Inhibition of insulin-like growth factor-1 receptor signaling enhances growth-inhibitory and proapoptotic effects of gefitinib (Iressa) in human breast cancer cells

Discovery of a 2,4-disubstituted pyrrolo[1,2-f][1,2,4]triazine inhibitor (BMS-754807) of insulin-like growth factor receptor (IGF-1R) kinase in clinical development

This report describes the biological activity, characterization, and SAR leading to 9d (BMS-754807) a small molecule IGF-1R kinase inhibitor in clinical development.

A selective eradication of human nonhereditary breast cancer cells by phenanthridine-derived polyADP-ribose polymerase inhibitors

Introduction

PARP-1 (polyADP-ribose polymerase-1) is known to be activated in response to DNA damage, and activated PARP-1 promotes DNA repair. However, a recently disclosed alternative mechanism of PARP-1 activation by phosphorylated externally regulated kinase (ERK) implicates PARP-1 in a vast number of signal-transduction networks in the cell. Here, PARP-1 activation was examined for its possible effects on cell proliferation in both normal and malignant cells.

Methods

In vitro (cell cultures) and in vivo (xenotransplants) experiments were performed.

Results

Phenanthridine-derived PARP inhibitors interfered with cell proliferation by causing G₂/M arrest in both normal (human epithelial cells MCF10A and mouse embryonic fibroblasts) and human breast cancer cells MCF-7 and MDA231. However, whereas the normal cells were only transiently arrested, G₂/M arrest in the malignant breast cancer cells was permanent and was accompanied by a massive cell death. In accordance, treatment with a phenanthridine-derived PARP inhibitor prevented the development of MCF-7 and MDA231 xenotransplants in female nude mice. Quiescent cells (neurons and cardiomyocytes) are not impaired by these PARP inhibitors.

Conclusions

These results outline a new therapeutic approach for a selective eradication of abundant nonhereditary human breast cancers.

Targeting insulin-like growth factor type 1 receptor in cancer therapy

It is believed that the insulin-like growth factor receptor type 1 (IGF-1R) signaling pathway plays a pivotal role in cancer growth, progression, and resistance to anticancer therapies. Strategies are being developed to block IGF-1R as an anticancer treatment. We reviewed several potential strategies for disrupting the IGF axis. We also reviewed the effects of two drugs that target the IGF-1R: monoclonal antibodies and tyrosine kinase inhibitors. Preliminary results of studies involving these agents provided a foundation for ongoing clinical trials, whose results in the near future will help us understand how to incorporate anti IGF-1R strategies into the current anticancer armamentarium.

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

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

Determinants of response to epidermal growth factor receptor tyrosine kinase inhibition in squamous cell carcinoma of the head and neck

Dramatic responses to epidermal growth factor receptor (EGFR) tyrosine kinase (TK) inhibitors may be seen in non-small cell lung cancers (NSCLCs) with a sensitizing mutation of the EGFR TK domain. It is not known how to predict response in patients with squamous cell carcinoma of the head and neck (SCCHN), where EGFR TK mutations are less frequent and where response rates in unselected patients are disappointing. We have characterized the intrinsic sensitivity of a panel of 18 SCCHN cell lines to gefitinib, an EGFR TK inhibitor, and have investigated correlations between putative markers of response and intrinsic sensitivity. Induction of G1 arrest was only seen in cell lines with GI(50) < 1 microM. Expression of EGFR, by three techniques, correlated with sensitivity to gefitinib. ERB-B2 expression appeared to influence sensitivity to gefitinib but ERB-B3 expression did not. While EGFR tyrosine kinase mutations were not detected, EGFR gene amplification was confirmed by fluorescence in situ hybridization in the most sensitive cell line. The number of cytosine adenine dinucleotide repeats in intron 1 of the EGFR gene did not correlate with sensitivity. E-cadherin expression was detected in cell lines with a range of sensitivities, whereas amphiregulin was secreted predominantly by sensitive cell lines. MET expression was an independent predictor of sensitivity to gefitinib, although neither expression nor phosphorylation of insulin-like growth factor 1 receptor correlated with intrinsic resistance. Breast receptor kinase (BRK) was more highly expressed in the sensitive cell lines, but siRNA knockdown of neither BRK nor MET affected sensitivity. Our data suggest that overexpression of EGFR and multiple related cell surface receptors may be associated with sensitivity to gefitinib and that differences between our data and the literature highlight that biomarkers of response are tumour type- and cell line-dependent.

Inhibition of the insulin-like growth factor 1 receptor pathway enhances the antitumor effect of cisplatin in human malignant mesothelioma cell lines

Human malignant mesothelioma (HMM) is a fatal tumor and is poorly responsive to current therapeutic regimens. The insulin-like growth factor 1 receptor (IGF-1R) pathway is activated in HMM cell lines and tissues. Treatment with AG1024, an inhibitor of the IGF-1R pathway, significantly decreased cell proliferation and attenuated the phosphorylation of Akt and p44/42. In addition, it significantly enhanced the cytotoxic effects of cisplatin in HMM cell lines. This study supports the conjecture that inhibition of the IGF-1R pathway may be a useful target for reducing toxicity and alleviating chemoresistance to traditional anticancer drugs in HMM patients.

Co-targeting the insulin-like growth factor I receptor enhances growth-inhibitory and pro-apoptotic effects of anti-estrogens in human breast cancer cell lines

The insulin-like growth factor I receptor (IGF1R) interacts with estrogen receptor-alpha (ERalpha) and HER2. We examined the effect of combinations of IGF1R antagonists (alpha-IR3, AG1024) and anti-estrogens (4-hydroxy tamoxifen, fulvestrant) in two human ER+ breast cancer cell lines: BT474 (HER2 overexpressing, IGF1R low) and MCF7 (HER2 non-overexpressing, IGF1R high). In BT474 cells, growth was inhibited by anti-estrogens, but not by IGF1R antagonists; however, adding IGF1R inhibitors to anti-estrogens enhanced growth inhibition. In MCF7 cells, growth was inhibited by IGF1R and ER antagonists and more so by their combination. In both cell lines, no single agents could induce apoptosis, but combining IGF1R inhibitors with anti-estrogens induced dramatic levels of apoptosis. IGF1R antagonists enhanced the ability of the anti-estrogens to inhibit ER transcriptional activity in BT474 cells, but not in MCF7 cells. The drug combination synergistically inhibited ER and IGF1R activity. Such combinations may be useful therapy for breast cancer.

The mechanisms of differential sensitivity to an insulin-like growth factor-1 receptor inhibitor (BMS-536924) and rationale for combining with EGFR/HER2 inhibitors

Overexpression and enhanced activity of insulin-like growth factor-I receptor (IGF-IR) in diverse tumor types make it an attractive target for cancer therapy. BMS-536924 is a potent small molecule inhibitor of IGF-IR, which shows antitumor activity in multiple tumor models, including sarcoma. To facilitate the development of IGF-IR inhibitors as cancer therapy, identification of biomarkers for selecting patients most likely to derive clinical benefit is needed. To do so, 28 sarcoma and neuroblastoma cell lines were screened for in vitro response to BMS-536924 to identify sensitive and resistant cell lines. Notably, Ewing's sarcoma, rhabdomyosarcoma, and neuroblastoma are more responsive to BMS-536924, suggesting these specific subtypes may represent potential targeted patient subpopulations for the IGF-IR inhibitor. Gene expression and protein profiling were performed on these cell lines, and candidate biomarkers correlating with intrinsic and/or acquired resistance to BMS-536924 were identified. IGF-I, IGF-II, and IGF-IR were highly expressed in sensitive cell lines, whereas IGFBP-3 and IGFBP-6 were highly expressed in resistant lines. Overexpression of epidermal growth factor receptor (EGFR) and its ligands in resistant cell lines may represent one possible resistance mechanism by the adaptation of IGF-IR-independent growth using alternative signaling pathways. Based on cross-talk between IGF-IR and EGFR pathways, combination studies to target both pathways were performed, and enhanced inhibitory activities were observed. These results provide a strategy for testing combinations of IGF-IR inhibitors with other targeted therapies in clinical studies to achieve improved patient outcomes. Further exploration of mechanisms for intrinsic and acquired drug resistance by these preclinical studies may lead to more rationally designed drugs that target multiple pathways for enhanced antitumor efficacy.

Cross-talk between the ErbB/HER family and the type I insulin-like growth factor receptor signaling pathway in breast cancer

Understanding the molecular mechanisms involved in tumorigenesis and their influence on clinical outcome is providing specific molecular markers for targeted therapy. Activation of tyrosine kinase receptors from the human epidermal growth factor receptor family (EGFR, HER2, HER3, HER4) and the insulin-like growth factor receptor I (IGF-IR) plays a key role in the initiation and progression of breast cancer. HER2 overexpression is a validated therapeutic target, as shown by the clinical efficacy of trastuzumab and lapatinib. However, only 25-30% of patients with HER2-overexpressing tumors respond to single-agent trastuzumab or lapatinib, and resistance develops even in responding patients. Therefore, to optimize therapeutic efficacy, it is urgent to elucidate the complex network of signaling pathways that develop in breast cancer cells. Signaling interactions have been reported between ErbB/HER family members and IGF-IR. As increased IGF-IR signaling has been implicated in trastuzumab resistance, agents targeting HER2, and IGF-IR could be potential therapeutic tools in breast cancers that develop resistance to HER2-directed therapy.

Mechanisms of resistance to ErbB-targeted cancer therapeutics

The ErbB receptors, such as EGFR, have been intensely pursued as targets for cancer therapeutics. However, a large percentage of patients who are initially responsive to ErbB-targeted therapies experience tumor recurrence and become refractory to therapy. In this issue of the JCI, Guix et al. demonstrate that downregulation of IGF-binding protein 3 (IGFBP-3) and -4, the negative regulators of IGF-I receptor signaling, contributes to the resistance of human squamous cell carcinomas to the EGFR inhibitor gefitinib (see the related article beginning on page 2609). Understanding the mechanisms involved in the resistance of some tumors to ErbB-targeted molecules may provide guidelines for developing more efficient therapeutic approaches.

The aromatase inhibitor letrozole and inhibitors of insulin-like growth factor I receptor synergistically induce apoptosis in in vitro models of estrogen-dependent breast cancer

Introduction

Endocrine-dependent, estrogen receptor positive breast cancer cells proliferate in response to estrogens, synthesized by the cytochrome p450 aromatase enzyme. Letrozole is a potent nonsteroidal aromatase inhibitor that is registered for the treatment of postmenopausal women with advanced metastatic breast cancers and in the neoadjuvant, early, and extended adjuvant indications. Because crosstalk exists between estrogen receptor and insulin-like growth factor I receptor (IGF-IR), the effect of combining a selective IGF-IR inhibitor (NVP-AEW541) with letrozole was assessed in two independent in vitro models of estrogen-dependent breast cancer.

Methods

MCF7 and T47D cells stably expressing aromatase (MCF7/Aro and T47D/Aro) were used as in vitro models of aromatase-driven breast cancer. The role of the IGF-IR pathway in breast cancer cells stimulated only by 17β-estradiol or androstenedione was assessed by proliferation assays. The combination of letrozole and NVP-AEW541 was assessed for synergy in inhibiting cell proliferation using Chou-Talalay derived equations. Finally, combination or single agent effects on proliferation and apoptosis were assessed using proliferation assays, flow cytometry, and immunoblotting.

Results

Both MCF7 and T47D cells, as well as MCF7/Aro and T47D/Aro, exhibited sensitivity to inhibition of 17β-estradiol dependent proliferation by NVP-AEW541. Letrozole combined with NVP-AEW541 synergistically inhibited androstenedione-dependent proliferation in aromatase-expressing cells with combination index values of 0.6 or less. Synergistic combination effects correlated with higher levels of apoptosis as compared with cells treated with the single agent alone. Treatment with either agent also appeared to inhibit IGF-IR signalling via phosphoinositide 3-kinase. Notably, IGF-IR inhibition had limited effect on estrogen-dependent proliferation in the cell lines, but was clearly required for survival, suggesting that the combination of letrozole and IGF-IR inhibition sensitizes cells to apoptosis.

Conclusion

Inhibition of the IGF-IR pathway and aromatase was synergistic in two independent estrogen-dependent in vitro models of breast cancer. Moreover, synergism of NVP-AEW541 and letrozole correlated with induction of apoptosis, but not cell cycle arrest, in the cell lines tested. Combination of IGF-IR inhibitors and letrozole may hold promise for the treatment of patients with estrogen-dependent breast cancers.

Insulin-like growth factor-1 receptor and ErbB kinase inhibitor combinations block proliferation and induce apoptosis through cyclin D1 reduction and Bax activation

The insulin-like growth factor-1 receptor (IGF-1R) and ErbB family of receptors are receptor tyrosine kinases that play important roles in cancer. Lack of response and resistance to therapies targeting ErbB receptors occur and are often associated with activation of the IGF-1R pathway. Combinations of agents that inhibit IGF-1R and ErbB receptors have been shown to synergistically block cancer cell proliferation and xenograft tumor growth. To determine the mechanism by which targeting both IGF-1R and ErbB receptors causes synergistic effects on cell growth and survival, we investigated the effects of combinations of selective IGF-1R and ErbB kinase inhibitors on proliferative and apoptotic signaling. We identified A431 squamous cell carcinoma cells as most sensitive to combinations of ErbB and IGF-1R inhibitors. The inhibitor combinations resulted in not only blockade of A431 cell proliferation, but also induced apoptosis, which was not seen with either agent alone. Upon examining phosphorylation states and expression levels of proteins in the IGF-1R and ErbB signaling pathways, we found a correlation between the ability of combinations to inhibit proliferation and to decrease levels of phosphorylated Akt and cyclin D1. In addition, the massive cell death induced by combined IGF-1R/ErbB inhibition was associated with Mcl-1 reduction and Bax activation. Thus, targeting both IGF-1R and ErbB receptors simultaneously results in cell cycle arrest and apoptosis through combined effects on Akt, cyclin D1, and Bax activation.

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.

Epithelial-to-mesenchymal transition and integrin-linked kinase mediate sensitivity to epidermal growth factor receptor inhibition in human hepatoma cells

Hepatocellular carcinoma (HCC) is associated with a poor prognosis due to late diagnoses and a lack of effective treatment options. Epidermal growth factor receptor (EGFR)-targeted therapies have been effective in other cancers. However, erlotinib and cetuximab have shown only modest efficacy in clinical trials of HCC. We examined epithelial-to-mesenchymal transition (EMT) as a determinant of sensitivity of HCC to EGFR inhibitors. A panel of 12 human hepatoma cell lines were classified as epithelial or mesenchymal based on their expression of E-cadherin and vimentin. The resulting classification correlated with a previous microarray analysis of human hepatoma cell lines whereby the mesenchymal cell lines were shown to have increased expression of genes involved in metastasis and invasion. Sensitivity to erlotinib, gefitinib, and cetuximab was assessed and the epithelial cell lines were found to be significantly more susceptible to all three agents. Analysis of the EGFR pathway showed that EMT status was independent of EGFR expression or downstream extracellular signal-regulated kinase activation and only the epithelial cell lines expressed ErbB3. Interestingly, mesenchymal cells resistant to EGFR inhibitors had increased AKT and signal transducer and activator of transcription-3 activation through elevated expression of integrin-linked kinase (ILK). Mesenchymal cell lines were therefore experimentally transformed with kinase-inactive ILK (KI-ILK) with a resulting decrease in ILK activity and activation of AKT. KI-ILK transformants showed increased sensitivity to EGFR inhibitors both in vitro and in an in vivo xenograft model. These data suggest that EMT predicts HCC sensitivity to EGFR-targeted therapies and that ILK is a novel target to overcome HCC resistance to EGFR inhibition.

Co-targeting insulin-like growth factor I receptor and HER2: dramatic effects of HER2 inhibitors on nonoverexpressing breast cancer

The insulin-like growth factor I receptor (IGFIR) and HER2 display important signaling interactions in breast cancer. We examined the effect of combinations of antagonists of these receptors using two human breast cancer cell lines: BT474 (HER2+, IGFIR low) and MCF7 (HER2 low, IGFIR high). In BT474 cells, growth was inhibited by HER2 antagonists but not by IGFIR antagonists; however, IGFIR antagonists enhanced the effect of HER2 inhibitors. In MCF7 cells, growth was inhibited by IGFIR antagonists but not by HER2 antagonists; however, HER2 antagonism enhanced the effect of IGFIR inhibitors. Synergistic inhibition of soft agar growth was also observed. Although HER2 and IGFIR antagonists individually only minimally affected cell cycle, their combination gave a small enhancement of their effects. No single receptor-targeting drug was capable of inducing apoptosis, but combining antagonists of both receptors induced a dramatic degree of apoptosis in both cell lines. Induction of apoptosis was most striking in MCF7 cells using a Herceptin/IGFIR antagonist combination despite these cells being HER2 nonoverexpressing. Toward understanding the mechanism of these effects, we detected coassociation IGFIR and HER2 in both cell lines. Specific inhibitors of one of these receptors could cross-inhibit the activity of the other. Targeting both receptors gave the maximal inhibition of their downstream extracellular signal-regulated kinase 1/2 and AKT signaling pathways. Hence, such drug combinations may be clinically useful and may be beneficial even in tumors in which single drugs are inactive, as exemplified by the effect of the HER2/IGFIR inhibitor combination in HER2 nonoverexpressing MCF7 cells.

The role of insulin receptors and IGF-I receptors in cancer and other diseases

There is evidence, both in vitro and in vivo, that receptor tyrosine kinases play a key role in the formation and progression of human cancer. In particular, the insulin-like growth factor receptor (IGF-IR), a tyrosine kinase receptor for IGF-I and IGF-II, has been well documented in cell culture, animal studies, and humans to play a role in malignant transformation, progression, protection from apoptosis, and metastasis. In addition, the hormone insulin (which is very closely related to the IGFs) and its tyrosine kinase receptor (the IR, which is very closely related to the IGR-IR) have been documented both in vitro and in vivo to play a key role in cancer biology. Indeed, several epidemiological studies have shown that insulin resistance status, characterized by hyperinsulinaemia, is associated with an increased risk for a number of malignancies, including carcinomas of the breast, prostate, colon and kidney. Recent data have elucidated some molecular mechanisms by which IR is involved in cancer. IR is over-expressed in several human malignancies. Interestingly, one of the two IR isoform (IR-A) is especially over-expressed in cancer. IR-A is the IR foetal isoform and has the peculiar characteristic to bind not only insulin but also IGF-II. In addition, the IR contributes to formation of hybrid receptors with the IGF-IR (HR). By binding to hybrid receptors, insulin may stimulate specific IGF-IR signalling pathways. Over-expression of IR-A is, therefore, a major mechanism of IGF system over-activation in cancer. In this respect, IR-A isoform and hybrid receptors should be regarded as potential molecular targets, in addition to IGF-IR, for novel anti-cancer therapy. These findings may have important implications for both the prevention and treatment of common human malignancies. They underline the concept that hyperinsulinaemia, associated with insulin resistance and obesity, should be treated by changes in life style and/or pharmacological approaches to avoid an increased risk for cancer. Moreover, native insulin and insulin analogue administration should be carefully evaluated in terms of the possible increase in cancer risk.

EGCG inhibits activation of the insulin-like growth factor (IGF)/IGF-1 receptor axis in human hepatocellular carcinoma cells

The receptor tyrosine kinase (RTK) insulin like growth factor-1 (IGF-1)/IGF-1 receptor (IGF-1R) axis plays an important role in the development of hepatocellular carcinoma (HCC). EGCG inhibits activation of the various types of RTKs and that this is associated with inhibition of multiple downstream signaling pathways. In this study we examined the effects of EGCG on activity of the IGF/IGF-1R axis in HepG2 human HCC cells which express constitutive activation of this axis. The level of phosphorylated (i.e. activated) form of the IGF-1R protein (p-IGF-1R) was increased in a series of human HCC cell lines when compared with the Hc normal human hepatocytes. EGCG preferentially inhibited growth of HepG2 cells when compared with Hc cells. Treatment of HepG2 cells with EGCG induced apoptosis and caused a decrease in the p-IGF-1R protein and its downstream signaling molecules including the p-ERK, p-Akt, p-Stat-3, and p-GSK-3β proteins, both in the absence or presence of ligand stimulation. EGCG also decreased the levels of both IGF-1 and IGF-2 proteins and mRNAs, but increased the levels of the IGFBP-3 protein. These findings suggest that EGCG can overcome the stimulatory effects of IGFs on the IGF-1R dependent signaling pathway, thus expanding the roles of EGCG as an inhibitor of critical RTKs involved in HCC cell proliferation. These results provide further evidence that EGCG may be useful in the chemoprevention or treatment of liver cancer.

Mechanisms of disease: signaling of the insulin-like growth factor 1 receptor pathway--therapeutic perspectives in cancer

The insulin-like growth factor 1 (IGF1) signaling pathway is implicated in the development of cancer. High levels of circulating IGF1 and certain genetic polymorphisms of IGF1 and IGFBP3 are associated with an increased risk of several common cancers. The IGF1 receptor (IGF1R) has been shown to be expressed in a wide range of tumors, and IGF1R signaling is crucial for tumor transformation and the survival of malignant cells. Several monoclonal antibodies and small-molecule inhibitors have been tested in preclinical studies and early-phase clinical studies. IGF1R signaling interferes with numerous growth factors and receptors such as VEGF and EGFR. In the experimental system, IGF1R signaling has been found to correlate with resistance to therapies based on the inhibition of EGFR and HER2. This Review highlights the most relevant studies in this exciting area of research, focusing in particular on the role of IGF1R in resistance to other receptor-targeted therapies for cancer.

Insulin receptor substrate-1 involvement in epidermal growth factor receptor and insulin-like growth factor receptor signalling: implication for Gefitinib ('Iressa') response and resistance

Classically the insulin receptor substrate-1 (IRS-1) is an essential component of insulin-like growth factor type 1 receptor (IGF-IR) signalling, providing an interface between the receptor and key downstream signalling cascades. Here, however, we show that in tamoxifen-resistant MCF-7 (Tam-R) breast cancer cells, that are highly dependent on epidermal growth factor receptor (EGFR) for growth, IRS-1 can interact with EGFR and be preferentially phosphorylated on tyrosine (Y) 896, a Grb2 binding site. Indeed, phosphorylation of this site is greatly enhanced by exposure of these cells, and other EGFR-positive cell lines, to EGF. Importantly, while IGF-II promotes phosphorylation of IRS-1 on Y612, a PI3-K recruitment site, it has limited effect on Y896 phosphorylation in Tam-R cells. Furthermore, EGF and IGF-II co-treatment, reduces the ability of IGF-II to phosphorylate Y612, whilst maintaining Y896 phosphorylation, suggesting that the EGFR is the dominant recruiter of IRS-1 in this cell line. Significantly, challenge of Tam-R cells with the EGFR-selective tyrosine kinase inhibitor gefitinib, for 7 days, reduces IRS-1/EGFR association and IRS-1 Y896 phosphorylation, while promoting IRS-1/IGF-IR association and IRS-1 Y612 phosphorylation. Furthermore, gefitinib significantly enhances IGF-II-mediated phosphorylation of IRS-1 Y612 and AKT in Tam-R cells. Importantly, induction of this pathway by gefitinib can be abrogated by inhibition/downregulation of the IGF-IR. Our data would therefore suggest a novel association exists between the EGFR and IRS-1 in several EGFR-positive cancer cell lines. This association acts to promote phosphorylation of IRS-1 at Y896 and drive MAPK signalling whilst preventing recruitment of IRS-1 by the IGF-IR and inhibiting signalling via this receptor. Treatment with gefitinib alters the dynamics of this system, promoting IGF-IR signalling, the dominant gefitinib-resistant growth regulatory pathway in Tam-R cells, thus, potentially limiting its efficacy.

siRNA mediated the type 1 insulin-like growth factor receptor and epidermal growth factor receptor silencing induces chemosensitization of liver cancer cells

PURPOSE

This study was to investigate if downregulation of IGF1R and EGFR by RNA interference (RNAi) would sensitize human liver cancer cells (HEPG2, Huh7 ) to adriamycin.

METHODS

HEPG2, Huh7 cell lines were transfected IGF1R siRNAs and EGFR siRNAs and IGF1R or EGFR mRNA level was determined by RT-PCR and Western-blot analysis. We investigated the effects of the adriamycin-induced apoptosis of these cells by TUNEL assay. Also we analyze caspase3, 8 and the phosphorylation levels of Akt and Erk by Western-blot. The p53 effect of adriamycin-induced cell death by inhibitors of EGFR/IGF1R is investigated by cell growth curves.

RESULTS

Transfection of an IGF1R and EGFR siRNAs resulted in substantial loss of IGF1R and EGFR mRNA of HEPG2, Huh7 cells relative to the control case. EGFR siRNA and IGF1R siRNA treatments increased the adriamycin-induced apoptosis of these cells. IGF1R siRNA and EGFR siRNA enhance a caspase-dependent cell death program. The phosphorylation levels of Akt and Erk were reduced by the combination of the two agents. The facilitation of adriamycin-induced cell death by inhibitors of EGFR/IGF1R is p53-independent.

CONCLUSIONS

The results indicate that the siRNA for IGF1R has a great potential for cancer therapy when combined with either a chemotherapeutic agent or siRNAs that targets EGFR.

Acquired resistance to erlotinib in A-431 epidermoid cancer cells requires down-regulation of MMAC1/PTEN and up-regulation of phosphorylated Akt

Erlotinib (Tarceva), an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, has clinical activity in advanced lung cancer, but disease that initially responds to erlotinib eventually progresses. The mechanism of this acquired resistance is unclear. We established two erlotinib-resistant pools of A-431 cells, a well-characterized epidermoid cancer cell line that constitutively overexpresses EGFR and is sensitive to erlotinib, by continuous exposure to erlotinib over a 6-month period. The extent of EGFR gene amplification or mutation of the EGFR tyrosine kinase domain was not altered in the resistant cells. Intracellular erlotinib concentrations, determined by liquid chromatography-tandem mass spectrometry, were almost the same in all three cell lines. Immunoprecipitation with EGFR antibody followed by detection with phosphotyrosine antibody revealed that erlotinib effectively reduced EGFR phosphorylation in both parental cells and resistant cells. Erlotinib induced mutated in multiple advanced cancers 1/phosphatase and tensin homologue (MMAC1/PTEN) and suppressed phosphorylated Akt (Ser(473)) but not in the erlotinib-resistant cells. Overexpression of MMAC1/PTEN by transfection with Ad.MMAC1/PTEN or by pharmacologic suppression of Akt activity restored erlotinib sensitivity in both resistant pools. Further, transfection of parental A-431 cells with constitutively active Akt was sufficient to cause resistance to erlotinib. We propose that acquired erlotinib resistance associated with MMAC1/PTEN down-regulation and Akt activation could be overcome by inhibitors of signaling through the phosphatidylinositol 3-kinase pathway.

Growth factor signalling in endocrine and anti-growth factor resistant breast cancer

Growth factors provide powerful mitogenic and survival signals to breast cancer cells and it is therefore not surprising that they are able to subvert inhibitory responses to anti-hormonal drugs. In this review we discuss several mechanisms by which this may be achieved and expand our observations to encompass recently emerging anti-growth factor treatments. The information presented is underpinned by inhibitor studies that show the targeting of such mechanisms in advance of anti-hormone or anti-growth factor resistance development is able to substantially delay this event, thus pointing the way forward to intelligent combination therapies relevant to the future management of breast cancer.

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.

The type 1 insulin-like growth factor receptor is over-expressed in bladder cancer

OBJECTIVE

To analyse bladder cancer biopsies and investigate the pattern of expression of the type 1 insulin-like growth factor receptor (IGF1R), a receptor tyrosine kinase that mediates tumour cell proliferation, motility and protection from apoptosis.

MATERIALS AND METHODS

Formalin-fixed specimens of bladder cancer (40 whole-mount, 80 cores on a tumour microarray) and normal bladder (15 samples) were stained immunohistochemically for the IGF1R. The IGF1R expression was also measured by quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) on RNA extracted from fresh frozen bladder cancers (61) and benign bladder (12).

RESULTS

Of the 15 samples of normal bladder, 14 showed negligible (1+) or light (2+) IGF1R immunostaining. By contrast moderate (3+) or heavy (4+) staining for IGF1R was detected in 89 (74%) of the 120 samples of malignant urothelium. Q-RT-PCR showed significantly higher levels of steady-state IGF1R mRNA in tumours (all cases, Ta-T4) than in normal bladder (P < 0.05), indicating up-regulation at the transcriptional level. This difference was particularly evident when comparing normal urothelium with superficial (Ta-T1) or invasive (T2-4) tumours; only the latter showed significant IGF1R over-expression at the RNA level (P < 0.05 vs normal bladder).

CONCLUSION

The IGF1R is up-regulated in bladder cancer compared with non-malignant bladder, and might contribute to a propensity for invasion.

Cdc42: an effector and regulator of ErbB1 as a strategic target in breast cancer therapy

ErbB1 and ErbB2 are often overexpressed in breast cancer. Overexpression of these receptors is correlated with poor prognosis. ErbB receptor-targeted therapies have been developed for the treatment of human breast cancer. While ErbB2 overexpression is usually caused by gene amplification, the mechanism for ErbB1 overexpression remains elusive. An important mechanism for the downregulation of ErbB1 is via Cbl-mediated receptor ubiquitination and degradation. Increasing evidence suggests that loss of Cbl-regulated ErbB1 degradation contributes to ErbB1 overexpression in cancer cells. Cdc42 is overexpressed in some breast cancers and evidence is accumulating that activated Cdc42 contributes to the accumulation of ErbB1 in cells through the regulation of c-Cbl function. Different therapeutic strategies targeting ErbB receptors and Cdc42 will be reviewed and discussed.

Heregulin beta1 drives gefitinib-resistant growth and invasion in tamoxifen-resistant MCF-7 breast cancer cells

INTRODUCTION

Resistance to anti-epidermal growth factor receptor (anti-EGFR) therapies is an emerging clinical problem. The efficacy of anti-EGFR therapies can be influenced by the presence of heregulins (HRGs), which can bind erbB3/4 receptors and can activate alternative signalling pathways. In the present study we have examined whether HRG signalling can circumvent EGFR blockade in an EGFR-positive tamoxifen-resistant MCF-7 (Tam-R) breast cancer cell line.

METHODS

Tam-R cells, incubated with the selective EGFR tyrosine kinase inhibitor gefitinib ('Iressa', ZD1839), were exposed to HRGbeta1 and the effects on erbB receptor dimerization profiles and on activation of associated downstream signalling components were assessed by immunoprecipitation, western blotting and immunocytochemistry. The effects of HRGbeta1 on gefitinib-treated Tam-R cell growth and invasion were also examined, and HRGbeta1 expression levels were assessed in breast cancer tissue by immunohistochemistry to address the potential clinical relevance of such a resistance mechanism.

RESULTS

In Tam-R cells, HRGbeta1 promoted erbB3/erbB2 and erbB3/EGFR heterodimerization, promoted ERK1/2 and AKT pathway activation and increased cell proliferation and invasion. Gefitinib prevented HRGbeta1-driven erbB3/EGFR heterodimerization, ERK1/2 activation and Tam-R cell proliferation, but HRGbeta1-driven erbB3/erbB2 heterodimerization, AKT activation and Tam-R cell invasion were maintained. A combination of gefitinib and the phosphatidylinositol 3-kinase inhibitor LY294002 effectively blocked HRGbeta1-mediated intracellular signalling activity, growth and invasion in Tam-R cells. Similarly, targeting erbB2 with trastuzumab in combination with gefitinib in Tam-R cells reduced HRGbeta1-induced erbB2 and ERK1/2 activity; however, HRGbeta1-driven AKT activity and cell growth were maintained while cell invasion was significantly enhanced with this combination. In clinical tissue all samples demonstrated cytoplasmic tumour epithelial HRGbeta1 protein staining, with expression correlating with EGFR positivity and activation of both AKT and ERK1/2.

CONCLUSION

HRGbeta1 can overcome the inhibitory effects of gefitinib on cell growth and invasion in Tam-R cells through promotion of erbB3/erbB2 heterodimerization and activation of the phosphatidylinositol 3-kinase/AKT signalling pathway. This may have implications for the effectiveness of anti-EGFR therapies in breast cancer as HRGbeta1 is enriched in many EGFR-positive breast tumours.

Impact of IGF-1R/EGFR cross-talks on hepatoma cell sensitivity to gefitinib

Epidermal growth factor receptor (EGFR)- and type 1 insulin-like growth factor receptor (IGF-1R)-dependent pathways are up-regulated in hepatocellular carcinoma (HCC), and cross-talks between both pathways have been described in other systems. Gefitinib, a specific EGFR inhibitor, has shown to reduce significantly, although not completely, HCC formation in rat cirrhotic liver. Here, we investigated whether IGF-1R-dependent pathways may interfere with EGFR signalling in hepatoma cells and, if so, whether such cross-talks may affect the antitumoral effect of gefitinib in these cells. We show that the proliferative action of IGF2 in HepG2 and Hep3B cells requires EGFR activation through the autocrine/paracrine release of amphiregulin. Thus, IGF2-induced extracellular signal-regulated kinase activity and DNA synthesis were inhibited by neutralizing antibodies against either EGFR or amphiregulin and by TAPI-1, a pharmalogical inhibitor of tumor necrosis factor-alpha converting enzyme, a sheddase of amphiregulin. Accordingly, IGF2 and EGF stimulating effects on cell proliferation were both strongly repressed by gefitinib. However, while gefitinib blocked Akt activation by EGF, it had no effect on Akt activation by IGF2 and did not cause apoptosis by its own. AG1024, a selective IGF-1R inhibitor, induced apoptosis and this effect was potentiated by gefitinib. In conclusion, we show that in HCC cells IGF2/IGF-1R activation triggers proliferative and survival signals through EGFR-dependent and -independent mechanisms, respectively. The IGF2/IGF-1R survival pathway may contribute to gefitinib resistance in these cells. Therefore, the inhibition of IGF2/IGF-1R signalling could potentiate the anti-tumoral effect of gefinitib in HCC.

Systems biology and combination therapy in the quest for clinical efficacy

Combinatorial control of biological processes, in which redundancy and multifunctionality are the norm, fundamentally limits the therapeutic index that can be achieved by even the most potent and highly selective drugs. Thus, it will almost certainly be necessary to use new 'targeted' pharmaceuticals in combinations. Multicomponent drugs are standard in cytotoxic chemotherapy, but their development has required arduous empirical testing. However, experimentally validated numerical models should greatly aid in the formulation of new combination therapies, particularly those tailored to the needs of specific patients. This perspective focuses on opportunities and challenges inherent in the application of mathematical modeling and systems approaches to pharmacology, specifically with respect to the idea of achieving combinatorial selectivity through use of multicomponent drugs.

New therapies for hepatocellular carcinoma

Hepatocellular carcinoma (HCC), one of the most common cancers worldwide, is often diagnosed at an advanced stage when most potentially curative therapies such as resection, transplantation or percutaneous and transarterial interventions are of limited efficacy. The fact that HCC is resistant to conventional chemotherapy, and is rarely amenable to radiotherapy, leaves this disease with no effective therapeutic options and a very poor prognosis. Therefore, the development of more effective therapeutic tools and strategies is much needed. HCCs are phenotypically and genetically heterogeneous tumors that commonly emerge on a background of chronic liver disease. However, in spite of this heterogeneity recent insights into the biology of HCC suggest that certain signaling pathways and molecular alterations are likely to play essential roles in HCC development by promoting cell growth and survival. The identification of such mechanisms may open new avenues for the prevention and treatment of HCC through the development of targeted therapies. In this review we will describe the new potential therapeutic targets and clinical developments that have emerged from progress in the knowledge of HCC biology, In addition, recent advances in gene therapy and combined cell and gene therapy, together with new radiotherapy techniques and immunotherapy in patients with HCC will be discussed.

Cross-talk between epidermal growth factor receptor and hypoxia-inducible factor-1alpha signal pathways increases resistance to apoptosis by up-regulating survivin gene expression

Although increasing evidence supports a link between epidermal growth factor receptor (EGFR) signaling and resistance to apoptosis, the mechanism by which the EGFR signaling pathway inhibits apoptosis is not well understood. In this study, we found that epidermal growth factor (EGF) stimulation increased the level of expression of the inhibitor of apoptosis protein survivin in breast cancer cells but not in normal mammary epithelial cells. We further demonstrated that activation of survivin gene expression is mediated by oxygen-independent hypoxia-inducible factor (HIF)-1alpha up-regulation in EGF-treated cancer cells. EGFR signaling activated the phosphoinositide 3-kinase/AKT pathway, subsequently increasing the level of HIF-1alpha under normoxic conditions. HIF-1alpha then activated survivin gene transcription through direct binding to the survivin promoter. Furthermore, we found that overexpression of HIF-1alpha small interfering RNA blocks EGF-induced survivin gene up-regulation and increases apoptosis induced by the chemotherapy drug docetaxel. However, transfection of a plasmid expressing HIF-1alpha gene activates survivin gene expression and reduces the apoptotic response. Our results demonstrate a novel pathway for EGFR signaling-mediated apoptosis resistance in human cancer cells. Although the role of HIF-1alpha in regulating cell survival under hypoxic conditions has been studied extensively, our results show that normoxic breast cancer cells utilize cross-talk between EGFR signals and HIF-1alpha to up-regulate the anti-apoptotic survivin gene, providing a strong rationale for the targeting of HIF-1alpha as a therapeutic approach for both hypoxic and normoxic tumor cells. Understanding key molecular events in EGFR signaling-induced apoptosis resistance should provide new information for the development of novel therapeutic agents targeting EGFR, HIF-1alpha, and/or survivin.

The role of the epidermal growth factor receptor in breast cancer

Recent trials of drug therapy targeting the erbB receptor HER2 have met with success in breast cancer. The epidermal growth factor receptor or EGFR is a closely related receptor from this same family that is involved in cellular signal transduction and tumor cell growth and survival. Emerging evidence indicates that EGFR is implicated in the development of hormone-resistant breast cancer, and that its activity is intertwined with estrogen receptor. Here, the role of EGFR in breast cancer is reviewed, and data from selected clinical trials of signal transduction inhibition of this cellular target are summarized.

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.

Expression of type 1 insulin-like growth factor receptor in marrow nucleated cells in malignant hematological disorders: correlation with apoptosis

To verify the expression of type 1 insulin-like growth factor receptor (IGF-IR) and its impact on hematopoietic cells apoptosis in myelodysplastic syndromes (MDS) and acute myeloid leukemias (AML), marrow samples from 16 patients with MDS and 16 patients with AML were examined along with 16 healthy donors as controls. Immunocytochemical methods (alkaline phosphatase anti-alkaline phosphatase) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (fluorescence) were used simultaneously on nucleated cell cytospins. The ratio of IGF-IR positive cells and apoptotic cells as well as the relationship between them were then analyzed separately. A quantitative real-time reverse transcriptase-polymerase chain reaction (PCR) was administrated for six MDS cases and two normal controls to validate IGF-IR expression detected by immunochemistry. In our assay, IGF-IR appeared to have higher to lower expression rate in turn from AML (86.8+/-13.8%) to MDS (56.8+/-14.3%) and then to normal controls (40.4+/-9.6%) (P<0.01 between each group). In MDS nucleated cells, IGF-IR showed stronger expression in refractory anemia with excess blasts (RAEB)/RAEB in transformation/chronic myelomonocytic leukemia subgroup when compared to RA/RA with ringed sideroblasts cases (64.1+/-3.2 vs 53.5+/-16.2%) (P>0.05). Nucleated cells from MDS marrow underwent more apoptosis (5.4+/-3.0%) than that in normal marrow (1.2+/-0.9%) (P<0.01) and AML marrow (0.3+/-0.4%) (also, P<0.01 between each compared group). For both AML and MDS cases, apoptotic signals presented mainly in individual IGF-IR negative cells (9.0+/-4.8%) and less so in IGF-IR positive cells (1.4+/-2.4%) (P<0.01). When analyzed by groups, cell number with IGF-IR expression showed a negative correlation to apoptotic cells amount (r=-0.852; P<0.01) but positive correlation to their blast count (r=0.677; P<0.01). Outcome from real-time quantitative PCR appeared to have a trend of enhanced IGF-IR expression in advanced MDS subtypes. In conclusion, overexpression of IGF-IR existed in hematopoietic cells in MDS and AML marrows, which appeared to be contributed to disease progress.