HER2-targeting Antibody-drug Conjugate Research Articles

Abstract PS11-06: Analysis of HER2 expression changes from breast primary to brain metastases including HER2 Low and impact on overall survival

Abstract Background: Previous studies have shown that breast cancer receptor subtype switching between matched primary and metastatic brain metastases (BrM) is common. HER2 expression at low levels, termed “HER2 Low”, has emerged as a new therapeutic biomarker for highly active antibody drug conjugates with potential intracranial activity. Trastuzumab deruxtecan is FDA approved for the treatment of HER2 Low and HER2 positive breast cancer with emerging evidence of CNS responses and clinical benefit in patients with BrM. This study aimed to investigate the relationship between HER2 expression including HER2-Low between matched breast cancer primary tumors and brain metastases. We also sought to evaluate the impact of low HER2 expression on overall survival in breast cancer brain metastases. Methods: We identified pts with MBC seen at least once at a single, NCI-designated center and had a diagnosis of BrM between 2003 and 2023. Of 1252 MBC pts with a diagnosis of BrM, 265 pts underwent resection/biopsy for BrM with available ER/PR/HER2 status. Only pts with available matched primary and BrM tissue were analyzed. HER2 expression was defined as: HER2+ (3+ or 2+/ISH amplified), HER2-Low (1+, 2+/ISH neg) or HER2-0 [by ASCO-CAP guidelines]. Estrogen receptor (ER) status was defined as ER≥1%. Multivariate overall survival (OS) analyses by Cox proportional hazard models were determined from time of BrM resection to death or last follow-up between HER2+, HER2-Low and HER2-0 patients controlling for ER and age. Results: 197 matched breast cancer primary and BrMs with available ER, PR, and HER2 testing were evaluated. Median age at BrM resection was 51 yrs. ER was positive in 48% (N=95) of BrMs. Of 265 resected BrMs, HER2 expression was found in 72%: 49.8% HER2+ (N=132), 22.2% HER2-Low (N=59), and 27.9% HER2-0 (N=74). HER2 expression by 197 primary tumors was: 57% HER2+ (N=112), 24% HER2-Low (N=48), 19% HER2 0 (N=37). Amongst 112 HER2+ primary tumors, 97% (N=109) had concordant HER2+ BrMs, 3 (2.6%) switched to HER2-Low, with 100% retaining some HER2 expression. Of 37 HER2-0 primaries, 35% (13/37) gained HER2-Low expression and 5.4% (2/37) gained HER2+ expression in the BrM. Amongst 48 HER2-Low primary tumors, half (52%) changed expression to either HER2+ (21%) or HER2-0 (31.2%) in the brain. 66 tumors had extracranial tissue biopsied prior to BrM resection available for HER2 analysis. Of 15 HER2-0 extracranial tumors, 47% gained HER2-Low and 13% gained HER2+ at time of BrMs. After adjusting for age and ER status at the time of BrMs, patients with HER2+ BrM had a statistically significant lower risk of death at time of follow up than those with HER2-Low BrM (HR=0.41, P=0.0006). The risk of death between patients with HER2-0 BrM did not differ from HER2-Low BrM after adjustment for ER and age (HR=0.96, p =0.9). Median survival from BrM resection was 12.4m, 16.1m, 47.6m for HER2-Low, HER2-0 and HER2+ respectively (p = .0004). Conclusions: HER2 expression amongst primary, extracranial and brain metastases is dynamic with frequent change. Over 40% of HER2-0 primary or extracranial tumors gain HER2 expression in the brain. These changes have therapeutic implications given HER2 targeting antibody drug conjugates with improved OS and emerging evidence of CNS activity, highlighting the need for better diagnostics, including those that do not require invasive tissue sampling, to determine HER2 status in the brain. Patients with HER2-Low and HER2-0 BrMs have inferior survival and are a clinical unmet need. Citation Format: Alyssa Pereslete, Melissa Hughes, Alyssa Patterson, Janet Files, Kyleen Nguyen, Lauren Buckley, Ashka Patel, Abigail Moore, Eric Winer, Tianyu Li, Sara Tolaney, Nancy Lin, Sarah Sammons. Analysis of HER2 expression changes from breast primary to brain metastases including HER2 Low and impact on overall survival [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 PS11-06.

Abstract PO4-14-12: Predicting Response to HER2 Tyrosine Kinase Inhibitors and Antibody Drug Conjugates in HER2 Mutant Invasive Lobular Carcinoma Using CRISPR/Cas9 Knock-in Cell lines and Patient-derived Organoids

Abstract Background: Activating mutations in ERBB2 (HER2) are enriched >4-fold in invasive lobular carcinoma (ILC) with a rate of up to 19% in metastatic ILC. ILC is a histologic subtype of breast cancer characterized by loss of E-cadherin (CDH1), suggesting a potential interaction between loss of CDH1 and mutations in ERBB2. Recent trials have demonstrated promising single agent efficacy using the irreversible pan-HER tyrosine kinase inhibitor (TKI), neratinib, in patients with metastatic ERBB2 mutant ILC. However, further studies on combination therapies with other anticancer agents are needed to increase response rate and progression free survival for these patients. HER2-targeted antibody drug conjugates (ADC), particularly trastuzumab deruxtecan (T-DXd), have shown great promise in HER2-low metastatic breast cancer. Yet, their efficacy as a single agent or with HER2 TKIs in HER2-low and -mutant ILC is unknown and warrants investigation. Methods: Past studies analyzing ERBB2 mutations used overexpression of ERBB2 mutant cDNA, but this approach does not faithfully recapitulate the human disease. To model ERBB2 missense mutations as found in human breast cancers, we used CRISPR-based prime editing to generate a panel of isogenic ILC cell lines and patient-derived organoids (PDO) harboring ERBB2 wild-type (WT) or ERBB2 mutations (S310F or V777L). Both of these ERBB2 mutations have been previously characterized and are known to be activating mutations. We then used them to test neratinib and other TKIs with ADCs, including T-DXd and trastuzumab emtansine (T-DM1). Results: We successfully introduced single copy, heterozygous activating ERBB2 mutations (S310F or V777L) into two ERBB2-nonamplified metastatic ILC cell lines (MDA-MB-134 and SUM44PE) and one ERBB2-nonamplified metastatic ILC PDO (IPM-BO-053). Positive clones carrying the mutations were verified by Sanger sequencing and droplet digital PCR and subsequently pooled together. We further demonstrated that these mutations hyperactivated HER2 and downstream signaling pathways. ILC cell lines harboring these mutations showed enhanced sensitivity to HER2 TKIs but not ADCs. In contrary, ERBB2 mutations did not alter responses of IPM-BO-053 PDOs to HER2 TKIs but significantly increased responses to ADCs. Interestingly, we also observed accelerated HER2 protein degradation upon heregulin stimulation in ERBB2 mutant ILC PDOs, suggesting activating ERBB2 mutations may enhance ADC/HER2 complex internalization, degradation, and release of payloads. Lastly, we explored drug synergy between HER2 TKIs and ADCs in isogenic IPM-BO-053 PDOs and found that combination of T-DXd and neratinib or afatinib showed synergy (Combination Index < 1). Conclusions: Although the reason for the discrepancies in drug response between ILC cell lines and PDOs is not clear, we hypothesize that response in 3D PDOs might be more faithfully representing response seen in patients. We will generate additional ILC PDOs with knock-in ERBB2 mutations to validate our findings. Irreversible HER2 TKIs, such as neratinib and afatinib, showed synergy with T-DXd in ERBB2 mutant ILC PDOs. This holds important therapeutic implications in light of current treatment options for ILC. In future experiments, we will test if neratinib or afatinib increases endocytic uptake of T-DXd using a fluorescently labeled endocytosis tracker. Further, an in-depth molecular characterization of our isogenic cell lines and PDOs models is ongoing to gain mechanistic insights into how activating ERBB2 mutations increase HER2 internalization and degradation. Our in vitro studies provide a strong foundation for in vivo testing of neratinib or afatinib with T-DXd for ERBB2 mutant ILC. Citation Format: Jie Bin Liu, Danielle Tseng, Jagmohan Hooda, Daniel Brown, Adrian Lee, Steffi Oesterreich. Predicting Response to HER2 Tyrosine Kinase Inhibitors and Antibody Drug Conjugates in HER2 Mutant Invasive Lobular Carcinoma Using CRISPR/Cas9 Knock-in Cell lines and Patient-derived Organoids [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 PO4-14-12.

Abstract PO3-18-11: A011801 (CompassHER2 RD): Postneoadjuvant T-DM1 + tucatinib/placebo in patients with residual HER2-positive invasive breast cancer

Abstract Background: Patients with HER2+ early breast cancer (EBC) and invasive residual disease (RD) after neoadjuvant therapy (NAT) have a higher risk of relapse than patients who have a pathologic complete response (pCR). Escalation of therapy in patients with RD using post-neoadjuvant T-DM1 has become the new standard of care, leading to improved invasive disease-free survival (iDFS), but patients with estrogen receptor (ER)-negative or nodal RD have suboptimal outcomes, and central nervous system recurrences are a challenge. More effective treatment strategies are urgently needed. Alliance A011801 (CompassHER2 RD) is an escalation trial for patients with high-risk HER2+ RD after neoadjuvant systemic therapy, evaluating the addition of the HER2 selective tyrosine kinase inhibitor (TKI) tucatinib to post-neoadjuvant T-DM1. Methods: Eligibility and Intervention: Patients with high-risk HER2+ RD (i.e., ER-, node-positive, or both) after a predefined course of neoadjuvant HER2-directed treatment are randomized 1:1 to adjuvant T-DM1 + placebo, vs. T-DM1 and tucatinib with adjuvant RT +/- ET. Eligibility criteria include completion of ≥ 6 cycles of NAT, including ≥ 9 weeks of paclitaxel and trastuzumab +/- pertuzumab. All chemotherapy (CT) must be completed preoperatively unless participating in EA1181 (~15-30% will be participants in the CompassHER2 pCR de-escalation companion trial [NCT04266249]; these patients must receive postoperative CT to complete ≥ 6 cycles prior to enrollment on A011801). Patients who received prior HER2-targeted TKIs or antibody-drug conjugates are ineligible. Objectives: The primary objective is to determine if iDFS is improved with addition of tucatinib to T-DM1 in patients with HER2+ EBC with RD after neoadjuvant systemic therapy; secondary endpoints include overall survival, breast cancer free survival, distant recurrence-free survival, brain metastases-free survival and disease-free survival. Correlative objectives include the association of i) tumor infiltrating lymphocyte (TILs) levels in the primary tumor and RD with iDFS, ii) TILs with tucatinib benefit, iii) iDFS and circulating tumor cells (CTC) at serial timepoints and iv) the magnitude of benefit of tucatinib (iDFS) in patients with/without detectable pretreatment CTCs. Quality of life and pharmacokinetic endpoints are also being evaluated. Statistics: A011801 is a prospective, double-blind, randomized, phase III superiority trial; stratified by i) receipt of postoperative CT (Y/N), ii) hormone receptor-status (+/-), and iii) pathologic lymph node status (+/-). The study targets an absolute difference of 5% in iDFS (control vs. experimental arm 82% & 87%, HR = 0.7), with a two-sided alpha of 0.05 and power of 80%. The sample size is 981; target accrual = 1031 patients; activation and estimated completion dates are 01/6/21 and ~ 01/2028. Accrual as of 7/10/2023: 438 patients. Support: U10CA180821, U10CA180882; Seagen Inc; https://acknowledgments.alliancefound.org. ClinicalTrials.gov Identifier: NCT04457596 Citation Format: Ciara O'Sullivan, Karla Ballman, Linda McCall, Tyler Zemla, Anna Weiss, Melissa Mitchell, Victoria Blinder, Nadine Tung, William Irvin, Myounghee Lee, Sailaja Kamaraju, Matthew Goetz, W. Fraser Symmans, Virginia Borges, Ian Krop, Ann Partridge, Lisa Carey. A011801 (CompassHER2 RD): Postneoadjuvant T-DM1 + tucatinib/placebo in patients with residual HER2-positive invasive 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 PO3-18-11.

Abstract PO4-15-08: Comprehensive genomic profiling of HER2-low advanced breast cancers

Abstract Background: With the recent approval of the HER2-targeted antibody-drug conjugate (ADC) trastuzumab deruxtecan (T-Dxd) for the treatment of HER2-low advanced breast cancers (aBC), [defined as HER2 immunohistochemistry (IHC) 1+, or 2+ with negative in-situ hybridization (ISH)], there is interest to understand whether this population represents a distinct molecular entity and if there are additional biomarkers that can improve patient selection for these therapies. Here, we examined 2086 aBC cases profiled with comprehensive genomic profiling (CGP) stratified by HER2 status (negative, low, and positive) and hormone receptor (HR) status (positive and negative). Methods: Hybrid-capture CGP targeting 324 genes was performed on advanced BC samples (FoundationOne®CDx). HER2 IHC status was abstracted from pathology reports while HER2 amplification status was abstracted from CGP. Results: We examined 2086 samples of aBC patients distributed as HER2-negative (n=657; IHC 0), HER2-low (n=1012, IHC 1+, 2+ ISH non-amplified), and HER2-positive (n=417; HER2 IHC 3+). HER2-low patients were significantly older than HER2-negative patients (median 60 v 57 years, p=0.0006). HER2-low cases were more common in HR-positive than in HR-negative disease (67% vs 46%, respectively). Overall, characteristics were generally similar for genetic ancestry and TMB-H frequency across all HER2-statuses. MSI-H was rare across all HER2-statuses groups. HER2-low cases were more likely to have alterations in GATA3 (12.6% v 6.5%), ESR1 (12.4% v 7.8%), FGFR2 (4.0% v 1.8%), AR (1.1% v 0.2%), and CDH1 (15.3% v 11.6%) and less likely to harbor alterations in TP53 (44.0% v 62.4%), RB1 (6.8% v 12%), NF1 (5.5% v 9.3%), and BRCA1 (3.0% v 5.2%) when compared to HER2-negative. Some genes showed a consistent pattern of decreased frequency as HER2-IHC expression decreased from HER2-positive to HER2-low and to HER2-negative (e.g. AR alterations seen in 2.6%, 1.1% and 0.2%, respectively) while others had a increasing frequency pattern (e.g. RB1 alterations observed in 2.4%, 6.8% and 12.0%; BRCA1 seen in 1.7%, 3% and 5.2%, respectively). However, some genomic characteristics were unique to the HER2-low population (e.g. TP53 seen in 69.5% of HER2-positive and 62.4% of HER2-negative, but at a lower frequency of 44% in HER2-low cases) [Table 1]. Within the HR-positive subgroup, a lower frequency of NF1 (4.4% v 10.4%), TP53 (30.6% v 41.1%), and RB1 (4.4% v 8.0%) and a higher frequency of AR (1.0% v 0.0%) and GATA3 (16.2% v 10.9%) were observed in HER2-low vs HER2-negative cases, while within the HR-negative subgroup there was a higher frequency of GATA3 (1.2% v 0.7%) and AR (1.2% v 0.4%) and trending lower frequency of TP53 (85.7% v 90.8%) and RB1 (14.3% v 17.4%) in the HER2-low vs. HER2-negative cases. Mutations in homologous recombination repair genes (BRCA1, BRCA2, PALB2) were less frequent in HER2-low cases vs. HER2-negative cases overall (8.4% v 10.7%) and in the HR-positive (3.6% v 5.6%) and HR-negative subgroups (10.6% v 17.4%). Consistent with this, the rate of scar-based HRD signature (HRDsig) was lower in the HER2-low vs. HER2-negative subgroup (15.9% v 20.4%, p=0.02). Conclusions: These data suggest the HER2-low aBC has distinct genomic alterations before and after stratification by HR-status when compared to HER2-negative and HER2-positive aBC cases. Higher prevalence of some potentially actionable alterations in HER2-low cases, including FGFR2, AR, and ESR1, may aid in patient selection and drug development considering new combination approaches. Table 1 Summary of comprehensive genomic profiling alterations observed in HER2-low aBC compared to HER2-positive and HER2-negative cases Citation Format: Adriana Kahn, Ethan Sokol, Jeffrey Ross, Maureen Pelletier, Neal Fischbach, Lajos Pusztai, Maryam Lustberg. Comprehensive genomic profiling of HER2-low advanced breast cancers [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 PO4-15-08.

A Single-Arm, Multicenter, Phase 2 Clinical Study of Recombinant Humanized Anti-HER2 Monoclonal Antibody-MMAE Conjugate (MRG002) in HER2-Positive Unresectable Locally Advanced or Metastatic Urothelial Carcinoma

BackgroundMRG002 is a novel HER2-targeted antibody-drug conjugate being investigated in the MRG002-006 trial to evaluate the efficacy and safety in HER2-positive urothelial carcinoma patients. MethodsThis is an open-label, single-arm, multicenter phase II study. Eligibility criteria included: histologically confirmed HER2 IHC 2+ or 3+ UC, prior received ≥1 standard treatment. Patients in this study received MRG002 every 3 weeks until progressive disease or unacceptable toxicity. The primary endpoint was confirmed ORR per RECIST 1.1. ResultsAs of February 24, 2023, a total of 43 patients were enrolled. The median age was 60. 9 patients were dosed at 2.6mg/kg and 34 patients were dosed at 2.2mg/kg. At baseline, most patients (29/43) received ≥ 2 lines of treatment and 35 (81.4%) patients had prior ICI therapy. FISH test was performed in 41 patients and 9 (22.0%) were positive. By the cut-off date, 41 patients were evaluable and the ORR was 53% (95%CI：38.9%-67.5%), with 6.9% CR, and the DCR was 83.7% (95%CI：70.0%-91.9%). The median PFS and OS for the 43 patients were 7.0 months (95%CI：5.4-NE) and 14.9 months (95%CI：11.9-NE), respectively. The ORR was 77.8% in 9 patients with positive HER2 FISH results. Most common treatment-related AEs were anemia (51.2%), alopecia (44.2%) and neutropenia (39.5%); most were grade 1 or 2. ConclusionPreliminary results of MRG002 demonstrated a clinically meaningful response in pretreated HER-2 positive unresectable locally advanced or metastatic UC patients. MRG002 at 2.2mg/kg was well tolerated with a manageable toxicity.

Abstract CT168: A phase 1/2a, multicenter, open-label, non-randomized first-in-human study to assess the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of DB-1310 (a HER3-targeting ADC) in patients with advanced/metastatic solid tumors

Abstract Background: Overexpression of epidermal growth factor receptor 3 (HER3 or ERBB3) has been reported in various cancers, including lung, prostate, head and neck, breast, and ovarian cancers, and is associated with disease progression and poor prognosis. DB-1310 is an antibody-drug conjugate (ADC) comprised of a humanized anti-HER3 IgG1 monoclonal antibody, covalently linked to a proprietary DNA topoisomerase I inhibitor (P1021) via a maleimide tetrapeptide-based cleavable linker, with a high drug-to-antibody ratio (~8). Preclinical studies of DB-1310 demonstrated promising antitumor activity in solid tumors and a tolerable safety profile, warranting further clinical development. Methods: This global, first-in-human, Phase 1/2a study includes dose escalation and expansion parts to assess the safety, tolerability, pharmacokinetics, and antitumor activity of DB-1310 in patients (pts) with pretreated advanced/metastatic solid tumors (NCT05785741). Eligible pts must have progressed on or after standard systemic anticancer treatments have ECOG PS ≤1, and evidence adequate organ function. Phase 1 part will evaluate 5 ascending dose levels of DB-1310 with a standard “3+3” design to identify the maximum tolerated dose (MTD) and/or recommended phase 2 dose (RP2D) in pts with advanced/metastatic solid tumors. Phase 2a part will initiate after MTD and/or RP2D are determined and enroll pts with non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) activating mutation, NSCLC without EGFR activating mutation, castration-resistant prostate cancer, head and neck squamous cell carcinoma, and HER2-positive (immunohistochemistry [IHC] 3+, or IHC 2+ and in situ hybridization-positive) breast cancer (BC). DB-1310 is administrated intravenously every 3 weeks as monotherapy, or plus trastuzumab in pts with HER2-positive BC only, until discontinuation criteria are met. The study plans to enroll approximately 95 pts in Phase 1 and 192 in Phase 2a from the United States and China. Citation Format: Aaron Lisberg, Shun Lu, Alexander Starodub, Harshad Amin, Julia Rotow, Lin Wu, Alexander Spira, Erika Hamilton, Weidi Shen, Liming Liu, Zhongyuan Zhu, Wei Gu, Yang Qiu, Rong Shi, Shengxue Liu. A phase 1/2a, multicenter, open-label, non-randomized first-in-human study to assess the safety, tolerability, pharmacokinetics, and preliminary antitumor activity of DB-1310 (a HER3-targeting ADC) in patients with advanced/metastatic solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT168.

Abstract CT159: Phase I trial of trastuzumab deruxtecan in combination with neratinib in solid tumors with HER2 alterations (NCI 10495)

Abstract Background: Human epidermal growth factor receptor 2 (HER2) overexpression, amplification, or mutation occurs across a variety of solid tumors. Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate (ADC) that has been approved by the FDA for HER2-overexpressed advanced breast, gastroesophageal cancers, HER2-low breast cancer, and HER2-mutated non-small cell lung cancer. However, some patients do not derive clinical benefit from T-DXd, and drug resistance is inevitable. Preclinical studies demonstrated that neratinib, an oral irreversible pan-HER tyrosine kinase inhibitor, can increase uptake of HER2-targeting ADCs, including ado-trastuzumab emtansine and T-DXd, in vivo. Enhanced uptake of ADC is postulated to be secondary to hindering HSP90 binding to the HER2 receptor, thereby inducing receptor ubiquitination and internalization. This finding was further confirmed in patient-derived xenograft models from two patients with HER2-mutated, but non-amplified, low-expressing advanced breast cancer. Therefore, we hypothesized that the combination of T-DXd and neratinib in patients with advanced solid tumors with a HER2 alteration will enhance the efficacy of T-DXd. As T-DXd and neratinib may have overlapping toxicities in patients, a phase I study to establish the safety of the combination is warranted. Methods: This is a multi-center, phase I clinical trial (NCT05372614, NCI 10495) with a 3+3 design to study the safety and tolerability of T-DXd and neratinib. The trial is supported by the National Cancer Institute Experimental Therapeutics Clinical Trials Network. Eligible patients have advanced solid tumors with HER2 overexpression, amplification by ISH/NGS, or an activating HER2 mutation. Up to 18 evaluable patients will be enrolled in the dose escalation portion (Part 1), and 12 patients will be enrolled in the pharmacodynamic cohort (Part 2). During Part 1, the maximum tolerated dose and recommended phase 2 dose will be determined for neratinib. The dose of T-DXd is fixed at 5.4 mg/kg. We are actively enrolling patients in Part 1. The primary endpoint is dose-limiting toxicities of the combination during the first 2 cycles of treatment (42 days). Key secondary objectives of the study include T-DXd payload (DXd/MAAA-1181a) in tumor tissue obtained before and after co-treatment with neratinib to assess the potential enhanced payload concentration with the combination and quantitative HER2 assessed by mass spectrometry using multiplex reaction monitoring. Citation Format: Andrew A. Davis, Ecaterina E. Dumbrava, Aparna Kalyan, Nataliya V. Uboha, Haider S. Mahdi, Reema A. Patel, Farshid Dayyani, Jessica Porzel, Whitney L. Hensing, Cynthia X. Ma, Ron Bose, Haeseong Park. Phase I trial of trastuzumab deruxtecan in combination with neratinib in solid tumors with HER2 alterations (NCI 10495) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT159.

Abstract 6006: Modeling antibody drug conjugate sensitivity using urothelial carcinoma patient-derived models

Abstract Introduction: Enfortumab Vedotin (EV), an antibody-drug conjugate (ADC) targeting Nectin-4, has emerged as a new standard-of-care for patients with metastatic urothelial cancer (UC). Promising results have also been observed in bladder cancer (BLCA) patients with ADCs targeting HER2. To identify predictive biomarkers of ADC sensitivity, we characterized a large and expanding biobank of patient-derived organoid (PDO) and xenograft (PDX) models for Nectin-4 and HER2 expression, and Nectin-4 and HER2-targeted ADC sensitivity. Methods: We generated 19 PDOs and 34 PDXs that reflect the genomic and biologic heterogeneity of human UC. A subset of these models was further characterized using a multiplatform approach, including bulk and single-cell DNA and RNA sequencing and immunoblot for Nectin-4 and HER2 expression. We leveraged these models to study the biologic determinants of sensitivity to EV and the HER2-targeted ADC trastuzumab deruxtecan (T-DXd). PDX models were treated with EV (5 mg/kg IV on day 1, 3, 6) or T-DXd (10 mg/kg IV on day 1, 21, 42) or vehicle only as control. We also studied sensitivity to T-DXd and EV, as well as to their cytotoxic payloads (exatecan and vedotin) in vitro using paired PDO models. Results: We observed high degree of variability of HER2 and Nectin-4 expression across UC PDOs and PDXs. In PDO models, sensitivity to EV correlated strongly with Nectin-4 expression, whereas HER2 expression was not strongly correlated with sensitivity to T-DXd. We also noted a poor correlation between Nectin-4 expression in PDOs and PDXs derived from the same patient. A subset of models, for example, SMBO-104 (ERBB2 wildtype with low HER2 expression), exhibited significantly greater sensitivity to EV than to T-DXd. Conversely, T-DXd was significantly more active than EV in SMBO-170, a model with ERBB2 amplification (~40 copies) and HER2 3+ expression. Sensitivity to exatecan, an analogue of the T-DXd payload deruxtecan, as measured by inhibition of cell proliferation and induction of apoptosis, was more predictive of T-DXd sensitivity than HER2 expression level. Conclusion: In this study, we generated and biologically characterized UC patient-derived models with the goal of identifying predictive biomarkers of sensitivity to Nectin-4 and HER2-targeted ADCs. We observed significant heterogeneity of HER2 and Nectin-4 expression across models. Models were identified in which T-DXd was superior to EV, and vice versa. Sensitivity to the T-DXd cytotoxic payload was more predictive of PDX response than HER2 expression levels, with significant tumor regression observed with T-DXd in BLCA models with low HER2 expression. Our data suggest that clinical trials of HER2-targeted ADCs such as T-DXd should not be restricted to patients with HER2 overexpression and that novel biomarkers will be needed to identify those UC patients most likely to benefit from FDA-approved and investigational ADCs. Citation Format: Xinran Tang, Ziyu Chen, Jasmine Thomas, Karan Nagar, John Christin, Naryan Rustgi, Sizhi Gao, Elisa de Stanchina, Jonathan Coleman, Michael Shen, Hikmat Al-Ahmadie, Gopa Iyer, Kwanghee Kim, David Solit. Modeling antibody drug conjugate sensitivity using urothelial carcinoma patient-derived models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6006.

Abstract 6352: Preclinical discovery of ARX622: A site-specific, TLR7 agonist, HER2-targeted immune-stimulatory antibody drug conjugate for treatment of multiple solid tumor types

Abstract Traditional antibody-drug conjugates leverage the specificity of antibodies to deliver cytotoxic payloads to tumor microenvironments (TMEs), thereby reducing systemic toxicities associated with non-targeted chemotherapeutics. Analogously, a novel class of immune-stimulating antibody conjugates (ISACs) has recently emerged to selectively deliver synthetic immune agonists to the TME without systemic immune activation. The first generation of ISACs and the majority of approved and investigational ADCs contain payloads linked to native lysine or cysteine residues, which can lead to heterogenous drug-antibody ratios (DARs), reduced antibody stability, and labile conjugation, all of which limit therapeutic index. Here we describe the generation and preclinical characterization of ARX622, a site-specific TLR7-selective agonist ISAC targeting HER2. To avoid the instability issues of previous generation ADCs and ISACs, ARX622 has a homogenous and stable DAR via oxime bond-mediated payload conjugation to a synthetic amino acid, para-acetyl phenylalanine (pAF), which is recombinantly incorporated at defined heavy chain positions. Similar to cytotoxic ADCs built on this site-specific conjugation platform, ARX622 ISAC and total mAb pharmacokinetic (PK) profiles in non-human primates (NHPs) are indistinguishable, demonstrating in vivo stability and minimal payload deconjugation. Accordingly, ARX622 displays an extended PK profile in mice compared to a DAR-matched random cysteine ISAC containing the same antibody and payload. In the presence of HER2-expressing cells, ARX622 selectively induces proinflammatory cytokine production, type I and III IFN secretion, and APC maturation. In a syngeneic tumor model, ARX622 promotes complete tumor regressions, immunologic memory, and epitope spreading. In xenograft systems, single doses of ARX622 induce complete regression of large, established tumors (>1000mm3), and robustly inhibit tumor growth in mice that have progressed through prior treatment with HER2-targeted mAbs or ADCs. In HER2-low xenografts, ARX622 monotherapy inhibits tumor growth, and promotes complete regression of late-stage (800mm3) tumors when sequentially combined with a HER2-ADC. Based on PK data at efficacious doses in mice and tolerated exposures in NHP toxicity studies, ARX622 has an estimated therapeutic index of ~60x. Taken together, ARX622’s mAb-like properties, high stability, broad immune mechanism induction, strong anti-tumor activity alone or in combination with ADCs, and wide therapeutic index make it a strong candidate for further development toward treating patients with a variety of HER2-expressing solid tumors. Citation Format: David Mills, Ji Young Kim, Erica Wood, Keith Tatsukawa, Nick Knudsen, Jay Nelson, Lillian Skidmore, Kedar GC, Hon Tran, Manoj Pal, Hamidreza Hashemi, Ying Buechler, Shawn Zhang, Dan O'Connor. Preclinical discovery of ARX622: A site-specific, TLR7 agonist, HER2-targeted immune-stimulatory antibody drug conjugate for treatment of multiple solid tumor types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6352.

Abstract 6581: DX126-262 combined with chemotherapy (Cisplatin and 5-Fu) demonstrates promising antitumor efficacy in HER2-positive gastric cancer

Abstract Gastric cancer is a common malignant tumor of the digestive system, and its morbidity and mortality rank among the top five in the world. Although significant progress has been made in cytotoxic chemotherapy, immunotherapy and targeted therapy in recent years, the long-term prognosis of patients with advanced or metastatic gastric cancer is still poor. Trastuzumab combined with chemotherapy is the first-line standard of care (SOC) for HER2-positive advanced or metastatic gastric cancer. Two ADC drugs targeting HER2, DS-8201 and RC-48, have also been approved for the treatment of gastric cancer. However, their limited clinical benefits and occurrence of adverse events still present a significant challenge. Therefore, minimizing the off-target toxicity and collateral damage while achieving significant chemotherapy efficacy has become the focus of gastric cancer treatment. DX126-262 is a novel HER2-targeting antibody-drug conjugate (ADC), generated by conjugating a Tubulysin B analogue to a recombinant humanized anti-HER2 monoclonal antibody through a linker containing branched hydrophilic polyethylene glycol, using thiol-maleimide chemistry to achieve drug antibody ratio (DAR) of 3.8. Previous studies have confirmed that DX126-262 monotherapy showed excellent efficacy in HER2-positive gastric cancer NCI-N87 cells in vitro and in vivo. And the efficacy has also been demonstrated in clinical trials (now in phase II, CTR20211871). Based on above results, we intended to further explore whether combination therapy of DX126-262 with Cisplatin and 5-FU can improve the anti-tumor efficacy compared with SOC (Herceptin plus Cisplatin and 5-FU) or DS-8201 monotherapy. The triple-drug combination therapy demonstrated much better therapeutic efficacy than single drug (DX126-262, Cisplatin, 5-FU, Herceptin, or DS-8201) or double-drug combination (Cisplatin plus 5-FU) or SOC (Herceptin plus Cisplatin and 5-FU) on human gastric cancer cells in vitro and in vivo. Meanwhile, triple-drug combination therapy did not exhibit superimposed toxicity, judging by the body weight of mice and hemal biochemistry assays. These results suggested that DX126-262 plus Cisplatin and 5-FU might be a promising strategy for treatment of HER2-positive advanced or metastatic gastric cancer in clinic. Citation Format: Xiaobo Cai, Min Cao, Huihui Guo, Qingliang Yang, Xiangfei Kong, Yong Du, Zhicang Ye, Zhixiang Guo, Lingli Zhang, Lu Bai, Junxiang Jia, Yunxia Zheng, Yongxiang Chen, Miaomiao Chen, Wei Zheng, Jun Zheng, Wenjun Li, Yuanyuan Huang, Mengmeng Liu, Zhongliang Fan, Hangbo Ye, Yifang Xu, Binbin Chen, Meng Dai, Robert Y. Zhao. DX126-262 combined with chemotherapy (Cisplatin and 5-Fu) demonstrates promising antitumor efficacy in HER2-positive gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6581.

Efficacy of Antibody Drug Conjugates Alone and in Combination with other Agents in Metastatic Urothelial Carcinoma: A Scoping Review

INTRODUCTION: Antibody drug conjugates represent a promising class of antineoplastic agents comprised of a monoclonal antibody linked to a potent cytotoxic payload for targeted delivery of chemotherapy to tumors. Various antibody drug conjugates have demonstrated impressive efficacy in patients with metastatic urothelial carcinoma in clinical trials, leading to two FDA approved therapies and several other agents and combinations in clinical development. MATERIALS AND METHODS: A comprehensive systematic review was undertaken utilizing the principles of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Queried databases included Ovid MEDLINE, Ovid Embase, Web of Science Core Collection and Cochrane CENTRAL Trials. The search sought to identify prospective therapeutic clinical trials in humans with metastatic urothelial carcinoma with a single-arm or randomized controlled trial design investigating antibody drug conjugate-containing regimens. RESULTS: The literature search yielded 4,929 non-duplicated articles, of which 30 manuscripts and conference abstracts were included, which derived from 15 clinical trials including 19 separate cohorts with efficacy outcome results. Eleven trials investigated ADC monotherapy, while two investigated combination regimens, and the remaining two studies were mixed. Five unique ADC targets were represented including Nectin-4, Trop-2, HER2, Tissue Factor, and SLITRK6. Twelve clinical trial cohorts required prior treatment (63%). Objective response rate was reported for all studies and ranged from 27–52% for ADC monotherapies and 34–75% for ADC plus anti-PD-1 agents. Time to event outcome reporting was highly variable. CONCLUSION: In addition to enfortumab vedotin and sacituzumab govitecan, various HER2-targeted antibody drug conjugates and ADC-anti-PD-1 combination regimens have demonstrated efficacy in clinical trials and are poised for clinical advancement.

Elucidating molecular mechanisms and therapeutic synergy: irreversible HER2-TKI plus T-Dxd for enhanced anti-HER2 treatment of gastric cancer

BackgroundHER2-targeted therapies have improved the outcomes of HER2-positive gastric cancer (GC), yet resistance remains a challenge. We sought to explore the effects of reversible and irreversible HER2 tyrosine kinase inhibitors (TKIs) alone or in combination with the HER2-targeting antibody drug conjugate trastuzumab deruxtecan (T-Dxd).MethodsThe effects of HER2-TKIs on HER2 and downstream signaling were evaluated via Western blotting. Proteasomal inhibitors and co-immunoprecipitation assays were performed to explore the role of proteasomal degradation in HER2 expression modulation, and immunofluorescence assays were employed to explore mechanisms of HER2 internalization. The synergistic potential of the irreversible HER2-TKI pyrotinib in combination with T-Dxd was validated using growth and viability assays in anti-HER2-positive GC cell cultures and tumor growth and immunohistochemical staining assays in a mouse xenograft model.ResultsOur study revealed that reversible HER2-TKIs elevated HER2 protein levels, whereas irreversible HER2-TKIs decreased them. Pyrotinib triggered HER2 degradation within the proteasome by promoting ubiquitination and dissociation from HSP90. Furthermore, pyrotinib substantially induced HER2 internalization, which led to improved cellular uptake of T-Dxd. The increased T-Dxd uptake was accompanied by greater efficacy in suppressing the growth of GC cells and enhanced anti-tumor effects in an animal model.ConclusionIn summary, our research reveals the molecular mechanisms of irreversible HER2-TKIs in regulating HER2 protein expression by promoting HER2 internalization. These findings advance our comprehension of targeted therapy for GC and provide a promising therapeutic combination strategy with enhanced efficacy against HER2-positive GC.

Comparison of trastuzumab emtansine, trastuzumab deruxtecan, and disitamab vedotin in a multiresistant HER2-positive breast cancer lung metastasis model

Human epidermal growth factor 2 (HER2)-positive breast cancer with lung metastases resistant to targeted agents is a common therapeutic challenge. Absence of preclinical lung metastasis models that are resistant to multiple anti-HER2 targeted drugs hampers the development of novel therapies. We established a novel HER2-positive breast cancer cell line (L-JIMT-1) with a high propensity to form lung metastases from the parenteral JIMT-1 cell line by injecting JIMT-1 cells into immunodeficient SCID mice. Lung metastases developed in all mice injected with L-JIMT-1 cells, and more rapidly and in greater numbers compared with the parental JIMT-1 cells. L-JIMT-1 cells expressed more epidermal growth factor receptor and HER2 than JIMT-1 cells. L-JIMT-1 cells were resistant to all five tyrosine kinase inhibitors tested in vitro (afatinib, erlotinib, lapatinib, sapitinib, and tucatinib). When we compared JIMT-1 and L-JIMT-1 sensitivity to three HER2-targeting antibody-drug conjugates (ADCs) trastuzumab emtansine (T-DM1), trastuzumab deruxtecan (T-DXd), and disitamab vedotin (DV) in vitro, JIMT-1 cells were resistant T-DXd, partially sensitive to T-DM1, and sensitive to DV, while L-JIMT-1 cells were resistant to both T-DM1 and T-DXd, but moderately sensitive to DV. In a mouse model, all three ADCs inhibited the growth of L-JIMT-1 lung metastases compared to a vehicle, but DV and T-DXd more strongly than T-DM1, and DV treatment led to the smallest tumor burden. The L-JIMT breast cancer lung metastasis model developed may be useful in the evaluation of anti-cancer agents for multiresistant HER2-positive advanced breast cancer.

Next-Generation HER2-Targeted Antibody-Drug Conjugates in Breast Cancer.

Human epidermal growth factor receptor 2 (HER2) tyrosine kinase is overexpressed in 20% of breast cancers and associated with a less favorable prognosis compared to HER2-negative disease. Patients have traditionally been treated with a combination of chemotherapy and HER2-targeted monoclonal antibodies such as trastuzumab and pertuzumab. The HER2-targeted antibody-drug conjugates (ADCs) trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd) represent a novel class of therapeutics in breast cancer. These drugs augment monoclonal antibodies with a cytotoxic payload, which is attached by a linker, forming the basic structure of an ADC. Novel combinations and sequential approaches are under investigation to overcome resistance to T-DM1 and T-DXd. Furthermore, the landscape of HER2-targeted therapy is rapidly advancing with the development of ADCs designed to attack cancer cells with greater precision and reduced toxicity. This review provides an updated summary of the current state of HER2-targeted ADCs as well as a detailed review of investigational agents on the horizon. Clinical trials are crucial in determining the optimal dosing regimens, understanding resistance mechanisms, and identifying patient populations that would derive the most benefit from these treatments. These novel ADCs are at the forefront of a new era in targeted cancer therapy, holding the potential to improve outcomes for patients with HER2-positive and HER2-Low breast cancer.

WUTSUP-02-II-Neo-Dis-Tis: Investigating the efficacy and safety of neoadjuvant tislelizumab plus disitamab vedotin with adjuvant tislelizumab in upper urinary tract carcinoma—A phase II multi-center study.

TPS718 Background: Upper tract urothelial carcinoma (UTUC) and urothelial bladder cancer (UBC) are frequently referred to as “disparate twins” despite their common tissue origin. They exhibit varying biological behaviors, prognostic outcomes, and responses to treatment. It is crucial to conduct dedicated clinical trials for UTUC as a separate entity rather than relying solely on UBC study results, giving that UTUC lags in evidence quantity and quality compared to UBC. Despite the superior outcomes of neoadjuvant treatment over adjuvant treatment in UBC trials, the currently available evidence for neoadjuvant therapy of UTUC remains limited in quantity and diversity, as the largest trial, POUT, is focused on adjuvant therapy. Additionally, the limited number of neoadjuvant trials for UTUC primarily utilize chemotherapy-based regimens, with little investigation into combination therapies. Of note, UTUC patients frequently have impaired renal functions, making a chemotherapy-independent approach a desirable alternative. On the other hand, given the short duration of neoadjuvant therapy, a combination therapy strategy appears to be necessary, especially with the increasing interest in immune therapy maintenance after surgery. Tislelizumab has demonstrated efficacy in patients with advanced or metastatic urothelial carcinoma. Disitamab Vedotin, a HER2-targeting antibody-drug conjugate (ADC), has demonstrated robust clinical efficacy in metastatic urothelial carcinoma patients with HER2 2+ or 3+ expression. Disitamab Vedotin in combination with PD-1 immunotherapy has shown remarkable results in locally advanced or metastatic urothelial carcinoma, regardless of HER2 expression, indicative of a synergistic effect between ADC and PD-1 immunotherapy. In this study, we aim to conduct a prospective phase II trial to investigate the efficacy and safety of neoadjuvant tislelizumab plus Disitamab Vedotin followed by adjuvant tislelizumab in patients with high-risk UTUC. Methods: This multi-center phase II trial aims to enroll 45 patients with histologically confirmed UTUC at clinical stage cT2-4N0M0 or cT1-4N1-2M0. Neoadjuvant therapy includes 4 cycles of Tislelizumab (200mg for each 3-week cycle) in combination with Disitamab Vedotin (2.0mg/kg for each 3-week cycle). Radical nephroureterectomy (including bladder cuff resection and regional lymph node dissection if indicated) will be performed if there is no obvious contraindication within 3-6 weeks after the final neoadjuvant therapy administration. Postoperative adjuvant treatment with 8 cycles of tislelizumab will be provided. The primary endpoint is pathological complete response rate. Secondary endpoints include overall survival, local recurrence free survival, distant metastasis free survival, FACT–G. Clinical trial information: ChiCTR2300067836 .

RC48-ADC versus BCG in adjuvant treatment of high-risk non-muscle-invasive bladder cancer with HER2 over-expression: A real-world retrospective study.

644 Background: Bladder cancer ranks as the tenth most prevalent malignancy globally, with non-muscle invasive bladder cancer (NMIBC) accounting for approximately 75% of cases. Patients diagnosed with high-risk NMIBC (HR-NMIBC) face a grim prognosis, characterized by a 5-year disease progression rate of up to 40%. Currently, the standard treatment for HR-NMIBC involves transurethral resection of bladder tumor (TURBT) followed by adjuvant intravesical Bacillus Calmette-Guérin (BCG) therapy. However, BCG infusion therapy is associated with prolonged duration, substantial costs, and a high frequency of toxic side effects. RC48-ADC, a novel humanized anti-HER2 antibody conjugated with monomethyl auristatin E, has shown promising efficacy with a manageable safety profile in patients with locally advanced or metastatic urothelial carcinoma (mUC) in a Phase II clinical trial (NCT03507166). Therefore, investigating the therapeutic potential of RC48-ADC in HR-NMIBC patients holds significant clinical importance. Methods: We conducted a retrospective analysis on patients diagnosed with HR-NMIBC exhibiting HER2 overexpression (≥ HER2 2+) who underwent adjuvant therapy with either RC48-ADC, a HER2-targeting antibody-drug conjugate, or BCG, at West China Hospital of Sichuan University between 2019 and 2023. The primary study endpoint was the twelve-month recurrence-free survival (RFS) rate, with safety assessments as secondary endpoints. Results: A total of thirty patients diagnosed with HR-NMIBC displaying HER2 overexpression were included in the study. Following TURBT, eleven patients received adjuvant therapy with RC48-ADC, while nineteen received adjuvant therapy with BCG. The median follow-up duration for patients receiving RC48-ADC and BCG adjuvant therapy was 7.3 and 16.43 months, respectively. Among patients treated with RC48-ADC, the twelve-month RFS rate was 100%, with one out of the 11 patients experiencing relapse after 14.2 months of RC48-ADC adjuvant therapy. In the BCG-treated group, the twelve-month RFS rate was 57.6%. However, Kaplan-Meier analysis revealed no statistically significant difference between these two groups (P=0.22). In the RC48-treated group, the most commonly reported treatment-related adverse events (TRAEs) included alopecia (45.5%), arthralgia (18.2%), and nausea (18.2%). A total of 27.7% of patients experienced grade 3 TRAEs, including alopecia, rash, and hypoesthesia, with no observations of grade 4 or grade 5 TRAEs. Conclusions: RC48-ADC has demonstrated promising efficacy with a manageable safety profile as an adjuvant therapy in patients with HR-NMIBC. RC48 may be an alternative adjuvant therapy for BCG in terms of the 12-month recurrence-free survival rate.

Development and validation of pharmacokinetics assays for a novel HER2-targeting antibody-drug conjugate (SHR-A1201): Application to its dose-escalation pharmacokinetic study

Approximately 25% of breast cancer patients with HER2 overexpression tend to have a high risk of disease progression and death. Various HER2-targeting therapies have been approved for treatment. Recently, a novel antibody-drug conjugate, SHR-A1201, is being researched and developed. For the pharmacokinetic study of SHR-A1201, suitable bioanalytical methods are needed for quantifying unconjugated cytotoxin, cytotoxin-conjugated antibodies and total antibodies. In this research, bioanalytical methods involving a highly sensitive LC-MS/MS assay for unconjugated cytotoxic payload DM1 in human plasma, ELISA strategies for DM1-conjugated trastuzumab and total trastuzumab in human serum were developed, validated and successfully applied to a phase I dose-escalation pharmacokinetic study of SHR-A1201. The pharmacokinetic properties and exposure-to-dose proportionality was evaluated for SHR-A1201. According to the bioanalytical method validation guidance, the bioanalytical methods were fully validated and the validation results met the acceptance criteria. The nonspecific binding of DM1 and dimer was avoided for the LC-MS/MS assay. In the dose-escalation pharmacokinetic study of SHR-A1201, a potential dose-proportional pharmacokinetics was observed over the dose from 1.2 mg/kg to 4.8 mg/kg. The validated bioanalytical strategies are robust and reproducible and these bioanalytical methods will contribute to better understanding of the pharmacokinetic properties of SHR-A1201.

Disitamab vedotin (RC48) plus toripalimab for HER2-expressing advanced gastric or gastroesophageal junction and other solid tumours: a multicentre, open label, dose escalation and expansion phase 1 trial

Although the antibody-drug conjugates (ADCs) have significantly improved the survival outcomes of patients with human epidermal receptor 2 (HER2)-expressing gastric or gastroesophageal junction (G/GEJ) cancer, the efficacy of ADC used as a single agent is limited. Therefore, it is necessary to investigate effective and safe combination regimens. Preclinical data indicated a synergetic antitumour effect of RC48 and programmed cell death protein 1 (PD-1) inhibitors. We aimed to evaluate the safety and efficacy of RC48 plus toripalimab in patients with HER2-expressing G/GEJ cancer and other solid tumours. This was a open-label, multicentre, phase 1 trial performed at three hospitals in China. Eligible patients had advanced G/GEJ cancer or other solid tumours with HER2 IHC≥1 or ISH positivity and were refractory to at least one line of treatment, or standard treatment was intolerable or unavailable for these patients. This study followed a "3+3" design with predefined RC48 dosages of 2.0mg/kg and 2.5mg/kg plus toripalimab 3mg/kg, once every 2 weeks (q2w). The primary objectives were to evaluate the safety and determine the recommended phase II dose (RP2D), and the secondary objectives included assessing the pharmacokinetics (PK) and preliminary efficacy. This study was registered with ClinicalTrials.gov, NCT04280341. Between July 13, 2020 and August 30, 2022, 56 patients, including 30 patients with G/GEJ cancer and 26 patients with other solid tumours, were enrolled and received RC48 plus toripalimab (n=7 for RC48 2.0mg/kg, toripalimab 3mg/kg, q2w; n=49 for RC48 2.5mg/kg, toripalimab 3mg/kg, q2w). No dose-limiting toxic effects occurred. The RP2D was declared as RC48 2.5mg/kg plus toripalimab 3mg/kg, q2w. The most common grade 3 adverse events were a decreased neutrophil count (n=13), and a decreased white blood cell count (n=7). The efficacy assessment was completed for 52 patients. Among patients with G/GEJ cancer (n=30), the confirmed objective response rate (ORR) was 43% (12/28, 95% CI 25, 63), median progression-free survival (PFS) was 6.2 months (95% CI 4.0, 6.9), median overall survival (OS) was 16.8 months (95% CI 7.2, NE). The ORR of patients with G/GEJ cancer receiving RP2D (n=24) reached 50% (11/22, 95% CI 28, 72), with median PFS of 5.1 months (95% CI 1.4, 7.3) and median OS of 14.0 months (95% CI 6.3, NE). Among patients with G/GEJ cancer who received RP2D, a clinical benefit was observed in both HER2-positive and low HER2 expressing populations, with an ORR of 56% (5/9, 95% CI 21, 86) vs. 46% (6/13, 95% CI 19, 75), median PFS of 7.8 months (95% CI 0.9, NE) vs. 5.1 months (95% CI 1.2, 6.9), median OS of NE months (95% CI 4.3, NE) vs. 14.0 months (95% CI 5.1, NE), respectively. Antitumour activity was also observed for other solid tumours, including breast cancer (5/13) and endometrial carcinoma (1/1). Our findings suggested that RC48 plus toripalimab had a manageable safety profile and showed encouraging efficacy in pretreated patients with HER2-positive and low HER2-expressing G/GEJ cancer. The findings of our phase 1 clinical trial support further investigation of HER2-targeted ADC plus immunotherapy in HER2-expressing G/GEJ cancer and pancancer treatment in the future. Beijing Municipal Medical Research Institutes, Beijing Medical Research Institute (Z200015).

Incidence of HER2-targeted antibody-drug conjugates-related cardiac events: a meta-analysis.

Background: Human epidermal growth factor receptor 2 (HER2)-targeted antibody-drug conjugate (ADC) has emerged as a hotspot for research and brought breakthroughs in the treatment of breast cancer and other solid tumors. While the occurrence of cardiac events (CEs) has yet not been systematically reported. Methods: The prospective clinical trials of marketed HER2-targeted ADCs were systematically searched in PubMed, Embase, Cochrane Library, and ClinicalTrials.gov from inception to May 2023. Two investigators independently extracted data with priority given to ClinicalTrials.gov, followed by peer-reviewed articles. Stata 15.0 software was used to perform the meta-analysis. The effect statistics were estimated as pooled incidence with 95% confidence intervals (CI). The primary objectives were to assess the incidence of all-grade and ≥3 /serious grades CEs related to HER2-targeted ADC. Our study strictly adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and has been registered on PROSPERO (NO. CRD42023440448). Results: After conducting a comprehensive literature search, initially 7000 relevant studies were identified, and eventually a total of 47 trials involving 10594 patients were included for analysis. The pooled incidence of all-grade and ≥3/serious grades CEs respectively were 4.7% [95% CI, 3.7-5.8%] and 0.6% (95% CI, 0.5-0.8%). The pooled incidence of CEs leading to dosage discontinuation was 0.8% (95% CI, 0.4-1.3%). Subgroup analysis revealed a significantly higher incidence of all-grade CEs in T-DXd treatment compared to T-DM1 treatment (7.7% versus 3.6%; p=0.017), as well as in phase I/II trials compared to phase III trials (6.9% versus 3.2%; p=0.002) and combination therapy compared to monotherapy (7.6% versus 3.9%; p=0.013). The electrocardiogram QT corrected interval prolonged was identified as the CE with the highest pooled incidence, occurring at a rate of 5.9% (95% CI, 3.3-8.5%). Conclusions: The incidence of CEs associated with HER2-targeted ADC is relatively low. However, it is crucial to enhance surveillance measures, particularly for T-DXd treatment and combination therapy.

Generation and Characterization of SORT1-Targeted Antibody-Drug Conjugate for the Treatment of SORT1-Positive Breast Tumor.

Antibody-drug conjugates (ADCs) have greatly improved the outcomes of advanced breast tumors. However, the treatment of breast tumors with existing ADCs is still hindered by many issues, such as tumor antigen heterogeneity and drug resistance. Therefore, ADCs against new targets would provide options for the treatment of these challenges. Sortilin-1 (SORT1) may be a promising target for ADC as it is upregulated in breast cancer. To evaluate the possibility of SORT1 as an ADC target, a humanized antibody_8D302 with high affinity against SORT1 was generated. Additionally, 8D302 was conjugated with MMAE and DXd to generate two ADCs_8D302-MMAE and 8D302-DXd, respectively. Both 8D302-MMAE and 8D302-DXd showed effective cytotoxicity against SORT1 positive breast tumor cell lines and induced bystander killing. Consequently, 8D302-MMAE showed relatively better anti-tumor activity than 8D302-DXd both in vitro and in vivo, but 8D302-DXd had superior safety profile and pharmacokinetics profile over 8D302-MMAE. Furthermore, SORT1 induced faster internalization and lysosomal trafficking of antibodies and had a higher turnover compared with HER2. Also, 8D302-DXd exhibited superior cell cytotoxicity and tumor suppression over trastuzumab-DXd, a HER2-targeted ADC. We hypothesize that the high turnover of SORT1 enables SORT1-targeted ADC to be a powerful agent for the treatment of SORT1-positive breast tumor.