HER2-directed Monoclonal Antibody Research Articles

Phase 3 study of disitamab vedotin with pembrolizumab vs chemotherapy in patients with previously untreated locally advanced or metastatic urothelial carcinoma that expresses HER2 (DV-001).

TPS4616 Background: Platinum-based chemotherapy (chemo) has been the standard first-line (1L) therapy for locally advanced or metastatic urothelial carcinoma (la/mUC). Recently, enfortumab vedotin, a nectin-4-directed antibody-drug conjugate (ADC) with a monomethyl auristatin E (MMAE) payload, plus pembrolizumab (pembro) showed improved survival over chemo. Human epidermal growth factor receptor 2 (HER2) expression (immunohistochemistry [IHC] 1+-3+) has been reported in approximately half of all patients (pts) across tumor types, including UC, and is a biomarker that may be associated with poor outcomes. Disitamab vedotin (DV; RC48-ADC) is an investigational ADC comprising a fully humanized HER2-directed monoclonal antibody, disitamab, conjugated to MMAE via a protease-cleavable mc-vc linker. DV elicits antitumor activity through multimodal mechanisms of action, including MMAE-mediated direct cytotoxicity, bystander effect, and immunogenic cell death. DV has shown encouraging activity with a manageable safety profile in pts with la/mUC—as a single agent in a HER2-expressing post-platinum setting (IHC 3+/2+; ORR, 50.5%; median [m]PFS, 5.9 months; mOS, 14.2 months) and in combination with a programmed cell death protein 1 (PD-1) inhibitor in all comers (ORR, 76.0% in treatment-naive pts; 83.3%, 64.3%, and 33.3% in HER2 IHC 3+/2+, IHC 1+, and IHC 0 subgroups, respectively). Improved outcomes observed with an MMAE payload plus PD-1 inhibition across the ADC landscape, along with DV data, provide a robust rationale for this phase 3 trial of DV with pembro in the 1L setting for HER2-expressing la/mUC. Methods: DV-001 (NCT05911295) is an open-label, randomized, multicenter, controlled phase 3 trial evaluating DV with pembro vs chemo in pts with previously untreated HER2-expressing la/mUC. Pts will be randomized 1:1 to Arm A or B. Pts in Arm A will receive DV IV every 2 weeks and pembro IV every 6 weeks. Treatment will continue until disease progression or intolerable toxicity; pembro will be administered for a maximum of 18 6-weekly infusions (approximately 2 years). Pts in Arm B will receive platinum-based chemo with gemcitabine IV on Days 1 and 8 of every 3-week cycle, and either cisplatin or carboplatin on Day 1 of every 3-week cycle for 4-6 cycles. Maintenance therapy with avelumab after completion of chemo may be given to eligible pts where approved and available. Pts must have previously untreated la/mUC, measurable disease per RECIST v1.1, ECOG PS of 0-2 and must be eligible for platinum-based chemo. HER2 expression must be determined using the VENTANA 4B5 HER2 IHC Assay centrally and using the most recent archival or fresh tumor sample. Primary endpoints include PFS per blinded independent central review and OS. Enrollment is ongoing in the US, Canada, and Australia and is planned globally. Clinical trial information: NCT05911295 .

Adjuvant or rescue disitamab vedotin (RC48-ADC) for high-risk non-muscle invasive bladder cancer with HER2 overexpression: A phase II multi-center study.

TPS4625 Background: Non-muscle invasive bladder cancer (NMIBC) comprises approximately three-quarters of newly diagnosed cases of bladder cancer. Based on the risk of disease progression, NMIBC is categorized into low, intermediate, and high risk, with high-risk NMIBC patients facing a 5-year disease progression rate of up to 40%. The current standard treatment for high-risk NMIBC involves transurethral resection of the bladder tumor (TURBT) combined with intravesical Bacillus Calmette-Guérin (BCG) instillation as adjuvant therapy. In cases of BCG instillation treatment failure, the standard approach is radical cystectomy. Multiple studies have reported HER2 positivity in 20-44% of NMIBC cases, and HER2 overexpression (immunohistochemistry ≥2+) is closely linked to the progression and adverse prognosis of bladder cancer. Consequently, HER2 may serve as a novel therapeutic target for bladder cancer. Disitamab Vedotin (DV; RC48-ADC) is an antibody-drug conjugate (ADC) comprising a fully humanized HER2-directed monoclonal antibody conjugated to monomethyl auristatin E (MMAE) via a protease-cleavable mc-vc linker. Results from a Phase II clinical trial (NCT03507166) suggest that Disitamab Vedotin exhibits favorable efficacy and safety in HER2-positive metastatic urothelial carcinoma patients who have previously failed chemotherapy. This clinical trial aims to investigate the efficacy and safety of RC48-ADC as adjuvant or rescue therapy for high-risk NMIBC with HER2 overexpression and to explore molecular biomarkers predicting the efficacy of RC48-ADC. Methods: This multicenter, Phase II clinical trial will enroll two cohorts: Cohort A, consisting of 52 patients undergoing first-line adjuvant therapy, and Cohort B, with 25 patients receiving rescue therapy after BCG instillation failure, both exhibiting HER2 overexpression in high-risk NMIBC. Following the Simon two-stage optimal design, the first stage will involve enrolling 19 patients in Cohort A and 12 patients in Cohort B. After safety and baseline assessments, both cohorts will undergo six cycles of treatment with RC48-ADC (120 mg intravenous infusion every two weeks), totaling 12 weeks of treatment. Primary endpoints include safety, 12-month recurrence-free rate (Cohort A), and 3-month clinical complete response rate (Cohort B). Secondary endpoints encompass the 6-month recurrence-free rate (Cohort A), duration of response (Cohort B), recurrence-free survival, progression-free survival, overall survival, and quality of life (assessed through eEuroQoL EQ-5D and FACT-BI). Additionally, exploratory endpoints will investigate the relationship between biomarkers in tumor tissues, blood, and urine, and treatment efficacy. Clinical trial information: NCT05996952 .

Abstract 1901: Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy in preclinical urothelial cancer models

Abstract Disitamab vedotin (DV, RC48-ADC) is an antibody-drug conjugate (ADC) that selectively delivers cytotoxic drug to HER2-expressing cancer cells. DV is composed of disitamab, a HER2-directed monoclonal antibody, and a vedotin linker-payload system, which enables conjugation of the microtubule-disrupting agent monomethyl auristatin E (MMAE) to the antibody via a protease-cleavable linker. The proposed mechanism of action (MOA) of DV occurs through direct cytotoxicity of HER2-expressing tumor cells following internalization of DV and intracellular release of MMAE. DV may also induce antitumor activity through bystander-mediated cytotoxicity of neighboring cells and via the inhibition of HER2 signaling pathways. Moreover, cellular response to MMAE includes the induction of immunogenic cell death and recruitment of immune cells to the tumor site. DV is currently being evaluated globally in subjects with HER2-expressing locally advanced or metastatic urothelial carcinoma (la/mUC) and has gained conditional approval in China following an overall response rate of 50.5% (pooled analysis from studies NCT03507166 and NCT03809013). RNA sequencing data from a large cohort of urothelial cancer patient tumors revealed expression of HER2 in many urothelial tumors; however, the relationship between HER2 expression and efficacy of DV is not well understood. Here, we sought to evaluate the antitumor activity of DV monotherapy in preclinical urothelial cancer models with varying levels of HER2 expression. Multiple patient-derived xenografts (PDX) and patient-derived 3D in vitro urothelial cancer models showed potent antitumor response to DV monotherapy in tumors with varying HER2 expression levels including HER2-low tumors. Overall, these findings support ongoing clinical trials in subjects with HER2-expressing la/mUC and provide scientific rationale to further explore DV monotherapy in HER2-positive and HER2-low urothelial cancer clinical settings. Citation Format: Renee Hein, Kelsi Willis, Gina LoMastro, Suhas Vasaikar, Vinita Gupta, Katie Snead, Sharsti Sandall, Anita Kulukian. Disitamab vedotin, a clinical stage HER2-directed antibody-drug conjugate, shows potent antitumor activity as a monotherapy in preclinical urothelial cancer 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 1901.

Phase II clinical study evaluating the efficacy and safety of disitamab vedotin combined with sintilimab and S-1 in the conversion treatment of HER2-overexpression unresectable gastric cancer.

TPS428 Background: Gastric cancer (GC) or gastroesophageal junction adenocarcinoma (GEJA) is the fifth commonest cancer and the fourth leading cause of cancer deaths worldwide. In about 30% to 40% of patients with advanced gastric cancer have lost the opportunity for radical surgery at the first diagnosis, and the overall 5-year survival rate is less than 50%. In recent years, conversion therapy has shown great promise. Disitamab vedotin is an antibody-drug conjugate comprising a novel HER2-directed monoclonal antibody, In previous study C008, RC48 showed a good safety profile and promising activity towards GC, and showed equivalent efficacy for HER2 IHC 2+ or HER2 IHC 3+ tumors. Methods: This study is a single-arm, phase II trial carry out at 16 academic hospitals in China, and will evaluate DV combined with Sintilimab and S-1 in patients with HER2-expressing unresectable gastric cancer. Eligible patients are at ≥ 18 to ≤ 75 years old; histologically confirmed, unresectable stage IV GC or GEJA; Single initial unresectable factor. For example, peritoneal metastasis (P1), Intraperitoneal free cancer cells positive (CY1), Paraaortic lymph node metastasis, liver metastasis (≤ 3 lesions, and ≤ 5 cm for a single lesion), ovarian metastasis; and documented histologically confirmed HER2 IHC 3+ or 2+; ECOG 0-1; at least one unresectable, measurable tumor lesion according to the RECIST version 1.1; adaptable function of the heart, liver, and kidney. 30 patients will be enrolled in this trial and receive Disitamab Vedotin(2.5mg/kg, IV, Q3W), Sintilimab (200 mg, IV, Q3W) and S-1 (twice daily on D1-14 are given at a dose calculate according to the body surface area and repeated every 3 weeks), until patients assessed by MDT to meet the criteria for surgical resection undergo gastrectomy. And the patients with peritoneal dissemination will combine with intraperitoneal administration of paclitaxel (60mg / m2, Q3W). The primary endpoint is R0 resection rate, Secondary endpoints include cORR, OS, RFS and safety. Seven patients have been enrolled in this study. Clinical trial information: NCT05627414 .

Phase 2 clinical study evaluating the efficacy and safety of disitamab vedotin with or without pembrolizumab in patients with HER2-expressing urothelial carcinoma (RC48G001).

TPS594 Background: Urothelial carcinoma (UC) is the 10th most diagnosed cancer worldwide, and nearly 50% of patients cannot tolerate the current first-line (1L) standard of care. There is a need to improve outcomes in 1L and later lines of therapy. HER2 is overexpressed in UC and may be associated with poor outcomes. Despite this, no HER2-directed therapies are currently approved for UC. Disitamab vedotin (DV; RC48-ADC) is an investigational antibody-drug conjugate comprising a novel HER2-directed monoclonal antibody, disitamab, conjugated to monomethyl auristatin E (MMAE) via a protease-cleavable mc-vc linker. DV elicits antitumor activity through multimodal mechanisms of action including MMAE-mediated direct cytotoxicity, bystander effect, and immunogenic cell death. Methods: RC48G001 (NCT04879329) is a phase 2, multi-cohort, open-label, multicenter trial to evaluate DV in patients with HER2-expressing locally advanced/metastatic UC (LA/mUC). Patients are enrolled in 3 cohorts based on prior treatment and tumor HER2 expression by immunohistochemistry (IHC) and gene amplification (via in situ hybridization [ISH]), assessed centrally. Cohorts A and B are enrolling patients who have received prior systemic therapy (1 or 2 lines, including platinum-containing chemotherapy) and whose tumors are HER2-positive (IHC 3+, or 2+ and ISH-positive) or HER2-low (IHC 2+ and ISH-negative, or IHC 1+), respectively. Cohort C is enrolling 1L treatment-naive patients in the LA/mUC setting, whose tumors have HER2-positive or HER2-low expression. Cohorts A and B will evaluate DV as monotherapy (intravenous [IV] administration, once every 2 weeks [Q2W]). Cohort C will evaluate DV (IV, Q2W) +/– pembrolizumab (IV, Day 1 of each 6-week cycle). Patients in all cohorts must have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 and an Eastern Cooperative Oncology Group Performance Status of 0–1 in Cohorts A and B, and 0–2 in Cohort C. The primary endpoint is confirmed objective response rate (cORR) per blinded independent central review (BICR). Secondary endpoints include cORR by investigator assessment, overall survival, duration of response, progression-free survival, disease control rate per RECIST v1.1 by BICR and investigator, safety, and pharmacokinetic parameters. Enrollment for all cohorts is ongoing in North America and Europe, and planned in Latin America, Asia-Pacific, and Israel. Clinical trial information: NCT04879329 .

1779TiP Phase II clinical study evaluating the efficacy and safety of disitamab vedotin in patients (pts) with HER2-expressing urothelial carcinoma (RC48G001)

More than 212,000 deaths annually are related to bladder cancer worldwide (Sung 2021), with 5-year survival rates of <5% in metastatic urothelial carcinoma (UC) (Witjes 2021). Nearly half of all pts cannot tolerate standard cisplatin-based first line (1L) chemotherapy and opportunity still exists to improve outcomes in both 1L and later lines of therapy. Human epidermal growth factor receptor 2 (HER2) is overexpressed in multiple malignant tumors and overexpression of HER2 may be associated with poor outcomes in UC (Zhao 2015). No HER2-directed therapies are currently approved for locally advanced unresectable or metastatic UC (LA/mUC). Disitamab vedotin (DV; RC48-ADC) is an investigational antibody–drug conjugate (ADC) comprised of a HER2-directed monoclonal antibody conjugated to monomethyl auristatin E (MMAE) via a protease-cleavable linker. DV elicits antitumor activity through MMAE-directed cytotoxicity and bystander effect (Li 2020). DV is conditionally approved in LA/mUC and gastric cancer in China and was granted Breakthrough Therapy designation by the FDA for second-line treatment of HER2-expressing LA/mUC after platinum-containing chemotherapy. RC48G001 (NCT04879329) is a phase 2, multicohort, open-label, multicenter trial to evaluate DV in pts with HER2-expressing LA/mUC. Pts are enrolled in 2 cohorts defined by HER2 expression (by immunohistochemistry [IHC]) and gene amplification (by in situ hybridization [ISH]) by central laboratory: Cohort A (IHC 3+, or 2+ and ISH+) and Cohort B (IHC 2+ and ISH-, or IHC 1+). Eligible pts must have measurable disease per RECIST v1.1, ECOG Performance Status of 0 or 1, and must have received 1 or 2 lines of prior systemic therapy, including 1 line of platinum-containing chemotherapy. The primary endpoint is confirmed objective response rate (ORR) assessed by blinded independent central review. Secondary endpoints include ORR assessed by investigator, duration of response, progression-free survival, disease control rate, overall survival, safety, and pharmacokinetic parameters. Enrollment for cohorts A and B is ongoing in North America and EU, and planned in LATAM, APAC, and Israel. NCT04879329. Under guidance of the authors, assistance in medical writing was provided by Hanna Thomsen, PhD, of Seagen Inc. and was funded by Seagen Inc. in accordance with Good Publication Practice (GPP3) guidelines. Seagen Inc.

Phase 2 trial of tucatinib plus trastuzumab deruxtecan in patients with HER2+ locally advanced or metastatic breast cancer with and without brain metastases (HER2CLIMB-04, trial in progress).

TPS1111 Background: Tucatinib is an oral reversible small-molecule tyrosine kinase inhibitor highly selective for human epidermal growth factor receptor 2 (HER2). Tucatinib is approved in the US for use in combination with trastuzumab and capecitabine in adult patients with HER2+ metastatic breast cancer (MBC), with and without brain metastases, who have received ≥1 prior anti–HER2-based regimens in the metastatic setting. Trastuzumab deruxtecan (T-DXd), an antibody–drug conjugate (ADC) comprising a HER2-directed monoclonal antibody conjugated to a topoisomerase I inhibitor payload, is also approved in the US for patients with HER2+ MBC. In HER2+ breast cancer (BC) xenograft models, tucatinib increased the antitumor activity of a HER2-directed ADC comprising a HER2-directed monoclonal antibody conjugated with 8 exatecan moieties (T-Ex) when compared to T-Ex alone (Kulukian et al 2019). While significant advances have been made in the treatment of patients with HER2+ BC, treatment of metastatic disease remains a clinical challenge due to limited treatment options. Methods: HER2CLIMB-04 (NCT04539938) is a single-arm, open-label, multicenter, phase 2 study evaluating the efficacy and safety of tucatinib plus T-DXd in previously treated patients aged ≥18 years with unresectable, locally advanced, or metastatic (LA/M) HER2+ BC. Patients must have prior treatment with a taxane and trastuzumab (with or without pertuzumab) in the LA/M setting or progressed within 6 months after neoadjuvant or adjuvant treatment involving a regimen including a taxane and trastuzumab (with or without pertuzumab). Patients with brain metastases, including active brain metastases, may be enrolled. A safety lead-in portion of the study with 10 patients who were followed for at least 1 cycle has been completed. This portion of the study demonstrated a manageable safety profile so the trial will enroll approximately 60 response-evaluable patients (including the 10 patients from the safety lead-in), evenly distributed between patients with and without brain metastases. The primary endpoint is confirmed objective response rate (cORR) by investigator assessment per RECIST 1.1. Secondary endpoints are progression-free survival (PFS), duration of response (DOR), disease control rate (DCR) by investigator assessment per RECIST 1.1, overall survival, and safety. Exploratory endpoints will include cORR, PFS, DCR, and DOR by independent central review per RECIST 1.1, pharmacokinetic analyses, biomarker analyses, and changes in patient-reported outcomes. Efficacy and safety will be summarized with descriptive statistics. Enrollment in the US began in late 2020. Clinical trial information: NCT04539938.

Immunotherapy for HER2-Positive Breast Cancer: Clinical Evidence and Future Perspectives.

Simple SummaryHuman epidermal growth factor receptor 2 (HER2) positive breast cancer is a heterogeneous disease. Among different therapeutic approaches, immunotherapies represent a relevant option for HER2-positive breast cancer patients, both in the adjuvant and metastatic setting. Starting from the dramatic clinical improvement observed with the advent of trastuzumab, which embodied a partly immune-mediated mechanism, a new wave of immunotherapies is now under investigation, including the novel HER2-directed monoclonal antibodies, the antibody–drug conjugates, the immune checkpoint inhibitors, the adoptive T-cell therapies, and therapeutic vaccines. In this narrative review, we present the most important clinical evidence on immunotherapy in HER2-positive breast cancer, and we critically discuss the uncertainties and opportunities in this evolving field of immune-oncology.Breast cancer is the most common malignancy among women worldwide, and HER2-positive breast cancer accounts for approximately 15% of all breast cancer diagnoses. The advent of HER2-targeting therapies has dramatically improved the survival of these patients, significantly reducing their risk of recurrence and death. However, as a significant proportion of patients ultimately develop resistance to these therapies, it is extremely important to identify new treatments to further improve their clinical outcomes. Immunotherapy has revolutionized the treatment and history of several cancer types, and it has already been approved as a standard of care for patients with triple-negative breast cancer. Based on a strong preclinical rationale, immunotherapy in HER2-positive breast cancer represents an intriguing field that is currently under clinical investigation. There is a close interplay between HER2-targeting therapies (both approved and under investigation) and the immune system, and several new immunotherapeutic strategies, including immune checkpoint inhibitors, CAR-T cells and therapeutic vaccines, are being studied in this disease. In this narrative review, we discuss the clinical evidence and the future perspectives of immunotherapy for patients with HER2-positive breast cancer.

Abstract OT1-13-01: HER2CLIMB-04: phase 2 trial of tucatinib + trastuzumab deruxtecan in patients with HER2+ locally advanced or metastatic breast cancer with and without brain metastases (trial in progress)

Abstract Background Tucatinib is an oral, reversible, small-molecule tyrosine kinase inhibitor highly selective for HER2 with minimal inhibition of the human epidermal growth factor receptor. Tucatinib is approved in the US for use in combination with trastuzumab and capecitabine in patients with HER2+ metastatic breast cancer, with and without brain metastases, who have received 1 or more prior anti-HER2-based regimens in the metastatic setting. Trastuzumab deruxtecan (T-DXd), an antibody-drug conjugate (ADC) comprising a HER2-directed monoclonal antibody conjugated to a topoisomerase I inhibitor payload, is approved in the US for patients with HER2+ metastatic breast cancer who have received 2 or more prior anti-HER2-based regimens in the metastatic setting. In HER2+ breast cancer xenograft models, tucatinib increased the antitumor activity of a HER2-directed ADC comprising a HER2-directed monoclonal antibody conjugated with 8 exatecan moieties (T-Ex) when compared to T-Ex alone (Kulukian, et al. (2019). Abstract P1-18-09. Proceedings of San Antonio Breast Cancer Symposium, December 10-14, 2019). While significant advances have been made in the treatment of patients with HER2+ breast cancer, treatment of metastatic disease remains a clinical challenge for which options are limited, particularly in patients with brain metastases. The HER2CLIMB-04 study is evaluating the efficacy and safety of tucatinib in combination with T-DXd in patients with HER2+ metastatic breast cancer following progression on 2 or more HER2-directed regimens in the metastatic setting. Trial Design HER2CLIMB-04 (NCT04539938) is a single-arm, open-label, multicenter, phase 2 study of tucatinib in combination with T-DXd in previously treated patients aged ≥18 years with unresectable, locally advanced, or metastatic HER2+ breast cancer. Patients with brain metastases, including active brain metastases, may be enrolled. A safety lead-in portion of the study will enroll 10 patients who will be followed for at least 1 cycle. If tucatinib combined with T-DXd has a manageable safety profile, the trial will enroll approximately 60 response-evaluable patients (including the 10 patients from the safety lead-in), approximately evenly distributed between patients with and without brain metastases. The primary endpoint is confirmed objective response rate (cORR) by investigator assessment per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1. Secondary endpoints are progression-free survival (PFS), duration of response (DoR), disease control rate (DCR) by investigator assessment per RECIST 1.1, OS, and safety. Exploratory endpoints will include cORR, PFS, DCR, and DoR by independent central review per RECIST 1.1, pharmacokinetic analyses, biomarker analyses, and changes in patient-reported outcomes using the European Quality of Life 5-Dimension 5-Level instrument. Efficacy and safety will be summarized with descriptive endpoints to describe continuous variables. For response rates, the 2-sided exact confidence interval using the Clopper-Pearson method will be calculated. Enrollment began in late 2020 at approximately 30 study sites in the US. Citation Format: Erika Hamilton, Lisa Carey, Jorge Ramos, Yiyi Chen, Ian Krop. HER2CLIMB-04: phase 2 trial of tucatinib + trastuzumab deruxtecan in patients with HER2+ locally advanced or metastatic breast cancer with and without brain metastases (trial in progress) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-13-01.

Combination of Pertuzumab and Trastuzumab in the Treatment of HER2-Positive Early Breast Cancer: A Review of the Emerging Clinical Data.

Human epidermal growth factor receptor type 2 (HER2) is a relevant and effective target in breast cancer. The development of monoclonal antibodies against HER2 has revolutionized the treatment of HER2-positive breast cancer. The humanized monoclonal antibody, trastuzumab, was the first in its class to be widely adopted. It was initially studied in the metastatic setting and then in the treatment of early-stage disease, demonstrating significant improvement in overall survival in both settings. The addition of pertuzumab further improved upon results achieved with trastuzumab and chemotherapy, specifically extending overall survival in patients with metastatic disease, lessening the risk of recurrence when used in the adjuvant setting, and improving pathologic complete response rate when utilized in the neoadjuvant setting. In this article, we review the studies that support the use of HER2-directed monoclonal antibodies in early-stage breast cancer both in the adjuvant and neoadjuvant settings and focus on the success of dual HER2-targeted therapy achieved with the combination of trastuzumab and pertuzumab. A newer way to administer these agents, specifically the subcutaneous formulation of pertuzumab and trastuzumab with recombinant human hyaluronidase, will also be discussed.

Abstract 4537: SBT6050, a HER2-directed TLR8 ImmunoTAC™therapeutic, is a potent human myeloid cell agonist that provides opportunity for single agent clinical activity

Abstract SBT6050, a novel therapeutic comprised of a potent toll-like receptor (TLR) 8 agonist conjugated to a HER2-directed monoclonal antibody that binds an epitope distinct from trastuzumab, is designed for systemic delivery and tumor-localized activation of human myeloid cells in the presence of moderate and high HER2-expressing tumor cells. Many solid tumors, including those expressing HER2, are refractory to immunotherapy due to immune-suppressive mechanisms, loss of HLA, low neoantigen availability, and/or minimal T cell infiltrates. These tumors frequently contain abundant populations of tumor-associated myeloid cells. Activation of these cells through TLR agonism has emerged as a promising approach in overcoming resistance mechanisms to current cancer immunotherapies. Unlike other endosomal TLRs such as TLR7 and TLR9, TLR8 is highly expressed in human myeloid cells known to be prevalent in human tumors such as conventional DCs and macrophages. TLR8's restricted myeloid cell expression removes the risk of inducing T cell death or tumor cell proliferation as described for other innate immune activators such as STING. Agonism of TLR8 in human myeloid cells activates a broad spectrum of anti-tumor immune mechanisms, including proinflammatory cytokine production, repolarization of suppressive myeloid cells and the priming of CTL responses. These functions cannot be replicated by a potent TLR7 agonist or with clinical agents such as resiquimod that agonize TLR7 and only weakly engage TLR8. Here we present data demonstrating the superiority of SBT6050 at activating human myeloid cells compared to HER2 antibody conjugates that use either a selective TLR7 agonist or resiquimod. In vitro studies with human immune cells show that SBT6050 potently induces multiple anti-tumor immune activities, including proinflammatory cytokine and chemokine production, inflammasome activation, direct activation of DCs and indirect T and NK cell cytolytic activity. Our data indicate the favorable profile of SBT6050 is likely due to efficient engagement of TLR8 in conjugate form and TLR8's unique expression profile, and not due to differences in the potency of the small molecule payloads. Using an SBT6050 mouse surrogate we show in vivo evidence for intratumoral TLR agonist activation of several myeloid driven anti-tumor pathways leading to curative single agent efficacy in both a T cell-excluded syngeneic tumor model and a xenograft model lacking T, B and NK cells. Collectively, these data demonstrate that SBT6050 displays an attractive functional profile unachievable with agonist-based antibody conjugates directed against other innate immune receptors. These data also highlight the potential for SBT6050 to be clinically active as a monotherapy. SBT6050 is projected to enter the clinic in 2020 for patients with moderate or high HER2-expressing tumors. Citation Format: Michael R. Comeau, Ty Brender, Monica Childs, Jamie Brevik, Damion Winship, Heather Metz, Jenny Chang, Jeffrey Adamo, Ben Setter, Hengyu Xu, Li-Qun Fan, Brenda Stevens, Sean W. Smith, Phil Tan, Robert DuBose, Yvette Latchman, Peter Baum, Valerie Odegard. SBT6050, a HER2-directed TLR8 ImmunoTAC™therapeutic, is a potent human myeloid cell agonist that provides opportunity for single agent clinical activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4537.

Novel HER2-targeted therapies for HER2-positive metastatic breast cancer.

Human epidermal growth factor receptor 2 (HER2) is overexpressed in approximately 20% of all breast cancers. Before the development of HER2-directed monoclonal antibodies, HER2-positive breast cancer was associated with a rather poor prognosis. With the advent of monoclonal HER2-targeting antibodies (trastuzumab and pertuzumab) and antibody-drug conjugates (trastuzumab emtansine [T-DM1] and trastuzumab deruxtecan), clinical outcomes for HER2-positive breast cancer have dramatically changed, and a greater proportion of patients in the nonmetastatic setting are cured. However, in the metastatic setting, resistance to anti-HER2 treatments still remains a major therapeutic challenge, underscoring the importance of developing novel HER2-directed therapies. Over the last year, there has been a dramatic shift in the current treatment paradigms for HER2-positive metastatic breast cancer, with recent U.S. Food and Drug Administration approvals of trastuzumab deruxtecan (DS-8201), neratinib, and tucatinib in combination with trastuzumab and capecitabine. The authors summarize recent phase 3 data with novel HER2-targeted therapies as well as phase 1 and 2 data with other novel HER2-targeting agents.

SBT6050, a HER2-directed TLR8 therapeutic, as a systemically administered, tumor-targeted human myeloid cell agonist.

3110 Background: Solid tumors are replete with myeloid cells which, when activated, drive potent anti-tumor responses. Clinical development of systemically administered myeloid cell agonists, however, has been hindered by acute toxicities due to peripheral activation of the targeted cell types. Intratumoral administration, the route of delivery typically used for innate immune/myeloid cell agonists, is limited by tumor accessibility and a dependence on abscopal responses. A systemically delivered myeloid cell agonist with tumor-localized activity has the potential to overcome challenges encountered with other innate immune/myeloid cell agonists in clinical development. Methods: SBT6050 is a novel therapeutic comprised of a potent toll-like receptor (TLR) 8 agonist payload conjugated to a HER2-directed monoclonal antibody. Delivery of the payload into the endosome of human myeloid cells, where TLR8 resides, requires the co-engagement of HER2 on tumor cells and Fc gamma receptor on human myeloid cells. Thus, SBT6050 is designed for systemic delivery and tumor-targeted activation of human myeloid cells. Results: Studies with human immune cells show that SBT6050 potently induces, in a HER2-dependent manner, multiple anti-tumor immune activities due to its direct activation of myeloid cells and the subsequent induction of T and NK cell cytolytic activity. SBT6050 is designed to activate human myeloid cells only in the presence of HER2-positive tumor cells with moderate (2+ by IHC) or high (3+ by IHC) expression levels. Tumor-localized activity has been demonstrated in mouse models using a SBT6050 mouse surrogate. Systemic delivery results in robust single agent efficacy in multiple mouse tumor models, even those engineered to lack T cells, without accompanying peripheral cytokine production. Trastuzumab and SBT6050 bind to distinct epitopes on HER2 and enhanced activity is observed when the two agents are combined. Conclusions: SBT6050 is a systemically administered, tumor-targeted myeloid cell agonist that demonstrates single agent efficacy in multiple mouse tumor models without peripheral cytokine production. A first-in-human study with SBT6050 is expected to begin this year for patients with HER2-expressing solid tumors.

Abstract PD4-09: Preclinical studies support the development of SBT6050, an anti-HER2 antibody conjugated to a potent TLR8 agonist, for treatment of moderate and high HER2-expressing tumors that lack pre-existing T cell infiltrate

Abstract Despite advances in treatment options for patients with HER2-expressing tumors, significant unmet medical need remains. Of note, checkpoint inhibition (CPI) therapy has been largely ineffective in HER2-expressing tumors, likely due to the absence of T cell infiltrate. We show here, however, that a large fraction of HER2-expressing tumors is replete with resident myeloid cells despite lacking T cells. Intratumoral activation of myeloid cells could be beneficial in breast cancer, as suggested by clinical studies with demonstrated responses in cutaneous breast cancer metastases after topical application of imiquimod, a relatively weak TLR agonist. Local administration, the typical delivery route used for innate immune/myeloid cell agonists, is limited by tumor accessibility and a dependence on abscopal responses. SBT6050 is a HER2-directed monoclonal antibody conjugated to a potent TLR8 agonist, allowing for systemic delivery of a myeloid cell agonist with activity localized to HER2-expressing tumor sites. SBT6050 is designed to activate human myeloid cells only in the presence of HER2-positivetumor cells with moderate (2+ by IHC) or high (3+ by IHC) expression levels. As previously described, SBT6050 is designed to drive tumor immunity through intratumoral pan-myeloid activation by inducing direct macrophage-mediated killing of tumor cells, repolarizing suppressive myeloid cell populations to a pro-immunogenic phenotype, augmenting dendritic cell priming of tumor-specific CTL responses, and facilitating tumor recruitment and infiltration of immune cell types, including T cells. Here, we present preclinical studies that provide additional support for the clinical evaluation of SBT6050 as a monotherapy as well as in combination with trastuzumab. SBT6050 is proficient at ADCC and ADCP and binds to an epitope distinct from trastuzumab. An SBT6050 mouse surrogate shows robust single agent efficacy in several tumor models, including an EMT6 breast cancer model, known to be CPI refractory due to low T cell infiltrate, engineered to express huHER2. Tumor-bearing mice treated with the SBT6050 surrogate had durable cures and were resistant to tumor rechallenge, indicating development of immunological memory. The SBT6050 surrogate was also more efficacious than unconjugated anti-HER2 mAb in HER2-positive xenograft models conducted in T cell deficient, but myeloid competent, mouse strains. These data demonstrate the benefit of tumor-directed myeloid cell activation, even in the absence of T cells. As trastuzumab and SBT6050 bind to distinct epitopes on HER2, we evaluated the combination of trastuzumab with SBT6050 in vitro or SBT6050 surrogate in vivo for enhanced activity. In vitro, SBT6050 did not impede trastuzumab’s blockade of HER2 signaling as evidenced by cell death of HER2-positive tumor cell lines. Furthermore, SBT6050 potently activates myeloid cells in a HER2-dependent manner in the presence of trastuzumab. In vivo studies assessing the combination of the SBT6050 surrogate with trastuzumab in HER2- positive xenograft models will support evaluating the combination in the clinic. SBT6050 is currently in preclinical development and is projected to enter the clinic in 2020. Citation Format: Valerie H Odegard, Kara Moyes, Monica Childs, Jamie Brevik, Damion Winship, Ty Brender, Heather Metz, Jenny R Chang, Jeffrey Adamo, Ben Setter, Hengyu Xu, Li-Qun Fan, Sean W Smith, Phil Tan, Robert DuBose, Yvette Latchman, Peter Baum. Preclinical studies support the development of SBT6050, an anti-HER2 antibody conjugated to a potent TLR8 agonist, for treatment of moderate and high HER2-expressing tumors that lack pre-existing T cell infiltrate [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr PD4-09.

Abstract 3271: A systemically administered, conditionally active TLR8 agonist for the treatment of HER2-expressing tumors

Abstract Clinical development of systemically administered myeloid cell agonists has been hindered by acute toxicities due to peripheral activation of the targeted cell types. Intratumoral administration, the route of delivery typically used for innate immune/myeloid cell agonists, is limited by tumor accessibility and a dependence on abscopal responses. Here, we describe an example of a new composition class, termed ImmunoTAC, that allows for systemic delivery of an immune modulator with activity localized to tumor sites and secondary lymphoid structures. Agonism of TLR8 in human myeloid cells drives anti-tumor immunity by inducing direct macrophage killing of tumor cells, repolarizing suppressive myeloid cell populations to a pro-immunogenic phenotype, and inducing dendritic cells to drive tumor-specific CTL responses. SBT6050 is an ImmunoTAC comprised of a novel, potent TLR8 agonist conjugated to a HER2-directed monoclonal antibody. SBT6050 is designed to activate human monocytes and macrophages only in the presence of HER2pos tumor cells with moderate (2+ by IHC) or high (3+ by IHC) expression levels. This activity is dependent upon the ability of the Fc domain of the antibody to engage Fcγ receptors on the surface of the myeloid cells. Additionally, SBT6050 potently activates conventional dendritic cells that, in turn, drive a Th1/CTL program in T cells. Systemic delivery of a SBT6050 surrogate in mice shows robust single agent efficacy in tumor models intrinsically resistant to checkpoint blockade, such as the previously characterized HER2+ CT26 syngeneic model. The intratumoral immune response is characterized by robust activation of tumor-associated myeloid cells, infiltration of neutrophils, persistent increases in local cytokine and chemokine production, decreases in Treg infiltrate, and the generation of a potent, neo-Ag specific anti-tumor CTL response. Mice cured with single-agent treatment are resistant to tumor rechallenge, demonstrating induction of long-lived immunological memory. In contrast to observations with small molecule TLR8 agonists, ImmunoTAC does not induce peripheral cytokine production or associated CRS-like toxicity in mice, consistent with the localized activity of the molecule. Silverback’s lead candidate, SBT6050, is currently in preclinical development for patients with moderate or high HER2-expressing tumors. More broadly, the data presented here describe a novel therapeutic modality that allows for systemic administration of immune modulators with tissue-localized activity. Citation Format: Kara Moyes, Ty Brender, Sean W. Smith, Hengyu Xu, Ben Setter, Li-Qun Fan, Rebecca Brunette, Justin Killebrew, Phil Tan, Craig Coburn, Peter Baum, Valerie Odegard. A systemically administered, conditionally active TLR8 agonist for the treatment of HER2-expressing tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3271.

Abstract P4-07-08: Budesonide and loperamide do not impact the cytotoxicity of neratinib or HER2-directed monoclonal antibodies in HER2+ breast cancer cell lines

Abstract Background: Neratinib is an irreversible pan-HER tyrosine kinase inhibitor with demonstrated clinical activity in HER2+ and HER2-mutated breast cancers. The main toxicity of neratinib is diarrhea, which is common in the absence of prophylaxis. Preclinical models suggest that neratinib-associated diarrhea may involve inflammatory, bile acid malabsorption and secretory factors. The phase II CONTROL study is currently investigating the prophylactic efficacy of the opioid receptor antagonist loperamide in combination with budesonide (a corticosteroid used for inflammatory gastrointestinal conditions) or colestipol (bile acid sequestrant) on neratinib-associated diarrhea in early-stage HER2+ breast cancer (NCT02400476). This in vitro study examines the impact of loperamide and budesonide on the anti-proliferative activity of neratinib or trastuzumab and pertuzumab in HER2+ or HER2-low breast cancer cell lines. Methods: HER2+ breast cancer cell lines SKBR3 (estrogen receptor [ER]–), BT474 (ER+), HCC1569 (ER–) and HER2-low, pertuzumab-sensitive MDA-MB-175-VII (ER+) breast cancer cells were investigated using a 5-day acid phosphatase-based proliferation assay to determine the concentrations required to inhibit growth by 50% (IC50). Fixed ratios of drugs were utilised in combination assays to generate Combination Index (CI) values (Calcusyn®) where available. Clinically relevant levels of neratinib, trastuzumab and pertuzumab were utilised in all experiments. Physiologically relevant levels of budesonide (˜4.2 nM) and loperamide (˜2.5 nM) were exceeded to provide IC50 values for these compounds. Results: All cell lines tested had neratinib IC50 values in the nM range (Table). Trastuzumab and the trastuzumab/pertuzumab combination did not exceed 50% inhibition in the HER2+ cell lines. In the HER2+ breast cancer cell lines tested, loperamide had no impact on neratinib activity in BT474, enhanced neratinib activity in SKBR3, and the combination of loperamide and neratinib proved synergistic in HCC1569 (CI = 0.77 +/– 0.2). Budesonide produced strong synergism in combination with neratinib in SKBR3 (CI = 0.27 +/– 0.03), had no impact on neratinib activity in BT474 and improved response to neratinib in HCC1569. Loperamide and budesonide improved the activity of trastuzumab and pertuzumab in all three HER2+ models tested, and had no impact on pertuzumab activity in MDA-MB-175-VII. Interestingly, neratinib proved synergistic in combination with pertuzumab in MDA-MB-175-VII (CI = 0.75 +/– 0.5 nM). Table.Anti-proliferative effects of agents testedBreast cancer cell lineNeratinib IC50, nMLoperamide IC50, nMBudesonide IC50, nMPertuzumab IC50, nMTrastuzumab (% inhibition, 2.5μg/ml)Trastuzumab/Pertuzumab (% inhibition, 2.5μg/ml)SKBR32.8 +/– 0.47.7 +/– 0.52.7 +/– 0.2NA26.3 +/– 1.3NABT4741.4 +/– 0.12.6 +/– 0.27 +/– 0.6NA40.1 +/– 4.3NAHCC156917.3 +/– 0.79.3 +/– 1.728.7 +/– 0.5No effectNo effect26.1 +/– 2.8MDA-MB-175-VII3 +/– 0.3&amp;gt; 20&amp;gt; 201.2 +/– 0.2NANANA = not acquired. Conclusions: Our preclinical results suggest that budesonide and loperamide do not antagonise the anti-proliferative activity of neratinib or HER2-directed monoclonal antibodies in HER2+ breast cancer cell lines. Citation Format: Collins DM, Gaynor N, Conlon N, Gullo G, Eustace AJ, Crown J. Budesonide and loperamide do not impact the cytotoxicity of neratinib or HER2-directed monoclonal antibodies in HER2+ breast cancer cell lines [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-07-08.

Rapidly quantifying drug sensitivity of dispersed and clumped breast cancer cells by mass profiling

Live cell mass profiling is a promising new approach for rapidly quantifying responses to therapeutic agents through picogram-scale changes in cell mass over time. A significant barrier in mass profiling is the inability of existing methods to handle pleomorphic cellular clusters and clumps, which are more commonly present in patient-derived samples or tissue cultures than are isolated single cells. Here we demonstrate automated Live Cell Interferometry (LCI) as a rapid and accurate quantifier of the sensitivity of single cell and colony-forming human breast cancer cell lines to the HER2-directed monoclonal antibody, trastuzumab (Herceptin). The relative sensitivities of small samples (<500 cells) of four breast cancer cell lines were determined tens-to-hundreds of times faster than is possible with traditional proliferation assays. These LCI advances in clustered sample assessment and speed open up the possibility for therapeutic response testing of patient-derived solid tumor samples, which are viable only for short periods ex vivo and likely to be in the form of cell aggregates and clusters.

Abstract P3-14-06: Pharmacokinetic (PK) Interaction Potential of Trastuzumab-DM1 (T-DM1) and Pertuzumab (P) in Pts with HER2-Positive, Locally Advanced or MBC: Results from a Phase 1b/2 Study

Abstract Introduction T-DM1 is an antibody-drug conjugate (ADC) composed of the cytotoxic DM1 conjugated to trastuzumab and retaining its antitumor properties. P is a HER2-directed monoclonal antibody that inhibits HER2 dimerization and subsequent signaling. The combination of T-DM1 and P has demonstrated synergistic antitumor activity in HER2-positive xenograft models. T-DM1 and P are expected to undergo proteolytic degradation with no significant involvement of cytochrome P450 isoenzymes. In contrast, DM1 is metabolized mainly by CYP3A4 and to a limited extent by CYP3A5. Therefore, a key component in evaluating this combination clinically is determining whether a PK-based drug interaction potential exists when these drugs are administered together. Assessment of PK-based therapeutic protein-ADC interaction potential is novel, as antibodies have typically been combined with chemotherapy in clinical studies. Methods This 3+3 dose escalation, open-label, phase 1b/2 study evaluated the safety, tolerability, PK, and efficacy of T-DM1 (3.0 mg/kg q3w or 3.6 mg/kg q3w [established phase 2 dose]) in combination with P (840 mg loading dose; 420 mg q3w thereafter) in pts with HER2-positive locally advanced or MBC. Because of the half-life of both agents, staggered dosing was not a practical approach to assess the PK interaction. Thus, both drugs were administered sequentially on Day 1 of each cycle. All pts receiving study treatment were evaluated for serum concentrations of T-DM1, total trastuzumab (conjugated and unconjugated to DM1), and plasma concentrations of DM1, at pre-specified time points. To avoid the interference of P with the quantification of total trastuzumab, a new assay that allows capturing trastuzumab in the presence of P was developed and validated. PK of T-DM1 and related analytes were compared with historical single agent data by population and/or noncompartmental analyses. Whether combination with P was a significant covariate of T-DM1 clearance and central volume of distribution (V1) was tested. The confidence intervals (CIs) of the ratios of clearance and V1 of combination to monotherapy were estimated. A CI containing 1 is indicative of comparable parameters. Results PK data were available for 63 pts. Combination with P was not a significant covariate of T-DM1 clearance and V1 (P&amp;gt;0.05 by the log likelihood ratio test). The combination to monotherapy ratios for clearance and V1 had a 95% CI of [0.90-1.04] and [0.95-1.06], respectively, indicating comparable clearance and V1 of combination and monotherapy. The average post-hoc Bayesian estimates of T-DM1 clearance and V1 in the presence of P were 0.69±0.14 L/day and 3.3±0.41 L, which were comparable with historical measures of 0.73±0.19 L/day and 3.4±0.57 L with monotherapy. The average maximal concentration of total trastuzumab in cycle 1 was 101±29 μg/ml in the 3.0 mg/kg TDM1 dose (n=3) and 98±32 μg/ml for the 3.6 mg/kg dose (n=60). The maximum DM1 level was &amp;lt;17 ng/mL at both T-DM1 doses. The PK of total trastuzumab and DM1 were also comparable with monotherapy (data not shown). Conclusions This assessment suggests that P does not alter the PK of T-DM1 when these drugs are administered together. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-14-06.