Acquired resistance to cetuximab is mediated by increased PTEN instability and leads cross-resistance to gefitinib in HCC827 NSCLC cells

Long non-coding RNAs in non-small cell lung cancer: implications for EGFR-TKI resistance

Non-small cell lung cancer (NSCLC) is one of the most common types of malignant tumors as well as the leading cause of cancer-related deaths in the world. The application of epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) has dramatically improved the prognosis of NSCLC patients who harbor EGFR mutations. However, despite an excellent initial response, NSCLC inevitably becomes resistant to EGFR-TKIs, leading to irreversible disease progression. Hence, it is of great significance to shed light on the molecular mechanisms underlying the EGFR-TKI resistance in NSCLC. Long non-coding RNAs (lncRNAs) are critical gene modulators that are able to act as oncogenes or tumor suppressors that modulate tumorigenesis, invasion, and metastasis. Recently, extensive evidence demonstrates that lncRNAs also have a significant function in modulating EGFR-TKI resistance in NSCLC. In this review, we present a comprehensive summary of the lncRNAs involved in EGFR-TKI resistance in NSCLC and focus on their detailed mechanisms of action, including activation of alternative bypass signaling pathways, phenotypic transformation, intercellular communication in the tumor microenvironment, competing endogenous RNAs (ceRNAs) networks, and epigenetic modifications. In addition, we briefly discuss the limitations and the clinical implications of current lncRNAs research in this field.

MicroRNAs as the critical regulators of tyrosine kinase inhibitors resistance in lung tumor cells

Lung cancer is the second most common and the leading cause of cancer related deaths globally. Tyrosine Kinase Inhibitors (TKIs) are among the common therapeutic strategies in lung cancer patients, however the treatment process fails in a wide range of patients due to TKIs resistance. Given that the use of anti-cancer drugs can always have side effects on normal tissues, predicting the TKI responses can provide an efficient therapeutic strategy. Therefore, it is required to clarify the molecular mechanisms of TKIs resistance in lung cancer patients. MicroRNAs (miRNAs) are involved in regulation of various pathophysiological cellular processes. In the present review, we discussed the miRNAs that have been associated with TKIs responses in lung cancer. MiRNAs mainly exert their role on TKIs response through regulation of Tyrosine Kinase Receptors (TKRs) and down-stream signaling pathways. This review paves the way for introducing a panel of miRNAs for the prediction of TKIs responses in lung cancer patients.

The Role of Akt in Acquired Cetuximab Resistant Head and Neck Squamous Cell Carcinoma: An In Vitro Study on a Novel Combination Strategy

The epidermal growth factor receptor (EGFR) is a therapeutic target in head and neck squamous cell carcinoma (HNSCC). Resistance to EGFR-targeted therapies, such as cetuximab, poses a challenging problem. This study aims to characterize acquired cetuximab resistance mechanisms in HNSCC cell lines by protein phosphorylation profiling. Through this, promising combination treatments can be identified to possibly overcome acquired cetuximab resistance in HNSCC. Protein phosphorylation profiling showed increased phosphorylation of Akt1/2/3 after cetuximab treatment in acquired cetuximab resistant cells compared to cetuximab sensitive cells, which was confirmed by western blotting. Based on this protein phosphorylation profile, a novel combination treatment with cetuximab and the Akt1/2/3 inhibitor MK2206 was designed. Synergy between cetuximab and MK2206 was observed in two cetuximab sensitive HNSCC cell lines and one acquired cetuximab resistant variant in simultaneous treatment schedules. In conclusion, this study demonstrates that increased Akt1/2/3 phosphorylation seems to be characteristic for acquired cetuximab resistance in HNSCC cell lines. Our results also show an additive to synergistic interaction between cetuximab and MK2206 in simultaneous treatment schedules. These data support the hypothesis that the combination of cetuximab with PI3K/Akt pathway inhibition might be a promising novel therapeutic strategy to overcome acquired cetuximab resistance in HNSCC patients.

[CRISPR/Cas9-mediated microRNA-21 knockout increased imatinib sensitivity in chronic myeloid leukemia cells]

目的

观察microRNA-21（miR-21）敲除对耐伊马替尼的人慢性髓性白血病细胞株K562/G01细胞在增殖、药物敏感性等方面的影响，初步探讨miR-21影响K562/G01细胞伊马替尼敏感性的可能机制。

方法

运用CRISPR/Cas9技术敲除K562/G01细胞的miR-21，经PCR筛选、Sanger测序鉴定和实时定量PCR检测获得miR-21敲除的单细胞克隆。扩增培养后，采用MTT法、细胞克隆形成实验检测miR-21敲除对K562/G01细胞增殖的影响。使用伊马替尼处理细胞后，用MTT法和Annexin Ⅴ-APC/7-AAD双染流式细胞检测法观察敲除miR-21后K562/G01细胞对伊马替尼的敏感性的变化。Western blot法检测miR-21敲除前后K562/G01细胞PTEN、AKT、p-AKT、PI3K、p-PI3K、P210^BCR-ABL、p-P210^BCR-ABL蛋白表达量的变化。

结果

成功构建了3个miR-21敲除的K562/G01单细胞克隆，CRISPR/Cas9介导的突变效率为7.12％～8.11％。miR-21敲除使K562/G01细胞的增殖受抑，野生型和1#、2#、6#单细胞克隆的克隆形成率依次为（57.67±8.25）％、（26.94±5.36）％、（7.17±2.11）％、（31.50±3.65）％，差异有统计学意义（P<0.05）。miR-21敲除使K562/G01细胞对伊马替尼的敏感性增加，野生型和1#、2#、6#单细胞克隆对伊马替尼的IC₅₀值分别为（21.92±1.36）µmol/ml、（3.98±0.39）µmol/ml、（5.38±1.01）µmol/ml、（9.24±1.36）µmol/ml，差异有统计学意义（P<0.05）。miR-21敲除后，其靶基因PTEN的蛋白表达水平未见明显变化，但PI3K、AKT信号分子的活化受到抑制，并且P210^BCR-ABL、p-P210^BCR-ABL蛋白表达也下调。

结论

miR-21敲除抑制K562/G01细胞增殖，提高其对伊马替尼的敏感性，这可能是通过抑制PI3K/AKT信号通路和BCR-ABL表达实现的。

Recent insights in the PI3K/Akt pathway as a promising therapeutic target in combination with EGFR-targeting agents to treat head and neck squamous cell carcinoma

Resistance to therapies targeting the epidermal growth factor receptor (EGFR), such as cetuximab, remains a major roadblock in the search for effective therapeutic strategies in head and neck squamous cell carcinoma (HNSCC). Due to its close interaction with the EGFR pathway, redundant or compensatory activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway has been proposed as a major driver of resistance to EGFR inhibitors. Understanding the role of each of the main proteins involved in this pathway is utterly important to develop rational combination strategies able to circumvent resistance. Therefore, the current work reviewed the role of PI3K/Akt pathway proteins, including Ras, PI3K, tumor suppressor phosphatase and tensing homolog, Akt and mammalian target of rapamycin in resistance to anti-EGFR treatment in HNSCC. In addition, we summarize PI3K/Akt pathway inhibitors that are currently under (pre)clinical investigation with focus on overcoming resistance to EGFR inhibitors. In conclusion, genomic alterations in and/or overexpression of one or more of these proteins are common in both human papillomavirus (HPV)-positive and HPV-negative HNSCC tumors. Therefore, downstream effectors of the PI3K/Akt pathway serve as promising drug targets in the search for novel therapeutic strategies that are able to overcome resistance to anti-EGFR treatment. Co-targeting EGFR and the PI3K/Akt pathway can lead to synergistic drug interactions, possibly restoring sensitivity to EGFR inhibitors and hereby improving clinical efficacy. Better understanding of the predictive value of PI3K/Akt pathway alterations is needed to allow the identification of patient populations that might benefit most from these combination strategies.

A preliminary analysis of interleukin-1 ligands as potential predictive biomarkers of response to cetuximab

BACKGROUND

The epidermal growth factor receptor (EGFR) monoclonal IgG1 antibody cetuximab is approved for first-line treatment of recurrent and metastatic (R/M) HNSCC as a part of the standard of care EXTREME regimen (platinum/5-fluorouracil/cetuximab). This regimen has relatively high response and disease control rates but is generally not curative and many patients will experience recurrent disease and/or metastasis. Therefore, there is a great need to identify predictive biomarkers for recurrence and disease progression in cetuximab-treated HNSCC patients to facilitate patient management and allow for treatment modification. The goal of this work is to assess the potential of activating interleukin-1 (IL-1) ligands (IL-1 alpha [IL-1α], IL-1 beta [IL-1β]) as predictive biomarkers of survival outcomes in HNSCC patients treated with cetuximab-based chemotherapy.

METHODS

Baseline gene, serum and tumor expression of interleukin-1 (IL-1) ligands were analyzed from The Cancer Genome Atlas (TCGA) database or clinical trials of cetuximab-based therapies and interrogated for associations with clinical outcome data.

RESULTS

High tumor gene expression of IL-1β was associated with a more favorable overall survival in cetuximab-treated HNSCC patients but not in non-cetuximab-treated patients. In HNSCC patients treated with cetuximab-based chemotherapy, higher gene and circulating levels of IL-1α and IL-1β were correlated with a more favorable progression free survival compared to patients with low or undetectable levels of IL-1 ligands.

CONCLUSIONS

These findings suggest that IL-1 ligands may function as predictive biomarkers for tumor response to cetuximab-based chemotherapy in HNSCC patients and warrants further investigation and validation in larger clinical studies.

Biodistribution, pharmacokinetics and radioimmunotherapy of 188Re-cetuximab in NCI-H292 human lung tumor-bearing nude mice

Background Cetuximab is a fully humanized IgG1 subclass monoclonal that binds specifically to the human epidermal growth factor receptor (EGFR). Although EGFR is expressed in normal cells, the overexpression of EGFR is detected in many human cancers, such as colon, rectum and lung tumors. In this study, cetuximab with a combination of radiotherapy nuclear ¹⁸⁸Re achieved better therapeutic effect on lung cancer. Methods¹⁸⁸Re-cetuximab administered by the i.v. route in human NCI-H292 lung tumor-bearing mice was investigated. NanoSPECT/CT images were taken to evaluate the distribution and tumor targeting of ¹⁸⁸Re-cetuximab in mice. The anti-tumor effect of ¹⁸⁸Re-cetuximab was assessed by the tumor growth inhibition, survival ratio. Results For nanoSPECT/CT imaging, a significant uptake in tumor was observed at 24 and 48 h following the injection of ¹⁸⁸Re-cetuximab. The anti-tumor effect of ¹⁸⁸Re-cetuximab was assessed by tumor growth inhibition and the survival ratio. The tumor-bearing mice treated with ¹⁸⁸Re-cetuximab showed a better mean tumor growth inhibition rate (MGI = 0.049) and longer median survival time and lifespan (62.50 d; 70.07%) than those treated with ¹⁸⁸Re-perrhenate and cetuximab only by single injection. A synergistic effect of tumor growth inhibition was observed with the combination index exceeding one for ¹⁸⁸Re-cetuximab (CI = 6.135 and 9.276). Conclusion The tumor targeting and localization of 188Re-cetuximab were confirmed in this study. Synergistic therapeutic efficacy was demonstrated for the radioimmunotherapy of ¹⁸⁸Re-cetuximab. The results of this study reveal the potential advantage and benefit obtained from ¹⁸⁸Re-cetuximab for diagnosis and therapy of oncology applications in the future.

Tumor-penetration and antitumor efficacy of cetuximab are enhanced by co-administered iRGD in a murine model of human NSCLC

Lung cancer is the leading cause of cancer-associated mortality, worldwide. For this reason, novel therapies are required for the treatment of this devastating disease. Cetuximab is a monoclonal antibody against epidermal growth factor receptor (EGFR), which is overexpressed in a variety of solid tumors, including non-small cell lung cancer (NSCLC). The therapeutic efficacy of cetuximab for NSCLC is limited to use as a monotherapy or in combination with chemotherapy. The objective of the present study was to develop a novel strategy to enhance the therapeutic efficacy of cetuximab for NSCLC by a co-administration with the tumor-penetrating internalizing RGD peptide (iRGD). Human NSCLC subcutaneous xenograft models established with the A549 cell line in nude mice were treated with 30 mg/kg cetuximab, 4 mg/kg iRGD, cetuximab plus iRGD or phosphate-buffered saline. The tumor-penetration, in vivo therapeutic efficacy and involved mechanism were evaluated. The present study showed that the A549 xenograft model is sensitive to the co-administration of cetuximab and iRGD. Treatment with cetuximab plus iRGD resulted in a significant increase in the tumor-penetration of cetuximab and tumor reduction compared with cetuximab monotherapy. In conclusion, iRGD enhances the effects of co-administered cetuximab in an NSCLC model. The combined application of cetuximab and iRGD may be a novel strategy to enhance the clinical therapeutic efficacy of cetuximab for the treatment of NSCLC.

Resistance of Nonmelanoma Skin Cancer to Nonsurgical Treatments. Part II: Photodynamic Therapy, Vismodegib, Cetuximab, Intralesional Methotrexate, and Radiotherapy

A wide range of treatments is now available for nonmelanoma skin cancer, including 5-fluorouracil, ingenol mebutate, imiquimod, diclofenac, photodynamic therapy, methotrexate, cetuximab, vismodegib, and radiotherapy. All are associated with high clinical and histologic response rates. However, some tumors do not respond due to resistance, which may be primary or acquired. Study of the resistance processes is a broad area of research that aims to increase our understanding of the nature of each tumor and the biologic features that make it resistant, as well as to facilitate the design of new therapies directed against these tumors. In this second article, having covered the topical treatments of nonmelanoma skin cancer, we review resistance to other nonsurgical treatments, such as monoclonal antibodies against basal and squamous cell carcinomas, intralesional chemotherapy, photodynamic therapy, and radiotherapy.

Study on chemotherapeutic sensitizing effect of nimotuzumab on different human esophageal squamous carcinoma cells

Esophageal cancer is one of the leading causes of mortality worldwide. Although, surgery, radio- and chemotherapy are used to treat the disease, the identification of new drugs is crucial to increase the curative effect. The aim of the present study was to examine the chemotherapeutic sensitizing effect of nimotuzumab (h-R3) and cisplatin cytotoxic drugs cisplatin (DDP) and 5-fluorouracil (5-FU) on esophageal carcinoma cells with two different epidermal growth factor receptor (EGFR) expressions. The expression of EGFR was detected in the human EC1 or EC9706 esophageal squamous cell carcinoma cell line using immunohistochemistry. The inhibitory effect of DDP and 5-FU alone or combined with h-R3 on EC1 or EC9706 cell proliferation was detected using an MTT assay. Flow cytometry and the TUNEL assay were used to determine the effect of single or combined drug treatment on cell apoptosis. The results showed that the expression of EGFR was low in EC1 cells but high in EC9706 cells. The inhibitory effect of the single use of h-R3 on EC1 or EC9706 cell proliferation was decreased. The inhibitory effect between single use of h-R3 alone and combined use of the chemotherapy drugs showed no statistically significant difference (P>0.05) on the EC1 cell growth rate, but showed a statistically significant difference (a=0.05) on EC9706 cell growth rate. The results detected by flow cytometry and TUNEL assay showed that the difference between single use of h-R3 alone and the control group was statistically significant with regard to the EC1 apoptosis rate effect (P<0.05), but not statistically significant for EC9706 (P>0.05). However, statistically significant differences were identified in the apoptotic rate of EC9706 cells between the h-R3 combined chemotherapy group and single chemotherapy group (P<0.05), but not on in the EC1 chemotherapy group (P>0.05). In conclusion, the sensitization effect of h-R3 on chemotherapy drugs is associated with the expression level of EGFR in EC1 or EC9706 cells. The cell killing effect of the combined use of h-R3 with DDP and 5-FU showed no obvious synergistic effect compared to the single-drug group, but only an additive effect.

Adaptive responses to antibody based therapy

Receptor tyrosine kinases (RTKs) represent a large class of protein kinases that span the cellular membrane. There are 58 human RTKs identified which are grouped into 20 distinct families based upon their ligand binding, sequence homology and structure. They are controlled by ligand binding which activates intrinsic tyrosine-kinase activity. This activity leads to the phosphorylation of distinct tyrosines on the cytoplasmic tail, leading to the activation of cell signaling cascades. These signaling cascades ultimately regulate cellular proliferation, apoptosis, migration, survival and homeostasis of the cell. The vast majority of RTKs have been directly tied to the etiology and progression of cancer. Thus, using antibodies to target RTKs as a cancer therapeutic strategy has been intensely pursued. Although antibodies against the epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) have shown promise in the clinical arena, the development of both intrinsic and acquired resistance to antibody-based therapies is now well appreciated. In this review we provide an overview of the RTK family, the biology of EGFR and HER2, as well as an in-depth review of the adaptive responses undertaken by cells in response to antibody based therapies directed against these receptors. A greater understanding of these mechanisms and their relevance in human models will lead to molecular insights in overcoming and circumventing resistance to antibody based therapy.

An integrated genome-wide approach to discover deregulated microRNAs in non-small cell lung cancer: Clinical significance of miR-23b-3p deregulation

In spite of significant technical advances, genesis and progression of non-small cell lung cancer (NSCLC) remain poorly understood. We undertook an integrated genetic approach to discover novel microRNAs that were deregulated in NSCLCs. A total 119 primary NSCLCs with matched normal were analyzed for genome-wide copy number changes. We also tested a subset of matched samples by microRNA expression array, and integrated them to identify microRNAs positioned in allelic imbalance area. Our findings support that most of the identified deregulated microRNAs (miR-21, miR-23b, miR-31, miR-126, miR-150, and miR-205) were positioned in allelic imbalance areas. Among microRNAs tested in independent 114 NSCLCs, overexpression of miR-23b was revealed to be a significantly poor prognostic factor of recurrence free survival (HR = 2.40, P = 0.005, 95%CI: 1.32–4.29) and overall survival (HR = 2.35, P = 0.005, 95%CI: 1.30–4.19) in multivariable analysis. In addition, overexpression of miR-23b in H1838 cell line significantly increased cell proliferation, while inhibition of miR-23b in H1437 and H1944 cell lines significantly decreased cell doubling time. In summary, integration of genomic analysis and microRNA expression profiling could identify novel cancer-related microRNAs, and miR-23b could be a potential prognostic marker for early stage NSCLCs. Further biological studies of miR-23b are warranted for the potential development of targeted therapy.

Enhancing tumor-targeting monoclonal antibodies therapy by PARP inhibitors

Monoclonal antibodies (mAbs) have become a successful therapeutic approach in cancer. However, some patients do not achieve long-term clinical benefit and most mAbs only exert modest effects as monotherapies. Therefore, combinations with chemotherapy are currently being investigated. Emerging studies have shown a synergistic therapeutic effect of PARP inhibitors and mAbs in cancer. PARP enzymes catalytically cleave β-NAD⁺ and transfer the ADP-ribose moiety to acceptor proteins, modifying their function. In here, we update recent data about the therapeutic effect of the combination of PARP inhibitors with mAbs in cancer treatment and discuss the molecular mechanisms involved in this synergy.

Phosphatidylinositol 3-kinase-AKT-mammalian target of rapamycin (PI3K-Akt-mTOR) signaling pathway in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a devastating disease with poor prognosis. Systemic chemotherapy has been the mainstay of treatment in advanced disease for many decades. Personalized targeted therapy such as epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) and crizotinib has significantly changed the treatment paradigm in NSCLC. The future success of development of molecular targeted therapy relies on the understanding of signal transduction pathways. The PI3K-Akt-mTOR pathway is commonly deregulated in human malignancy including NSCLC. Therefore, this pathway is a target for many therapeutic developments. This review will provide an overview of PI3K-Akt-mTOR signaling pathway, genetic alterations activating the pathway and clinical therapeutic development of pathway inhibitors.

Pharmacogenomics of EGFR-targeted therapies in non-small cell lung cancer: EGFR and beyond

Commonly observed aberrations in epidermal growth factor receptor (EGFR) signaling have led to the development of EGFR-targeted therapies for various cancers, including non–small cell lung cancer (NSCLC). EGFR mutations and overexpression have further been shown to modulate sensitivity to these EGFR-targeted therapies in NSCLC and several other types of cancers. However, it is clear that mutations and/or genetic variations in EGFR alone cannot explain all of the variability in the responses of patients with NSCLC to EGFR-targeted therapies. For instance, in addition to EGFR genotype, genetic variations in other members of the signaling pathway downstream of EGFR or variations in parallel receptor tyrosine kinase (RTK) pathways are now recognized to have a significant impact on the efficacy of certain EGFR-targeted therapies. In this review, we highlight the mutations and genetic variations in such genes downstream of EGFR and in parallel RTK pathways. Specifically, the directional effects of these pharmacogenetic factors are discussed with a focus on two commonly prescribed EGFR inhibitors: cetuximab and erlotinib. The results of this comprehensive review can be used to optimize the treatment of NSCLC with EGFR inhibitors. Furthermore, they may provide the rationale for the design of subsequent combination therapies that involve the inhibition of EGFR.

Sym004, a novel EGFR antibody mixture, can overcome acquired resistance to cetuximab

The epidermal growth factor receptor (EGFR) is a central regulator of tumor progression in a variety of human cancers. Cetuximab is an anti-EGFR monoclonal antibody that has been approved for head and neck and colorectal cancer treatment, but many patients treated with cetuximab don't respond or eventually acquire resistance. To determine how tumor cells acquire resistance to cetuximab, we previously developed a model of acquired resistance using the non-small cell lung cancer line NCI-H226. These cetuximab-resistant (Ctx(R)) cells exhibit increased steady-state EGFR expression secondary to alterations in EGFR trafficking and degradation and, further, retained dependence on EGFR signaling for enhanced growth potential. Here, we examined Sym004, a novel mixture of antibodies directed against distinct epitopes on the extracellular domain of EGFR, as an alternative therapy for Ctx(R) tumor cells. Sym004 treatment of Ctx(R) clones resulted in rapid EGFR degradation, followed by robust inhibition of cell proliferation and down-regulation of several mitogen-activated protein kinase pathways. To determine whether Sym004 could have therapeutic benefit in vivo, we established de novo Ctx(R) NCI-H226 mouse xenografts and subsequently treated Ctx(R) tumors with Sym004. Sym004 treatment of mice harboring Ctx(R) tumors resulted in growth delay compared to mice continued on cetuximab. Levels of total and phospho-EGFR were robustly decreased in Ctx(R) tumors treated with Sym004. Immunohistochemical analysis of these Sym004-treated xenograft tumors further demonstrated decreased expression of Ki67, and phospho-rpS6, as well as a modest increase in cleaved caspase-3. These results indicate that Sym004 may be an effective targeted therapy for Ctx(R) tumors.

Resistance of oral squamous cell carcinoma cells to cetuximab is associated with EGFR insensitivity and enhanced stem cell-like potency

Cetuximab, a specific anti-epidermal growth factor receptor (EGFR) monoclonal antibody, is used in cancer treatment. Although development of resistance to cetuximab is well recognized, the underlying mechanisms remain unclear. In the present study, we characterized cetuximab-resistant oral squamous cell carcinoma (OSCC) cell lines. The human OSCC cell lines HSC3, HSC4 and SAS were used in the present study. Effects of inhibitors including cetuximab on growth in cells were assessed by MTT assays. Southern blotting and immunofluorescence analysis were performed to examine protein expression and localization. Sphere formation was used to characterize stem cell-like properties. Floating aggregation culture was used for anchorage-independent growth. Cetuximab inhibited proliferation of HSC3 and HSC4 cells, but not SAS cells. Proliferation of all three cell lines was inhibited by the EGFR/ErbB2/ErbB4 inhibitor II. The EGFR inhibitor AG1478 strongly inhibited HSC3 and HSC4 proliferation, but that of SAS cells only moderately. EGFR proteins were localized on cell surface and phosphorylated in all three cell lines. SAS cells could proliferate in serum-free monolayer culture and formed spheres from single cells in floating culture. HSC3 and HSC4 could not proliferate under serum-free culture conditions and could not form spheres. Growth of SAS spheres required serum, and was inhibited by both AG1478 and cetuximab. Thus, cetuximab-resistant SAS cells not only engaged in EGFR-independent growth but also exhibited stem cell-like properties. However, growth was EGFR-dependent in aggregation culture, and the SAS cell aggregates became cetuximab-sensitive. This suggests that cetuximab sensitivity is not only cell-type-dependent but is also affected by the growth microenvironment.

Emerging EGFR antagonists for breast cancer

INTRODUCTION

The EGFR has been associated with the pathogenesis and progression of breast cancer. Treatment based on an EGFR target is emerging as a promising option, especially in combination with conventional therapies. Unfortunately, there are no validated predictor biomarkers, and combinatorial treatments are meeting new resistance.

AREAS COVERED

The purpose of this review is to summarize the existing treatments and the current research based on targeting the EGFR pathway.

EXPERT OPINION

The existing EGFR treatments in breast cancer have shown limited benefit. The combination of the monoclonal antibody cetuximab and platinum salts achieves a 15 - 20% response rate. The effectiveness of tyrosine kinase inhibitors is not completely clear, showing modest or no benefits. Gefitinib treatment has offered some promising results in estrogen receptor + breast cancer. However, it has not been identified as a predictive factor for the appropriate selection of patients. Radioimmunotherapy with anti-EGFR radiolabeled antibodies is a promising strategy in BRCA-mutated breast cancer, but it still requires clinical confirmation. Nevertheless, the crosstalk between pathways frequently leads to treatment resistance. Current research is focused on increasing knowledge about the mechanisms of response and the discovery of predictive markers. Targeting several pathways simultaneously and a correct selection of patients seem essential.

Targeting AKT with the allosteric AKT inhibitor MK-2206 in non-small cell lung cancer cells with acquired resistance to cetuximab

The epidermal growth factor receptor (EGFR) is a central regulator of tumor progression in human cancers. Cetuximab is an anti-EGFR monoclonal antibody that has been approved for use in oncology. Despite clinical success the majority of patients do not respond to cetuximab and those who initially respond frequently acquire resistance. To understand how tumor cells acquire resistance to cetuximab we developed a model of resistance using the non-small cell lung cancer line NCI-H226. We found that cetuximab-resistant (Ctx (R) ) clones manifested strong activation of EGFR, PI3K/AKT and MAPK. To investigate the role of AKT signaling in cetuximab resistance we analyzed the activation of the AKT pathway effector molecules using a human AKT phospho-antibody array. Strong activation was observed in Ctx (R) clones for several key AKT substrates including c-jun, GSK3β, eIF4E, rpS6, IKKα, IRS-1 and Raf1. Inhibition of AKT signaling by siAKT1/2 or by the allosteric AKT inhibitor MK-2206 resulted in robust inhibition of cell proliferation in all Ctx (R) clones. Moreover, the combinational treatment of cetuximab and MK-2206 resulted in further decreases in proliferation than either drug alone. This combinatorial treatment resulted in decreased activity of both AKT and MAPK thus highlighting the importance of simultaneous pathway inhibition to maximally affect the growth of Ctx (R) cells. Collectively, our findings demonstrate that AKT activation is an important pathway in acquired resistance to cetuximab and suggests that combinatorial therapy directed at both the AKT and EGFR/MAPK pathways may be beneficial in this setting.

MiR-21 overexpression is associated with acquired resistance of EGFR-TKI in non-small cell lung cancer

BACKGROUND AND PURPOSE

With the increasing use of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) in patients with advanced non-small cell lung cancer (NSCLC), its acquired resistance has become a major clinical problem. Recent studies revealed that miR-21 was involved into the resistance of cytotoxic agents. The aim of this study was to investigate its role in the acquired resistance of NSCLC to EGFR-TKI.

METHODS

EGFR-TKI-sensitive human lung adenocarcinoma cell line PC9 and the acquired resistant cell line, PC9R, were used. Lentiviral vectors were used to infect PC9 or PC9R to regulate the miR-21 expression. The expression of targeted proteins PTEN and PDCD4 was controlled by RNA interference. MicroRNA array, RT-PCR and TaqMan MicroRNA Assays were used to detect miR-21 expression. The MTT and Annexin V assays were used to determine proliferation and apoptosis. Western Blot and immunohistochemistry were used to analyze target protein expression (PTEN, PDCD4, Akt, p-Akt). We also constructed PC9R xenograft tumor model to observe the relationship between miR-21 and EGFR-TKI resistance in vivo and validated it in the clinical serum specimens of NSCLC patients treated with EGFR-TKI.

RESULT

MiR-21 was overexpressed in the EGFR-TKI resistant cell line PC9R relative to PC9. The level of miR-21 was reversely correlated with the expression of PTEN and PDCD4 and positive correlated with PI3K/Akt pathway. Inhibiting miR-21 with lentivirus vector induces apoptosis in PC9R cell line and inhibiting miR-21with ASO suppressed tumor growth in nude mice treated with EGFR-TKI. Furthermore, serum miR-21 expression in NSCLC patients treated with EGFR-TKI was significantly higher at the time of acquiring resistance than at baseline (p<0.01).

CONCLUSION

miR-21 is involved in acquired resistance of EGFR-TKI in NSCLC, which is mediated by down-regulating PTEN and PDCD4 and activating PI3K/Akt pathway.

PIK3CA, BRAF, and PTEN status and benefit from cetuximab in the treatment of advanced colorectal cancer--results from NCIC CTG/AGITG CO.17

PURPOSE

Cetuximab improves survival in patients with K-ras wild-type advanced colorectal cancer. We examined the predictive and prognostic significance of additional biomarkers in this setting, in particular BRAF, PIK3CA, and PTEN.

EXPERIMENTAL DESIGN

Available colorectal tumor samples were analyzed from the CO.17 study. BRAF mutations were identified in tumor-derived DNA by direct sequencing and PIK3CA mutations were identified using a high-resolution melting screen with confirmation by sequencing. PTEN expression by immunohistochemistry (IHC) was performed on tissue microarrays. For each biomarker, prognostic and predictive effects were examined using a Cox model with tests for treatment-biomarker interaction.

RESULTS

A total of 572 patients with pretreated colorectal cancer were randomly assigned to receive cetuximab or best supportive care (BSC). Of 401 patients assessed for BRAF status, 13 (3.2%) had mutations. Of 407 patients assessed for PIK3CA status, 61 (15%) had mutations. Of 205 patients assessed for PTEN, 148 (72%) were negative for IHC expression. None of BRAF, PIK3CA, or PTEN was prognostic for overall or progression-free survival in the BSC arm. None was predictive of benefit from cetuximab, either in the whole study population or the K-ras wild-type subset. In the K-ras wild-type subgroup, the overall survival adjusted HR according to BRAF mutation status was 1.39 (interaction P = 0.69), PIK3CA mutation status HR = 0.79 (interaction P = 0.63), and PTEN expression HR = 0.75 (interaction P = 0.61).

CONCLUSIONS

In chemotherapy-refractory colorectal cancer, neither PIK3CA mutation status nor PTEN expression were prognostic, nor were they predictive of benefit from cetuximab. Evaluation of predictive significance of BRAF mutations requires a larger sample size.

Preclinical modeling of EGFR-specific antibody resistance: oncogenic and immune-associated escape mechanisms

To define the molecular basis of secondary resistance to epidermal growth factor receptor (EGFR)-specific antibodies is crucial to increase clinical benefit in patients. The limited access to posttreatment tumor samples constitutes the major barrier to conduct these studies, representing preclinical experimentation as a useful alternative. Anti-EGFR antibody-based therapy has been reported to mediate tumor regression by interrupting oncogenic signals and, more recently, by inducing antitumor immunological responses. However, resistance models have been focused only on tumor escape associated with EGFR blockade, whereas studies describing immune-associated escape mechanisms have not been reported thus far. To address this idea, we modeled resistance induction in D122 metastasis-bearing C57BL/6 mice treated with 7A7 (an anti-murine EGFR antibody). Similarly to patients receiving EGFR-specific antibodies, 7A7 resistance promotion represents an important drawback to successful therapy. Characterization of primary cultures derived from metastasis in 7A7-treated mice revealed a high frequency of tumor variants resistant to in vivo and in vitro antibody treatment. We showed, for the first time, the convergence of alterations in oncogenic and immunological pathways in 7A7-resistant variants. To identify key molecules behind resistance, seven 7A7-resistant variants were screened. HER3 overexpression and PTEN deficiency leading to hyperactivation of protumoral downstream signaling were found in these variants as a consequence of 7A7-mediated EGFR inhibition. Concomitantly, we found a high percentage of resistant variants carrying abnormalities in the constitutive and/or interferon gamma (IFN-γ)-inducible major histocompatibility complex I (MHC-I) expression. A significant decrease in mRNA levels for MHC-I heavy chains, β2-microglogulin and antigen processing machinery genes as well as transcriptional alterations in IFN-γ pathway components were identified as the main mechanisms underlying MHC-I expression defects in 7A7-resistant variants. Notably, these defects have not been previously associated with EGFR-specific antibody resistance, providing novel immunological escape mechanisms. This study has strong implications for the development of new combination strategies to overcome anti-EGFR antibodies refractoriness.

Acquired resistance to cetuximab is associated with the overexpression of Ras family members and the loss of radiosensitization in head and neck cancer cells

PURPOSE

Cetuximab in combination with radiation therapy is used to treat patients with head and neck squamous cell carcinoma (HNSCC). In the present study, the mechanism of acquired resistance to cetuximab in HNSCC cells was investigated in vitro.

MATERIAL AND METHODS

The HNSCC cell lines UT5 and SAS and UT5 cells with acquired resistance to cetuximab (UT5R9) were used. The radiotoxicity potentials of cetuximab and inhibitors of PI3K, MAPK and farnesylation were tested using a clonogenic survival assay. Western blotting was used to evaluate protein expression. The levels of EGFR ligands were detected by ELISA.

RESULTS

Cetuximab inhibited proliferation and induced radiosensitization in UT5 cells but not in SAS cells. In comparison with UT5 cells, cetuximab-resistant SAS cells markedly overexpressed the K-Ras, H-Ras and N-Ras proteins, as detected by Western blotting. Resistance in UT5R9 cells was associated with the overexpression of the K-Ras, H-Ras and N-Ras proteins as well as an increase in the autocrine production of the EGFR ligands amphiregulin and transforming growth factor α (TGFα). UT5R9 cells were significantly more radioresistant than UT5 cells. Radioresistant UT5R9 cells were not radiosensitized by cetuximab, but knocking down H-RAS and N-RAS with siRNA and targeting Ras farnesylation using the farnesyltransferase inhibitor lonafarnib induced radiosensitization in these cells. Targeting PI3K and MEK revealed that the activation of the PI3K/Akt pathway but not the MAPK/ERK pathway is associated with radioresistance in UT5R9 cells.

CONCLUSION

Targeting Ras and PI3K activity improves the outcome of irradiation in cetuximab-resistant HNSCC cell lines in vitro.

Glycolysis inhibition sensitizes non-small cell lung cancer with T790M mutation to irreversible EGFR inhibitors via translational suppression of Mcl-1 by AMPK activation

The secondary EGF receptor (EGFR) T790M is the most common mechanism of resistance to reversible EGFR-tyrosine kinase inhibitors (TKI) in patients with non-small cell lung cancer (NSCLC) with activating EGFR mutations. Although afatinib (BIBW2992), a second-generation irreversible EGFR-TKI, was expected to overcome the acquired resistance, it showed limited efficacy in a recent phase III clinical study. In this study, we found that the inhibition of glycolysis using 2-deoxy-d-glucose (2DG) improves the efficacy of afatinib in H1975 and PC9-GR NSCLC cells with EGFR T790M. Treatment with the combination of 2DG and afatinib induced intracellular ATP depletion in both H1975 and PC9-GR cells, resulting in activation of AMP-activated protein kinase (AMPK). AMPK activation played a central role in the cytotoxicity of the combined treatment with 2DG and afatinib through the inhibition of mTOR. The alteration of the AMPK/mTOR signaling pathway by the inhibition of glucose metabolism induced specific downregulation of Mcl-1, a member of the antiapoptotic Bcl-2 family, through translational control. The enhancement of afatinib sensitivity by 2DG was confirmed in the in vivo PC9-GR xenograft model. In conclusion, this study examined whether the inhibition of glucose metabolism using 2DG enhances sensitivity to afatinib in NSCLC cells with EGFR T790M through the regulation of the AMPK/mTOR/Mcl-1 signaling pathway. These data suggest that the combined use of an inhibitor of glucose metabolism and afatinib is a potential therapeutic strategy for the treatment of patients with acquired resistance to reversible EGFR-TKIs due to secondary EGFR T790M.

miRNA-200c increases the sensitivity of breast cancer cells to doxorubicin through the suppression of E-cadherin-mediated PTEN/Akt signaling

Doxorubicin (ADR) is successfully used to treat breast cancer, however, it is often associated with the acquired resistance of breast cancer cells which eliminates the therapeutic efficiency of ADR, leading to relapse and a poorer prognosis. It has been reported that microRNA-200c (miRNA-200c), a non-coding RNA, is important in the epithelial to mesenchymal transition (EMT) and metastasis in breast cancer cells. Recent evidence demonstrated that miRNA-200c is also regulated in chemotherapeutic drug resistance, however, the precise mechanism by which this occurs remains unclear. In this study, we demonstrated that the loss of miRNA-200c correlates with the acquired resistance of breast cancer cells to ADR. In addition, the loss of miRNA-200c correlated with decreased levels of E-cadherin and PTEN, and increased levels of ZEB1 and phospho-Akt (p-Akt) in ADR-resistant breast cancer cells (MCF-7/ADR cells). More importantly, we demonstrated that the gain of miRNA-200c results in an increased sensitivity of cells to ADR, downregulation of ZEB1, upregulation of E-cadherin and PTEN, and inactivation of Akt signaling. Following the co-transfection of E-cadherin siRNA, the miRNA-200c-mediated regulation of Akt signaling and PTEN was inhibited. Results of the present study also demonstrated that Akt signaling is involved in the ADR resistance of breast cancer cells since LY294002, an inhibitor of Akt signaling, partially restored the sensitivity of MCF-7/ADR cells to ADR. In conclusion, miRNA-200c inhibited Akt signaling through its effects on E-cadherin and PTEN, resulting in the inhibition of ADR resistance in breast cancer cells.

Overcoming acquired resistance to anticancer therapy: focus on the PI3K/AKT/mTOR pathway

BACKGROUND

Most targeted anticancer therapies, as well as cytotoxic and radiation therapies, are encumbered by the development of secondary resistance by cancer cells. Resistance is a complex phenomenon involving multiple mechanisms, including activation of signaling pathways such as phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR). Novel strategies to overcome resistance by targeting these signaling pathways are being evaluated.

METHODS

PubMed and key cancer congress abstracts were searched until July 2012 for preclinical and clinical data relating to the PI3K/AKT/mTOR pathway and anticancer treatment resistance, and use of PI3K/AKT/mTOR inhibitors in resistant cancer cell lines and patient populations.

RESULTS

Activation of the PI3K/AKT/mTOR pathway is frequently implicated in resistance to anticancer therapies, including biologics, tyrosine kinase inhibitors, radiation, and cytotoxics. As such, inhibitors of the PI3K/AKT/mTOR pathway are being rapidly evaluated in preclinical models and in clinical studies to determine whether they can restore therapeutic sensitivity when given in combination. In breast cancer, non-small-cell lung cancer, and glioblastoma, we find compelling preclinical evidence to show that inhibitors of PI3K or mTOR can restore sensitivity in resistant cells. Although clinical evidence is less mature, a recent Phase III study with the mTORC1 inhibitor everolimus in patients with advanced breast cancer resistant to aromatase inhibition and several Phase I/II studies with PI3K inhibitors demonstrate proof-of-concept, warranting future clinical evaluation.

CONCLUSION

Current preclinical and clinical evidence suggest that inhibitors of the PI3K/AKT/mTOR pathway could have utility in combination with other anticancer therapies to circumvent resistance by cancer cells. Multiple clinical studies are ongoing.

Development of PI3K/AKT/mTOR pathway inhibitors and their application in personalized therapy for non-small-cell lung cancer

Lung cancer is a common disease with more than 1.6 million new cases diagnosed worldwide in 2008. Treatments for patients with advanced disease are rarely curative, and responses to therapy are often followed by relapse, which highlights the large unmet need for novel therapies. Recent advances in cancer treatment have focused on personalized therapy, whereby patients are treated with agents that best target the molecular drivers of their disease. Thus, a better understanding of the pathways that drive cancer or drug resistance is of critical importance. One such example is the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, which is activated in many lung cancer patients and represents a target for therapy. PI3K/AKT/mTOR pathway activation has also been observed in tumors resistant to agents targeting upstream receptor tyrosine kinases. Agents that target this pathway have the potential to shut down survival pathways, and are being explored both in the setting of pathway-activating mutations and for their ability to restore sensitivity to upstream signaling targeted agents. Here, we examine the frequency of mutations activating the PI3K/AKT/mTOR pathway, review the novel agents being explored to target this pathway, and explore the potential role of the inhibition of this pathway in the clinical development of these agents.

Hepatocyte growth factor induces resistance to anti-epidermal growth factor receptor antibody in lung cancer

INTRODUCTION

Epidermal growth factor receptor (EGFR) is an attractive drug target in lung cancer, with several anti-EGFR antibodies and small-molecule inhibitors showing efficacy in lung cancer patients. Patients, however, may develop resistance to EGFR inhibitors. We demonstrated previously that hepatocyte growth factor (HGF) induced resistance to EGFR tyrosine kinase inhibitors in lung cancers harboring EGFR mutations. We therefore determined whether HGF could induce resistance to the anti-EGFR antibody (EGFR Ab) cetuximab in lung cancer cells, regardless of EGFR gene status.

METHODS

Cetuximab sensitivity and signal transduction in lung cancer cells were examined in the presence or absence of HGF, HGF-producing fibroblasts, and cells tranfected with the HGF gene in vitro and in vivo.

RESULTS

HGF induced resistance to cetuximab in H292 (EGFR wild) and Ma-1(EGFR mutant) cells. Western blotting showed that HGF-induced resistance was mediated by the Met/Gab1/Akt signaling pathway. Resistance of H292 and Ma-1 cells to cetuximab was also induced by coculture with lung fibroblasts producing high levels of HGF and by cells stably transfected with the HGF gene. This resistance was abrogated by treatment with anti-HGF neutralizing antibody.

CONCLUSIONS

HGF-mediated resistance is a novel mechanism of resistance to EGFR Ab in lung cancers, with fibroblast-derived HGF inducing cetuximab resistance in H292 tumors in vivo. The involvement of HGF-Met-mediated signaling should be assessed in acquired resistance to EGFR Ab in lung cancer, regardless of EGFR gene status.

Where now for anti-EGF receptor therapies in colorectal cancer?

Current US FDA-approved monoclonal antibodies targeting the EGF receptor (EGFR) include cetuximab and panitumumab. In this article, we discuss the clinical evidence concerning the use of monoclonal antibodies targeting the EGFR in the setting of advanced colorectal cancer and the emergence of predictive molecular biomarkers. In addition, we also consider the evidence surrounding the evolution of anti-EGFR-resistance mechanisms evoked by targeted anti-EGFR therapy and potential therapeutic strategies that may counteract resistant tumor growth.

Resistance to EGF receptor-targeted monoclonal antibodies in the management of advanced colorectal cancer

SUMMARY Molecular markers that predict benefit associated with treatments for advanced colon cancer are now part of routine clinical practice. Monoclonal antibodies that target the EGF receptor have been shown to lack efficacy in cancers that have KRAS gene mutations. The antibodies are now used exclusively for patients with KRAS wild-type colon cancer. Such cancers may not respond to EGF receptor-targeted therapy at all. Those that initially respond will eventually develop resistance and inevitably progress. We will review mechanisms of primary and secondary resistance to EGF receptor monoclonal antibody therapy and suggest strategies to overcome resistance.

[Research progress on resistance mechanisms of epidermal growth factor receptor tyrosine kinase inhibitors in non-small cell lung cancer]

With a greater understanding of tumor biology, novel molecular-targeted strategies that block cancer progression pathways have been evaluated as a new therapeutic approach for treating non-small cell lung cancer (NSCLC). Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib and erlotinib, show favorable response to EGFR mutant lung cancer in some populations of NSCLC patients. However, the efficacy of EGFR-TKIs is limited by either primary (de novo) or acquired resistance after therapy. This review will focus on recently identified mechanisms of primary and acquired resistance to EGFR TKIs and strategies currently being employed to overcome resistance.

Epithelial to mesenchymal transition in an epidermal growth factor receptor-mutant lung cancer cell line with acquired resistance to erlotinib

INTRODUCTION

Mesenchymal status is related to "inherent resistance" to gefitinib or erlotinib in non-small cell lung cancer without epidermal growth factor receptor(EGFR) mutations. In addition, a recent report showed that the epithelial to mesenchymal transition (EMT) plays a role in acquired resistance to gefitinib in A549 cells, which harbor a KRAS mutation. However, recent clinical studies revealed that gefitinib or erlotinib are highly effective in the treatment of non-small cell lung cancer with EGFR mutations.

METHODS

We developed resistant cells (HCC4006ER) from erlotinib-sensitive HCC4006 cells harboring an EGFR deletion mutation by chronic exposure to increasing concentrations of erlotinib. Acquired resistance mechanisms of HCC4006ER cells were analyzed.

RESULTS

Neither known resistance mechanisms nor novel molecules that may confer erlotinib resistance were identified using candidate or comprehensive analyses. In addition, HCC4006ER cells lost dependency for EGFR. However, we found that HCC4006ER cells acquired a mesenchymal phenotype and exhibited down-regulation of E-cadherin expression (2.7 × 10 times compared with parental cells). We also found that the histone deacetylase inhibitor, MS-275, restored E-cadherin expression and moderate sensitivity to erlotinib in HCC4006ER cells, on the other hand, transforming growth factor beta, an inducer of EMT, led to moderate erlotinib resistance in HCC4006 parental cells.

CONCLUSIONS

This is the first report of a relationship between EMT and erlotinib acquired resistance in an erlotinib sensitive EGFR-mutant lung cancer cell line. Our results indicate that it would be important to consider the influence of EMT in the development of treatments against acquired resistance to gefitinib or erlotinib.

Cell signaling molecules as drug targets in lung cancer: an overview

PURPOSE OF REVIEW

Lung being one of the vital and essential organs in the body, lung cancer is a major cause of mortality in the modern human society. Lung cancer can be broadly subdivided into nonsmall cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Although NSCLC is sometimes treated with surgery, the advanced and metastatic NSCLC and SCLC usually respond better to chemotherapy and radiation. The most important targets of these chemotherapeutic agents are various intracellular signaling molecules. The primary focus of this review article is to summarize the description of various cell signaling molecules involved in lung cancer development and their regulation by chemotherapeutic agents.

RECENT FINDINGS

Extensive research work in recent years has identified several cellular signaling molecules that may be intricately involved in the complexity of lung cancer. Some of these cell signaling molecules are epidermal growth factor receptors, vascular endothelial growth factor receptors, mammalian target of rapamycin, mitogen-activated protein kinase phosphatase-1, peroxisome proliferator-activated receptor-gamma, matrix metalloproteinases and receptor for advanced glycation end-products.

SUMMARY

The present review will strengthen our current knowledge regarding the efficacy of the above-mentioned cell signaling molecules as potential beneficial drug targets against lung cancer.

Checks and balances: interplay of RTKs and PTPs in cancer progression

In recent years, targeted therapies for receptor tyrosine kinases (RTKs) have shown initial promise in the clinical setting for the treatment of several tumors driven by these oncogenic signaling pathways. Unfortunately, clinical relapse due to acquired resistance to these molecular therapeutics is common. An improved understanding of how tumors bypass the inhibitory effects of RTK-targeted therapies has revealed a rich myriad of possible mechanisms for acquired resistance. Protein tyrosine phosphatases (PTPs) can function as oncogenes or tumor suppressors to either enhance or suppress RTK signaling. Recent studies suggest that the loss or gain of function of PTP's can significantly impinge on RTK signaling during tumor progression. Here we review the interplay between RTKs and PTPs as an emerging mechanism for acquired resistance to RTK-targeted therapies, that may aid in the design of improved therapies to prevent and overcome resistance in treatments for cancer patients.

Molecular mechanisms of resistance to the EGFR monoclonal antibody cetuximab

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase belonging to the HER family of receptor tyrosine kinases. Receptor activation upon ligand binding leads to down stream activation of the PI3K/AKT, RAS/RAF/MEK/ERK and PLCγ/PKC pathways that influence cell proliferation, survival and the metastatic potential of tumor cells. Increased activation by gene amplification, protein overexpression or mutations of the EGFR has been identified as an etiological factor in a number of human epithelial cancers (e.g., NSCLC, CRC, glioblastoma and breast cancer). Therefore, targeting the EGFR has been intensely pursued as a cancer treatment strategy over the last two decades. To date, five EGFR inhibitors, including three small molecule tyrosine kinase inhibitors (TKIs) and two monoclonal antibodies have gained FDA approval for use in oncology. Both approaches to targeting the EGFR have shown clinical promise and the anti-EGFR antibody cetuximab is used to treat HNSCC and CRC. Despite clinical gains arising from use of cetuximab, both intrinsic resistance and the development of acquired resistance are now well recognized. In this review we focus on the biology of the EGFR, the role of EGFR in human cancer, the development of antibody-based anti-EGFR therapies and a summary of their clinical successes. Further, we provide an in depth discussion of described molecular mechanisms of resistance to cetuximab and potential strategies to circumvent this resistance.