Novel Estrogen Receptor-Targeted Agents for Breast Cancer

Addressing Sexual Health in Breast Cancer Survivors: Evidence-Based Practices and Clinical Considerations

OPINION STATEMENT

Sexual health concerns are extremely prevalent among breast cancer survivors. The treatments used to treat and cure breast cancer - surgical removal of part or the whole breast, chemotherapy, radiation, and endocrine therapy - can have devastating impact on sexual function. Unfortunately, most patients are not given adequate preparation for these impending effects and can be blindsided by the resulting loss of sexual desire, vaginal dryness and decreased lubrication, pain with sex, vaginal stenosis, loss of nipple and breast sensation, muted or loss of orgasms and the resulting impact on sexuality and intimate relationships. Education about female sexual health is still lacking in most training programs and few cancer centers offer sexual health programs for cancer survivors. Oncology professionals and others who provide care for patients with breast cancer have the opportunity address sexual health, a vital aspect of quality of life. A focus on training and education, development of sexual health programs, and focus on sexual health in research is vital.

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.

Extended adjuvant endocrine therapy in early breast cancer: finding the individual balance

Endocrine therapy (ET) is a cornerstone in the management of patients with hormone receptor-positive early breast cancer, which accounts for over 70% of cases worldwide. The efficacy of adjuvant ET for 5 years in reducing the risk of recurrence and improving survival outcomes is well documented. However, the risk for late relapses, occurring >5 years after initial treatment, has prompted exploration of longer treatment durations. Extending ET beyond the traditional 5-year period offers additional benefit in reducing the risk of recurrence and improving long-term outcomes. Nevertheless, determining the optimal duration and identifying suitable candidates for extended therapy is often nuanced. This review aims to comprehensively evaluate the current landscape of extended ET in breast cancer management. It provides an overview of the rationale behind extending endocrine treatment in both premenopausal and postmenopausal women, with a focus on clinical trials and observational studies supporting extended therapy. Furthermore, it emphasizes the significance of considering associated toxicities in patient management. It also explores novel strategies involving the combination of ET with new drugs, leading to an evolution of treatment paradigms that may make the need for extended therapy obsolete.

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.

Oral selective estrogen receptor degraders for breast cancer treatment: focus on pharmacological differences

PURPOSE

The management of hormone receptor-positive (HR +) breast cancer (BC) relies on endocrine therapy (ET), with a primary focus on disrupting estrogen receptor (ER) signaling due to its critical role in BC tumorigenesis and progression. While effective for both early-stage and advanced breast cancers, ET frequently encounters resistance mechanisms, including both ligand-dependent and ligand-independent trajectories, ultimately leading to disease progression.

METHODS

We searched PubMed, EMBASE and Scopus databases to review the current evidence on the use of novel oral selective estrogen receptor degraders (SERDs) for the treatment of HR+ BC.

CONCLUSIONS

Somatic activating mutations of the estrogen receptor 1 (ESR1) gene are known to sustain ER activity, boost ER-dependent gene transcription, and foster resistance to ET. The most significant gap remains after treatment failure with ET and cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, where fulvestrant monotherapy typically results in a median progression-free survival of 2-3 months. Novel compounds, including oral SERDs, have been explored for their potential to overcome therapeutic resistance, both as monotherapy and in combination with other targeted therapies. Herein, we provide an overview on the latest findings on oral SERDs, examining their mechanism of action, safety data, and pharmacokinetics and pharmacodynamics profiles.

Assessing the causal relationship between plasma proteins and osteoporosis: novel insights into pathological mechanisms and therapeutic implications

Identifying dysregulated plasma proteins in osteoporosis (OP) progression offers insights into prevention and treatment. This study found 8 such proteins associated with OP, suggesting them as therapy targets. This discovery may cut drug development costs and improve personalized treatments.

PURPOSE

This study aims to identify potential therapeutic targets for OP using summary data-based Mendelian randomization (SMR) and colocalization analysis methods. Furthermore, we seek to explore the biological significance and pharmacological value of these drug targets.

METHODS

To identify potential therapeutic targets for OP, we conducted SMR and colocalization analysis. Plasma protein (pQTL, exposure) data were sourced from the study by Ferkingstad et al. (n = 35,559). Summary statistics for bone mineral density (BMD, outcome) were obtained from the GWAS Catalog (n = 56,284). Additionally, we utilized enrichment analysis, protein-protein interaction (PPI) network analysis, drug prediction, and molecular docking to further analyze the biological significance and pharmacological value of these drug targets.

RESULTS

In the SMR analysis, while 20 proteins showed significance, only 8 potential drug targets (GCKR, ERBB3, CFHR1, GPN1, SDF2, VTN, BET1L, and SERPING1) received support from colocalization (PP.H4 > 0.8). These proteins are closely associated with immune function in terms of biological significance. Molecular docking also demonstrated favorable binding of drugs to proteins, consistent with existing structural data, further substantiating the pharmacological value of these targets.

CONCLUSIONS

The study identified 8 potential drug targets for OP. These prospective targets are believed to have a higher chance of success in clinical trials, thus aiding in prioritizing OP drug development and reducing development costs.

The landscape of combining immune checkpoint inhibitors with novel Therapies: Secret alliances against breast cancer

This review focuses on the immune checkpoint inhibitors (ICIs) in the context of breast cancer (BC) management. These innovative treatments, by targeting proteins expressed on both tumor and immune cells, aim to overcome tumor-induced immune suppression and reactivate the immune system. The potential of this approach is the subject of numerous clinical studies. Here, we explore the key studies and emerging therapies related to ICIs providing a detailed analysis of their specific and combined use in BC treatment.

Oral SERDs changing the scenery in hormone receptor positive breast cancer, a comprehensive review

BACKGROUND

Primary and acquired endocrine resistance remains a major issue in the treatment of hormone receptor positive breast cancer. Acquired resistance often results from estrogen receptor 1 (ESR1) mutations leading to estrogen independent estrogen receptor activation. Selective estrogen receptor degraders (SERDs) induce degradation of this receptor, thereby overcoming this resistance. The intramuscular administration and modest efficacy of fulvestrant, the first SERD, triggered development of oral, more potent SERDs. This narrative review gives an overview of the current evidence regarding this new drug class.

METHODS

Medline/PubMed and Embase database were screened using a systematic search strategy. We assessed the San Antonio Breast Cancer Symposium abstract reports, the European Society of Medical Oncology (ESMO) and American Society of Clinical Oncology (ASCO) meeting resources by applying the following terms: 'SERD', 'giredestrant', 'elacestrant', 'imlunestrant', 'amcenestrant', 'camizestrant' and 'rintodestrant'.

CLINICALTRIALS

gov was consulted to include ongoing trials.

RESULTS

The search retrieved 1191 articles. After screening, 108 articles were retained. In the phase 3 EMERALD trial, elacestrant demonstrated benefit in progression free survival (PFS) in second line metastatic disease in postmenopausal women or men, leading to Food and Drug Administration (FDA) and European Medicines Agency (EMA) approval for the ESR1 mutated population. This PFS advantage was more pronounced among patients who had priorly received at least 12 months of a cyclin-dependent kinases 4/6 inhibitor (CDK4/6i). In the phase 2 SERENA-2 trial, camizestrant improved PFS as second line treatment. However, trials of giredestrant and amcenestrant failed to show PFS benefit in second line metastatic setting. In the preoperative setting, several oral SERDs resulted in a significant reduction of tumoral proliferation. Furthermore, many trials are still in progress.

CONCLUSION

Oral SERDs constitute an exciting new drug class. Ongoing and future research will further refine the role of these drugs next to standard endocrine treatments and targeted therapies.

Updates in Systemic Treatment of Hormone Receptor-Positive Early-Stage Breast Cancer

OPINION STATEMENT

Hormone-receptor positive (HR +) and human epidermal growth factor receptor 2 (HER2) negative early breast cancer (eBC) is a heterogeneous disease with several contributing factors for increased risk of recurrence, including tumor features, individual biomarkers, and genomic risk. The current standard approach in the management of HR + /HER2neg eBC includes chemotherapy and endocrine therapy (ET), and additional therapies based on risk profile, menopausal status, and genetics are sometimes appropriate. The risk of recurrence is more pronounced in patients with high-risk eBC including large tumor size, nodal involvement, high proliferative index, and genetic predisposition. In premenopausal patients with high-risk eBC, ovarian function suppression in combination with adjuvant ET improves survival. In postmenopausal patients, extended aromatase inhibitor (AI) therapy can be considered. Recent trials have identified novel treatment approaches to reduce the risk of recurrence in high-risk HR + /HER2neg eBC including the addition of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors to adjuvant ET. For patients with germline BRCA1/BRCA2 mutations, adjuvant poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors have been shown to improve overall survival (OS). However, despite these recent advances, the risk of recurrence remains substantial, highlighting an area of unmet need. There are several ongoing clinical trials further investigating the role of CDK 4/6 inhibitors and immunotherapy in high-risk HR + /HER2neg eBC.

Standardized molecular pathology workflow for ctDNA-based ESR1 testing in HR+/HER2- metastatic breast cancer

Mutations in the estrogen receptor alpha gene (ESR1) can lead to resistance to endocrine therapy (ET) in hormone receptor-positive (HR+)/ HER2- metastatic breast cancer (MBC). ESR1 mutations can be detected in up to 40 % of patients pretreated with ET in circulating tumor DNA (ctDNA). Data from prospective randomized trials highlight those patients with HR+/HER2- MBC with detectable ESR1 mutations experience better outcomes when receiving novel selective estrogen receptor degraders (SERDs). There is a high need for optimizing ESR1 testing strategies on liquid biopsy samples in HR+/HER2- MBC, including a hugh quality workflow implementation and molecular pathology reporting standardization. Our manuscript aims to elucidate the clinical and biological rationale for ESR1 testing in MBC, while critically examining the currently available guidelines and recommendations for this specific type of molecular testing on ctDNA. The objective will extend to the critical aspects of harmonization and standardization, specifically focusing on the pathology laboratory workflow. Finally, we propose a clear and comprehensive model for reporting ESR1 testing results on ctDNA in HR+/HER2- MBC.

The vitamin D analog EB1089 sensitizes triple-negative breast cancer cells to the antiproliferative effects of antiestrogens

PURPOSE

Patients bearing estrogen receptor (ER)α-negative breast cancer tumors confront poor prognosis and are typically unresponsive to hormone therapy. Previous studies have shown that calcitriol, the active vitamin D metabolite, can induce ERα expression in ERα-negative cells. EB1089, a calcitriol analog with reduced calcemic effects, exhibits greater potency than calcitriol in inhibiting cancer cell growth. However, the impact of EB1089 on ERα expression in triple-negative breast cancer (TNBC) cells remains unexplored. This study aims to investigate whether EB1089 could induce functional ERα expression in TNBC cell lines, potentially enabling the antiproliferative effects of antiestrogens.

MATERIALS AND METHODS

TNBC cell lines HCC1806 and HCC1937 were treated with EB1089, and ERα expression was analyzed using real-time PCR and Western blots. The transcriptional activity of induced ERα was evaluated through a luciferase reporter assay. The antiproliferative effects of tamoxifen and fulvestrant antiestrogens were assessed using the sulforhodamine B assay in the EB1089-treated cells.

RESULTS

Our findings indicated that EB1089 significantly induced ERα mRNA and protein expression in TNBC cells. Moreover, EB1089-induced ERα exhibited transcriptional activity and effectively restored the inhibitory effects of antiestrogens, thereby suppressing cell proliferation in TNBC cells.

CONCLUSION

EB1089 induced the expression of functional ERα in TNBC cells, restoring the antiproliferative effects of antiestrogens. These results highlight the potential of using EB1089 as a promising strategy for re-establishment of the antiproliferative effect of antiestrogens as a possible management for TNBC. This research lays the foundation for potential advancements in TNBC treatment, offering new avenues for targeted and effective interventions.

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.

Current Status and Future Perspectives of Antibody-Drug Conjugates in Hormone Receptor-Positive Breast Cancer

Breast cancer is the most common cancer type in women. The vast majority of breast cancer patients have hormone receptor-positive (HR+) tumors. In advanced HR+ breast cancer, the combination of endocrine therapy with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors is considered the standard of care in the front-line setting. Nevertheless, resistance to hormonal therapy and CDK4/6 inhibitors eventually occurs, leading to progression of the disease. Antibody-drug conjugates (ADCs) comprise a promising therapeutic choice with significant efficacy in patients with HR+ breast cancer, which is resistant to endocrine treatment. ADCs typically consist of a cytotoxic payload attached by a linker to a monoclonal antibody that targets a specific tumor-associated antigen, offering the advantage of a more selective delivery of chemotherapy to cancer cells. In this review, we focus on the ADC mechanisms of action, their toxicity profile and therapeutic uses as well as on related biomarkers and future perspectives in advanced HR+ breast cancer.

Pharmacological insights on novel oral selective estrogen receptor degraders in breast cancer

The therapeutic landscape of estrogen receptor (ER)-positive breast cancer includes endocrine treatments with aromatase inhibitors (AIs), selective estrogen receptor modulators (SERMs), and selective estrogen receptor degraders (SERDs). Fulvestrant is the first approved SERD with proven efficacy and good tolerability in clinical practice. However, drug resistance, low receptor affinity, and parental administration stimulated the search for new oral SERDs opening a new therapeutic era in ER + breast cancer. Elacestrant is an orally bioavailable SERD that has been recently approved by the FDA for postmenopausal women with ER+, human epidermal growth factor receptor 2-negative (HER2-), estrogen receptor 1 (ESR1)-mutated advanced or metastatic breast cancer with disease progression following at least one line of endocrine therapy. Other molecules of the same class currently tested in clinical trials are amcenestrant, giredestrant, camizestrant, and imlunestrant. The current review article offers a detailed pharmacological perspective of this emerging drug class, which may help with their possible future clinical applications.

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.

Germacrone: A Multi-targeting Sesquiterpene with Promising Anti-cancer and Chronic Disease Applications

BACKGROUND

Germacrone, a naturally occurring active compound found in essential oils extracted from medicinal plants within the Zingiberaceae family, has garnered attention for its potential therapeutic applications. Extensive research has highlighted its multi-targeting capabilities, positioning it as a promising treatment for various chronic diseases, including cancer, cardiovascular conditions, and neurodegenerative disorders like Alzheimer's disease.

OBJECTIVE

This review aims to provide a comprehensive overview of germacrone as a scaffold for developing multi-targeting drugs with therapeutic potential against a range of chronic disorders. The study delves into the molecular mechanisms that underlie the therapeutic effects of germacrone and explores its potential targets, including NF-κB, PI3K/AKT/mTOR, p53, JAK/STAT, caspase, apoptosis, and autophagy induction.

METHODS

A systematic review of literature databases was conducted to gather relevant studies on germacrone and its therapeutic applications. The molecular mechanisms and potential targets of germacrone were examined to elucidate its multi-targeting capabilities.

RESULTS

Germacrone exhibits significant potential in the management of chronic diseases, with demonstrated effects on various cellular pathways. The review highlights its impact on NF-κB, PI3K/AKT/mTOR, p53, JAK/STAT, caspase, apoptosis, and autophagy induction, showcasing its versatility in targeting multiple pathways associated with chronic conditions. Germacrone has emerged as a promising candidate for the treatment of diverse chronic diseases. The understanding of its multi-targeting capabilities, coupled with its natural origin, positions it as a valuable scaffold for developing therapeutics.

CONCLUSION

The exploration of germacrone as a structural framework for multi-targeting drugs offers a potential avenue to enhance efficacy while minimizing potential side effects. Further research and clinical trials are warranted to validate the therapeutic potential of germacrone in diverse medical contexts.

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.

Potential value of ctDNA monitoring in metastatic HR + /HER2 - breast cancer: longitudinal ctDNA analysis in the phase Ib MONALEESASIA trial

BACKGROUND

There is increasing interest in the use of liquid biopsies, but data on longitudinal analyses of circulating tumor DNA (ctDNA) remain relatively limited. Here, we report a longitudinal ctDNA analysis of MONALEESASIA, a phase Ib trial evaluating the efficacy and safety of ribociclib plus endocrine therapy (ET) in Asian patients with hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer.

METHODS

MONALEESASIA enrolled premenopausal and postmenopausal Japanese and postmenopausal non-Japanese Asian patients. All patients received ribociclib with ET (letrozole, fulvestrant, or tamoxifen with goserelin). ctDNA was analyzed using a targeted next-generation sequencing panel of 572 cancer-related genes and correlated by best overall response (BOR).

RESULTS

Five hundred seventy-four cell-free DNA samples from 87 patients were tested. The most frequently altered genes at baseline included PIK3CA (29%) and TP53 (22%). Treatment with ribociclib plus ET decreased ctDNA in most patients at the first on-treatment time point, regardless of dose or ET partner. Patients with partial response and stable disease had lower ctDNA at baseline that remained low until data cutoff if no progressive disease occurred. Most patients with progressive disease as the best response had higher ctDNA at baseline that remained high at the end of treatment. For patients with partial response and stable disease with subsequent progression, ctDNA increased towards the end of treatment in most patients, with a median lead time of 83 days (14-309 days). In some patients with BOR of partial response who experienced disease progression later, specific gene alterations and total ctDNA fraction increased; this was sometimes observed concurrently with the development of new lesions without a change in target lesion size. Patients with alterations in PIK3CA and TP53 at baseline had shorter median progression-free survival compared with patients with wild-type PIK3CA and TP53, 12.7 and 7.3 months vs 19.2 and 19.4 months, respectively (P = .016 and P = .0001, respectively).

CONCLUSIONS

Higher ctDNA levels and PIK3CA and TP53 alterations detected at baseline were associated with inferior outcomes. On-treatment ctDNA levels were associated with different patterns based on BOR. Longitudinal tracking of ctDNA may be useful for monitoring tumor status and detection of alterations with treatment implications.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02333370 . Registered on January 7, 2015.