The upgraded role of HER3 and HER4 receptors in breast cancer

HER3 receptor and its role in the therapeutic management of metastatic breast cancer

Metastatic breast cancer (mBC) poses a significant threat to women's health and is a major cause of malignant neoplasms in women. Human epidermal growth factor receptor (HER)3, an integral member of the ErbB/HER receptor tyrosine kinase family, is a crucial activator of the phosphoinositide-3 kinase/protein kinase B signaling pathway. HER3 overexpression significantly contributes to the development of resistance to drugs targeting other HER receptors, such as HER2 and epidermal growth factor receptors, and plays a crucial role in the onset and progression of mBC. Recently, numerous HER3-targeted therapeutic agents, such as monoclonal antibodies (mAbs), bispecific antibodies (bAbs), and antibody-drug conjugates (ADCs), have emerged. However, the efficacy of HER3-targeted mAbs and bAbs is limited when used individually, and their combination may result in toxic adverse effects. On the other hand, ADCs are cytotoxic to cancer cells and can bind to target cells through antibodies, which highlights their use in targeted HER3 therapy for mBC. This review provides an overview of recent advancements in HER3 research, historical initiatives, and innovative approaches in targeted HER3 therapy for metastatic breast cancer. Evaluating the advantages and disadvantages of current methods may yield valuable insights and lessons.

The role of the NDRG1 in the pathogenesis and treatment of breast cancer

Breast cancer (BC) is the leading cause of cancer death in women. This disease is heterogeneous, with clinical subtypes being estrogen receptor-α (ER-α) positive, having human epidermal growth factor receptor 2 (HER2) overexpression, or being triple-negative for ER-α, progesterone receptor, and HER2 (TNBC). The ER-α positive and HER2 overexpressing tumors can be treated with agents targeting these proteins, including tamoxifen and pertuzumab, respectively. Despite these treatments, resistance and metastasis are problematic, while TNBC is challenging to treat due to the lack of suitable targets. Many studies examining BC and other tumors indicate a role for N-myc downstream-regulated gene-1 (NDRG1) as a metastasis suppressor. The ability of NDRG1 to inhibit metastasis is due, in part, to the inhibition of the initial step in metastasis, namely the epithelial-to-mesenchymal transition. Paradoxically, there are also reports of NDRG1 playing a pro-oncogenic role in BC pathogenesis. The oncogenic effects of NDRG1 in BC have been reported to relate to lipid metabolism or the mTOR signaling pathway. The molecular mechanism(s) of how NDRG1 regulates the activity of multiple signaling pathways remains unclear. Therapeutic strategies that up-regulate NDRG1 have been developed and include agents of the di-2-pyridylketone thiosemicarbazone class. These compounds target oncogenic drivers in BC cells, suppressing the expression of multiple key hormone receptors including ER-α, progesterone receptor, androgen receptor, and prolactin receptor, and can also overcome tamoxifen resistance. Considering the varying role of NDRG1 in BC pathogenesis, further studies are required to examine what subset of BC patients would benefit from pharmacopeia that up-regulate NDRG1.

Mechanisms of Endocrine Resistance in Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) breast cancer (BC) accounts for approximately 70% of all breast invasive tumors. Endocrine therapy (ET) represents the standard treatment for HR + BC. Most patients, however, eventually develop resistance to ET, which limits their effectiveness and poses a major challenge for the management of HR + BC. Several mechanisms that contribute to ET resistance have been described. One of the most common mechanisms is the upregulation of alternative signaling pathways that can bypass estrogen dependency, such as activation of the PI3K/Akt/mTOR as well as mitogen-activated protein kinase (MAPK) and the insulin-like growth factor 1 receptor (IGF-1R) pathways. Another common mechanism of endocrine resistance is the acquisition of activating mutations of ESR1, which encodes for the estrogen receptor, that lead to structural changes of the receptor, prevent the binding to anti-estrogen drugs and result in constitutive activation of the receptor, even in the absence of estrogens. Epigenetic changes, such as DNA methylation and histone modifications, can also contribute to ET resistance by altering the expression of genes that are involved in estrogen signaling. Understanding the mechanisms of resistance to ET is crucial for the development of new therapies that can overcome resistance and improve outcomes for patients with HR + BC.

Beyond HER2: Targeting the ErbB receptor family in breast cancer

Targeting the HER2 oncogene represents one of the greatest advances in the treatment of breast cancer. HER2 is one member of the ERBB-receptor family, which includes EGFR (HER1), HER3 and HER4. In the presence or absence of underling genomic aberrations such as mutations or amplification events, intricate interactions between these proteins on the cell membrane lead to downstream signaling that encourages cancer growth and proliferation. In this Review, we contextualize efforts to pharmacologically target the ErbB receptor family beyond HER2, with a focus on EGFR and HER3. Preclinical and clinical efforts are synthesized. We discuss successes and failures of this approach to date, summarize lessons learned, and propose a way forward that invokes new therapeutic modalities such as antibody drug conjugates (ADCs), combination strategies, and patient selection through rational biomarkers.

The landscape of chimeric antigen receptor T cell therapy in breast cancer: Perspectives and outlook

Chimeric antigen receptor-T (CAR-T) cell therapy is a revolutionary adoptive cell therapy, which could modify and redirect T cells to specific tumor cells. Since CAR-T cell therapy was first approved for B cell-derived malignancies in 2017, it has yielded unprecedented progress in hematological tumors and has dramatically reshaped the landscape of cancer therapy in recent years. Currently, cumulative evidence has demonstrated that CAR-T cell therapy could be a viable therapeutic strategy for solid cancers. However, owing to the immunosuppressive tumor microenvironment (TME) and heterogenous tumor antigens, the application of CAR-T cell therapy against solid cancers requires circumventing more challenging obstacles. Breast cancer is characterized by a high degree of invasiveness, malignancy, and poor prognosis. The review highlights the underlying targets of CAR-T cell therapy in breast cancer, summarizes the challenges associated with CAR-T cell therapy, and proposes the strategies to overcome these challenges, which provides a novel approach to breast cancer treatment.

Clinical development of antibody-drug conjugates in triple negative breast cancer: Can we jump higher?

INTRODUCTION

Triple negative breast cancer (TNBC) is an aggressive BC subtype, associated with higher rates of relapse in the primary disease setting and shorter overall survival upon metastatic relapse. The advent of antibody-drug conjugates (ADC), able to deliver selectively potent chemotherapeutic agents, has demonstrated promising clinical activity, with the first approval of an ADC, i.e. Sacituzumab Govitecan, in the metastatic setting. The main scope of this paper is to provide the most recent data indicating the promise of this novel class of drugs, as potential tools to improve clinical outcomes of patients diagnosed with TNBC.

AREAS COVERED

In this article, upon review of the main characteristics of TNBC, and those of ADCs, an overview of the data from clinical trials assessing ADCs in TNBC will be provided, including those that led to the first approval of such a drug for patients with metastatic disease; furthermore, several other ADCs targeting different proteins (over)expressed by TNBC undergo clinical development. Combinations of ADCs with other targeted agents are discussed; the most pertinent considerations for improving the chances of successful clinical development of ADCs in TNBC are provided.

EXPERT OPINION

ADCs are a potent class of targeted anticancer assets, with demonstrated efficacy against metastatic TNBC. Such assets could further improve clinical outcomes of patients with TNBC, and successful development depends upon: i) successful triaging of patients with the right ADC, ii) technical optimization of ADCs to maximize the efficacy, while reducing toxicity, and iii) assess rationally chosen combinations with synergistic antitumor activity and acceptable safety profile.

Small Molecule Compounds of Natural Origin Target Cellular Receptors to Inhibit Cancer Development and Progression

Receptors are macromolecules that transmit information regulating cell proliferation, differentiation, migration and apoptosis, play key roles in oncogenic processes and correlate with the prognoses of cancer patients. Thus, targeting receptors to constrain cancer development and progression has gained widespread interest. Small molecule compounds of natural origin have been widely used as drugs or adjuvant chemotherapeutic agents in cancer therapies due to their activities of selectively killing cancer cells, alleviating drug resistance and mitigating side effects. Meanwhile, many natural compounds, including those targeting receptors, are still under laboratory investigation for their anti-cancer activities and mechanisms. In this review, we classify the receptors by their structures and functions, illustrate the natural compounds targeting these receptors and discuss the mechanisms of their anti-cancer activities. We aim to provide primary knowledge of mechanistic regulation and clinical applications of cancer therapies through targeting deregulated receptors.

Landscape of Epidermal Growth Factor Receptor Heterodimers in Brain Metastases

Simple Summary

HER2+ breast cancer patients are treated with agents that tag HER2+ tumour cells for elimination by the immune system, down-modulate HER2 activity and/or block the formation of HER2 dimers, including the neuregulin-1 receptor, HER2-HER3. HER2-targeted therapies prolong survival by lowering the risk of relapse, but do not prevent brain metastases. The reasons for this are not fully understood. We quantified HER2-HER3 dimers in 203 brain metastases, and 34 primary breast tumour samples. Dimer frequency was relatively high in brain metastases from breast, ovarian, lung and kidney cancers, and in brain metastases compared to patient-matched breast tumours; but did not reliably correlate with HER2/HER3 expression or activation. In in vitro experiments, pertuzumab failed to suppress HER2-HER3 dimers in HER2+ breast cancer cells provided with a saturating concentration of neuregulin-1. These findings may provide insights about the differences in intracranial versus extracranial efficacy of HER2-targeted therapies.

Abstract

HER2+ breast cancer patients have an elevated risk of developing brain metastases (BM), despite adjuvant HER2-targeted therapy. The mechanisms underpinning this reduced intracranial efficacy are unclear. We optimised the in situ proximity ligation assay (PLA) for detection of the high-affinity neuregulin-1 receptor, HER2-HER3 (a key target of pertuzumab), in archival tissue samples and developed a pipeline for high throughput extraction of PLA data from fluorescent microscope image files. Applying this to a large BM sample cohort (n = 159) showed that BM from breast, ovarian, lung and kidney cancers have higher HER2-HER3 levels than other primary tumour types (melanoma, colorectal and prostate cancers). HER2 status, and tumour cell membrane expression of pHER2(Y^1221/1222) and pHER3(Y¹²²²) were positively, but not exclusively, associated with HER2-HER3 frequency. In an independent cohort (n = 78), BM had significantly higher HER2-HER3 levels than matching primary tumours (p = 0.0002). For patients who had two craniotomy procedures, HER2-HER3 dimer levels were lower in the consecutive lesion (n = 7; p = 0.006). We also investigated the effects of trastuzumab and pertuzumab on five different heterodimers in vitro: HER2-EGFR, HER2-HER4, HER2-HER3, HER3-HER4, HER3-EGFR. Treatment significantly altered the absolute frequencies of individual complexes in SKBr3 and/or MDA-MB-361 cells, but in the presence of neuregulin-1, the overall distribution was not markedly altered, with HER2-HER3 and HER2-HER4 remaining predominant. Together, these findings suggest that markers of HER2 and HER3 expression are not always indicative of dimerization, and that pertuzumab may be less effective at reducing HER2-HER3 dimerization in the context of excess neuregulin.

The Yin and Yang of ERBB4: Tumor Suppressor and Oncoprotein

ERBB4 (HER4) is a member of the ERBB family of receptor tyrosine kinases, a family that includes the epidermal growth factor receptor (EGFR/ERBB1/HER1), ERBB2 (Neu/HER2), and ERBB3 (HER3). EGFR and ERBB2 are oncoproteins and validated targets for therapeutic intervention in a variety of solid tumors. In contrast, the role that ERBB4 plays in human malignancies is ambiguous. Thus, here we review the literature regarding ERBB4 function in human malignancies. We review the mechanisms of ERBB4 signaling with an emphasis on mechanisms of signaling specificity. In the context of this signaling specificity, we discuss the hypothesis that ERBB4 appears to function as a tumor suppressor protein and as an oncoprotein. Next, we review the literature that describes the role of ERBB4 in tumors of the bladder, liver, prostate, brain, colon, stomach, lung, bone, ovary, thyroid, hematopoietic tissues, pancreas, breast, skin, head, and neck. Whenever possible, we discuss the possibility that ERBB4 mutants function as biomarkers in these tumors. Finally, we discuss the potential roles of ERBB4 mutants in the staging of human tumors and how ERBB4 function may dictate the treatment of human tumors. SIGNIFICANCE STATEMENT: This articles reviews ERBB4 function in the context of the mechanistic model that ERBB4 homodimers function as tumor suppressors, whereas ERBB4-EGFR or ERBB4-ERBB2 heterodimers act as oncogenes. Thus, this review serves as a mechanistic framework for clinicians and scientists to consider the role of ERBB4 and ERBB4 mutants in staging and treating human tumors.

Development of recombinant biomimetic nano-carrier for targeted gene transfer to HER3 positive breast cancer

Human epidermal growth factor receptor 3 (HER3) has rapidly gained much attention as a promising target for cancer treatment. The increasing recognition of HER3 roles in a number of HER family-driven cancers has led to studies aimed at targeting this receptor and developing HER3-targeted platforms with the ability to deliver therapeutic genes. We have previously indicated that the flexible linker and one unit of RALA in affibody-based platform could target HER3 and deliver its cargo. Based on the previous finding, in a new class of affibody-based platforms, we used two different linkers and RALA units and then compared their effectiveness on targeting and delivering specified genes to HER3 positive cells. Our results clearly showed that our biopolymeric platforms can successfully condense DNA into nanoparticles and object the overexpressed HER3 receptors and then transfer specific genes. Our affibody-based platform containing a rigid linker and one RALA unit presents an adequate transfection efficacy and low toxicity (based on MTT and apoptosis assays), however, the platform containing two RALA units and a flexible linker demonstrated high transfection efficacy while having modest toxicity in HER3 positive breast cancer cells. This may pave the way for further innovative applications of recombinant biopolymer when stable and economical productions need to be definitely considered.

Potent dual EGFR/Her4 tyrosine kinase inhibitors containing novel (1,2-dithiolan-4-yl)acetamides

Modifications at C₆ and C₇ positions of 3-cyanoquinolines 6 and 7 led to potent inhibitors of the ErbB family of kinases particularly against EGFR^WT and Her4 enzymes in the radioisotope filter binding assay. The lead (4, SAB402) displayed potent dual biochemical activities with EGFR^WT/Her4 IC₅₀ ratio of 80 due to its potent inhibition of Her4 activity (IC₅₀ 0.03 nM), however, the selectivity towards activating mutations (EGFR^L858R, EGFR^ex19del) was decreased. Inhibitor 4 also exhibited excellent growth inhibition in seven different cancer types and reduced cell viability in female NMRI nude mice in the intraperitoneally implanted hollow fibers which have been loaded with MOLT-4 (leukemia) and NCI-H460 (NSCLC) cells in a statistically significant manner.

Clinicopathologic significance of nuclear HER4 and phospho-YAP(S127) in human breast cancers and matching brain metastases

Background

Human epidermal growth factor receptor-4 (HER4) and yes-associated protein-1 (YAP) are candidate therapeutic targets in oncology. YAP's transcriptional coactivation function is modulated by the HER4 intracellular domain (HER4-ICD) in vitro, but the clinical relevance of this has not been established. This study investigated the potential for targeting the HER4-YAP pathway in brain metastatic breast cancer.

Methods

We performed immuno-phenotypic profiling of pathway markers in a consecutive breast cancer series with 25 years of clinical follow up (n = 371), and patient-matched breast and metastatic brain tumours (n = 91; 30 pairs).

Results

Membrane localisation of phospho-HER4 [pHER4(Y¹¹⁶²)] was infrequent in primary breast cancer, but very frequent in brain metastases (5.9% versus 75% positive), where it was usually co-expressed with pHER3(Y¹²⁸⁹) (p < 0.05). The presence of YAP in tumour cell nuclei was associated directly with nuclear pERK5(T²¹⁸/Y²¹⁰) (p = 0.003). However, relationships with disease-specific survival depended on oestrogen receptor (ER) status. Nuclear pYAP(S¹²⁷) was associated with smaller, good prognostic ER+ breast tumours (log-rank hazard-ratio 0.53; p = 9.6E^-03), but larger, poor prognostic triple-negative cancers (log-rank hazard-ratio 2.78; p = 1.7E^-02), particularly when co-expressed with nuclear HER4-ICD (p = 0.02). This phenotype was associated with stemness and mitotic instability markers (vimentin, SOX9, ID1, SPAG5, TTK, geminin; p < 0.05). YAP expression in brain metastases was higher than matched primary tumours; specifically, nuclear pYAP(S¹²⁷) in ER-negative cases (p < 0.05). Nuclear YAP was detected in ~70% of ER-negative, HER4-activated brain metastases.

Discussion

Our findings suggest that the canonical-mechanism where Hippo pathway-mediated phosphorylation of YAP ostensibly excludes it from the nucleus is dysfunctional in breast cancer. The data are consistent with pYAP(S¹²⁷) having independent transcriptional functions, which may include transducing neuregulin signals in brain metastases. Consistent with mechanistic studies implicating it as an ER co-factor, nuclear pYAP(S¹²⁷) associations with breast cancer clinical outcomes were dependent on ER status.

Conclusion

Preclinical studies investigating HER4 and nuclear YAP combination therapy strategies are warranted.

Combined HER3-EGFR score in triple-negative breast cancer provides prognostic and predictive significance superior to individual biomarkers

Epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 3 (HER3) have been investigated as triple-negative breast cancer (TNBC) biomarkers. Reduced EGFR levels can be compensated by increases in HER3; thus, assaying EGFR and HER3 together may improve prognostic value. In a multi-institutional cohort of 510 TNBC patients, we analyzed the impact of HER3, EGFR, or combined HER3-EGFR protein expression in pre-treatment samples on breast cancer-specific and distant metastasis-free survival (BCSS and DMFS, respectively). A subset of 60 TNBC samples were RNA-sequenced using massive parallel sequencing. The combined HER3-EGFR score outperformed individual HER3 and EGFR scores, with high HER3-EGFR score independently predicting worse BCSS (Hazard Ratio [HR] = 2.30, p = 0.006) and DMFS (HR = 1.78, p = 0.041, respectively). TNBCs with high HER3-EGFR scores exhibited significantly suppressed ATM signaling and differential expression of a network predicted to be controlled by low TXN activity, resulting in activation of EGFR, PARP1, and caspases and inhibition of p53 and NFκB. Nuclear PARP1 protein levels were higher in HER3-EGFR-high TNBCs based on immunohistochemistry (p = 0.036). Assessing HER3 and EGFR protein expression in combination may identify which adjuvant chemotherapy-treated TNBC patients have a higher risk of treatment resistance and may benefit from a dual HER3-EGFR inhibitor and a PARP1 inhibitor.

Negative feedback regulation of ErbB4 tyrosine kinase activity by ERK-mediated non-canonical phosphorylation

ErbB4 receptor tyrosine kinase has four different isoforms that are classified based on variants in the extracellular juxtamembrane domain (JM-a and JM-b) and the C-terminal region (CYT-1 and CYT-2). Here, we used the JM-b/CYT-1 isoform to investigate the roles of serine/threonine phosphorylation in MEK-ERK-dependent feedback inhibition. TPA as an activator of the ERK pathway markedly induced ErbB4 phosphorylation at Thr-674, the conserved common feedback site in the intracellular JM domain, which resulted in the downregulation of tyrosine autophosphorylation. We also identified Ser-1026 as an ErbB4-specific ERK target site in the CYT-1 region. Moreover, double mutations (Thr-674/Ser-1026 to Ala) significantly upregulated ErbB4 activation, indicating that Thr-674 and Ser-1026 are cooperatively involved in negative feedback regulation. Given the fact that ErbB4 mutation is one of the most common genetic alterations in melanoma cells, we demonstrated that a typical oncogenic ErbB4 mutant was resistant to the negative feedback regulation to maintain a highly active status of tyrosine kinase activity. Together, these findings indicate that feedback mechanisms are key switches determining oncogenic potentials of ErbB receptor kinases.

HER3 targeting potentiates growth suppressive effects of the PI3K inhibitor BYL719 in pre-clinical models of head and neck squamous cell carcinoma

BYL719 is a PI3K inhibitor that has demonstrated efficacy in the treatment of head and neck squamous cell carcinoma. BYL719 exerts its therapeutic effect by suppressing AKT and other proliferative signaling mechanisms. Despite PI3K inhibition and AKT suppression, residual activity of protein S6, a core marker of proliferative activation, has been observed. HER3, either via dimerization or activation by its ligand neurgeulin (NRG), is known to activate PI3K. Thus, we hypothesized that co-targeting HER3 and PI3K would lead to greater suppression of the PI3K-AKT signaling pathway and greater tumor suppression than with BYL719 alone. We investigated biochemical expression and activation of the HER3-PI3K-AKT-S6 pathway in HNSCC cell lines and patient-derived xenografts (PDXs). Antitumor effects of HER3 and PI3K inhibitors alone and in combination were evaluated in cell culture and murine models. Treatment of HNSCC cell lines with BYL719 significantly reduced AKT activation and suppressed tumor growth. However, S6 was persistently activated despite suppression of AKT. Combination treatment with KTN3379, a monoclonal antibody targeted against HER3, and BYL719 led to enhanced suppression of in vitro and in vivo cancer growth and durable suppression of AKT and S6. Therefore, inhibition of HER3 with KTN3379 enhanced the effects of PI3K inhibition in pre-clinical HNSCC models. These data support co-targeting HER3 and PI3K for the treatment of HSNCC.

Expressions and clinical significance of HER4 and CD44 in sinonasal mucosal malignant melanoma

Sinonasal mucosal malignant melanoma (SNMMM) is a rare disease. The aim of this study was to investigate the expressions of HER4 and CD44 in human SNMMM tissues and their relationship with the clinicopathological features and prognosis of patients. In total, 64 paraffin-embedded samples of SNMMM treated in our hospital from 29 December 1999 to 24 June 2011 were collected. HER4 and CD44 were detected in the tissues of SNMMM by immunohistochemistry. The differences in the HER4 and CD44 expressions in the tissues were evaluated and matched with clinicopathological parameters and the survival rate, respectively. The positive rates of the HER4 and CD44 expressions were 70.3 and 65.6%, respectively; the positive expression of HER4 was correlated with a positive expression of CD44 (P<0.05). The positive expression of HER4 was correlated with the prognosis of SNMMM patients (P<0.05). There was no significant correlation between a positive expression of CD44 and the prognosis of patients (P>0.05). The expressions of HER4 and CD44 were not significantly correlated with sex, age, pigment, tumor site, etc. (P>0.05). Our results further emphasize a correlation between HER4 and CD44 expressions in SNMMM tissues and point out that a positive HER4 expression might be an important factor in valuing the prognosis of patients with SNMMM.

Evaluation of the prognostic value of all four HER family receptors in patients with metastatic breast cancer treated with trastuzumab: A Hellenic Cooperative Oncology Group (HeCOG) study

In the current study, we performed a complete analysis, with four different methods, of all four HER family receptors, in a series of patients with metastatic breast cancer treated with trastuzumab-based regimens and evaluated their prognostic value. Formalin-fixed paraffin-embedded tumor tissue samples were collected from 227 patients, considered to be HER2-positive when assessed at the local laboratories. We evaluated gene amplification, copy number variations (CNVs), mRNA and protein expression of all four HER family members. In addition, our analysis included the evaluation of several other factors by immunohistochemistry (IHC), such as pHER2^Tyr1221/1222, pHER2^Tyr877 and PTEN. Central review of HER2 status by IHC and fluorescence in situ hybridization revealed that of the 227 patients, only 139 (61.2%) were truly HER2-positive. Regarding the 191 patients treated with trastuzumab as first-line therapy, median time to progression (TTP) was 15.3 and 10.4 months for HER2-positive and HER2-negative participants, respectively, whereas median survival was 50.4 and 38.1 months, respectively. In HER2-positive patients, high HER3 mRNA expression was of favorable prognostic significance for TTP and survival (HR = 0.43, 95% CI 0.21–0.88, Wald’s p = 0.022 and HR = 0.43, 95% CI 0.21–0.88, p = 0.021, respectively), while EGFR copy gain and EGFR protein expression were associated with higher risk for disease progression in HER2-negative patients (HR = 3.53, 95% CI 1.19–10.50, p = 0.023 and HR = 3.37, 95% CI 1.12–10.17, p = 0.031, respectively). Positive HER3 protein expression was a favorable factor for TTP in HER2-negative patients (HR = 0.43, 95% CI 0.22–0.84, p = 0.014). In the multivariate analysis, only EGFR copy gain retained its prognostic significance for TTP in the HER2-negative population (HR = 3.96, 95% CI 1.29–12.16, p = 0.016), while high HER3 mRNA expression retained its favorable prognostic significance for TTP in the HER2-positive subgroup (HR = 0.47, 95% CI 0.23–0.99, p = 0.048). The present study suggests that EGFR copy gain represents a negative prognostic factor for TTP in HER2-negative patients with metastatic breast cancer treated with trastuzumab. In addition, high HER3 mRNA expression appears to be of favorable prognostic significance for TTP in HER2-positive patients. Given the small number of patients included in the current analysis and the retrospective nature of the study, our findings should be validated in larger cohorts.

Silencing human epidermal growth factor receptor-3 radiosensitizes human luminal A breast cancer cells

Endocrine therapy and radiotherapy are the main treatments for luminal A breast cancer. However, drug and radiotherapy resistance could occur during long‐term treatment, leading to local recurrence and distant metastasis. Some studies have found that drug resistance might be related to human epidermal growth factor receptor‐3 (HER3) overexpression. However, whether HER3 plays a role in radiotherapy resistance is unknown. The purpose of this study is to elucidate the effect of HER3 in radiotherapy and to assess whether HER3 could be a potential target for radiosensitivity. We used retroviruses to construct stable low expression of HER3 in MCF‐7 and ZR75‐1cells. The CCK‐8 assay was used to observe proliferation. Colony‐forming assay was used to detect radiosensitivity. Flow cytometry was used to observe the cell cycle and apoptosis. Immunofluorescence assay was used to detect the number of γH2AX foci in the nucleus with or without ionizing radiation (IR). Western blot analysis was used to verify the change of relative proteins. Nude mice were used to observe tumor growth in vivo. In our study, silencing HER3 reduced cell proliferation and clone formation ability after IR, so silencing HER3 increased the sensitivity of luminal A breast cancer cells to radiotherapy. In terms of radiosensitivity mechanisms, it is suggested that the silencing of HER3 enhanced IR‐induced DNA damage, reduced DNA repair, and increased apoptosis and G₂/M arrest. In addition, silencing HER3 combined with IR clearly inhibited the transplanted tumor growth in vivo. Therefore, we concluded that HER3 played a role in radiotherapy resistance. Silencing HER3 increased the radiosensitivity of luminal A breast cancer cells and HER3 could be a potential target for radiosensitivity.

Synergistic Targeting HER2 and EGFR with Bivalent Aptamer-siRNA Chimera Efficiently Inhibits HER2-Positive Tumor Growth

HER2 overexpression is identified on 20–30% breast cancer and other cancers at different levels. Although HER2 targeted monoclonal antibody combined with chemical drugs has shown improved outcomes in HER2 expressing patients, drug resistance and toxicity have limited their efficacy. To overcome drug resistance, cotargeting  multiple HER receptors was proven to be effective. EGFR/HER2 dimerization can active PI3K/AKT pathway, and resistance to HER2-targeted drugs is associated with upregulation of EGFR. Here, we developed a novel HER2/EGFR targeted nucleic acid therapeutic to address current drug limits. The new therapeutic is constructed by fusing HER2 aptamer-EGFR siRNA sense strand with HER2 aptamer-EGFR siRNA antisense strand into one molecule: a bivalent HER2 aptamer-EGFR siRNA aptamer chimera (HEH). In breast cancer cell lines, HEH can be selectively taken up into HER2 expressing cells and successfully silence EGFR gene and down regulate HER2 expression. In breast cancer xenograft models, HEH is capable of triggering cell apoptosis, decreasing HER2 and EGFR expression, and suppressing tumor growth. The therapeutic efficacy of HEH is superior to HER2 aptamer only, which suggests that HEH has synergistic effect by targeting HER2 and EGFR. This study demonstrated that HEH has great potential as a new HER2 targeted drug to address toxicity and resistance of current drugs and may provide a cure for many HER2 positive cancers.

HDAC6 inhibitor TST strengthens the antiproliferative effects of PI3K/mTOR inhibitor BEZ235 in breast cancer cells via suppressing RTK activation

NVP-BEZ235 (BEZ235), an available dual PI3K/mTOR inhibitor, showed antitumor effect and provided a therapy strategy in carcinomas. However, the acquired upregulation of multiple receptor tyrosine kinases (RTKs) by NVP-BEZ235 in tumors limits its clinical efficacy. HDAC6, a class II histone deacetylase, is associated with expressions of multiple RTKs. The aim of this study was to detect whether co-treatment with HDAC6 inhibitor Tubastatin A (TST) would enhance the anticancer effects of BEZ235 in breast cancer cells. In this study, we described that treatment of breast cancer cell lines (T47D, BT474, and MDA-MB-468) with BEZ235 significantly triggered PI3K/mTOR signaling inactivation and increased multiple RTK expression, including EGFR, HER2, HER3, IGF-1 receptor, insulin receptor, and their phosphorylation levels. The adding of TST destabilized these RTKs in those breast cancer cells. Co-treatment with BEZ235 and TST reduced cell proliferative rate by strengthening Akt inactivation. In addition, the combination of these two drugs also cooperatively arrested cell cycle and DNA synthesis. In conclusion, the co-treatment with PI3K/mTOR inhibitor BEZ235 and HDAC6 inhibitor TST displayed additive antiproliferative effects on breast cancer cells through inactivating RTKs and established a rationable combination therapy to treat breast cancer.

Subtyping Of Triple Negative Breast Carcinoma On The Basis Of RTK Expression

Background: "Triple-negative breast cancers" (TNBC) comprise a heterogeneous group of about 15% of invasive BCs lacking the expression of estrogen and progesterone receptors (ER, PR) and the expression of HER2 (ERBB2) and are therefore no established candidates for targeted treatment options in BC, i.e., endocrine and anti-HER2 therapy. The aim of the present study was to use gene expression profiling and immunohistochemical (IHC) characterization to identify receptor tyrosine kinase (RTK) profiles that would allow patient stratification for the purposes of target-oriented personalized tumor therapy in TNBC. Methods: Twenty-nine cases of TNBC selected according to routine diagnostic IHC/cytogenetic criteria were examined by reverse transcription polymerase chain reaction (RT-PCR). RTK mRNA expression profiles were generated for a total of 31 tumor-relevant biomarkers, mainly belonging to the IGF- and EGF-receptor families but also including biomarkers related to downstream signaling. Protein expression of selected biomarkers was investigated by IHC. Results: Hierarchical cluster analysis revealed a dichotomous differentiation pattern amongst TNBCs. A significant difference in gene expression was observed for 16 of the 31 RTK-associated tumor relevant biomarkers between the two newly identified TNBC subgroups. The findings were verified at the posttranslational level by the IHC data. The RTKs HER4, IGF-1R and IGF-2R and the hormone receptors ER and PR below the IHC detection limit play a central role in the differentiation of the two TNBC subgroups. Observed survival was reported as Kaplan-Meier estimates and point towards an improved survival of patients with RTK-high with superior three-year survival rate of 100% compared to RTK-low gene signatures with superior three-year survival rate of 60% (log-rank test, p-value = 0.022). Conclusion: Gene-expression and IHC analysis of the EGF and IGF receptor families and biomarkers associated with downstream signaling point to the existence of two distinct TNBC subtypes. The RTKs HER4, IGF-1R, IGF-2R and the hormone receptors ER and PR appear to be of particular importance here. Based on survival analysis the differentiation of TNBC with RTK-high and RTK-low gene signatures seems to be of prognostic relevance. Additionally, correlation analysis of the relationship between RTKs and ER suggests co-regulatory mechanisms that may have potential significance in new therapeutic approaches.

Assessment of Specificity of an Adenovirus Targeted to HER3/4

Gene therapy with viral vectors, such as adenovirus (Ad), targeted to the human epidermal growth factor receptors 3 and 4 (HER3/4) are potentially useful for cancer therapy. Testing the expression of a reporter gene from these viruses in target cells is essential to determine functionality of the targeted virus. A competition assay with a relevant ligand (heregulin, HRG) can provide convincing evidence that blocking binding to the HER3/4 receptor results in decreased reporter gene expression. Labeling individual viruses with a fluorescent molecule allows examination of the targeted virus in specific steps in the infection. Virus internalization into cell lines can be determined using antibody-labeled receptors, and the virus colocalization with receptors can also be visualized. Characterization of a targeted virus in this fashion is important to demonstrate that the targeting of the virus functions in an expected manner, and provides support for larger-scale testing of the virus. Information acquired in these experiments may also be useful to inform and improve on the design of future targeted viruses.

Human epidermal growth factor receptor 3 in head and neck squamous cell carcinomas

Human epidermal growth factor receptor 3 (HER3) is a member of the human epidermal growth factor receptor (HER) family. The main characteristic of HER3 is that it does not possess tyrosine kinase activity, unlike other HERs. The role of HER3 in tumorigenesis has now been recognized, particularly in head and neck squamous cell carcinomas (HNSCCs). Despite conflicting studies, HER3 was found to be overexpressed in HNSCC samples, and correlates with disease progression and poor survival, especially when it is coexpressed with other HERs. HER3 is a significant factor in HNSCC treatment resistance. Indeed, HER3 is a major mechanism described for cetuximab resistance because of modification of epidermal growth factor receptor (EGFR) internalization and by phosphotidylinositol-3-kinase (PI3K)/AKT signaling pathway activation. HER3 also affects resistance to tyrosine kinase inhibitors (TKIs) and thereby promotes treatment escape and radiotherapy resistance by activation of the survival signaling pathway. To counteract this, pharmacologic inhibitors of HER3 are currently in development and could significantly improve HNSCC treatment. © 2016 Wiley Periodicals, Inc. Head Neck 38: E2412-E2418, 2016.

Nuclear HER4 mediates acquired resistance to trastuzumab and is associated with poor outcome in HER2 positive breast cancer

The role of HER4 in breast cancer is controversial and its role in relation to trastuzumab resistance remains unclear. We showed that trastuzumab treatment and its acquired resistance induced HER4 upregulation, cleavage and nuclear translocation. However, knockdown of HER4 by specific siRNAs increased trastuzumab sensitivity and reversed its resistance in HER2 positive breast cancer cells. Preventing HER4 cleavage by a γ-secretase inhibitor and inhibiting HER4 tyrosine kinase activity by neratinib decreased trastuzumab-induced HER4 nuclear translocation and enhanced trastuzumab response. There was also increased nuclear HER4 staining in the tumours from BT474 xenograft mice and human patients treated with trastuzumab. Furthermore, nuclear HER4 predicted poor clinical response to trastuzumab monotherapy in patients undergoing a window study and was shown to be an independent poor prognostic factor in HER2 positive breast cancer. Our data suggest that HER4 plays a key role in relation to trastuzumab resistance in HER2 positive breast cancer. Therefore, our study provides novel findings that HER4 activation, cleavage and nuclear translocation influence trastuzumab sensitivity and resistance in HER2 positive breast cancer. Nuclear HER4 could be a potential prognostic and predictive biomarker and understanding the role of HER4 may provide strategies to overcome trastuzumab resistance in HER2 positive breast cancer.

Intracellular antigens as targets for antibody based immunotherapy of malignant diseases

This review discusses the potential use of intracellular tumor antigens as targets of antibody-based immunotherapy for the treatment of solid tumors. In addition, it describes the characteristics of the intracellular tumor antigens targeted with antibodies which have been described in the literature and have been identified in the authors' laboratory. Finally, the mechanism underlying the trafficking of the intracellular tumor antigens to the plasma membrane of tumor cells are reviewed.

Nodes-and-connections RNAi knockdown screening: identification of a signaling molecule network involved in fulvestrant action and breast cancer prognosis

Although RNA interference (RNAi) knockdown screening of cancer cell cultures is an effective approach to predict drug targets or therapeutic/prognostic biomarkers, interactions among identified targets often remain obscure. Here, we introduce the nodes-and-connections RNAi knockdown screening that generates a map of target interactions through systematic iterations of in silico prediction of targets and their experimental validation. An initial RNAi knockdown screening of MCF-7 human breast cancer cells targeting 6560 proteins identified four signaling molecules required for their fulvestrant-induced apoptosis. Signaling molecules physically or functionally interacting with these four primary node targets were computationally predicted and experimentally validated, resulting in identification of four second-generation nodes. Three rounds of further iterations of the prediction–validation cycle generated third, fourth and fifth generation of nodes, completing a 19-node interaction map that contained three predicted nodes but without experimental validation because of technical limitations. The interaction map involved all three members of the death-associated protein kinases (DAPKs) as well as their upstream and downstream signaling molecules (calmodulins and myosin light chain kinases), suggesting that DAPKs play critical roles in the cytocidal action of fulvestrant. The in silico Kaplan–Meier analysis of previously reported human breast cancer cohorts demonstrated significant prognostic predictive power for five of the experimentally validated nodes and for three of the prediction-only nodes. Immunohistochemical studies on the expression of 10 nodal proteins in human breast cancer tissues not only supported their prognostic prediction power but also provided statistically significant evidence of their synchronized expression, implying functional interactions among these nodal proteins. Thus, the Nodes-and-Connections approach to RNAi knockdown screening yields biologically meaningful outcomes by taking advantage of the existing knowledge of the physical and functional interactions between the predicted target genes. The resulting interaction maps provide useful information on signaling pathways cooperatively involved in clinically important features of the malignant cells, such as drug resistance.

Evaluation of the prognostic significance of HER family mRNA expression in high-risk early breast cancer: a Hellenic Cooperative Oncology Group (HeCOG) validation study

Background

The aim of the study was to evaluate the prognostic ability of the transcriptional profiling of the HER family genes in early breast cancer, as a validation analysis of another previously published HeCOG study.

Methods

RNA was extracted from 663 formalin-fixed paraffin-embedded (FFPE) tumor tissue samples of high-risk early breast cancer patients enrolled in the randomized HE10/00 trial. Relative mRNA expression of all four HER family members was assessed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

Results

In compliance with our previous study, the overall agreement between qRT-PCR and IHC/FISH for HER2 status determination was good (69%). Likewise, the overall concordance between qRT-PCR and IHC for EGFR status was high (81%). In line with our previously reported data, we demonstrated a positive association between HER2 and HER3 mRNA expression. Similarly, mRNA expression of HER3 and HER4 was positively associated with each other and negatively associated with EGFR. Regarding relationships with clinico-pathological parameters, our findings are also in agreement with our previous results. Generally, increased EGFR and HER2 mRNA expression was related to unfavorable, whereas high HER3 and HER4 mRNA expression was associated with favorable clinico-pathological parameters. In univariate analysis, no significant association between EGFR, HER2 and HER3 mRNA expression and overall survival (OS) or disease-free survival (DFS) was demonstrated. However, high EGFR protein expression was associated with significantly shorter OS (log-rank, p = 0.015). In compliance with our previously published data, increased HER4 mRNA expression had a significantly favorable prognostic value in terms of OS (p = 0.044) and DFS (p = 0.047). In multivariate analysis, among all HER receptors, only EGFR protein expression was found to affect OS (Wald’s p = 0.028) and DFS (p = 0.015) independently. Concerning the combined expression of all four HER family receptors, the combination of high EGFR, high HER2, low HER3 and low HER4 mRNA expression was associated with a trend for shorter OS (log-rank, p = 0.065) and significantly worse DFS (p = 0.033), compared with all other co-expression profiles.

Conclusions

These data indicate that qRT-PCR may represent a valid alternative method for evaluating the expression of HER family members in FFPE breast carcinoma tissue samples.

Trial registration

Australian New Zealand Clinical Trials Registry ACTRN12609001036202

Combining lapatinib and pertuzumab to overcome lapatinib resistance due to NRG1-mediated signalling in HER2-amplified breast cancer

Acquired resistance to lapatinib, an inhibitor of EGFR and HER2 kinases, is common. We found that reactivation of EGFR, HER2 and HER3 occurred within 24 hours of lapatinib treatment after their initial dephosphorylation. This was associated with increased expression of NRG1 in cells treated with lapatinib. Exogenous NRG1 partially rescued breast cancer cells from growth inhibition by lapatinib. In addition, both parental and lapatinib-resistant breast cancer cells were sensitive to SGP1, which inhibits binding of NRG1 and other HER3 ligands. Addition of pertuzumab to lapatinib further inhibited NRG1-induced signalling, which was not fully inhibited by either drug alone. In animal model, a combination of pertuzumab to lapatinib induced a greater tumor regression than either lapatinib or pertuzumab monotherapy. This novel combination treatment may provide a promising strategy in clinical HER2-targeted therapy and may inhibit a subset of lapatinib-resistant breast cancer, although the group of patients that will respond to this therapy requires further stratification.

HER-3 peptide vaccines/mimics: Combined therapy with IGF-1R, HER-2, and HER-1 peptides induces synergistic antitumor effects against breast and pancreatic cancer cells

The human epidermal growth factor receptor 3 (HER-3/ErbB3) is a unique member of the human epidermal growth factor family of receptors, because it lacks intrinsic kinase activity and ability to heterodimerize with other members. HER-3 is frequently upregulated in cancers with epidermal growth factor receptor (EGFR/HER-1/ErbB1) or human epidermal growth factor receptor 2 (HER-2/ErBB2) overexpression, and targeting HER-3 may provide a route for overcoming resistance to agents that target EGFR or HER-2. We have previously developed vaccines and peptide mimics for HER-1, HER-2 and vascular endothelial growth factor (VEGF). In this study, we extend our studies by identifying and evaluating novel HER-3 peptide epitopes encompassing residues 99-122, 140-162, 237-269 and 461-479 of the HER-3 extracellular domain as putative B-cell epitopes for active immunotherapy against HER-3 positive cancers. We show that the HER-3 vaccine antibodies and HER-3 peptide mimics induced antitumor responses: inhibition of cancer cell proliferation, inhibition of receptor phosphorylation, induction of apoptosis and antibody dependent cellular cytotoxicity (ADCC). Two of the HER-3 epitopes 237-269 (domain II) and 461-479 (domain III) significantly inhibited growth of xenografts originating from both pancreatic (BxPC3) and breast (JIMT-1) cancers. Combined therapy of HER-3 (461-471) epitope with HER-2 (266-296), HER-2 (597-626), HER-1 (418-435) and insulin-like growth factor receptor type I (IGF-1R) (56-81) vaccine antibodies and peptide mimics show enhanced antitumor effects in breast and pancreatic cancer cells. This study establishes the hypothesis that combination immunotherapy targeting different signal transduction pathways can provide effective antitumor immunity and long-term control of HER-1 and HER-2 overexpressing cancers.

Biomarkers for predicting response to tyrosine kinase inhibitors in drug-sensitive and drug-resistant human bladder cancer cells

The epidermal growth factor receptor (EGFR) family is reportedly overexpressed in bladder cancer, and tyrosine kinase inhibitors (TKIs) have been suggested as treatment. Gefitinib (Iressa®) is a selective inhibitor of the EGFR and lapatinib is a dual inhibitor of both the EGFR and HER2 (human EGFR type 2 receptor). Both compounds compete with the binding of ATP to the tyrosine kinase domain of the respective receptors to inhibit receptor autophosphorylation causing suppression of signal transduction. Unfortunately, resistance to these inhibitors is a major clinical issue. The purpose of the present study was to use protein array analysis to compare the signaling pathway(s) induced by gefitinib and lapatinib, in UM-UC-5 (drug-sensitive) and UM-UC-14 (drug-resistant) bladder cancer cells and to identify molecular markers that may be useful predictors of their efficacy. The results revealed that phosphorylation of EGFR, HER3, Met and ERK1/2 was markedly overexpressed in the sensitive cell line (UM-UC-5) and was strongly inhibited by the TKIs. Other notable differences included decreased phosphorylation of RSK, GSK3, AMPK, Akt and c-Jun by TKIs in the sensitive cells. In contrast, phosphorylated p53 was highly expressed in the resistant cell line (UM-UC-14) and TKIs had no effect in the resistant cells. Overall results suggest that phosphorylated HER3, ERK1/2 and p53 may be used as biomarkers to determine the sensitivity of bladder cancers to TKIs. In particular, a combination of these markers may be more likely to predict the sensitivity to TKIs.

Structural analysis of the EGFR/HER3 heterodimer reveals the molecular basis for activating HER3 mutations

The human epidermal growth factor receptor (HER) tyrosine kinases homo- and heterodimerize to activate downstream signaling pathways. HER3 is a catalytically impaired member of the HER family that contributes to the development of several human malignancies and is mutated in a subset of cancers. HER3 signaling depends on heterodimerization with a catalytically active partner, in particular epidermal growth factor receptor (EGFR) (the founding family member, also known as HER1) or HER2. The activity of homodimeric complexes of catalytically active HER family members depends on allosteric activation between the two kinase domains. To determine the structural basis for HER3 signaling through heterodimerization with a catalytically active HER family member, we solved the crystal structure of the heterodimeric complex formed by the isolated kinase domains of EGFR and HER3. The structure showed HER3 as an allosteric activator of EGFR and revealed a conserved role of the allosteric mechanism in activation of HER family members through heterodimerization. To understand the effects of cancer-associated HER3 mutations at the molecular level, we solved the structures of two kinase domains of HER3 mutants, each in a heterodimeric complex with the kinase domain of EGFR. These structures, combined with biochemical analysis and molecular dynamics simulations, indicated that the cancer-associated HER3 mutations enhanced the allosteric activator function of HER3 by redesigning local interactions at the dimerization interface.

CNS metastases in breast cancer patients: prognostic implications of tumor subtype

Development of brain metastases (BM) in breast cancer leads to limited survival. The therapeutical options are limited. There are less data about the risk factors and prognostic importance in BM. Objective is to investigate predictors of central nervous system metastases and outcome after diagnosis of BM according to tumor subtype. Based on medical records, 80 consecutive patients with primary non-metastatic operable breast cancer, treated at Department of Gynecology, University of Tübingen, and who developed BM during follow-up, were retrospectively analyzed. Clinicopathological parameters and their prognostic impact were evaluated. A node involvement (40 %), ER/PR negative (53.75 vs. 61.25 %), triple negative (28.75 %) and HER2+ status (40 %) were associated with BM. BM in breast cancer patients lead to a shortened survival. In cerebral metastatic breast cancer patients with HER2-negative and triple-negative, patients had significant shorter survival after detection of BM compared with HER2-positive and non-triple-negative patients (p = 0.001; p = 0.03). Risk of BM varies significantly by subtype. Understanding the biology of metastases can help categorize patients into prognostically useful categories and tailor treatment regimens for individual patients. Prospective clinical trials would be required for evaluating the potential role of screening for asymptomatic BM and of treatment of triple-negative patients.

Design and evaluation of radiolabeled tracers for tumor imaging

The growing understanding of tumor biology and the identification of tumor-specific genetic and molecular alterations, such as the overexpression of membrane receptors and other proteins, allows for personalization of patient management using targeted therapies. However, this puts stringent demands on the diagnostic tools used to identify patients who are likely to respond to a particular treatment. Radionuclide molecular imaging is a promising noninvasive method to visualize and characterize the expression of such targets. A number of different proteins, from full-length antibodies and their derivatives to small scaffold proteins and peptide receptor-ligands, have been applied to molecular imaging, each demonstrating strengths and weaknesses. Here, we discuss the concept of molecular targeting and, in particular, molecular imaging of cancer-associated targets. Additionally, we describe important biotechnological considerations and desired features when designing and developing tracers for radionuclide molecular imaging.

Flotillin depletion affects ErbB protein levels in different human breast cancer cells

The ErbB3 receptor is an important regulator of cell growth and carcinogenesis. Among breast cancer patients, up to 50-70% have ErbB3 overexpression and 20-30% show overexpressed or amplified ErbB2. ErbB3 has also been implicated in the development of resistance to several drugs used against cancers driven by ErbB1 or ErbB2. One of the main challenges in ErbB-targeting therapy is to inactivate signaling mediated by ErbB2-ErbB3 oncogenic receptor complexes. We analyzed the regulatory role of flotillins on ErbB3 levels and ErbB2-ErbB3 complexes in SKBR3, MCF7 and MDA-MB-134-VI human breast cancer cells. Recently, we described a mechanism for interfering with ErbB2 signaling in breast cancer and demonstrated a molecular complex of flotillin scaffolding proteins with ErbB2 and Hsp90. In the present study, flotillins were found to be in a molecular complex with ErbB3, even in cells without the presence of ErbB2 or other ErbB receptors. Depletion of either flotillin-1 or flotillin-2 resulted in downregulation of ErbB3 and a selective reduction of ErbB2-ErbB3 receptor complexes. Moreover, flotillin-2 depletion resulted in reduced activation of Akt and MAPK signaling cascades, and as a functional consequence of flotillin depletion, breast cancer cells showed an impaired cell migration. Altogether, we provide data demonstrating a novel and functional role of flotillins in the regulation of ErbB protein levels and stabilization of ErbB2-ErbB3 receptor complexes. Thus, flotillins are crucial regulators for oncogenic ErbB function and potential targets for cancer treatment.

HSP90 inhibitor AUY922 abrogates up-regulation of RTKs by mTOR inhibitor AZD8055 and potentiates its antiproliferative activity in human breast cancer

mTOR inhibition led to activation of upstream receptor tyrosine kinases (RTKs) and AKT, which may attenuate the efficacy of mTOR kinase inhibitors. We sought to discover efficient drug combination with mTOR inhibitors by elucidating the survival feedback loops induced by mTOR inhibition in breast cancer. The feedback signaling upon treatment of mTOR inhibitor AZD8055 was determined and the combinatorial activity of AZD8055 and HSP90 inhibitor AUY922 in cell signaling and proliferation were detected. Treatment of breast cancer T47D cells with AZD8055 induced activation of AKT and phosphatidylinositol 3-kinase (PI3K), which was accompanied with increase in expression of multiple upstream proteins including EGFR, HER2, HER3 and IRS-1. Different RTKs were revealed to be responsible for the reactivation of AKT by AZD8055 in different breast cancer cell lines. Down-regulation of these proteins differentially enhanced the antiproliferative activity of AZD8055. AZD8055 and AUY922 displayed synergistic effect against a panel of human breast cancer cells irrespective their genotype, which was associated with enhanced cell cycle arrest and inhibition of DNA synthesis. AUY922 destabilized multiple tested tyrosine kinases and abrogated activation of AKT induced by AZD8055. AZD8055 also inhibited up-regulation of HSP70 and HSP27 upon AUY922 treatment. Cotreatment of these two drugs demonstrated synergistic activity against triple negative MDA-MB-468 xenograft without enhanced toxicity. The combination of AZD8055 and AUY922 demonstrated synergistic activity against various types of breast cancer and established a mechanistic rationale for a combination approach using catalytic mTOR kinase inhibitor and HSP90 inhibitor in the treatment of breast cancer.

Regulation of angiogenesis via Notch signaling in breast cancer and cancer stem cells

Breast cancer angiogenesis is elicited and regulated by a number of factors including the Notch signaling. Notch receptors and ligands are expressed in breast cancer cells as well as in the stromal compartment and have been implicated in carcinogenesis. Signals exchanged between neighboring cells through the Notch pathway can amplify and consolidate molecular differences, which eventually dictate cell fates. Notch signaling and its crosstalk with many signaling pathways play an important role in breast cancer cell growth, migration, invasion, metastasis and angiogenesis, as well as cancer stem cell (CSC) self-renewal. Therefore, significant attention has been paid in recent years toward the development of clinically useful antagonists of Notch signaling. Better understanding of the structure, function and regulation of Notch intracellular signaling pathways, as well as its complex crosstalk with other oncogenic signals in breast cancer cells will be essential to ensure rational design and application of new combinatory therapeutic strategies. Novel opportunities have emerged from the discovery of Notch crosstalk with inflammatory and angiogenic cytokines and their links to CSCs. Combinatory treatments with drugs designed to prevent Notch oncogenic signal crosstalk may be advantageous over λ secretase inhibitors (GSIs) alone. In this review, we focus on the more recent advancements in our knowledge of aberrant Notch signaling contributing to breast cancer angiogenesis, as well as its crosstalk with other factors contributing to angiogenesis and CSCs.

Prognostic significance of human epidermal receptor (HER)- 3 immunohistochemical expression in patients with metastatic breast cancer

BACKGROUND

Previous reports have shown that human epidermal receptor (HER)-3 overexpression may be associated with poor prognosis in patients with breast cancer, but results have been conflicting. In this study, we sought to investigate the prognostic significance of HER-3 immunohistochemical expression in patients with metastatic breast cancer.

METHODS

We retrospectively analyzed HER-3 immunohistochemical expression profiles in 45 paraffin-embedded specimens from patients who had been treated between 1996 and 2006 in the Department of Oncology of the Uludag University School of Medicine, Bursa, Turkey. Membranous or cytoplasmic dominant expression patterns of HER-3 were analyzed using the Rajkumar score and a cytoplasmic 4-point scoring system, respectively. Progression-free survival (PFS) and overall survival (OS) served as the main outcome measures.

RESULTS

The median PFS in the study participants was 9 months (interquartile range: 4.5-13 months), whereas the median OS was 20 months (interquartile range: 7.5-28 months). Categorization of the patient population according to HER-3 positive immunohistochemical expression did not reveal any statistically significant difference in terms of both PFS (p=0.70) and OS (p=0.81). The results of multivariable Cox regression analysis indicated that tumor size was the only independent predictor of PFS, whereas estrogen and progesterone receptor status was independently associated with OS.

CONCLUSIONS

HER-3 immunohistochemical expression did not correlate with outcomes in Turkish patients with metastatic breast cancer. Although our results suggest that HER-3 expression in cancer specimens is not of prognostic significance, further prospective studies are warranted to confirm these results.

Inverse regulation of EGFR/HER1 and HER2-4 in normal and malignant human breast tissue

Cross-talk between the estrogen and the EGFR/HER signalling pathways has been suggested as a potential cause of resistance to endocrine therapy in breast cancer. Here, we determined HER1-4 receptor and neuregulin-1 (NRG1) ligand mRNA expression levels in breast cancers and corresponding normal breast tissue from patients previously characterized for plasma and tissue estrogen levels. In tumours from postmenopausal women harbouring normal HER2 gene copy numbers, we found HER2 and HER4, but HER3 levels in particular, to be elevated (2.48, 1.30 and 22.27 –fold respectively; P<0.01 for each) compared to normal tissue. Interestingly, HER3 as well as HER4 were higher among ER+ as compared to ER- tumours (P=0.004 and P=0.024, respectively). HER2 and HER3 expression levels correlated positively with ER mRNA (ESR1) expression levels (r=0.525, P=0.044; r=0.707, P=0.003, respectively). In contrast, EGFR/HER1 was downregulated in tumour compared to normal tissue (0.13-fold, P<0.001). In addition, EGFR/HER1 correlated negatively to intra-tumour (r=-0.633, P=0.001) as well as normal tissue (r=-0.556, P=0.006) and plasma estradiol levels (r=-0.625, P=0.002), suggesting an inverse regulation between estradiol and EGFR/HER1 levels. In ER+ tumours from postmenopausal women, NRG1 levels correlated positively with EGFR/HER1 (r=0.606, P=0.002) and negatively to ESR1 (r=-0.769, P=0.003) and E2 levels (r=-0.542, P=0.020). Our results indicate influence of estradiol on the expression of multiple components of the HER system in tumours not amplified for HER2, adding further support to the hypothesis that cross-talk between these systems may be of importance to breast cancer growth in vivo.

Immunohistochemical analysis of the monoclonal antibody 4B5 in breast tissue expressing human epidermal growth factor receptor 4 (HER4)

AIMS

A recent study examining the specificity of human epidermal growth factor receptor (HER) 2 pharmacodiagnostic antibodies demonstrated that CB11 and 4B5 stain both HER2-transfected and HER4-transfected cell lines. However, there has been no evidence showing that 4B5 has affinity for HER4 in clinically obtained tissues, and, if so, whether this has any impact on the assessment of HER2. We therefore sought to determine the expression of membrane-bound HER4 in clinical breast carcinomas, and evaluate its impact on the clinical utility of 4B5 in determining HER2 status.

METHODS AND RESULTS

Breast carcinomas were assessed by immunohistochemistry (IHC) for membrane-bound HER4 using anti-HER4 clone E200. HER2 expression in these cases was then assessed using anti-HER2 clone 4B5, and a reference clone, SP3. In all 117 membrane HER4-positive cases (out of 241), 4B5 scored equal to or less than the reference anti-HER2 clone SP3. Eighteen cases were positive for membrane-bound HER4 by E200 and negative by 4B5, including a membrane HER4 level 3+ case.

CONCLUSIONS

No cross-reactivity of 4B5 with membrane-bound HER4 was identified in the clinical IHC analysis of formalin-fixed paraffin-embedded breast carcinoma cases as evidenced by the HER4 antibody clone E200.

Oncogenic ERBB3 mutations in human cancers

The human epidermal growth factor receptor (HER) family of tyrosine kinases is deregulated in multiple cancers either through amplification, overexpression, or mutation. ERBB3/HER3, the only member with an impaired kinase domain, although amplified or overexpressed in some cancers, has not been reported to carry oncogenic mutations. Here, we report the identification of ERBB3 somatic mutations in ~11% of colon and gastric cancers. We found that the ERBB3 mutants transformed colonic and breast epithelial cells in a ligand-independent manner. However, the mutant ERBB3 oncogenic activity was dependent on kinase-active ERBB2. Furthermore, we found that anti-ERBB antibodies and small molecule inhibitors effectively blocked mutant ERBB3-mediated oncogenic signaling and disease progression in vivo.

IL-1 and EGF regulate expression of genes important in inflammation and cancer

This review focuses on the mechanisms by which the expression of specific genes is regulated by two proteins that are important in inflammation and cancer, namely the pro-inflammatory cytokine interleukin (IL)-1β and epidermal growth factor (EGF). In the review the receptors that recognize factors that cause inflammation are described with main focus on the receptors associated with activation of IL-1β. The function of IL-1β and pathways leading to activation of transcription factors, particularly NFκB and Elk-1 are analyzed. Then the mechanisms of EGF action, with particular emphasis of the activation of Elk-1 are illustrated. The link between aberrant signaling of EGF receptor family members and cancer development is explained. The relationship between inflammation and tumorigenesis is discussed.

Association of ErbB1-4 expression in invasive breast cancer with clinicopathological characteristics and prognosis

BACKGROUND

Human epidermal growth factor receptor type 2 (Her2)/ErbB2 plays a key role in the initiation and progression of invasive breast cancer. However, the prognostic relevance to breast cancer patients of the other ErbB family members has long been a matter of debate.

METHODS

In a series of 250 primary invasive breast cancer patients, we performed a comprehensive analysis of ErbB1-4 at the levels of mRNA expression and gene copy number using real-time quantitative PCR. The relationship between the status of ErbB1-4 and the clinicopathological characteristics or prognosis was evaluated.

RESULTS

The mRNA expression of ErbB2, but not the other ErbB genes, was significantly correlated to copy number (P = 0.0005). ErbB3 and ErbB4 mRNA expression were positively correlated to each other (P < 0.0001). The mRNA expression of ErbB1/2 was inversely correlated to estrogen receptor (ER) and progesterone receptor (PgR) positivity, although mRNA expression of ErbB3/4 was positively correlated to ER and PgR positivity. Kaplan-Meier survival analysis showed that ErbB1 mRNA expression was associated with reduced survival. Neither ErbB2 nor ErbB3 mRNA expression had any association with survival, because half of the patients with Her2-positive tumors were treated with trastuzumab. High ErbB4 mRNA expression showed good prognosis with respect to breast cancer-specific survival

CONCLUSIONS

ErbB3 and ErbB4 mRNA expression, as well as well as that of ErbB1 and ErbB2, could be histopathological factors. ErbB3 mRNA was highly expressed in ER-positive tumors and has controversial prognostic value. ErbB4 mRNA expression was well correlated with ER positivity and good prognosis, indicating that ErbB4 may contribute to ER-dependent growth.

Molecular analysis of HER2 signaling in human breast cancer by functional protein pathway activation mapping

PURPOSE

Targeting of the HER2 protein in human breast cancer represents a major advance in oncology but relies on measurements of total HER2 protein and not HER2 signaling network activation. We used reverse-phase protein microarrays (RPMA) to measure total and phosphorylated HER2 in the context of HER family signaling to understand correlations between phosphorylated and total levels of HER2 and downstream signaling activity.

EXPERIMENTAL DESIGN

Three independent study sets, comprising a total of 415 individual patient samples from flash-frozen core biopsy samples and formalin-fixed and paraffin-embedded (FFPE) surgical and core samples, were analyzed via RPMA. The phosphorylation and total levels of the HER receptor family proteins and downstream signaling molecules were measured in laser capture microdissected (LCM) enriched tumor epithelium from 127 frozen pretreatment core biopsy samples and whole-tissue lysates from 288 FFPE samples and these results were compared with FISH and immunohistochemistry (IHC).

RESULTS

RPMA measurements of total HER2 were highly concordant (>90% all sets) with FISH and/or IHC data, as was phosphorylation of HER2 in the FISH/IHC(+) population. Phosphorylation analysis of HER family signaling identified HER2 activation in some FISH/IHC(-) tumors and, identical to that seen with FISH/IHC(+) tumors, the HER2 activation was concordant with EGF receptor (EGFR) and HER3 phosphorylation and downstream signaling endpoint activation.

CONCLUSIONS

Molecular profiling of HER2 signaling of a large cohort of human breast cancer specimens using a quantitative and sensitive functional pathway activation mapping technique reveals IHC(-)/FISH(-)/pHER2(+) tumors with HER2 pathway activation independent of total HER2 levels and functional signaling through HER3 and EGFR.