Trastuzumab Emtansine Research Articles

Abstract 4518: Proteolysis targeting chimera (PROTAC)-driven internalization of antibodies targeting oncogenic cell surface receptors

Abstract Antibody-drug conjugates (ADCs) are increasingly being used in clinic, and many novel ADCs are being tested in clinical trials. Most ADCs act by delivering cytotoxic payloads into target cells. The activity of most ADCs is predicated upon internalization to release the cytotoxic payloads intracellularly to act on the malignant cells. The degree of ADC internalization is incomplete or absent for many cell surface targets, limiting the activity of ADCs. PROTACs are heterobifunctional molecules that result in the polyubiquitylation of their targets by inducing proximity with E3 ligases. The proteasome then recognizes the poly-ubiquitin chains and degrades these targets. We hypothesized that PROTACs that act on the same targets as ADCs could improve the internalization and efficacy of these ADCs. Using multiple cell lines derived from breast, lung or pancreatic cancers that express the oncogenic cell surface proteins EGFR (ERBB1), HER2 (ERBB2) or MET (HGF), we measured antibody internalization with live cell imaging. Antibodies were labeled with a pH sensitive reagent that fluoresces red (640 nm) upon exposure to acidic environments. Fluorescence was measured over time to create an area under the curve which was compared between the cell lines that were treated with and without PROTACs. Antibody internalization was observed in all cell lines that expressed the targets recognized by the antibodies. The addition of PROTACs targeting the same oncogenic cell surface proteins as the antibodies significantly increased antibody internalization beyond that observed without PROTACs. Internalization of antibodies was confirmed by measuring intracellular immunoglobulins by Western blot. Antibody internalization with PROTACs was dose-dependent, increased over time and was blocked by either the clatharin inhibitor Dyngo4a or the proteasome inhibitor MG132. In the case of HER2 for which there are FDA-approved anti-HER2 ADCs, the cytotoxicity of trastuzumab emtansine (TDM1) significantly increased with the addition of a HER2-targeting PROTAC across a range of doses. PROTACs that target the same oncogenic cell surface proteins as antibodies improve antibody internalization and ADC cytotoxicity, in a process dependent upon clatharin and the proteasome. This novel application of PROTACs may impact the use of ADCs, and provides a rationale to combine these agents in clinical trials. Citation Format: Ezequiel J. Tolosa, Lin Yang, Jennifer Ayers-Ringler, Jayapal Mallareddy, Janet Schaefer-Klein, Farhad Kosari, Amar Natarajan, Aaron S. Mansfield. Proteolysis targeting chimera (PROTAC)-driven internalization of antibodies targeting oncogenic cell surface receptors [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 4518.

Abstract 5857: Trastuzumab deruxtecan resistance can be mediated by payload resistance or secondary extracellular ERBB2 mutations but sensitivity to HER2 tyrosine kinase inhibitors is maintained

Abstract Among NSCLC patients, the most common HER2 mutation is the exon 20 insertion mutation, Y772dupYVMA, which accounts for over 40% of all HER2 mutations in lung cancer. Trastuzumab deruxtecan (T-DXd), a HER2 antibody-drug conjugate (ADC), received FDA approval for the treatment of HER2 mutant NSCLC yielding a confirmed objective response of 52% and a median duration of response of greater than 9 months. Unfortunately, patients that initially respond to T-DXd will eventually acquire resistance, and the mechanisms of resistance as well as effective targeting strategies to overcome resistance are not yet elucidated. We generated Ba/F3 cells expressing the HER2 YVMA insertion mutation with acquired resistance to T-DXd by culturing cells in T-DXd until resistance occurred. T-DXd resistant cells retained expression of HER2, but were resistant to the payload, deruxtecan, as well as other topoisomerase inhibitors. T-DXd resistant cells exhibited loss of topoisomerase I, a previously reported mechanism of topoisomerase inhibitor resistance. In parallel, we generated a PDX model of acquired T-DXd resistance and observed sustained expression of HER2 but loss of TOP1 in resistant tumors. T-DXd resistant cell lines were sensitive to payloads with alternate mechanisms of action including maytansine and likewise retained sensitivity to the HER2 ADC trastuzumab emtansine (T-DM1) which utilizes DM1 as a payload. Given that T-DXd resistant cells retained HER2 expression, we assessed whether they were sensitive to HER2 tyrosine kinase inhibitors (TKI). T-DXd resistant cells remained highly sensitive to HER2 TKIs including poziotinib, afatinib, BI-4142, and BI-1622. To investigate whether genomic alterations of HER2 could facilitate HER2 ADC resistance, we utilized the LentiMutate approach which employs an error-prone HIV-1 reverse transcriptase to produce a high frequency of mutations to identify resistance-associated mutations in cells treated with a HER2 ADC. Sequencing analysis revealed that resistant cells had an enrichment in point mutations within HER2 domain IV (D582N, F595C/S, E580K, C623Y), which includes the binding site of trastuzumab. To validate the impact of these mutations on HER2 ADC resistance, we generated cells expressing a HER2 exon 20 insertion in combination with the observed domain IV mutations. D582N and F695C/S co-mutations conferred resistance to T-DXd and T-DM1 but not to HER2 TKIs. These data demonstrate that resistance to T-DXd can be mediated by loss of sensitivity to the ADC payload in which case ADCs bearing payloads with alternate mechanisms of action as well as HER2 TKIs retain anti-tumor cell activity. Moreover, resistance to trastuzumab-based ADCs can also be mediated by secondary mutations within domain IV of HER2. However, these resistance mutations do not diminish HER2 TKI activity. Citation Format: Monique B. Nilsson, Xiuning Le, Junqin He, Xiaoxing Yu, Xiaofang Huo, Ashwani Kumar, Alissa Poteete, Qian Huang, Ralf Kittler, John Heymach. Trastuzumab deruxtecan resistance can be mediated by payload resistance or secondary extracellular ERBB2 mutations but sensitivity to HER2 tyrosine kinase inhibitors is maintained [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 5857.

Abstract 2377: HER2-ADC efficacy is rooted in its induction of immunogenic cell death with FcGR activation and a systemic bystander effect

Abstract Background: T-DXd is an antibody-drug conjugate (ADC) targeting HER2 that has demonstrated superior clinical efficacy over previous HER2-targeting agent Trastuzumab emtansine (T-DM1). Notably, T-Dxd is clinically effective in breast cancers (BC) with a range of HER2 expression. While its purported mechanism of action (MOA) involves its cleavable linker leading to bystander killing, it remains unclear how this potential MOA accounts for efficacy in HER2-low cancers or the role FCGR-mediated signaling and immune induction plays in its clinical efficacy. Method: In vitro studies utilized co-culture, internalization, FCGR activation, ADCP, flow cytometry, and gene expression by QRT-PCR and ELISA assays. Assessments of tumor antigen-specific T cell stimulation involved JEDI T cells. In vivo studies were conducted using in vivo implantation of HER2+ and HER2- cells, PK assessments of T-Dxd/DM1 and therapeutic effects determined using an endogenous HER2 transgenic mouse model that measured HER2-specific adaptive immune responses, in combination with immune checkpoint blockade anti-CD47. Results: T-Dxd elicited a systemic bystander effect that was only partially dependent on HER2 expression, mediated by specific cathepsins in the extracellular TME. Notably, T-Dxd cytotoxicity induced immunogenic cell death (ICD), while also retaining the ability to engage FCGRs to promote ADCP and innate immune activation. ICD was mediated by secretion of specific Dxd driven DAMPs (HMGB1 and eATP), resulting in TLR4/STING activation. ICD and FCGR activation along with antigen ADCP together elicited myeloid cell activation (CD80, CD40) and antigen presentation, resulting in effective expansion of tumor antigen-specific T cells responses, demonstrated by co-culture assays using EGFP/HER2+ BC cells and CD8+ JEDI T cells. T cell activation required TLR4 and STING pathways while in vivo, T-Dxd anti-tumor responses associated with augmented HER2-specific T and B cell responses. However, T-Dxd also induced CD47 to limit phagocytosis. But, the use of CD47/SIRPa blocking antibodies dramatically enhanced CD8+ T cell expansion in vitro and anti-tumor efficacy in vivo upon T-Dxd treatment. Conclusion: Our study demonstrates that T-Dxd is cleavable in HER2 negative BC in vivo, which permits more widespread Dxd activity against HER2 low BC. Critically, Dxd elicits ICD, resulting in innate immune stimulation of myeloid cells, which when combined with FCGR activation and ADCP, leads to a striking induction of tumor-specific adaptive immunity. This combination was unique to T-Dxd, which may underlie its clinical superior efficacy. However, T-Dxd activity also elicits suppressive CD47 expression which could be negated using CD47/SIRPA blockade. We found that this combination dramatically enhanced T-Dxd resulted therapeutic efficacy, thus supporting clinical exploration of these combinations. Citation Format: Li-Chung Tsao, Xingru Ma, John S. Wang, Timothy N. Trotter, Tao Wang, Jun-Ping Wei, Gang-jun Lei, Jason McBane, Ping Fan, Ivan Spasojevic, Zachary C. Hartman. HER2-ADC efficacy is rooted in its induction of immunogenic cell death with FcGR activation and a systemic bystander effect [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 2377.

Effects of trastuzumab emtansine on canine urothelial carcinoma cells in vitro and in vivo.

Urothelial carcinoma (UC) is the most common malignancy of the urinary tract in dogs and has aggressive behaviour. Although human epidermal growth factor receptor 2 (HER2) is a known therapeutic target with evidence in canine UC, the efficacy of anti-HER2 antibody drugs remains unknown. This study aimed to investigate the effects of anti-HER2 antibody drugs including trastuzumab and trastuzumab emtansine (T-DM1) on canine UC cell lines in vitro and in vivo. Four canine UC cell lines (Nene, TCCUB, Love, and Sora) were used. In western blotting, HER2 protein expression was observed in all the cell lines. Although both trastuzumab and T-DM1 showed dose-dependent growth inhibitory activity in the cell lines, T-DM1 showed much stronger activity than that of trastuzumab. In flow cytometry analyses with the canine UC cell line (Sora), T-DM1 but not trastuzumab significantly increased the percentages of early and late apoptotic cells in annexin V apoptotic assays and the sub-G1 phase fraction in cell cycle analyses. For the in vivo experiment, the canine UC cells (Sora) were subcutaneously injected into nude mice. Four days after inoculation, trastuzumab, T-DM1, or vehicle was administered intraperitoneally once a week for three times. Tumour volumes were significantly smaller in the T-DM1 group compared to the trastuzumab and vehicle control groups. These findings indicate that T-DM1 exerts a stronger antitumour effect than that of trastuzumab on canine UC cells in vitro and in vivo, possibly by inducing apoptosis due to DM1.

Neoadjuvant–adjuvant pertuzumab in HER2-positive early breast cancer: final analysis of the randomized phase III PEONY trial

The randomized, multicenter, double-blind, placebo-controlled, phase III PEONY trial (NCT02586025) demonstrated significantly improved total pathologic complete response (primary endpoint) with dual HER2 blockade in HER2-positive early/locally advanced breast cancer, as previously reported. Here, we present the final, long-term efficacy (secondary endpoints: event-free survival, disease-free survival, overall survival) and safety analysis (62.9 months’ median follow-up). Patients (female; n = 329; randomized 2:1) received neoadjuvant pertuzumab/placebo with trastuzumab and docetaxel, followed by adjuvant 5-fluorouracil, epirubicin, and cyclophosphamide, then pertuzumab/placebo with trastuzumab until disease recurrence or unacceptable toxicity, for up to 1 year. Five-year event-free survival estimates are 84.8% with pertuzumab and 73.7% with placebo (hazard ratio 0.53; 95% confidence interval 0.32–0.89); 5-year disease-free survival rates are 86.0% and 75.0%, respectively (hazard ratio 0.52; 95% confidence interval 0.30–0.88). Safety data are consistent with the known pertuzumab safety profile and generally comparable between arms, except for diarrhea. Limitations include the lack of ado-trastuzumab emtansine as an option for patients with residual disease and the descriptive nature of the secondary, long-term efficacy endpoints. PEONY confirms the positive benefit:risk ratio of neoadjuvant/adjuvant pertuzumab, trastuzumab, and docetaxel treatment in this patient population.

Clinical Outcomes of Patients with HER2 Positive Metastatic Breast Cancer to the Brain, with First-Line Trastuzumab, Pertuzumab and Chemotherapy, in a Real-World Setting.

In this observational study, we analyzed the treatment patterns and clinical outcomes of patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (mBC) who developed brain metastases during their disease in a 2.7 million-member public health-provider in Israel. Newly diagnosed patients with mBC who initiated first-line treatment between January 2013 and June 2021 were identified. Time on treatment (ToT) and overall survival (OS) were assessed at a minimum of 6 months follow-up (cutoff: December 2021). We identified a total of 61 patients: 98.4% females, median age 50 years (IQR = 44-63), 85% invasive ductal tumors, 44% hormone receptor positive, 51% performance status 0-1. The median duration of follow-up was 6.2 years. All patients initiated a combination treatment of trastuzumab, pertuzumab, and chemotherapy (TPC), and 72% moved to second-line treatment during the study follow-up period (82% ado-trastuzumab emtansine). The median ToT for first-line and second-line treatments were 16.9 months (95% CI = 13.9-27.7) and 7.9 months (95% CI = 5.6-10.9), respectively. The median overall survival (OS) was 45.5 months (95% CI = 35.4-71.2) from the initiation of first-line treatment. When considering the timing of brain metastases, the median OS was 36.3 months (95% CI = 10.0-NR) for those diagnosed upfront (n = 15, 25%), 59.1 months (95% CI = 32.5-NR) for those diagnosed while on TPC (n = 25, 41%), and 40.8 months (95% CI = 35.4-NR) for those diagnosed at a later stage (n = 21, 34%). The median OS from brain metastases diagnosis was 25.1 months (95% CI = 17.0-34.6). Patients with upfront brain involvement at the time of mBC diagnosis had shorter survival compared to those who started TPC without brain metastases. Nonetheless, the overall results from this study compare favorably with previous studies and contribute to understanding the value of traditional treatment options, which will serve as a baseline for future treatment strategies in the real-world setting.

Charting the Course in Sequencing Antibody-Drug Conjugates in Breast Cancer.

Based on the unprecedented results observed in recent clinical trials, antibody-drug conjugates (ADCs) have revolutionized the treatment algorithm of metastatic breast cancer (mBC). The strategy of sequencing different ADCs in other lines of therapy is highly attractive, but the proportion of patients who have undergone such a strategy in the context of published clinical trials is still limited, especially for modern ADCs. HER2-positive disease is primarily managed with a sequence of different ADCs. Historically, trastuzumab emtansine (T-DM1) has been the most commonly used ADC for both early and metastatic HER2-positive disease. Considering the recent evidence related to trastuzumab deruxtecan (T-DXd), it is expected to assume the role of the main ADC in our clinical practice. Herein, we report a retrospective analysis of the sequence of different ADCs relying on available published data from clinical trials.

Addressing Residual Disease in HER2-Positive and Triple-Negative Breast Cancer: What Is Next?

To summarize the treatment strategies for patients with human epidermal growth factor receptor 2 (HER2)-positive disease and triple-negative breast cancer (TNBC) who have residual disease after preoperative systemic therapy. There has been a shift towards neoadjuvant systemic therapy for selected patients with HER2-positive and TNBC. Assessing the tumor's response to therapy provides prognostic information and allows individualization of the postoperative treatment for these patients based on the tumor response to neoadjuvant therapy. Patients with TNBC with residual disease after neoadjuvant therapy can be treated with pembrolizumab, capecitabine, or olaparib. Those with HER2-positive disease are treated with adjuvant trastuzumab emtansine. The treatment of early breast cancer has evolved significantly, and patient outcomes continue to improve. As better treatments are developed, we will need biomarkers to determine which patients may benefit from certain therapies to continue to improve outcomes by right-sizing treatments and limiting toxicities.

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.

Estimating Public Economic Gains from Early Breast Cancer and Curative Treatment: A Case Study in Human Epidermal Growth Factor Receptor (HER-2) Positive Targeted Therapies.

Cancer diagnosis influences the choices that patients make regarding current and future labor market activity. These choices have implications for governments based on resulting changes in taxes paid and benefits received. In this analysis we explore how human growth receptor 2 (HER2)-positive residual invasive breast cancer and different treatments influence government accounts excluding health costs. HER2-positive early breast cancer (eBC) health states from a published disease model were used to establish likelihood of working and wage impact at different stages of disease. The indirect productivity losses for an average woman aged 49years were translated into fiscal consequences to government by applying an established government perspective-modeling framework. The fiscal projections (discounted) include gross tax revenue by disease stage, government transfer costs related to time off work and early retirement ,and net fiscal balance (e.g., gross taxes-transfers) in three countries Canada, Portugal, and Brazil. The net fiscal balance in Canada for a healthy woman was C$109,551 compared with a HER2-positive eBC woman treated with trastuzumab emtansine (C$69,767) or trastuzumab (C$62,971). A similar pattern was observed in the three countries but reflecting the overall tax burden in each country, labor force activity, and available public benefits. Age at diagnosis was an important determinant of the likely net fiscal balance, as this influences the remaining working years. Women diagnosed with HER2-positive eBC were estimated to pay less lifetime gross taxes and receive more in sickness benefits compared with healthy women. Treatments that improve outcomes are likely to offer fiscal gains for government from improved work force participation.

Antibody and antibody fragments site-specific conjugation using new Q-tag substrate of bacterial transglutaminase

During the last few years Antibody-Drug Conjugates (ADCs) have become one of the most active and very promising therapeutic weapons. Lessons learned from the traditional chemical conjugations (via lysine or cysteine residues of the antibodies) and the clinical studies of the developed ADCs have recently paved the way to the improvement of the conjugation technologies. Use of site-specific conjugation is considered as the promising path for improving the design and development of homogeneous ADCs with controlled Drug-Antibody ratio (DAR). Moreover, some of these conjugations can be applied to antibody fragments such as Fab, scfv and VHH for which random and chemical conjugation showed significant limitations. In this study, we identified a novel small peptide substrate (Q-tag) with high affinity and specificity of bacterial transglutaminase which can be genetically fused to different formats of antibodies of interest for the development of enzymatic site-specific conjugation we named “CovIsolink” platform. We describe the synthesis of chemically defined drugs conjugation in which the site and stoichiometry of conjugation are controlled using a genetically encoded Q-tag peptide with specific amino acids which serves as a substrate of bacterial transglutaminase. This approach has enabled the generation of homogeneous conjugates with DAR 1,7 for full IgG and 0,8 drug ratio for Fab, scfv and VHH antibody fragments without the presence of significant amounts of unconjugated antibody and fragments. As a proof of concept, Q-tagged anti Her-2 (human IgG1 (Trastuzumab) and the corresponding fragments (Fab, scfv and VHH) were engineered and conjugated with different aminated-payloads. The corresponding Cov-ADCs were evaluated in series of in vitro and in vivo assays, demonstrating similar tumor cell killing potency as Trastuzumab emtansine (Kadcyla®) even with lower drug-to-antibody ratio (DAR).

A pharmacovigilance study on antibody-drug conjugate (ADC)-related neurotoxicity based on the FDA adverse event reporting system (FAERS).

Background: Antibody-drug conjugates (ADCs) are a relatively new class of anticancer agents that use monoclonal antibodies to specifically recognize tumour cell surface antigens. However, off-target effects may lead to severe adverse events. This study evaluated the neurotoxicity of ADCs using the FDA Adverse Event Reporting System (FAERS) database. Research design and methods: Data were extracted from the FAERS database for 2004 Q1 to 2022 Q4. We analysed the clinical characteristics of ADC-related neurological adverse events (AEs). We used the reporting odds ratio (ROR) and proportional reporting ratio (PRR) for the disproportionality analysis to evaluate the potential association between AEs and ADCs. Results: A total of 562 cases of neurological AEs were attributed to ADCs. The median age was 65years old [(Min; Max) = 3; 92]. Neurotoxic signals were detected in patients receiving brentuximab vedotin, enfortumab vedotin, polatuzumab vedotin, trastuzumab emtansine, gemtuzumab ozogamicin, inotuzumab ozogamicin, and trastuzumab deruxtecan. The payloads of brentuximab vedotin, enfortumab vedotin, polatuzumab vedotin, and trastuzumab emtansine were microtubule polymerization inhibitors, which are more likely to develop neurotoxicity. We also found that brentuximab vedotin- and gemtuzumab ozogamicin-related neurological AEs were more likely to result in serious outcomes. The eight most common ADC-related nervous system AE signals were peripheral neuropathy [ROR (95% CI) = 16.98 (14.94-19.30), PRR (95% CI) = 16.0 (14.21-18.09)], cerebral haemorrhage [ROR (95% CI) = 9.45 (7.01-12.73), PRR (95% CI) = 9.32 (6.95-12.50)], peripheral sensory neuropathy [ROR (95% CI) = 47.87 (33.13-69.19), PRR (95% CI) = 47.43 (32.93-68.30)], polyneuropathy [ROR (95% CI) = 26.01 (18.61-36.33), PRR (95% CI) = 25.75 (18.50-35.86)], encephalopathy [ROR (95% CI) = 5.16 (3.32-8.01), PRR (95% CI) = 5.14 (3.32-7.96)], progressive multifocal leukoencephalopathy [ROR (95% CI) = 22.67 (14.05-36.58), PRR (95% CI) = 22.52 (14.01-36.21)], taste disorder [ROR (95% CI) = 26.09 (15.92-42.76), PRR (95% CI) = 25.78 (15.83-42.00)], and guillain barrier syndrome [ROR (95% CI) = 17.844 (10.11-31.51), PRR (95% CI) = 17.79 (10.09-31.35)]. The mortality rate appeared to be relatively high concomitantly with AEs in the central nervous system. Conclusion: ADCs may increase the risk of neurotoxicity in cancer patients, leading to serious mortality. With the widespread application of newly launched ADC drugs, combining the FAERS data with other data sources is crucial for monitoring the neurotoxicity of ADCs. Further studies on the potential mechanisms and preventive measures for ADC-related neurotoxicity are necessary.

Abstract B030: ABC101-1, a novel microtubule inhibitor antibody-drug conjugate targeting HER2, has potent anti-tumor activity in a breast cancer model

Abstract Background: ABC101-1 is an antibody-drug conjugate (ADC) targeting receptor tyrosine-protein kinase erbB-2, also known as HER2. ABC101-1 consists of a humanized IgG1 monoclonal antibody called trastuzumab conjugated to a microtubulin inhibitor, DM1, through interchain cysteines with a drug-to-antibody ratio (DAR) of 8. Our novel non-cleavable linker platform using maleimide as a connector enabled the construction of homogeneous ABC101-1 with DAR of 8, via a straightforward process resulting in high conjugation yield. Employing non-cleavable linkers may ensure that the cytotoxic drug is delivered stably to tumor cells, enhancing the therapeutic efficacy of ADC. Herein, we describe anti-breast cancer activity through in vitro cytotoxicity and in vivo efficacy, pharmacokinetics, and binding affinity of ABC101-1. Methods: In vitro cytotoxicity of ADC and linker-payload was evaluated by measuring cell viability using Cell Count Kit-8 (CCK8) analysis. In vivo anti-tumor activity was investigated using SKBR3 cell line-derived xenograft (CDX) model. A pharmacokinetic (PK) profile was assessed by performing indirect ELISA to determine concentrations of total mAb in the serum. The binding affinity of ABC101-1 to HER2 protein was assessed using the indirect ELISA measuring the concentrations of total mAb. Results: In this study, ABC101-1 exhibited potent in vitro cytotoxicity with picomolar activity on HER2-positive breast cancer cell line. In the CDX breast cancer model, ABC101-1 led to stronger tumor growth inhibition in both early and late phases than ado-trastuzumab emtansine (DAR 3.5) at the same dose. Also, the favorable pharmacokinetic profile of ABC101-1 was observed, along with the preserved antigen-binding ability upon the conjugation to linker-payload. Conclusions: ABC101-1 displayed preclinical efficacy in in vitro and in vivo studies as well as a favorable PK, thereby suggesting its therapeutic potential as an anti-tumor drug in breast cancer therapy. This study would reveal that our novel linker platform is a promising and efficient strategy to develop effective and homogeneous ADCs with DAR 8. Our finding may support the further pre-clinical evaluation of ABC101-1. Citation Format: Seo Woo Kim, Hana Yu, Geon Ho Lee, Tae Gyu Lim, Minji Jeong, Hyeonjoo Hwang, Jee Eun Moon, Yong Beom Lee, Sung-Ha Jin, Jin Hyun Jeong. ABC101-1, a novel microtubule inhibitor antibody-drug conjugate targeting HER2, has potent anti-tumor activity in a breast cancer model [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B030.

Abstract A026: An alternative to HER2 IHC 0/1+/2+ status to predict which clinically HER2-negative patients will respond to anti-HER2 therapies: A rationale for the likely superiority of quantitative HER2 pathway RPPA measurements

Abstract Immunohistochemistry (IHC) may not accurately measure HER2 levels and does not reflect HER2 activity/phosphorylation in HER2-negative patients in the HER2 LOW (IHC 1+/2+) and ULTRA-LOW (IHC 0) range [PMID: 35595825). Yet, accurate quantification of HER2 may be key for predicting response to antibody drug conjugates (ADC) such as fam-trastuzumab-deruxtecan-nxki (T-DxD). We showed previously that response to the receptor tyrosine kinase inhibitor (RTKI) neratinib and the ADC ado-trastuzumab emtansine (TDM-1) can be predicted by phospho(p) HER2 Y1248 and pEGFR Y1173, but not total HER2, in TN and HER2+ pts, respectively (PMID: 34741023; 32914002). We now utilize I-SPY2 TRIAL data to explore further relationships between HER2 IHC, Reverse Phase Protein Array (RPPA)-based quantitative HER2 measurement and a HER2 Activation Response Predictive Signature (HARPS) as candidate response predictors for HER2low-targeted agents. Tumors from 395 HER2-negative patients (HR+=200, TN=195) from 8 arms of the I-SPY2 TRIAL had HER2 IHC/FISH data, along with RPPA-based HER2, pHER2 Y1248 and pEGFR Y1173 data from Laser Capture Microdissection (LCM)-enriched tumor epithelium. Of these tumors, 37% (145/395) were HER2 IHC 0, 42% (168/395) were IHC 1+ and 21% (82/395) were IHC 2+. RPPA-based HARPS was categorized as HARPS+ (pHER2-high/pEGFR-high) or HARPS- (pHER2-low and/or pEGFR-low) using previously established combined cut points. Association between quantitative protein values and HER2 IHC was assessed using ANOVA/Tukey tests. Association between endpoint quartiles and IHC was assessed using chi-squared/posthoc tests. RPPA quantitative HER2 total protein levels were associated with HER2 IHC (Tukey p<1E-09), however, the median and ranges of HER2 expression highly overlapped between HER2 IHC 0, 1+ and 2+ (e.g. HER2=0.44 [0.27 - 0.6] in IHC 0 vs 0.69 [0.42-1.0] in IHC 2+). A significant number (34%) of HER2 IHC 0 tumors expressed HER2 above the median level in the HER2 LOW population. While pHER2 and HARPS status were not associated with HER2 IHC class, HARPS associated with total HER2 overall (chi-squared p=8E-05) and in TNBC (chi-squared p=2.4E-06). We found that 42% (81/195) of TNBC were HARPS+, as were 44% (40/89) of HER2 ULTRA-LOW and 40% (41/104) of HER2 LOW tumors. Our results reveal general disconcordance between IHC and RPPA quantitative HER2, with a third of HER2 IHC 0 tumors expressing HER2 and thus, potentially responsive to ADCs such as T-DxD or TDM1. The high proportion of HER2 ULTRA-LOW TNBC tumors classified HARPS+ by our CLIA-based assay identifies tumors predicted to respond to HER2-directed TKI therapies, representing a cohort with actionable HER2 biology missed by IHC. As HER2Low targeted therapies enter ISPY 2.2, we will test the hypothesis that quantitative HER2 is most predictive for HER2 ADCs, and HARPS is most predictive for RTKIs. Citation Format: Julia Wulfkuhle, Denise M. Wolf, Angela DeMichele, Christina Yau, Laura van ‘t Veer, Hope S. Rugo, Lajos Pusztai, Lamorna Brown-Swigart, Gillian L. Hirst, Rosa I. Gallagher, Amy L. Delson, Alexander D. Borowsky, Laura J. Esserman, Paula R. Pohlmann, Emanuel F. Petricoin. An alternative to HER2 IHC 0/1+/2+ status to predict which clinically HER2-negative patients will respond to anti-HER2 therapies: A rationale for the likely superiority of quantitative HER2 pathway RPPA measurements [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A026.

Advances in the study of marketed antibody-drug Conjugates (ADCs) for the treatment of breast cancer.

Breast cancer continues to have a high incidence rate among female malignancies. Despite significant advancements in treatment modalities, the heterogeneous nature of breast cancer and its resistance to various therapeutic approaches pose considerable challenges. Antibody-drug conjugates (ADCs) effectively merge the specificity of antibodies with the cytotoxicity of chemotherapeutic agents, offering a novel strategy for precision treatment of breast cancer. Notably, trastuzumab emtansine (T-DM1) has provided a new therapeutic option for HER2-positive breast cancer patients globally, especially those resistant to conventional treatments. The development of trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) has further broadened the applicability of ADCs in breast cancer therapy, presenting new hopes for patients with low HER2 expression and triple-negative breast cancer. However, the application of ADCs presents certain challenges. For instance, their treatment may lead to adverse reactions such as interstitial lung disease, thrombocytopenia, and diarrhea. Moreover, prolonged treatment could result in ADCs resistance, complicating the therapeutic process. Economically, the high costs of ADCs might hinder their accessibility in low-income regions. This article reviews the structure, mechanism of action, and clinical trials of commercially available ADCs for breast cancer treatment, with a focus on the clinical trials of the three drugs, aiming to provide insights for clinical applications and future research.

Branched pegylated linker-auristatin to control hydrophobicity for the production of homogeneous minibody-drug conjugate against HER2-positive breast cancer

Trastuzumab emtansine (Kadcyla®) was the first antibody-drug conjugate (ADC) approved by the Food and Drug Administration in 2013 against a solid tumor, and the first ADC to treat human epidermal growth factor receptor 2 positive (HER2+) breast cancer. However, this second generation ADC is burden by several limitations included heterogeneity, limited activity against heterogeneous tumor (regarding antigen expression) and suboptimal tumor penetration. To address this, different development strategies are oriented towards homogeneous conjugation, new drugs, optimized linkers and/or smaller antibody formats. To reach better developed next generation ADCs, a key parameter to consider is the management of the hydrophobicity associated with the linker-drug, increasing with and limiting the drug-to-antibody ratio (DAR) of the ADC. Here, an innovative branched pegylated linker was developed, to control the hydrophobicity of the monomethyl auristatin E (MMAE) and its cathepsin B-sensitive trigger. This branched pegylated linker-MMAE was then used for the efficient generation of internalizing homogeneous ADC of DAR 8 and minibody-drug conjugate of DAR 4, targeting HER2. Both immunoconjugates were then evaluated in vitro and in vivo on breast cancer models. Interestingly, this study highlighted that the minibody-MMAE conjugate of DAR 4 was the best immunoconjugate regarding in vitro cellular internalization and cytotoxicity, gamma imaging, ex vivo biodistribution profile in mice and efficient reduction of tumor size in vivo. These results are very promising and encourage us to explore further fragment-drug conjugate development.

The HER2-directed antibody-drug conjugate DHES0815A in advanced and/or metastatic breast cancer: preclinical characterization and phase 1 trial results

Approved antibody-drug conjugates (ADCs) for HER2-positive breast cancer include trastuzumab emtansine and trastuzumab deruxtecan. To develop a differentiated HER2 ADC, we chose an antibody that does not compete with trastuzumab or pertuzumab for binding, conjugated to a reduced potency PBD (pyrrolobenzodiazepine) dimer payload. PBDs are potent cytotoxic agents that alkylate and cross-link DNA. In our study, the PBD dimer is modified to alkylate, but not cross-link DNA. This HER2 ADC, DHES0815A, demonstrates in vivo efficacy in models of HER2-positive and HER2-low cancers and is well-tolerated in cynomolgus monkey safety studies. Mechanisms of action include induction of DNA damage and apoptosis, activity in non-dividing cells, and bystander activity. A dose-escalation study (ClinicalTrials.gov: NCT03451162) in patients with HER2-positive metastatic breast cancer, with the primary objective of evaluating the safety and tolerability of DHES0815A and secondary objectives of characterizing the pharmacokinetics, objective response rate, duration of response, and formation of anti-DHES0815A antibodies, is reported herein. Despite early signs of anti-tumor activity, patients at higher doses develop persistent, non-resolvable dermal, ocular, and pulmonary toxicities, which led to early termination of the phase 1 trial.

Cardiotoxicity from anti-HER-2 therapies in patients with HER-2 positive breast cancer

HER-2 positive (+) breast cancer (BC) accounts for 20-25% of BC, it is more aggressive, and it has a lower survival rate. Since the approval of trastuzumab in 1998, other HER-2-targeted therapies such as pertuzumab and trastuzumab emtansine (TDM1) have been introduced, improving patient survival. However, cardiotoxicity is an adverse effect of these treatments. To estimate the incidence of cardiotoxicity with trastuzumab, trastuzumab/pertuzumab, and TDM1 in women with HER-2 + BC treated over a 6-year period at the Hospital de Clínicas and the Hospital Departamental de Soriano. Observational, descriptive, and retrospective study which included patients with HER-2 + BC treated with trastuzumab, trastuzumab/pertuzumab, or TDM1. 81 patients were included, with a cardiotoxicity incidence of 23.4%. Cardiotoxicity was determined by a > 10% decrease in left ventricular ejection fraction (LVEF) (57.9%) and a LVEF < 50% evident during treatment (42.1%). Only 1 patient presented symptomatic heart failure. 63.1% of those who discontinued treatment due to cardiotoxicity managed to resume it. No relationship was evident between cardiovascular history or the administration regimen and the development of cardiotoxicity. The study showed a cardiotoxicity incidence similar to the international one. Most did not present cardiac toxicity, and if they did, it was asymptomatic and reversible.

Molecular imaging predicts lack of T-DM1 response in advanced HER2-positive breast cancer (final results of ZEPHIR trial)

Efficacy of the human epidermal growth factor receptor (HER)2-targeting trastuzumab emtansine (T-DM1) in breast cancer (BC) relies on HER2 status determined by immunohistochemistry or fluorescence in-situ hybridization. Heterogeneity in HER2 expression, however, generates interest in “whole-body” assessment of HER2 status using molecular imaging. We evaluated the role of HER2-targeted molecular imaging in detecting HER2-positive BC lesions and patients unlikely to respond to T-DM1. Patients underwent zirconium-89 (89Zr) trastuzumab (HER2) PET/CT and [18F]-2-fluoro-2-deoxy-D-glucose (FDG) PET/CT before T-DM1 initiation. Based on 89Zr-trastuzumab uptake, lesions were visually classified as HER2-positive (visible/high uptake) or HER2-negative (background/close to background activity). According to proportion of FDG-avid tumor load showing 89Zr-trastuzumab uptake (entire/dominant part or minor/no part), patients were classified as HER2-positive and HER2-negative, respectively. Out of 265 measurable lesions, 93 (35%) were HER2-negative, distributed among 42 of the 90 included patients. Of these, 18 (19%) lesions belonging to 11 patients responded anatomically (>30% decrease in axial diameter from baseline) after three T-DM1 cycles, resulting in an 81% negative predictive value (NPV) of the HER2 PET/CT. In combination with early metabolic response assessment on FDG PET/CT performed before the second T-DM1 cycle, NPVs of 91% and 100% were reached in predicting lesion-based and patient-based (RECIST1.1) response, respectively. Therefore, HER2 PET/CT, alone or in combination with early FDG PET/CT, can successfully identify BC lesions and patients with a low probability of clinical benefit from T-DM1.