Activation Of ErbB Receptors Research Articles

The Ectodomain Shedding of E-cadherin by ADAM15 Supports ErbB Receptor Activation

The zinc-dependent disintegrin metalloproteinases (a disintegrin and metalloproteinases (ADAMs) have been implicated in several disease processes, including human cancer. Previously, we demonstrated that the expression of a catalytically active member of the ADAM family, ADAM15, is associated with the progression of prostate and breast cancer. The accumulation of the soluble ectodomain of E-cadherin in human serum has also been associated with the progression of prostate and breast cancer and is thought to be mediated by metalloproteinase shedding. Utilizing two complementary models, overexpression and stable short hairpin RNA-mediated knockdown of ADAM15 in breast cancer cells, we demonstrated that ADAM15 cleaves E-cadherin in response to growth factor deprivation. We also demonstrated that the extracellular shedding of E-cadherin was abrogated by a metalloproteinase inhibitor and through the introduction of a catalytically inactive mutation in ADAM15. We have made the novel observation that this soluble E-cadherin fragment was found in complex with the HER2 and HER3 receptors in breast cancer cells. These interactions appeared to stabilize HER2 heterodimerization with HER3 and induced receptor activation and signaling through the Erk pathway, supporting both cell migration and proliferation. In this study, we provide evidence that ADAM15 catalyzes the cleavage of E-cadherin to generate a soluble fragment that in turn binds to and stimulates ErbB receptor signaling.

2005 ORAL Breast cancer incidence in relation to oestrogen hormone receptor status in Denmark 1994–2005

Overexpression of ErbB2 has been found in approximately 25–30% of human breast cancers and has been shown to render the cancer cells more resistant to chemotherapy. However, it is not clear whether ErbB2 overexpression renders the cells more resistant to specific anti-cancer drugs or renders the cells more resistant to a broad range of anti-cancer drugs. It is not clear how the function of ErbB2 in drug resistance is related to expression and activation of the other ErbB receptors. In this communication, we showed that several breast cancer cell lines including BT20, BT474, MCF-7, MDA-MB-453, and SKBR-3 cells had a similar pattern of resistance to a broad range of anti-cancer drugs including 5-Fluorouracil, Cytoxan, Doxorubincin, Taxol, and Vinorelbin, suggesting a mechanism of multidrug resistance. High expression of P-glycoprotein and the ErbB receptors contribute to drug resistance of these breast cancer cells; however, overexpression of ErbB2 alone is not a major factor in determining drug resistance. To further determine the role of the ErbB receptors in drug resistance, we selected various NIH 3T3 cell lines that specifically expressed EGF receptor (EGFR), ErbB2, ErbB3, EGFR/ErbB2, EGFR/ErbB3, or ErbB2/ErbB3. A cytotoxicity assay showed that expression of ErbB2 alone did not significantly enhance drug resistance, whereas coexpression of either EGFR or ErbB3 with ErbB2 significantly enhanced drug resistance. Moreover, ErbB2 was highly phosphorylated in NIH 3T3 cells that coexpress ErbB2 with either EGFR or ErbB3, but not in NIH 3T3 cells that express ErbB2 alone. Together, our results suggest that coexpression of EGFR or ErbB3 with ErbB2 induces high phosphorylation of ErbB2 and renders the cells more resistant to various anti-cancer drugs.

Human Breast Cancer Cells Selected for Resistance to Trastuzumab In vivo Overexpress Epidermal Growth Factor Receptor and ErbB Ligands and Remain Dependent on the ErbB Receptor Network

We have investigated mechanisms of acquired resistance to the HER2 antibody trastuzumab in BT-474 human breast cancer cells. BT-474 xenografts established in athymic nude mice were eliminated by trastuzumab. Continuous cell lines (HR for Herceptin resistant) were generated from tumors that recurred in the presence of continuous antibody therapy. The isolated cells behaved resistant to trastuzumab in culture as well as when reinjected into nude mice. They retained HER2 gene amplification and trastuzumab binding and were exquisitely sensitive to peripheral blood mononuclear cells ex vivo in the presence of the antibody. The HR cells exhibited higher levels of phosphorylated epidermal growth factor receptor (EGFR) and EGFR/HER2 heterodimers. Phosphorylation of HER2 in HR cells was inhibited by the EGFR tyrosine kinase inhibitors erlotinib and gefitinib. Gefitinib also inhibited the basal association of p85 with phosphorylated HER3 in HR cells. Both inhibitors as well as the dual EGFR/HER2 inhibitor, lapatinib, induced apoptosis of the HR cells in culture. Growth of established HR5 xenografts was inhibited by erlotinib in vivo. In addition, the HR cells overexpressed EGFR, transforming growth factor alpha, heparin-binding EGF, and heregulin RNAs compared with the parental trastuzumab-sensitive cells. These results are consistent with the inability of trastuzumab to block the heterodimerization of HER2 and suggest that amplification of ligand-induced activation of ErbB receptors is a plausible mechanism of acquired resistance to trastuzumab that should be investigated in primary mammary cancers.

Phase I Clinical and Pharmacodynamic Evaluation of Oral CI-1033 in Patients with Refractory Cancer

To determine the tolerability and pharmacokinetics of CI-1033 given daily for 7 days of a 21-day cycle. Tumor response and changes in erbB receptor tyrosine kinase activity in tumor and skin tissue were examined, and modulation of potential biomarkers in plasma was explored. This was a dose-finding phase I study in patients with advanced solid malignancies. Patients were evaluated for safety, pharmacokinetics, and tumor response. Pharmacodynamic markers, such as Ki67, p27, and erbB receptor status, were assessed in tumor and skin tissue using immunohistochemical and immunoprecipitation methodologies. Plasma biomarkers HER2, vascular endothelial growth factor, interleukin-8, and matrix metalloproteinase-9 were evaluated using immunologic techniques. Fifty-three patients were enrolled in the study. Dose-limiting toxicity (emesis, persistent rash, and mouth ulcer) was observed at 750 mg. The maximum tolerated dose was 650 mg. There were no confirmed objective responses. CI-1033 treatment showed down-regulation of epidermal growth factor receptor, HER2, and Ki67 in a variety of tumor tissues and up regulation of p27 in skin tissue. Plasma HER2 was reduced following CI-1033 administration, but no consistent change in vascular endothelial growth factor, interleukin-8, or matrix metalloproteinase-9 was noted. CI-1033 plasma concentrations were proportional to dose. The safety and pharmacokinetic profile of CI-1033 was favorable for multidose oral administration. Evidence of modulation of erbB receptor activity in tumor and skin tissue was accompanied by changes in markers of proliferation and cell cycle inhibition. Additional clinical trials are warranted in defining the role of CI-1033 in the treatment of cancer and further assessing the utility of antitumor markers.

Quantitative Transcriptional Control of ErbB Receptor Signaling Undergoes Graded to Biphasic Response for Cell Differentiation

ErbB receptor ligands, epidermal growth factor (EGF) and heregulin (HRG), induce dose-dependent transient and sustained intracellular signaling, proliferation, and differentiation of MCF-7 breast cancer cells, respectively. In an effort to delineate the ligand-specific cell determination mechanism, we investigated time course gene expressions induced by EGF and HRG that induce distinct cellular phenotypes in MCF-7 cells. To analyze independently the effects of ligand dosage and time for gene expression, we developed a statistical method for estimating the two effects. Our results indicated that signal transduction pathways convey quantitative properties of the dose-dependent activation of ErbB receptor to early transcription. The results also implied that moderate changes in the expression levels of a number of genes, not the predominant regulation of a few specific genes, might cooperatively work at the early stage of the transcription for determining cell fate. However, the EGF- and HRG-induced distinct signal durations resulted in the ligand-oriented biphasic induction of proteins after 20 min. The selected gene list and HRG-induced prolonged signaling suggested that transcriptional feedback to the intracellular signaling results in a graded to biphasic response in the cell determination process and that each ErbB receptor is inextricably responsible for the control of amplitude and duration of cellular biochemical reactions.

Polycystic kidney disease: genes, proteins, animal models, disease mechanisms and therapeutic opportunities

An increased understanding of the genetic, molecular and cellular mechanisms responsible for the development of polycystic kidney disease has laid out the foundation for the development of rational therapies. Many animal models where these therapies can be tested are currently available. This review summarizes the rationale for these treatments, the results of preclinical trials and the prospects for clinical trials, some already in early phases of implementation.

Radiotherapy-induced signal transduction

Exposure of tumor cells to ionizing radiation causes compensatory activation of multiple intracellular survival signaling pathways to maintain viability. In human carcinoma cells, radiation exposure caused an initial rapid inhibition of protein tyrosine phosphatase function and the activation of ERBB receptors and downstream signaling pathways. Radiation-induced activation of extracellular regulated kinase (ERK)1/2 promoted the cleavage and release of paracrine ligands in carcinoma cells which caused re-activation of ERBB family receptors and intracellular signaling pathways. Blocking ERBB receptor phosphorylation or ERK1/2 pathway activity using small-molecule inhibitors of kinases for a short period of time following exposure (3 h) surprisingly protected tumor cells from the toxic effects of ionizing radiation. Prolonged exposure (48-72 h) of tumor cells to inhibition of ERBB receptor/ERK1/2 function enhanced radiosensitivity. In addition to ERBB receptor signaling, expression of activated forms of RAS family members and alterations in p53 mutational status are known to regulate radiosensitivity apparently independent of ERBB receptor function; however, changes in RAS or p53 mutational status, in isogenic HCT116 cells, were also noted to modulate the expression of ERBB receptors and ERBB receptor paracrine ligands. These alterations in receptor and ligand expression correlated with changes in the ability of HCT116 cells to activate ERK1/2 and AKT after irradiation, and to survive radiation exposure. Collectively, our data in multiple human carcinoma cell lines argues that tumor cells are dynamic and rapidly adapt to any single therapeutic challenge, for example, radiation and/or genetic manipulation e.g. loss of activated RAS function, to maintain tumor cell growth and viability.

γ‐Tocotrienol inhibits ErbB3‐dependent PI3K/Akt mitogenic signalling in neoplastic mammary epithelial cells

The antiproliferative effects of gamma-tocotrienol are associated with suppression in epidermal growth factor (EGF)-dependent phosphatidylinositol-3-kinase (PI3K)/PI3K-dependent kinase-1 (PDK-1)/Akt mitogenic signalling in neoplastic mammary epithelial cells. Studies were conducted to investigate the direct effects of gamma-tocotrienol treatment on specific components within the PI3K/PDK-1/Akt mitogenic pathway. +SA cells were grown in culture and maintained in serum-free media containing 10 ng/ml EGF as a mitogen. Treatment with 0-8 microm gamma-tocotrienol resulted in a dose-responsive decrease in the +SA cell growth and a corresponding decrease in phospho-Akt (active) levels. However, gamma-tocotrienol treatment had no direct inhibitory effect on Akt or PI3K enzymatic activity, suggesting that the inhibitory effects of gamma-tocotrienol occur upstream of PI3K, possibly at the level of the EGF-receptor (ErbB1). Additional studies were conducted to determine the effects of gamma-tocotrienol on ErbB receptor activation. Results showed that gamma-tocotrienol treatment had little or no effect on ErbB1 or ErbB2 receptor tyrosine phosphorylation, a prerequisite for substrate interaction and signal transduction, but did cause a significant and progressive decrease in the ErbB3 tyrosine phosphorylation. Because ErbB1 or ErbB2 receptors form heterodimers with the ErbB3 receptor, and ErbB3 heterodimers have been shown to be the most potent activators of PI3K, these findings strongly suggest that the antiproliferative effects of gamma-tocotrienol in neoplastic +SA mouse mammary epithelial cells are mediated by a suppression in ErbB3-receptor tyrosine phosphorylation and subsequent reduction in PI3K/PDK-1/Akt mitogenic signalling.

Neuregulin-1/erbB-Activation Improves Cardiac Function and Survival in Models of Ischemic, Dilated, and Viral Cardiomyopathy

We evaluated the therapeutic potential of a recombinant 61-residue neuregulin-1 (beta2a isoform) receptor-active peptide (rhNRG-1) in multiple animal models of heart disease. Activation of the erbB family of receptor tyrosine kinases by rhNRG-1 could provide a treatment option for heart failure, because neuregulin-stimulated erbB2/erbB4 heterodimerization is not only critical for myocardium formation in early heart development but prevents severe dysfunction of the adult heart and premature death. Disabled erbB-signaling is also implicated in the transition from compensatory hypertrophy to failure, whereas erbB receptor-activation promotes myocardial cell growth and survival and protects against anthracycline-induced cardiomyopathy. rhNRG-1 was administered IV to animal models of ischemic, dilated, and viral cardiomyopathy, and cardiac function and survival were evaluated. Short-term intravenous administration of rhNRG-1 to normal dogs and rats did not alter hemodynamics or cardiac contractility. In contrast, rhNRG-1 improved cardiac performance, attenuated pathological changes, and prolonged survival in rodent models of ischemic, dilated, and viral cardiomyopathy, with the survival benefits in the ischemic model being additive to those of angiotensin-converting enzyme inhibitor therapy. In addition, despite continued pacing, rhNRG-1 produced global improvements in cardiac function in a canine model of pacing-induced heart failure. These beneficial effects make rhNRG-1 promising as a broad-spectrum therapeutic for the treatment of heart failure due to a variety of common cardiac diseases.

ErbB receptor regulation by dexamethasone in mouse type II epithelial cells

Glucocorticoids stimulate foetal surfactant synthesis. Therefore, they are used in impending pre-term birth. One mechanism of action on surfactant synthesis is through the induction of neuregulin (NRG) secretion by foetal lung fibroblasts. The direct effects on signalling pathways, and specifically on erbB receptors in foetal type II cell surfactant synthesis, are less well understood. The present authors studied the effect of known promoters of foetal surfactant synthesis (namely dexamethasone and mature (i.e. NRG-containing) fibroblast-conditioned medium (FCM)) on erbB receptor activation, protein content and dimerisation patterns in foetal mouse lung type II cells. Dexamethasone inhibited surfactant synthesis in immature type II cells at day (d)16 of gestation, while the mature FCM had stimulatory effects. Both treatments directly stimulated surfactant synthesis in more mature (d17) cells. At this gestational day, dexamethasone had only a small effect on phosphorylation, but it stimulated the protein levels of all four erbB receptors. Dexamethasone effects were distinct from those of mature FCM, which stimulated both protein content and phosphorylation of all erbB receptors and of the signalling intermediate phospholipase Cgamma. Dexamethasone modulated erbB receptor dimerisation patterns, such that erbB2 became the main dimerisation partner for erbB4. In conclusion, dexamethasone signalling involves erbB receptors in foetal type II cells, in a manner similar to, but distinct from, neuregulin-containing fibroblast-conditioned medium signalling.

Targeting ADAMS and ERBBs in lung cancer

Aberrant ERBB receptor activity contributes to the development of many human cancers. Receptor overexpression, kinase domain (KD) mutations, and autocrine ligand production contribute to ERBB activation in human tumors. ERBB-targeted tyrosine kinase inhibitors (TKIs) and monoclonal antibodies are used in cancer treatment; however, clinical hurdles, including patient selection and TKI resistance, need to be overcome in order to optimize therapy. This minireview will discuss recent findings on possible mechanisms leading to ERBB-targeted therapy resistance and potential means to overcome them.

Ligand‐independent regulation of ErbB4 receptor phosphorylation by activated ras

The ErbB family of receptor tyrosine kinases regulates cell growth, differentiation and survival. Activation of the receptors is induced by specific growth factors in an autocrine, paracrine or juxtacrine manner. The activated ErbB receptors turn on a large variety of signaling cascades, including the prominent Ras-dependent signaling pathways. The activated Ras can induce secretion of growth factors such as EGF and neuregulin, which activate their respective receptors. In the present study, we demonstrate for the first time that activated Ras can activate ErbB4 receptor in a ligand-independent manner. Expression of constitutively active H-Ras(12V), K-Ras(12V) or N-Ras(13V) in PC12-ErbB4 cells induced ErbB4-receptor phosphorylation, indicating that each of the most abundant Ras isoforms can induce receptor activation. NRG-induced phosphorylation of ErbB4 receptor was blocked by the soluble ErbB4 receptor, which had no effect on the Ras-induced receptor phosphorylation. Moreover, conditioned medium from H-Ras(12V)-transfected PC12-ErbB4 cells had no effect on receptor phosphorylation. It thus indicates that Ras induces ErbB4 phosphorylation in a ligand-independent manner. Each of the Ras effector domain mutants, H-Ras(12V)S35, H-Ras(12V)C40, and H-Ras(12V)G37, which respectively activate Raf1, PI3K, and RalGEF, induced a small but significant receptor phosphorylation. The PI3K inhibitor LY294002 and the MEK inhibitor PD98059 caused a partial inhibition of the Ras-induced ErbB4 receptor phosphorylation. Using a mutant ErbB4 receptor, which lacks kinase activity, we demonstrated that the Ras-mediated ErbB4 phosphorylation depends on the kinase activity of the receptor and facilitates ligand-independent neurite outgrowth in PC12-ErbB4 cells. These experiments demonstrate a novel mechanism controlling ErbB receptor activation. Ras induces ErbB4 receptor phosphorylation in a non-autocrine manner and this activation depends on multiple Ras effector pathways and on ErbB4 kinase activity.

Expression of heregulin by mouse mammary tumor cells: Role in activation of ErbB receptors

The inappropriate activation of one or more members of the ErbB family of receptor tyrosine kinases [ErbB-1 (EGFR), ErbB-2, ErbB-3, ErbB-4] has been linked with oncogenesis. ErbB-2 is frequently coexpressed with ErbB-3 in breast cancer cells and in the presence of the ligand heregulin (HRG) the ErbB-2/ErbB-3 receptors form a signaling heterodimer that can affect cell proliferation and apoptosis. The major goal of the present study was to determine whether endogenous HRG causes autocrine/paracrine activation of ErbB-2/ErbB-3 and contributes to the proliferation of mammary epithelial tumor cells. Tyrosine-phosphorylated (activated) ErbB-2 and ErbB-3 receptors were detected in the majority of extracts from tumors that had formed spontaneously or as a result of oncogene expression. HRG-1 transcripts and protein were found in the epithelial cells of most of these mouse mammary tumors. Various mouse mammary cell lines also contained activated ErbB-2/ErbB-3 and HRG transcripts. A approximately 50 kDa C-terminal fragment of pro-HRG was detected, which indicates that the HRG-1 precursor is readily processed by these cells. It is likely that the secreted mature HRG activated the ErbB-2/3 receptors. Addition of an antiserum against HRG to the mammary epithelial tumor cell line TM-6 reduced ErbB-3 Tyr-phosphorylation. Treatment with HRG-1 siRNA oligonucleotides or infection with a retroviral construct to stably express HRG siRNA effectively reduced HRG protein levels, ErbB-2/ErbB-3 activation, and the rate of proliferation, which could be reversed by the addition of HRG. The cumulative findings from these experiments show that coexpression of the HRG ligand contributes to activation of ErbB-2/Erb-3 in mouse mammary tumor cells in an autocrine or paracrine fashion.

Electrostatic interactions of peptides flanking the tyrosine kinase domain in the epidermal growth factor receptor provides a model for intracellular dimerization and autophosphorylation

The mechanism by which ligand-activated EGFR induces autophosphorylation via dimerization is not fully understood. Structural studies have revealed an extracellular loop mediated receptor dimerization. We have previously presented experimental data showing the involvement of a positive 13 amino acid peptide (R645-R657; P13+) from the intracellular juxtamembrane domain (JM) of EGFR important for intracellular dimerization and autophosphorylation. A model was presented that suggest that P13+ interacts with a negative peptide (D979-E991; P13-) positioned distal to the tyrosine kinase domain in the opposite EGFR monomer. The present work shows additional data strengthening this model. In fact, by analyzing protein sequences of 21 annotated ErbB proteins from 9 vertebrate genomes, we reveal the high conservation of peptides P13+ and P13- with regard to their sequence as well as their position relative to the tyrosine kinase (TK) domain. Moreover in silico structure modeling of these ErbB intracellular domains supports a general electrostatic P13+/P13- interaction, implying that the C-terminal of one receptor monomer is facing the TK domain of the other monomer in the receptor dimer and vice versa. This model provides new insights into the molecular mechanism of ErbB receptor activation and suggests a new strategy to pharmacologically interfering with ErbB receptor activity.

Differential Localization of ErbB Receptor Ensembles Influences Their Signaling in Hippocampal Neurons

Our studies indicate that ErbB complexes participate in both survival and synaptic plasticity signals of hippocampal neurons but in a manner that depends on the subcellular localization of the receptor ensembles. Using dissociated hippocampal cultures, we found that neurons, rather than glial cells, are the primary targets of ErbB receptor ligands such as epidermal growth factor and heregulin. Further investigation demonstrated that ErbB receptors distribute differentially in hippocampal neurons with the epidermal growth factor receptor confined to neural cell bodies and the p185(c-neu) and ErbB4 receptors distributed to both neural soma and neurites. Activation of ErbB receptor and downstream signaling molecules were observed in neurites only after heregulin stimulation. The receptor complex which mediated neurite located signals was the p185(c-neu)/ErbB4 heterodimer. Colocalization of p185(c-neu), but not epidermal growth factor receptor, with postsynaptic density protein 95 suggests that the heregulin signaling contributes to synapse specific activities. However, the epidermal growth factor receptor complex mediates physiological survival signals, as neuronal survival was enhanced by epidermal growth factor, rather than heregulin. Collectively, these studies indicate that different ErbB ensembles localize to different locations on the neuron to mediate distinct signals and functions.

Activation of ErbB receptors by 1,4-naphthoquinones

Activation of ErbB receptors by 1,4-naphthoquinones

Inhibition by transmembrane peptides of chimeric insulin receptors.

Receptor tyrosine kinases play essential roles in cell proliferation and differentiation. We have recently shown that peptides corresponding to the transmembrane domains of the epidermal growth factor (EGF) and ErbB2 receptors inhibit their corresponding receptor activation in cancer cell lines. We extend this observation to cells transfected with chimeric insulin receptors where the transmembrane domain has been replaced by that of the EGF receptor or a mutated Erb2 domain. Peptides corresponding to the transmembrane domains of the EGF receptor and ErbB2 are able to inhibit specifically the autophosphorylation of insulin receptors with the corresponding domain. This inhibitory effect is correlated with the propensity of the different transmembrane domains to self-associate in a genetic reporter assay. Thus, our data strengthen the notion that transmembrane domains are involved in erbB receptor activation, and that these receptors can be modulated by inhibiting protein-protein interactions within the membrane.

The Antitumor and Antiangiogenic Activity of Vascular Endothelial Growth Factor Receptor Inhibition Is Potentiated by ErbB1 Blockade

Receptor tyrosine kinases of the ErbB family play important roles in the control of tumor growth. Vascular endothelial growth factor (VEGF) stimulates endothelial cell proliferation, enhances vascular permeability, and plays an important role in tumor vascularization. We evaluated the effects of selective VEGF receptor (VEGFR; PTK787/ZK222584) and ErbB (PKI166 and ZD1839) inhibitors on tumor growth and angiogenesis and asked whether additional therapeutic benefit was conferred by combination treatment. The antitumor activity of each inhibitor alone or in combination was assessed in human cancer models in immunocompromised mice. ErbB receptor expression and activation of downstream signaling pathway was evaluated in both tumor and endothelial cells. Both ErbB inhibitors significantly enhanced the antitumor activity of PTK787/ZK222584. In vitro, ErbB1 inhibition blocked VEGF release by tumor cells and proliferation of both tumor and endothelial cells. In an in vitro angiogenesis assay, epidermal growth factor (EGF) stimulated the release of VEGF by smooth muscle cells resulting in increased angiogenesis, a response blocked by administration of PTK787/ZK222584. Under basal condition, both ZD1839 and PTK787/ZK222584 blocked sprouting, likely via inhibition of an autocrine ErbB1 loop and VEGFR signaling, respectively, in endothelial cells. In conditions of limiting VEGF, EGF plays an important role in endothelial cell proliferation, survival, and sprouting. We have shown that activation of ErbB1 triggers a plethora of effects, including direct effects on tumor and endothelial cells and indirect effects mediated via induction of VEGF release. Simultaneous blockade of ErbB1 and VEGFR pathways results in a cooperative antitumor effect, indicating that this combination may represent a valid therapeutic strategy.

The ErbB Receptors and their Ligands in Cancer: An Overview

This review article provides an overview on the most recent advances on the role of ErbB receptors and growth factors of the epidermal growth factor (EGF)-family of peptides in cancer pathogenesis and progression. The ErbB tyrosine kinases and the EGF-like peptides form a complex system. In fact, the interactions occurring between receptors and ligands of these families affect the type and the duration of the intracellular signals that derive from receptor activation. Interestingly, activation of ErbB receptors is also driven by different classes of membrane receptor, suggesting that ErbB kinases can amplify growth promoting signals carried by different pathways. The importance of ErbB receptors and EGF-like peptides in development of organs and tissues has been demonstrated by using different mouse models. In vitro and in vivo studies have also shown that ErbB receptors and their ligands can act as transforming genes. However, evidence suggests that cooperation of different receptors and ligands is necessary to induce a fully transformed phenotype. Indeed, co-expression of different ErbB receptors and EGF-like growth factors is a common phenomenon in human primary carcinomas. This observation suggests that the growth and the survival of carcinoma cells is sustained by a network of receptors/ligands of the ErbB family. In this respect, the contemporary expression of different ErbB tyrosine kinases and/or EGF-like growth factors in human carcinomas might also affect tumor response to target based agents directed against the ErbB receptor/ligand system.

Efficacy of erbB specific tyrosine kinase inhibitors in thyroid carcinoma cells

The expression and activation of epidermal growth factor receptor (EGFR) and related erbB receptors is associated with thyroid tumorigenesis. Besides an enhanced proliferation, cell survival and angiogenesis, activation of erbB receptors may be associated with resistance to cytotoxic drugs. In our study we analyzed the expression of erbB receptor family members in thyroid carcinoma cells. Furthermore, we studied whether inhibition of erbB receptors may influence proliferation and increase sensitivity towards chemotherapeutic drugs in undifferentiated thyroid carcinoma cells. We found that FTC133, SW1736 and HTh74 thyroid carcinoma cells expressed high levels of EGFR, while HTh7 and C643 cells showed no EGFR expression. ErbB2 expression was moderat in SW1736, HTh7 and C643 cells and negative in FTC133 and HTh74 cells. ErbB4 was expressed in all cell lines except C643. Treatment with 1.0–5.0µM of the tyrosine kinase inhibitor CL387785 (CL) resulted in an inhibition of FTC133, HTh74 and C643 cells. SW1736 and HTh7 cells were not inhibited but unexpectedly showed increased proliferation with low concentrations (0.1–1.0µM CL) perhaps due to autocrine stimulation processes. All cell lines were insensitive to cisplatin up to concentrations of 2.0µg/ml. Doxorubicin showed a slight but significant inhibitory effect at 0.2–1.0µM. Gemcitabine (0.02–0.05µg/ml) was effective in FTC133, SW1736 and C643 cells. Neither CL nor the additionally used tyrosine kinase inhibitor PD153035 (PD) had an effect on cisplatin, doxorubicin or gemcitabine sensitivity. In contrast, camptothecin exhibited an effective inhibition of FTC133 and SW1736 cells (0,02µg/ml). Interestingly, the lower sensitivity of HTh7 cells to camptothecin could be increased by tyrosine kinase inhibition with 0.5µM CL or 0,2µM PD. In conclusion, inhibition of tyrosine kinases may be an effective approach to decrease proliferation of chemo-insensitive thyroid carcinoma cells. Treatment with tyrosine kinase inhibitors may thus become clinically relevant for treatment of undifferentiated thyroid carcinomas.