Crystal structure of the complex of human epidermal growth factor and receptor extracellular domains

Glioblastoma mutations alter EGFR dimer structure to prevent ligand bias

The epidermal growth factor receptor (EGFR) is frequently mutated in human cancer^1,2, and is an important therapeutic target. EGFR inhibitors have been successful in lung cancer, where mutations in the intracellular tyrosine kinase domain activate the receptor¹, but not in glioblastoma multiforme (GBM)³, where mutations occur exclusively in the extracellular region. Here we show that common extracellular GBM mutations prevent EGFR from discriminating between its activating ligands⁴. Different growth factor ligands stabilize distinct EGFR dimer structures⁵ that signal with different kinetics to specify or bias outcome^5,6. EGF itself induces strong symmetric dimers that signal transiently to promote proliferation. Epiregulin (EREG) induces much weaker asymmetric dimers that drive sustained signalling and differentiation⁵. GBM mutations reduce the ability of EGFR to distinguish EREG from EGF in cellular assays, and allow EGFR to form strong (EGF-like) dimers in response to EREG and other low-affinity ligands. Using X-ray crystallography, we further show that the R84K GBM mutation symmetrizes EREG-driven extracellular dimers so that they resemble dimers normally seen with EGF. By contrast, a second GBM mutation, A265V, remodels key dimerization contacts to strengthen asymmetric EREG-driven dimers. Our results argue for an important role of altered ligand discrimination by EGFR in GBM, with potential implications for therapeutic targeting.

Fluorescence Imaging of Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitor Resistance in Non-Small Cell Lung Cancer

Simple Summary

Lung cancer is the leading cause of cancer-related deaths, with a low (<21%) 5-year survival rate. Lung cancer is often driven by the misfunction of molecules on the surface of cells of the epithelium, which orchestrate mechanisms by which these cells grow and proliferate. Beyond common non-specific treatments, such as chemotherapy or radiotherapy, among molecular-specific treatments, a number of small-molecule drugs that block cancer-driven molecular activity have been developed. These drugs initially have significant success in a subset of patients, but these patients systematically develop resistance within approximately one year of therapy. Substantial efforts towards understanding the mechanisms of resistance have focused on the genomics of cancer progression, the response of cells to the drugs, and the cellular changes that allow resistance to develop. Fluorescence microscopy of many flavours has significantly contributed to the last two areas, and is the subject of this review.

Abstract

Non-small cell lung cancer (NSCLC) is a complex disease often driven by activating mutations or amplification of the epidermal growth factor receptor (EGFR) gene, which expresses a transmembrane receptor tyrosine kinase. Targeted anti-EGFR treatments include small-molecule tyrosine kinase inhibitors (TKIs), among which gefitinib and erlotinib are the best studied, and their function more often imaged. TKIs block EGFR activation, inducing apoptosis in cancer cells addicted to EGFR signals. It is not understood why TKIs do not work in tumours driven by EGFR overexpression but do so in tumours bearing classical activating EGFR mutations, although the latter develop resistance in about one year. Fluorescence imaging played a crucial part in research efforts to understand pro-survival mechanisms, including the dysregulation of autophagy and endocytosis, by which cells overcome the intendedly lethal TKI-induced EGFR signalling block. At their core, pro-survival mechanisms are facilitated by TKI-induced changes in the function and conformation of EGFR and its interactors. This review brings together some of the main advances from fluorescence imaging in investigating TKI function and places them in the broader context of the TKI resistance field, highlighting some paradoxes and suggesting some areas where super-resolution and other emerging methods could make a further contribution.

Structural Insight and Development of EGFR Tyrosine Kinase Inhibitors

Lung cancer has a high prevalence, with a growing number of new cases and mortality every year. Furthermore, the survival rate of patients with non-small-cell lung carcinoma (NSCLC) is still quite low in the majority of cases. Despite the use of conventional therapy such as tyrosine kinase inhibitor for Epidermal Growth Factor Receptor (EGFR), which is highly expressed in most NSCLC cases, there was still no substantial improvement in patient survival. This is due to the drug’s ineffectiveness and high rate of resistance among individuals with mutant EGFR. Therefore, the development of new inhibitors is urgently needed. Understanding the EGFR structure, including its kinase domain and other parts of the protein, and its activation mechanism can accelerate the discovery of novel compounds targeting this protein. This study described the structure of the extracellular, transmembrane, and intracellular domains of EGFR. This was carried out along with identifying the binding pose of commercially available inhibitors in the ATP-binding and allosteric sites, thereby clarifying the research gaps that can be filled. The binding mechanism of inhibitors that have been used clinically was also explained, thereby aiding the structure-based development of new drugs.

EGFR-Targeted Photodynamic Therapy

The epidermal growth factor receptor (EGFR) plays a pivotal role in the proliferation and metastatization of cancer cells. Aberrancies in the expression and activation of EGFR are hallmarks of many human malignancies. As such, EGFR-targeted therapies hold significant potential for the cure of cancers. In recent years, photodynamic therapy (PDT) has gained increased interest as a non-invasive cancer treatment. In PDT, a photosensitizer is excited by light to produce reactive oxygen species, resulting in local cytotoxicity. One of the critical aspects of PDT is to selectively transport enough photosensitizers to the tumors environment. Accordingly, an increasing number of strategies have been devised to foster EGFR-targeted PDT. Herein, we review the recent nanobiotechnological advancements that combine the promise of PDT with EGFR-targeted molecular cancer therapy. We recapitulate the chemistry of the sensitizers and their modes of action in PDT, and summarize the advantages and pitfalls of different targeting moieties, highlighting future perspectives for EGFR-targeted photodynamic treatment of cancer.

Allosteric activation of preformed EGF receptor dimers by a single ligand binding event

Aberrant activation of the epidermal growth factor receptor (EGFR) by mutations has been implicated in a variety of human cancers. Elucidation of the structure of the full-length receptor is essential to understand the molecular mechanisms underlying its activation. Unlike previously anticipated, here, we report that purified full-length EGFR adopts a homodimeric form in vitro before and after ligand binding. Cryo-electron tomography analysis of the purified receptor also showed that the extracellular domains of the receptor dimer, which are conformationally flexible before activation, are stabilized by ligand binding. This conformational flexibility stabilization most likely accompanies rotation of the entire extracellular domain and the transmembrane domain, resulting in dissociation of the intracellular kinase dimer and, thus, rearranging it into an active form. Consistently, mutations of amino acid residues at the interface of the symmetric inactive kinase dimer spontaneously activate the receptor in vivo. Optical observation also indicated that binding of only one ligand activates the receptor dimer on the cell surface. Our results suggest how oncogenic mutations spontaneously activate the receptor and shed light on the development of novel cancer therapies.

Fluorescently tagged nanobodies and NanoBRET to study ligand-binding and agonist-induced conformational changes of full-length EGFR expressed in living cells

Introduction

The Epidermal Growth Factor Receptor is a member of the Erb receptor tyrosine kinase family. It binds several ligands including EGF, betacellulin (BTC) and TGF-α, controls cellular proliferation and invasion and is overexpressed in various cancer types. Nanobodies (VHHs) are the antigen binding fragments of heavy chain only camelid antibodies. In this paper we used NanoBRET to compare the binding characteristics of fluorescent EGF or two distinct fluorescently labelled EGFR directed nanobodies (Q44c and Q86c) to full length EGFR.

Methods

Living HEK293T cells were stably transfected with N terminal NLuc tagged EGFR. NanoBRET saturation, displacement or kinetics experiments were then performed using fluorescently labelled EGF ligands (EGF-AF488 or EGF-AF647) or fluorescently labelled EGFR targeting nanobodies (Q44c-HL488 and Q86c-HL488).

Results

These data revealed that the EGFR nanobody Q44c was able to inhibit EGF binding to full length EGFR, while Q86c was able to recognise agonist bound EGFR and act as a conformational sensor. The specific binding of fluorescent Q44c-HL488 and EGF-AF488 was inhibited by a range of EGFR ligands (EGF> BTC>TGF-α).

Discussion

EGFR targeting nanobodies are powerful tools for studying the role of the EGFR in health and disease and allow real time quantification of ligand binding and distinct ligand induced conformational changes.

Epitope Mapping of an Anti-HER2 Monoclonal Antibody (H2Mab-181) Using Enzyme-Linked Immunosorbent Assay

Human epidermal growth factor receptor 2 (HER2) is a type I transmembrane 185 kDa protein expressed in various types of normal or cancer cells. Overexpression of HER2 is found in many cancers and is related to cell proliferation, differentiation, and migration. We recently developed a novel anti-HER2 monoclonal antibody, H₂Mab-181, by immunizing mice with the purified recombinant extracellular domain of HER2. H₂Mab-181 can specifically and sensitively detect HER2 not only in flow cytometry and Western blotting for gastric cancer cell lines, but also in immunohistochemical analyses for gastric cancer tissues. In this study, we analyzed the binding epitope of H₂Mab-181 to HER2 using enzyme-linked immunosorbent assay (ELISA). Results showed that the H₂Mab-181 epitope was determined to be Gly383, Asp384, Ala386, Asn388, and Pro391 by ELISA.

Harnessing Reversed Allosteric Communication: A Novel Strategy for Allosteric Drug Discovery

Allostery is a fundamental and extensive mechanism of intramolecular signal transmission. Allosteric drugs possess several unique pharmacological advantages over traditional orthosteric drugs, including greater selectivity, better physicochemical properties, and lower off-target toxicity. However, owing to the complexity of allosteric regulation, experimental approaches for the development of allosteric modulators are traditionally serendipitous. Recently, the reversed allosteric communication theory has been proposed, providing a feasible tool for the unbiased detection of allosteric sites. Herein, we review the latest research on the reversed allosteric communication effect using the examples of sirtuin 6, epidermal growth factor receptor, 3-phosphoinositide-dependent protein kinase 1, and Related to A and C kinases (RAC) serine/threonine protein kinase B and recapitulate the methodologies of reversed allosteric communication strategy. The novel reversed allosteric communication strategy greatly expands the horizon of allosteric site identification and allosteric mechanism exploration and is expected to accelerate an end-to-end framework for drug discovery.

Signalling dynamics in embryonic development

In multicellular organisms, cellular behaviour is tightly regulated to allow proper embryonic development and maintenance of adult tissue. A critical component in this control is the communication between cells via signalling pathways, as errors in intercellular communication can induce developmental defects or diseases such as cancer. It has become clear over the last years that signalling is not static but varies in activity over time. Feedback mechanisms present in every signalling pathway lead to diverse dynamic phenotypes, such as transient activation, signal ramping or oscillations, occurring in a cell type- and stage-dependent manner. In cells, such dynamics can exert various functions that allow organisms to develop in a robust and reproducible way. Here, we focus on Erk, Wnt and Notch signalling pathways, which are dynamic in several tissue types and organisms, including the periodic segmentation of vertebrate embryos, and are often dysregulated in cancer. We will discuss how biochemical processes influence their dynamics and how these impact on cellular behaviour within multicellular systems.

Therapeutic advances in non-small cell lung cancer: Focus on clinical development of targeted therapy and immunotherapy

Lung cancer still contributes to nearly one-quarter cancer-related deaths in the past decades, despite the rapid development of targeted therapy and immunotherapy in non-small cell lung cancer (NSCLC). The development and availability of comprehensive genomic profiling make the classification of NSCLC more precise and personalized. Most treatment decisions of advanced-stage NSCLC have been made based on the genetic features and PD-L1 expression of patients. For the past 2 years, more than 10 therapeutic strategies have been approved as first-line treatment for certain subgroups of NSCLC. However, some major challenges remain, including drug resistance and low rate of overall survival. Therefore, we discuss and review the therapeutic strategies of NSCLC, and focus on the development of targeted therapy and immunotherapy in advanced-stage NSCLC. Based on the latest guidelines, we provide an updated summary on the standard treatment for NSCLC. At last, we discussed several potential therapies for NSCLC. The development of new drugs and combination therapies both provide promising therapeutic effects on NSCLC.

Structural basis of cytokine-mediated activation of ALK family receptors

Anaplastic lymphoma kinase (ALK)¹ and the related leukocyte tyrosine kinase (LTK)² are recently deorphanized receptor tyrosine kinases³. Together with their activating cytokines, ALKAL1 and ALKAL2^4-6 (also called FAM150A and FAM150B or AUGβ and AUGα, respectively), they are involved in neural development⁷, cancer^7-9 and autoimmune diseases¹⁰. Furthermore, mammalian ALK recently emerged as a key regulator of energy expenditure and weight gain¹¹, consistent with a metabolic role for Drosophila ALK¹². Despite such functional pleiotropy and growing therapeutic relevance^13,14, structural insights into ALK and LTK and their complexes with cognate cytokines have remained scarce. Here we show that the cytokine-binding segments of human ALK and LTK comprise a novel architectural chimera of a permuted TNF-like module that braces a glycine-rich subdomain featuring a hexagonal lattice of long polyglycine type II helices. The cognate cytokines ALKAL1 and ALKAL2 are monomeric three-helix bundles, yet their binding to ALK and LTK elicits similar dimeric assemblies with two-fold symmetry, that tent a single cytokine molecule proximal to the cell membrane. We show that the membrane-proximal EGF-like domain dictates the apparent cytokine preference of ALK. Assisted by these diverse structure-function findings, we propose a structural and mechanistic blueprint for complexes of ALK family receptors, and thereby extend the repertoire of ligand-mediated dimerization mechanisms adopted by receptor tyrosine kinases.

Structures of the HER2-HER3-NRG1β complex reveal a dynamic dimer interface

Human epidermal growth factor receptor 2 (HER2) and HER3 form a potent pro-oncogenic heterocomplex^1-3 upon binding of growth factor neuregulin-1β (NRG1β). The mechanism by which HER2 and HER3 interact remains unknown in the absence of any structures of the complex. Here we isolated the NRG1β-bound near full-length HER2-HER3 dimer and, using cryo-electron microscopy, reconstructed the extracellulardomain module, revealing unexpected dynamics at the HER2-HER3 dimerization interface. We show that the dimerization arm of NRG1β-bound HER3 is unresolved because the apo HER2 monomer does not undergo a ligand-induced conformational change needed to establish a HER3 dimerization arm-binding pocket. In a structure of the oncogenic extracellular domain mutant HER2(S310F), we observe a compensatory interaction with the HER3 dimerization arm that stabilizes the dimerization interface. Both HER2-HER3 and HER2(S310F)-HER3 retain the capacity to bind to the HER2-directed therapeutic antibody trastuzumab, but the mutant complex does not bind to pertuzumab. Our structure of the HER2(S310F)-HER3-NRG1β-trastuzumab Fab complex reveals that the receptor dimer undergoes a conformational change to accommodate trastuzumab. Thus, similar to oncogenic mutations, therapeutic agents exploit the intrinsic dynamics of the HER2-HER3 heterodimer. The unique features of a singly liganded HER2-HER3 heterodimer underscore the allosteric sensing of ligand occupancy by the dimerization interface and explain why extracellular domains of HER2 do not homo-associate via a canonical active dimer interface.

A molecular mechanism for the generation of ligand-dependent differential outputs by the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that couples the binding of extracellular ligands, such as EGF and transforming growth factor-α (TGF-α), to the initiation of intracellular signaling pathways. EGFR binds to EGF and TGF-α with similar affinity, but generates different signals from these ligands. To address the mechanistic basis of this phenomenon, we have carried out cryo-EM analyses of human EGFR bound to EGF and TGF-α. We show that the extracellular module adopts an ensemble of dimeric conformations when bound to either EGF or TGF-α. The two extreme states of this ensemble represent distinct ligand-bound quaternary structures in which the membrane-proximal tips of the extracellular module are either juxtaposed or separated. EGF and TGF-α differ in their ability to maintain the conformation with the membrane-proximal tips of the extracellular module separated, and this conformation is stabilized preferentially by an oncogenic EGFR mutation. Close proximity of the transmembrane helices at the junction with the extracellular module has been associated previously with increased EGFR activity. Our results show how EGFR can couple the binding of different ligands to differential modulation of this proximity, thereby suggesting a molecular mechanism for the generation of ligand-sensitive differential outputs in this receptor family.

NADPH Oxidase and Epidermal Growth Factor Receptor Are Promising Targets of Phytochemicals for Ultraviolet-Induced Skin Carcinogenesis

The skin acts as the primary defense organ that protects the body from the external environment. Skin cancer is one of the most common cancers in the world. Skin carcinogenesis is usually caused by cell degeneration due to exposure to ultraviolet (UV) radiation, which causes changes in various signaling networks, disrupting the homeostasis of single skin cells. In this review, we summarize the roles of nicotinamide adenine dinucleotide phosphate oxidase (NOX) and epidermal growth factor receptor (EGFR) in UV-induced skin carcinogenesis. Furthermore, we describe the crosstalk that exists between NOX, EGFR, and protein tyrosine phosphatase κ and its oncogenic downstream signaling pathways. Chemoprevention is the use of chemical compounds to recover the healthy status of the skin or delay cancer development. Current evidence from in vitro and in vivo studies on chemopreventive phytochemicals that target NOX, EGFR, or both, as major regulators of skin carcinogenesis will also be discussed.

EGFR transactivates RON to drive oncogenic crosstalk

Crosstalk between different receptor tyrosine kinases (RTKs) is thought to drive oncogenic signaling and allow therapeutic escape. EGFR and RON are two such RTKs from different subfamilies, which engage in crosstalk through unknown mechanisms. We combined high-resolution imaging with biochemical and mutational studies to ask how EGFR and RON communicate. EGF stimulation promotes EGFR-dependent phosphorylation of RON, but ligand stimulation of RON does not trigger EGFR phosphorylation – arguing that crosstalk is unidirectional. Nanoscale imaging reveals association of EGFR and RON in common plasma membrane microdomains. Two-color single particle tracking captured formation of complexes between RON and EGF-bound EGFR. Our results further show that RON is a substrate for EGFR kinase, and that transactivation of RON requires formation of a signaling competent EGFR dimer. These results support a role for direct EGFR/RON interactions in propagating crosstalk, such that EGF-stimulated EGFR phosphorylates RON to activate RON-directed signaling.

The EGF Domains of MUC4 Oncomucin Mediate HER2 Binding Affinity and Promote Pancreatic Cancer Cell Tumorigenesis

Simple Summary

A feature of pancreatic cancer (PC) is the frequent overexpression of tyrosine kinase membrane receptor HER2 along with its membrane partner the MUC4 oncomucin in the early stages of the pancreatic carcinogenesis. However, therapeutic approaches targeting HER2 in PC are not efficient. MUC4 could indeed represent an alternative therapeutic strategy to target HER2 signaling pathway, but this approach needs to characterize MUC4/HER2 interaction at the molecular level. In this study, we successfully showed the impact of the EGF domains of MUC4 on HER2 binding affinity and demonstrated their “growth factor-like” biological activities in PC cells. Moreover, homology models of the MUC4_EGF/HER2 complexes allowed identification of binding hotspots mediating binding affinity with HER2 and PC cell proliferation. These results allow a better understanding of the mechanisms involved in the MUC4/HER2 complex formation and may lead to the design of potential MUC4/HER2 inhibitors.

Abstract

The HER2 receptor and its MUC4 mucin partner form an oncogenic complex via an extracellular region of MUC4 encompassing three EGF domains that promotes tumor progression of pancreatic cancer (PC) cells. However, the molecular mechanism of interaction remains poorly understood. Herein, we decipher at the molecular level the role and impact of the MUC4_EGF domains in the mediation of the binding affinities with HER2 and the PC cell tumorigenicity. We used an integrative approach combining in vitro bioinformatic, biophysical, biochemical, and biological approaches, as well as an in vivo study on a xenograft model of PC. In this study, we specified the binding mode of MUC4_EGF domains with HER2 and demonstrate their “growth factor-like” biological activities in PC cells leading to stimulation of several signaling proteins (mTOR pathway, Akt, and β-catenin) contributing to PC progression. Molecular dynamics simulations of the MUC4_EGF/HER2 complexes led to 3D homology models and identification of binding hotspots mediating binding affinity with HER2 and PC cell proliferation. These results will pave the way to the design of potential MUC4/HER2 inhibitors targeting the EGF domains of MUC4. This strategy will represent a new efficient alternative to treat cancers associated with MUC4/HER2 overexpression and HER2-targeted therapy failure as a new adapted treatment to patients.

Syndecans and Their Synstatins: Targeting an Organizer of Receptor Tyrosine Kinase Signaling at the Cell-Matrix Interface

Receptor tyrosine kinases (RTKs) and integrin matrix receptors have well-established roles in tumor cell proliferation, invasion and survival, often functioning in a coordinated fashion at sites of cell-matrix adhesion. Central to this coordination are syndecans, another class of matrix receptor, that organize RTKs and integrins into functional units, relying on docking motifs in the syndecan extracellular domains to capture and localize RTKs (e.g., EGFR, IGF-1R, VEGFR2, HER2) and integrins (e.g., αvβ3, αvβ5, α4β1, α3β1, α6β4) to sites of adhesion. Peptide mimetics of the docking motifs in the syndecans, called “synstatins”, prevent assembly of these receptor complexes, block their signaling activities and are highly effective against tumor cell invasion and survival and angiogenesis. This review describes our current understanding of these four syndecan-coupled mechanisms and their inhibitory synstatins (SSTN_IGF1R, SSTN_VEGFR2, SSTN_VLA-4, SSTN_EGFR and SSTN_HER2).

Expanding the Disorder-Function Paradigm in the C-Terminal Tails of Erbbs

ErbBs are receptor tyrosine kinases involved not only in development, but also in a wide variety of diseases, particularly cancer. Their extracellular, transmembrane, juxtamembrane, and kinase folded domains were described extensively over the past 20 years, structurally and functionally. However, their whole C-terminal tails (CTs) following the kinase domain were only described at atomic resolution in the last 4 years. They were shown to be intrinsically disordered. The CTs are known to be tyrosine-phosphorylated when the activated homo- or hetero-dimers of ErbBs are formed. Their phosphorylation triggers interaction with phosphotyrosine binding (PTB) or Src Homology 2 (SH2) domains and activates several signaling pathways controling cellular motility, proliferation, adhesion, and apoptosis. Beyond this passive role of phosphorylated domain and site display for partners, recent structural and function studies unveiled active roles in regulation of phosphorylation and interaction: the CT regulates activity of the kinase domain; different phosphorylation states have different compaction levels, potentially modulating the succession of phosphorylation events; and prolines have an important role in structure, dynamics, and possibly regulatory interactions. Here, we review both the canonical role of the disordered CT domains of ErbBs as phosphotyrosine display domains and the recent findings that expand the known range of their regulation functions linked to specific structural and dynamic features.

A novel EGFR inhibitor suppresses survivin expression and tumor growth in human gefitinib-resistant EGFR-wild type and -T790M non-small cell lung cancer

Tyrosine kinase inhibitors of epidermal growth factor receptor (EGFR-TKIs) are currently used therapy for non-small cell lung cancer (NSCLC) patients; however, drug resistance during cancer treatment is a critical problem. Survivin is an anti-apoptosis protein, which promotes cell proliferation and tumor growth that highly expressed in various human cancers. Here, we show a novel synthetic compound derived from gefitinib, do-decyl-4-(4-(3-(4-(3-chloro-4-fluorophenylamino)-7-methoxyquinazolin-6-yloxy)propyl) piper-azin-1-yl)-4-oxobutanoate, which is named as SP101 that inhibits survivin expression and tumor growth in both the EGFR-wild type and -T790M of NSCLC. SP101 blocked EGFR kinase activity and induced apoptosis in the A549 (EGFR-wild type) and H1975 (EGFR-T790M) lung cancer cells. SP101 reduced survivin proteins and increased active caspase 3 for inducing apoptosis. Ectopic expression of survivin by a survivin-expressed vector attenuated the SP101-induced cell death in lung cancer cells. Moreover, SP101 inhibited the gefitinib-resistant tumor growth in the xenograft human H1975 lung tumors of nude mice. SP101 substantially reduced survivin proteins but conversely elicited active caspase 3 proteins in tumor tissues. Besides, SP101 exerted anticancer abilities in the gefitinib resistant cancer cells separated from pleural effusion of a clinical lung cancer patient. Consistently, SP101 decreased the survivin proteins and the patient-derived xenografted lung tumor growth in nude mice. Anti-tumor ability of SP101 was also confirmed in the murine lung cancer model harboring EGFR T790M-L858R. Together, SP101 is a new EGFR inhibitor with inhibiting survivin that can be developed for treating EGFR wild-type and EGFR-mutational gefitinib-resistance in human lung cancers.

Anti-EGFR Binding Nanobody Delivery System to Improve the Diagnosis and Treatment of Solid Tumours

BACKGROUND

Epidermal Growth Factor Receptor (EGFR) and members of its homologous protein family mediate transmembrane signal transduction by binding to a specific ligand, which leads to regulated cell growth, differentiation, proliferation and metastasis. With the development and application of Genetically Engineered Antibodies (GEAs), Nanobodies (Nbs) constitute a new research hot spot in many diseases. A Nb is characterized by its low molecular weight, deep tissue penetration, good solubility and high antigen-binding affinity, the anti-EGFR Nbs are of significance for the diagnosis and treatment of EGFR-positive tumours.

OBJECTIVE

This review aims to provide a comprehensive overview of the information about the molecular structure of EGFR and its transmembrane signal transduction mechanism, and discuss the anti-EGFR-Nbs influence on the diagnosis and treatment of solid tumours.

METHODS

Data were obtained from PubMed, Embase and Web of Science. All patents are searched from the following websites: the World Intellectual Property Organization (WIPO®), the United States Patent Trademark Office (USPTO®) and Google Patents.

RESULTS

EGFR is a key target for regulating transmembrane signaling. The anti-EGFR-Nbs for targeted drugs could effectively improve the diagnosis and treatment of solid tumours.

CONCLUSION

EGFR plays a role in transmembrane signal transduction. The Nbs, especially anti- EGFR-Nbs, have shown effectiveness in the diagnosis and treatment of solid tumours. How to increase the affinity of Nb and reduce its immunogenicity remain a great challenge.

An Anti-HER2 Monoclonal Antibody H2Mab-41 Exerts Antitumor Activities in Mouse Xenograft Model Using Dog HER2-Overexpressed Cells

Overexpression of human epidermal growth factor receptor 2 (HER2) has been reported in a variety of cancer types, including breast, lung, gastric, pancreatic, and colorectal cancers. Trastuzumab, a humanized anti-HER2 monoclonal antibody (mAb), has been shown to provide significant survival benefits in HER2-overexpressing breast cancer and gastric cancer patients. Previously, an anti-HER2 mAb, H₂Mab-41 (IgG_2b, kappa), was developed in our laboratory and its antitumor activity was demonstrated in mouse xenograft models of human colon cancer. The present study aimed to investigate the ability of H₂Mab-41 to induce antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) in dog HER2 (dHER2)-overexpressed cell lines, and thus exert its antitumor activity against dHER2-overexpressed tumors in vivo. Flow cytometry results demonstrated the cross-reactivity of H₂Mab-41 with dHER2. Further evaluation of interaction between H₂Mab-41 and dHER2-overexpressed CHO-K1 (CHO/dHER2) cells indicated moderate binding affinity of H₂Mab-41 toward dHER2, with a dissociation constant (K_D) of 2.6 × 10^-8 M. In vitro analysis revealed that the administration of H₂Mab-41 induced high levels of ADCC and CDC in CHO/dHER2 cells. Furthermore, intraperitoneal administration of H₂Mab-41 in mouse xenograft models of CHO/dHER2 resulted in significant inhibition of tumor development compared to the control mouse IgG. Thus, the findings of the present study demonstrated the in vivo safety and efficacy of H₂Mab-41, highlighting its suitability to be included as a part of a therapeutic regimen for dHER2-expressing canine cancers.

Development of a Novel Anti-HER2 Monoclonal Antibody H2Mab-181 for Gastric Cancer

Human epidermal growth factor receptor 2 (HER2) is a type I transmembrane 185 kDa protein. HER2 is expressed in a variety of normal tissue types and cancer cells. HER2 is associated with cell proliferation, differentiation, and migration. The overexpression of HER2 has been observed in a number of cancers, including breast and gastric cancers. Gastric cancer is one of the most common cancers worldwide, with an annual case rate of ∼1 million people diagnosed with the disease. Trastuzumab is a humanized anti-HER2 monoclonal antibody (mAb) that has been utilized in gastric cancer therapy. In this study, we have developed a novel anti-HER2 mAb, H₂Mab-181 (IgG₁, kappa), through the immunization of mice with a purified recombinant extracellular domain of HER2. H₂Mab-181 can specifically and sensitively detect HER2 in both flow cytometry and Western blot applications in gastric cancer cell lines and can also be utilized in immunohistochemical analyses of gastric cancer tissues. Together, H₂Mab-181 could be useful for the diagnosis and therapy in gastric cancers.

Versatile Mitogenic and Differentiation-Inducible Layer Formation by Underwater Adhesive Polypeptides

Artificial materials have no biological functions, but they are important for medical devices such as artificial organs and matrices for regenerative medicine. In this study, mitogenic and differentiation-inducible materials are devised via the simple coating of polypeptides, which contain the sequence of epidermal growth factor or insulin-like growth factor with a key amino acid (3,4-dihydroxyphenylalanine) of underwater adhesive proteins. The adhesive polypeptides prepared via solid-phase synthesis form layers on various substrates involving organic and inorganic materials to provide biological surfaces. Through the direct activation of cognate receptors on interactive surfaces, the materials enable increased cell growth and differentiation compared to that achieved by soluble growth factors. This superior growth and differentiation are attributed to the long-lasting signal transduction (triggered by the bound growth factors), which do not cause receptor internalization and subsequent downregulation.

Free energy perturbation guided Synthesis with Biological Evaluation of Substituted Quinoline derivatives as small molecule L858R/T790M/C797S mutant EGFR inhibitors targeting resistance in Non-Small Cell Lung Cancer (NSCLC)

Two different schemes of novel substituted quinoline derivatives were designed and synthesized via simple reaction steps and conditions. A comparative molecular docking study was carried out on two different types of EGFR enzymes which include wild-type (PDB: 4I23) and T790M mutated (PDB: 2JIV) respectively. Compounds were also validated upon T790M/C797S mutated (PDB ID: 5D41) EGFR enzyme at the allosteric binding site. Free energy perturbations were carried out to determine the absolute binding free energy of a protein-ligand complex in the form of ΔG_binding, which in turn provided 4ab and 5ad as the most potential contenders through the structural enhancement in the determined initial scaffolds. Anticancer activity of the synthesized derivatives was examined against HCC827, H1975 (L858R/T790M), A549, and HT-29 cell lines by standard MTT assay. Compound 4ad (6-chloro-2-(isoindolin-2-yl)-4-methylquinoline) has shown excellent inhibitory activities against mutant EGFR kinase with IC₅₀ value 0.91 µM. The potency of compounds 4ab, 4ad and 5adwas compared throughan insilicoADMET study.

Advances of Targeted Therapy for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the common and fatal malignancies, which is a significant global health problem. The clinical applicability of traditional surgery and other locoregional therapies is limited, and these therapeutic strategies are far from satisfactory in improving the outcomes of advanced HCC. In the past decade, targeted therapy had made a ground-breaking progress in advanced HCC. Those targeted therapies exert antitumor effects through specific signals, including anti-angiogenesis or cell cycle progression. As a standard systemic therapy option, it tremendously improves the survival of this devastating disease. Moreover, the combination of targeted therapy with immune checkpoint inhibitor (ICI) has demonstrated more potent anticancer effects and becomes the hot topic in clinical studies. The combining medications bring about a paradigm shift in the treatment of advanced HCC. In this review, we presented all approved targeted agents for advanced HCC with an emphasis on their clinical efficacy, summarized the advances of multi-target drugs in research for HCC and potential therapeutic targets for drug development. We also discussed the exciting results of the combination between targeted therapy and ICI.

Discovery of Cyclic Peptidomimetic Ligands Targeting the Extracellular Domain of EGFR

It is very promising to target the extracellular domain of epidermal growth factor receptor (EGFR) for developing novel and selective anticancer therapies. Herein, we report the discovery of a novel small molecule, M-2-5, from a one-bead-two-compound (OBTC) cyclic γ-AApeptide library. The molecule was found to bind tightly to the extracellular domain of EGFR. Intriguingly, this molecule could also effectively antagonize EGF-stimulated EGFR phosphorylation and downstream signal transduction. Furthermore, together with its remarkable resistance to proteolytic degradation, M-2-5 was shown to effectively inhibit cell proliferation and migration in vitro and suppresses the growth of tumor in the A549 xenograft model in vivo, highlighting its potential therapeutic application for cancer treatment.

Src family kinases, adaptor proteins and the actin cytoskeleton in epithelial-to-mesenchymal transition

Over a century of scientific inquiry since the discovery of v-SRC but still no final judgement on SRC function. However, a significant body of work has defined Src family kinases as key players in tumor progression, invasion and metastasis in human cancer. With the ever-growing evidence supporting the role of epithelial-mesenchymal transition (EMT) in invasion and metastasis, so does our understanding of the role SFKs play in mediating these processes. Here we describe some key mechanisms through which Src family kinases play critical role in epithelial homeostasis and how their function is essential for the propagation of invasive signals. Video abstract.

Signaling pathways in cancer-associated fibroblasts and targeted therapy for cancer

To flourish, cancers greatly depend on their surrounding tumor microenvironment (TME), and cancer-associated fibroblasts (CAFs) in TME are critical for cancer occurrence and progression because of their versatile roles in extracellular matrix remodeling, maintenance of stemness, blood vessel formation, modulation of tumor metabolism, immune response, and promotion of cancer cell proliferation, migration, invasion, and therapeutic resistance. CAFs are highly heterogeneous stromal cells and their crosstalk with cancer cells is mediated by a complex and intricate signaling network consisting of transforming growth factor-beta, phosphoinositide 3-kinase/AKT/mammalian target of rapamycin, mitogen-activated protein kinase, Wnt, Janus kinase/signal transducers and activators of transcription, epidermal growth factor receptor, Hippo, and nuclear factor kappa-light-chain-enhancer of activated B cells, etc., signaling pathways. These signals in CAFs exhibit their own special characteristics during the cancer progression and have the potential to be targeted for anticancer therapy. Therefore, a comprehensive understanding of these signaling cascades in interactions between cancer cells and CAFs is necessary to fully realize the pivotal roles of CAFs in cancers. Herein, in this review, we will summarize the enormous amounts of findings on the signals mediating crosstalk of CAFs with cancer cells and its related targets or trials. Further, we hypothesize three potential targeting strategies, including, namely, epithelial-mesenchymal common targets, sequential target perturbation, and crosstalk-directed signaling targets, paving the way for CAF-directed or host cell-directed antitumor therapy.

EGFR extracellular domain III expressed in Escherichia coli with SEP tag shows improved biophysical and functional properties and generate anti-sera inhibiting cancer cell growth

The epidermal growth factor receptor extracellular domain III (EGFR-ECDIII) protein is a promising target of anti-cancer research, and its production in Escherichia coli would thus represent significant benefits. However, despite its moderate size (19 kDa), the expression of EGFR-ECDIII in E.coli is hampered by the presence of multiple cysteines producing misfolded proteins with incorrect S-S bonds. In our study, we show that a short 12-residue solubility enhancing peptide (SEP) tag containing nine arginines (C9R) attached at the C-terminus of EGFR-ECDIII reduces the inclusion body formation and increases the final yield by six times (20 mg/L). EGFR-ECDIII-C9R purified from the soluble fraction eluted as a sharp single RP-HPLC peak, suggesting a single S-S bond pairing. Biophysical characterization using circular dichroism, fluorescence, and light scattering confirmed its native-like properties together with reversible thermal denaturation. The binding activity of EGFR-ECDIII-C9R to anti-EGFR-VHH7D12, a single-domain antibody with specific binding to the ECDIII, was assessed by sandwich ELISA. Further, we produced anti-EGFR-ECDIII-C9R antisera in mouse models and anti-sera inhibited A431 cancer cells' growth. These results demonstrate that the SEP tag enables the rapid production of the multiple disulfide-bonded EGFR-ECDIII in E. coli having native-like biophysical properties and producing neutralizing antibodies.

Discovery of Potent EGFR Inhibitors With 6-Arylureido-4-anilinoquinazoline Derivatives

According to the classical pharmacophore fusion strategy, a series of 6-arylureido-4-anilinoquinazoline derivatives ( Compounds 7a - t ) were designed, synthesized, and biologically evaluated by the standard CCK-8 method and enzyme inhibition assay. Among the title compounds, Compounds 7a , 7c , 7d , 7f , 7i , 7o , 7p , and 7q exhibited promising anti-proliferative bioactivities, especially Compound 7i , which had excellent antitumor activity against the A549, HT-29, and MCF-7 cell lines (IC₅₀ = 2.25, 1.72, and 2.81 μM, respectively) compared with gefitinib, erlotinib, and sorafenib. In addition, the enzyme activity inhibition assay indicated that the synthesized compounds had sub-micromolar inhibitory levels (IC₅₀, 11.66-867.1 nM), which was consistent with the results of the tumor cell line growth inhibition tests. By comparing the binding mechanisms of Compound 7i (17.32 nM), gefitinib (25.42 nM), and erlotinib (33.25 nM) to the EGFR, it was found that Compound 7i could extend into the effective region with a similar action conformation to that of gefitinib and interact with residues L85, D86, and R127, increasing the binding affinity of Compound 7i to the EGFR. Based on the molecular hybridization strategy, 14 compounds with EGFR inhibitory activity were designed and synthesized, and the action mechanism was explored through computational approaches, providing valuable clues for the research of antitumor agents based on EGFR inhibitors.

Discovery of Hyperstable Noncanonical Plant-Derived Epidermal Growth Factor Receptor Agonist and Analogs

Here, we report the discovery of the first plant-derived and noncanonical epidermal growth factor receptor (EGFR) agonist, the 36-residue bleogen pB1 from Pereskia bleo of the Cactaceae family. We show that bleogen pB1 is a low-affinity EGFR agonist using a suite of chemical, biochemical, cellular, and animal experiments which include incisor eruption and wound-healing mouse models. A focused positional scanning pB1 library of Ala- and d-amino acid scans yielded a high-affinity pB1 analog, [K29k]pB1, with a 60-fold-improved EGFR affinity and mitogenicity. We show that the potency of [K29k]pB1 and the epidermal growth factor (EGF) is comparable in a diabetic mouse wound-healing model. We also show that both bleogen pB1 and [K29k]pB1 are hyperstable, being >100-fold more stable than EGF against proteolytic degradation. Overall, our discovery of a noncanonical proteolytic-resistant EGFR agonist scaffold could open new avenues for developing wound healing and skin regeneration therapeutics and biomaterials.

Role of Glycans on Key Cell Surface Receptors That Regulate Cell Proliferation and Cell Death

Cells undergo proliferation and apoptosis, migration and differentiation via a number of cell surface receptors, most of which are heavily glycosylated. This review discusses receptor glycosylation and the known roles of glycans on the functions of receptors expressed in diverse cell types. We included growth factor receptors that have an intracellular tyrosine kinase domain, growth factor receptors that have a serine/threonine kinase domain, and cell-death-inducing receptors. N- and O-glycans have a wide range of functions including roles in receptor conformation, ligand binding, oligomerization, and activation of signaling cascades. A better understanding of these functions will enable control of cell survival and cell death in diseases such as cancer and in immune responses.

Isatin-Hydrazones with Multiple Receptor Tyrosine Kinases (RTKs) Inhibitory Activity and In-Silico Binding Mechanism

Recently, we have reported a series of isatin hydrazone, two of them, namely, 3-((2,6-dichlorobenzylidene)hydrazono)indolin-2-one (1) and 3-((2-chloro-6-fluorobenzylidene)hydrazono)indolin-2-one (2) having potent cytotoxicity, showing cyclin-dependent kinases (CDK2) inhibitory activity and bearing recommended drug likeness properties. Since both compounds (1 and 2) showed inhibitory activity against CDK2, we assumed it would also have multiple receptor tyrosine kinases (RTKs) inhibitory activity. Considering those points, here, above-mentioned two isatin hydrazone 1 and 2 were synthesized using previously reported method for further investigation of their potency on RTKs (EGFR, VEGFR-2 and FLT-3) inhibitory activity. As expected, Compound 1 exhibited excellent inhibitory activity against epidermal growth factor receptor (EGFR, IC50 = 0.269 µM), vascular epidermal growth factor receptor 2 (VEGFR-2, IC50 = 0.232 µM) and FMS-like tyrosine kinase-3 (FLT-3, IC50 = 1.535 µM) tyrosine kinases. On the other hand, Compound 2 also exhibited excellent inhibitory activity against EGFR (IC50 = 0.369 µM), VEGFR-2 (IC50 = 0.266 µM) and FLT-3 (IC50 = 0.546 µM) tyrosine kinases. A molecular docking study with EGFR, VEGFR-2 and FLT-3 kinase suggested that both compounds act as type I ATP competitive inhibitors against EGFR and VEGFR-2, and type II ATP non-competitive inhibitors against FLT-3.

An anti-HER2 nanobody binds to its antigen HER2 via two independent paratopes

High-resolution structural data of complexes between antibodies and membrane receptors still represent a demanding task. In this study, we used complementary sets of experimental data to obtain a structural model of the complex formed by the human epidermal growth factor receptor 2 (HER2) and its specific nanobody A10. First we identified by NMR the residues that bind or rearrange as a consequence of the complex formation. In parallel, the complex was cross-linked, digested and the resulting peptides were characterized by mass-spectrometry to define maximal distance restraints between HER2 and A10 amino acids in their complex. These independent datasets guided a docking process, refined by molecular dynamics simulations, to develop a model of the complex and estimate per-residue free-energy contributions. Such a model explains the experimental data and identifies a second, non-canonical paratope, located in the region opposite to the conventional nanobody paratope, formed by the hypervariable loop regions LH1 and LH3. Both paratopes contributed substantially to the overall affinity by binding to independent HER2 epitopes. Nanobody mutants with substitution of key interaction residues, as indicated by the model, possess significantly lower affinity for HER2. This is the first described case of a "natural" biparatopic nanobody, directly selected by in-vitro panning.

Loss of CPAP causes sustained EGFR signaling and epithelial-mesenchymal transition in oral cancer

Higher epidermal growth factor receptor (EGFR) signaling can contribute to tumor metastasis and resistance to therapies in oral squamous cell carcinoma (OSCC). EGFR signaling can promote epithelial-mesenchymal transition (EMT) in OSCC. EMT is a process by which epithelial cells acquire invasive properties and it can contribute to tumor metastasis. Not only do the abnormal functions of microtubule and microtubule-organizing centers (MTOC) such as centrosomes lead to cancers, but also the malignant tissues are characterized by aberrant centriolar features and amplified centrosomes. Microtubule inhibition therapies increase the sensitivity to EGFR targeting drugs in various cancers. In this study, we show that the loss of expression of a microtubule/tubulin binding protein, centrosomal protein 4.1-associated protein (CPAP), which is critical for centriole biogenesis and normal functioning of the centrosome, caused an increase in the EGFR levels and its signaling and, enhanced the EMT features and invasiveness of OSCC cells. Further, depletion of CPAP enhanced the tumorigenicity of these cells in a xeno-transplant model. Importantly, CPAP loss-associated EMT features and invasiveness of multiple OSCC cells were attenuated upon depletion of EGFR in them. On the other hand, we found that CPAP protein levels were higher in EGF treated OSCC cells as well as in oral cancer tissues, suggesting that the frequently reported aberrant centriolar features of tumors are potentially a consequence, but not the cause, of tumor progression. Overall, our novel observations show that, in addition to its known indispensable role in centrosome biogenesis, CPAP also plays a vital role in suppressing tumorigenesis in OSCC by facilitating EGFR homeostasis.

In-Cell Single-Molecule Analysis of Molecular State and Reaction Kinetics Coupling

Cellular signaling is regulated by the spatiotemporal dynamics and kinetics of molecular behavior. To investigate the mechanisms at the molecular level, fluorescence single-molecule analysis is an effective method owing to the direct observation of individual molecules in situ in cells and the results in quantitative information about the behavior. The integration of machine learning into this analysis modality enables the acquisition of behavioral features at all time points of all molecules. As a case study, we described a hidden Markov model-based approach to infer the molecular states of mobility and clustering for epidermal growth factor receptor (EGFR) along a single-molecule trajectory. We reveal a scheme of the receptor signaling through the dynamic coupling of the mobility and clustering states under the influence of a local membrane structure. As the activation process progressed, EGFR generally converged to an immobile cluster. This state exhibited high affinity with a specific cytoplasmic protein, shown by two-color single-molecule analysis, and could be a platform for downstream signaling. The method was effective for elucidating the biophysical mechanisms of signaling regulation when comprehensive analysis is possible for a huge number and multiple molecular species in the signaling pathway. Thus, a fully automated system for single-molecule analysis, in which indispensable expertise was replicated using artificial intelligence, has been developed to enable in-cell large-scale analysis. This system opens new single-molecule approaches for pharmacological applications as well as the basic sciences.

Identification of Vinyl Sulfone Derivatives as EGFR Tyrosine Kinase Inhibitor: In Vitro and In Silico Studies

Epidermal growth factor receptor (EGFR), overexpressed in many types of cancer, has been proved as a high potential target for targeted cancer therapy due to its role in regulating proliferation and survival of cancer cells. In the present study, a series of designed vinyl sulfone derivatives was screened against EGFR tyrosine kinase (EGFR-TK) using in silico and in vitro studies. The molecular docking results suggested that, among 78 vinyl sulfones, there were eight compounds that could interact well with the EGFR-TK at the ATP-binding site. Afterwards, these screened compounds were tested for the inhibitory activity towards EGFR-TK using ADP-Glo™ kinase assay, and we found that only VF16 compound exhibited promising inhibitory activity against EGFR-TK with the IC₅₀ value of 7.85 ± 0.88 nM. In addition, VF16 showed a high cytotoxicity with IC₅₀ values of 33.52 ± 2.57, 54.63 ± 0.09, and 30.38 ± 1.37 µM against the A431, A549, and H1975 cancer cell lines, respectively. From 500-ns MD simulation, the structural stability of VF16 in complex with EGFR-TK was quite stable, suggesting that this compound could be a novel small molecule inhibitor targeting EGFR-TK.

Galectins as modulators of receptor tyrosine kinases signaling in health and disease

Receptor tyrosine kinases (RTKs) constitute a large group of cell surface proteins that mediate communication of cells with extracellular environment. RTKs recognize external signals and transfer information to the cell interior, modulating key cellular activities, like metabolism, proliferation, motility, or death. To ensure balanced stream of signals the activity of RTKs is tightly regulated by numerous mechanisms, including receptor expression and degradation, ligand specificity and availability, engagement of co-receptors, cellular trafficking of the receptors or their post-translational modifications. One of the most widespread post-translational modifications of RTKs is glycosylation of their extracellular domains. The sugar chains attached to RTKs form a new layer of information, so called glyco-code that is read by galectins, carbohydrate binding proteins. Galectins are family of fifteen lectins implicated in immune response, inflammation, cell division, motility and death. The versatility of cellular activities attributed to galectins is a result of their high abundance and diversity of their cellular targets. A various sugar specificity of galectins and the differential ability of galectin family members to form oligomers affect the spatial distribution and the function of their cellular targets. Importantly, galectins and RTKs are tightly linked to the development, progression and metastasis of various cancers. A growing number of studies points on the close cooperation between RTKs and galectins in eliciting specific cellular responses. This review focuses on the identified complexes between galectins and RTK members and discusses their relevance for the cell physiology both in healthy tissues and in cancer.

Dealing with NSCLC EGFR mutation testing and treatment: A comprehensive review with an Italian real-world perspective

Since their discovery, relevant efforts have been made to optimize the detection approaches to EGFR mutations as well as the clinical management of EGFR-mutated NSCLC. The recent shift from single gene testing to novel comprehensive detection platforms along with the development of new generation tyrosine kinase inhibitors, targeting both common and uncommon EGFR-mutations, is leading to a progressive increase in the number of patients who may benefit from targeted approaches, with subsequent impact on their long-term survival and quality of life. However, a prompt and adequate implementation of the most recent diagnostic and treatment advances in the routine practice often remains critical to be specifically addressed. In this review we provide a complete and updated overview of the different detection platforms and therapeutic options currently available for the clinical management of advanced EGFR-positive NSCLC, summarizing scientific evidence and describing molecular testing as well as treatment practice in the real-word scenario.

Anti-EGFR antibody 528 binds to domain III of EGFR at a site shifted from the cetuximab epitope

Antibodies have been widely used for cancer therapy owing to their ability to distinguish cancer cells by recognizing cancer-specific antigens. Epidermal growth factor receptor (EGFR) is a promising target for the cancer therapeutics, against which several antibody clones have been developed and brought into therapeutic use. Another antibody clone, 528, is an antagonistic anti-EGFR antibody, which has been the focus of our antibody engineering studies to develop cancer drugs. In this study, we explored the interaction of 528 with the extracellular region of EGFR (sEGFR) via binding analyses and structural studies. Dot blotting experiments with heat treated sEGFR and surface plasmon resonance binding experiments revealed that 528 recognizes the tertiary structure of sEGFR and exhibits competitive binding to sEGFR with EGF and cetuximab. Single particle analysis of the sEGFR-528 Fab complex via electron microscopy clearly showed the binding of 528 to domain III of sEGFR, the domain to which EGF and cetuximab bind, explaining its antagonistic activity. Comparison between the two-dimensional class average and the cetuximab/sEGFR crystal structure revealed that 528 binds to a site that is shifted from, rather than identical to, the cetuximab epitope, and may exclude known drug-resistant EGFR mutations.

Human RNase3 immune modulation by catalytic-dependent and independent modes in a macrophage-cell line infection model

The human RNase3 is a member of the RNaseA superfamily involved in host immunity. RNase3 is expressed by leukocytes and shows broad-spectrum antimicrobial activity. Together with a direct antimicrobial action, RNase3 exhibits immunomodulatory properties. Here, we have analysed the transcriptome of macrophages exposed to the wild-type protein and a catalytic-defective mutant (RNase3-H15A). The analysis of differently expressed genes (DEGs) in treated THP1-derived macrophages highlighted a common pro-inflammatory "core-response" independent of the protein ribonucleolytic activity. Network analysis identified the epidermal growth factor receptor (EGFR) as the main central regulatory protein. Expression of selected DEGs and MAPK phosphorylation were inhibited by an anti-EGFR antibody. Structural analysis suggested that RNase3 activates the EGFR pathway by direct interaction with the receptor. Besides, we identified a subset of DEGs related to the protein ribonucleolytic activity, characteristic of virus infection response. Transcriptome analysis revealed an early pro-inflammatory response, not associated to the protein catalytic activity, followed by a late activation in a ribonucleolytic-dependent manner. Next, we demonstrated that overexpression of macrophage endogenous RNase3 protects the cells against infection by Mycobacterium aurum and the human respiratory syncytial virus. Comparison of cell infection profiles in the presence of Erlotinib, an EGFR inhibitor, revealed that the receptor activation is required for the antibacterial but not for the antiviral protein action. Moreover, the DEGs related and unrelated to the protein catalytic activity are associated to the immune response to bacterial and viral infection, respectively. We conclude that RNase3 modulates the macrophage defence against infection in both catalytic-dependent and independent manners.

Thirty Years of HER3: From Basic Biology to Therapeutic Interventions

HER3 is a pseudokinase member of the EGFR family having a role in both tumor progression and drug resistance. Although HER3 was discovered more than 30 years ago, no therapeutic interventions have reached clinical approval to date. Because the evidence of the importance of HER3 is accumulating, increased amounts of preclinical and clinical trials with HER3-targeting agents are emerging. In this review article, we discuss the most recent HER3 biology in tumorigenic events and drug resistance and provide an overview of the current and emerging strategies to target HER3.

PINK1-Mediated Inhibition of EGFR Dimerization and Activation Impedes EGFR-Driven Lung Tumorigenesis

EGFR is established as a driver of lung cancer, yet the regulatory machinery underlying its oncogenic activity is not fully understood. PTEN-induced kinase 1 (PINK1) kinase is a key player in mitochondrial quality control, although its role in lung cancer and EGFR regulation is unclear. In this study, we show that PINK1 physically directly interacts with EGFR via the PINK1 C-terminal domain (PINK1-CTD) and the EGFR tyrosine kinase domain. This interaction constituted an endogenous steric hindrance to receptor dimerization and inhibited EGFR-mediated lung carcinogenesis. Depletion of PINK1 from lung cancer cells promoted EGFR dimerization, receptor activation, EGFR downstream signaling, and tumor growth. In contrast, overexpression of PINK1 or PINK1-CTD suppressed EGFR dimerization, activation, downstream signaling, and tumor growth. These findings identify key elements in the EGFR regulatory cascade and illustrate a new direction for the development of anti-EGFR therapeutics, suggesting translational potential of the PINK1-CTD in lung cancer. SIGNIFICANCE: This study identifies PINK1 as a critical tumor suppressor that impedes EGFR dimerization and highlights PINK1-CTD as a potential therapeutic agent in EGFR-driven lung cancer.

Beyond history and "on a roll": The list of the most well-studied human protein structures and overall trends in the protein data bank

Of the roughly 20,000 canonical human protein sequences, as of January 20, 2021, 7,077 proteins have had their full or partial, medium- to high-resolution structures determined by x-ray crystallography or other methods. Which of these proteins dominate the protein data bank (the PDB) and why? In this paper, we list the 273 top human protein structures based on the number of their PDB entries. This set of proteins accounts for more than 40% of all available human PDB entries and represent past trends as well as current status for protein structural biology. We briefly discuss the relationship which some of the prominent protein structures have with protein research as a whole and mention their relevance to human diseases. The top-10 soluble and membrane proteins are all well-known (most of their first structures being deposited more than 30 years ago). Overall, there is no dramatic change in recent trends in the PDB. Remarkably, the number of structure depositions has grown nearly exponentially over the last 10 or more years (with a doubling time of 7 years for proteins, obtained from any organism). Growth in human protein structures is slightly faster (at 5.9 years). The information in this paper may be informative to senior scientists but also inspire researchers who are new to protein science, providing the year 2021 snap-shot for the state of protein structural biology.

Trastuzumab Blocks the Receiver Function of HER2 Leading to the Population Shifts of HER2-Containing Homodimers and Heterodimers

HER2, a member of the Erythroblastosis Protein B/Human Epidermal Growth Factor Receptor (ErbB/HER) family of receptor tyrosine kinase, is overexpressed in 20~30% of human breast cancers. Trastuzumab, a HER2-targeted therapeutic monoclonal antibody, was developed to interfere with the homodimerization of HER2 in HER2-overexpressing breast cancer cells, which attenuates HER2-mediated signaling. Trastuzumab binds to the domain IV of the HER2 extracellular domain and does not directly block the dimerization interface of HER2-HER2 molecules. The three-dimensional structures of the tyrosine kinase domains of ErbB/HER family receptors show asymmetrical packing of the two monomers with distinct conformations. One monomer functions as an activator, whereas the other acts as a receiver. Once activated, the receiver monomer phosphorylates the activator or other proteins. Interestingly, in our previous work, we found that the binding of trastuzumab induced phosphorylation of HER2 with the phosphorylation pattern of HER2 that is different from that mediated by epidermal growth factor (EGF) in human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Binding of trastuzumab to HER2 promoted an allosteric effect of HER2, in both tyrosine kinase domain and ectodomain of HER2 although details of allosteric regulation were missing. In this study, we utilized molecular dynamics (MD) simulations to model the allosteric consequences of trastuzumab binding to HER2 homodimers and heterodimers, along with the apo forms as controls. We focused on the conformational changes of HER2 in its monomeric and dimeric forms. The data indicated the apparent dual role of trastuzumab as an antagonist and an agonist. The molecular details of the simulation provide an atomic level description and molecular insight into the action of HER2-targeted antibody therapeutics.

Bisphenol S and Epidermal Growth Factor Receptor Signaling in Human Placental Cytotrophoblasts

BACKGROUND

Bisphenol S (BPS) is an endocrine-disrupting chemical and the second most abundant bisphenol detected in humans. In vivo BPS exposure leads to reduced binucleate cell number in the ovine placenta. Binucleate cells form by cellular fusion, similar to the human placental syncytiotrophoblast layer. Given that human placental syncytialization can be stimulated through epidermal growth factor (EGF), we hypothesized that BPS would reduce human cytotrophoblast syncytialization through disruption of EGF receptor (EGFR) signaling.

OBJECTIVE

We tested whether BPS interferes EGFR signaling and disrupts human cytotrophoblast syncytialization.

METHODS

We first tested BPS competition for EGFR using an EGF/EGFR AlphaLISA assay. Using human primary term cytotrophoblast cells (hCTBs) and MDA-MD-231 cells, a breast cancer cell line with high EGFR expression, we evaluated EGFR downstream signaling and tested whether BPS could inhibit the EGF response by blocking EGFR activation. We also evaluated functional end points of EGFR signaling, including EGF endocytosis, cell proliferation, and syncytialization.

RESULTS

BPS blocked EGF binding in a dose-dependent manner and reduced EGF-mediated phosphorylated EGFR in both cell types. We further confirmed that BPS acted as an EGFR antagonist as shown by a reduction in EGF internalization in both hCTBs and MDA-MD-231 cells. Finally, we demonstrated that BPS interfered with EGF-mediated cell processes, such as cell proliferation in MDA-MD-231 cells and syncytialization in hCTBs. EGF-mediated, but not spontaneous, hCTB syncytialization was fully blocked by BPS (200 ng/mL), a dose within urinary BPS concentrations detected in humans.

CONCLUSIONS

Given the role of EGFR in trophoblast proliferation and differentiation during placental development, this study suggests that exposures to BPS at environmentally relevant concentrations may result in placenta dysfunction, affecting fetal growth and development. https://doi.org/10.1289/EHP7297.

Design of epidermal growth factor immobilization on 3D biocompatible scaffolds to promote tissue repair and regeneration

Exogenous application of human epidermal growth factor (hEGF) stimulates epidermal wound healing. The aim of this study was to develop bioconjugates based on hEGF mimicking the protein in its native state and thus suitable for tissue engineering applications, in particular for treating skin-related disorders as burns. Ribonuclease A (RNase A) was used to investigate a number of different activated-agarose carriers: cyanogen bromide (CNBr)-activated-agarose and glyoxyl-agarose showed to preserve the appropriate orientation of the protein for receptor binding. EGF was immobilized on these carriers and immobilization yield was evaluated (100% and 12%, respectively). A peptide mapping of unbound protein regions was carried out by LC-MS to take evidence of the residues involved in the immobilization and, consequently, the flexibility and surface accessibility of immobilized EGF. To assess cell proliferative activities, 10, 25, 50, and 100 ng/mL of each immobilized EGF sample were seeded on fibroblast cells and incubated for 24, 48 and 72 h. The immobilized growth factor showed significantly high cell proliferative activity at 50 and 100 ng/mL compared to control and soluble EGF. Although both of the immobilized samples show dose-dependency when seeded with high number of fibroblast cells, CNBr-agarose-EGF showed a significantly high activity at 100 ng/mL and 72 h incubation, compared to glyoxyl-agarose-EGF.

Review on Epidermal Growth Factor Receptor (EGFR) Structure, Signaling Pathways, Interactions, and Recent Updates of EGFR Inhibitors

The epidermal growth factor receptor (EGFR) belongs to the ERBB family of tyrosine kinase receptors. EGFR signaling cascade is a key regulator in cell proliferation, differentiation, division, survival, and cancer development. In this review, the EGFR structure and its mutations, signaling pathway, ligand binding and EGFR dimerization, EGF/EGFR interaction, and the progress in the development of EGFR inhibitors have been explored.

Computational and Synthetic approach with Biological Evaluation of Substituted Quinoline derivatives as small molecule L858R/T790M/C797S triple mutant EGFR inhibitors targeting resistance in Non-Small Cell Lung Cancer (NSCLC)

New substituted quinoline derivatives were designed and synthesized via a five-step modified Suzuki coupling reaction. A comparative molecular docking study was carried out on two different types of EGFR enzymes which include wild-type (PDB: 4I23) and T790M mutated (PDB: 2JIV) respectively. Compounds were also validated upon T790M/C797S mutated (PDB ID: 5D41) EGFR enzyme at the allosteric binding site. All docking studies confirmed high potency and flexibility towards wild type as well as a mutated enzyme. Anticancer activity of the synthesized derivatives was examined against HCC827, H1975 (L858R/T790M/C797S and L858R/T790M), A549, and HT-29 cell lines by standard MTT assay. Most of the quinoline derivatives revealed a significant cytotoxic effect. The IC50 values of 4-(4-methylquinolin-2-yl)phenyl 4-(chloromethyl)benzoate (5j) were found to be 0.0042 µM, 0.02 µM, 1.91 µM, 3.82 µM and 3.67 µM while IC50 values of osimertinib were 0.0040 µM, 0.02 µM, ND, 0.99 µM and 1.22 µM, respectively. Compound 5j has shownexcellent inhibitory activities against EGFR kinases triple mutant with IC 50 value 1.91 µM. It was observed that, compared to H1975, A549 and A431 cell lines, synthesized compounds significantly inhibited proliferation of the HCC827 cell line. These data suggested that synthesized compounds showed promising selective anticancer activity against tumor cells harboring EGFR Del E746-A750. The potency of compound 5j was compared through molecular dynamic simulations andan insilicoADMET study. QSAR models were generated and the best model was correctly compared with respect to predicted and observed activity of compounds. The built model will assist to design, refine and construct novel substituted quinoline derivatives as potent EGFR inhibitors in near future.