A Randomized, Open-label, Presurgical, Window-of-Opportunity Study Comparing the Pharmacodynamic Effects of the Novel Oral SERD AZD9496 with Fulvestrant in Patients with Newly Diagnosed ER+ HER2- Primary Breast Cancer

A phase I dose escalation and expansion trial of the next-generation oral SERD camizestrant in women with ER-positive, HER2-negative advanced breast cancer: SERENA-1 monotherapy results

BACKGROUND

SERENA-1 (NCT03616587) is a phase I, multi-part, open-label study of camizestrant in pre- and post-menopausal women with estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer. Parts A and B aim to determine the safety and tolerability of camizestrant monotherapy and define doses for clinical evaluation.

PATIENTS AND METHODS

Women aged ≥18 years with metastatic or recurrent ER+, HER2- breast cancer, refractory (or intolerant) to therapy, were assigned 25 mg up to 450 mg once daily (QD; escalation) or 75, 150, or 300 mg QD (expansion). Safety and tolerability, antitumor efficacy, pharmacokinetics, and impact on mutations in the estrogen receptor gene (ESR1m) circulating tumor (ct)DNA levels were assessed.

RESULTS

By 9 March 2021, 108 patients received camizestrant monotherapy at 25-450 mg doses. Of these, 93 (86.1%) experienced treatment-related adverse events (TRAEs), 82.4% of which were grade 1 or 2. The most common TRAEs were visual effects (56%), (sinus) bradycardia (44%), fatigue (26%), and nausea (15%). There were no TRAEs grade 3 or higher, or treatment-related serious adverse events at doses ≤150 mg. Median tmax was achieved ∼2-4 h post-dose at all doses investigated, with an estimated half-life of 20-23 h. Efficacy was observed at all doses investigated, including in patients with prior cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) and/or fulvestrant treatment, with and without baseline ESR1 mutations, and with visceral disease, including liver metastases.

CONCLUSIONS

Camizestrant is a next-generation oral selective ER antagonist and degrader (SERD) and pure ER antagonist with a tolerable safety profile. The pharmacokinetics profile supports once-daily dosing, with evidence of pharmacodynamic and clinical efficacy in heavily pre-treated patients, regardless of ESR1m. This study established 75-, 150-, and 300-mg QD doses for phase II testing (SERENA-2, NCT04214288 and SERENA-3, NCT04588298).

Influence of tumor microenvironment on the different breast cancer subtypes and applied therapies

Despite the significant improvements made in breast cancer therapy during the last decades, this disease still has increasing incidence and mortality rates. Different targets involved in general processes, like cell proliferation and survival, have become alternative therapeutic options for this disease, with some of them already used in clinic, like the CDK4/6 inhibitors for luminal A tumors treatment. Nevertheless, there is a demand for novel therapeutic strategies focused not only on tumor cells, but also on their microenvironment. Tumor microenvironment (TME) is a very complex and dynamic system that, more than surrounding and supporting tumor cells, actively participates in tumor development and progression. During the last decades, it has become clear that the cellular and acellular components of TME differ between the various breast cancer subtypes and shape the differences regarding their severity and prognosis. The pivotal role of the TME in controlling tumor growth and influencing responses to therapy represents a potential source for novel targets and therapeutic strategies. In this review, we present a description of the multiple therapeutic options used for different breast cancer subtypes, as well as the influence that the TME may exert on the development of the disease and on the response to the distinct therapies, which in some cases may explain their failure by the occurrence of relapses and resistance. Furthermore, the ongoing studies focused on the use of TME components for developing potential cancer treatments are described.

AMEERA-4: a randomized, preoperative window-of-opportunity study of amcenestrant versus letrozole in early breast cancer

BACKGROUND

Window-of-opportunity (WOO) studies provide insights into the clinical activity of new drugs in breast cancer.

METHODS

AMEERA-4 (NCT04191382) was a WOO study undertaken to compare the pharmacodynamic effects of amcenestrant, a selective estrogen receptor degrader, with those of letrozole in postmenopausal women with newly diagnosed, operable estrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER+/HER2-) breast cancer. Women were randomized (1:1:1) to receive amcenestrant 400 mg, amcenestrant 200 mg, or letrozole 2.5 mg once daily for 14 days before breast surgery. The primary endpoint was change in Ki67 between baseline and Day 15 (i.e., day of surgery).

RESULTS

Enrollment was stopped early because of slow recruitment, in the context of the COVID-19 pandemic. The modified intent-to-treat population consisted of 95 study participants with baseline and post-treatment Ki67 values, whereas the safety population included 104 participants who had received at least one dose of study medication. Relative change from baseline in Ki67 was - 75.9% (95% confidence interval [CI] - 81.9 to - 67.9) for amcenestrant 400 mg, - 68.2% (- 75.7 to - 58.4) for amcenestrant 200 mg, and - 77.7% (- 83.4 to - 70.0) for letrozole (geometric least-squares mean [LSM] estimates). Absolute change in ER H-score from baseline (LSM estimate) was - 176.7 in the amcenestrant 400 mg arm, - 202.9 in the amcenestrant 200 mg arm, and - 32.5 in the letrozole arm. There were no Grade ≥ 3 treatment-related adverse events.

CONCLUSIONS

Both amcenestrant and letrozole demonstrated antiproliferative activity in postmenopausal women with previously untreated, operable ER+/HER2- breast cancer and had good overall tolerability.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04191382 https://clinicaltrials.gov/ct2/show/NCT04191382 . Registered 9 December 2019.

Neoadjuvant endocrine therapy in ER-positive breast cancer: evolution, indication, and tailored treatment strategy

In recent years, endocrine therapy (ET), an effective systemic treatment for the management of estrogen receptor (ER)-positive breast cancers, has regained interest as a neoadjuvant therapy based on evidence that ET can fulfill the aim of neoadjuvant systemic treatment for tumor shrinkage as well as elucidate important clinical information on endocrine sensitivity that enables the prognostication of patients. Moreover, neoadjuvant endocrine therapy (NET) potentially provides an opportunity for early assessment of the clinical efficacy of novel agents. Furthermore, recently reported trials have generated evidence for a more tailored approach for perioperative management of ER-positive breast cancer using clinical and molecular biomarkers, and this has provided a rationale that enables the broadening of clinical indications for NET. This review discusses the current evidence for NET, the evolution of NET trials, clinical indications, and NET-based treatment strategies.

Identification of Novel Dual-Target Estrogen Receptor α Degraders with Tubulin Inhibitory Activity for the Treatment of Endocrine-Resistant Breast Cancer

Endocrine resistance remains a significant problem in the clinical treatment of estrogen receptor α-positive (ERα+) breast cancer (BC). In this study, we developed a series of novel dual-functional ERα degraders based on a bridged bicyclic scaffold with selenocyano (SeCN) side chains. These compounds displayed potent ERα degradation and tubulin depolymerization activity. Among them, compounds 35s and 35t exhibited the most promising antiproliferative and ERα degradation activity in multiple ERα+ BC cell lines bearing either wild-type or mutant ERα. Meanwhile, compounds 35s and 35t disrupted the microtubule network by restraining tubulin polymerization, evidenced by 35t inducing cell cycle arrest in the G2/M phase. In MCF-7 and LCC2 xenograft models, compounds 35s and 35t remarkably suppressed tumor growth without noticeable poisonousness. Finally, this study provided guidance for developing new dual-target antitumor drug candidates for the ERα+ BC therapy, especially for the resistant variant.

Selective Estrogen receptor degraders (SERDs) for the treatment of breast cancer: An overview

Discovery of SERDs has changed the direction of anticancer research, as more than 70% of breast cancer cases are estrogen receptor positive (ER+). Therapies such as selective estrogen receptor modulators (SERM) and aromatase inhibitors (AI's) have been effective, but due to endocrine resistance, SERDs are now considered essential therapeutics for the treatment of ER+ breast cancer. The present review deliberates the pathophysiology of SERDs from the literature covering various molecules in clinical trials. Estrogen receptors active sites distinguishing characteristics and interactions with currently available FDA-approved drugs have also been discussed. Designing strategy of previously reported SERDs, their SAR analysis, in silico, and the biological efficacy have also been summarized along with appropriate examples.

Targeted protein degrader development for cancer: advances, challenges, and opportunities

Anticancer-targeted therapies inhibit various kinases implicated in cancer and have been used in clinical settings for decades. However, many cancer-related targets are proteins without catalytic activity and are difficult to target using traditional occupancy-driven inhibitors. Targeted protein degradation (TPD) is an emerging therapeutic modality that has expanded the druggable proteome for cancer treatment. With the entry of new-generation immunomodulatory drugs (IMiDs), selective estrogen receptor degraders (SERDs), and proteolysis-targeting chimera (PROTAC) drugs into clinical trials, the field of TPD has seen explosive growth in the past 10 years. Several challenges remain that need to be tackled to increase successful clinical translation of TPD drugs. We present an overview of the global landscape of clinical trials of TPD drugs over the past decade and summarize the clinical profiles of new-generation TPD drugs. In addition, we highlight the challenges and opportunities for the development of effective TPD drugs for future successful clinical translation.

Molecular Biomarker Expression in Window of Opportunity Studies for Oestrogen Receptor Positive Breast Cancer-A Systematic Review of the Literature

Simple Summary

Window of opportunity (WoO) trials allow the opportunity to assess the use of drugs in breast cancer research before treatment has commenced. The aim of this review of the literature is to review WoO trials in patients with oestrogen receptor-positive (ER+) breast cancer to help guide treatment. This will be useful for patients who receive drug treatment before surgery, or as an alternative to surgery in older, more frail adults.

Abstract

Window of opportunity (WoO) trials create the opportunity to demonstrate pharmacodynamic parameters of a drug in vivo and have increasing use in breast cancer research. Most breast cancer tumours are oestrogen receptor-positive (ER+), leading to the development of multiple treatment options tailored towards this particular tumour subtype. The aim of this literature review is to review WoO trials pertaining to the pharmacodynamic activity of drugs available for use in ER+ breast cancer in order to help guide treatment for patients receiving neoadjuvant and primary endocrine therapy. Five databases (EMBASE, Cochrane, MEDLINE, PubMed, Web of Science) were searched for eligible studies. Studies performed in treatment-naïve patients with histologically confirmed ER+ breast cancer were included if they acquired pre- and post-treatment biopsies, compared measurement of a proteomic biomarker between these two biopsies and delivered treatment for a maximum mean duration of 31 days. Fifteen studies were eligible for inclusion and covered six different drug classes: three endocrine therapies (ETs) including aromatase inhibitors (AIs), selective oestrogen receptor modulators (SERMs), selective oestrogen receptor degraders (SERDs) and three non-ETs including mTOR inhibitors, AKT inhibitors and synthetic oestrogens. Ki67 was the most frequently measured marker, appearing in all studies. Progesterone receptor (PR) and ER were the next most frequently measured markers, appearing five and four studies, respectively. All three of these markers were significantly downregulated in both AIs and SERDs; Ki67 alone was downregulated in SERMs. Less commonly assessed markers including pS6, pGSH3B, FSH and IGF1 were downregulated while CD34, pAKT and SHBG were significantly upregulated. There were no significant changes in the other biomarkers measured such as phosphate and tensin homolog (PTEN), Bax and Bcl-2.WoO studies have been widely utilised within the ER+ breast cancer subtype, demonstrating their worth in pharmacodynamic research. However, research remains focused upon routinely measured biomarkers such ER PR and Ki67, with an array of less common markers sporadically used.

The Present and Future of Clinical Management in Metastatic Breast Cancer

Regardless of the advances in our ability to detect early and treat breast cancer, it is still one of the common types of malignancy worldwide, with the majority of patients decease upon metastatic disease. Nevertheless, due to these advances, we have extensively characterized the drivers and molecular profiling of breast cancer and further dividing it into subtypes. These subgroups are based on immunohistological markers (Estrogen Receptor-ER; Progesterone Receptor-PR and Human Epidermal Growth Factor Receptor 2-HER-2) and transcriptomic signatures with distinct therapeutic approaches and regiments. These therapeutic approaches include targeted therapy (HER-2+), endocrine therapy (HR+) or chemotherapy (TNBC) with optional combination radiotherapy, depending on clinical stage. Technological and scientific advances in the identification of molecular pathways that contribute to therapy-resistance and establishment of metastatic disease, have provided the rationale for revolutionary targeted approaches against Cyclin-Dependent Kinases 4/6 (CDK4/6), PI3 Kinase (PI3K), Poly ADP Ribose Polymerase (PARP) and Programmed Death-Ligand 1 (PD-L1), among others. In this review, we focus on the comprehensive overview of epidemiology and current standard of care treatment of metastatic breast cancer, along with ongoing clinical trials. Towards this goal, we utilized available literature from PubMed and ongoing clinical trial information from clinicaltrials.gov to reflect the up to date and future treatment options for metastatic breast cancer.

Biomarkers for Systemic Therapy in Metastatic Breast Cancer: ASCO Guideline Update

PURPOSE

To update the ASCO biomarkers to guide systemic therapy for metastatic breast cancer (MBC) guideline.

METHODS

An Expert Panel conducted a systematic review to identify randomized clinical trials and prospective-retrospective studies from January 2015 to January 2022.

RESULTS

The search identified 19 studies informing the evidence base.

RECOMMENDATIONS

Candidates for a regimen with a phosphatidylinositol 3-kinase inhibitor and hormonal therapy should undergo testing for PIK3CA mutations using next-generation sequencing of tumor tissue or circulating tumor DNA (ctDNA) in plasma to determine eligibility for alpelisib plus fulvestrant. If no mutation is found in ctDNA, testing in tumor tissue, if available, should be used. Patients who are candidates for poly (ADP-ribose) polymerase (PARP) inhibitor therapy should undergo testing for germline BRCA1 and BRCA2 pathogenic or likely pathogenic mutations to determine eligibility for a PARP inhibitor. There is insufficient evidence for or against testing for a germline PALB2 pathogenic variant to determine eligibility for PARP inhibitor therapy in the metastatic setting. Candidates for immune checkpoint inhibitor therapy should undergo testing for expression of programmed cell death ligand-1 in the tumor and immune cells to determine eligibility for treatment with pembrolizumab plus chemotherapy. Candidates for an immune checkpoint inhibitor should also undergo testing for deficient mismatch repair/microsatellite instability-high to determine eligibility for dostarlimab-gxly or pembrolizumab, as well as testing for tumor mutational burden. Clinicians may test for NTRK fusions to determine eligibility for TRK inhibitors. There are insufficient data to recommend routine testing of tumors for ESR1 mutations, for homologous recombination deficiency, or for TROP2 expression to guide MBC therapy selection. There are insufficient data to recommend routine use of ctDNA or circulating tumor cells to monitor response to therapy among patients with MBC.Additional information can be found at www.asco.org/breast-cancer-guidelines.

A real-world US study of recurrence risks using combined clinicopathological features in HR-positive, HER2-negative early breast cancer

Aim: To assess invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in hormone receptor-positive, HER2-negative early breast cancer with combined clinicopathological criteria from monarchE, a phase III study of abemaciclib. Methods: US electronic health records were used to compare outcomes between high-risk (≥4 lymph nodes, or 1-3 lymph nodes and grade 3, tumor ≥5 cm, or Ki-67 ≥20%) versus nonhigh-risk groups using Kaplan-Meier methods and Cox regression models. Results: The high-risk group (n = 557) was at higher risk for IDFS and DRFS events than the nonhigh-risk group (n = 3471). IDFS events (hazard ratio: 3.07; 95% CI: 2.45-3.83) and DRFS events (hazard ratio: 3.15; 95% CI: 2.49-3.97) were significantly higher for the high-risk group. Conclusion: Risk of recurrence was three-times greater in the high-risk group, highlighting the need for better therapies.

Andrographolide Inhibits ER-Positive Breast Cancer Growth and Enhances Fulvestrant Efficacy via ROS-FOXM1-ER-α Axis

Estrogen receptor (ER)-positive breast cancer is the main subtype of breast cancer (BRCA) with high incidence and mortality. Andrographolide (AD), a major active component derived from the traditional Chinese medicine Andrographis paniculate, has substantial anti-cancer effect in various tumors. However, the antitumor efficacy and the underlying molecular mechanisms of AD on ER-positive breast cancer are poorly understood. In the present study, we demonstrated that andrographolide (AD) significantly inhibited the growth of ER-positive breast cancer cells. Mechanistically, AD suppressed estrogen receptor 1 (ESR1, encodes ER-α) transcription to inhibit tumor growth. Further studies revealed that AD induced ROS production to down-regulate FOXM1-ER-α axis. Conversely, inhibiting ROS production with N-acetylcysteine (NAC) elevated AD-decreased ER-α expression, which could be alleviated by FOXM1 knockdown. In addition, AD in combination with fulvestrant (FUL) synergistically down-regulated ER-α expression to inhibit ER-positive breast cancer both in vitro and in vivo. These findings collectively indicate that AD suppresses ESR1 transcription through ROS-FOXM1 axis to inhibit ER-positive breast cancer growth and suggest that AD might be a potential therapeutic agent and fulvestrant sensitizer for ER-positive breast cancer treatment.

Understanding and overcoming tumor heterogeneity in metastatic breast cancer treatment

Rational development of targeted therapies has revolutionized metastatic breast cancer outcomes, although resistance to treatment remains a major challenge. Advances in molecular profiling and imaging technologies have provided evidence for the impact of clonal diversity in cancer treatment resistance, through the outgrowth of resistant clones. In this Review, we focus on the genomic processes that drive tumoral heterogeneity and the mechanisms of resistance underlying metastatic breast cancer treatment and discuss implications for future treatment strategies.

Endocrine Treatment for Breast Cancer Patients Revisited-History, Standard of Care, and Possibilities of Improvement

PURPOSE OF REVIEW

Due to the findings of current studies and the approval of novel substances for the therapy of hormone-receptor-positive breast cancer patients, the established standards of endocrine treatment are changing. The purpose of this review is to give an overview of the history of endocrine treatment, to clarify its role in the present standard of care, and to discuss the possibilities of improvement.

RECENT FINDINGS

Tamoxifen, aromatase inhibitors, and fulvestrant are the main drugs that have been used for decades in the therapy of hormone-receptor-positive breast cancer patients. However, since a relevant number of women suffer at some point from disease recurrence or progression, several novel substances are being investigated to overcome resistance mechanisms by interfering with certain signaling pathways, such as the PI3K/AKT/mTOR or the CDK4/6 pathways. mTOR and CDK4/6 inhibitors were the first drugs approved for this purpose and many more are in development.

SUMMARY

Endocrine treatment is one of the best tolerable cancer therapies available. Continuous investigation serves to improve patients' outcomes and modernize the current standard of care. Considering the resistance mechanisms and substances analyzed against these, endocrine treatment of hormone-receptor-positive breast cancer is on the brink of a new era.

Accelerating drug access from advanced to early breast cancer: the special case of oral selective estrogen receptor degraders

PURPOSE OF REVIEW

For hormone receptor positive breast cancer, the development of endocrine resistance commonly occurs, presenting as either disease progression in the metastatic setting or recurrence during or following adjuvant endocrine therapy. Various mechanisms of resistance have been described. In order to reduce or overcome endocrine resistance, there has been substantial interest in developing potent and orally bioavailable selective estrogen receptor degraders (SERDs) for metastatic disease and select patients with early-stage estrogen receptor positive breast cancer.

RECENT FINDINGS

At least 11 oral SERDs have entered clinical development. We review current studies in both the metastatic and neoadjuvant/adjuvant setting and present the available evidence of benefit and toxicity for these novel agents. Further characterization of changes to tissue-based biomarkers such as estrogen receptor, progesterone receptor and Ki67 expression and blood-based biomarkers such as ctDNA and estrogen receptor 1 mutation may help to refine therapeutic strategies, combinations, and patient selection to identify women who are most likely to benefit from these novel endocrine agents.

SUMMARY

Although SERDs have clear therapeutic potential based on nonclinical studies and have demonstrated early signs of activity in phase I and II studies in the metastatic setting, ongoing research is needed to clarify when and in whom these agents may have greatest clinical benefit.

Oral Selective Estrogen Receptor Degraders (SERDs) as a Novel Breast Cancer Therapy: Present and Future from a Clinical Perspective

Estrogen receptor-positive (ER+) is the most common subtype of breast cancer. Endocrine therapy is the fundamental treatment against this entity, by directly or indirectly modifying estrogen production. Recent advances in novel compounds, such as cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), or phosphoinositide 3-kinase (PI3K) inhibitors have improved progression-free survival and overall survival in these patients. However, some patients still develop endocrine resistance after or during endocrine treatment. Different underlying mechanisms have been identified as responsible for endocrine treatment resistance, where ESR1 gene mutations are one of the most studied, outstanding from others such as somatic alterations, microenvironment involvement and epigenetic changes. In this scenario, selective estrogen receptor degraders/downregulators (SERD) are one of the weapons currently in research and development against aromatase inhibitor- or tamoxifen-resistance. The first SERD to be developed and approved for ER+ breast cancer was fulvestrant, demonstrating also interesting activity in ESR1 mutated patients in the second line treatment setting. Recent investigational advances have allowed the development of new oral bioavailable SERDs. This review describes the evolution and ongoing studies in SERDs and new molecules against ER, with the hope that these novel drugs may improve our patients’ future landscape.

From Pure Antagonists to Pure Degraders of the Estrogen Receptor: Evolving Strategies for the Same Target

Pure antiestrogens, or selective estrogen receptor degraders (SERDs), have proven to be effective in treating breast cancer that has progressed on tamoxifen and/or aromatase inhibitors. However, the only FDA-approved pure antiestrogen, fulvestrant, is limited in efficacy by its low bioavailability. The search for orally bioavailable SERDs has continued for nearly as long as the clinical history of the injection-only fulvestrant. Oral SERDs that have been developed and tested in patients ranged from nonsteroidal ER binders containing an acrylic acid or amino side chain to bifunctional proteolysis-targeting chimera (PROTAC) pure ER degraders. Structural evolution in the development of oral SERD molecules has been closely associated with quantifiable ER-degrading potency, as seen in the structural comparison analysis of acrylic acid and basic amino side-chain-bearing SERDs. Failure to improve on fulvestrant in the clinical trials by numerous acidic SERDs and early basic SERDs is blamed on tolerability and/or insufficient efficacy, which will likely be overcome by the new-generation basic SERD molecules and PROTAC ER degraders with improved oral bioavailability, low toxicity, and superior efficacy of receptor degradation.

Endocrine Resistance in Breast Cancer: The Role of Estrogen Receptor Stability

Therapy of hormone receptor positive breast cancer (BCa) generally targets estrogen receptor (ER) function and signaling by reducing estrogen production or by blocking its interaction with the ER. Despite good long-term responses, resistance to treatment remains a significant issue, with approximately 40% of BCa patients developing resistance to ET. Mutations in the gene encoding ERα, ESR1, have been identified in BCa patients and are implicated as drivers of resistance and disease recurrence. Understanding the molecular consequences of these mutations on ER protein levels and its activity, which is tightly regulated, is vital. ER activity is in part controlled via its short protein half-life and therefore changes to its stability, either through mutations or alterations in pathways involved in protein stability, may play a role in therapy resistance. Understanding these connections and how ESR1 alterations could affect protein stability may identify novel biomarkers of resistance. This review explores the current reported data regarding posttranslational modifications (PTMs) of the ER and the potential impact of known resistance associated ESR1 mutations on ER regulation by affecting these PTMs in the context of ET resistance.

Endocrine-Resistant Breast Cancer: Mechanisms and Treatment

BACKGROUND

Endocrine treatment is one of the most effective therapies for estrogen receptor-positive breast cancer. However, most tumors will develop resistance to endocrine therapy as the cancer progresses. This review focuses on the mechanisms and markers of endocrine-resistant breast cancer. In addition, current and future strategies to overcome endocrine resistance are discussed.

SUMMARY

Several molecular mechanisms of endocrine resistance have been identified, including alterations in the ESR1 gene or in the PIK3CA/mTOR pathway. Meanwhile, CDK4/6, mTOR, and PI3K inhibition have shown to improve the efficacy of endocrine treatment and new promising approaches are being developed.

KEY MESSAGE

Overcoming primary or acquired resistance to endocrine treatment remains a major challenge. Since the molecular mechanisms of endocrine resistance are manifold, optimal combination and sequencing strategies will have to be developed in the future.