Aberrant Activation Of Epidermal Growth Factor Receptor Research Articles

329 Mechanisms of Cutaneous Adverse Events during Targeted Cancer Therapy

Aberrant activation of EGFR is seen in many solid cancers, which has led to the development of EGFR-targeted anti-cancer therapies. However, the epidermal growth factor receptor (EGFR) plays an important role in hair morphogenesis and the maintenance of skin homeostasis. Therefore, cancer patients receiving EGFR inhibitors commonly develop a papulopustular rash, pruritus and dry skin. Severe adverse events may require interruption of an otherwise effective therapy. Mice with genetic ablation of EGFR in epidermal cells develop skin inflammation which closely mimics the hallmarks of EGFR inhibition in humans.

The Role of the Epidermal Growth Factor Receptor in Diabetic Kidney Disease.

The epidermal growth factor receptor (EGFR) is expressed in numerous cell types in the adult mammalian kidney and is activated by a family of EGF-like ligands. EGFR activation has been implicated in a variety of physiologic and pathophysiologic functions. There is increasing evidence that aberrant EGFR activation is a mediator of progressive kidney injury in diabetic kidney disease. This review will highlight recent studies indicating its potential role and mechanisms of injury of both glomerular and tubular cells in development and progression of diabetic kidney disease.

Stable and EGF-Induced Temporal Interactome Profiling of CBL and CBLB Highlights Their Signaling Complex Diversity.

The epidermal growth factor receptor (EGFR) signal modulates cell proliferation, migration, and survival. Aberrant activation of EGFR constitutes the major cause of various cancers. Receptor ubiquitination and degradation mediated by CBL proteins play negative regulatory roles and control the intensity and duration of the signaling. With the construction of stable cell lines inducibly expressing FLAG-tagged CBL or CBLB, we identified 102 and 82 stable interacting proteins of CBL and CBLB, respectively, through the affinity purification followed by mass spectrometry (AP-MS) approach. Time-resolved profiling at six different time points combined with functional annotations of the temporal interactomes provides insights into the dynamic assembly of signal proteins upon EGFR signaling activation. Comparison between the interactomes of CBL and CBLB indicates their redundant but also complementary functions. Importantly, we validated the stable association of EPS15L1 and ITSN2 and temporal association of TNK2 to both CBL and CBLB through biochemical assays. Collectively, these results offer a useful resource for CBL and CBLB interactomes and highlight their prominent and diverse roles in the EGFR signaling network.

Chronicles of EGFR Tyrosine Kinase Inhibitors: Targeting EGFR C797S Containing Triple Mutations.

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase widely expressed in many cancers such as non-small cell lung cancer (NSCLC), pancreatic cancer, breast cancer, and head and neck cancer. Mutations such as L858R in exon 21, exon 19 truncation (Del19), exon 20 insertions, and others are responsible for aberrant activation of EGFR in NSCLC. First-generation EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib and erlotinib have clinical benefits for EGFR-sensitive (L858R and Del19) NSCLC patients. However, after 10-12 months of treatment with these inhibitors, a secondary T790M mutation at the gatekeeper position in the kinase domain of EGFR was identified, which limited the clinical benefits. Second-generation EGFR irreversible inhibitors (afatinib and dacomitinib) were developed to overcome this T790M mutation. However, their lack of selectivity toward wild-type EGFR compromised their clinical benefits due to serious adverse events. Recently developed third-generation irreversible EGFR TKIs (osimertinib and lazertinib) are selective toward driving mutations and the T790M mutation, while sparing wild-type EGFR activity. The latest studies have concluded that their efficacy was also compromised by additional acquired mutations, including C797S, the key residue cysteine that forms covalent bonds with irreversible inhibitors. Because second- and third-generation EGFR TKIs are irreversible inhibitors, they are not effective against C797S containing EGFR triple mutations (Del19/T790M/C797S and L858R/T790M/C797S). Therefore, there is an urgent unmet medical need to develop next-generation EGFR TKIs that selectively inhibit EGFR triple mutations via a non-irreversible mechanism.

Mechanistic insights into differential requirement of receptor dimerization for oncogenic activation of mutant EGFR and its clinical perspective

The epidermal growth factor receptor (EGFR), a member of the ErbB family (EGFR, ErbB2, ErbB3 and ErbB4), plays a crucial role in regulating various cellular responses such as proliferation, differentiation, and survival. As a result, aberrant activation of EGFR, mostly mediated through different classes of genomic alterations occurring within EGFR, is closely associated with the pathogenesis of numerous human cancers including lung adenocarcinoma, glioblastoma, and colorectal cancer. Thus, specific suppression of oncogenic activity of mutant EGFR with its targeted drugs has been routinely used in the clinic as a very effective anti-cancer strategy in treating a subset of tumors driven by such oncogenic EGFR mutants. However, the clinical efficacy of EGFR-targeted therapy does not last long due to several resistance mechanisms that emerge in the patients following the drug treatment. Thus, there is an urgent need for the development of novel therapeutic tactics specifically targeting mutant EGFR with the focus on the unique biological features of various mutant EGFR. Regarding this point, our review specifically emphasizes the recent findings about distinct requirements of receptor dimerization and autophosphorylation, which are critical steps for enzymatic activation of EGFR and signaling cascades, respectively, among wildtype and mutant EGFR and further discuss their clinical significance. In addition, the molecular mechanisms regulating EGFR dimerization and enzymatic activity by a key negative feedback inhibitor Mig6 as well as the clinical use for developing potential novel drugs targeting it are described in this review.

DETERMINATION OF THE THREE‐DIMENSIONAL STRUCTURE OF FULL‐LENGTH HUMAN EPIDERMAL GROWTH FACTOR RECEPTOR BY CRYO‐ELECTRON TOMOGRAPHY

Human epidermal growth factor receptor (EGFR) plays vital roles in cellular processes including cell proliferation, survival, motility and differentiation. Mice lacking EGFR die shortly after birth due to multi‐organ failure. Aberrant activation of EGFR is implicated in many human cancers. EGFR is synthesized as a single‐pass transmembrane protein, which consists of an extracellular ligand‐binding domain and an intracellular kinase domain separated by a single transmembrane domain. While crystal structures of EGFR domains are available, three‐dimensional structural determination of the full‐length EGFR has not been successful so far. In the conference, we will present cryo‐electron tomography structures of the intact human EGFR in the presence of bound EGF ligand. We successfully purified the full‐length EGFR with autophosphorylation activity upon EGF stimulation. We then prepared vitrified specimens and collected 30 tilt series projections spanning −60 to +60 degrees, with tilt increments of 0.5 degrees, using a FEI Titan Krios at 39,000× magnification and □1–2 μm underfocus. Tilt series data was analyzed with COMET software. These three‐dimensional structures of the full‐length EGFR are invaluable for understanding of mechanisms underlying activation of EGFR by ligand binding.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Therapeutic effects of gefitinib-encapsulated thermosensitive injectable hydrogel in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is one of the most widespread musculoskeletal diseases worldwide, which remains an intractable clinical challenge. The aim of this study is to investigate the therapeutic potential of the small molecule gefitinib (an epidermal growth factor receptor (EGFR) inhibitor) in ameliorating IVD degeneration. Aberrant EGFR activation levels were detected in both human and rat degenerative IVDs, which prompted us to investigate the functional roles of EGFR by utilizing inducible cartilage-specific EGFR-deficient mice. We demonstrated that conditional EGFR deletion in mice increased nucleus pulposus (NP) extracellular matrix (ECM) production and autophagy marker activation while MMP13 expression decreased. These outcomes are comparable to the use of a controlled-release injectable thermosensitive hydrogel of gefitinib to block EGFR activity in a puncture-induced rat model. We also conducted a case series study involving patients with non-small cell lung cancer and IVD degeneration who received gefitinib treatment from 2010 to 2015. Gefitinib-treated patients displayed a relative slower disc degenerating progression, in contrast to control subjects. These findings thus provide evidence that suppression of EGFR by the FDA-approved drug gefitinib can protect IVD degeneration in rats, implying the potential application of gefitinib as a small molecule drug for treating IVD degeneration.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease.

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

AKT-STAT3 Pathway as a Downstream Target of EGFR Signaling to Regulate PD-L1 Expression on NSCLC cells.

While cancer development and progression can be controlled by cytotoxic T cells, it is also known that tumor-specific CD8+T cells become functionally impaired by acquiring a group of inhibitory receptors known as immune checkpoints. Amongst those, programmed death-1 (PD-1) is one of the most recognized negative regulators of T cell function. In non-small lung cancers (NSCLCs), the aberrant activation of epidermal growth factor receptor (EGFR) is known to induce PD-L1 expression and further the treatment with gefitinib, a tyrosine kinase inhibitor (TKI) for EGFR, decrease the expression of PD-L1 on NSCLC. Given the acquired resistance to gefitinib treatment frequently observed by developing secondary-site mutations limiting its efficacy, it is important to understand the downstream mechanism of activated-EGFR signaling for regulating PD-L1 in NSCLC. In this study, we demonstrated that AKT-STAT3 pathway could be a potential target for regulating the surface expression of PD-L1 on NSCLCs with aberrant EGFR activity and, further, the inhibition of AKT or STAT3 activity could down-regulate the expression of PD-L1 even in gefitinib-resistant NSCLCs. These results highlight an importance of AKT-STAT3 pathway as a promising target for potentiating anti-tumor immune responses by regulating PD-L1 expression on cancer cells with aberrant EGFR activity.

Abstract 750: Overcoming resistance to anti-EGFR therapy in non-small cell lung cancer with a T-type Ca2+ channels inhibitor

Abstract This study's aim was to define a novel molecular target and to develop an effective agent capable of overcoming intrinsic and acquired resistance to anti-EGFR therapy. Despite introduction of new therapies, lung cancer is a major cause of cancer death. One of its characteristics is the expression and activation of epidermal growth factor receptor (EGFR). Activating mutations in EGFR are present in approximately 20% of patients with non-small cell lung cancer (NSCLC), mostly in never-smokers. While most patients initially respond to treatment with anti-EGFR therapy, essentially all patients develop acquired drug resistance. T-type calcium channels, are present in lung cancer and support cell proliferation. Importantly, their expression often coincides with abnormal expression or mutations in EGFR. In this study, we investigated the effects of T-type channel inhibition on NSCLC survival and resistance to targeted therapy in vitro. We used a panel of cell lines differing in EGFR mutation status and sensitivity to EGFR tyrosine kinase inhibitors (TKIs). Our results show that T-type channel inhibitors alone arrest cells in the G1/G0 phase of the cell cycle and induce cell death. The treatment reduces activity of both PI3K/AKT/mTOR and JAK2/STAT5 pathways, often upregulated as a mechanism of acquired resistance to TKIs. Importantly, combined treatment with TKI, gefitinib, and T-type channels inhibitor, mibefradil, resulted in synergistic growth inhibition. Our results demonstrate a connection between T-type Ca2+ channels and aberrant EGFR activity in NSCLC, and provide the rationale for future use of two targeted therapies together. Since T-type calcium channel inhibitors are already undergoing clinical trials, our discoveries could be quickly translated into clinical practice. Citation Format: Barbara Dziegielewska, Lloyd S. Gray, Jaroslaw Dziegielewski. Overcoming resistance to anti-EGFR therapy in non-small cell lung cancer with a T-type Ca2+ channels inhibitor. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 750. doi:10.1158/1538-7445.AM2015-750

Pancreatic oncogenic signaling cascades converge at Protein Kinase D1

Pancreatic oncogenic signaling cascades converge at Protein Kinase D1

Gefitinib-mediated Reactive Oxygen Specie (ROS) Instigates Mitochondrial Dysfunction and Drug Resistance in Lung Cancer Cells

Therapeutic benefits offered by tyrosine kinase inhibitors (TKIs), such as gefitinib (Iressa) and erlotinib (Tarceva), are limited due to the development of resistance, which contributes to treatment failure and cancer-related mortality. The aim of this study was to elucidate mechanistic insight into cellular perturbations that accompany acquired gefitinib resistance in lung cancer cells. Several lung adenocarcinoma (LAD) cell lines were screened to characterize epidermal growth factor receptor (EGFR) expression and mutation profile. To circumvent intrinsic variations between cell lines with respect to response to drug treatments, we generated gefitinib-resistant H1650 clone by long-term, chronic culture under gefitinib selection of parental cell line. Isogenic cells were analyzed by microarray, Western blot, flow cytometry, and confocal and transmission electron microscope. We observed that although chronic gefitinib treatment provided effective action against its primary target (aberrant EGFR activity), secondary effects resulted in increased cellular reactive oxygen species (ROS). Gefitinib-mediated ROS correlated with epithelial-mesenchymal transition, as well as striking perturbation of mitochondrial morphology and function. However, gefitinib treatment in the presence of ROS scavenger provided a partial rescue of mitochondrial aberrations. Furthermore, withdrawal of gefitinib from previously resistant clones correlated with normalized expression of epithelial-mesenchymal transition genes. These findings demonstrate that chronic gefitinib treatment promotes ROS and mitochondrial dysfunction in lung cancer cells. Antioxidants may alleviate ROS-mediated resistance.

Regulation of EGFR nanocluster formation by ionic protein-lipid interaction.

The abnormal activation of epidermal growth factor receptor (EGFR) is strongly associated with a variety of human cancers but the underlying molecular mechanism is not fully understood. By using direct stochastic optical reconstruction microscopy (dSTORM), we find that EGFR proteins form nanoclusters in the cell membrane of both normal lung epithelial cells and lung cancer cells, but the number and size of clusters significantly increase in lung cancer cells. The formation of EGFR clusters is mediated by the ionic interaction between the anionic lipid phosphatidylinositol-4,5-bisphosphate (PIP2) in the plasma membrane and the juxtamembrane (JM) region of EGFR. Disruption of EGFR clustering by PIP2 depletion or JM region mutation impairs EGFR activation and downstream signaling. Furthermore, JM region mutation in constitutively active EGFR mutant attenuates its capability of cell transformation. Collectively, our findings highlight the key roles of anionic phospholipids in EGFR signaling and function, and reveal a novel mechanism to explain the aberrant activation of EGFR in cancers.

A bispecific transmembrane antibody simultaneously targeting intra- and extracellular epitopes of the epidermal growth factor receptor inhibits receptor activation and tumor cell growth

Epidermal growth factor receptor (EGFR) plays an important role in essential cellular processes such as proliferation, survival and migration. Aberrant activation of EGFR is frequently found in human cancers of various origins and has been implicated in cancer pathogenesis. The therapeutic antibody cetuximab (Erbitux) inhibits tumor growth by binding to the extracellular domain of EGFR, thereby preventing ligand binding and receptor activation. This activity is shared by the single chain antibody fragment scFv(225) that contains the same antigen binding domain. The unrelated EGFR-specific antibody fragment scFv(30) binds to the intracellular domain of the receptor and retains antigen binding upon expression as an intrabody in the reducing environment of the cytosol. Here, we used scFv(225) and scFv(30) domains to generate a novel type of bispecific transmembrane antibody termed 225.TM.30, that simultaneously targets intra- and extracellular EGFR epitopes. Bispecific 225.TM.30 and related membrane-anchored monospecific 225.TM and TM.30 proteins carrying extracellular scFv(225) or intracellular scFv(30) antibody fragments linked to a transmembrane domain were expressed in EGFR-overexpressing tumor cells using a doxycycline-inducible retroviral system. Induced expression of 225.TM.30 and 225.TM, but not TM.30 reduced EGFR surface levels and ligand-induced EGFR activation, while all three molecules markedly inhibited tumor cell growth. Co-localization of 225.TM with EGFR was predominantly found on the cell surface, while interaction with 225.TM.30 and TM.30 proteins resulted in the redistribution of EGFR to perinuclear compartments. Our data demonstrate functionality of this novel type of membrane-anchored intrabodies in tumor cells and suggest distinct modes of action of mono- and bispecific variants.

Tyrosine Phosphorylation of Mig6 Reduces Its Inhibition of the Epidermal Growth Factor Receptor

Under physiological conditions, epidermal growth factor receptor (EGFR) tyrosine kinase activity is tightly controlled through the coordinated action of both positive and negative regulators. Aberrant EGFR activation occurs frequently in many cancer types, and the endogenous EGFR feedback inhibitor, Mig6/RALT, is more efficiently phosphorylated by oncogenic EGFR variants. We have utilized expressed protein ligation to generate semisynthetic Tyr394 phosphorylated and unphosphorylated forms of the Mig6 protein and shown that phosphorylation of Mig6 reduces its ability to inhibit purified, near full-length EGFR (tEGFR). We also demonstrate that the kinetic parameters of tEGFR are similar whether solubilized in detergent or reconstitutued in nanodisc bilayers. These findings suggest a mechanism by which EGFR and its family members evade negative regulation by Mig6 under pathological conditions.

Abstract 1810: Analysis of EGFRvIII mediated responses driven by JNK2 in Glioblastoma Multiforme.

Abstract The most malignant central nervous system cancer, Glioblastoma Mulitforme (GBM), accounts for the majority of primary brain cancer-related deaths (Porter, McCarthy et al. 2010) and has an average post-diagnostic survival rate of just over 14 months (Behin, Hoang-Xuan et al. 2003; Stupp, Mason et al. 2005; Louis, Ohgaki et al. 2007). The epidermal growth factor receptor (EGFR) (Wong, Ruppert et al. 1992; Mukasa, Wykosky et al. 2010) has been shown to play central roles in GBM tumorigenesis and therapeutic resistance and reports have indicated that ∼50% of all GBMs display aberrant activation of EGFR and of these ∼50% also express a ligand-independent, constitutively active mutant, EGFRvIII (Nishikawa, Ji et al. 1994) that is associated with increased tumorigenecity and mortality (Heimberger, Hlatky et al. 2005; Heimberger, Suki et al. 2005). In addition, several reports have indicated that the c-Jun N-terminal kinase 2 (JNK2) is activated in the majority of GBM tumors when compared to normal brain tissue (Antonyak, Kenyon et al. 2002; Tsuiki, Tnani et al. 2003; Cui, Han et al. 2006) and JNK2 activation strongly correlates with both GBM histological grade and expression of EGFR (Li, Wang et al. 2008). Current therapies specifically targeting the EGFR have limited success and the universal resurgence of tumors post-treatment occurs due to infiltrating tumor cells that escape initial surgery and exhibit profound resistance to irradiation and current chemotherapy treatments (Claes, Idema et al. 2007). Therefore, the identification of novel tractable targets for improved therapeutics and the molecular and genetic profiling of GBMs continues to be a necessity. To this end we have compared the gene expression profiles of U87 GBM cells with cells expressing EGFRvIII (U87EGFRvIII) and specifically studied genes modulated by JNK2 using microarray analysis comparing U87EGFRvIII cells expressing either short hairpin RNA directed against JNK2 (U87EGFRvIIIshJNK2) or a non-silencing control (U87EGFRvIIIshNS). Gene expression profiles revealed 390 EGFRvIII-induced genes that were significantly associated with targeted loss of JNK2 expression by a minimum of 2 fold on comparison to non-silencing controls. JNK2 modulated gene clusters related to cell movement were revealed with Ingenuity Pathway Analysis (IPA) and included interesting genes such as HGF, MMP7, FGF10, PDGFRA and IGFBP5. Ultimately, these studies, allowed us to further understand the molecular mechanisms driving EGFRvIII-induced tumorigenesis and such knowledge will ultimately enhance our ability to develop an efficacious GBM therapy that can increase the effectiveness of clinically approved drugs. Citation Format: Vanessa Saunders, Mohammad Fallahi-Sichani, Yuan Yuan Ling, Derek Duckett. Analysis of EGFRvIII mediated responses driven by JNK2 in Glioblastoma Multiforme. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1810. doi:10.1158/1538-7445.AM2013-1810

Aberrantly activated EGFR contributes to enhanced IL-8 expression in COPD airways epithelial cells via regulation of nuclear FoxO3A

BackgroundDecreased activity of forkhead transcription factor class O (FoxO)3A, a negative regulator of NF-κB-mediated chemokine expression, is implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Previously, we showed...

Hyperactivation of constitutively dimerized oncogenic EGF receptors by autocrine loops

The epidermal growth factor (EGF) receptor (EGFR) has a key role in normal embryonic development, adult tissue homeostasis and many pathological processes, in particular tumour formation. Aberrant EGFR activation occurs in many cancer types, and inhibition of this receptor is a promising anti-tumour strategy. Besides overexpression of the wild-type receptor, mutated oncogenic EGFR variants are often associated with malignant transformation. In human non-small-cell lung cancers, kinase mutants of the EGFR are rather common. Human glioblastoma often express the truncated EGFRvIII version as well as other dimerized and permanently activated mutants of the receptor, which are considered as tumour drivers. Similarly, the mutated and dimerized EGFR variant Xiphophorus melanoma receptor kinase (Xmrk) is causative for the development of malignant pigment cell tumours in medaka and Xiphophorus melanoma models. It is generally believed that oncogenic receptors that are active due to dimerizing mutations are ligand independent. Here, we show that different EGFR variants from fish and human efficiently induce autocrine loops by inducing EGFR ligands such as amphiregulin and HB-EGF. Importantly, the pre-dimerized oncogenic EGFR versions Xmrk from Xiphophorus and human EGFR(C600F), though already active in absence of ligands, respond to ligand stimulation with enhanced oncogenic signalling. In summary, our data show that autocrine or paracrine loops are still acting on pre-dimerized oncogenic EGFRs and contribute to their pro-tumorigenic signalling.

A two-tiered mechanism of EGFR inhibition by RALT/MIG6 via kinase suppression and receptor degradation

Signaling by epidermal growth factor receptor (EGFR) must be controlled tightly because aberrant EGFR activity may cause cell transformation. Receptor-associated late transducer (RALT) is a feedback inhibitor of EGFR whose genetic ablation in the mouse causes phenotypes due to EGFR-driven excess cell proliferation. RALT inhibits EGFR catalytic activation by docking onto EGFR kinase domain. We report here an additional mechanism of EGFR suppression mediated by RALT, demonstrating that RALT-bound EGF receptors undergo endocytosis and eventual degradation into lysosomes. Moreover, RALT rescues the endocytic deficit of EGFR mutants unable to undergo either endocytosis (Dc214) or degradation (Y1045F) and mediates endocytosis via a domain distinct from that responsible for EGFR catalytic suppression. Consistent with providing a scaffolding function for endocytic proteins, RALT drives EGFR endocytosis by binding to AP-2 and Intersectins. These data suggest a model in which binding of RALT to EGFR integrates suppression of EGFR kinase with receptor endocytosis and degradation, leading to durable repression of EGFR signaling.

Abstract 619: Dual targeted therapies to overcome tyrosin kinase inhibitors resistant in epidermal growth factor receptor (EGFR) expression of lung cancer

Abstract Background: Non-small cell lung cancer (NSCLS) comprises about 80% of all lung cancers. The regular treatments for NSCLC are surgery, chemotherapy, radiotherapy and EGFR-targeted therapy. EGFR is frequently mutated and amplified in lung adenocarcinom as sensitive to EGFR inhibitors. The EGFR-targeted therapy, Gefitinib and Erlotinib, significantly improves disease free survival. However, it was not possible to predict super-responder of gefitinib degree of EGFR expression as a single agent. There is an imposing need for new rationally designed regimens to overcome Gefitinib resistance. The other tyrosine kinase inhibitor, Lapatinib, is a small-molecule inhibitor targeting both the HER2 and the epidermal growth factor receptor (EGFR) in solid tumors. We hypothesized that this aberrant activation of EGFR may contribute to Gefitinib resistance and dual blocking EGFR activation with EGFR and ERBB2 inhibitor will re-sensitize HER family in lung cancers. Experimental Design: In the in vitro study, cancer cells with EGFR wild type or mutation type were treated with Tyrosine kinase inhibitor, Gefitinib, Lapatinib, or combined treatments. The responses of cells to Gefitinib or/and Lapatinib treatments were evaluated by MTS proliferation, apoptosis assay, soft agar colony formation assay and western blot. In the in vivo study, pulmonary xenograft tumors were established in ICR/SCID mouse and treated with vehicle control, Gefitinib, Lapatinib, or Gefitinib plus Lapatinib for 4 weeks. Tumor volume were monitored and further studied by immunohistochemistry on collected tumors. Results: We selected multiple pairs of EGFR wild type and mutation type. The EGFR mutation cells have more effect under single tyrosine kinase inhibitor (Gefitinib) treatment compared with EGFR wild type cells. Dual inhibition of EGFR activation sensitized EGFR expression pulmonary cancer cells to Gefitinib treatment. Compared with single treatment, combined treatment led to a significantly more effective inhibition of cell proliferation and induced apoptosis. In a mouse pulmonary xenograft model, combination therapy with Gefitinib and Lapatinib dramatically inhibited EGFR wild type tumor growth. Conclusions: Since the EGFR family inhibitor, Lapatinib is currently under Phase III clinical trial, combining Gefitinib with this Lapatinib, dual EGFR inhibitors is a clinically applicable strategy and a promising combinatory targeted anti-cancer therapy to overcome EGFR wild type mediated Gefitinib resistance. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 619.