ErbB-2 amplification inhibits down-regulation and induces constitutive activation of both ErbB-2 and epidermal growth factor receptors

HER2-Positive Gastric Cancer and Antibody Treatment: State of the Art and Future Developments

Despite a decreasing incidence in Western countries, gastric cancer is among the most common cancer subtypes globally and is associated with one of the highest tumor-related mortality rates. Biomarkers play an increasing role in the treatment against gastric cancer. HER2 was one of the first biomarkers that found its way into clinical practice. Since the ToGA trial, trastuzumab has been part of first-line palliative chemotherapy in metastatic or unresectable gastric cancer. HER2-targeting agents, such as the tyrosine kinase inhibitor lapatinib, the antibody drug conjugate (ADC) trastuzumab-emtansine or dual HER2 inhibition (pertuzumab and trastuzumab), have been investigated in the second-line setting but led to negative study results. More recently, the ADC trastuzumab-deruxtecan was authorized after the failure of trastuzumab-based treatment. However, further improvements in HER2-directed therapy are required as resistance mechanisms and HER2 heterogeneity limit the existing treatment options. This review aims to give an overview of the current standard-of-care HER2-directed therapy in gastric cancer, as well as its challenges and future developments.

The ErbB Signaling Network and Its Potential Role in Endometrial Cancer

Endometrial cancer (EC) is the second most common malignancy of the female reproductive system worldwide. The updated EC classification emphasizes the significant role of various signaling pathways such as PIK3CA-PIK3R1-PTEN and RTK/RAS/β-catenin in EC pathogenesis. Some of these pathways are part of the EGF system signaling network, which becomes hyperactivated by various mechanisms and participates in cancer pathogenesis. In EC, the expression of ErbB receptors is significantly different, compared with the premenopausal and postmenopausal endometrium, mainly because of the increased transcriptional activity of ErbB encoding genes in EC cells. Moreover, there are some differences in ErbB-2 receptor profile among EC subgroups that could be explained by the alterations in pathophysiology and clinical behavior of various EC histologic subtypes. The fact that ErbB-2 receptor expression is more common in aggressive EC histologic subtypes (papillary serous and clear cell) could indicate a future role of ErbB-targeted therapies in well-defined EC subgroups with overexpression of ErbB receptors.

EGFR trafficking: effect of dimerization, dynamics, and mutation

Spontaneous dimerization of EGF receptors (EGFR) and dysregulation of EGFR signaling has been associated with the development of different cancers. Under normal physiological conditions and to maintain homeostatic cell growth, once EGFR signaling occurs, it needs to be attenuated. Activated EGFRs are rapidly internalized, sorted through early endosomes, and ultimately degraded in lysosomes by a process generally known as receptor down-regulation. Through alterations to EGFR trafficking, tumors develop resistance to current treatment strategies, thus highlighting the necessity for combination treatment strategies that target EGFR trafficking. This review covers EGFR structure, trafficking, and altered surface expression of EGFR receptors in cancer, with a focus on how therapy targeting EGFR trafficking may aid tyrosine kinase inhibitor treatment of cancer.

Structure and dynamics of the EGFR/HER2 heterodimer

HER2 belongs to the human epidermal growth factor receptor tyrosine kinase family. Its overexpression or hyperactivation is a leading cause for multiple types of cancers. HER2 functions mainly through dimerization with other family members, such as EGFR. However, the molecular details for heterodimer assembly have not been completely understood. Here, we report cryo-EM structures of the EGF- and epiregulin-bound EGFR/HER2 ectodomain complexes at resolutions of 3.3 Å and 4.5 Å, respectively. Together with the functional analyses, we demonstrate that only the dimerization arm of HER2, but not that of EGFR, is essential for their heterodimer formation and signal transduction. Moreover, we analyze the differential membrane dynamics and transient interactions of endogenous EGFR and HER2 molecules in genome-edited cells using single-molecule live-cell imaging. Furthermore, we show that the interaction with HER2 could allow EGFR to resist endocytosis. Together, this work deepens our understanding of the unique structural properties and dynamics of the EGFR/HER2 complex.

Breakthroughs in the Systemic Treatment of HER2-Positive Advanced/Metastatic Gastric Cancer: From Singlet Chemotherapy to Triple Combination

Gastric cancer is heterogeneous in morphology, biology, genomics, and treatment response. Alterations in human epidermal growth factor receptor 2 (HER2) overexpression, microsatellite instability (MSI) status, programmed death-ligand 1 (PD-L1) levels, and fibroblast growth factor receptor 2 (FGFR2) can be used as biomarkers. Since the combination of fluoropyrimidine/platinum plus trastuzumab that was investigated in the ToGA trial was approved as a standard of care in HER2-positive patients in 2010, no other agents showed efficacy in the first- (HELOISE, LOGiC, JACOB trials) and second- (TyTAN, GATSBY, T-ACT trials) line treatments. Despite the success in treating breast cancer, various anti-HER2 agents, including a monoclonal antibody (pertuzumab), an antibody-drug conjugate (ADC; trastuzumab emtansine [T-DM1]), and a small molecule (lapatinib) failed to translate into clinical benefits until the KEYNOTE-811 (first-line) and DESTINY-Gastri01 (≥second-line) trials were conducted. The incorporation of HER2-directed treatment with immune checkpoint inhibitors in the form of a monoclonal antibody or ADC is now approved as a standard treatment. Despite the promising results of new agents (engineered monoclonal antibodies, bi-specific antibodies, fusion proteins, and small molecules) in the early phase of development, the management of HER2-positive gastric cancer requires further optimization to achieve precision medicine with a chemotherapeutic backbone. Treatment resistance is a complex process that can be overcome using a combination of chemotherapy, targeted agents, and immune checkpoint inhibitors, including novel agents. HER2 status must be reassessed in patients undergoing anti-HER2 treatment with disease progression after the first-line treatment. As a general guideline, patients who need systemic treatment should receive chemotherapy plus targeted agents, anti-angiogenic agents, immune checkpoint inhibitors, or their combinations.

Mutant forms of EGFR promote HER2 trafficking through efficient formation of HER2-EGFR heterodimers

INTRODUCTION

Human epidermal growth factor receptor 2 (HER2) forms homodimers and is retained at the surface of cancer cells positive for HER2 amplification. The dimerization, internalization, and intracellular trafficking of HER2 in cancer cells without HER2 amplification have remained uncharacterized, however.

MATERIALS AND METHODS

HER2 homodimers and heterodimers were detected in various cell lines with the use of an in situ proximity ligation assay. The effects of wild-type or mutant forms of epidermal growth factor receptor (EGFR) on intracellular trafficking of HER2 were examined by live-cell imaging. The sensitivity of cell lines without HER2 amplification to ado-trastuzumab emtansine (T-DM1), an anti-HER2 (trastuzumab)-cytotoxic drug conjugate (ADC) was also investigated.

RESULTS

HER2 preferentially formed heterodimers with EGFR rather than homodimers and was rapidly internalized together with EGFR in cells without HER2 amplification. HER2-EGFR heterodimers were more abundant and HER2 was more efficiently transferred to lysosomes in such cells with than in those without EGFR activating mutations. T-DM1 showed a high cytotoxic efficacy in the cells with EGFR mutations, suggesting that mutant forms of EGFR promote the transfer of HER2-bound T-DM1 to lysosomes through efficient formation of HER2-EGFR heterodimers.

CONCLUSION

Our findings reveal that HER2 trafficking is affected by EGFR, especially by mutant forms of the receptor, and they provide a rationale for the use of HER2-targeting ADCs in the treatment of EGFR-mutated lung cancer.

Improved intratumoral penetration of IL12 immunocytokine enhances the antitumor efficacy

Tumor-targeting antibody (Ab)-fused cytokines, referred to as immunocytokines, are designed to increase antitumor efficacy and reduce toxicity through the tumor-directed delivery of cytokines. However, the poor localization and intratumoral penetration of immunocytokines, especially in solid tumors, pose a challenge to effectively stimulate antitumor immune cells to kill tumor cells within the tumor microenvironment. Here, we investigated the influence of the tumor antigen-binding kinetics of a murine interleukin 12 (mIL12)-based immunocytokine on tumor localization and diffusive intratumoral penetration, and hence the consequent antitumor activity, by activating effector T cells in immunocompetent mice bearing syngeneic colon tumors. Based on tumor-associated antigen HER2-specific Ab Herceptin (HCT)-fused mIL12 carrying one molecule of mIL12 (HCT-mono-mIL12 immunocytokine), we generated a panel of HCT-mono-mIL12 variants with different affinities (K D) mainly varying in their dissociation rates (k off) for HER2. Systemic administration of HCT-mono-mIL12 required an anti-HER2 affinity above a threshold (K D = 130 nM) for selective localization and antitumor activity to HER2-expressing tumors versus HER2-negative tumors. However, the high affinity (K D = 0.54 or 46 nM) due to the slow k off from HER2 antigen limited the depth of intratumoral penetration of HCT-mono-mIL12 and the consequent tumor infiltration of T cells, resulting in inferior antitumor activity compared with that of HCT-mono-mIL12 with moderate affinity of (K D = 130 nM) and a faster k off. The extent of intratumoral penetration of HCT-mono-mIL12 variants was strongly correlated with their tumor infiltration and intratumoral activation of CD4+ and CD8+ T cells to kill tumor cells. Collectively, our results demonstrate that when developing antitumor immunocytokines, tumor antigen-binding kinetics and affinity of the Ab moiety should be optimized to achieve maximal antitumor efficacy.

HER2-targeted advanced metastatic gastric/gastroesophageal junction adenocarcinoma: treatment landscape and future perspectives

Recently, the global incidence of gastric/gastroesophageal junction (G/GEJ) cancer has remained high. China is also a large country with a high gastric cancer (GC) incidence rate, where the cases of GC account for 40% of all cases worldwide. More than 90% of GEJ cancers are the adenocarcinoma pathological type. Patients with early-stage G/GEJ adenocarcinoma may have a better prognosis after surgery. In contrast, patients with advanced metastatic G/GEJ adenocarcinoma usually choose comprehensive treatment based on systemic pharmacotherapy, but the subsequent long-term survival is not optimistic. The discovery of various biomarkers, especially microsatellite instability (MSI), programmed cell death-ligand 1 (PD-L1), human epidermal growth factor receptor 2 (HER2), tumor mutational burden (TMB) and Epstein-Barr virus (EBV), has led to the identification of an increasing number of targeted populations and has greatly improved the clinical efficacy of treatments for G/GEJ adenocarcinoma. The ToGA trial added trastuzumab to standard chemotherapy, showed improved survival of patients with HER2-positive advanced G/GEJ adenocarcinoma and brought these patients into a new era of HER2-targeted therapy. Moreover, many HER2-targeted agents have been developed and studied in patients with advanced HER2-positive G/GEJ adenocarcinoma who have demonstrated excellent clinical outcomes. However, many patients experience disease progression with HER2-targeted therapy; hence, new anti-HER2 drugs keep being developed, significantly reducing HER2 resistance. This paper reviews HER2-targeted drugs for advanced metastatic G/GEJ adenocarcinoma, potential resistance mechanisms and future directions.

Imaging Endocytosis Dynamics in Health and Disease

Endocytosis is a critical process for cell growth and viability. It mediates nutrient uptake, guarantees plasma membrane homeostasis, and generates intracellular signaling cascades. Moreover, it plays an important role in dead cell clearance and defense against external microbes. Finally, endocytosis is an important cellular route for the delivery of nanomedicines for therapeutic treatments. Thus, it is not surprising that both environmental and genetic perturbation of endocytosis have been associated with several human conditions such as cancer, neurological disorders, and virus infections, among others. Over the last decades, a lot of research has been focused on developing advanced imaging methods to monitor endocytosis events with high resolution in living cells and tissues. These include fluorescence imaging, electron microscopy, and correlative and super-resolution microscopy. In this review, we outline the major endocytic pathways and briefly discuss how defects in the molecular machinery of these pathways lead to disease. We then discuss the current imaging methodologies used to study endocytosis in different contexts, highlighting strengths and weaknesses.

Development and Evaluation of Competitive Inhibitors of Trastuzumab-HER2 Binding to Bypass the Binding-Site Barrier

Our group has developed and experimentally validated a strategy to increase antibody penetration in solid tumors through transient inhibition of antibody-antigen binding. In prior work, we demonstrated that 1HE, an anti-trastuzumab single domain antibody that transiently inhibits trastuzumab binding to HER2, increased the penetration of trastuzumab and increased the efficacy of ado-trastuzumab emtansine (T-DM1) in HER2+ xenograft bearing mice. In the present work, 1HE variants were developed using random mutagenesis and phage display to enable optimization of tumor penetration and efficacy of trastuzumab-based therapeutics. To guide the rational selection of a particular 1HE mutant for a specific trastuzumab-therapy, we developed a mechanistic pharmacokinetic (PK) model to predict within-tumor exposure of trastuzumab/T-DM1. A pharmacodynamic (PD) component was added to the model to predict the relationship between intratumor exposure to T-DM1 and the corresponding therapeutic effect in HER2+ xenografts. To demonstrate the utility of the competitive inhibition approach for immunotoxins, PK parameters specific for a recombinant immunotoxin were incorporated into the model structure. Dissociation half-lives for variants ranged from 1.1 h (for variant LG11) to 107.9 h (for variant HE10). Simulations predicted that 1HE co-administration can increase the tumor penetration of T-DM1, with inhibitors with longer trastuzumab binding half-lives relative to 1HE (15.5 h) further increasing T-DM1 penetration at the expense of total tumor uptake of T-DM1. The PK/PD model accurately predicted the response of NCI-N87 xenografts to treatment with T-DM1 or T-DM1 co-administered with 1HE. Model predictions indicate that the 1HE mutant HF9, with a trastuzumab binding half-life of 51.1 h, would be the optimal inhibitor for increasing T-DM1 efficacy with a modest extension in the median survival time relative to T-DM1 with 1HE. Model simulations predict that LG11 co-administration will dramatically increase immunotoxin penetration within all tumor regions. We expect that the mechanistic model structure and the wide range of inhibitors developed in this work will enable optimization of trastuzumab-cytotoxin penetration and efficacy in solid tumors.

Extensive conformational and physical plasticity protects HER2-HER3 tumorigenic signaling

Surface-targeting biotherapeutic agents have been successful in treating HER2-amplified cancers through immunostimulation or chemodelivery but have failed to produce effective inhibitors of constitutive HER2-HER3 signaling. We report an extensive structure-function analysis of this tumor driver, revealing complete uncoupling of intracellular signaling and tumorigenic function from regulation or constraints from their extracellular domains (ECDs). The canonical HER3 ECD conformational changes and exposure of the dimerization interface are nonessential, and the entire ECDs of HER2 and HER3 are redundant for tumorigenic signaling. Restricting the proximation of partner ECDs with bulk and steric clash through extremely disruptive receptor engineering leaves tumorigenic signaling unperturbed. This is likely due to considerable conformational flexibilities across the span of these receptor molecules and substantial undulations in the plane of the plasma membrane, none of which had been foreseen as impediments to targeting strategies. The massive overexpression of HER2 functionally and physically uncouples intracellular signaling from extracellular constraints.

Emerging HER2-directed therapeutic agents for gastric cancer in early phase clinical trials

INTRODUCTION

HER2 positive gastric cancer is a distinct subgroup overexpressing the HER2 receptor. For a decade, first-line Trastuzumab was the only licensed HER2-directed therapy for HER2 positive advanced gastric cancer following results from the ToGA trial in 2010 demonstrating a survival benefit when added to chemotherapy. Within the last year, significant advances have taken place in the field of HER2-directed gastric cancer therapy.

AREAS COVERED

This review discusses pivotal clinical trial results and summarises current clinical trials of HER2-directed therapy in gastric cancer. Evidence for HER2-directed antibodies, immunotherapy, immune stimulating antibody conjugates, antibody-drug conjugates (including DESTINY trial results) and tyrosine kinase inhibitors are placed into clinical context. Key challenges including resistance mechanisms and drug toxicities are outlined. Search terms 'HER2' and 'gastric cancer' were entered into ClinicalTrials.gov, Pubmed and Google. Only English-language studies were included.

EXPERT OPINION

Clinical management of HER2 positive gastric cancer patients is likely to change significantly over the next 5 years. Checkpoint inhibition is likely to be used alongside HER2-directed therapy and chemotherapy first-line in advanced disease. Trastuzumab deruxtecan is likely to be offered second-line and beyond. The sheer number of clinical trials of HER2-directed therapy in gastric cancer are testament to progress and potential.

Comprehensive analysis of the ErbB receptor family in pediatric nervous system tumors and rhabdomyosarcoma

BACKGROUND

There is a paucity of knowledge regarding pediatric biomarkers, including the relevance of ErbB pathway aberrations in pediatric tumors. We investigated the occurrence of ErbB receptor aberrations across different pediatric malignancies, to identify patterns of ErbB dysregulation and define biomarkers suitable for patient enrichment in clinical studies.

PROCEDURE

Tissue samples from 297 patients with nervous system tumors and rhabdomyosarcoma were analyzed for immunohistochemical expression or gene amplification of epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2). Exploratory analyses of HER3/HER4 expression, and mRNA expression of ErbB receptors/ligands (NanoString) were performed. Assay validation followed general procedures, with additional validation to address Clinical Laboratory Improvement Amendments (CLIA) requirements.

RESULTS

In most tumor types, samples with high ErbB receptor expression were found with heterogeneous distribution. We considered increased/aberrant ErbB pathway activation when greater than or equal to two EGFR/HER2 markers were simultaneously upregulated. ErbB pathway dysregulation was identified in ∼20%-30% of samples for most tumor types (medulloblastoma/primitive neuroectodermal tumors 31.1%, high-grade glioma 27.1%, neuroblastoma 22.7%, rhabdomyosarcoma 23.1%, ependymoma 18.8%), 4.2% of diffuse intrinsic pontine gliomas, and no recurrent or refractory low-grade astrocytomas. In medulloblastoma/primitive neuroectodermal tumors and neuroblastoma, this was attributed mainly to high EGFR polysomy/HER2 amplification, whereas EGFR gene amplification was observed in some high-grade glioma samples. EGFR/HER2 overexpression was most prevalent in ependymoma.

CONCLUSIONS

Overexpression and/or amplification of EGFR/HER2 were identified as potential enrichment biomarkers for clinical trials of ErbB-targeted drugs.

Quantification of EGFR-HER2 Heterodimers in HER2-Overexpressing Breast Cancer Cells Using Liquid-Phase Electron Microscopy

Currently, breast cancer patients are classified uniquely according to the expression level of hormone receptors, and human epidermal growth factor receptor 2 (HER2). This coarse classification is insufficient to capture the phenotypic complexity and heterogeneity of the disease. A methodology was developed for absolute quantification of receptor surface density ρ_R, and molecular interaction (dimerization), as well as the associated heterogeneities, of HER2 and its family member, the epidermal growth factor receptor (EGFR) in the plasma membrane of HER2 overexpressing breast cancer cells. Quantitative, correlative light microscopy (LM) and liquid-phase electron microscopy (LPEM) were combined with quantum dot (QD) labeling. Single-molecule position data of receptors were obtained from scanning transmission electron microscopy (STEM) images of intact cancer cells. Over 280,000 receptor positions were detected and statistically analyzed. An important finding was the subcellular heterogeneity in heterodimer shares with respect to plasma membrane regions with different dynamic properties. Deriving quantitative information about EGFR and HER2 ρ_R, as well as their dimer percentages, and the heterogeneities thereof, in single cancer cells, is potentially relevant for early identification of patients with HER2 overexpressing tumors comprising an enhanced share of EGFR dimers, likely increasing the risk for drug resistance, and thus requiring additional targeted therapeutic strategies.

The membrane-linked adaptor FRS2β fashions a cytokine-rich inflammatory microenvironment that promotes breast cancer carcinogenesis

Human breast cancer develops after a long period of latency under premalignant conditions. Strategies to target the premalignant conditions have yet to materialize since the molecular mechanisms remain obscure. Here, we discovered that FRS2β, expressed in a subset of mammary epithelial cells, directly activates nuclear factor–κB (NF-κB) and drives the initiation and promotion of the stroma-rich premalignant conditions. The FRS2β-triggered activation of NF-κB takes place in the early endosomes, the organelles, which have not been believed to be a major place for NF-κB signaling. The endosome signaling should be a novel focus for targeting therapy for prevention of breast cancer. This work paves a new way to develop preventive strategies of breast tumor development.

Although it is held that proinflammatory changes precede the onset of breast cancer, the underlying mechanisms remain obscure. Here, we demonstrate that FRS2β, an adaptor protein expressed in a small subset of epithelial cells, triggers the proinflammatory changes that induce stroma in premalignant mammary tissues and is responsible for the disease onset. FRS2β deficiency in mouse mammary tumor virus (MMTV)–ErbB2 mice markedly attenuated tumorigenesis. Importantly, tumor cells derived from MMTV-ErbB2 mice failed to generate tumors when grafted in the FRS2β-deficient premalignant tissues. We found that colocalization of FRS2β and the NEMO subunit of the IκB kinase complex in early endosomes led to activation of nuclear factor–κB (NF-κB), a master regulator of inflammation. Moreover, inhibition of the activities of the NF-κB–induced cytokines, CXC chemokine ligand 12 and insulin-like growth factor 1, abrogated tumorigenesis. Human breast cancer tissues that express higher levels of FRS2β contain more stroma. The elucidation of the FRS2β–NF-κB axis uncovers a molecular link between the proinflammatory changes and the disease onset.

A DNA Aptamer That Inhibits the Aberrant Signaling of Fibroblast Growth Factor Receptor in Cancer Cells

Growth factor receptors are activated through dimerization by the binding of their ligands and play pivotal roles in normal cell function. However, the aberrant activity of the receptors has been associated with cancer malignancy. One of the main causes of the aberrant receptor activation is the overexpression of receptors and the resultant formation of unliganded receptor dimers, which can be activated in the absence of external ligand molecules. Thus, the unliganded receptor dimer is a promising target to inhibit aberrant signaling in cancer. Here, we report an aptamer that specifically binds to fibroblast growth factor receptor 2b and inhibits the aberrant receptor activation and signaling. Our investigation suggests that this aptamer inhibits the formation of the receptor dimer occurring in the absence of external ligand molecules. This work presents a new inhibitory function of aptamers and the possibility of oligonucleotide-based therapeutics for cancer.

Mechanisms for Regulating and Organizing Receptor Signaling by Endocytosis

Intricate relationships between endocytosis and cellular signaling, first recognized nearly 40 years ago through the study of tyrosine kinase growth factor receptors, are now known to exist for multiple receptor classes and to affect myriad physiological and developmental processes. This review summarizes our present understanding of how endocytosis orchestrates cellular signaling networks, with an emphasis on mechanistic underpinnings and focusing on two receptor classes-tyrosine kinase and G protein-coupled receptors-that have been investigated in particular detail. Together, these examples provide a useful survey of the current consensus, uncertainties, and controversies in this rapidly advancing area of cell biology.

Anti-EGFR therapy in metastatic colorectal cancer: mechanisms and potential regimens of drug resistance

Cetuximab and panitumumab, as the highly effective antibodies targeting epidermal growth factor receptor (EGFR), have clinical activity in the patients with metastatic colorectal cancer (mCRC). These agents have good curative efficacy, but drug resistance also exists at the same time. The effects of KRAS, NRAS, and BRAF mutations and HER2 amplification on the treatment of refractory mCRC have been elucidated and the corresponding countermeasures have been put forward. However, the changes in EGFR and its ligands, the mutations or amplifications of PIK3CA, PTEN, TP53, MET, HER3, IRS2, FGFR1, and MAP2K1, the overexpression of insulin growth factor-1, the low expression of Bcl-2-interacting mediator of cell death, mismatch repair-deficient, and epigenetic instability may also lead to drug resistance in mCRC. Although the emergence of drug resistance has genetic or epigenetic heterogeneity, most of these molecular changes relating to it are focused on the key signaling pathways, such as the RAS/RAF/mitogen-activated protein kinase or phosphatidylinositol 3-kinase/Akt/mammalian target of the rapamycin pathway. Accordingly, numerous efforts to target these signaling pathways and develop the novel therapeutic regimens have been carried out. Herein, we have reviewed the underlying mechanisms of the resistance to anti-EGFR therapy and the possible implications in clinical practice.

Developing effective combination therapy for pancreatic cancer: An overview

Pancreatic cancer is a fatal disease. The five-year survival for patients with all stages of this tumor type is less than 10%, with a majority of patients dying from drug resistant, metastatic disease. Gemcitabine has been a standard of care for the treatment of pancreatic cancer for over 20 years, but as a single agent gemcitabine is not curative. Since the only therapeutic option for the over 80 percent of pancreatic cancer patients ineligible for surgical resection is chemotherapy with or without radiation, the last few decades have seen a significant effort to develop effective therapy for this disease. This review addresses preclinical and clinical efforts to identify agents that target molecular characteristics common to pancreatic tumors and to develop mechanism-based combination approaches to therapy. Some of the most promising combinations include agents that inhibit transcription dependent on BET proteins (BET bromodomain inhibitors) or that inhibit DNA repair mediated by PARP (PARP inhibitors).

Beclin 1 Promotes Endosome Recruitment of Hepatocyte Growth Factor Tyrosine Kinase Substrate to Suppress Tumor Proliferation

Beclin 1 has nonautophagic functions that include its ability to regulate endocytic receptor trafficking. However, the contribution of this function to tumor suppression is poorly understood. Here, we provide in vivo evidence that Beclin 1 suppresses tumor proliferation by regulating the endocytic trafficking and degradation of the EGFR and transferrin (TFR1) receptors. Beclin 1 promoted endosomal recruitment of hepatocyte growth factor tyrosine kinase substrate (HRS), which was necessary for sorting surface receptors to intraluminal vesicles for signal silencing and lysosomal degradation. In tumors with low Beclin 1 expression, endosomal HRS recruitment was diminished and receptor function was sustained. Collectively, our results demonstrate a novel role for Beclin 1 in impeding tumor growth by coordinating the regulation of key growth factor and nutrient receptors. These data provide an explanation for how low levels of Beclin 1 facilitate tumor proliferation and contribute to poor cancer outcomes. SIGNIFICANCE: Beclin 1 controls the trafficking fate of growth regulatory receptors to suppress tumor proliferation.

Breast cancer brain metastasis: molecular mechanisms and directions for treatment

The development of brain metastasis (BM) of breast cancer is usually a late event with deleterious effect on the prognosis. Treatment options for intracerebral seeding of breast cancer are limited and, so far, nonspecific. Molecular detailing of subsequent events of penetration, seeding, and outgrowth in brain is highly relevant for developing therapeutic strategies to treat, or prevent, BM.We scrutinize recent literature for molecules and pathways that are operative in the formation of breast cancer BM. We also summarize current data on therapeutic efforts to specifically address BM of breast cancer. Data on molecular pathways underlying the formation of BM of breast cancer are sketchy and to some extent inconsistent. The molecular makeup of BM differs from that of the primary tumors, as well as from metastases at other sites. Current efforts to treat breast cancer BM are limited, and drugs used have proven effects on the primary tumors but lack specificity for the intracerebral tumors.More basic research is necessary to better characterize BM of breast cancer. Apart from the identification of drug targets defined by the intracerebral tumors, also targets in the molecular pathways involved in passing the blood-brain barrier and intracerebral tumor cell growth should be revealed.

Etiologic Role of Kinases in the Progression of Human Cancers and Its Targeting Strategies

Cancer is one of the dominant causes of death worldwide while lifelong prognosis is still inauspicious. The maturation of the cancer is seen as a process of transformation of a healthy cell into a tumor-sensitive cell, which is held entirely at the cellular, molecular, and genetic levels of the organism. Tyrosine kinases can play a major, etiologic role in the inception of malignancy and devote to the uncontrolled proliferation of cancerous cells and the progression of a tumor as well as the development of metastatic disease. Angiogenesis and oncogene activation are the major event in cell proliferation. The growth of a tumor and metastasis are fully depending on angiogenesis and lymphangiogenesis triggered by chemical signals from tumor cells in a phase of rapid growth. Tyrosine kinase inhibitors are compounds that inhibit tyrosine kinases and effective in targeting angiogenesis and blocking the signaling pathways of oncogenes. Small molecule tyrosine kinase inhibitors like afatinib, erlotinib, crizotinib, gefitinib, and cetuximab are shown to a selective cut off tactic toward the constitutive activation of an oncogene in tumor cells, and thus contemplated as promising therapeutic approaches for the diagnosis of cancer and malignancies.

Targeting promiscuous heterodimerization overcomes innate resistance to ERBB2 dimerization inhibitors in breast cancer

Background

The oncogenic receptor tyrosine kinase (RTK) ERBB2 is known to dimerize with other EGFR family members, particularly ERBB3, through which it potently activates PI3K signalling. Antibody-mediated inhibition of this ERBB2/ERBB3/PI3K axis has been a cornerstone of treatment for ERBB2-amplified breast cancer patients for two decades. However, the lack of response and the rapid onset of relapse in many patients now question the assumption that the ERBB2/ERBB3 heterodimer is the sole relevant effector target of these therapies.

Methods

Through a systematic protein-protein interaction screen, we have identified and validated alternative RTKs that interact with ERBB2. Using quantitative readouts of signalling pathway activation and cell proliferation, we have examined their influence upon the mechanism of trastuzumab- and pertuzumab-mediated inhibition of cell growth in ERBB2-amplified breast cancer cell lines and a patient-derived xenograft model.

Results

We now demonstrate that inactivation of ERBB3/PI3K by these therapeutic antibodies is insufficient to inhibit the growth of ERBB2-amplified breast cancer cells. Instead, we show extensive promiscuity between ERBB2 and an array of RTKs from outside of the EGFR family. Paradoxically, pertuzumab also acts as an artificial ligand to promote ERBB2 activation and ERK signalling, through allosteric activation by a subset of these non-canonical RTKs. However, this unexpected activation mechanism also increases the sensitivity of the receptor network to the ERBB2 kinase inhibitor lapatinib, which in combination with pertuzumab, displays a synergistic effect in single-agent resistant cell lines and PDX models.

Conclusions

The interaction of ERBB2 with a number of non-canonical RTKs activates a compensatory signalling response following treatment with pertuzumab, although a counter-intuitive combination of ERBB2 antibody therapy and a kinase inhibitor can overcome this innate therapeutic resistance.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1127-y) contains supplementary material, which is available to authorized users.

Studies on the Dual Activity of EGFR and HER-2 Inhibitors Using Structure-Based Drug Design Techniques

HER-2 and EGFR are biological targets related to the development of cancer and the discovery and/or development of a dual inhibitor could be a good strategy to design an effective drug candidate. In this study, analyses of the chemical properties of a group of substances having affinity for both HER-2 and EGFR were carried out with the aim of understanding the main factors involved in the interaction between these inhibitors and the biological targets. Comparative analysis of molecular interaction fields (CoMFA) and comparative molecular similarity index analysis (CoMSIA) techniques were applied on 63 compounds. From CoMFA analyses, we found for both HER-2 (r² calibration = 0.98 and q²_cv = 0.83) and EGFR (r² calibration = 0.98 and q²_cv = 0.73) good predictive models. Good models for CoMSIA technique have also been found for HER-2 (r² calibration = 0.92 and q²_cv = 0.74) and EGFR (r² calibration = 0.97 and q²_cv = 0.72). The constructed models could indicate some important characteristics for the inhibition of the biological targets. New compounds were proposed as candidates to inhibit both proteins. Therefore, this study may guide future projects for the development of new drug candidates for the treatment of breast cancer.

Composite regulation of ERK activity dynamics underlying tumour-specific traits in the intestine

Acting downstream of many growth factors, extracellular signal-regulated kinase (ERK) plays a pivotal role in regulating cell proliferation and tumorigenesis, where its spatiotemporal dynamics, as well as its strength, determine cellular responses. Here, we uncover the ERK activity dynamics in intestinal epithelial cells (IECs) and their association with tumour characteristics. Intravital imaging identifies two distinct modes of ERK activity, sustained and pulse-like activity, in IECs. The sustained and pulse-like activities depend on ErbB2 and EGFR, respectively. Notably, activation of Wnt signalling, the earliest event in intestinal tumorigenesis, augments EGFR signalling and increases the frequency of ERK activity pulses through controlling the expression of EGFR and its regulators, rendering IECs sensitive to EGFR inhibition. Furthermore, the increased pulse frequency is correlated with increased cell proliferation. Thus, ERK activity dynamics are defined by composite inputs from EGFR and ErbB2 signalling in IECs and their alterations might underlie tumour-specific sensitivity to pharmacological EGFR inhibition.

The ERK signalling pathway regulates homeostasis of the intestinal epithelium. Here the authors identify two modes of ERK activity generated independently from EGFR and ErbB2 receptor and whose balance in cancer is shifted by Wnt pathway activation, resulting in enhanced sensitivity to EGFR inhibitors.

MicroRNA and HER2-overexpressing cancer

The discovery of microRNAs (miRNAs) has opened up new avenues for studying cancer at the molecular level, featuring a post-genomic era of biomedical research. These non-coding regulatory RNA molecules of ~22 nucleotides have emerged as important cancer biomarkers, effectors, and targets. In this review, we focus on the dysregulated biogenesis and function of miRNAs in cancers with an overexpression of the proto-oncogene HER2. Many of the studies reviewed here were carried out in breast cancer, where HER2 overexpression has been extensively studied and HER2-targeted therapy practiced for more than a decade. MiRNA signatures that can be used to classify tumors with different HER2 status have been reported but little consensus can be established among various studies, emphasizing the needs for additional well-controlled profiling approaches and meta-analyses in large and well-balanced patient cohorts. We further discuss three aspects of microRNA dysregulation in or contribution to HER2-associated malignancies or therapies: (a) miRNAs that are up- or down-regulated by HER2 and mediate the downstream signaling of HER2; (b) miRNAs that suppress the expression of HER2 or a factor in HER2 receptor complexes, such as HER3; and (c) miRNAs that affect responses to anti-HER2 therapies. The regulatory mechanisms are elaborated using mainly examples of miR-205, miR-125, and miR-21. Understanding the regulation and function of miRNAs in HER2-overexpressing tumors shall shed new light on the pathogenic mechanisms of microRNAs and the HER2 proto-oncogene in cancer, as well as on individualized or combinatorial anti-HER2 therapies.

FGFR1 and HER1 or HER2 co-amplification in breast cancer indicate poor prognosis

Human epidermal growth factor receptor 1 or 2 (HER1/2), and fibroblast growth factor receptor 1 (FGFR1) signaling serve critical roles in the progression of breast cancer; however, cross-talk between HER1/2 and FGFR1 signaling has not been extensively studied. In the present study, the copy number variation status of FGFR1 and HER1/2, and the clinical implications and prognostic relevance of this, were evaluated in invasive ductal breast cancer (IDC) tissue samples. Quantitative polymerase chain reaction and fluorescence in situ hybridization were used to assess gene copy number variation in IDC samples, and the clinical characteristics and survival curves of patients with IDC were analyzed. The amplification of FGFR1 was identified in 16.0% of the samples (12 of 75), of HER1 in 26.7% (20 of 75), of HER2 in 37.3% (28 of 75), and of FGFR1 and HER1/2 simultaneously in 8.0% (6 of 75). FGFR1 and HER1/2 co-amplification were significantly correlated with distant metastasis (P=0.035), recurrence (P=0.026) and decreased disease-free survival time (P=0.042). This was the case for patients undergoing endocrine therapy (P=0.002) and chemotherapy (P=0.044). Taken together, the results indicate that patients with FGFR1 and HER1/2 co-amplification may exhibit a less favorable prognosis compared with patients with either FGFR1, HER1/2 amplification or without amplification.

The effects of trastuzumab on HER2-mediated cell signaling in CHO cells expressing human HER2

BACKGROUND

Targeted therapy with trastuzumab has become a mainstay for HER2-positive breast cancer without a clear understanding of the mechanism of its action. While many mechanisms have been suggested for the action of trastuzumab, most of them are not substantiated by experimental data. It has been suggested that trastuzumab functions by inhibiting intracellular signaling initiated by HER2, however, the data are very controversial. A major issue is the different cellular background of various breast cancer cells lines used in these studies. Each breast cancer cell line has a unique expression profile of various HER receptors, which could significantly affect the effects of trastuzumab.

METHODS

To overcome this problem, in this research we adopted a cell model that allow us to specifically examine the effects of trastuzumab on a single HER receptor without the influence of other HER receptors. Three CHO cell lines stably expressing only human EGFR (CHO-EGFR), HER2 (CHO-K6), or HER3 (CHO-HER3) were used. Various methods including cytotoxicity assay, immunoblotting, indirect immunofluorescence, cross linking, and antibody-dependent cellular cytotoxicity (ADCC) were employed in this research.

RESULTS

We showed that trastuzumab did not bind EGFR and HER3, and thus did not affect the homodimerization and phosphorylation of EGFR and HER3. However, overexpression of HER2 in CHO cells, in the absence of other HER receptors, resulted in the homodimerization of HER2 and the phosphorylation of HER2 at all major pY residues. Trastuzumab bound to HER2 specifically and with high affinity. Trastuzumab inhibited neither the homodimerization of HER2, nor the phosphorylation of HER2 at most phosphotyrosine residues. Moreover, trastuzumab did not inhibit the phosphorylation of ERK and AKT in CHO-K6 cells, and did not inhibit the proliferation of CHO-K6 cells. However, trastuzumab induced strong ADCC in CHO-K6 cells.

CONCLUSION

We concluded that, in the absence of other HER receptors, trastuzumab exerts its antitumor activity through the induction of ADCC, rather than the inhibition of HER2-homodimerization and phosphorylation.

EGFR Trafficking in Physiology and Cancer

Signaling from the epidermal growth factor receptor (EGFR) elicits multiple biological responses, including cell proliferation, migration, and survival. Receptor endocytosis and trafficking are critical physiological processes that control the strength, duration, diversification, and spatial restriction of EGFR signaling through multiple mechanisms, which we review in this chapter. These mechanisms include: (i) regulation of receptor density and activation at the cell surface; (ii) concentration of receptors into distinct nascent endocytic structures; (iii) commitment of the receptor to different endocytic routes; (iv) endosomal sorting and postendocytic trafficking of the receptor through distinct pathways, and (v) recycling to restricted regions of the cell surface. We also highlight how communication between organelles controls EGFR activity along the endocytic route. Finally, we illustrate how abnormal trafficking of EGFR oncogenic mutants, as well as alterations of the endocytic machinery, contributes to aberrant EGFR signaling in cancer.

Targeted Therapies for the Treatment of Brain Metastases in Solid Tumors

Brain metastases are a major cause of morbidity and mortality in cancer patients. While the mainstay treatment comprises surgery and radiation therapy, the role of systemic agents remains controversial. In general, it has been presumed that poor blood-brain barrier (BBB) penetration and inherently more resistant metastatic brain disease preclude a favorable systemic treatment approach. However, a better understanding of tumor biology and the subsequent development of targeted drugs have reawakened interest in systemic therapy. Despite still limited brain distribution, a variety of targeted drugs have demonstrated activity in brain metastases in early clinical trials. Nevertheless, disease progression commonly occurs, and it remains to be elucidated whether limited CNS drug distribution or the acquisition of resistant metastatic clones must be held responsible for this prognosis. Moreover, micrometastatic brain disease beyond an intact BBB-and ultimately prevention of brain metastasis formation-may generally remain inaccessible for first-generation targeted agents with poor CNS penetration. To overcome limited brain distribution and possibly emerging acquired resistance, highly potent next-generation targeted drugs with enhanced CNS distribution have been developed. In view of this emerging but yet undefined role of targeted therapies in the treatment of brain metastases from solid tumors, this review aims to summarize the current knowledge from clinical trials and discusses clinically relevant obstacles to overcome.

Endometrial Carcinoma: Specific Targeted Pathways

Endometrial cancer (EC) is the most common gynecologic malignancy in the western world with more than 280,000 cases per year worldwide. Prognosis for EC at early stages, when primary surgical resection is the most common initial treatment, is excellent. Five-year survival rate is around 70 %.Several molecular alterations have been described in the different types of EC. They occur in genes involved in important signaling pathways. In this chapter, we will review the most relevant altered pathways in EC, including PI3K/AKT/mTOR, RAS-RAF-MEK-ERK, Tyrosine kinase, WNT/β-Catenin, cell cycle, and TGF-β signaling pathways. At the end of the chapter, the most significant clinical trials will be briefly discussed.This information is important to identify specific targets for therapy.

MEK inhibitors induce Akt activation and drug resistance by suppressing negative feedback ERK-mediated HER2 phosphorylation at Thr701

Targeting the MEK/ERK pathway has been viewed as a promising strategy for cancer therapy. However, MEK inhibition leads to the compensatory PI3K/AKT activation and thus contributes to the desensitization of cancer cells to MEK inhibitors. The underlying molecular mechanism of this event is not yet understood. In this study, our data showed that the induction of Akt activity by MEK inhibitors was specifically observed in HER2‐positive breast cancer cells. Silence of HER2, or overexpression of HER2 kinase‐dead mutant, prevents the induction of Akt activation in response to MEK inhibition, indicating HER2 as a critical regulator for this event. Furthermore, HER2 Thr701 was demonstrated as a direct phosphorylation target of ERK1/2. Inhibition of this specific phosphorylation prolonged the dimerization of HER2 with EGFR in a clathrin‐dependent manner, leading to the enhanced activation of HER2 and EGFR tyrosine kinase and their downstream Akt pathway. These results suggest that suppression of ERK‐mediated HER2 Thr701 phosphorylation contributes to MEK inhibitor‐induced Akt activation.

Inhibition of MHC-I by Brucella abortus is an early event during infection and involves EGFR pathway

Brucella abortus is able to persist inside the host despite the development of potent CD8+ T-cell responses. We have recently reported the ability of B. abortus to inhibit the interferon-γ-induced major histocompatibility complex (MHC)-I cell surface expression on human monocytes. This phenomenon was due to the B. abortus-mediated retention of MHC-I molecules within the Golgi apparatus and was dependent on bacterial viability. However, the implications of bacterial virulence or replicative capacity and the signaling pathways remained unknown. Here we demonstrated that the B. abortus mutant strains RB51 and virB10- are able to inhibit MHC-I expression in the same manner as wild-type B. abortus, even though they are unable to persist inside human monocytes for a long period of time. Consistent with this, the phenomenon was triggered early in time and could be observed at 8 h postinfection. At 24 and 48 h, it was even stronger. Regarding the signaling pathway, targeting epidermal growth factor (EGF) receptor (EGFR), ErbB2 (HER2) or inhibition of tumor necrosis factor-α-converting enzyme, one of the enzymes which generates soluble EGF-like ligands, resulted in partial recovery of MHC-I surface expression. Moreover, recombinant EGF and transforming growth factor-α as well as the combination of both were also able to reproduce the B. abortus-induced MHC-I downmodulation. Finally, when infection was performed in the presence of an extracellular signal-regulated kinase 1/2 (Erk1/2) inhibitor, MHC-I surface expression was significantly recovered. Overall, these results describe how B. abortus evades CD8+ T-cell responses early during infection and exploits the EGFR-ERK signaling pathway to escape from the immune system and favor chronicity.

Targeted Treatment of Esophagogastric Cancer

Adenocarcinoma of the esophagogastric junction (EGJ) and stomach remains one of the most common causes of cancer-related death worldwide. Although there is increasing data on the mutational landscape of esophagogastric cancer, phase III trials often yield negative results, and there is a paucity of approved targeted agents. For the time being, the subset of patients carrying HER2-positive metastatic tumors can receive trastuzumab in addition to chemotherapy. Furthermore, ramucirumab has been found to be active both as a single agent and in combination with paclitaxel. Herein, we give an overview of currently approved targeted treatments for locally advanced/resectable as well as unresectable/metastatic EGJ/gastric adenocarcinoma, summarizing the underlying clinical studies. Moreover, further potential targets still under investigation are presented.

Trastuzumab in the management of gastroesophageal cancer: patient selection and perspectives

The addition of trastuzumab to the treatment of a subset of patients with advanced gastric and gastroesophageal junction cancers showing HER2 positivity has been shown to confer clinical benefit; however, questions remain over the optimal methods for defining and selecting such patients. This review provides an overview of current standards for assessing HER2 positivity, the evolving treatment landscape for HER2-positive gastric and esophageal cancers and the challenges and potential future directions in optimal patient selection for HER2-targeted therapy.

Metastatic human epidermal growth factor receptor 2-positive breast cancer: Management, challenges, and future directions

HER2 is over-expressed or amplified in 15-20% of breast cancer. Significant progress has been made in the treatment of metastatic HER2+ breast cancer. This is largely due to successful targeting of the HER2 pathway. There are several approved agents in the metastatic setting. However, treatment resistance frequently develops and tumors eventually progress. In recent years, our understanding of mechanisms of resistance has evolved. It is generally accepted now that HER2-positive breast cancer is not one disease. New therapeutic strategies and a tailored approach to management are necessary to maximize patient outcomes and minimize toxicity.

The Under-Appreciated Promiscuity of the Epidermal Growth Factor Receptor Family

Each member of the epidermal growth factor receptor (EGFR) family plays a key role in normal development, homeostasis, and a variety of pathophysiological conditions, most notably in cancer. According to the prevailing dogma, these four receptor tyrosine kinases (RTKs; EGFR, ERBB2, ERBB3, and ERBB4) function exclusively through the formation of homodimers and heterodimers within the EGFR family. These combinatorial receptor interactions are known to generate increased interactome diversity and therefore influence signaling output, subcellular localization and function of the heterodimer. This molecular plasticity is also thought to play a role in the development of resistance toward targeted cancer therapies aimed at these known oncogenes. Interestingly, many studies now challenge this dogma and suggest that the potential for EGFR family receptors to interact with more distantly related RTKs is much greater than currently appreciated. Here we discuss how the promiscuity of these oncogenic receptors may lead to the formation of many unexpected receptor pairings and the significant implications for the efficiency of many targeted cancer therapies.

17AAG-induced internalisation of HER2-specific Affibody molecules

The geldanamycin derivative 17-allylamino-17-demethoxygeldanamycin (17-AAG) is known to induce internalisation and degradation of the otherwise internalisation-resistant human epidermal growth factor receptor 2 (HER2) receptor. In the present study, 17-AAG was used to increase internalisation of the HER2-specific Affibody molecule ABY-025. The cellular redistribution of halogen-labelled ²¹¹At-ABY-025 and radiometal-labelled ¹¹¹In-ABY-025 following treatment with 17-AAG was studied. 17-AAG treatment of SKOV-3 human ovarian carcinoma and SKBR-3 human breast carcinoma cells to some extent shifted the localisation of ¹¹¹In-ABY-025 from the cell surface to intracellular compartments in the two cell lines. ABY-025 labelled with the high-linear energy transfer α emitter ²¹¹At was also internalised to a higher degree; however, due to its physiological properties, this nuclide was excreted faster. The results indicate that 17-AAG may be used to facilitate cell-specific intracellular localisation of a suitable cytotoxic or radioactive agent coupled to ABY-025 in HER2-overexpressing cells.

HER2-HER3 dimer quantification by FLIM-FRET predicts breast cancer metastatic relapse independently of HER2 IHC status

Overexpression of HER2 is an important prognostic marker, and the only predictive biomarker of response to HER2-targeted therapies in invasive breast cancer. HER2-HER3 dimer has been shown to drive proliferation and tumor progression, and targeting of this dimer with pertuzumab alongside chemotherapy and trastuzumab, has shown significant clinical utility. The purpose of this study was to accurately quantify HER2-HER3 dimerisation in formalin fixed paraffin embedded (FFPE) breast cancer tissue as a novel prognostic biomarker.FFPE tissues were obtained from patients included in the METABRIC (Molecular Taxonomy of Breast Cancer International Consortium) study. HER2-HER3 dimerisation was quantified using an improved fluorescence lifetime imaging microscopy (FLIM) histology-based analysis. Analysis of 131 tissue microarray cores demonstrated that the extent of HER2-HER3 dimer formation as measured by Förster Resonance Energy Transfer (FRET) determined through FLIM predicts the likelihood of metastatic relapse up to 10 years after surgery (hazard ratio 3.91 (1.61-9.5), p = 0.003) independently of HER2 expression, in a multivariate model. Interestingly there was no correlation between the level of HER2 protein expressed and HER2-HER3 heterodimer formation. We used a mathematical model that takes into account the complex interactions in a network of all four HER proteins to explain this counterintuitive finding.Future utility of this technique may highlight a group of patients who do not overexpress HER2 protein but are nevertheless dependent on the HER2-HER3 heterodimer as driver of proliferation. This assay could, if validated in a group of patients treated with, for instance pertuzumab, be used as a predictive biomarker to predict for response to such targeted therapies.

Bimolecular complementation affinity purification (BiCAP) reveals dimer-specific protein interactions for ERBB2 dimers

The dynamic assembly of multiprotein complexes is a central mechanism of many cell signaling pathways. This process is key to maintaining the spatiotemporal specificity required for an accurate, yet adaptive, response to rapidly changing cellular conditions. We describe a technique for the specific isolation and downstream proteomic characterization of any two interacting proteins, to the exclusion of their individual moieties and competing binding partners. We termed the approach bimolecular complementation affinity purification (BiCAP) because it combines the use of conformation-specific nanobodies with a protein-fragment complementation assay with affinity purification. Using BiCAP, we characterized the specific interactome of the epidermal growth factor receptor (EGFR) family member ERBB2 when in the form of a homodimer or when in the form of a heterodimer with either EGFR or ERBB3. We identified dimer-specific interaction patterns for key adaptor proteins and identified a number of previously unknown interacting partners. Functional analysis for one of these newly identified partners revealed a noncanonical mechanism of extracellular signal-regulated kinase (ERK) activation that is specific to the ERBB2:ERBB3 heterodimer and acts through the adaptor protein FAM59A in breast cancer cells.

Conservation of protein abundance patterns reveals the regulatory architecture of the EGFR-MAPK pathway

Various genetic mutations associated with cancer are known to alter cell signaling, but it is not clear whether they dysregulate signaling pathways by altering the abundance of pathway proteins. Using a combination of RNA sequencing and ultrasensitive targeted proteomics, we defined the primary components-16 core proteins and 10 feedback regulators-of the epidermal growth factor receptor (EGFR)-mitogen-activated protein kinase (MAPK) pathway in normal human mammary epithelial cells and then quantified their absolute abundance across a panel of normal and breast cancer cell lines as well as fibroblasts. We found that core pathway proteins were present at very similar concentrations across all cell types, with a variance similar to that of proteins previously shown to display conserved abundances across species. In contrast, EGFR and transcriptionally controlled feedback regulators were present at highly variable concentrations. The absolute abundance of most core proteins was between 50,000 and 70,000 copies per cell, but the adaptors SOS1, SOS2, and GAB1 were found at far lower amounts (2000 to 5000 copies per cell). MAPK signaling showed saturation in all cells between 3000 and 10,000 occupied EGFRs, consistent with the idea that adaptors limit signaling. Our results suggest that the relative stoichiometry of core MAPK pathway proteins is very similar across different cell types, with cell-specific differences mostly restricted to variable amounts of feedback regulators and receptors. The low abundance of adaptors relative to EGFR could be responsible for previous observations that only a fraction of total cell surface EGFR is capable of rapid endocytosis, high-affinity binding, and mitogenic signaling.

Targeted Therapy in Brain Metastases: Ready for Primetime?

Brain metastasis is a serious complication of cancer that causes significant morbidity for patients. Over the last decade, numerous new driver somatic mutations have been recognized and targeted therapies are changing the landscape of treatment in lung cancer, breast cancer, and melanoma, which are also the three most common cancers that result in brain metastases. The common actionable mutations include the EGFR mutation and anaplastic lymphoma kinase (ALK) translocations in non-small cell lung cancer, the HER2 mutation in breast cancer, and the BRAF mutation in melanoma. However, most of the early trials with targeted agents excluded patients with brain metastases. With a better understanding of the biology, several recent trials of targeted therapy that focus on brain metastases have been reported and others are ongoing. Novel agents with better penetration across the blood-brain barrier are currently being investigated for patients with brain metastases. In this review, we discuss the current state of use and future directions of targeted therapies in brain metastases.

Spatio-Temporal Parameters of Endosomal Signaling in Cancer: Implications for New Treatment Options

The endo/lysosomal system in cells provides membranous platforms to assemble specific signaling complexes and to terminate signal transduction, thus, is essential for physiological signaling. Endocytic organelles can significantly extend signaling of activated cell surface receptors, and may additionally provide distinct locations for the generation of specific signaling outputs. Failures of regulation at different levels of endocytosis, recycling, degradation as well as aberrations in specific endo/lysosomal signaling pathways, such as mTORC1, might lead to different diseases including cancer. Therefore, a better understanding of spatio‐temporal compartmentalization of sub‐cellular signaling might provide an opportunity to interfere with aberrant signal transduction in pathological processes by novel combinatorial therapeutic approaches. J. Cell. Biochem. 117: 836–843, 2016. © 2015 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals Inc.

Exosome mediated communication within the tumor microenvironment

It is clear that exosomes (endosome derived vesicles) serve important roles in cellular communication both locally and distally and that the exosomal process is abnormal in cancer. Cancer cells are not malicious cells; they are cells that represent 'survival of the fittest' at its finest. All of the mutations, abnormalities, and phenomenal adaptations to a hostile microenvironment, such as hypoxia and nutrient depletion, represent the astute ability of cancer cells to adapt to their environment and to intracellular changes to achieve a single goal - survival. The aberrant exosomal process in cancer represents yet another adaptation that promotes survival of cancer. Cancer cells can secrete more exosomes than healthy cells, but more importantly, the content of cancer cells is distinct. An illustrative distinction is that exosomes derived from cancer cells contain more microRNA than healthy cells and unlike exosomes released from healthy cells, this microRNA can be associated with the RNA-induced silencing complex (RISC) which is required for processing mature and biologically active microRNA. Cancer derived exosomes have the ability to transfer metastatic potential to a recipient cell and cancer exosomes function in the physical process of invasion. In this review we conceptualize the aberrant exosomal process (formation, content selection, loading, trafficking, and release) in cancer as being partially attributed to cancer specific differences in the endocytotic process of receptor recycling/degradation and plasma membrane remodeling and the function of the endosome as a signaling entity. We discuss this concept and, to advance comprehension of exosomal function in cancer as mediators of communication, we detail and discuss exosome biology, formation, and communication in health and cancer; exosomal content in cancer; exosomal biomarkers in cancer; exosome mediated communication in cancer metastasis, drug resistance, and interfacing with the immune system; and discuss the therapeutic manipulation of exosomal content for cancer treatment including current clinical trials of exosomal therapeutics. Often referred to as cellular nanoparticles, understanding exosomes, and how cancer cells use these cellular nanoparticles in communication is at the cutting edge frontier of advancing cancer biology.

Activation of EGFR, HER2 and HER3 by neurotensin/neurotensin receptor 1 renders breast tumors aggressive yet highly responsive to lapatinib and metformin in mice

A present challenge in breast oncology research is to identify therapeutical targets which could impact tumor progression. Neurotensin (NTS) and its high affinity receptor (NTSR1) are up regulated in 20% of breast cancers, and NTSR1 overexpression was shown to predict a poor prognosis for 5 year overall survival in invasive breast carcinomas. Interactions between NTS and NTSR1 induce pro-oncogenic biological effects associated with neoplastic processes and tumor progression. Here, we depict the cellular mechanisms activated by NTS, and contributing to breast cancer cell aggressiveness. We show that neurotensin (NTS) and its high affinity receptor (NTSR1) contribute to the enhancement of experimental tumor growth and metastasis emergence in an experimental mice model. This effect ensued following EGFR, HER2, and HER3 over-expression and autocrine activation and was associated with an increase of metalloproteinase MMP9, HB-EGF and Neuregulin 2 in the culture media. EGFR over expression ensued in a more intense response to EGF on cellular migration and invasion. Accordingly, lapatinib, an EGFR/HER2 tyrosine kinase inhibitor, as well as metformin, reduced the tumor growth of cells overexpressing NTS and NTSR1. All cellular effects, such as adherence, migration, invasion, altered by NTS/NTSR1 were abolished by a specific NTSR1 antagonist. A strong statistical correlation between NTS-NTSR1-and HER3 (p< 0.0001) as well as NTS-NTSR1-and HER3- HER2 (p< 0.001) expression was found in human breast tumors. Expression of NTS/NTSR1 on breast tumoral cells creates a cellular context associated with cancer aggressiveness by enhancing epidermal growth factor receptor activity. We propose the use of labeled NTS/NTSR1 complexes to enlarge the population eligible for therapy targeting HERs tyrosine kinase inhibitor or HER2 overexpression.

Neurotensin (NTS) and its receptor (NTSR1) causes EGFR, HER2 and HER3 over-expression and their autocrine/paracrine activation in lung tumors, confirming responsiveness to erlotinib

Alterations in the signaling pathways of epidermal growth factor receptors (HERs) are associated with tumor aggressiveness. Neurotensin (NTS) and its high affinity receptor (NTSR1) are up regulated in 60% of lung cancers. In a previous clinical study, NTSR1 overexpression was shown to predict a poor prognosis for 5 year overall survival in a selected population of stage I lung adenocarcinomas treated by surgery alone. In a second study, shown here, the frequent and high expression of NTSR1 was correlated with a pejorative prognosis in 389 patients with stage I to III lung adenocarcinoma, and was an independent prognosis marker. Interactions between NTS and NTSR1 induce pro-oncogenic biological effects associated with neoplastic processes and tumor progression. Here we highlight the cellular mechanisms activated by Neurotensin (NTS) and its high affinity receptor (NTSR1) contributing to lung cancer cell aggressiveness. We show that the NTS autocrine and/or paracrine regulation causes EGFR, HER2, and HER3 over-expression and activation in lung tumor cells. The EGFR and HER3 autocrine activation is mediated by MMP1 activation and EGF "like" ligands (HB-EGF, Neuregulin 1) release. By establishing autocrine and/or paracrine NTS regulation, we show that tumor growth is modulated according to NTS expression, with a low growth rate in those tumors that do not express NTS. Accordingly, xenografted tumors expressing NTS and NTSR1 showed a positive response to erlotinib, whereas tumors void of NTSR1 expression had no detectable response. This is consistent with the presence of a NTS autocrine loop, leading to the sustained activation of EGFR and responsible for cancer aggressiveness. We propose the use of NTS/NTSR1 tumor expression, as a biomarker for the use of EGFR tyrosine kinase inhibitors in patients lacking EGFR mutation.