Bispecific Antibody Fusion Protein Research Articles

First-in-class PD-1/IL-2 bispecific antibody fusion protein IBI363 in patients with advanced melanoma: Safety and efficacy results from a phase I study.

9562 Background: Despite great success of immunotherapy (IO) in advanced melanoma, there remains unmet clinical needs for IO resistant and cold tumors. IBI363 is a first-in-class PD-1/IL-2α-bias bispecific antibody fusion protein which could block PD-1 checkpoint and activate α-bias IL-2 to rejuvenate exhausted tumor-specific T cells. Herein, we report updated results from the phase I study to evaluate safety and efficacy of IBI363 in pts with advanced melanoma. Methods: Eligible pts with advanced melanoma who failed or intolerant to standard therapy were enrolled to receive IBI363 intravenously at different dose levels ranging from 100-2000 μg/kg QW/Q2W/Q3W. Primary objective of the study was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR), disease control rate (DCR), duration of response (DoR) and progression free survival (PFS). Results: As of January 11, 2024, 67 pts were enrolled (females: 55.2%, median age: 59.0 years, ECOG PS 1: 74.6%, prior treatment lines ≥2: 59.7%, prior IO: 89.6%). There were 17 pts with cutaneous melanoma, 22 pts with acral melanoma, 25 pts with mucosal melanoma and 3 pts with unknown primary melanoma. The median treatment duration was 12.0 weeks (range: 2.0-43.6) with 38 pts (56.7%) still on treatment. Most comment reason for end of treatment was disease progression in 25 pts (37.3%). All pts were included in safety analysis. Treatment-emergent adverse events (TEAEs) occurred in 63 (94.0%) pts. Grade ≥3 TEAEs and TRAEs occurred in 16 (23.9%) and 12 (17.9%) pts. Common TEAEs (≥20%) were arthralgia (34.3%), hyperthyroidism (29.9%), anemia (25.4%). TEAE leading to treatment discontinuation occurred in 1 (1.5%) pt.No pts had TEAEs leading to death. Pts with at least 1 post-baseline tumor assessment were included in efficacy evaluable set. In all evaluable pts (n=57), the best overall response was partial response (PR) in 16 pts, stable disease (SD) in 25 pts and progressive disease (PD) in 16 pts. The overall ORR was 28.1% (95%CI: 17.0-41.5%) and DCR was 71.9% (95%CI: 58.5-83.0). In pts had prior IO (n=52), ORR was 21.2% (95%CI: 11.1-34.7) and DCR was 67.3% (95%CI: 52.9-79.7). In 1 mg/kg Q2W pts had prior IO (n=25), ORR was 32.0% (95%CI: 14.9-53.5) and DCR was 80.0% (95%CI: 59.3-93.2). The DoR and PFS data were immature at the time of analysis. Biomarker analysis in baseline tumor region observed significantly higher CD8 T cell infiltration (measured by cell positivity and density) in PR/SD patients than PD patients (p<0.05). More updated data on safety and efficacy will be presented at the meeting. Conclusions: In pts with advanced melanoma, IBI363 showed encouraging efficacy in different tumor subtypes and in pts wit prior IO. The safety profiles were acceptable and manageable. Further clinical development of IBI363 in melanoma are ongoing both in China and overseas. Clinical trial information: NCT05460767 .

First-in-class PD-1/IL-2 bispecific antibody fusion protein IBI363 in patients with other solid tumors: Safety and efficacy results from a phase I study.

e14593 Background: IBI363 is a first-in-class PD-1/IL-2α-bias bispecific antibody fusion protein which could block PD-1 checkpoint and rejuvenate exhausted tumor-specific T cells by cis-activating α-bias IL-2. It was well tolerated and showed encouraging efficacy in patients (pts) with advanced melanoma, non-small cell lung cancer and colorectal cancer. Herein, we report a phase I study of IBI363 in patients (pts) with other solid tumors. Methods: Eligible pts with advanced biliary tract cancer (BTC), head and neck squamous cell carcinoma (HNSCC), cervical cancer (CC) and ovarian cancer (OC) who failed or intolerant to standard therapy were enrolled. IBI363 was intravenously administered at different dose levels ranging from 600 to 1500 μg/kg QW/Q2W/Q3W. Primary objective of the study was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR) and disease control rate (DCR). Results: As of January 26, 2024, 24 pts were enrolled including 13 pts with BTC, 3 pts with HNSCC, 4 pts with CC and 4 pts with OC. In BTC, 6 (46.2%) pts received IBI363 treatment for more than 3 months and the maximum treatment duration was 7 months. In HNSCC, CC and OC, the maximum treatment duration was 4.6, 6.2 and 6.5 months respectively. Pts with at least 1 tumor assessment were included in efficacy evaluable set (n = 18). The overall ORR was 22.2% and DCR was 77.8%. In 11 evaluable pts with BTC, best overall response (BOR) was confirmed partial response (cPR) in 1 pt (600 μg/kg Q2W, immunotherapy (IO)-failed), stable disease (SD) in 9 pts (including 6 pts with tumor regression) and progressive disease (PD) in 1 pt. ORR was 9.1% and DCR was 90.9%. In 2 evaluable pts with HNSCC, 1 pt had cPR (600 μg/kg Q2W, IO-naïve, PD-L1 expression negative) and 1 pt had PD. In 3 evaluable pts with CC, 1 pt had cPR (1000 μg/kg Q2W, IO-failed), 1 pt had SD and 1 pt had PD. In 2 evaluable pts with OC, 1 pt had cPR (1000 μg/kg Q2W, platinum-resistant) and 1 pt had PD. All cPR pts had previous 1-2 lines of treatments and had tumor regression ranging from 45% to 87%. Durable tumor responses were observed with cPR remained at week 30 in BTC and remained at week 24 in HNSCC, CC and OC. In 4 pts with cPR, 3 pts still on treatment and 1 pt with HNSCC received curative resection. No new safety signals of IBI363 were observed. More updated data on safety and efficacy will be presented at the meeting. Conclusions: IBI363 showed promising and durable efficacy in pts with various solid tumors including refractory tumors such as BTC and IO or platinum-resistant tumors such as CC and OC. Further clinical investigations on these tumors using IBI363 alone or in combination with other treatments are ongoing. Clinical trial information: NCT05460767 .

IMM2510, an anti-PD-L1/VEGF bispecific antibody fusion protein, in patients with advanced solid tumors: A phase I dose-escalation study.

e14506 Background: IMM2510 is a novel bispecific antibody fusion protein targeting PD-L1 and VEGF. The preclinical study demonstrated that IMM2510 induced significantly stronger anti-tumor activity than either monotherapy or combination of PD-L1 inhibitor and anti-VEGF antibody through blocking the PD-1/PD-L1 pathway and thus activate T cells and reducing VEGF-mediated tumor angiogenesis as well as an enhanced ADCC effect. We previously disclosed the preliminary clinical data of IMM2510, and here we further report safety and efficacy results of IMM2510 in the phase I dose escalation study. Methods: A phase I, multicenter, open-label, dose-escalation study, was designed to evaluate the safety, efficacy, recommended phase II dose (RP2D), and pharmacokinetics (PK) of IMM2510 in patients (pts) with advanced solid tumors. The study was designed with an accelerated titration followed by a standard 3+3 design. IMM2510 (0.007, 0.03, 0.1, 0.3, 1.0, 3.0, 6.0, 10.0, 20.0 mg/kg) was administered intravenously Q2W as monotherapy. Results: As of Dec 21, 2023, 33 pts had received IMM2510 at 9 dose levels (0.007-20.0 mg/kg), the median age was 57 years (range 36-74), the median prior line of therapy was 3 (range 1-13), and 27.3% pts received prior anti PD-1/PD-L1 inhibitor therapies. Treatment-related adverse events (TRAEs) occurred in 32 pts (97.0%). Most TRAEs were grade 1 or 2. The most common TRAEs (≥ 20%) of all grades were infusion related reaction (IRR) (72.7%), platelet count decreased (39.4%), anemia (33.3%) and diarrhea (21.2%). Grade ≥3 TRAEs occurred in 11 pts (33.3%). Grade ≥3 TRAEs (≥5%) were IRR (9.1%), platelet count decreased (6.1%), lymphocyte count decreased (6.1%) and diarrhea (6.1%). TRAEs leading to treatment discontinuation occurred in 3 pts (9.1%) which were IRR, hypersensitivity and pyrexia, respectively. No DLT occurred. In 25 response evaluable pts, 3 pts had confirmed PR: 1 pt with sq-NSCLC (onco-driver gene negative, previous IO treatment failure) at 3 mg/kg with tumor shrinkage 46% and still on the treatment with treatment duration over 20 months; 1 pt with sq-NSCLC at 10 mg/kg with tumor shrinkage about 32% along with treatment duration 9.4 months; 1 pt with thymus adeno-squamous carcinoma (PD-L1 CPS 80) at 20 mg/kg with tumor shrinkage over 53% and still remains on the treatment along with treatment duration 8.1 months. In addition, 7 pts with BOR SD and 4 of them had over 15% decreased tumor burden (1 cervical cancer at 3 mg/kg, 2 non-sq NSCLC at 10 and 20 mg/kg respectively, 1 ovarian cancer at 20 mg/kg). The half-life of IMM2510 in 20.0mg/kg dose group was around 6.8 days. The RP2D was determined to be 20.0 mg/kg. Conclusions: IMM2510 is well tolerated in general and preliminary anti-tumor activity in solid tumors is encouraging. The phase Ib/II is ongoing to enroll patients. Clinical trial information: NCT05972460 .

Dual blockade of CD47 and CD24 signaling using a novel bispecific antibody fusion protein enhances macrophage immunotherapy

CD47 and its receptor SIRPα act as a dominant anti-phagocytic, ‘don’t eat me’ signal. Recent studies reveal CD24 as a novel target for cancer immunotherapy by macrophages in ovarian cancer and breast cancer. However, whether simultaneous blockade of CD47 and CD24 by bispecific antibody may result in a potential synergy is still unclear. In the present study, we for the first time designed and developed a bispecific antibody fusion protein, PPAB001 for co-targeting CD47 and CD24. Data demonstrate that simultaneous blockade of CD47/SIRPα and CD24/Siglec-10 signaling by PPAB001 potently promoted macrophage phagocytosis of tumor cells. Compared to single CD47 or CD24-targeting agent, PPAB001 was more effective in inhibiting tumor growth in both mouse 4T-1 syngeneic and human SK-OV-3 xenogeneic tumor models. Mechanistically, we found that PPAB001 therapy markedly increased the proportion of tumor-infiltrating macrophages and upregulated IL-6 and TNF-α levels that were representative macrophage inflammatory cytokines. Notably, an increased ratio of M1/M2 in tumor-infiltrating macrophages in the mice treated with PPAB001 suggested that the dual blockade may promote the transition of macrophages from M2 to M1. Taken together, our data supported the development of PPAB001 as a novel immunotherapeutic in the treatment of CD47 and CD24 double positive cancers.

Safety and efficacy of HB0025, an anti-PD-1/VEGF bispecific antibody fusion protein, in patients with advanced solid tumors: Preliminary results from an FIH trial.

2589 Background: HB0025 is a recombinant humanized anti-PD-L1 monoclonal antibody-VEGFR1 fusion Protein. Nonclinical data both in vitro and vivo have shown high-affinity binding to both targets as well as the inhibition of tumor growth in animal models. Here, we present preliminary safety and efficacy data from a dose escalation phase I study of HB0025. Methods: Eligible patients(pts) were ≥18 years old (ECOG PS 0–1) who had advanced solid tumors (NSCLC, gynecological tumors, digestive system tumors, etc.) and failed standard treatment. This phase 1 dose escalation includes accelerated titration (0.01, 0.03, 0.1 and 0.3mg/kg) and conventional 3+3 dose escalation (1.0, 3.0, 6.0, 10, 12, 20, and 30.0 mg/kg). HB0025 is administered intravenously every 14 days (Q2W). Objectives include evaluation of safety, pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, and antitumor activity. Adverse events (AEs) were reported with CTCAE v5.0 and DLTs were evaluated within a 28-day window. Results: As of Aug 30th 2022, 30 pts including 8 male and 22 female from Caucasian and Mongoloid have received HB0025 at doses of 0.01 mg/kg (n=1), 0.03 mg/kg (n=2), 0.1 mg/kg (n=1), 0.3 mg/kg (n=1),1.0 mg/kg (n=3), 3.0 mg/kg (n=7), 6.0mg/kg (n=7), 10.0 mg/kg (n=5), and 12.0mg/kg (n=3) Q2W. Overall, the median age was 55 years and the median lines of previous treatment was four. Of the 22 evaluable pts dosed at ≥ 3 mg/kg Q2W, the ORR was 9.1% (2/22) and the disease control rate (DCR) was 50% [11/22]. Among the 2 responders, a CR (colorectal ca) pt whose prior therapy was no immune checkpoint inhibitor (ICI) or bevacizumab have continued more than 36 weeks; and a PR (NSCLC) pt with duration more than 18 weeks whose tumor was 60.2% regression and prior ICI failure. Till the date of submission, the therapy was continuing for the CR and PR pts. Treatment-related adverse events (TRAEs) occurred in 83.3% of pts. The grade 3 TRAEs occurred in 20% [6/30] and treatment-related SAEs occurred in 13.3% [4/30]. One DLT occurred in the 12.0mg/kg cohort. No death occurred related to HB0025. TRAEs leading to treatment discontinuation occurred in 13.3% of pts [4/30]. The most frequent TRAEs were hypertriglyceridemia (23.3%), hypercholesterolemia (23.3%), anemia (16.7%), alanine aminotransferase increase (16.7%), and proteinuria (13.3%). Conclusions: HB0025 shows manageable safety and promising anti-tumor activity in pts with various solid tumors. To better characterize the risk-benefit profile, HB0025 is currently enrolled at 20.0 mg/kg Q2W and is being explored at doses 10 mg/kg in expansion cohorts. The future data, including PK, PD and ADA will be presented. Clinical trial information: NCT04678908 .

Abstract 2887: Three dimensional colon cancer organoids model the response to CEA CD3 T cell engagers

Abstract Rationale: The CEA-CD3 T cell bispecific antibody cibisatamab (CEA-TCB) is currently undergoing clinical trials. Here we study its performance against three-dimensional tumor organoids in cocultures with T cells as compared to a higher affinity CEACAM5-CD3 (CEACAM5-TCB) bispecific antibody using time-lapse confocal microscopy. Methods: Pre-labelled spheroids derived from colon cancer cell lines and primary organoids derived from four colorectal cancer surgical specimens, which expressed different graded levels of CEA, were exposed in cocultures to T lymphocytes. Cocultures were treated with CEA-CD3 T-cell engagers and were followed by live confocal microscopy. Caspase 3 activation detected in real-time was used as an indicator of tumor cell death. Co-cultures were also set up with autologous tumor-associated fibroblasts to test the co-stimulatory effect of a fibroblast activated protein (FAP)- targeted 4-1BBL bispecific antibody fusion protein currently undergoing clinical trials. Results: Tumor-cell killing of 3D colon carcinoma cultures was dependent on the levels of surface CEA expression, in such a way that the lower affinity agent (CEA-TCB) did not mediate killing by human preactivated T cells below a certain CEA expression threshold, while the high affinity construct (CEACAM5-TCB) remained active on the low CEA expressing organoids. Modelling heterogeneity in the levels of CEA expression by coculturing CEA high and low organoids showed measurable but weak bystander killing. Cocultures of tumor organoids, autologous fibroblasts and T cells allowed to observe a costimulatory effect of anti-FAP-4-1BBL both to release IFNγ and to attain more efficacious tumor cell killing. Conclusion: Three-dimensional tumor cocultures with T cells using live confocal microscopy provide suitable models to test the requirements for colon-cancer redirected killing as elicited by CEA-targeted T-cell engagers undergoing clinical trials and treatment allow combinations to be tested in a relevant preclinical system. Citation Format: Alvaro Teijeira, Itziar Migueliz, Saray Garasa, Marina Bacac, Christian Klein, Ignacio Melero. Three dimensional colon cancer organoids model the response to CEA CD3 T cell engagers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2887.

Three-dimensional colon cancer organoids model the response to CEA-CD3 T-cell engagers.

Rationale: The CEA-CD3 T cell bispecific antibody cibisatamab (CEA-TCB) is currently undergoing clinical trials. Here we study its performance against three-dimensional tumor organoids in cocultures with T cells as compared to a higher affinity CEACAM5-CD3 (CEACAM5-TCB) bispecific antibody using time-lapse confocal microscopy.Methods: Pre-labelled spheroids derived from colon cancer cell lines and primary organoids derived from four colorectal cancer surgical specimens, which expressed different graded levels of CEA, were exposed in cocultures to T lymphocytes. Cocultures were treated with CEA-CD3 T-cell engagers and were followed by live confocal microscopy. Caspase 3 activation detected in real-time was used as an indicator of tumor cell death. Co-cultures were also set up with autologous tumor-associated fibroblasts to test the co-stimulatory effect of a fibroblast activated protein (FAP)- targeted 4-1BBL bispecific antibody fusion protein currently undergoing clinical trials.Results: Tumor-cell killing of 3D colon carcinoma cultures was dependent on the levels of surface CEA expression, in such a way that the lower affinity agent (CEA-TCB) did not mediate killing by human preactivated T cells below a certain CEA expression threshold, while the high affinity construct (CEACAM5-TCB) remained active on the low CEA expressing organoids. Modelling heterogeneity in the levels of CEA expression by coculturing CEA high and low organoids showed measurable but weak bystander killing. Cocultures of tumor organoids, autologous fibroblasts and T cells allowed to observe a costimulatory effect of anti-FAP-4-1BBL both to release IFNγ and to attain more efficacious tumor cell killing.Conclusion: Three-dimensional tumor cocultures with T cells using live confocal microscopy provide suitable models to test the requirements for colon-cancer redirected killing as elicited by CEA-targeted T-cell engagers undergoing clinical trials and treatment allow combinations to be tested in a relevant preclinical system.

A novel bispecific antibody fusion protein co-targeting EGFR and CD47 with enhanced therapeutic index.

To promote targeting specificity of anti-CD47 agents, we have constructed a novel bispecific antibody fusion protein against EGFR and CD47, which may minimize the "off-target" effects caused by CD47 expression on red blood cells. The novel bispecific antibody fusion protein, denoted as Bi-SP could simultaneously bind to EGFR and CD47 and exhibited potent phagocytosis-stimulation effects in vitro. Bi-SP treatment with a low dose more effectively inhibited tumor growth than either EGFR-targeting antibody, Pan or the SIRPα variant-Fc (SIRPαV-Fc) in the A431 xenograft tumor model. In addition, the treatment with Bi-SP produced less red blood cell (RBC) losses than the SIRPαV-Fc treatment, suggesting its potential use for minimizing RBC toxicity in therapy. Bi-SP with improved therapeutic index has the potential to treat CD47+ and EGFR+ cancers in clinics.

242P - Biomarker Analysis of a Phase 1 Study of Mm-111, a Bispecific Her2/Her3 Antibody Fusion Protein, in Combination with Multiple Treatment Regimens in Patients with Advanced Her2 Positive Solid Tumors

ABSTRACT Aim: Activation of HER2/HER3 heterodimers by HER3's ligand heregulin (HRG) is a putative resistance mechanism for HER2-targeted therapies. MM-111 is a HER2/HER3 bispecific antibody fusion protein designed to inhibit HRG activated HER3 signaling in HER2+ tumors. This study evaluated biomarkers in patient samples from a multi-arm Phase 1 study of MM-111 combined with standard of care HER2-targeting regimens: capecitabine + cisplatin + trastuzumab (T); lapatinib (L) +/- T; paclitaxel (P) + T; L + P + T; docetaxel + T. All patients were required to have advanced HER2+ cancer. Methods: The following biomarkers were assessed in formalin fixed, paraffin-embedded archived tissue: HER2 by 5 methods including immunohistochemistry (IHC) scored using 0/1 + /2 + /3+ and image analysis (optical density) systems, quantitative immunofluorescence (qIF), fluorescent in situ hybridization (FISH), and reverse transcription polymerase chain reaction (PCR); HER3 by qIF and PCR; and HRG, betacellulin, and EGF receptor by PCR. Results: 86 patients [46 breast, 15 gastro-esophageal (GE), 11 bladder, 14 other cancers] were treated and archived tissue was received from 71 patients. All 71 samples were assessable by IHC, 69 by qIF, 64 by FISH, and 46 by PCR. The 5 HER2 assessments correlated well with each other and the correlations were independent of indication. Compared to other indications, patients with GE cancer tended to have higher HRG and HER3 expression. Stratified by indication and treatment, increased HER2 expression correlated with longer progression free survival (PFS) across all patients, particularly GE patients, but the relative contribution of MM-111 or trastuzumab could not be determined. Higher betacellulin expression was associated with longer PFS for regimens containing lapatinib. Conclusions: This study supports use of the described biomarker assays for analysis of samples from a randomized Phase 2 study of MM-111 in HER2+ GE cancer. Biomarker analyses of archived and newly acquired biopsy samples will be performed in the Phase 2 study to provide further insight for the role of HER2, HER3, and HRG in the response of HER2+ cancer to MM-111-containing therapy. Disclosure: A. Kudla, B. Adiwijaya, V. Paragas, K. Kawash, S. Frye, C.F. McDonaghand V. Moyo: Employee of Merrimack Pharmaceuticals with stock options; A.A. Garcia: Recipient of research funding from Merrimack Pharmaceuticals; C.S. Denlinger: Recipient of research funding from Merrimack Pharmaceuticals. P. Conkling: Recipient of funding from Virginia Oncology Associates and US Oncology. S. Anthony: Consultant for Paradigm.All other authors have declared no conflicts of interest.

A phase I and pharmacologic study of MM-111, a bispecific HER2/HER3 antibody fusion protein, in combination with multiple treatment regimens in patients with advanced HER2-positive solid tumors.

TPS3111 Background: The HER2/HER3 oncogenic heterodimer is a potent HER receptor pairing with respect to strength of interaction, receptor tyrosine phosphorylation, and downstream signaling through mitogen activated protein kinase and phosphoinositide-3 kinase pathways. MM-111 is a novel bispecific antibody fusion protein that inhibits ligand activated HER3 signaling through abrogation of ligand binding specifically in HER2 overexpressing tumors. In preclinical models of HER2+ solid tumors, MM-111 inhibits ligand-induced HER3 phosphorylation, cell cycle progression, and tumor growth. HER2 is a well-established target of anticancer agents such as trastuzumab and lapatinib, specifically in breast and gastric tumors. Preclinical data demonstrate that MM-111 potentiates the antitumor activity of both trastuzumab and lapatinib and this phase I study seeks to determine if MM-111 can be safely used in combination with various standard of care HER2 targeting regimens, namely; (1) trastuzumab, cisplatin and, capecitabine, (2) trastuzumab and lapatinib, and (3) trastuzumab and paclitaxel. Methods: This is a multi-arm phase I, open label, multicenter, dose-escalation study of MM-111 in an add-on design that evaluates the safety, pharmacokinetics (PK), and anti-tumor activity of MM-111 in combination. Each arm is designed to run as a separate phase I study to address safety and tolerability of each combination. For eligibility, patients are required to have documented advanced HER2-positive cancer, with adequate bone marrow, hepato-renal and cardiac function. The dose escalation for each arm utilizes a standard “3 + 3” design with MM-111 dosed initially at a moderate dose of 10 mg/kg and escalated up to 20 mg/kg to identify a phase II dose in combination with each regimen. Once the maximum tolerated dose or phase II dose is identified, expansion cohorts will accrue to further evaluate these combinations. The flexibility of the design allows additional combinations arms to be added. Key exploratory analyses will include an evaluation of safety, PK, and efficacy as evidenced by best overall response and duration of response.

Abstract 1888: MM-111, a bispecific HER2 and HER3 antibody, inhibits trastuzumab-resistant tumor cell growth

Abstract Amplification of human epidermal growth factor receptor 2 (HER2) occurs in approximately 25% of breast cancers and is associated with increased disease recurrence and poor prognosis. Trastuzumab, a monoclonal antibody targeting HER2, has demonstrated clinical benefit in HER2 over-expressing tumors. However, acquired resistance and disease progression is widely observed in patients treated with trastuzumab. In this experiment our objectives were to dissect the dynamic, molecular mechanisms involved in acquired resistance to trastuzumab and to determine whether MM-111, a novel bispecific antibody fusion protein that specifically targets the HER2/HER3 heterodimer and blocks heregulin binding to HER3, has activity in trastuzumab-resistant tumor cells. BT474 cells were cultured in the presence of trastuzumab and cells were periodically tested for response to trastuzumab and MM-111. Samples were also collected for protein and RNA analyses. Resistance to trastuzumab gradually increased in BT474 cells after four months of exposure to trastuzumab, as measured by a cell proliferation assay. Quantitative flow cytometry analysis showed EGFR, HER2, and HER3 levels on the cell surface of resistant cells were similar to the parental cells. Phospho-protein kinase antibody arrays revealed that signaling pathways associated with the ERK cascade were activated during the development of drug resistance. Western blotting further confirmed that phosphorylation of EGFR, ERK, CREB, c-Jun, and AFT-1 was increased in the resistant cells. Real-time polymerase chain reaction also showed transcript levels of HER ligands, including HRG1α, HRG1α, betacellulin, amphiregulin, epigen, TGFβ, and HB-EGF, dramatically increased in tumor cells that acquired resistance to trastuzumab. Compared to the BT474 parental cells, MM-111 showed a greater inhibition in trastuzumab-resistant cells in a spheroid growth assay. Furthermore, trastuzumab-resistant cells became more sensitive to gefitinib and erlotinib, both EGFR inhibitors. The combination of gefitinib or erlotinib with MM-111 showed greater inhibition than either drug alone. In conclusion, our data suggest that one mechanism by which HER2 overexpressing breast cancer cells develop resistance to trastuzumab is to up-regulate ligand-dependent EGFR and HER3 signaling pathways. The use of MM-111 and EGFR inhibitors may provide an effective therapeutic strategy for the treatment of trastuzumab-resistant cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1888. doi:1538-7445.AM2012-1888

A phase I/II study of MM-111, a novel bispecific antibody that targets the ErB2/ErB3 heterodimer, in combination with trastuzumab in advanced refractory HER2-positive breast cancer.

TPS119 Background: The ErbB2/ErbB3 oncogenic heterodimer is the most potent ErbB receptor pairing with respect to strength of interaction, receptor tyrosine phosphorylation, and downstream signaling through mitogen activated protein kinase and phosphoinositide-3 kinase pathways. MM-111 is a novel bispecific antibody fusion protein that specifically targets the ErbB2/ErbB3 heterodimer and abrogates binding of ErbB3’s ligand heregulin. In preclinical models of HER-2+ solid tumors, MM-111 inhibits ligand-induced ErbB3 phosphorylation, cell cycle progression, and tumor growth. ErbB2 (HER2) is a well established target of anticancer agents such as trastuzumab and lapatinib for HER2+ cancers, specifically breast and gastric. ErbB3 signaling has emerged as an important mechanism of resistance to ErbB2 (HER-2) targeted agents in clinical use, and preclinical data demonstrates that MM-111 potentiates the antitumor activity of trastuzumab. This first-in-human phase I/II study evaluates the safety and tolerability of MM-111 in combination with trastuzumab and preliminarily explores efficacy in HER-2+ advanced breast cancer (ABC). Methods: This is a phase I/II, open label, multicenter, dose-escalation study that will evaluate the safety, pharmacokinetics (PK), and efficacy of MM-111 + trastuzumab. There is a dose escalation phase followed by an expansion cohort. The dose escalation phase utilizes a standard “3 + 3” design where doses of MM-111 will be escalated until the phase II dose is identified in combination with trastuzumab given at the approved dose and regimen. Once the MTD or phase II dose is identified, an expansion cohort will be enrolled to further evaluate the safety and efficacy of doublet. Key exploratory analyses will include an evaluation of safety and efficacy and levels of expression and/or amplification of HER2 and heregulin. As of January 1 2011, cohorts 1 thru 2 have been completed without DLT. A total of 7 patients have been treated. Enrollment to cohort 3 is ongoing.

Abstract 655: Combination of MM-111, an ErbB2/ErbB3 bispecific antibody, with endocrine therapies as an effective strategy for treatment of ER+/HER2+ breast cancer

Abstract Approximately 75% of breast cancers are estrogen receptor (ER) positive. Although endocrine therapies such as tamoxifen, fulvestrant, and letrozole have demonstrated significant efficacy in treating ER+ breast cancer patients, intrinsic or acquired resistance has limited their success. Recent studies suggest that crosstalk between ErbB receptor signaling and ER signaling may contribute to resistance to endocrine therapy. Overexpression of human epidermal growth factor receptor 2 (HER2, synonymous with ErbB2) and upregulation of the ErbB3 ligand heregulin are associated with poor prognosis and reduced overall survival. MM-111 is a novel bispecific antibody fusion protein that specifically targets the ErbB2/ErbB3 heterodimer and blocks heregulin binding to ErbB3. MM-111 inhibits ligand-induced ErbB3 phosphorylation, tumor cell cycle progression, and tumor growth when ErbB2 is overexpressed. We hypothesized that combination of endocrine therapies with MM-111 may improve anti-tumor efficacy. In an estrogen-stimulated BT474-M3 ER-positive breast cancer cell three-dimensional spheroid assay, MM-111, when used as a single agent, showed growth inhibitory effects similar to the anti-estrogen drugs tamoxifen and fulvestrant. Combination of MM-111 with anti-estrogen therapy showed superior activity to either drug alone. In the presence of heregulin, MM-111 maintained its growth inhibitory activity, whereas the inhibitory effect of tamoxifen and fulvestrant was diminished. This suggests that activation of ErbB3 confers tumor cell resistance to anti-estrogen therapies. When both estrogen and heregulin were present, the combination of MM-111 and the anti-estrogen drugs demonstrated a significantly greater inhibitory effect than either drug alone. Western blot analysis showed that treatment of BT-474-M3 cells with the combination of MM-111 and the anti-estrogen drugs significantly increased apoptosis markers such as cytochrome C and BAX. Furthermore, an in vivo BT474-M3 xenograft model showed resistance to tamoxifen treatment (5 mg/pellet, 60-day release). In this xenograft model MM-111 sensitized tumor response to tamoxifen and the combination treatment dramatically inhibited tumor growth. In conclusion, the combination of MM-111 and endocrine therapies may provide a potent regimen that overcomes acquired resistance to endocrine therapies in ER+, ErbB2-overexpressing breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 655. doi:10.1158/1538-7445.AM2011-655

Abstract P6-15-15: MM-111 - A Novel Bispecific Antibody Targeting HER-2/HER-3 Z Heterodimer: Safety and Tolerability in a First-In Human Phase I/II Study in Patients with Refractory HER2-Positive (HER-2+) Cancers

Abstract Background: The ErbB2/ErbB3 oncogenic heterodimer is the most potent ErbB receptor pairing with respect to strength of interaction, receptor tyrosine phosphorylation, and downstream signaling through mitogen activated protein kinase and phosphoinositide-3 kinase pathways. ErbB3 signaling has emerged as an important mechanism of resistance to ErbB2 (HER-2) targeted agents in clinical use (Sergina et al Nature 2007, Garrett et al SABCS 2009 abstract 63). MM-111 is a novel bispecific antibody fusion protein that specifically targets the ErbB2/ErbB3 heterodimer and abrogates ligand binding. In preclinical models of HER-2+ gastric, breast, ovarian and lung cancers, MM-111 inhibits ligand-induced ErbB3 phosphorylation, cell cycle progression, and tumor growth. This first-inhuman phase 1-2 study evaluates the safety and tolerability of MM-111 and preliminarily explores efficacy in HER-2+ advanced breast cancer (ABC). The safety data obtained during the Phase 1 dose escalation portion of this study provide the basis of this report. Methods: Patients (pts) with histologically confirmed HER-2+ advanced solid tumors progressing or recurring on standard therapy; aged ≥18 years; ECOG PS ≥2 and adequate organ function were eligible for phase I. Pts with stable CNS lesions were also eligible. A Modified Fibonacci schema was used for dose escalation in Phase I. Primary endpoints for Phase 1 were determination of maximum tolerated dose/maximum feasible dose while secondary endpoints included determination of dose-limiting toxicity, adverse events, and pharmacokinetic (PK) and immunogenicity profiles of MM-111. MM-111 was administered intravenously weekly in 4-week cycles. Results: 12 pts (11 ABC and 1 gastric cancer) were treated: median age 59 (range 36-82), median PS 1 (range 0-1), 11♂:1♀, median numberof prior therapies 7 (3-12). A total 19 courses (median 2; range 1-2) of therapy was administered at 4 dose-levels (3 mg/kg, 6mg/kg, 12mg/kg and 20 mg/kg respectively). Common adverse events reported included pain (n=7) fatigue (n=4), dyspepsia (n = 3) and pyrexia (n = 3). There were no treatment interruptions due to adverse events. No dose limiting toxicities were observed and there has been no evidence of cardiotoxicity or immunogenicity to date. PK data indicate dose proportionality at the dose-levels explored and supports weekly dosing. Conclusions: MM-111 is well tolerated at the doses levels studied and the PK profile suggests that weekly dosing is feasible. Enrollment to phase II is anticipated to commence shortly. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-15-15.

A phase I/II and pharmacologic study of MM-111 in patients with advanced, refractory HER2-positive (HER2+) cancers.

TPS169 Background: The ErbB2/ErbB3 oncogenic heterodimer is the most potent ErbB receptor pairing with respect to strength of interaction, ligand–induced tyrosine phosphorylation, and downstream signaling through mitogen-activated protein kinase and phosphoinositide-3 kinase pathways. Recently, ErbB3 signaling has emerged as an important hypothesized mechanism of resistance to ErbB2 (HER2) targeted agents in clinical use (Sergina et al. Nature 2007; Garrett et al. SABCS 2009 abstract 63). MM-111 is a novel bispecific antibody fusion protein that specifically targets the ErbB2/ErbB3 heterodimer and blocks ligand binding to ErbB3. In HER2+ gastric, breast, ovarian, and lung cancer cell lines and xenografts, MM-111 inhibits ligand-induced ErbB3 phosphorylation, tumor cell cycle progression, and tumor growth. This first-in-human phase I-II study evaluates the safety and tolerability of MM-111 and provides preliminary efficacy data in HER-2+ advanced breast cancer (ABC). Methods: Patients (pts) aged ≥ 18 years with histologically confirmed HER2+ advanced solid tumors that have progressed or recurred on standard therapy or for which no standard therapy exists, and adequate performance status, bone marrow reserve, and organ function, are eligible for the phase I portion. Phase II is restricted to pts with HER2+ ABC who have progressed on prior trastuzumab or lapatinib therapy. Pts with stable central nervous system lesions are eligible. Phase I employs a standard 3 + 3 dose escalation design. Once the maximum tolerated (MTD) or feasible dose (MFD) is determined, up to 25 additional pts with HER2+ ABC will be enrolled, for a planned total of 40-49 pts in both phases. Primary endpoints are determination of MTD/MFD (phase I) and 6-month progression-free survival (phase II). Secondary endpoints include determination of dose-limiting toxicity, adverse event, pharmacokinetic, and immunogencity profiles of MM-111, as well as overall response and clinical benefit rates of MM-111 in HER2+ ABC. MM-111 is administered intravenously weekly in 4-week cycles. 8 pts have been enrolled in the phase I portion (7 ABC, 1 advanced gastric cancer), and enrollment in the phase I portion is ongoing. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Merrimack Pharmaceuticals Merrimack Pharmaceuticals Merrimack Pharmaceuticals Chemotherapy Foundation Merrimack Pharmaceuticals Merrimack Pharmaceuticals

Abstract 3485: MM-111, an ErbB2/ErbB3 bispecific antibody with potent activity in ErbB2-overexpressing cells, positively combines with trastuzumab to inhibit growth of breast cancer cells driven by the ErbB2/ErbB3 oncogenic unit

Abstract MM-111 is a novel bispecific antibody fusion protein which targets the ErbB2/ErbB3 oncogenic unit, blocking activation of the phosphatidylinositol 3-kinase (PI3K) pro-survival pathway. The anti-ErbB2 arm of MM-111 binds with high affinity to the ErbB2 receptor, which localizes the bispecific molecule to ErbB2 over-expressing tumor cells and promotes binding of the anti-ErbB3 arm to the ErbB3 receptor. MM-111 binding to ErbB3 results in inhibition of ErbB3 signaling by blocking the binding of the ErbB3 physiological ligand heregulin. MM-111 treatment of ErbB2 overexpressing cancer cells inhibits activation of the PI3K pathway with sub-nanomolar potency, blocks cell cycle progression and attenuates tumor cell growth in multiple xenograft models. ErbB2 over-expressing tumor cells are addicted to growth signals provided by the ligand-activated ErbB2/ErbB3 heterodimer. Activation of downstream PI3K pathway signaling also occurs through ligand-independent ErbB2/ErbB2 homodimers and ErbB2/ErbB3 heterodimers. Recently the ErbB2-targeted therapeutic antibody trastuzumab was shown to inhibit basal ErbB3 signaling in the absence of ligand stimulation, purportedly by interrupting ligand-independent ErbB2/ErbB3 heterodimers formed through overexpression of ErbB2. However, in these studies trastuzumab did not effectively block ligand-induced activation of the ErbB2/ErbB3 oncogenic unit. Indeed, there is emerging evidence that ligand-induced ErbB3 activation may have an important role in resistance to trastuzumab. As MM-111 and trastuzumab have distinct and potentially complimentary effects on signaling in cells overexpressing ErbB2, we hypothesized that their combination may synergistically effect inhibition of tumor cell growth driven by the ErbB2/3 signaling network. Our data demonstrate that MM-111 and trastuzumab positively combine to inhibit breast cancer growth in multiple in vitro breast cancer models expressing ErbB2 and ErbB3. Further, in the BT-474 breast cancer xenograft model the combination of MM-111 and trastuzumab results in greater inhibition of tumor growth and an increased number of completely regressed tumors compared to the monotherapy treatment groups. Pharmacodynamic analysis of samples from these studies show that repeated administration of the combined therapeutic agents results in strong inhibition of the ErbB3/PI3K pathway. In conclusion, we show that MM-111 and trastuzumab inhibit the growth of ErbB2 over-expressing breast tumors with distinct mechanisms that act synergistically in combination. Concurrent treatment with MM-111 and trastuzumab may provide a potent therapeutic regimen for ErbB2-overexpressing breast cancer patients and potentially deter acquired resistance to trastuzumab through ErbB3 activation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3485.

A bispecific single-chain antibody fusion protein for targeted depletion of autoreactive B cells via unstimulated human T lymphocytes

Autoantigen-specific B cells are culprits in the pathogenesis of many autoimmune diseases either through the production of autoreactive antibodies or as very effective antigen-presenting cells. A general depletion of B cells by a CD20-specific monoclonal IgG1 antibody has recently been validated as an effective strategy for treating rheumatoid arthritis. However, general elimination of B cells can lead to immunosuppression and increased risk of infection. In search for a more specific approach, we have generated a fusion protein for the antigen-specific targeting of autoreactive B cells for re-directed lysis by resting human T lymphocytes. We describe the design, purification and characterization of MOGxanti-CD3, a single-chain bispecific antibody fusion protein recognizing B cell receptors specific for the human myelin oligodendrocyte glycoprotein (MOG) and to CD3 on human T cells. MOGxAnti-CD3 induced selective and very efficient redirected lysis of MOG-reactive B cells through freshly isolated, unstimulated human T cells. Fusions between autoantigens and an anti-CD3 single-chain antibody may be suitable to develop very specific therapeutic approaches for the selective depletion of autoreactive B cells in autoimmune diseases.

A bispecific single-chain antibody fusion protein for targeted depletion of autoreactive B cells via unstimulated human T lymphocytes

Autoantigen-specific B cells are culprits in the pathogenesis of many autoimmune diseases either through the production of autoreactive antibodies or as very effective antigen-presenting cells. A general depletion of B cells by a CD20-specific monoclonal IgG1 antibody has recently been validated as an effective strategy for treating rheumatoid arthritis. However, general elimination of B cells can lead to immunosuppression and increased risk of infection. In search for a more specific approach, we have generated a fusion protein for the antigen-specific targeting of autoreactive B cells for re-directed lysis by resting human T lymphocytes. We describe the design, purification and characterization of MOGxanti-CD3, a single-chain bispecific antibody fusion protein recognizing B cell receptors specific for the human myelin oligodendrocyte glycoprotein (MOG) and to CD3 on human T cells. MOGxAnti-CD3 induced selective and very efficient redirected lysis of MOG-reactive B cells through freshly isolated, unstimulated human T cells. Fusions between autoantigens and an anti-CD3 single-chain antibody may be suitable to develop very specific therapeutic approaches for the selective depletion of autoreactive B cells in autoimmune diseases.