HER2-targeting Antibody-drug Conjugate Research Articles

329TiP KATE3: A phase III study of trastuzumab emtansine (T-DM1) in combination with atezolizumab or placebo in patients with previously treated HER2-positive and PD-L1–positive locally advanced or metastatic breast cancer

T-DM1, a HER2-targeted antibody–drug conjugate, and atezolizumab, a PD-L1-targeted monoclonal antibody, have shown clinical benefit in HER2-positive and triple-negative breast cancer (BC), respectively. In addition to its cytotoxic effects, T-DM1 potentiates antitumor immunity with a synergistic effect observed in preclinical models when combining PD-L1 and HER2 inhibitors. Exploratory analyses of the randomized, phase 2 KATE2 study suggested a progression free survival (PFS) and overall survival (OS) benefit with atezolizumab plus T-DM1 compared to T-DM1 alone in pre-treated patients with HER2-positive and PD-L1-positive locally advanced (LA)/metastatic (M)BC. These data support further study of T-DM1 plus atezolizumab in this patient population. KATE3 (NCT04740918) is an ongoing randomized, multicenter, double-blind, Phase 3 study of T-DM1 with atezolizumab or placebo in trastuzumab- (± pertuzumab) and taxane-pretreated LA/MBC with centrally-determined HER2-positive and PD-L1–positive (assessed ≤6 months before study entry) unresectable LA/MBC. Patients must have received ≤2 prior lines of therapy for MBC and experienced disease progression during or after LA/MBC therapy or during or within 6 months after (neo)adjuvant therapy. Previous adjuvant T-DM1 is allowed if disease recurrence occurred >6 months after completing T-DM1 treatment. Previous treatment with CD137 agonists and PD-(L)1–targeted agents is allowed. Patients are randomized 1:1 to 3-weekly cycles of T-DM1 3.6 mg/kg and atezolizumab 1200 mg or T-DM1 3.6 mg/kg and placebo. Randomization is stratified by hormone receptor status, disease status, and world region. The multiple primary endpoints are investigator-assessed PFS and OS. Secondary endpoints include objective response rate, response duration, PFS assessed by a blinded independent central review committee, PFS and OS in those with brain metastases at baseline, central nervous system PFS, patient-reported outcomes, and safety. Approximately 350 patients will be enrolled at approximately 175 sites worldwide. NCT04740918. Medical writing support was provided by Tracy McNally, PhD, and Holly Strausbaugh, PhD, on behalf of Twist Medical, LLC, and funded by F. Hoffmann-La Roche, Ltd. F. Hoffmann-La Roche, Ltd.

LBA15 Primary outcome of the phase III SYD985.002/TULIP trial comparing [vic-]trastuzumab duocarmazine to physician’s choice treatment in patients with pre-treated HER2-positive locally advanced or metastatic breast cancer

[vic-]Trastuzumab duocarmazine (SYD985, Byondis B.V., NL) is a novel HER2-targeting antibody–drug conjugate comprised of trastuzumab bound to a linker drug containing duocarmycin. TULIP assessed the efficacy of SYD985 in advanced HER2-positive breast cancer.

LBA1 Trastuzumab deruxtecan (T-DXd) vs trastuzumab emtansine (T-DM1) in patients (Pts) with HER2+ metastatic breast cancer (mBC): Results of the randomized phase III DESTINY-Breast03 study

T-DXd is a HER2-targeting antibody–drug conjugate approved for pts with advanced HER2+ mBC based on the results from DESTINY-Breast01 (NCT03248492). This is the first report of DESTINY-Breast03 (NCT03529110), a multicenter, open-label, randomized phase 3 study comparing the efficacy and safety of T-DXd vs T-DM1 in pts with HER2+ mBC previously treated with trastuzumab and taxane. This is the first reported randomized study of T-DXd in BC.

LBA55 Primary analysis of a phase II single-arm trial of trastuzumab deruxtecan (T-DXd) in western patients (Pts) with HER2-positive (HER2+) unresectable or metastatic gastric or gastroesophageal junction (GEJ) cancer who progressed on or after a trastuzumab-containing regimen

Overexpression and/or amplification of HER2 occurs in ∼20% of gastric or GEJ cancers. In DESTINY-Gastric01, the HER2-targeted antibody-drug conjugate T-DXd improved response and overall survival vs physician’s choice irinotecan/paclitaxel in pts from Japan/Korea with locally advanced or metastatic HER2+ gastric/GEJ cancer who progressed on ≥2L therapy including trastuzumab. Here, we report data from the single-arm, phase 2 DESTINY-Gastric02 trial, the first 2L study of T-DXd in Western pts with HER2+ gastric/GEJ cancer.

284P Trastuzumab emtansine (T-DM1) in Asian patients with previously treated HER2-positive locally advanced (LA) or metastatic breast cancer (MBC): Data from the phase III EMILIA study

The phase 3 EMILIA study (NCT00829166) was initiated based on phase 1 and 2 data identifying the HER2-targeted antibody-drug conjugate T-DM1 as a potential therapy for HER2-positive advanced breast cancer previously treated with trastuzumab (H) and taxane (T). We report a subgroup analysis of Asian patients enrolled in Asia.

Preclinical evaluation of MRG002, a novel HER2-targeting antibody-drug conjugate with potent antitumor activity against HER2-positive solid tumors.

ERBB2 is a proto-oncogene of multiple cancers including breast and gastric cancers with HER2 protein overexpression or gene amplification and has been proven clinically as a valid target for these cancers. HER2-targeting agents such as Herceptin®, Kadcyla® and ENHERTU® have been approved by the FDA for the treatment of breast cancer, but these drugs still face the challenge of acquired resistance and/or severe adverse reactions in clinical use. Therefore, there is significant unmet medical need for developing new agents that are more effective and safer for patients with advanced HER2-positive solid tumors including breast and gastric cancers. We report here the making of MRG002, a novel HER2-targeted antibody drug conjugate (ADC), and preclinical characterization including pharmacology, pharmacodynamics and toxicology and discuss its potential as a novel agent for treating patients with HER2-positive solid tumors. MRG002 exhibited similar antigen binding affinity but much reduced antibody-dependent cellular cytotoxicity (ADCC) activity compared to trastuzumab. In addition to potent in vitro cytotoxicity, MRG002 showed tumor regression in both high- and medium-to-low HER2 expressing in vivo xenograft models. Furthermore, MRG002 showed enhanced antitumor activity when used in combination with an anti-PD-1 antibody. Main findings from toxicology studies are related to the payload and are consistent with literature report of other ADCs with monomethyl auristatinE. MRG002 has demonstrated a favorable toxicity profile and potent antitumor activities in the breast and gastric PDX models with varying levels of HER2 expression, and/or resistance to trastuzumab or T-DM1. A phase I clinical study of MRG002 in patients with HER2-positive solid tumors is ongoing (CTR20181778).

Abstract 1090: Overcoming trastuzumab resistance using trastuzumab deruxtecan (T-DXd), a HER2 targeting antibody drug conjugate, in HER2 amplified gastric cancer

Abstract HER2 is amplified in 7% to 20% of gastric cancer (GC) and is associated with poor clinical outcome. Trastuzumab, HER2-targeting antibody, has already been successfully employed for the treatment of HER2 amplified metastatic GC patients. However, most GC patients who achieved an initial response to the trastuzumab-based regimen developed resistance within 1 year after treatment. In this study, we aimed to investigate the efficacy and biological mechanism of trastuzumab deruxtecan (T-DXd) for overcoming trastuzumab resistance in HER2 amplified GC cell lines. We established four trastuzumab resistant cell lines from HER2 amplified GC cell lines by trastuzumab dose-escalation treatment; YCC-33TR, YCC-38TR, NCI-N87TR, and SNU-216TR. Next, we compared the anti-tumor efficacy of trastuzumab and T-DXd (Daiichi Sankyo, Japan), a HER2-targeting antibody-drug conjugate (ADC), in parental and trastuzumab resistant cell lines. Drug sensitivities were determined by the inhibition rates (IR) at 100μg/ml using cell viability assay. Both in baseline and in post-treatment drug responses, expression levels of proteins such as HER2, Erk, Akt, H2A.X and cPARP were detected by western blotting. The parental cell lines were sensitive to trastuzumab, while four trastuzumab resistant (TR) cell lines demonstrated significant resistance to trastuzumab (p<0.05). Compared with the parental cell lines, pHER2 expression was increased in trastuzumab resistant cell lines, and HER2 expression was decreased but still remained at a high level, suggesting that T-DXd can bind to HER2. As expected, T-DXd was sensitive in both parental and trastuzumab resistant cell lines. In detail, sensitivity to T-DXd in parental and resistant cells were as follows: YCC-33 vs YCC-33TR (79.6% vs 90.7%), YCC-38 vs YCC-38TR (94.4% vs 76.5%), NCI-N87 vs NCI-N87TR (83.8% vs 82.6%), and SNU-216 vs SNU-216TR (58.3% vs 42.6%). When treated with T-DXd to trastuzumab resistant cell lines, the expression levels of HER2 and HER2-related molecules showed various patterns for each cell line, and the expression levels of pH2A.X or cPARP were increased compared to trastuzumab treatment. It seems that T-DXd acts to cause DNA damage and induce apoptosis in parental and trastuzumab resistant cell lines. In summary, the established trastuzumab resistant cell lines retained high HER2 expression, and both HER2 amplified parental and trastuzumab resistant cell lines were sensitive to T-DXd. Our data indicated that T-DXd may have a potential therapeutic effect to overcome trastuzumab resistance in GC. Citation Format: Juin Park, Inhye Jeong, Sun Kyoung Kang, Seo Young Yu, Woo Sun Kwon, Tae Soo Kim, Jihyun Hwang, Hyun Cheol Chung, Sun Young Rha. Overcoming trastuzumab resistance using trastuzumab deruxtecan (T-DXd), a HER2 targeting antibody drug conjugate, in HER2 amplified gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1090.

Abstract 514: Specific anti-HER2 host immunity conferred by HER2-targeted antibody drug conjugate therapy and checkpoint blockade

Abstract Using HER2-targeted antibody drug conjugates (ADC), we tested the therapeutic efficacy, direct impact on cancer stem cells (CSCs), and potential added benefit when combined with PD-L1 blockade in immunocompetent mouse tumor models. Two murine mammary tumor models were used in this study: D2F2/E2, a cell line resulting from stable transfection of parental D2F2 murine mammary tumor cells with wild-type human HER2, and 4T1-HER2, derived from parental 4T1 by stable transduction with wild-type human HER2. We demonstrate that HER2-targeted ADC treatment induced both cellular and humoral anti-HER2 adaptive immune responses which effectively targeted both bulk tumor and cancer stem cells. We recently investigated induction of host immunity using a tumor re-challenge strategy in tumor free animals subjected to ADC or ADC + anti-PD-L1 therapy. D2F2/E2 tumor-bearing mice were treated with ADC or ADC + anti-PD-L1 to generate tumor free mice. These tumor free animals were re-challenged with the relevant tumor D2F2/E2 or irrelevant tumor WT 4T1 respectively. While all the tumor free animals re-challenged with WT 4T1 showed aggressive tumor growth, ADC-treated tumor free animals re-challenged with D2F2/E2 demonstrated significantly (p<0.0001) slower tumor growth compared with the age-matched naive mice, and this protection was significantly (p=0.0078) enhanced in ADC + anti-PD-L1-treated tumor free animals, resulting in completely rejection of the re-challenge and thus documenting immunological memory formation. B cell activation was obvious by the significant upregulation of Ki67 and GL7 CD86 on both CD45+CD19+ tumor-infiltration lymphocytes (TILs) and splenocytes. B cell differentiation was evident by the upregulation of GL7 on both TILs and splenocytes, as well as the expression of CD138 on splenotytes. We found that IgG1 was the predominant isotype in treated mice vs. IgG2a, IgG2b, IgG3, and ADC + anti-PD-L1 dual treatment drastically increased the amount of IgG1 in serum. In addition, ADC+ anti-PD-L1 dual treatment significantly increased the frequency of CD8+IFNγ+ cells in TILs. Both ADC alone (p=0.0004) and ADC+anti-PD-L1 dual treatment (p=0.01) significantly decreased CD4+FoxP3+ regulatory T cells. These results provide evidence that HER2-targeted ADC + anti-PD-L1 immunotherapy-induced B cell activation and differentiation along with the modulation of T cell subsets could confer host anti-HER2 immunity. Citation Format: You Qin, Hannah E. Dobson, Frank I. Comer, Alfred E. Chang, Max S. Wicha, Qiao Li. Specific anti-HER2 host immunity conferred by HER2-targeted antibody drug conjugate therapy and checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 514.

A narrative review of advances in treatment and survival prognosis of HER2-positive malignant lung cancers.

Human epidermal growth factor receptor 2 (HER2), as a receptor tyrosine kinase of EGF receptor family, whose mutation is often associated with even if less frequency but poor prognosis and shorter survival in pulmonary malignant tumor. HER2 status include mutation, overexpression, amplification and also some rare genotypes, detected by next generation sequencing (NGS), immunohistochemistry (IHC), and also fluorescence in situ hybridization (FISH). Different genotypes represent different therapeutic targets and indicate different clinical prognosis concluded by previous studies. Unfortunately, no standard guidelines for first-line treatment are widely recognized, and current therapeutic schedules include chemotherapy, radiotherapy, targeted therapy, and immunotherapy. Especially for patients with advanced metastasis, chemotherapy is based as a systemic therapy using studies of breast cancer or EGFR-positive lung adenocarcinoma as a template. Studies already explored treatment including EGFR tyrosine kinase inhibitors (TKIs) such as gefitinib and afatinib, and also trastuzumab and its conjugation like HER2-targeted antibody-drug conjugate trastuzumab emtansine (T-DM1) and conjugate trastuzumab deruxtecan (T-DXd). Also, he researches explored combination therapy with chemotherapy and TKIs or monoclonal antibodies. This review describes commonly used therapies for HER2-positive/HER2-overexpression patients and general relationship between genotypes of HER2, drug selection and final prognosis in order to provide suggestions for future diagnosis and treatment.

Relative Risk of Peripheral Neuropathy With Ado-Trastuzumab Emtansine (T-DM1) Compared to Taxane-Based Regimens in Human Epidermal Growth Factor Receptor 2 (HER2)-Positive Cancers: A Systematic Review and Meta-Analysis.

BackgroundPeripheral neuropathy (PN), especially peripheral sensory neuropathy (PSN), is significant toxicity of taxanes, the most used class of microtubule inhibitors for human epidermal growth factor receptor 2 (HER2)-positive breast cancer patients. Ado-trastuzumab emtansine (T-DM1) is a HER2-targeted antibody-drug conjugate, consisting of trastuzumab and a microtubule inhibitor DM1, which has been approved for HER2-positive breast cancer. T-DM1 has also been found to cause significant PN, including PSN.MethodsWe conducted a systematic review and meta-analysis of phase 3 randomized controlled trials using T-DM1 in the experimental arm and a taxane-based regimen in the control arm to determine the relative risk of PN and PSN associated with T-DM1 as compared to taxanes. A total of 1,857 patients were included in the analysis. The Cochran-Mantel-Haenszel method and the random-effects model were used to calculate the pooled risk ratio (RR) with a 95% confidence interval (CI) for all-grade and grade ≥3 PN and PSN. ResultsThe relative risks of all-grade PN and all-grade PSN were lower with T-DM1 compared to taxanes. The pooled RR of all-grade PN was 0.59, 95% CI: 0.39-0.89, P = 0.01, and the pooled RR of all-grade PSN was 0.58, 95% CI: 0.46-0.74, P < 0.0001.ConclusionsOur meta-analysis demonstrated that T-DM1 is associated with a relatively lower risk of all-grade PN and PSN than the taxane-based regimens for HER2-positive cancers. It could be an area of consideration in selecting therapy for HER2-positive breast cancer patients at high risk of developing or having pre-existing PN and PSN.

Treatment and prognosis of advanced triple-negative breast cancer patients with HER2-low expression: A 15-year retrospective study.

e13046 Background: There is some tumor defined HER2 1+ or 2+ by IHC and negative in FISH as HER2 low expression in common triple-negative breast cancer (TNBC). This subset is considered to be a new subtype of HER2-low BC, which might benefit from HER2-targeted antibody drug conjugate (ADC). Therefore, it could preliminarily understand on treatment status and treatment needs of HER2-low BC by analysis of the distribution, treatment patterns and prognosis of HER2-low BC in advanced TNBC. Methods: This was a retrospective study which included HR-negative, HER2 IHC 0/1+/2+ and FISH negative ABC patients (pts) diagnosed from June 2006 to September 2020, with recurrence and de novo metastatic cancer at a single institution in China. The cut-off date of follow-up was 31 December 2020. The baseline characteristics, first- and second-line therapies and the clinical outcomes were reported. Results: In total of 195 pts with complete follow-up data were included into final analysis. HR-negative, HER2 IHC 0 pts (triple negative, TN pts) were 61.5% (n = 120), and HR- negative, HER2 IHC 1 + / 2 + and FISH negative pts (HER2-low pts) were 38.5% (n = 75). The baseline characteristics and treatment patterns of HER2-low pts and TN pts were similar. The median age of pts at diagnosis was 48 years old while 54.4% pts were premenopausal. About 80% pts were recurrence, and 27.6% of them received neoadjuvant chemotherapy. The median disease-free interval (DFI) in early stage was 15.5 months, with 66.0% pts for DFI≥12 months. 56.4% of the pts presented with visceral metastasis. The most common sites of metastasis were lung (35.4%), lymph node (27.7%), soft tissue (24.1%), liver (20.5%), bone (20.5%), and brain (6.2%). The most commonly used regimens for first- and second-line were combination chemotherapy, which were 74.7% and 65.3%, respectively; paclitaxel (55.6%) and platinum (43.8%) were the most commonly used drugs for the first-line treatment. Only 14.4% and 3.6% pts received targeted combination therapy and immunotherapy in advanced setting, respectively. In TN and HER2-low ABC pts, the median PFS of first-line treatment were both 7.2 months, and the median OS was 17.2 months and 17.0 months, respectively. In DFI≥12 months and DFI&lt;12 months subgroup, the median PFS was 8.4 months vs. 4.7 months, with a median OS of 17.8 months vs. 14.4 months, respectively. No significant different was observed between HER2-low pts and TN pts. Conclusions: Based on this observational cohort study, there is no significant difference in the current treatment patterns and prognosis between HER2-low pts and TN pts. However, with the emergence of HER2-targeted ADC therapy, HER2-low ABC pts which were commonly defined as TNBC may benefit from these novel therapies. The recurrence subgroup with DFI≥12 months presented a trend of longer OS, suggesting the therapy mode and response in early stage should be considered in advanced TNBC treatment.

TRIO-US B-12 TALENT: Phase II neoadjuvant trial evaluating trastuzumab deruxtecan with or without anastrozole for HER2-low, HR+ early stage breast cancer.

TPS603 Background: Although patients with hormone receptor-positive (HR+)/HER2-negative breast cancer (BC) frequently respond clinically to neoadjuvant treatment, fewer than 10% achieve a pathologic complete response (pCR) with standard chemotherapy or endocrine therapy, even in combination with targeted agents such as CDK4/6 inhibitors. Thus, finding more effective therapies for this disease remains an area of unmet need. HER2 amplification is a known driver of endocrine resistance and HER2 protein may be expressed at a low level (IHC 1+ or 2+) in up to 60% of HR+ BC. Trastuzumab deruxtecan (DS-8201a, T-DXd) is a novel HER2-targeting antibody drug conjugate (ADC) that is FDA approved for HER2-positive metastatic BC and has demonstrated promising clinical efficacy in HER2-low BC with an objective response rate of ̃37%. The aim of TALENT (TRIO-US B-12) is to evaluate the clinical activity and toxicity of neoadjuvant T-DXd either alone or in combination with endocrine therapy in patients with HR+/HER2-low early BC. Methods: TRIO-US B-12 TALENT (NCT04553770) is an ongoing randomized, multicenter, open-label, two-stage, phase II neoadjuvant trial for participants with early stage, HR+, HER2-low expressing (1+ or 2+ by IHC) BC. Eligible participants include men and women with previously untreated, operable invasive BC greater than 2.0 cm (cT2) in size. Pts with recurrent or metastatic BC, or inflammatory BC are excluded. Pts are randomized 1:1 to receive six cycles of T-DXd (5.4 mg/kg IV q21 days) either alone or in combination with anastrozole (1 mg PO QD). Men and pre/peri menopausal women randomized to the anastrozole arm also receive standard of care GnRH agonist. Stratification factors include HER2 expression (1+ or 2+) and menopausal status. Tumor tissue is taken at baseline, cycle 1 day 17-21, and at surgery. Blood samples are taken at four time points for biomarker analysis. The primary endpoint is pCR rate (breast and lymph node) at definitive surgery. In stage I, 58 participants will be randomized (29/arm). If &gt;2 participants in an arm achieve pCR, that arm will expand (stage II) to enroll an additional 15 participants (total of 44/arm). A pCR rate of &gt;10% (5/44) would be considered favorable, warranting further evaluation of the treatment in a larger trial. Other endpoints include safety, changes in Ki67 expression, Residual Cancer Burden index, biomarker analysis (including serial cfDNA analysis), and health-related quality of life. As of January 2021, four participants have enrolled. Conclusions: To our knowledge this is the only ongoing study evaluating T-DXd with or without endocrine therapy for HR+, HER2-low breast cancer in the neoadjuvant setting. The study will shed light on clinical activity and biomarkers, which may guide larger confirmatory studies for patients with HR+, HER2-low early breast cancer. Clinical trial information: NCT04553770.

RC48-ADC, a HER2-targeting antibody-drug conjugate, in patients with HER2-positive and HER2-low expressing advanced or metastatic breast cancer: A pooled analysis of two studies.

1022 Background: Currently, there are no standard ≥3 line regimens recommended for HER2-positive (IHC 3+, or IHC 2+/FISH+) advanced or metastatic breast cancer, and no recommended HER2-targeting treatment for HER2-low expressing (IHC 2+/FISH-, or IHC 1+) population. RC48-ADC is an innovative HER2-targeting antibody-drug conjugate with a cleavable linker and a potent microtubule inhibitor payload MMAE that has a bystanding effect in tumor cell killing. Methods: C001 CANCER (NCT02881138) was a dose-escalation phase I study (0.5, 1.0, 1.5, 2.0, and 2.5 mg/kg) with the 3+3 design among HER2-positive patients. C003 CANCER (NCT03052634) was a phase Ib study with 1.5, 2.0, and 2.5 mg/kg doses in the HER2-positive subgroup and 2.0 mg/kg dose in both IHC 2+/FISH-, and IHC 1+ HER2-low expressing subgroup. C003 CANCER is currently ongoing for IHC 1+ patients. Pooled analysis of the two studies was conducted for the efficacy and safety of RC48-ADC in HER2-positive or HER2-low expressing subgroups. Results: At the time of data cutoff (December 31, 2020), 118 female breast cancer patients were enrolled and treated with RC48-ADC. 70 patients (59.3%) were HER2-positive and 48 patients (40.7%) were HER2-low expressing. At baseline, 77 patients (65.3%) had liver metastases, 50 patients (42.4%) were ECOG PS 1, 47 patients (39.8%) had received ≥3 prior chemotherapy regimens. In the HER2-positive subgroup, ORRs for 1.5, 2.0, and 2.5 mg/kg doses were 22.2% (95% CI: 6.4%, 47.6%), 42.9% (95% CI: 21.8%, 66.0%), and 40.0% (95% CI: 21.1%, 61.3%). mPFSs for 1.5, 2.0, and 2.5 mg/kg cohorts were 4.0 months (95% CI: 2.6, 7.6), 5.7 months (95% CI: 5.3, 8.4) and 6.3 months (95% CI: 4.3, 8.8). In the HER2-low expressing subgroup, the ORR and mPFS were 39.6% (95% CI: 25.8%, 54.7%) and 5.7 months (95% CI: 4.1, 8.3). ORR and mPFS for IHC2+/FISH- patients were 42.9% (15/35) and 6.6 months (95% CI: 4.1, 8.5). For IHC1+ patients, even though the COVID-19 pandemic led to treatment postpone for some patients, ORR and mPFS reached 30.8% (4/13) and 5.5 months (95% CI: 2.7, 11.0). The common treatment-related adverse events (TRAEs) were AST increased (64.4%), ALT increased (59.3%), hypoesthesia (58.5%), white blood cell count decreased (48.3%), and neutrophil count decreased (47.5%); most were grade 1-2 in severity. Neutrophil count decreased (16.9%), GGT increased (12.7%), and fatigue (11.9%) were the grade 3 and above TRAEs occurring in ≥ 10% of the overall population. Conclusions: RC48-ADC showed consistent efficacy in HER2-positive and HER2-low expressing subgroups. The 2.0 mg/kg Q2W showed a more favorable benefit-risk ratio than other dose levels. No new safety signals were observed. Further studies are initiated to evaluate the efficacy and safety of RC48-ADC in various settings. Clinical trial information: NCT02881138; NCT03052634 .

Prevalence of HER2 low in breast cancer subtypes using the VENTANA anti-HER2/neu (4B5) assay.

1021 Background: Breast cancer patients with HER2 low expression by immunohistochemistry (IHC), defined as IHC1+ or IHC2+ without gene amplification (ISH-) do not respond to conventional anti-HER2 therapies such as trastuzumab or pertuzumab. The HER2-targeted antibody-drug conjugate (ADC) trastuzumab deruxtecan (T-DXd) showed efficacy in late line HER2-overexpressing patients, with some responses in patients with low HER2 expression. Two of the market leading IHC IVDs are Dako Herceptest and Ventana 4B5. T-DXd is being investigated in HER2 low patients as determined by the VENTANA anti-HER2/neu (4B5) assay in the phase III DESTINY-Breast04 study. There is a paucity of information on prevalence of IHC1+/2+ in different breast cancer subtypes, which this study aims to address. Methods: HER2 status was calculated from 3750 consecutive primary or metastatic breast cancer patient samples successfully stained using the 4B5 assay and scored locally according to ASCO/CAP 2018 guidelines. Samples were obtained from 3 anatomic pathology labs that support networks of US community hospitals. 500 additional breast cancer samples, pre-selected to include a range of IHC staining (concordance cohort), were stained with both 4B5 and HercepTest (Dako/Agilent) and scored (IHC0, IHC1+, IHC2+, IHC3+) at a central laboratory. Results: Prevalence of HER2 categories in 3750 consecutive breast cancer samples is presented in the table below. &gt;50% of estrogen-receptor positive (ER+ve) and progesterone receptor positive (PR+ve) subtypes are HER2 low. In the 500 sample concordance cohort, 28.0% were IHC1+/2+ using the 4B5 assay compared with 11.6% using HercepTest. HercepTest identified IHC1+/2+ staining in 21.6% [95%CI:15.1,29.4] of the patients classified as IHC1+/2+ by 4B5. 98.3% [95%CI: 96.2, 99.5] of samples IHC0 by 4B5 were also IHC0 by Herceptest. Conclusions: HER2 IHC1+/2+ (ISH-) by Ventana 4B5 represent a significant proportion of breast cancer patients and more than 50% of ER+ve and PR+ve subtypes. The 4B5 assay classed several patients as IHC1+/2+ that are IHC0 by Herceptest, but almost all patients IHC0 by 4B5 were also IHC0 by Herceptest.[Table: see text]

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

TPS595 Background: Patients (pts) with HER2+ early breast cancer (EBC) and invasive residual disease (RD) after neoadjuvant therapy (NAT) have a higher risk of relapse than pts with a pathologic complete response (pCR). Post neoadjuvant T-DM1 has improved invasive disease-free survival (iDFS), but pts with estrogen receptor (ER)-negative or nodal RD have suboptimal outcomes and recurrences in the central nervous system are a problem. More effective treatment strategies are needed. The CompassHER2 trials, EA1181 and A011801, leverage pCR to tailor post neoadjuvant therapy in HER2+ EBC. EA1181 is a NAT de-escalation trial of a taxane, trastuzumab and pertuzumab (THP) in clinical stage II-III HER2+ EBC; pts with a pCR complete HP +/- adjuvant radiation (RT) +/- endocrine therapy (ET). A011801 is an escalation trial for pts with high risk HER2+ RD after NAT, examining addition of the HER2 selective tyrosine kinase inhibitor (TKI) tucatinib to adjuvant T-DM1. Methods: Eligibility and Intervention: Pts. with high-risk HER2+ RD (e.g. ER-,node-positive, or both) after a predefined course of neoadjuvant HER2-directed treatment are randomized 1:1 to adjuvant T-DM1+ placebo (pb), vs. T-DM1 and tucatinib with adjuvant RT +/- ET. Eligibility criteria include completion of ≥ 6 cycles of NAT, including ≥ 9 weeks of T and H +/- P. All chemotherapy (CT) must be completed preoperatively unless participating in EA1181 (̃15-30% enrollees); these pts must receive postoperative CT to complete ≥ 6 cycles prior to enrollment on A011801. Pts who received prior HER2-targeted TKIs or antibody-drug conjugates are ineligible. Objectives: The primary objective is to determine if iDFS is higher with addition of T-DM1 to tucatinib in pts with HER2+ EBC with RD after NAT; 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 pts with/without detectable pretreatment CTCs. Quality of life and pharmacokinetic endpoints will also be 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% &amp; 87%, HR = 0.7), with a two-sided alpha of 0.05 and power of 80%. The sample size is 981; target accrual = 1031 pts; activation and completion dates are 01/6/21 and ̃ 01/2028. Support: U10CA180821, U10CA180882; Seagen Inc; ClinicalTrials.gov Identifier: NCT04457596 Clinical trial information: NCT04457596.

Visualization of Intratumor Pharmacokinetics of [fam-] Trastuzumab Deruxtecan (DS-8201a) in HER2 Heterogeneous Model Using Phosphor-integrated Dots Imaging Analysis

Abstract Purpose: We assessed the intratumor pharmacokinetics of [fam-] trastuzumab deruxtecan, T-DXd (known as DS-8201a), a novel HER2-targeted antibody–drug conjugate, using phosphor-integrated dots (PID)-imaging analysis to elucidate its pharmacologic mechanism. Experimental Design: We used two mouse xenograft models administered T-DXd at the concentration of 4 mg/kg: (i) a heterogeneous model in which HER2-positive and HER2-negative cell lines were mixed, and (ii) a homogeneous model in which both cell types were transplanted separately into the same mouse. PID imaging involved immunostaining using novel high-intensity fluorescent nanoparticles. The distribution of T-DXd was assessed by PID imaging targeting the parent antibody, trastuzumab, and the payload, DXd, in serial frozen sections, respectively. Results: After T-DXd administration in the heterogeneous model, HER2 expression tended to decrease in a time-dependent manner. The distribution of trastuzumab and DXd was observed by PID imaging along the HER2-positive area throughout the observation period. A detailed comparison of the PID distribution between trastuzumab and DXd showed that trastuzumab matched almost perfectly with the HER2-positive area. In contrast, DXd exhibited widespread distribution in the surrounding HER2-negative area as well. In the HER2-negative tumor of the homogeneous model, the PID distribution of trastuzumab and DXd remained extremely low throughout the observation period. Conclusions: Our results suggest that T-DXd is distributed to tumor tissues via trastuzumab in a HER2-dependent manner and then to adjacent HER2-negative areas. We successfully visualized the intratumor distribution of T-DXd and its mechanism of action, the so-called “bystander effect.”

Switchable CAR-T Cells Outperformed Traditional Antibody-Redirected Therapeutics Targeting Breast Cancers.

Various antibody-redirected immunotherapeutic approaches, including antibody-drug conjugates (ADCs), bispecific antibodies (bsAbs), and chimeric antigen receptor-T (CAR-T) cells, have been devised to produce specific activity against various cancer types. Using genetically encoded unnatural amino acids, we generated a homogeneous Her2-targeted ADC, a T cell-redirected bsAb, and a FITC-modified antibody capable of redirecting anti-FITC CAR-T (switchable CAR-T; sCAR-T) cells to target different Her2-expressing breast cancers. sCAR-T cells showed activity against Her2-expressing tumor cells comparable to that of conventional anti-Her2 CAR-T cells and superior to that of ADC- and bsAb-based approaches. To prevent antigen escape, we designed bispecific sCAR-T cells targeting both the Her2 receptor and IGF1R, which showed an overall improved activity against cancer cells with low Her2 expression. This study increases our understanding of various explored cancer therapeutics and underscores the efficient application of sCAR-T cells as a promising therapeutic option for breast cancer patients with low or heterogeneous antigen expression.

Dolaflexin: A Novel Antibody-Drug Conjugate Platform Featuring High Drug Loading and a Controlled Bystander Effect.

After significant effort over the last 30 years, antibody-drug conjugates (ADC) have recently gained momentum as a therapeutic modality, and nine ADCs have been approved by the FDA to date, with additional ADCs in late stages of development. Here, we introduce dolaflexin, a novel ADC technology that overcomes key limitations of the most common ADC platforms with two key features: a higher drug-to-antibody ratio and a novel auristatin with a controlled bystander effect. The novel, cell permeable payload, auristatin F-hydroxypropylamide, undergoes metabolic conversion to the highly potent, but less cell permeable auristatin F to balance the bystander effect through drug trapping within target cells. We conducted studies in mice, rats, and cynomolgus monkeys to complement in vitro characterization and contrasted the performance of dolaflexin with regard to antitumor activity, pharmacokinetic properties, and safety in comparison with the ADC platform utilized in the approved ADC ado-trastuzumab emtansine (T-DM1). A HER2-targeted dolaflexin ADC was shown to have a much lower threshold of antigen expression for potent cell killing in vitro, was effective in vivo in tumors with low HER2 expression, and induced tumor regressions in a xenograft model that is resistant to T-DM1.

HER2-targeted antibody-drug conjugate induces host immunity against cancer stem cells

We previously tested HER2-targeted antibody-drug conjugates (ADCs) in immunocompromised (SCID) mice, precluding evaluation of host immunity, impact on cancer stem cells (CSCs), and potential benefit when combined with PD-L1 blockade. In this study, we tested HER2-targeted ADC in two immunocompetent mouse tumor models. HER2-targeted ADC specifically inhibited the growth of HER2-expressing tumors, prolonged animal survival, and reduced HER2+ and PD-L1+ cells. ADC+ anti-PD-L1 antibody augmented therapeutic efficacy, modulated immune gene signatures, increased the number and function of CD3+ and CD19+ tumor-infiltrating lymphocytes (TILs), induced tumor antigen-specific immunological memory, stimulated B cell activation, differentiation, and IgG1 production both systemically and in the tumor microenvironment. In addition, ADC therapy modulated Tcell subsets and their activation in TILs. Furthermore, HER2-targeted ADC reduced the number and tumorigenicity of ALDHhi CSCs. This study demonstrates that HER2-targeted ADC effectively targets ALDHhi CSCs and this effect is augmented by co-administration of anti-PD-L1 antibody.

Exatecan Antibody Drug Conjugates Based on a Hydrophilic Polysarcosine Drug-Linker Platform

We herein report the development and evaluation of a novel HER2-targeting antibody–drug conjugate (ADC) based on the topoisomerase I inhibitor payload exatecan, using our hydrophilic monodisperse polysarcosine (PSAR) drug-linker platform (PSARlink). In vitro and in vivo experiments were conducted in breast and gastric cancer models to characterize this original ADC and gain insight about the drug-linker structure–activity relationship. The inclusion of the PSAR hydrophobicity masking entity efficiently reduced the overall hydrophobicity of the conjugate and yielded an ADC sharing the same pharmacokinetic profile as the unconjugated antibody despite the high drug-load of the camptothecin-derived payload (drug–antibody ratio of 8). Tra-Exa-PSAR10 demonstrated strong anti-tumor activity at 1 mg/kg in an NCI-N87 xenograft model, outperforming the FDA-approved ADC DS-8201a (Enhertu), while being well tolerated in mice at a dose of 100 mg/kg. In vitro experiments showed that this exatecan-based ADC demonstrated higher bystander killing effect than DS-8201a and overcame resistance to T-DM1 (Kadcyla) in preclinical HER2+ breast and esophageal models, suggesting potential activity in heterogeneous and resistant tumors. In summary, the polysarcosine-based hydrophobicity masking approach allowsfor the generation of highly conjugated exatecan-based ADCs having excellent physicochemical properties, an improved pharmacokinetic profile, and potent in vivo anti-tumor activity.