Estrogen Receptor Degrader Research Articles

Abstract C032: The impact of neoadjuvant endocrine therapy (NET) in ER+ breast cancer tumor microenvironment and metastasis

Abstract Breast cancer is the most common cancer in women worldwide and the second leading cause of death. The Estrogen Receptor positive (ER+) subtype constitutes approximately 80% of the yearly 250,000 breast cancer diagnoses in the US. Anti-estrogen endocrine therapy, administered either pre- or post-operatively, is the cornerstone treatment for all stages of breast cancer. Pre- operative or neoadjuvant endocrine therapy (NET) reduces pre-surgical tumor burden, improves surgical outcome, and provides prognostic information. Although the treatment often has a favorable initial response, about 20% of patients eventually develop resistance and recurrent disease, even decades after the primary diagnosis.We hypothesized that resistance in NET is mediated through pro-metastatic changes in the tumor microenvironment affecting either (i) dissemination machinery or (ii) cancer cell phenotype.The main mode of breast cancer hematogenous dissemination to distant sites is through intravasation portals called Tumor Microenvironment of Metastasis (TMEM) doorways. Each TMEM doorway consists of a tumor cell overexpressing the actin-regulatory protein MENA, a Tie2high/ VEGFAhigh macrophage and an endothelial cell, all in direct contact. TMEM doorway activity leads to vascular opening events, during which tumor cells located in areas around TMEM doorways intravasate and disseminate to secondary sites. Therefore, to investigate the impact of NET on cancer cell dissemination, we evaluated its effect on (i) TMEM doorway score (the number of TMEM doorways per tissue area), (ii) TMEM doorway opening, (iii) the number of circulating tumor cells and (iv) the number of disseminated tumor cells. We used the orthotopic MCF7 breast cancer xenograft model grown in NOD/SCID mice and tested two drugs widely used in NET, Fulvestrant (a Selective Estrogen Receptor Degrader) and Tamoxifen (a Selective Estrogen Receptor Modulator). NET did not affect the TMEM doorway score, TMEM doorway activity, the number of CTCs or the number of DTCs. We are now focused on evaluating the effect of NET on the density of cancer cells which are upregulated in programs of invasion, stemness, and dormancy. This “Triple Threat Phenotype (TTP)” gives tumor cells an enhanced ability to disseminate to and colonize distant organs. To this effect we will stain primary MCF7 tumors from NET and vehicle-treated mice for markers of invasiveness (MENA), stemness (SOX9) and dormancy (NR2F1). Detecting any changes in the phenotype of metastatic tumor cells following NET will help us understand underlying mechanisms of endocrine therapy resistance and may lead to new therapeutic targets and improve patient outcomes. Citation Format: Anastasia Aristoteleia Chondronikola, Dimitra Anastasiadou, Aliona Zintiridou, Camille L. Duran, Nicole Barth, Burcu Karadal-Ferrena, Erika Pereira-Zambalde, Lina Ariyan, Suryansh Shukla, George S. Karagiannis, David Entenberg, John S. Condeelis, Maja H. Oktay. The impact of neoadjuvant endocrine therapy (NET) in ER+ breast cancer tumor microenvironment and metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C032.

Insulin-like growth factor-binding protein-3 is induced by tamoxifen and fulvestrant and modulates fulvestrant response in breast cancer cells

IntroductionInsulin-like growth factor binding protein-3 (IGFBP-3) exerts varying effects on estrogen receptor alpha (ERα)-positive and triple-negative breast cancer (TNBC) cells. In ERα-positive cells, IGFBP-3 is antiproliferative and proapoptotic. In contrast, IGFBP-3 stimulates proliferation in triple-negative breast cancer (TNBC) cells via EGFR activation.MethodsTo identify potential mechanisms that underlie the opposing effects of IGFBP-3 on these two breast cancer subtypes, IGFBP-3 expression was determined in cell line models of both ERα-positive breast cancer and TNBC, and cells were treated with antiestrogens tamoxifen and fulvestrant. Results and discussionMCF-7 and T-47D cells expressed low levels of IGFBP-3 when compared to MDA-MB-231 and MDA-MB-468 cells. MCF-7 cells with acquired resistance to the selective estrogen receptor degrader fulvestrant expressed high IGFBP-3 and MCF-7 cells with constitutive IGFBP-3 expression were fulvestrant resistant. IGFBP-3 expression was increased in all cell lines upon treatment with fulvestrant or the selective estrogen receptor modulator tamoxifen and both fulvestrant and tamoxifen increased TNBC cell proliferation. Further, IGFBP-3 expression was increased by treatment with the GPER1 agonist G-1 and attenuated upon treatment with P17, a YAP/TAZ inhibitor. These data suggest that IGFBP-3 modulates breast cancer cells and is a mediator of breast cancer cell response to fulvestrant and tamoxifen.

Development of a Commercial Manufacturing Process for Vepdegestrant, an Orally Bioavailable PROTAC Estrogen Receptor Degrader for the Treatment of Breast Cancer

Development of a Commercial Manufacturing Process for Vepdegestrant, an Orally Bioavailable PROTAC Estrogen Receptor Degrader for the Treatment of Breast Cancer

Camizestrant, a next-generation oral SERD, versus fulvestrant in post-menopausal women with oestrogen receptor-positive, HER2-negative advanced breast cancer (SERENA-2): a multi-dose, open-label, randomised, phase 2 trial

Resistance to endocrine therapies in hormone receptor-positive breast cancer is challenging. We aimed to assess the next-generation oral selective oestrogen receptor degrader (SERD) and complete oestrogen receptor antagonist, camizestrant, versus the first-approved SERD, fulvestrant, in post-menopausal women with oestrogen receptor-positive, HER2-negative, advanced breast cancer. SERENA-2 is an open-label, randomised, phase 2 trial that is being conducted at 74 study centres across Asia, Europe, the Middle East, and North America. Female patients aged 18 years or older who were post-menopausal with histologically or cytologically confirmed metastastic or locoregional oestrogen receptor-positive, HER2-negative breast cancer, an Eastern Cooperative Oncology Group or WHO performance status of 0 or 1, and disease recurrence or progression on at least one line of endocrine therapy, and no more than one previous endocrine therapy in the advanced setting. Patients were initially randomly assigned (1:1:1:1) to receive oral camizestrant once daily at 75 mg, 150 mg, or 300 mg (until the 300 mg group was closed), or fulvestrant intramuscularly at 500 mg (per label). Randomisation was managed through an interactive web-based system and stratified by previous treatment with CDK4/6 inhibitors and presence of liver and/or lung metastases. The primary objective was to determine clinical efficacy of camizestrant versus fulvestrant at each dose level using the primary endpoint of investigator-assessed progression-free survival, per Response Evaluation Criteria in Solid Tumours (version 1.1), assessed by intention to treat in all randomly assigned patients (full analysis set). No formal statistical comparison for the efficacy analysis of the camizestrant 300 mg dose versus fulvestrant was to be performed. Safety analyses included all randomly assigned patients who received at least one dose of study treatment. This study is registered with ClinicalTrials.gov, NCT04214288, and is ongoing. Between May 11, 2020, and Aug 10, 2021, 240 patients were randomly assigned to receive camizestrant 75 mg (n=74), 150 mg (n=73), 300 mg (n=20), or fulvestrant (n=73), and were included in the full analysis set. All patients received at least one dose of study drug. Median follow-up was 16·6 months (IQR 12·9-19·4) for the camizestrant 75 mg group, 16·3 months (12·9-18·3) for the camizestrant 150 mg group, and 14·7 months (12·7-20·1) for the fulvestrant 500 mg group. Median progression-free survival was 7·2 months (90% CI 3·7-10·9) with camizestrant 75 mg, 7·7 months (5·5-12·9) with camizestrant 150 mg, and 3·7 months (2·0-6·0) with fulvestrant. The hazard ratio for camizestrant 75 mg versus fulvestrant was 0·59 (90% CI 0·42-0·82; p=0·017), and the hazard ratio for camizestrant 150 mg versus fulvestrant was 0·64 (0·46-0·89; p=0·0090). Treatment-related adverse events occurred in 39 (53%) of 74 patients in the camizestrant 75 mg group, 49 (67%) of 73 patients in the camizestrant 150 mg group, 14 (70%) of 20 patients in the camizestrant 300 mg group, and 13 (18%) of 73 patients in the fulvestrant group. No single grade 3 or worse treatment-emergent adverse event occurred in more than two (3%) patients in any group. Serious treatment-emergent adverse events occurred in six (8%) patients in the camizestrant 75 mg group, seven (10%) patients in the camizestrant 150 mg group, two (10%) patients in the camizestrant 300 mg group, and four (5%) patients in the fulvestrant group. No treatment-related deaths occurred. Camizestrant at 75 and 150 mg showed a significant benefit in progression-free survival versus fulvestrant. These results support further development of camizestrant for the treatment of oestrogen receptor-positive, HER2-negative breast cancer. AstraZeneca.

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.

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.

637P AC699, a novel chimeric estrogen receptor degrader, in a phase I study in breast cancer

637P AC699, a novel chimeric estrogen receptor degrader, in a phase I study in breast cancer

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.

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.

Estrogen Receptor Blockade Potentiates Immunotherapy for Liver Metastases by Altering the Liver Immunosuppressive Microenvironment.

The immune microenvironment of the liver plays a major role in controlling the expansion of hepatic metastases and is regulated by estrogen. We show that treatment of tumor-bearing mice with an estrogen receptor degrader potentiated an anti-metastatic effect of immunotherapy. Our results provide mechanistic insight into clinical findings and a rationale for evaluating the efficacy of combination anti-estrogen and immunotherapy for prevention and/or treatment of hepatic metastases in female patients.

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.

Novel Treatment Strategies for Hormone Receptor (HR)-Positive, HER2-Negative Metastatic Breast Cancer.

Estrogen receptor (ER)-positive breast cancer (BC) is the most common BC subtype. Endocrine therapy (ET) targeting ER signaling still remains the mainstay treatment option for hormone receptor (HR)-positive BC either in the early or in advanced setting, including different strategies, such as the suppression of estrogen production or directly blocking the ER pathway through SERMs-selective estrogen receptor modulators-or SERDs-selective estrogen receptor degraders. Nevertheless, the development of de novo or acquired endocrine resistance still remains challenging for oncologists. The use of novel ET combined with targeted drugs, such as cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, has significantly improved long-term outcome rates, thus changing the therapeutic algorithm for metastatic BC (MBC) and recently the therapeutic strategy in the adjuvant setting for early high-risk BC. Eluding the resistance to CDK4/6 inhibitors combined with ET is currently an unmet medical need, and there is disagreement concerning the best course of action for patients who continue to progress after this combination approach. Genetic changes in the tumor along its growth uncovered by genomic profiling of recurrent and/or metastatic lesions through tumor and/or liquid biopsies may predict the response or resistance to specific agents, suggesting the best therapeutic strategy for each patient by targeting the altered ER-dependent pathway (novel oral SERDs and a new generation of anti-estrogen agents) or alternative ER-independent signaling pathways such as PI3K/AKT/mTOR or tyrosine kinase receptors (HER2 mutations or HER2 low status) or by inhibiting pathways weakened through germline BRCA1/2 mutations. These agents are being investigated as single molecules and in combination with other target therapies, offering promising weapons to overcome or avoid treatment failure and propose increasingly more personalized treatment approaches. This review presents novel insights into ET and other targeted therapies for managing metastatic HR+/HER2- BC by exploring potential strategies based on clinical evidence and genomic profiling following the failure of the CDK4/6i and ET combination.

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.