Structural analysis of the epitopes on erbB2 interacted with inhibitory or non-inhibitory monoclonal antibodies

Cell surface protein aggregation triggers endocytosis to maintain plasma membrane proteostasis

The ability of cells to manage consequences of exogenous proteotoxicity is key to cellular homeostasis. While a plethora of well-characterised machinery aids intracellular proteostasis, mechanisms involved in the response to denaturation of extracellular proteins remain elusive. Here we show that aggregation of protein ectodomains triggers their endocytosis via a macroendocytic route, and subsequent lysosomal degradation. Using ERBB2/HER2-specific antibodies we reveal that their cross-linking ability triggers specific and fast endocytosis of the receptor, independent of clathrin and dynamin. Upon aggregation, canonical clathrin-dependent cargoes are redirected into the aggregation-dependent endocytosis (ADE) pathway. ADE is an actin-driven process, which morphologically resembles macropinocytosis. Physical and chemical stress-induced aggregation of surface proteins also triggers ADE, facilitating their degradation in the lysosome. This study pinpoints aggregation of extracellular domains as a trigger for rapid uptake and lysosomal clearance which besides its proteostatic function has potential implications for the uptake of pathological protein aggregates and antibody-based therapies.

Challenges in Detection of Serum Oncoprotein: Relevance to Breast Cancer Diagnostics

Breast cancer is a highly prevalent malignancy that shows improved outcomes with earlier diagnosis. Current screening and monitoring methods have improved survival rates, but the limitations of these approaches have led to the investigation of biomarker evaluation to improve early diagnosis and treatment monitoring. The enzyme-linked immunosorbent assay (ELISA) is a specific and robust technique ideally suited for the quantification of protein biomarkers from blood or its constituents. The continued clinical relevancy of this assay format will require overcoming specific technical challenges, including the ultra-sensitive detection of trace biomarkers and the circumventing of potential assay interference due to the expanding use of monoclonal antibody (mAb) therapeutics. Approaches to increasing the sensitivity of ELISA have been numerous and include employing more sensitive substrates, combining ELISA with the polymerase chain reaction (PCR), and incorporating nanoparticles as shuttles for detection antibodies and enzymes. These modifications have resulted in substantial boosts in the ability to detect extremely low levels of protein biomarkers, with some systems reliably detecting antigen at sub-femtomolar concentrations. Extensive utilization of mAb therapies in oncology has presented an additional contemporary challenge for ELISA, particularly when both therapeutic and assay antibodies target the same protein antigen. Resolution of issues such as epitope overlap and steric hindrance requires a rational approach to the design of diagnostic antibodies that takes advantage of modern antibody generation pipelines, epitope binning techniques and computational methods to strategically target biomarker epitopes. This review discusses technical strategies in ELISA implemented to date and their feasibility to address current constraints on sensitivity and problems with interference in the clinical setting. The impact of these recent advancements will depend upon their transformation from research laboratory protocols into facile, reliable detection systems that can ideally be replicated in point-of-care devices to maximize utilization and transform both the diagnostic and therapeutic monitoring landscape.

Molecular modeling of polynucleotide complexes

Delivery of polynucleotides into patient cells is a promising strategy for treatment of genetic disorders. Gene therapy aims to either synthesize desired proteins (DNA delivery) or suppress expression of endogenous genes (siRNA delivery). Carriers constitute an important part of gene therapeutics due to limitations arising from the pharmacokinetics of polynucleotides. Non-viral carriers such as polymers and lipids protect polynucleotides from intra and extracellular threats and facilitate formation of cell-permeable nanoparticles through shielding and/or bridging multiple polynucleotide molecules. Formation of nanoparticulate systems with optimal features, their cellular uptake and intracellular trafficking are crucial steps for an effective gene therapy. Despite the great amount of experimental work pursued, critical features of the nanoparticles as well as their processing mechanisms are still under debate due to the lack of instrumentation at atomic resolution. Molecular modeling based computational approaches can shed light onto the atomic level details of gene delivery systems, thus provide valuable input that cannot be readily obtained with experimental techniques. Here, we review the molecular modeling research pursued on critical gene therapy steps, highlight the knowledge gaps in the field and providing future perspectives. Existing modeling studies revealed several important aspects of gene delivery, such as nanoparticle formation dynamics with various carriers, effect of carrier properties on complexation, carrier conformations in endosomal stages, and release of polynucleotides from carriers. Rate-limiting steps related to cellular events (i.e. internalization, endosomal escape, and nuclear uptake) are now beginning to be addressed by computational approaches. Limitations arising from current computational power and accuracy of modeling have been hindering the development of more realistic models. With the help of rapidly-growing computational power, the critical aspects of gene therapy are expected to be better investigated and direct comparison between more realistic molecular modeling and experiments may open the path for design of next generation gene therapeutics.

Deregulation of HER2 downstream signaling in breast cancer cells by a cocktail of anti-HER2 scFvs

Human epidermal growth factor receptor 2 (HER2) is overexpressed in 30% of patients with breast cancer. HER2 targeting is the mainstay of targeted therapy for the treatment of invasive breast cancers. Due to biological and therapeutic advantages, single chain fragment variable (scFv) antibodies have emerged as promising alternative therapeutics. In this study, we assessed the capability of three scFvs against HER2 extracellular domains (II, III, IV) in deregulation of some key signaling mediators that have important roles in growth, survival, angiogenesis, and cell migration of breast tumor cells. Downregulation of activated Akt (p-Akt), increase of p27 protein levels, and downregulation of HER1, HER2, HER3 and epidermal growth factor (EGF), CXCR3, CXCL10, and MMP2 were observed following treatment of breast cancer cells (SKBR3 cell line) with the scFvs and their combination. Our results suggest that the combination of the three scFvs could be considered as an effective cocktail on HER2 tumorgenic signaling pathways that leads to tumor growth suppression and death.

Linear and conformational B cell epitope prediction of the HER 2 ECD-subdomain III by in silico methods

Human epidermal growth factor receptor 2 (HER2) is a member of the epidermal growth factor receptor family of receptor tyrosine kinases that play important roles in all processes of cell development. Their overexpression is related to many cancers, including examples in the breast, ovaries and stomach. Anticancer therapies targeting the HER2 receptor have shown promise, and monoclonal antibodies against subdomains II and IV of the HER2 extra-cellular domain (ECD), Pertuzumab and Herceptin, are currently used in treatments for some types of breast cancers. Since anti HER2 antibodies targeting distinct epitopes have different biological effects on cancer cells; in this research linear and conformational B cell epitopes of HER2 ECD, subdomain III, were identified by bioinformatics analyses using a combination of linear B cell epitope prediction web servers such as ABCpred, BCPREDs, Bepired, Bcepred and Elliprro. Then, Discotope, CBtope and SUPERFICIAL software tools were employed for conformational B cell epitope prediction. In contrast to previously reported epitopes of HER2 ECD we predicted conformational B cell epitopes P1C: 378-393 (PESFDGDPASNTAPLQ) and P2C: 500-510 (PEDECVGEGLA) by the integrated strategy and and P4: PESFDGD-X-TAPLQ; P5: PESFDGDP X TAPLQ; P6: ESFDGDP X NTAPLQP; P7: PESFDGDP-X-NTAPLQ; P8: ESFDG-XX-TAPLQPEQL and P9: ESFDGDP- X-NTAPLQP by SUPERFICIAL software. These epitopes could be further used as peptide antigens to actively immune mice for development of new monoclonal antibodies and peptide cancer vaccines that target different epitopes or structural domains of HER2 ECD.

Anti-HER-2 engineering antibody ChA21 inhibits growth and induces apoptosis of SK-OV-3 cells

Background and Aims

Anti-HER-2 antibodies targeting distinct epitopes have different biological functions on cancer cells. In a previous study, we demonstrated that anti-HER-2 engineering antibody ChA21 was able to bind to subdomain I of HER-2 extracellular domain. In this study, The effects of ChA21 on growth and apoptosis against ovarian carcinoma cell SK-OV-3 over-expressing HER-2 in vitro and in vivo were investigated.

Methods

Cell growth inhibition was evaluated by MTT assay. Apoptosis was detected by TUNEL stain, transmission electron microscopy and flow cytometry on cultured cells and tissue sections from nude mice xenografts. The apoptosis-related proteins Bax and Bcl-2 were assessed by immunohistochemistry.

Results

We found that treatment of ChA21 caused a dose-dependent decrease of cell proliferation in vitro and a significant inhibition of tumor growth in vivo. ChA21 therapy led to a significant increase in the induction of apoptosis, and up-regulated the expression of Bax, while the expression of Bcl-2 was down-regulated.

Conclusion

These data suggest that ChA21 inhibits the growth and induces apoptosis of SK-OV-3 via regulating the balance between Bax and Bcl-2.

Epitope mapping and structural analysis of an anti‐ErbB2 antibody A21: Molecular basis for tumor inhibitory mechanism

Anti-ErbB2 antibodies targeting distinct epitopes can have different biological functions on cancer cells. A21 prepared by surface epitope masking (SEM) method is a tumor-inhibitory anti-ErbB2 monoclonal antibody. Previously we engineered a single chain chimeric antibody chA21 with potential for therapy of ErbB2-overexpressing tumors. Here, we mapped the A21 epitope on ErbB2 extracellular domain (ECD) by screening a combinatorial phage display peptide library, serial subdomain deletion, and mutagenesis scanning. X-ray crystal structure of the A21 scFv fragment at 2.1 A resolution was also determined. A molecular model of Ag-Ab complex was then constructed based on the crystal structures of the A21 scFv and ErbB2 ECD. Some of biological functions of the A21 mAb and its derivative antibodies including their tumor cell growth inhibition and effects on the expression, internalization, and phosphorylation of ErbB2 receptor were also investigated. The results showed that A21 recognized a conformational epitope comprising a large region mostly from ErbB2 extracellular subdomain I with several surface-exposed residues important for the binding affinity. These data provide unique functional properties of A21 that are quite different from two broadly used anti-ErbB2 mAbs, Herceptin and 2C4. It suggested that the A21 epitope may be another valuable target for designing new anti-ErbB2 therapeutics.

De novo design of ErbB2 epitope targeting fusion protein stabilized by coiled coil structure

The extracellular cysteine-rich domains of ErbB2 receptors play important roles in ligand binding and receptor dimerization. The aim of the present study was to design a novel peptide exerting cytostatic effect toward ErbB2-overexpressing tumors based on one of the cysteine-rich domain (S1) of ErbB2. In order to create a stable molecule with unique structural and binding property, a chimeric molecule PL45 composed of ErbB2 S1 domain targeting peptide and the five stranded coiled coil domain from cartilage oligomeric matrix protein (COMP) was generated. PL45 was efficiently expressed in Escherichia coli and exhibited remarkable thermal and pH stability. It was capable of interfering with dimerization of ErbB2 and inhibiting the growth of ErbB2-overexpressing tumor cells in vitro and in vivo. The results provide evidence that the coiled coil structure can be used as a new scaffold to stabilize short peptides with potential application for anti-cancer immunotherapy and S1 domain of ErbB2 is a promising target for drug design.

Growth inhibition of breast cancer cell lines overexpressing Her2/neu by a novel internalized fully human Fab antibody fragment

The Her2/neu oncogene is overexpressed in various human cancers of epithelial origin and is associated with increased metastatic potential and poor prognosis. Blocking the Her2/neu signalling has been the focus of most therapeutic approaches. In this paper, the Her2/neu extracellular domain expressed in soluble form in yeast Pichia pastoris was used in order to isolate a fully human Fab fragment from a combinatorial Fab phage display library, derived from invaded lymph nodes of a breast cancer patient. The isolated fully human Fab63 binds specifically the native Her2/neu receptor and competes with Herceptin for binding to soluble Her2/neu receptor. In Her2/neu overexpressing cancer cells, Fab63 is rapidly internalized and has significant antiproliferative effects, where ligand-independent mechanisms dominate signal induction. Moreover, in the presence of the ligand heregulin, growth inhibition was also detected by Fab63. The human Fab63 is a non-immunogenic agent with unique properties that can be applied in diagnosis and cancer therapy, with great potential for further manipulation towards the generation of an effective anticancer molecule.

Sequestering ErbB2 in endoplasmic reticulum by its autoinhibitor from translocation to cell surface: An autoinhibition mechanism of ErbB2 expression

ErbB2 is differentially overexpressed in tumor versus host tissues, suggesting that an autoregulation mechanism may modulate the expression of ErbB2 and control cell growth. A truncated ErbB2 extracellular domain, herstatin has been shown to bind to ErbB2 and inhibit the growth of tumor cells expressing ErbB2. In the present study, the interaction of herstatin and ErbB2 in vivo was observed by confocal microscopy. The aggregation of ErbB2 and herstatin was found in endoplasmic reticulum (ER). The decrease of ErbB2 on the cell surface was accompanied with the increased colocalization of ErbB2 and herstatin in the cytoplasm, suggesting that the formation of ErbB2/herstatin complex may prevent transit from ER to cell surface of ErbB2. The formation of ErbB2 and herstatin complex was further confirmed by immunoprecipitation. The results demonstrate that sequestering ErbB2 molecules intracellularly by herstatin may be a possible mechanism of the cell growth inhibition.

In vivo identification of the interaction site of ErbB2 extracellular domain with its autoinhibitor

Direct interference with the transforming potential of ErbB2 has become a subject of great interest. Disruption of critical ErbB2 ectodomain interactions may lead to novel therapeutic approaches for the treatment of various tumors. The ErbB receptor signaling can be inhibited by rationally designed peptide mimetics based on the subdomains of ErbB ectodomain. The mimetics can bind to the ErbB receptor specifically and block inter-receptor interactions, resulting in the growth inhibition of ErbB2-overexpressing cells in vitro. In this study, three-dimensional structure of herstatin, an autoinhibitor of ErbB2 and ErbB2 ectodomain complex was constructed by computer-aided molecular modeling. The binding site on ErbB2 ectodomain for herstatin was determined at S1 domain. The mutants of ErbB2 ectodomain were constructed. The interactions of ErbB2 ectodomain and its mutants with herstatin were analyzed for the first time in living cells that coexpressed herstatin and ErbB2 ectodomain or the mutants. The S1 domain in ErbB2 ectodomain was verified as the interaction site with herstatin by immunoprecipitation, confocal microscopy, and fluorescence resonance energy transfer (FRET). The binding region of herstatin on ErbB2 ectodomain might be a potential target region for the drug design.

Reorganization of ErbB family and cell survival signaling after Knock-down of ErbB2 in colon cancer cells

The role of the ErbB family in supporting the malignant phenotype was characterized by stable transfection of a single chain antibody (ScFv5R) against ErbB2 containing a KDEL endoplasmic reticulum retention sequence into GEO human colon carcinoma cells. The antibody traps ErbB2 in the endoplasmic reticulum, thereby down-regulating cell surface ErbB2. The transfected cells showed inactivation of ErbB2 tyrosine phosphorylation and reduced heterodimerization of ErbB2 and ErbB3. This resulted in greater sensitivity to apoptosis induced by growth deprivation and delayed tumorigenicity in vivo. Furthermore, decreased heterodimerization of ErbB2 and ErbB3 led to a reorganization in ErbB function in transfected cells as heterodimerization between epidermal growth factor receptor (EGFR) and ErbB3 increased, whereas ErbB3 activation remained almost the same. Importantly, elimination of ErbB2 signaling resulted in an increase in EGFR expression and activation in transfected cells. Increased EGFR activation contributed to the sustained cell survival in transfected cells.