Selective Estrogen Receptor Degrader Research Articles

Long-term estrogen-deprived estrogen receptor α-positive breast cancer cell migration assisted by fatty acid 2-hydroxylase.

The risk of breast cancer (BC) recurrence is high in postmenopausal women, though the underlying molecular mechanisms are not yet fully understood. We developed a long-term estrogen-deprived (LTED) cell line from MCF-7 cells, which we used as an in vitro model for aromatase inhibitor (AI)-resistant estrogen receptor α (ERα)-positive postmenopausal BC. We also describe the involvement of fatty acid 2-hydroxylase (FA2H) in the modulation of LTED cell migration. Small interfering RNA specific to FA2H (siFA2H) could reduce cell migration, whereas the introduction of plasmid expressing FA2H, but not its inactive mutant, resulted in enhanced migration. Moreover, proliferation of the LTED cells was not affected by modulation of FA2H expression. Fulvestrant (FUL), a selective estrogen receptor degrader used to treat AI-resistant ERα-positive postmenopausal BC, was found to induce degradation of ERα together with a decrease in ER-mediated transcription; however, FA2H protein expression and migration remained unchanged. Overall, the findings of this study suggest that FA2H is one of the drivers of LTED cell migration, and that LTED cells resistant to FUL therapy may be involved in malignancy and metastatic mechanisms.

Pharmacologic Induction of ERα SUMOylation Disrupts Its Chromatin Binding.

Estrogen receptor α (ERα)-positive breast cancer patients are typically treated with ERα inhibitors, including selective estrogen receptor modulators (SERMs) and selective estrogen receptor degraders (SERDs). However, the distinct pharmacological properties of various ERα inhibitors remain incompletely understood. In this study, we employed formaldehyde cross-linking followed by ERα immunoprecipitation and mass spectrometry to reveal that fulvestrant, the first FDA-approved SERD, induces the interaction between ERα and SUMO E3 ligases PIAS1 and PIAS2. Biochemical and genomic assays confirmed that fulvestrant induces SUMOylation of ERα, which inhibits ERα's binding to chromatin DNA. In addition, raloxifene (a SERM) and elacestrant (the first FDA-approved oral SERD) were identified as compounds that similarly induce ERα SUMOylation and inhibit its chromatin interaction. Our findings reveal a mechanism by which select ERα inhibitors disrupt ERα function through SUMOylation, offering insights for the development of next-generation ERα-targeted therapies.

8595 Brain Penetration Impedes SERD Efficacy in Breast Cancer Pre-clinical Models

Abstract Disclosure: S.E. Wardell: None. B. Chakraborty: None. S. Artham: None. M.A. Newlin: None. M. Kirkland: None. C. Chang: None. D.P. McDonnell: None. Most breast cancers express the estrogen receptor (ER, ESR1), and agents that target ER remain the cornerstone of interventions used to treat this disease at all stages. Aromatase inhibitors (AI), which block estrogen synthesis, and the selective ER downregulator (SERD) fulvestrant were developed with the goal of achieving absolute inhibition of ER signaling in tumors. However, it has been assumed that the clinical efficacy (and utility) of fulvestrant is somewhat limited by its poor pharmaceutical properties and the requirement that it be administered by intramuscular injection. This, together with the observation that the activating ESR1 mutations selected for during AI treatment are not effectively inhibited by fulvestrant, encouraged the development of new classes of SERDs that achieve sufficient exposure to saturate and degrade ER in tumors. The recent approval of the second-generation SERD elacestrant for the treatment of breast cancers harboring ESR1 mutations was a major advance in approaches to target ER in advanced breast cancer. Several additional oral SERDs have been developed and evaluated as potential treatments for advanced metastatic breast cancer. Despite showing substantial efficacy in pre-clinical assays that assess ER downregulation and gene transcription, and notably equivalent antitumor activities in cell line derived and PDX tumors in immunocompromised mice, the clinical development of the majority of these SERDs has been discontinued for lack of efficacy. In reviewing the available clinical data across many SERD programs, we noted that some drugs demonstrated a paradoxical, non-linear response curve with higher doses exhibiting less efficacy than lower doses. Probing this pharmacology in animal models we determined that the ability of SERDs to cross the blood brain barrier and attenuate ER signaling in the hypothalamus was a key differentiator of SERDs. In validated syngeneic models of breast cancer, we observed doses of fulvestrant having confirmed brain exposure stimulated tumor growth independent of tumor ER-status. We evaluated the ability of several next generation SERDs for their brain penetrance and demonstrated that SERD presence in the brain was associated with a stimulatory effect on tumor growth. Interestingly, administration of a low dose of 17b-estradiol (E2) together with a brain excluded SERD further repressed tumor growth, highlighting a potentially beneficial anti-tumor role for estrogen signaling in the brain. Furthermore, combination of a brain excluded SERM with E2 also resulted in increased tumor growth repression; thus, ER downregulation is dispensable for the cooperative activity observed for estrogens administered together with a peripheral ER antagonist. These data suggest that differences in tissue pharmacology, as opposed to differences in ability to degrade ER, is likely to be a major differentiator of ER modulators. Presentation: 6/3/2024

8018 Improving Anti-Breast Cancer Activities by Optimizing Torsion Angle Energies

Abstract Disclosure: D.R. Zak: None. E.C. Fink: None. G.R. Hancock: None. K.S. Young: None. S.W. Fanning: None. Overexpression of estrogen receptor alpha (ER-alpha) is found in 70% of breast cancer tumors. Normally, ER-alpha remains inactive and sequestered in the cytoplasm until estrogen binds to the ligand-binding domain (LBD) to enable nuclear translocation, coregulator recruitment, and subsequent activation of proliferative ER-alpha-dependent transcriptomic profiles. The majority of breast cancers are treated successfully with ER-targeted endocrine therapies, but hotspot ER-alpha LBD mutants are selected for, namely Y537S and D538G causing therapeutic resistance, relapse, and aggressive metastatic disease. The selective estrogen receptor modulator (SERM) lasofoxifene (laso) and selective estrogen receptor degrader (SERD) elacestrant (RAD1901) are chemically distinctive and show great promise in the ER-alpha mutant setting with potent anti-tumor effects and improved side effect profiles compared to the standard-of-care SERD fulvestrant (ICI). To elucidate the structural-transcriptional relationships of these ligands, we created a laso/RAD1901 chemical hybrid T6I-29 that demonstrated both canonical and unexpected therapeutic mechanisms of action. However, it possesses reduced anti-proliferative potency compared to ICI. We hypothesized that minor chemical changes to T6I-29 could improve potency while maintaining its favorable pharmaceutical profiles. To address this hypothesis, we performed quantum mechanical calculations of a series of T6I-derivatives. The addition of a methyl linker within the scaffold core significantly improved the torsion angle energies of the ligand binding pose. Multiple derivatives were synthesized based on these computations. The new compound T6I-B2 exerted profound anti-proliferative effects on breast cancer cells and adopted a unique ligand binding pose within the LBD. This approach shows that T6I-SERM potency can be improved by optimizing ligand torsion angle energies. Presentation: 6/3/2024

Induction of the TEAD Co-activator VGLL1 by Estrogen Receptor-Targeted Therapy Drives Resistance in Breast Cancer.

Resistance to endocrine therapies (ET) is common in estrogen receptor (ER) positive breast cancer, and most relapsed patients die with ET-resistant disease. While genetic mutations provide explanations for some relapses, mechanisms of resistance remain undefined in many cases. Drug-induced epigenetic reprogramming has been shown to provide possible routes to resistance. By analyzing histone H3 lysine 27 acetylation (H3K27ac) profiles and transcriptional reprogramming in models of ET resistance, we discovered that selective ER degraders (SERDs), such as fulvestrant, promote expression of VGLL1, a co-activator for TEAD transcription factors. VGLL1, acting via TEADs, promoted expression of genes that drive growth of fulvestrant-resistant breast cancer cells. Pharmacological disruption of VGLL1/TEAD4 interaction inhibited VGLL1/TEAD-induced transcriptional programs to prevent growth of resistant cells. EGFR was among the VGLL1/TEAD-regulated genes, and VGLL1-directed EGFR upregulation sensitized fulvestrant-resistant breast cancer cells to EGFR inhibitors. Taken together, these findings identify VGLL1 as a transcriptional driver in ET resistance and advance therapeutic possibilities for relapsed ER+ breast cancer patients.

Ionizable Drugs Enable Intracellular Delivery of Co-Formulated siRNA.

Targeting complementary pathways in diseases such as cancer can be achieved with co-delivery of small interfering ribonucleic acid (siRNA) and small molecule drugs; however, current formulation strategies are typically limited to one, but not both. Here, ionizable small molecule drugs and siRNA are co-formulatedin drug-rich nanoparticles. Ionizable analogs of the selective estrogen receptor degrader fulvestrant self-assemble into colloidal drug aggregates and cause endosomal disruption, allowing co-delivery of siRNA against a non-druggable target. siRNA is encapsulated in lipid-stabilized, drug-rich colloidal nanoparticles where the ionizable lipid used in conventional lipid nanoparticles is replaced with an ionizable fulvestrant analog. The selection of an appropriate phospholipid and formulation buffer enables endocytosis and potent reporter gene knockdown in cancer cells. Importantly, siRNA targeting cyclin E1 is effectively delivered to drug-resistant breast cancer cells, demonstrating the utility of this approach. This strategy opens the possibility of using ionizable drugs to co-deliver RNA and ultimately improve therapeutic outcomes.

Discovery of non-antiproliferative selective estrogen receptor degraders (SERDs) based on scaffold optimization of elacestrant

Elacestrant, the first oral selective estrogen receptor degrader (SERD), has been approved for ER positive breast cancer in 2023. Recent study showed that elacestrant has moderate pharmacokinetic property and the oral bioavailability is 11 %. In this study, we have performed docking analyses of elacestrant with different cytochrome P450 isoforms. The results indicated that tetrahydronaphthalene scaffold of elacestrant located closely to Heme iron center of P450s and might undergo rapid metabolism by CYP3A4. Therefore, we have changed the tertiary carbon atom to nitrogen atom of the scaffold to attenuate the metabolic effect. The most interesting finding is that compound B16 exhibited significant degradation of ERα at 5 μM but didn't show antiproliferative activity at high concentrations in MCF-7 and T47D cells. Compound B16 may serve as an ER probe to investigate ER status in ER positive breast cancer cells.

Molecular Modeling Studies of Similar Molecules to Selective Estrogen Receptor Degrader Elacestrant as Inhibitors of SARS-COV-2.

Coronavirus 2019 (COVID-19) is a disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) strain. Many anticancer compounds have been repurposed as effective anti-coronavirus agents and are currently in a clinical trial to be evaluated for treatment. Elacestrant is a novel selective estrogen receptor degrader (SERD). A fingerprint Tanimoto-based 2-dimensional similarity search was performed in the PubChem database using elacestrant as a prototype. The chemical compounds were downloaded, and virtual screening, molecular docking, and molecular dynamics were further used to identify the most active molecules in the binding pocket SARS-COV-2 main protease. Eight compounds with superior docking score, gscore, and glide binding energy were identified. Molecular dynamic simulations (MD) were performed at 100 ns to remove the false interactions between the receptor and the active ligands. The results showed that all the compounds displayed good stability. Further, the ADMET results showed that compounds CID58023104 was observed to be deemed a hit compound; hence, CID58023104 and could be optimize, derivatize, and explore for further development as an anti-coronavirus agent targeting SARS-COV-2 main protease.

Use of differential scanning calorimetry as a rapid, effective in-process check method for impurity quantitation of an early clinical batch of Giredestrant (GDC-9545)

Giredestrant (GDC-9545) is a selective estrogen receptor degrader (SERD) that was developed for treatment of ER+/HER2− metastatic breast cancer. An anhydrous crystalline tartrate salt was identified as the solid form suitable for clinical development. An early clinical batch of the active pharmaceutical ingredient (API)/drug substance failed to pass the GMP purity specifications owing to the presence of a substantial amount of high molecular weight impurities (oligomers), as determined by size exclusion chromatography. Several trial rework batches were manufactured using various re-slurry and recrystallization conditions to purge impurities in the drug substance to adhere to purity specifications. Based on the melting point depression of the API in presence of oligomers in these rework batches, a differential scanning calorimetry method was developed to quantify impurity content as a function of melting point onset of the API. This thermal analysis method was used as a surrogate for chromatography as a rapid, effective in-process check method for impurity quantitation to enable the timely release of the final reworked clinical batch. Post release, the % w/w oligomer value determined by calorimetry was in excellent agreement to that obtained by size exclusion chromatography.

Current and Novel Treatment Options in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer.

Metastatic breast cancer (mBC) remains an incurable disease, and most patients will experience disease progression during their treatment course. Although endocrine therapy remains the mainstay of treatment for hormone receptor-positive/human epidermal growth factor receptor 2-negative mBC, significant progress has been and continues to be made in the treatment of this BC subtype. The discovery of molecular markers, mutations in key cellular pathways, and genomic signatures have led to the development of novel and targeted agents, such as antibody-drug conjugates, oral selective estrogen receptor downregulators, and inhibitors of the PI3K/AKT/mTOR pathway. This has resulted in significant improvements in the survival and quality of life of patients. With the increasing number of treatment options for patients, appropriate drug sequencing remains a challenge. Treatment discussions should involve patient-physician shared decision making, with consideration of genomic data, previous lines of therapy, side effect profiles, and clinical trial enrollment.

OBHSA, a novel selective estrogen receptor degrader, overcomes tamoxifen resistance through cell cycle arrest and unfolded protein response-mediated apoptosis in breast cancer

Breast cancer (BC) is a highly heterogeneous tumor that has surpassed lung cancer as the most frequently diagnosed cancer in women. In clinical practice,the primary approach for treating estrogen receptor alpha (ERα)-positive BC is through endocrine therapy, which involves targeting the ERα using medications like tamoxifen and fulvestrant. However, the problem of de novo or acquired resistance poses a significant clinical challenge, emphasizing the critical need for the development of novel therapeutic strategies. In this regard, we have successfully designed and developed a novel selective estrogen receptor degrader (SERD) called OBHSA, which specifically targets and degrades ERα, demonstrating remarkable efficacy. Our findings revealed the effectiveness of OBHSA in inhibiting the proliferation of various BC cells, including both tamoxifen-sensitive and tamoxifen-resistant BC cells, indicating its great potential to overcome endocrine resistance. In terms of mechanism, we discovered that OBHSA overcame tamoxifen resistance through two distinct pathways. Firstly, OBHSA degraded cyclin D1 in an ERα-dependent manner, thereby blocking the cell cycle. Secondly, OBHSA induced an elevation in intracellular reactive oxygen species, triggering an excessive activation of the unfolded protein response (UPR) and ultimately leading to apoptotic cell death. In summary, our finding demonstrated that OBHSA exerts anti-tumor effects by inducing cell cycle arrest and UPR-mediated apoptosis. These findings hold promise for the development of novel therapeutic drugs targeting endocrine-resistant BC.

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

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. 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). 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.

Elacestrant in the treatment landscape of ER-positive, HER2-negative, ESR1-mutated advanced breast cancer: a contemporary narrative review.

Estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer with ESR1 mutations presents a significant therapeutic challenge due to its adaptive resistance mechanisms to chemotherapy, especially endocrine treatment. Elacestrant, a novel oral selective estrogen receptor degrader (SERD), has emerged as a promising agent in this treatment-resistant era. A comprehensive search was conducted on pivotal clinical trials, including the RAD1901-005 Trial, EMERALD TRIAL, ELIPSE, and ELEVATE, focusing on their methodologies, patient populations, treatment regimens, and outcomes. This narrative review describes the available preclinical and clinical evidence on elacestrant, focusing on its pharmacodynamics, pharmacokinetics, efficacy, and safety within the existing literature. Elacestrant has demonstrated excellent activity against ESR1 mutations associated with resistance to first-line endocrine therapies. Clinical trials have shown improved progression-free survival in patients with advanced ER+/HER2-, ESR1-mutated breast cancer. Safety profiles indicate a tolerable side effect spectrum consistent with other agents. Its oral bioavailability offers a convenient alternative to injectable SERDs, with potential implications for patient adherence and quality of life. The review also discusses the comparative efficacy of elacestrant relative to existing endocrine therapies and its possible use in combination regimens. Ongoing clinical trials assessing elacestrant and other SERDs will yield data that might aid clinicians in determining the optimal selection and order of endocrine treatment drugs for ER+ breast cancer. The integration of targeted and immunotherapeutic agents with traditional chemotherapy represents a pivotal shift in Breast Cancer treatment, moving towards more personalized and effective regimens.

A review of endocrine therapy for hormone-dependent breast cancer

Purpose of the study: to provide current data on pharmacotherapy of hormone-dependent breast cancer (hdBC) and to consider the feasibility of introducing new hormone therapy drugs for breast cancer into clinical practice. Material and Methods. We analyzed 80 publications available Pubmed, Springer, Cochrane Library, etc. concerning the study of pharmacological characteristics of various groups of drugs for the treatment of hdBC, of which 49 were included in this review. Results. Currently, there are several approaches to the treatment of hdBC. Selective estrogen receptor modulators and aromatase inhibitors are the most studied and frequently used drugs. The cyclin-dependent kinase 4/6 inhibitors can be present in both the first- and second-line therapy. Currently, close attention is paid to the development of new drugs based on genomic profiling of the tumor, which is the standard of treatment for hdBC, and contributes to the personalization of therapy. Conclusion. Further development of drugs holds great promise for increasing overall survival and more accurate prognosis, response to conventional systemic therapy, and individualization of pharmacotherapy for hdBC. However, further research and development of new drugs is required. In this regard, the introduction of oral selective estrogen receptor degraders into practice and the development of new drugs that block estrogen-dependent and independent signaling to estrogen receptors are the most promising trends.

The anti-aromatase and anti-estrogenic activity of plant products in the treatment of estrogen receptor-positive breast cancer

Despite being the focal point of decades of research, female breast cancer (BC) continues to be one of the most lethal cancers in the world. Given that 80 % of all diagnosed BC cases are estrogen receptor-positive (ER+) with carcinogenesis driven by estrogen-ERα signalling, current standard of care (SOC) hormone therapies are geared towards modulating the function and expression levels of estrogen and its receptors, ERα and ERβ. Currently, aromatase inhibitors (AIs), selective ER modulators (SERMs) and selective ER degraders (SERDs) are clinically prescribed for the management and treatment of ER+ BC, with the anti-aromatase activity of AIs abrogating estrogen biosynthesis, while the anti-estrogenic SERMs and SERDs antagonise and degrade the ER, respectively. The use of SOC hormone therapies is, however, significantly hampered by the onset of severe side-effects and the development of resistance. Given that numerous studies have reported on the beneficial effects of plant compounds and/or extracts and the multiple pathways through which they target ER+ breast carcinogenesis, recent research has focused on the use of dietary chemopreventive agents for BC management. When combined with SOC treatments, several of these plant components and/or extracts have demonstrated improved efficacy and/or synergistic impact. Moreover, despite a lack of in vivo investigations, plant products are generally reported to have a lower side-effect profile than SOC therapies and are therefore thought to be a safer therapeutic choice. Thus, the current review summarizes the findings from the last five years regarding the anti-aromatase and anti-estrogenic activity of plant products, as well as their synergistic anti-ER+ BC effects in combination with SOC therapies.

Mass Balance, Metabolic Pathways, Absolute Bioavailability, and Pharmacokinetics of Giredestrant in Healthy Subjects.

Giredestrant is a potent and selective small-molecule estrogen receptor degrader. The objectives of this study were to assess the absolute bioavailability (aBA) of giredestrant and to determine the mass balance, routes of elimination, and metabolite profile of [14C]giredestrant. In part 1 (mass balance), a single 30.8-mg oral dose of [14C]giredestrant (105 µCi) was administered to women of nonchildbearing potential (WNCBP; n = 6). The mean recovery of total radioactivity in excreta was 77.0%, with 68.0% of the dose excreted in feces and 9.04% excreted in urine over a 42-day sample collection period. The majority of the circulating radioactivity (56.8%) in plasma was associated with giredestrant. Giredestrant was extensively metabolized, with giredestrant representing only 20.0% and 1.90% of the dose in feces and urine, respectively. All metabolites in feces resulted from oxidative metabolism and represented 44.7% of the dose. In part 2 (aBA), WNCBP (n = 10) received an oral (30-mg capsule) or intravenous (30-mg solution) dose of giredestrant. The aBA of giredestrant after oral administration was 58.7%. Following the intravenous dose, giredestrant had a plasma clearance and volume of distribution of 5.31 L/h and 266 L, respectively. In summary, giredestrant was well tolerated, rapidly absorbed, and showed moderate oral bioavailability with low recovery of the dose as parent drug in excreta. Oxidative metabolism followed by excretion in feces was identified as the major route of elimination of giredestrant. SIGNIFICANCE STATEMENT: This study provides definitive insight into the absorption, distribution, metabolism, and excretion of giredestrant in humans. The results show that giredestrant exhibits low clearance, a high volume of distribution, and moderate oral bioavailability in humans. In addition, the data show that oxidative metabolism followed by excretion in feces is the primary elimination route of giredestrant in humans. These results will be used to further inform the clinical development of giredestrant.

A window-of-opportunity (WOO) trial of giredestrant +/- LHRHa vs anastrozole+LHRHa in premenopausal women with ER+/HER2- early breast cancer (EBC; IBCSG 67-22; PREcoopERA).

TPS628 Background: Adjuvant endocrine therapy (ET) for premenopausal women with ER+/HER2- EBC often includes ovarian function suppression (OFS) via a GnRH or LHRH agonist (LHRHa) plus an aromatase inhibitor (AI) or tamoxifen. Younger age is associated with lower rates of ET adherence indicating side effects are less acceptable to these women. The development of drug regimens without OFS are clearly an unmet medical need in this setting. New oral selective ER degraders (SERDs) are emerging as potentially useful ETs in the (neo)adjuvant settings. Giredestrant is an efficient and potent SERD and a full antagonist, which translates into better anti-proliferation activity than known SERDs. PREcoopERA is a WOO trial aiming to determine, among premenopausal women with ER+/HER2- EBC: if giredestrant+LHRHa provides greater anti-proliferative activity than anastrozole+LHRHa; and if giredestrant without LHRHa provides similar (non-inferior) anti-proliferative activity to giredestrant+LHRHa. Results would provide rationale for subsequent (neo)adjuvant clinical trials. Methods: PREcoopERA (NCT05896566) is a randomized, open-label, 3-arm, WOO trial evaluating the anti-proliferative activity and safety of the oral SERD giredestrant +/- LHRHa triptorelin, as compared to the AI anastrozole + triptorelin. Eligible are premenopausal women with untreated ER+/HER2- operable stage I-III (excl. T4) EBC, with Ki-67 ≥10%. 220 women will be randomized in 2:2:1 ratio to giredestrant (30 mg/d po for 4 weeks until rebiopsy) + triptorelin (3.75 mg IM on D1); giredestrant alone; or anastrozole (1 mg/d po) + triptorelin. Rebiopsy is planned for D29, either during primary surgery or standalone procedures. The primary endpoint is change in Ki-67 labeling index between pre-treatment diagnostic tumor biopsy and post-treatment rebiopsy, as assessed by the IBCSG Pathology Office. Sample size of 80:80:40 randomized women are planned to test superiority of 4 weeks giredestrant+triptorelin vs anastrozole+triptorelin to reduce Ki-67 (hypothesized percentage changes -80% vs -65%) and to test non-inferiority of 4 weeks giredestrant vs giredesrant+triptorelin (within 10% as non-inferiority margin). The trial was activated on 9 October 2023. The first woman was enrolled on 25 January 2024. Clinical trial information: NCT05896566 .

Artificial intelligence (AI) –powered H&E whole-slide image (WSI) analysis to predict recurrence in hormone receptor positive (HR+) early breast cancer (EBC).

571 Background: The recurrence risk (RS) based on transcriptomic profiles or Ki-67 level of HR+ EBC has been used for adjuvant treatment decisions and may also aid selecting patients who could benefit from novel treatments including CDK4/6 inhibitor or oral selective estrogen receptor degraders (SERDs). Artificial intelligence-powered H&E whole slide image (WSI) models can be a practical approach for this biomarker without the need of additional tissue samples. We developed ML-based models of histopathologic features from an H&E WSI to approximate RS of 21-gene assay (OncotypeDx) using various algorithms of different complexities. Methods: The development dataset was composed of 1,009 cases from TCGA-BRCA with gene expression profiles and 483 EBC cases from Samsung Medical Center with RS results. The prediction model was developed in two-stages. First, Lunit SCOPE, an AI-powered H&E WSI analyzer, detects various cell types and segments tissue areas resulting in various cell densities in tissue regions of interest. Next, four traditional ML models were applied on top of the first stage results. In addition, a deep learning model based on multiple instance learning (DL-MIL) was developed using three features: a supervised convolutional neural network, a supervised cell detection model, and an AI-based pathology profiling analyzer, for extracting semantic contents. The model performance was validated using two independent EBC test sets: 248 cases for comparison with the RS results (set 1), and 708 cases with DFS (set 2). Results: The cross-validation performance of the four traditional ML algorithms had area under the curve of receiver operating characteristics curve (AUROC) ranging from 0.728 to 0.779, where mitotic cell density, tumor cell density, and fibroblast density in cancer area were the variables with the highest importance for all four models. The DL-MIL model had cross validation performance of AUROC 0.831. In test set 1, DL-MIL model showed the highest discrimination with AUROC of 0.828 compared to traditional ML models where logistic regression showed the highest discrimination with AUROC of 0.786 (Table). The DL-MIL model showed the highest performance among the models to predict DFS with hazard ratio (HR) of 2.48 (1.47-4.18). Conclusions: Histopathomic models can accurately predict the RS of high risk as well as poor DFS from only H&E WSIs. These AI models can be a practical tool for treatment selection including emerging drugs such as SERDs. [Table: see text]

Preliminary results from a phase 1 study of AC699, an orally bioavailable chimeric estrogen receptor degrader, in patients with advanced or metastatic breast cancer.

3074 Background: Endocrine therapy is a critical component of treatment for over 200,000 patients diagnosed yearly with estrogen receptor positive (ER+)/HER2- breast cancer. Although selective ER degraders (SERDs) have improved progression-free survival in this patient population, as monotherapy they have shown very limited overall response rates (ORR). AC699 is a novel chimeric degrader that binds, ubiquitinates and degrades ERα by bringing it into close proximity with an E3 ligase. This mechanism of action may result in greater specificity and more complete target blockade compared to SERDs. Initial results from the ongoing first-in-human dose escalation study of AC699 (NCT05654532) are presented here. Methods: The study employed a 3+3 design, with the option of adding backfill patients to each cohort cleared and deemed safe. Patients must have had locally advanced or metastatic ER+/HER2- breast cancer and received at least 2 prior lines of endocrine treatment, or at least 1 prior line if combined with a CDK4/6 inhibitor. AC699 was administered orally once daily in 28-day cycles. Tumor responses were assessed every 2 cycles using RECIST v1.1 criteria. The relationship between ESR1 mutational status and anti-tumor activity was investigated as an exploratory analysis. Results: A total of 22 patients had received AC699 in 3 dose cohorts (100, 200 and 300 mg) at the time of data cutoff. The median age was 61 years and the median lines of prior therapy was 5 (range 2-10). Prior treatments included CDK4/6 inhibitor (100%), aromatase inhibitor (91%), fulvestrant (82%), novel oral SERD or covalent antagonist (SERCA) (23%), and ER chimeric degrader (14%). Eighteen patients had measurable disease while 4 had bone lesions only. There were no dose-limiting toxicities, dose reductions or discontinuations for treatment-related AEs, and the maximum tolerated dose was not reached. The most common treatment-emergent AEs were fatigue (23%), dehydration (18%) and nausea (18%). All treatment-related AEs were Grade 1 or 2, including nausea (18%) and hot flushes (14%). Fifteen patients had at least 1 scan before the data cutoff date and of these, 3 were not evaluable for ORR due to having bone lesions only. Among the 12 evaluable patients, 4 (33%) achieved partial response: 3 confirmed and one unconfirmed. The clinical benefit rate (CBR) which also includes patients with stable disease ≥24 weeks was 42% (5/12). In the subgroup of evaluable patients harboring a confirmed ESR1 mutation, the ORR was 67% (4/6), the CBR was 83% (5/6) and the median time on treatment was 168 days (range 56-336), with 4 of 7 patients still receiving AC699. Conclusions: Preliminary data from the ongoing phase 1 trial evaluating AC699 indicate promising safety, tolerability, and anti-tumor activity, at doses up to 300 mg orally once daily. A phase 2 study will begin enrolling in early 2024. Clinical trial information: NCT05654532 .

Genomic alterations (GA) in ESR1, PIK3CA, AKT1, and PTEN in HR(+)HER2(-) patients (pts) with metastatic breast cancer (MBC): Co-occurrence and prevalence along treatment course.

1060 Background: The standard of care for HR(+) HER2(-) MBC is evolving with new biomarker-guided drugs, including novel selective estrogen receptor degraders (SERDs) for pts with ESR1 mutations (mut) and PIK3CA and AKT inhibitors for pts with alterations in the PI3K pathway (PIK3CA, AKT1, and PTEN). This study aimed to evaluate the co-occurrence and the prevalence of these GA in different metastatic lines of therapy in real-world practice for MBC. Methods: This study included pts with HR(+) HER2(-) MBC who underwent genomic testing using Foundation Medicine tissue or liquid comprehensive genomic profiling assays, with specimens collected within 60 days of therapy initiation. Clinical data were obtained by the nationwide (US-based) de-identified Flatiron Health and Foundation Medicine real-world clinicogenomic breast cancer database (FH-FMI CGDB), originated from ~280 US cancer clinics (~800 sites of care) between 01/2011-06/2023. The prevalence of ESR1mut, PIK3CAmut, AKT1, PTENmut, and PTEN copy loss were calculated in tissue (TBx) and liquid biopsies (LBx) collected at time of 1st, 2nd, and 3rd lines of therapy. The co-occurrence of GA in TBx was evaluated. Results: Among patients with a TBx collected around therapy initiation (n=2,536), 81.5% (2,066) was collected at 1st, 10.2% (258) at 2nd, and 8.3% (212) at 3rd line. Among patients with a LBx collected around therapy initiation (n=545), 47% (256) was collected at 1st, 33.2% (181) at 2nd, and 19.8% (108) at 3rd line. In TBx, the prevalence of GA detected in 1st, 2nd, and 3rd lines were 58.6% (1,210), 67.4% (174), and 71.2% (151), respectively. In LBx, the prevalence was 42.7% (121), 65.7% (119), and 60.1% (65), respectively. Among LBx with tumor fraction ³1%, the prevalence was 67.9% (74/109), 89.1% (81/91), and 84.3% (43/51). Among patients with a GA detected in TBx 1st (n=1,210), 2nd (n=174), and 3rd (n=151) lines, both ESR1mut and a PIK3 pathway GA was detected in 7.4% (90), 12.1% (21), and 23.8% (36), respectively. Conclusions: In our dataset, 42-59% of patients with HR(+) HER2(-) MBC have at least one GA detected by TBx or LBx in 1st line, with prevalence increasing in later lines of therapy to 60-71% due to acquisition of an ESR1mut. PTEN copy loss is detected at much higher rates in TBx than LBx, consistent with the known inherent limitations of ctDNA testing. Serial genomic testing with LBx with reflex TBx if alterations are not identified should strongly be considered with the recent approvals of several molecularly targeted agents for HR(+) HER2(-) MBC. [Table: see text]