Cancer stem cell-driven efficacy of trastuzumab (Herceptin): towards a reclassification of clinically HER2-positive breast carcinomas

Clinically HER2+ (cHER2+) breast cancer (BC) can no longer be considered a single BC disease entity in terms of trastuzumab responsiveness. Here we propose a framework for predicting the response of cHER2+ to trastuzumab that integrates the molecular distinctions of intrinsic BC subtypes with recent knowledge on cancer stem cell (CSC) biology. First, we consider that two interchangeable populations of epithelial-like, aldehyde dehydrogenase (ALDH)-expressing and mesenchymal-like, CD44⁺CD24^−/low CSCs can be found in significantly different proportions across all intrinsic BC subtypes. Second, we overlap all the intrinsic subtypes across cHER2+ BC to obtain a continuum of mixed phenotypes in which one extreme exhibits a high identity with ALDH+ CSCs and the other extreme exhibits a high preponderance of CD44⁺CD24^−/low CSCs. The differential enrichment of trastuzumab-responsive ALDH+ CSCs versus trastuzumab-refractory CD44⁺CD24^−/low CSCs can explain both the clinical behavior and the primary efficacy of trastuzumab in each molecular subtype of cHER2+ (i.e., HER2-enriched/cHER2+, luminal A/cHER2+, luminal B/cHER2+, basal/cHER2+, and claudin-low/cHER2+). The intrinsic plasticity determining the epigenetic ability of cHER2+ tumors to switch between epithelial and mesenchymal CSC states will vary across the continuum of mixed phenotypes, thus dictating their intratumoral heterogeneity and, hence, their evolutionary response to trastuzumab. Because CD44⁺CD24^−/low mesenchymal-like CSCs distinctively possess a highly endocytic activity, the otherwise irrelevant HER2 can open the door to a type of “Trojan horse” approach by employing antibody-drug conjugates such as T-DM1, which will allow a rapid and CSC-targeted delivery of cytotoxic drugs to therapeutically manage trastuzumab-unresponsive basal/cHER2+ BC. Contrary to the current dichotomous model used clinically, our model proposes that a reclassification of cHER2+ tumors based on the spectrum of molecular BC subtypes might inform on their CSC-determined sensitivity to trastuzumab, thus providing a better delineation of the predictive value of cHER2+ in BC by incorporating CSCs-driven intra-tumor heterogeneity into clinical decisions.     

A Tumor initiating cell-enriched prognostic signature for HER2+:ERα? breast cancer; rationale,new features,controversies and future directions

The high intra- and inter-tumor heterogeneity of many types of cancers, including breast cancer (BC), poses great challenge to development of subtype-specific prognosis. In BC, the classification of tumors as either ERα⁺ (Luminal A and Luminal B), HER2⁺ (ERα⁺ or ERα⁻) or triple-negative (TNBC)(Basal-like, claudin-low) guides both prognostication and therapy. Indeed, prognostic signatures for ERα⁺ BC are being incorporated into clinical use. However, these signatures distinguish between luminal A (low risk) and Luminal B (high risk) BC; signatures that identify low/high risk patients with luminal B BC are yet to be developed. Likewise, no signature is in clinical use for HER2⁺ or TNBC. The major obstacles to development of robust signatures stem from diversity of BC, clonal evolution and heterogeneity within each subtype. We have recently generated a prognostic signature for HER2⁺:ERα⁻ BC based on the identification of genes that were differentially expressed in a tumor-initiating cell (TIC)-enriched fraction versus non-TIC fraction from a mouse model of HER2⁺ BC (MMTV-Hers/Neu). Here we describe the rationale behind development of this prognosticator, and present new features of the signature, including elevated PI3K pathway activity and low TNFalpha and IFNgamma signaling in high-risk tumors. In addition, we address controversies in the field such as whether random gene expression signatures significantly associate with cancer outcome. Finally, we suggest a guideline for development of prognostic signatures and discuss future directions.     

Pre-clinical study of drug combinations that reduce breast cancer burden due to aberrant mTOR and metabolism promoted by LKB1 loss

Cancer therapies that simultaneously target activated mammalian target of rapamycin (mTOR) and cell metabolism are urgently needed. The goal of our study was to identify therapies that effectively inhibited both mTOR activity and cancer cell metabolism in primary tumors in vivo. Using our mouse model of spontaneous breast cancer promoted by loss of LKB1 expression in an ErbB2 activated model; referred to as LKB1^−/−NIC mice, we evaluated the effect of novel therapies in vivo on primary tumors. Treatment of LKB1^−/−NIC mice with AZD8055 and 2-DG mono-therapies significantly reduced mammary gland tumorigenesis by inhibiting mTOR pathways and glycolytic metabolism; however simultaneous inhibition of these pathways with AZD8055/2-DG combination was significantly more effective at reducing tumor volume and burden. At the molecular level, combination treatment inhibited mTORC1/mTORC2 activity, selectively inhibited mitochondria function and blocked MAPK pro-survival signaling responsible for the ERK-p90RSK feedback loop. Our findings suggest that loss of LKB1 expression be considered a marker for metabolic dysfunction given its role in regulating AMPK and mTOR function. Finally, the outcome of our pre-clinical study confirms therapies that simultaneously target mTORC1/mTORC2 and glycolytic metabolism in cancer produce the best therapeutic outcome for the treatment of patients harboring metabolically active HER2 positive breast cancers.     

HER2 Positive and HER2 Negative Classical Type Invasive Lobular Carcinomas: Comparison of Clinicopathologic Features

Human epidermal growth factor receptor 2 (HER2) positive (+) classical type invasive lobular carcinoma (cILC) of the breast is extremely rare and its clinicopathologic features have not been well characterized. We compared features of HER2(+) and HER2 negative (−) cILCs. A total of 29 cases were identified from the clinical database at our institution from 2011-2019; 9 were HER2(+) cILC tumors and 20 were HER2(−) cILC tumors. The results reveal that HER2(+) cILC group had significantly increased Ki-67 expression and reduced estrogen receptor (ER) expression compared to HER2(−) cILC group (both p < 0.05). In addition, HER2(+) cILCs tended to be diagnosed at a younger age and more common in the left breast, and appeared to have a higher frequency of nodal or distant metastases. These clinicopathologic features suggest HER2(+) cILC tumors may have more aggressive behavior than their HER2(−) counterpart although both groups of tumors showed similar morphologic features. Future directions of the study: (1) To conduct a multi-institutional study with a larger case series of HER2(+) cILC to further characterize its clinicopathologic features; (2) to compare molecular profiles by next generation sequencing (NGS) assay between HER2(+) cILC and HER2(−) cILC cases to better understand tumor biology of this rare subset of HER2(+) breast cancer; and (3) to compare molecular characteristics of HER2(+) cILC and HER2(+) high grade breast cancer in conjunction with status of tumor response to anti-HER2 therapy to provide insight to management of this special type of low grade breast cancer to avoid unnecessary treatment and related toxicity     

Heregulin-HER3-HER2 signaling promotes matrix metalloproteinase-dependent blood-brain-barrier transendothelial migration of human breast cancer cell lines

HER2-positive breast tumors are associated with a high risk of brain relapse. HER3 is thought to be an indispensible signaling substrate for HER2 (encoded by ERBB2) and is induced in breast cancer-brain metastases, though the molecular mechanisms by which this oncogenic dimer promotes the development of brain metastases are still elusive. We studied the effects of the HER3-HER2 ligand, heregulin (neuregulin-1, broadly expressed in the brain), on luminal breast cancer cell lines in vitro. Treatment of SKBr3 (ERBB2-amplified), MDA-MB-361 (ERBB2-amplified, metastatic brain tumor-derived) and MCF7 (HER2-positive, not ERBB2-amplified) cells with exogenous heregulin increased proliferation and adhesive potential, concomitant with induction of cyclin D1 and ICAM-1, and suppression of p27. All three cell lines invaded through matrigel toward a heregulin chemotactic signal in transwell experiments, associated with activation of extracellular cathepsin B and matrix metalloproteinase-9 (MMP-9). Moreover, heregulin induced breast cancer cell transmigration across a tight barrier of primary human brain microvascular endothelia. This was dependent on the activity of HER2, HER3 and MMPs, and was completely abrogated by combination HER2-HER3 blockade using Herceptin^® and the humanized HER3 monoclonal antibody, EV20. Collectively these data suggest mechanisms by which the HER3-HER2 dimer promotes development of metastatic tumors in the heregulin-rich brain microenvironment.     

MicroRNA-21 links epithelial-to-mesenchymal transition and inflammatory signals to confer resistance to neoadjuvant trastuzumab and chemotherapy in HER2-positive breast cancer patients

Patients with primary HER2-positive breast cancer benefit from HER2-targeted therapies. Nevertheless, a significant proportion of these patients die of disease progression due to mechanisms of drug resistance. MicroRNAs (miRNAs) are emerging as critical core regulators of drug resistance that act by modulating the epithelial- to-mesenchymal transition (EMT) and cancer-related immune responses. In this study, we investigated the association between the expression of a specific subset of 14 miRNAs involved in EMT processes and immune functions and the response to neoadjuvant trastuzumab and chemotherapy in 52 patients with HER2-overexpressing breast tumors. The expression of only a single miRNA, miR-21, was significantly associated with residual disease (p = 0.030) and increased after trastuzumab-chemotherapy (p = 0.012). A target prediction analysis coupled with in vitro and in vivo validations revealed that miR-21 levels inversely correlated with the expression of PTEN (rs = −0.502; p = 0.005) and PDCD4 (rs = −0.426; p = 0.019), which differentially influenced the drug sensitivity of HER2-positive breast cancer cells. However, PTEN expression was only marginally associated with residual disease. We further demonstrated that miR-21 was able to affect the response to both trastuzumab and chemotherapy, triggering an IL-6/STAT3/NF-κB-mediated signaling loop and activating the PI3K pathway. Our findings support the ability of miR-21 signaling to sustain EMT and shape the tumor immune microenvironment in HER2-positive breast cancer. Collectively, these data provide a rationale for using miR-21 expression as a biomarker to select trastuzumab-chemotherapy-resistant HER2-positive breast cancer patients who may benefit from treatments containing PI3K inhibitors or immunomodulatory drugs.     

The HER2 amplicon includes several genes required for the growth and survival of HER2 positive breast cancer cells

About 20% of breast cancers are characterized by amplification and overexpression of the HER2 oncogene. Although significant progress has been achieved for treating such patients with HER2 inhibitor trastuzumab, more than half of the patients respond poorly or become resistant to the treatment. Since the HER2 amplicon at 17q12 contains multiple genes, we have systematically explored the role of the HER2 co-amplified genes in breast cancer cell growth and their relation to trastuzumab resistance. We integrated aCGH data of the HER2 amplicon from 71 HER2 positive breast tumors and 10 cell lines with systematic functional RNA interference analysis of 23 core amplicon genes with several phenotypic endpoints in a panel of trastuzumab responding and non-responding HER2 positive breast cancer cells. Silencing of HER2 caused a greater growth arrest and apoptosis in the responding compared to the non-responding cell lines, indicating that the resistant cells are inherently less dependent on the HER2 pathway. Several other genes in the amplicon also showed a more pronounced effect when silenced; indicating that expression of HER2 co-amplified genes may be needed to sustain the growth of breast cancer cells. Importantly, co-silencing of STARD3, GRB7, PSMD3 and PERLD1 together with HER2 led to an additive inhibition of cell viability as well as induced apoptosis. These studies indicate that breast cancer cells may become addicted to the amplification of several genes that reside in the HER2 amplicon. The simultaneous targeting of these genes may increase the efficacy of the anti-HER2 therapies and possibly also counteract trastuzumab resistance. The observed additive effects seem to culminate to both apoptosis and cell proliferation pathways indicating that these pathways may be interesting targets for combinatorial treatment of HER2+ breast cancers.     

Cyclin D1 is a direct target of JAG1-mediated Notch signaling in breast cancer

The Notch ligand, JAG1 is associated with breast cancer recurrence. Herein, we report on a genomics approach to elucidate mechanisms downstream of JAG1 that promote breast cancer growth. In a survey of 46 breast cancer cell lines, we found that triple negative (TN; basal and mesenchymal ER-, PR-, and Her2-negative) lines express JAG1 at significantly higher levels than do HER2⁺ or luminal (ER⁺) Her2⁻ cell lines. In contrast to the luminal lines tested (T47D and MCF7), TN breast cancer cell lines (HCC1143 and MDA MB231) display high-level JAG1 expression and growth inhibition with RNA interference-induced JAG1 down-regulation. We used microarray profiling of TN tumor cells transfected with JAG1 siRNA to identify JAG1-regulated genes (P ≤ 0.005; fold change ≥1.5). Among JAG1-regulated genes identified, cyclin D1 was found to be a direct target of NOTCH1 and NOTCH3. We show that JAG1 down-regulation reduces direct binding of Notch to the cyclin D1 promoter, reduced cyclin D1 expression and inhibition of cell cycle progression through the cyclin D1-dependant G1/S checkpoint. Furthermore, we show that cyclin D1 and JAG1 expression correlate in TN breast cancer expression datasets. These data suggest a model whereby JAG1 promotes cyclin D1-mediated proliferation of TN breast cancers.     

Sensitization of breast cancer to Herceptin by redox active nanoparticles

Herceptin-resistant tumor relapse remains a major clinical issue responsible for the poor prognosis of HER2⁺ breast cancer. Understanding the underlying mechanisms and finding a therapeutic solution are of paramount urgency to improve the patient management. Here we report that anticancer redox active cerium oxide nanoparticles (CONPs) can potently sensitize the cancer cells to the cytotoxicity of Herceptin. By comparing between Herceptin-sensitive and Herceptin-resistant human breast cancer cell lines under normoxic as well as hypoxic culture conditions, we found that in the presence of CONPs, Herceptin can kill the Herceptin-resistant cells equally effectively as it kills the Herceptin-sensitive cells under the hypoxic, but not normoxic, culture conditions by inhibiting the cell viability, survival and proliferation. Signaling analysis reveals that under the normoxic conditions, the levels of hypoxia induced factor 1α as well as vascular endothelial growth factor are higher in the Herceptin-resistant cells than that in the Herceptin-sensitive cells and are strongly induced once the culture is switched to the hypoxic conditions, which can be potently suppressed by CONPs. Treatment with CONPs plus Herceptin significantly slows down the primary tumor growth and lung metastasis of the Herceptin-resistant cells in a xenograft mouse model of orthotopic breast cancer through inhibiting the cell proliferation and survival as well as tumor angiogenesis. These results shed new lights on the mechanisms underlying the Herceptin resistance of the HER2⁺ breast cancer and provide insights into introducing CONPs-like agents to Herceptin-based therapy to improve treatment outcomes.     

Sortilin‐related receptor is a druggable therapeutic target in breast cancer

In breast cancer, the currently approved anti‐receptor tyrosine‐protein kinase erbB‐2 (HER2) therapies do not fully meet the expected clinical goals due to therapy resistance. Identifying alternative HER2‐related therapeutic targets could offer a means to overcome these resistance mechanisms. We have previously demonstrated that an endosomal sorting protein, sortilin‐related receptor (SorLA), regulates the traffic and signaling of HER2 and HER3, thus promoting resistance to HER2‐targeted therapy in breast cancer. This study aims to assess the feasibility of targeting SorLA using a monoclonal antibody. Our results demonstrate that anti‐SorLA antibody (SorLA ab) alters the resistance of breast cancer cells to HER2 monoclonal antibody trastuzumab in vitro and in ovo. We found that SorLA ab and trastuzumab combination therapy also inhibits tumor cell proliferation and tumor cell density in a mouse xenograft model of HER2‐positive breast cancer. In addition, SorLA ab inhibits the proliferation of breast cancer patient‐derived explant three‐dimensional cultures. These results provide, for the first time, proof of principle that SorLA is a druggable target in breast cancer.     

AZD8931, an equipotent,reversible inhibitor of signaling by epidermal growth factor receptor (EGFR), HER2, and HER3: preclinical activity in HER2 non-amplified inflammatory breast cancer models

Introduction

Epidermal growth factor receptor (EGFR) overexpression has been associated with prognostic and predictive value in inflammatory breast cancer (IBC). Epidermal growth factor receptor 2 (HER2) overexpression is observed at a higher rate in IBC compared with noninflammatory breast cancer. Current clinically available anti-HER2 therapies are effective only in patients with HER2 amplified breast cancer, including IBC. AZD8931 is a novel small-molecule equipotent inhibitor of EGFR, HER2, and HER3 signaling. In this study, we investigated the antitumor activity of AZD8931 alone or in combination with paclitaxel using preclinical models of EGFR-overexpressed and HER2 non-amplified IBC cells.

Methods

Two IBC cell lines SUM149 and FC-IBC-02 derived from pleural effusion of an IBC patient were used in this study. Cell growth and apoptotic cell death were examined in vitro. For the in vivo tumor growth studies, IBC cells were orthotopically transplanted into the mammary fat pads of immunodeficient mice. AZD8931 was given by daily oral gavage at doses of 25 mg/kg, 5 days/week for 4 weeks. Paclitaxel was subcutaneously injected twice weekly.

Results

AZD8931 significantly suppressed cell growth of IBC cells and induced apoptosis of human IBC cells in vitro. Significantly, we showed that AZD8931 monotherapy inhibited xenograft growth and the combination of paclitaxel + AZD8931 was demonstrably more effective than paclitaxel or AZD8931 alone treatment at delaying tumor growth in vivo in orthotopic IBC models.

Conclusion

AZD8931 single agent and in combination with paclitaxel demonstrated signal inhibition and antitumor activity in EGFR-overexpressed and HER2 non-amplified IBC models. These results suggest that AZD8931 may provide a novel therapeutic strategy for the treatment of IBC patients with HER2 non-amplified tumors.     

ADAM10 mediates trastuzumab resistance and is correlated with survival in HER2 positive breast cancer

Trastuzumab prolongs survival in HER2 positive breast cancer patients. However, resistance remains a challenge. We have previously shown that ADAM17 plays a key role in maintaining HER2 phosphorylation during trastuzumab treatment. Beside ADAM17, ADAM10 is the other well characterized ADAM protease responsible for HER ligand shedding. Therefore, we studied the role of ADAM10 in relation to trastuzumab treatment and resistance in HER2 positive breast cancer. ADAM10 expression was assessed in HER2 positive breast cancer cell lines and xenograft mice treated with trastuzumab. Trastuzumab treatment increased ADAM10 levels in HER2 positive breast cancer cells (p≤0.001 in BT474; p≤0.01 in SKBR3) and in vivo (p≤0.0001) compared to control, correlating with a decrease in PKB phosphorylation. ADAM10 inhibition or knockdown enhanced trastuzumab response in naïve and trastuzumab resistant breast cancer cells. Trastuzumab monotherapy upregulated ADAM10 (p≤0.05); and higher pre-treatment ADAM10 levels correlated with decreased clinical response (p≤0.05) at day 21 in HER2 positive breast cancer patients undergoing a trastuzumab treatment window study. Higher ADAM10 levels correlated with poorer relapse-free survival (p≤0.01) in a cohort of HER2 positive breast cancer patients. Our studies implicate a role of ADAM10 in acquired resistance to trastuzumab and establish ADAM10 as a therapeutic target and a potential biomarker for HER2 positive breast cancer patients.     

Targeting HER3 with miR-450b-3p suppresses breast cancer cells proliferation

In breast cancer cells, heterodimerization of HER2 and HER3 plays important and dominant roles in the functionality and transformation of HER-mediated pathways, in particular the PI3K/Akt survival pathway. HER3 was considered as a major signaling hub in HER2-amplified cancers. Inhibition of HER3 expression may therefore represent a rational therapeutic approach to breast cancers where HER2/HER3-mediated signaling plays a role in tumorigenesis and progression. miRNAs exerts important roles in regulating gene expressions by binding to and repressing target mRNAs. Here we reported that miRNA-450b-3p inhibits HER3 expression by directly targeting 3′ UTR of HER3 mRNA and represses the downstream signal transductions of HER family. Overexpression of miRNA-450b-3p in SKBR3 cells inhibits cells clonogenic potential and enhances their sensitivity to trastuzumab, a monoclonal antibody that binds to the HER2 receptor, or doxorubicin through repressing proliferative signal pathways mediated by HER3/HER2/PI3K/AKT. Furthermore, we found that breast cancer patients with tumors that demonstrating upregulated HER3 (>2-fold) and downregulated miR-450b-3p (>2-fold) expressions compared with the paired adjacent non-tumorous tissues showed significantly poorer overall survival (P < 0.05). Our study identified miRNA-450b-3p as a new tumor repressor and also provided some evidences suggesting that downregulation of miR-450b-3p expression with concurrent overexpression of HER3 may serve as a prognostic biomarker for poor overall survival in breast cancer patients.     

PAQR3 expression is downregulated in human breast cancers and correlated with HER2 expression

PAQR3 is a newly discovered tumor suppressor and its functional role in breast cancer has not been well characterized. We report here that PAQR3 is associated with the progression and survival of human patients with breast cancer, as well as cell proliferation and migration of human breast cancer cells. PAQR3 mRNA level was robustly downregulated in human breast cancer samples compared with their corresponding para-cancerous histological normal tissues (n = 82, P < 0.0001). The mRNA level of PAQR3 was negatively correlated with HER2 expression (P < 0.0001) and disease-free survival of the patients (P < 0.0001). PAQR3 overexpression inhibited cell proliferation, colony formation and migration of breast cancer cells including MCF7, SKBR3, MDA-MD-231, MDA-MD-468 and MDA-MD-453 cells. Knockdown of PAQR3 in MDA-MD-231 cells elevated cell proliferation and migration. Inhibition of HER2 by trastuzumab increased PAQR3 expression in SKBR3 cells. In conclusion, PAQR3 expression is frequently downregulated in human breast cancers inversely correlated with HER2 expression. PAQR3 is able to modulate the proliferation and migration of breast cancer cells. Our data indicate that PAQR3 functions as a tumor suppressor in the development of human breast cancers.     

Detection of HER2-positive Circulating Tumor Cells Using the LiquidBiopsy System in Breast Cancer

Background

Most previous studies of circulating tumor cells (CTCs) are based on the CellSearch platform, but CellSearch has a number of limitations. This study aimed to use the LiquidBiopsy system and immunofluorescence to test the human epidermal growth factor receptor 2 (HER2) status of CTCs in patients with breast cancer.

HER family kinase domain mutations promote tumor progression and can predict response to treatment in human breast cancer

Resistance to HER2‐targeted therapies remains a major obstacle in the treatment of HER2‐overexpressing breast cancer. Understanding the molecular pathways that contribute to the development of drug resistance is needed to improve the clinical utility of novel agents, and to predict the success of targeted personalized therapy based on tumor‐specific mutations. Little is known about the clinical significance of HER family mutations in breast cancer. Because mutations within HER1/EGFR are predictive of response to tyrosine kinase inhibitors (TKI) in lung cancer, we investigated whether mutations in HER family kinase domains are predictive of response to targeted therapy in HER2‐overexpressing breast cancer. We sequenced the HER family kinase domains from 76 HER2‐overexpressing invasive carcinomas and identified 12 missense variants. Patients whose tumors carried any of these mutations did not respond to HER2 directed therapy in the metastatic setting. We developed mutant cell lines and used structural analyses to determine whether changes in protein conformation could explain the lack of response to therapy. We also functionally studied all HER2 mutants and showed that they conferred an aggressive phenotype and altered effects of the TKI lapatinib. Our data demonstrate that mutations in the finely tuned HER kinase domains play a critical function in breast cancer progression and may serve as prognostic and predictive markers.