Drug-resistant HER2-positive breast cancer: Molecular mechanisms and overcoming strategies

Proximity-induced membrane protein degradation for cancer therapies

The selective modulation of membrane proteins presents a significant challenge in drug development, particularly in cancer therapies. However, conventional small molecules and biologics often face significant hurdles in effectively targeting membrane-bound proteins, largely due to the structural complexity of these proteins and their involvement in intricate cellular processes. In light of these limitations, proximity-induced protein modulation has recently emerged as a transformative approach. It leverages molecule-induced proximity strategies to commandeer endogenous cellular machinery for precise protein manipulation. One of these modulatory strategies is protein degradation, wherein membrane-targeting degraders derived from proximity-induction approaches offer a unique therapeutic avenue by inducing the irreversible removal of key oncogenic and immune-regulatory proteins to combat cancer. This review explores the fundamental principles underlying proximity-driven membrane protein degradation, highlighting key strategies such as LYTACs, PROTABs, TransTACs, and IFLD that are reshaping targeted cancer therapy. We discuss recent technological advancements in the application of proximity-induced degraders across breast cancer, lung cancer, immunotherapy, and other malignancies, underscoring how these innovative approaches have demonstrated significant therapeutic potential. Lastly, while these emerging technologies offer significant promise, they still face substantial limitations, including drug delivery, selectivity, and resistance mechanisms that need to be addressed to achieve successful clinical translation.

Pyrotinib and Nab-Paclitaxel in HER2-Positive Breast Cancer (PANHER Trial): A Prospective, Single-Arm, Phase II Trial

Trastuzumab and pertuzumab combined with chemotherapy represent the standard therapy for first-line treatment of HER2-positive metastatic breast cancer (BC). Due to challenges related to availability and cost in China, it is necessary to explore treatments involving tyrosine kinase inhibitors (TKIs). In this multicenter, single-arm, open-label phase II trial, patients with HER2-positive BC were enrolled from seven hospitals in China. Patients received oral pyrotinib 400 mg once daily and intravenous nab-paclitaxel 125 mg/m2 on days 1, 8, and 15 of each 28-day cycle until disease progression or intolerable toxicity. The primary endpoint was the objective response rate (ORR). Between December 2019 and December 2021, 51 patients were enrolled. Among all enrolled patients, 48 had at least one response evaluation. Of these evaluable patients, 39 patients achieved responses, resulting in a positive study outcome. The ORR was 76.5% (95% CI, 62.5%-87.2%), and the disease control rate was 94.1% (95% CI, 83.8-98.8). As of January 24, 2024, the median follow-up duration was 29.2 months (IQR, 24.9-33.2). The median progression-free survival was 14.6 months (95% CI, 8.0-24.2), and the median overall survival was not reached. Forty-nine patients (96.1%) developed grade ≥ 3 adverse events (AEs). The most common grade ≥ 3 AEs were decreased neutrophil count (43.1%), decreased white blood cell count (43.1%), and diarrhea (23.5%). Pyrotinib combined with nab-paclitaxel demonstrated promising efficacy for HER2-positive advanced breast cancer, with an acceptable safety profile. Trial Registration: chictr.org, ChiCTR1900023653.

Molecular Subtypes and Mechanisms of Breast Cancer: Precision Medicine Approaches for Targeted Therapies

Breast cancer remains one of the most prevalent diseases worldwide, primarily affecting women. Its heterogeneous nature poses a significant challenge in the development of effective and targeted treatments. Molecular characterization has enabled breast cancer to be classified into four main subtypes: luminal A, luminal B, HER2-positive, and triple-negative breast cancer, based on hormone receptor expression and HER2 status. A deeper understanding of these molecular markers and their associated signaling pathways, such as MAPK and PI3K/AKT, is essential for improving prognosis and optimizing treatment strategies. Currently, several therapeutic agents are utilized in neoadjuvant and adjuvant therapies, often in combination with surgical interventions. However, emerging evidence highlights the growing challenge of drug resistance, which significantly limits the efficacy of existing treatments. Addressing this issue may require innovative approaches, including combination therapies and precision medicine strategies, tailored to the molecular profile of each patient. Therefore, a comprehensive understanding of the pathophysiologic mechanisms driving breast cancer progression and resistance is crucial for the development of advanced targeted therapies with greater precision and efficacy. This review aims to explore recent advancements in molecular research related to breast cancer subtypes and provide a critical analysis of current therapeutic approaches within the framework of precision medicine.

Druggable Molecular Networks in BRCA1/BRCA2-Mutated Breast Cancer

Mutations in the tumor suppressor genes BRCA1 and BRCA2 are associated with the triple-negative breast cancer phenotype, particularly aggressive and hard-to-treat tumors lacking estrogen, progesterone, and human epidermal growth factor receptor 2. This research aimed to understand the metabolic and genetic links behind BRCA1 and BRCA2 mutations and investigate their relationship with effective therapies. Using the Cytoscape software, two networks were generated through a bibliographic analysis of articles retrieved from the PubMed-NCBI database. We identified 98 genes deregulated by BRCA mutations, and 24 were modulated by therapies. In particular, BIRC5, SIRT1, MYC, EZH2, and CSN2 are influenced by BRCA1, while BCL2, BAX, and BRIP1 are influenced by BRCA2 mutation. Moreover, the study evaluated the efficacy of several promising therapies, targeting only BRCA1/BRCA2-mutated cells. In this context, CDDO-Imidazolide was shown to increase ROS levels and induce DNA damage. Similarly, resveratrol decreased the expression of the anti-apoptotic gene BIRC5 while it increased SIRT1 both in vitro and in vivo. Other specific drugs were found to induce apoptosis selectively in BRCA-mutated cells or block cell growth when the mutation occurs, i.e., 3-deazaneplanocin A, genistein or daidzein, and PARP inhibitors. Finally, over-representation analysis on the genes highlights ferroptosis and proteoglycan pathways as potential drug targets for more effective treatments.

Targeting PCSK9, through an innovative cVLP-based vaccine, enhanced the therapeutic activity of a cVLP-HER2 vaccine in a preclinical model of HER2-positive mammary carcinoma

BACKGROUND

HER2-targeted therapies have revolutionized the treatment of HER2-positive breast cancer patients, leading to significant improvements in tumor response rates and survival. However, resistance and incomplete response remain considerable challenges. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition is a novel therapeutic strategy for the management of dyslipidemia by enhancing the clearance of low-density lipoprotein cholesterol receptors, however recent evidence also shows links between PCSK9 and cancer cells. We present an innovative immunization approach combining capsid virus-like particle (cVLP)-based vaccines against HER2 and PCSK9.

METHODS

The therapeutic activity of the combined vaccine was evaluated in female mice challenged with HER2-positive mammary carcinoma cells. Controls included untreated mice and mice treated with cVLP-PCSK9 and cVLP-HER2 as standalone therapies. Antibodies elicited by vaccinations were detected through ELISA immunoassay. The functional activity of the antibodies was tested in 3D-soft agar assay on human HER2 +  +  + trastuzumab sensitive and resistant cells.

RESULTS

Mice vaccinated with cVLP-HER2 + cVLP-PCSK9 displayed tumor regression from the 40th day after cell challenge in 100% of mice remaining tumor-free even 4 months later. In contrast, 83% of mice treated with cVLP-HER2 vaccine alone experienced an initial tumor regression, followed by tumor relapse in 60% of subjects. Untreated mice and mice treated with the cVLP-PCSK9 vaccine alone developed progressive tumors within 1-2 months after cell injection. The combined vaccine approach elicited strong anti-human HER2 antibody responses (reaching 1-2 mg/ml range) comprising multiple immunoglobulins isotypes. cVLP-PCSK9 vaccine elicited anti-PCSK9 antibody responses, resulting in a marked reduction in PCSK9 serum levels. Although the anti-PCSK9 response was reduced when co-administered with cVLP-HER2, it remained significant. Moreover, both cVLP-HER2 + cVLP-PCSK9 and cVLP-HER2 alone induced anti-HER2 antibodies able to inhibit the 3D growth of human HER2 +  +  + BT-474 and trastuzumab-resistant BT-474 C5 cells. Strikingly, antibodies elicited by the combined vaccination were more effective than those elicited by the cVLP-HER2 vaccine alone in the inhibition of trastuzumab-resistant C5 cells.

CONCLUSIONS

The results indicate that cVLP-PCSK9 vaccination shows adjuvant activity when combined with cVLP-HER2 vaccine, enhancing its therapeutic efficacy against HER2-positive breast cancer and holding promise in overcoming the challenges posed by resistance and incomplete responses to HER2-targeted therapy.

Heterogeneity in Cancer

Cancer heterogeneity is a major challenge in oncology, complicating diagnosis, prognostication, and treatment. The clinical heterogeneity of cancer, which leads to differential treatment outcomes between patients with histopathologically similar cancers, is attributable to molecular diversity manifesting through genetic, epigenetic, transcriptomic, microenvironmental, and host biology differences. Heterogeneity is observed between patients, individual metastases, and within individual lesions. This review discusses clinical implications of heterogeneity, emphasizing need for personalized approaches to overcome challenges posed by cancer's diverse presentations. Understanding of emerging molecular diagnostic and analytical techniques can provide a view into the multidimensional complexity of cancer heterogeneity. With over 90% of cancer-related deaths associated with metastasis, we additionally explore the role heterogeneity plays in treatment resistance and recurrence of metastatic lesions. Molecular insights from next-generation sequencing, single-cell transcriptomics, liquid biopsy technology, and artificial intelligence will facilitate the development of combination therapy regimens that can potentially induce lasting and even curative treatment outcomes.

Therapeutic potential of anti-ErbB3 chimeric antigen receptor natural killer cells against breast cancer

ErbB3 is markedly overexpressed in breast cancer cells and is associated with resistance and metastasis. Additionally, ErbB3 expression levels are positively correlated with low densities of tumor-infiltrating lymphocytes, a marker of poor prognosis. Consequently, ErbB3 is a promising therapeutic target for cancer immunotherapy. Here, we report the generation of ErbB3-targeted chimeric antigen receptor (CAR)-modified natural killer (NK) cells by transducing cord blood-derived primary NK cells using vsv-g envelope-pseudotyped lentiviral vectors. Transduced cells displayed stable CAR-expressing activity and increased cytotoxicity against ErbB3-positive breast cancer cell lines. Furthermore, anti-ErbB3 (aErbB3) CAR-NK cells strongly reduced the tumor burden in the SK-BR-3 xenograft mouse model without observable side effects. These findings underscore the potential of aErbB3 CAR-NK cells as targeted immunotherapy for ErbB3-positive breast cancer, suggesting a promising alternative to conventional treatments.

Pyrotinib induces cell death in HER2-positive breast cancer via triggering HSP90-dependent HER2 degradation and ROS/HSF-1-dependent oxidative DNA damage

HER2-positive breast cancer (HER2+ BC) is distinguished by its poor prognosis, propensity for early onset, and high risk of recurrence and metastasis. Consequently, anti-HER2-targeted therapy has emerged as a principal strategy in the treatment of this form of breast cancer. Pyrotinib, a novel irreversible pan-HER2 tyrosine kinase inhibitor, has brought fresh hope to patients with advanced HER2+ breast cancer. In this study, we conducted a comprehensive exploration of pyrotinib's antitumor mechanism. The in vitro results showed that pyrotinib significantly inhibited SKBR3 cells viability and induced apoptosis by promoting HER2 endocytosis and ubiquitylation, leading to HER2 degradation through the displacement of HSP90 from HER2. Beyond targeting the HER2 signaling pathway, pyrotinib also induced DNA damage, which was mediated by the activation of the reactive oxygen species/heat shock factor 1 signaling pathway and the downregulation of proliferating cell nuclear antigen expression. Furthermore, the in vivo results demonstrated a pronounced anticancer effect of pyrotinib in the SKBR3 xenograft mouse model, concomitant with a reduction in HER2 expression. In summary, our findings provide novel insights into the mechanism of pyrotinib in the treatment of HER2+ BC.

Mechanism of miRNAs and miRNA-mRNA Regulatory Networks in Modulating Drug Resistance in HER2-Positive Breast Cancer: An Integrative Bioinformatics Approach

BACKGROUND

HER2-positive breast cancer is an aggressive subtype where innate/acquired resistance to targeted drugs remains a challenge. This study aims to uncover the underlying mechanisms of HER2 drug resistance through miRNA analysis and target identification.

METHODS

MiRNA datasets were systematically retrieved from the GEO database, and differential expression analysis was conducted for both miRNA and mRNA datasets. Functional analyses were also conducted to validate the identified miRNAs and assess their clinical relevance.

RESULTS

We identified 113 differentially expressed miRNAs (DEMs) and 923 target genes. Validation was performed using external mRNA datasets, and intersection with significant genes identified 110 overlapping genes associated with HER2 drug resistance. Further analyses included functional enrichment, construction of a protein-protein interaction (PPI) network, identification of key hub genes such as BCL2, FOS, and CXCR4, and assessment of clinical relevance through survival analysis and immunohistochemistry (IHC) assessments.

CONCLUSIONS

This integrative approach unveils a complex landscape of HER2 drug resistance in breast cancer, identifying crucial miRNAs, target genes, and significant pathways. The findings offer novel insights into the mechanisms governing drug resistance and highlight the potential for enhancing therapeutic strategies. Future studies are necessary for experimental validation to further explore the complex mechanisms involved.

Resistance mechanisms and prospects of trastuzumab

Breast cancer that overexpresses Human Epidermal Growth Factor Receptor 2 (HER2+) due to gene amplification or overexpression constitutes 15-20% of all breast cancer cases. Trastuzumab, the first FDA-approved monoclonal antibody targeting HER2, serves as the standard first-line treatment for HER2-positive advanced breast cancer, as recommended by multiple clinical guidelines.Currently, accumulated clinical evidence reveals a considerable degree of variability in the response of HER2+ breast cancer to trastuzumab treatment. Specifically, over 50% of patients either do not respond to or develop resistance against trastuzumab.The specific mechanisms of resistance to trastuzumab are currently unclear. This paper aims to review the existing research on the resistance mechanisms of trastuzumab, based on its target, from aspects such as genetic loci, molecular structure, signaling pathways, and the tumor microenvironment and to outline current research progress and new strategies.

Targeted Sequencing of HER2-Positive Breast Cancer Mutations Revealed a Potential Association between PIK3CA and Trastuzumab Resistance

BACKGROUND

Different molecular subtypes, including HER2-positive, have been identified in breast cancer. The overexpression of HER2 triggers downstream signaling pathways such as the PI3K/AKT/mTOR pathway. Until recently, trastuzumab has been used as a single HER2-targeted therapy in Egypt. However, resistance to trastuzumab has been reported. Previous studies have demonstrated the genetic variants that affect the trastuzumab response. However in Egypt, few studies investigated molecular biomarkers such as p53 that might affect the trastuzumab response. Therefore, we aimed to extend the genetics workup of Her2 + BC to include important oncogenes and other vital cancer pathways.

METHODS

Formalin-fixed paraffin-embedded samples were collected from 24 HER2+ BC Egyptian patients, twelve patients in complete remission for 2 years or more from the start of trastuzumab and twelve resistant patients who relapsed or developed metastasis within 2 years from the start of trastuzumab. Somatic mutations in hotspot regions of 17 genes were further investigated using next-generation sequencing.

RESULTS

Among the total number of identified variants (106 variants), PIK3CA showed the most frequent variants, with more variants occurring in the resistant group than in the responsive group (P= 0.004). The frequency of PIK3CA mutations was greater in resistant patients than in responsive patients (P= 0.036). Additionally, there was a significant correlation between PIK3CA mutations and pathological complete response (pCR) (P=0.036). Most of PIK3CA variants in resistant patients were detected in exon 9 and 20. The PIK3CA variants His1047Tyr, Glu545Lys, His701Pro, Lys111Glu, Val344Gly and Tyr1021Cys were found only in the resistant patients, suggesting that they are associated with trastuzumab resistance.

CONCLUSION

PIK3CA variants were more frequent in resistant HER2+ BC patients than in responsive patients, with a significant correlation between PIK3CA mutation and a lower pCR rate. PIK3CA variants within exon 9 and 20 (such as Glu545Lys and His1047Tyr respectively) were associated with trastuzumab resistance.

pH-tailored delivery of a multitarget anticancer benzimidazole derivative using a PEGylated β-cyclodextrin-curcumin functionalized nanocomplex

In this study, we aimed to enhance the bioavailability of a benzimidazole derivative with potent anticancer potential through a nano-based approach. Benzimidazole-loaded polyethylene glycol-β-cyclodextrin-functionalized curcumin nanocomplex (BMPE-Cur) was prepared and characterized for its physicochemical properties and drug release profiles under different pH conditions. In addition, the biological activities of the nanocomplex including antioxidant potentials and pro-apoptogenic properties, against HepG2, PC3, and the chemo-resistant MCF-7-ADR cell lines relative to the normal Wi-38 cell line were in vitro assessed and compared with those of the free benzimidazole compound. In addition to FTIR, XRD, and NMR spectral studies, a polymeric nanocomplex with an average particle size of 467.7 nm and high stability was successfully developed, as indicated by the negative zeta potential (-28.24 mV). The nanocomplex also showed prolonged pH-sensitive sustained drug release under conditions that replicated the tumor's extra/intracellular pH. The formulated nanocomplex also demonstrated potent radical scavenging capacity owing to the inclusion of curcumin, a known radical quencher. In addition, compared with the free compound, BMPE-Cur induced DNA fragmentation-driven cell cycle arrest in HepG2, PC3, and MCF-7-ADR cells at the G1/S, G1 & S phases; respectively, with remarkable selectivity. In conclusion, the newly formulated BMPE-Cur nanocomplex represents an attractive multitarget anticancer candidate.

Establishment of a trastuzumab-resistant extramammary Paget disease model: loss of PTEN as a potential mechanism

BACKGROUND/OBJECTIVES

Extramammary Paget disease (EMPD) is a rare, cutaneous intraepithelial adenocarcinoma typically treated with wide local excision. Unfortunately, a number of patients with metastases show poor responses to chemotherapy. While some studies have explored trastuzumab's effectiveness against EMPD positive for human epidermal growth factor receptor 2 (HER2), trastuzumab resistance (TR) may emerge after anti-HER2 therapy.

METHODS/SUBJECTS

In this study, we established TR EMPD patient-derived xenografts (PDX) that replicated the histological and HER2 expression traits of naive EMPD tumours.

RESULTS

Cancer gene analyses revealed a loss of the PTEN gene in TR tumours, which was further confirmed by immunohistochemical staining and immunoblotting to test for protein expression levels. Reduced PTEN levels correlated with increased protein kinase B (Akt) phosphorylation and p27 downregulation, suggesting a potential mechanism for trastuzumab resistance in EMPD cells. In the trastuzumab-sensitive EMPD-PDX mouse model, PTEN inhibitors partially restored trastuzumab-mediated tumour regression. The TR EMPD-PDX responded favourably to targeted therapy (lapatinib, abemaciclib, palbociclib) and chemotherapy (eribulin, docetaxel, trastuzumab deruxtecan).

CONCLUSIONS

This study demonstrates an innovative TR EMPD-PDX model and introduces promising antineoplastic effects with various treatments for TR EMPD tumours.

Key target genes related to anti-breast cancer activity of ATRA: A network pharmacology, molecular docking and experimental investigation

All-trans retinoic acid (ATRA) has promising activity against breast cancer. However, the exact mechanisms of ATRA's anticancer effects remain complex and not fully understood. In this study, a network pharmacology and molecular docking approach was applied to identify key target genes related to ATRA's anti-breast cancer activity. Gene/disease enrichment analysis for predicted ATRA targets was performed using the Database for Annotation, Visualization and Integrated Discovery (DAVID), the Comparative Toxicogenomics Database (CTD), and the Gene Set Cancer Analysis (GSCA) database. Protein-Protein Interaction Network (PPIN) generation and analysis was conducted via Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) and cytoscape, respectively. Cancer-associated genes were evaluated using MyGeneVenn from the CTD. Differential expression analysis was conducted using the Tumor, Normal, and Metastatic (TNM) Plot tool and the Human Protein Atlas (HPA). The Glide docking program was used to predict ligand-protein binding. Treatment response predication and clinical profile assessment were performed using Receiver Operating Characteristic (ROC) Plotter and OncoDB databases, respectively. Cytotoxicity and gene expression were measured using MTT/fluorescent assays and Real-Time PCR, respectively. Molecular functions of ATRA targets (n = 209) included eicosanoid receptor activity and transcription factor activity. Some enriched pathways included inclusion body myositis and nuclear receptors pathways. Network analysis revealed 35 hub genes contributing to 3 modules, with 16 of them were associated with breast cancer. These genes were involved in apoptosis, cell cycle, androgen receptor pathway, and ESR-mediated signaling, among others. CCND1, ESR1, MMP9, MDM2, NCOA3, and RARA were significantly overexpressed in tumor samples. ATRA showed a high affinity towards CCND1/CDK4 and MMP9. CCND1, ESR1, and MDM2 were associated with poor treatment response and were downregulated after treatment of the breast cancer cell line with ATRA. CCND1 and ESR1 exhibited differential expression across breast cancer stages. Therefore, some part of ATRA's anti-breast cancer activity may be exerted through the CCND1/CDK4 complex.

Hallmarks of cancer resistance

This review explores the hallmarks of cancer resistance, including drug efflux mediated by ATP-binding cassette (ABC) transporters, metabolic reprogramming characterized by the Warburg effect, and the dynamic interplay between cancer cells and mitochondria. The role of cancer stem cells (CSCs) in treatment resistance and the regulatory influence of non-coding RNAs, such as long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), are studied. The chapter emphasizes future directions, encompassing advancements in immunotherapy, strategies to counter adaptive resistance, integration of artificial intelligence for predictive modeling, and the identification of biomarkers for personalized treatment. The comprehensive exploration of these hallmarks provides a foundation for innovative therapeutic approaches, aiming to navigate the complex landscape of cancer resistance and enhance patient outcomes.

siRNA treatment targeting integrin α11 overexpressed via EZH2-driven axis inhibits drug-resistant breast cancer progression

BACKGROUND

Breast cancer, the most prevalent cancer in women worldwide, faces treatment challenges due to drug resistance, posing a serious threat to patient survival. The present study aimed to identify the key molecules that drive drug resistance and aggressiveness in breast cancer cells and validate them as therapeutic targets.

METHODS

Transcriptome microarray and analysis using PANTHER pathway and StemChecker were performed to identify the most significantly expressed genes in tamoxifen-resistant and adriamycin-resistant MCF-7 breast cancer cells. Clinical relevance of the key genes was determined using Kaplan-Meier survival analyses on The Cancer Genome Atlas dataset of breast cancer patients. Gene overexpression/knockdown, spheroid formation, flow cytometric analysis, chromatin immunoprecipitation, immunocytochemistry, wound healing/transwell migration assays, and cancer stem cell transcription factor activation profiling array were used to elucidate the regulatory mechanism of integrin α11 expression. Tumour-bearing xenograft models were used to demonstrate integrin α11 is a potential therapeutic target.

RESULTS

Integrin α11 was consistently upregulated in drug-resistant breast cancer cells, and its silencing inhibited cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT) while restoring sensitivity to anticancer drugs. HIF1α, GLI-1, and EZH2 contributed the most to the regulation of integrin α11 and EZH2 expression, with EZH2 being more necessary for EZH2 autoinduction than HIF1α and GLI-1. Additionally, unlike HIF1α or EZH2, GLI-1 was the sole transcription factor activated by integrin-linked focal adhesion kinase, indicating GLI-1 as a key driver of the EZH2-integrin α11 axis operating for cancer stem cell survival and EMT. Kaplan-Meier survival analysis using The Cancer Genome Atlas (TCGA) dataset also revealed both EZH2 and integrin α11 could be strong prognostic factors of relapse-free and overall survival in breast cancer patients. However, the superior efficacy of integrin α11 siRNA therapy over EZH2 siRNA treatment was demonstrated by enhanced inhibition of tumour growth and prolonged survival in murine models bearing tumours.

CONCLUSION

Our findings elucidate that integrin α11 is upregulated by EZH2, forming a positive feedback circuit involving FAK-GLI-1 and contributing to drug resistance, cancer stem cell survival and EMT. Taken together, the results suggest integrin α11 as a promising prognostic marker and a powerful therapeutic target for drug-resistant breast cancer.

Targeting Sphingosine-1-Phosphate Signaling in Breast Cancer

In recent years, newly emerging therapies, such as immune checkpoint inhibitors and antibody-drug conjugates, have further improved outcomes for breast cancer patients. However, recurrent and metastatic breast cancer often eventually develops resistance to these drugs, and cure is still rare. As such, the development of new therapies for refractory breast cancer that differ from conventional mechanisms of action is necessary. Sphingosine-1-phosphate (S1P) is a key molecule with a variety of bioactive activities, including involvement in cancer cell proliferation, invasion, and metastasis. S1P also contributes to the formation of the cancer microenvironment by inducing surrounding vascular- and lymph-angiogenesis and regulating the immune system. In this article, we outline the basic mechanism of action of S1P, summarize previous findings on the function of S1P in cancer cells and the cancer microenvironment, and discuss the clinical significance of S1P in breast cancer and the therapeutic potential of targeting S1P signaling.

miRNAs as biomarkers of therapeutic response to HER2-targeted treatment in breast cancer: A systematic review

Breast cancer is the most common type of lethal cancer in women globally. Women have a 1 in 8 chance of developing breast cancer in their lifetime. Among the four primary molecular subtypes (luminal A, luminal B, HER2+, and triple-negative), HER2+ accounts for 20-25 % of all breast cancer and is rather aggressive. Although the treatment outcome of HER2+ breast cancer patients has been significantly improved with anti-HER2 agents, primary and acquired drug resistance present substantial clinical issues, limiting the benefits of HER2-targeted treatment. MicroRNAs (miRNAs) play a central role in regulating acquired drug resistance. miRNA are single-stranded, non-coding RNAs of around 20-25 nucleotides, known for essential roles in regulating gene expression at the post-transcriptional level. Increasing evidence has demonstrated that miRNA-mediated alteration of gene expression is associated with tumorigenesis, metastasis, and tumor response to treatment. Comprehensive knowledge of miRNAs as potential markers of drug response can help provide valuable guidance for treatment prognosis and personalized medicine for breast cancer patients.

Reduced Tumor Volume and Increased Necrosis of Human Breast Tumor Xenograft in Mice Pretreated by a Cocktail of Three Specific Anti-HER2 scFvs

PURPOSE

We aimed to assess the effects of a cocktail comprising three specific anti- HER2 scFvs on breast tumor formation in a xenograft mouse model and to evaluate quantitative changes in the tumor using stereological analysis.

METHODS

Three specific anti-HER2 phage antibodies were produced from a scFv-library using phage display technology. The cell binding capacities of the antibodies were assessed via FACS analysis. Soluble forms of the antibodies were prepared by infecting HB2151-E. coli cells and purified using a centrifugal ultrafiltration method. The purification process was evaluated by SDSPAGE analysis. Two forms of scFv cocktails were prepared, soluble scFv and phage-scFv cocktail, which contained an equal amount/phage of each of the three antibodies. Inbred female BALB/c mice were pretreated with 5 and 20 mg/kg of the soluble scFv cocktail and 1011 phage-scFv cocktail/ kg. The mice were then injected with 2×106 SKBR-3 human breast cancer cells. Total tumor, inflammatory and non-inflammatory volumes were estimated using the Cavalieri principle after preparing photomicrograph slides.

RESULTS

The anti-HER2 scFvs showed significantly higher binding to SKBR-3 cells compared to the isotype control. SDS-PAGE analysis confirmed the high purification of the scFvs. Stereological analysis revealed that the group pretreated with 20 mg/kg of the soluble scFv cocktail exhibited the highest reductions in total tumor volume, non-inflammatory volume, and inflammatory volume, with reductions of 73%, 78%, and 72%, respectively, compared to PBS-pretreated mice (P-value < 0.0001). The volumetric ratio of necrotic tissue to total tumor volume increased by 2.2-fold and 2- fold in the 20 mg/kg of soluble scFv cocktail and phage-scFv cocktail groups, respectively, compared to the PBS-treated mice (P-value < 0.05).

CONCLUSION

Pre-treatment with a 20 mg/kg anti-HER2 scFv cocktail resulted in a significant reduction in tumor volume and increased necrotic area in a human breast cancer xenograft model, indicating the remarkable anti-tumor effect of the cocktail in vivo.

Targeted Delivery of Potent Chemical Drugs and RNAi to Drug-Resistant Breast Cancer Using RNA-Nanotechnology and RNA-Ligand Displaying Extracellular vesicles

This review describes a new technology to treat breast-cancer-drug-resistance by targeting the ABC as the multi-homo-subunit ATPase, enlightening by the Christmas-lighting budge with serial circuit and the asymmetrical homo-hexamer of the phi29 DNA packaging motor with sequential revolving mechanism. Chemotherapeutics has been widely used in breast cancer treatments, but drug resistance has raised a serious concern. RNA therapeutics has emerged as the third milestone in pharmaceutical drug development. RNA nanoparticles are dynamic, mild, and deformative, resulting in spontaneous, rapid, and efficient accumulation in tumor vasculature after IV injection. Their negative charge and favorable size bypass the nonspecific targeting of vital organs and normal cells. This motile and deformable nature also led to the fast passing of glomerular filters and their movement into the urine for rapid body clearance for those non-tumor-accumulated nanoparticles, resulting in undetectable toxicity. Extracellular vesicles have shown potential as a delivery system for RNAi and chemotherapeutic drugs in vivo, contributing to the efficacy of cancer remission. However, the lack of cell-targeting ligands on extracellular vesicles and the nonspecific entry into healthy cells has led to safety concerns. This review addresses how to apply RNA nanotechnology and RNA-ligand displaying extracellular vesicles for specific delivery to breast cancer. The particular focus is on using and combining the RNA and extracellular vesicle technology to deal with breast cancer drug resistance. The targeting capabilities and drug safety can be improved through extracellular vesicle engineering techniques, such as affixing ligands on the extracellular vesicle surface utilizing arrow-tail RNA nanoparticles, ultimately addressing off-target effects and toxicity. Using RNA ligands for specific targeting and the efficient membrane fusion of extracellular vesicles has enabled the development of ligand-displayed extracellular vesicles capable of delivering both RNAi and chemical drugs to cells with precision, effectively inhibiting tumor growth. The negative charge inherent in the vesicles results in electrostatic repulsion, reducing non-specific binding to healthy cells that contain negatively charged lipid membranes. By leveraging the principles of RNA nanotechnology, the engineering of extracellular vesicles offers a promising avenue for addressing breast cancer drug resistance. This review also discusses applying the series of circuit mechanisms in Christmas-decorating-lighting to develop effective therapeutics to combat breast cancer chemoresistance by targeting the ABC drug transporter and breast cancer surface receptors.

Molecular Profile of Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is a relatively uncommon but highly aggressive primary liver cancer that originates within the liver. The aim of this study is to review the molecular profile of intrahepatic cholangiocarcinoma and its implications for prognostication and decision-making. This comprehensive characterization of ICC tumors sheds light on the disease's underlying biology and offers a foundation for more personalized treatment strategies. This is a narrative review of the prognostic and therapeutic role of the molecular profile of ICC. Knowing the molecular profile of tumors helps determine prognosis and support certain target therapies. The molecular panel in ICC helps to select patients for specific therapies, predict treatment responses, and monitor treatment responses. Precision medicine in ICC can promote improvement in prognosis and reduce unnecessary toxicity and might have a significant role in the management of ICC in the following years. The main mutations in ICC are in tumor protein p53 (TP53), Kirsten rat sarcoma virus (KRAS), isocitrate dehydrogenase 1 (IDH1), and AT-rich interactive domain-containing protein 1A (ARID1A). The rate of mutations varies significantly for each population. Targeting TP53 and KRAS is challenging due to the natural characteristics of these genes. Different stages of clinical studies have shown encouraging results with inhibitors of mutated IDH1 and target therapy for ARID1A downstream effectors. Fibroblast growth factor receptor 2 (FGFR2) fusions are an important target in patients with ICC. Immune checkpoint blockade can be applied to a small percentage of ICC patients. Molecular profiling in ICC represents a groundbreaking approach to understanding and managing this complex liver cancer. As our comprehension of ICC's molecular intricacies continues to expand, so does the potential for offering patients more precise and effective treatments. The integration of molecular profiling into clinical practice signifies the dawn of a new era in ICC care, emphasizing personalized medicine in the ongoing battle against this malignancy.

Saeed H, del Solar V, López-Hernández JE, Michel A, Mathew J, Lewis JS, Contel M. Shifting the Antibody-Drug Conjugate Paradigm: A Trastuzumab-Gold-Based Conjugate Demonstrates High Efficacy against Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer Mouse Model

Antibody-drug conjugates (ADCs) combine the selectivity of monoclonal antibodies (mAbs) with the efficacy of chemotherapeutics to target cancers without toxicity to normal tissue. Clinically, most chemotherapeutic ADCs are based on complex organic molecules, while the conjugation of metallodrugs to mAbs has been overlooked, despite the resurgent interest in metal-based drugs as cancer chemotherapeutics. In 2019, we described the first gold ADCs containing gold-triphenylphosphane fragments as a proof of concept. The ADCs (based on the antibody trastuzumab) were selective and highly active against HER2-positive breast cancer cells. In this study, we developed site-specific ADCs (Thio-1b and Thio-2b) using the cysteine-engineered trastuzumab derivative THIOMAB antibody technology with gold(I)-containing phosphanes and a maleimide-based linker amenable to bioconjugation (1b and 2b). In addition, we developed lysine-directed ADCs with gold payloads based on phosphanes and N-heterocyclic carbenes featuring an activated ester moiety (2c and 5c) with trastuzumab (Tras-2c and Tras-5c) and another anti-HER2 antibody, pertuzumab (Per-2c and Per-5c). Both sets of ADCs demonstrated significant anticancer potency in vitro assays. Based on these results, one ADC (Tras-2c), containing the [Au(PEt3)] fragment present in FDA-approved auranofin, was selected for an in vivo antitumor efficacy study. Immunocompromised mice xenografted with the HER2-positive human cancer cell line SKBR-3 exhibited almost complete tumor reduction and low toxicity with intravenous administration of Tras-2c. With this highly selective targeting system, we demonstrated that a subnanomolar cytotoxicity profile in cells is not required for an impressive antitumor effect in a mouse xenograft model.

Cost-utility analysis of trastuzumab deruxtecan versus trastuzumab emtansine in HER2-positive metastatic breast cancer in Chinese setting

PURPOSE

Trastuzumab deruxtecan (T-DXd) expressed substantial improvement in the progression-free survival and overall survival contrasted with trastuzumab emtansine (T-DM1) in patients with HER2-positive metastatic breast cancer (mBC), becoming the second-line standard of care, promisingly. We aim to estimate the cost-utility of T-DXd versus T-DM1 in HER2-positive mBC from the Chinese healthcare perspective.

METHODS

A partitioned survival model was applied to examine the cost-utility of T-DXd versus T-DM1. Clinical patients and outcome data were sourced from the DESTINY-Breast 03 trial. Costs and utilities were sourced in Chinese setting. Total costs, quality-adjusted life months (QALMs), and an incremental cost-utility ratios (ICUR) were calculated for cost-utility analysis. The willingness-to-pay threshold was set at $3188/QALM. Univariate, scenario, and probabilistic sensitivity analyses were performed.

RESULTS

T-DXd group gained ∆QALM of 7.09 months and ∆Cost of $304,503 compared with T-DM1 therapy, which caused an ICUR of $42,936/QALM. The results of sensitivity analyses confirmed the base-case findings. Furthermore, T-DXd must reduce the price to enter the Chinese mainland market. At least when the cycle cost of T-DXd is reduced to $2975, T-DXd has an 83.3% chance of becoming a better choice.

CONCLUSIONS

T-DXd appears to be not cost effective compared with T-DM1 for HER2-positive mBC patients previously treated with trastuzumab and a taxane.

MAF1 is a predictive biomarker in HER2 positive breast cancer

RNA polymerase III transcription is pivotal in regulating cellular growth and frequently deregulated in various cancers. MAF1 negatively regulates RNA polymerase III transcription. Currently, it is unclear if MAF1 is universally deregulated in human cancers. Recently, MAF1 expression has been demonstrated to be altered in colorectal and liver carcinomas and Luminal B breast cancers. In this study, we analyzed clinical breast cancer datasets to determine if MAF1 alterations correlate with clinical outcomes in HER2-positive breast cancer. Using various bioinformatics tools, we screened breast cancer datasets for alterations in MAF1 expression. We report that MAF1 is amplified in 39% of all breast cancer sub-types, and the observed amplification co-occurs with MYC. MAF1 amplification correlated with increased methylation of the MAF1 promoter and MAF1 protein expression is significantly decreased in luminal, HER2-positive, and TNBC breast cancer subtypes. MAF1 protein expression is also significantly reduced in stage 2 and 3 breast cancer compared to normal and significantly decreased in all breast cancer patients, regardless of race and age. In SKBR3 and BT474 breast cancer cell lines treated with anti-HER2 therapies, MAF1 mRNA expression is significantly increased. In HER2-positive breast cancer patients, MAF1 expression significantly increases and correlates with five years of relapse-free survival in response to trastuzumab treatment, suggesting MAF1 is a predictive biomarker in breast cancer. These data suggest a role for MAF1 alterations in HER2-positive breast cancer. More extensive studies are warranted to determine if MAF1 serves as a predictive and prognostic biomarker in breast cancer.

Investigation of Tumor Heterogeneity Using Integrated Single-Cell RNA Sequence Analysis to Focus on Genes Related to Breast Cancer-, EMT-, CSC-, and Metastasis-Related Markers in Patients with HER2-Positive Breast Cancer

Human epidermal growth factor receptor 2 (HER2) protein, which is characterized by the amplification of ERBB2, is a molecular target for HER2-overexpressing breast cancer. Many targeted HER2 strategies have been well developed thus far. Furthermore, intratumoral heterogeneity in HER2 cases has been observed with immunohistochemical staining and has been considered one of the reasons for drug resistance. Therefore, we conducted an integrated analysis of the breast cancer single-cell gene expression data for HER2-positive breast cancer cases from both scRNA-seq data from public datasets and data from our cohort and compared them with those for luminal breast cancer datasets. In our results, heterogeneous distribution of the expression of breast cancer-related genes (ESR1, PGR, ERBB2, and MKI67) was observed. Various gene expression levels differed at the single-cell level between the ERBB2-high group and ERBB2-low group. Moreover, molecular functions and ERBB2 expression levels differed between estrogen receptor (ER)-positive and ER-negative HER2 cases. Additionally, the gene expression levels of typical breast cancer-, CSC-, EMT-, and metastasis-related markers were also different across each patient. These results suggest that diversity in gene expression could occur not only in the presence of ERBB2 expression and ER status but also in the molecular characteristics of each patient.

Clinical Impact of New Treatment Strategies for HER2-Positive Metastatic Breast Cancer Patients with Resistance to Classical Anti-HER Therapies

HER2-positive breast cancer accounts for 15-20% of all breast cancer cases. This subtype is characterized by an aggressive behavior and poor prognosis. Anti-HER2 therapies have considerably improved the natural course of the disease. Despite this, relapse still occurs in around 20% of patients due to primary or acquired treatment resistance, and metastasis remains an incurable disease. This article reviews the main mechanisms underlying resistance to anti-HER2 treatments, focusing on newer HER2-targeted therapies. The progress in anti-HER2 drugs includes the development of novel antibody-drug conjugates with improvements in the conjugation process and novel linkers and payloads. Moreover, trastuzumab deruxtecan has enhanced the efficacy of trastuzumab emtansine, and the new drug trastuzumab duocarmazine is currently undergoing clinical trials to assess its effect. The combination of anti-HER2 agents with other drugs is also being evaluated. The addition of immunotherapy checkpoint inhibitors shows some benefit in a subset of patients, indicating the need for useful biomarkers to properly stratify patients. Besides, CDK4/6 and tyrosine kinase inhibitors are also included in the design of new treatment strategies. Lapitinib, neratinib and tucatinib have been approved for HER2-positive metastasis patients, however clinical trials are currently ongoing to optimize combined strategies, to reduce toxicity, and to better define the useful setting. Clinical research should be strengthened along with the discovery and validation of new biomarkers, as well as a deeper understanding of drug resistance and action mechanisms.

Overview on Current Trends and Emerging Therapies in the Chemotherapy of Patients with Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer

Over the past few decades, significant progress has been made in the management of human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC) due to the development of targeted therapies. However, HER2-positive BC is an aggressive subtype, posing significant challenges, including treatment resistance and disease recurrence. Current standard treatment options for HER2-positive BC include combinations of chemotherapy drugs, targeted therapies such as trastuzumab and pertuzumab, and hormone therapies. However, some important limitations of these treatments, such as resistance and adverse effects, are reported. Also, we showed emerging therapeutic options, such as novel chemotherapy agents, antibody-drug conjugates, and immune checkpoint inhibitors, and discussed their mechanisms of action, potential benefits, and potential future directions in the field.

Pyrotinib plus capecitabine for trastuzumab-resistant, HER2-positive advanced breast cancer (PICTURE): a single-arm, multicenter phase 2 trial

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.

The Role of HER2 Status in the Biliary Tract Cancers

Despite recent advances, biliary tract cancer (BTC) is traditionally known as being hard to treat with a poor prognosis. Recent state-of-the-art genomic technologies such as next-generation sequencing (NGS) revolutionized cancer management and shed light on the genomic landscape of BTCs. There are ongoing clinical trials to assess the efficacy of HER2-blocking antibodies or drug conjugates in BTCs with HER2 amplifications. However, HER2 amplifications may not be the sole eligibility factor for these clinical trials. In this review, we aimed to comprehensively examine the role of somatic HER2 alterations and amplifications in patient stratification and provide an overview of the current state of ongoing clinical trials.

HDAC Inhibition Restores Response to HER2-Targeted Therapy in Breast Cancer via PHLDA1 Induction

The downregulation of Pleckstrin Homology-Like Domain family A member 1 (PHLDA1) expression mediates resistance to targeted therapies in receptor tyrosine kinase-driven cancers. The restoration and maintenance of PHLDA1 levels in cancer cells thus constitutes a potential strategy to circumvent resistance to inhibitors of receptor tyrosine kinases. Through a pharmacological approach, we identify the inhibition of MAPK signalling as a crucial step in PHLDA1 downregulation. Further ChIP-qPCR analysis revealed that MEK1/2 inhibition produces significant epigenetic changes at the PHLDA1 locus, specifically a decrease in the activatory marks H3Kme3 and H3K27ac. In line with this, we show that treatment with the clinically relevant class I histone deacetylase (HDAC) inhibitor 4SC-202 restores PHLDA1 expression in lapatinib-resistant human epidermal growth factor receptor-2 (HER2)+ breast cancer cells. Critically, we show that when given in combination, 4SC-202 and lapatinib exert synergistic effects on 2D cell proliferation and colony formation capacity. We therefore propose that co-treatment with 4SC-202 may prolong the clinical efficacy of lapatinib in HER2+ breast cancer patients.

Axillary Downstaging and the Impact of Clinical Axillary Status on Efficacy of Neoadjuvant Therapy for HER2-Positive Breast Cancer: A Network Meta-Analysis

Background: Lymph node downstaging and the achievement of total-pCR (ypT0/is ypN0) after neoadjuvant therapy are of great importance in HER-2 positive breast cancer. We aim to provide an overall review of neoadjuvant regimens for lymph node downstaging and to indirectly compare the total-pCR by various neoadjuvant regimens with network meta-analysis in HER2-positive patients according to their clinical lymph node status. Methods: Five English databases were searched comprehensively and systematically for relevant RCTs and case-control studies. The data extracted from the included studies were analyzed with the use of Review Manager 5.3 or STATA 15.0 software. Results: A total of 1508 published manuscripts were identified, and 17 studies including 4747 patients were finally included in our analysis. The network meta-analysis of total-pCR showed that dual-target therapy is significantly better than single-target therapy in clinically node-positive patients, and carboplatin performed significantly better than anthracycline in single-target condition. Lapatinib performed poorly in clinically node-positive patients. However, lapatinib in combination with trastuzumab was ranked at the top in the clinically node-negative group, and pertuzumab showed dissatisfied performance in contrast to the primacy of pertuzumab in clinically node-positive groups. Conclusion: In summary, different lymph node statuses led to the diverse first choice of neoadjuvant regimen. We highly recommended TCbHP as the first choice for the neoadjuvant treatment in clinically node-positive HER-2 positive breast cancer. Since lapatinib with trastuzumab ranked top in the clinically node-negative group, we looked forward to discovering the potential value of TKI in clinically node-negative patients, which needs further analysis in the future.

Clinical updates on tyrosine kinase inhibitors in HER2-positive breast cancer

Breast cancer (BC) is caused by epigenetic modifications and genetic heterogeneity and exhibits various histological feature. HER2+ (Human epidermal growth factor receptor 2) is a more aggressive type of breast cancer, diagnosis and prognosis are difficult for HER2+ BC. Anti-HER2+ inhibitors have been effectively used for patient treatment. High mortality rate is reported in HER2+ BC, due to availability of limited therapeutic options. Despite advances in systemic medications to treat metastatic breast cancer (MBC), HER2-positive MBC is still challenging for patients and treating clinicians. The clinical characteristics of the disease have changed after treatment with HER2-targeted therapy. Various types of Tyrosine kinase inhibitors (TKIs) have been developed to treat patients with HER2+ BC including afatinib, lapatinib, neratinib, tucatinib, and pyrotinib, have been developed as HER2-targeted therapies. The antibody-drug conjugates adotrastuzumab, emtansine, famtrastuzumab, and deruxtecan, as well as the anti-HER2 monoclonal antibody pertuzumab are used in both early-stage and metastatic situations, either alone or in conjunction with chemotherapy and other HER2-targeting therapies. The emergence of drug resistance in anti-HER2 therapies has been observed. To overcome drug resistance and limited efficacy in current treatment options, nano formulations can be used in patients with HER2+ BC treatment. Anti-HER2 ligands can be used in various nano formulations to target HER2 receptors. Here we will discuss, targeted TKIs in patients with HER2+ BC, clinical studies of HER2+ targeted TKIs, mechanisms of resistance to HER2-directed therapies with new implications of TKIs in HER2+ MBC (metastatic breast cancer) and anti-HER2 ligand in various nano formulations to target HER2 receptors.

HER2 mRNA Levels, Estrogen Receptor Activity and Susceptibility to Trastuzumab in Primary Breast Cancer

While the results thus far demonstrate the clinical benefit of trastuzumab in breast cancer (BC), some patients do not respond to this drug. HER2 mRNA, alone or combined with other genes/biomarkers, has been proven to be a powerful predictive marker in several studies. Here, we provide evidence of the association between HER2 mRNA levels and the response to anti-HER2 treatment in HER2-positive BC patients treated with adjuvant trastuzumab and show that this association is independent of estrogen receptor (ER) tumor positivity. While HER2 mRNA expression was significantly correlated with HER2 protein levels in ER-negative tumors, no correlation was found in ER-positive tumors, and HER2 protein expression was not associated with relapse risk. Correlation analyses in the ER-positive subset identified ER activity as the pathway inversely associated with HER2 mRNA. Associations between HER2 levels and oncogene addiction, as well as between HER2 activation and trastuzumab sensitivity, were also observed in vitro in HER2-positive BC cell lines. In ER-positive but not ER-negative BC cells, HER2 transcription was increased by reducing ligand-dependent ER activity or inducing ER degradation. Accordingly, HER2 mRNA levels in patients were found to be inversely correlated with blood levels of estradiol, the natural ligand of ER that induces ER activation. Moreover, low estradiol levels were associated with a lower risk of relapse in HER2-positive BC patients treated with adjuvant trastuzumab. Overall, we found that HER2 mRNA levels, but not protein levels, indicate the HER2 dependency of tumor cells and low estrogen-dependent ER activity in HER2-positive tumors.

The reversal of anti-HER2 resistance in advanced HER2-positive breast cancer using apatinib: two cases reports and literature review

BACKGROUND

Human epidermal growth factor receptor 2 (HER2)-targeted treatment has yielded a notable clinical benefit in patients with HER2-positive breast cancer. However, nearly 50% of patients still suffer disease progression due to resistance to HER2-targeted therapy. After the failure of macromolecular monoclonal antibodies (mAbs) therapy, we can choose small molecule tyrosine kinase inhibitors (TKIs) to reverse HER2 resistance. When small molecule TKIs resistance, we can use mAb combined with small molecule TKI, or antibody-drug conjugates (ADCs) to reverse HER2 resistance. However, then due to the availability and price of ADCs, patients may not use them. Consequently, new therapeutic approaches are required to overcome HER2-targeted therapy resistance. Vascular endothelial growth factor and its receptors (VEGF/VEGFRs) promote tumor angiogenesis. They can also activate downstream signaling pathways to promote tumorigenesis. VEGFR is a key regulator of the tyrosine kinase signaling pathway and may be a potential target in HER2-positive breast cancer. Apatinib is a small molecule TKI that specifically binds to VEGFR2 and thus exerts an antitumor effect. Although there is no definite indication for apatinib in breast cancer, it has a good benefit in advanced gastric cancer.

CASE DESCRIPTION

The two patients we reported were both HER2-positive breast cancer who we followed for more than 10 years. After the failure of multi-line anti-HER2 treatment, apatinib combined with anti-HER2 treatment had PFS of 8.4 months and 10.6 months, respectively. One patient had grade 2 hand-foot syndrome. The other had grade 2 leukopenia and grade 2 thrombocytopenia, both of them improved after control. And the best response of them were PR and SD, respectively.

CONCLUSIONS

Our cases demonstrate that, in HER2-positive breast cancer patients with HER2-targeted resistance, apatinib may be able to reverse HER2 resistance. These two cases suggest an alternative method for clinical HER2-targeted treatment of drug-resistant breast cancer patients and provide new insights for future research.