Case Report: Prolonged Clinical Benefit of ESG401, a Novel Trophoblast Cell-Surface Antigen 2 (Trop-2) Antibody-Drug Conjugate (ADC), in a Patient with Endocrine- Refractory Hormone Receptor-Positive, HER-2 Negative Metastatic Breast Cancer

Case Report: Prolonged Clinical Benefit of ESG401, a Novel Trophoblast Cell-Surface Antigen 2 (Trop-2) Antibody-Drug Conjugate (ADC), in a Patient with Endocrine- Refractory Hormone Receptor-Positive, HER-2 Negative Metastatic Breast Cancer | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report Case Report: Prolonged Clinical Benefit of ESG401, a Novel Trophoblast Cell-Surface Antigen 2 (Trop-2) Antibody-Drug Conjugate (ADC), in a Patient with Endocrine- Refractory Hormone Receptor-Positive, HER-2 Negative Metastatic Breast Cancer Jing Zhao, Fengbo Huang, Xia Xu, Yan Zhang, Xiaoyan Xing, Jian Huang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4429017/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Breast cancer (BC) remains a leading cause of cancer-related mortality in women, with hormone receptor-positive (HR+) tumors accounting for a significant proportion of cases. Despite advancements in endocrine therapy (ET), resistance remains a challenge in metastatic settings. The use of cyclin-dependent kinases 4/6 (CDK4/6) inhibitors in combination with endocrine therapy has notably improved survival. In China, when patients develop resistance to CDK4/6 inhibitors (CDK4/6i) or face financial constraints that prevent their use, chemotherapy becomes the standard treatment approach. This highlights an urgent need for effective treatments following CDK4/6i therapy. ESG401 is a novel Trop2-directed antibody-drug conjugate (ADC) with promising preclinical and early clinical efficacy and safety data. We report a case of a 61-year-old female with HR + HER2- metastatic breast cancer (MBC) who developed resistance to fulvestrant and subsequent chemotherapy but achieved a durable partial response (PR) lasting more than 22.5 months following ESG401 treatment. This case underscores the potential role of Trop2-directed ADCs, such as ESG401, in overcoming endocrine resistance and providing meaningful clinical benefit in heavily pretreated patients with HR+/HER2- MBC. Furthermore, the patient's exceptionally long clinical benefit distinguishes her from other patients receiving ESG401 treatment. Further exploration of the use of ESG401 in HR + HER2- MBC patients, as well as a deeper understanding of the characteristics of patients that may impact sustained efficacy, in expanded clinical trials is warranted. Hormone receptor-positive Metastatic breast cancer Endocrine resistance Trop2 Antibody‒drug conjugate Figures Figure 1 Figure 2 Figure 3 Introduction Breast cancer (BC) remains the most frequently diagnosed cancer, accounting for approximately 24.5% of all new cancer cases in 2020, and is the primary cause of cancer-related mortality in women(Sung et al., 2021 ). Hormone receptor-positive (HR+) tumors constitute 70–80% of all breast cancers(Masood, 1992 ). Due to the strong dependency of breast tumor development on the estrogen-estrogen receptor (ER) axis, estrogen suppression therapy and ER antagonists are the main treatments for hormone receptor-positive HER2-negative (HR + HER2-) metastatic breast cancer (MBC). However, not all patients exhibit a favorable response to endocrine therapy (ET). Primary and acquired resistance to ET remains a challenge. Several studies have revealed that endocrine therapy combined with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) has the potential to overcome resistance to ET and significantly improve survival rates(Cristofanilli et al., 2016 ; Slamon et al., 2020 ; Sledge et al., 2020 ). Additionally, alternative options such as PIK3CA inhibitors(Rugo et al., 2021 ), mTOR inhibitors(Baselga et al., 2012 ), AKT inhibitors(Turner et al., 2023 ), and emerging oral selective estrogen receptor degraders (SERDs) are gaining attention as later-line treatments(Bidard et al., 2022 ). However, the accessibility of some of these treatments is limited in China. For patients who have exhausted endocrine therapy-based options, single-agent chemotherapy remains the standard of care. However, later-line chemotherapy is associated with limited effectiveness, reduced quality of life, and significant toxicity, highlighting the pressing unmet medical needs of these individuals. ESG401 is a novel antibody-drug conjugate (ADC) comprising a humanized IgG1 monoclonal antibody targeting trophoblast cell-surface antigen 2 (Trop-2) linked to the topoisomerase I inhibitor SN-38 via a proprietary stable-cleavable linker with a drug-to-antibody ratio (DAR) of 8. The preliminary results of a phase I/II study in locally advanced/metastatic solid tumors revealed that ESG401 is safe and well tolerated with promising efficacy in heavily pretreated patients(Ma et al., 2023 ). Here, we report a patient with HR+/HER2- MBC who exhibited primary resistance to fulvestrant and had received multiple prior chemotherapy treatments but demonstrated a durable response lasting more than 22 months after treatment with ESG401. At the time of writing, the patient has maintained this response and is still receiving treatment, demonstrating excellent effectiveness and tolerability to ESG401. This case highlights the prolonged clinical benefit achieved by this patient following ESG401 treatment. Case presentation In October 2019, a 61-year-old female patient presented to our hospital for the detection of multiple lung nodules by computed tomography (CT). She was diagnosed with lobular breast cancer (luminal B subtype) and underwent a modified radical mastectomy 5 years prior. She underwent adjuvant chemotherapy (epirubicin and cyclophosphamide followed by docetaxel) and received letrozole as adjuvant endocrine therapy until admission. The chest CT revealed numerous pulmonary nodules, thickening of the bilateral pleural nodules, and enlarged lymph nodes in the mediastinum (Fig. 1 A-B). Endobronchial ultrasound-guided transbronchial needle aspiration of the mediastinum lymph node confirmed the recurrence of ER-positive, PR-negative, and HER2 2+/fluorescence in situ hybridization-negative breast cancer (Fig. 1 C-G). Metastases were not found in the brain, bones, or abdomen. She was diagnosed with metastatic lobular BC (lung, lymph node and pleural). The patient was recommended to receive CDK4/6i-based endocrine therapy but could not afford it at that time. Fulvestrant monotherapy was administered. However, a CT scan performed 3 months later revealed significant growth in the lung nodules and a new mass in the liver (Fig. 2 ), indicating primary resistance to endocrine therapy. Then, the patient underwent nine cycles of albumin-bound paclitaxel (200 mg, administered intravenously on Days 1 and 8 every 21 days) as second-line therapy, achieving a partial response (PR), followed by maintenance therapy with capecitabine. The progression-free survival (PFS) time was 13.6 months. Eribulin (2 mg, administered intravenously on Day 1 and Day 8, every 21 days) was then initiated as third-line therapy, resulting in another PR. Maintenance treatment with eribulin was continued for 14.7 months. In May 2022, progression of the liver metastatic lesion was observed (Fig. 2 ). The patient was recommended to participate in a phase I/II clinical trial designed to evaluate the safety and antitumor effects of ESG401 (Shanghai Escugen Biotechnology Co., Ltd. Shanghai, China) in solid tumors (NCT04892342). ESG401 is a novel ADC with a humanized IgG1 antibody against the Trop2 antigen and the small molecule SN-38, which is a topoisomerase I inhibitor. An innovative stable and cleavable linker was used to combine the antibody to the payload with a DAR of 8. After providing informed consent, the patient received ESG401 treatment (12 mg/kg intravenously on Day 1, Day 8, and Day 15 every 28 days) on May 25, 2022. Trop2 status was assessed via IHC, revealing an H-score of 250, which was considered to be a high expression of Trop2. (Fig. 1 H). After two treatment cycles, the CT scan showed a significant reduction in the size of the liver metastases, from 33 mm to 17 mm (a reduction of 48.5%), the overall efficacy of the patient was determined as PR according to RECIST 1.1. Four weeks later, the PR was confirmed. Subsequently, the patient's lesions further decreased, with a total reduction in the sum of the longest diameters of the target lesions of 52.6%. At the time of writing (May 2024), the patient had sustained a beneficial response for 23.6 months. The latest CT scan from March 21, 2024, revealed a sustained PR for the liver mass. Although a lung nodule has gradually gotten larger, the overall assessment of efficacy is still a PR. The pharmacokinetic profile of this patient indicates that, irrespective of whether they received a single or multiple doses of ESG401, the concentrations of both the total antibody and the intact ADC remained similar. However, the concentration of SN-38 was significantly lower compared to the total antibody and ESG401, with a maximum concentration (Cmax) of 6.5 ng/ml and an area under the curve (AUC) of 136 ng·h/ml. The pharmacokinetics (PK) profiles of total antibody and ADC drug are very similar, indicating that ESG401 is very stable in circulation (Fig. 3 ). The patient has experienced very mild and easily manageable adverse reactions, including grade 2 neutropenia, grade 1 diarrhea, and anemia, during ESG401 treatment. The patient maintains an excellent performance status and has a high quality of life. Discussion Endocrine resistance, which refers to resistance to estrogen or ER suppression, remains a significant hurdle for patients with HR+/HER2- BC. For MBC, primary endocrine resistance is defined as disease progression during the first 6 months of first-line ET(Hanker et al., 2020 ). The mechanism is intricate and potentially linked to modifications in the estrogen receptor pathway (e.g., ESR1 mutations) or upstream signaling pathways of growth factors (e.g., the PI3K/Akt/mTOR pathway) (Hart et al., 2015 ). In the last two decades, there have been notable advancements in the discovery and approval of novel medications targeting the ER and upstream signaling pathways. Among the drugs available in China, CDK4/6i combined with fulvestrant is the standard treatment for patients who have progressed on aromatase inhibitors (AIs). In our specific case, the patient opted against receiving CDK4/6i treatment due to financial limitations and subsequently experienced rapid progression while on fulvestrant monotherapy. In addition to chemotherapy, the mTOR inhibitor everolimus in combination with exemestane is a favorable option, potentially prolonging PFS in patients who are refractory to nonsteroidal AIs(Baselga et al., 2012 ). Nevertheless, the relatively high toxicity profile of everolimus limits its utilization. ADCs are a class of targeted therapies that consist of monoclonal antibodies conjugated with cytotoxic drugs. The monoclonal antibody component enables specific recognition and binding to cancer cell surface antigens, while the cytotoxic drug payload delivers a potent anticancer effect directly to tumor cells. Trastuzumab emtansine (T-DM1) is the first approved ADC that targets HER2(Verma et al., 2012 ). Compared with T-DM1, trastuzumab deruxtecan (T-DXd), another ADC that targets HER2, has been shown to improve survival outcomes in patients with HER2-positive MBC(Hurvitz et al., 2023 ); it also improves survival outcomes in patients with MBC with low HER2 expression compared to those receiving standard chemotherapy(Modi et al., 2022 ). Trop-2 is another target of interest in breast cancer. It was initially identified in 1981 as a protein prominently present on the surface of trophoblast cells(Lipinski et al., 1981 ). However, subsequent studies revealed its intricate involvement in cancer cell processes, including growth, proliferation, migration, invasion, and survival(Zaman et al., 2019 ). In breast cancer, expression of the TROP-2 gene has been identified across all subtypes, with particularly elevated levels observed in HR + HER2-negative and triple-negative breast cancer (TNBC) compared to HER2-positive disease (Vidula et al., 2022 ). Elevated TROP-2 expression was correlated with poorer survival outcomes(Ambrogi et al., 2014 ). Sacituzumab govitecan (SG) is the first ADC directed against Trop-2 and was recently approved in China for patients with metastatic triple-negative breast cancer (mTNBC) who have undergone two or more lines of chemotherapy. SG consists of a humanized anti-Trop-2 monoclonal antibody linked to SN-38 via a hydrolysable CL2A linker.(Bardia, 2020 ) In HR + HER2- MBC patients resistant to endocrine therapy, sacituzumab govitecan significantly increased the median progression-free survival (mPFS) (5.5 months vs. 4.0 months) and median overall survival (mOS) (14.4 months vs. 11.2 months) compared to that with conventional chemotherapy. (Rugo et al., 2022 ). However, safety analysis revealed a greater incidence of adverse events (AEs) in the SG group, with notable neutropenia, diarrhea, nausea, vomiting, alopecia, and fatigue. The hydrolysable CL2A linker, which is designed for extracellular hydrolysis, leads to an earlier release of free SN-38 into the circulation, leading to a higher peak cytotoxin concentration, a higher exposure and potentially contributing to an increase in AEs(Tarcsa et al., 2020 ). Compared to investigator’s choice of chemotherapy, another Trop2-targeted ADC called datopotamab deruxtecan (Dato-DXd) led to significant improvement in PFS (6.9 months vs. 4.9 months) and presented a favorable safety profile in a phase III trial for HR+/HER2- MBC (Bardia et al., 2022 ). These studies demonstrate that Trop2-directed ADCs offer substantial promise as a novel therapeutic approach for HR+/HER2- MBC. An optimal linker for an ADC should possess adequate stability to transport the payload to the desired site while also exhibiting sufficient lability to release an effective quantity of payload either within the tumor or in the tumor microenvironment (TME)(Tarantino et al., 2023 ). ESG401 is a novel ADC directed toward Trop2 that utilizes an innovative stable cleavable linker designed to conjugate SN38 to a humanized monoclonal antibody targeting Trop2 with a DAR of 8. The cytotoxic effects of SN38 on ESG401 occur only after it is taken up by tumor cells into lysosomes and released through the action of tissue proteases, reducing the diffusion of the free cytotoxic payload into circulation. It showed that the longer half-life of intact ADC in the patient than SG (49.0 vs.23.4 hours), with lower exposure of SN38, reflected in the ratio of SN38 to ADC (0.002% vs. 0.07%). Furthermore, the pharmacokinetic evaluation of the patient, the same as other patients from the trial, exhibited notably reduced maximum concentration (Cmax) levels (6.5 vs. 98.0 ng/ml) and area under the curve (AUC) values (136 vs. 3696 ng·h/ml) for SN-38 when contrasted with the published pharmacokinetic profile of SG 25 . These PK characteristics suggest that ESG401 is more stable in circulation. This may mechanistically explain the patient's milder off-target toxicities, such as neutropenia, nausea, and diarrhea. The toxicity profile of ESG401 was moderate, as reported 10 , the most frequent treatment-related adverse events (TRAEs) of Grade 3 or higher were leukopenia (29%) and neutropenia (31%). There were no Grade 3 or higher events of thrombocytopenia, diarrhea, skin rash, or oral mucositis. This profile is attributed to the stability of the ADC molecule conferred by the proprietary linker of ESG401 and the reduced release of free payload in the system, thereby minimizing off-target toxicity. The cleavable linker and membrane-permeable payload SN-38 enable it to exert a “bystander effect” (Kawato et al., 1991 ). In tumor-bearing mouse models, compared with tumors treated with SG, tumors treated with ESG401 had higher levels of and longer exposure to both free SN38 and total SN38 within tumor tissues. The combination of decreased serum release and increased exposure of SN-38 within tumor tissues indicated the reliable efficacy and exceptional safety of ESG401 in an animal model. Initial findings from a phase I/II clinical trial assessing the safety, tolerability, pharmacokinetics, and antitumor effects of ESG401 in patients with locally advanced or metastatic solid tumors have been reported(Ma et al., 2023 ). Thirty-five heavily treated patients (with a median of 4 (2–10) prior lines of treatment) were enrolled. Among 33 patients assessed for efficacy, the ORR and DCR across various dosage regimens were 36.4% (12/33) and 63.6% (21/33), respectively. Specifically, in a subgroup of 13 patients receiving therapeutically relevant doses of HR+/HER2- MBC, the ORR and DCR were 62% (8/13) and 77% (10/13), respectively. These promising efficacy signals suggest a favorable treatment effect of ESG401 for HR+/HER2- MBC, which is consistent with the case of this patient with exceptionally long clinical benefit that we have reported. In our case, the patient who rapidly progressed on fulvestrant and subsequently received two additional lines of chemotherapy achieved a significant PR following treatment with ESG401. This favorable response lasted for more than 22.5 months with excellent tolerance and good quality of life, exceeding the duration achieved with previous chemotherapy; this response period was also much longer than the published mPFS from studies using SG (5.5 months) and Dato-Dxd (6.8 months) in the same indication population. This may be attributed to the high TROP2 expression, low tumor burden, good performance status, and excellent efficacy of ESG401. Some possible underlying unveiled reasons may have an impact as well. Further exploration of these factors that may contribute to the patient's prolonged duration response will help to further elucidate the mechanism of drug action and provide meaningful guidance for the treatment of such patients. Moreover, diverse reactions to ESG401 were observed in hepatic and pulmonary lesions, emphasizing the heterogeneous nature of tumors. Variability in TROP2 expression across distinct metastatic loci in breast cancer has been documented(Kojima;, 2024). Re-evaluation through lung metastasis re-biopsy at the onset of progressive disease (PD) could offer valuable insights into the resistance mechanisms of ESG401, thus guiding subsequent therapeutic strategies. In conclusion, for patients with endocrine-refractory HR+/HER2- MBC, Trop2-directed ADCs represent an optimal choice for later lines of therapy. Enhanced ADC engineering holds significant promise for maximizing both the efficacy and safety of these agents. ESG401 has demonstrated favorable tolerability with promising signs of efficacy in heavily pretreated patients. Further investigations through expanded clinical trials in HR+/HER2- MBC, as well as a deeper understanding of the characteristics of patients that may impact sustained efficacy, are warranted. Declarations Ethics declarations This case was approved by Ethics Committee of the Second Affiliated Hospital, Zhejiang University School of Medicine (2021-437). Informed consent was obtained from the patient. Funding None Conflicts of interest All the Authors declare that there are no conflicts of interest. The manuscript has been read and approved by all the authors Author Contributions Jing Zhao and Xiaoyan Xing wrote the main manuscript text, Fengbo Huang and Xia Xu prepared figures, Yan Zhang and Fuming Qiu involved in the management of patients, Jian Huang and Fuming Qiu conducted this project. All authors reviewed the manuscript. References Ambrogi F, Fornili M, Boracchi P et al. Trop-2 is a determinant of breast cancer survival. PLoS One. 2014, 9: e96993. Bardia A. A closer look at sacituzumab govitecan-hziy. Clin Adv Hematol Oncol. 2020, 18: 715-7. Bardia A, Kalinsky K, Tsurutani J et al. 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Fulvestrant plus palbociclib versus fulvestrant plus placebo for treatment of hormone-receptor-positive, her2-negative metastatic breast cancer that progressed on previous endocrine therapy (paloma-3): Final analysis of the multicentre, double-blind, phase 3 randomised controlled trial. Lancet Oncol. 2016, 17: 425-39. Hanker AB, Sudhan DR, Arteaga CL. Overcoming endocrine resistance in breast cancer. Cancer Cell. 2020, 37: 496-513. Hart CD, Migliaccio I, Malorni L, Guarducci C, Biganzoli L, Di Leo A. Challenges in the management of advanced, er-positive, her2-negative breast cancer. Nat Rev Clin Oncol. 2015, 12: 541-52. Hurvitz SA, Hegg R, Chung WP et al. Trastuzumab deruxtecan versus trastuzumab emtansine in patients with her2-positive metastatic breast cancer: Updated results from destiny-breast03, a randomised, open-label, phase 3 trial. Lancet. 2023, 401: 105-17. Kawato Y, Aonuma M, Hirota Y, Kuga H, Sato K. 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Trastuzumab deruxtecan in previously treated her2-low advanced breast cancer. N Engl J Med. 2022, 387: 9-20. Rugo HS, Bardia A, Marme F et al. Sacituzumab govitecan in hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer. J Clin Oncol. 2022, 40: 3365-76. Rugo HS, Lerebours F, Ciruelos E et al. Alpelisib plus fulvestrant in pik3ca-mutated, hormone receptor-positive advanced breast cancer after a cdk4/6 inhibitor (bylieve): One cohort of a phase 2, multicentre, open-label, non-comparative study. Lancet Oncol. 2021, 22: 489-98. Slamon DJ, Neven P, Chia S et al. Overall survival with ribociclib plus fulvestrant in advanced breast cancer. N Engl J Med. 2020, 382: 514-24. Sledge GW, Jr., Toi M, Neven P et al. The effect of abemaciclib plus fulvestrant on overall survival in hormone receptor-positive, erbb2-negative breast cancer that progressed on endocrine therapy-monarch 2: A randomized clinical trial. JAMA Oncol. 2020, 6: 116-24. Sung H, Ferlay J, Siegel RL et al. Global cancer statistics 2020: Globocan estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin. 2021, 71: 209-49. Tarantino P, Ricciuti B, Pradhan SM, Tolaney SM. Optimizing the safety of antibody-drug conjugates for patients with solid tumours. Nat Rev Clin Oncol. 2023, 20: 558-76. Tarcsa E, Guffroy MR, Falahatpisheh H, Phipps C, Kalvass JC. Antibody-drug conjugates as targeted therapies: Are we there yet? A critical review of the current clinical landscape. Drug Discov Today Technol. 2020, 37: 13-22. Turner NC, Oliveira M, Howell SJ et al. Capivasertib in hormone receptor-positive advanced breast cancer. N Engl J Med. 2023, 388: 2058-70. Verma S, Miles D, Gianni L et al. Trastuzumab emtansine for her2-positive advanced breast cancer. N Engl J Med. 2012, 367: 1783-91. Vidula N, Yau C, Rugo H. Trophoblast cell surface antigen 2 gene (tacstd2) expression in primary breast cancer. Breast Cancer Res Treat. 2022, 194: 569-75. Zaman S, Jadid H, Denson AC, Gray JE. Targeting trop-2 in solid tumors: Future prospects. Onco Targets Ther. 2019, 12: 1781-90. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4429017","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":305601389,"identity":"fa6c05bd-8507-495f-87f7-04e76576a495","order_by":0,"name":"Jing Zhao","email":"","orcid":"","institution":"Second Affiliated Hospital of Zhejiang University","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Zhao","suffix":""},{"id":305601390,"identity":"90bd3e2b-cbcc-4e3b-a4f3-cc0633be092f","order_by":1,"name":"Fengbo Huang","email":"","orcid":"","institution":"Second Affiliated Hospital of Zhejiang University","correspondingAuthor":false,"prefix":"","firstName":"Fengbo","middleName":"","lastName":"Huang","suffix":""},{"id":305601395,"identity":"24aa0944-11d0-4967-87ad-be2a1db643d0","order_by":2,"name":"Xia Xu","email":"","orcid":"","institution":"Jinhua Central Hospital","correspondingAuthor":false,"prefix":"","firstName":"Xia","middleName":"","lastName":"Xu","suffix":""},{"id":305601396,"identity":"a37fde5c-5f30-4182-b6f8-93956a29c53d","order_by":3,"name":"Yan Zhang","email":"","orcid":"","institution":"Second Affiliated Hospital of Zhejiang University","correspondingAuthor":false,"prefix":"","firstName":"Yan","middleName":"","lastName":"Zhang","suffix":""},{"id":305601397,"identity":"550d9d83-f29b-4228-84f3-a8d34518dc0f","order_by":4,"name":"Xiaoyan Xing","email":"","orcid":"","institution":"Shanghai Escugen Biotechnology Co., Ltd","correspondingAuthor":false,"prefix":"","firstName":"Xiaoyan","middleName":"","lastName":"Xing","suffix":""},{"id":305601398,"identity":"b5cb4f6b-b071-4536-92ff-f962fe25ea65","order_by":5,"name":"Jian Huang","email":"","orcid":"","institution":"Second Affiliated Hospital of Zhejiang University","correspondingAuthor":false,"prefix":"","firstName":"Jian","middleName":"","lastName":"Huang","suffix":""},{"id":305601399,"identity":"8d057918-cf68-4013-b88e-8af17ffb2065","order_by":6,"name":"Fuming Qiu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYDACZgaGDwwMEgwM7A0MBkA+YwMRWhhngLXwHCBWCwNYCxBIJEB4BLXwHecxbObNsciTj3z+oJiHwUZ2wwHmZw/waZE8DNKyTaLY8HZCgjEPQ5rxhgNs5gb4tBgc5jF/DNSSuHF2wgGglsOJGw7wsEkQ0AK2JXHjzIMNQC3/SdAyX4KZAajlAGEtkofZChvnArVs4EljMJxjkGw88zCbGV4tfOcPb2x4u60ucX778WcGbyrsZPuONz/Dq4XhAMyFBxjYDMCRyYxXPZIW+QYG5geEFI+CUTAKRsHIBABDf0fVhmSxLQAAAABJRU5ErkJggg==","orcid":"","institution":"Second Affiliated Hospital of Zhejiang University","correspondingAuthor":true,"prefix":"","firstName":"Fuming","middleName":"","lastName":"Qiu","suffix":""}],"badges":[],"createdAt":"2024-05-16 06:55:30","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4429017/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4429017/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":57708434,"identity":"630df4ba-06ff-49a6-abbd-d6c727aff2de","added_by":"auto","created_at":"2024-06-04 15:18:14","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3212134,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Representative computed tomography (CT) scan images of the lung. (B) CT scan images of mediastinum lymph node metastases (white arrow). (C) Hematoxylin and eosin-stained(HE) section of a metastatic mediastinal lymph node (20×). (D-F) Immunohistochemistry (IHC) staining for ER, PR, and c-erbB-2 (HER2) expression in the metastatic mediastinal lymph node. (G) Fluorescence in situ hybridization (FISH) of the metastatic mediastinum lymph node revealed negative HER2 amplification. (H) Immunohistochemistry (IHC) staining for TROP2 expression in the metastatic mediastinal lymph node.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4429017/v1/a4f9f30ed0ff7ff50c74cb33.jpg"},{"id":57708433,"identity":"4a2a717c-bc09-48b6-82ad-d6e5270da7fb","added_by":"auto","created_at":"2024-06-04 15:18:13","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1173862,"visible":true,"origin":"","legend":"\u003cp\u003eImaging evolution of the patient treatment timeline and image efficacy evaluation.\u003c/p\u003e","description":"","filename":"Figure2v3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4429017/v1/721b404c456d5fdeef85fa1d.jpg"},{"id":57708432,"identity":"73b39df6-d2af-49c6-81bd-9dcfb91d7a2a","added_by":"auto","created_at":"2024-06-04 15:18:13","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":219574,"visible":true,"origin":"","legend":"\u003cp\u003eThe plasma drug concentration-time curve of ESG-401, total antibody and SN-38 of the patient\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4429017/v1/ee7fc787eae47be22bb6d51c.jpg"},{"id":57709494,"identity":"b9e20799-8a2e-4148-ae48-769064fca656","added_by":"auto","created_at":"2024-06-04 15:34:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4083876,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4429017/v1/e6f5fd9e-8412-47c1-9117-c31a2c41f250.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Case Report: Prolonged Clinical Benefit of ESG401, a Novel Trophoblast Cell-Surface Antigen 2 (Trop-2) Antibody-Drug Conjugate (ADC), in a Patient with Endocrine- Refractory Hormone Receptor-Positive, HER-2 Negative Metastatic Breast Cancer","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBreast cancer (BC) remains the most frequently diagnosed cancer, accounting for approximately 24.5% of all new cancer cases in 2020, and is the primary cause of cancer-related mortality in women(Sung et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Hormone receptor-positive (HR+) tumors constitute 70\u0026ndash;80% of all breast cancers(Masood, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Due to the strong dependency of breast tumor development on the estrogen-estrogen receptor (ER) axis, estrogen suppression therapy and ER antagonists are the main treatments for hormone receptor-positive HER2-negative (HR\u0026thinsp;+\u0026thinsp;HER2-) metastatic breast cancer (MBC). However, not all patients exhibit a favorable response to endocrine therapy (ET). Primary and acquired resistance to ET remains a challenge.\u003c/p\u003e \u003cp\u003eSeveral studies have revealed that endocrine therapy combined with cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) has the potential to overcome resistance to ET and significantly improve survival rates(Cristofanilli et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Slamon et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sledge et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Additionally, alternative options such as PIK3CA inhibitors(Rugo et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), mTOR inhibitors(Baselga et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), AKT inhibitors(Turner et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), and emerging oral selective estrogen receptor degraders (SERDs) are gaining attention as later-line treatments(Bidard et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, the accessibility of some of these treatments is limited in China. For patients who have exhausted endocrine therapy-based options, single-agent chemotherapy remains the standard of care. However, later-line chemotherapy is associated with limited effectiveness, reduced quality of life, and significant toxicity, highlighting the pressing unmet medical needs of these individuals.\u003c/p\u003e \u003cp\u003eESG401 is a novel antibody-drug conjugate (ADC) comprising a humanized IgG1 monoclonal antibody targeting trophoblast cell-surface antigen 2 (Trop-2) linked to the topoisomerase I inhibitor SN-38 via a proprietary stable-cleavable linker with a drug-to-antibody ratio (DAR) of 8. The preliminary results of a phase I/II study in locally advanced/metastatic solid tumors revealed that ESG401 is safe and well tolerated with promising efficacy in heavily pretreated patients(Ma et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Here, we report a patient with HR+/HER2- MBC who exhibited primary resistance to fulvestrant and had received multiple prior chemotherapy treatments but demonstrated a durable response lasting more than 22 months after treatment with ESG401. At the time of writing, the patient has maintained this response and is still receiving treatment, demonstrating excellent effectiveness and tolerability to ESG401. This case highlights the prolonged clinical benefit achieved by this patient following ESG401 treatment.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eIn October 2019, a 61-year-old female patient presented to our hospital for the detection of multiple lung nodules by computed tomography (CT). She was diagnosed with lobular breast cancer (luminal B subtype) and underwent a modified radical mastectomy 5 years prior. She underwent adjuvant chemotherapy (epirubicin and cyclophosphamide followed by docetaxel) and received letrozole as adjuvant endocrine therapy until admission. The chest CT revealed numerous pulmonary nodules, thickening of the bilateral pleural nodules, and enlarged lymph nodes in the mediastinum (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-B). Endobronchial ultrasound-guided transbronchial needle aspiration of the mediastinum lymph node confirmed the recurrence of ER-positive, PR-negative, and HER2 2+/fluorescence in situ hybridization-negative breast cancer (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC-G). Metastases were not found in the brain, bones, or abdomen. She was diagnosed with metastatic lobular BC (lung, lymph node and pleural). The patient was recommended to receive CDK4/6i-based endocrine therapy but could not afford it at that time. Fulvestrant monotherapy was administered. However, a CT scan performed 3 months later revealed significant growth in the lung nodules and a new mass in the liver (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), indicating primary resistance to endocrine therapy. Then, the patient underwent nine cycles of albumin-bound paclitaxel (200 mg, administered intravenously on Days 1 and 8 every 21 days) as second-line therapy, achieving a partial response (PR), followed by maintenance therapy with capecitabine. The progression-free survival (PFS) time was 13.6 months. Eribulin (2 mg, administered intravenously on Day 1 and Day 8, every 21 days) was then initiated as third-line therapy, resulting in another PR. Maintenance treatment with eribulin was continued for 14.7 months.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn May 2022, progression of the liver metastatic lesion was observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The patient was recommended to participate in a phase I/II clinical trial designed to evaluate the safety and antitumor effects of ESG401 (Shanghai Escugen Biotechnology Co., Ltd. Shanghai, China) in solid tumors (NCT04892342). ESG401 is a novel ADC with a humanized IgG1 antibody against the Trop2 antigen and the small molecule SN-38, which is a topoisomerase I inhibitor. An innovative stable and cleavable linker was used to combine the antibody to the payload with a DAR of 8. After providing informed consent, the patient received ESG401 treatment (12 mg/kg intravenously on Day 1, Day 8, and Day 15 every 28 days) on May 25, 2022. Trop2 status was assessed via IHC, revealing an H-score of 250, which was considered to be a high expression of Trop2. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eH). After two treatment cycles, the CT scan showed a significant reduction in the size of the liver metastases, from 33 mm to 17 mm (a reduction of 48.5%), the overall efficacy of the patient was determined as PR according to RECIST 1.1. Four weeks later, the PR was confirmed. Subsequently, the patient's lesions further decreased, with a total reduction in the sum of the longest diameters of the target lesions of 52.6%. At the time of writing (May 2024), the patient had sustained a beneficial response for 23.6 months. The latest CT scan from March 21, 2024, revealed a sustained PR for the liver mass. Although a lung nodule has gradually gotten larger, the overall assessment of efficacy is still a PR. The pharmacokinetic profile of this patient indicates that, irrespective of whether they received a single or multiple doses of ESG401, the concentrations of both the total antibody and the intact ADC remained similar. However, the concentration of SN-38 was significantly lower compared to the total antibody and ESG401, with a maximum concentration (Cmax) of 6.5 ng/ml and an area under the curve (AUC) of 136 ng\u0026middot;h/ml. The pharmacokinetics (PK) profiles of total antibody and ADC drug are very similar, indicating that ESG401 is very stable in circulation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The patient has experienced very mild and easily manageable adverse reactions, including grade 2 neutropenia, grade 1 diarrhea, and anemia, during ESG401 treatment. The patient maintains an excellent performance status and has a high quality of life.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eEndocrine resistance, which refers to resistance to estrogen or ER suppression, remains a significant hurdle for patients with HR+/HER2- BC. For MBC, primary endocrine resistance is defined as disease progression during the first 6 months of first-line ET(Hanker et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The mechanism is intricate and potentially linked to modifications in the estrogen receptor pathway (e.g., ESR1 mutations) or upstream signaling pathways of growth factors (e.g., the PI3K/Akt/mTOR pathway) (Hart et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In the last two decades, there have been notable advancements in the discovery and approval of novel medications targeting the ER and upstream signaling pathways. Among the drugs available in China, CDK4/6i combined with fulvestrant is the standard treatment for patients who have progressed on aromatase inhibitors (AIs). In our specific case, the patient opted against receiving CDK4/6i treatment due to financial limitations and subsequently experienced rapid progression while on fulvestrant monotherapy. In addition to chemotherapy, the mTOR inhibitor everolimus in combination with exemestane is a favorable option, potentially prolonging PFS in patients who are refractory to nonsteroidal AIs(Baselga et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Nevertheless, the relatively high toxicity profile of everolimus limits its utilization.\u003c/p\u003e \u003cp\u003eADCs are a class of targeted therapies that consist of monoclonal antibodies conjugated with cytotoxic drugs. The monoclonal antibody component enables specific recognition and binding to cancer cell surface antigens, while the cytotoxic drug payload delivers a potent anticancer effect directly to tumor cells. Trastuzumab emtansine (T-DM1) is the first approved ADC that targets HER2(Verma et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Compared with T-DM1, trastuzumab deruxtecan (T-DXd), another ADC that targets HER2, has been shown to improve survival outcomes in patients with HER2-positive MBC(Hurvitz et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e); it also improves survival outcomes in patients with MBC with low HER2 expression compared to those receiving standard chemotherapy(Modi et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Trop-2 is another target of interest in breast cancer. It was initially identified in 1981 as a protein prominently present on the surface of trophoblast cells(Lipinski et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1981\u003c/span\u003e). However, subsequent studies revealed its intricate involvement in cancer cell processes, including growth, proliferation, migration, invasion, and survival(Zaman et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In breast cancer, expression of the TROP-2 gene has been identified across all subtypes, with particularly elevated levels observed in HR\u0026thinsp;+\u0026thinsp;HER2-negative and triple-negative breast cancer (TNBC) compared to HER2-positive disease (Vidula et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Elevated TROP-2 expression was correlated with poorer survival outcomes(Ambrogi et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSacituzumab govitecan (SG) is the first ADC directed against Trop-2 and was recently approved in China for patients with metastatic triple-negative breast cancer (mTNBC) who have undergone two or more lines of chemotherapy. SG consists of a humanized anti-Trop-2 monoclonal antibody linked to SN-38 via a hydrolysable CL2A linker.(Bardia, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) In HR\u0026thinsp;+\u0026thinsp;HER2- MBC patients resistant to endocrine therapy, sacituzumab govitecan significantly increased the median progression-free survival (mPFS) (5.5 months vs. 4.0 months) and median overall survival (mOS) (14.4 months vs. 11.2 months) compared to that with conventional chemotherapy. (Rugo et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, safety analysis revealed a greater incidence of adverse events (AEs) in the SG group, with notable neutropenia, diarrhea, nausea, vomiting, alopecia, and fatigue. The hydrolysable CL2A linker, which is designed for extracellular hydrolysis, leads to an earlier release of free SN-38 into the circulation, leading to a higher peak cytotoxin concentration, a higher exposure and potentially contributing to an increase in AEs(Tarcsa et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Compared to investigator\u0026rsquo;s choice of chemotherapy, another Trop2-targeted ADC called datopotamab deruxtecan (Dato-DXd) led to significant improvement in PFS (6.9 months vs. 4.9 months) and presented a favorable safety profile in a phase III trial for HR+/HER2- MBC (Bardia et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These studies demonstrate that Trop2-directed ADCs offer substantial promise as a novel therapeutic approach for HR+/HER2- MBC.\u003c/p\u003e \u003cp\u003eAn optimal linker for an ADC should possess adequate stability to transport the payload to the desired site while also exhibiting sufficient lability to release an effective quantity of payload either within the tumor or in the tumor microenvironment (TME)(Tarantino et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). ESG401 is a novel ADC directed toward Trop2 that utilizes an innovative stable cleavable linker designed to conjugate SN38 to a humanized monoclonal antibody targeting Trop2 with a DAR of 8. The cytotoxic effects of SN38 on ESG401 occur only after it is taken up by tumor cells into lysosomes and released through the action of tissue proteases, reducing the diffusion of the free cytotoxic payload into circulation. It showed that the longer half-life of intact ADC in the patient than SG (49.0 vs.23.4 hours), with lower exposure of SN38, reflected in the ratio of SN38 to ADC (0.002% vs. 0.07%). Furthermore, the pharmacokinetic evaluation of the patient, the same as other patients from the trial, exhibited notably reduced maximum concentration (Cmax) levels (6.5 vs. 98.0 ng/ml) and area under the curve (AUC) values (136 vs. 3696 ng\u0026middot;h/ml) for SN-38 when contrasted with the published pharmacokinetic profile of SG\u003csup\u003e25\u003c/sup\u003e. These PK characteristics suggest that ESG401 is more stable in circulation. This may mechanistically explain the patient's milder off-target toxicities, such as neutropenia, nausea, and diarrhea. The toxicity profile of ESG401 was moderate, as reported\u003csup\u003e10\u003c/sup\u003e, the most frequent treatment-related adverse events (TRAEs) of Grade 3 or higher were leukopenia (29%) and neutropenia (31%). There were no Grade 3 or higher events of thrombocytopenia, diarrhea, skin rash, or oral mucositis. This profile is attributed to the stability of the ADC molecule conferred by the proprietary linker of ESG401 and the reduced release of free payload in the system, thereby minimizing off-target toxicity.\u003c/p\u003e \u003cp\u003eThe cleavable linker and membrane-permeable payload SN-38 enable it to exert a \u0026ldquo;bystander effect\u0026rdquo; (Kawato et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). In tumor-bearing mouse models, compared with tumors treated with SG, tumors treated with ESG401 had higher levels of and longer exposure to both free SN38 and total SN38 within tumor tissues. The combination of decreased serum release and increased exposure of SN-38 within tumor tissues indicated the reliable efficacy and exceptional safety of ESG401 in an animal model. Initial findings from a phase I/II clinical trial assessing the safety, tolerability, pharmacokinetics, and antitumor effects of ESG401 in patients with locally advanced or metastatic solid tumors have been reported(Ma et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Thirty-five heavily treated patients (with a median of 4 (2\u0026ndash;10) prior lines of treatment) were enrolled. Among 33 patients assessed for efficacy, the ORR and DCR across various dosage regimens were 36.4% (12/33) and 63.6% (21/33), respectively. Specifically, in a subgroup of 13 patients receiving therapeutically relevant doses of HR+/HER2- MBC, the ORR and DCR were 62% (8/13) and 77% (10/13), respectively. These promising efficacy signals suggest a favorable treatment effect of ESG401 for HR+/HER2- MBC, which is consistent with the case of this patient with exceptionally long clinical benefit that we have reported.\u003c/p\u003e \u003cp\u003eIn our case, the patient who rapidly progressed on fulvestrant and subsequently received two additional lines of chemotherapy achieved a significant PR following treatment with ESG401. This favorable response lasted for more than 22.5 months with excellent tolerance and good quality of life, exceeding the duration achieved with previous chemotherapy; this response period was also much longer than the published mPFS from studies using SG (5.5 months) and Dato-Dxd (6.8 months) in the same indication population. This may be attributed to the high TROP2 expression, low tumor burden, good performance status, and excellent efficacy of ESG401. Some possible underlying unveiled reasons may have an impact as well. Further exploration of these factors that may contribute to the patient's prolonged duration response will help to further elucidate the mechanism of drug action and provide meaningful guidance for the treatment of such patients. Moreover, diverse reactions to ESG401 were observed in hepatic and pulmonary lesions, emphasizing the heterogeneous nature of tumors. Variability in TROP2 expression across distinct metastatic loci in breast cancer has been documented(Kojima;, 2024). Re-evaluation through lung metastasis re-biopsy at the onset of progressive disease (PD) could offer valuable insights into the resistance mechanisms of ESG401, thus guiding subsequent therapeutic strategies.\u003c/p\u003e \u003cp\u003eIn conclusion, for patients with endocrine-refractory HR+/HER2- MBC, Trop2-directed ADCs represent an optimal choice for later lines of therapy. Enhanced ADC engineering holds significant promise for maximizing both the efficacy and safety of these agents. ESG401 has demonstrated favorable tolerability with promising signs of efficacy in heavily pretreated patients. Further investigations through expanded clinical trials in HR+/HER2- MBC, as well as a deeper understanding of the characteristics of patients that may impact sustained efficacy, are warranted.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cem\u003eEthics declarations\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis case was approved by\u0026nbsp;Ethics Committee of the Second Affiliated Hospital, Zhejiang University School of Medicine (2021-437). Informed consent was obtained from the patient.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eFunding\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eNone\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eConflicts of interest\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the Authors declare that there are no conflicts of interest.\u003c/p\u003e\n\u003cp\u003eThe manuscript has been read and approved by all the authors\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003e\u003cem\u003eAuthor Contributions\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJing Zhao and \u0026nbsp; Xiaoyan Xing wrote the main manuscript text, Fengbo Huang and Xia Xu prepared figures, Yan Zhang and Fuming Qiu \u0026nbsp; involved in the management of patients, Jian Huang and Fuming Qiu conducted this project. All authors reviewed the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAmbrogi F, Fornili M, Boracchi P et al. Trop-2 is a determinant of breast cancer survival. PLoS One. 2014, 9: e96993.\u003c/li\u003e\n\u003cli\u003eBardia A. A closer look at sacituzumab govitecan-hziy. Clin Adv Hematol Oncol. 2020, 18: 715-7.\u003c/li\u003e\n\u003cli\u003eBardia A, Kalinsky K, Tsurutani J et al. Datopotamab deruxtecan (dato-dxd), a trop2 antibody-drug conjugate, vs investigators\u0026apos; choice of chemotherapy (icc) in previously-treated, inoperable or metastatic hormone-receptor (hr) positive, her2-negative (hr+/her2-) breast cancer: Tropion-breast01. Annals of Oncology. 2022, 33: S663-S.\u003c/li\u003e\n\u003cli\u003eBaselga J, Campone M, Piccart M et al. Everolimus in postmenopausal hormone-receptor-positive advanced breast cancer. N Engl J Med. 2012, 366: 520-9.\u003c/li\u003e\n\u003cli\u003eBidard FC, Kaklamani VG, Neven P et al. Elacestrant (oral selective estrogen receptor degrader) versus standard endocrine therapy for estrogen receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer: Results from the randomized phase iii emerald trial. J Clin Oncol. 2022, 40: 3246-56.\u003c/li\u003e\n\u003cli\u003eCristofanilli M, Turner NC, Bondarenko I et al. Fulvestrant plus palbociclib versus fulvestrant plus placebo for treatment of hormone-receptor-positive, her2-negative metastatic breast cancer that progressed on previous endocrine therapy (paloma-3): Final analysis of the multicentre, double-blind, phase 3 randomised controlled trial. Lancet Oncol. 2016, 17: 425-39.\u003c/li\u003e\n\u003cli\u003eHanker AB, Sudhan DR, Arteaga CL. Overcoming endocrine resistance in breast cancer. Cancer Cell. 2020, 37: 496-513.\u003c/li\u003e\n\u003cli\u003eHart CD, Migliaccio I, Malorni L, Guarducci C, Biganzoli L, Di Leo A. Challenges in the management of advanced, er-positive, her2-negative breast cancer. Nat Rev Clin Oncol. 2015, 12: 541-52.\u003c/li\u003e\n\u003cli\u003eHurvitz SA, Hegg R, Chung WP et al. Trastuzumab deruxtecan versus trastuzumab emtansine in patients with her2-positive metastatic breast cancer: Updated results from destiny-breast03, a randomised, open-label, phase 3 trial. Lancet. 2023, 401: 105-17.\u003c/li\u003e\n\u003cli\u003eKawato Y, Aonuma M, Hirota Y, Kuga H, Sato K. Intracellular roles of sn-38, a metabolite of the camptothecin derivative cpt-11, in the antitumor effect of cpt-11. Cancer Res. 1991, 51: 4187-91.\u003c/li\u003e\n\u003cli\u003eKojima; MOTSY. Abstract po3-15-12: Expression and co-expression patterns of trop2 and her2 in breast cancer: Implications for bispecific antibody-drug conjugate therapy. Cancer Res. 2024, 84: Abstract PO3-15-2.\u003c/li\u003e\n\u003cli\u003eLipinski M, Parks DR, Rouse RV, Herzenberg LA. Human trophoblast cell-surface antigens defined by monoclonal antibodies. Proc Natl Acad Sci U S A. 1981, 78: 5147-50.\u003c/li\u003e\n\u003cli\u003eMa F, Qiu F, Tong Z et al. Preliminary results from a first-in-human study of esg401, a trophoblast cell-surface antigen 2 (trop2) antibody drug conjugate (adc), in patients with locally advanced/ metastatic solid tumors. Journal of Clinical Oncology. 2023, 41.\u003c/li\u003e\n\u003cli\u003eMasood S. Estrogen and progesterone receptors in cytology: A comprehensive review. Diagn Cytopathol. 1992, 8: 475-91.\u003c/li\u003e\n\u003cli\u003eModi S, Jacot W, Yamashita T et al. Trastuzumab deruxtecan in previously treated her2-low advanced breast cancer. N Engl J Med. 2022, 387: 9-20.\u003c/li\u003e\n\u003cli\u003eRugo HS, Bardia A, Marme F et al. Sacituzumab govitecan in hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer. J Clin Oncol. 2022, 40: 3365-76.\u003c/li\u003e\n\u003cli\u003eRugo HS, Lerebours F, Ciruelos E et al. Alpelisib plus fulvestrant in pik3ca-mutated, hormone receptor-positive advanced breast cancer after a cdk4/6 inhibitor (bylieve): One cohort of a phase 2, multicentre, open-label, non-comparative study. Lancet Oncol. 2021, 22: 489-98.\u003c/li\u003e\n\u003cli\u003eSlamon DJ, Neven P, Chia S et al. Overall survival with ribociclib plus fulvestrant in advanced breast cancer. N Engl J Med. 2020, 382: 514-24.\u003c/li\u003e\n\u003cli\u003eSledge GW, Jr., Toi M, Neven P et al. The effect of abemaciclib plus fulvestrant on overall survival in hormone receptor-positive, erbb2-negative breast cancer that progressed on endocrine therapy-monarch 2: A randomized clinical trial. JAMA Oncol. 2020, 6: 116-24.\u003c/li\u003e\n\u003cli\u003eSung H, Ferlay J, Siegel RL et al. Global cancer statistics 2020: Globocan estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin. 2021, 71: 209-49.\u003c/li\u003e\n\u003cli\u003eTarantino P, Ricciuti B, Pradhan SM, Tolaney SM. Optimizing the safety of antibody-drug conjugates for patients with solid tumours. Nat Rev Clin Oncol. 2023, 20: 558-76.\u003c/li\u003e\n\u003cli\u003eTarcsa E, Guffroy MR, Falahatpisheh H, Phipps C, Kalvass JC. Antibody-drug conjugates as targeted therapies: Are we there yet? A critical review of the current clinical landscape. Drug Discov Today Technol. 2020, 37: 13-22.\u003c/li\u003e\n\u003cli\u003eTurner NC, Oliveira M, Howell SJ et al. Capivasertib in hormone receptor-positive advanced breast cancer. N Engl J Med. 2023, 388: 2058-70.\u003c/li\u003e\n\u003cli\u003eVerma S, Miles D, Gianni L et al. Trastuzumab emtansine for her2-positive advanced breast cancer. N Engl J Med. 2012, 367: 1783-91.\u003c/li\u003e\n\u003cli\u003eVidula N, Yau C, Rugo H. Trophoblast cell surface antigen 2 gene (tacstd2) expression in primary breast cancer. Breast Cancer Res Treat. 2022, 194: 569-75.\u003c/li\u003e\n\u003cli\u003eZaman S, Jadid H, Denson AC, Gray JE. Targeting trop-2 in solid tumors: Future prospects. Onco Targets Ther. 2019, 12: 1781-90.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Hormone receptor-positive, Metastatic breast cancer, Endocrine resistance, Trop2, Antibody‒drug conjugate","lastPublishedDoi":"10.21203/rs.3.rs-4429017/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4429017/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBreast cancer (BC) remains a leading cause of cancer-related mortality in women, with hormone receptor-positive (HR+) tumors accounting for a significant proportion of cases. Despite advancements in endocrine therapy (ET), resistance remains a challenge in metastatic settings. The use of cyclin-dependent kinases 4/6 (CDK4/6) inhibitors in combination with endocrine therapy has notably improved survival. In China, when patients develop resistance to CDK4/6 inhibitors (CDK4/6i) or face financial constraints that prevent their use, chemotherapy becomes the standard treatment approach. This highlights an urgent need for effective treatments following CDK4/6i therapy. ESG401 is a novel Trop2-directed antibody-drug conjugate (ADC) with promising preclinical and early clinical efficacy and safety data. We report a case of a 61-year-old female with HR\u0026thinsp;+\u0026thinsp;HER2- metastatic breast cancer (MBC) who developed resistance to fulvestrant and subsequent chemotherapy but achieved a durable partial response (PR) lasting more than 22.5 months following ESG401 treatment. This case underscores the potential role of Trop2-directed ADCs, such as ESG401, in overcoming endocrine resistance and providing meaningful clinical benefit in heavily pretreated patients with HR+/HER2- MBC. Furthermore, the patient's exceptionally long clinical benefit distinguishes her from other patients receiving ESG401 treatment. Further exploration of the use of ESG401 in HR\u0026thinsp;+\u0026thinsp;HER2- MBC patients, as well as a deeper understanding of the characteristics of patients that may impact sustained efficacy, in expanded clinical trials is warranted.\u003c/p\u003e","manuscriptTitle":"Case Report: Prolonged Clinical Benefit of ESG401, a Novel Trophoblast Cell-Surface Antigen 2 (Trop-2) Antibody-Drug Conjugate (ADC), in a Patient with Endocrine- Refractory Hormone Receptor-Positive, HER-2 Negative Metastatic Breast Cancer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-04 15:18:09","doi":"10.21203/rs.3.rs-4429017/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3be54102-938f-4e41-9981-b0b2a6ef9a12","owner":[],"postedDate":"June 4th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-04T15:18:11+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-04 15:18:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4429017","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4429017","identity":"rs-4429017","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}