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At least 55 records · Page 3Linked to original sources
PubMed2004

Dual-agent molecular targeting of the epidermal growth factor receptor (EGFR): combining anti-EGFR antibody with tyrosine kinase inhibitor.

Molecular inhibition of epidermal growth factor receptor (EGFR/HER1) signaling is under active investigation as a promising cancer treatment strategy. We examined the potency of EGFR inhibition achieved by combining anti-EGFR monoclonal antibody and tyrosine kinase inhibitor, which target extracellular and intracellular domains of the receptor, respectively. We specifically studied the combination of cetuximab (Erbitux, C225; ImClone Systems, New York, NY) with either gefitinib (Iressa, ZD1839; AstraZeneca, Macclesfield, UK) or erlotinib (Tarceva, OSI-774; Genentech, South San Francisco, CA) across a variety of human cancer cells. The combination of cetuximab plus gefitinib or erlotinib enhanced growth inhibition over that observed with either agent alone. As measured by immunostaining, inhibition of EGFR phosphorylation with the combination of cetuximab plus gefitinib or erlotinib was augmented over that obtained with single-agent therapy in head and neck (H&N) cancer cell lines. Phosphorylation inhibition of downstream effector molecules [mitogen-activated protein kinase (MAPK) and AKT] also was enhanced in tumor cells treated with the combination of cetuximab plus gefitinib or erlotinib. Flow cytometry and immunoblot analysis demonstrated that treatment of H&N tumor cells with cetuximab in combination with either gefitinib or erlotinib amplified the induction of apoptosis. Following establishment of cetuximab-resistant cell lines, we observed that gefitinib or erlotinib retained the capacity to inhibit growth of lung and H&N tumor cells that were highly resistant to cetuximab. Treatment with gefitinib or erlotinib, but not cetuximab, also could further inhibit the activation of downstream effectors of EGFR signaling in cetuximab-resistant cells, including MAPK and AKT. These data suggest that tyrosine kinase inhibitors may further modulate intracellular signaling that is not fully blocked by extracellular anti-EGFR antibody treatment. Finally, animal studies confirmed that single EGFR inhibitor treatment resulted in partial and transient tumor regression in human lung cancer xenografts. In contrast, more profound tumor regression and regrowth delay were observed in mice treated with the combination of cetuximab and gefitinib or erlotinib. Immunohistochemical staining, which demonstrated significant reduction of the proliferative marker proliferating cell nuclear antigen in mice treated with dual EGFR inhibitors, further supported this in vivo observation. Together, these data suggest that combined treatment with distinct EGFR inhibitory agents can augment the potency of EGFR signaling inhibition. This approach suggests potential new strategies to maximize effective target inhibition, which may improve the therapeutic ratio for anti-EGFR-targeted therapies in developing clinical trials.

Animals↗
PubMed1994

Emergence of MCF-7 cells overexpressing a transfected epidermal growth factor receptor (EGFR) under estrogen-depleted conditions: evidence for a role of EGFR in breast cancer growth and progression.

Overexpression of epidermal growth factor receptor (EGFR) is correlated with loss of estrogen receptor and poor prognosis in breast cancer. To investigate this phenomenon, we transfected a cytomegalovirus expression vector directing the expression of EGFR into estrogen receptor-positive MCF-7 breast cancer cells and into a clone of MCF-7 cells previously transfected with transforming growth factor alpha. Cells arising from single clones or pooled polyclonal populations maintained in charcoal-stripped calf serum, a medium devoid of estrogen, overexpressed EGFR. Switching these cells to a medium containing fetal calf serum or charcoal-stripped calf serum plus 17 beta-estradiol resulted in the emergence of a population expressing low EGFR levels. Loss of expression was not a consequence of nonspecific repression of the cytomegalovirus promoter, because expression of the fibroblast growth factor (FGF)-4 complementary DNA in a similar vector was not lost in fetal calf serum. While loss of EGFR overexpression in fetal calf serum was seen at both the protein and mRNA levels, Southern blotting shows that this was not due to loss of the transfected gene. Subclones of a cell population with low EGFR expression were capable of increasing expression upon estrogen withdrawal, demonstrating that the changes in EGFR expression were reversible and suggesting a growth advantage conferred by EGFR overexpression under these restrictive growth conditions. Overexpression of EGFR did not result in loss of ER expression. These results suggest a role for overexpression of EGFR in the growth of estrogen receptor-positive breast cancer cells in the absence of estrogen.

Animals↗
PubMed2000

Immunoelectron microscope analysis of epidermal growth factor receptor (EGFR) in isolated Mytilus galloprovincialis (Lam.) digestive gland cells: evidence for ligand-induced changes in EGFR intracellular distribution.

In mammalian cells, the binding of epidermal growth factor (EGF) to its receptor (EGFR), a glycoprotein with intrinsic tyrosine kinase activity, leads to the pleiotropic responses to EGF. Among these, a negative feedback response by stimulation of receptor internalization and lysosomal degradation, this attenuating signal transduction. In this work, data are reported on the identification of specific EGFRs in isolated digestive gland cells from the marine mussel (Mytilus galloprovincialis Lam.) By immunoelectron microscopy. In control digestive cells, EGFR immunoreactivity was mainly associated with cytoplasmic membrane structures and, to a lesser extent, the cell membrane. The presence of EGFR-like receptors was confirmed by Western blotting of digestive gland cell extracts with two different monoclonal antibodies that recognize either intracellular or extracellular epitopes. The addition of mammalian EGF resulted in significant time and temperature-dependent changes in EGFR subcellular distribution in mussel cells. In cells exposed to EGF for 0-15 min at 4 degrees C, the distribution of EGFR was not significantly different from that of the control cells. On the other hand, at 18 degrees C, an increased labelling along the cell membrane was observed after 5-10 min after EGF addition, with a concomitant decrease in the cytoplasmic signal. Moreover, after 20 min of exposure to EGF, ligand binding apparently resulted in EGFR compartmentation within the lysosomes. These observations were confirmed by quantitative analysis of EGFR labelling at different times of EGF exposure. Similar results were obtained utilizing the two different monoclonal antibodies. The results indicate that, in mussel digestive cells, the binding of heterologous EGF to specific receptors induces a negative feedback response by stimulating the lysosomal degradation of EGFR, thus suggesting the presence of mechanisms responsible for receptor downregulation similar to those observed in mammalian cells.

Animals↗
PubMed2005

Engineering and characterisation of chimeric monoclonal antibody 806 (ch806) for targeted immunotherapy of tumours expressing de2-7 EGFR or amplified EGFR.

We report the generation of a chimeric monoclonal antibody (ch806) with specificity for an epitope on the epidermal growth factor receptor (EGFR) that is different from that targeted by all other anti-EGFR therapies. Ch806 antibody is reactive to both de2-7 and overexpressed wild-type (wt) EGFR but not native EGFR expressed in normal tissues at physiological levels. Ch806 was stably expressed in CHO (DHFR -/-) cells and purified for subsequent characterisation and validated for use in preliminary immunotherapy investigations. Ch806 retained the antigen binding specificity and affinity of the murine parental antibody. Furthermore, ch806 displayed enhanced antibody-dependent cellular cytotoxicity against target cells expressing the 806 antigen in the presence of human effector cells. Ch806 was successfully radiolabelled with both iodine-125 and indium-111 without loss of antigen binding affinity or specificity. The radioimmunoconjugates were stable in the presence of human serum at 37 degrees C for up to 9 days and displayed a terminal half-life (T(1/2beta)) of approximately 78 h in nude mice. Biodistribution studies undertaken in BALB/c nude mice bearing de2-7 EGFR-expressing or amplified EGFR-expressing xenografts revealed that (125)I-labelled ch806 failed to display any significant tumour retention. However, specific and prolonged tumour localisation of (111)In-labelled ch806 was demonstrated with uptake of 31%ID g(-1) and a tumour to blood ratio of 5 : 1 observed at 7 days postinjection. In vivo therapy studies with ch806 demonstrated significant antitumour effects on established de2-7 EGFR xenografts in BALB/c nude mice compared to control, and both murine 806 and the anti-EGFR 528 antibodies. These results support a potential therapeutic role of ch806 in the treatment of suitable EGFR-expressing tumours, and warrants further investigation of the potential of ch806 as a therapeutic agent.

Animals↗
PubMed2005

Combined treatment with EGFR inhibitors and arsenite upregulated apoptosis in human EGFR-positive melanomas: a role of suppression of the PI3K-AKT pathway.

Epidermal growth factor receptor (EGFR) is expressed, albeit at low or intermediate levels, in human melanomas at the different stages of tumor progression. Coexpression of EGFR with its ligand TGFalpha indicates their role in paracrine and autocrine growth regulation of melanomas. As it was previously observed for several types of cancer, specific inhibitors of EGFR-mediated signaling may reduce antiapoptotic properties of cancer cells and sensitize them to cytotoxic drugs. We recently reported that arsenite, particularly in combination with inhibitors of the PI3K-AKT and mitogen-activated protein kinase (MAPK) kinase (MEK)-extracellular signal-regulated kinase (ERK) pathways, induces high levels of apoptosis in different melanomas. Since EGFR signaling operates via activation of the PI3K-AKT and MEK-ERK pathways, we suggested that the combination of arsenite and EGFR inhibitors might also effectively induce apoptosis in melanoma. Here, we demonstrate that a moderate concentration of arsenite (5-10 muM) indeed upregulates apoptosis induced by EGFR inhibitors in EGFR-positive melanomas. In contrast, induction of apoptosis in melanomas with negligible surface expression of EGFR or with defective EGFR signaling requires direct suppression of the PI3K-AKT and MAPK pathways by specific pharmacological inhibitors in the presence of arsenite. Under these conditions, metastatic melanoma cell lines undergo TNF-related apoptosis-inducing ligand (TRAIL)- and tumor necrosis factor alpha (TNFalpha)-mediated apoptosis. Taken together, these data provide additional approaches in sensitizing melanomas to the cytotoxic effects of specific inhibitors of survival pathways.

Apoptosis↗
PubMed2006

The epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478 increases the formation of inactive untethered EGFR dimers. Implications for combination therapy with monoclonal antibody 806.

The epidermal growth factor receptor (EGFR) has at least two fundamental conformations: an inactive tethered conformation and an active untethered, ligand-bound "back-to-back" dimer, which may be part of an oligomeric complex. Monoclonal antibody (mAb) 806 is an EGFR-specific antibody that only binds a transitional form of the receptor after it untethers but before forming the back-to-back, ligated, active oligomer. We have shown that AG1478, a tyrosine kinase inhibitor of the EGFR, synergistically inhibits the growth of tumors overexpressing EGFR when used in combination with mAb 806 but the mechanism for this was not elucidated (Johns, T. G., Luwor, R. B., Murone, C., Walker, F., Weinstock, J., Vitali, A. A., Perera, R. M., Jungbluth, A. A., Stockert, E., Old, L. J., Nice, E. C., Burgess, A. W., and Scott, A. M. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 15871-15876). We now show that AG1478 increases binding of mAb 806 to the cell surface through two distinct mechanisms: an immediate effect on the conformation of EGFR and a longer term increase in cell surface under-glycosylated EGFR, an event known to increase mAb 806 reactivity. Cross-linking studies demonstrated the presence of spontaneously occurring mAb 806-reactive dimers on the surface of cells overexpressing EGFR, which are rapidly increased by AG1478. Because they react with mAb 806, these dimers must exist in a conformation distinct from the ligated back-to-back dimer. Indeed, we detected similar dimers in 293T cells expressing the EGFR lacking the small dimerization/activation arm essential to the formation of the back-to-back dimer. Thus, some of the EGFR on the cell surface of cancer cells must exist as an untethered dimer that adopts a previously unreported conformation that is inactive. This information was used to optimize the therapeutic synergy between mAb 806 and AG1478 in a xenograft model.

Animals↗
PubMed2006

Epidermal growth factor receptor (EGFR) antibody down-regulates mutant receptors and inhibits tumors expressing EGFR mutations.

Activating mutations in the kinase domain of the EGF receptor have been reported in non-small cell lung cancer. The majority of tumors expressing these mutants are sensitive to ATP mimetics that inhibit the EGFR tyrosine kinase. The effect of antibodies that bind to the ectodomain of the receptor is less clear. We report herein the effects and mechanisms of action of the antibody cetuximab in lung cancer cells that naturally express receptor mutations and in ErbB-null 32D hematopoietic cells transfected with mutant EGFR. Treatment with cetuximab down-regulated EGFR levels and inhibited cell growth both in vitro and in vivo. This was associated with inhibition of ligand-independent EGFR signaling. These effects were seen in 32D cells arguing the growth inhibitory action was not because of the blockade of autocrine ligand action. Both antibody-induced EGFR down-regulation and inhibition of growth required receptor dimerization as monovalent Fab fragments only eliminated receptor levels or reduced cell proliferation in the presence of antihuman IgG. Finally, cetuximab inhibited growth of H1975 lung cancer cells and xenografts, which expressed L858R/T790M EGFR and were resistant to EGFR tyrosine kinase inhibitors. These data suggest that cetuximab is an effective therapy against mutant EGFR-expressing cancer cells and thus can be considered in combination with other anti-EGFR molecules.

Animals↗
PubMed2026

Enozertinib Is a Selective, Brain-Penetrant EGFR Inhibitor for Treating Non-Small Cell Lung Cancers with EGFR Exon 20 and Atypical Mutations.

UNLABELLED: EGFR mutations are common oncogenic drivers in non-small cell lung cancer (NSCLC), and approximately half of patients develop brain metastases over the course of their disease. Patients with nonclassic EGFR mutations, such as insertions in exon 20, are a high unmet need with a worse prognosis compared with patients with classic EGFR mutations. Here, we describe the discovery and development of enozertinib (formerly ORIC-114), a highly brain-penetrant, orally bioavailable, irreversible inhibitor that targets EGFR exon 20 mutations with unparalleled kinome selectivity. Preclinical studies revealed strong potency and tumor regressions driven by enozertinib across a broad range of atypical EGFR-mutant models. In a phase I clinical trial of enozertinib in patients with advanced NSCLC bearing atypical mutations in EGFR, a patient harboring an EGFR exon 20 insertion experienced sustained complete response of all systemic and brain metastases. Together, these findings identify enozertinib as a promising investigational inhibitor to address the unmet need for brain-penetrant therapies in NSCLC with EGFR exon 20 insertions or other atypical mutations. SIGNIFICANCE: Preclinical and initial phase I clinical data demonstrate the potency, kinome selectivity, efficacy, and brain penetration of enozertinib in NSCLC with EGFR exon 20 insertions and atypical mutations, warranting further clinical development.

Carcinoma, Non-Small-Cell Lung↗
PubMed2006

Signaling via ErbB2 and ErbB3 associates with resistance and epidermal growth factor receptor (EGFR) amplification with sensitivity to EGFR inhibitor gefitinib in head and neck squamous cell carcinoma cells.

PURPOSE: The epidermal growth factor receptor (EGFR) inhibitor gefitinib (Iressa) has shown antitumor activity in clinical trials against cancers, such as non-small cell lung cancer and head and neck squamous cell carcinoma (HNSCC). Research on non-small cell lung cancer has elucidated factors that may predict response to gefitinib. Less is known about molecular markers that may predict response to gefitinib in HNSCC patients. EXPERIMENTAL DESIGN: We analyzed possible associations of responsiveness to gefitinib with molecular markers of the EGFR/ErbB receptor family signaling pathway using 10 established HNSCC lines in vitro. IC50 of gefitinib sensitivity was determined using clonogenic survival assays. ErbB signaling was assessed by Western and real-time reverse transcription-PCR analyses of EGFR, ErbB2, ErbB3, and ErbB4 expression levels as well as by phosphorylation analysis of pEGFR, pErbB2, pErbB3, pAkt, and pErk. EGFR sequences encoding kinase domain and EGFR gene copy numbers were determined by cDNA sequencing and real-time PCR, respectively. Finally, responsiveness to gefitinib was compared with responsiveness to the anti-EGFR antibody cetuximab (Erbitux). RESULTS: Expression levels of pErbB2 (P = 0.02) and total ErbB3 protein (P = 0.02) associated with resistance to gefitinib. Combining gefitinib with pertuzumab (Omnitarg), an antibody targeting ErbB2 heterodimerization, provided additional growth-inhibitory effect over gefitinib alone on relatively gefitinib-resistant HNSCC cell lines. The same markers did not predict resistance to cetuximab. In contrast, a similar trend suggesting association between EGFR gene copy number and drug sensitivity was observed for both gefitinib (P = 0.0498) and cetuximab (P = 0.053). No activating EGFR mutations were identified. CONCLUSIONS: EGFR amplification may predict sensitivity to gefitinib in HNSCC. However, other EGFR/ErbB receptor family members than EGFR may contribute to resistance to gefitinib. ErbB2 and ErbB3 may have potential as predictive markers and as therapeutic targets for combination therapy in treatment of HNSCC with gefitinib.

Antibodies, Monoclonal↗
PubMed2005

Enhanced efficacy of radioimmunotherapy with 90Y-CHX-A''-DTPA-hu3S193 by inhibition of epidermal growth factor receptor (EGFR) signaling with EGFR tyrosine kinase inhibitor AG1478.

PURPOSE: Monoclonal antibodies and tyrosine kinase inhibitors specific for the epidermal growth factor receptor (EGFR) have been shown to enhance the effect of external beam radiation on EGFR-positive tumors. The effect of EGFR signaling abrogation by EGFR tyrosine kinase inhibitor on the efficacy of radioimmunotherapy has not been reported previously. This study investigated the effect of EGFR tyrosine kinase inhibition on the efficacy of radioimmunotherapy in a human cancer xenograft model. EXPERIMENTAL DESIGN: The humanized anti-Lewis Y antibody hu3S193 and the EGFR tyrosine kinase inhibitor AG1478 were studied. BALB/c nude mice were engrafted with A431 squamous carcinoma cells. Initial biodistribution properties of the 90Y-CHX-A''-DTPA-hu3S193 were evaluated in this model. In therapy experiments, cohorts of four to five xenografted mice were treated with saline as placebo, 0.4 mg AG1478 i.p. (six doses over 2 weeks), single i.v. injections of unlabeled hu3S193, or 90Y-CHX-A''-DTPA-hu3S193 (12.5, 25, 50, or 100 microCi). The combination of 0.4 mg AG1478 i.p. and 25 microCi 90Y-CHX-A''-DTPA-hu3S193 i.v. was subsequently evaluated in the A431 model. RESULTS: 90Y-CHX-A''-DTPA-hu3S193 retained excellent immunoreactivity after radiolabeling. The biodistribution study showed excellent uptake in tumor (90.33 +/- 38.84%ID/g) peaking at 24 to 72 hours after injection and with prolonged retention. 90Y-CHX-A''-DTPA-hu3S193 significantly inhibited A431 xenograft growth at 25, 50, and 100 microCi doses. The combination of 0.4 mg AG1478 with a single dose of 25 microCi 90Y-CHX-A''-DTPA-hu3S193 resulted in a significant enhancement of efficacy compared with either agent alone (P = 0.013). CONCLUSIONS: The efficacy of radioimmunotherapy with 90Y-CHX-A''-DTPA-hu3S193 is significantly enhanced by EGFR tyrosine kinase inhibitor AG1478. Further investigations of dosing regimens using EGFR tyrosine kinase inhibitors and radioimmunotherapy in the treatment of EGFR expressing tumors are warranted.

Animals↗
PubMed2002

Brain tumors in mice are susceptible to blockade of epidermal growth factor receptor (EGFR) with the oral, specific, EGFR-tyrosine kinase inhibitor ZD1839 (iressa).

Iressa (ZD1839) is a p.o.-active, selective, epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) that blocks signal transduction pathways implicated in cancer cell proliferation, survival, and host-dependent processes promoting cancer growth. EGFR is up-regulated in primary malignant tumors of the central nervous system (CNS) and in many systemic tumors that metastasize to the CNS. The purpose of our study was to evaluate the efficacy and toxicity of p.o.-administered ZD1839 for the treatment of established intracerebral (i.c.) tumors expressing EGFR or the tumorigenic mutated variant EGFRvIII, which is constitutively phosphorylated. Oral administration of ZD1839 at 50 or 100 mg/kg/day for 3 weeks in athymic mice with established i.c. A431 human epidermoid carcinoma expressing EGFR increased median survival by 88% (P = 0.009) and 105% (P < 0.001), respectively. Additionally, there was no evidence of systemic or CNS toxicity. However, ZD1839 failed to inhibit either s.c. or i.c. in vivo tumor growth when tumorigenicity was conferred by EGFRvIII. Western blotting revealed that treatment with ZD1839 virtually ablated phosphorylation of EGFR Tyr-1173 in A431 tumors. However, treatment of NR6M tumors with ZD1839 only partially decreased phosphorylation of EGFRvIII Tyr-1173 while up-regulating overall expression, suggesting that EGFRvIII may not be susceptible to the same molecular mechanisms of tyrosine kinase inhibition as EGFR. In conclusion, ZD1839 is active in a brain tumor model expressing EGFR, but not EGFRvIII, as EGFR mutations may lead to relative therapeutic resistance. On the basis of these observations, we believe that clinical trials of ZD1839 against brain tumors expressing EGFR are warranted, but that special consideration should be given to tumors that coexpress EGFRvIII.

3T3 Cells↗
PubMed2026

Targeting EGFR-Mutant Non-Small Cell Lung Cancer in Asia: An Update on Monotherapy and Combination Therapy&#xa0;With EGFR Inhibitors.

EGFR-mutant lung cancer represents a major subtype of non-small cell lung cancer in Asia, with particularly high prevalence in never-smokers, women, and patients with adenocarcinoma histology. Although this clinicopathologic enrichment has been recognized for more than two decades, the mechanisms underlying the excess frequency of EGFR-mutant disease in Asian populations remain only partially understood. Accumulating evidence suggests a multifactorial basis involving host genetic susceptibility and diversity, endogenous mutational processes and exogenous exposures such as ambient particulate matter. In particular, recent genomic and experimental studies support a tumour-promotion framework in which inflammatory microenvironmental cues may facilitate the outgrowth of pre-existing oncogenic clones, while mutational signatures provide genomic footprints of these processes. In parallel, the treatment landscape for EGFR-mutant non-small cell lung cancer has evolved substantially with successive generations of EGFR tyrosine kinase inhibitors (EGFR-TKIs), leading to marked improvements in survival. However, acquired resistance remains inevitable in most patients with advanced disease and is driven by both genetic and non-genetic mechanisms, including secondary EGFR alterations, bypass pathway activation, TP53-associated genomic instability, adaptive mutagenesis, and drug-tolerant persister states. These insights have provided a strong rationale for combination strategies beyond EGFR-TKI monotherapy. In this review, we summarize current understanding of the epidemiology and biological basis of EGFR-mutant lung cancer in Asia and discuss the preclinical rationale and emerging clinical evidence supporting combination approaches with chemotherapy, anti-angiogenic agents, and EGFR/MET-directed therapies.

EGFR mutations↗
PubMed2001

A strong intronic enhancer element of the EGFR gene is preferentially active in high EGFR expressing breast cancer cells.

Hormone-independent human breast cancer is characterized by estrogen receptor (ER) loss and the acquisition of high epidermal growth factor receptor (EGFR) levels. Despite the tendency for an inverse correlation between EGFR and ER, EGFR is a strong prognostic indicator for poor survival rate independent of ER status suggesting that EGFR overexpression is an important step in the progression to estrogen independence. We have previously shown that several DNase I hypersensitive sites which correspond to potential regulatory regions reside within the EGFR gene first intron exclusively in hormone-independent breast cancer cells. CAT assays investigating the transcriptional activity of the first intron of EGFR indicate that a 140 bp region has an enhancer ability specifically in these hormone-independent breast cancer cells. The DNA-protein interaction that occurs in this enhancer was localized to a 35 bp region and displayed enhancer-like activity in the same hormone-independent breast cancer cells. Furthermore, the protein that binds to this 35 bp region seems to be ubiquitous in the cell lines tested but in higher abundance in high EGFR expressing cells. Identifying the specific regulatory elements involved in EGFR up-regulation could lead to the development of therapies for preventing and treating estrogen-independent breast cancer.

Base Sequence↗
PubMed2001

ZD1839 (Iressa), a novel epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, potently inhibits the growth of EGFR-positive cancer cell lines with or without erbB2 overexpression.

Overexpression of the growth factor receptors EGFR and erbB2 occurs frequently in several human cancers and is associated with aggressive tumour behaviour and poor patient prognosis. We have investigated the effects of ZD1839 (Iressa), a novel EGFR tyrosine kinase inhibitor, on the growth, in vitro and in vivo, of human cancer cell lines expressing various levels of EGFR and erbB2. Proliferation of EGFR-overexpressing A431 and MDA-MB-231 cells in vitro was potently inhibited (50%-70%) by ZD1839 with half-maximally effective doses in the low nanomolar range. In parallel, ZD1839 blocked autophosphorylation of EGFR and prevented activation of PLC-gamma 1, ERK MAP kinases and PKB/Akt by EGF. It also inhibited proliferation in EGFR(+) cancer cell lines overexpressing erbB2 (SKBr3, SKOV3, BT474) by between 20% and 80%, effects which correlated with inhibition of EGF-dependent erbB2 phosphorylation and activation of ERK MAP kinase and PKB/Akt in SKOV3 cells. Oral administration of ZD1839 inhibited the growth of MDA-MB-231 and SKOV3 tumours, established as xenografts in athymic mice, by 71% and 32%, respectively. Growth inhibition coincided with reduced proliferation but no change in apoptotic index. Collectively, these results show that ZD1839, at the doses studied, is a potent inhibitor of proliferation not only in cells overexpressing EGFR but also in EGFR(+) cells that overexpress erbB2.

Cell Division↗
PubMed2006

Planning for intracavitary anti-EGFR radionuclide therapy of gliomas. Literature review and data on EGFR expression.

Targeting with radionuclide labelled substances that bind specifically to the epidermal growth factor receptor, EGFR, is considered for intracavitary therapy of EGFR-positive glioblastoma multiforme, GBM. Relevant literature is reviewed and examples of EGFR expression in GBM are given. The therapeutical efforts made so far using intracavitary anti-tenascin radionuclide therapy of GBM have given limited effects, probably due to low radiation doses to the migrating glioma cells in the brain. Low radiation doses might be due to limited penetration of the targeting agents or heterogeneity in the expression of the target structure. In this article we focus on the possibilities to target EGFR on the tumour cells instead of an extracellular matrix component. There seems to be a lack of knowledge on the degree of intratumoral variation of EGFR expression in GBM, although the expression seemed rather homogeneous over large areas in most of the examples (n=16) presented from our laboratory. The observed homogeneity was surprising considering the genomic instability and heterogeneity that generally characterises highly malignant tumours. However, overexpression of EGFR is, at least in primary GBMs, one of the steps in the development of malignancy, and tumour cells that lose or downregulate EGFR will probably be outgrown in an expanding tumour cell population. Thus, loss of EGFR expression might not be the critical factor for successful intracavitary radionuclide therapy. Instead, it is likely that the penetration properties of the targeting agents are critical, and detailed studies on this are urgent.

Antibodies↗
PubMed2006

Nuclear EGFR signalling network in cancers: linking EGFR pathway to cell cycle progression, nitric oxide pathway and patient survival.

Emerging evidences suggest the existence of a new mode of epidermal growth factor receptor (EGFR) signalling pathway in which activated EGFR undergoes nuclear translocalization and subsequently regulates gene expression and potentially mediates other cellular processes. This signalling route is distinct from the better-characterized, traditional EGFR pathway that involves transduction of mitogenic signals through activation of multiple signalling cascades. Transcriptional activity of nuclear EGFR appears to depend on its C-terminal transactivation domain and its physical and functional interaction with other transcription factors that contain DNA-binding activity. Likely via its ability to upregulate gene expression, nuclear EGFR pathway is associated with major characteristics of more aggressive tumours: increased proliferative potential, nitric oxide synthesis, and accelerated G1/S cell cycle progression. A role of nuclear EGFR in prognostic prediction is further suggested in patients with breast carcinomas and oropharyngeal squamous cell carcinomas. It is noted that significant advances were made towards the knowledge of the nuclear EGFR pathway; however, many aspects of this new pathway remain unresolved and will be discussed in this review. As a number of other receptor tyrosine kinases (RTKs) and cytokine receptors also undergo similar nuclear translocalization, a better understanding of the physiological and malignant nature of the nuclear EGFR pathway will likely shed light into the biology of cancer with nuclear RTKs.

Animals↗
PubMed2004

Interactions of EGFR and caveolin-1 in human glioblastoma cells: evidence that tyrosine phosphorylation regulates EGFR association with caveolae.

Epidermal growth factor receptor (EGFR) amplification and type III mutation (EGFRvIII), associated with constitutive tyrosine kinase activation and high malignancy, are commonly observed in glioblastoma tumors. The association of EGFR and EGFRvIII with caveolins was investigated in human glioblastoma cell lines, U87MG and U87MG-EGFRvIII. Caveolin-1 expression, determined by RT-PCR, real-time quantitative PCR and Western blot, was upregulated in glioblastoma cell lines (two-fold) and tumors (20-300-fold) compared to primary human astrocytes and nonmalignant brain tissue, respectively. U87MG-EGFRvIII expressed higher levels of caveolin-1 than U87MG. In contrast, the expression of caveolin-2 and -3 were downregulated in glioblastoma cells compared to astrocytes. A colocalization of EGFR, but not of EGFRvIII, with lipid rafts and caveolin-1 was observed by immunocytochemistry. Association of EGFR and EGFRvIII with caveolae, assessed in vitro by binding to caveolin scaffolding domain peptides and in vivo by immunocolocalization studies in cells and caveolae-enriched cellular fraction, was phosphorylation-dependent: ligand-induced phosphorylation of EGFR resulted in dissociation of EGFR from caveolae. In contrast, inhibition of the EGFRvIII constitutive tyrosine phosphorylation by AG1478 increased association of EGFRvIII with caveolin-1. AG1478 also increased caveolin-1 expression and reduced glioblastoma cell growth in a semi-solid agar. The evidence suggests that the phosphorylation-regulated sequestration of EGFR in caveolae may be involved in arresting constitutive or ligand-induced signaling through EGFR responsible for glial cell transformation.

Caveolin 1↗
PubMed2004

Continual expression of Rab5(Q79L) causes a ligand-independent EGFR internalization and diminishes EGFR activity.

The amount of cell-surface Epidermal Growth Factor Receptor (EGFR) available to secreted ligand (EGF) dictates a cell's ability to mediate cell proliferation, differentiation or migration. Multiple factors regulate EGFR cell-surface expression including the rates of protein synthesis and protein degradation, and the endocytic trafficking of both stimulated and unstimulated EGFR. Rab5 is a 25 kDa protein that is localized to the plasma membrane and the early endosome. Its exact molecular function, however, remains controversial. We have used stable and transient expression systems in HeLa cells to examine the consequence of continual, overexpression of wild-type and activated mutants of rab5 on EGFR localization and signaling. Continual expression of constitutively activated mutants of rab5 causes a ligand-independent redistribution of EGFRs into intracellular vesicles that can not be blocked with an antagonistic antibody. The net result is a decrease in the level of cell-surface EGFRs available for ligand stimulation. Thus, rab5 activation regulates EGFR signaling by facilitating the internalization of the unliganded EGFR.

Animals↗