Antisense oligonucleotides targeting the epidermal growth factor receptor inhibit proliferation, induce apoptosis, and cooperate with cytotoxic drugs in human cancer cell lines

Targeting the Epidermal Growth Factor Receptor with Molecular Degraders: State-of-the-Art and Future Opportunities

Epidermal growth factor receptor (EGFR) is an oncogenic drug target and plays a critical role in several cellular functions including cancer cell growth, survival, proliferation, differentiation, and motility. Several small-molecule tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs) have been approved for targeting intracellular and extracellular domains of EGFR, respectively. However, cancer heterogeneity, mutations in the catalytic domain of EGFR, and persistent drug resistance limited their use. Different novel modalities are gaining a position in the limelight of anti-EGFR therapeutics to overcome such limitations. The current perspective reflects upon newer modalities, importantly the molecular degraders such as PROTACs, LYTACs, AUTECs, and ATTECs, etc., beginning with a snapshot of traditional and existing anti-EGFR therapies including small molecule inhibitors, mAbs, and antibody drug conjugates (ADCs). Further, a special emphasis has been made on the design, synthesis, successful applications, state-of-the-art, and emerging future opportunities of each discussed modality.

Inhibition of Epidermal Growth Factor Receptor Signaling by Antisense Oligonucleotides as a Novel Approach to Epidermal Growth Factor Receptor Inhibition

We report a novel method to inhibit epidermal growth factor receptor (EGFR) signaling using custom morpholino antisense oligonucleotides (ASOs) to drive expression of dominant negative mRNA isoforms of EGFR by ASO-induced exon skipping within the transmembrane (16) or tyrosine kinase domains (18 and 21). In vivo ASO formulations induced >95% exon skipping in several models of nonsmall cell lung cancer (NSCLC) and were comparable in efficacy to erlotinib in reducing colony formation, cell viability, and migration in EGFR mutant NSCLC (PC9). However, unlike erlotinib, ASOs maintained their efficacy in both erlotinib-resistant subclones (PC9-GR) and wild-type overexpressing EGFR models (H292), in which erlotinib had no significant effect. The most dramatic ASO-induced phenotype resulted from targeting the EGFR kinase domain directly, which resulted in maximal inhibition of phosphorylation of EGFR, Akt, and Erk in both PC9 and PC9GR cells. Phosphoproteomic mass spectrometry confirmed highly congruent impacts of exon 16-, 18-, and 21-directed ASOs compared with erlotinib on PC9 genome-wide cell signaling. Furthermore, EGFR-directed ASOs had no impact in EGFR-independent NSCLC models, confirming an EGFR-specific therapeutic mechanism. Further exploration of synergy of ASOs with existing tyrosine kinase inhibitors may offer novel clinical models to improve EGFR-targeted therapies for both mutant and wild-type NSCLC patients.

Composites of Nucleic Acids and Boron Clusters (C2B10H12) as Functional Nanoparticles for Downregulation of EGFR Oncogene in Cancer Cells

Epidermal growth factor receptor (EGFR) is one of the most promising molecular targets for anticancer therapy. We used boron clusters as a platform for generation of new materials. For this, functional DNA constructs conjugated with boron clusters (B-ASOs) were developed. These B-ASOs, built from 1,2-dicarba-closo-dodecaborane linked with two anti-EGFR antisense oligonucleotides (ASOs), form with their complementary congeners torus-like nanostructures, as previously shown by atomic force microscope (AFM) and transmission electron cryo-microscopy (cryo-TEM) imaging. In the present work, deepened studies were carried out on B-ASO's properties. In solution, B-ASOs formed four dominant complexes as confirmed by non-denaturing polyacrylamide gel electrophoresis (PAGE). These complexes exhibited increased stability in cell lysate comparing to the non-modified ASO. Fluorescently labeled B-ASOs localized mostly in the cytoplasm and decreased EGFR expression by activating RNase H. Moreover, the B-ASO complexes altered the cancer cell phenotype, decreased cell migration rate, and arrested the cells in the S phase of cell cycle. The 1,2-dicarba-closo-dodecaborane-containing nanostructures did not activate NLRP3 inflammasome in human macrophages. In addition, as shown by inductively coupled plasma mass spectrometry (ICP MS), these nanostructures effectively penetrated the human squamous carcinoma cells (A431), showing their potential applicability as anticancer agents.

Advances in covalent kinase inhibitors

This comprehensive review details recent advances, challenges and innovations in covalent kinase inhibition within a 10 year period (2007–2018).

Expression, purification, and characterization of the native intracellular domain of human epidermal growth factor receptors 1 and 2 in Escherichia coli

Human epidermal growth factor receptors (EGFR) are an important target in drug discovery in terms of both protein-small-molecule interactions and protein-protein interactions. In this work, the isolation of a stable soluble protein of the tyrosine kinase domain of EGFR in Escherichia coli expression has been accomplished. This successful study presents the expression and purification conditions to obtain a stable soluble protein of the active tyrosine kinase domain of EGFR (EGFR-TK) and ErbB2 (ErbB2-TK) in a bacterial system, albeit in relatively low yields. The recombinant gene was inserted into a pColdI vector and recombinant protein was expressed at low temperature. Purification of EGFR-TK and ErbB2-TK took place under the same conditions by purified supernatant using a diethylaminoethyl sepharose column followed by anion exchange and size-exclusion chromatography columns. The final yields of purified EGFR-TK and ErbB2-TK were 8.4 and 9.5 mg per liter of culture, respectively. Determination of EGFR-TK and ErbB2-TK was performed via enzyme activity with commercial drugs. The IC₅₀ values of erlotinib and afatinib against EGFR-TK were 13.09 nM and 2.36 nM respectively, while the IC₅₀ values of lapatinib and afatinib against ErbB2-TK were 24.69 nM and 1.36 nM, respectively. These results confirmed that soluble proteins of the active intracellular domain of the HERs family were successfully expressed and purified in a bacterial system. The new protein expression and purification protocol will greatly facilitate the enzymatic inhibition and structural studies of this protein for drug discovery.

Biocompatible ELR-Based Polyplexes Coated with MUC1 Specific Aptamers and Targeted for Breast Cancer Gene Therapy

The search for new and biocompatible materials with high potential for improvement is a challenge in gene delivery applications. A cell type specific vector made of elastin-like recombinamer (ELR) and aptamers has been specifically designed for the intracellular delivery of therapeutic material for breast cancer therapy. A lysine-enriched ELR was constructed and complexed with plasmid DNA to give positively charged and stable polyplexes. Physical characterization of these polyplexes showed a particle size of around 140 nm and a zeta potential of approximately +40 mV. The incorporation of MUC1-specific aptamers into the polyplexes resulted in a slight decrease in zeta potential but increased cell transfection specificity for MCF-7 breast cancer cells with respect to a MUC1-negative tumor line. After showing the transfection ability of this aptamer-ELR vector which is facilitated mainly by macropinocytosis uptake, we demonstrated its application for suicide gene therapy using a plasmid containing the gene of the toxin PAP-S. The strategy developed in this work about using ELR as polymeric vector and aptamers as supplier of specificity to deliver therapeutic material into MUC1-positive breast cancer cells shows promising potential and continues paving the way for ELRs in the biomedical field.

Epidermal growth factor receptor targeting in cancer: a review of trends and strategies

The epidermal growth factor receptor (EGFR) is a cell-surface receptor belonging to ErbB family of tyrosine kinase and it plays a vital role in the regulation of cell proliferation, survival and differentiation. However; EGFR is aberrantly activated by various mechanisms like receptor overexpression, mutation, ligand-dependent receptor dimerization, ligand-independent activation and is associated with development of variety of tumors. Therefore, specific EGFR inhibition is one of the key targets for cancer therapy. Two major approaches have been developed and demonstrated benefits in clinical trials for targeting EGFR; monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs). EGFR inhibitors like, cetuximab, panitumumab, etc. (mAbs) and gefitinib, erlotinib, lapatinib, etc. (TKIs) are now commercially available for treatment of variety of cancers. Recently, many other agents like peptides, nanobodies, affibodies and antisense oligonucleotide have also shown better efficacy in targeting and inhibiting EGFR. Now a days, efforts are being focused to identify molecular markers that can predict patients more likely to respond to anti-EGFR therapy; to find out combinatorial approaches with EGFR inhibitors and to bring new therapeutic agents with clinical efficacy. In this review we have outlined the role of EGFR in cancer, different types of EGFR inhibitors, preclinical and clinical status of EGFR inhibitors as well as summarized the recent efforts made in the field of molecular EGFR targeting.

Breast cancer subtypes: response to radiotherapy and potential radiosensitisation

Radiotherapy (RT) is of critical importance in the locoregional management of early breast cancer. Over 50% of patients receive RT at some time during the treatment of their disease, equating to over 500 000 patients worldwide receiving RT each year. Unfortunately, not all patients derive therapeutic benefit and some breast cancers are resistant to treatment, as evidenced by distant metastatic spread and local recurrence. Prediction of individual responses to RT may allow a stratified approach to this treatment permitting those patients with radioresistant tumours to receive higher doses of RT (total and/or tumour cavity boost doses) and/or radiosensitising agents to optimise treatment. Also, for those patients unlikely to respond at all, it would prevent harmful side effects occurring for no therapeutic gain. More selective targeting would better direct National Health Service resources, ease the burden on heavily used treatment RT machines and reduce the economic cost of cancer treatment. Unfortunately, there are no robust and validated biomarkers for predicting RT outcome. We review the available literature to determine whether classification of breast cancers according to their molecular profile may be used to predict successful response to, or increased morbidity from, RT. Class-specific biomarkers for targeting by radiosensitising agents are also discussed.

Gefitinib (ZD1839) increases the efficacy of cisplatin in ovarian cancer cells

We examined the effect of gefitinib (ZD1839), a selective epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor, on cytotoxicity to cisplatin, EGFR downstream signaling, apoptosis and the association between the inhibition of DNA repair by gefitinib and the expression of DNA-dependent protein kinase (DNA-PK) using three ovarian cancer cell lines. In the presence of gefitinib, cisplatin-induced growth inhibition and apoptosis were significantly enhanced in Caov-3 and RMG-1 cells, which express EGFR, and in A2780, which lacks EGFR but expresses HER-2. Gefitinib significantly inhibited the cisplatin-induced ERK and Akt activation in Caov-3 and RMG-1 cells but not in A2780 cells. In all three cell lines, there was delayed repair of DNA intrastrand cross-links damaged by cisplatin used in combination with gefitinib, compared with cisplatin alone. The reduction in DNA-PK levels persisted when cells were exposed to combinations of cisplatin and gefitinib in all cell lines. Moreover, the delayed repair was cancelled by anti-HER2 small-interfering RNA transfection in A2780 cells. These results suggest that combination therapy with cisplatin and gefitinib may increase the therapeutic efficacy of cisplatin by blocking EGFR downstream signaling and/or inhibiting DNA repair in ovarian cancer.

EGFR(s) in aging and carcinogenesis of the gastrointestinal tract

Cells of the gastrointestinal (GI) mucosa are subject to a constant process of renewal which, in normal adults, reflects a balance between the rates of cell production and cell loss. Detailed knowledge of these events is, therefore, essential for a better understanding of the normal aging processes as well as many GI diseases, particularly malignancy, that represent disorders of tissue growth. In general, many GI dysfunctions, including malignancy, increase with advancing age, and aging itself is associated with alterations in structural and functional integrity of the GI tract. Although the regulatory mechanisms for age-related increase in the incidence of GI-cancers are yet to be fully delineated, recent evidence suggests a role for epidermal growth family receptors and its family members {referred to as EGFR(s)} in the development and progression of carcinogenesis during aging. The present communication discusses the involvement of EGFR(s) in regulating events of GI cancers during advancing age and summarizes the current available therapeutics targeting these receptors. The current review also describes the effectiveness of ErbB inhibitors as well as combination therapies. Additionally, the involvement of GI stem cells in the development of the age-related rise in GI cancers is emphasized.

Molecular imaging metrics to evaluate response to preclinical therapeutic regimens

Molecular imaging comprises a range of techniques, spanning not only several imaging modalities but also many disease states and organ sites. While advances in new technology platforms have enabled a deeper understanding of the cellular and molecular basis of malignancy, reliable non-invasive imaging metrics remain an important tool for both diagnostics and patient management. Furthermore, the non- invasive nature of molecular imaging can overcome shortcomings associated with traditional biological approaches and provide valuable information relevant to patient care. Integration of information from multiple imaging techniques has the potential to provide a more comprehensive understanding of specific tumor characteristics, tumor status, and treatment response.

Emerging drugs to treat squamous cell carcinomas of the head and neck

IMPORTANCE OF THE FIELD

Head and neck squamous cell carcinoma (HNSCC) is the eighth leading cause of cancer death worldwide. Despite advances in surgery and chemoradiation therapy, there has been little improvement in survival rates over the past 4 decades. Additionally, surgery and chemoradiotherapy have serious side effects. The development of agents with greater efficacy and tolerability is needed.

AREAS COVERED IN THIS REVIEW

EGFR is the only proven molecular target for HNSCC therapy. Cetuximab, the sole FDA-approved molecular targeted HNSCC therapy, and other potential targeted therapies are being evaluated in preclinical, clinical and post-marketing studies. Here, we review the emerging targets for biological agents in HNSCC and the rationale for their selection.

WHAT THE READER WILL GAIN

Key information in the development of new drug targets and the emergence of new biomarkers are discussed. Readers will gain insight regarding the limitations of current therapies, the impact of recently approved targeted therapies and the influence that predictive biomarkers will have on drug development.

TAKE HOME MESSAGE

The head and neck cancer drug market is rapidly evolving. Coordination between drug and biomarker development efforts may soon yield targeted therapies that can achieve the promise of personalized cancer medicine.

Evaluation of folate-PAMAM for the delivery of antisense oligonucleotides to rat C6 glioma cells in vitro and in vivo

In the current study, we evaluated the efficiency of folate-polyamidoamine dendrimers conjugates (FA-PAMAM) for the in situ delivery of therapeutic antisense oligonucleotides (ASODN) that could inhibit the growth of C6 glioma cells. Folic acid was coupled to the surface amino groups of G5-PAMAM dendrimer (G5D) through a 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide bond, and ASODNs corresponding to rat epidermal growth factor receptor (EGFR) were then complexed with FA-PAMAM. At an ASODN to PAMAM ratio of 16:1, agarose electrophoresis indicated that antisense oligonucleotides were completely complexed with PAMAM or FA-PAMAM. The ASODN transfection rates mediated by FA-PAMAM and PAMAM were superior to oligofectamine, resulting in greater suppression of EGFR expression and glioma cell growth. Stereotactic injection of EGFR ASODN:FA-PAMAM complexes into established rat C6 intracranial gliomas resulted in greater suppression of tumor growth and longer survival time of tumor-bearing rats compared with PAMAM and oligofectamine-mediated EGFR-ASODN therapy. The current study demonstrates the suitability of folate-PAMAM dendrimer conjugates for efficient EGFR ASODN delivery into glioma cells, wherein they release the ASODN from the FA-PAMAM to knock down EGFR expression in C6 glioma cells, both in vitro and in vivo. FA-PAMAM may thus represent a novel delivery system for short oligonucleotides in glioma-targeted therapy.

Epidermal growth factor receptor signaling in nonsmall cell lung cancer

Epidermal growth factor is a 170-kd protein that binds to a specific tyrosine kinase receptor, epidermal growth factor receptor (EGFR), on the cell surface. EGFR function is dysregulated in various malignancies including nonsmall cell lung cancer (NSCLC) leading to activation of several signal transduction pathways including K-RAS, PIK3, and STAT3 and STAT5, that promote cell cycle progression, proliferation, invasion, angiogenesis, and inhibit apoptosis. EGFR overexpression is seen in a majority of cases of NSCLC, but its prognostic role is controversial. EGFR inhibitors currently undergoing clinical trials in NSCLC include monoclonal antibodies or small molecule tyrosine kinase inhibitors. The only EGFR inhibitor currently approved for the treatment of NSCLC is erlotinib, a small molecule tyrosine kinase inhibitor. Although women, nonsmokers, patients with adenocarcinoma and patients with Asian ethnicity seem to have better outcomes with erlotinib, the factors predictive for response to these agents are currently the focus of investigation.

The biological effect of 125I seed continuous low dose rate irradiation in CL187 cells

Background

To investigate the effectiveness and mechanism of ¹²⁵I seed continuous low-dose-rate irradiation on colonic cell line CL187 in vitro.

Methods

The CL187 cell line was exposed to radiation of ⁶⁰Coγ ray at high dose rate of 2 Gy/min and ¹²⁵I seed at low dose rate of 2.77 cGy/h. Radiation responses to different doses and dose rates were evaluated by colony-forming assay. Under ¹²⁵I seed low dose rate irradiation, a total of 12 culture dishes were randomly divided into 4 groups: Control group, and 2, 5, and 10 Gy irradiation groups. At 48 h after irradiation, apoptosis was detected by Annexin and Propidium iodide (PI) staining. Cell cycle arrests were detected by PI staining. In order to investigate the influence of low dose rate irradiation on the MAPK signal transduction, the expression changes of epidermal growth factor receptor (EGFR) and Raf under continuous low dose rate irradiation (CLDR) and/or EGFR monoclonal antibodies were determined by indirect immunofluorescence.

Results

The relative biological effect (RBE) for ¹²⁵I seeds compared with ⁶⁰Co γ ray was 1.41. Apoptosis rates of CL187 cancer cells were 13.74% ± 1.63%, 32.58% ± 3.61%, and 46.27% ± 3.82% after 2 Gy, 5 Gy, and 10 Gy irradiation, respectively; however, the control group apoptosis rate was 1.67% ± 0.19%. G₂/M cell cycle arrests of CL187 cancer cells were 42.59% ± 3.21%, 59.84% ± 4.96%, and 34.61% ± 2.79% after 2 Gy, 5 Gy, and 10 Gy irradiation, respectively; however, the control group apoptosis rate was 26.44% ± 2.53%. P < 0.05 vs. control groups by Student's t-test were found in every treated group both in apoptosis and in G₂/M cell cycle arrest. After low dose rate irradiation, EGFR and Raf expression increased, but when EGFR was blocked by a monoclonal antibody, EGFR and Raf expression did not change.

Conclusion

¹²⁵I seeds resulted in more effective inhibition than ⁶⁰Co γ ray high dose rate irradiation in CL187 cells. Apoptosis following G₂/M cell cycle arrest was the main mechanism of cell-killing effects under low dose rate irradiation. CLDR could influence the proliferation of cells via MAPK signal transduction.

Dose-dependent and sequence-dependent cytotoxicity of erlotinib and docetaxel in head and neck squamous cell carcinoma

The purpose of this study was to determine whether the efficacy of taxoid treatment combined with epidermal growth factor receptor (EGFR) inhibition is dose and sequence dependent in head and neck squamous cell carcinoma. Three head and neck squamous cell carcinoma cell lines, chosen on the basis of their diverse EGFR expression levels, were treated with docetaxel, erlotinib, or both. The combination index was calculated using the Chou-Talalay equation. Propidium iodide staining with fluorescence-activated cell sorting analysis was used to evaluate the effects of drugs on cell cycle changes. Western blot analysis was used to determine the effects of agents on cell signaling pathways. Administration of low-dose docetaxel (0.1-3 nmol/l) concurrently or before erlotinib had additive cytotoxic effects in two cell lines but was antagonistic in one line, whereas low-dose docetaxel after erlotinib was synergistic in all cell lines. In contrast, high-dose docetaxel (40 nmol/l) resulted in more apoptosis when given before, rather than after or concurrently with, erlotinib. Low-dose docetaxel induced an accumulation of cells in the sub-G0 phase of the cell cycle with no mitotic arrest or apoptosis, whereas high-dose docetaxel induced mitotic arrest and apoptosis. The low and high doses of docetaxel had opposite effects on EGFR expression: a decrease and an increase, respectively. The dose of docetaxel affects sequence-dependent cytotoxicity when docetaxel is combined with an EGFR inhibitor. The mechanism for this difference is a combination of the dose-dependent effects of docetaxel on the mode of cell death and on EGFR expression.

The efficacy and toxicity of EGFR in the settings of radiotherapy: Focus on published clinical trials

Basic research in solid malignant tumours has led to a wealth of knowledge about this disease process and about novel ways to more effectively target our therapies. Laboratory research continues to identify novel therapeutic targets and moreover, clinical research is identifying effective new treatment regimens. Many preclinical studies in this area have targeted the epidermal growth factor receptor (EGFR) signalling pathway to increase radiosensitivity. The in vitro rationale for targeting EGFR and concurrent ionising radiation is well established, but to date, rare clinical data could provide proof-of-principle. Here we report all the different published clinical trials focusing on efficacy and toxicity in order to clarify and to summarise the present state-of-the-art of this particularly promising combination in solid tumour management.

Rational bases for the development of EGFR inhibitors for cancer treatment

Growth factor receptors and their ligands not only regulate normal cell processes but have been also identified as key regulators of human cancer formation. The epidermal growth factor receptor (EGFR/ErbB1/HER1) belongs to the ErbB/HER-family of tyrosine kinase receptors (RTKs). These trans-membrane proteins are activated following binding with peptide growth factors of the EGF-family of proteins. Several evidences suggest that cooperation of multiple ErbB receptors and ligands is required for the induction of cell transformation. In this respect, EGFR, upon activation, sustains a complex and redundant network of signal transduction pathways with the contribution of other trans-membrane receptors. EGFR has been found to be expressed and altered in a variety of malignancies and clearly it plays a significant role in tumor development and progression, including cell proliferation, regulation of apoptotic cell death, angiogenesis and metastatic spread. Moreover, amplification of the EGFR gene and mutations in the EGFR tyrosine kinase domain have been recently reported in human carcinomas. As a result, investigators have developed approaches to inhibit the effects of EGFR activation, with the aim of blocking tumor growth and invasion. A number of agents targeting EGFR, including specific antibodies directed against its ligand-binding domain and small molecules inhibiting its tyrosine kinase activity are either in clinical trials or are already approved for clinical treatment. This article reviews the EGFR role in carcinogenesis and tumor progression as rational bases for the development of specific therapeutic inhibitors.

Overcoming resistance to molecularly targeted anticancer therapies: Rational drug combinations based on EGFR and MAPK inhibition for solid tumours and haematologic malignancies

Accumulating evidence suggests that cancer can be envisioned as a "signaling disease", in which alterations in the cellular genome affect the expression and/or function of oncogenes and tumour suppressor genes. This ultimately disrupts the physiologic transmission of biochemical signals that normally regulate cell growth, differentiation and programmed cell death (apoptosis). From a clinical standpoint, signal transduction inhibition as a therapeutic strategy for human malignancies has recently achieved remarkable success. However, as additional drugs move forward into the clinical arena, intrinsic and acquired resistance to "targeted" agents becomes an issue for their clinical utility. One way to overcome resistance to targeted agents is to identify genetic and epigenetic aberrations underlying sensitivity/resistance, thus enabling the selection of patients that will most likely benefit from a specific therapy. Since resistance often ensues as a result of the concomitant activation of multiple, often overlapping, signaling pathways, another possibility is to interfere with multiple, cross-talking pathways involved in growth and survival control in a rational, mechanism-based, fashion. These concepts may be usefully applied, among others, to agents that target two major signal transduction pathways: the one initiated by epidermal growth factor receptor (EGFR) signaling and the one converging on mitogen-activated protein kinase (MAPK) activation. Here, we review the molecular mechanisms of sensitivity/resistance to EGFR inhibitors, as well as the rationale for combining them with other targeted agents, in an attempt to overcome resistance. In the second part of the paper, we review MAPK-targeted agents, focusing on their therapeutic potential in haematologic malignancies, and examine the prospects for combinations of MAPK inhibitors with cytotoxic agents or other signal transduction-targeted agents to obtain synergistic anti-tumour effects.

European Society for Medical Oncology 2006: meeting highlights on targeted therapies. Istanbul, Turkey, 29 September-3 October 2006

Considerable advances in our understanding of the complex cellular, molecular and genetic mechanisms underlying tumorigenesis over the last decade have contributed to the development of novel and improved targeted therapies in cancer intervention. These novel therapies interfere specifically with signaling pathways essential for tumor cell proliferation, survival and migration, they may be able to inhibit tumor growth and metastasis effectively, with fewer severe adverse events than seen with existing chemotherapeutic interventions, which have a narrow therapeutic index and are associated with severe toxic side effects. Among the most recent advances in anticancer treatments are therapies that target novel cellular entities, such as epidermal growth factor receptor and vascular endothelial growth factor. Monoclonal antibodies and protein tyrosine kinase inhibitors represent two classes among these promising new therapeutic interventions. During the European Society for Medical Oncology Congress 2006 (Istanbul, Turkey, 29 September-3 October) new and emerging biological therapies have represented a central argument of research. These highlights summarize the most interesting studies concerning molecular agents, such as panitumumab, lapatinib, sunitinib, sorafenib, erlotinib, bevacizumab and cetuximab, to provide a comprehensive overview of the important points and news about this area of research discussed during the meeting.

Small interfering RNA targeting epidermal growth factor receptor enhances chemosensitivity to cisplatin, 5-fluorouracil and docetaxel in head and neck squamous cell carcinoma

Overexpression of epidermal growth factor receptor (EGFR) has been found in various epithelial malignancies, including head and neck squamous cell carcinoma (HNSCC), and is associated with increased tumor growth, metastasis, resistance to chemotherapeutic agents and poor prognosis. As such, EGFR is a potential target for antitumor therapy and several EGFR inhibitors have been investigated in preclinical or clinical settings. In the present study, we used small interfering RNA (siRNA) to downregulate EGFR expression while evaluating the effect of EGFR siRNA on cell proliferation, and the combined effects with cisplatin, 5-fluorouracil (5-FU) and docetaxel in HNSCC. Furthermore, HNSCC xenografts were treated with EGFR siRNA alone or in combination with cisplatin, and tumor growth was examined. EGFR expression, proliferation, angiogenesis and apoptosis index were evaluated by immunohistochemistry. The results showed that EGFR siRNA efficiently downregulated EGFR expression and inhibited cell growth of HNSCC. Treatment with EGFR siRNA in combination with cisplatin, 5-FU and docetaxel enhanced chemosensitivity with a significant increase in apoptosis. EGFR siRNA delivered by atelocollagen enhanced the antitumor effect of cisplatin in the HNSCC xenograft model. These cumulative results suggest that EGFR siRNA combined with cisplatin, 5-FU and docetaxel may be a feasible strategy to enhance the effects of chemotherapy in patients with HNSCC.

The complexity of targeting EGFR signalling in cancer: from expression to turnover

The epidermal growth factor receptor (ErbB1 or EGFR) has been found to be altered in a variety of human cancers. A number of agents targeting these receptors, including specific antibodies directed against the ligand-binding domain of the receptor and small molecules that inhibit kinase activity are either in clinical trials or are already approved for clinical treatment. However, identifying patients that are likely to respond to such treatments has been challenging. As a consequence, it still remains important to identify additional alterations of the tumor cell that contribute to the response to EGFR-targeted agents. While EGFR-mediated signalling pathways have been well established, there is still a rather limited understanding of how intracellular protein-protein interactions, ubiquitination, endocytosis and subsequent degradation of EGFR contribute to the determination of sensitivity to EGFR targeting agents and are emerging areas of investigation. This review primarily focuses on the basic signal transduction pathways mediated through activated membrane bound and/or endosomal EGFR and emphasizes the need to co-target additional proteins that function either upstream or downstream of EGFR to improve cancer therapy.

Cooperative inhibitory effect of ZD1839 (Iressa) in combination with 17-AAG on glioma cell growth

ZD1839 ("Iressa") is an orally active, selective epidermal growth factor (EGF) receptor-tyrosine kinase inhibitor. We evaluated the antitumor activity of ZD1839 in combination with HSP90 antagonist, 17-AAG in malignant human glioma cell lines. ZD1839 independently produced a dose-dependent inhibition of cellular proliferation in glioma cells grown in culture with time- and dose-dependent accumulation of cells in G(1) phase of the cell cycle on flow cytometric analysis, although the concentrations required for optimal efficacy were at or above the limits of clinically achievable levels. Because the heat shock protein (HSP) is involved in the conformational maturation of a number of signaling proteins critical to the proliferation of malignant glioma cells, we hypothesized that the HSP90 inhibitor 17-AAG would potentiate ZD 1839-mediated glioma cytotoxicity by decreasing the activation status of EGF receptor, as well as down regulating the levels of other relevant signaling effectors. We, therefore, examined the effects of ZD1839 and 17-AAG, alone and in combination, on signal transduction and apoptosis in a series of malignant glioma cell lines. Simultaneous exposure to these inhibitors significantly induced cell death and quantitative analysis revealed that interaction between ZD1839 and 17-AAG-induced cytotoxicity was synergistic, leading to a pronounced increase in active caspase-3 and PARP cleavage. No significant growth inhibition or caspase activation was seen in control cells. The enhanced cytotoxicity of this combination was associated with diminished Akt activation and a significant downregulation of EGFR receptor, Raf-1 and mitogen activated protein kinase (MAPK). Cells exposed to 17-AAG and ZD1839 displayed a significant reduction in cell cycle regulatory proteins, such as CDK4 and CDK6. Taken together, these findings suggest that ZD1839, an EGF receptor tyrosine kinase inhibitor, plays a critical role in regulating the apoptotic response to 17-AAG and that multi-site targeting of growth signaling and cell survival pathways could provide a potent strategy to treat patients with malignant gliomas.

Molecular biology of epidermal growth factor receptor inhibition for cancer therapy

Understanding the role of the epidermal growth factor receptor (EGFR) in cellular signalling processes underlying malignancy has enabled the development of rationally designed EGFR-targeted therapeutics. Strategies have been devised to interfere with the EGFR signalling at three different levels: at the extracellular level, competing with ligand binding; at the intracellular level, inhibiting the activation of the tyrosine kinase; or at the mRNA level, modulating the expression of the EGFR protein. Each of these strategies has proven to have an antitumour effect mediated by events such as inhibition of cell proliferation, induction of apoptosis, decrease of cellular invasion and migration; and/or inhibition of angiogenesis. Furthermore, the combination of these strategies with traditional chemotherapy or radiotherapy has generally resulted in enhanced antitumour effects. Likewise, the benefit of interfering simultaneously with different signalling pathways has been documented to improve tumour growth inhibition. These preclinical results have encouraged clinical studies that led to the FDA approval of three drugs. However, finding the perfect strategy for each individual patient appears to be a limiting factor, demanding further research to be able to generate relevant molecular expression profiles on a case-to-case basis. Taken together, a successful EGFR inhibition will require a better understanding of signalling pathways in combination with the development of rationally designed effective molecules.

Interaction of the epidermal growth factor receptor and the DNA-dependent protein kinase pathway following gefitinib treatment

The epidermal growth factor receptor (EGFR) is an important target for cancer therapy. We previously showed that the EGFR inhibitor gefitinib modulated repair of DNA damage following exposure to cisplatin and etoposide involving the DNA-dependent protein kinase (DNA-PK) pathway. In this study, we specifically investigated the effect of EGFR inhibition by gefitinib on functional activity of DNA-PK in cancer cell lines and the interaction between EGFR and DNA-PK. The effects of DNA-PK inhibition by wortmannin and small interfering RNA to the catalytic subunit of DNA-PK (DNA-PK(CS)) on cell proliferation and DNA interstrand cross-link repair were investigated in the human MCF-7 breast cancer cell line and compared with the effects of gefitinib. DNA-PK activity was quantitated and expression measured by immunoblotting following gefitinib treatment. Immunoprecipitation experiments were done with and without gefitinib in MCF-7 cells, the AR42J pancreas cell line with high EGFR, and the human MDA-453 breast cancer cell line expressing low EGFR. Nuclear and cytoplasmic extracts were immunoblotted with antibody to DNA-PK(CS) to determine if gefitinib treatment altered cellular expression. Reduction of DNA-PK activity by wortmannin and expression by small interfering RNA to DNA-PK(CS) sensitized cells to cisplatin and inhibited repair of cisplatin-induced interstrand cross-links. Gefitinib treatment reduced DNA-PK activity in MCF-7 and AR42J but not MDA-453 cells. Immunoprecipitation experiments showed interaction between EGFR and DNA-PK(CS) in a dose-dependent and time-dependent manner following gefitinib treatment in MCF-7 and AR42J but not MDA-453 cells. Gefitinib treatment reduced nuclear expression and increased cytosolic expression of DNA-PK(CS) in MCF-7 and AR42J but not MDA-453 cells. Treatment with gefitinib modulates association of EGFR and DNA-PK(CS). This is correlated with decreased function of DNA-PK(CS). Inhibition of DNA-PK(CS) may be an important factor in sensitization to chemotherapy and radiation following treatment with inhibitors of the EGFR pathway.

CD95-mediated apoptosis of human glioma cells: modulation by epidermal growth factor receptor activity

The death ligands CD95L and Apo2L/TRAIL are promising investigational agents for the treatment of malignant glioma. EGFR is overexpressed in a significant proportion of malignant gliomas in vivo. Here, we report that CD95L-induced cell death is enhanced by EGFR inhibition using tyrphostine AG1478 in 7 of 12 human malignant glioma cell lines. Conversely, CD95-mediated and Apo2L-induced cell death are both inhibited by overexpression of EGFR in LN-229 cells. CD95L-induced cell death augmented by AG1478 is accompanied by enhanced processing of caspase 8. LN-229 cells overexpressing the viral caspase inhibitor, crm-A, are not sensitized to CD95L-induced cell death by AG1478, indicating that EGFR exerts its antiapoptotic properties through a caspase 8-dependent pathway. These data define a modulatory effect of EGFR-activity on death ligand-induced apoptosis and indicate that EGFR inhibition is likely to improve the efficacy of death ligand-based cancer therapies. Furthermore, it is tempting to speculate that EGFR amplification protects tumor cells from death ligand-mediated host immune responses in vivo and that EGFR's effects on death receptor-mediated apoptosis may explain the anti-tumor effects of non-cytotoxic, unarmed anti-EGFR family antibodies.

Potential role of short hairpin RNA targeting epidermal growth factor receptor in growth and sensitivity to drugs of human lung adenocarcinoma cells

Upregulation of expression and activation of epidermal growth factor receptor (EGFR) is involved in the development and progression of a wide range of human cancers. The present study aims at determining gene-silencing effects of vector-based short hairpin RNA (shRNA) targeting EGFR on receptor expression and cell growth and evaluating its modulation of responsiveness to drugs in human lung adenocarcinoma cells (HLAC). A vector-based polymerase 3-promotor system was used to express shRNA targeting EGFR in HLAC lines (A549 and SPC-A1). EGFR was detected by immunofluorescence staining and quantified by Western blot. The effect of shRNA targeting EGFR on tumor cell growth was assessed by colony formation assay, cell cycle and apoptosis by flow cytometry, and the responsiveness of HLAC lines to cytotoxic drugs by 3-[4,5-dimethylthiozol-2yl]-2,5-diphenyltetrazolium bromide [MTT] assay. Vectors expressing shRNA against EGFR significantly downregulated receptor expression by 74 and 85% and the colony number by 63 and 69% in A549 and SPC-A1, respectively. Vector-based shRNA against EGFR caused G1 arrest, induced apoptosis, and subsequently increased the sensitivity to cisplatin, doxorubicin and paclitaxel by about four- to seven-fold in both HLAC lines. Our data suggest that vector-based shRNA could be considered as an alternative to effectively inhibit EGFR expression in HLACs, probably with the higher efficacy in combination therapies with conventional chemotherapeutic drugs.

Blockade of EGFR and ErbB2 by the novel dual EGFR and ErbB2 tyrosine kinase inhibitor GW572016 sensitizes human colon carcinoma GEO cells to apoptosis

Coexpression of the epidermal growth factor receptor (EGFR) family receptors is found in a subset of colon cancers, which may cooperatively promote cancer cell growth and survival, as heterodimerization is known to provide for diversification of signal transduction. Recently, efforts have been made to develop novel 4-anilinoquinazoline and pyridopyrimidine derivatives to inhibit EGFR and ErbB2 kinases simultaneously. In this study, we tested the efficacy of a novel reversible dual inhibitor GW572016 compared with the selective EGFR and ErbB2 tyrosine kinase inhibitors (TKI) AG1478 and AG879 and their combination, using the human colon adenocarcinoma GEO mode. GEO cells depend on multiple ErbB receptors for aberrant growth. A synergistic effect on inhibition of cell proliferation associated with induction of apoptosis was observed from the combination of AG1478 and AG879. Compared with AG1478 or AG879, the single TKI compound GW572016 was a more potent inhibitor of GEO cell proliferation and was able to induce apoptosis at lower concentrations. Western blot analysis revealed that AG1478 and AG879 were unable to suppress both EGFR and ErbB2 activation as well as the downstream mitogen-activated protein kinase (MAPK) and AKT pathways as single agents. In contrast, GW572016 suppressed the activation of EGFR, ErbB2, MAPK, and AKT in a concentration-dependent manner. Finally, in vivo studies showed that GW572016 treatment efficiently blocked GEO xenograft growth at a dose range of 30 to 200 mg/kg with a twice-daily schedule. In summary, our study indicates that targeting both EGFR and ErbB2 simultaneously could enhance therapy over that of single agents directed at EGFR or ErbB2 in cancers that can be identified as being primarily heterodimer-dependent.

Gene therapy for carcinoma of the breast

In view of the limited success of available treatment modalities for breast cancer, alternative and complementary strategies need to be developed. The delineation of the molecular basis of breast cancer provides the possibility of specific intervention by gene therapy through the introduction of genetic material for therapeutic purposes. In this regard, several gene therapy approaches for carcinoma of the breast have been developed. These approaches can be divided into six broad categories: (1) mutation compensation, (2) molecular chemotherapy, (3) proapoptotic gene therapy, (4) antiangiogenic gene therapy, (5) genetic immunopotentiation, and (6) genetic modulation of resistance/sensitivity. Clinical trials for breast cancer have been initiated to evaluate safety, toxicity, and efficacy. Combined modality therapy with gene therapy and chemotherapy or radiation therapy has shown promising results. It is expected that as new therapeutic targets and approaches are identified and advances in vector design are realized, gene therapy will play an increasing role in clinical breast cancer treatment.

Epidermal growth factor inhibition in solid tumours

The epidermal growth factor receptor (EGFR) plays an important role in the carcinogenesis of many human malignancies and is therefore an attractive target against which anticancer therapy may be effective. At present, there are two ways in which this may be achieved clinically: antibodies against EGFR and inhibitors of the EGFR tyrosine kinase. This review describes presently approved agents cetuximab (monoclonal EGFR antibody), gefitinib and erlotinib (EGFR tyrosine kinase inhibitors) in detail. Efficacy data for these agents in various human malignancies is presented. Various other agents that are in the early stages of development at present have also been mentioned.

Epidermal growth factor receptor inhibitors in the treatment of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death in both men and women. Despite the introduction of the newer cytotoxic agents in NSCLC treatment during the last decade the survival rates of patients have reached a plateau. New strategies are clearly needed to improve treatment outcomes. Epidermal growth factor receptor (EGFR) has a key role in cancer development and progression and has been recognised as a target of increasing importance in NSCLC. Gefitinib, erlotinib and cetuximab are EGFR-targeting agents that are being extensively evaluated in NSCLC. EGFR inhibitors demonstrate significant clinical activity in approximately 10-20% of pretreated NSCLC patients. Somatic mutations in the kinase domain of the receptor have been shown to be associated with enhanced sensitivity to EGFR inhibitors. However, four large Phase III randomised, placebo-controlled trials of gefitinib and erlotinib in combination with standard platinum-based first-line chemotherapy failed to show any survival benefit in patients receiving the study drugs. Possible reasons include patient selection, drug scheduling, trial design or other factors. Active research is ongoing to improve the efficacy of EGFR inhibitors as monotherapy or in combination with other treatment modalities.

A universal strategy for stable intracellular antibodies

The expression of intracellular antibodies (intrabodies) in mammalian cells has provided a powerful tool to manipulate microbial and cellular signalling pathways in a highly precise manner. However, several technical hurdles have thus far restricted their more widespread use. In particular, single-chain antibodies (scFvs) have been reported to fold poorly in the reducing environment of the cytoplasm and as such there has been a reluctance to use scFv-phage libraries as a source of intrabodies unless a preselection step was applied to identify these rare scFvs that could fold properly in the absence of disulfide bonds. Recently, we reported that scFvs can be efficiently expressed within the cytoplasm of bacteria when fused at the C-terminus of the Escherichia coli maltose-binding protein (MBP). Here, we demonstrate that such MBP-scFvs are similarly stabilized when expressed in the mammalian cell cytoplasm as well as other compartments. This was demonstrated by comparing MBP-scFv fusions to the corresponding unfused scFvs that activate a defective beta-galactosidase enzyme, others that neutralize the wild-type beta-galactosidase enzyme, and an antibody that blocks the epidermal growth factor receptor. In all cases, the MBP-scFvs significantly outperformed their unfused counterparts. Our results suggest that fusion of scFvs to MBP, and possibly to other "chaperones in the context of a fusion protein", may provide a universal approach for efficient expression of intrabodies in the mammalian cell cytoplasm. This strategy should allow investigators to bypass much of the in vitro scFv characterization that is often not predictive of in vivo intrabody function and provide a more efficient use of large native and synthetic scFv-phage libraries already in existence to identify intrabodies that will be active in vivo.

Combined effects of Cantide and chemotherapeutic drugs on inhibition of tumor cells’ growth in vitro and in vivo

AIM: To investigate the combination effect of hTERT antisense oligonucleotide “Cantide” and three chemotherapeutic drugs (cisplatin, 5-fluorouracil (5-FU) and adriamycin (ADM)) on inhibiting the proliferation of HepG2, BGC and A549 cell lines in vitro, and to investigate the efficacy of Cantide used in combination with cisplatin (DDP) in vivo.

METHODS: Cantide was transfected into these tumor cells by Lipofectin, and cell growth activity was calculated by microcytotoxicity assay. In vivo study, cells of HepG2 were implanted in Balb/c nude mice for 4 d. Then Cantide, DDP and Cantide+DDP were given intraperitoneally for 24 d respectively. The body weights of the tumor-bearing animals and their tumor mass were measured later to assess the effect of combination therapy in the nude mice. To evaluate the interaction of Cantide and these chemotherapeutic drugs, SAS software and Jin Zhengjun method were used.

RESULTS: Combination treatments with 0.1 μmol/L Cantide reduced the IC₅₀ of DDP, 5-FU and ADM from 1.07, 4.15 and 0.29 μg/mL to 0.25, 1.52 and 0.12 μg/mL respectively. The inhibition ability of DDP, 5-FU and ADM respectively in combination with Cantide in these tumor cells was higher than that of these drugs alone (P<0.0001). And synergism (Q≥1.15) was observed at the lower concentration of DDP (≤1 μg/mL), 5-FU (≤10 μg/mL) and ADM (≤0.1 μg/mL) with combination of Cantide. In vivo, combination treatment with Cantide and DDP produced the greater growth inhibition of human liver carcinoma cells HepG2 in nude mice (0.65±0.19 g tumor) compared with that when only one of these drugs was used (Cantide group: 1.05±0.16 g tumor, P = 0.0009<0.001; DDP group: 1.13±0.09 g tumor, P = 0.0001<0.001).

CONCLUSION: These findings indicate that Cantide may enhance therapeutic effectiveness of chemotherapeutic drugs over a wide range of tumor cells in vitro, and the combination use of Cantide and DDP can produce much higher inhibition rates, as compared with when either of these drugs was used only in vivo.

The epidermal growth factor receptor as a target for colorectal cancer therapy

The epidermal growth factor receptor (EGFR) is the prototypical member of the erbB receptor family. The EGFR axis is activated by a variety of ligands that are crucial in the formation and propagation of many tumors, including colorectal cancer, through their effects on cell signaling pathways, cellular proliferation, control of apoptosis, and angiogenesis. The importance of the EGFR axis in tumorigenesis and tumor progression makes it an attractive target for the development of anticancer therapies. A variety of targeting strategies to exploit the role of EGFR in tumors have been employed. The most highly developed of these anti-EGFR approaches are the monoclonal antibodies and the tyrosine kinase inhibitors (TKIs). Clinical evaluations of these compounds have yielded some promising results. The role of the EGFR axis in colorectal cancer formation and progression is reviewed and the clinical development of these anticancer EGFR-targeted drugs is reviewed and updated.

Antisense glutaminase inhibition decreases glutathione antioxidant capacity and increases apoptosis in Ehrlich ascitic tumour cells

Glutamine is an essential amino acid in cancer cells and is required for the growth of many other cell types. Glutaminase activity is positively correlated with malignancy in tumours and with growth rate in normal cells. In the present work, Ehrlich ascites tumour cells, and their derivative, 0.28AS-2 cells, expressing antisense glutaminase mRNA, were assayed for apoptosis induced by methotrexate and hydrogen peroxide. It is shown that Ehrlich ascites tumour cells, expressing antisense mRNA for glutaminase, contain lower levels of glutathione than normal ascites cells. In addition, 0.28AS-2 cells contain a higher number of apoptotic cells and are more sensitive to both methotrexate and hydrogen peroxide toxicity than normal cells. Taken together, these results provide insights into the role of glutaminase in apoptosis by demonstrating that the expression of antisense mRNA for glutaminase alters apoptosis and glutathione antioxidant capacity.

Epidermal Growth Factor Receptor as a Novel Therapeutic Target in Anaplastic Thyroid Carcinomas

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive human malignancies, with a median survival of up to 6 months. Such a bad prognosis under the present treatment procedures suggests the need for novel approaches in the management of this disease. Since some epidermal growth factor receptor (EGFR) inhibitors are now in clinical trials and few data are available concerning EGFR expression in anaplastic thyroid carcinomas, we tried to estimate a possible overexpression of this receptor in a larger tumor series. Twenty-five ATCs, including 3 ATCs with poorly differentiated thyroid carcinoma (PDTC) parts, were immunohistochemically investigated with a mouse monoclonal antibody directed against EGFR (EGFR pharmDX kit). The tumors revealed primarily a distinct membranous staining pattern, and in several tumor cells an additional cytoplasmic reactivity could be observed. The anaplastic carcinomas presented with 5 of 25 (20%) without EGFR reaction, 10 of 25 (40%) with reactivity, and 10 of 25 (40%) with overexpression of the receptor. All ATCs with PDTC parts (100%) showed EGFR overexpression. Cytoplasmic reactivity was observed in 56% of all ATCs. A significant correlation was calculated for EGFR overexpression and cytoplasmic staining (P = 0.036). Concerning receptor overexpression, ATCs were significantly different from ATCs with PDTC parts (P = 0.023). For the first time, we present EGFR overexpression in ATC in a larger tumor series, demonstrating that EGFR overexpression is a common finding in ATC. For at least one-third of all anaplastic thyroid carcinomas, EGFR seems to be a promising agent for the targeted molecular therapy of these extraordinarily aggressive tumors.

Targeted delivery of antisense oligodeoxynucleotides to folate receptor-overexpressing tumor cells

A major problem in exploring the full potential of antisense ODN is the lack of a safe and efficient delivery system. In this study a new method has been developed that is highly efficient in encapsulating ODN inside folate receptor (FR)-targeted lipid vesicles. ODN formulated in these vesicles were efficiently protected from degradation by nucleases compared to free ODN. Folate efficiently mediated intracellular delivery of ODN to KB tumor cells that overexpress FR. Delivery of EGFR antisense ODN via FR-targeted lipid vesicles resulted in a significant down-regulation of EGFR expression in KB cells and cell growth inhibition, far more efficient than that with free ODN or ODN encapsulated in ligand-free lipid vesicles. Intracellular delivery of EGFR antisense ODN also sensitized KB cells to doxorubicin (DOX) treatment. Thus targeted delivery of ODN via this novel lipid vector may have potential in treating tumors that overexpress FR.

Modulation of DNA Repair In vitro after Treatment with Chemotherapeutic Agents by the Epidermal Growth Factor Receptor Inhibitor Gefitinib (ZD1839)

PURPOSE

The epidermal growth factor receptor (EGFR) is commonly expressed in human tumors and provides a target for therapy. Gefitinib (Iressa, ZD1839) is a quinazoline derivative that inhibits EGFR tyrosine kinase activity. Gefitinib demonstrated anticancer efficacy in vivo, and although experiments in vitro have suggested that inhibition of EGFR modulates the activity of chemotherapeutic agents, the mechanism of this interaction is unclear. We investigated mechanisms for this modulation.

EXPERIMENTAL DESIGN

The antiproliferative effect of gefitinib alone or combined with cisplatin, melphalan, and etoposide was determined in a human breast (MCF-7) cancer cell line. Using the alkaline single-cell gel electrophoresis (comet) assay, we investigated kinetics of DNA damage and repair after treatment with the chemotherapeutic drugs combined with gefitinib. To investigate whether the phosphatidylinositol 3'-kinase pathway was contributing to repair-inhibition produced by gefitinib, cells were exposed to chemotherapy in combination with the phosphatidylinositol 3'-kinase inhibitor LY294002.

RESULTS

A superadditive (synergistic) increase in growth inhibition for combined treatment with gefitinib was found for cisplatin and etoposide, but not with melphalan. There was delayed repair of DNA strand breaks after treatment with etoposide combined with gefitinib, and repair of DNA interstrand cross-links produced by cisplatin is delayed in combination with gefitinib. Inhibition of cell proliferation and DNA repair was identical in cells treated with LY294002. Immunoprecipitation of cell extracts demonstrated that after exposure to gefitinib, there was an association between EGFR and DNA-PK(CS).

CONCLUSION

Gefitinib acts through inhibition of repair of cisplatin and etoposide-induced DNA damage; this effect is mimicked by inhibitors of the phosphatidylinositol 3'-kinase suggesting similar mechanisms of action.

Targeting the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a member of the erbB family of tyrosine kinase receptors (RTK). The EGFR is involved in cell proliferation, metastasis and angiogenesis, and is expressed in a large proportion of epithelial tumours. The two main classes of EGFR inhibitors in clinical trials are the RTK inhibitors and the monoclonal antibodies. The clinical development of EGFR inhibitors has introduced new challenges to the design of phase I, II, and III trials. Both classes of agents can be safely administered at doses sufficient to inhibit the EGFR system. Receptor tyrosine kinase inhibitors have been extensively evaluated in non-small-cell lung cancer. In this setting, gefitinib has demonstrated activity in patients who fail initial chemotherapy. Monoclonal antibodies have been developed in combination with cytotoxic chemotherapy in several tumour types, most notably colorectal and head and neck cancer. The preliminary results suggest an increase in response rate and time to progression with the combination of cetuximab and chemotherapy in both disease models. Future issues in the development of EGFR inhibitors include the identification of biologic predictors of response, combination with other targeted agents, and their utilisation in earlier stage malignancies.

Blockade of epidermal growth factor- or heregulin-dependent ErbB2 activation with the anti-ErbB2 monoclonal antibody 2C4 has divergent downstream signaling and growth effects

Due to heterodimerization and a variety of stimulating ligands, the ErbB receptor system is both diverse and flexible, which proves particularly advantageous to the aberrant signaling of cancer cells. However, specific mechanisms of how a particular receptor contributes to generating the flexibility that leads to aberrant growth regulation have not been well described. We compared the utilization of ErbB2 in response to epidermal growth factor (EGF) and heregulin stimulation in colon carcinoma cells. Anti-ErbB2 monoclonal antibody 2C4 blocked heregulin-stimulated phosphorylation of ErbB2 and ErbB3; activation of mitogen-activated protein kinase (MAPK), phosphatidylinositol 3'-kinase (PI3K), and Akt; proliferation; and anchorage-independent growth. 2C4 blocked EGF-mediated phosphorylation of ErbB2 and inhibited PI3K/Akt and anchorage-independent growth but did not affect ErbB1 or MAPK. Immunoprecipitations showed that ErbB3 and Grb2-associated binder (Gab) 1 were phosphorylated and associated with PI3K activity after heregulin treatment and that Gab1 and Gab2, but not ErbB3, were phosphorylated and associated with PI3K activity after EGF treatment. These data show that monoclonal antibody 2C4 inhibited all aspects of heregulin signaling as well as anchorage-independent and monolayer growth. Furthermore, we identify ErbB2 as a critical component of EGF signaling to the Gab1/Gab2-PI3K-Akt pathway and anchorage-independent growth, but EGF stimulation of MAPK and monolayer growth can occur efficiently without the contribution of ErbB2.

Combining EGFR inhibitors with radiation or chemotherapy: will preclinical studies predict clinical results?

PURPOSE

To highlight some of the preclinical data that examine the interaction of epidermal growth factor receptor (EGFR) inhibitors with radiotherapy and chemotherapy.

METHODS AND MATERIALS

Recognition of the EGFR as an important regulator of tumor cell growth in the early 1980s stimulated the development of a series of molecules specifically designed to inhibit EGFR signaling as anticancer agents. Many of these agents have now matured and are in advanced clinical trial investigations, with tumor response rates on the order of 10-20% identified across a variety of human malignancies. Initially designed primarily as "cytostatic" agents, as opposed to "cytotoxic" agents, it is possible that the EGFR inhibitors will realize their optimal clinical impact when delivered in concert with conventional cytotoxic modalities such as radiotherapy and/or chemotherapy.

RESULTS

Despite very strong in vitro and in vivo preclinical results, several major gaps remain in our knowledge regarding the EGFR inhibitor mechanisms of interaction with radiotherapy and chemotherapy, with considerable selection bias in the publication of preclinical data available to date.

CONCLUSION

By acknowledging the limitations of the available preclinical data and by expanding our mechanistic understanding of EGFR inhibitor function in representative tumor model systems, we should enhance our capacity to predict the most rational and successful methods to combine EGFR inhibitors with cytotoxic modalities in future clinical trials.

Epidermal growth factor receptor: a promising target in solid tumours

The epidermal growth factor receptor (EGFR) is expressed in a wide variety of solid tumours. It has been demonstrated that the EGFR-associated signaling pathway plays an important role in carcinogenesis and cancer progression. In the new therapeutic paradigm of molecular-targeted cancer therapy, interference with intracellular signaling cascades is an appealing treatment approach. Inhibitory strategies under study include monoclonal antibodies, tyrosine kinase inhibitors, EGFR-ligand conjugates, EGFR immunoconjugates, and antisense oligonucleotides. Many of these strategies have demonstrated efficacy against EGFR-expressing tumour cells in preclinical studies, prompting a large number of clinical trials. In particular, clinical studies using monoclonal antibody blockade and EGFR tyrosine kinase inhibitors have suggested that EGFR blockade is a well-tolerated and effective treatment strategy; however, more trials are needed to precisely define how these agents will fit into modern cancer care.

Bcl-x(L) antisense oligonucleotides radiosensitise colon cancer cells

Advanced colon cancer is a malignancy with poor response to various treatment modalities including ionising radiation (IR) and chemotherapy. Both IR and chemotherapeutic agents have been shown to act by inducing apoptosis, a type of cell death antagonised by the Bcl-x_L gene product. Since approximately 60% of human colon cancers express Bcl-x_L, it was the aim of this study to explore the potential of Bcl-x_L antisense oligonucleotides as a novel radiosensitisation strategy. Caco-2 colon cancer cells were treated with Bcl-x_L antisense oligonucleotides in combination with IR or cisplatin, and Bcl-x_L protein expression, apoptosis, cell viability and clonogenic survival were examined. Bcl-x_L antisense oligonucleotide specifically reduced the Bcl-x_L protein level by almost 50% in Caco-2 cells. The decreased threshold for the induction of apoptosis resulted in a 300% increase of apoptosis after IR or cisplatin treatment and led to a 60% reduction of cell proliferation beyond response rates achieved with IR. These data suggest that Bcl-x_L is an important factor contributing to the treatment resistance of human colon cancer. Specific reduction of Bcl-x_L protein levels by antisense oligonucleotides qualifies as a promising therapeutic strategy for colon cancer that may help overcome resistance and improve clinical outcome in this malignancy.

Silibinin sensitizes human prostate carcinoma DU145 cells to cisplatin- and carboplatin-induced growth inhibition and apoptotic death

In several recent studies, we have shown that silibinin inhibits the growth of human prostate cancer cells (PCA) both in vitro and in vivo. Here, we investigated the effect of silibinin in combination with cisplatin and carboplatin on human PCA DU145 cell growth and apoptosis. Cisplatin alone at 2 microg/ml dose produced 48% cell growth inhibition, whereas a combination with 50-100 microM silibinin resulted in 63-80% (p<0.05-0.001) growth inhibition. Similarly, compared to 68% growth inhibition at 20 microg/ml carboplatin, addition of 50-100 microM doses of silibinin caused 80-90% inhibition (p<0.005-0.001). In the studies assessing the effect of these combinations on cell cycle progression, a combination of cisplatin or carboplatin with silibinin resulted in a stronger G2-M arrest, compared to these agents alone showing a moderate G2-M and G1 arrests in case of cisplatin and silibinin, and a complete S phase arrest with carboplatin, respectively. A stronger G2-M arrest by these combinations was accompanied by a substantial decrease in the levels of cdc2, cyclin B1 and cdc25C. Silibinin/platinum compound combinations were also effective in inducing apoptosis where cisplatin and carboplatin when combined with silibinin enhanced apoptosis from 8 to 15% and from 20 to 40%, respectively. Apoptosis induction was further confirmed by PARP and caspases 3, 9 and 7 whose cleaved levels were also enhanced by combination treatment. In addition, there was a significant increase in cytochrome c release in the cytosol following treatment of DU145 cells with these combinations. Together, these results show a substantial increase in the efficacy of platinum compounds on human PCA cells, when combined with silibinin, which provide a rationale for further investigations with these combinations.

Messenger RNA expression profiling of genes involved in epidermal growth factor receptor signalling in human cancer cells treated with scanning array-designed antisense oligonucleotides

Scanning oligodeoxynucleotide (ODN) arrays appear promising in vitro tools for the prediction of effective antisense reagents but their usefulness has not yet been reported in mammalian systems. In this study, we have evaluated the use of scanning ODN arrays to predict efficacious antisense ODNs targeting the human epidermal growth factor receptor (EGFR) mRNA in a human epidermoid cancer cell line and in primary human glioma cells. Hybridisation accessibility profile of the first 120nt in the coding region of the human EGFR mRNA was determined by hybridising a radiolabelled EGFR transcript to a scanning array of 2684 antisense sequences ranging from monomers to 27-mers. Two ODNs, AS1 and AS2, complementary to accessible sequences within the EGFR mRNA, were designed and their ability to hybridise to EGFR mRNA was further confirmed by in vitro RNase H-mediated cleavage assays. Phosphorothioate-modified 21-mer AS1 and AS2 ODNs inhibited the growth of an established human A431 cancer cell line as well as primary glioma cells from human subjects when delivered as cationic lipoplexes. In contrast, scrambled controls and AS3-an antisense ODN complementary to an inaccessible site in EGFR mRNA-were inactive. Western blots showed that AS1 ODN exhibited a dose-dependent inhibition of EGFR protein expression in A431 cells in the nanomolar range. Microarray-based gene expression profiling studies of A431 cells treated with the 21-mer phosphorothioate AS1 ODN demonstrated successful inhibition of downstream signalling molecules further confirming the effective inhibition of EGFR expression in human cancer cells by antisense ODNs designed by scanning ODN array technology.

Status of epidermal growth factor receptor antagonists in the biology and treatment of cancer

The epidermal growth factor receptor (EGFR) is a tyrosine kinase receptor of the ErbB family that is abnormally activated in many epithelial tumors. Receptor activation leads to recruitment and phosphorylation of several downstream intracellular substrates, leading to mitogenic signaling and other tumor-promoting cellular activities. In human tumors, receptor overexpression correlates with a more aggressive clinical course. Taken together, these observations indicate that the EGFR is a promising target for cancer therapy. Monoclonal antibodies directed at the ligand-binding extracellular domain and low-molecular weight inhibitors of the receptor's tyrosine kinase are currently in advanced stages of clinical development. These agents prevent ligand-induced receptor activation and downstream signaling, which results in cell cycle arrest, promotion of apoptosis, and inhibition of angiogenesis. They also enhance the antitumor effects of chemotherapy and radiation therapy. In patients, anti-EGFR agents can be given safely at doses that fully inhibit receptor signaling, and single-agent activity has been observed against a variety of tumor types, including colon carcinoma, non-small-cell lung cancer, head and neck cancer, ovarian carcinoma, and renal cell carcinoma. Although antitumor activity is significant, responses have been seen in only a minority of the patients treated. In some clinical trials, anti-EGFR agents enhanced the effects of conventional chemotherapy and radiation therapy. Ongoing research efforts are directed at the selection of patients with EGFR-dependent tumors, identification of the differences among the various classes of agents, and new clinical development strategies.