Treatment of human breast cancer cells with antisense RNA to the type I insulin-like growth factor receptor inhibits cell growth, suppresses tumorigenesis, alters the metastatic potential, and prolongs survival in vivo

The cancer glycocode as a family of diagnostic biomarkers, exemplified by tumor-associated gangliosides

One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode).A class of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs) are presented here as potential diagnostics for detecting cancer, especially at early stages, as the biological function of TMGs makes them etiological. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention. Diagnosis is critical to reducing cancer mortality but many cancers lack efficient and effective diagnostic tests, especially for early stage disease. Ideal diagnostic biomarkers are etiological, samples are preferably obtained via non-invasive methods (e.g. liquid biopsy of blood or urine), and are quantitated using assays that yield high diagnostic sensitivity and specificity for efficient diagnosis, prognosis, or predicting response to therapy. Validated biomarkers with these features are rare. While the advent of proteomics and genomics has led to the identification of a multitude of proteins and nucleic acid sequences as cancer biomarkers, relatively few have been approved for clinical use. The use of multiplex arrays and artificial intelligence-driven algorithms offer the option of combining data of known biomarkers; however, for most, the sensitivity and the specificity are below acceptable criteria, and clinical validation has proven difficult. One strategic solution to this problem is to expand the biomarker families beyond those currently exploited. One unexploited family of cancer biomarkers comprise glycoproteins, carbohydrates, and glycolipids (the Tumor Glycocode). Here, we focus on a family of glycolipid cancer biomarkers, the tumor-marker gangliosides (TMGs). We discuss the diagnostic potential of TMGs for detecting cancer, especially at early stages. We include prior studies from the literature to summarize findings for ganglioside quantification, expression, detection, and biological function and its role in various cancers. We highlight the examples of TMGs exhibiting ideal properties of cancer diagnostic biomarkers, and the application of GD2 and GD3 for diagnosis of early stage cancers with high sensitivity and specificity. We propose that a quantitative matrix of the Cancer Biomarker Glycocode and artificial intelligence-driven algorithms will expand the menu of validated cancer biomarkers as a step to resolve some of the challenges in cancer diagnosis, and yield a combination that can identify a specific cancer, in a tissue-agnostic manner especially at early stages, to enable early intervention.

SNIP1 Recruits TET2 to Regulate c-MYC Target Genes and Cellular DNA Damage Response

The TET2 DNA dioxygenase regulates gene expression by catalyzing demethylation of 5-methylcytosine, thus epigenetically modulating the genome. TET2 does not contain a sequence-specific DNA-binding domain, and how it is recruited to specific genomic sites is not fully understood. Here we carried out a mammalian two-hybrid screen and identified multiple transcriptional regulators potentially interacting with TET2. The SMAD nuclear interacting protein 1 (SNIP1) physically interacts with TET2 and bridges TET2 to bind several transcription factors, including c-MYC. SNIP1 recruits TET2 to the promoters of c-MYC target genes, including those involved in DNA damage response and cell viability. TET2 protects cells from DNA damage-induced apoptosis dependending on SNIP1. Our observations uncover a mechanism for targeting TET2 to specific promoters through a ternary interaction with a co-activator and many sequence-specific DNA-binding factors. This study also reveals a TET2-SNIP1-c-MYC pathway in mediating DNA damage response, thereby connecting epigenetic control to maintenance of genome stability.

Therapeutic Potency of Nanoformulations of siRNAs and shRNAs in Animal Models of Cancers

RNA Interference (RNAi) has brought revolutionary transformations in cancer management in the past two decades. RNAi-based therapeutics including siRNA and shRNA have immense scope to silence the expression of mutant cancer genes specifically in a therapeutic context. Although tremendous progress has been made to establish catalytic RNA as a new class of biologics for cancer management, a lot of extracellular and intracellular barriers still pose a long-lasting challenge on the way to clinical approval. A series of chemically suitable, safe and effective viral and non-viral carriers have emerged to overcome physiological barriers and ensure targeted delivery of RNAi. The newly invented carriers, delivery techniques and gene editing technology made current treatment protocols stronger to fight cancer. This review has provided a platform about the chronicle of siRNA development and challenges of RNAi therapeutics for laboratory to bedside translation focusing on recent advancement in siRNA delivery vehicles with their limitations. Furthermore, an overview of several animal model studies of siRNA- or shRNA-based cancer gene therapy over the past 15 years has been presented, highlighting the roles of genes in multiple cancers, pharmacokinetic parameters and critical evaluation. The review concludes with a future direction for the development of catalytic RNA vehicles and design strategies to make RNAi-based cancer gene therapy more promising to surmount cancer gene delivery challenges.

Mammary tumors that become independent of the type I insulin-like growth factor receptor express elevated levels of platelet-derived growth factor receptors

BACKGROUND

Targeted therapies are becoming an essential part of breast cancer treatment and agents targeting the type I insulin-like growth factor receptor (IGF-IR) are currently being investigated in clinical trials. One of the limitations of targeted therapies is the development of resistant variants and these variants typically present with unique gene expression patterns and characteristics compared to the original tumor.

RESULTS

MTB-IGFIR transgenic mice, with inducible overexpression of the IGF-IR were used to model mammary tumors that develop resistance to IGF-IR targeting agents. IGF-IR independent mammary tumors, previously shown to possess characteristics associated with EMT, were found to express elevated levels of PDGFRα and PDGFRβ. Furthermore, these receptors were shown to be inversely expressed with the IGF-IR in this model. Using cell lines derived from IGF-IR-independent mammary tumors (from MTB-IGFIR mice), it was demonstrated that PDGFRα and to a lesser extent PDGFRβ was important for cell migration and invasion as RNAi knockdown of PDGFRα alone or PDGFRα and PDGFRβ in combination, significantly decreased tumor cell migration in Boyden chamber assays and suppressed cell migration in scratch wound assays. Somewhat surprisingly, concomitant knockdown of PDGFRα and PDGFRβ resulted in a modest increase in cell proliferation and a decrease in apoptosis.

CONCLUSION

During IGF-IR independence, PDGFRs are upregulated and function to enhance tumor cell motility. These results demonstrate a novel interaction between the IGF-IR and PDGFRs and highlight an important, therapeutically relevant pathway, for tumor cell migration and invasion.

Molecular target characterization and antimyeloma activity of the novel, insulin-like growth factor 1 receptor inhibitor, GTx-134

PURPOSE

Therapeutic strategies that target insulin-like growth factor 1 receptor (IGF-1R) hold promise in a wide variety of cancers including multiple myeloma (MM). In this study, we describe GTx-134, a novel small-molecule inhibitor of IGF-1R and insulin receptor (IR) and characterized its antitumor activity in preclinical models of MM.

EXPERIMENTAL DESIGN

The activity of GTx-134 as a single agent and in combination was tested in MM cell lines and primary patient samples. Downstream effector proteins and correlation with apoptosis was evaluated. Cytotoxcity in bone marrow stroma coculture experiments was assessed. Finally, the in vivo efficacy was evaluated in a human myeloma xenograft model.

RESULTS

GTx-134 inhibited the growth of 10 of 14 myeloma cell lines (<5 μmol/L) and induced apoptosis. Sensitivity to GTx-134 correlated with IGF-1R signal inhibition. Expression of MDR-1 and CD45 were associated with resistance to GTx-134. Coculture with insulin-growth factor-1 (IGF-1) or adherence to bone marrow stroma conferred modest resistance, but did not overcome GTx-134-induced cytotoxicity. GTx-134 showed in vitro synergies when combined with dexamethasone or lenalidomide. Further, GTx-134 enhanced the activity of PD173074, a fibroblast growth factor receptor 3 (FGFR3) inhibitor, against t(4;14) myeloma cells. Therapeutic efficacy of GTx-134 was shown against primary cells and xenograft tumors. Although dysregulation of glucose homeostasis was observed in GTx-134-treated mice, impairment of glucose tolerance was modest.

CONCLUSIONS

These studies support the potential therapeutic efficacy of GTx-134 in MM. Further, they provide a rationale for clinical application in combination with established antimyeloma treatments and novel targeted therapies.

Dual epidermal growth factor receptor (EGFR)/insulin-like growth factor-1 receptor (IGF-1R) inhibitor: a novel approach for overcoming resistance in anticancer treatment

Small molecule inhibitors of epidermal growth factor receptors (EGFR) have been found to show a good initial response in cancer patients but during the course of treatment, patients develop resistance after a few weeks of time. Development of secondary mutations or over-activation of insulin like growth factor (IGF-1R) pathway are a few of the several mechanisms proposed to explain the resistance. To study the effect of dual inhibition of EGFR and IGF-1R in overcoming the resistance, three strategies were envisaged and are reported in this manuscript: 1) a virtual predictive tumor model, 2) in vitro experimental data using a combination of EGFR and IGF-1R inhibitors and 3) in vitro experimental data using in house dual inhibitors. Findings reported in this manuscript suggest that simultaneous inhibition of IGF-1R and EGFR either by combination of two inhibitors or by dual kinase inhibitors is more efficacious compared to single agents. In vitro cell based experiments conducted using epidermoid cancer cell line, A431 and an EGFR mutant cell line, H1975 along with virtual predictions reported here suggests that dual inhibition of EGFR and IGF-1R is a viable approach to overcome EGFR resistance.

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.

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.

ErbB2 enhances mammary tumorigenesis, oncogene-independent recurrence and metastasis in a model of IGF-IR-mediated mammary tumorigenesis

Background

The type I insulin-like growth factor receptor (IGF-IR) and ErbB2 (Her-2) are receptor tyrosine kinases implicated in human breast cancer. Both proteins are currently the subject of targeted therapeutics that are used in the treatment of breast cancer or which are in clinical trials. The focus of this study was to utilize our inducible model of IGF-IR overexpression to explore the interaction of these two potent oncogenes.

Results

ErbB2 was overexpressed in our RM11A cell line, a murine tumor cell line that overexpresses human IGF-IR in an inducible manner. ErbB2 conferred an accelerated tumor onset and increased tumor incidence after injection of RM11A cells into the mammary glands of syngeneic wild type mice. This was associated with increased proliferation immediately after tumor cell colonization of the mammary gland; however, this effect was lost after tumor establishment. ErbB2 overexpression also impaired the regression of established RM11A tumors following IGF-IR downregulation and enhanced their metastatic potential.

Conclusion

This study has revealed that even in the presence of vast IGF-IR overexpression, a modest increase in ErbB2 can augment tumor establishment in vivo, mediate resistance to IGF-IR downregulation and facilitate metastasis. This supports the growing evidence suggesting a possible advantage of using IGF-IR and ErbB2-directed therapies concurrently in the treatment of 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.

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.

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.

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.

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.

Reversibility and recurrence of IGF-IR-induced mammary tumors

The type-I insulin-like growth factor receptor (IGF-IR) is frequently overexpressed in breast cancer and therapeutic agents targeting IGF-IR are currently in development. The ultimate success of anti-IGF-IR therapies will depend on the extent to which established tumors remain dependent upon IGF-IR signaling for sustained growth. To investigate the potential benefits and pitfalls of targeting IGF-IR, we used a doxycycline inducible mouse model of IGF-IR initiated breast cancer. We found that downregulation of IGF-IR results in tumor-size-dependent regression to an undetectable state. Partially regressed tumors almost always resumed growth in the absence of doxycycline and a proportion of tumors that regressed to an undetectable state ultimately recurred. This re-emergence of tumor growth in the absence of doxycycline was facilitated by IGF-IR-dependent and IGF-IR-independent mechanisms. Tumor escape from IGF-IR dependence was associated with an epithelial to mesenchymal transition and upregulation of transcriptional repressors of E-cadherin. These results suggest that tumors initiated by IGF-IR have the ability to become independent of this initiating oncogene, and IGF-IR independence is associated with characteristics consistent with an epithelial to mesenchymal transition.

The insulin-like growth factor system and its receptors: A potential novel anticancer target

The current generation of novel anticancer therapies that are in preclinical and clinical development are based on exploiting our increasing understanding of the molecular and cellular basis of cancer development and progression. Accelerated rates of cell division and proliferation have been postulated to predispose to the development of malignant disease. The insulin-like growth factor (IGF) signaling system has an important physiological role in regulating cellular proliferation and apoptosis. This function has led to considerable interest in its relevance to neoplasia over the last decade. In this review, we give an overview of the IGF system physiology, discuss the epidemiological significance of IGF signaling and neoplasia, and review the preclinical and clinical studies in targeting IGF receptors as cancer therapies.

Knockdown of insulin-like growth factor 1 receptor enhances chemosensitivity to cisplatin in human lung adenocarcinoma A549 cells

The effects of RNA interference-mediated insulin-like growth factor 1 receptor (IGF1R) gene silencing in response to cisplatin (DDP) in the lung cancer cell line A549 in vivo and in vitro were investigated using two plasmids expressing short hairpin RNA (shRNA) to IGF1R. A549 cells were transfected with plasmids expressing each shRNA and then treated with DDP. Semi-quantitative reverse transcription-PCR and Western blot analysis were used to detect the expression of IGF1R. MTT assay, flow cytometry and tumor growth assay in athymic nude mice were used to assess the chemosensitivity to DDP following IGF1R knockdown. Our data showed that the transfection of A549 cells with shRNA resulted in specific silencing of IGF1R by 78.9% at the mRNA level and by 89.8% at the protein level. Down-regulation of IGF1R significantly enhanced cell sensitivity to DDP, decreased the IC50 of DDP in A549 cells at 24 h, 48 h and 72 h, and retained 77.5% of A549 cells in the G0/G1 phase. Furthermore, shRNA-mediated silencing of IGF1R in combination with DDP treatment enhanced the suppression of tumor growth in both size and weight by more than 60% and increased apoptosis by more than 75% when compared with the controls in vivo. Suppression of IGF1R gene expression by shRNA enhances the chemosensitivity of A549 cells to DDP both in vitro and in vivo, indicating the therapeutic potential of RNA interference as a method for gene therapy in treating lung cancer.

Targeting the type 1 insulin-like growth factor receptor as a treatment for cancer

BACKGROUND

The type 1 insulin-like growth factor receptor (IGF1R) plays a critical role in transformation, invasion and apoptosis protection, and is an attractive cancer treatment target.

OBJECTIVE

To review IGF1R antibodies and kinase inhibitors that are in preclinical and clinical development, and to discuss questions that will influence the success of this approach in clinical practice.

METHODS

This review is drawn from published literature, meeting abstracts and online resources.

RESULTS/CONCLUSION

IGF1R blockade is generally well tolerated although it can induce hyperglycaemia. Single-agent activity has been documented in Ewing's sarcoma but not thus far in common solid tumours. Key issues include identification of factors that influence sensitivity to IGF1R blockade, and how most effectively to combine IGF1R inhibitors with other treatments.

Cytochrome p450 epoxygenase promotes human cancer metastasis

Cytochrome P450 (CYP) epoxygenases convert arachidonic acid to four regioisomeric epoxyeicosatrienoic acids (EET), which exert diverse biological activities in a variety of systems. We previously reported that the CYP2J2 epoxygenase is overexpressed in human cancer tissues and cancer cell lines and that EETs enhance tumor growth, increase carcinoma cell proliferation, and prevent apoptosis of cancer cells. Herein, we report that CYP epoxygenase overexpression or EET treatment promotes tumor metastasis independent of effects on tumor growth. In four different human cancer cell lines in vitro, overexpression of CYP2J2 or CYP102 F87V with an associated increase in EET production or addition of synthetic EETs significantly induced Transwell migration (4.5- to 5.5-fold), invasion of cells (3- to 3.5-fold), cell adhesion to fibronectin, and colony formation in soft agar. In contrast, the epoxygenase inhibitor 17-ODYA or infection with the antisense recombinant adeno-associated viral vector (rAAV)-CYP2J2 vector inhibited cell migration, invasion, and adhesion with an associated reduction in EET production. CYP overexpression also enhanced metastatic potential in vivo in that rAAV-CYP2J2-infected MDA-MB-231 human breast carcinoma cells showed 60% more lung metastases in athymic BALB/c mice and enhanced angiogenesis in and around primary tumors compared with control cells. Lung metastasis was abolished by infection with the antisense rAAV-CYP2J2 vector. CYP epoxygenase overexpression or EET treatment up-regulated the prometastatic matrix metalloproteinases and CD44 and down-regulated the antimetastatic genes CD82 and nm-23. Together, these data suggest that CYP epoxygenase inhibition may represent a novel approach to prevent metastasis of human cancers.

Aggressive breast cancer cells are dependent on activated Abl kinases for proliferation, anchorage-independent growth and survival

Mutant Abl kinases (such as BCR-Abl) drive the development of leukemia; however little is known regarding whether Abl kinases contribute to the development or progression of solid tumors. We recently demonstrated that endogenous Abl kinases (c-Abl, Arg) are activated by deregulated ErbB receptors and Src kinases, and drive invasion of aggressive breast cancer cells. In this study, we examined whether activation of endogenous Abl kinases affects transformation, proliferation and survival, which are major contributors to breast cancer development and metastatic progression. Using a pharmacological inhibitor and RNAi, we demonstrate that activation of endogenous Abl kinases dramatically promotes breast cancer cell proliferation and anchorage-independent growth in serum, as well as survival following nutrient deprivation. Activation of Abl kinases mediates phosphorylation of STAT3, and promotes proliferation by accelerating G(1) --> S progression. Moreover, we identify IGF-1R as a novel upstream activator of endogenous Abl kinases, and demonstrate that Abl kinase activation is required for IGF-1-stimulated cell cycle progression in breast cancer cells. Since activation of Abl kinases affects multiple steps of breast cancer development and progression, Abl kinase inhibitors are likely to be effective agents for the treatment of breast cancers containing highly active Abl kinases.

A novel, potent, and selective insulin-like growth factor-I receptor kinase inhibitor blocks insulin-like growth factor-I receptor signaling in vitro and inhibits insulin-like growth factor-I receptor dependent tumor growth in vivo

Insulin-like growth factor-I receptor (IGF-IR) and its ligands, IGF-I and IGF-II, are up-regulated in a variety of human cancers. In tumors, such as colorectal, non-small cell lung, ovarian, and pediatric cancers, which may drive their own growth and survival through autocrine IGF-II expression, the role of IGF-IR is especially critical. Here, we present a novel small-molecule IGF-IR kinase inhibitor, cis-3-[3-(4-methyl-piperazin-l-yl)-cyclobutyl]-1-(2-phenyl-quinolin-7-yl)-imidazo[1,5-a]pyrazin-8-ylamine (PQIP), which displayed a cellular IC(50) of 19 nmol/L for inhibition of ligand-dependent autophosphorylation of human IGF-IR with 14-fold cellular selectivity relative to the human insulin receptor. PQIP showed minimal activity against a panel of 32 other protein kinases. It also abolished the ligand-induced activation of downstream phosphorylated AKT and phosphorylated extracellular signal-regulated kinase 1/2 in both IGF-IR transfectant cells and a GEO human colorectal cancer cell line. Analysis of GEO cells revealed a significant level of both phosphorylated IGF-IR and IGF-II expression. Furthermore, inactivation of IGF-II in conditioned GEO culture medium by a neutralizing antibody diminished IGF-IR activation, indicating the presence of a functional IGF-II/IGF-IR autocrine loop in GEO cells. Once daily oral dosing of PQIP induced robust antitumor efficacy in GEO xenografts. The antitumor efficacy correlated with the degree and duration of inhibition of tumor IGF-IR phosphorylation in vivo by this compound. Moreover, when mice were treated for 3 days with a dose of PQIP that maximally inhibited tumor growth, only minor changes in blood glucose were observed. Thus, PQIP represents a potent and selective IGF-IR kinase inhibitor that is especially efficacious in an IGF-II-driven human tumor model.

Silencing of the type 1 insulin-like growth factor receptor increases the sensitivity to apoptosis and inhibits invasion in human lung adenocarcinoma A549 cells

The type 1 insulin-like growth factor receptor (IGF-1R), which is over-expressed or activated in many human cancers, including lung cancer, mediates cancer cell proliferation and metastasis. Several studies indicate that blocking IGF-1R expression can inhibit tumor cell proliferation and metastasis. In this study, inhibition of the endogenous IGF-1R by recombinant adenoviruses encoding short hairpin RNAs against IGF-1R was found to significantly suppress IGF-1R expression, arrest the cell cycle, enhance the apoptotic response, and inhibit proliferation, adhesion, invasion and migration in A549 cells. Moreover, silencing IGF-1R decreases the expression of invasive-related genes including matrix metalloproteinase-2 (MMP-2), MMP-9, and urokinase-plasminogen activator (u-PA), and the phosphorylation of Akt and ERK1/2. These results suggest that the silencing of IGF-1R has the potential to be an effective cancer gene therapy strategy for human lung cancer.

1,3-Disubstituted-imidazo[1,5-a]pyrazines as insulin-like growth-factor-I receptor (IGF-IR) inhibitors

A series of novel 8-amino-1,3-disubstituted-imidazo[1,5-a]pyrazines was designed and synthesized as IGF-IR inhibitors.

Activation of Abl tyrosine kinases promotes invasion of aggressive breast cancer cells

The Abl family of nonreceptor tyrosine kinases consists of two related proteins, c-Abl and Abl-related gene (Arg). Activated forms of the Abl kinases (BCR-Abl, Tel-Abl, and Tel-Arg) induce the development of human leukemia; it is not known, however, whether Abl kinases are activated in solid tumors or whether they contribute to tumor development or progression. Previously, we showed that Abl kinases are activated downstream of growth factor receptors, Src family kinases, and phospholipase Cgamma1 (PLCgamma1) in fibroblasts and influence growth factor-mediated proliferation, membrane ruffling, and migration. Growth factor receptors, Src kinases, and PLCgamma1 are deregulated in many solid tumors and drive tumor invasion and metastasis. In this study, we found that Abl kinases are constitutively activated, in highly invasive breast cancer cell lines, downstream of deregulated ErbB receptors and Src kinases. Furthermore, activation of Abl kinases promotes breast cancer cell invasion, as treatment of cells with the Abl kinase inhibitor, STI571, or silencing c-Abl and Arg expression with RNA interference dramatically inhibits Matrigel invasion. This is the first evidence that (a) Abl kinases are deregulated and activated in a nonhematopoietic cancer, (b) activation of Abl kinases in breast cancer cells occurs via a novel mechanism, and (c) constitutive activation of Abl kinases promotes invasion of breast cancer cells. These data suggest that pharmacologic inhibitors targeted against Abl kinases could potentially be useful in preventing breast cancer progression in tumors harboring activated Abl kinases.

Insulin-Like Growth Factor (IGF) family and prostate cancer

There is abundant in vitro, animal and epidemiologic evidence to suggest that the Insulin-Like Growth Factor (IGF) family is a multi-component network of molecules which is involved in the regulation of both physiological and pathological growth processes in prostate. The IGF family plays a key role in cellular metabolism, differentiation, proliferation, transformation and apoptosis, during normal development and malignant growth. This family also seem essential in prostate cancer bone metastases, angiogenesis and androgen-independent progression. Therapeutic alternatives in men with progressive prostate cancer after androgen ablation are very limited. More effective therapies are needed for these patients. Pharmacologic interventions targeting the IGF family are being devised. Such strategies include reduction of IGF-I levels (growth hormone-releasing hormone antagonists, somatostatin analogs), reduction of functional IGF-I receptor levels (antisense oligonucleotides, small interfering RNA), inhibition of IGF-IR and its signalling (monoclonal antibodies, small-molecule tyrosine kinase inhibitors) and Insulin-Like Growth Factor Binding Proteins.

Inhibitors of insulin-like growth factor signaling: a therapeutic approach for breast cancer

The peptide growth factors IGF-I and IGF-II not only play a role in the development of the mammary gland but are also implicated in breast cancer. Several reagents disrupting IGF signaling have been developed and clinical trials validating IGF signaling as a target in cancer therapy are underway. This review highlights the approaches to inhibiting IGF signaling in breast cancer.

Insulin-like growth factor-I receptor signaling and resistance in breast cancer

Insulin-like growth factor-I receptor (IGF-IR) signaling is involved in many fundamental adverse aspects of cancer cell biology, such as proliferation, cell survival and migration. Its anti-apoptotic properties have implicated the receptor in mediating decreased sensitivity to chemotherapeutic drugs and radiation treatment; however, data are emerging that also indicates a role for IGF-IR signaling in resistance, not only to antihormones but also to antigrowth factor strategies such as agents that target the erb family of receptors. As such, IGF-IR is clearly an attractive therapeutic target for the treatment of cancer, including breast cancer, where there is evidence of clinical prominence of the IGF-IR pathway and, as such, numerous strategies are currently in development to inhibit IGF-IR signaling. This review focuses on the ability of the IGF-IR to contribute to resistance mechanisms that support breast cancer cell growth in the presence of antihormones and antigrowth factors and discusses methods to maximize antitumor effects by combination regimens cotargeting the IGF-IR that may delay, or even prevent, progression to the resistant phenotype.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

Tissue-Type Plasminogen Activator Is Upregulated in Metastatic Breast Cancer Cells Exposed to Insulin-Like Growth Factor—I

The insulin-like growth factor (IGF) system plays an important role in breast tumorigenesis. Breast cancer cells express the type I IGF receptor (IGF-IR) and respond to IGFs in the environment. Tissue-type plasminogen activator (tPA) has been shown to be associated with neoplastic transformation and the invasive phenotype for highly aggressive tumors; however, its role in breast cancer remains unclear. We asked whether there is a relationship between the IGF system and tPA in estrogen receptor-negative breast cancer cells that could contribute to invasion. When MDA-MB-435s breast cancer cells were exposed to IGF-I, tPA messenger RNA (mRNA) was upregulated in a time-dependent fashion. Tissue-type plasminogen activator protein accumulation was also increased in a similar manner. The invasiveness of MDA-MB-435s cells was enhanced in the presence of IGF-I. When the MDA-MB-435s cells were stably transfected with an antisense IGF-IR expression construct, the transfectants expressed high levels of IGF-IR antisense, dramatically reduced levels of endogenous IGF-IR, and a decrease in relative staining intensity for IGF-IR protein. A marked suppression in tPA mRNA expression occurred in MDA-MB-435s cells accompanying inhibition of IGF-IR. When cells carrying the antisense IGF-IR expression construct were exposed to IGF-I, tPA protein accumulation was significantly lower than that of control transfected cells. To our knowledge, this study is the first to show a relationship between the IGF system and tPA. Strategies that target the IGF/tPA pathway could provide alternative treatments for patients with certain types of metastatic breast cancer.

Combination therapy enhances the inhibition of tumor growth with the fully human anti-type 1 insulin-like growth factor receptor monoclonal antibody CP-751,871

PURPOSE

The insulin-like growth factor (IGF) signaling pathway is implicated in cellular mitogenesis, angiogenesis, tumor cell survival, and tumorigenesis. Inhibition of this pathway results in decreased cell growth, inhibition of tumor formation in animal models, and increased apoptosis in cells treated with cytotoxic chemotherapy. We generated and characterized a human monoclonal antibody that targeted the IGF receptor.

EXPERIMENTAL DESIGN

By use of XenoMouse technology, we generated CP-751,871, a fully human IgG2 antibody with high affinity (K(d) = 1.5 nmol/L) for human IGF-1R and evaluated its biological, pharmacologic, and antitumor properties.

RESULTS

This antibody blocks binding of IGF-1 to its receptor (IC(50) 1.8 nmol/L), IGF-1-induced receptor autophosphorylation (IC(50) 0.42 nmol/L) and induced the down-regulation of IGF-1R in vitro and in tumor xenografts. The extent of IGF-1R down-regulation in vivo was proportional to CP-751,871 concentrations in the serum of tumor-bearing mice. Pharmacokinetic profiles in cynomolgus monkeys indicated a close to linear increase of exposure following i.v. dosing of antibody in the range of 3 to 100 mg/kg. CP-751,871 showed significant antitumor activity both as a single agent and in combination with Adriamycin, 5-fluorouracil, or tamoxifen in multiple tumor models. A biomarker assay was developed to establish the relationship between circulating antibody concentrations and down-regulation of IGF-1R in peripheral blood cells. The concentration of CP-751,871 required to down-regulate 50% of IGF-1R on peripheral blood cells was 0.3 nmol/L.

CONCLUSION

These data suggest that inhibition of the IGF cascade by use of this monoclonal antibody may be of clinical benefit in the treatment of human cancers.

c-myc-induced hepatocarcinogenesis in the absence of IGF-I receptor

Numerous tumours, including hepatocarcinomas, produce IGFs, and some depend on these growth factors in a paracrine or autocrine fashion. We have shown that c-myc-induced experimental hepatocarcinogenesis is associated with enhanced production of IGF-II. To assess the role of the IGF-I receptor (IGF-IR) in hepatocarcinogenesis, we generated conditional mutant mice that overexpressed c-myc and were knocked out for IGF-IR specifically in the liver. We compared these mice with littermate controls that also overexpressed c-myc but had wild-type IGF-IR alleles. We found that the pretumoral phase, induced by early c-myc expression and characterised by increased cell proliferation, was largely unaffected by the lack of IGF-IR. To our further surprise, hepatocellular carcinomas (HCCs) lacking IGF-IR readily developed and progressed at the same rate as control HCCs. At 9 months, all c-myc transgenic mice displayed well-differentiated multifocal tumours, regardless of whether their livers-and their tumours-were able to produce IGF-IR. Levels of IRS-1 and IRS-2 were elevated in all tumours in the presence or absence of IGF-IR, suggesting that the signalling pathway downstream of IGF-IR is activated via IGF-IR-independent mechanisms in HCC. In conclusion, the deregulation of IGF signalling pathways, which often occurs during liver tumorigenesis, does not necessarily require IGF-IRs, and hepatic IGF-IR alone may not play a determinant role in c-myc-induced hepatocarcinogenesis.

A recombinant humanized anti-insulin-like growth factor receptor type I antibody (h7C10) enhances the antitumor activity of vinorelbine and anti-epidermal growth factor receptor therapy against human cancer xenografts

Interaction of insulin-like growth factor receptor I (IGF-IR) with its ligands has been reported to induce cell proliferation, transformation and blockade of cell apoptotic functions. IGF-IR is overexpressed on numerous tumor cell types and its blockade could be of importance for anti-cancer therapy. We have generated a humanized anti-IGF-IR antibody h7C10 that blocks in vitro IGF-I and IGF-II-induced cell proliferation of MCF-7 breast cancer cells. Analysis of the IGF-I transduction cascade demonstrated that the humanized anti-IGF-IR antibody and its murine parental form block IGF-I-induced tyrosine phosphorylation, both its beta-chain and IRS-1 tyrosine phosphorylation. This presumably leads to cell cycle arrest and, consequently, growth inhibition. Treatment of nude mice bearing either human breast cancer cells (MCF-7) or non small lung cancer cells (A549) with h7C10, or its murine parental form 7C10, inhibited significantly tumor growth. An almost complete inhibition of A549 tumor growth was observed when mice were treated with the anti-IGF-IR antibody combined with either a chemotherapeutic agent, Vinorelbine or an anti-epidermal growth factor receptor (EGFR) antibody, 225. Combined therapy prolonged significantly the life span of mice in an orthotopic in vivo model of A549; the combination of the anti-IGF-IR antibody with an anti-EGFR antibody was superior to the Vinorelbine combination. The present results indicate that the humanized anti-IGF-IR antibody h7C10 has a great potential for cancer therapy when combined with either a chemotherapeutic agent or an antibody that targets other growth factor receptors, such as the epidermal growth factor receptor.

The insulin like growth factor-1 receptor (IGF-1R) as a drug target: novel approaches to cancer therapy

The insulin-like growth factor 1 receptor (IGF-1R) is an important signaling molecule in cancer cells and plays an essential role in the establishment and maintenance of the transformed phenotype. Inhibition of IGF-1R signaling thus appears to be a promising strategy to interfere with the growth and survival of cancer cells. Different classes of molecules, e.g., antisense RNA, monoclonal antibodies and dominant negative IGF-1R gene variants, have been employed towards this aim. These agents have been able to reverse the transformed phenotype in several rodent and human cancer cell lines. The application of peptide aptamers specifically binding to the IGF-1R represents a novel approach to target IGF-1R signaling. The integration of peptide aptamers into targeted protein degradation vehicles and their transduction into cells allows the temporary elimination of the receptor protein. This review summarizes recently published data about inhibition of IGF-1R signaling and provides a perspective on upcoming possibilities.

Inhibition of in vivo breast cancer growth by antisense oligodeoxynucleotides to type I insulin-like growth factor receptor mRNA involves inactivation of ErbBs, PI-3K/Akt and p42/p44 MAPK signaling pathways but not modulation of progesterone receptor activity

The present study addresses the effect of targeting type I insulin-like growth factor receptor (IGF-IR) with antisense strategies in in vivo growth of breast cancer cells. Our research was carried out on C4HD tumors from an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in Balb/c mice. We employed two different experimental strategies. With the first one we demonstrated that direct intratumor injection of phosphorothioate antisense oligodeoxynucleotides (AS[S]ODNs) to IGF-IR mRNA resulted in a significant inhibition of C4HD tumor growth. In the second experimental strategy, we assessed the effect of intravenous (i.v.) injection of AS [S]ODN on C4HD tumor growth. This systemic treatment also resulted in significant reduction in tumor growth. The antitumor effect of IGF-IR AS[S]ODNs in both experimental protocols was due to a specific antisense mechanism, since growth inhibition was dose-dependent and no abrogation of tumor proliferation was observed in mice treated with phosphorothioate sense ODNs (S[S]ODNs). In addition, IGF-IR expression was inhibited in tumors from mice receiving AS[S]ODNs, as compared to tumors from control groups. We then investigated signal transduction pathways modulated in vivo by AS[S]ODNs treatment. Tumors from AS[S]ODN-treated mice of both intratumoral and intravenous protocols showed a significant decrease in the degree of insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation. Activation of two of the main IGF-IR signaling pathways, phosphatidylinositol 3-kinase (PI-3K)/Akt and p42/p44 mitogen-activated protein kinases (MAPK) was abolished in tumors growing in AS[S]ODN-treated animals. Moreover, ErbB-2 tyrosine phosphorylation was blocked by in vivo administration of AS[S]ODNs. On the other hand, we found no regulation of either progesterone receptor expression or activity by in vivo AS[S]ODNs administration. Our results for the first time demonstrated that breast cancer growth can be inhibited by direct in vivo administration of IGF-IR AS[S]ODNs.

The insulin-like growth factor system in advanced breast cancer

Despite improvements in therapy, the prognosis for advanced breast cancer is poor and a search for new treatment targets and key regulators of tumour growth is warranted. Extensive data are available on the importance of the insulin-like growth factor (IGF) system in growth regulation of breast cancer cell lines in vitro, indicating that the IGF-I receptor (IGF-IR), IGF-I (and IGF-II) function as survival factors, while IGF binding protein (IGFBP)-3 may act as a growth inhibitor. There is a tight link between the growth regulatory pathways of IGFs and oestrogens in oestrogen-receptor(OR)-positive breast cancer cells. In vivo studies indicate a role of IGF-I and IGF-IR in breast cancer development. However, the importance of the IGF system in metastatic and highly aggressive breast tumours in vivo is not clear, and therapeutic strategies designed to interrupt IGF signalling have not yet proved to be an effective treatment modality in patients with metastatic breast cancer.

In vivo antitumor activity of NVP-AEW541-A novel, potent, and selective inhibitor of the IGF-IR kinase

IGF-IR-mediated signaling promotes survival, anchorage-independent growth, and oncogenic transformation, as well as tumor growth and metastasis formation in vivo. NVP-AEW541 is a pyrrolo[2,3-d]pyrimidine derivative small molecular weight kinase inhibitor of the IGF-IR, capable of distinguishing between the IGF-IR (IC50 = 0.086 microM) and the closely related InsR (IC50 = 2.3 microM) in cells. As expected for a specific IGF-IR kinase inhibitor, NVP-AEW541 abrogates IGF-I-mediated survival and colony formation in soft agar at concentrations that are consistent with inhibition of IGF-IR autophosphorylation. In vivo, this orally bioavailable compound inhibits IGF-IR signaling in tumor xenografts and significantly reduces the growth of IGF-IR-driven fibrosarcomas. Thus, NVP-AEW541 represents a class of selective, small molecule IGF-IR kinase inhibitors with proven in vivo antitumor activity and potential therapeutic application.

Anti-insulin-like growth factor strategies in breast cancer

The insulin-like growth factors (IGF-I and -II) are potent mitogens and survival factors for both normal and malignant breast cells. These effects are mediated primarily through the IGF-I receptor (IGF-IR), which is significantly overexpressed and highly activated in breast tumors. The IGF-binding proteins are competitive inhibitors of IGF/IGF-IR interaction, limiting cellular proliferation and survival. Higher serum IGF-I levels or an increased ratio of IGF-I to IGF binding protein-3 is associated with an increased risk of developing breast cancer. Hence, interest in the IGF system as a potential target for the development of novel antineoplastic therapies has ensued. Several strategies to interrupt IGF-IR signaling are currently being evaluated for the treatment of breast cancer, including suppression of IGF production, reduction of functional IGF-IR levels, neutralization of IGF action, and inhibition of IGF-IR activation.

IGF-1 receptor contributes to the malignant phenotype in human and canine osteosarcoma

To further define the role of insulin-like growth factor-1 (IGF-1) and its receptor (IGF-1R) in osteosarcoma (OS), human OS cell lines with low (SAOS-2) and high (SAOS-LM2) metastatic potential and three canine OS-derived cell lines were studied. Cell lines were evaluated for: IGF-1R expression; expression of IGF binding proteins (IGFBPs); effect of IGF-1 on tumor cell growth, invasion, expression of urokinase plasminogen activator (uPA), and soluble uPA receptor (suPAR), and; ectopic and orthotopic tumorigenicity of the canine OS cells in athymic mice. All cell lines exhibited steady-state mRNA expression of IGF-1R. The SAOS-2 and SAOS-LM2 cells expressed 9,138 and 10,234 cell-associated binding sites, respectively. Canine OS cells expressed from 1,728 to 3,883 binding sites. Two IGF-1-treated cell lines displayed enhanced proliferation. Two cell lines formed colonies in semisolid media, and IGF-1 increased colony number. Matrigel invasion was enhanced in one cell line following IGF-1 treatment. uPA and suPAR were unchanged in SAOS-2 and SAOS-LM2 cells following IGF-1 treatment, but the highly metastatic OS line SAOS-LM2 expressed five times more suPAR and displayed enhanced invasion compared to the parental, low metastatic SAOS-2. IGFBP-5 was detected in four of five cell lines, and IGFBP-3 was detected in two canine OS cell lines. Two canine OS lines were tumorigenic, and one metastasized spontaneously. In conclusion, OS cells express IGF-1R, which can contribute to their growth and invasion. There is suggestive evidence that increasing receptor number may contribute to in vivo tumorigenesis. Additional studies are needed to determine how IGF-1/IGF-1R interactions contribute to the malignant phenotype of OS.

Growth factor receptors as therapeutic targets: strategies to inhibit the insulin-like growth factor I receptor

Neoplastic transformation is often related to abnormal activation of growth factor receptors and their signaling pathways. The concept of targeting specific tumorigenic receptors and/or signaling molecules has been validated by the development and successful clinical application of drugs acting against the epidermal growth factor receptor 2 (HER2/neu, Erb2), the epidermal growth factor receptor 1 (EGFR, HER1), the Brc-Abl kinase, the platelet-derived growth factor receptor, and c-kit. This review will focus on the next promising therapeutic target, the insulin-like growth factor I receptor (IGF-IR). IGF-IR has been implicated in a number of neoplastic diseases, including several common carcinomas. From a pharmaceutical standpoint, of particular importance is that IGF-IR appears to be required for many transforming agents (genetic, viral, chemical) to act, but is not obligatory for the function of normal adult cells. The tumorigenic potential of IGF-IR is mediated through its antiapoptotic and transforming signaling, and in some cases through induction of prometastatic pathways. Preclinical studies demonstrated that downregulation of IGF-IR reversed the neoplastic phenotype and sensitized cells to antitumor treatments. The strategies to block IGF-IR function employed anti-IGF-IR antibodies, small-molecule inhibitors of the IGF-IR tyrosine kinase, antisense oligodeoxynucleotides and antisense RNA, small inhibitory RNA, triple helix, dominant-negative mutants, and various compounds reducing ligand availability. The experience with these strategies combined with the knowledge gained with current anti-growth factor receptor drugs should streamline the development of anti-IGF-IR therapeutics.

Suppression of mammary gland tumorigenesis in diabetic rats

The aim of this study was to compare mammary gland tumorigenesis in diabetic and non-diabetic rats. Streptozotocin and N-nitroso-N-methylurea were used to induce diabetes and mammary tumors, respectively. A suppression of mammary carcinogenesis in diabetic rats was shown by a longer latency period, a lower number of tumors per animal and a smaller final tumor volume. An 84% of the lesions developed in diabetic animals were benign tumors. Eighty day-old diabetic rats had significantly lower plasma levels of total-IGF-I and insulin versus non-diabetic rats. We postulate that the decrease in the total IGF-I and insulin levels during the promotion phase of carcinogenesis in this model plays an important role in retarding the tumor development in diabetic animals and in favoring the development of benign mammary lesions.

Effects of insulin-like growth factors-IR and -IIR antisense gene transfection on the biological behaviors of SMMC-7721 human hepatoma cells

BACKGROUND AND AIMS

Insulin-like growth factors (IGFs) are closely related to hepatocellular carcinoma growth. The study aim was to investigate the effects of IGF-IR and IGF-IIR antisense gene transfection on the biological behaviors of SMMC-7721 human hepatoma cells.

METHODS

7721-IGF-IR-AS cells (human hepatoma SMMC-7721 cells transfected with IGF-IR antisense gene in our previous study) were transfected with a plasmid vector expressing IGF-IIR cDNA in the antisense orientation by DOTAP liposome.7721-IGF-R-AS cells were obtained by selection with G418 and hygromycin. Morphological changes of the cells were observed with optic and electron microscopes. In vitro growth of the 7721-IGF-R-AS cells was observed with a soft agar test, MTT test and with naked mice inoculation test in vivo.

RESULTS

The following changes were found in the SMMC-7721 cells after being transfected with the IGF-IR and IGF-IIR antisense genes: (i) the degree of malignancy of the tumor cells as revealed by cell morphology was ameliorated; (ii) the growth capability of the tumor cells in soft agar and their tumorigenicity in naked mice were significantly depressed. However, in the control groups, the SMMC-7721 cells transfected both with IGF-IR and IGF-IIR sense cDNA and SMMC-7721 cells transfected without any external genes, had no such changes. However, the cell growth curves had no significant differences among these three groups.

CONCLUSION

IGF-IR and IGF-IIR antisense genes could significantly restrain the malignant behavior of human hepatoma cells and might be useful in investigating a potential route for hepatocellular carcinoma gene therapy.

Functional role of alpha-actinin, PI 3-kinase and MEK1/2 in insulin-like growth factor I receptor kinase regulated motility of human breast carcinoma cells

Within epithelial tissue, cells are held together by specialized lateral junctions. At particular stages of development and in pathological processes such as metastasis, cells break down the intercellular junctions, separate from the epithelial sheet and migrate individually. Despite the importance of these processes, little is understood about the regulatory mechanisms of active cell separation. In view of the effects of insulin-like growth factor I (IGF-I) on mammary gland development and cancer, we developed a model using MCF-7 human breast cancer cells in which the process of cell separation can be induced by IGF-I. The separation was enhanced in MCF-7 cells overexpressing the IGF-IR and blocked in the cells expressing a dead-kinase mutant of this receptor. Activation of the IGF-IR resulted in a rapid formation of motile actin microspikes at the regions of cell-cell contacts, disorganization of mature adherens junctions and the onset of cell migration. In cell separation, the signaling between the IGF-IR kinase and actin required phosphatidylinositol 3 (PI 3)-kinase-generated phospholipids but not MAP kinases and was mediated by alpha-actinin. The activity of MEK1/2 kinases was needed for consecutive cell migration. This work also defined a new function for alpha-actinin. Upon IGF-IR activation, green fluorescence protein (GFP)-labeled alpha-actinin concentrated at the base of actin microspikes. Deletion of the N-terminal actin-binding domain of alpha-actinin prevented this redistribution, indicating that this domain is necessary. Detection of the C-terminal tail of alpha-actinin reduced the number of microspikes, showing that alpha-actinin has a role in the development of microspikes and is not passively reorganized with filamentous actin. We suggest that the signaling pathway from the IGF-IR kinase through the PI-3 kinase to alpha-actinin participates in the rapid organization of actin into microspikes at the cell-cell junctions and leads to active cell separation, whereas signaling through ERK1/2 MAP kinases controls cell migration following cell separation.

Peripheral lymph node stromal cells can promote growth and tumorigenicity of breast carcinoma cells through the release of IGF-I and EGF

The regional lymph nodes draining primary breast carcinomas are generally the first site to be invaded by disseminating tumor cells. The extent of lymph node involvement remains the most reliable indicator for staging and prognosis of breast cancer. We have investigated host-tumor interactions between breast carcinoma cells and the lymph node stroma, which may control the outcome of lymph node infiltration. In a previous study, we identified integrin-mediated cell adhesion as a correlate of the metastatic potential of human and rat carcinoma cells. Our present objective was to determine whether lymphatic stromal cells can affect cancer cell growth through the elaboration of growth-modulating factors. Two lymphatic stromal cell lines, ST-A4 and ST-B12, were established from normal rat lymph node stromal cell cultures. SFM conditioned by these cells increased the proliferation of human (Hs578T and MCF-7) and rat (TMT-081) breast carcinoma cells by up to 7-fold and augmented their ability to form colonies in semisolid agar by up to 41-fold. This effect was specific as normal, diploid human breast epithelial cells (Hs578Bst), a nontumorigenic, immortalized human breast epithelial cell line (MCF-10A) and a nonmetastatic rat mammary carcinoma cell line (MT-W9B) had either no or reduced responses. RT-PCR analysis revealed that both lymph node stromal cell lines expressed mRNA transcripts for multiple growth factors, including IGF-I, EGF, HGF and PDGF-alpha, and produced detectable levels of IGF-I, EGF and PDGF-alpha, as assessed by Western blotting. Antibody-mediated depletion assays identified IGF-I and EGF as the major mitogenic factors in the CM. The identification of these cells raises the possibility that the lymph node microenvironment may contribute actively to the process of cancer cell dissemination.

Induction of fascin spikes in breast cancer cells by activation of the insulin-like growth factor-I receptor

Insulin-like growth factor-I receptor (IGF-IR) signaling contributes to the formation of mammary carcinomas and has chiefly been studied with regard to the proliferative and anti-apoptotic effects of IGF-IR signaling. However, IGF-IR activation also affects the actin cytoskeleton and alterations in cell migratory behavior are of known importance for the malignant conversion and metastasis of epithelial cells. The actin-binding protein fascin is found in cell projections and spikes that are involved in the locomotion of mesenchymal cells. Fascin expression is typically low in normal epithelial cells, but is markedly upregulated in several types of carcinomas. Here, we also demonstrate increased fascin expression in breast carcinoma cell lines and adopt MCF-7 human mammary carcinoma cells that over-express wild-type or kinase-inactivated forms of the IGF-IR as a model system to test the hypothesis that IGF-IR activation induces fascin projections. We show that the time-dependent dissociation of cell colonies that occurs upon receptor activation by IGF-I involves the formation of dynamic, fascin-containing lateral cell projections that co-localize with ruffling membranes in association with protrusive activity and cell migratory phenotype. The molecular mechanism of these effects is completely dependent on IGF-IR tyrosine kinase activity and is mediated by a phosphatidylinositol (PI) 3-kinase-dependent process. In demonstrating transduction of fascin spike assembly by activation of a peptide growth factor receptor, these novel data reveal a wide role for fascin spikes in cell motility and provide new insight into the complex effects of IGF-IR signaling on actin cytoskeletal organization.

Gene targets of antisense therapies in breast cancer

Advances in molecular and cell biology have led to further understanding of the mechanisms of malignant growth and metastasis in human breast cancer cells. Initiation and progression of breast cancer results from mutations and the abnormal expression of many genes that control cellular proliferation, differentiation, invasion, metastasis and sensitivity to therapy (chemotherapy and radiation therapy). Inhibition of host immunity also plays a role in breast cancer progression. Many genes have been selected as targets for antisense therapy, including HER-2/neu, PKA, TGF-alpha, EGFR, TGF-beta, IGFIR, P12, MDM2, BRCA, Bcl-2, ER, VEGF, MDR, ferritin, transferrin receptor, IRE, C-fos, HSP27, C-myc, C-raf and metallothionein genes. The strategy behind antisense therapy is the development of specific therapeutic agents that aim to correct the mutations and abnormal expression of cellular genes in breast tumour cells by decreasing gene expression, inducing degradation of target mRNA and causing premature termination of transcription. Many in vitro and in vivo studies have investigated the therapeutic efficacy of oligonucleotides and antisense RNAs. These studies have demonstrated specific inhibition of tumour cell growth by antisense therapy and have shown synergistic inhibitory effects between antisense oligonucleotides or antisense RNA and conventional chemotherapeutic drugs used in the treatment of breast cancer. Antisense oligonucleotides have been modified to improve their ability to penetrate cells, bind to gene sequences and downregulate target gene function. Many delivery systems for antisense RNA and antisense oligonucleotides have been developed, including virus vectors (retrovirus, adenovirus and adeno-associate virus) and liposomes, to carry the antisense RNA or oligonucleotides through the cell membrane into the cytoplasm and nucleus of the tumour cells. However, in order to determine their feasibility antisense therapies need to be further investigated to determine their antitumour activity, pharmacokinetics and toxicity in breast cancer patients.

Treatment of murine breast cancer cells with antisense RNA to the type I insulin-like growth factor receptor decreases the level of plasminogen activator transcripts, inhibits cell growth in vitro, and reduces tumorigenesis in vivo

AIMS

To establish that cells from the murine mammary carcinoma cell line, EMT6, express type I insulin-like growth factor receptor (IGF-IR), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA). To investigate the role of IGF-IR in growth, transformation, and tumorigenesis in addition to its relation to tPA and uPA in EMT6 cells. To assess the suitability of the EMT6/syngeneic mouse model for studying the role of IGF-IR in tumorigenesis.

METHODS

The presence of transcripts for IGF-IR, tPA, and uPA was determined by northern blot analysis using poly (A(+)) RNA derived from EMT6 cells transfected with an antisense IGF-IR construct or a construct lacking the antisense IGF-IR insert. Flow cytometry was used to measure IGF-IR protein. Assays were performed to determine cell proliferation, transformation, and the tumorigenicity of antisense IGF-IR transfected EMT6 cells and control transfected EMT6 cells.

RESULTS

There was strong expression of IGF-IR, tPA, and uPA in EMT6 cells. EMT6 cells from clones carrying antisense IGF-IR displayed a significant decrease in cell proliferation and lost the ability to form colonies in soft agar. A decrease in tumour size occurred when cells carrying the antisense IGF-IR were injected into syngeneic mice. Reduced expression of tPA and uPA was seen in EMT6 cells carrying the antisense IGF-IR construct.

CONCLUSIONS

The IGF-IR plays a role in the progression, transformation, and tumorigenesis of EMT6 murine mammary carcinoma cells. The suppression of IGF-IR mRNA in EMT6 cells decreases tPA and uPA expression. EMT6 cells and the syngeneic mouse provide a suitable model for studying the role of IGF-IR in breast tumour progression.

Effectiveness of insulin-like growth factor I receptor antisense strategy against Ewing's sarcoma cells

The insulin-like growth factor I receptor (IGF-IR) plays an essential role in the establishment and maintenance of transformed phenotype of Ewing's sarcoma (ES) cells, and interference with the IGF-IR pathways by a neutralizing antibody causes reversal of the malignant potential of this neoplasm. In this paper, we stably transfected an IGF-IR antisense mRNA expression plasmid in an ES cell line to determine the effectiveness of antisense strategies against the in vitro and in vivo growth of ES cells. Doxorubicin sensitivity of TC-71 cells expressing antisense targeted to IGF-IR mRNA was also examined. Cells carrying antisense IGF-IR had a reduced expression of the receptor, a modest decrease in cell proliferation, a significant increase in anoikis-induced apoptosis, and a severely reduced ability to form colonies in soft agar. Moreover, TC/AS cells showed a marked reduction in their motility. In vivo, when cells carrying antisense IGF-IR were injected subcutaneously in nude mice, tumor formation was delayed and survival increased. Metastatic ability of ES cells was also significantly reduced. Furthermore, TC/AS clones showed a significantly higher sensitivity to doxorubicin - a major drug in the treatment of ES. These results indicate that inhibiting IGF-IR by antisense strategies may be relevant to the clinical treatment of ES patients by reducing the malignant potential of these cells and enhancing the effectiveness of chemotherapy.