We describe how dynamic and multilayer interactions give rise to the multifunctional role of the IGF/INS axis. Furthermore, we summarise the importance of the regulatory IGF/INS network in cancer, and discuss the possibilities and limitations of therapies targeting the IGF/INS axis with reference to ongoing clinical trials concerning the blockage of IGF1R in several types of cancer.

Compensatory insulin receptor (IR) activation on inhibition of insulin-like growth factor-1 receptor (IGF-1R): rationale for cotargeting IGF-1R and IR in cancer

Insulin-like growth factor-1 receptor (IGF-1R) is a receptor tyrosine kinase (RTK) and critical activator of the phosphatidylinositol 3-kinase-AKT pathway. IGF-1R is required for oncogenic transformation and tumorigenesis. These observations have spurred anticancer drug discovery and development efforts for both biological and small-molecule IGF-1R inhibitors. The ability for one RTK to compensate for another to maintain tumor cell viability is emerging as a common resistance mechanism to antitumor agents targeting individual RTKs. As IGF-1R is structurally and functionally related to the insulin receptor (IR), we asked whether IR is tumorigenic and whether IR-AKT signaling contributes to resistance to IGF-1R inhibition. Both IGF-1R and IR(A) are tumorigenic in a mouse mammary tumor model. In human tumor cells coexpressing IGF-1R and IR, bidirectional cross talk was observed following either knockdown of IR expression or treatment with a selective anti-IGF-1R antibody, MAB391. MAB391 treatment resulted in a compensatory increase in phospho-IR, which was associated with resistance to inhibition of IRS1 and AKT. In contrast, treatment with OSI-906, a small-molecule dual inhibitor of IGF-1R/IR, resulted in enhanced reduction in phospho-IRS1/phospho-AKT relative to MAB391. Insulin or IGF-2 activated the IR-AKT pathway and decreased sensitivity to MAB391 but not to OSI-906. In tumor cells with an autocrine IGF-2 loop, both OSI-906 and an anti-IGF-2 antibody reduced phospho-IR/phospho-AKT, whereas MAB391 was ineffective. Finally, OSI-906 showed superior efficacy compared with MAB391 in human tumor xenograft models in which both IGF-1R and IR were phosphorylated. Collectively, these data indicate that cotargeting IGF-1R and IR may provide superior antitumor efficacy compared with targeting IGF-1R alone.

Insulin receptor (IR) pathway hyperactivity in IGF-IR null cells and suppression of downstream growth signaling using the dual IGF-IR/IR inhibitor, BMS-754807

The biology of IGF-IR/IR signaling was studied in normal mouse embryonic fibroblasts (MEFs) that were either wild type (wt), heterozygous (het), or null for the IGF-IR. The ability of IGF-I, IGF-II, or insulin to stimulate serum-starved MEFs was characterized by gene expression profiling and biochemical analyses for activation of downstream signals. Each genotypic group of MEFs exhibited distinct patterns of expression both while resting and in response to stimulation. The insulin receptor (IR) pathway in IGF-IR null MEFs was hypersensitive to insulin ligand stimulation resulting in greater AKT phosphorylation than in wt or het MEFs stimulated with the same ligand. Interestingly, the IR pathway hypersensitivity in IGF-IR null MEFs occurred with no observed changes in the levels of IR isoforms A or B. A new small molecule IGF-IR inhibitor (BMS-754807), having equipotent activity against both IGF-IR and IR, proved effective in suppressing both AKT and ERK phosphorylation from both the IGF-IR and IR pathways by all three ligands tested in wt, het, and null MEFs. The use of a dual IGF-IR/IR inhibitor addresses concerns about the use of growth inhibiting therapies directed against the IGF-IR receptor in certain cancers. Lastly, comparison of the antiproliferative effects (IC(50)s) of various compounds in wt vs. null MEFs demonstrates that genetically characterized MEFs provide a simple and inexpensive tool with which to define compounds as having mostly on-target or off-target IGF-IR activities because off-target compounds affect both wt and null MEFs equally.

Combination of two insulin-like growth factor-I receptor inhibitory antibodies targeting distinct epitopes leads to an enhanced antitumor response

The insulin-like growth factor-I receptor (IGF-IR) is a cell surface receptor tyrosine kinase that mediates cell survival signaling and supports tumor progression in multiple tumor types. We identified a spectrum of inhibitory IGF-IR antibodies with diverse binding epitopes and ligand-blocking properties. By binding distinct inhibitory epitopes, two of these antibodies, BIIB4 and BIIB5, block both IGF-I and IGF-II binding to IGF-IR using competitive and allosteric mechanisms, respectively. Here, we explored the inhibitory effects of combining BIIB4 and BIIB5. In biochemical assays, the combination of BIIB4 and BIIB5 improved both the potency and extent of IGF-I and IGF-II blockade compared with either antibody alone. In tumor cells, the combination of BIIB4 and BIIB5 accelerated IGF-IR downregulation and more efficiently inhibited IGF-IR activation as well as downstream signaling, particularly AKT phosphorylation. In several carcinoma cell lines, the antibody combination more effectively inhibited ligand-driven cell growth than either BIIB4 or BIIB5 alone. Notably, the enhanced tumor growth-inhibitory activity of the BIIB4 and BIIB5 combination was much more pronounced at high ligand concentrations, where the individual antibodies exhibited substantially reduced activity. Compared with single antibodies, the BIIB4 and BIIB5 combination also significantly further enhanced the antitumor activity of the epidermal growth factor receptor inhibitor erlotinib and the mTOR inhibitor rapamycin. Moreover, in osteosarcoma and hepatocellular carcinoma xenograft models, the BIIB4 and BIIB5 combination significantly reduced tumor growth to a greater degree than each single antibody. Taken together, our results suggest that targeting multiple distinct inhibitory epitopes on IGF-IR may be a more effective strategy of affecting the IGF-IR pathway in cancer.

Mutual interaction and reciprocal down-regulation between c-met and insulin receptor substrate-1

The insulin receptor substrate-1 (IRS-1) and c-met, the receptor for the hepatocyte growth factor (HGF) co-immuno-precipitate from lysates treated with the respective antibodies. The interaction between IRS-1 and c-met requires a tyrosyl phosphorylated IRS-1 and results in reciprocal down-regulation. IRS-1 inhibits cell motility, while the activated c-met promotes it. These and other results suggest an explanation for reports in the literature indicating that c-met levels are high and IRS-1 levels are low in human cancer metastases.

Obesity, hyperinsulinemia and breast cancer: novel targets and a novel role for metformin

The relationship between obesity, metabolic syndrome, diabetes and cancer has been recognized for many years. Multiple studies conducted in the last 20 years have identified molecular mechanisms responsible for this phenomenon. Elucidation of the important role of insulin, IGF receptor, mTOR and AMP-activated protein kinase in breast cancer biology has led to the development and subsequent clinical evaluation of novel targeted therapies, including IGF-1 receptor-specific antibodies or tyrosine kinase inhibitors and inhibitors of mTOR. There is also a growing interest in the use of metformin, which has been shown to possess antitumor activity resulting from activation of AMP-activated protein kinase and subsequent inhibiton of mTOR, as well as from decreased circulating insulin levels. Metformin has been shown to inhibit proliferation, invasion and angiogenesis of neoplastic cells and to overcome resistance of breast cancer to chemotherapy, hormonal therapy and HER2 inhibition. Recently, metformin has been demonstrated to inhibit breast cancer stem cell growth and to synergize with chemotherapy in suppression of tumor growth and prolongation of survival of breast tumor-bearing animals. Several currently ongoing Phase II and III clinical studies are evaluating the therapeutic efficacy of metformin in the treatment of early and advanced breast cancer patients.

Update on human polyomaviruses and cancer

Over 50 years of polyomavirus research has produced a wealth of insights into not only general biologic processes in mammalian cells, but also, how conditions can be altered and signaling systems tweaked to produce transformation phenotypes. In the past few years three new members (KIV, WUV, and MCV) have joined two previously known (JCV and BKV) human polyomaviruses. In this review, we present updated information on general virologic features of these polyomaviruses in their natural host, concentrating on the association of MCV with human Merkel cell carcinoma. We further present a discussion on advances made in SV40 as the prototypic model, which has and will continue to inform our understanding about viruses and cancer.

Workflow comparison for label-free, quantitative secretome proteomics for cancer biomarker discovery: method evaluation, differential analysis, and verification in serum

The cancer cell secretome has emerged as an attractive subproteome for discovery of candidate blood-based biomarkers. To choose the best performing workflow, we assessed the performance of three first-dimension separation strategies prior to nanoLC-MS/MS analysis: (1) 1D gel electrophoresis (1DGE), (2) peptide SCX chromatography, and (3) tC2 protein reversed phase chromatography. 1DGE using 4-12% gradient gels outperformed the SCX and tC2 methods with respect to number of identified proteins (1092 vs 979 and 580, respectively), reproducibility of protein identification (80% vs 70% and 72%, respectively, assessed in biological N = 3). Reproducibility of protein quantitation based on spectral counting was similar for all 3 methods (CV: 26% vs 24% and 24%, respectively). As a proof-of-concept of secretome proteomics for blood-based biomarker discovery, the gradient 1DGE workflow was subsequently applied to identify IGF1R-signaling related proteins in the secretome of mouse embryonic fibroblasts transformed with human IGF1R (MEF/Toff/IGF1R). VEGF and osteopontin were differentially detected by LC-MS/MS and verified in secretomes by ELISA. Follow-up in serum of mice bearing MEF/Toff/IGF1R-induced tumors showed an increase of osteopontin levels paralleling tumor growth, and reduction in the serum of mice in which IGF1R expression was shut off and tumor regressed.

Defining the pathway to insulin-like growth factor system targeting in cancer

The insulin-like growth factors (IGFs; IGF-1 and IGF-2) play central roles in cell growth, differentiation, survival, transformation and metastasis. The biologic effects of the IGFs are mediated by the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase with homology to the insulin receptor (IR). Dysregulation of the IGF system is well recognized as a key contributor to the progression of multiple cancers, with IGF-1R activation increasing the tumorigenic potential of breast, prostate, lung, colon and head and neck squamous cell carcinoma (HNSCC). Despite this relationship, targeting the IGF-1R has only recently undergone development as a molecular cancer therapeutic. As it has taken hold, we are witnessing a robust increase and interest in targeting the inhibition of IGF-1R signaling. This is accentuated by the list of over 30 drugs, including monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs) that are under evaluation as single agents or in combination therapies. The IGF-binding proteins (IGFBPs) represent the third component of the IGF system consisting of a class of six soluble secretory proteins. They represent a unique class of naturally occurring IGF-antagonists that bind to and sequester IGF-1 and IGF-2, inhibiting their access to the IGF-1R. Due to their dual targeting of the IGFs without affecting insulin action, the IGFBPs are an untapped "third" class of IGF-1R inhibitors. In this commentary, we highlight some of the significant aspects of and prospects for targeting the IGF-1R and describe what the future may hold.

Northwestern profiling of potential translation-regulatory proteins in human breast epithelial cells and malignant breast tissues: evidence for pathological activation of the IGF1R IRES

Genes involved in the control of cell proliferation and survival (those genes most important to cancer pathogenesis) are often specifically regulated at the translational level, through RNA-protein interactions involving the 5'-untranslated region of the mRNA. IGF1R is a proto-oncogene strongly implicated in human breast cancer, promoting survival and proliferation of tumor cells, as well as metastasis and chemoresistance. Our lab has focused on the molecular mechanisms regulating IGF1R expression at the translational level. We previously discovered an internal ribosome entry site (IRES) within the 5'-untranslated region of the human IGF1R mRNA, and identified and functionally characterized two individual RNA-binding proteins, HuR and hnRNP C, which bind the IGF1R 5'-UTR and differentially regulate IRES activity. Here we have developed and implemented a high-resolution northwestern profiling strategy to characterize, as a group, the full spectrum of sequence-specific RNA-binding proteins potentially regulating IGF1R translational efficiency through interaction with the 5'-untranslated sequence. The putative IGF1R IRES trans-activating factors (ITAFs) are a heterogeneous group of RNA-binding proteins including hnRNPs originating in the nucleus as well as factors tightly associated with ribosomes in the cytoplasm. The IGF1R ITAFs can be categorized into three distinct groups: (a) high molecular weight external ITAFs, which likely modulate the overall conformation of the 5'-untranslated region of the IGF1R mRNA and thereby the accessibility of the core functional IRES; (b) low molecular weight external ITAFs, which may function as general chaperones to unwind the RNA, and (c) internal ITAFs which may directly facilitate or inhibit the fundamental process of ribosome recruitment to the IRES. We observe dramatic changes in the northwestern profile of non-malignant breast cells downregulating IGF1R expression in association with acinar differentiation in 3-D culture. Most importantly, we are able to assess the RNA-binding activities of these putative translation-regulatory proteins in primary human breast surgical specimens, and begin to discern positive correlations between individual ITAFs and the malignant phenotype. Together with our previous findings, these new data provide further evidence that pathological dysregulation of IGF1R translational control may contribute to development and progression of human breast cancer, and breast metastasis in particular.

A human monoclonal antibody against insulin-like growth factor-II blocks the growth of human hepatocellular carcinoma cell lines in vitro and in vivo

Elevated expression of insulin-like growth factor-II (IGF-II) is frequently observed in a variety of human malignancies, including breast, colon, and liver cancer. As IGF-II can deliver a mitogenic signal through both IGF-IR and an alternately spliced form of the insulin receptor (IR-A), neutralizing the biological activity of this growth factor directly is a potential alternative option to IGF-IR-directed agents. Using a Fab-displaying phage library and a biotinylated precursor form of IGF-II (1-104 amino acids) as a target, we isolated Fabs specific for the E-domain COOH-terminal extension form of IGF-II and for mature IGF-II. One of these Fabs that bound to both forms of IGF-II was reformatted into a full-length IgG, expressed, purified, and subjected to further analysis. This antibody (DX-2647) displayed a very high affinity for IGF-II/IGF-IIE (K(D) value of 49 and 10 pmol/L, respectively) compared with IGF-I (approximately 10 nmol/L) and blocked binding of IGF-II to IGF-IR, IR-A, a panel of insulin-like growth factor-binding proteins, and the mannose-6-phosphate receptor. A crystal complex of the parental Fab of DX-2647 bound to IGF-II was resolved to 2.2 A. DX-2647 inhibited IGF-II and, to a lesser extent, IGF-I-induced receptor tyrosine phosphorylation, cellular proliferation, and both anchorage-dependent and anchorage-independent colony formation in various cell lines. In addition, DX-2647 slowed tumor progression in the Hep3B xenograft model, causing decreased tumoral CD31 staining as well as reduced IGF-IIE and IGF-IR phosphorylation levels. Therefore, DX-2647 offers an alternative approach to targeting IGF-IR, blocking IGF-II signaling through both IGF-IR and IR-A.

Nuclear export and mitochondrial and endoplasmic reticulum localization of IGF-binding protein 3 regulate its apoptotic properties

Tumor suppression by IGF-binding protein 3 (IGFBP3) may occur in an IGF-independent manner, in addition to its role as a regulator of IGF bioavailability. After secretion, IGFBP3 is internalized, rapidly localized to the nucleus, and is later detected in the cytoplasm. We identified a putative nuclear export sequence (NES) in IGFBP3 between amino acids 217 and 228, analogous to the leucine-rich NES sequence of p53 and HIV Rev. Mutation of the NES prevents nucleocytoplasmic shuttling of IGFBP3 and blocks its ability to induce apoptosis. Targeting of IGFBP3 to the mitochondria and endoplasmic reticulum (ER) was confirmed by co-localization with organelle markers using fluorescence confocal microscopy and subcellular fractionation. Mitochondrial targeting was also demonstrated in vivo in IGFBP3-treated prostate cancer xenografts. These results show that IGFBP3 shuttles from the nucleus to the mitochondria and ER, and that nuclear export is essential for its effects on prostate cancer apoptosis.

Insulin-like growth factors I and II receptors in the breast cancer survival disparity among African-American women

OBJECTIVE

African-American (AA) women with breast cancer are more likely to have advanced disease at diagnosis, higher risk of recurrence and poorer prognosis than Caucasian (CA) women. We have recently shown higher insulin-like growth factor II (IGF-II) expression in paired breast tissue samples from AA women as compared to CA women. IGF-II is a potent mitogen that induces cell proliferation and survival signals through activation of the IGF-I and Insulin receptors (IGF-IR, IR) while IGF-II circulating levels are regulated by cellular uptake through the IGF2 receptor. We hypothesize that differential expression of the IGF1R and IGF2R among AA and CA women potentiates IGF-II mitogenic effects, thus contributing to the health disparity observed between these ethnic groups.

DESIGN

We examined IGF-IR and IGF2R mRNA, protein expression and IGF1R phosphorylation in paired breast tissue samples from AA and CA women by Real Time-PCR, Western blot analysis, immunohistochemistry and ELISA techniques.

RESULTS

Our results showed significantly increased expression of IGF1R in AA normal tissues as compared to CA normal tissues. IGF1R expression was similar between AA normal and malignant tissues, while IGF1R, IRS-1 and Shc phosphorylation was significantly higher in AA tumor samples. Significantly higher levels of IGF2R were found in CA tumor samples as compared to AA tumor samples.

CONCLUSIONS

We conclude that IGF1R and IGF2R differential expression may contribute to the increased risk of malignant transformation in young AA women and to the more aggressive breast cancer phenotype observed among AA breast cancer patients and represent, along with IGF-II, potential therapeutic targets in breast cancer.

Effect of type 1 insulin-like growth factor receptor targeted therapy on chemotherapy in human cancer and the mechanisms involved

INTRODUCTION

Chemotherapy is administered only to patients with advanced cancers, typically to modest avail. Hence, the search for innovative approaches to treat cancer is growing rapidly. One such approach involves targeting molecular pathways identified as encouraging tumor growth and maintenance, particularly the type 1 insulin-like growth factor (IGF-1) and its receptor (IGF-1R) pathway that is important in conferring chemoresistance.

MATERIALS AND METHODS

This study focuses on IGF-1R targeted therapy, which will enhance chemotherapy efficacy, through reviewing recent literature from PubMed and Medline databases.

CONCLUSION

This review examines data and strategies addressing an approach conquering chemoresistance through the combination of IGF-1R targeted therapy and chemotherapy in cancer patients, as well as the mechanisms by which IGF-1R acts as a target. This will impact on future research on treatment selection, thereby improving patient prognosis.