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Introduction: Trastuzumab is commonly used to treat human epidermal growth factor receptor-2-positive (HER2+) breast cancer, but its efficacy is often limited by chemotherapy resistance. Recent studies have indicated that long non-coding RNAs (lncRNAs) play important roles in tumor progression and response to therapy. However, the regulatory mechanisms associating lncRNAs and trastuzumab resistance remain unknown. Methods: Quantitative polymerase chain reaction was performed to detect the expression of related genes. Western blot and immunofluorescence assays were used to evaluate protein expression levels. A series of gain- or loss-of-function assays confirmed the function of AGAP2-AS1 in trastuzumab resistance, both in vitro and in vivo. RNA immunoprecipitation and pull-down analyses were conducted to verify the interaction between METTL3/YTHDF2 and lncRNA AGAP2-AS1. Results: AGAP2-AS1 was upregulated in trastuzumab-resistant cells and SKBR-3R-generated xenografts in nude mice. Silencing AGAP2-AS1 significantly decreased trastuzumab-induced cytotoxicity both in vitro and in vivo. Furthermore, m6A methylation of AGAP2-AS1 was reduced in trastuzumab-resistant cells compared to that in parental cells. In addition, METTL3 increased m6A methylation of AGAP2-AS1, which finally induced the suppressed AGAP2-AS1 expression. Moreover, YTHDF2 was essential for METTL3-mediated m6A methylation of AGAP2-AS1. Functionally, AGAP2-AS1 regulated trastuzumab resistance by inducing autophagy and increasing ATG5 expression. Conclusion: we demonstrated that METTL3/YTHDF2-mediated m6A methylation increased the expression of AGAP2-AS1, which could promote trastuzumab resistance in breast cancer. AGAP2-AS1 regulates trastuzumab resistance by inducing autophagy. Therefore, AGAP2-AS1 may be a promising predictive biomarker and therapeutic target in patients with breast cancer. [ABSTRACT FROM AUTHOR]

HER2-targeted therapies, such as Trastuzumab (Tz), have significantly improved the clinical outcomes for patients with HER2+ breast cancer (BC). However, treatment resistance remains a major obstacle. To elucidate functional and metabolic changes associated with acquired resistance, we characterized protein profiles of BC Tz-responder spheroids (RSs) and non-responder spheroids (nRSs) by a proteomic approach. Three-dimensional cultures were generated from the HER2+ human mammary adenocarcinoma cell line BT-474 and a derived resistant cell line. Before and after a 15-day Tz treatment, samples of each condition were collected and analyzed by liquid chromatography–mass spectrometry. The analysis of differentially expressed proteins exhibited the deregulation of energetic metabolism and mitochondrial pathways. A down-regulation of carbohydrate metabolism and up-regulation of mitochondria organization proteins, the tricarboxylic acid cycle, and oxidative phosphorylation, were observed in nRSs. Of note, Complex I-related proteins were increased in this condition and the inhibition by metformin highlighted that their activity is necessary for nRS survival. Furthermore, a correlation analysis showed that overexpression of Complex I proteins NDUFA10 and NDUFS2 was associated with high clinical risk and worse survival for HER2+ BC patients. In conclusion, the non-responder phenotype identified here provides a signature of proteins and related pathways that could lead to therapeutic biomarker investigation. [ABSTRACT FROM AUTHOR]

Simple Summary: HER2-positive breast cancer, treated with trastuzumab, often develops resistance within a year in about 50% of patients. This study identifies ITGβ3 as a key factor in promoting resistance by upregulating stem cell markers through the Notch signaling pathway. Combining trastuzumab with the integrin inhibitor cilengitide significantly reduces these markers, suggesting a potential therapeutic approach to overcoming resistance. HER2-positive breast cancer, characterised by overexpressed HER2 levels, is associated with aggressive tumour behaviour and poor prognosis. Trastuzumab is a standard treatment; however, approximately 50% of patients develop resistance within one year. This study investigates the role of ITGβ3 in promoting stemness and resistance in HER2-positive breast cancer cell lines (HCC1599 and SKBR3). The findings demonstrate that chronic exposure to trastuzumab upregulates stem cell markers (SOX2, OCT4, KLF4, NANOG, SALL4, ALDH, BMI1, Nestin, Musashi 1, TIM3, CXCR4). Given the documented role of RGD-binding integrins in drug resistance and stemness, we specifically investigated their impact on resistant cells. Overexpression of ITGβ3 enhances the expression of these stem cell markers, while silencing ITGβ3 reduces their expression, suggesting a major role for ITGβ3 in maintaining stemness and resistance. Further analysis reveals that ITGβ3 activates the Notch signalling pathway, known for regulating stem cell maintenance. The combination of trastuzumab and cilengitide, an integrin inhibitor, significantly decreases the expression of stem cell markers in resistant cells, indicating a potential therapeutic strategy to overcome resistance. These results identify the importance of ITGβ3 in mediating stemness and trastuzumab resistance through Notch signalling in HER2-positive breast cancer, offering new approaches for enhancing treatment efficacy. [ABSTRACT FROM AUTHOR]

Breast cancer antiestrogen resistance 4 (BCAR4) has been suggested that can modulate cell behavior, resulting in tumorigenesis and chemoresistance. However, the underlying mechanisms of BCAR4 in trastuzumab resistance (TR) is still elusive. Here, we explored the function and the underlying mechanism of BCAR4 involving in TR. We found that BCAR4 is significantly upregulated in trastuzumab‐resistant BC cells. Knockdown of BCAR4 could sensitize the BC cells to trastuzumab and suppress epithelial–mesenchymal transition (EMT). Mechanically, BCAR4 promotes yes‐associated protein 1 (YAP1) expression by competitively sponging miR‐665, to activated TGF‐β signaling. Reciprocally, YAP1 could occupy the BCAR4 promoter to enhance its transcription, suggesting that there exists a positive feedback regulation between YAP1 and BCAR4. Targeting the BCAR4/miR‐665/YAP1 axis may provide a novel insight of therapeutic approaches for TR in BC. [ABSTRACT FROM AUTHOR]

Simple Summary: tRF-27 has been identified as upregulated in both naïve trastuzumab-resistant HER2-positive breast cancer cells and patient samples, positioning it as a potential biomarker. However, the underlying mechanisms of this upregulation remain unclear. This study proposes that the abnormal transcription of specific tRNA-Cys-GCA isodecoders in naïve trastuzumab-resistant cells might contribute to the accumulation of tRF-27. Additionally, the reduction in H3K27me3 modifications at these tRNA genes, attributed to imbalances in histone modification enzymes, appears to influence tRNA transcription alterations. Building upon these findings, our research demonstrates that the application of a demethylase inhibitor may offer a potential strategy to overcome trastuzumab resistance. tRNA-derived fragments (tRFs) play crucial roles in cancer progression. Among them, tRF-27 has been identified as a key factor in promoting naïve trastuzumab resistance in HER2-positive breast cancer. However, the origin of tRF-27 remains uncertain. In this study, we propose that the upregulated expression of specific cysteine tRNAs may lead to the increased accumulation of tRF-27 in trastuzumab-resistant JIMT1 cells. Mechanistically, the reduced inhibitory H3K27me3 modification at the promoter regions of tRF-27-related tRNA genes in JIMT1 cells, potentially resulting from decreased EZH2 and increased KDM6A activity, may be a critical factor stimulating the transcriptional activity of these tRNA genes. Our research offers fresh insights into the mechanisms underlying elevated tRF-27 levels in trastuzumab-resistant breast cancer cells and suggests potential strategies to mitigate trastuzumab resistance in clinical treatments. [ABSTRACT FROM AUTHOR]

Simple Summary: A major hurdle in trastuzumab therapy remains acquired resistance within some HER2+ patients. Mechanisms contributing to, and as a consequence of, resistance remain elusive. Here, we investigate the spatiotemporal change in cell states within two cell lines—trastuzumab-sensitive (BT474) and -resistant (BT474R) HER2+ cancer cells in the presence of two endogenous ligands, epidermal growth factor (EGF) and neuregulin1/heregulin (HRG). We measure the HER2 receptor organization dynamics, signaling state, chromatin accessibility, and bioenergetics in both cell lines. Our measurements reveal significant alterations in a ligand-dependent manner within both cell lines. To the best of our knowledge, this study represents a novel attempt at systematically characterizing the effect of ligands on HER2 overexpressing cells, emphasizing their pivotal role. It provides critical insights into the dynamics of trastuzumab resistance in these cancers. Trastuzumab therapy in HER2+ breast cancer patients has mixed success owing to acquired resistance to therapy. A detailed understanding of downstream molecular cascades resulting from trastuzumab resistance is yet to emerge. In this study, we investigate the cellular mechanisms underlying acquired resistance using trastuzumab-sensitive and -resistant cancer cells (BT474 and BT474R) treated with endogenous ligands EGF and HRG across time. We probe early receptor organization through microscopy and signaling events through multiomics measurements and assess the bioenergetic state through mitochondrial measurements. Integrative analyses of our measurements reveal significant alterations in EGF-treated BT474 HER2 membrane dynamics and robust downstream activation of PI3K/AKT/mTORC1 signaling. EGF-treated BT474R shows a sustained interferon-independent activation of the IRF1/STAT1 cascade, potentially contributing to trastuzumab resistance. Both cell lines exhibit temporally divergent metabolic demands and HIF1A-mediated stress responses. BT474R demonstrates inherently increased mitochondrial activity. HRG treatment in BT474R leads to a pronounced reduction in AR expression, affecting downstream lipid metabolism with implications for treatment response. Our results provide novel insights into mechanistic changes underlying ligand treatment in BT474 and BT474R and emphasize the pivotal role of endogenous ligands. These results can serve as a framework for furthering the understanding of trastuzumab resistance, with therapeutic implications for women with acquired resistance. [ABSTRACT FROM AUTHOR]

Background: Trastuzumab resistance accounts for chemotherapy failure in gastric cancer patients in clinical practice. The significance of long non-coding RNAs (lncRNAs) in the maintenance of drug resistance in gastric cancer has been already underlined. Method: This study aimed to identify the specific role of lncRNA-ATB in gastric cancer progression and trastuzumab resistance. The downstream miRs of lncRNA-ATB and target genes of miRs were predicted by bioinformatics analysis and verified using dual luciferase reporter assay. Loss- and gain-function assays were performed to explore the roles of lncRNA-ATB, miR-200c, and zinc-finger protein 217 (ZNF217) in the cell functions and trastuzumab resistance of a trastuzumab-resistant gastric cancer cell line (NCI-N87-TR). Result: LncRNA-ATB was upregulated, while miR-200c was downregulated. Depletion of lncRNA-ATB or miR-200c elevation led to a decrease in malignant properties of NCI-N87-TR cells. LncRNA-ATB could negatively target miR- 200c, which in turn inversely targeted and reduced the expression of ZNF217. Silencing of ZNF217 could inhibit cell viability and migration. Conclusion: lncRNA-ATB promoted the progression and trastuzumab resistance of gastric cancer by repressing miR-200c via ZNF217 upregulation. [ABSTRACT FROM AUTHOR]

Background: Patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer and primary resistance to trastuzumab have a poor clinical outcome and lack good evidence to inform clinical decision. This study investigated the efficacy and safety of pyrotinib plus capecitabine in this population. Methods: This phase 2 trial was conducted at 16 sites in China. Patients received oral pyrotinib 400 mg once daily and capecitabine 1000 mg/m2 twice a day on days 1–14 of each 21-day cycle until disease progression or intolerable toxicity. The primary endpoint was investigator-assessed progression-free survival (PFS). Results: Between June 2019 and September 2021, 100 patients were enrolled with a median age of 51 years (range, 24–69). All patients had been treated with trastuzumab and 21 (21.0%) patients had prior use of pertuzumab. As of August 31, 2022, the median follow-up duration was 20.1 months (range, 1.3–38.2). The median PFS was 11.8 months (95% confidence interval [CI], 8.4–15.1), which crossed the pre-specified efficacy boundary of 8.0 months. The objective response rate was 70.0% (70/100), with a median duration of response of 13.8 months (95% CI, 10.2–19.3). The disease control rate was 87.0% (87/100). The median overall survival was not reached. The most common grade ≥ 3 treatment-emergent adverse event was diarrhea (24 [24.0%]). No treatment-related deaths occurred. Conclusions: Pyrotinib plus capecitabine can be considered to be a treatment option in HER2-positive advanced breast cancer patients who have shown primary resistance to trastuzumab. Even in the era of modern anti-HER2 treatments, this clinical setting warrants more investigations to meet unmet needs. Trial registration: ClinicalTrials.gov, NCT04001621. Retrospectively registered on June 28, 2019. [ABSTRACT FROM AUTHOR]

Breast cancer is the most common cancer in women. The human epidermal growth factor receptor 2 (HER2) overexpressing subtype is related to poor prognosis with an aggressive phenotype and is reported as one of the most commonly seen subtypes. Trastuzumab is prevalently used as a treatment method for HER2+ breast cancer however, resistance to the drug frequently occurs following the treatment. MicroRNAs (miRNAs) are 19-23 nucleotide long small RNAs, which regulate gene expression at posttranscriptional level and studies show that there are differentially expressed miRNAs between drug sensitive and resistant groups, indicating that they might have some key roles in drug effectiveness. In this study, the aim is to find out the role of miR-216b-5p in trastuzumab resistance. SK-BR-3 cells developed resistance to trastuzumab after continuous treatment with increasing concentrations of the drug for 6 months. To investigate the effect of miR-216b-5p on cancer cell behavior in resistance state, proliferation, motility, and invasion capacities of these resistant cells were analyzed by xCELLigence real-time cell analyzer. To further understand the molecular mechanisms underlying the regulation of resistant SK-BR-3 cells by miR-216b-5p, microarray analysis was performed. Apoptosis analysis was also performed since the pathway enrichment analysis pointed out cell death related pathways. The proliferation, motility, and invasion capacities of the miR-216b-5p transfected resistant cells were diminished compared to sensitive cells. We identified the necroptosis signaling pathway as the result of microarray and pathway enrichment analyses. STAT1, IRF9, and PKR were validated as the significant elements of the pathway, which are also the putative targets of miR-216b-5p. Our apoptosis analysis showed that a significant amount of trastuzumab resistant SK-BR-3 cells entered to late apoptosis/necrosis stage upon miR-216b-5p overexpression, it could be concluded that reexpression of miR-216b-5p sensitizes trastuzumab resistance through necroptosis in breast cancer. [ABSTRACT FROM AUTHOR]

[Display omitted] • ELF3-MED23 hotspot was efficiently deciphered by using customized small molecules. • ELF3-MED23 PPI depends on specific H-bondings to upregulate HER2 expression. • PPI inhibitory activity of YK1 was specific to ELF3-MED23. • YK1-mediated specific H-bond interruption induces promising anticancer activities. • Anticancer effect of YK1 was even significant against trastuzumab-refractory clones. • YK1 held highly drug-like properties showing favorable PK profile. HER2 overexpression induces cancer aggression and frequent recurrences in many solid tumors. Because HER2 overproduction is generally followed by gene amplification, inhibition of protein–protein interaction (PPI) between transcriptional factor ELF3 and its coactivator MED23 has been considered an effective but challenging strategy. This study aimed to determine the hotspot of ELF3-MED23 PPI and further specify the essential residues and their key interactions in the hotspot which are controllable by small molecules with significant anticancer activity. Intensive biological evaluation methods including SEAP, fluorescence polarization, LC-MS/MS-based quantitative, biosensor, GST-pull down assays, and in silico structural analysis were performed to determine hotspot of ELF3-MED23 PPI and to elicit YK1, a novel small molecule PPI inhibitor. The effects of YK1 on possible PPIs of MED23 and the efficacy of trastuzumab were assessed using cell culture and tumor xenograft mouse models. ELF3-MED23 PPI was found to be specifically dependent on H-bondings between D400, H449 of MED23 and W138, I140 of ELF3 for upregulating HER2 gene transcription. Employing YK1, we confirmed that interruption on these H-bondings significantly attenuated the HER2-mediated oncogenic signaling cascades and exhibited significant in vitro and in vivo anticancer activity against HER2-overexpressing breast and gastric cancers even in their trastuzumab refractory clones. Our approach to develop specific ELF3-MED23 PPI inhibitor without interfering other PPIs of MED23 can finally lead to successful development of a drug resistance-free compound to interrogate HER2 biology in diverse conditions of cancers overexpressing HER2. [ABSTRACT FROM AUTHOR]

BACKGROUND: The albumin-bilirubin (ALBI) score is a novel indicator of liver function. Some studies showed that the ALBI score was a predictive marker for the prognosis and efficacy of drug therapy in malignancies. We aimed to assess the predicted role of ALBI score in the sensitivity to therapy with trastuzumab in patients with human epidermal growth factor receptor 2 (HER2) positive breast cancer (BC). The clinical data of 226 HER2-positive BC patients at the Harbin Medical University Cancer Hospital from January 2017 and December 2018 were retrospectively collected. The ALBI score was calculated with serum albumin and bilirubin before diagnosis. The associations between ALBI score and trastuzumab resistance were analyzed by logistic regression analyses. The patients with trastuzumab resistance had higher ALBI scores compared with the patients without trastuzumab resistance. Moreover, there were weak correlations between the ALBI score and lymph node status (P = 0.093). In addition, multivariate analysis revealed that the ALBI score was an independent prognostic factor for trastuzumab resistance in HER2-positive BC. High ALBI score is associated with trastuzumab resistance in HER2-positive BC. Future studies are needed. [ABSTRACT FROM AUTHOR]

Trastuzumab plus chemotherapy is the standard of care for the first-line treatment of patients with HER2+ advanced esophagogastric (EG) cancer. Nevertheless, patients frequently develop resistance. In preclinical models, we identified the overexpression of Fibroblast Growth Factor Receptor (FGFR) 3 as a mechanism potentially involved in trastuzumab-acquired resistance. FGFR inhibition could be a potential mechanism as a second-line treatment. In this Simon's two-stage phase 2, single arm study, patients with advanced EG cancer refractory to trastuzumab-containing therapies received pemigatinib, an inhibitor of FGFR. The primary end point was the 12-week progression-free survival rate. Translational analyses were performed on tissue and plasma samples. Eight patients were enrolled in the first stage. Although the 6-week disease control rate was 25%, only one patient achieved a stable disease after 12 weeks of treatment. The trial was discontinued before the second stage. Two out of six evaluable tumor samples expressed FGFR3. No FGFRs amplification was detected. HER2 amplification was lost in three out of eight patients. Three patients had an high Tumor Mutational Burden, and two of them are significantly long-term survivors. These results do not support the therapeutic efficacy of targeting FGFR in unselected patients with advanced EG cancer, who are refractory to trastuzumab-containing therapies. [ABSTRACT FROM AUTHOR]

Simple Summary: Cortactin (CTTN) is an actin-binding protein that is mainly known for its ability to promote cancer progression. It is unclear, however, whether CTTN affects tumor initiation and anti-tumor drug resistance in breast cancer. Here, we investigated the potential role of CTTN as a novel poor prognostic biomarker and possible therapeutic target of trastuzumab resistance for HER2 positive breast cancer. Our findings showed that CTTN enhances tumor initiation and increases anti-HER2 drug resistance by activating the DKK-1/Wnt/β-catenin signaling pathway. CTTN-induced cancer stem cell-like properties were reversed by treatment of β-catenin/TCF inhibitor. Furthermore, combinational treatment with trastuzumab and β-catenin/TCF inhibitor overcame CTTN-induced trastuzumab resistance. These results suggest that combined treatment of trastuzumab and Wnt signaling inhibitors could be an effective therapeutic strategy to treat HER2+ breast tumors expressing high levels of CTTN. Collectively, we suggest that CTTN could be a potential target for treatment of trastuzumab resistance in HER2 positive breast cancer patients. Background: Despite the therapeutic success of trastuzumab, HER2 positive (HER2+) breast cancer patients continue to face significant difficulties due to innate or acquired drug resistance. In this study we explored the potential role of CTTN in inducing trastuzumab resistance of HER2+ breast cancers. Methods: Genetic changes of CTTN and survival of HER2+ breast cancer patients were analyzed in multiple breast cancer patient cohorts (METABRIC, TCGA, Kaplan-Meier (KM) plotter, and Hanyang University cohort). The effect of CTTN on cancer stem cell activity was assessed using the tumorsphere formation, ALDEFLUOR assay, and by in vivo xenograft experiments. CTTN-induced trastuzumab resistance was assessed by the sulforhodamine B (SRB) assay, colony formation assays, and in vivo xenograft model. RNA-seq analysis was used to clarify the mechanism of trastuzumab resistance conferred by CTTN. Results: Survival analysis indicated that CTTN overexpression is related to a poor prognosis in HER2+ breast cancers (OS, p = 0.05 in the Hanyang University cohort; OS, p = 0.0014 in KM plotter; OS, p = 0.008 and DFS, p = 0.010 in METABRIC). CTTN overexpression-induced cancer stem cell-like characteristics in experiments of tumorsphere formation, ALDEFLUOR assays, and in vivo limiting dilution assays. CTTN overexpression resulted in trastuzumab resistance in SRB, colony formation assays, and in vivo xenograft models. Mechanistically, the mRNA and protein levels of DKK-1, a Wnt antagonist, were downregulated by CTTN. Treatment of the β-catenin/TCF inhibitor reversed CTTN-induced cancer stem cell-like properties in vitro. Combination treatment with trastuzumab and β-catenin/TCF inhibitor overcame trastuzumab resistance conferred by CTTN overexpression in in vitro colony formation assays. Conclusions: CTTN activates DKK-1/Wnt/β-catenin signaling to induce trastuzumab resistance. We propose that CTTN is a novel biomarker indicating a poor prognosis and a possible therapeutic target for overcoming trastuzumab resistance. [ABSTRACT FROM AUTHOR]

Human epidermal growth factor receptor 2-positive (HER2+) breast cancer is characterized by invasive growth, rapid metastasis and chemoresistance. Trastuzumab is an effective treatment for HER2+ breast cancer; however, trastuzumab resistance leads to cancer relapse and metastasis. CKLF-like MARVEL transmembrane domain-containing 6 (CMTM6) has been considered as a new immune checkpoint for tumor-induced immunosuppression. The role of CMTM6 in trastuzumab resistance remains unknown. Here, we uncover a role of CMTM6 in trastuzumab-resistant HER2+ breast cancer. CMTM6 expression was upregulated in trastuzumab-resistant HER2+ breast cancer cell. Patients with high CMTM6 expressing HER2+ breast cancer had worse overall and progression-free survival than those with low CMTM6 expression. In vitro, CMTM6 knockdown inhibited the proliferation and migration of HER2+ breast cancer cells, and promoted their apoptosis, while CMTM6 overexpression reversed these effects. CMTM6 and HER2 proteins were co-localized on the surface of breast cancer cells, and CMTM6 silencing reduced HER2 protein levels in breast cancer cells. Co-immunoprecipitation revealed that CMTM6 directly interacted with HER2 in HER2+ breast cancer cells, and CMTM6 overexpression inhibited HER2 ubiquitination. Collectively, these findings highlight that CMTM6 stabilizes HER2 protein, contributing to trastuzumab resistance and implicate CMTM6 as a potential prognostic marker and therapeutic target for overcoming trastuzumab resistance in HER2+ breast cancer. [ABSTRACT FROM AUTHOR]

Background: The emergence of de novo or intrinsic trastuzumab resistance is exceedingly high in breast cancer that is HER2 positive and correlates with an abundant cancer stem cell (CSC)-like population. We sought to examine the capacity of β-escin, an anti-inflammatory drug, to address trastuzumab resistance in HER2-positive breast cancer cells. Methods: The effect of β-escin on trastuzumab-resistant and -sensitive cell lines in vitro was evaluated for apoptosis, expression of HER2 family members, and impact on CSC-like properties. An in vivo model of trastuzumab-resistant JIMT-1 was used to examine the efficacy and toxicity of β-escin. Results: β-escin induced mitochondrial-mediated apoptosis accompanied by reactive oxygen species (ROS) production and increased active p18Bax fragmentation, leading to caspase-3/-7 activation. Attenuation of CSC-related features by β-escin challenge was accompanied by marked reductions in CD44high/CD24low stem-like cells and aldehyde dehydrogenase 1 (ALDH1) activity as well as hindrance of mammosphere formation. β-escin administration also significantly retarded tumor growth and angiogenesis in a trastuzumab-resistant JIMT-1 xenograft model via downregulation of CSC-associated markers and intracellular domain HER2. Importantly, β-escin selectively inhibited malignant cells and was less toxic to normal mammary cells, and no toxic effects were found in liver and kidney function in animals. Conclusions: Taken together, our findings highlight β-escin as a promising candidate for the treatment of trastuzumab-resistant HER2-positive breast cancers. [ABSTRACT FROM AUTHOR]

Trastuzumab is the first-line therapy for human epidermal growth factor receptor 2-positive (HER2+) breast cancer, but often patients develop acquired resistance. Although other agents are in clinical use to treat trastuzumab-resistant (TR) breast cancer; still, the patients develop recurrent metastatic disease. One of the primary mechanisms of acquired resistance is the shedding/loss of the HER2 extracellular domain, where trastuzumab binds. We envisioned any new agent acting downstream of the HER2 should overcome trastuzumab resistance. The mixed lineage kinase 3 (MLK3) activation by trastuzumab is necessary for promoting cell death in HER2+ breast cancer. We designed nanoparticles loaded with MLK3 agonist ceramide (PPP-CNP) and tested their efficacy in sensitizing TR cell lines, patient-derived organoids, and patient-derived xenograft (PDX). The PPP-CNP activated MLK3, its downstream JNK kinase activity, and down-regulated AKT pathway signaling in TR cell lines and PDX. The activation of MLK3 and down-regulation of AKT signaling by PPP-CNP induced cell death and inhibited cellular proliferation in TR cells and PDX. The apoptosis in TR cells was dependent on increased CD70 protein expression and caspase-9 and caspase-3 activities by PPP-CNP. The PPP-CNP treatment alike increased the expression of CD70, CD27, cleaved caspase-9, and caspase-3 with a concurrent tumor burden reduction of TR PDX. Moreover, the expressions of CD70 and ceramide levels were lower in TR than sensitive HER2+ human breast tumors. Our in vitro and preclinical animal models suggest that activating the MLK3-CD70 axis by the PPP-CNP could sensitize/overcome trastuzumab resistance in HER2+ breast cancer. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to explore the role of galectin‐3 in human epidermal growth factor receptor 2 (HER2)‐positive breast cancer cells and the potential mechanism. Methods: Kaplan–Meier (KM)‐plot and The Cancer Genome Atlas (TCGA) databases were used to study the role of galectin‐3 in the prognosis of HER2‐positive breast cancer. The effects of galectin‐3 on cell proliferation, migration, invasion, and colony formation ability in HER2‐positive breast cancer cells were examined. The relationship between galectin‐3 and important components in the HER2 pathways, including HER2, epidermal growth factor receptor (EGFR), protein kinase B (AKT), and phosphatase and tensin homolog (PTEN), was further studied. Lentivirus and CRISPR/Cas9 were used to construct stable cell lines. Cell counting kit‐8 (CCK‐8) and apoptosis assays were used to study the relationship between galectin‐3 and trastuzumab. The effect of galectin‐3 on cell stemness was studied by mammosphere formation assay. The effects of galectin‐3 on stemness biomarkers and the Notch1 pathway were examined. Tumorigenic models were used to evaluate the effects of galectin‐3 on tumorigenesis and the therapeutic effect of trastuzumab in vivo. Results: HER2‐positive breast cancer patients with a high expression level of LGALS3 (the gene encoding galectin‐3) messenger RNA (mRNA) showed a poor prognosis. Galectin‐3 promoted cancer malignancy through phosphoinositide 3‐kinase (PI3K)/AKT signaling pathway activation and upregulated stemness by activating the Notch1 signaling pathway in HER2‐positive breast cancer cells. These two factors contributed to the enhancement of trastuzumab resistance in cells. Knockout of LGALS3 had a synergistic therapeutic effect with trastuzumab both in vitro and in vivo. Conclusions: Galectin‐3 may represent a prognostic predictor and therapeutic target for HER2‐positive breast cancer. [ABSTRACT FROM AUTHOR]

Trastuzumab resistance presents a significant challenge in the treatment of HER2+ breast cancer, necessitating the investigation of combination therapies to overcome this resistance. Honokiol, a compound with broad anticancer activity, has shown promise in this regard. This study aims to discover the effect of honokiol in increasing trastuzumab sensitivity in HER2+ trastuzumab-resistant breast cancer cells HCC1954 and the underline mechanisms behind. A bioinformatics study performed to explore the most potential target hub gene for honokiol in HER2+ breast cancer. Honokiol, trastuzumab and combined treatment cytotoxicity activity was then evaluated in both parental HCC1954 and trastuzumab resistance (TR-HCC1954) cells using MTT assay. The expression levels of these hub genes were then analyzed using qRT-PCR and those that could not be analyzed were subjected to molecular docking to determine their potential. Honokiol showed a potent cytotoxicity activity with an IC 50 of 41.05 μM and 69.61 μM in parental HCC1954 and TR-HCC1954 cell line respectively. Furthermore, the combination of honokiol and trastuzumab resulted in significant differences in cytotoxicity in TR-HCC1954 cells at specific concentrations. Molecular docking and the qRT-PCR showed that the potential ERα identified from the bioinformatics analysis was affected by the treatment. Our results show that honokiol has the potential to increase the sensitivity of trastuzumab in HER2+ trastuzumab resistant breast cancer cell line HCC1954 by affecting regulating estrogen receptor signaling. Further research is necessary to validate these findings. [Display omitted] • Using bioinformatics to explore the potential target hub gene of honokiol in HER2+ trastuzumab-resistant breast cancer cells. • Honokiol increased the sensitivity of trastuzumab in trastuzumab-resistant HCC1954 breast cancer cells. • ERα as the potential target of honokiol in overcoming breast cancer resistance towards trastuzumab. [ABSTRACT FROM AUTHOR]

The specific human epidermal growth factor receptor 2 (HER2)-targeting monoclonal antibody trastuzumab shows considerable clinical efficacy in patients with HER2-overexpressing breast cancer. However, about 20% of patients who receive trastuzumab in the adjuvant setting relapse, and approximately half of patients with metastatic HER2-positive breast cancer develop resistance to trastuzumab within 1 year. Although the mechanism of trastuzumab resistance has been explored broadly, whether and how angiogenesis participates in trastuzumab resistance is unclear. Here, we examined the association between angiogenesis and trastuzumab resistance by using a trastuzumab-resistant cell line (SKBR3-TR). Compared with that from the parental trastuzumab-sensitive SKBR3 cells, the culture supernatant from SKBR3-TR cells significantly increased the sprouting of endothelial cells. To identify intercellular features that contribute to the induction of endothelial tube formation, proteomics revealed that α-crystallin B chain (αB-crystallin) was upregulated in SKBR3-TR cells. Moreover, silencing of αB-crystallin significantly repressed SKBR3-TR-induced tube formation, and knockdown of αB-crystallin in SKBR3-TR cells suppressed the activation of mechanistic target of rapamycin (mTOR) in endothelial cells. In addition, treatment with rapamycin, an inhibitor of mTOR, reversed the SKBR3-TR-induced promotion of tube formation. In summary, αB-crystallin enhanced the ability of SKBR3-TR cells to activate mTOR in endothelial cells and thus promote angiogenesis. • Increased αB-crystallin level of SKBR3-TR cells promoted tube formation by HAECs. • Silencing αB-crystallin in SKBR3-TR cells suppresses p-mTOR in endothelial cells. • Rapamycin suppressed tube formation in HAECs induced by SKBR3-TR cells. [ABSTRACT FROM AUTHOR]

Background: To date, many efforts have been made to understand the resistance mechanism of trastuzumab in human epidermal growth factor receptor 2 (HER2)-positive breast and gastric cancer. However, there is still a huge unmet medical need for patients with trastuzumab resistance. Methods: In our study, we generated four trastuzumab-resistant (HR) cancer cell lines from ERBB2-amplified gastric and biliary tract cancer cell lines (SNU-216, NCI-N87, SNU-2670, and SNU-2773). Results: Here, we found higher PD-L1 expression in trastuzumab-resistant (HR) HER2-positive cancer cells than in parental cells, and blocking PD-L1 reversed the resistance to trastuzumab in HR cells. Trastuzumab upregulated PD-L1 expression via NF-κB activation in both parental and HR cells, however, led to DNA damage only in parental cells. The WEE1 inhibitor adavosertib, which downregulates PD-L1 expression, enhanced trastuzumab efficacy by blocking BRCA1-CMTM6-PD-L1 signals and the HER2-CDCP-1-SRC axis. Additionally, the levels of galectin-9, CD163, FoxP3, and CTLA-4 were diminished by blocking WEE1 in the presence of human PBMCs in vitro. Conclusion: Taken together, the strategy of co-targeting HER2 and WEE1 could overcome resistance to trastuzumab in HER2-positive cancers, supporting further clinical development in HER2-positive cancer patients. [ABSTRACT FROM AUTHOR]

Over-expression of the human epidermal growth factor receptor-2 (HER2) is related to aggressive tumors and poor prognosis in breast cancer. Trastuzumab (TRA) resistance leads to tumor recurrence and metastasis, resulting in poor prognosis in HER2-positive breast cancer. POU Class 4 Homeobox 1 (POU4F1) is a member of the POU domain family transcription factors, and has a key role in regulating cancers. However, its effects on TRA-resistant HER2-positive breast cancer are still vague. In the present study, we found that POU4F1 expression was dramatically increased in clinical breast cancer specimens with TRA resistance. Higher POU4F1 was also detected in HER2-positive breast cancer cells with TRA resistance than that of the parental ones. Poor prognosis was detected in breast cancer patients with high POU4F1 expression. Under TRA treatment, POU4F1 knockdown significantly reduced the proliferative capacity of HER2-positive breast cancer cells with TRA resistance. POU4F1 silence also sensitized resistant HER-positive breast cancer cells to TRA treatment in vivo using a xenograft mouse model, along with the markedly reduced tumor growth rate and tumor weight. Moreover, we found that POU4F1 deletion greatly decreased the activation of mitogen-activated or extracellular signal-regulated protein kinase kinases 1 and 2 (MEK1/2) and extracellular-regulated kinase 1/2 (ERK1/2) signaling pathways in breast cancer cells with TRA resistance. Migration and invasion were also effectively hindered by POU4F1 knockdown in TRA-resistant HER2-positive breast cancer cells. Notably, we found that POU4F1 deletion-improved chemosensitivity of HER2-positive breast cancer cells with drug-resistance to TRA treatment was closely associated with the blockage of ERK1/2 signaling. Collectively, our findings reported a critical role of POU4F1 in regulating TRA resistance, and demonstrated the underlying molecular mechanisms in HER2-positive breast cancer. Thus, POU4F1 may be a promising prognostic and therapeutic target to develop effective treatment for overcoming TRA resistance. • POU4F1 suppression reduces the proliferation and tumor growth in HER2-positive breast cancer. • POU4F1 knockdown inhibits migration and invasion in HER2-positive breast cancer cells through mediating ERK1/2 signaling. • POU4F1 is clinically correlated with the activation of MEK/ERK signaling in breast cancer. [ABSTRACT FROM AUTHOR]

Although trastuzumab has greatly improved the outcome of HER2-positive breast cancer, the emergence of resistance hampers its clinical benefits. Trastuzumab resistance is a multi-factorial consequence predominantly due to presence of cancer stem-like cells (CSCs). AZD1775, a potent anti-cancer agent targeting WEE1 kinase to drive tumor cells with DNA damage to premature mitosis, has previously shown high efficacies when targeting different cancers with a well-tolerated cytotoxic profile, but has not been evaluated in trastuzumab-resistant (TrR) breast cancer. We sought to investigate the effect of AZD1775 on cancer stem-like cell (CSC) properties, apoptosis, cell cycle regulation in TrR breast cancer. Our study for the first time demonstrated that AZD1775 induces apoptosis and arrests TrR cells at G2/M phase. More importantly, AZD1775 effectively targeted CSC properties by suppressing MUC1 expression levels. AZD1775 administration also induced apoptosis in our in-house patient-derived tumor cell line at passage 0, implying its significant clinical relevance. These findings highlight the potential clinical application of AZD1775 in overcoming trastuzumab resistance in breast cancer. [ABSTRACT FROM AUTHOR]

Background: Although trastuzumab provides significant clinical benefit for HER2-positive breast cancers, responses are limited by the emergence of resistance. Recent evidence suggests that long noncoding RNAs (lncRNAs) play important roles in tumorigenesis and chemoresistance. However, the regulatory mechanism of lncRNAs in trastuzumab resistance is not well established to date. In this research, we identified the differentially expressed lncRNA and investigated its regulatory role in trastuzumab resistance of breast cancer. Methods: LncRNA microarray and qRT-PCR were performed to identify the dysregulated lncRNAs. Transmission electron microscopy, differential ultracentrifugation and qRT-PCR were used to verify the existence of exosomal AFAP1-AS1 (actin filament associated protein 1 antisense RNA 1). Bioinformatics prediction, RNA fluorescence in situ hybridization (RNA-FISH) and immunoprecipitation assays were performed to identify the direct interactions between AFAP1-AS1 and other associated targets, such as AU-binding factor 1 (AUF1) and ERBB2. Finally, a series gain- or loss-functional assays were done to prove the precise role of AFAP1-AS1 in trastuzumab resistance. Results: AFAP1-AS1 was screened out due to its higher expression in trastuzumab-resistant cells compared to sensitive cells. Increased expression of AFAP1-AS1was associate with poorer response and shorter survival time of breast cancer patients. AFAP1-AS1 was upregulated by H3K27ac modification at promoter region, and knockdown of AFAP1-AS1 reversed trastuzumab resistance. Moreover, extracellular AFAP1-AS1 secreted from trastuzumab resistant cells was packaged into exosomes and then disseminated trastuzumab resistance of receipt cells. Mechanically, AFAP1-AS1 was associated with AUF1 protein, which further promoted the translation of ERBB2 without influencing the mRNA level. Conclusion: Exosomal AFAP1-AS1 could induce trastuzumab resistance through associating with AUF1 and promoting ERBB2 translation. Therefore, AFAP1-AS1 level may be useful for prediction of trastuzumab resistance and breast cancer treatment. [ABSTRACT FROM AUTHOR]

Background: Although an immense effort has been made to develop a novel biomarker for response to trastuzumab, no reliable biomarkers are available to guide management, expect for HER2. The aim of this study was to examine the relationship between microRNA (miRNA) expression and resistance to trastuzumab. Methods: Differentially expressed miRNAs between trastuzumab‐resistant and trastuzumab‐sensitive cell lines were analyzed using microarrays. We performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses to determine the functions of differentially expressed miRNA and their targeted genes. Furthermore, the protein–protein interactions (PPI) network was analyzed. Serum samples were collected from patients with HER2‐positive breast cancer who were treated with trastuzumab. We validated the miRNAs expression levels by quantitative reverse‐transcription polymerase chain reaction (qRT‐PCR) in these serums. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the predictive performance of the miRNA. Results: Using miRNA microarrays, 151 miRNAs that significant differentially expressed between the trastuzumab‐resistant and sensitive cells were identified, including 46 upregulated and 105 downregulated miRNAs. Results of real‐time PCR confirmed seven miRNAs in cell lines. PI3K‐Akt signaling pathway was involved in regulating biological function according to KEGG analysis. Compared with the serums of trastuzumab‐sensitive patients, three miRNAs, namely miR‐200b, miR‐135b, and miR‐29a, were identified to be upregulated, and miR‐224 was downregulated in the trastuzumab‐resistant serums. ROC analysis showed that four miRNAs were correlated with trastuzumab resistance. Furthermore, three subnetwork modules of PPI network were obtained. Conclusion: The results indicated that miRNAs were reliable predictive biomarkers for response to trastuzumab. [ABSTRACT FROM AUTHOR]

Trastuzumab is a successful, rationally designed therapy that provides significant clinical benefit for human epidermal growth factor receptor-2 (HER2)-positive breast cancer patients. However, about half of individuals with HER2-positive breast cancer do not respond to trastuzumab treatment because of various resistance mechanisms, including but not limited to: 1) shedding of the HER2 extracellular domain, 2) steric hindrance (e.g., MUC4 and MUC1), 3) parallel pathway activation (this is the general mechanism cited in the quote above), 4) perturbation of downstream signaling events (e.g., PTEN loss or PIK3CA mutation), and 5) immunologic mechanisms (such as FcR polymorphisms). EPHA5, a receptor tyrosine kinase, has been demonstrated to act as an anticancer agent in several cancer cell types. In this study, deletion of EPHA5 can significantly increase the resistance of HER2-positive breast cancer patients to trastuzumab. To investigate how EPHA5 deficiency induces trastuzumab resistance, clustered regularly interspaced short palindromic repeat technology was used to create EPHA5-deficient variants of breast cancer cells. EPHA5 deficiency effectively increases breast cancer stem cell (BCSC)-like properties, including NANOG, CD133+, E-cadherin expression, and the CD44+/CD24-/low phenotype, concomitantly enhancing mammosphere-forming ability. EPHA5 deficiency also caused significant aggrandized tumor malignancy in trastuzumab-sensitive xenografts, coinciding with the up-regulation of BCSC-related markers and intracellular Notch1 and PTEN/AKT signaling pathway activation. These findings highlight that EPHA5 is a potential prognostic marker for the activity of Notch1 and better sensitivity to trastuzumab in HER2-positive breast cancer. Moreover, patients with HER2-positive breast cancers expressing high Notch1 activation and low EPHA5 expression could be the best candidates for anti-Notch1 therapy. [ABSTRACT FROM AUTHOR]

Resistance to trastuzumab has become a limiting factor for therapeutic efficacy of human epidermal growth factor 2 (HER2)-positive breast cancer. Different expression levels of miRNAs in cancer cells have been associated with poor prognosis and response to chemotherapy. The aim of this study was to evaluate miRNAs that were thought to be associated with HER2-positive breast cancer chemoresistance. In this study, the relative expression of candidate miRNAs to U6 RNA was evaluated in trastuzumab-resistant and trastuzumab-sensitive cells using relative real-time PCR. Our results demonstrated that miR-23b-3p, miR-195-5p, miR-656-5p, and miR-340-5p were significantly dysregulated. For the first time in this study, these miRNAs were identified to be involved in trastuzumab resistance. TargetScan and miRDB were then used for predicting the potential targets of the candidate miRNAs. Our results also revealed that the predicted potential targets of these miRNAs were strongly associated with drug resistance pathways. As a relative expression of candidate miRNAs was statistically different in trastuzumab-resistant and trastuzumab-sensitive cells, their potential targets were involved in drug resistance pathways. We strongly hypothesized the dysregulation of miRNAs as a possible mechanism of trastuzumab resistance. We also assumed that the strategic manipulation of these regulatory networks might be a possible therapeutic strategy to improve the results of chemotherapy for this resistance. However, more research is needed to evaluate the role of these miRNAs in the acquisition of trastuzumab resistance. [ABSTRACT FROM AUTHOR]

Recently, miRNAs have been regarded as potential candidates for mediating therapeutic functions by targeting genes related to drug response. In this study, we suggested that plasma miRNAs may be correlated with response to trastuzumab in HER2-positive breast cancer patients. To determine whether miR-195, miR-23b-3p, miR-1246, and miR-34c-3p are involved in trastuzumab resistance, we screened their expressions in the BT-474 cell line, which was followed by plasma analysis from 20 trastuzumab-resistant HER2-positive breast cancer patients and 20 nonresistance subjects. Then, TargetScan, Pictar, and miRDB were applied to find the possible targets of the selected miRNAs. In addition, the expression status of admitted targets was evaluated. Our results showed that in resistant BT-474 cells, miR-1246, and miR-23b-3p were significantly upregulated, and miR-195-5p and miR-34c-3p were downregulated. In plasma analysis, we found miR-195-5p, miR-34c-3p, and miR-1246 meaningfully diminished in the resistant group, while the expression of miR-23b-3p was not statistically different. The expression levels of confirmed targets by qRT-PCR showed that the expression of RAF1, AKT3, c-MET, CCND1, PHLPP2, MYB, MAP2K1, and PTEN was significantly upregulated, while the expression of CCNG2 was significantly downregulated. The networks of miRNAs with their confirmed targets improved comprehension of miRNA-mediated therapeutic responses to trastuzumab and might be proposed for more characterization of miRNA functions. Moreover, these data indicated that miR-195-5p, miR-34c-3p, and miR-1246 could be possible biomarkers for prognosis and early detection of the trastuzumab-resistant group from the sensitive group of HER2-positive breast cancer patients. • Resistance to trastuzumab is a major issue for HER2-positive breast cancer treatment. • miRNAs could be biomarkers for disease diagnosis, prognosis, and treatment. • Altered miRNA expression may help detect trastuzumab-resistant patients quickly. • miR-195, −34c, and − 1246 dysregulation might be biomarkers for trastuzumab resistance. [ABSTRACT FROM AUTHOR]

Abstract Introduction Although targeting human epidermal growth factor receptor 2 (HER2) is a meaningful treatment in HER2-positive breast cancer, ultimately resistance develops. Androgen receptor (AR) expression and immune cell infiltration are thought to be involved in trastuzumab response and may, therefore, be of interest as additional targets for therapy in HER2-positive breast cancer. Aim To improve insights into the presence among AR expression, immune cell infiltration and HER2, we analysed HER2-positive breast tumours. Methods Primary tumours of 221 patients treated with trastuzumab for metastatic disease were selected. HER2 status was centrally confirmed. AR, T-cells (CD3 and CD8), programmed cell death protein 1 (PD-1) and PD-1 ligand 1 immunohistochemical staining and M2 tumour-associated macrophages (TAMs; CD68 and CD163) immunofluorescence were performed. Tumour-infiltrating lymphocytes were evaluated by haematoxylin and eosin staining. Results Sufficient tumour material was available for 150 patients. Oestrogen receptor was expressed in 51.3% of the tumours and AR in 81.3% of the tumours. AR expression was inversely correlated with M2 TAM (Pearson's r = −0.361, P < 0.001), CD3+ (r = −0.199, P < 0.030) and CD8+ (r = −0.212, P < 0.021) T-cell infiltration. Clustering analysis showed high immune cell infiltration in AR low-expressing tumours, and low immune cell infiltration in AR-high expressing tumours. Conclusion AR expression inversely correlates with immune cell infiltration in HER2-positive breast cancer. Highlights • Androgen receptor (AR) expression was studied in human epidermal growth factor receptor 2–positive advanced breast cancer. • AR expression was negatively correlated with immune cell infiltration. • The strongest negative correlation with immune cell infiltration was with M2 tumour-associated macrophages. • A subgroup was identified with low immune cell infiltration and high AR expression. [ABSTRACT FROM AUTHOR]

Background/Aims: Resistance to trastuzumab remains a common challenge to HER-2 positive breast cancer. Up until now, the underlying mechanism of trastuzumab resistance is still unclear. tRNA-derived small non-coding RNAs, a new class of small non-coding RNA (sncRNAs), have been observed to play an important role in cancer progression. However, the relationship between tRNA-derived fragments and trastuzumab resistance is still unknown. Methods: We detected the levels of tRNA-derived fragments expression in normal breast epithelial cell lines, trastuzumab-sensitive and -resistant breast cancer cell lines using high-throughput sequencing. qRT-PCR was conducted to validate the differentially expressed fragments in serums from trastuzumab-sensitive and -resistant patients. A receiver operating characteristic (ROC) curve analysis was performed to evaluate the power of specific tRNA-derived fragments. Progression-free survival (PFS) was analyzed using Cox-regression. Results: Our sequence results showed that tRNA-derived fragments were differentially expressed in the HBL-100, SKBR3, and JIMT-1 cell lines. tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN were found significantly upregulated in trastuzumab-resistant patients compared to sensitive individuals, and the ROC analysis showed that tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN were correlated with trastuzumab resistance. In a multivariate analysis, higher levels of tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN expression were associated with significantly shorter PFS in patients with metastatic HER-2 positive breast cancer. Conclusion: Our results suggest that tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN play important roles in trastuzumab resistance. Patients with high levels of tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN expression benefitted less from trastuzumab-based therapy than those that express lower-levels of these molecules. tRF-30-JZOYJE22RR33 and tRF-27-ZDXPHO53KSN may be potential biomarkers and intervention targets in the clinical treatment of trastuzumab-resistant breast cancer. [ABSTRACT FROM AUTHOR]

Fulvestrant is a pure estrogen receptor (ER) antagonist approved for the treatment of metastatic ER positive breast cancer in postmenopausal women with disease progression following antiestrogen therapy. The clinical results of fulvestrant demonstrated encouraging activity in tumors in spite of HER2 positivity, but data about its use after progression on anti-HER2 agents are limited. Partial responses and durations of response of 12, 25, and 38 months in three cases with multiple metastases of ER positive and HER2 positive breast cancer were observed; all patients had been treated with 1–4 regimens of an anti-HER2 agent in combination with chemotherapy or an aromatase inhibitor before the initiation of fulvestrant. Fulvestrant is a valuable option with limited toxicity and durable response in metastatic HER2 and ER positive breast cancer after progression on anti-HER2 agents as well. Therapeutic benefit even in extensive skin metastases and (irradiated) brain metastases may be expected. Further investigations are warranted to establish where it fits into the multimodal management of ER and HER positive breast cancer. [ABSTRACT FROM AUTHOR]

Trastuzumab, the first targeted antibody against human epidermal growth factor receptor 2 (HER2), has been used to treat gastric cancer patients with HER2 overexpression. However, trastuzumab resistance often occurs following an initial period of benefits, and the underlying mechanisms remain largely unclear. The present study revealed that collagen type IV α1 chain (COL4A1), whose expression is upregulated in gastric cancer tissues and trastuzumab‑resistant gastric cancer cells, may potentially confer trastuzumab resistance in gastric cancer. By performing bioinformatics analysis of 2 microarray datasets, the present study initially identified COL4A1, overexpressed in gastric cancer tissues and trastuzumab‑resistant gastric cancer cells, as a potential candidate for inducing trastuzumab resistance. The drug resistance function of COL4A1 in gastric cancer was then validated by performing protein/gene interactions and biological process annotation analyses, and further validated by analyzing the functionality of microRNAs that target COL4A1 mRNA. Collectively, these data indicated that COL4A1 may confer trastuzumab resistance in gastric cancer. [ABSTRACT FROM AUTHOR]

Trastuzumab is recommended for the treatment of human epidermal growth factor receptor 2‑positive adenocarcinoma of the esophagogastric junction (AEG) in combination with chemotherapy; however, drug resistance has severely affected its clinical application. The present study aimed to investigate the effect of sex determining region Y‑box 9 (SOX9), a prognostic marker in adjuvant oncological settings, on AEG cell proliferation and apoptosis in the presence or absence of trastuzumab. Furthermore, the molecular mechanism underlying the role of SOX9 in trastuzumab resistance was explored. ESO26 cells were treated with various concentrations of trastuzumab, and trastuzumab induced SOX9 expression in a concentration‑dependent manner, as determined by reverse transcription‑quantitative polymerase chain reaction and western blotting analyses. Transfection of ESO26 cells with SOX9 small interfering RNA was conducted to knock down SOX9 expression, and the results of MTT and flow cytome­try assays demonstrated that SOX9 knockdown sensitized ESO26 cells to trastuzumab by inhibiting cell proliferation and enhancing cell apoptosis. In addition, it was observed that the trastuzumab‑induced phosphorylation of AKT was suppressed by SOX9 knockdown. In conclusion, the present study demonstrated that SOX9 participated in trastuzumab resistance by affecting cell proliferation and apoptosis, and indicated that SOX9 may exert its effect on trastuzumab resistance via activation of the phosphatidylinositol-3-kinase/AKT signaling pathway. This study identified a novel mechanism underlying trastuzumab resistance in vitro and may be useful in improving the efficacy of trastuzumab treatment. [ABSTRACT FROM AUTHOR]

Breast cancer resistance to the monoclonal erbB2/HER2 antibody trastuzumab (or herceptin) has become a significant obstacle in clinical targeted therapy of HER2-positive breast cancer. Previous research demonstrated that such drug resistance may be related to dysregulation of miRNA expression. Here, we found that knockdown of the long non-coding RNA, urothelial cancer associated 1 (UCA1), can promote the sensitivity of human breast cancer cells to trastuzumab. Mechanistically, UCA1 knockdown upregulated miR-18a and promoted miR-18a repression of Yes-associated protein 1 (YAP1). A luciferase reporter assay confirmed the association of miR-18a with wild-type UCA1 but not with UCA1 mutated at the predicted miR-18a-binding site. The direct targeting of YAP1 by miR-18a was verified by the observation that miR-18a mimic suppressed luciferase expression from a construct containing the YAP1 3′ untranslated region. Meanwhile, reciprocal repression of UCA1 and miR-18a were found to be Argonaute 2-dependent. Knockdown of YAP1 recapitulated the effect of UCA1 silencing by reducing the viability of trastuzumab-treated breast cancer cells, whereas inhibition of miR-18a abrogated UCA1 knockdown-induced improvement of trastuzumab sensitivity in breast cancer cells. These findings demonstrate that the UCA1/miR-18a/YAP1 axis plays an important role in regulating the sensitivity of breast cancer cells to trastuzumab, which has implications for the development of novel approaches to improving breast cancer responses to targeted therapy. [ABSTRACT FROM AUTHOR]

Although trastuzumab provides significant clinical benefit for HER2-positive breast cancers, responses are limited by the emergence of resistance. Trastuzumab resistance is a multi-factorial phenomenon thought to arise from the presence of cancer stem cells and interactions between truncated p95HER2 and HER family members. Flubendazole (FLU) is a potent anthelmintic agent with an exceptional safety profile. Evidence also suggests that it can act as an anticancer agent in several cancer cell types. We sought to investigate the effect of FLU on apoptosis, HER2/Akt signaling, breast cancer stem cell (BCSC)-like properties and trastuzumab resistance in HER2-positive breast cancer cells. FLU treatment induced apoptosis, associated with a significant downregulation of truncated p95HER2, phospho-HER2, phospho-HER3 and phospho-Akt levels, as well as suppression of HER2/HER3 hetero-dimerization in both trastuzumab-sensitive and –resistant lines. FLU effectively targeted BCSC-like properties including aldehyde dehydrogenase 1 (ALDH1) expression and the CD44 high /CD24 low phenotype, concomitant with a suppression of mammosphere-forming ability. FLU administration also caused significant tumor suppression in trastuzumab-resistant xenografts, coinciding with the downregulation of BCSC-related markers and intracellular HER2. These findings highlight the mechanisms of action of FLU in overcoming trastuzumab resistance in breast cancer. [ABSTRACT FROM AUTHOR]

Background/Aims: Trastuzumab is an important treatment used for patients with Her-2-positive breast cancer, but an increasing incidence of trastuzumab resistance has been observed clinically during the past decade. Aberrant microRNA (miR) expression levels are correlated with prognosis and response to trastuzumab in breast cancer. MiR-129-5p is downregulated in trastuzumab-resistant human breast cancer cells (JIMT-1), but its potential function and underlying mechanism remain unclear. Methods: Quantitative RT-PCR (qRT-PCR) was used to determine the expression levels of miR-129-5p and its potential target genes. The effects of miR-129-5p on cell responses to trastuzumab were analyzed by CCK-8 and flow cytometry assays in Her-2-positive breast cancer cells (SKBR-3 and JIMT-1). Bio-informatics analyses were performed to predict target genes of miR-129-5p, and luciferase assays were carried out to confirm the binding of miR-129-5p and rpS6. Results: MiR-129-5p, which was downregulated and predicted to target rpS6 in trastuzumab-resistant breast cancer cells, enhanced the sensitivity of breast cancer cells to trastuzumab by reducing the expression of rpS6. Moreover, the overexpression of rpS6 reversed the sensitivity of cells to trastuzumab induced by miR-129-5p. Conclusions: MiR-129-5p sensitized Her-2-positive breast cancer to trastuzumab by downregulating rpS6. These findings provide novel insights into the common role of rpS6 and its related molecular mechanisms in mediating trastuzumab-resistance in Her-2-positive breast cancers. [ABSTRACT FROM AUTHOR]

Background and Aim: Resistance to trastuzumab has been a critical barrier to targeted therapy of HER 2- positive (Human Epidermal Growth Factor Receptor 2) breast cancers. MicroRNAs (miRNAs) are known as decisive core regulators of drug resistance that modulate the epithelial-to-mesenchymal transition (EMT) and cancer-related immune responses. The present study aimed at examining the expression of miR-141 in trastuzumab-resistant and trastuzumab-sensitive BT-474 breast cancer cells. Materials and Methods: In this experimental study, trastuzumab-resistant BT-474 cells were generated by continuous in-vitro culture of BT-474 cells in the presence of trastuzumab for six months. The relative expression of miR-141 to U6 RNA was then evaluated in trastuzumab-resistant and trastuzumab-sensitive cells using Relative Real-Time PCR. Mann-Whitney test was used to compare the difference between the two groups. Results: There was a significant difference between the survival rates of resistant BT-474 cells and sensitive cells in the MTT test in the presence of different concentrations of trastuzumab showing that BT-474 breast cancer cells have turned resistant to this drug under long-term culture (P=0.001). Also, the expression of miR-141 in trastuzumab-resistant cells was significantly reduced by four times compared with the BT-474 parent cells (P=0.049). Conclusion: Down-regulation of miR-141 in trastuzumab-resistant BT-474 cells might be one possible mechanism for resistance against trastuzumab and an indication of the role of this microRNA in controlling the metastasis pathway. [ABSTRACT FROM AUTHOR]

Background Resistance to the HER2-targeted antibody trastuzumab remains to be a major clinical challenge in the treatment of HER2-positive breast cancer. Hyper-activation of STAT3 is proposed to be a predictive biomarker of trastuzumab resistance. However, the precise mechanism(s) remains poorly defined. Evidence is emerging that HIF-1α, a central downstream element of STAT3 pathway, serves a pivotal role in the complex signaling network with subsequent diverse cellular events. Material and methods We have established trastuzumab resistant SKBR3 cells (SKBR3-TR). The cell viability, apoptosis as well as western blot, siRNA transfection and co-immunoprecipitation assays were performed to evaluate the involvement of STAT3/HIF-1α in modulation of trastuzumab resistance. Results We found that in SKBR3-TR cells and conditioned medium-treated parental cells, constitutive phosphorylated STAT3 coincided with prominent up-regulation of HIF-1α which was accompanied with PTEN attenuation. Moreover, the inhibition of STAT3 activation by Stattic and/or genetically STAT3 knocking down decreased HIF-1α level in SKBR3-TR cells. Additionally, treatment with Stattic and/or STAT3 siRNA engendered the up-regulation of PTEN protein in STAT3-inhibited resistant cells. Restoration of PTEN was also observed following siRNA-mediated silencing of HIF-1α expression. Moreover, down-regulation of HIF-1α caused a reduction in the HES-1 content. Further study with HES-1 specific siRNA revealed the elevation of PTEN expression in HES-1 knock-down trastuzumab resistant cells. Conclusion The impairment of STAT3-HIF-1α-HES-1 pathway restored trastuzumab sensitivity through up-regulation of PTEN protein. General significance These findings highlighted the signal integrator role of HIF-1α in STAT3-mediated trastuzumab resistance induction which would be valuable in designing more efficient chemosensitization strategies. [ABSTRACT FROM AUTHOR]

Despite of the effectiveness of the anti-ErbB2 humanized antibody trastuzumab, trastuzumab resistance emerges as a major and common clinical problem. Thus, circumventing trastuzumab resistance has become an urgent need. Recently, Src inhibitor saracatinib has drawn great attention for its key role in trastuzumab response. As shown in our previous study, H2-18, an anti-ErbB2 antibody, could potently induce programmed cell death (PCD) in trastuzumab-resistant breast cancer cells. Here we combined H2-18 and a Src inhibitor, saracatinib, and studied the antitumor activity of this drug combination in trastuzumab-resistant breast cancer cell lines. The results showed that H2-18 and saracatinib could synergistically inhibit cell proliferation of BT-474, SKBR-3, HCC-1954 and HCC-1419 breast cancer cell lines in vitro. H2-18 plus saracatinib could also inhibit the HCC-1954 tumor growth more effectively in vivo than each drug alone. H2-18 plus saracatinib showed a significantly more potent PCD-inducing activity compared with either H2-18 or saracatinib alone. We conclude that enhanced PCD may contribute to the superior antitumor efficacy of this combination therapy. The combination of H2-18 and SRC inhibitor has the potential to be translated into clinic. [ABSTRACT FROM AUTHOR]

HER2-positive breast tumors are known to harbor cancer stem-like cell populations and are associated with an aggressive tumor phenotype and poor clinical outcomes. Disulfiram (DSF), an anti-alcoholism drug, is known to elicit cytotoxicity in many cancer cell types in the presence of copper (Cu). The objective of the present study was to investigate the mechanism of action responsible for the induction of apoptosis by DSF/Cu and its effect on cancer stem cell properties in HER2-positive breast cancers in vitro and in vivo. DSF/Cu treatment induced apoptosis, associated with a marked decrease in HER2, truncated p95HER2, phospho-HER2, HER3, phospho-HER3 and phospho-Akt levels, and p27 nuclear accumulation. This was accompanied by the eradication of cancer stem-like populations, concomitant with the suppression of aldehyde dehydrogenase 1 (ALDH1) activity and mammosphere formation. DSF administration resulted in a significant reduction in tumor growth and an enhancement of apoptosis, as well as HER2 intracellular domain (ICD) and ALDH1A1 downregulation. Our results demonstrate that DSF/Cu induces apoptosis and eliminates cancer stem-like cells via the suppression of HER2/Akt signaling, suggesting that DSF may be potentially effective for the treatment of HER2-positive cancers. [ABSTRACT FROM AUTHOR]

Objective Uterine serous carcinomas (USC) harbor simultaneous HER2 (ERBB2) over-expression and gain of function mutations in PIK3CA . These concurrent alterations may uncouple single agent anti-HER2 therapeutic efficacy making inhibition of the mammalian target of rapamycin (mTOR) a promising option to heighten anti-tumor response. Methods Both in vitro and in vivo experiments were conducted to assess proliferation, cell death and anti-tumor activity of ridaforolimus, lapatinib and combination lapatinib, trastuzumab (L/T) and ridaforolimus. With institutional approval, NOD/SCID mice bearing xenografts of non-immortalized, HER2 gene amplified cell lines (ARK1, ARK2) with and without PIK3CA gene mutations were divided into four arm cohorts. Ridaforolimus was administered alone and in combination with L/T. Tumor volumes were assessed and posttreatment analysis was performed. Results We observed dose dependent in vitro abrogation of downstream target proteins including phospho-AKT and phospho-S6. In both in vivo models, single agent ridaforolimus impaired xenograft tumor growth. Combination ridaforolimus and L/T, however, further improved the observed anti-tumor activity only in the ARK1 model with the PIK3CA gene mutation (E542K). The addition of mTOR inhibition to dual HER2 blockade added no additional anti-tumor effects in the ARK2 xenografts. Western blot and immunohistochemical analysis of downstream pathway alterations following in vivo treatment revealed dual HER2 blockade with ridaforolimus was necessary to induce apoptosis, decrease proliferation and abrogate phospho-S6 protein expression in the PIK3CA mutated model. Conclusions These pilot data suggest that PIK3CA gene mutation may be an effective biomarker for selecting those HER2 over-expressing USC tumors most likely to benefit from mTOR inhibition. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the growth inhibitory effects of of trastuzumab-resistant SK-BR-3R cells with combination of trastuzumab and NSC 74859 and further explore the mechanism involved. Methods: Trastuzumab-resistant SK-BR-3 cells was characterized and cell proliferation of SK-BR-3R upon treatment with trastuzumab, NSC 74859 or trastuzumab plus NSC 74859 were evaluated by MTT assay. Subsequently, nude mice bearing subcutaneous SK-BR-3R cells xenograft tumor model was set up to evaluate the tumor growth inhibition upon combinational treatment. Additionally, the levels of phosphorylated HER2, STAT3 and AKT were detected by western blot assay. Results: Trastuzumab-resistant SK-BR-3 cell line were obtained and characterized by MTT assay. Next, Trastuzumab(50 nmol/L) plus NSC 74859(50 μmol/L) exhibited significant inhibitory effect compared with either agent alone by MTT assay, showing statistical difference; Furthermore, combinatorial treatment with trastuzumab plus NSC 74859 resulted in a significant benefit over either agent alone in SK-BR-3R xenograft models. Finally, combined treatment of trastuzumab and NSC 74859 suppressed HER2, STAT3 and AKT phosphorylation in SK-BR-3R cells. Conclusions: Combination treatment of trastuzumab with NSC 74859 markedly inhibited the growth of SK-BR-3R cells. Suppression of PI3K/AKT pathway in SK-BR-3R cells could explain the inhibitory effects upon combinational treatment. To conclude, this study will provide a new regimen for treating the trastuzumab-resistant breast cancer in clinics. [ABSTRACT FROM AUTHOR]

Development of resistance against cancer therapeutic agents is a common problem in cancer management. Trastuzumab resistance is one of the challenges in management of HER-2-positive breast cancer patients resulting in breast cancer progression, metastasis, and patient poor outcome. The aim of this study is to determine the alteration in gene expression in response to Trastuzumab resistance after long-term exposure to Trastuzumab. The Trastuzumab-resistant MDA-MB-453 (MDA-MB-453/TR) cell line was developed by exposing cells to 10 μM Trastuzumab continuously for 6 months. Sensitivity toward Trastuzumab was tested using cell viability assays. The acquisition of an epithelial-to mesenchymal transition (EMT) phenotype was also observed in parallel with the development of resistance. Based on the real-time-based PCR array technology, several genes were altered affecting multiple networks. The most up-regulated genes were TGF-β1 and EGF, and IGFBP-3. These genes are known to have a critical role in Trastuzumab resistance in breast cancer cell lines and/or in the acquisition of EMT. They are also recognized for their role in cancer progression and metastasis. These alterations indicate that the development of Trastuzumab resistance is multifactorial and involves a development of a mesenchymal like phenotype. [ABSTRACT FROM AUTHOR]

Despite the efficacy of trastuzumab in treating HER2-positive breast cancer patients, a significant proportion of patients relapse after treatment. The role of C-X-C chemokine receptor type 4 (CXCR4) in trastuzumab resistance was studied only in cell lines and the underlying mechanisms remain largely unclear. This study investigated the role of CXCR4 in trastuzumab resistance in breast cancer patients and explored the possible underlying mechanisms. The study was performed retrospectively on tissue samples from 62 breast cancer patients including 42 who were treated with trastuzumab and chemotherapy and 20 who received chemotherapy alone in adjuvant setting. Expression levels of CXCR4 and its regulators hypoxia-inducible factor 1-alpha (HIF-1α), tristetraprolin (TTP), human antigen R (HuR), itchy E3 ubiquitin protein ligase (ITCH), miR-302a and miR-494 were determined and their associations with tumor recurrence and disease-free survival were analyzed. In trastuzumab-treated patients, high CXCR4 expression was associated with recurrence and was an independent predictor of progression risk after therapy. CXCR4 correlated positively with its transcriptional regulator, HIF-1α, and negatively with its post-translational regulator, ITCH. HIF-1α, HuR and ITCH were significantly associated with clinical outcome. In chemotherapy-treated patients, neither CXCR4 nor any of its regulators were associated with recurrence or predicted disease progression risk after chemotherapy. In conclusion, this study suggests a potential role for CXCR4 in recurrence after trastuzumab-based therapy in human breast cancer that could be mediated, at least in part, by hypoxia and/or decreased ubiquitination. These findings highlight the potential utility of CXCR4 as a promising target for enhancing trastuzumab therapeutic outcome. [Display omitted] • This clinical investigation reports potential CXCR4 role in trastuzumab resistance. • High CXCR4 was associated with recurrence after trastuzumab-based therapy. • CXCR4 was an independent predictor of progression risk after trastuzumab therapy. • High CXCR4 could be mediated by hypoxia and/or decreased ubiquitination. • CXCR4 was not associated with and did not predict recurrence after chemotherapy. [ABSTRACT FROM AUTHOR]

Objective: To identify clinically relevant predictive biomarkers of trastuzumab resistance. Material and methods: MTT, FACS assays, immunoblotting and immunocytochemistry were used to phenotypically characterize drug responses of two cell models BT474R and SKBR3R. Student'st-test and Spearman's correlation were applied for statistic analysis. Results: The activity of a downstream effector of the HER2 pathway phosphorylated ribosomal protein S6 (p-rpS6), was suppressed by trastuzumab in the parental cell lines yet remained unchanged in the resistant cells following treatment. The level of p-rpS6 was inversely correlated to the drug induced growth inhibition of trastuzumab-resistant cells when they are treated with selected HER2 targeting drugs. Conclusion: p-rpS6 is a robust post-treatment indicator of HER2 pathway-targeted therapy resistance. [ABSTRACT FROM PUBLISHER]

Background: The likelihood of recurrence in patients with breast cancer who have HER2-positive tumors is relatively high, although trastuzumab is a remarkably effective drug in this setting. Signal transducer and activator of transcription 3 protein (STAT3), a transcription factor that is persistently tyrosine-705 phosphorylated (pSTAT3) in response to numerous oncogenic signaling pathways, activates downstream proliferative and anti-apoptotic pathways. We hypothesized that pSTAT3 expression in HER2-positive breast cancer will confer trastuzumab resistance. Methods: We integrated reverse phase protein array (RPPA) and gene expression data from patients with HER2-positive breast cancer treated with trastuzumab in the adjuvant setting. Results: We show that a pSTAT3-associated gene signature (pSTAT3-GS) is able to predict pSTAT3 status in an independent dataset (TCGA; AUC = 0.77, P = 0.02). This suggests that STAT3 induces a characteristic set of gene expression changes in HER2-positive cancers. Tumors characterized as high pSTAT3-GS were associated with trastuzumab resistance (log rank P = 0.049). These results were confirmed using data from the prospective, randomized controlled FinHer study, where the effect was especially prominent in HER2-positive estrogen receptor (ER)-negative tumors (interaction test P = 0.02). Of interest, constitutively activated pSTAT3 tumors were associated with loss of PTEN, elevated IL6, and stromal reactivation. Conclusions: This study provides compelling evidence for a link between pSTAT3 and trastuzumab resistance in HER2-positive primary breast cancers. Our results suggest that it may be valuable to add agents targeting the STAT3 pathway to trastuzumab for treatment of HER2-positive breast cancer. [ABSTRACT FROM AUTHOR]

Background Subsets of high grade endometrial cancer (EnCa) over-express HER2 (ERBB2), yet clinical trials have failed to demonstrate any anti-tumor activity utilizing trastuzumab, an approved platform for HER2 positive breast cancer (BrCa). A truncated p95HER2 variant lacking the trastuzumab binding site may confer resistance. The objective of this investigation was to characterize the expression of the p95HER2 truncated variant in EnCa. Materials and methods With institutional approval, 86 high grade EnCa tumors were identified with tumor specimens from surgeries performed between 2000 and 2011. Clinical data were collected and all specimens underwent tumor genotyping, HER2 immunohistochemistry (IHC, HercepTest(r)), HER2 fluorescent in situ hybridization (FISH), along with total HER2 (H2T) and p95HER2 assessment with VeraTag(r) testing. Regression models were used to compare a cohort of 86 breast tumors selected for equivalent HER2 protein expression. Results We identified 44 high grade endometrioid and 42 uterine serous carcinomas (USC). IHC identified high HER2 expression (2 + or 3 +) in 59% of the tumors. HER2 gene amplification was observed in 16 tumors (12 USC, 4 endometrioid). Both HER2 gene amplification and protein expression correlated with H2T values. High p95HER2 expression above 2.8 RF/mm² was observed in 53% (n = 54) with significant correlation with H2T levels. When matched to a cohort of 107 breast tumors based on HercepTest HER2 expression, high grade EnCa presented with higher p95 levels (p < 0.001). Conclusions These data demonstrate that compared to BrCa, high grade EnCa expresses higher levels of p95HER2 possibly providing rationale for the trastuzumab resistance observed in EnCa. [ABSTRACT FROM AUTHOR]

Resistance to trastuzumab is frequently observed during the treatment of patients with human epidermal growth factor 2 (HER2)-positive metastatic breast cancers. The aim of the present study was to determine if the phosphorylated proline-rich Akt substrate of 40 kDa (phospho-PRAS40Thr246), a novel biomarker for phosphoinositol-3 kinase (PI3K) pathway activation, could predict the response of HER2-positive metastatic breast cancers to treatment with trastuzumab. Formalin-fixed, paraffin-embedded tumor tissue samples were retrospectively collected from 55 trastuzumab-treated patients. Next, the expression of phospho-PRAS40Thr246 and phosphatase and tensin homolog (PTEN) was assessed by immunohistochemistry. In total, five common phosphoinositol-3 kinase α catalytic subunit mutations, namely E542K, E545K, E545D, H1047R and H1047L, were identified by the amplification-refractory mutation system, using the allele-specific polymerase chain reaction. The activation of the PI3K pathway, as determined by low PTEN expression or the presence of oncogenic PIK3CA mutations, was observed in 49.1% (27 cases) of the 55 HER2-positive metastatic breast cancer tissues. In total, 40% of the tumors were defined as being phospho-PRAS40Thr246 -positive. Furthermore, the results revealed that phospho-PRAS40Thr246 expression was associated with the PI3K pathway activation status and an increased risk of tumor progression in HER2-positive metastatic breast cancer patients who had received trastuzumab-based therapy. Therefore, phospho-PRAS40Thr246 expression levels may reflect the PI3K pathway activation status and act as a biomarker for HER2-amplified breast cancer patients who are unlikely to respond to trastuzumab-based therapy. [ABSTRACT FROM AUTHOR]

HER2-positive (HER2 +) breast cancer accounts for 18%–20% of all breast cancer cases and has the second poorest prognosis among breast cancer subtypes. Trastuzumab, the first Food and Drug Administration-approved targeted therapy for breast cancer, established the era of personalized treatment for HER2 + metastatic disease. It is well tolerated and improves overall survival and time-to-disease progression; with chemotherapy, it is part of the standard of care for patients with HER2 + metastatic disease. However, many patients do not benefit from it because of resistance. Substantial research has been performed to understand the mechanism of trastuzumab resistance and develop combination strategies to overcome the resistance. In this review, we provide insight into the current pipeline of drugs used in combination with trastuzumab and the degree to which these combinations have been evaluated, especially in patients who have experienced disease progression on trastuzumab. We conclude with a discussion of the current challenges and future therapeutic approaches to trastuzumab-based combination therapy. [ABSTRACT FROM AUTHOR]

Background: Trastuzumab (Tmab) resistance is a major clinical problem to be resolved in patients with HER2-positive gastric cancers. However, in contrast to the situation for HER2-positive breast cancer lines, the Tmab-resistant gastric cancer preclinical models that are needed to develop a new therapy to overcome this problem are not yet available. Methods: We developed three new cell lines from HER2 gene-amplified gastric cancer cell lines (GLM-1, GLM-4, NCI N-87) by a new in vivo selection method consisting of the repeated culture of small residual peritoneal metastasis but not subcutaneous tumor after Tmab treatment. We then evaluated the anti-tumor efficacy of lapatinib for these Tmab-resistant cells. Results: We successfully isolated two Tmab-resistant cell lines (GLM1-HerR2(3), GLM4-HerR2) among the three tested cell lines. These resistant cells differed from the parental cells in their flat morphology and rapid growth in vitro, but HER2, P95HER2 expression, and Tmab binding were essentially the same for the parental and resistant cells. MUC4 expression was up- or downregulated depending on the cell line. These resistant cells were still sensitive to lapatinib, similar to the parental cells, in vitro. This growth inhibition of the Tmab-resistant cells by lapatinib was due to both G1 cell-cycle arrest and apoptosis induction via effective blockade of the PI3K/Akt and MAPK pathways. A preclinical study confirmed that the Tmab-resistant tumors are significantly susceptible to lapatinib. Conclusion: These results suggest that lapatinib has antitumor activity against the Tmab-resistant gastric cancer cell lines, and that these cell lines are useful for understanding the mechanism of Tmab resistance and for developing a new molecular therapy for Tmab-resistant HER2-positive gastric cancers. [ABSTRACT FROM AUTHOR]

ERBB2 gene amplification occurs in about one quarter of breast carcinomas (BCs) and identifies a distinct clinical subset of BC. The introduction in the clinic of Trastuzumab, a humanized monoclonal antibody (mAb) directed to the ERBB2 extracellular domain, has had a great impact on the therapeutic management of ERBB2+ BC. Yet, not all patients respond to Trastuzumab and resistance develops also among patients that initially benefit from Trastuzumab-based regimens. Pre-clinical studies have discovered several mechanisms through which tumor cells may escape from Trastuzumab-mediated ERBB2 inhibition. These include rewiring of the ErbB signaling network, loss of ERBB2 expression, expression of ERBB2 isoforms refractory to Trastuzumab inhibition, vicarious signaling by non-ErbB tyrosine kinases and constitutive activation of downstream signaling routes, such as the PI3K pathway. While the relative contribution of each of these mechanisms to establishing Trastuzumab resistance in the clinical setting is not fully understood, much attention has been focused on abating resistance by achieving complete blockade of ERBB2-containing dimers. This approach, propelled by the development of novel anti-ERBB2 therapeutics, has led to the recent approval of Lapatinib, Pertuzumab and T-DM1 as additional anti-ERBB2 therapeutics in BC. However, full success is far from being achieved and resistance to ERBB2 targeting remains a relevant problem in the clinical management of BC. Herein, we provide an overview of biological and molecular bases underpinning resistance to ERBB2 therapeutics in BC, discuss outstanding issues in the field of ERBB2 therapeutic targeting and elaborate on future directions of translational research on ERBB2+ breast cancer. [ABSTRACT FROM AUTHOR]