Novel endocrine therapies: What is next in estrogen receptor positive, HER2 negative breast cancer?

Decoding Clinical Trials in Metastatic Breast Cancer: Practical Insights for Optimal Therapy Sequencing

The art of sequencing therapy in the management of breast cancer is a multifaceted challenge that demands the careful integration of clinical trial data, real-world evidence, and individualized patient factors to guide treatment decisions. As the therapeutic landscape evolves rapidly with new agents and combinations, clinicians are confronted with critical decisions on how best to order treatments to maximize benefit, minimize toxicity, and preserve future options. For patients with estrogen receptor-positive (ER+) disease, this review discusses how emerging resistance patterns after cyclin-dependent kinase 4 and 6 inhibitors require careful re-evaluation of subsequent endocrine and targeted therapies, as well as chemotherapy, emphasizing the need for evidence-based strategies and ethical crossover designs in clinical trials. In addition, for both ER+ and ER- metastatic breast cancer (MBC) with nonoverexpressed human epidermal growth factor receptor 2 (HER2), this review highlights pivotal trials investigating antibody-drug conjugates (ADCs)-including trastuzumab deruxtecan, sacituzumab govitecan, and datopotamab deruxtecan-and the challenges related to control arm selection and crossover that may affect outcome interpretation. Finally, for patients with HER2-positive disease, the review explores first-line and maintenance strategies-including insights from landmark trials like CLEOPATRA and PATINA-and addresses the impact of brain metastases on sequencing decisions. By critically appraising current data and identifying gaps in biomarker-guided and sequencing-specific strategies, this review provides practical insights to inform clinical practice and optimize personalized treatment plans for patients with MBC.

Patient preferences for treatments in hormone receptor-positive/HER2-negative metastatic breast cancer in Italy: a discrete choice experiment study

Hormone receptor (HR) positive (HR +) and human epidermal growth factor receptor 2 (HER2) negative (aka HER2 -) breast cancer (BC) is the most frequently diagnosed subtype. Recent development of next-generation endocrine therapies (e.g. selective estrogen receptor degraders (SERDs); third-generation aromatase inhibitors (AI) and targeted therapies (e.g., CDK4/6, PI3K, and mTOR inhibitors)) as well as antibody drugs conjugates (ADC, eg. T-DXd and SG) showed promising results with meaningful improvements in survival for patients with metastatic HR + HER2 - BC. Therapy selection is mainly based on clinical, tumor pathological and molecular characteristics as well as on efficacy based on trial data, nevertheless, side effect profiles are key differentiators of treatments in the metastatic setting. Therefore, understanding how patients evaluate various treatment attributes and how these change in different clinical situations is fundamental toward the choice of optimal therapeutic strategies for treating metastatic HR + HER2 - Stage IV patients. Here, we investigated treatment preferences of a total of 102 stage IV HR + HER2 - breast cancer patients in Italy by developing and applying a survey instrument based on discrete choice experiment (DCE). Treatment efficacy was the top valued attribute across all patient segments and the second most important attribute was the risk of grade ≥ 3 adverse events (AE). Overall, therapies with better outcomes of PFS or AE grade 3 or higher would have a higher impact on the preference to choose a treatment from a patient perspective.

PROteolysis TArgeting Chimera (PROTAC) Estrogen Receptor Degraders for Treatment of Estrogen Receptor-Positive Advanced Breast Cancer

The estrogen receptor (ER) signaling pathway is a key driver of breast cancer, primarily through the activation of genes that promote tumor cell survival and growth. The recommended first-line treatment for ER-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer is endocrine therapy plus a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor. However, most patients experience disease progression, and there is no clear standard of care in the second-line setting. Thus, novel treatments in the advanced setting are needed. In this narrative review, we describe the unique mechanisms of action of a new class of drugs called PROteolysis TArgeting Chimera (PROTAC) ER degraders. Unlike other ER-targeted therapies, these small molecules harness the body's primary intracellular natural protein disposal machinery, the ubiquitin-proteasome system, to directly induce ER degradation. Vepdegestrant (ARV-471) is the furthest advanced PROTAC ER degrader currently in clinical development. Preclinical data demonstrate increased tumor growth inhibition with vepdegestrant alone or in combination with CDK4/6 inhibitors compared with the selective ER degrader fulvestrant. In a first-in-human phase 1/2 clinical study, vepdegestrant administered orally as monotherapy or in combination with palbociclib showed promising clinical activity and a favorable safety profile in patients with heavily pretreated ER+/HER2- advanced breast cancer. Several other PROTAC ER degraders (AC699, ERD-3111, ERD-4001, and HP568) are in early development and have demonstrated activity in preclinical breast cancer models, with some recently entering clinical trials. The data highlight the potential for PROTAC ER degraders to be a new backbone therapy in breast cancer.

Estrogen receptor expression in human tumors: A tissue microarray study evaluating more than 18,000 tumors from 149 different entities

Estrogen receptor (ER) is a ligand-activated transcription factor with a critical role in development and function of multiple organ systems and a well-established drug target for breast cancer. To comprehensively evaluate ER expression in normal and tumor tissues, a tissue microarray containing 18,560 samples from 149 different tumor types and subtypes and 608 samples of 76 different normal tissue types was analyzed by immunohistochemistry (IHC). ER positivity was found in 55 different tumor types including 26 entities with at least one strongly positive tumor. ER positivity strongly predominated in breast neoplasms (81.1%) and in other gynecological tumors (39.4%) while only 0.8% of non-gynecological and non-mammary tumors showed ER positivity. Among these, ER staining - often at lower intensity - especially occurred in neuroendocrine neoplasms (up to 9.1%), salivary gland tumors (up to 8.3%), and in squamous cell carcinomas of different sites of origin (up to 6.7%). In invasive breast carcinoma (NST), reduced ER immunostaining was linked to high pT (p < 0.0001), high grade (p < 0.0001), distant metastasis (p = 0.0012), HER2 positivity (p < 0.0001), PR negativity (p < 0.0001) and shorter overall survival (p = 0.0576). In serous high-grade ovarian cancer, reduced ER staining was linked to nodal metastasis (p = 0.0012). ER staining was unrelated to histopathological features in 145 analyzable endometroid endometrial carcinomas. Within non-mammary, non-gynecological, non-prostate, and non-testicular tumors, ER positivity was more common in tumors from female (1.4% of 2528) than from male patients (0.6% of 3228; p = 0.0003). In summary, our data provide a ranking list of tumor entities according to their prevalence of ER positivity and shows that ER can be strongly expressed in a small number of non-breast and non-gynecological tumors which could potentially represent a diagnostic pitfall in a cancer of unknown primary but also represents a therapeutic opportunity.

New Promising Steroidal Aromatase Inhibitors with Multi-Target Action on Estrogen and Androgen Receptors for Breast Cancer Treatment

Background/Objectives: Endocrine therapies that comprise anti-estrogens and aromatase inhibitors (AIs) are the standard treatment for estrogen receptor-positive (ER+) (Luminal A) breast cancer-the most prevalent subtype. However, the emergence of resistance restricts their success by causing tumor relapse and re-growth, which demands a switch towards other therapeutic approaches in order to minimize or overcome resistance. Indeed, this clinical limitation highlights the search for new molecules to improve cancer treatment. Recently, strategies that address multiple targets have been emerging, and multi-target drugs have the potential to become the future anti-cancer molecules. Our group has been searching for new multi-target compounds, and as part of this, our study aims to understand the anti-cancer and multi-target potential of three new steroidal aromatase inhibitors (AIs): 7α-methylandrost-4-en-17-one (6), 7α-methylandrost-4-ene-3,17-dione (10a) and androsta-4,9(11)-diene-3,17-dione (13). Methods: Their in vitro actions and molecular mechanisms were elucidated in a sensitive ER+ aromatase-overexpressing breast cancer cell line, MCF-7aro cells, as well as in an AI-resistant ER+ breast cancer cell line, LTEDaro cells. Results: All the new AIs (10 µM) prevented the proliferation of MCF-7aro cells by arresting cell cycle progression. Interestingly, all AIs (10 µM) act as androgen receptor (AR) agonists and modulate ER levels, synthesis and signaling to induce the apoptosis of ER+ breast cancer cells. Additionally, these new AIs (10 µM) also re-sensitize resistant cells by promoting apoptosis, offering a therapeutic benefit. Conclusions: Overall, new steroidal polypharmacological compounds have been discovered that, by acting as AIs, ER modulators and AR agonists, impair ER+ breast cancer cell growth. Overall, this study is a breakthrough on drug discovery as it presents new molecules with appealing anti-cancer properties and multi-target action for the treatment of ER+ breast cancer.

Estrogen Signaling in Early-Stage Breast Cancer: Impact on Neoadjuvant Chemotherapy and Immunotherapy

Neoadjuvant chemoimmunotherapy (NACIT) has been shown to improve pathologic complete response (pCR) rates and survival outcomes in stage II-III triple-negative breast cancer (TNBC). Promising pCR rate improvements have also been documented for selected patients with estrogen receptor-positive (ER+) human epidermal growth factor receptor 2-negative (HER2-) breast cancer (BC). However, one size does not fit all and predicting which patients will benefit from NACIT remains challenging. Accurate predictions would be useful to minimize immune-related toxicity, which can be severe, irreversible, and potentially impact fertility and quality of life, and to identify patients in need of alternative treatments. This review aims to capitalize on the existing translational and clinical evidence on predictors of treatment response in patients with early-stage BC treated with neoadjuvant chemotherapy (NACT) and NACIT. It summarizes evidence suggesting that NACT/NACIT effectiveness may correlate with pre-treatment tumor characteristics, including mutational profiles, ER expression and signaling, immune cell presence and spatial organization, specific gene signatures, and the levels of proliferating versus quiescent cancer cells. However, the predominantly qualitative and descriptive nature of many studies highlights the challenges in integrating various potential response determinants into a validated, comprehensive, and multimodal predictive model. The potential of novel multi-modal approaches, such as those based on artificial intelligence, to overcome current challenges remains unclear, as these tools are not free from bias and shortcut learning. Despite these limitations, the rapid evolution of these technologies, coupled with further efforts in basic and translational research, holds promise for improving treatment outcome predictions in early HER2- BC.

Comprehensive review of drug resistance in mammalian cancer stem cells: implications for cancer therapy

Cancer remains a significant global challenge, and despite the numerous strategies developed to advance cancer therapy, an effective cure for metastatic cancer remains elusive. A major hurdle in treatment success is the ability of cancer cells, particularly cancer stem cells (CSCs), to resist therapy. These CSCs possess unique abilities, including self-renewal, differentiation, and repair, which drive tumor progression and chemotherapy resistance. The resilience of CSCs is linked to certain signaling pathways. Tumors with pathway-dependent CSCs often develop genetic resistance, whereas those with pathway-independent CSCs undergo epigenetic changes that affect gene regulation. CSCs can evade cytotoxic drugs, radiation, and apoptosis by increasing drug efflux transporter activity and activating survival mechanisms. Future research should prioritize the identification of new biomarkers and signaling molecules to better understand drug resistance. The use of cutting-edge approaches, such as bioinformatics, genomics, proteomics, and nanotechnology, offers potential solutions to this challenge. Key strategies include developing targeted therapies, employing nanocarriers for precise drug delivery, and focusing on CSC-targeted pathways such as the Wnt, Notch, and Hedgehog pathways. Additionally, investigating multitarget inhibitors, immunotherapy, and nanodrug delivery systems is critical for overcoming drug resistance in cancer cells.

Imlunestrant, an Oral Selective Estrogen Receptor Degrader, as Monotherapy and in Combination With Targeted Therapy in Estrogen Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer: Phase Ia/Ib EMBER Study

PURPOSE

Imlunestrant is a next-generation oral selective estrogen receptor (ER) degrader designed to deliver continuous ER target inhibition, including in ESR1-mutant breast cancer. This phase Ia/b trial determined the recommended phase II dose (RP2D), safety, pharmacokinetics, and efficacy of imlunestrant, as monotherapy and in combination with targeted therapy, in ER-positive (ER+) advanced breast cancer (ABC) and endometrial endometrioid cancer. The ER+/human epidermal growth factor receptor 2-negative (HER2-) ABC experience is reported here.

METHODS

An i3+3 dose-escalation design was used, followed by dose expansions of imlunestrant as monotherapy or in combination with abemaciclib with or without aromatase inhibitor (AI), everolimus, or alpelisib. Imlunestrant was administered orally once daily and with the combination partner per label.

RESULTS

Overall, 262 patients with ER+/HER2- ABC were treated (phase Ia, n = 74; phase Ib, n = 188). Among patients who received imlunestrant monotherapy (n = 114), no dose-limiting toxicities or discontinuations occurred. At the RP2D (400 mg once daily), patients (n = 51) reported grade 1-2 nausea (39.2%), fatigue (39.2%), and diarrhea (29.4%). Patients at RP2D had received previous cyclin-dependent kinase 4/6 inhibitor (CDK4/6i; 92.2%), fulvestrant (41.2%), and chemotherapy (29.4%) for ABC and achieved a median progression-free survival (mPFS) of 7.2 months (95% CI, 3.7 to 8.3). Among patients who received imlunestrant + abemaciclib (n = 42) and imlunestrant + abemaciclib + AI (n = 43), most (69.4%) were treatment-naïve for ABC; all were CDK4/6i-naïve. Patients treated with imlunestrant + everolimus (n = 42)/alpelisib (n = 21) had received previous CDK4/6i (100%), fulvestrant (34.9%), and chemotherapy (17.5%) for ABC. No new safety signals or interactions with partnered drugs were observed. The mPFS was 19.2 months (95% CI, 13.8 to not available) for imlunestrant + abemaciclib and was not reached for imlunestrant + abemaciclib + AI. The mPFS with imlunestrant + everolimus/alpelisib was 15.9 months (95% CI, 11.3 to 19.1)/9.2 months (95% CI, 3.7 to 11.1). Antitumor activity was evident regardless of ESR1 mutation status.

CONCLUSION

Imlunestrant, as monotherapy or in combination with targeted therapy, had a manageable safety profile with evidence of preliminary antitumor activity in ER+/HER2- ABC.

Chemotherapy Combined With Endocrine Therapy: Old Wine in a New Bottle?

Both chemotherapy (CT) and endocrine therapy (ET) play important roles in the systemic treatment of breast cancer (BC). However, previous studies have shown an antagonistic effect when CT and ET are administered simultaneously. Therefore, sequential administration is more effective than combined administration. The current guidelines and consensus recommend a sequential schedule of CT and ET for patients with hormone receptor-positive (HR+) BC. However, with the continuous introduction of new endocrine drugs, the question of whether the simultaneous administration of CT and ET is superior to sequential therapy has surfaced again as a hot topic of clinical concern. Recent studies have shown that the combination of certain chemotherapeutic agents with endocrine drugs has a synergistic effect. This review aims to summarize the new advances achieved in recent years on the old topic of CT combined with ET in the treatment of BC.

Targeted protein degradation: current molecular targets, localization, and strategies

Targeted protein degradation (TPD) has revolutionized drug discovery by selectively eliminating specific proteins within and outside the cellular context. Over the past two decades, TPD has expanded its focus beyond well-established targets, exploring diverse proteins beyond cancer-related ones. This evolution extends the potential of TPD to various diseases. Notably, TPD can target proteins at demanding locations, such as the extracellular matrix (ECM) and cellular membranes, presenting both opportunities and challenges for future research. In this review, we comprehensively examine the exciting opportunities in the burgeoning field of TPD, highlighting different targets, their cellular environment, and innovative strategies for modern drug discovery.

Heteroaryl Group Containing Trisubstituted Alkenes: Synthesis and Anti-Tumor Activity

Pancreatobililary cancers are fatal solid tumors that pose a significant threat to human life. It is imperative to investigate novel small molecule active compounds for controlling these cancers. Heterocyclic compounds (e. g. gemcitabine) and multi-substituted alkenes (e. g. resveratrol) are commonly applied in tumor treatment. Researchers have proposed that the synthesis of new trisubstituted alkenes containing heteroaromatic rings by combining these two scaffolds may be a fresh strategy to develop new active molecules. In this study, we utilized alkenyl bromide and heteroaryl boronic acid as substrates, employing Suzuki coupling to generate a series of triarylethylenes featuring nitrogen, oxygen, and sulfur atoms. Through in vitro experiments, the results indicated that some compounds exhibited remarkable anti-tumor efficacy (e. g. IC50[3be, GBC-SD]=0.13 μM and IC50[3be, PANC-1]=0.27 μM). The results further demonstrated that the antitumor efficacy of these compounds was dependent on the heteroatom, π-system, skeleton-bonding site, and substituent type.

Protection of HT22 neuronal cells against chemically-induced ferroptosis by catechol estrogens: protein disulfide isomerase as a mechanistic target

Ferroptosis is a form of regulated cell death, characterized by excessive iron-dependent lipid peroxidation. Biochemically, ferroptosis can be selectively induced by erastin through glutathione depletion or through inhibition of glutathione peroxidase 4 by RSL3, which leads to accumulation of cytotoxic lipid reactive oxygen species (ROS). Protein disulfide isomerase (PDI) was recently shown to mediate erastin/RSL3-induced ferroptosis and thus also become a new target for protection against chemically-induced ferroptosis. The present study aims to identify endogenous compounds that can protect against erastin/RSL3-induced ferroptotic cell death. We find that 2-hydroxyestrone, 2-hydroxyestradiol, 4-hydroxyestrone and 4-hydroxyestradiol, four major endogenous catechol estrogens, are effective inhibitors of PDI, and can strongly protect against chemically-induced ferroptotic cell death in cultured HT22 mouse hippocampal neuronal cells. The CETSA assay showed that these catechol estrogens can bind to PDI in live cells. PDI knockdown attenuates the protective effect of these catechol estrogens against chemically-induced ferroptosis. Mechanistically, inhibition of PDI's catalytic activity by catechol estrogens abrogates erastin/RSL3-induced dimerization of nitric oxide synthase, thereby preventing the subsequent accumulation of cellular nitric oxide, ROS and lipid-ROS, and ultimately ferroptotic cell death. In addition, joint treatment of cells with catechol estrogens also abrogates erastin/RSL3-induced upregulation of nitric oxide synthase protein levels, which also contributes to the cytoprotective effect of the catechol estrogens. In conclusion, the present study demonstrates that the catechol estrogens are protectors of HT22 neuronal cells against chemically-induced ferroptosis, and inhibition of PDI's catalytic activity by these estrogens contributes to a novel, estrogen receptor-independent mechanism of cytoprotection.

Breast cancer immunotherapy: Realities and advances

Breast cancer (BC) is the most common malignant tumor and the main cause of death in women worldwide. With increased knowledge regarding tumor escape mechanisms and advances in immunology, many new antitumor strategies such as nonspecific immunotherapies, monoclonal antibodies, anticancer vaccines, and oncolytic viruses, among others, make immunotherapy a promising approach for the treatment of BC. However, these approaches still require meticulous assessment and readjustment as resistance and modest response rates remain important barriers. In this article, we aim to summarize the most recent data available in BC immunotherapy to include the results of ongoing clinical trials and approved therapies used as monotherapies or in combination with conventional treatments.

Advances in the mechanism of CDK4/6 inhibitor resistance in HR+/HER2- breast cancer

Among women, breast cancer is the most prevalent form of a malignant tumour. Among the subtypes of breast cancer, hormone receptor (HR) positive and human epidermal growth factor receptor (HER2) negative kinds make up the biggest proportion. The advent of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, which are dependent on cell cycle proteins, has greatly enhanced the prognosis of patients with advanced HR+/HER2- breast cancer. This is a specific treatment that stops the growth of cancer cells by preventing them from dividing. Nevertheless, the drug resistance of the disease unavoidably impacts the effectiveness of treatment and the prognosis of patients. This report provides a thorough analysis of the current research advancements about the resistance mechanism of CDK4/6 inhibitors in HR+/HER2- breast cancer. It presents an in-depth discussion from numerous viewpoints, such as aberrant cell cycle regulation and changes in signalling pathways. In response to the drug resistance problem, subsequent treatment strategies are also being explored, including switching to other CDK4/6 inhibitor drugs, a combination of novel endocrine therapeutic agents, an optimal combination of targeted therapies and switching to chemotherapy. An in-depth study of the resistance mechanism can assist in identifying creative tactics that can overcome or postpone drug resistance, alleviate the problem of restricted treatment strategies following drug resistance and enhance the prognosis of patients.

Eribulin plus carboplatin combination for HER2-negative metastatic breast cancer: a multicenter, real-world cohort study

BACKGROUND

Pre-clinical data suggests a potential synergistic effect of eribulin and platinum. However, clinical data on the combination for metastatic breast cancer (mBC) is lacking. We evaluated the efficacy and safety of eribulin plus carboplatin (ErCb) in patients with mBC.

PATIENTS AND METHODS

This multicenter, real-world cohort study included patients with pre-treated metastatic triple negative breast cancer (TNBC) or endocrine-refractory hormone receptor (HR) positive, HER2-negative mBC who received ErCb. Eribulin (1.4 mg/m2) and carboplatin (target AUC = 2) were administered intravenously on day 1 and 8 of 21-day cycle. Objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and adverse events (AEs) were evaluated.

RESULTS

From March 2022 to December 2023, a cohort of 37 patients were recruited to the study. Among them, 22 patients have TNBC and 15 have HR + HER2 - mBC. Of the 22 patients with TNBC, 8 had an initial diagnosis of the HR + HER2 - subtype. The median treatment was 6 cycles (range, 2 - 8 cycles). In the full cohort, TNBC, and HR + HER2 - subgroup, the ORR were 51.4%, 54.5% and 46.7%, the DCR were 81.1%, 81.8% and 80%, and the median PFS were 5 months, 5 months, and 5.2 months, respectively. The median OS was 12.7 months in the entire cohort and 12.8 months in TNBC subgroup. The most common grade 3/4 hematological AEs were neutropenia (37.8%), leukopenia (35.1%), febrile neutropenia (10.8%), thrombocytopenia (5.4%), and anemia (2.7%). No grade 3/4 non-hematological AEs were observed.

CONCLUSION

ErCb demonstrated favorable efficacy and tolerability in patients with heavily pre-treated mBC, especially TNBC. The findings of the current study warrant further investigation of the application of this combination in earlier lines of mBC treatment.

Unveiling the Mechanism of Compound Ku-Shen Injection in Liver Cancer Treatment through an Ingredient-Target Network Analysis

BACKGROUND

Compound Ku-Shen Injection (CKI) is a traditional Chinese medicine preparation derived from Ku-Shen and Bai-Tu-Ling, commonly used in the adjunctive treatment of advanced cancers, including liver cancer. However, the underlying mechanisms of CKI's effectiveness in cancer treatment are not well defined.

METHODS

This study employs network pharmacology to investigate the traditional Chinese medicine (TCM) compatibility theory underlying CKI's action in treating liver cancer, with findings substantiated by molecular docking and in vitro experiments. Sixteen active components were identified from CKI, along with 193 potential targets for treating liver cancer. Key therapeutic target proteins, including EGFR and ESR1, were also identified. KEGG enrichment results showed that the neuroactive ligand-receptor interaction, cAMP signaling pathway, and serotonergic synapses make up the key pathway of CKI in the treatment of liver cancer. Molecular docking results confirmed that the key active ingredients effectively bind to the core targets. CCK-8 cytotoxic experiment results show that the CKI key components of oxymatrine and matrine can inhibit the growth of HepG2 liver cancer cell proliferation. A Western blot analysis revealed that oxymatrine suppresses the expression of EGFR, contributing to its therapeutic efficacy against liver cancer.

CONCLUSION

our study elucidated the therapeutic mechanism of CKI in treating liver cancer and unveiled the underlying principles of its TCM compatibility through its mode of action.

Enhanced desmosome assembly driven by acquired high-level desmoglein-2 promotes phenotypic plasticity and endocrine resistance in ER+ breast cancer

Acquired resistance to endocrine treatments remains a major clinical challenge. In this study, we found that desmoglein-2 (DSG2) plays a major role in acquired endocrine resistance and cellular plasticity in ER+ breast cancer (BC). By analysing the well-established fulvestrant-resistant ER+ BC model using single-cell RNA-seq, we revealed that ER inhibition leads to a specific increase in DSG2 in cancer cell populations, which in turn enhances desmosome formation in vitro and in vivo and cell phenotypic plasticity that promotes resistance to treatment. DSG2 depletion reduced tumorigenesis and metastasis in fulvestrant-resistant xenograft models and promoted fulvestrant efficiency. Mechanistically, DSG2 forms a desmosome complex with JUP and Vimentin and triggers Wnt/PCP signalling. We showed that elevated DSG2 levels, along with reduced ER levels and an activated Wnt/PCP pathway, predicted poor survival, suggesting that a DSG2high signature could be exploited for therapeutic interventions. Our analysis highlighted the critical role of DSG2-mediated desmosomal junctions following antiestrogen treatment.

Mechanisms of sensitivity and resistance to CDK4/CDK6 inhibitors in hormone receptor-positive breast cancer treatment

Cell cycle dysregulation is a hallmark of cancer that promotes eccessive cell division. Cyclin-dependent kinase 4 (CDK4) and cyclin-dependent kinase 6 (CDK6) are key molecules in the G1-to-S phase cell cycle transition and are crucial for the onset, survival, and progression of breast cancer (BC). Small-molecule CDK4/CDK6 inhibitors (CDK4/6i) block phosphorylation of tumor suppressor Rb and thus restrain susceptible BC cells in G1 phase. Three CDK4/6i are approved for the first-line treatment of patients with advanced/metastatic hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) BC in combination with endocrine therapy (ET). Though this has improved the clinical outcomes for survival of BC patients, there is no established standard next-line treatment to tackle drug resistance. Recent studies suggest that CDK4/6i can modulate other distinct effects in both BC and breast stromal compartments, which may provide new insights into aspects of their clinical activity. This review describes the biochemistry of the CDK4/6-Rb-E2F pathway in HR+ BC, then discusses how CDK4/6i can trigger other effects in BC/breast stromal compartments, and finally outlines the mechanisms of CDK4/6i resistance that have emerged in recent preclinical studies and clinical cohorts, emphasizing the impact of these findings on novel therapeutic opportunities in BC.

PROTAC: Novel degradable approach for different targets to treat breast cancer

The revolutionary Proteolysis Targeting Chimera (PROTACs) have the exciting potential to reshape the pharmaceutical industry landscape by leveraging the ubiquitin-proteasome system for targeted protein degradation. Breast cancer, the most prevalent cancer in women, could be treated using PROTAC therapy. Although substantial work has been conducted, there is not yet a comprehensive overview or progress update on PROTAC therapy for breast cancer. Hence, in this article, we've compiled recent research progress focusing on different breast cancer target proteins, such as estrogen receptor (ER), BET, CDK, HER2, PARP, EZH2, etc. This resource aims to serve as a guide for future PROTAC-based breast cancer treatment design.

Pure estrogen receptor antagonists potentiate capecitabine activity in ESR1-mutant breast cancer

The ESR1 ligand binding domain activating mutations are the most prevalent genetic mechanism of acquired endocrine resistance in metastatic hormone receptor-positive breast cancer. These mutations confer endocrine resistance that remains estrogen receptor (ER) dependent. We hypothesized that in the presence of the ER mutations, continued ER blockade with endocrine therapies that target mutant ER is essential for tumor suppression even with chemotherapy treatment. Here, we conducted comprehensive pre-clinical in vitro and in vivo experiments testing the efficacy of adding fulvestrant to fluorouracil (5FU) and the 5FU pro-drug, capecitabine, in models of wild-type (WT) and mutant ER. Our findings revealed that while this combination had an additive effect in the presence of WT-ER, in the presence of the Y537S ER mutation there was synergy. Notably, these effects were not seen with the combination of 5FU and selective estrogen receptor modulators, such as tamoxifen, or in the absence of intact P53. Likewise, in a patient-derived xenograft (PDX) harboring a Y537S ER mutation the addition of fulvestrant to capecitabine potentiated tumor suppression. Moreover, multiplex immunofluorescence revealed that this effect was due to decreased cell proliferation in all cells expressing ER and was not dependent on the degree of ER expression. Taken together, these results support the clinical investigation of the combination of ER antagonists with capecitabine in patients with metastatic hormone receptor-positive breast cancer who have experienced progression on endocrine therapy and targeted therapies, particularly in the presence of an ESR1 activating mutation.

Phase II randomized trial comparing metronomic anthracycline-containing chemotherapy versus standard schedule in untreated HER2 negative advanced breast cancer: activity and quality of life results of the GOIM 21003 trial

BACKGROUND

Optimizing chemotherapy to achieve disease and symptoms control is a noteworthy purpose in advanced breast cancer (ABC). We reported the activity and quality of life of a phase II study, comparing metronomic regimen with standard schedule as first line chemotherapy for ABC.

METHODS

Patients with HER2 negative ABC were randomized to non-pegylated liposomal doxorubicin (NPLD, 60 mg/m2 every 3 weeks) and cyclophosphamide (CTX, 600 mg/m2 every 3 weeks) (Arm A) or NPLD (20 mg/m2 day, on day 1, 8 and 15 every 4 weeks) and metronomic daily oral CTX 50 mg (ARM B). Primary end-points were overall response rate (ORR) and quality of life, secondary progression-free survival (PFS), overall survival (OS) and toxicity.

RESULTS

From August 2012 to December 2017, 121 patients were enrolled, 105 evaluable. Median follow-up was 21.3 months. Most patients had hormone receptor positive. ORR was 43 % in arm A and 50 % in arm B. Median PFS was 8.9 months in arm A and 6,4 months in arm B. There was no difference in OS. Total score was not clinically different between the two arms. Grade 4 neutropenia was observed in 12 patients and 16 patients respectively; alopecia G2 in 41 % (77 %) vs 14 (27 %) in arm A and in arm B respectively. One cardiac toxicity was observed (arm A).

CONCLUSIONS

First line metronomic chemotherapy for HER2 negative ABC had similar clinical activity and quite better tolerability than standard schedule and could be considered a further treatment option when chemotherapy is indicated.

Adverse event signal mining and serious adverse event influencing factor analysis of fulvestrant based on FAERS database

Fulvestrant, as the first selective estrogen receptor degrader, is widely used in the endocrine treatment of breast cancer. However, in the real world, there is a lack of relevant reports on adverse reaction data mining for fulvestrant. To perform data mining on adverse events (AEs) associated with fulvestrant and explore the risk factors contributing to severe AEs, providing a reference for the rational use of fulvestrant in clinical practice. Retrieved adverse event report information associated with fulvestrant from the U.S. Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) database, covering the period from market introduction to September 30, 2023. Suspicious AEs were screened using the reporting odds ratio (ROR) and proportional reporting ratio methods based on disproportionality analysis. Univariate and multivariate logistic regression analyses were conducted on severe AEs to explore the risk factors associated with fulvestrant-induced severe AEs. A total of 6947 reports related to AEs associated with fulvestrant were obtained, including 5924 reports of severe AEs and 1023 reports of non-severe AEs. Using the disproportionality analysis method, a total of 210 valid AEs were identified for fulvestrant, with 45 AEs (21.43%) not listed in the product labeling, involving 11 systems and organs. The AEs associated with fulvestrant were sorted by frequency of occurrence, with neutropenia (325 cases) having the highest number of reports. By signal strength, injection site pruritus showed the strongest signal (ROR = 658.43). The results of the logistic regression analysis showed that concurrent use of medications with extremely high protein binding (≥ 98%) is an independent risk factor for severe AEs associated with fulvestrant. Age served as a protective factor for fulvestrant-related AEs. The co-administration of fulvestrant with CYP3A4 enzyme inhibitors did not show statistically significant correlation with the occurrence of severe AEs. Co-administration of drugs with extremely high protein binding (≥ 98%) may increase the risk of severe adverse reactions of fulvestrant. Meanwhile, age (60-74 years) may reduce the risk of severe AEs of fulvestrant. However, further clinical research is still needed to explore and verify whether there is interaction between fulvestrant and drugs with high protein binding through more clinical studies.

The discovery of potent USP2/USP8 dual-target inhibitors for the treatment of breast cancer via structure guided optimization of ML364

USP2 and USP8 are crucial in the development and progression of breast cancer, primarily through the stabilization of protein substrates such as Her2 and ERα. The dual-target inhibitor ML364, targeting both USP2 and USP8, has garnered significant interest in recent research. In this study, we developed a series of ML364 derivatives using ligand-based drug design strategies. The standout compound, LLK203, demonstrated enhanced inhibitory activity, showing a 4-fold increase against USP2 and a 9-fold increase against USP8, compared to the parent molecule. In MCF-7 breast cancer cells, LLK203 effectively degraded key proteins involved in cancer progression and notably inhibited cell proliferation. Moreover, LLK203 exhibited potent in vivo efficacy in the 4T1 homograft model, while maintaining a low toxicity profile. These results underscore the potential of LLK203 as a promising dual-target inhibitor of USP2/USP8 for breast cancer treatment.

Therapeutic evolution in HR+/HER2- breast cancer: from targeted therapy to endocrine therapy

Breast cancer, a complex and varied disease, has four distinct subtypes based on estrogen receptor and human epidermal growth factor receptor 2 (HER2) levels, among which a significant subtype known as HR+/HER2-breast cancer that has spurred numerous research. The prevalence of breast cancer and breast cancer-related death are the most serious threats to women's health worldwide. Current progress in treatment strategies for HR+/HER2-breast cancer encompasses targeted therapy, endocrine therapy, genomic immunotherapy, and supplementing traditional methods like surgical resection and radiotherapy. This review article summarizes the current epidemiology of HR+/HER2-breast cancer, introduces the classification of HR+/HER2-breast cancer and the commonly used treatment methods. The mechanisms of action of various drugs, including targeted therapy drugs and endocrine hormone therapy drugs, and their potential synergistic effects are deeply discussed. In addition, clinical trials of these drugs that have been completed or are still in progress are included.

Therapeutic targeting of p90 ribosomal S6 kinase

The Serine/Threonine protein kinase family, p90 ribosomal S6 kinases (RSK) are downstream effectors of extracellular signal regulated kinase 1/2 (ERK1/2) and are activated in response to tyrosine kinase receptor or G-protein coupled receptor signaling. RSK contains two distinct kinase domains, an N-terminal kinase (NTKD) and a C-terminal kinase (CTKD). The sole function of the CTKD is to aid in the activation of the NTKD, which is responsible for substrate phosphorylation. RSK regulates various homeostatic processes including those involved in transcription, translation and ribosome biogenesis, proliferation and survival, cytoskeleton, nutrient sensing, excitation and inflammation. RSK also acts as a major negative regulator of ERK1/2 signaling. RSK is associated with numerous cancers and has been primarily studied in the context of transformation and metastasis. The development of specific RSK inhibitors as cancer therapeutics has lagged behind that of other members of the mitogen-activated protein kinase signaling pathway. Importantly, a pan-RSK inhibitor, PMD-026, is currently in phase I/1b clinical trials for metastatic breast cancer. However, there are four members of the RSK family, which have overlapping and distinct functions that can vary in a tissue specific manner. Thus, a problem for transitioning a RSK inhibitor to the clinic may be the necessity to develop isoform specific inhibitors, which will be challenging as the NTKDs are very similar to each other. CTKD inhibitors have limited use as therapeutics as they are not able to inhibit the activity of the NTKD but could be used in the development of proteolysis-targeting chimeras.

Hereditary breast and ovarian cancer: from genes to molecular targeted therapies

Hereditary familial tumors constitute 10-15% of all malignancies and present opportunities for the identification of therapeutic approaches against specific germline genetic defects. Hereditary breast and ovarian cancer (HBOC) syndrome, which is linked to the pathogenic mutations of the breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) genes, is an important research model for personalized therapeutic approaches for specific germline mutations. HBOC is characterized by multiple cases of breast and ovarian carcinoma in association with other tumors (prostate, pancreas and stomach carcinoma) within the same family branch, a young age of onset (<36 years), bilaterality and an autosomal dominant pattern of inheritance. Counseling, evaluation of the clinical criteria for the diagnosis of HBOC, and the performance of genetic testing allow for the identification of subjects with BRCA1/2 mutations and provide crucial information for clinical and therapeutic management. The identification of a BRCA gene mutation has therapeutic implications for women with metastatic and non-metastatic breast cancer. In the therapeutic setting of BRCA+ breast cancer, treatment with poly (ADP-ribose) polymerase (PARP) inhibitors, which keep cancer cells from repairing their damaged DNA and cause cell death, is remarkable. This review summarizes the evidence demonstrating the value of BRCA1/2 status as a diagnostic and prognostic tool and as a predictive biomarker in the personalized approach to hereditary BRCA + cancers.

ESR1 mutations in HR+/HER2-metastatic breast cancer: Enhancing the accuracy of ctDNA testing

Activating mutations of the estrogen receptor alpha gene (ESR1) are common mechanisms of endocrine therapy (ET) resistance in hormone receptor-positive (HR + )/Human Epidermal Growth Factor Receptor 2 (HER2)-negative metastatic breast cancer (MBC). Recent clinical findings emphasize that both old and new generations of selective ER degraders (SERDs) demonstrate enhanced clinical effectiveness in patients with MBC who have detectable ESR1 mutations via liquid biopsy. This stands in contrast to individuals with MBC carrying these mutations and undergoing conventional endocrine monotherapies like aromatase inhibitors (AIs). Liquid biopsy, particularly the analysis of circulating tumor DNA (ctDNA), has emerged as a promising, minimally invasive alternative to conventional tissue-based testing for identifying ESR1 mutations. Within the context of the PADA-1 and EMERALD trials, distinct molecular methodologies and assays, specifically digital droplet PCR (ddPCR) and next-generation sequencing (NGS), have been employed to evaluate the mutational status of ESR1 within ctDNA. This manuscript critically examines the advantages and indications of various ctDNA testing methods on liquid biopsy for HR+/HER2-negative MBC. Specifically, we delve into the capabilities of ddPCR and NGS in identifying ESR1 mutations. Each methodology boasts unique strengths and limitations: ddPCR excels in its analytical sensitivity for pinpointing hotspot mutations, while NGS offers comprehensive coverage of the spectrum of ESR1 mutations. The significance of meticulous sample handling and timely analysis is emphasized, acknowledging the transient nature of cfDNA. Furthermore, we underscore the importance of detecting sub-clonal ESR1 mutations, as these variants can exert a pivotal influence on predicting both endocrine therapy resistance and responsiveness to SERDs. In essence, this work discusses the role of ctDNA analysis for detecting ESR1 mutations and their implications in tailoring effective therapeutic strategies for HR+/HER2- MBC.

Clinician's guide to targeted estrogen receptor degradation using PROTAC in patients with estrogen receptor-positive metastatic breast cancer

PURPOSE OF REVIEW

Metastatic breast cancer (MBC) remains a major clinical challenge, necessitating the development of innovative therapeutic strategies. Estrogen receptor (ER) degradation using proteolysis-targeting chimeras (PROTAC) has emerged as a promising approach for overcoming acquired resistance to endocrine therapy. This review will summarize recent findings, highlighting the role of ER degradation by PROTAC in patients with MBC.

RECENT FINDINGS

The application of PROTAC technology for ER degradation has demonstrated initial success in preclinical and early clinical studies. PROTACs, consisting of an ER-targeting moiety, an E3 ubiquitin ligase-recruiting moiety, and a linker, facilitate ER ubiquitination and subsequent proteasomal degradation. Yet, significant challenges persist in the clinical translation of ER degradation by PROTAC. These include the optimization of PROTAC design, elucidation of mechanisms underlying resistance to PROTAC-induced ER degradation, and identification of predictive biomarkers for patient stratification. Additionally, addressing potential off-target effects and toxicity profiles remains a critical aspect of developing PROTAC-based therapies.

SUMMARY

Recent data demonstrate the potential of ER degradation by PROTAC as a therapeutic strategy for patients with MBC. Continued research efforts and development of synergistic combinations are crucial for further advancing PROTAC-based therapies and improving outcomes in patients with MBC.

HATS off to KAT6A/B inhibitors: A new way to target estrogen-receptor-positive breast cancer

Inhibitors for the KAT6 family of histone acetyltransferases (HATs) have been actively pursued due to the oncogenic roles of KAT6A in human cancer. CTx-648 is a novel KAT6A/B inhibitor with excellent pharmacokinetic properties and in vivo efficacy that represents a promising new treatment strategy for estrogen-receptor-positive breast cancer.

Recent Developments in the Therapeutic Landscape of Advanced or Metastatic Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) disease is the most frequently diagnosed subtype of breast cancer. Among tumor subtypes, natural course of HR+ breast cancer is indolent with favorable prognosis compared to other subtypes such as human epidermal growth factor protein 2-positive disease and triple-negative disease. HR+ tumors are dependent on steroid hormone signaling and endocrine therapy is the main treatment option. Recently, the discovery of cyclin-dependent kinase 4/6 inhibitors and their synergistic effects with endocrine therapy has dramatically improved treatment outcome of advanced HR+ breast cancer. The demonstrated efficacy of additional nonhormonal agents, such as targeted therapy against mammalian target of rapamycin and phosphatidylinositol 3-kinase signaling, poly(ADP-ribose) polymerase inhibitors, antibody-drug conjugates, and immunotherapeutic agents have further expanded the available therapeutic options. This article reviews the latest advancements in the treatment of HR+ breast cancer, and in doing so discusses not only the development of currently available treatment regimens but also emerging therapies that invite future research opportunities in the field.

The Treatment Landscape of Elderly Patients with Hormone Receptor-Positive Her2 Negative Advanced Breast Cancer: Current Perspectives and Future Directions

Breast cancer (BC) in elderly women is an increasing health issue due to demographic changes. BC tends to present later and may receive less than standard treatment options. More often, BC in elderly patients is endocrine-positive (HR+). The treatment of elderly patients with metastatic BC (mBC) represents a therapeutic challenge. In recent years, the treatment landscape of patients that are HR+/Her2-negative has changed due to the introduction in clinical practice of new targeted drugs, which have improved patient outcomes. Elderly patients are a small percentage of all patients enrolled in clinical trials and, to date, there are no standardized guidelines that define the best treatment option for this patient population. This can lead to undertreatment or overtreatment, impacting patient morbidity and mortality. Geriatric Assessment tools to tailor the treatment in elderly patients are underused because they are long and difficult to apply in a busy routine clinical practice. For all these reasons, there is an urgent need to produce data about the best treatment for elderly patients with HR+ mBC. Herein, we report data from randomized clinical trials and real-world evidence on the therapeutic options for HR+ Her2-negative mBC elderly patients and explore future treatment directions.

Targeted Degradation of CDK4/6: An Innovative Approach to Overcoming Cancer Drug Resistance

Targeted protein degradation has emerged as a powerful approach for the selective elimination of disease-causing proteins. Cyclin-dependent kinases 4 and 6 (CDK4/6) are of significant interest in cancer research due to their crucial role in cell cycle regulation. However, resistance to CDK4/6 inhibitors is a considerable challenge. This Patent Highlight showcases the recent advances in strategies to degrade CDK4/6 to overcome drug resistance, explicitly focusing on proteolysis-targeting chimeras (PROTACs) and molecular glue degraders.