Molecular architecture of the ErbB2 extracellular domain homodimer

SpyMask enables combinatorial assembly of bispecific binders

Bispecific antibodies are a successful and expanding therapeutic class. Standard approaches to generate bispecifics are complicated by the need for disulfide reduction/oxidation or specialized formats. Here we present SpyMask, a modular approach to bispecifics using SpyTag/SpyCatcher spontaneous amidation. Two SpyTag-fused antigen-binding modules can be precisely conjugated onto DoubleCatcher, a tandem SpyCatcher where the second SpyCatcher is protease-activatable. We engineer a panel of structurally-distinct DoubleCatchers, from which binders project in different directions. We establish a generalized methodology for one-pot assembly and purification of bispecifics in 96-well plates. A panel of binders recognizing different HER2 epitopes were coupled to DoubleCatcher, revealing unexpected combinations with anti-proliferative or pro-proliferative activity on HER2-addicted cancer cells. Bispecific activity depended sensitively on both binder orientation and DoubleCatcher scaffold geometry. These findings support the need for straightforward assembly in different formats. SpyMask provides a scalable tool to discover synergy in bispecific activity, through modulating receptor organization and geometry.

Electrochemical Cellulase-Linked ELASA for Rapid Liquid Biopsy Testing of Serum HER-2/neu

Non-invasive liquid biopsy assays for blood-circulating biomarkers of cancer allow both its early diagnosis and treatment monitoring. Here, we assessed serum levels of protein HER-2/neu, overexpressed in a number of aggressive cancers, by the cellulase-linked sandwich bioassay on magnetic beads. Instead of traditional antibodies we used inexpensive reporter and capture aptamer sequences, transforming the enzyme-linked immuno-sorbent assay (ELISA) into an enzyme-linked aptamer-sorbent assay (ELASA). The reporter aptamer was conjugated to cellulase, whose digestion of nitrocellulose film electrodes resulted in the electrochemical signal change. ELASA, optimized relative aptamer lengths (dimer vs monomer and trimer), and assay steps allowed 0.1 fM detection of HER-2/neu in the 10% human serum in 1.3 h. Urokinase plasminogen activator and thrombin as well as human serum albumin did not interfere, and liquid biopsy analysis of serum HER-2/neu was similarly robust but 4 times faster and 300 times cheaper than both electrochemical and optical ELISA. Simplicity and low cost of cellulase-linked ELASA makes it a perspective diagnostic tool for fast and accurate liquid biopsy detection of HER-2/neu and of other proteins for which aptamers are available.

Biased activation of the receptor tyrosine kinase HER2

HER2 belongs to the ErbB sub-family of receptor tyrosine kinases and regulates cellular proliferation and growth. Different from other ErbB receptors, HER2 has no known ligand. Activation occurs through heterodimerization with other ErbB receptors and their cognate ligands. This suggests several possible activation paths of HER2 with ligand-specific, differential response, which has so far remained unexplored. Using single-molecule tracking and the diffusion profile of HER2 as a proxy for activity, we measured the activation strength and temporal profile in live cells. We found that HER2 is strongly activated by EGFR-targeting ligands EGF and TGFα, yet with a distinguishable temporal fingerprint. The HER4-targeting ligands EREG and NRGβ1 showed weaker activation of HER2, a preference for EREG, and a delayed response to NRGβ1. Our results indicate a selective ligand response of HER2 that may serve as a regulatory element. Our experimental approach is easily transferable to other membrane receptors targeted by multiple ligands.

Rational Design, Synthesis and Biological Evaluation of Novel Pyrazoline-Based Antiproliferative Agents in MCF-7 Cancer Cells

Breast cancer is a disease in which cells in the breast divide continuously without control. There are great limitations in cancer chemotherapy. Hence, it is essential to search for new cancer therapeutics. Herein, a novel series of EGFR/HER2 dual inhibitors has been designed based on the hybridization of thiazole and pyrazoline fragments. The synthesized compounds were screened for their anti-proliferative activity against MCF-7 breast cancer cell line and MCF-10 normal breast cell line. Interestingly, synthesized compounds 6e and 6k showed very potent antiproliferative activity towards MCF-7 with IC50 values of 7.21 and 8.02 µM, respectively. Furthermore, enzymatic assay was performed against EGFR and HER2 to prove the dual inhibitory action. Compounds 6e and 6k showed potent inhibitory activity for EGFR with IC50 of 0.009 and 0.051 µM, respectively, and for HER2 with IC50 of 0.013 and 0.027 µM, respectively. Additionally, compounds 6e and 6k significantly stimulated apoptotic breast cancer cell death. Compound 6e was further explored for its anticancer activity in vivo using a Xenograft model. Moreover, computational modeling studies, ADMET studies and toxicity prediction were performed to investigate their potential drug candidates.

Whole-exome sequencing reveals a comprehensive germline mutation landscape and identifies twelve novel predisposition genes in Chinese prostate cancer patients

Prostate cancer is the most inheritable cancer with approximately 42% of disease risk attributed to inherited factors by studies of twins, indicating the importance of additional genetic screening to identify predisposition variants. However, only DNA damage repair (DDR) genes have been investigated thoroughly in prostate cancer. To determine the comprehensive germline mutation landscape in Chinese prostate cancer patients, we performed whole exome sequencing in 100 Han Chinese patients with prostate cancer in Hong Kong and identified deleterious germline mutations. A total of 36 deleterious germline variants in 25 genes were identified in 29% patients. Variants were found in eight pathways, including DNA methylation, DDR, and tyrosine-protein kinase. These findings were validated in an independent Chinese cohort of 167 patients with prostate cancer in Shanghai. Seven common deleterious-variant-containing genes were found in discovery cohort (7/25, 28%) and validation cohort (7/28, 25%) with three genes not described before (LDLR, MYH7 and SUGCT) and four genes previously reported (FANCI, ITGA6, PABPC1 and RAD54B). When comparing with that of a cohort of East Asian healthy individuals, 12 non-DDR novel potential predisposition genes (ADGRG1, CHD4, DNMT3A, ERBB3, GRHL1, HMBS, LDLR, MYH7, MYO6, NT5C2, NUP98 and SUGCT) were identified using the discovery and validation cohorts, which have not been previously reported in prostate cancer patients in all ethnic groups. Taken together, this study reveals a comprehensive germline mutation landscape in Chinese prostate cancer patients and discovers 12 novel non-DDR predisposition genes to lay the groundwork for the optimization of genetic screening.

Prostate cancer is the most inheritable cancer with about 42% of disease risk attributed to inherited factors, indicating the importance of additional genetic screening to identify predisposition variants. However, only DNA damage repair (DDR) genes have been studied thoroughly in prostate cancer. To determine the comprehensive germline mutation landscape in Chinese prostate cancer patients, we performed whole exome sequencing in 100 Han Chinese patients with prostate cancer in Hong Kong and identified deleterious germline mutations. A total of 36 deleterious germline variants in 25 genes were identified in 29% patients. Variants were found in eight pathways, including DNA methylation, DDR, and tyrosine-protein kinase. These findings were validated in an independent Chinese cohort of 167 patients with prostate cancer in Shanghai. Seven common deleterious-variant-containing genes were found in discovery cohort and validation cohort with three genes not described before (LDLR, MYH7 and SUGCT) and four genes previously reported. When comparing with that of a cohort of East Asian healthy individuals, 12 non-DDR novel potential predisposition genes were identified using the discovery and validation cohorts, which have not been previously reported in prostate cancer patients in all ethnic groups.

"Shedding" light on HER4 signaling in normal and malignant breast tissues

Receptor Tyrosine Kinases of the Epidermal Growth Factor Receptor Family play a pivotal role as drivers of carcinogenesis and uncontrolled cell growth for a variety of malignancies, not least for breast cancer. Besides the estrogen receptor, the HER2 receptor was and still is a representative marker for advanced taxonomic sub-differentiation of breast cancer and emerged as one of the first therapeutic targets for antibody based therapies. Since the approval of trastuzumab for the therapy of HER2-positive breast cancer in 1998 anti-HER2 treatment strategies are being modified, refined, and successfully combined with complementary treatments, nevertheless there is still potential for improvement. The HER2 relatives, namely HER1 (i.e., EGFR), HER3 and HER4 share a high degree of molecular homology and together form a functional unit for signal transmission. Under regular conditions, receptor coexpression patterns and receptor interaction represent key parameters for signaling robustness, which ensures cellular growth control and enables tissue differentiation. In addition, treatment efficiency of e.g., an anti-HER2 targeting is substantially determined by the expression pattern of HER receptors on target cells. Within the receptor family, the HER4 plays a particular role and is engaged in exceptional signaling activities. A favorable prognostic impact has been attributed to HER4 expression in breast cancer under specific molecular conditions. HER4-specific cellular effects are initially determined by a ligand-dependent or -independent receptor activation. Essential processes as cell growth and proliferation, cell differentiation, and apoptotic cell death can be initiated by this receptor. This review gives an overview of the role of HER4 in normal and malignant breast epithelial cells and tissues. Specific mechanism of HER4 activation and subsequent intracellular signaling will be described by taking a focus on effects provoked by receptor shedding. HER4 activities and specific effects will be correlated to breast cancer subtypes and the impact of HER4 on course and outcome of disease will be considered. Moreover, current and potential therapeutic approaches will be discussed.

Potent anti-tumor immune response and tumor growth inhibition induced by HER2 subdomain fusion protein in a mouse tumor model

PURPOSE

Several approaches have so far been employed to establish anti-tumor immunity by targeting HER2 protein. Active immunization with recombinant HER2 subdomains has previously been demonstrated to induce potent immune response and tumor growth inhibition. In the present study, we investigated the immunogenicity and tumor inhibitory effect of a fusion protein consisting of human HER2 extracellular subdomain (ECD-DI + II) together with T-helper cell epitopes of Tetanus toxin (p2 and p30).

METHODS

BALB/c mice were immunized with two recombinant proteins (DI + II and p2p30-DI + II) emulsified in 4 different adjuvants. Anti-DI + II antibody response, cytokine profile, frequency of splenic CD25⁺FOXP3⁺ regulatory T cells (Tregs) and CD8⁺CD107a⁺ cytotoxic T lymphocytes (CTLs) were assessed in the immunized mice. To assess the anti-tumor effect, the immunized mice were subcutaneously challenged with HER2-overexpressing tumor cells and the tumor growth was determined.

RESULTS

Both recombinant proteins were able to induce comparable levels of ECD-DI + II-specific antibodies. Immunization with p2p30-DI + II resulted in a significant increase in the level of Interferon-gamma (IFN-γ) secretion compared to DI + II protein and significantly higher frequency of CTLs and lower frequency of Tregs. The number of mice that remained tumor-free until day 120 was significantly higher in p2p30-DI + II vaccinated groups.

CONCLUSIONS

Our data suggest that the p2p30-DI + II fusion protein together with CpG adjuvant induces more potent anti-tumor immune responses in a mouse tumor model. Accordingly, this formulation might be considered as a potential immunotherapeutic approach in HER2⁺ cancers.

It Takes More than Two to Tango: Complex, Hierarchal, and Membrane-Modulated Interactions in the Regulation of Receptor Tyrosine Kinases

The search for an understanding of how cell fate and motility are regulated is not a purely scientific undertaking, but it can also lead to rationally designed therapies against cancer. The discovery of tyrosine kinases about half a century ago, the subsequent characterization of certain transmembrane receptors harboring tyrosine kinase activity, and their connection to the development of human cancer ushered in a new age with the hope of finding a treatment for malignant diseases in the foreseeable future. However, painstaking efforts were required to uncover the principles of how these receptors with intrinsic tyrosine kinase activity are regulated. Developments in molecular and structural biology and biophysical approaches paved the way towards better understanding of these pathways. Discoveries in the past twenty years first resulted in the formulation of textbook dogmas, such as dimerization-driven receptor association, which were followed by fine-tuning the model. In this review, the role of molecular interactions taking place during the activation of receptor tyrosine kinases, with special attention to the epidermal growth factor receptor family, will be discussed. The fact that these receptors are anchored in the membrane provides ample opportunities for modulatory lipid-protein interactions that will be considered in detail in the second part of the manuscript. Although qualitative and quantitative alterations in lipids in cancer are not sufficient in their own right to drive the malignant transformation, they both contribute to tumor formation and also provide ways to treat cancer. The review will be concluded with a summary of these medical aspects of lipid-protein interactions.

Integrated approach to functional analysis of an ERBB2 variant of unknown significance detected by a cancer gene panel test

Purpose

Dealing with variants of unknown significance (VUS) is an important issue in the clinical application of NGS-based cancer gene panel tests. We detected a novel ERBB2 extracellular domain VUS, c.1157A > G p.(E401G), in a cancer gene panel test. Since the mechanisms of activation by ERBB2 extracellular domain (ECD) variants are not fully understood, we aimed to clarify those mechanisms and the biological functions of ERBB2 E401G.

Methods

ERBB2 E401G was selected as VUS for analysis because multiple software tools predicted its pathogenicity. We prepared ERBB2 expression vectors with the E401G variant as well as vectors with S310F and E321G, which are known to be activating mutations. On the basis of wild-type ERBB2 or mutant ERBB2 expression in cell lines without ERBB2 amplification or variants, we evaluated the phosphorylation of human epidermal growth factor receptor 2 and related proteins, and investigated with molecular dynamics (MD) simulation the mechanisms conferred by the variants. The biological effects of ERBB2 E401G were also investigated, both in vitro and in vivo.

Results

We found that ERBB2 E401G enhances C-terminal phosphorylation in a way similar to S310F. MD simulation analysis revealed that these variants maintain the stability of the EGFR-HER2 heterodimer in a ligand-independent manner. Moreover, ERBB2 E401G-transduced cells showed an increased invasive capacity in vitro and an increased tumor growth capacity in vivo.

Conclusion

Our results provide important information on the activating mechanisms of ERBB2 extracellular domain (ECD) variants and illustrate a model workflow integrating wet and dry bench processes for the analysis of VUS detected with cancer gene panel tests.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13402-021-00656-3.

Glycosylation promotes the cancer regulator EGFR-ErbB2 heterodimer formation - molecular dynamics study

ErbB family of receptor tyrosine kinases play significant roles in cellular differentiation and proliferation. Mutation or overexpression of these receptors leads to several cancers in humans. The family has four homologous members including EGFR, ErbB2, ErbB3, and ErbB4. From which all except the ErbB2 bind to growth factors via the extracellular domain to send signals to the cell. However, dimerization of the ErbB receptor occurs in extracellular, transmembrane, and intracellular domains. The ErbB receptors are known to form homodimers and heterodimers in the active form. Heterodimerization increases the variety of identified ligands and signaling pathways that can be activated by these receptors. Furthermore, glycosylation of the ErbB receptors has shown to be critical for their stability, ligand binding, and dimerization. Here, atomistic molecular dynamics simulations on the glycosylated and unglycosylated heterodimer showed that the EGFR-ErbB2 heterodimer is more stable in its dynamical pattern compared to the EGFR-EGFR homodimer. This increased stability is regulated by maintaining the dimeric interface by the attached glycans. It was also shown that the presence of various glycosylation sites within the ErbB2 growth factor binding site leads to occlusion of this site by the glycans that inhibit ligand binding to ErbB2 and participate in further stabilization of the heterodimer construct. Putting together, glycosylation seems to promote the heterodimer formation within the ErbB family members as the dominant molecular mechanism of activation for these receptors.

Engineering an anti-HER2 biparatopic antibody with a multimodal mechanism of action

The receptor tyrosine kinase HER2 acts as oncogenic driver in numerous cancers. Usually, the gene is amplified, resulting in receptor overexpression, massively increased signaling and unchecked proliferation. However, tumors become frequently addicted to oncogenes and hence are druggable by targeted interventions. Here, we design an anti-HER2 biparatopic and tetravalent IgG fusion with a multimodal mechanism of action. The molecule first induces HER2 clustering into inactive complexes, evidenced by reduced mobility of surface HER2. However, in contrast to our earlier binders based on DARPins, clusters of HER2 are thereafter robustly internalized and quantitatively degraded. This multimodal mechanism of action is found only in few of the tetravalent constructs investigated, which must target specific epitopes on HER2 in a defined geometric arrangement. The inhibitory effect of our antibody as single agent surpasses the combination of trastuzumab and pertuzumab as well as its parental mAbs in vitro and it is effective in a xenograft model.

Structural and dynamic characterization of the C-terminal tail of ErbB2: Disordered but not random

ErbB2 (or HER2) is a receptor tyrosine kinase overexpressed in some breast cancers and associated with poor prognosis. Treatments targeting the receptor extracellular and kinase domains have greatly improved disease outcome in the last 20 years. In parallel, the structures of these domains have been described, enabling better mechanistic understanding of the receptor function and targeted inhibition. However, the ErbB2 disordered C-terminal cytoplasmic tail (CtErbB2) remains very poorly characterized in terms of structure, dynamics, and detailed functional mechanism. Yet, it is where signal transduction is triggered via phosphorylation of tyrosine residues and carried out via interaction with adaptor proteins. Here, we report the first description, to our knowledge, of the ErbB2 disordered tail at atomic resolution using NMR, complemented by small-angle x-ray scattering. We show that although no part of CtErbB2 has any fully populated secondary or tertiary structure, it contains several transient α-helices and numerous transient polyproline II helices, populated up to 20 and 40%, respectively, and low but significant compaction. The presence of some structural elements suggests, along the lines of the results obtained for EGFR (ErbB1), that they may have a functional role in ErbB2's autoregulation processes. In addition, the transient formation of polyproline II helices is compliant with previously suggested interactions with SH3 domains. All in all, our in-depth structural study opens perspectives in the mechanistic understanding of ErbB2.

Mechanisms and potential interventions associated with the cardiotoxicity of ErbB2-targeted drugs: Insights from in vitro, in vivo, and clinical studies in breast cancer patients

Breast cancer is the most frequently occurring cancer among women worldwide. Human epidermal growth factor receptor 2 (HER2 or ErbB2) is overexpressed in between 20 and 25% of invasive breast cancers and is associated with poor prognosis. Trastuzumab, an anti-ErbB2 monoclonal antibody, reduces cancer recurrence and mortality in HER2-positive breast cancer patients, but unexpectedly induces cardiac dysfunction, especially when used in combination with anthracycline-based chemotherapy. Novel approved ErbB2-targeting drugs, including lapatinib, pertuzumab, and trastuzumab-emtansine, also potentially cause cardiotoxicity, although early clinical studies demonstrate their cardiac safety profile. Unfortunately, the mechanism involved in causing the cardiotoxicity is still not completely understood. In addition, the use of preventive interventions against trastuzumab-induced cardiac dysfunction, including angiotensin-converting enzyme inhibitors and beta-blockers, remain controversial. Thus, this review aims to summarize and discuss the evidence currently available from in vitro, in vivo, and clinical studies regarding the mechanism and potential interventions associated with the cardiotoxicity of ErbB2-targeted drugs.

EGF-Containing Membrane-Bound Mucins: A Hidden ErbB2 Targeting Pathway?

Membrane-bound mucins belong to a heterogeneous family of large O-glycoproteins involved in numerous cancers and inflammatory diseases of the epithelium. Some of them are also involved in protein-protein interactions, with receptor tyrosine kinase ErbB2, and fundamental and clinical data showed that these complexes have a detrimental impact on cancer outcome, thus raising interest in therapeutic targeting. This paper aims to demonstrate that MUC3, MUC4, MUC12, MUC13, and MUC17 have a common evolutionary origin and share a common structural organization with EGF-like and SEA domains. Theoretical structure-function relationship analysis of the conserved domains indicated that the studied membrane-bound mucins share common biological properties along with potential specific functions. Finally, the potential druggability of these complexes is discussed, revealing ErbB2-related pathways of cell signaling to be targeted.

Almeida J, Melo A, D. S. Cordeiro MN, Cabo Verde S, H. Gümüş Z, S. Moreira I, D. G. Correia J, Melo R. Dynamical Rearrangement of Human Epidermal Growth Factor Receptor 2 upon Antibody Binding: Effects on the Dimerization

Human epidermal growth factor 2 (HER2) is a ligand-free tyrosine kinase receptor of the HER family that is overexpressed in some of the most aggressive tumours. Although it is known that HER2 dimerization involves a specific region of its extracellular domain, the so-called “dimerization arm”, the mechanism of dimerization inhibition remains uncertain. However, uncovering how antibody interactions lead to inhibition of HER2 dimerization is of key importance in understanding its role in tumour progression and therapy. Herein, we employed several computational modelling techniques for a molecular-level understanding of the interactions between HER and specific anti-HER2 antibodies, namely an antigen-binding (Fab) fragment (F0178) and a single-chain variable fragment from Trastuzumab (scFv). Specifically, we investigated the effects of antibody-HER2 interactions on the key residues of “dimerization arm” from molecular dynamics (MD) simulations of unbound HER (in a total of 1 µs), as well as ScFv:HER2 and F0178:HER2 complexes (for a total of 2.5 µs). A deep surface analysis of HER receptor revealed that the binding of specific anti-HER2 antibodies induced conformational changes both in the interfacial residues, which was expected, and in the ECDII (extracellular domain), in particular at the “dimerization arm”, which is critical in establishing protein–protein interface (PPI) interactions. Our results support and advance the knowledge on the already described trastuzumab effect on blocking HER2 dimerization through synergistic inhibition and/or steric hindrance. Furthermore, our approach offers a new strategy for fine-tuning target activity through allosteric ligands.

Visualisation of HER2 homodimers in single cells from HER2 overexpressing primary formalin fixed paraffin embedded tumour tissue

Background

HER2 is considered as one of the most important, predictive biomarkers in oncology. The diagnosis of HER2 positive cancer types such as breast- and gastric cancer is usually based on immunohistochemical HER2 staining of tumour tissue. However, the current immunohistochemical methods do not provide localized information about HER2’s functional state. In order to generate signals leading to cell growth and proliferation, the receptor spontaneously forms homodimers, a process that can differ between individual cancer cells.

Materials and methods

HER2 overexpressing tumour cells were dissociated from formalin-fixed paraffin-embedded (FFPE) patient’s biopsy sections, subjected to a heat-induced antigen retrieval procedure, and immobilized on microchips. HER2 was specifically labelled via a two-step protocol involving the incubation with an Affibody-biotin compound followed by the binding of a streptavidin coated quantum dot (QD) nanoparticle. Cells with membrane bound HER2 were identified using fluorescence microscopy, coated with graphene to preserve their hydrated state, and subsequently examined by scanning transmission electron microscopy (STEM) to obtain the locations at the single molecule level. Label position data was statistically analysed via the pair correlation function, yielding information about the presence of HER2 homodimers.

Results

Tumour cells from two biopsies, scored HER2 3+, and a HER2 negative control sample were examined. The specific labelling protocol was first tested for a sectioned tissue sample of HER2-overexpressing tumour. Subsequently, a protocol was optimized to study HER2 homodimerization in single cells dissociated from the tissue section. Electron microscopy data showed membrane bound HER2 in average densities of 201–689 proteins/μm². An automated, statistical analysis of well over 200,000 of measured protein positions revealed the presence of HER2 homodimers in 33 and 55% of the analysed images for patient 1 and 2, respectively.

Conclusions

We introduced an electron microscopy method capable of measuring the positions of individually labelled HER2 proteins in patient tumour cells from which information about the functional status of the receptor was derived. This method could take HER2 testing a step further by examining HER2 homodimerization directly out of tumour tissue and may become important for adjusting a personalized antibody-based drug therapy.

Electronic supplementary material

The online version of this article (10.1186/s10020-019-0108-z) contains supplementary material, which is available to authorized users.

Mechanisms of Receptor Tyrosine-Protein Kinase ErbB-3 (ERBB3) Action in Human Neoplasia

It is well established that the epidermal growth factor (EGF) receptor, receptor tyrosine-protein kinase erbB-2 (ERBB2)/human EGF receptor 2 (HER2), and, to a lesser extent, ERBB4/HER4, promote the pathogenesis of many types of human cancers. In contrast, the role that ERBB3/HER3, the fourth member of the ERBB family of receptor tyrosine kinases, plays in these diseases is poorly understood and, until recently, underappreciated. In large part, this was because early structural and functional studies suggested that ERBB3 had little, if any, intrinsic tyrosine kinase activity and, thus, was unlikely to be an important therapeutic target. Since then, however, numerous publications have demonstrated an important role for ERBB3 in carcinogenesis, metastasis, and acquired drug resistance. Furthermore, somatic ERBB3 mutations are frequently encountered in many types of human cancers. Dysregulation of ERBB3 trafficking as well as cooperation with other receptor tyrosine kinases further enhance ERBB3's role in tumorigenesis and drug resistance. As a result of these advances in our understanding of the structure and biochemistry of ERBB3, and a growing focus on the development of precision and combinatorial therapeutic regimens, ERBB3 is increasingly considered to be an important therapeutic target in human cancers. In this review, we discuss the unique structural and functional features of ERBB3 and how this information is being used to develop effective new therapeutic agents that target ERBB3 in human cancers.

A germline alteration of ERBB2 increases the risk of breast cancer in Chinese Han women with a familial history of malignant tumors

Previous studies have demonstrated that a family history of breast cancer is considered a risk factor, and hereditary factors may be involved in breast cancer pathogenesis. Next-generation sequencing techniques were used to analyze 111 cancer-associated genes in patients with breast cancer with a familial history of malignant tumors in the pre-experiment and a novel variant, receptor tyrosine-protein kinase erbB-2 (ERBB2) c.338G>A: p.R113Q was identified in two cases of breast cancer. ERBB2 is considered an important oncogene, and overexpression or mutation of the ERBB2 gene may lead to the occurrence or metastasis of tumors. To assess a potential association between rs185670819 and breast cancer, 117 patients with breast cancer and a familial history of any cancer, who were diagnosed by experienced pathologists at the Xijing Hospital (Shaanxi, China) between July 2015 and December 2016, were recruited. The presence of the missense variant was confirmed using bi-directional Sanger sequencing of samples from the patients with breast cancer and 250 healthy controls. The effects of the missense mutation on the structure and function of ERBB2 were analyzed in silico. The missense variant, R113Q, in patients with breast cancer with a familial history of malignant tumors in China, was present in 8 patients [6.8% (95% CI: 3.21–13.45)] and 3 of 250 healthy controls [1.2% (95% CI: 0.31–3.76; OR=6.04, 95% CI: 1.573–23.214, P=0.009)]. Of the 8 patients with the R113Q variant, 6 patients had a family history of cancer of the digestive system. The present study suggests that ERBB2 c.338G>A: p.R113Q may be a potential risk factor in the development and progression of breast cancer.

Inhibition of HER2-Positive Breast Cancer Growth by Blocking the HER2 Signaling Pathway with HER2-Glycan-Imprinted Nanoparticles

Blocking the HER2 signaling pathway has been an effective strategy in the treatment of HER2-positive breast cancer. It mainly relies on the use of monoclonal antibodies and tyrosine-kinase inhibitors. Herein, we present a new strategy, the nano molecularly imprinted polymer (nanoMIP). The nanoMIPs, imprinted using HER2 N-glycans, could bind almost all HER2 glycans and suppress the dimerization of HER2 with other HER family members, blocking the downstream signaling pathways, thereby inhibiting HER2+ breast cancer growth. In vitro experiments demonstrated that the nanoMIPs specifically targeted HER2+ cells and inhibited cell proliferation by 30 %. In vivo experiments indicated that the mean tumor volume of the nanoMIP-treated group was only about half of that of the non-treated groups. This study provides not only a new possibility to treat of HER2+ breast cancer but also new evidence to boost further development of nanoMIPs for cancer therapy.

The Effects of Pertuzumab and Its Combination with Trastuzumab on HER2 Homodimerization and Phosphorylation

Pertuzumab (Perjeta) is an anti-HER2 monoclonal antibody that is used for treatment of HER2-positive breast cancers in combination with trastuzumab (Herceptin) and docetaxel and showed promising clinical outcomes. Pertuzumab is suggested to block heterodimerization of HER2 with EGFR and HER3 that abolishes canonical function of HER2. However, evidence on the exact mode of action of pertuzumab in homodimerization of HER2 are limited. In this study, we investigated the effect of pertuzumab and its combination with trastuzumab on HER2 homodimerization, phosphorylation and whole gene expression profile in Chinese hamster ovary (CHO) cells stably overexpressing human HER2 (CHO-K6). CHO-K6 cells were treated with pertuzumab, trastuzumab, and their combination, and then HER2 homodimerization and phosphorylation at seven pY sites were investigated. The effects of the monoclonal antibodies on whole gene expression and the expression of cell cycle stages, apoptosis, autophagy, and necrosis were studied by cDNA microarray. Results showed that pertuzumab had no significant effect on HER2 homodimerization, however, trastuzumab increased HER2 homodimerization. Interestingly, pertuzumab increased HER2 phosphorylation at Y1127, Y1139, and Y1196 residues, while trastuzumab increased HER2 phosphorylation at Y1196. More surprisingly, combination of pertuzumab and trastuzumab blocked the phosphorylation of Y1005 and Y1127 of HER2. Our results also showed that pertuzumab, but not trastuzumab, abrogated the effect of HER2 overexpression on cell cycle in particular G1/S transition, G2/M transition, and M phase, whereas trastuzumab abolished the inhibitory effect of HER2 on apoptosis. Our findings confirm that pertuzumab is unable to inhibit HER2 homodimerization but induces HER2 phosphorylation at some pY sites that abolishes HER2 effects on cell cycle progress. These data suggest that the clinical effects of pertuzumab may mostly through the inhibition of HER2 heterodimers, rather than HER2 homodimers and that pertuzumab binding to HER2 may inhibit non-canonical HER2 activation and function in non-HER-mediated and dimerization-independent pathway(s).

Mechanisms Underlying the Action and Synergism of Trastuzumab and Pertuzumab in Targeting HER2-Positive Breast Cancer

Human epidermal growth factor receptor (HER) 2 (HER2) is overexpressed in 20⁻30% of breast cancers. HER2 is a preferred target for treating HER2-positive breast cancer. Trastuzumab and pertuzumab are two HER2-targeted monoclonal antibodies approved by the Food and Drug Administration (FDA) to use as adjuvant therapy in combination with docetaxel to treat metastatic HER2-positive breast cancer. Adding the monoclonal antibodies to treatment regimen has changed the paradigm for treatment of HER2-positive breast cancer. Despite improving outcomes, the percentage of the patients who benefit from the treatment is still low. Continued research and development of novel agents and strategies of drug combinations is needed. A thorough understanding of the molecular mechanisms underlying the action and synergism of trastuzumab and pertuzumab is essential for moving forward to achieve high efficacy in treating HER2-positive breast cancer. This review examined and analyzed findings and hypotheses regarding the action and synergism of trastuzumab and pertuzumab and proposed a model of synergism based on available information.

Phytoestrogens and mycoestrogens interacting with breast cancer proteins

Breast cancer is a highly heterogeneous disease influenced by the hormonal microenvironment and the most common malignancy in women worldwide. Some phytoestrogens and mycoestrogens have been epidemiologically linked as risk factors or protectors, however their mechanisms of action are complex and not fully understood. The aim of this study was to predict the potential of 36 natural xenoestrogens to interact with 189 breast cancer proteins using AutoDock Vina. In order to validate our protocol, an in silico docking pose and binding site determination was compared with the crystallographic structure and the power of prediction to distinguish between ligand and decoys was evaluated through a receiver operating characteristic curve (ROC) of the resultant docking affinities and in vitro data. The best affinity score was obtained for glyceollin III interacting with the sex hormone binding globulin (-11.9 Kcal/mol), a plasma steroid transport protein that regulates sex steroids bioavailability. Other natural xenoestrogens such as beta-carotene, chrysophanol 8-O-beta-d-glucopyranoside and glyceollin I, also presented good affinity for proteins related to this disease and the validation was successful. This study may help to prioritize compounds for toxicity tests or drug development from natural scaffolds, and to elucidate their mechanisms of action.

Combating acquired resistance to trastuzumab by an anti-ErbB2 fully human antibody

Trastuzumab resistance is a common problem that impedes the effectiveness of trastuzumab in ErbB2-amplified cancers. About 70% of ErbB2-amplified breast cancers do not respond to trastuzumab (de novo resistance), and the majority of the trastuzumab-responsive cancers progress within 1 year (acquired resistance). Different mechanisms exist between de novo and acquired resistance. Innate resistance mechanisms are mainly independent of ErbB2 receptor activity, and acquired resistance involves with alterations depending on ErbB2 activity. We previously reported H2-18, an ErbB2 domain I-specific antibody, which could circumvent de novo resistance to trastuzumab. Here, we modeled the development of acquired resistance by treating human gastric cancer cell line NCI-N87 with trastuzumab to obtain the trastuzumab-resistant subline, NCI-N87-TraRT. Next, we investigated the antitumor efficacy of H2-18 in NCI-N87-TraRT cell line. H2-18 exhibited a significantly greater antitumor activity in NCI-N87-TraRT tumor-bearing nude mice than pertuzumab and trastuzumab, either alone or in combination. The unique ability of H2-18 to overcome acquired resistance may be attributable to its potent programmed cell death-inducing activity, which was probably mediated by RIP1-ROS-JNK-c-Jun pathway. In conclusion, H2-18 may have the potential as an effective agent to circumvent acquired resistance to trastuzumab in ErbB2-overexpressing cancers.

An anti-ErbB2 fully human antibody circumvents trastuzumab resistance

Trastuzumab, an anti-HER2/ErbB2 humanized antibody, has shown great clinical benefits in ErbB2-positive breast cancer treatment. Despite of its effectiveness, response rate to trastuzumab is limited and resistance is common. Here, we developed a new anti-ErbB2 antibody, denoted as H2-18, which was isolated from a phage display human antibody library. Previous studies have demonstrated that trastuzumab recognizes the juxtamembrane region of domain IV, and pertuzumab, another humanized ErbB2-specific antibody, binds to ErbB2 near the center of domain II. Our crystallographic analysis showed that the epitope recognized by H2-18 is within domain I of the ErbB2 molecule. H2-18 potently induced programmed cell death (PCD) in both trastuzumab-sensitive and -resistant breast cancer cell lines, while trastuzumab and pertuzumab, either used alone or in combination, only exhibits very weak PCD-inducing activity. More importantly, H2-18 could inhibit the growth of trastuzumab-resistant breast cancer cells far more effectively than trastuzumab plus pertuzumab, both in vitro and in vivo. In conclusion, H2-18 shows a unique ability to overcome trastuzumab resistance, suggesting that it has the great potential to be translated to the clinic.

Heregulin-expressing HER2-positive breast and gastric cancer exhibited heterogeneous susceptibility to the anti-HER2 agents lapatinib, trastuzumab and T-DM1

Background

Overexpression of heregulin, a HER3 ligand, is one mechanism that confers resistance to the anti-HER2 agents trastuzumab and lapatinib. We investigated the impact of heregulin expression on the efficacy of HER2-targeted therapeutic agents, including trastuzumab, trastuzumab emtansine (T-DM1) and lapatinib, in vitro and in vivo and evaluated the heregulin messenger RNA (mRNA) levels in specimens from patients with HER2-positive breast or gastric cancer.

Results

Cell proliferation and apoptosis assays demonstrated that heregulin conferred robust resistance to lapatinib and trastuzumab via HER3-Akt pathway activation followed by survivin overexpression; however, heregulin conferred minimal or no resistance to T-DM1 and paclitaxel. The heregulin mRNA level of one of 10 patients was up-regulated after the acquisition of resistance to trastuzumab-based therapy.

Materials and Methods

SK-BR-3, NCI-N87, BT-474, MDA-MB-453, HCC1954, SNU-216 and 4-1ST cells were pharmacologically treated with recombinant heregulin or transfected with the heregulin gene. We also assessed the expression of heregulin mRNA in HER2-positive breast or gastric cancer samples before and after trastuzumab-based therapy using a RT-PCR-based method.

Conclusions

mRNA up-regulation of heregulin was observed in clinical breast cancer specimens during trastuzumab-based treatment, but heregulin overexpression had a limited effect on the sensitivity to T-DM1 in vitro and in vivo.

Liquid-phase electron microscopy of molecular drug response in breast cancer cells reveals irresponsive cell subpopulations related to lack of HER2 homodimers

The development of drug resistance in cancer poses a major clinical problem. An example is human epidermal growth factor receptor 2 (HER2) overexpressing breast cancer often treated with anti-HER2 antibody therapies, such as trastuzumab. Since drug resistance is rooted mainly in tumor cell heterogeneity, we examined the drug effect in different subpopulations of SKBR3 breast cancer cells, and compared the results with a drug resistant cell line, HCC1954. Correlative light microscopy and liquid-phase scanning transmission electron microscopy (STEM) were used to quantitatively analyze HER2 responses upon drug binding, whereby many tens of whole cells were imaged. Trastuzumab was found to selectively cross-link and down regulate HER2 homodimers from the plasma membranes of bulk cancer cells. In contrast, HER2 resided mainly as monomers in rare subpopulations of resting- and cancer stem cells (CSCs), and these monomers were not internalized after drug binding. The HER2 distribution was hardly influenced by trastuzumab for the HCC1954 cells. These findings show that resting cells and CSCs are irresponsive to the drug, and thus point towards a molecular explanation behind the origin of drug resistance. This analytical method is broadly applicable to study membrane protein interactions in the intact plasma membrane, while accounting for cell heterogeneity.

Protein lysine methyltransferase SMYD3 is involved in tumorigenesis through regulation of HER2 homodimerization

HER2 is a receptor tyrosine kinase, which is amplified and overexpressed in a subset of human cancers including breast and gastric cancers, and is indicated in its involvement in progression of cancer. Although its specific ligand(s) has not been detected, HER2 homodimerization, which is critical for its activation, is considered to be dependent on its expression levels. Here, we demonstrate a significant role of HER2 methylation by protein lysine methyltransferase SMYD3 in HER2 homodimerization. We found that SMYD3 trimethylates HER2 protein at lysine 175. HER2 homodimerization was enhanced in the presence of SMYD3, and substitution of lysine 175 of HER2 with alanine (HER2-K175A) reduced the formation of HER2 homodimers. Furthermore, HER2-K175A revealed lower level of autophosphorylation than wild-type HER2. We also identified that knockdown of SMYD3 attenuated this autophosphorylation in breast cancer cells. Our results imply that SMYD3-mediated methylation of HER2 at Lysine 175 may regulate the formation of HER2 homodimer and subsequent autophosphorylation and suggest that the SMYD3-mediated methylation pathway seems to be a good target for development of novel anti-cancer therapy.

Molecular and hydrodynamic properties of human epidermal growth factor receptor HER2 extracellular domain and its homodimer: Experiments and multi-scale simulations

BACKGROUND

In a broad range of human carcinomas gene amplification leads to HER2 overexpression, which has been proposed to cause spontaneous dimerization and activation in the absence of ligand. This makes HER2 attractive as a therapeutic target. However, the HER2 homodimerization mechanism remains unexplored. It has been suggested that the "back-to-back" homodimer does not form in solution. Notwithstanding, very recently the crystal structure of the HER2 extracellular domain homodimer formed with a "back-to-head" interaction has been resolved. We intend to explore the existence of such interactions.

METHODS

A combination of experiments, molecular dynamics and hydrodynamic modeling were used to monitor the transport properties of HER2 in solution.

RESULTS & CONCLUSIONS

We have detected the HER2 extracellular domain homodimer in solution. The results show a high degree of molecular flexibility, which ultimately leads to quite higher values of the intrinsic viscosity and lower values of diffusion coefficient than those corresponding to globular proteins. This flexibility obeys to the open conformation of the receptor and to the large fluctuations of the different domains. We also report that for obtaining the correct hydrodynamic constants from the modeling one must consider the glycosylation of the systems.

GENERAL SIGNIFICANCE

Conformational features of epidermal growth factor receptors regulate their hydrodynamic properties and control their activity. It is essential to understand the dynamics of these systems and the role of the specific domains involved. To find biophysical correlations between dynamics and macroscopic transport properties is of general interest for researches working in this area. This article is part of a Special Issue entitled "Biochemistry of Synthetic Biology - Recent Developments" Guest Editor: Dr. Ilka Heinemann and Dr. Patrick O'Donoghue.

Targeting EGFR/HER2 heterodimerization with a novel anti-HER2 domain II/III antibody

HER2, a ligand-free tyrosine kinase receptor of the HER family, is frequently overexpressed in breast cancer. The anti-HER2 antibody trastuzumab has shown significant clinical benefits in metastatic breast cancer. Despite the effectiveness of trastuzumab, its efficacy remains variable and often modest. Thus, there is an urgent need to improve ErbB2-targeting therapy. Here, we describe a novel anti-HER2 antibody, 7C3, which was developed using hybridoma technique. Structural analysis confirms that the epitope of this antibody is in domain II/III of HER2. Moreover, a structural conformation change was observed in HER2 in complex with 7C3. Interestingly, this novel anti-HER2 antibody exhibits efficacy in blocking HER2/EGFR heterodimerization and signaling. The results highlight the different function role of HER2 domains and the unique potential of 7C3 to inhibit the HER2/EGFR heterodimer, which may complement current anti-HER2 treatments.

Fcab-HER2 Interaction: a Ménage à Trois. Lessons from X-Ray and Solution Studies

The crystallizable fragment (Fc) of the immunoglobulin class G (IgG) is an attractive scaffold for the design of novel therapeutics. Upon engineering the C-terminal loops in the CH3 domains, Fcabs (Fc domain with antigen-binding sites) can be designed. We present the first crystal structures of Fcabs, i.e., of the HER2-binding clone H10-03-6 having the AB and EF loop engineered and the stabilized version STAB19 derived by directed evolution. Comparison with the crystal structure of the Fc wild-type protein reveals conservation of the overall domain structures but significant differences in EF-loop conformations. Furthermore, we present the first Fcab-antigen complex structures demonstrating the interaction between the engineered Fcab loops with domain IV of HER2. The crystal structures of the STAB19-HER2 and H10-03-6-HER2 complexes together with analyses by isothermal titration calorimetry, SEC-MALS, and fluorescence correlation spectroscopy show that one homodimeric Fcab binds two HER2 molecules following a negative cooperative binding behavior.

Inhibition of HER3 activation and tumor growth with a human antibody binding to a conserved epitope formed by domain III and IV

Human epidermal growth factor receptor 3 (HER3, also known as ErbB3) has emerged as relevant target for antibody-mediated tumor therapy. Here, we describe a novel human antibody, IgG 3-43, recognizing a unique epitope formed by domain III and parts of domain IV of the extracellular region of HER3, conserved between HER3 and mouse ErbB3. An affinity of 11 nM was determined for the monovalent interaction. In the IgG format, the antibody bound recombinant bivalent HER3 with subnanomolar affinity (K_D = 220 pM) and HER3-expressing tumor cells with EC₅₀ values in the low picomolar range (27 - 83 pM). The antibody competed with binding of heregulin to HER3-expressing cells, efficiently inhibited phosphorylation of HER3 as well as downstream signaling, and induced receptor internalization and degradation. Furthermore, IgG 3-43 inhibited heregulin-dependent proliferation of several HER3-positive cancer cell lines and heregulin-independent colony formation of HER2-overexpressing tumor cell lines. Importantly, inhibition of tumor growth and prolonged survival was demonstrated in a FaDu xenograft tumor model in SCID mice. These findings demonstrate that by binding to the membrane-proximal domains III and IV involved in ligand binding and receptor dimerization, IgG 3-43 efficiently inhibits activation of HER3, thereby blocking tumor cell growth both in vitro and in vivo.

A computational analysis of in vivo VEGFR activation by multiple co-expressed ligands

The splice isoforms of vascular endothelial growth A (VEGF) each have different affinities for the extracellular matrix (ECM) and the coreceptor NRP1, which leads to distinct vascular phenotypes in model systems expressing only a single VEGF isoform. ECM-immobilized VEGF can bind to and activate VEGF receptor 2 (VEGFR2) directly, with a different pattern of site-specific phosphorylation than diffusible VEGF. To date, the way in which ECM binding alters the distribution of isoforms of VEGF and of the related placental growth factor (PlGF) in the body and resulting angiogenic signaling is not well-understood. Here, we extend our previous validated cell-level computational model of VEGFR2 ligation, intracellular trafficking, and site-specific phosphorylation, which captured differences in signaling by soluble and immobilized VEGF, to a multi-scale whole-body framework. This computational systems pharmacology model captures the ability of the ECM to regulate isoform-specific growth factor distribution distinctly for VEGF and PlGF, and to buffer free VEGF and PlGF levels in tissue. We show that binding of immobilized growth factor to VEGF receptors, both on endothelial cells and soluble VEGFR1, is likely important to signaling in vivo. Additionally, our model predicts that VEGF isoform-specific properties lead to distinct profiles of VEGFR1 and VEGFR2 binding and VEGFR2 site-specific phosphorylation in vivo, mediated by Neuropilin-1. These predicted signaling changes mirror those observed in murine systems expressing single VEGF isoforms. Simulations predict that, contrary to the 'ligand-shifting hypothesis,' VEGF and PlGF do not compete for receptor binding at physiological concentrations, though PlGF is predicted to slightly increase VEGFR2 phosphorylation when over-expressed by 10-fold. These results are critical to design of appropriate therapeutic strategies to control VEGF availability and signaling in regenerative medicine applications.