Endocrine Therapy In ER Research Articles

65 (PB053): Effect of tasurgratinib as an orally available FGFR1-3 inhibitor on resistance to a CDK4/6 inhibitor and endocrine therapy in ER(+)/HER2 (-) breast cancer preclinical models

65 (PB053): Effect of tasurgratinib as an orally available FGFR1-3 inhibitor on resistance to a CDK4/6 inhibitor and endocrine therapy in ER(+)/HER2 (-) breast cancer preclinical models

224 (PB212): AI-enhanced high-content imaging to identify effective compound combinations with CDK4/6 inhibitor and endocrine therapy in ER+ HER2- breast cancer

224 (PB212): AI-enhanced high-content imaging to identify effective compound combinations with CDK4/6 inhibitor and endocrine therapy in ER+ HER2- breast cancer

Quantitative evaluation of the efficacy and safety profiles of two types of targeted inhibitors combined with endocrine therapy in ER+/HER2- metastatic breast cancer.

The aim of this study was to quantitatively compare the efficacy and safety of CDK4/6 inhibitors and PI3K/AKT/mTOR inhibitors for ER+/HER2- metastatic breast cancer. A parametric survival function was used to analyze the time course of overall survival (OS) and progression-free survival (PFS). The objective response rate (ORR) and the incidence of any grade and grade 3-4 adverse events were summarized using the random-effects model of a single-arm meta-analysis. This study included 44 arms from 48 publications, with a total sample size of 7881 patients. Our study revealed that CDK4/6 inhibitors had a median OS of 40.7 months, a median PFS of 14.8 months, and an ORR of 40%, whereas PI3K/AKT/mTOR inhibitors had a median OS of 29.8 months, a median PFS of 8.3 months, and an ORR of 20%. Additionally, this study also found that the proportion of patients with visceral metastases and specific endocrine therapy used in combination significantly impact OS and PFS. In terms of adverse events, CDK4/6 inhibitors exhibited a relatively high incidence of hematological adverse events. Our study provides solid quantitative evidence for the first-line recommendation of CDK4/6 inhibitors combined with endocrine therapy for ER+/HER2- metastatic breast cancer in clinical guidelines.

Single-cell and bulk sequencing analysis to evaluate the oncogenic role of PDE3A in pan-cancer and validation in breast cancer.

e15128 Background: PDE3A is involved in critical physiological processes through the hydrolysis of cycle AMP (cAMP) and GMP (cGMP). Its role in the occurrence and progression of cancer has recently attracted attention, but carcinogenic mechanism in pan-cancer has not been fully elucidated. Methods: We explored the expression, prognostic and diagnostic value, mutation, methylation, immune infiltration, and signaling pathway enrichment analysis of PDE3A in pan-cancer by combining multiple bioinformatics databases and single-cell sequencing analysis. Furthermore, we verified the protein and mRNA expression levels of PDE3A and investigated its oncogenic role in the progression of breast cancer (BRCA). Results: PDE3A was expressed at lower levels than normal tissues in most cancers and showed a wonderful prognostic value. PDE3A was strongly correlated with immune cells, especially cancer-associated fibroblast (CAF), and was involved in various vital signaling pathways. Furthermore, PDE3A could facilitate BRCA progression by promoting cells invasion and migration, and it may be associated with the efficacy of endocrine therapy in ER+ BRCA. Conclusions: We provided new insights into the carcinogenic effect of PDE3A in pan-cancer. PDE3A may be a potential biomarker for cancer diagnosis and prognosis, and it is also a promising target for cancer immunotherapy.

Abstract PO5-23-10: Development of a long-term in vitro assay able to identify compounds that can overcome resistance to CDK4/6 inhibitor plus endocrine therapy in ER+ HER2- breast cancer

Abstract CDK4/6 inhibitor plus endocrine therapy (ET) has emerged as the standard of care first line therapy in ER+ HER2- breast cancer. While this combination has shown the ability to extend overall survival, nearly all patients acquire resistance and progress after 2-3 years. Subsequently, interest has turned to identifying a third partner compound that can be integrated into the CDK4/6i plus ET backbone regimen with the goal of overcoming resistance and driving a deeper response. However, a comprehensive assay-based workflow proficient in identifying compounds with the most promising potential is lacking. To fill this need, we set out to develop a high-throughput in vitro assay with relevant multi-faceted readouts to assess the efficacy of potential triplet combinations using 12 human ER+ breast cancer lines. For this assay, cells were engineered to express nuclear RFP to enable accurate cell counting using basic imaging techniques in 384 well plates. Each third partner compound was tested at two different doses and, in addition to the triplet combination (CDK4/6i + ET + third partner), single agent as well as double agent combinations were investigated. The assay was imaged and re-dosed every 5 days until day 15. On day 15, the compounds were washed out and the cells underwent a 25-day drug holiday to monitor relapse. Duplicate plates of all conditions were monitored and imaged every two hours for 24 hours for live cell staining of apoptosis markers. Additional duplicate plates were fixed and stained on days 5 and 15 for markers of senescence and cell cycle. Images were subsequently fed into a python-based algorithm to determine the percentage of cell population expressing the various markers and phenotypic correlates were extracted. We are looking for triplet combinations that induce a deeper cell cycle arrest, senescence, and/or cell death compared with the CDK4/6 inhibitor plus ET only treatment. Our drug holiday results will help elucidate the treatments able to continue to induce suppression once washed out, indicating treatment options that may induce long-lasting, possibly irreversible effects on the cells. Finally, by extracting phenotypic correlates from brightfield images we hope to cluster the various compounds in their effects across cell lines of diverse backgrounds to help understand the best way to benefit multiple patient populations. Overall, the assay will be able to identify and differentiate various therapeutic combinations based on cell count, senescence, and cell death. The format of this assay enables depth of analysis not accessible using other techniques such as FACS, including full dose-response curves, combination matrices, and longitudinal analyses. Additionally, the assay can be modified to evaluate any number of cellular markers and can be useful across a number of applications. The approach developed here will be foundational in discovering next-step strategies for patients with therapy resistance. Citation Format: Stephanie Kronstadt, Neil Umbreit, Matt Niederst, Rens Janssens. Development of a long-term in vitro assay able to identify compounds that can overcome resistance to CDK4/6 inhibitor plus endocrine therapy in ER+ HER2- breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-23-10.

Abstract PO4-04-01: Antitumor activity and safety of sacibertinib (Hemay022) in combination with endocrine therapy in patients with ER and HER2 both positive metastatic breast cancer: A phase Ib study

Abstract Abstract PURPOSE Sacibertinib (Hemay022) is a novel irreversible tyrosine kinase inhibitor (TKI) blocking epidermal growth factor receptor and human epidermal growth factor receptor 2 (HER2). This study aimed to explore the safety and efficacy of sacibertinib plus endocrine therapy in patients with estrogen receptor-positive ( PATIENTS AND METHODS Using a phase 1b 3+3 dose escalation and expansion study design, patients with ER+/HER2+ MBC were treated with sacibertinib (200mg-500mg daily) plus endocrine therapy including exemestane, letrozole, fulvestrant. The safety, pharmacokinetic and clinical efficacy, including objective response rate (ORR), clinical benefit rate (CBR), disease control rate (DCR) and progression-free survival (PFS) were assessed. RESULTS A total of 55 ER+/HER2+ MBC patients pretreated with chemotherapy and anti-HER2 therapy were enrolled in the study between March, 2018 and July, 2021. The incidence of ORR ranged from 17.6% to 42.9%, DCR ranged from 63.0% to 86.8%, CBR ranged from 42.3% to 69.7%, and the overall median PFS was 9.0 (95% CI, 5.5 ~ 11.00) months. In the 400 mg Sacibertinib plus exemestane cohort (N = 18), ORR was 38.9% (7/18), DCR was 72.2%(13/18), CBR was 66.7%(12/18), and median PFS was 8.9 months; In the 500 mg Sacibertinib plus exemestane cohort (N = 12), ORR was 25.0%(3/12), DCR was 100.0%(12/12), CBR was 50.0%(6/12), and median PFS was 9.0 months. The ORR, CBR, and DCR were better in the 400 mg and above dose cohorts than in the 200 mg and 300 mg cohorts. The DCR of the 500 mg combined with exemestane cohort was better than that of the other dose cohorts. Sacibertinib plus endocrine therapy was well-tolerated without dose-limiting toxicities. The most frequent grade 3 adverse events included diarrhoea (9.1%), leucopenia(5.5%), neutropenia (3.6%). One (1.8%) had grade 4 hydropericardium. CONCLUSION Sacibertinib plus endocrine therapy had a favorable safety profile and antitumor activity in patients with ER+/HER2+ MBC, 400-500mg daily showed more efficacy, supporting further assessment in randomized studies. This figure showed response of Sacibertinib plus endocrine therapy in ER+/HER2+ metastatic breast cancer. Citation Format: Hui-Ping Li, Qingyuan Zhang, Ruyan Zhang, Yaxin Liu, Xianjun Hu. Antitumor activity and safety of sacibertinib (Hemay022) in combination with endocrine therapy in patients with ER and HER2 both positive metastatic breast cancer: A phase Ib study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-04-01.

Abstract PO4-01-09: The Prognostic Impact of Adjuvant Endocrine Therapy by Age for Patients with Small Estrogen Receptor-Positive (ER+), Human Epidermal Growth Factor 2 Negative (HER2-) Breast Cancer

Abstract Backgrounds: We previously reported an analysis of the impact of adjuvant endocrine therapy (ET) for patients with ER+ and HER2- T1a/bN0M0 breast cancer (BC) at ASCO 2023 (Abstract #538). For the whole cohort, adjuvant ET significantly reduced distant metastases, but the absolute overall survival (OS) difference was small. The presence of medical comorbidities related to treatment toxicity and the estimated life-expectancy differ based on age, affecting the clinical impact of ET. There may be settings where comorbidities result in a sufficiently short, expected OS such that the benefit of ET will not outweigh risk. In multivariate analysis, age (<55 vs >55) was not an independent risk factor for distant metastasis. Here we evaluate the impact of adjuvant ET for ER+/HER2- T1a/bN0M0 breast cancer by age-specific subgroups, focusing on younger (< 40) and older (>65) population. Methods: This is a multicenter retrospective cohort study that evaluated the impact of adjuvant ET for patents with ER+/HER2- T1a/bN0M0 BC who underwent primary breast cancer surgery between 2008 and 2012 in 47 institutes of the Japan Clinical Oncology Group (JCOG). We analyzed distant metastatic-free survival (DMFS) and OS using Kaplan-Meier estimates with log-rank test in patients treated with and without ET in each of three age-specific subgroups (<40, 41-64 and 65> years of age). Results: Median follow-up was 9.2 years; the median age of the entire cohort was 55 years. Of 4756 eligible patients, 417 patients were age 65 (1025 (82%) with ET and 227 (18%) without ET). Of all 3989 (84%) patients with ET (2053 (51%) with Tamoxifen, 2142 (54%) with Aromatase inhibitor, 595 (15%) with LH-RH analog and 76 (2%) with others, includes duplicates). In the < 40 subgroup, 9-year DMFS was 97.2% with ET and 91.0% without ET (p=0.023) and 9-year OS was 97.8% with ET and 97.0% without ET (p=0.954). In the > 65 subgroup), 9-year DMFS was 92.6% with ET and 84.0% without ET (p< 0.01) and 9-year OS was 93.8% with ET and 84.9% without ET (p< 0.01). In those aged 41-64, no significant difference was observed in both 9-year DMFS and OS between patients with and without ET (p=0.328 and p=0.731, respectively) See Table for details. Conclusions: Adjuvant endocrine therapy was associated with improved distant metastatic-free survival in the younger (<40) and older (>65) population in this large Japanese dataset and was associated with improved overall survival in those >65. Our findings suggest clinically relevant benefit from ET in both younger and older unselected patients with very small ER+ BC. The lack of benefit in patients aged 41-64 is likely due to individual tumor and treatment factors, which will be evaluated and described in detail at the meeting. Table. The 9-year DMFS and OS of each age-specific three subgroups. *They are analyzed by using Kaplan-Meier estimates with log-rank test between patients treated with and without ET. Citation Format: Yuko Takahashi, Shinsuke Sasada, Naoto Kondo, Hiroya Hashimoto, Kaori Terata, Kumiko Kida, Yasuaki Sagara, Yoichi Naito, Keisei Anan, Takayuki Ueno, Akihiko Suto, Chizuko Kanbayashi, Mina Takahashi, Rikiya Nakamura, Toshiyuki Ishiba, Michiko Tsuneizumi, Seiichiro Nishimura, Yukinori Ozaki, Akihiko Shimomura, Takehiko Sakai, Tsuguo Iwatani, Hideo Shigematsu, Kenji Tamura, Tomomi Fujisawa, Takashi Hojo, Fumitaka Hara, Tadahiko Shien, Hiroji Iwata. The Prognostic Impact of Adjuvant Endocrine Therapy by Age for Patients with Small Estrogen Receptor-Positive (ER+), Human Epidermal Growth Factor 2 Negative (HER2-) Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-01-09.

Riluzole Suppresses Growth and Enhances Response to Endocrine Therapy in ER+ Breast Cancer.

Resistance to endocrine therapy in estrogen receptor-positive (ER+) breast cancer remains a significant clinical problem. Riluzole is FDA-approved for the treatment of amyotrophic lateral sclerosis. A benzothiazole-based glutamate release inhibitor with several context-dependent mechanism(s) of action, riluzole has shown antitumor activity in multiple malignancies, including melanoma, glioblastoma, and breast cancer. We previously reported that the acquisition of tamoxifen resistance in a cellular model of invasive lobular breast cancer is accompanied by the upregulation of GRM mRNA expression and growth inhibition by riluzole. We tested the ability of riluzole to reduce cell growth, alone and in combination with endocrine therapy, in a diverse set of ER+ invasive ductal and lobular breast cancer-derived cell lines, primary breast tumor explant cultures, and the estrogen-independent, ESR1-mutated invasive lobular breast cancer patient-derived xenograft model HCI-013EI. Single-agent riluzole suppressed the growth of ER+ invasive ductal and lobular breast cancer cell lines in vitro, inducing a histologic subtype-associated cell cycle arrest (G0-G1 for ductal, G2-M for lobular). Riluzole induced apoptosis and ferroptosis and reduced phosphorylation of multiple prosurvival signaling molecules, including Akt/mTOR, CREB, and Fak/Src family kinases. Riluzole, in combination with either fulvestrant or 4-hydroxytamoxifen, additively suppressed ER+ breast cancer cell growth in vitro. Single-agent riluzole significantly inhibited HCI-013EI patient-derived xenograft growth in vivo, and the combination of riluzole plus fulvestrant significantly reduced proliferation in ex vivo primary breast tumor explant cultures. Riluzole may offer therapeutic benefits in diverse ER+ breast cancers, including lobular breast cancer.

ORACLE-RIPA study: A phase II, randomized, open-label, parallel-group study comparing the immune modulation effect of neoadjuvant ribociclib, palbociclib, and abemaciclib in early ER+/HER2- breast cancer.

TPS632 Background: CDK4/6 inhibitors (CDK4/6i), ribociclib, palbociclib, and abemaciclib, provide similar progression-free survival (PFS) benefits when combined with endocrine therapy in ER+/HER2- metastatic breast cancer (MBC) patients. However, not all CDK4/6i have demonstrated overall-survival (OS) benefits in their respective phase III trials. Both, ribociclib and abemaciclib, have shown significant OS benefits in ER+/HER2- MBC patients, but palbociclib has not. Because of similar benefits of the 3 CDK4/6i on PFS, the OS benefit is likely not a result of differences in their synergistic efficacy of a CDK4/6i with endocrine therapy. CDK4 inhibition on cancer cells can also result in upregulation of MHC-I and MHC-II expression on cell surface and Rb-dependent interferon-gamma secretion. CDK6 inhibition might inhibit T cell and NK cell proliferation causing a negative effect on the tumor microenvironment. CDK6 inhibition can also reduce regulatory T cell numbers and increase cytokine production to enhance cytotoxic T cell function. Thus, we hypothesize that the differential impact of the 3 CDK4/6i on OS might be resulting from different immunomodulation effects. To investigate the functional alterations of the CDK4/6i on the BC microenvironment, the neoadjuvant treatment setting is best to compare the immune modulation effects of CDK4/6i from pre-treatment and post-treatment tumor tissues. Methods: This phase II multicenter, randomized, open-label, parallel-group study evaluates the immunomodulation effects of the 3 different CDK4/6i (ribociclib, palbociclib, or abemaciclib) combined with letrozole in neoadjuvant early ER+/HER2- breast cancer patients. A total of 20 patients will be enrolled into each treatment arm. The major inclusion criteria are female patients aged ≥ 20 years old, having a histologically and/or cytologically confirmed diagnosis of ER+ ( > 10%) and/or PR+, HER2 negative (IHC 0+/1+, or IHC 2+ plus FISH negative) breast cancer, stage II/III, and adequate organ function. The treatment will12 weeks of letrozole plus a CDK4/6i. Premenopausal patients will receive GnRH agonist. Breast tumor biopsy, blood and stool samples will be collected prospectively at the time prior to treatment initiation, at 2 weeks after treatment, and at surgery. A description summary will be utilized to compare the results between the 3 CDK4/6i. The trial results will address questions about differences or similarities of the 3 CDK4/6i within the same study. The study is currently enrolling at 3 medical centers s in Taiwan. Clinical trial information: Pending formal number assignment .

Efficacy of oral selective estrogen receptor degraders (SERD)s in the treatment of estrogen receptor positive (ER+), HER2-negative metastatic breast cancer (MBC): A stratified analysis of the ESR1 wild type (wt) and mutant (mt) subgroups.

1096 Background: Oral SERDs are a novel drug class developed to counteract endocrine resistance due to ESR1 mutations. Several SERDs have emerged from phase 2 and 3 trials, and the FDA has most recently limited approval for Elacestrant to patients with ESR1mt tumours despite PFS benefit in the overall population. Questions remain on whether patients with ESR1wt tumours stand to benefit from SERDs. We conducted an IPD meta-analysis of the trials EMERALD, SERENA2, ACELERA and AMEERA3 to compare survival outcomes of SERDs in the 2nd or 3rd line setting against endocrine therapy (ET), using KMSubtraction to unveil HRs of unreported ESR1wt subgroups from AMEERA3 and EMERALD. Meta-analysis results were stratified by ESR1 status. Methods: RCTs investigating the efficacy of novel SERDs versus ET for ER+, HER2- MBC, and which reported the Kaplan Meier (KM) plots of progression free survival (PFS) were selected after a systematic search of Embase and PubMed from inception until January 21,2023. A graphical reconstructive algorithm was applied to estimate time-to-event outcomes from reported KM plots in all overall and reported subgroup cohorts, deriving IPD. A bipartite matching algorithm, KMSubtraction was used to subtract patients in the reported subgroup from the overall cohort, to derive survival data for unreported ESR1wt subgroups. An IPD meta-analysis was then performed, pooling data by ESR1 mutation. Results: A total of 1216 patients were included in this analysis. In the pooled analysis of the overall cohort, PFS benefit was observed with SERDs compared to treatment of physician's choice (TPC) (HR 0.787, 95%CI 0.683-0.908, p<0.001). In the ESR1mt subgroup SERDs demonstrated improved PFS (HR 0.557, 95%CI 0.440-0.705, p<0.001) compared with TPC. In the ESR1wt subgroup, SERDs demonstrated no significant PFS benefit (HR 0.948, 95%CI 0.790-1.137, p=0.565) when compared to TPC. KMSubtraction was implemented on AMEERA3 to reveal survival data in ESR1wt subgroup. Amcenestrant revealed no significant PFS difference in the ESR1wt population (HR 1.197, 95% CI 0.857-1.670, p=0.291) when compared to ET. Additionally, a separate analysis of EMERALD was performed using KMSubtraction to derive survival data of the ESR1wt subgroup comparing Elacestrant vs Fulvestrant. No significant PFS difference was observed between the 2 agents in the ESR1wt population (HR 0.832, 95% CI 0.587-1.178, p=0.299). Conclusions: Our results suggest that PFS benefit in the overall population is mainly driven by the ESR1mt subgroup. These findings are in line with the recent FDA approval of Elacestrant for patients with ESR1mt tumours. [Table: see text]

Comprehensive analysis of a cuproptosis-related ceRNA network implicates a potential endocrine therapy resistance mechanism in ER-positive breast cancer

BackgroundWhile adjuvant endocrine therapy (ET) may decrease the mortality rate of estrogen receptor-positive (ER+) breast cancer (BC), the likelihood of relapse and metastasis due to ET resistance remains high. Cuproptosis is a recently discovered regulated cell death (RCD), whose role in tumors has yet to be elucidated. Thus, there is a need to study its specific regulatory mechanism in resistance to ET in BC, to identify novel therapeutic targets.MethodsThe prognostic cuproptosis-related genes (CRGs) in ER+ BC were filtered by undergoing Cox regression and least absolute shrinkage and selection operator (LASSO) regression analyses in TCGA-BRCA, and a CRGs risk signature was constructed using the correlation coefficient. Immune infiltration analysis, immune function analysis, tumor microenvironment (TME) analysis, immune checkpoint analysis, immunotherapy response analysis, drug sensitivity analysis, and pathway activation analysis were carried out among the high- and low-risk groups in turn. The central CRG of cuproptosis in ER+ BC resistance to ET was acquired through the intersection of protein interaction network (PPI) analysis, genes differentially expressed (DEGs) between human BC cells LCC9 and MCF-7 (GSE159968), and CRGs with prognostic significance in TCGA-BRCA ER+ BC. The miRNAs upstream of the core CRGs were predicted based on the intersection of 4 databases, miRDB, RNA22, miRWalk, and RNAlnter. Candidate miRNAs consisted of the intersection of predicted miRNAs and miRNAs differentially expressed in the LCC9 and MCF-7 cell lines (GSE159979). Candidate lncRNAs were the intersection of the differential lncRNAs from the LCC9 and MCF-7 cell lines and the survival-related lncRNAs obtained from a univariate Cox regression analysis. Pearson's correlation analysis was performed between mRNA-miRNA, miRNA-lncRNA, and mRNA-lncRNA expression separately.ResultsWe constructed A risk signature of 4-CRGs to predict the prognosis of ER+ BC in TCGA-BRCA, a risk score = DLD*0.378 + DBT*0.201 + DLAT*0.380 + ATP7A*0.447 was used as the definition of the formula. There were significant differences between the high- and low-risk groups based on the risk score of 4-CRGs in aspects of immune infiltration, immune function, expression levels of immune checkpoint genes, and signaling pathways. DLD was determined to be the central CRG of cuproptosis in ER+ BC resistance to ET through the intersection of the PPI network analysis, DEGs between LCC9 and MCF-7 and 4-CRGs. Two miRNAs hsa-miR-370-3p and hsa-miR-432-5p were found taking DLD mRNA as a target, and the lncRNA C6orf99 has been hypothesized to be a competitive endogenous RNA that regulates DLD mRNA expression by sponging off hsa-miR-370-3p and hsa-miR-432-5p.ConclusionThis study built a prognostic model based on genes related to cuproptosis in ER+ BC. We considered DLD to be the core gene associated with resistance to ET in ER+ BC via copper metabolism. The search for promising therapeutic targets led to the establishment of a cuproptosis-related ceRNA network C6orf99/hsa-miR-370-3p and hsa-miR-432-5p/DLD.

Abstract 4852: Metabolomic rewiring in endocrine therapy resistant estrogen receptor positive breast cancer

Abstract Breast cancer (BC) is one of the most commonly diagnosed cancers worldwide and the most common in women in the United States. The majority of the BC are estrogen receptor alpha positive (ER+) and are likely to respond to endocrine therapy. Tamoxifen and fulvestrant are the most widely used hormonal treatments for ER+ BC. However, nearly half of patients receiving endocrine therapy suffer from the risk of recurrence due to either intrinsic or acquired resistance. Thus, it is vital to understand the mechanisms of resistance to endocrine therapy in ER+ BC. Metabolic reprogramming is one of the significant hallmarks of cancer and it is now known that many tumors utilize mitochondrial oxidative phosphorylation (OXPHOS) for their energy needs. Our lab previously reported that metastatic triple-negative breast cancer (TNBC), which does not express ER, has a high energy dependency on mitochondrial fatty acid beta-oxidation (FAO). In this project, we developed a gene signature by integrating the transcriptomic, metabolomic, and lipidomic data from FAO rate-limiting gene (CPT1) modulated TNBC cells. Our signature represented the FAO-regulated gene set relevant to metabolic or lipidomic changes. We discovered a significant reliance on this TNBC signature in endocrine-resistant ER+ BC. Clinical data suggests that our gene signature predicts the survival of endocrine-treated ER+ BC patients. Though increased fatty acid consumption is reported in tamoxifen-resistant cells, the role of FAO in endocrine treatment resistance is largely unclear. We then analyzed the metabolic reprogramming in ER+ BC cell lines after tamoxifen or fulvestrant therapy. Molecular, genetic, and metabolic analyses suggested that endocrine therapy-induce AMPK-FAO-OXPHOS signal activation in ER+ BC cells. Furthermore, the knockdown of CPT1, the rate-limiting enzyme of FAO, or treatment with FAO inhibitors significantly enhanced the response to endocrine therapies. We have also reported that FAO induces the autophosphorylation of the c-Src proto-oncogene in TNBC tumors. Thus, we analyzed this phenomenon in the endocrine-resistant ER+ BC cells. As expected, endocrine therapy-induced FAO activated the Src pathway in ER+ BC also. Moreover, in vitro, and in vivo studies confirmed that endocrine-resistant ER+ BC cells have increased sensitivity to FAO, OXPHOS, and Src inhibitors. Finally, analysis of clinical data suggests that low expression of FAO rate-limiting genes in the ER+ primary tumors have better recurrence-free and distant metastasis-free survival after endocrine therapy. Overall, our findings suggest that the gene signature generated from FAO-modulated TNBC cells predicts response to endocrine therapy in ER+ BC. Moreover, metabolic reprogramming in endocrine-resistant ER+ tumors induce FAO, OXPHOS, and Src pathways, providing potential targets to overcome endocrine-resistance ER+ BC patients. Citation Format: Songyeon Ahn, Junhyoung Park, Sandra L. Grimm, Badrajee WB Piyarathna, Nagireddy Putluri, Gokul Das, Cristian Coarfa, Benny A. Kaipparettu. Metabolomic rewiring in endocrine therapy resistant estrogen receptor positive breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4852.

P113 MRI Patterns in the evaluation of pathological response after Neoadjuvant Endocrine therapy in ER+/HER2- Breast Cancer and Implications on Surgical Planning

P113 MRI Patterns in the evaluation of pathological response after Neoadjuvant Endocrine therapy in ER+/HER2- Breast Cancer and Implications on Surgical Planning

Abstract P4-01-37: Discontinuation of HER2+ targeted therapy among cancer survivors with metastatic HER2+ breast cancer: A case report

Abstract Background: Anti-HER2 directed therapy (aHER2tx) has significantly improved survival outcomes in patients with HER2-positive metastatic breast cancer (HMBC). Current United States (US) and European oncology practice guidelines recommend continuing aHER2tx until intolerable side effects or disease progression. It is estimated that 10-15% of treated patients (pts) may achieve prolonged complete remission (CR). Currently, the optimal duration of aHER2tx in patients achieving a CR is unknown. A PubMed literature search identified 7 case reports outside of the US that describe pts who remain in CR after discontinuation of aHER2tx. To our knowledge, this is the first analysis of similar cases in the US. Method: We identified pts with a diagnosis of HMBC who discontinued aHER2tx between January 1, 2010, to June 30, 2021, at a large integrated healthcare system in the US. Pts were included if they had discontinued aHER2tx for at least one year. Data collection included demographics, histology, confirmed sites of metastatic disease (mets), local and systemic treatment (tx) before and after aHER2tx discontinuation, documented radiographic response, and reason to discontinue aHER2tx. Data collection ended on June 30, 2022. Results: Our case report identified 15 pts (mean age at diagnosis 53.0 ± 13.2) based on inclusion criteria. Baseline demographics and characteristics are listed in Table 1. Common clinical characteristics of the cohort include mean age at mets diagnosis is 56 years, postmenopausal status (67%), invasive ductal carcinoma (87%), ER-negative (60%), HER2-positive 3+ by IHC (93%), de-novo mets (60%), multiple sites (93%) and multi-organ mets (87%). Among the cohort, 6 pts (40%) received prior adjuvant therapy, then later recurred, and of these only one had received HER2-based adjuvant tx. In all pts, first line therapy for mets included chemotherapy and aHER2tx, except one pt received endocrine therapy (ET) and aHER2tx. A CR was achieved in all but one pt (93%) with one line of aHER2tx consisting of trastuzumab (H) ± pertuzumab (P). One pt (7%) received local tx to all metastatic sites. In 13 pts, the median time to first radiologic complete response (RCR) after first line therapy for mets was 4 months (Interquartile (IQR) 3-15). Two cases were not included as we were unable to determine time to initial response after tx. All pts had confirmed RCR at the time of aHER2tx discontinuation. Median duration of aHER2tx was 8.3 years (IQR 4.8-9.5), including a median of 6.3 years (IQR 2.8-8.8) on maintenance aHER2tx. Twelve pts (80%) were off all therapy, and 3 pts (20%) continued ET for ER+ disease at the last follow-up (f/u). Patient preference (47%) was the most common reason for stopping aHER2tx. The median disease-free survival off aHER2tx was 4.8 years (IQR 3.1-6.2) and all pts were alive without evidence of disease at last f/u. Conclusion: A subset of HMBC pts successfully discontinued aHER2tx without experiencing recurrence with a median of 4.8 years off therapy in a US cohort. In this case report, common clinical features like strong HER2 overexpression, no prior aHER2tx, and achieving RCR while on first line aHER2tx with H ± P are potential indicators for prolonged CR after discontinuing aHER2tx. Future studies with a comparator group are needed to fully understand the pt population who may safely stop aHER2tx after a CR. Table 1: Baseline Demographics and Clinical Characteristics Citation Format: Lai Fong Hui, Nina N. Shah, Rita L. Hui. Discontinuation of HER2+ targeted therapy among cancer survivors with metastatic HER2+ breast cancer: A case report [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-37.

Prolylcarboxypeptidase promotes IGF1R/HER3 signaling and is a potential target to improve endocrine therapy response in estrogen receptor positive breast cancer

ABSTRACT Prolylcarboxypeptidase (PRCP) is a lysosomal serine protease that cleaves peptide substrates when the penultimate amino acid is proline. Previous studies have linked PRCP to blood-pressure and appetite control through its ability to cleave peptide substrates such as angiotensin II and α-MSH. A potential role for PRCP in cancer has to date not been widely appreciated. Endocrine therapy resistance in breast cancer is an enduring clinical problem mediated in part by aberrant receptor tyrosine kinase (RTK) signaling. We previously found PRCP overexpression promoted 4-hydroxytamoxifen (4-OHT) resistance in estrogen receptor-positive (ER+) breast cancer cells. Currently, we tested the potential association between PRCP with breast cancer patient outcome and RTK signaling, and tumor responsiveness to endocrine therapy. We found high PRCP protein levels in ER+ breast tumors associates with worse outcome and earlier recurrence in breast cancer patients, including patients treated with TAM. We found a PRCP specific inhibitor (PRCPi) enhanced the response of ER+ PDX tumors and MCF7 tumors to endoxifen, an active metabolite of TAM in mice. We found PRCP increased IGF1R/HER3 signaling and AKT activation in ER+ breast cancer cells that was blocked by PRCPi. Thus, PRCP is an adverse prognostic marker in breast cancer and a potential target to improve endocrine therapy in ER+ breast cancers.

OR16-5 Riluzole suppresses growth and enhances response to endocrine therapy in ER+ breast cancer

Abstract Approximately 75% of breast cancers are classified as hormone receptor-positive, most of which are estrogen receptor alpha-positive (ER+), which is the primary driver of growth in these tumors. Consequently, endocrine or anti-estrogen therapy is used for treatment. However, despite the benefits of endocrine therapeutics, treatment-resistant relapse is a significant problem that affects 30-50% of patients who initially respond to endocrine therapy. Therefore, studying resistance to endocrine therapy is critical for breast cancer research.We have shown that invasive lobular breast cancer (ILC) cells resistant to the anti-estrogen tamoxifen increase their expression of metabotropic glutamate receptors (GRMs/mGluRs). GRMs are well-known to play important roles in learning and memory in the brain and protect neurons from excitotoxicity (cell death caused by prolonged exposure to neurotransmitters). It is now appreciated that this pro-survival function of GRMs can be highjacked by cancer cells, including breast cancer. Thus, targeting GRM signaling could prove a valuable therapeutic strategy. We chose to target the GRM signaling pathway with the FDA-approved drug Riluzole currently being used to treat amyotrophic lateral sclerosis.In this study, we test the ability of Riluzole to reduce cell growth, alone and in combination with endocrine therapy, in a diverse set of ER+ invasive ductal and lobular breast cancer-derived cell lines, primary breast tumor explant cultures, and the estrogen-independent, ESR1-mutated, ILC-derived patient-derived xenograft model HCI-013EI. In addition to measuring tumor growth rate and size, primary tumors and organs were collected for immunohistochemistry analysis.Riluzole as a single agent suppressed the growth of ER+ invasive ductal and lobular breast cancer cell lines in vitro, inducing differential histologic subtype-associated cell cycle arrest (G0-G1 for ductal, G2-M for lobular). In tamoxifen-resistant ILC cells, Riluzole induced apoptotic and ferroptotic cell death, and inhibited phosphorylation of focal adhesion kinase. Riluzole combined with either fulvestrant or 4-hydroxytamoxifen additively or synergistically suppressed ER+ breast cancer cell growth in vitro. Using proliferating cell nuclear antigen (PCNA) staining as a proxy for cell proliferation, the combination of Riluzole plus Fulvestrant significantly reduced PCNA in a patient-derived explant model (t-test p = 0.013). The in vivo experiment showed reduced tumor size and growth between the control and combination treatments. However, unlike in the in vitro experiment, there was little difference between the single-agent fulvestrant and the combination groups. The observed difference between the in vitro and in vivo study may be attributed to the bioavailability of Riluzole in mice.In conclusion, our results show that Riluzole enhances response to endocrine therapy in ER+ breast cancer. Presentation: Sunday, June 12, 2022 12:00 p.m. - 12:15 p.m.

Co-targeting CDK2 and CDK4/6 overcomes resistance to aromatase and CDK4/6 inhibitors in ER+ breast cancer

Resistance to aromatase inhibitor (AI) treatment and combined CDK4/6 inhibitor (CDK4/6i) and endocrine therapy (ET) are crucial clinical challenges in treating estrogen receptor-positive (ER+) breast cancer. Understanding the resistance mechanisms and identifying reliable predictive biomarkers and novel treatment combinations to overcome resistance are urgently needed. Herein, we show that upregulation of CDK6, p-CDK2, and/or cyclin E1 is associated with adaptation and resistance to AI-monotherapy and combined CDK4/6i and ET in ER+ advanced breast cancer. Importantly, co-targeting CDK2 and CDK4/6 with ET synergistically impairs cellular growth, induces cell cycle arrest and apoptosis, and delays progression in AI-resistant and combined CDK4/6i and fulvestrant-resistant cell models and in an AI-resistant autocrine breast tumor in a postmenopausal xenograft model. Analysis of CDK6, p-CDK2, and/or cyclin E1 expression as a combined biomarker in metastatic lesions of ER+ advanced breast cancer patients treated with AI-monotherapy or combined CDK4/6i and ET revealed a correlation between high biomarker expression and shorter progression-free survival (PFS), and the biomarker combination was an independent prognostic factor in both patients cohorts. Our study supports the clinical development of therapeutic strategies co-targeting ER, CDK4/6 and CDK2 following progression on AI-monotherapy or combined CDK4/6i and ET to improve survival of patients exhibiting high tumor levels of CDK6, p-CDK2, and/or cyclin E1.

Abstract 4123: Real-world data to identify the genomic association with response to CDK4/6i + Endocrine therapy in ER+ breast cancer patients

Abstract Background Real-world data (RWD) has been increasingly used for drug development. RWD coupled with genomic data provides an opportunity to identify the association between certain genomic alterations and response to current standard of care (SOC). Such analyses may help identify predictive biomarkers to select patients who will benefit most from SOC, and/or potential therapeutic nodes that can be pharmacologically targeted to overcome resistance to SOC. Methods We obtained Flatiron CGDB Breast Cancer (as of Q3 2020 release) data set. This data set includes clinical and genomic data from 6,918 breast cancer patients. Time to treatment discontinuation (TTD) was used as real world outcome. We performed two types of genomic-outcome association analysis: 1) Use Cox proportional hazards regression model to identify which baseline mutation (mutation occurred prior to the treatment) could predict the outcome; and 2) use Fisher exact test to identify which mutations are enriched in post-treatment tumors samples, compared to pre-treatment tumor samples. Result We found TP53 mutation is associated with shorter TTD for Palbociclib + Aromatase inhibitor (AI); Palbociclib + Fulvestrant; and endocrine monotherapy. It is consistent with the reports that TP53 mutation is poor prognostic factor (ref). Interestingly, ESR1 mutation is associated with shorter TTD for Palbociclib + AI and AI monotherapy; but not associated with TTD for Palbociclib + Fulvestrant or Fulvestrant monotherapy. On the other hand, MYC amplification is associated shorter TTD for Palbociclib + Fulvestrant or Fulvestrant monotherapy. We found that genes associated with Palbociclib + Endocrine are by and large same as those associated with endocrine monotherapy; suggesting the association is largely driven by endocrine treatment. Comparison of post-treatment vs. pre-treatment analysis found that ESR1 mutation is enriched in post treatment of AI; but not Fulvestrant. Conclusion We demonstrated that real-world clinicogenomic data could identify the biologically meaningful genomic biomarkers that are associated with real world response. This study warrants the further investigation of novel genomic biomarkers identified from the analysis. Citation Format: Kun Yu, Tenghui Chen, Manav Korpal, Ping Zhu, Zhaojie Zhang, Lihua Yu, Yonghong Xiao. Real-world data to identify the genomic association with response to CDK4/6i + Endocrine therapy in ER+ breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4123.

96P PAM50-based ROR indexes as a tool to individualize the use of neoadjuvant endocrine therapy in ER+/HER2- breast cancer

Neoadjuvant endocrine therapy (NET) is an attractive scenario to find novel biomarkers in oestrogen receptor-positive/HER2-negative breast cancer (ER+/HER2- BC). In this context, PAM50 multigene panel has been validated as a relapse predictor. This study aims to determine if PAM50-derived risk of recurrence (ROR) indexes at diagnosis correlate with biomarkers of response to NET.

Adjuvant and neoadjuvant therapy of ER+ / HER2– breast cancer

Even early-stage breast cancer is a heterogeneous disease, so the optimal treatment depends on the pathological characteristics of the tumor. The vast majority of breast tumors (80%) are classified as estrogen receptor positive (ER+) with varying degrees of ER expression. The benefit of endocrine therapy is small with low ER staining (1–10%), occurring in less than 2% of all cases of ER+ breast cancer. Genetic analyzes are valuable for administration of adjuvant chemotherapy prior to endocrine therapy in ER+ / HER2– pN0–pN1c breast cancer. But such tests are not yet widely available. In practical work, when planning adjuvant and neoadjuvant therapy for patients with ER+ / HER2– breast cancer, pathological assessment of the expression of ER, PR, Ki‑67, as well as the tumor grade (G) remains important. The use of drugs to overcome resistance to endocrine therapy: PI3-kinase inhibitors (taselisib), CDK 4/6 inhibitors (palbociclib, abemaciclib, ribociklib), mTOR inhibitors (everolimus) can enhance the effect of neoadjuvant and adjuvant endocrine therapy.