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

Vepdegestrant for the treatment of HR+/HER2- breast cancer

INTRODUCTION

The treatment of advanced hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer has been improved through the development of endocrine therapy (ET) and targeted agents. However, resistance to ET, particularly caused by ESR1 mutations, has not been fully addressed.

AREAS COVERED

Vepdegestrant is a first-in-class, selective, and orally bioavailable PROteolysis TArgeting Chimera (PROTAC) estrogen receptor (ER) degrader. Preclinical studies have suggested promising activity of vepdegestrant irrespective of ESR1 genotypes. Phase I and II clinical studies have revealed a favorable safety profile and encouraging efficacy of vepdegestrant as a single agent and in combination with other targeted agents.

EXPERT OPINION

The results of the phase III VERITAC-2 study, comparing vepdegestrant with fulvestrant, are expected to be available in 2025, and will provide the first data on the true clinical significance of vepdegestrant. Several phase III studies of combinations with vepdegestrant including + atirimociclib (a cyclin-dependent kinase 4 inhibitor) have been or are planned to be conducted. The results of these may not only transform the treatment landscape for advanced HR+/HER2- breast cancer but may pave the way for PROTAC as a new class of anti-cancer drugs that may make previously undruggable targets druggable.

Methyl-oxazolomycin A: A novel oxazolomycin analog with potent selective estrogen receptor degrading activity in breast cancer cells

Breast cancer (BC), the most prevalent malignancy in women worldwide, is categorized according to the expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) in tumor cells. Approximately 70% of all BCs are ER-positive and HER2-negative, and estrogen binding to the ER plays a vital role in BC development. We previously reported that methyl-oxazolomycin A, a natural compound isolated from Streptomyces sp. in soil, exhibited selective antiproliferative activity against ER-positive BC cells compared to triple-negative BC cells not expressing ER, PR, and HER2. The present study aimed to elucidate the molecular mechanisms underlying the antiproliferative activity of methyl-oxazolomycin A in two ER-positive BC lines, MCF-7 and T-47D. Methyl-oxazolomycin A effectively reduced the protein levels of ERα via proteasomal degradation while also reducing the protein levels of phosphorylated ERα. Notably, methyl-oxazolomycin A demonstrated potent antiproliferative activity in tamoxifen-resistant MCF-7 cells and downregulated the protein expression of phosphorylated ERα at Tyr537, which SERDs such as fulvestrant fail to target. The antiproliferative activity of methyl-oxazolomycin A was associated with the induction of the G0/G1 cell cycle arrest through the modulation of cell cycle checkpoint protein expression. Prolonged treatment with methyl-oxazolomycin A led to an increase in the production of reactive oxygen species and induced apoptosis. These findings, which detail the mechanisms underlying the antiproliferative activity of methyl-oxazolomycin A, support its potential as a novel agent targeting ER-positive BC cells.

Characterization of SUSD3 as a novel prognostic biomarker and therapeutic target for breast cancer

BACKGROUND

Breast cancer (BC) remains a significant global health challenge, contributing substantially to cancer-related deaths worldwide. Its prevalence and associated death rates remain alarmingly high, highlighting the persistent public health burden. The objective of this study was to systematically examine the involvement of SUSD3 (Sushi Domain-Containing 3) in BC, highlighting its crucial role in the pathogenesis and progression of this disease.

METHODS

BC-related gene microarray data, along with corresponding clinicopathological information, were obtained from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Leveraging TIMER and HPA databases, we conducted comparative analyses to evaluate SUSD3 expression in BC. We then analyzed the association between SUSD3 and clinical traits, as well as the prognostic value of SUSD3. SUSD3-related differential expression genes (DEGs) were sent for analysis utilizing GO, KEGG, and GSEA. We utilized SUSD3 mRNA expression to assess immune cells' scores in BC tissues calculated by single-sample enrichment analyses based on "CIBERSORT" R package. Drug sensitivity analysis was used to screen potential drugs sensitive to SUSD3. R software was used for statistical analyses and graphical representation of the data.

RESULTS

Our findings confirmed a significant upregulation of SUSD3 expression in BC, which correlated with a favorable prognosis. Clinical correlation analysis further emphasized the strong association between SUSD3 expression and key clinical parameters like estrogen receptor (ER) status, progesterone receptor (PR) status, stage, and T classification in breast cancer. Univariate and multivariate Cox regression analyses showed that SUSD3 could be used as an independent prognostic factor for BC. Differentially expressed genes (DEGs) co-expressed with SUSD3 were significantly associated with various biological processes, such as the cell cycle, DNA replication, p53 signaling pathway, cancer-related pathways, and Wnt signaling pathway, as indicated by gene set enrichment analysis (GSEA). Furthermore, our analysis demonstrated that SUSD3 generally exhibited negative associations with immune modulators. Drug sensitivity analysis revealed positive correlations between SUSD3 and the efficacy of Fulvestrant, Raloxifene, and Fluphenazine.

CONCLUSION

The research emphasizes the significance of SUSD3 as a potential marker for BC, providing insights into the underlying molecular mechanisms implicated in tumorigenesis. SUSD3 holds promise in helping the classification of breast cancer pathological groups, predicting prognosis, and facilitating targeted therapy.

Simulated Galactic Cosmic Radiation Exposure-Induced Mammary Tumorigenesis in ApcMin/+ Mice Coincides with Activation of ERα-ERRα-SPP1 Signaling Axis

BACKGROUND

Exposure to galactic cosmic radiation (GCR) is a breast cancer risk factor for female astronauts on deep-space missions. However, the specific signaling mechanisms driving GCR-induced breast cancer have not yet been determined.

METHODS

This study aimed to investigate the role of the estrogen-induced ERα-ERRα-SPP1 signaling axis in relation to mammary tumorigenesis in female ApcMin/+ mice exposed to simulated GCR (GCRsim) at 100-110 days post-exposure.

RESULTS

In GCRsim-exposed mice, we observed marked elevations in serum estradiol, increased ductal overgrowth, ERα activation, and upregulation of ERα target genes with pro-tumorigenic functions in mammary tissues that was coupled with a higher mammary tumorigenesis, relative to control. Additionally, the ERα target gene Esrra, which encodes ERRα, was also upregulated along with its oncogenic target gene Spp1, indicating the activation of the ERα-ERRα-SPP1 axis in mouse mammary tissues after GCRsim exposure. Using a human tissue microarray and human breast cancer gene expression analysis, we also highlighted the conserved nature of the ERα-ERRα-SPP1 signaling in human breast cancer development.

CONCLUSIONS

We identified the ERα-ERRα-SPP1 signaling axis as a potential key mediator in GCR-induced breast cancer with conserved activation in human breast cancer. These findings suggest that targeting this pathway could serve as a potential target for therapeutic intervention to safeguard female astronauts during and after a prolonged outer space mission.

Current Therapeutic Opportunities for Estrogen Receptor Mutant Breast Cancer

Estrogen receptor α (ERα) drives two out of three breast cancers and therefore ERα is a major therapeutic target for ER-positive breast cancer patients. Drugs that inhibit ERα activity or block estrogen synthesis in the body are currently being used in the clinic to treat ER-positive breast cancer and have been quite successful in controlling breast cancer progression for the majority of patients. However, ER-positive breast cancer often becomes resistant to these endocrine therapies, leading to endocrine-resistant metastatic breast cancer, a very aggressive cancer that leads to death. Recent large-scale genomic studies have revealed a series of activating somatic mutations in the ERα gene (ESR1) in endocrine-resistant metastatic breast cancer patients. Of these, Y537S and D538G mutations are found at a much higher rate in patients with metastatic breast cancer. Remarkably, these mutations produce an ERα with much higher transcriptional activity than wild type in the absence of estradiol, and traditional endocrine therapy has poor efficacy against ER mutants. Therefore, the development of new drugs that target ER mutants is an unmet clinical need for endocrine-resistant metastatic breast cancer. This review summarizes the recent preclinical and clinical trials targeting estrogen receptor mutant breast cancer.

Endocrine therapy for early breast cancer in the era of oral selective estrogen receptor degraders: challenges and future perspectives

PURPOSE OF REVIEW

Growth and survival of hormone receptor positive breast cancer cells are dependent on circulating hormones (e.g., estrogen and progesterone). Endocrine therapy improved outcomes in both early and advanced hormone receptor positive breast cancer. These treatments include drugs with different mechanisms of action, namely selective estrogen receptor modulators (SERM), aromatase inhibitors, and selective estrogen receptor degraders (SERDs). SERDs represent estrogen receptor antagonists, favoring its degradation and thus interfering with proliferation genes transcription and activation. Fulvestrant is the first approved SERD, administered intramuscularly for treating advanced breast cancer.

RECENT FINDINGS

Oral SERDs have been tested to overcome the limitation of the intramuscular administration, and to increase SERD bioavailability. Recently, an oral SERD, Elacestrant, has been approved by the Food and Drug Administration (FDA) for patients carrying an ESR1 mutation. In fact, oral SERDs seem to be effective in tumors harboring ESR1 mutations, a well known mechanism of resistance to endocrine therapy (especially aromatase inhibitors).

SUMMARY

More recently, oral SERDs have been tested in patients with early hormone receptor positive breast cancer, although their impact on survival and in this curative setting compared to standard endocrine therapy still needs to be elucidated. The best timing and duration of SERD administration and specific biomarkers in (neo)adjuvant setting remain largely unknown.

Oral SERDs alone or in combination with CDK 4/6 inhibitors in breast cancer: Current perspectives and clinical trials

Over the past few decades, first-line therapy for treating advanced and metastatic HR+/HER2-breast cancer has transformed due to the introduction of adjuvant endocrine therapy with cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i). However, there is an unmet need for novel classes of endocrine therapy with superior efficacy to improve treatment outcomes and overcome CDK4/6i resistance. New generation selective estrogen receptor degraders (SERDs), orally administered and with higher bioavailability, could potentially be the novel compounds to meet this emerging need. In this paper, we review accredited clinical studies on the combining effects of CDK4/6 inhibitors and oral SERDs, report efficacy of treatment data when available, and provide a framework for future research focusing on these promising agents.